Science the silicon crystal surface, Yin says, although an experiment could be designed using EXAFS (extended x-ray absorption fine structure spectroscopy) that would show whether the predicted silicon-silicon bond length is correct. The Berkeley workers are not planning to do this experiment. Instead, they want to push their study of surfaces to transition metal systems because of their importance in many catalytic processes. The researchers see other applications of the theoretical model to the study of semiconductors and electron-lattice interactions in superconductivity. Rebecca Rawls, Washington
Chemical data support archaeological theory An anthropologist from the U.S. and an archaeologist and a chemist from South Africa believe they can show that maize became an important cultivated crop and staple in the diet of peoples in the Amazon River region of South America between about 800 BC and 400 AD. This conclusion is contrary to the prevailing view that maize was not important to the prehistoric peoples of the Amazon basin. The team is composed of Nikolaas J. van der Merwe, an archaeologist at the University of Capetown, South Africa; Anna C. Roosevelt of the Museum of the American Indian, New York City; and J. C. Vogel of the National Physical Research Laboratory of South Africa in Pretoria. Their findings are published in a recent issue of Nature [292, 536 (1981)]. Although there are some archaeological relics that support the notion that people living in this region ate maize, most of the data on which the researchers base their case are chemical and come from studying carbon isotope ratios in the skeletons of prehistoric people in the Orinoco River valley in Parmana, Venezuela. The gist of the chemical argument is that in maize, carbon dioxide initially is laid down in plant material in four-carbon carboxylic acids, rather than as the three-carbon phosphoglyceric acid found in most food plants. The carbon compounds found in C4 plants have a different 13 C/ 12 C ratio from those in C3 plants, and this difference is transmitted to animals that depend on maize as their major carbon source. Thus, if maize, or some other C4 plant, was a major source of 36
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food for the people of the Parmana area or for their livestock, the parts of their remains that contain carbon will show a skewed 13 C/ 12 C ratio that is characteristic of carbon from C4 plants. The researchers examined the bone collagen of the remains of humans who lived in the Parmana area during three different periods—2100 to 800 BC, 800 BC to 400 AD, and 400 to 1500 AD—using a mass spectrometry technique. The results show a substantial shift during the middle period from a predominately C3 diet to a diet that contained 80% or more C 4 foods. Such an argument does not prove that it was maize and not some other C4 plant that these early peoples were eating. The researchers also have investigated the plants that grow in the Amazonian ecosystem and find that, besides maize, there are a few C4 grasses there that provide food for certain small mammals. These mammals are too small, however, to make it likely that they ever comprised 80% of the diet of humans living in the region. There are carbonized plant remains that show that maize was known in the region during the period, and there are samples of grinding tools that could have been used to grind maize. Thus, the researchers argue, the most likely source of the C4 plants in these people's diet is maize, and to provide 80% of their diet it must have been cultivated. Other archaeological evidence indicates that the population of the Parmana region grew 15-fold during the period from 800 BC to 400 AD. This great increase in the concentration of people in this region, and the subsequent development of a complex society there could have come about because the people had learned to cultivate maize as their major food source, the researchers conclude. D
Proton NMR probes intact red blood cells Proton nuclear magnetic resonance spectra for small molecules inside intact red blood cells can be obtained using a technique that eliminates many of the numerous and interfering signals produced there by hemoglobin protein molecules. These spectra then can be used to interpret intracellular processes. Chemistry professor Dallas L. Rabenstein, of the University of Alberta in Edmonton, described such re-
Rabenstein: eliminate envelope
search to the 28th Congress of the International Union of Pure & Applied Chemistry in Vancouver, B.C. Rabenstein, postdoctoral fellow Anvar A. Isab, and graduate students David W. Brown and R. Steven Reid use a double-pulsed, Fourier transform NMR technique to obtain the spectra. According to Rabenstein, the spectra from a simple Fourier transform NMR experiment on red blood cells is a relatively featureless envelope that yields no information on individual molecular species. The envelope is due to the large number of proton resonances from the hemoglobin molecule. "What we have to do," Rabenstein says, "is eliminate the envelope to obtain individual peaks on which to focus." Rabenstein takes advantage of differences in spin-spin relaxation time, which are designated T2. The shorter T 2 is, the faster the NMR signals from that molecule decay. T2 is a function of a number of parameters, Rabenstein says, one of which is molecular size. Hemoglobin, with a molecular weight of about 65,000, has a much shorter T2 than many smaller molecules of interest with molecular weights between 100 and 400. Rabenstein uses two pulses with a 60-millisecond delay between the first and second pulse, which is directed opposite to the first pulse. Data are taken 60 milliseconds after the second pulse. According to Rabenstein, the first pulse orients the proton nuclei, and the second pulse acts to focus the nuclei of interest. Because spin-spin relaxation for hemoglobin protons is much faster than for protons on
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Our Anhydrous Sulfolane is a highly-polar compound useful as a plasticizer and as a rea c t i o n solvent in the production of pharmaceuticals and specialty chemicals. As a major supplier, with major resources behind us, you can count on Phillips expert feedstock control to give you high quality and assured supply. For a copy of our fullcolor Hydrocarbons and Sulfur Chemicals Price List #24, write on your company letterhead to 14C4 Phillips Building, Bartlesville, OK 74004. Overseas inquiries should be directed to N. V Phillips Petroleum Chemicals SA., Schoonhees, B-3980 Tessenderlo, Belgium.
