Importance of Carbon

Carbon is the chemical element with symbol C and atomic number 6. It is a member of group 14 on the periodic table. The name "carbon" comes from Latin language carbo, coal.

• Carbon is Non-metallic
• Tetravalent
• Has three naturally occurring isotopes ( ¹²C and ¹³C is stable, ¹⁴C is radioactive)
• Has many allotropes of which the best known are graphite, diamond, and amorphous carbon

Carbon is the 15th most abundant element in the Earth's crust, and the fourth most abundant element in the universe by mass after hydrogen, helium, and oxygen. It is present in all known lifeforms, and in the human body carbon is the second most abundant element by mass (about 18.5%) after oxygen. This abundance, along with the unique diversity of organic compounds and their unusual catenation ability at the temperatures commonly encountered on Earth, make this element the chemical basis of all known life.

Formation of the carbon atomic nucleus requires a nearly simultaneous triple collision of alpha particles (helium nuclei) within the core of a giant or supergiant star. This happens in conditions of > 100 megakelvin temperature and helium concentration that the rapid expansion and cooling of the early universe prohibited, and therefore no significant carbon was created during the Big Bang.

Carbon is essential to all known living systems, and without it life as we know it could not exist. The major economic use of carbon other than food and wood is in the form of hydrocarbons, most notably the fossil fuel methane gas and crude oil (petroleum). Crude oil is used by the petrochemical industry to produce, amongst others, gasoline and kerosene, through a distillation process, in refineries.

Cellulose is a natural, carbon-containing polymer produced by plants in the form of cotton, linen, and hemp. Cellulose is mainly used for maintaining structure in plants. Commercially valuable carbon polymers of animal origin include wool, cashmere and silk. Plastics are made from synthetic carbon polymers, often with oxygen and nitrogen atoms included at regular intervals in the main polymer chain. The raw materials for many of these synthetic substances come from crude oil.

Organometallic compounds by definition contain at least one carbon-metal bond. A wide range of such compounds exist; major classes include simple alkyl-metal compounds (e.g. tetraethyllead), η²-alkene compounds (e.g. Zeise's salt, and η³-allyl compounds (e.g. allylpalladium chloride dimer; metallocenes containing cyclopentadienyl ligands (e.g. ferrocene); and transition metal carbene complexes.

Carbon black is used as the black pigment in printing ink, artist's oil paint and water colours, carbon paper, automotive finishes, India ink and laser printer toner. Carbon black is also used as a filler in rubber products such as tyres and in plastic compounds. Activated charcoal is used as an adsorbent in filter material in applications as diverse as gas masks, water purification and kitchen extractor hoods and in medicine to absorb toxins, poisons, or gases from the digestive system. Carbon is used in chemical reduction at high temperatures.

Coke is used to reduce iron ore into iron. Case hardening of steel is achieved by heating finished steel components in carbon powder. Carbides of silicon, tungsten, boron and titanium, are among the hardest known materials, and are used as abrasives in cutting and grinding tools. Carbon compounds make up most of the materials used in clothing, such as natural and synthetic textiles and leather, and almost all of the interior surfaces in the built environment other than glass, stone and metal.

HPLC

High-performance liquid chromatography (or high-pressure liquid chromatography, HPLC) is a chromatographic technique that can separate a mixture of compounds, and is used in biochemistry and analytical chemistry to identify, quantify and purify the individual components of the mixture.

High performance liquid chromatography is basically a highly improved form of column chromatography. Instead of a solvent being allowed to drip through a column under gravity, it is forced through under high pressures of up to 400 atmospheres. That makes it much faster.

It also allows you to use a very much smaller particle size for the column packing material which gives a much greater surface area for interactions between the stationary phase and the molecules flowing past it. This allows a much better separation of the components of the mixture.

The other major improvement over column chromatography concerns the detection methods which can be used. These methods are highly automated and extremely sensitive.

HPLC utilizes different types of stationary phase (typically, hydrophobic saturated carbon chains), a pump that moves the mobile phase(s) and analyte through the column, and a detector that provides a characteristic retention time for the analyte. The detector may also provide other characteristic information (i.e. UV/Vis spectroscopic data for analyte if so equipped). Analyte retention time varies depending on the strength of its interactions with the stationary phase, the ratio/composition of solvent(s) used, and the flow rate of the mobile phase.

The output will be recorded as a series of peaks - each one representing a compound in the mixture passing through the detector and absorbing UV light.

Plasma

Plasma was first identified in a Crookes tube, and so described by Sir William Crookes in 1879 (he called it "radiant matter").
 Plasma, in physics, fully ionized gas of low density, containing approximately equal numbers of positive and negative ions . It is electrically conductive and is affected by magnetic fields. The study of plasma, called plasma physics, is especially important in research efforts to produce a controlled thermonuclear reaction . Such a reaction requires extremely high temperatures; it has been computed that a temperature of about 10 million degrees Celsius would be needed to initiate the reaction between deuterium and tritium.

By passing a very high electric current through plasma great heat is produced and, simultaneously, an electromagnetic field is created, causing the plasma to withdraw from the walls of its container. The contraction of the plasma, called the pinch effect, prevents the container from being destroyed, but the effect may become unstable too quickly for the fusion reaction. The properties of plasma are distinct from those of the ordinary states of matter, and for this reason many scientists consider plasma a fourth state of matter. Interstellar gases, as well as the matter inside stars, are thought to be in the form of plasma, thus making plasma a common form of matter in the universe.

Like gas, plasma does not have a definite shape or a definite volume unless enclosed in a container; unlike gas, in the influence of a magnetic field, it may form structures such as filaments, beams and double layers. Some common plasmas are stars and neon signs.

Chemistry: Lab-on-a-chip

Chemistry: Lab-on-a-chip

Chemistry: Diffuse interstellar bands.

Chemistry: Diffuse interstellar bands.

Diffuse interstellar bands.

Diffuse interstellar bands (DIBs) are absorption features seen in the spectra of astronomical objects in our galaxy. They are caused by the absorption of light by the interstellar medium. More than 200 bands are seen, in ultraviolet, visible and infrared wavelengths.

