Studies on amine hydrothiocyanates. IV. Thermal decomposition studies using TG

The thermal decomposition of piperidine hydrothiocyanate, piperazine hydrothiocyanate, and the dihydrothiocyanates of ethylenediamine and 1,3-diaminopropane has been studied using TG. Piperidine hydrothiocyanate decomposes in a single step while the dihydrothiocyanates follow more complicated decomposition patterns yielding H₂S and half of the organic moiety first. The second step involves the loss of H₂S and the remainder of the organic moiety. In each case, complex polymeric materials result. Piperazine hydrothiocyanate also decomposes in two steps, the first involving the loss of half of the piperazine and the second involving the loss of piperazine and H₂S. Kinetic parameters have been determined for all these reactions.     

Structural requirements in chiral diphosphine-rhodium complexes. VIII. Asymmetric hydrogenation of N-acetyldehydroamino acids with rhodium(I) complexes containing chiral carbocyclic analogues of DIOP.

Z--acetamidocinnamic acid was hydrogenated with neutral diphosphine-rhodium(I) complexes containing trans-1,2-bis(diphenylphosphinomethyl) cycloalkanes to give N-acetylphenylalanine: 86 % e.e.-(R) [(1R,2R)-cyclobutane]; 63 % e.e.-(R) [(1R,2R)-cyclopentane]; 35 % e.e.-(S) [(1S,2S)-cyclohexane]; and 82 % e.e.-(R) [(2R,3R)-DIOP]. Similarly, -acetamidoacrylic acid was hydrogenated to give N-acetylalanine: 72 % e.e.-(R) [(1R,2R)-cyclobutane]; 72 % e.e.-(R) [(1R,2R)-cyclopentane]; 40 % e.e.-(S) [(1S,2S)-cyclohexane]; and 73 % e.e.-(R) [(2R,3R)-DIOP].     

Chemical models of the hydrophobic interaction: Apparent molal volumes and heat capacities of three symmetrical bolaform electrolytes and their homologous monomers in aqueous solution at 25°C

The densities and volumetric specific heats of aqueous solutions of Bu₃NHBr, Pent₃NHCl, and three diazonium salts, HN?Oct₃?NHBr₂, HN?Dec₃?NHCl₂, and Bu₃N?Oct?NBu₃Br₂, have been measured at 25°C. From these data, the apparent molal volumes φ _v and apparent molal heat capacities φ _c have been calculated and are reported here. In the series of compounds chosen, the diazonium (higher homologs) can be regarded as dimers of the alkyl-substituted ammonium ions (lower homologs), and these systems are examined as chemical models for the hydrophobic interaction. With the three homologous pairs studied here, the chemical model predicts that the strong interaction (limitingly, chemical binding) of two hydrocarbon chains in water leads to a major decrease in both φ _v and φ _c of the interacting solutes, ca.?22 cm³-mole^?1 and ?200 J-^oK^?1-mole^?1. These predictions constitute limiting behavior — useful, but not sufficient, to explain the observed concentration dependence of φ _v and φ _c in aqueous solutions of the lower homologs Bu₃NHBr, Pent₃NHCl, and Bu₄NBr. An explanation for the concentration dependence of φ _c is suggested with reference to ultrasonic relaxation data.     

Characterization of peptides by liquid chromatography/electrospray ionization mass spectrometry using silver nitrate as a post-column complexant

Two model peptides, des-Arg1-bradykinin (DAB) and bradykinin (B), were cationized by Ag+ after their separation by reversed-phase liquid chromatography (RPLC) prior to mass spectrometry (MS). Silver nitrate solution was used as a post-column reagent. The RPLC and MS experimental conditions were optimized using flow injection in order to obtain sufficiently abundant silver adducts to permit MS/MS experiments. The use of water-methanol with 0.1% formic acid as mobile phase allowed a good chromatographic separation of the two peptides with a polymeric stationary phase and sufficiently abundant silver-containing adducts, [M + Ag + H]2+ and [M + 2Ag]2+. The gas-phase dissociation of [DAB + Ag + H]2+ and [DAB + 2Ag]2+ led to interpretable mass spectra during the on-line cationization experiment. Most of the ions obtained by dissociating [DAB + Ag + H]2+ and [DAB + 2Ag]2+ species are silver-containing ions but the ions produced depend on the parent. The ions coming from the dissociation of the doubly charged silver adducts [DAB + Ag + H]2+ or [DAB + 2Ag]2+ are of interest compared with those coming from the singly charged silver species or doubly charged protonated species. The fragmentation of the doubly charged silver adducts provides ions over the entire mass range. Although the presence of several prolines in des-Arg1-bradykinin prevents the formation of some expected ions, the observation of triplets [an-H + Ag]+, [bn-H + Ag]+ and [bn + OH + Ag]+ produced by the dissociation of on-line Ag(+)-cationized peptides could contribute to greater success of automatic sequencing of peptides.     

Unimolecular gas-phase reactions of the methyl acetoacetate radical cation. Oxygen atom permutation via ion-molecule complexes

The reactions of metastable decomposing methyl acetoacetate (a mixture of keto a ad enol tautomers) are reported and discussed. The unimolecular fragmentations of the tautomers are different. The metastable decomposing radical cation of the keto form displays four specific ions: [M –CO]⁺˙, [M – CH₂O]⁺˙, [M – CH₂CO]⁺˙ and m/z 43. The results derived from D-, ¹³C- and ¹⁸O-labelled precursors together with thermochemical data have been used to study the mechanisms. Experimental results indicate that an unexpected isomerization occurs before dissociation. It formally corresponds to oxygen atom permutation of the two carbonyl groups without participation of the carbon atoms. This remarkable process is interpreted in terms of a mechanism involving ion-molecule complexes.     

Structural requirements in chiral diphosphine-rhodium complexes. VI. Inhibition of the asymmetric hydrogenation of Z-methyl-α-acetamidocinnamate catalyed by diop-rhodium catalyst in the presence of Z-adamantyl or bornyl-α-acetamidocinnamate.

The half-life period (6.6 mm.) for the hydrogenation of Z-methyl-a-acetamidocinnamate (catalyzed by a neutral DIOPRh complex) was found to be the same when the Me ester reduction was performed in the presence of equimolar quantities of the corresponding i-Pr or t-Bu ester unsaturated stbstrates. Neither the Me nor the i-Pr or t-Bu esters underwent appreciable Z,E-isomerization. The formation of N-acetylphenylalanine methyl ester product suffered inhibition when the hydrogenation reaction was performed in the presence of the corresponding bornyl or 1-adamantyl unsaturated esters (half-life period of the Me ester: 27 ~ 40 mm., respectively. The greater the inhibition of the Me ester unsaturated substrate, the more the bulky inhibitor itself underwent Z,E-isomerization. In the presence of inhibitors, the Me unsaturated substrate did not undergo appreciable Z,E-isomerization.