Jiří Dybal

A Proton Complex of p-tert-Butylcalix[4]arene-tetrakis(N,N-dimethylthioacetamide): NMR Evidence and Probable Structure

Using 1H and 13C NMR together with density functional theoretical (DFT) calculations, it is shown that p-tert-butylcalix[4]arene-tetrakis(N,N-dimethylthioacetamide) (1) forms a stable equimolecular complex with proton in the form of hydroxonium ion in nitrobenzene-d 5. Protons were offered by hydrogen bis(1,2-dicarbollyl) cobaltate (HDCC) and converted to hydroxonium ions by traces of water. The complex 1·H3O+ adopts a slightly asymmetric but rapidly motionally averaged conformation, which is distinctly more cone-like than ligand 1. The hydroxonium ion H3O+ is bound partly to thiocarbonyl sulphur atoms and partly to phenoxy oxygen atoms of 1 by strong hydrogen bonds and other electrostatic interactions.

Experimental Evidence for Unusual Protonation of Tetraethyl p-tert-Butylcalix[4]arene Tetraacetate and the Most Probable Structure of the Resulting Complex

Using 1H and 13C NMR, FT IR spectroscopy together with quantum mechanical DFT calculations, we show that tetraethyl p-tert-butylcalix[4]arene tetraacetate (1) forms a stable equimolecular complex with proton in the form of hydroxonium ion in acetonitrile-d 3. Protons for this complex were offered by hydrogen bis(1,2-dicarbollyl) cobaltate (HDCC) and converted to hydroxonium ions by traces of water. The complex 1·H3O+ adopts a slightly asymmetric conformation, which is distinctly more cone-like than ligand 1. According to spectral evidence, the hydroxonium ion H3O+ is bound mainly to three of the phenoxy oxygen atoms of 1 by strong hydrogen bonds leaving the ester carbonyl groups, which are the usual coordination site for metal cations, free. Theoretical DFT calculations support the bonding to phenoxy oxygen atoms but slightly prefer a structure with one of the carbonyls being involved in the coordination.

Purification of the specific immunoglobulin G1 by immobilized metal ion affinity chromatography using nickel complexes of chelating porous and nonporous polymeric sorbents based on poly(methacrylic esters). Effect of polymer structure

Ni2+ complexes of the chelating nonporous and porous bead sorbents based on methacrylic esters crosslinked with ethylene dimethacrylate were used in isolation of the horseradish peroxidase-specific immunoglobulin IgG1 from the crude mouse ascitic fluid by immobilized metal ion affinity chromatography (IMAC). Iminodiacetic and aspartic acids were attached to porous poly(glycidyl methacrylate) beads differing in size, morphology and chemical composition. Ethylenediaminetriacetic acid and quinolin-8-ol chelating groups were attached mainly to the surface hydroxyl groups in nonporous poly(diethylene glycol methacrylate) beads through spacers. The latter sorbents exhibited better kinetic characteristics than the former but a very low IgG1 sorption capacity. In a single-step IMAC procedure, the best efficiency in the specific IgG1 purification was obtained with porous sorbents (recovery 92%, purity 73%). Differences in IMAC separations are discussed from the point of view of morphology of polymer beads as well as of the type and concentration of chelating ligands.

Blends of poly(ethylene oxide)/poly(methyl methacrylate). An i.r. and n.m.r. study

Abstract I.r. and high-resolution solid-state 13C n.m.r. spectra, as well as proton relaxation times T1H and T1ϱH of poly(ethylene oxide) (PEO)/atactic poly(methyl methacrylate) (a-PMMA) blends in the solid state, with PEO weight fractions of 10, 30, 50 and 70% were measured. Infra-red spectra of pure PEO with various molecular weights were also measured. The measurements indicate that no large changes in the content of the ttt conformational structure of PEO with blending occur. In the blends containing 30% PEO or less, only a negligible amount of crystalline PEO has been found. From the T1H and T1ϱH relaxation times it follows that all the blends studied are completely homogeneous on the scale of 20–70 nm; at the same time at least part of the PMMA and PEO chains are intimately mixed in the amorphous phase with the average size of the PMMA domains being below 6 nm, T1H values and 13C n.m.r. linewidths indicate changes in the mobility of polymer segments with blending.

Copolymerization of tetraethoxysilane and dimethyl(diethoxy)silane studied by 29Si NMR and ab initio calculations of 29Si NMR chemical shifts

Abstract Copolymerization of tetraethoxysilane (TEOS) and dimethyl(diethoxy)silane (DMDEOS) was studied by means of the 29Si NMR spectroscopy and ab initio quantum chemical calculations. 29Si NMR spectra of reaction mixtures of TEOS and DMDEOS were effectively measured by a slightly modified DEPT experiment, in which the pulse sequence is divided into two parts and all pulses on protons are replaced by selective pulses. Quantum chemical ab initio calculation of structures and 29Si NMR chemical shifts of some reaction products were used in signal assignment. The assignment of the signals to corresponding structure units is not yet unambiguous; however, a semiquantitative analysis of relations in the reaction mixture of TEOS and DMDEOS could be done. Although the reactivity of the DMDEOS monomer is much higher in comparison with TEOS, the arising gel is not strictly phase separated and copolymerization of both monomers occurs. In the first stages of the process, resulting oligomers are composed of 70% of DMDEOS structure units. In the final stages of polycondensation, domains of the TEOS structure units are formed, which can act as linking units between cyclic oligomers.