The origin of DIBs was unknown and hotly disputed for many years, and the DIBs were long believed to be due to polycyclic aromatic hydrocarbons and other large carbon-bearing molecules. However, no agreement of the bands could be found with laboratory measurements or with theoretical calculations.

The great problem with DIBs, apparent from the earliest observations, was that their central wavelengths did not correspond with any known spectral lines of any ion or molecule, and so the material which was responsible for the absorption could not be identified. A large number of theories were advanced as the number of known DIBs grew, and determining the nature of the absorbing material (the 'carrier') became a crucial problem in astrophysics.

One important observational result is that the strengths of most DIBs are not correlated with each other. This means that there must be many carriers, rather than one carrier responsible for all DIBs. Also significant is that the strength of DIBs is broadly correlated with the extinction. Extinction is caused by dust in the interstellar medium, and so DIBs are likely to be also due to dust or something related to it.

The existence of sub-structure in DIBs supports the idea that they are caused by molecules. Substructure results from band heads in the rotational band contour and from isotope substitution. In a molecule containing, say, three carbon atoms, some of the carbon will be in the form of the carbon-13 isotope, so that while most molecules will contain three carbon-12 atoms, some will contain two C¹² atoms and one C¹³ atom, much less will contain one C¹² and two C¹³s, and a very small fraction will contain three C¹³ molecules. Each of these forms of the molecule will create an absorption line at a slightly different rest wavelength.

The most likely candidate molecules for producing DIBs are thought to be large carbon-bearing molecules, which are common in the interstellar medium. Polycyclic aromatic hydrocarbons, long carbon-chain molecules, and fullerenes are all potentially important.

In recent years, very high resolution spectrographs on the world's most powerful telescopes have been used to observe and analyse DIBs . Spectral resolutions of 0.005 nm are now routine using instruments at observatories such as the European Southern Observatory at Cerro Paranal, Chile, and the Anglo-Australian Observatory in Australia, and at these high resolutions, many DIBs are found to contain considerable sub-structure.

Lab-on-a-chip

A lab-on-a-chip (LOC) is a device that integrates one or several laboratory functions on a single chip of only millimeters to a few square centimeters in size. LOCs deal with the handling of extremely small fluid volumes down to less than pico liters. Lab-on-a-chip devices are a subset of MEMS devices and often indicated by "Micro Total Analysis Systems" (µTAS) as well.

Microfluidics is a broader term that describes also mechanical flow control devices like pumps and valves or sensors like flowmeters and viscometers. However, strictly regarded "Lab-on-a-Chip" indicates generally the scaling of single or multiple lab processes down to chip-format, whereas "µTAS" is dedicated to the integration of the total sequence of lab processes to perform chemical analysis. The term "Lab-on-a-Chip" was introduced later on when it turned out that µTAS technologies were more widely applicable than only for analysis purposes.


Chip materials and fabrication technologies
The basis for most LOC fabrication processes is photolithography. Initially most processes were in silicon, as these well-developed technologies were directly derived from semiconductor fabrication. Because of demands for e.g. specific optical characteristics, bio- or chemical compatibility, lower production costs and faster prototyping, new processes have been developed such as glass, ceramics and metal etching, deposition and bonding, PDMS processing (e.g., soft lithography), thick-film- and stereolithography as well as fast replication methods via electroplating, injection molding and embossing. Furthermore the LOC field more and more exceeds the borders between lithography-based microsystem technology, nano technology and precision engineering.


Advantages of LOCs
LOCs may provide advantages, which are specific to their application. Typical advantages are:

1. low fluid volumes consumption (less waste, lower reagents costs and less required sample volumes for diagnostics)
2. faster analysis and response times due to short diffusion distances, fast heating, high surface to volume ratios, small heat capacities.
3. better process control because of a faster response of the system (e.g. thermal control for exothermic chemical reactions)
4. compactness of the systems due to integration of much functionality and small volumes
5. massive parallelization due to compactness, which allows high-throughput analysis
6. lower fabrication costs, allowing cost-effective disposable chips, fabricated in mass production
7. safer platform for chemical, radioactive or biological studies because of integration of functionality, smaller fluid volumes and stored energies

For the chips to be used in areas with limited resources, many challenges must be overcome. In developed nations, the most highly valued traits for diagnostic tools include speed, sensitivity, and specificity; but in countries where the healthcare infrastructure is less well developed, attributes such ease of use and shelf life must also be considered. The reagents that come with the chip, for example, must be designed so that they remain effective for months even if the chip is not kept in a climate-controlled environment. Chip designers must also keep cost, scalability, and recyclability in mind as they choose what materials and fabrication techniques to use.


One active area of LOC research involves ways to diagnose and manage HIV infections. Around 40 million people are infected with HIV in the world today, yet only 1.3 million of these people receive anti-retroviral treatment. Around 90% of people with HIV have never been tested for the disease. Measuring the number of CD4+ T lymphocytes in a person’s blood is an accurate way to determine if a person has HIV and to track the progress of an HIV infection. At the moment, flow cytometry is the gold standard for obtaining CD4 counts, but flow cytometry is a complicated technique that is not available in most developing areas because it requires trained technicians and expensive equipment.

LASER

Light amplification by stimulated emission of radiation (LASER or laser) is a mechanism for emitting electromagnetic radiation, typically light or visible light, via the process of stimulated emission. The emitted laser light is usually a spatially coherent, narrow low-divergence beam, that can be manipulated with lenses. In laser technology, "coherent light" denotes a light source that produces light of in-step waves of identical frequency, phase, and polarization.



Design


A laser consists of a gain medium inside a highly reflective optical cavity, as well as a means to supply energy to the gain medium. The gain medium is a material with properties that allow it to amplify light by stimulated emission. In its simplest form, a cavity consists of two mirrors arranged such that light bounces back and forth, each time passing through the gain medium. Typically one of the two mirrors, the output coupler, is partially transparent. The output laser beam is emitted through this mirror.


Light of a specific wavelength that passes through the gain medium is amplified (increases in power); the surrounding mirrors ensure that most of the light makes many passes through the gain medium, being amplified repeatedly. Part of the light that is between the mirrors (that is, within the cavity) passes through the partially transparent mirror and escapes as a beam of light.


