Correction of diffraction effects in confocal raman microspectroscopy

A mathematical approach developed to correct depth profiles of wet-chemically modified polymer films obtained by confocal Raman microscopy is presented which takes into account scattered contributions originated from a diffraction-limited laser focal volume. It is demonstrated that the problem can be described using a linear Fredholm integral equation of the first kind which correlates apparent and true Raman intensities with the depth resolution curve of the instrument. The calculations of the corrected depth profiles show that considerable differences between apparent and corrected depth profiles exist at the surface, especially when profiles with strong concentration gradients are dealt with or an instrument with poor depth resolution is used. Degrees of modification at the surface obtained by calculation of the corrected depth profiles are compared with those measured by FTIR-ATR and show an excellent concordance.</p

CYP2C19 pharmacogenetics in advanced cancer: compromised function independent of genotype

CYP2C19 is a drug-metabolising enzyme involved in the metabolism of a number of chemotherapeutic agents including cyclophosphamide. Variants of the CYP2C19 gene result in a loss of function polymorphism, which affects approximately 3% of the Caucasian population. These individuals are poor metabolisers (PM) of a wide range of medications including omeprazole (OMP). In healthy subjects PM can be identified through homozygous variant genotype. However, a discordance between CYP2C19 genotype and phenotype has been reported previously in a small study of cancer patients. To investigate whether CYP2C19 activity was decreased in patients with advanced cancer, CYP2C19 genotype was determined in 33 advanced cancer patients using PCR-RFLP analysis for the two important allelic variants (*2,681G>A and *3,636G>A) and the activity of the enzyme was evaluated using the CYP2C19 probe drug OMP. The activity of the drug-metabolising enzyme CYP2C19 was severely compromised in advanced cancer patients, resulting in a PM status in 37% of the patients who had normal genotype. This is significantly (P<0.0005) higher than that would be predicted from the genotypic status of these patients. There was no evidence of a correlation between compromised CYP2C19 activity and any of the proinflammatory cytokines or acute phase response proteins studied. However, there was preliminary evidence of an association between PM status and low body mass (P=0.03). There is increasing interest in using pharmacogenetics to ‘individualise medicine', however, the results of this study indicate that in a cancer population genotyping for CYP2C19 would significantly underestimate the number of phenotypic PM of drugs, such as cyclophosphamide, which may be metabolised by this enzyme

Syndiotactic polystyrene/ethylbenzene complex: Chain conformations and phase behaviour

Syndiotactic polystyrene (sPS) has been studied, primarily in the delta (solvent-stabilised) and gamma phases. Crystallisation from dilute ethylbenzene solution at 40 degrees C leads to a lamellar morphology, with a similar unit cell for the polymer/solvent complex as that proposed by Chatani et al for the sPS/toluene complex [1]. As the temperature is raised, the X-ray long period increases in the temperature range of decomplexation, becoming constant in the gamma phase before increasing again on annealing in the alpha phase. Neutron scattering measurements show negligible isotopic fractionation and only a small increase in the radius of gyration in the plane of the sedimented delta phase mats (R-xy) with increasing molecular weight. Together with model simulations which reproduce satisfactorily both the form of Kratky plots and the values for R-xy, this evidence points strongly towards a sheetlike structure (as is obtained for other non-complexing solution-grown polymer crystals). Increases in R-xy and changes in the scattering curves from those characteristic of sheetlike structures in the gamma phase are interpreted as indicating movement of crystal stems out of the sheers

Molecular dimensions in the delta and gamma phases of syndiotactic polystyrene, using small angle neutron scattering

The delta phase of syndiotactic polystyrene/ethylbenzene has previously been shown to involve a sheet-like arrangement of crystal stems, with superfolding at higher molecular weights. SANS measurements have been made using tilted samples in order to separate in-plane and out-of-plane radii of gyration. Use of intensities from the whole area of the detector allows the determination of these quantities with good precision. Comparison between the out-of-plane radius and the long spacing determined from small angle X-ray measurements shows close agreement for the lower molecular weight ((M) over bar(w), = 42 700) in both delta and gamma phases, while R-z is a factor of 2 larger for the higher molecular weight ((M) over bar(w) = 124500). This indicates that each molecule occupies a single lamella at the lower molecular weight and, on average, two lamellae at the higher one, in both delta and gamma phases. This provides clear evidence of tie molecules at the higher molecular weight, and also implies that the delta to gamma phase transition only involves a reorganisation of chain segments within those lamellae which originally contained the molecule. (C) 1999 Elsevier Science Ltd. All rights reserved

Mixed crystal infrared spectroscopy of uniaxially drawn polyethylene films

Blends of fully deuterated polyethylene with unlabeled polymer have been studied using Fourier transform infrared (FT-IR) spectroscopy. Melt quenched samples were drawn at 1 mm min(-1), clamped, and cooled with liquid nitrogen. The CD2 bending vibration is sensitive to the local molecular arrangement. Changes in band components were related to (1) crystallization of amorphous polymer; (2) the untwisting of spherulite ribbons perpendicular to the draw direction; and (3) coarse slip. Measurement of remaining doublet splittings enabled estimates of surviving crystallite block sizes to be made. In addition, CH2 wagging and rocking bands showed evidence of increasingly defective crystals and of a Martensitic transformation to the monoclinic crystal form

Structural information from progression bands in the FTIR spectra of long chain n-alkanes

