Showing papers on "Reactivity (chemistry) published in 1971"

Zerovalent platinum chemistry. Part VI. The reactions of bis- and tris-triphenylphosphineplatinum(0) with hydrogen sulphide, hydrogen selenide, sulphur, and related molecules

Abstract: The reactions of Pt(PPh3)n(n= 2 or 3) with H2M, HMPh, and M (M = S or Se) to form adducts have been studied. The reactivity of the products towards soft and hard reagents has been investigated and compared with that of related H2M, HMPh, and M adducts of some RhI and IrI triphenylphosphine complexes. The results agree with the proposed mechanisms of poisoning of metal surfaces by species such as H2M or M.

Reaction of diethyl pyrocarbonate with nucleic acid components. Adenosine.

Abstract: The use of diethyl pyrocarbonate as a nuclease inhibitor in the preparation of RNA of high molecular weight has prompted a study of the possible reactions of this compound with nucleic acid components under the conditions generally employed for providing inhibition. The first substrate investigated was adenine, which has been found to undergo ring opening with the formation of 5(4)-N-carbethoxyaminoimidazole-4(5)-N'-carbethoxycarboxamidine (II). This product was converted efficiently to isoguanine by treatment with ammonia. The structure of II was established by spectroscopy. For comparisons of reactivity and of spectroscopic and chromatographic properties with the adenine-diethyl pyrocarbonate product, the compounds 9-carbethoxyadenine, 6-N-carbethoxyaminopurine (V), and 6-ethylaminopurine were made; compound V was made by employing the 1-ethoxyethyl protecting group in the synthetic sequence. Purine compounds can be converted to 9-(1-ethoxyethyl) derivatives simply by refluxing in acetal. The facile reaction of adenine with diethyl pyrocarbonate illustrates the importance of gaining information as to the fate of various nucleic acid components in the presence of diethyl pyrocarbonate. The successful preparation of high molecular weight, biologically active RNA depends on the rapid inactivation of nucleases in the early steps of the isolation. Conservation of biological activity upon prolonged storage also requires the total absence of nuclease activity in these preparations. Interest in specific nuclease inhibitors was often motivated by these considerations. Recently the inhibitory activity of diethyl pyrocarbonate (DEP) (ethoxyformic anhydride) was utilized in the isolation of high molecular weight RNA.'2 This bactericidal agent3 was shown to convert pri mary and secondary amines into carbamic acid esters (urethans). More recent investigations have demonstrated that amino acids and proteins reacted in a similar way and were converted into N-carbethoxy derivatives at either free a-amino groups or the z-aminio group of lysine.5 6 In spite of these substitutions, it was concluded that irreversible inactivationl of enzymatic activity was most probably due to conformational chainges resultiing in insolubility.5 Subsequently, it was shown by others that the insolubility of proteins after reaction with DEP may be attributed to formation of intermolecular covaleint bonds, possibly as a result of a much more complicated reaction iinvolving both amino and carboxylic groups.7'8 In addition to these findings it was also reported

EPR Pulse Radiolysis Studies of the Hydrogen Atom in Aqueous Solution. I. Reactivity of the Hydrogen Atom

Abstract: The transient properties of hydrogen and deuterium atoms produced by pulse radiolysis in water have been studied by EPR. Details of the EPR instrumentation are described. From decay characteristics of the EPR signal on addition of various solutes, rate constants for the reaction of atomic hydrogen with various classes of molecules have been determined. Agreement of our results with prior indirect determinations is, in general, good. The isotope effect is also in agreement with expectation.

