Showing papers on "Reactivity (chemistry) published in 1973"

Conjugates of Immunoglobulin G with Different Fluorochromes. I. Characterization by Anionic‐exchange Chromatography

Abstract: The conjugation of purified IgG for 1 hour at room temperature and pH 9.5 was found to be a simple and reproducible method useful with FITC. MRITC. RBITC and RB200SC fluorochromes. Anionic-exchange chromatography revealed some difference between conjugates with two batches of FITC and with two batches of MRITC from the same commercial source. Storage of FITC and MRITC as dry powders had only a minor deleterious effect. These fluorochromes as well as fresh solutions of RB200SC produced satisfactory conjugates; but reliable information about their properties could only be obtained from chromatographic analyses. High-affinity reactions apparently gave rise to optimum conjugates and depended on addition of small amounts of fluoruchrome; increased amounts of fluorochrome favoured low-affinity reactions with resulting over-coupling. This was a problem mainly with FITC and RB200SC. RBITC as well as aged solutions of RB200SC produced undue reduction in the isoelectric point of IgG relatively to degree of coupling. Species differences in IgG were found to influence the reactivity of FITC and MRITC.

Kinetics of diffusion-controlled reaction between chemically asymmetric molecules. II. Approximate steady-state solution

Abstract: The previously published equation for the rate of a diffusion-limited bimolecular reaction between chemically asymmetric molecules is studied numerically for the case that one of the reactant molecules is uniform. The results are reproduced quite well by a simple approximate chemical-kinetic steady-state scheme and, in principle, allow estimates of the size of the reactive region and of the activation-controlled rate to be made from the observed dependence of rate on solvent viscosity. The simple scheme is easily generalized to the case of two nonuniform reactants. In general, restriction of reactivity to some fraction of the molecular surface (i.e., a steric factor) must reduce the observable reaction rate, but to an extent which is moderated by the rotational diffusion of the reactant molecules.

Reactivity of co-ordinated ligands. Part XV. Formation of complexes containing Group V donor atoms and metal–carbon σ-bonds

Abstract: The reactions of various palladium(II) and platinum(II) species with a number of ligands which may function as electron pair donors while simultaneously forming metal–carbon σ-bonds have been examined. Compounds containing metal–carbon σ-bonds have been obtained for NN-2-trimethylbenzylamine, N-benzylpiperid-4-one, 1-phenyl-NN-dimethylcyclohexylamine, triphenylmethylamine, N-methyltriphenylmethylamine, benzophenone phenylhydrazone, and benzo[h]quinoline. Various substitution and displacement reactions of some similar derivatives have also been examined.

Reactivity and interface characteristics of titanium-alumina composites

Abstract: The reaction kinetics between α-Ti alloys and single crystal sapphire, the phase composition and morphology of the reaction-zone, and the phase compatibility in the system Ti-Al-O were investigated as part of a study to determine the feasibility of fabricating useful Al2O3-reinforced titanium matrix composites. In the temperature range 650 to 1000° C titanium reduces Al2O3 to form a complex reaction layer consisting of two distinct zones; an inner zone adjacent to the Al2O3 of a TiO phase containing isolated particles of (Ti, Al)2O3, presumably, and an outer zone of a Ti3Al phase adjacent to the Ti matrix. The isothermal growth of the reaction layer follows a parabolic rate law. The temperature dependence of the rate constants fits an Arrhenius equation yielding activation energies of 50 to 52 kcal/mol. The high Al alloys, except Ti-6Al-2Sn-4Mo-2Zr, reacted more rapidly than pure Ti indicating that Al diffusion through the reaction zone may be the rate-limiting step.

The meso-reactivity of porphyrins and related compounds. Part VI. Oxidative cleavage of the haem system. The four isomeric biliverdins of the IX series

Abstract: The oxidative cleavage of haemin in aqueous pyridine under various conditions (ascorbic acid–oxygen; hydrazine–oxygen; and ascorbic acid–hydrogen peroxide) gives four isomeric biliverdins of the IX series which have been isolated (from a much improved ascorbic acid–oxygen reaction) as their crystalline dimethyl esters. The properties of the four isomers are described. On the basis of mass and n.m.r. spectra, structures are assigned to all four isomers for the first time. A key observation in the n.m.r. spectra of these compounds is the chemical shift of the heteroaryl methyl group. The implications of these results are discussed.

