Extensive Chemical Modification Research Articles

Characterization of biomass pyrolysis tars produced in the relative absence of extraparticle secondary reactions

Product distributions from the atmospheric pressure pyrolysis of sugar-cane bagasse and silver birch were determined in a wire-mesh reactor as a function of temperature (300–900 °C) and heating rate (1–1000 K s −1), over a range of holding times between 0 and 100 s. Major groups of components present in the tars were identified by g.c.-m.s.. Above 500 °C when increasing the heating rate from 1 to 1000 K s −1 in experiments using holding times longer than several seconds, tar yields were observed to increase by about 10 wt% to nearly 54% w/w daf bagasse; total volatile yields increased by similar amounts. Number average molecular masses ( MM n ) of tars determined by vapour pressure osmometry (v.p.o.) were in the range 150–250 Da, those of silver birch tars being systematically larger than those of sugar-cane bagasse by 15–30 Da. For both sets of tars, MM n were observed to decrease with increasing temperature between 400 °C and 600 °C, but remained unchanged between 600 °C and 900 °C. The molecular masses were also observed to decline with increasing heating rate. Lignocellulosic substrates appear to cleave readily to give relatively small, compact and relatively stable molecules able to evaporate completely at temperatures around 500 °C. Extensive chemical modification of primary products appears to result from intraparticle secondary reactions, these reactions being intensified during pyrolysis at higher heating rates. Whilst the wire-mesh reactor configuration appears not to alter tar yields or structures subsequent to release from parent substrate particles, comparison with tars obtained at 600 °C in a ‘hot-rod’ (fixed-bed) reactor suggests that whilst overall yields may be adversely affected and the relative abundance of some major components altered, extraparticle secondary reactions do not substantially change the character of the tar at this temperature.

Phthalocyanine and Its Polymers

Abstract Copper and metal free phthalocyanines are wide band gap semiconductors with remarkable chemical and thermal stability, giving them device potential. Extensive structural and chemical modifications are required to achieve the necessary improvement in carrier mobility, control of electronic properties, and processability. In this paper some of the important developments in modifying the properties of phthalocyanines by chemical modification and polymerisation are reviewed. New results are reported in the μ-bridged phthalocyanines, including doping by ion implantation, band width determination by plasma absorption spectroscopy, and the influence of gases on the Seebeck coefficient. Infra-red photoconduction in two-dimensional polymers using light chopped at variable frequency is also reported.

Chemical development of astemizole‐like compounds

AbstractNewly synthesized diphenylbutylpiperidine derivatives were devoid of neuroleptic activity but were moderately active histamine antagonists in vitro. Their structural relation to classical antihistamines was not evident, but the requirement of a piperidino‐2‐aminobenzimidazole core was confirmed by the synthesis of R 39848, which was more potent. About 500 new compounds related to R 39848 were synthesized by varying in particular the alkyl and aralkyl groups implanted on the piperidine, benzimidazole, and bridging amine nitrogen. Potency, oral activity, and long duration of action in the compound 48/80 lethality test in rats prompted the selection of R 43512 (astemizole) for detailed pharmacological studies. Antiallergic specificity and lack of central effects were the conclusions of all studies, and the higher clinical effectiveness of astemizole was in agreement with a dosage that is not limited by central or other side effects. More extensive chemical modifications of the astemizole molecule were explored, and it is possible that some recent compounds may either have an increased antiallergic effectiveness (R 57959) or be useful in other indications because of a different profile of peripheral actions.

Kinetics of cholesterol and phospholipid exchange between Mycoplasma gallisepticum cells and lipid vesicles. Alterations in membrane cholesterol and protein content.

The kinetics of exchange of radiolabeled cholesterol and phospholipids between intact Mycoplasma gallisepticum cells and unilamellar lipid vesicles were investigated over a wide range of cholesterol/phospholipid molar ratio. The change in cholesterol/phospholipid molar ratio was achieved by adapting the sterol-requiring M. gallisepticum to grow in cholesterol-poor media, providing cells with decreased unesterified cholesterol content. At least 90% of the cholesterol molecules in unsealed M. gallisepticum membranes underwent exchange at 37 degrees C as a single kinetic pool in the presence of albumin (2%, w/v). However, we observed biphasic exchange kinetics with intact cells, indicating that cholesterol translocation from the inner to outer monolayers was rate-limiting in the exchange process. Approximately 50% of the cholesterol molecules were localized in each kinetic pool, independent of the cholesterol/phospholipid molar ratio in the cells and vesicles. A striking change in the kinetic parameters for cholesterol exchange occurred between 20 and 26 mol % cholesterol; for example, when the cholesterol/phospholipid molar ratio was decreased from 0.36 to 0.25, the half-time for equilibration of the two cholesterol pools at 37 degrees C decreased from 4.6 +/- 0.5 to 2.5 +/- 0.1 h. Phospholipid exchange rates were also enhanced on decreasing the membrane cholesterol content. The ability of cholesterol to modulate its own exchange rate, as well as that of phospholipids, is suggested to arise from the sterol's ability to regulate membrane lipid order. Extensive chemical modification of the membrane surface by cross-linking of some of the protein constituents with 1,4-phenylenedimaleimide decreased the cholesterol exchange rate. Depletion of membrane proteins by treatment of growing cultures with chloramphenicol increased the cholesterol exchange rate, possibly because of removal of some of the protein mass that may impede lipid translocation. The observations that phospholipid exchange was one order of magnitude slower than cholesterol exchange and that dimethyl sulfoxide, potassium thiocyanate, and potassium salicylate enhanced the cholesterol exchange rate are consistent with a mechanism involving lipid exchange by diffusion through the aqueous phase.

