Well-graphitized synthetic

The hetero-DA reaction with azadienes, a well known synthetic method for obtaining nitrogen heterocycles, suffers from some difficulties, because of the low reactivity of the diene. For example, azadiene 2 did not react with DMAD under the action of conventional heating [22], Sequential exposure to MW irradiation (30 W) for 10 min on a graphite support (Tmax = 171 °C) led to the adduct 7 with 60% conversion (50% in isolated product) [26, 27]. An equivalent yield was obtained by ultrasonic irradiation of the neat reaction mixture at 50 °C for 50 h [29]. 

In the solid state, three allotropes of carbon (diamond, graphite, and fullerene Fig. 1) are well-established. Synthetic approaches to other carbon allotropes, including poly-ynes, cvclo[ ]carbons and other carbon networks have been surveyed.1 The chemistry of fullerenes, the so-called third form of carbon, and of the closely related carbon nanotubes, has been extensively detailed.2 4 The molecule C2o may be the smallest fullerene, although other structures have been suggested (Fig. 2).5 It is highly reactive and has been produced in only miniscule amounts in a mass spectrometer from a highly brominated dodecahedrane. 

During the next 15 years there were a number of additional innovations in the application of HPHT technology to the synthesis of industrial superabrasives, virtually all of which were pioneered by GE—the Superabrasives business working in close collaboration with the Corporate Research and Development laboratory. In 1956, Wentorf synthesized cubic boron nitride (cBN). Boron nitride does not exist in nature, but the hexagonal form of BN, which has a structure very similar to that of graphite, was a well known synthetic material. The second-hardest material known, cBN has much better abrasion resistance with ferrous alloys and oxidation resistance than diamond. The best catalyst-solvents for cBN synthesis are alkali- and alkaline-earth nitrides and related inorganic salts. GE introduced cBN commercially in 1969 under the tradename Borazon cBN. 

Natural phospholipids, sterols, glycopepetides, lipopeptides, polyether lipids, and sulfo-lipids, as well as synthetic amphiphiles and even certain silanes, can assemble to form bilayer lipid membranes (BLMs), which can be free or supported on mercury, gold, silver, graphite, clay, etc. [121-123]. Amphiphilic membrane proteins and soluble proteins mod-... 

Other advances in material science have helped humans mimic nature in the production of certain materials. For example, in the last half of the twentieth century we have learned how to produce synthetic diamonds. Diamonds were first produced commercially in the 1950s by General Electric by subjecting graphite to temperatures of 2,500°C and pressures approaching 100,000 atmospheres. Currently, well over a hundred companies produce synthetic diamonds. 

The necessary atomic mobility can be provided by heating to about 1500 K (area D in Fig. 1). Various departures from ideality make it difficult to prepare pure wurtzitic carbon, even when the best graphite is used. The products obtained so far always contain some ordinary diamond as well as remnant graphite, parts of which are compressed by the nearby diamond regions. Hence, many physical properties of wurtzitic carbon are not well-known. It has been found in the Canyon Diablo meteorite and in some shock-made diamond from DuPont, but not in regular synthetic industrial diamond. This form of carbon has been given the name lonsdaleite. 

Because of the complex behaviour to be expected for natural nucleic acids, it is only natural that considerable effort has been devoted to studies of the electrochemical properties of their monomeric units, and defined analogues of these, as well as of synthetic oligo- and polynucleotides. A variety of techniques has been applied for this purpose, and some of the details and findings are covered in several reviews 19 24). Most investigations have dealt with electroreduction processes 15 20,24,25). Only relatively recently has attention been directed to possible electrooxidation of nucleic acids and their constituents with the aid of the graphite electrode which, in comparison with the mercury electrode, possesses a much greater accessible range of positive potentials 26 29). 

---