15N-NMR spectroscopy. III. Neighboring residue effects in sequence polymers containing glycylglycine units

The tripeptides Phe-Gly-Gly, β-Ala-Gly-Gly, and ?-Aca-Gly-Gly as well as the peptide derivatives δ-isothiocyanatovaleroyl-Gly-Gly and ?-isothiocyanatocaproyl-Gly-Gly were synthesized by using known methods so that the peptide nitrogen between the two glycyl residues was isotopically enriched in ¹⁵N to a level of 0.8–0.9%. These monomer units were then used to produce the sequence polymers (Phe-Gly-Gly)_n, (β-Ala-Gly-Gly)_n, (δ-Ava-Gly-Gly)_n, and (?-Aca-Gly-Gly)_n. The 18.24 MHz ¹⁵N-NMR spectra of the oligo- and polypeptides were obtained by using trifluoroacetic acid as solvent, since the solutions have relatively low viscosity and exhibit a strong negative nuclear Overhauser enhancement of the ¹⁵N signals. For comparison, ¹⁵N-NMR spectra of the homopolymers (Gly)_n, (β-Ala)_n, (γ-Abu)_n, (δ-Ava)_n, and (?-Aca)_n were also recorded. The ¹⁵N signals from the ω-aminoacyl residues in the sequence polymers appear up to 11 ppm upfield of the signals observed for the homopolyamides. The ¹⁵N signals from the two glycyl residues are separated by 3–7 ppm. Comparison with the ¹³C-NMR spectra of the same polymers indicates that ¹⁵N-NMR is better suited for the characterization and sequence analysis of these types of polymers.     

Determination of low dose concentration profiles in solids by means of (n,p) and (n, α) reactions

The isotopes³He,⁶Li,⁷Be and¹⁰B exhibit extremely large cross sections, between 1 and 48 kilobarn, for (n, p) or (n, α) reactions with thermal neutrons. Together with now available extracted thermal neutron fluxes of 10⁽ n·cm⁻²·sec⁻¹ or more, these reactions present a highly sensitive method of detecting the mentioned light elements in any heavy matrix material. Through the experimentally determined energy losses of the emitted protons or α-particles, also well resolved depth profiles can be obtained, as demonstrated here for some relevant examples from semiconductor and fusion technology.     

Über den Dissoziationszustand von geschmolzenem Natriumdiwolframat (Na2W2O7)

Kordes and Nolte are of the opinion that, on melting, Na₂W₂O₇ dissociates according to the reaction whereas Gelsing et al. assume a dissociation into Na⁺ ions and a mixture of chains of WO₄ tetrahedra (WO, W₂O, W₃O, etc.). In the present paper it is demonstrated that a dissociation according to the ideas of Gelsing et al. can excellently explain the cryometric results found by Kordes and Nolte themselves. The dissociation scheme proposed by Gelsing et al., is even more likely than that proposed by Kordes and Nolte when the results of surface tension measurements reported by Gossink and Stevels are taken into account.     

Binding energy of lithium halide molecules

A semi-empirical open shell model of sigma bonded systems has been employed to calculate the binding energies for diatomic lithium halides. The repulsion between the atomic cores is taken as the Coulomb repulsion term $\text{1}\text{R}{}_{12}$ modified by the presence of electronic cores. This modification has been estimated from the repulsion term in the Rittner potential function. The agreement with the experimental values is quite satisfactory but the extension of the same method to alkali hydrides results in gross discrepancies. The results are discussed in the light of other results.     

Reactions of Titanium Alkoxides with N-Methylaminoalcohols

N-methylaminoalkoxides of titanium of the type Ti(OR)_4?n(O · CHR′ · CH₂ · NR″R?)_n where R = Et and Pr¹; n = 1–4; and R′ = R″ = H, R? = Me; R′ = H, R″ = R? = Me; R′ = R″ = R? = Me, synthesized by the reactions of titanium alkoxides with aminoalcohols, show interesting variations in their properties like physical state, volatility and molecular complexity. I.r. and p.m.r. spectra of these derivatives have been recorded. A few interchange reactions with methanol and tert-butanol have also been carried out. These aminoalkoxides get cleaved with acetyl chloride and undergo insertion reactions with phenylisocyanate, thus providing the first examples of insertion reactions in such derivatives.     

Carbon suboxide and some of its reactions

The reaction of carbon suboxide with a number of 2-amino-1,3,4-thiadiazoles has given the corresponding pyrimido[1,2-b]-1,3,4-thiadiazoles     

Ab initio MO-SCF calculation on a model of anomalous water

Ab initio calculations are carried out on the planar hexamer model of anomalous water using a variety of basis sets. The results are compared to results of similar calculations on free water and water in the ice I-like puckered ring configurations.

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Zusammenfassung Es werden ab initio-Rechnungen für das planare Hexamer-Modell von anomalem Wasser unter Verwendung mehrerer BasissÄtze durchgeführt. Die Ergebnisse werden mit Resultaten Ähnlicher Rechnungen über freies Wasser und Wasser in der I-Eis Ähnlichen Konfiguration verzerrter Ringe verglichen.

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Résumé Calculs ab initio sur le modèle hexamérique plan de l'eau anormale en utilisant différentes bases. Les résultats sont comparés à ceux de calculs similaires sur l'eau libre et sur l'eau dans une configuration cyclique compacte analogue à celle de la glace I.

     

INTRAMOLECULAR EXCIPLEX FORMATION IN Nα-ACETYL-1-PYRENYLALANYL-1-METHYLTRYPTOPHAN METHYLESTER

Abstract— The synthesis, absorption and emission properties of erythro (e) and threo (t) Na-acetyl-1-pyrenylalanyl-1-methyltryptophan methylester (APTE) are reported. From the dependency of the exciplex emission maximum on the solvent polarity, the exciplex dipole moment of erythro and threo APTE were calculated. The evolution of the ratio of the quantum yield of exciplex emission and the quantum yield of emission from the locally excited state is correlated with solvent polarity and with the tendency of the solvent to interact with the peptide chain through hydrogen bonding. It is shown that solvents, inert towards the peptide function, shift the equilibrium between the two ground state conformations towards C₇, in which an exciplex geometry can be reached. Hydrogen accepting solvents shift the conformational equilibrium towards C₅, which cannot form an exciplex directly within the lifetime of excited pyrene.     

Gmelin handbook of inorganic chemistry, 8th edit., S — Sulfur-Nitrogen Compounds,Part 2: Compounds with Sulfur of Oxidation Number IV: Springer-Verlag,Berlin, Heidelberg,New York,Tokyo, 1985, xiv + 333 pages,DM 1144, ISBN 3-540-93512-6

A close examination of the ESR spectrum of a paramagnetic complex formed from bis(ethoxythiocarbonyl)sulfide and dimanganese decacarbonyl has revealed, for the first in this type of radical adduct, ₁₃C hyperfine coupling in natural abundance from the carbonyl ligands.