János Rohonczy

Structural characterization of gel-derived calcium silicate systems

The main aim of this study is to synthesize calcium silicate ceramics that exhibit suitable properties to be used for biomedical applications. In the present work, attention was paid to the understanding of processing-structure relationships. A particular effort was made to clarify the identification of Ca-O-Si bonds by means of spectroscopy. The calcium silicate systems were prepared via a sol-gel route, varying the chemical compositions, the catalyst concentration, and the temperature and time of aging and heat treatment. The processes and the phases evolved during the sol-gel procedure were determined. The bond systems were investigated by Fourier transform infrared (FTIR) and (29)Si magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy and the aggregate structures by scanning electron microscopy (SEM), small-angle neutron scattering (SANS), small-angle X-ray scattering (SAXS), wide-angle X-ray scattering (WAXS), and X-ray diffraction (XRD) measurements.

Pseudosymmetry and chiral discrimination in optical resolution via diastereoisomeric salt formation. The crystal structures of (R)- and (S)-N-methylamphetamine bitartrates (RMERTA and SMERTA)

The structures of the diastereoisomeric salts of (R)- and (S)-N-methylamphetamine bitartrates (RMERTA and SMERTA) have been determined by X-ray crystallography. Comparison of these crystal structures provides an insight into the mechanism of optical resolution via diastereoisomeric salt formation. The very small difference between the two crystal structures indicates that specific interactions such as CH⋯O interactions may play an important role in molecular recognition.

Preparation and characterization of brominated polyethersulfones

A novel derivative of aromatic polyethersulfone (PES) was obtained by bromination. Victrex PES was reacted with bromine under various conditions: in solution, in suspension, and without solvent; with or without catalyst; and at low and elevated temperatures. Practically no bromination occurred in solution; in the other cases, brominated PESs to various extents were obtained. The degree of substitution (DS) varied between 0.3 and 2.3. It was found that no catalyst is required for this reaction; the temperature, the concentrations of bromine and of polymer in the reaction mixture, and the duration of the reaction are the determinant factors of the DS. The modified polymers were characterized by elemental analysis, 1H-NMR, 13C-NMR, and PGC-MS, and their thermal properties were investigated by TGA and DSC methods. Further transformations of brominated PES as well as other new chemical reactions of PES will be the subject of later publications.

Trimethylsilylated N-alkyl-substituted carbamates: III. Structure of trimethylsilyl-N,N-diisopropyl carbamate in solid phase and in solution☆

Abstract The conformers of trimethylsilyl- N , N -diisopropyl carbamate were studied by 1 H NMR spectroscopy. The barriers to rotation by isopropyl groups and to the rotation around the amide bond, and the population of the conformers were determined from the coalescence temperature of the methyne signal. Single crystal X-ray diffraction studies revealed that the crystal had formed from preferred conformer in solution. The mirror symmetric conformer is stabilized by an intramolecular CH ⋯ O hydrogen bond and by an intramolecular O ⋯ Si donor-acceptor interaction.

In situ IR and NMR spectroscopic investigation of the formation and structure of protonated diacetylketene tetrachloroaluminate

In situ IR and multinuclear NMR are used to monitor the formation of protonated diacetylketene tetrachloroaluminate (1) in the reaction of acetyl chloride and AlCl3 in both dichloromethane and in 1-butyl-3-methylimidazolium chloride ([bmim]Cl). The existence of a fast equilibrium between two enolic forms of protonated diacetylketene (with [AlCl4]− as the counterion) is established. The structure of 1 is determined by the rarely used 13C{1H}–13C{1H} COSY experiment.

Aqueous solubilization of [60]fullerene via inclusion complex formation and the hydration of C60

Natural and substituted cyclodextrins (CDs), as well as some calixarenes, have been investigated with respect to their solubilization of C60 in water. Underivatized γ-CD is proved to have unique solubilizing power among the possible complexing agents as it produces stable solutions and solids containing real 1∶2 complexes. The differences in the appearance of the solutions (magenta or brown colour) are explained by the hydration of the C60 within the supramolecule. The composition and structure of the complexes are proved by chemical analyses, X-ray diffraction, atomic force microscopy and solid state NMR.

Simulation of DNMR spectra using propagator formalism and Monte Carlo method

A new program-ProMoCS-is presented for the simulation of dynamic nuclear magnetic resonance spectra. Its algorithm is based on the Monte Carlo method as the one of the previously introduced MC-DNMR but the theory of ProMoCS is explained by using the statistical approach of propagator formalism. Our new program is suitable for the calculation of dynamic NMR spectra of spin systems up to 12 1/2 spin nuclei, several conformers and any type of exchange between them. Mutual exchange of coupled spins can be simulated as well. While it keeps the main advantage of the Monte Carlo based method: calculation with significantly smaller matrices as compared with programs based on the simulation of the average density matrix, the maximum number of nuclei is increased significantly. Thus spectra of such systems can be simulated that was impossible previously.

Two N-Aryl-Substituted Silyl Carbamates

Trimethylsilyl N-(4-bromophenyl)carbamate, C10H14BrNO2Si, and trimethylsilyl N-tert-butyl-N-phenylcarbamate, C14H23NO2Si, are both important silylating agents. The structures of both molecules are dominated by a plane containing a remarkably large number of atoms. The planes are organized by delocalization around the carbamate moiety. A quasi-pentacoordination of the Si atom in both compounds is also described.

Fast calculation of DNMR spectra on CUDA‐enabled graphics card

During the past few years, general‐purpose graphics processing units (GPGPUs) have become rather popular in the high performance computing community. In this study, we present an implementation of the simulation of dynamic nuclear magnetic resonance (DNMR) spectra. The algorithm is based on the kinetic Monte Carlo method and therefore can benefit from the multithreaded architecture of the GPGPU. By careful optimization of the algorithm a 30–100‐fold speed increase could be achieved.

Chemical processing of new piezoelectric materials

Low-density piezoelectric aluminosilicate aerogels were prepared by sol-gel technology. In order to reinforce the fragile aluminosilicate aerogels, the inorganic component was mixed with organic polymers (polyacrylic acid, polyvinyl acetate and polydimethylsiloxane) prior to gelation. The strength of the composite gels increases by a factor of two or three. The piezoelectricity of the composite gels changes variously depending on the kind and content of the organic polymers. The aerogel containing polyvinyl acetate shows negligible piezoelectricity. The use of polydimethylsiloxane decreases the piezoelectricity by 50% and polyacrylic acid increases it by 100%. The chemical structures of the composite gels were investigated by means of 27Al and 29Si magic angle spinning nuclear magnetic resonance, infrared spectroscopy and small angle x-ray scattering. The structure and the Al incorporation have strong effects on the piezoelectricity. The higher the amounts of bonded Al atoms in the silica network the higher the intensity of the piezoelectricity is.