Intermediate band to conduction band optical absorption in ZnTeO

ZnTe doped with high concentrations of oxygen has been proposed in previous works as an intermediate band (IB) material for photovoltaic applications. The existence of extra optical transitions related to the presence of an IB has already been demonstrated in this material and it has been possible to measure the absorption coefficient of the transitions from the valence band (VB) to the IB. In this study, we present the first measurement of the absorption coefficient associated with transitions from the IB to the conduction band (CB) in ZnTeO. The samples used are 4-mum-thick ZnTe layers with or without O in a concentration ~10 19 cm -3, which have been grown on semiinsulating GaAs substrates by molecular beam epitaxy (MBE). The IB-CB absorption coefficient peaks for photon energies ~0.4 eV. It is extracted from reflectance and transmittance spectra measured using Fourier transform infrared (FTIR) spectroscopy. Under typical FTIR measurement conditions (low light intensity, broadband spectrum), the absorption coefficient in IB-to-CB transitions reaches 700 cm -1. This is much weaker than the one observed for VB-IB absorption. This result is consistent with the fact that the IB is expected to be nearly empty of electrons under equilibrium conditions in ZnTe(O).

trans/cis (Z/E) photoisomerization of the chromophore of photoactive yellow protein is not a prerequisite for the initiation of the photocycle of this photoreceptor protein

The chromophore of photoactive yellow protein (PYP) (i.e., 4-hydroxycinnamic acid) has been replaced by an analogue with a triple bond, rather than a double bond (by using 4-hydroxyphenylpropiolic acid in the reconstitution, yielding hybrid I) and by a “locked” chromophore (through reconstitution with 7-hydroxycoumarin-3-carboxylic acid, in which a covalent bridge is present across the vinyl bond, resulting in hybrid II). These hybrids absorb maximally at 464 and 443 nm, respectively, which indicates that in both hybrids the deprotonated chromophore does fit into the chromophore-binding pocket. Because the triple bond cannot undergo cis/trans (or E/Z) photoisomerization and because of the presence of the lock across the vinyl double bond in hybrid II, it was predicted that these two hybrids would not be able to photocycle. Surprisingly, both are able. We have demonstrated this ability by making use of transient absorption, low-temperature absorption, and Fourier-transform infrared (FTIR) spectroscopy. Both hybrids, upon photoexcitation, display authentic photocycle signals in terms of a red-shifted intermediate; hybrid I, in addition, goes through a blue-shifted-like intermediate state, with very slow kinetics. We interpret these results as further evidence that rotation of the carbonyl group of the thioester-linked chromophore of PYP, proposed in a previous FTIR study and visualized in recent time-resolved x-ray diffraction experiments, is of critical importance for photoactivation of PYP.

Efficient exchange of the primary quinone acceptor QA in isolated reaction centers of Rhodopseudomonas viridis

A key step in the conversion of solar energy into chemical energy by photosynthetic reaction centers (RCs) occurs at the level of the two quinones, QA and QB, where electron transfer couples to proton transfer. A great deal of our understanding of the mechanisms of these coupled reactions relies on the seminal work of Okamura et al. [Okamura, M. Y., Isaacson, R. A., & Feher, G. (1975) Proc. Natl. Acad. Sci. USA 88, 3491–3495], who were able to extract with detergents the firmly bound ubiquinone QA from the RC of Rhodobacter sphaeroides and reconstitute the site with extraneous quinones. Up to now a comparable protocol was lacking for the RC of Rhodopseudomonas viridis despite the fact that its QA site, which contains 2-methyl-3-nonaprenyl-1,4-naphthoquinone (menaquinone-9), has provided the best x-ray structure available. Fourier transform infrared difference spectroscopy, together with the use of isotopically labeled quinones, can probe the interaction of QA with the RC protein. We establish that a simple incubation procedure of isolated RCs of Rp. viridis with an excess of extraneous quinone allows the menaquinone-9 in the QA site to be almost quantitatively replaced either by vitamin K1, a close analogue of menaquinone-9, or by ubiquinone. To our knowledge, this is the first report of quinone exchange in bacterial photosynthesis. The Fourier transform infrared data on the quinone and semiquinone vibrations show a close similarity in the bonding interactions of vitamin K1 with the protein at the QA site of Rp. viridis and Rb. sphaeroides, whereas for ubiquinone these interactions are significantly different. The results are interpreted in terms of slightly inequivalent quinone–protein interactions by comparison with the crystallographic data available for the QA site of the two RCs.