The process of supplying the energy required for the amplification is called pumping. The energy is typically supplied as an electrical current or as light at a different wavelength. Such light may be provided by a flash lamp or perhaps another laser. Most practical lasers contain additional elements that affect properties such as the wavelength of the emitted light and the shape of the beam.




Types and operating principles
 
Gas lasers


Gas lasers using many gases have been built and used for many purposes.


The helium-neon laser (HeNe) emits at a variety of wavelengths and units operating at 633 nm are very common in education because of its low cost.


Carbon dioxide lasers can emit hundreds of kilowatts[14] at 9.6 µm and 10.6 µm, and are often used in industry for cutting and welding. The efficiency of a CO2 laser is over 10%.


Argon-ion lasers emit light in the range 351-528.7 nm. Depending on the optics and the laser tube a different number of lines is usable but the most commonly used lines are 458 nm, 488 nm and 514.5 nm.


A nitrogen transverse electrical discharge in gas at atmospheric pressure (TEA) laser is an inexpensive gas laser producing UV light at 337.1 nm.


Metal ion lasers are gas lasers that generate deep ultraviolet wavelengths. Helium-silver (HeAg) 224 nm and neon-copper (NeCu) 248 nm are two examples. These lasers have particularly narrow oscillation linewidths of less than 3 GHz (0.5 picometers),[16] making them candidates for use in fluorescence suppressed Raman spectroscopy



Chemical lasers


Chemical lasers are powered by a chemical reaction, and can achieve high powers in continuous operation. For example, in the Hydrogen fluoride laser (2700-2900 nm) and the Deuterium fluoride laser (3800 nm) the reaction is the combination of hydrogen or deuterium gas with combustion products of ethylene in nitrogen trifluoride. They were invented by George C. Pimentel



Excimer lasers


Excimer lasers are powered by a chemical reaction involving an excited dimer, or excimer, which is a short-lived dimeric or heterodimeric molecule formed from two species (atoms), at least one of which is in an excited electronic state. They typically produce ultraviolet light, and are used in semiconductor photolithography and in LASIK eye surgery. Commonly used excimer molecules include F2 (fluorine, emitting at 157 nm), and noble gas compounds (ArF [193 nm], KrCl [222 nm], KrF [248 nm], XeCl [308 nm], and XeF [351 nm]).



Solid-state lasers


Solid-state laser materials are commonly made by "doping" a crystalline solid host with ions that provide the required energy states. For example, the first working laser was a ruby laser, made from ruby (chromium-doped corundum). The population inversion is actually maintained in the "dopant", such as chromium or neodymium. Formally, the class of solid-state lasers includes also fiber laser, as the active medium (fiber) is in the solid state. Practically, in the scientific literature, solid-state laser usually means a laser with bulk active medium, while wave-guide lasers are caller fiber lasers.


"Semiconductor lasers" are also solid-state lasers, but in the customary laser terminology, "solid-state laser" excludes semiconductor lasers, which have their own name.


Neodymium is a common "dopant" in various solid-state laser crystals, including yttrium orthovanadate (Nd:YVO4), yttrium lithium fluoride (Nd:YLF) and yttrium aluminium garnet (Nd:YAG). All these lasers can produce high powers in the infrared spectrum at 1064 nm. They are used for cutting, welding and marking of metals and other materials, and also in spectroscopy and for pumping dye lasers. These lasers are also commonly frequency doubled, tripled or quadrupled to produce 532 nm (green, visible), 355 nm (UV) and 266 nm (UV) light when those wavelengths are needed.


Ytterbium, holmium, thulium, and erbium are other common "dopants" in solid-state lasers. Ytterbium is used in crystals such as Yb:YAG, Yb:KGW, Yb:KYW, Yb:SYS, Yb:BOYS, Yb:CaF2, typically operating around 1020-1050 nm. They are potentially very efficient and high powered due to a small quantum defect. Extremely high powers in ultrashort pulses can be achieved with Yb:YAG. Holmium-doped YAG crystals emit at 2097 nm and form an efficient laser operating at infrared wavelengths strongly absorbed by water-bearing tissues. The Ho-YAG is usually operated in a pulsed mode, and passed through optical fiber surgical devices to resurface joints, remove rot from teeth, vaporize cancers, and pulverize kidney and gall stones.


Titanium-doped sapphire (Ti:sapphire) produces a highly tunable infrared laser, commonly used for spectroscopy as well as the most common ultrashort pulse laser.


Thermal limitations in solid-state lasers arise from unconverted pump power that manifests itself as heat and phonon energy. This heat, when coupled with a high thermo-optic coefficient (dn/dT) can give rise to thermal lensing as well as reduced quantum efficiency. These types of issues can be overcome by another novel diode-pumped solid-state laser, the diode-pumped thin disk laser. The thermal limitations in this laser type are mitigated by using a laser medium geometry in which the thickness is much smaller than the diameter of the pump beam. This allows for a more even thermal gradient in the material. Thin disk lasers have been shown to produce up to kilowatt levels of power

Dye lasers



Dye lasers use an organic dye as the gain medium. The wide gain spectrum of available dyes allows these lasers to be highly tunable, or to produce very short-duration pulses (on the order of a few femtoseconds)


Free electron lasers


Free electron lasers, or FELs, generate coherent, high power radiation, that is widely tunable, currently ranging in wavelength from microwaves, through terahertz radiation and infrared, to the visible spectrum, to soft X-rays. They have the widest frequency range of any laser type. While FEL beams share the same optical traits as other lasers, such as coherent radiation, FEL operation is quite different. Unlike gas, liquid, or solid-state lasers, which rely on bound atomic or molecular states, FELs use a relativistic electron beam as the lasing medium, hence the term free electron.




Uses
 
The first application of lasers visible in the daily lives of the general population was the supermarket barcode scanner, introduced in 1974. The laserdisc player, introduced in 1978, was the first successful consumer product to include a laser, but the compact disc player was the first laser-equipped device to become truly common in consumers' homes, beginning in 1982, followed shortly by laser printers.


