Vibrationally mediated photodissociation of nitrous acid

Hitherto unobserved overtone and combination bands of nitrous acid have been investigated by Fourier-transform infrared absorption spectroscopy and through the resonance enhancements they provide in the two-photon excition spectrum for forming OH(X) photofragments. Analysis of the band profiles associated with the second and third O—H stretching overtones of trans-HONO, and of the energy disposal into the OH(X) fragments resulting from two-photon dissociation mediated by these overtone levels, provide some clues as to the mechanism for intramolecular vibrational energy redistribution (IVR) within these vibrationally excited molecules. The work serves to highlight further the extreme sensitivity of vibrationally mediated photodissociation (VMP) as a means of revealing weak O—H stretching overtones, even in situations (as here) where the species of interest is but a minor constituent of an equilibrium mixture.

Single amino acid substitutions in puroindoline-b mutants influence lipid binding properties

External reflectance Fourier transform infrared (ER-FTIR) spectroscopy and surface pressure measurements have been used to characterize the interaction of wild-type puroindoline-b (Pin-b) and two mutant forms featuring single residue substitutions-namely, Gly-46 to Ser-46 (Pin-bH) and Trp-44 to Arg-44 (Pin-bS)-with condensed-phase monolayers of zwitterionic (L-alpha-dipalmitoylphosphatidylcholine, DPPC) and anionic (L-alpha-dipalmitoylphosphatidyl-dl-glycerol, DPPG) phospholipids. The interaction with anionic DPPG monolayers, monitored by surface pressure isotherms, was influenced significantly by mutations in Pin-b (p < 0.05); wild-type Pin-b showed the highest surface pressure change of 10.6 +/- 1.0 mN m(-1), followed by Pin-bH (7.9 +/- 1.6 mN m(-1)) and Pin-bS (6.3 +/- 1.0 mN m(-1)), and the surface pressure isotherm kinetics were also different in each case. Integrated Amide I peak areas from corresponding ER-FTIR spectra confirmed the differences in adsorption kinetics, but also showed that differences in adsorbed amount were less significant, suggesting that mutations influence the degree of penetration into DPPG films. All Pin-b types showed evidence of interaction with DPPC films, detected as changes in surface pressure (5.6 +/- 1.1 mN m(-1)); however, no protein peaks were detected in the ER-FTIR spectra, which indicated that the interaction was via penetration with limited adsorption at the lipid/water interface. The expression of Pin-b mutants is linked to wheat endosperm hardness; therefore, the data presented here suggest that the lipid binding properties may be pivotal within the mechanism for this quality trait. In addition, the data suggest antimicrobial activities of Pin-b mutants would be lower than those of the wild-type Pin-b, because of decreased selectivity toward anionic phospholipids.

Analysis of red and yellow ochre samples from Clearwell Caves and Catalhoyuk by vibrational spectroscopy and other techniques

Ochre samples excavated from the neolithic site at Qatalhoyuk, Turkey have been compared with "native" ochres from Clearwell Caves, UK using infrared spectroscopy backed up by Raman spectroscopy, scanning electron microscopy (with energy-dispersive X-rays (EDX) analysis), powder X-ray diffraction, diffuse reflection UV-Vis and atomic absorption spectroscopies. For the Clearwell Caves ochres, which range in colour from yellow-orange to red-brown, it is shown that the colour is related to the nature of the chromophore present and not to any differences in particle size. The darker red ochres contain predominantly haematite while the yellow ochre contains only goethite. The ochres from Qatalhoyuk contain only about one-twentieth of the levels of iron found in the Clearwell Caves ochres. The iron oxide pigment (haematite in all cases studied here) has been mixed with a soft lime plaster which also contains calcite and silicate (clay) minerals. (C) 2003 Elsevier B.V. All rights reserved.

Using a water-soluble melamine-formaldehyde resin to improve the hardness of Norway spruce wood

Samples of Norway spruce wood were impregnated with a water-soluble melamine formaldehyde resin by using short-term vacuum treatment and long-term immersion, respectively. By means of Fourier transform infrared (FTIR) spectroscopy and UV microspectrophotometry, it was shown that only diffusion during long-term immersion leads to sufficient penetration of melamine resin into the wood structure, the flow of liquids in Norway spruce wood during vacuum treatment being greatly hindered by aspirated pits. After an immersion in aqueous melamine resin solution for 3 days, the resin had penetrated to a depth > 4 mm, which, after polymerization of the resin, resulted in an improvement of hardness comparable to the hardwood beech. A finite element model describing the effect of increasing depth of modification on hardness demonstrated that under the test conditions chosen for this study, a minimum impregnation depth of 2 mm is necessary to achieve an optimum increase in hardness. (C) 2004 Wiley Periodicals, Inc.

