Heinz Böhlig

FTIR-spectroscopic characterization of phosphocholine-headgroup model compounds

Abstract The polar headgroups are an important molecular subregion of phospholipids since they mediate a substantial part of the interactions emerging with other constituents of biological membranes, be it inherent macromolecules (proteins) or water as forming the natural environment. FTIR spectroscopy is well proven for characterizing aspects of weak interactions, above all hydrogen bonding. We have used this method to study solid deposits of a number of selected lipid models, such as choline, acetylcholine and methylphosphocholine (MePC), and compared them with the common phospholipid dimyristoylglycerophosphocholine (DMPC), at different degrees of hydration, which were varied via relative humidity (RH). At low RHs, only MePC and DMPC take up considerable amounts of water, thus elucidating the essential role of phosphate groups in the first stages of lipid hydration. The progress of PC-headgroup hydration can be sensitively monitored by the wavenumber decrease of the band owing to antisymmetric PO 2 − stretching vibration. Concomitant variations of the spectral parameters of ν CH bands of MePC reveal that conformational changes may simultaneously occur in the headgroup. Surprisingly to us, the model compounds display qualitative differences in the appearance of their ν CH bands, which are most probably a result of substituent effects.

Vibrational analysis of benzothiazoline-2-thione

Abstract Infrared and Raman spectra of solid benzothiazoline-2-thione (BTT) have been measured in the range 4000–50 cm −1 and 4000–200 cm −1 , respectively. Force constants and vibrational frequencies of BTT and 2-mercapto-benzothiazole have been determined by means of quantum chemical calculations on the basis of the density functional theory. An assignment has been made for the normal vibrations using the calculated vibrational frequencies and the potential energy distribution. In spite of the probability of the existence of 2-mercapto-benzothiazole within a tautomeric equilibrium, there is no indication of its presence besides the neat BTT.

Structure of adsorption complexes of water in zeolites of different types studied by infrared spectroscopy and inelastic neutron scattering

We combined the results of diffuse reflectance infrared Fourier transform spectroscopic (DRIFTS) measurements (4000–1500 cm−1) and inelastic neutron scattering (INS) (5–100 meV) to study the structure of adsorption complexes of water in zeolites of types FAU and MFI exchanged with alkali metal cations. In the case of faujasites, at relatively high water loadings we observe correlation between the position of the broad band at about 3400–3500 cm−1 arising from OH-stretching of hydrogen bonded water molecules and the basicity of framework oxygen atoms of the zeolite. This result indicates that at these water loadings a significant number of water molecules forms hydrogen bonds to framework oxygen. Temperature-programmed DRIFT studies show that depending on the type of exchanged cation (Li-LSX, NaX) the position of the band at about 3400–3500 cm−1 changes suddenly in the temperature region 400–450 K and then remains stable upon further increase of the temperature. The observed behavior is caused by the formation of smaller, more strongly bonded water-cation clusters from the large web-like structures as a significant number of water molecules is removed. Bands due to hydrogen bond stretchings (O–H⋯O) and up to three librations of water molecules are observed in the INS spectra in the regions 15–44 meV and 44–89 meV respectively. The observed shifts of the band positions for different water loadings are in agreement with the results of DRIFT studies.

Approximate Assignment of Vibrational Frequencies of the NaX Framework

Summary On the basis of systematically developed subunit cluster models of NaX zeolite framework normal coordinate analyses have been carried out by means of WILSONs GF matrix method intending to understand the corresponding experimental vibrational spectra. An approximate assignment of vibrational frequencies of the NaX zeolite framework is given on the basis of calculated eigenvalues, potential energy distributions and eigenvectors. The results are discussed in connection with the FLANIGEN conception of internal and external vibrations.