The low temperature FTIR spectrum of long chain n-alkanes has been investigated in the region between the C–C stretching and CH2 twisting fundamentals (1050–1133 cm−1). With successive annealing and cooling stages, extended chain crystals of n-C198H398 show an improvement in the regularity of the progression bands observed. This is related to a ‘perfecting’ of the crystals. A once-folded sample of the same alkane shows additional features between 1050 and 1100 cm−1, attributed to resonance modes from a tight (110) fold. These disappear on transformation to the extended form, to be replaced by progression bands. Assignment of the individual bands enables the length of the all-trans chain to be estimated and this method is used to show that centre-branched long chain n-alkanes have a folded conformation. It is also shown that the chain length derived from such FTIR data for a 1:1 molar mixture of n-C162H326 and n-C246H494 is consistent with a triple layer superlattice structure. </p

Conformationally sensitive infrared vibrations of the syndiotactic polystyrene/ethylbenzene complex

The 920-960 cm(-1) region of the infrared spectrum of the delta phase syndiotactic polystyrene/ethylbenzene predominantly involves bands arising from helical structures and has been studied here as a function of heating temperature. Curve fitting and deconvolution showed the necessity, for annealing temperatures above 120 degrees C, of adding a third component at 940 cm(-1) to peaks at 934 and 943 cm(-1). The 934 and 943 cm(-1) peaks behave as a doublet, primarily due to the delta phase, with the splitting increasing on annealing. The 940 cm(-1) peak is solely due to the gamma phase helix. Importantly, these assignments provide the opportunity for using these bands for further studies of complexation/decomplexation in such systems. The reduction in absorbance of 934 and 943 cm(-1) peaks occurs at a lower temperature than the rise in the 940 cm(-1) absorbance, and this is attributed to disordering of the delta phase helices prior to reformation as gamma phase helices. Similar measurements using deuterated syndiotactic polystyrene also showed helix and zigzag bands, but without a predominantly delta phase helix peak. Solvent peaks in the deuterated syndiotactic polystyrene/ethylbenzene system were used to monitor the delta to gamma phase transition. In combination with DSC and TGA data, the melting temperature of the alpha phase was found to be depressed by 7 degrees C for the deuterated polymer, while the delta to gamma phase transition temperature was shown to be around 24 degrees C higher

Molecular changes on drawing isotopic blends of polyethylene and ethylene copolymers. Part 2. MCIRS studies

The technique of mixed crystal FTIR spectroscopy has been applied to uniaxially drawn isotopic blends of linear polyethylene and ethylene copolymers. Following the drawing of melt-quenched samples at 1 mm minK1, clamped samples were cooled with liquid nitrogen. Analysis of the CD2 bending vibration of the ‘guest’ perdeuterated species enabled the arrangement of crystal stems to be characterised. Changes in band components observed were identified with the processes of polymer crystallisation, the untwisting of lamellar ribbons perpendicular to the draw direction and coarse slip. For example, the appearance of new doublets or increased splittings is related to crystallisation, while an increase in singlet band area, at least at higher draw ratios, is indicative of coarse slip. Crystallisation appears to be complete at a draw ratio of 4 for a linear polyethylene sample with low guest molecular weight. For similar copolymer ‘guest’ molecular weights, the processes identified above are delayed to higher levels of deformation. This was attributed to copolymer branches hindering both crystallisation and chain translation through lamellae. Estimates of the crystallite block size present after drawing enable a quantitative description of coarse slip to be obtained. A progressive increase in width of the central singlet for two of these samples is tentatively ascribed to variations in molecular strain.</p

Molecular changes on drawing isotopic blends of polyethylene and ethylene copolymers: 1. Static and time-resolved sans studies

Small angle neutron scattering (sans) has been used to observe changes in molecular orientation on deformation of isotopic, melt quenched blends of linear polyethylene and copolymers with butyl and hexyl branches, using uniaxial drawing. In no case was there evidence of significant isotopic fractionation either before or during deformation. Samples left clamped in the neutron beam following deformation showed no evidence of molecular relaxation, while significant changes in molecular orientation with time were observed for samples unclamped after deformation. This latter behaviour could be fitted adequately by a single exponential decay and the relaxation time was found to be of the order of tens of minutes. This relaxation time increased with both increasing molecular weight and the presence of branching. For samples drawn to draw ratios of up to 3.0, the anisotropy in the radius of gyration was compared with predictions for affine deformation. Only in the cases of linear labelled guest molecules in either a linear or copolymer host were significant departures from the affine model observed: no such departures were found for copolymer guest molecules. This is interpreted in terms of a delay in crystallite disruption until higher draw ratios for copolymer guest molecules with respect to linear guest.</p

Neutron scattering studies of syndiotactic polystyrene/ethylbenzene

The neutron scattering observed from delta-phase samples of syndiotactic polystyrene (sPS)/ethylbenzene is shown to be consistent with sheet-like arrangements of crystal stems arranged along the a direction. Adjacent stems therefore show an alternation in helicity. Simulations based on a statistical model have been used to calculate statistical parameters, such as the probability of adjacency (P-A) for which optimum agreement is found for a value of 0.8. Radii of gyration obtained from simulations are in good agreement with experimental values. The molecular weight range studied appears to cover the change from a single-sheet structure to a superfolded double sheet. The same stem statistics (with P-A = 0.8) apply, irrespective of molecular weight. Scattering data from the gamma phase of sPS are well reproduced by a model involving some movement of stems out of the planes of the sheets. (C) 1998 Elsevier Science Ltd. All rights reserved