Polymer-mediated disruption of drug crystallinity

Ibuprofen (IB), a BCS Class II compound, is a highly crystalline substance with poor solubility properties. Here we report on the disruption of this crystalline structure upon intimate contact with the polymeric carrier cross-linked polyvinylpyrrolidone (PVP-CL) facilitated by low energy simple mixing. Whilst strong molecular interactions between APIs and carriers within delivery systems would be expected on melting or through solvent depositions, this is not the case with less energetic mixing. Simple mixing of the two compounds resulted in a significant decrease in the differential scanning calorimetry (DSC) melting enthalpy for IB, indicating that approximately 30% of the crystalline content was disordered. This structural change was confirmed by broadening and intensity diminution of characteristic IB X-ray powder diffractometry (PXRD) peaks. Unexpectedly, the crystalline content of the drug continued to decrease upon storage under ambient conditions. The molecular environment of the mixture was further investigated using Fourier transform infrared (FT-IR) and Fourier transform Raman (FT-Raman) spectroscopy. These data suggest that the primary interaction between these components of the physical mix is hydrogen bonding, with a secondary mechanism involving electrostatic/hydrophobic interactions through the IB benzene ring. Such interactions and subsequent loss of crystallinity could confer a dissolution rate advantage for IB. (C) 2006 Elsevier B.V. All rights reserved.

Self-assembly and hydrogelation of an amyloid peptide fragment

The self-assembly of a fragment of the amyloid beta peptide that has been shown to be critical in amyloid fibrillization has been studied in aqueous solution. There are conflicting reports in the literature on the fibrillization of A beta (16-20), i.e., KLVFF, and our results shed light on this. In dilute solution, self-assembly of NH2-KLVFF-COOH is strongly influenced by aromatic interactions between phenylalanine units, as revealed by UV spectroscopy and circular dichroism. Fourier transform infrared (FTIR) spectroscopy reveals beta-sheet features in spectra taken for more concentrated solutions and also dried films. X-ray diffraction and cryo-transmission electron microscopy (cryo-TEM) provide further support for beta-sheet amyloid fibril formation. A comparison of cryo-TEM images with those from conventional dried and negatively stained TEM specimens highlights the pronounced effects of sample preparation on the morphology. A comparison of FTIR data for samples in solution and dried samples also highlights the strong effect of drying on the self-assembled structure. In more concentrated phosphate-buffered saline (PBS) solution, gelation of NH2-KLVFF-COOH is observed. This is believed to be caused by screening of the electrostatic charge on the peptide, which enables beta sheets to aggregate into a fibrillar gel network. The rheology of the hydrogel is probed, and the structure is investigated by light scattering and small-angle X-ray scattering.

Multi-responsive hydrogels based on N-isopropylacrylamide and sodium alginate

Hydrogels consisting of sodium alginate and N-isopropylacrylamide covalently crosslinked with N,N′-methylenebisacrylamide were prepared. The mixed-interpenetrated networks obtained were characterized using elemental analysis, Fourier transform infrared and Raman spectroscopy, swelling measurements and environmental scanning electron microscopy. The thermo- and pH-responsive properties of these hydrogels were evidenced by their swelling behaviour, which depended also on the amount of crosslinking agent and hydrogel composition.

Use of in situ FT-Raman spectroscopy to study the kinetics of the transformation of carbamazepine polymorphs

The solid-state transformation of carbamazepine from form III to form I was examined by Fourier Transform Raman spectroscopy. Using a novel environmental chamber, the isothermal conversion was monitored in situ at 130◦C, 138◦C, 140◦C and 150◦C. The rate of transformation was monitored by taking the relative intensities of peaks arising from two C H bending modes; this approach minimised errors due to thermal artefacts and variations in power intensities or scattering efficiencies from the samples in which crystal habit changed from a characteristic prism morphology (form III) to whiskers (form I). The solid-state transformation at the different temperatures was fitted to various solid-state kinetic models of which four gave good fits, thus indicating the complexity of the process which is known to occur via a solid–gas–solid mechanism. Arrhenius plots from the kinetic models yielded activation energies from 344 kJ mol−1 to 368 kJ mol−1 for the transformation. The study demonstrates the value of a rapid in situ analysis of drug polymorphic type which can be of value for at-line in-process control.