Some of the other applications include:


Medicine: Bloodless surgery, laser healing, surgical treatment, kidney stone treatment, eye treatment, dentistry


Industry: Cutting, welding, material heat treatment, marking parts


Defense: Marking targets, guiding munitions, missile defence, electro-optical countermeasures (EOCM), alternative to radar, blinding enemy troops.


Research: Spectroscopy, laser ablation, laser annealing, laser scattering, laser interferometry, LIDAR, laser capture microdissection


Product development/commercial: laser printers, CDs, barcode scanners, thermometers, laser pointers, holograms, bubblegrams.


Laser lighting displays: Laser light shows


Cosmetic skin treatments: acne treatment, cellulite and striae reduction, and hair removal.

BLOOM ENERGY

Bloom Energy Corporation, a Silicon Valley-based


company committed to changing the way people generate and consume energy, announced

today the availability of the Bloom Energy Server, a patented solid oxide fuel cell (SOFC)

technology that provides a cleaner, more reliable, and more affordable alternative to both today’s

electric grid as well as traditional renewable energy sources. The Bloom Energy Server provides

distributed power generation, allowing customers to efficiently create their own electricity onsite.

The company introduced its groundbreaking technology at an event hosted today at eBay Inc.

headquarters along with California Governor Arnold Schwarzenegger, General Colin Powell, and

several of its early customers.

Built using abundant and affordable materials, Bloom’s fuel cell technology is fundamentally

different from the legacy “hydrogen” fuel cells most people are familiar with. The Bloom Energy

Server is distinct in four primary ways: it uses lower cost materials, provides unmatched efficiency

in converting fuel to electricity, has the ability to run on a wide range of renewable or traditional

fuels, and is more easily deployed and maintained.

Unlike traditional renewable energy technologies, like solar and wind, which are intermittent,

Bloom’s technology can provide renewable power 24/7.

Each Bloom Energy Server provides 100 kilowatts (kW) of power in roughly the footprint of a

parking space. Each system generates enough power to meet the needs of approximately 100

average U.S. homes or a small office building. For more power, customers simply deploy multiple

Energy Servers side by side. The modular architecture allows customers to start small and “pay

as they grow”.
 
Powder to Power – How It Works


Founded in 2001, Bloom Energy can trace its roots to the NASA Mars space program. For NASA,

Sridhar and his team were charged with building technology to help sustain life on Mars using

solar energy and water to produce air to breath and fuel for transportation. They soon realized

that their technology could have an even greater impact here on Earth and began work on what

would become the Bloom Energy Server.

The Bloom Energy Server converts air and nearly any fuel source – ranging from natural gas to a


wide range of biogases – into electricity via a clean electrochemical process, rather than dirty


combustion. Even running on a fossil fuel, the systems are approximately 67% cleaner than a

typical coal-fired power plant. When powered by a renewable fuel, they can be 100% cleaner.

Each Energy Server consists of thousands of Bloom's fuel cells – flat, solid ceramic squares


made from a common sand-like "powder."
 
About Bloom Energy


Bloom Energy is a provider of breakthrough solid oxide fuel cell technology that generates clean,

highly-efficient power onsite from virtually any fuel source. Bloom Energy’s mission is to make

clean, reliable energy affordable for everyone in the world. The Bloom Energy Server is currently

producing power for several Fortune 500 companies.

Chemicals-Risk

The 20th century has seen the birth of three Ages, each with profound social implications. These have been called the Nuclear Age, the Electronic Age and the Chemical Age. The latter is the oldest (beginning ca. 1930), and although its impact has been less dramatic than the other two, its consequences have more thoroughly and deeply permeated our day-to-day lives. Our local grocery, hardware, garden and drug stores carry an impressive array of commonly used chemical "tools", such as detergents, adhesives, lubricants, fabrics, pesticides, pharmaceutical drugs, vitamins and a multitude of fabricated plastic items. Industrial applications of chemical tools include explosives, heat-transfer gases and liquids, specialized coatings, fire retardants and high-performance plastic components.




Despite our widespread use of chemical tools, indeed some might say because of our reliance on them, many people fear exposure to these materials, and have deep concerns regarding the use, storage and disposal of chemicals. Paradoxically, we find our desires for more abundant consumer goods, energy and personal mobility in conflict with maintenance of a healthful environment. To be sure, environmental degradation, with accompanying threats to health and disruption of ecosystems, is not a new phenomenon. From the earliest recorded history, human disturbance of the environment by deforestation, air pollution from cooking and heating fires, and careless sewage and waste disposal has been noted. Today, as global populations grow and per capita energy use and material consumption increases, pollution problems are exacerbated, and previously unnoticed secondary effects manifest themselves.


Every day we take risks and avoid others. About 250 people in the U.S. are electrocuted every year in accidents involving home wiring or appliances. This represents a risk of death of about 8*10-7 per year (250 divided by the U.S. population) or 6*10-6 per lifetime (75 yr.). Nevertheless, most of us choose to live in electrically wired homes, and make extensive use of electrical appliances. Likewise, many people would be unwilling to live within 20 miles of a nuclear power plant, yet accept (even request) a 4,000 times greater radiation dose from medical x-rays or 6,500 times greater cosmic radiation at altitudes of a mile or more.




The concept of risk and the notion of uncertainty are closely related. The lifetime risk of dying from cancer is roughly 22%, and is somewhat greater for those who smoke. However, even if an individual is a heavy smoker, we cannot say with certainty he(she) will die of lung cancer. On the other hand, if that individual is dying as the result of a serious automobile accident, the risk of dying from cancer drops to nearly zero.



Using Chemicals
As with any other kind of tool, chemicals must be handled correctly, with proper care and precaution. Although chemicals vary in the hazards they present, it is generally wise to treat all chemicals as though they are potentially dangerous. Among the recognized hazardous properties of chemicals are: explosiveness, flammability, corrosiveness, irritation, sensitivity, toxicity and radioactivity. One of the most useful sources of information about chemical hazards is the material safety data sheet (MSDS). Information about these data sheets is available at MSDSonline. It is an interesting excercise to examine the MSDS for common chemicals such as acetic acid (vinegar) and naphthalene (mothballs).