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C&ENAug. 31, 1981
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Phillips has your Sulfur Chemical Mercaptans Ethyl mercaptan η-Propyl mercaptan iso-Propyl mercaptan η-Butyl mercaptan sec-Butyl mercaptan iso-Butyl mercaptan tert-Butyl mercaptan n-Hexyl mercaptan Cyclohexyl mercaptan n-Octyl mercaptan tert-Octyl mercaptan tert-Nonyl mercaptan n-Dodecyl mercaptan tert-Dodecyl mercaptan tert-Tetradecyl mercaptan tert-Hexadecyl mercaptan tert-Mixed mercaptans (C», C12) (C12, C 14 , L i e )
2-Mercaptoethanol Benzyl mercaptan Sulfides Ethylthioethanol Di-n-butyl sulfide Di-tert-butyl sulfide Ethylthioacetate Phenylthioethanol
Science smaller molecules, the signals from the hemoglobin protons have decayed completely by the time the spectrum is taken. The result, Rabenstein says, is an NMR spectrum with observable peaks from a number of molecules including glucose-free glycine, ala nine, and glutathione. Rabenstein uses two peaks from glutathione to study the binding of methylmercury in red blood cells and how various drugs affect that binding. Methylmercury is highly toxic. Ac cording to Rabenstein, about 10% of the body burden of methylmercury is in the blood and, of that, about 90% is in the red blood cells. Glutathione is an amino acid with a sulfhydryl group that forms a complex with methyl mercury, and this causes a chemical shift in the resonance signal from a
Technology
Methane reforming to stay key hydrogen source
Disulfides Di-tert-butyl disulfide Di-tert-dodecyl disulfide Di-n-butyl disulfide Polysulfides Di-tert-butyl polysulfide Sulfones Sulfolane (anhydrous) Sulfolane-W Sulfolene New Developmental Sulfur Chemicals From Phillips: We can now produce developmental to commercial quanti ties of Di-n-propyl and Di-sec-butyl disulfides, Ethanedithiol, Thiodiglycol and Di-tert-nonylpolysulfide.
Future production of hydrogen, whether for making conventional chemicals or for high-volume use as a fuel, seems limited to those processes already in existence, unless some major technological breakthrough appears. A projection by Thomas Whaley, research manager in the In stitute of Gas Technology's energy systems department in Chicago, supports the belief that even in the beginning of the next century steam reforming of methane will remain the process of choice—with a coal-based process becoming firmly lodged in second place. After that follow numerous spe cialty processes that have significant, if smaller, contributions to make to hydrogen production, Whaley told the summer national meeting of the
PHILLIPS CHEMICAL
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American Institute of Chemical En gineers in Detroit. Despite somewhat diminished enthusiasm for water splitting via nuclear-heat-driven processes, the search continues for an efficient thermochemical scheme. High-temperature steam electrolysis in a fusion reactor is the newest sug gestion. . Catalytic steam reforming of light hydrocarbons, particularly methane, is now the least costly way of pro ducing large volumes of hydrogen when natural gas is readily available. If higher-molecular-weight hydro carbons are used, cost increases ac cordingly, but is still low. Hydrogen purity of 93% is good enough for ammonia production, the chief consumer of hydrogen at present, Whaley points out. For other
Steam reforming is cheapest route to hydrogen Process
Steam reforming Partial oxidation Partial oxidation Steam-irona Electrolysis, conventional Electrolysis, solid polymer electrolyte
A S U B S I D I A R Y OF PHILLIPS P E T R O L E U M
proton bound to a carbon near that group. "The rate of exchange of methyl mercury on and off glutathione's sulfhydryl group is sufficiently rapid that there is always only one signal," Rabenstein says. "The position of that resonance is a linear function of the amount of complex formed." Rabenstein says his data show that methylmercury binds at least six times more strongly to glutathione than to hemoglobin, which also con tains sulfhydryl groups. By adding various compounds to "poison" red blood cells and observ ing the effect on the resonance posi tion, Rabenstein can evaluate the potential of the compounds as agents for treating methylmercury poison ing. Π
Feedstock/raw material cost
Methane/$2.00 per million Btu Residual oil/$2.35 per million Btu Coal/$1.17 per million Btu Coal/$1.00 per million Btu Water/3 cents per kWh Water/3 cents per kWh
Thermal efficiency
Hydrogen cost, $ per 1000 standard cu ft
74% 83
$1.61 2.69
$ 4.76 8.23
3.66 2.56 6.83 4.45
11.20 7.84 20.90 13.62
59 63 76b 78b
Hydrogen cost, $ per million Btu
a Includes 2 cents per kWh credit for by-product electric power, b Electric power to hydrogen (does not include the efficiencies involved in generating electricity). Note: Based on 100 million standard cu ft per day of hydrogen; 90% stream factor. Source: Institute of Gas Technology
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