Absolute high spectral resolution measurements of surface solar radiation for detection of water vapour continuum absorption

Solar-pointing Fourier transform infrared (FTIR) spectroscopy offers the capability to measure both the fine scale and broadband spectral structure of atmospheric transmission simultaneously across wide spectral regions. It is therefore suited to the study of both water vapour monomer and continuum absorption behaviours. However, in order to properly address this issue, it is necessary to radiatively calibrate the FTIR instrument response. A solar-pointing high-resolution FTIR spectrometer was deployed as part of the ‘Continuum Absorption by Visible and Infrared radiation and its Atmospheric Relevance’ (CAVIAR) consortium project. This paper describes the radiative calibration process using an ultra-high-temperature blackbody and the consideration of the related influence factors. The result is a radiatively calibrated measurement of the solar irradiation at the ground across the IR region from 2000 to 10 000 cm−1 with an uncertainty of between 3.3 and 5.9 per cent. This measurement is shown to be in good general agreement with a radiative-transfer model. The results from the CAVIAR field measurements are being used in ongoing studies of atmospheric absorbers, in particular the water vapour continuum.

Ruminal dry matter and nitrogen degradation in relation to condensed tannin and protein molecular structures in sainfoin (Onobrychis viciifolia) and lucerne (Medicago sativa).

Sainfoin is a temperate legume that contains condensed tannins (CT), i.e. polyphenols that are able to bind proteins and thus reduce protein degradation in the rumen. A reduction in protein degradation in the rumen can lead to a subsequent increase in amino acid flow to the small intestine. The effects of CT in the rumen and the intestine differ according to the amount and structure of CT and the nature of the protein molecular structure. The objective of the present study was to investigate the degradability in the rumen of three CT-containing sainfoin varieties and CT-free lucerne in relation to CT content and structure (mean degree of polymerization, proportion of prodelphinidins and cis-flavanol units) and protein structure (amide I and II bands, ratio of amide I-to-amide II, α-helix, β-sheet, ratio of α-helix-to-β-sheet). Protein molecular structures were identified using Fourier transform/infrared-attenuated total reflectance (FT/IR-ATR) spectroscopy. The in situ degradability of three sainfoin varieties (Ambra, Esparcette and Villahoz) was studied in 2008, during the first growth cycle at two harvest dates (P1 and P2, i.e. 5 May and 2 June, respectively) and at one date (P3) during the second growth cycle (2 June) and these were compared with a tannin-free legume, lucerne (Aubigny). Loss of dry matter (DMDeg) and nitrogen (NDeg) in polyester bags suspended in the rumen was measured using rumen-fistulated cows. The NDeg of lucerne compared with sainfoin was 0·80 v. 0·77 at P1, 0·78 v. 0·65 at P2 and 0·79 v. 0·70 at P3, respectively. NDeg was related to the rapidly disappearing fraction (‘a’) fraction (r=0·76), the rate of degradation (‘c’) (r=0·92), to the content (r=−0·81) and structure of CT. However, the relationship between NDeg and the slowly disappearing fraction (‘b’) was weak. There was a significant effect of date and species×date, for NDeg and ‘a’ fraction. The secondary protein structure varied with harvest date (species×date) and was correlated with the fraction ‘b’. Both tannin and protein structures influenced the NDeg degradation. CT content and structure were correlated to the ‘a’ fraction and to the ‘c’. Features of the protein molecular secondary structure were correlated to the ‘b’ fraction.

Using paint to investigate fires: an ATR-IR study of the degradation of paint samples upon heating

Fire investigation is a challenging area for the forensic investigator. The aim of this work was to use spectral changes to paint samples to estimate the temperatures to which a paint has been heated. Five paint samples (one clay paint, two car paints, one metallic paint, and one matt emulsion) have been fully characterized by a combination of attenuated total reflectance Fourier transform infrared (ATR-IR), Raman, X-ray fluorescence spectroscopy and powder X-ray diffraction. The thermal decomposition of these paints has been investigated by means of ATR-IR and thermal gravimetric analysis. Clear temperature markers are observed in the ATR-IR spectra namely: loss of m(C = O) band, >300°C; appearance of water bands on cooling, >500°C; alterations to m(Si–O) bands due to dehydration of silicate clays, >700°C; diminution of m(CO3) and d(CO3) modes of CaCO3, >950°C. We suggest the possible use of portable ATR-IR for nondestructive, in situ analysis of paints.