Solid-state NMR study of structure, size and dynamics of domains in hybrid siloxane networks

Structure, size and dynamics of domains of hybrid siloxane networks prepared by copolymerization of tetraethoxysilane (TEOS) and dimethyl(diethoxy)silane (DMDEOS) were studied by several techniques of solid-state 1 H and 29 Si NMR spectroscopy as well as by ab initio quantum chemical calculations. T1r ( 1 H) relaxation times, dipolar dephasing and spin diffusion experiments confirmed the existence of nanoheterogeneous system with random, bicontinuous morphology. The size of domains of TEOS homopolymer is about 1.3‐2.8 nm, the size of copolymer phase being larger, ca. 4.0‐6.8 nm. Quantum chemical ab initio calculations of geometry and the principal values of 29 Si NMR chemical shift tensor and the isotropic chemical shift confirmed our structural predictions that copolymers with polycyclic structure units are formed. The accord of calculated values with those experimentally determined was sufficiently good.q 2000 Elsevier Science Ltd. All rights reserved.

Structural transformation of polyethylene phase in oriented polyethylene/polypropylene blends: a hierarchical structure approach

Injection-moulded specimens of polyethylene/polypropylene blends were drawn at room temperature and subsequently annealed at 140°C, i.e. above the melting temperature of polyethylene, but below the melting temperature of isotactic polypropylene. Structural transformations of the polyethylene phase were assessed at several levels of hierarchical structure by polarised FTIR spectroscopy with photoacoustic detection, DSC, WAXS and SAXS analyses, and dynamic mechanical analysis. The results indicate reorientation of polyethylene chains, corresponding rearrangement of crystalline lamellae and healing of interfibrillar flaws upon annealing.

Microdomain structure and chain orientation in polypropylene/polyethylene blends investigated by micro-Raman confocal imaging spectroscopy

Compositional domain structure of blends of isotactic polypropylene with linear polyethylene and chain orientation of neat polymers and of the blends were assessed by micro-Raman confocal imaging spectroscopy and FT Raman spectroscopy. The results were correlated with polarised photoacoustic FTIR and with DSC. The surface and inner parts of compression-moulded, injection-moulded and drawn specimens were compared. Polymer domains in the blends and domains of different orientation were identified. The larger size of the polymer domains and lower chain orientation in the core of the specimens prepared by injection-moulding were explained by different cooling conditions of the melt. Possibilities and limitations of the micro-Raman confocal spectroscopy method were discussed.

Detection of aniline oligomers on polyaniline-gold interface using resonance Raman scattering.

In situ deposited conducting polyaniline films prepared by the oxidation of aniline with ammonium peroxydisulfate in aqueous media of various acidities on gold and silicon supports were characterized by Raman spectroscopy. Enhanced Raman bands were found in the spectra of polyaniline films produced in the solutions of weak acids or in water on gold surface. These bands were weak for the films prepared in solutions of a strong acid on a gold support. The same bands are present in the Raman spectra of the reaction intermediates deposited during aniline oxidation in water or aqueous solutions of weak or strong acids on silicon removed from the reaction mixture at the beginning of the reaction. Such films are formed by aniline oligomers adsorbed on the surface. They were detected on the polyaniline-gold interface using resonance Raman scattering on the final films deposited on gold. The surface resonance Raman spectroscopy of the monolayer of oligomers found in the bulk polyaniline film makes this method advantageous in surface science, with many applications in electrochemistry, catalysis, and biophysical, polymer, or analytical chemistry.

Application of capillary affinity electrophoresis and density functional theory to the investigation of valinomycin-lithium complex.

Capillary affinity electrophoresis (CAE) and quantum mechanical density functional theory (DFT) have been applied to the investigation of interactions of valinomycin (Val), a macrocyclic dodecadepsipeptide antibiotic ionophore, with lithium cation Li(+). Firstly, from the dependence of effective electrophoretic mobility of Val on the Li(+) ion concentration in the background electrolyte (BGE) (methanolic solution of 50mM chloroacetic acid, 25 mM Tris, pH(MeOH) 7.8, 0-40 mM LiCl), the apparent binding (stability) constant (K(b)) of Val-Li(+) complex in methanol was evaluated as logK(b)=1.50+/-0.24. The employed CAE method include correction of the effective mobilities measured at ambient temperature, at different input power (Joule heating) and at variable ionic strength of the BGEs to the mobilities related to the reference temperature 25 degrees C and to the constant ionic strength 25 mM. Secondly, using DFT calculations, the most probable structures of the non-hydrated Val-Li(+) and hydrated Val-Li(+) x 3H(2)O complex species were predicted.