Of all the hazardous properties noted above, toxicity seems to constitute the greatest concern in the minds of the public. Contrary to popular belief, the fact that a substance is toxic does not mean it will always kill people or animals exposed to it. Virtually all substances are lethal if taken in sufficient amount. As noted by the Swiss Physician Paracelsus, It is the dose that makes the poison! Thus, 1.5 grams of arsenic trioxide will kill a 180 pound man; 2 milligrams will not. Small amounts of vitamin D (ca. 10 micrograms per day) are necessary for good health, but in larger amounts it is more toxic than arsenic compounds.


Humans vary considerably in their sensitivity to natural and synthetic chemicals. Strawberry, peanut and latex allergies are relatively common, and reports of asthma-like symptoms on exposure to synthetic plasticizers exist. A more complex and less well-defined syndrome, known as multiple chemical sensitivity, is the subject of medical controversy, although it is very real to those who suffer its effects. One thing is certain. If you wish to avoid exposure to chemicals, the planet earth is a poor place to live.








 

CLAYS

Clay minerals are hydrous aluminium phyllosilicates, sometimes with variable amounts of iron, magnesium, alkali metals, alkaline earths and other cations. Clays have structures similar to the micas and therefore form flat hexagonal sheets. Clay minerals are common weathering products (including weathering of feldspar) and low temperature hydrothermal alteration products. Clay minerals are very common in fine grained sedimentary rocks such as shale, mudstone and siltstone and in fine grained metamorphic slate and phyllite.




Clays are ultra fine grained (normally considered to be less than 2 micrometres in size on standard particle size classifications) and so require special analytical techniques. Standards include x-ray diffraction, electron diffraction methods, various spectroscopic methods such as Mossbauer spectroscopy, infrared spectroscopy, and EDS or energy dispersive spectroscopy. These methods should always augment standard polarized light microscopy, a technique which is sometimes overlooked but often where fundamental occurrences or petrologic relationships are established.



Clays are commonly referred to as 1:1 or 2:1. Clays are fundamentally built of tetrahedral sheets and octahedral sheets, as described in the Structure section below. A 1:1 clay would consist of one tetrahedral sheet and one octahedral sheet, and examples would be kaolinite and serpentine. A 2:1 clay consists of an octahedral sheet sandwiched between two tetrahedral sheets, and examples are illite, smectite, attapulgite, and chlorite (although chlorite has an external octahedral sheet often referred to as "brucite").



Structure


Like all phyllosilicates, clay minerals are characterised by two-dimensional sheets of corner sharing SiO4 and AlO4 tetrahedra. These tetrahedral sheets have the chemical composition (Al,Si)3O4, and each tetrahedron shares 3 of its vertex oxygen atoms with other tetrahedra forming a hexagonal array in two-dimensions. The fourth vertex is not shared with another tetrahedron and all of the tetrahedra "point" in the same direction (i.e. all of the unshared vertices are on the same side of the sheet).



In clays the tetrahedral sheets are always bonded to octahedral sheets formed from small cations, such as aluminium or magnesium, coordinated by six oxygen atoms. The unshared vertex from the tetrahedral sheet also form part of one side of the octahedral sheet but an additional oxygen atom is located above the gap in the tetrahedral sheet at the center of the six tetrahedra. This oxygen atom is bonded to a hydrogen atom forming an OH group in the clay structure. Clays can be categorised depending on the way that tetrahedral and octahedral sheets are packaged into layers. If there is only one tetrahedral and one octahedral group in each layer the clay is known as a 1:1 clay. The alternative, known as a 2:1 clay, has two tetrahedral sheets with the unshared vertex of each sheet pointing towards each other and forming each side of the octahedral sheet.



Bonding between the tetrahedral and octahedral sheets requires that the tetrahedral sheet becomes corrogated or twisted, causing ditrigonal distortion to the hexagonal array, and the octahedral sheet is flattened. This minimizes the overall bond-valence distortions of the crystallite.



Depending on the composition of the tetrahedral and octahedral sheets, the layer will have no charge, or will have a net negative charge. If the layers are charged this charge is balanced by interlayer cations such as Na+ or K+. In each case the interlayer can also contain water. The crystal structure is formed from a stack of layers interspaced with the interlayers.

Named Reactions

Link: http://www.chem.wisc.edu/areas/reich/syntheses/syntheses.htm

Link: http://www.organic-chemistry.org/namedreactions/

Chemistry: Organic synthesis

Chemistry: Organic synthesis

Organic synthesis

Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has developed into one of the most important branches of organic chemistry. There are two main areas of research fields within the general area of organic synthesis: total synthesis and methodology.

Total synthesis

A total synthesis is the complete chemical synthesis of complex organic molecules from simple, commercially available (petrochemical) or natural precursors. In a linear synthesis there is a series of steps which are performed one after another until the molecule is made- this is often adequate for a simple structure. The chemical compounds made in each step are usually referred to as synthetic intermediates.
The "father" of modern organic synthesis is regarded as Robert Burns Woodward, who received the 1965 Nobel Prize for Chemistry for several brilliant examples of total synthesis such as his 1954 synthesis of strychnine.

Asymmetric synthesis

Asymmetric synthesis, also called chiral synthesis, enantioselective synthesis or stereoselective synthesis, is organic synthesis which introduces one or more new and desired elements of chirality.This is important in the field of pharmaceuticals because the different enantiomers or diastereomers of a molecule often have different biological activity.

There are three main approaches to asymmetric synthesis:
chiral pool synthesis
chiral auxiliaries
asymmetric catalysis

In practice, a mixture of all three is often used in order to maximize the advantages of each method.


Methodology

Each step of a synthesis involves a chemical reaction, and reagents and conditions for each of these reactions need to be designed to give a good yield and a pure product, with as little work as possible. A method may already exist in the literature for making one of the early synthetic intermediates, and this method will usually be used rather than "trying to reinvent the wheel". However most intermediates are compounds that have never been made before, and these will normally be made using general methods developed by methodology researchers. To be useful, these methods need to give high yields and to be reliable for a broad range of substrates. Methodology research usually involves three main stages- discovery, optimisation, and studies of scope and limitations. The discovery requires extensive knowledge of and experience with chemical reactivities of appropriate reagents. Optimisation is where one or two starting compounds are tested in the reaction under a wide variety of conditions of temperature, solvent, reaction time, etc., until the optimum conditions for product yield and purity are found.


