Acid studies

The AMBER and CHARMM force fields are best suited for protein and nucleic acid studies. 

Case a, i is well illustrated by the arsenite-induced oxidation of manganese(II) by chromic acid, studied by Lang and Zwerina. The overall equation of this induced reaction is... 

In 1962 Olah repotted the NMR spectrum of the t-butyl cation in superacid solution, [1] and NMR was thenceforth the ex rimental method of choice for studies of intermediates in solution acid chemistry. The inhomogeneous nature and diversity of solid acid systems will ensure that no one experimental technique will so completely dominate as NMR has in solution studies, but the contributions and potential of NMR to solid acid studies are clearly such as to put it on an equal footing with reaction studies, infrared, TPD, diffraction methods and calorimetry. 

Wolter O, Heitbaum J. 1984. The adsorption of CO on a porous Pt-electrode in sulfuric acid studied by DEMS. Ber Bunsenges Phys Chem 88 6-10. 

The potential for coordination depends on the oxy substituents.82 Alkoxy substituents are usually chelated, whereas highly hindered silyloxy groups usually do not chelate. Trimethylsiloxy groups are intermediate in chelating ability. The extent of chelation also depends on the Lewis acid. Studies with a-alkoxy and (3-alkoxy aldehydes with lithium enolates found only modest diastereoselectivity.83... 

W.J. Muizebelt, M.W.F. Nielen, Oxidative crosslinking of unsaturated fatty acids studied with mass spectrometry, Journal of Mass Spectrometry, 31, 545 554 (1996). 

M.P. Colombini, R. Fuoco, A. Giacomelli, B. Muscatello, Characterization of Proteinaceous Binders in Wall Painting Samples by Microwave Assisted Acid Hydrolysis and GC MS Determination of Amino Acids, Studies in Conservation, 43, 33 41 (1998). 

The Mechanism of the Oxydation of Uric Acid Studied with Isotopic... 

Solutions of Ru3(CO)i2 in carboxylic acids are active catalysts for hydrogenation of carbon monoxide at low pressures (below 340 atm). Methanol is the major product (obtained as its ester), and smaller amounts of ethylene glycol diester are also formed. At 340 atm and 260°C a combined rate to these products of 8.3 x 10 3 turnovers s-1 was observed in acetic acid solvent. Similar rates to methanol are obtainable in other polar solvents, but ethylene glycol is not observed under these conditions except in the presence of carboxylic acids. Studies of this reaction, including infrared measurements under reaction conditions, were carried out to determine the nature of the catalyst and the mechanism of glycol formation. A reaction scheme is proposed in which the function of the carboxylic acid is to assist in converting a coordinated formaldehyde intermediate into a glycol precursor. 

Finally, in many cases the acidity equilibria cannot be measured but the rate of proton transfer or transmetallation can be measured to give an ionic or ion pair kinetic acidity. Studies using the rates of proton transfer have included the use of isotopes such as tritium and deuterium5,6. The rate is then used to calculate the Brpnsted slope, a, by plotting the logarithm of the proton transfer rate against the pK, as determined by the equilibrium acidity, for a series of compounds. From this plot, the approximate pKa of an unknown compound can be determined by comparison of the same type of compounds. 

The combination of dicyclopentadienylzirconium dichloride and silver perchlorate activates armed glycosyl sulfoxides in dichloromethane between -20 °C and room temperature, but only very simple acceptors were studied [335]. Other Lewis and Bronsted acids studied include the environmentally benign europium, lanthanum and ytterbium triflates [336], certain polyoxometallates [337], sulfated zirconia [338] and Nafion H [338]. 

Abate G, Masini JC. Complexation of Cd(II) and Pb(II) with humic acids studies by anodic stripping voltammetry using differential equilibrium functions and discrete site models. Org. Geochem. 2002 33 1171-1182. 

Except for phthalic acid, all other carboxylic acids studied induce considerable increases in the light compared to the dark values (the relatively high rate of iron oxide dissolution induced by oxalic acid has been extensively studied (5,8). Phthalic acid actually appears to stabilize the iron oxide against photodissolution despite the solution phase complex exhibiting some photoactivity. 

NMR properties, 33 213, 274 in sheet silicate studies, 33 128-137 for zeolite acidity studies, 33 275-279 Hydrogen sulfide... 

Prins reaction, heteropolyacid catalysis, 41 156 Probe molecules, 42 119 acidic dissociation constant, 38 210 NMR solid acidity studies, 42 139-140 acylium ions, 42 139, 160 aldehydes, 42 162-163 alkyl carbenium ions, 42 154-157 allyl cation, 42 143-144 ammonia, 42 172-174 arenium ions, 42 150-154 carbonium ions, 42 157-160 chalcogenenonium ions, 42 161-162 cyclopentenyl cations, 42 140-143 indanyl cations, 42 144-147 ketones, 42 162,163-165 nitrogen-containing compounds, 42 165-170... 

The lowfield sense of nonequivalence for the methyl doublet of methylphenylphosphinothioic acid studied by Harger (71) is readily... 

Bylund J, Kunz T, Valmsen K, Oliw EH. 1998. Cytochromes P450 with bisallylic hydroxylation activity on arachidonic and linoleic acids studied with human recombinant enzymes and with human and rat liver microsomes. J Pharmacol Exp Ther 284 51-60. 

Despite considerable biochemical work, high-resolution crystal structure determination of native RNase A and S, and some medium-resolution studies of RNase A-inhibitor complexes, a number of questions existed concerning the details of the catalytic mechanism and the role of specific amino acids. Study of the low-temperature kinetics and three-dimensional structures of the significant steps of the ribonuclease reaction was designed to address the following questions. 

Ruthenium(III) catalyses the oxidative decarboxylation of butanoic and 2-methylpropanoic acid in aqueous sulfuric acid. ° Studies of alkaline earth (Ba, Sr) metal alkoxides in amide ethanolysis and of alkali metal alkoxide clusters as highly effective transesterification catalysts were covered earlier. Kinetic studies of the ethanolysis of 5-nitroquinol-8-yl benzoate (228) in the presence of lithium, sodium, or potassium ethoxide revealed that the highest catalytic activity is observed with Na+.iio... 

Before entering the perraeator for salt removal, the feed is either acidified or modified with proprietary chemicals for scale control. While both approaches have their followers, despite its handicaps, acid dosing today appears predominant in the industry in fact some RO permeator manufacturers will only warranty their product for acid. Studies to be initiated shortly at our laboratory should hopefully quantitatively evaluate the relative merits of these approaches. It is hoped that at least equivalence if not superiority for proprietary scale control chemicals will be unequivocally established so that one can drop acid use and satisfy many who are justifiably reluctant to use acid, for reasons familiar to all. 

Vibrational spectroscopy of adsorbed probe molecules is one of the most powerful tools to assess the acidic properties of catalysts. Acidity studies of dealumi-nated Y zeolites (main active component of FCC catalysts) or other zeolitic catalysts are reported using mostly Fourier Transform Infrared Spectroscopy (FTIR) with CO adsorption at 77 K or FTIR-pyridine/substituted pyridines adsorption at 425 K [22-26]. FTIR acidity studies of commercial FCC catalysts are even more scarce... 

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