Monitoring the GAP catalyzed H-Ras GTPase reaction at atomic resolution in real time

The molecular reaction mechanism of the GTPase-activating protein (GAP)-catalyzed GTP hydrolysis by Ras was investigated by time resolved Fourier transform infrared (FTIR) difference spectroscopy using caged GTP (P3-1-(2-nitro)phenylethyl guanosine 5′-O-triphosphate) as photolabile trigger. This approach provides the complete GTPase reaction pathway with time resolution of milliseconds at the atomic level. Up to now, one structural model of the GAP⋅Ras⋅GDP⋅AlFx transition state analog is known, which represents a “snap shot” along the reaction-pathway. As now revealed, binding of GAP to Ras⋅GTP shifts negative charge from the γ to β phosphate. Such a shift was already identified by FTIR in GTP because of Ras binding and is now shown to be enhanced by GAP binding. Because the charge distribution of the GAP⋅Ras⋅GTP complex thus resembles a more dissociative-like transition state and is more like that in GDP, the activation free energy is reduced. An intermediate is observed on the reaction pathway that appears when the bond between β and γ phosphate is cleaved. In the intermediate, the released Pi is strongly bound to the protein and surprisingly shows bands typical of those seen for phosphorylated enzyme intermediates. All these results provide a mechanistic picture that is different from the intrinsic GTPase reaction of Ras. FTIR analysis reveals the release of Pi from the protein complex as the rate-limiting step for the GAP-catalyzed reaction. The approach presented allows the study not only of single proteins but of protein–protein interactions without intrinsic chromophores, in the non-crystalline state, in real time at the atomic level.

Obtenção de gel mucoadesivo de nistatina para o tratamento da candidíase oral. Desenvolvimento e caracterização de dispersões sólidas de nistatina

A nistatina (NYS) é o fármaco de primeira escolha no tratamento da candidíase oral, que frequentemente acomete mais os indivíduos imunocomprometidos e pacientes com outras desordens (diabetes não tratada, neoplasias, imunodeficiências). No mercado brasileiro, a NYS é encontrada na forma de suspensão oral aquosa, onde o procedimento para sua administração consiste em bochechar o medicamento. Apesar de haver a indicação de que se mantenha o contato direto entre fármaco e a mucosa oral, na qual se encontra a Candida spp., o que aumentaria expressivamente o sucesso terapêutico, a suspensão não apresenta tal propriedade. Assim, a NYS que é fármaco com ação efetiva contra a candidíase oral, é considerada pertencente à Classe IV do Sistema de Classificação Biofarmacêutica, ou seja, apresenta baixa solubilidade e baixa permeabilidade. A baixa solubilidade pode comprometer sua disponibilidade na cavidade oral, e consequentemente, sua ação farmacológica. Diante desse quadro, o objetivo do presente trabalho foi o desenvolvimento de dispersões sólidas de NYS para o tratamento da candidíase oral, e sua posterior incorporação em gel mucoadesivo oral, favorecendo a formulação no local de ação. As dispersões sólidas são sistemas farmacêuticos, onde um fármaco pouco solúvel em água encontra-se dispersado em um carreador, no estado sólido. Os carreadores normalmente são hidrofílicos, o que permite que esses sistemas sejam empregados para aumentar a solubilidade aquosa do fármaco. Assim, foram desenvolvidas as dispersões sólidas de NYS, pelo método de eliminação do solvente, empregando como carreadores, lactose, HPMC, poloxamer 407 e poloxamer 188. Essas foram submetidas à caracterização por análise térmica, usando os ensaios de calorimetria exploratória diferencial (DSC) e termogravimetria/termogravimetria derivada (TG/DTG). Dentre essas dispersões sólidas, aquelas que se mostraram com comportamento térmico sugerindo a formação de um novo \"sistema\", foram analisadas por meio de ensaio de solubilidade. Dessa forma, a formulação NYS DS G2 (49) se destacou, pois apresentou maior solubilidade em água (4,484 mg/mL); em pH 5,5 (4,249 mg/mL) e em pH 7,0 (4,293 mg/mL), ou seja, houve um aumento de 1,426 vezes em água; 4,227 vezes em pH 5,5; e 2,743 vezes em pH 7,0. Essa formulação foi, por fim avaliada por difração de raio-X e espectroscopia de infravermelho com transformada de Fourier, técnicas que corroboraram com a análise térmica quanto à indicação de formação da dispersão sólida. Por sua vez, essa dispersão sólida foi incorporada em 4 bases de géis mucoadesivos de carbopol ® 934 PNF, alterando apenas a concentração do polímero (0,5; 1,0; 1,5; 2,0 %p/p). Foi observado que a liberação de NYS DS G2 (49) foi superior, quando comparada à liberação de NYS MP a partir do gel, e através do ensaio de mucoadesão, percebeu-se que os géis desenvolvidos apresentaram propriedades mucoadesivas compatíveis com relatos na literatura, independentemente da quantidade de carbopol ® empregada. As características reológicas foram distintas, e foi observado que as formulações Gel A e Gel B, que possuem menor quantidade de polímero, tiverem um indicativo de comportamento de fluido newtoniano, diferente dos demais, o que pode não ser desejado para esse tipo de forma farmacêutica tópica e semi-sólida. Ao final desse trabalho, pode-se concluir que foi possível desenvolver um sistema farmacêutico na forma de dispersão sólida com maior solubilidade que a NYS pura, e sua incorporação em uma forma farmacêutica mucoadesiva, e que a liberação da NYS na forma DS foi muito superior que o fármaco na forma \"convencional\", o que permite que a NYS esteja mais disponível na cavidade oral, e também junto à mucosa bucal, o que levaria a efeito farmacológico mais efetivo do antifúngico.