Link: http://www.chem.wisc.edu/areas/reich/syntheses/syntheses.htm

Organometallic chemistry

Organometallic chemistry is the study of chemical compounds containing bonds between carbon and a metal.Since many compounds without such bonds are chemically similar, an alternative may be compounds containing metal-element bonds of a largely covalent character. Organometallic chemistry combines aspects of inorganic chemistry and organic chemistry.


Organometallic compounds are also known as organo-inorganics, metallo-organics and metalorganics. Organometallic compounds are distinguished by the prefix "organo-" e.g. organopalladium compounds. Examples of such organometallic compounds include all Gilman Reagents, which contain lithium and copper. Tetracarbonyl nickel, and ferrocene are examples of organometallic compounds containing transition metals. Other examples include organomagnesium compounds like iodo(methyl)magnesium MeMgI, diethylmagnesium (Et2Mg), and all Grignard reagents; organolithium compounds such as butyllithium (BuLi), organozinc compounds such as chloro(ethoxycarbonylmethyl)zinc (ClZnCH2C(=O)OEt); and organocopper compounds such as lithium dimethylcuprate (Li+[CuMe2]–).

In addition to the traditional metals, lanthanides, actinides, and semimetals, elements such as boron, silicon, arsenic, and selenium are considered to form organometallic compounds, e.g. organoborane compounds such as triethylborane (Et3B).

Structure and properties

The metal-carbon bond in organometallic compounds is generally of character intermediate between ionic and covalent. Primarily ionic metal-carbon bonds are encountered either when the metal is very electropositive (as in the case of the alkali metals) or when the carbon-containing ligand exists as a stable carbanion. Carbanions can be stabilized by resonance (as in the case of the aromatic cyclopentadienyl anion) or by the presence of electron-withdrawing substituents (as in the case of the triphenylmethyl anion). Hence, the bonding in compounds like sodium acetylide and triphenylmethylpotassium is primarily ionic. On the other hand, the ionic character of metal-carbon bonds in the organometallic compounds of transition metals, poor metals, and metalloids tends to be intermediate, owing to the middle-of-the-road electronegativity of such metals.

Organometallic compounds with bonds that have characters in between ionic and covalent are very important in industry, as they are both relatively stable in solutions and relatively ionic to undergo reactions. Two important classes are organolithium and Grignard reagents. In certain organometallic compounds such as ferrocene or dibenzenechromium, the pi orbitaStructure and properties.


Organometallic compounds undergo several important reactions:


oxidative addition and reductive elimination
transmetalation
carbometalation
Hydrometalation
electron transfer
beta-hydride elimination
organometallic substitution reaction
carbon-hydrogen bond activation
cyclometalation
Migratory insertion

Fullerene chemistry

Fullerene chemistry is a field of organic chemistry devoted to the chemical properties of fullerenes.Research in this field is driven by the need to functionalize fullerenes and tune their properties. For example fullerene is notoriously insoluble and adding a suitable group can enhance solubility. By adding a polymerizable group, a fullerene polymer can be obtained. Functionalized fullerenes are divided into two classes:
exohedral with substituents outside the cage
endohedral fullerenes with trapped molecules inside the cage.

Chemical properties of fullerenes.

Fullerene or C60 is soccer-ball-shaped or Ih with 12 pentagons and 20 hexagons. According to Euler's theorem these 12 pentagons are required for closure of the carbon network consisting of n hexagons and C60 is the first stable fullerene because it is the smallest possible to obey this rule. In this structure none of the pentagons make contact with each other. Both C60 and its relative C70 obey this so-called isolated pentagon rule (IPR). The next homologue C84 has 24 IPR isomers of which several are isolated and another 51,568 non-IPR isomers. Non-IPR fullerenes have thus far only been isolated as endohedral fullerenes such as Tb3N@C84 with two fused pentagons at the apex of an egg-shaped cage

Because of the molecule's spherical shape the carbon atoms are highly pyramidalized, which has far-reaching consequences for reactivity. It is estimated that strain energy constitutes 80% of the heat of formation. The conjugated carbon atoms respond to deviation from planarity by orbital rehybridization of the sp² orbitals and pi orbitals to a sp2.27 orbital with a gain in p-character. The p lobes extend further outside the surface than they do into the interior of the sphere and this is one of the reasons a fullerene is electronegative. The other reason is that the empty low-lying pi* orbitals also have high s character.

The double bonds in fullerene are not all the same. Two groups can be identified: 30 so-called [6,6] double bonds connect two hexagons and 60 [5,6] bonds connect a hexagon and a pentagon. Of the two the [6,6] bonds are shorter with more double-bond character and therefore a hexagon is often represented as a cyclohexatriene and a pentagon as a pentalene or [5]radialene.

Fullerene reactions

Fullerenes tend to react as electrophiles. An additional driving force is relief of strain when double bonds become saturated. Key in this type of reaction is the level of functionalization i.e. monoaddition or multiple additions and in case of multiple additions their topological relationships (new substituents huddled together or evenly spaced).

Fullerenes react as electrophiles with a host of nucleophiles in nucleophilic additions. The intermediary formed carbanion is captured an electrophile. Examples of nucleophiles are Grignard reagents and organolithium reagents. For example the reaction of C60 with methylmagnesium chloride stops quantitatively at the penta-adduct with the methyl groups centered around a cyclopentadienyl anion which is subsequently protonated [5]. Another nucleophilic reaction is the Bingel reaction.

Fullerene reacts with chlorobenzene and aluminium chloride in a Friedel-Crafts alkylation type reaction. In this hydroarylation the reaction product is the 1,2-addition adduct (Ar-CC-H) [6].

The [6,6] bonds of fullerenes react as dienes or dienophiles in cycloadditions for instance Diels-Alder reactions. 4-membered rings can be obtained by [2+2]cycloadditions for instance with benzyne. An example of a 1,3-dipolar cycloaddition to a 5-membered ring is the Prato reaction.