Dinitrogen release from arylpentazole: A picosecond time-resolved infrared, spectroelectrochemical, and DFT computational study

p-(Dimethylamino)phenyl pentazole, DMAP-N5 (DMAP = Me2N−C6H4), was characterized by picosecond transient infrared spectroscopy and infrared spectroelectrochemistry. Femtosecond laser excitation at 310 or 330 nm produces the DMAP-N5 (S1) excited state, part of which returns to the ground state (τ = 82 ± 4 ps), while DMAP-N and DMAP-N3 (S0) are generated as double and single N2-loss photoproducts with η ≈ 0.14. The lifetime of DMAP-N5 (S1) is temperature and solvent dependent. [DMAP-N3]+ is produced from DMAP-N5 in a quasireversible, one-electron oxidation process (E1/2 = +0.67 V). Control experiments with DMAP-N3 support the findings. DFT B3LYP/6-311G** calculations were used to identify DMAP-N5 (S1), DMAP-N3 +, and DMAP-N in the infrared spectra. Both DMAP-N5 (S1) and [DMAP-N5]+ have a weakened N5 ring structure.

Hyperbranched polymers containing oxazoline monomers andsuccinic anhydride: applications in fast drying, low solvent coating formulations

tMelt-polycondensation of succinic acid anhydride with oxazoline-based diol monomers gave hyper-branched polymers with carboxylicacids terminal groups.1H NMR and quantitative13C NMRspectroscopy coupled with DEPT-13513C NMR experiment showed high degrees of branching (over 60%).Esterification of the acid end groups by addition of citronellol at 160◦C produced novel white spirit solubleresins which were characterized by Fourier transform-infrared (FTIR) spectroscopy, gel permeation chro-matography (GPC), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Blendsof the new hyperbranched materials with commercial alkyd resins resulted in a dramatic, concentrationdependent drop in viscosity. Solvent-borne coatings were formulated containing the hyperbranchedpolymers. Dynamic mechanical analysis studies revealed that the air drying rates of the new coatingsystems were enhanced compared with identical formulations containing only commercial alkyd resins.

Spectral design of temperature-invariant narrow bandpass filters for the mid-infrared

The ability of narrow bandpass filters to discriminate wavelengths between closely-separated gas absorption lines is crucial in many areas of infrared spectroscopy. As improvements to the sensitivity of infrared detectors enables operation in uncontrolled high-temperature environments, this imposes demands on the explicit bandpass design to provide temperature-invariant behavior. The unique negative temperature coefficient (dn/dT<0) of Lead-based (Pb) salts, in combination with dielectric materials enable bandpass filters with exclusive immunity to shifts in wavelength with temperature. This paper presents the results of an investigation into the interdependence between multilayer bandpass design and optical materials together with a review on invariance at elevated temperatures.

Biomineralisation by earthworms: an investigation into the stability and distribution of amorphous calcium carbonate

Background Many biominerals form from amorphous calcium carbonate (ACC), but this phase is highly unstable when synthesised in its pure form inorganically. Several species of earthworm secrete calcium carbonate granules which contain highly stable ACC. We analysed the milky fluid from which granules form and solid granules for amino acid (by liquid chromatography) and functional group (by Fourier transform infrared (FTIR) spectroscopy) compositions. Granule elemental composition was determined using inductively coupled plasma-optical emission spectroscopy (ICP-OES) and electron microprobe analysis (EMPA). Mass of ACC present in solid granules was quantified using FTIR and compared to granule elemental and amino acid compositions. Bulk analysis of granules was of powdered bulk material. Spatially resolved analysis was of thin sections of granules using synchrotron-based μ-FTIR and EMPA electron microprobe analysis. Results The milky fluid from which granules form is amino acid-rich (≤ 136 ± 3 nmol mg−1 (n = 3; ± std dev) per individual amino acid); the CaCO3 phase present is ACC. Even four years after production, granules contain ACC. No correlation exists between mass of ACC present and granule elemental composition. Granule amino acid concentrations correlate well with ACC content (r ≥ 0.7, p ≤ 0.05) consistent with a role for amino acids (or the proteins they make up) in ACC stabilisation. Intra-granule variation in ACC (RSD = 16%) and amino acid concentration (RSD = 22–35%) was high for granules produced by the same earthworm. Maps of ACC distribution produced using synchrotron-based μ-FTIR mapping of granule thin sections and the relative intensity of the ν2: ν4 peak ratio, cluster analysis and component regression using ACC and calcite standards showed similar spatial distributions of likely ACC-rich and calcite-rich areas. We could not identify organic peaks in the μ-FTIR spectra and thus could not determine whether ACC-rich domains also had relatively high amino acid concentrations. No correlation exists between ACC distribution and elemental concentrations determined by EMPA. Conclusions ACC present in earthworm CaCO3 granules is highly stable. Our results suggest a role for amino acids (or proteins) in this stability. We see no evidence for stabilisation of ACC by incorporation of inorganic components.