Stabilisation of low softening point petroleum pitch fibres by HNO3

This paper deals with the stabilisation of low softening point pitch fibres obtained from petroleum pitches using HNO3 as oxidising agent. This method presents some advantages compared with conventional methods: pitches with low softening point (SP) can be used to prepare carbon fibres (CF), the stabilisation time has been reduced, the CF yields are similar to those obtained after general methods of stabilisation, and the initial treatments to increase SP when low SP pitches are used to prepare CF, are avoided. The parent pitches were characterised by different techniques such as diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), elemental analysis and solvent extraction with toluene and quinoline. The interaction between HNO3 and the pitch fibres, as well as the changes occurring during the heat treatment, have been followed by DRIFTS.

Kinetic study of the decompositions involved in the thermal degradation of commercial azodicarbonamide

The transitions and reactions involved in the thermal treatment of several commercial azodicarbonamides (ADC) in an inert atmosphere have been studied by dynamic thermogravimetry analysis (TGA), mass spectrometry and Fourier transform infrared (FTIR) spectroscopy. A pseudo-mechanistic model, involving several competitive and non-competitive reactions, has been suggested and applied to the correlation of the weight loss data. The model applied is capable of accurately representing the different processes involved, and can be of great interest in the understanding and quantification of such phenomena, including the simulation of the instantaneous amount of gases evolved in a foaming process. In addition, a brief discussion on the methodology related to the mathematical modeling of TGA data is presented, taking into account the complex thermal behaviour of the ADC.

Characterization and electrochemical properties of conducting nanocomposites synthesized from p-anisidine and aniline with titanium carbide by chemical oxidative method

A novel polymer/TiC nanocomposites “PPA/TiC, poly(PA-co-ANI)/TiC and PANI/TiC” was successfully synthesized by chemical oxidation polymerization at room temperature using p-anisidine and/or aniline monomers and titanium carbide (TiC) in the presence of hydrochloric acid as a dopant with ammonium persulfate as oxidant. These nanocomposites obtained were characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and thermogravimetric analysis (TGA). XRD indicated the presence of interactions between polymers and TiC nanoparticle and the TGA revealed that the TiC nanoparticles improve the thermal stability of the polymers. The electrical conductivity of nanocomposites is in the range of 0.079–0.91 S cm−1. The electrochemical behavior of the polymers extracted from the nanocomposites has been analyzed by cyclic voltammetry. Good electrochemical response has been observed for polymer films; the observed redox processes indicate that the polymerisation on TiC nanoparticles produces electroactive polymers. These nanocomposite microspheres can potentially used in commercial applications as fillers for antistatic and anticorrosion coatings.

Standard infrared prism spectra.

Vol. 57 has title: Standard infrared grating spectra.

Infrared spectra of polymers and resins.

Cover title: Infrared spectra of plastics and resins.

