Effect of chain length on the conformation and T cell recognition of synthetic hemagglutinin fragments

Circular dichroism and Fourier-transform infrared spectroscopies were used to compare the conformational mobility of 13-mer peptides covering the 317-329 region of the envelope protein hemagglutinin of human influenza A virus subtypes H1, H2 and H3 with that of their truncated deca- and nonapeptide analogs. These peptides were demonstrated to bind to the murine I-Ed major histocompatibility complex encoded class II and human HLA-B*2705 class I molecules. Despite the amino acid substitutions in the three 13-mer subtype sequences, no significant differences in the conformational properties could be shown. Deletion of the N-terminal three residues resulted in a shift to an increased alpha-helical conformer population in the 317-329 H1 peptide and the breakage of the 3(10) or weakly H-bonded (nascent) alpha-helix in the H2 and H3 peptides. The conformational change observed upon deletion did not influence the efficiency of I-Ed peptide interaction, however, the C-terminal Arg had a beneficial effect both on MHC class II and class I binding without causing any remarkable change in solution conformation.     

Synthesis,spectroscopic and thermal characterization of new metal-containing isocyanate-based polymers

Journal of Thermal Analysis and Calorimetry - To overcome the polyurethanes low heat resistance and obtain new PU-based materials, in continuation of our research in the synthesis of hybrid...     

Ab initio calculations for XPS chemical shifts of poly(vinyl-trifluoroacetate) using trimer models

X-ray photoelectron spectra (XPS) of the polymer poly(vinyl-trifluoroacetate) show C(1s) binding energy shifts which are unusual because they are influenced by atoms which are several bonds away from the probed atom. In this work, the influence of the trifluoroacetate substituent on the 1s ionization potential of the carbon atoms of the polyethylene chain is investigated theoretically using mono-substituted, diad and triad models of trimers representing the polymer. Carbon 1s ionization energies are calculated by the Hartree–Fock theory employing Koopmans' theorem. The influence of the configuration and conformation of the functional groups as well as the degree of substitution are found to be important determinants of XPS spectra. It is further found that the 1s binding energy correlates in a linear fashion, with the total electrostatic potential at the position of the probe atom, and depends not only on nearest neighbor effects. This may have implications for the interpretation of high-resolution XP spectra.     

Rearrangement Reactions of Tritylcarbenes: Surprising Ring Expansion and Computational Investigation

As a rule, acetylides and sulfonyl azides do not undergo electrophilic azide transfer because 1,2,3‐triazoles are usually formed. We show now that treatment of tritylethyne with butyllithium followed by exposure to 2,4,6‐triisopropylbenzenesulfonyl azide leads to products that are easily explained through the generation of short‐lived tritylethynyl azide and its secondary product cyanotritylcarbene. Furthermore, it is demonstrated that tritylcarbenes generally do not produce triphenylethenes exclusively, as was stated in the literature. Instead, these carbenes always yielded also (diphenylmethylidene)cycloheptatrienes (heptafulvenes) as side products. This result is supported by static DFT, coupled cluster, and ab initio molecular dynamics calculations. From these investigations, the fused bicyclobutane intermediate was found to be essential for heptafulvene formation. Although the bicyclobutane is also capable of rearranging to the triphenylethene product, only the heptafulvene pathway is reasonable from the energetics. The ethene is formed straight from cyanotritylcarbene.     

Development of novel LpxC inhibitors: chiral-pool synthesis of C-triazolyl glycosides

The Zn²⁺-dependent deacetylase LpxC plays an important role in the biosynthesis of the cell wall of Gram-negative bacteria and therefore represents an interesting target for the development of novel antibiotics. In a 10-step, chiral pool synthesis starting from d-mannose (3), a series of C-aryl furanosidic hydroxamic acids bearing a 1,4-disubstituted triazole ring in α-configuration at the furanose moiety was stereoselectively synthesized and tested for inhibitory activity against LpxC. The key step of the synthesis comprises a Cu(I) catalyzed Huisgen cycloaddition of terminal alkyne 10 with various azides to introduce diversity to the potential LpxC inhibitors. The X-ray crystal structure of the click product 11e proves the stereochemistry at the anomeric center and the substitution pattern of the triazole ring. The synthesized compounds did not inhibit LpxC.     

