Biomedical subjects

H W Siesler

Publications and source records attributed to H W Siesler.

9 recordsLinked to original sources

PubMed2006

Solid state characterization of olanzapine polymorphs using vibrational spectroscopy.

FT-Raman, infrared and near infrared investigations of two polymorphs of olanzapine are presented, establishing the main features that allow the discrimination of these crystalline forms using vibrational spectroscopic methods. Ab initio calculations on the basis of the density functional theory were used to determine the stable conformations. The calculated vibrational spectra were compared to the experimental ones in order to identify the conformers corresponding to each polymorph and to assign the vibrational bands to the internal vibrations of the olanzapine molecule. Our results support the hydrogen bonding pattern proposed by the reported crystalline structure and provide valuable information on the structural and thermodynamical relationship between the investigated polymorphs.

Antipsychotic Agents↗

PubMed2005

Near-infrared spectroscopic observation of the ageing process in archaeological wood using a deuterium exchange method.

The ageing degradation of the fine wood structure of dry-exposed archaeological wood was investigated by Fourier transform near-infrared spectroscopy with the aid of a deuterium exchange method. The archaeological wood sample was taken from an old wooden temple in Japan (late 7th century), which has been designated as a UNESCO world heritage site. Comparing the analytical results with those of a modern wood sample of the same species, the ageing process of archaeological wood was clarified as a change in the state of order on a macromolecular structural level. It can be concluded from NIR spectra that the amorphous region, and partially semi-crystalline region, in cellulose, hemicellulose, and lignin decreased by the ageing degradation, whereas the crystalline region in cellulose was not affected by the ageing. The accessibility of the diffusant to effect H/D-exchange was monitored by an OH-related absorption band obtained from FT-NIR transmission spectroscopy and characteristically varied with the ageing process of the wood samples, the absorption bands characteristic of a specific state of order and the diffusion agent. Finally, we proposed a morphological model to describe the variation of the fine structure of the microfibrils in the cell wall with ageing degradation. The state of microfibrils changed loosely by ageing, so that elementary fibrils were arranged loosely under 5 A, whereas several elementary fibrils in the modern wood were arranged in very close proximity under 3 A to each other.

Archaeology↗

PubMed2003

Electric-field-induced reorientation of liquid crystalline p-cyanophenyl-p-n-alkylbenzoates: a time-resolved study by fourier transform infrared transmission and attenuated total reflection spectroscopy.

Time-resolved polarization Fourier transform infrared (FT-IR) transmission and attenuated total reflection (ATR) spectroscopy were applied to investigate the reorientation phenomena of the three members of the homologous series of nematic liquid crystalline p-cyanophenyl-p-n-alkylbenzoates 6CPB, 7CPB, and 10CPB under the external perturbation of an electric field. In conjunction with a newly constructed measurement cell, this method allowed us to differentiate the response of the LC system in the surface layer and in the bulk of the cell at different temperatures and voltages. The relaxation time of the LC molecules close to the wall of the cell was found to be shorter than in the bulk. However, at a field strength of 7 V, the initial orientation in the bulk preceeds the analogous process in the surface region.

Anisotropy↗

PubMed2003

Near-infrared spectroscopic monitoring of the diffusion process of deuterium-labeled molecules in wood. Part I: softwood.

The diffusion process of several molecules (D2O, n-butanol (OD) and t-butanol (OD)) in softwood (Sitka spruce) was investigated by means of a deuterium exchange method and Fourier transform near-infrared (FT-NIR) polarization spectroscopy. The location of OH groups in different states of order of cellulose in wood was clarified by analyzing the FT-NIR transmission spectra ranging from 7200 to 6000 cm(-1). Four absorption bands were assigned to 2 x v(OH) absorptions of the amorphous regions, OH groups in semi-crystalline regions, and two types of intramolecular hydrogen-bonded OH groups in the crystalline regions, respectively. The saturation level of accessibility was very different for these absorption bands (i.e., 70-80, 60, and 40-50% for the amorphous, semi-crystalline, and crystalline regions, respectively). However, the saturation accessibilities for each absorption band varied little with molecular structure and geometry of the diffusants. The diffusion rate of D2O was much faster than that of n-butanol (OD) and t-butanol (OD) for all states of orders. The size effect of the butanols led to slight differences in the diffusive transport in the crystalline regions.

1-Butanol↗

PubMed2003

Near-infrared spectroscopic monitoring of the diffusion process of deuterium-labeled molecules in wood. Part II: hardwood.

Fourier transform near-infrared (FT-NIR) transmission spectroscopy was applied to monitor the diffusion process of deuterium-labeled molecules in hardwood (Beech). The results are compared with previous data obtained on softwood (Sitka spruce) in order to consistently understand the state of order in cellulose of wood. The saturation accessibility and diffusion rate varied characteristically with the OH groups in different states of order in the wood substance, the diffusants, and the wood species, respectively. The variation of saturation accessibility should be associated with the fundamental difference of the fine structure such as the microfibrils in the wood substance. The effect of the anatomical cellular structure on the accessibility was reflected in the variation of the diffusion rate with the wood species. The size effect of the diffusants also played an important role for the diffusion process in wood. Since the volumetric percentage of wood fibers and wood rays is relatively similar, the dichroic effects due to the anisotropy of the cellulose chains were apparently diminished. Finally, we proposed a new interpretation of the fine structure of the microfibrils in the cell wall by comparing a series of results from hardwood and softwood. Each elementary fibril in the hardwood has a more homogeneous arrangement in the microfibrils compared to that in the softwood.