Immobilization of aluminum chloride on MCM-41 as a new catalyst system for liquid-phase isopropylation of naphthalene

A great deal of effort has been made at searching for alternative catalysts to replace conventional Lewis acid catalyst aluminum trichloride (AlCl3). In this paper, immobilization of AlCl3 on mesoporous MCM-41 silica with and without modification was carried out. The catalytic properties of the immobilized catalyst systems for liquid-phase isopropylation of naphthalene were studied and compared with those of H/MCM-41 and H/mordenite. The structures of the surface-immobilized aluminum chloride catalysts were studied and identified by using solid-state magic angle spinning nuclear magnetic resonance (MAS NMR), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), nitrogen adsorption, and X-ray diffraction (XRD) techniques. The catalytic activity of the immobilized catalysts was found to be similar to that of acidic mordenite zeolite. A significant enhancement in the selectivity of 2,6-diisopropylnaphthalene (2,6-DIPN) was observed over the immobilized aluminum chloride catalysts. Immobilization of aluminum chloride on mesoporous silica coupled with surface silylation is a promising way of developing alternative catalyst system for liquid-phase Friedel-Crafts alkylation reactions. (C) 2002 Elsevier Science B.V. All rights reserved.

The cell wall galactans from Australian representatives of the genus Meristotheca (solieriaceae, rhodophyta)

The Solieriaceae, has the largest number of genera (16-18) of any family in the carrageenophyte order Gigartinales. One of these genera, Meristotheca, consists of three or four species of foliose, erect to prostrate plants sporadically recorded from the tropics of both hemispheres. The hot-water-soluble polysaccharides from Australian representatives of the type species, M. papulosa, and M. procumbens from Lord Howe Island have been characterized by compositional assays, linkage analysis, and Fourier transform infrared and C-13-nuclear magnetic resonance spectroscopy. The results show that polysaccharides from both species are similar, being predominantly composed of 4-linked 3,6-anhydro-alpha-D-galactopyranose 2-sulphate alternating with 3-linked beta-D-galactopyranose 4-sulphate, as is typical of iota-carrageenan. Small proportions of the 3-linked units occur as the pyruvated residue 4,6-O-(1-carboxyethylidene)-beta-D-galactopyranose, and other minor variations from idealized iota-carrageenan were also detected. The polysaccharides from representatives of Meristotheca are comparable to those of other solieriacean algae analysed to date, but the minor structural variations suggest a closer chemotaxonomic affinity with noneucheumoid genera of the Solieriaceae, such as Sarconema, Solieria, and Tikvahiella, than to the eucheumoid genera Eucheuma, Kappaphycus and Betaphycus (tribe Eucheumatoideae) from which most kappa- and iota-carrageenans are commercially extracted.

Poly(hydroxyether of phenolphthalein) and its blends with poly(ethylene oxid)

Poly(hydroxyether of phenolphthalein) (PPH) was synthesized through the polycondensation of phenolphthalein with epichlorohydrin. It was characterized by Fourier transform infrared (FTIR) spectroscopy, NMR spectroscopy, and differential scanning calorimetry (DSC). The miscibility of the blends of PPH with poly(ethylene oxide) (PEO) was established on the basis of the thermal analysis results. DSC showed that the PPH/PEO blends prepared via casting from N,N-dimethylformamide possessed single, composition-dependent glass-transition temperatures. Therefore, the blends were miscible in the amorphous state for all compositions. FTIR studies indicated that there were competitive hydrogen-bonding interactions with the addition of PEO to the system, which were involved with (OHO)-O-. . .=C

Distribution of melamine in polyester-melamine surface coatings cured under nonisothermal conditions

The influence of experimental cure parameters on the diffusion of reactive species in polyester-melamine thermoset coatings during curing has been investigated with X-ray photoelectron spectroscopy and attenuated total reflectance Fourier transform infrared. The diffusion of melamine plays a vital role in the curing process and, therefore, in the ultimate properties of coatings. At a low (

A nearly idealized 6 '-O-methylated t-carrageenan from the Australian red alga Claviclonium ovatum (Acrotylaceae, Gigartinales)

The polysaccharides extracted from Claviclonium ovatum were studied by a combination of compositional assays, reductive partial hydrolysis, linkage analysis, Fourier Transform infrared (FTIR) spectroscopy, and C-13, H-1, and C-13/H-1 heteronuclear multiple quantum correlation (HMQC) two-dimensional nuclear magnetic resonance (NMR) spectroscopy. The chemical and spectroscopic data showed that the alkali-modified C. ovatum polysaccharides are composed of a nearly idealized repeating unit of 6'-O-methylcarrabiose 2,4'-disulfate (the repeating unit of 6-O-methylated iota-earrageenan), although some minor components were also present. The C. ovatum galactans are the most highly methylated carrageenans reported. (C) 2004 Elsevier Ltd. All rights reserved.