Cation- and/or anion-directed reaction routes. Could the desolvation pattern of isostructural coordination compounds be related to their molecular structure?

The crystal and molecular structure of [Cu(ampf)(ClO₄)(MeOH)₂]ClO₄, (1), ampf = N,N′-bis(4-acetyl-5-methylpyrazol-3-yl)formamidine, determined by X-ray crystallography is described and compared with the structurally related copper(II) complexes, formed under similar experimental conditions, using Cu^II salts with different anions. The complex formation is discussed in view of the structures of cobalt(II) and nickel(II) complexes with the same organic ligand and different anions, also formed under similar reaction conditions. Solvent molecules coordinated to the central atom play an important role in biologic systems. To get a better insight into the desolvation mechanism, in this study the desolvation pattern of 1 is presented. As in literature little attention is paid to the desolvation mechanism of solvate complexes, the desolvation mechanism of three, potentially biologically active isostructural pairs of octahedral Ni^II and Co^II compounds with ampf and dmpc (3,5-dimethyl-1H-pyrazole-1-carboxamidine) ligands are evaluated and compared with the desolvation of 1. The results of the thermal data are discussed on the basis of structural features of the compounds. The minor differences in structures of the related compounds cannot be straightforwardly connected with the different solvent evaporation mechanism. To explain the differences found in desolvation pattern in isostructural Co^II and Ni^II complexes the Jahn-Teller effect is proposed.     

Thermal decomposition of new chlorido(p-cymene) ruthenium(II) complexes containing N-alkylphenothiazines

The thermal decomposition of [RuCl₂(η⁶-p-cymene)]₂ (1) and its biologically active N-alkylphenothiazine compounds of composition L[RuCl₃(η⁶-p-cymene)] where L = CPH⁺ (2), TFH⁺·HCl (3), and TRH⁺ (4) (chlorpromazine hydrochloride, CP·HCl; trifluoperazine dihydrochloride, TF·2HCl; and thioridazine hydrochloride, TR·HCl, respectively) has been studied. The crystal and molecular structure of compound 3 was determined earlier by single crystal X-ray diffraction analysis. The thermal data were collected by simultaneous TG/DSC measurements. For evolved gas detection, the qualitative reaction of chlorides with AgNO₃ in an acidic solution was applied. The measurements were carried out in the temperature range to 700 °C in nitrogen atmosphere. Compounds of L[RuCl₃(η⁶-p-cymene)] crystallize with water or water/2-propanole. On the basis of thermal data, the trend in the solvent bonding energies was assessed.     

Thermal stability of polyurethane materials based on castor oil as polyol component

Preparation of the series of polyurethane elastomers and its nanocomposites from castor oil (a vegetable triglyceride) and different isocyanates (aromatic: toluene diisocyanate, TDI and aliphatic: isophorone diisocyanate, IPDI) is described. The synthesis was carried out in bulk and without catalyst by a one-step reactive process. Different elastomers were prepared by using several stoichiometric imbalances. For polyurethane nanocomposites based on TDI, titanium(IV) oxide nanoparticles was used. The thermal properties of the materials are discussed on the basis of simultaneous TG-DSC measurements results and TMDSC data. TMDSC results show that T _g increases with increasing r = NCO/OH ratio. Namely, with increasing NCO/OH ratio the cross-linkage density increases and as a consequence, the chain mobility decreases, resulting in a higher T _g. It was estimated that the T _g of the samples decreased as the nanofiller content increased due to the changes in the segmental mobility in polyurethane materials. Thermal data refers to increased stability of nanocomposites compared with that of the unfilled elastomers.