The determination of molecular orientation in uniaxially compressed PMMA by X-ray scattering

A procedure is presented for obtaining full molecular orientation information from wide angle X-ray scattering patterns of deformed non-crystalline polymers. The method is based on the analysis of experimental and calculated scattering patterns into their spherical harmonics. The results obtained for PMMA are compared with values predicted by the pseudo affine and affine deformation schemes.

A two-dimensional X-ray scattering system for in-situ time-resolving studies of polymer structures subjected to controlled deformations

A two-dimensional X-ray scattering system developed around a CCD-based area detector is presented, both in terms of hardware employed and software designed and developed. An essential feature is the integration of hardware and software, detection and sample environment control which enables time-resolving in-situ wide-angle X-ray scattering measurements of global structural and orientational parameters of polymeric systems subjected to a variety of controlled external fields. The development and operation of a number of rheometers purpose-built for the application of such fields are described. Examples of the use of this system in monitoring degrees of shear-induced orientation in liquid-crystalline systems and crystallization of linear polymers subsequent to shear flow are presented.

Penciclovir solubility in Eudragit films: a comparison of X-ray, thermal, microscopic and release rate techniques

The solubility of penciclovir (C10N5O3H17) in a novel film formulation designed for the treatment of cold sores was determined using X-ray, thermal, microscopic and release rate techniques. Solubilities of 0.15–0.23, 0.44, 0.53 and 0.42% (w/w) resulted for each procedure. Linear calibration lines were achieved for experimentally and theoretically determined differential scanning calorimetry (DSC) and X-ray powder diffractometry (XRPD) data. Intra- and inter-batch data precision values were determined; intra values were more precise. Microscopy was additionally useful for examining crystal shape, size distribution and homogeneity of drug distribution within the film. Whereas DSC also determined melting point, XRPD identified polymorphs and release data provided relevant kinetics.

Quantitative analysis of mannitol polymorphs: X-ray powder diffractometry—exploring preferred orientation effects

Mannitol is a polymorphic pharmaceutical excipient, which commonly exists in three forms: alpha, beta and delta. Each polymorph has a needle-like morphology, which can give preferred orientation effects when analysed by X-ray powder diffractometry (XRPD) thus providing difficulties for quantitative XRPD assessments. The occurrence of preferred orientation may be demonstrated by sample rotation and the consequent effects on X-ray data can be minimised by reducing the particle size. Using two particle size ranges (less than 125 and 125–500�microns), binary mixtures of beta and delta mannitol were prepared and the delta component was quantified. Samples were assayed in either a static or rotating sampling accessory. Rotation and reducing the particle size range to less than�125 microns halved the limits of detection and quantitation to 1 and 3.6%, respectively. Numerous potential sources of assay errors were investigated; sample packing and mixing errors contributed the greatest source of variation. However, the rotation of samples for both particle size ranges reduced the majority of assay errors examined. This study shows that coupling sample rotation with a particle size reduction minimises preferred orientation effects on assay accuracy, allowing discrimination of two very similar polymorphs at around the 1% level

Preventing carbon contamination of optical devices for X-rays: the effect of oxygen on photon-induced dissociation of CO on platinum

Platinum is one of the most common coatings used to optimize mirror reflectivity in soft X-ray beamlines. Normal operation results in optics contamination by carbon-based molecules present in the residual vacuum of the beamlines. The reflectivity reduction induced by a carbon layer at the mirror surface is a major problem in synchrotron radiation sources. A time-dependent photoelectron spectroscopy study of the chemical reactions which take place at the Pt(111) surface under operating conditions is presented. It is shown that the carbon contamination layer growth can be stopped and reversed by low partial pressures of oxygen for optics operated in intense photon beams at liquidnitrogen temperature. For mirrors operated at room temperature the carbon contamination observed for equivalent partial pressures of CO is reduced and the effects of oxygen are observed on a long time scale.

Unraveling the electronic structures of low-valent naphthalene and anthracene iron complexes: x-ray, spectroscopic, and density functional theory studies