Fullerenes are easily hydrogenated by several methods with C60H18 and C60H36 being most studied hydrofullerenes[citation needed]. However, completely hydrogenated C60H60 is only hypothetical because of large strain. Highly hydrogenated fullerenes are not stable, prolonged hydrogenation of fullerenes by direct reaction with hydrogen gas at high temperature conditions results in collapse of cage structure with formation of polycyclic aromatic hydrocarbons.
Although more difficult than reduction, oxidation of fullerene is possible for instance with oxygen and osmium tetraoxide

Fullerenes react in electrophilic additions as well. The reaction with bromine can add up to 24 bromine atoms to the sphere. The record holder for fluorine addition is C60F48. According to in silico predictions the as yet elusive C60F60 may have some of the fluorine atoms in endo positions (pointing inwards) and may resemble a tube more than it does a sphere [7]
Fullerenes react with carbenes to methanofullerenes

Chemistry: Combinatorial chemistry

http://books.google.co.in/books?id=IgiJTVsbeoYC&dq=combinatorial+chemistry&printsec=frontcover&source=bl&ots=T5ArPuA_M1&sig=ghxNUo8E06fUs1ynv7IlxpF-SDI&hl=en&ei=q6OrSs2sCceutgeqgvGtCA&sa=X&oi=book_result&ct=result&resnum=10#v=onepage&q=&f=falseChemistry: Combinatorial chemistry

Combinatorial chemistry

Combinatorial chemistry is a technique by which large numbers of structurally distinct molecules may be synthesised in a time and submitted for pharmacological assay. The key of combinatorial chemistry is that a large range of analogues is synthesised using the same reaction conditions, the same reaction vessels. In this way, the chemist can synthesise many hundreds or thousands of compounds in one time instead of preparing only a few by simple methodology.Combinatorial chemistry involves the rapid synthesis or the computer simulation of a large number of different but structurally related molecules or materials

Synthesis of molecules in a combinatorial fashion can quickly lead to large numbers of molecules. For example, a molecule with three points of diversity (R1, R2, and R3) can generate NR1*NR2*NR3 possible structures, where NR1 ,NR2 , and NR3 are the number of different substituents utilized.

Although combinatorial chemistry has only really been taken up by industry since the 1990s, its roots can be seen as far back as the 1960s when a researcher at Rockefeller University, Bruce Merrifield, started investigating the solid-phase synthesis of peptides. Professor Pieczenik, a colleague of Nobel Laureate Merrifield synthesized the first combinatorial library. In the 1980s researcher H. Mario Geysen developed this technique further, creating arrays of different peptides on separate supports but not a combinatorial library based on random synthesis.

In its modern form, combinatorial chemistry has probably had its biggest impact in the pharmaceutical industry. Researchers attempting to optimize the activity profile of a compound create a 'library' of many different but related compounds. Advances in robotics have led to an industrial approach to combinatorial synthesis, enabling companies to routinely produce over 100,000 new and unique compounds per year.

In order to handle the vast number of structural possibilities, researchers often create a 'virtual library', a computational enumeration of all possible structures of a given pharmacophore with all available reactants. Such a library can consist of thousands to millions of 'virtual' compounds. The researcher will select a subset of the 'virtual library' for actual synthesis, based upon various calculations and criteria.
Combinatorial chemistry is one of the important new methodologies developed by researchers in the pharmaceutical industry to reduce the time and costs associated with producing effective and competitive new drugs.

By accelerating the process of chemical synthesis, this method is having a profound effect on all branches of chemistry, but especially on drug discovery. Through the rapidly evolving technology of combi-chemistry, it is now possible to produce compound libraries to screen for novel bioactivities. This powerful new technology has begun to help pharmaceutical companies to find new drug candidates quickly, save significant money in preclinical development costs and ultimately change their fundamental approach to drug discovery.


Development of Combinatorial Chemistry
---------------------------------------------------------------------------

From a historical perspective, the research efforts made in classical combinatorial chemistry can be briefly outlined in three phases:

In the early 1990s, the initial efforts in the combinatorial chemistry arena were driven by the improvements made in high-throughput screening (HTS) technologies. This led to a demand for access to a large set of compounds for biological screening.

To keep up with this growing demand, chemists were under constant pressure to produce compounds in vast numbers for screening purposes. For practical reasons, the molecules in the first phase were simple peptides (or peptide-like) and lacked the structural complexity commonly found in modern organic synthesis literature.

The second phase started in the late 1990s, when chemists became aware that it is not just about numbers; but something was missing in compounds produced in a combinatorial fashion. Emphasis was thus shifted towards quality rather than quantity.

Like the first phase, the third phase had its origin in progress made by the biomedical community. As the scientific community moved into the post-genomic chemical biology age, there was a growing demand in understanding the role of newly discovered proteins and their interactions with other bio-macromolecules (i.e. other proteins and DNA or RNA). For example, the early goals of the biomedical research community were centered on the identification of small-molecule ligands for biological targets, such as G-protein-coupled receptors (GPCRs) and enzymes.

However, the current challenges are moving in the direction of understanding bio-macromolecular (i.e. protein-protein, protein-DNA/RNA) interactions and how small molecules could be utilized as useful chemical probes in systematic dissection of these interactions. By no means will this be a trivial undertaking! The development of biological assays towards understanding biomacromolecular interactions is equally challenging as the need for having access to useful small molecule chemical probes.

Supramolecular Chemistry.

What is supramolecular chemistry?

It has been described as ‘chemistry beyond the molecule’, whereby a ‘supermolecule’ is a
species that is held together by non-covalent interactions between two or more
covalent molecules or ions. It can also be described as ‘lego™ chemistry’ in which
each lego™ brick represents a molecular building block and these blocks are held
together by intermolecular interactions (bonds), of a reversible nature, to form
a supramolecular aggregate. These intermolecular bonds include electrostatic
interactions, hydrogen bonding, – interactions, dispersion interactions and
hydrophobic or solvophobic effects.

Supramolecular Chemistry: The study of systems involving aggregates of molecules
or ions held together by non-covalent interactions, such as electrostatic interactions,
hydrogen bonding, dispersion interactions and solvophobic effects.