Inelastic neutron scattering and infrared spectroscopic study of furan adsorption on alkali-metal cation-exchanged faujasites

Inelastic neutron scattering (INS) as well as infrared (IR) transmission and diffuse reflection infrared Fourier transform (DRIFT) spectra of furan adsorbed on Li-LSX, NaY, NaX, K-LSX, and CsNaX zeolites have been measured in the range 2000-200 and 4000-1300 cm(-1), respectively. On the basis of an assignment of normal modes of furan taken from the literature and our own quantum chemical calculations of vibrational frequencies, the observed frequency shifts between bulk furan and furan adsorbed on the zeolites mentioned above have been interpreted in view of the interactions between furan and zeolite. For an explanation of frequency shifts of CH out-of-plane bendings, CH stretchings and some ring vibrations, it has to be assumed that in addition to the interaction between furan and the corresponding cation of the zeolite, a further interaction between the CH bonds and lattice oxygen atoms exists.

Schwingungsverhalten des syn- und anti-acetaldoxims: 1. Mitt. Schwingungsspektren

Abstract The infrared spectra of CH3CHNOH, CH3CHNOD, CH3CDNOD and CD3CDNOD have been recorded and studied. On the basis of the symmetry properties the normal vibrations were assigned by comparison.

Schwingungsverhalten des syn- und anti-acetaldoxims: 2. Mitt. normalkoordinatenbehandlung

Abstract Normal coordinate calculations on CH 3 CHNOH, CH 3 CHNOD, CH 3 CDNOD and CD 3 CDNOD have been carried out applying the general harmonic valence force field. The calculated frequencies of the normal vibrations considered agree satisfactorily with the corresponding values obtained from the spectra. The potential energy distributions have also been calculated; they were used to interpret the behaviour of characteristic vibrations.

Characterization of Extra-framework Cations in Zeolites. A temperature-programmed desorption (TPD) study

We have investigated the interaction of a few 5-ring organic compounds (cyclopentane, cyclopentene, furan, 2-methylfuran, 2,5-dihydrofuran and tetrahydrofuran) with alkali-metal cation-exchanged faujasites (LSX, X and Y types) by means of temperature-programmed desorption (TPD). The desorption behavior at higher temperatures of all probe molecules on the sodium ion containing faujasites with different Si/Al ratios reflects the higher cation content of zeolites with greater aluminum content. Only the desorption profiles of tetrahydrofuran and 2,5-dihydrofuran show, depending on the kind of cation, additional desorption features at higher temperatures. Using a regularization method, desorption energy distribution functions for furan and tetrahydrofuran were calculated. The calculated desorption energy distributions clearly illustrate the very different adsorption behavior of furan and tetrahydrofuran which leads to large differences in the binding energies between the corresponding adsorption complexes.

Investigation of the non-isothermal water desorption on alkali-metal cation-exchanged X-type zeolites: a temperature-programmed diffuse reflection infrared Fourier transform spectroscopic (TP-DRIFTS) study

The non-isothermal desorption of water on alkali-metal cation-exchanged X-type zeolites was investigated by means of temperature-programmed diffuse reflection infrared Fourier transform spectroscopy (TP-DRIFTS). Based on the areas under the DRIFT spectra recorded at temperature intervals of 10 K, the desorption profiles could be calculated. Their shape is principally identical to the desorption curves obtained by conventional TPD (EGD/EGA). Using a numerical regularisation method, desorption energy distribution functions have been calculated. The assignment of several characteristic bands to differently bonded water molecules and explanations for certain observed trends have been given.

Schwingungsanalyse konformerer 1-Brombutane

Zusammenfassung Die Infrarot- und Ramanspektren von n-Butylbromid wurden im flussigen Zustand aufgenommen. Mit Hilfe einer Normalkoordinatenanalyse gelang es, die auftretenden Banden den Konformationen TT, TG, GT und GG zuzuordnen. Im Bereich 500–390 cm −1 befindet sich ein “Konformerenfenster”, das die eindeutige Identifikation der vier Konformeren gestattet.