Naphthalene and anthracene transition metalates are potent reagents, but their electronic structures have remained poorly explored. A study of four Cp*-substituted iron complexes (Cp* = pentamethylcyclopentadienyl) now gives rare insight into the bonding features of such species. The highly oxygen- and water-sensitive compounds [K(18-crown- 6){Cp*Fe(η4-C10H8)}] (K1), [K(18-crown-6){Cp*Fe(η4-C14H10)}] (K2), [Cp*Fe(η4-C10H8)] (1), and [Cp*Fe(η4-C14H10)] (2) were synthesized and characterized by NMR, UV−vis, and 57Fe Mössbauer spectroscopy. The paramagnetic complexes 1 and 2 were additionally characterized by electron paramagnetic resonance (EPR) spectroscopy and magnetic susceptibility measurements. The molecular structures of complexes K1, K2, and 2 were determined by single-crystal X-ray crystallography. Cyclic voltammetry of 1 and 2 and spectroelectrochemical experiments revealed the redox properties of these complexes, which are reversibly reduced to the monoanions [Cp*Fe(η4-C10H8)]− (1−) and [Cp*Fe(η4-C14H10)]− (2−) and reversibly oxidized to the cations [Cp*Fe(η6-C10H8)]+ (1+) and [Cp*Fe(η6-C14H10)]+ (2+). Reduced orbital charges and spin densities of the naphthalene complexes 1−/0/+ and the anthracene derivatives 2−/0/+ were obtained by density functional theory (DFT) methods. Analysis of these data suggests that the electronic structures of the anions 1− and 2− are best represented by low-spin FeII ions coordinated by anionic Cp* and dianionic naphthalene and anthracene ligands. The electronic structures of the neutral complexes 1 and 2 may be described by a superposition of two resonance configurations which, on the one hand, involve a low-spin FeI ion coordinated by the neutral naphthalene or anthracene ligand L, and, on the other hand, a low-spin FeII ion coordinated to a ligand radical L•−. Our study thus reveals the redox noninnocent character of the naphthalene and anthracene ligands, which effectively stabilize the iron atoms in a low formal, but significantly higher spectroscopic oxidation state.

Oxidoalkoxidovanadium(V) complexes: synthesis, characterization and comparison of X-ray crystal structures

The reaction of VO(acac)(2) with the ONO-chelator obtained by the condensation of salicylaldehyde with 2-hydroxybenzoylhydrazine (H2L) in a monohydric alcohol. (ROH) medium produces VO(OR)L]-type oxidoalkoxido complexes (1-7) where R = Me, Pr-n, Pr-i, Bu-n, Bu-i, Bu-t and (n)Pen. All the complexes show the metal atom to have a five-coordinate square pyramidal environment, although in some complexes there is an additional weak V center dot center dot center dot O interaction in the sixth axial position. In acetonitrile medium and in the presence of a cis-diol (ethylene glycol), H2L reacts with VO(acac)(2) to form a six-coordinate complex, [VO(OCH2CH2OH)L] (8). When the reaction is carried out in acetonitrile medium in the presence of 2-amino ethanol, a completely different type of product containing the square pyramidal complex anion [VO2L](-) associated with the cation [NH3CH2CH2OH](+) is obtained. It was noted previously that on being reacted with monodentate nitrogen donor bases B (which are stronger than pyridine), the [VO(OR)L] complexes react to form the same complex anion [VO2L](-) associated with the corresponding cation [BH](+). The coordination environment around the V(V) acceptor center of the water soluble [BH](+)[VO2L](-)satisfies one of the several requirements for an efficient antidiabetic vanadium species such as water solubility, nature of donor atoms of the ligand and their disposition around the VO2+ acceptor center.

Peroxidative bromination and oxygenation of organic compounds: synthesis, X-ray crystal structure and catalytic implications of mononuclear and binuclear oxovanadium(V) complexes containing Schiffbase ligands

Treatment of of (R,R)-N,N-salicylidene cyclohexane 1,2-diamine(H(2)L(1)) in methanol with aqueous NH(4)VO(3) solution in perchloric acid medium affords the mononuclear oxovanadium(V) complex [VOL(1)(MeOH)]-ClO(4) (1) as deep blue solid while the treatment of same solution of (R,R)-N,N-salicylidene cyclohexane 1,2-diamine(H(2)L(1)) with aqueous solution of VOSO(4) leads to the formation of di-(mu-oxo) bridged vanadium(V) complex [VO(2)L(2)](2) (2) as green solid where HL(2) = (R,R)-N-salicylidene cyclohexane 1,2-diamine. The ligand HL(2) is generated in situ by the hydrolysis of one of the imine bonds of HL(1) ligand during the course of formation of complex [VO(2)L(2)](2) (2). Both the compounds have been characterized by single crystal X-ray diffraction as well as spectroscopic methods. Compounds 1 and 2 are to act as catalyst for the catalytic bromide oxidation and C-H bond oxidation in presence of hydrogen peroxide. The representative substrates 2,4-dimethoxy benzoic acid and para-hydroxy benzoic acids are brominated in presence of H(2)O(2) and KBr in acid medium using the above compounds as catalyst. The complexes are also used as catalyst for C-H bond activation of the representative hydrocarbons toluene, ethylbenzene and cyclohexane where hydrogen peroxide acts as terminal oxidant. The yield percentage and turnover number are also quite good for the above catalytic reaction. The oxidized products of hydrocarbons have been characterized by GC Analysis while the brominated products have been characterized by (1)H NMR spectroscopic studies.