Supramolecular chemistry is a multidisciplinary field which impinges on
various other disciplines, such as the traditional areas of organic and inorganic
chemistry, needed to synthesise the precursors for a supermolecule, physical
chemistry, to understand the properties of supramolecular systems and computational
modelling to understand complex supramolecular behaviour. A great
deal of biological chemistry involves supramolecular concepts and in addition
a degree of technical knowledge is required in order to apply supramolecular
systems to the real world, such as the development of nanotechnological devices.


Supramolecular chemistry can be split into two broad categories;

• host–guest chemistry
• self-assembly

The host component is defined as an organic molecule or ion whose binding sites converge
in the complex. The guest component is any molecule or ion whose binding sites
diverge in the complex.1 A binding site is a region of the host or guest that is
of the correct size, geometry and chemical nature to interact with the other species.

Host–guest complexes include biological systems, such as enzymes and their substrates, with enzymes being the host and the substrates the guest. In terms of coordination chemistry,
metal–ligand complexes can be thought of as host–guest species, where large
(often macrocyclic) ligands act as hosts for metal cations. If the host possesses a
permanent molecular cavity containing specific guest binding sites, then it will
generally act as a host both in solution and in the solid state and there is a
reasonable likelihood that the solution and solid state structures will be similar
to one another. On the other hand, the class of solid state inclusion compounds
only exhibit host–guest behaviour as crystalline solids since the guest is bound
within a cavity that is formed as a result of a hole in the packing of the host
lattice. Such compounds are generally termed clathrates from the Greek klethra,
meaning ‘bars’.

Where there is no significant difference in size and no species is acting as a host for another, the non-covalent joining of two or more species is termed self-assembly. Strictly, self-assembly is an equilibrium between two or more molecular components to produce an aggregate with a
structure that is dependent only on the information contained within the chemical
building blocks.

Nature itself is full of supramolecular systems, for example, deoxyribonucleic
acid (DNA) is made up from two strands which self-assemble via hydrogen
bonds and aromatic stacking interactions to form the famous double helical
structure.

Host–Guest Chemistry: The study of large ‘host’ molecules that are capable of
enclosing smaller ‘guest’ molecules via non-covalent interactions.

Self-Assembly: The spontaneous and reversible association of two or more
components to form a larger, non-covalently bound aggregate.

Binding Site: A region of a molecule that has the necessary size, geometry
and functionalities to accept and bind a second molecule via non-covalent
interactions.

Thermionic emission; Cold Cathode

Thermionic emission is the heat-induced flow of charge carriers from a surface or over a potential-energy barrier. This occurs because the thermal energy given to the carrier overcomes the forces restraining it. The charge carriers can be electrons or ions, and in older literature are sometimes referred to as "thermions". After emission, a charge will initially be left behind in the emitting region that is equal in magnitude and opposite in sign to the total charge emitted. But if the emitter is connected to a battery, then this charge left behind will be neutralized by charge supplied by the battery, as the emitted charge carriers move away from the emitter, and finally the emitter will be in the same state as it was before emission. The thermionic emission of electrons is also known as thermal electron emission.
The classical example of thermionic emission is the emission of electrons from a hot metal cathode into a vacuum (known as the Edison effect) used in vacuum tubes. However, the term "thermionic emission" is now used to refer to any thermally excited charge emission process, even when the charge is emitted from one solid-state region into another. This process is crucially important in the operation of a variety of electronic devices and can be used for power generation or cooling. The magnitude of the charge flow increases dramatically with increasing temperature. However, vacuum emission from metals tends to become significant only for temperatures over 1000 K. The science dealing with this phenomenon has been known as thermionics, but this name seems to be gradually falling into disuse.

Cold cathode
Cold cathode is an element used within some Nixie tubes, gas discharge lamps, gas filled tubes, and vacuum tubes. The term 'cold cathode' refers to the fact that the cathode is not independently heated. In spite of this, the cathode itself may still operate at temperatures as high as if the cathode were heated.
Cold cathode fluorescent lamps (CCFLs) are usually also called cold cathodes. Neon lamps are a very common example of a cold cathode lamp.
Cold Cathodes remain popular for LCD backlighting and enthusiast computer case modders.

Electron emission
A cathode is any electrode that emits electrons. When used in electrical and electronic devices (most fluorescent lamps, vacuum tubes, etc.), the cathode is explicitly heated, creating a hot cathode. By taking advantage of thermionic emission, electrons can overcome the work function of the cathode without an electric field to pull the electrons out. But if sufficient voltage is present, electrons can still be stripped even out of a cathode operating at ambient temperature. Because it is not deliberately heated, such a cathode is referred to as a cold cathode, although several mechanisms may eventually cause the cathode to become quite hot once it is operating. Most cold cathode devices are filled with a gas which can be ionized. A few cold cathode devices contain a vacuum.

Thermoelectric effect
The thermoelectric effect is the direct conversion of temperature differences to electric voltage and vice versa. A thermoelectric device creates a voltage when there is a different temperature on each side. Conversely when a voltage is applied to it, it creates a temperature difference (known as the Peltier effect). At atomic scale (specifically, charge carriers), an applied temperature gradient causes charged carriers in the material, whether they are electrons or holes, to diffuse from the hot side to the cold side, similar to a classical gas that expands when heated; hence, the thermally-induced current.
This effect can be used to generate electricity, to measure temperature, to cool objects, or to heat them or cook them. Because the direction of heating and cooling is determined by the sign of the applied voltage, thermoelectric devices make very convenient temperature controllers.
Traditionally, the term thermoelectric effect or thermoelectricity encompasses three separately identified effects, the Seebeck effect, the Peltier effect, and the Thomson effect. In many textbooks, thermoelectric effect may also be called the Peltier–Seebeck effect. This separation derives from the independent discoveries of French physicist Jean Charles Athanase Peltier and Estonian-German physicist Thomas Johann Seebeck. Joule heating, the heat that is generated whenever a voltage is applied across a resistive material, is somewhat related, though it is not generally termed a thermoelectric effect (and it is usually regarded as being a loss mechanism due to non-ideality in thermoelectric devices). The Peltier–Seebeck and Thomson effects can in principle be thermodynamically reversible, whereas Joule heating is not.