Silicon difluoride, a carbene analog - Its reactions and properties

Abstract: Silicon difluoride reactions and properties, describing production from commercial silicon tetrafluoride and versatility of reactions with organic and inorganic compounds

The Mechanism of Contact Elimination, A Contribution to Understanding the Function of Polar Catalysts

Abstract: The current ideas of organic chemists based on the work of Ingold and his school are applied to heterogeneous catalytic eliminations (mostly from haloalkanes and aliphatic alcohols). It is deduced from the activity of the catalysts, the reactivity of the substrates (reactants), and the primary product distribution that these eliminations proceed by a heterolytic mechanism similar to that involved in the liquid phase. The activity of the catalysts (salts and oxides) increases with increasing charge and decreasing radius of the cations and with increasing basicity of the anions. The reactivity of the substrates behaves in much the same manner as in the liquid phase. In contrast with the liquid-phase reaction, the cis-olefins are frequently favored as primary products. The stereospecificity of the reaction is determined from the relative strengths of the interactions between the catalyst cation and the leaving group X−, and between the catalyst anion and the leaving proton. Only trans elimination has so far been found in the concerted mechanism.

The Streptococcal Cell Wall: Structure, Antigenic Composition, and Reactivity with Lysozyme

Abstract: The biochemical and immunochemical structures of cell walls of many Lancefieldgrouped streptococci have been determined over the past 15 years. Through the work of Krause,'L McCarty,2 Slade and Slamp,3 and others, much has been learned. A brief summary of their findings follows. Figure 1 is Krause'sl diagrammatic representation of the group A streptococcal cell surface. There is an outer capsule of hyaluronic acid; many cariogenic cells instead possess dextran or levan capsules. A proteinaceous cell wall layer contains the typespecific (M, T, and R) antigens of the group A organism; cariogenic streptococci appear to lack such cell wall proteins. The group-specific antigen of the group A organism is associated with the polysaccharide layer, which contains only rhamnose and Nacetylglucosamine. Figure 2 shows the cell wall carbohydrates of groups A, A-variant, and group C streptococci."2 The haptenic moiety of the group A polysaccharide is a terminal N-acetylglucosamine residue attached by a beta linkage to a backbone that consists largely of rhamnose. If the amino sugar constituent is lost by genetic alteration, the terminal rhamnose residues become the antigenic determinants for the resulting group A-variant organism. A terminal N-acetylgalactosamine moiety is the antigenic determinant in the group C polysaccharide, which contains mostly rhamnose and amino sugar. As will be seen, many oral streptococci possess even more complex cell wall polysaccharides. The antigenic significance of these carbohydrates is the object of our current research.

Ketenoide Reaktionsweise eines mesoionischen Oxazolons‐(5)

Abstract: Die aus 3-Methyl-2.4-diphenyl-oxazolium-5-olat (1) mit Azomethinen, Diisopropyl-carbodiimid und 1-Morpholino-cyclopenten erhaltenen 1:1-Addukte gehen nicht aus 1.3-Dipolaren Cycloadditionen hervor, sondern leiten sich als 2+24-Cycloaddukte von mit 1 valenztautomeren [Methyl-benzoyl-amino]-phenylketen (4) ab. Ketenoid Reactivity of a Mesoionic Oxazol-5-one 3-Methyl-2.4-diphenyloxazolium-5-olate combines with azomethines, diisopropylcarbodiimide and 1-morpholinocyclopentene to form 1:1-adducts. These are not the result of 1.3-dipolar cycloadditions of 1, but rather are 2+24-cycloadducts which are derived from a valency tautomer, the [N-benzoyl-methylamino]-phenylketene (4).

Synthesis of Some Stable 7-Halo-1,4-thiazepines. Potential Substituted Penam Precursors

Abstract: The synthesis of some new 3-carbomethoxy-5-oxoperhydro-1,4-thiazepines is described. Halogenation studies led to the preparation of three potential substituted penam ring precursors: 6,7-dibromo-3-carbomethoxy-5-oxoperhydro-1,4-thiazepine, 3-carbomethoxy-6,7-dichloro-5-oxoperhydro-1,4-thiazepine, and 3-carbomethoxy-7-chloro-6,6-dimethyl-5-oxoperhydro-1,4-thiazepine. Preliminary studies on the reactivity of these α-halothioethers showed that methanolysis to the corresponding methoxy-thiazepines may be carried out in nearly quantitative yields in the case of the first two derivatives; the third compound, on the other hand, led to an open-chain dehydrohalogenated product where C-7 is converted to the corresponding dimethyl acetal.