1-Butanol↗

PubMed2002

Time-resolved infrared spectroscopic study of the switching dynamics of a surface-stabilized ferroelectric liquid crystal.

The orientation dynamics of a ferroelectric liquid crystal with a naphthalene ring (FLC-3) during the electric-field-induced switching between two surface-stabilized states was investigated by means of time-resolved Fourier-transform infrared spectroscopy. Time-resolved infrared spectra of the planar-aligned cell of FLC-3 were measured as a function of the polarization angle ranging from 0 degree to 180 degrees under a rectangular electric field +/-40 V with a 5-kHz repetition rate in the smectic-C* (Sm-C*) phase at 137 degrees C. From these spectra details about the mutual arrangement of different molecular segments at all the delay times in the Sm-C* phase were derived. It was found that the C=O group in the core moiety exhibits a dynamical behavior different from that in the chiral moiety during the electric-field-induced switching between the two surface-stabilized states. The most important finding in the present study is that during the electric-field-induced switching the FLC molecule not only rotates around the layer normal, but also revolves around its own long axis. Furthermore, time-resolved infrared spectroscopy revealed that each group in the core moiety passes almost simultaneously through the projection of the layer normal in the cell window during the dynamic switching.

Journal Article↗

PubMed2001

Polarized infrared spectroscopic study on the orientation of the molecules in the smectic-C* phase of a ferroelectric liquid crystal with a naphthalene ring: alternative theory for the analysis of polarization-angle-dependent intensity changes.

A theory to explain the polarization-angle dependence of polarized infrared spectra of a ferroelectric liquid crystal in the surface-stabilized ferroelectric liquid crystal state is proposed. It describes the relationship between the intensity of the absorption bands and the polarization angle of the infrared radiation. Using this theory the polarization-angle dependence of the infrared band intensities was analyzed for a ferroelectric liquid crystal with a naphthalene ring and two phenyl rings with a stacked layer structure in the smectic-C* phase. The polarization-angle-dependent spectra were measured at 137 degrees C under external dc electric fields of +40 and -40 V to investigate the orientation of the molecules. Plots of the infrared absorbance versus polarization angle for representative bands were subjected to a curve fitting procedure by a least squares method. From the curves obtained the orientation of the transition dipole moments with respect to the molecular long axis and the orientation of the molecular long axis with respect to the rubbing direction of the cell were estimated based upon the suggested theory. The polarization-angle-dependent infrared spectra obtained were also analyzed by two-dimensional (2D) correlation spectroscopy. The 2D correlation analysis clearly detects a slight phase difference in the polarization-angle dependence which is hardly recognized in ordinary plots of the intensity changes in the infrared bands. The 2D correlation analysis allows us to separate asymmetric and symmetric stretching bands due to the chiral methyl group from those arising from other methyl groups in the alkyl chains.

Journal Article↗

PubMed2000

Monitoring the melt-extrusion transesterification of ethylene-vinylacetate copolymer by self-modeling curve resolution analysis of on-line near-infrared spectra.

The transesterification of molten ethylene-vinylacetate (EVA) copolymers by octanol with sodium methoxide as catalyst in an extruder has been monitored by on-line near infrared (NIR) spectroscopy. A total of 60 NIR spectra were acquired for 37 min with the last spectrum recorded 31 min after the addition of octanol and catalyst was stopped. The experimental spectra show strong baseline fluctuations which are corrected for by multiplicative scatter correction (MSC). The chemometric methods of the orthogonal projection approach (OPA) and multivariate curve resolution (MCR) were used to resolve the spectra and to derive concentration profiles of the species. The detailed analysis reveals the absence of completely pure variables which leads to small errors in the calculation of pure spectra. The initial estimation of a concentration that is necessary as an input parameter for MCR also presents a non-trivial task. We obtained results that were not ideal but applicable for practical concentration control. They enable a fast monitoring of the process in real-time and resolve the spectra of the EVA copolymer and the ethylene-vinyl alcohol (EVAL) copolymer to be very close to the reference spectra. The chemometric methods used and the decomposed spectra are discussed in detail.

Journal Article↗

PubMedDate not supplied

Two-dimensional/ATR infrared correlation spectroscopic study on water diffusion in a poly(epsilon-caprolactone) matrix.

In the present contribution, two-dimensional ATR-FTIR spectroscopy was used to study the diffusion of water in poly(epsilon-caprolactone) (PCL). In the spectral region of the nu(OH) stretching vibration of water, four absorption bands (3635, 3560, 3411, and 3220 cm(-1)) can be identified. The higher wavenumber band pair at 3635 and 3560 cm(-1) is assigned to the antisymmetric and symmetric OH stretching vibrations, respectively, of water which is partially hydrogen-bonded to the carbonyl groups of PCL, whereas the lower frequency band pair at 3411 (antisymmetric) and 3220 cm(-1) (symmetric) is attributed to the OH stretching vibrations of bulk water which is fully hydrogen-bonded to other water molecules. From the asynchronous map of a 2D correlation analysis of spectra recorded during the diffusion of water into PCL, it was concluded that during the diffusion process the water molecules first penetrate into the free volume (microvoids) of the PCL matrix or are molecularly dispersed in the polymer matrix and then form hydrogen bonds with the C=O groups of the polymer.

Biocompatible Materials↗