Formation and cure of novolacs: NMR study of transient molecules

Abstract: High-resolution magnetic resonance spectroscopy has been used to investigate three areas of novolac resin chemistry: first, the lifetimes of glycol species in formalin under acid and base conditions and the reactivity of methylene glycol towards alcohols; second, the in situ identification of novolac resin intermediates; third, the novolac–hexamethylenetetramine cure mechanisms. It is shown that the mean lifetime of a given glycol species is an order of magnitude shorter under basic conditions than under an acid of equal normality. The ratio of the equilibrium constants for the addition of methylene glycol to methanol, benzyl alcohol, and phenol was measured as 70:20:1. New reactive intermediates were discovered while monitoring the reaction of phenol and formalin. The reactions of various phenols with hexamethylenetetramine were studied, and short-lived benzoxazines were detected at 100–120°C whenever ortho hydrogen was available on the phenolic nucleus. The NMR peak assignments in the reaction sequence: benzoxazine, dibenzylamine, tribenzylamine, diphenylmethane are presented. Spectra of the very elusive p-benzylamines of 2,6-xylenol were recorded at 100–155°C. At 170°C, the lifetimes of these p-benzylamines are too short to afford proton resonance spectra. No evidence of hexahydrotriazine or (CH2 = N-CH2)3N type structures was found in 100 MHz NMR spectra of reaction mixtures of a phenol and hexamethylene-tetramine.

Pulse radiolysis of dithiothreitol.

Abstract: Dithiothreitol has been used in model experiments to investigate its free radical reactivity in relation to its properties as a radioprotector. Absolute rate constants for the reaction of this sulf...

Cyclooligomerization with Transition Metal Catalysts

Abstract: This report is concerned not only with the syntheses of new ring systems and the preparation of derivatives of known rings but also with new types of catalysts based upon, e. g., nickel, iron, molybdenum, manganese, and palladium. The broad applicability of the methylene insertion reaction as a method for identifying mono- and di-methyl-substituted eight-, ten-, and twelve-membered rings is also demonstrated. A further section is concerned with the possible mechanism of CC bond formation in transition metal complexes; several earlier suggestions have been revised in the light of new experimental data. In addition, experimental results are discussed which indicate that the reactivity and selectivity of the complexes formed by the nickel-ligand catalyst and olefins or alkynes depend upon the structure of the ligands.

Thermally stable polymers derived from 2,3,5,6‐tetraaminopyridine

Abstract: The stable trihydrochloride salt of 2,3,5,6-tetraaminopyridine (TAP) has been found to be a versatile intermediate to a variety of thermally stable polymers such as polybenzimidazoles (PBI), polyimidazopyrrolones (pyrrones), and polybenzimidazobenzophenanthroline (BB polymer). The controlled reactivity of two of the four amino sites of TAP · 3HCl towards diacid halides and dianhydrides makes possible the preparation of high molecular weight, soluble polyamide prepolymers at mild temperatures. PBI, pyrrones, and BB polymer are obtained from the linear polyamide precursors by heating at 150–375°C. Unoptimized cyclized polymers were aged isothermally in air at 600°F (316°C) and found to be superior to analogous polymers described in the literature. Weight retentions of up to 97% were observed after 500 hr in air at 600°F.

Mechanism of reaction of carbon monoxide with phenyllithium

Abstract: The product mixtures obtained by reaction between phenyllithium and carbon monoxide in diethyl ether, followed by hydrolysis, include benzophenone (1). a,a-diphenylacetophenone (2), benzil (3), a,a-diphenyl- a-hydroxyacetophenone (4), benzpinacot (5), a-hydroxyacetophenone (6), 1,3,3-triphenylpropane-1,2-dione (7), 1,3,3-triphenylpropan-1-one-2,3-diol (8). and benzhydrol (9). Compounds 1, 2, 6,7, and 8 are produced in signifi- cant yields i 3,4,5, and 9 are produced in trace quantities. Spectroscopic studies establish dilithium benzophenone dianion (18) as the first long-lived intermediate formed in this reaction; qualitative correlations between the basicity of a number of organolithium reagents and their reactivity toward carbon monoxide suggests, but does not prove, that benzoyllithium is a precursor of 18. Labeling experiments indicate that the products ultimately isolated following hydrolysis of the reaction mixture are derived from at least two pathways which compete for the initially formed 18. One involves combination of l8 with 1 equiv of phenyllithium and 1 equiv of carbon monoxide, followed by elimination of I equiv of lithium oxide. yielding 17, the lithium enolate of 2; a second involves com- bination of 18 with 1 equiv of phenyllithium and 2 equiv of carbon monoxide. yielding 22,the trilithium trianion of 8. Hydrolysis of l7 yields 2 directly. Hydrolysis of 22 yields 8; reverse aldol reactions involving 8 or its pre- cursors generate 1 and 6. The mechanism proposed to account for the major products of the reaction of phenyl- lithium and carbon monoxide is outlined in Scheme III" On the basis of this scheme, plausible paths to the minor products of the reaction are proposed.