Chemical modification potentiates the biological activities of 2-5A and its congeners.

Chemical modification of p5'A2'(p5'A2')np5'A by a periodate oxidation/Schiff base formation/borohydride reduction cycle gave a series of 2-5A analogues in which the ribose of the 2'-terminal nucleotide was transformed to an N-substituted morpholine (azahexapyranose). 2',5'-Oligoriboadenylate 5'-monophosphates bearing this modification were 5-10 times more potent as antagonists of the action of 2-5A or poly(I).poly(C) than was unmodified p5'A2'p5'A2'p5'A. Application of this modification to the tetramer triphosphate ppp5'A2'p5'A2'p5'A2'p5'A resulted in an analogue with 10 times the activity of ppp5'A2'p5'A2'p5'A (2-5A trimer triphosphate) as an inhibitor of protein synthesis or activator of the 2-5A-dependent endoribonuclease. This activator of the 2-5A-dependent endoribonuclease. This new 2-5A analogue, the most potent 2-5A derivative reported to date, inhibited translation in extracts of mouse L-cells programmed with encephalomyocarditis virus RNA at a concentration of 10(-10) M (concentration for half-maximal inhibition). All such N-substituted morpholine modified 2',5'-oligoriboadenylates were found to be extremely resistant to degradation by L-cell extracts under conditions where unmodified 2-5A or its derivatives were quickly destroyed. These data demonstrate the necessity for an intact terminal ribose ring for the action of the 2-5A phosphodiesterase. Thus, extensive chemical modification of 2' terminus of 2-5A may be possible without adversely affecting its biological activity while endowing it with other favorable properties such as resistance to degradation.

The Efficacy of 4-Amino-6-Trichloroethenyl-1,3-Benzenedisulphonamide Against Liver Fluke in Sheep and Cattle

Extensive chemical modification and biological testing of benzenesulphonamides resulted in the selection of 4-amino-6-trichloroethenyl-1,3-benzenedisulphonamide as the most promising fasciolicide in this series. Dosages of 10 and 15 mg/kg were 97 and 92% effective against immature liver flukes in calves and sheep respectively. Mature flukes in both sheep and cattle were removed by a single dose of 3 · 75 mg/kg.

Structural relationships of sugars to taste.

Chemical modification of sugars and their simple analogues indicates that these types of compound are almost always sweet, bitter, or bitter/sweet; hence, the two basic tastes may be intimately associated features of the same molecule. Stepwise modification at each chiral center around the sugar ring allows the sapid functions in these molecules to be mapped and leads to the inescapable conclusion that sugar molecules may be "polarized" on taste bud receptors, so that one end of the molecule elicits sweetness and the other bitterness. However, more extensive chemical modification evidently causes the molecule to realign itself in entirely different ways on the receptor. In most oligosaccharides only one sugar residue is likely to bind to the taste receptor, and this is probably a nonreducing end group, because the anomeric center of glucopyranose types of structure does not appear to affect sweetness. Sweetness depresses bitterness and bitterness depresses sweetness. Hence, it is not possible to make structural comparisons between analogues without correcting for these effects. However, some semiquantitative studies have established the value of current hydrogen bond theories of sweetness and the ideal oxygen-oxygen interorbital spacings for sweetness criteria in sugar molecules.

The reaction of sulphuric acid with lysozyme and horse globin.

Lysozyme and horse globin have been treated with concentrated sulphuric acid to produce the N→O acyl shift. Results showed the reaction to be incomplete. Extensive chemical modification of the tyrosine, phenylalanine, tryptophan, and cystine residues occurs. Peptides obtained by degrading the modified protein with hydroxylamine could not be resolved either by paper chromatography or paper electrophoresis.