Fiber-optic infrared spectroelectrochemical studies of six-coordinate manganese nitrosyl porphyrins in nonaqueous media

The redox behavior of the six-coordinate (por)Mn(NO)(1-MeIm) (por = tetraphenylporphyrin dianion (TPP), tetratolylporphyrin dianion (TTP), or tetra-p-methoxyphenylporphyrin dianion (T(p-OMe)PP)) complexes were examined by cyclic voltammetry at room temperature and at -78 degrees C in two nonaqueous solvents (CH2Cl2 and THF) at a Pt disk electrode. In CH2Cl2 at room temperature, the compounds undergo four oxidations and two reductions within the solvent limit; in THF, the compounds undergo one oxidation and three reductions. In both solvents, the first oxidation represents a chemically irreversible one-electron process involving the rapid loss of nitric oxide. The oxidation occurs at the MnNO site as judged from bulk electrolysis, UV-vis spectroscopy at room temperature, and IR spectroelectrochemistry at room temperature and at -78 degrees C. The second oxidation, accessible in CH2Cl2, is also chemically irreversible and occurs at the porphyrin ring; the third and the fourth oxidations are, on the other hand, chemically reversible but also occur at the porphyrin ring. The first reduction is chemically irreversible in CH2Cl2, occurs at the porphyrin ring, and is followed by loss of NO. In THF, the first reduction is chemically reversible and is followed by reversible loss of NO.     

THE POSSIBLE PRESENCE OF A THIRD INTERMEDIATE FOR IODOPSIN AT -195°C*

Abstract— From the theoretical analysis of the time variation of the change in absorbance of chicken iodopsin solution (at—195°C), the formation of a new intermediate during bleaching has been suggested.     

Iodopsin, a red-sensitive cone visual pigment in the chicken retina.

The vertebrate retina contains two kinds of visual cells: rods, responsible for twilight (scotopic) vision (black and white discrimination); and cones, responsible for daylight (photopic) vision (color discrimination). Here we attempt to explain some of their functional differences and similarities in terms of their visual pigments. In the chicken retina there are four types of single cones and a double cone; each of the single cones has its own characteristic oil droplet (red, orange, blue, or colorless) and the double cone is composed of a set of principal and accessory members, the former of which has a green-colored oil droplet. Iodopsin, the chicken red-sensitive cone visual pigment, is located at outer segments of both the red single cones and the double cones, while the other single cones and the rod contain their own visual pigments with different absorption spectra. The diversity in absorption spectra among these visual pigments is caused by the difference in interaction between chromophore (11-cis retinal) and protein moiety (opsin). However, the chromophore-binding pocket in iodopsin is similar to that in rhodopsin. The difference in absorption maxima between both pigments could be explained by the difference in distances between the protonated Schiff-bases at the chromophore-binding site and their counter ions in iodopsin and rhodopsin. Furthermore, iodopsin has a unique chloride-binding site whose chloride ion serves for the red-shift of the absorption maximum of iodopsin. Visual pigment bleaches upon absorption of light through several intermediates and finally dissociates into all-trans retinal and opsin. That the sensitivity of cones is lower than rods cannot be explained by the relative photosensitivity of iodopsin to rhodopsin, but may be understood to some extent by the short lifetime of an enzymatically active intermediate (corresponding to metarhodopsin II) produced in the photobleaching process of iodopsin. The rapid formation and decay of the meta II-intermediate of iodopsin compared with metarhodopsin II are not contradictory to the rapid generation and recovery of cone receptor potential compared with rod receptor potential. The rapid recovery of the cone receptor potential may be due to a more effective shutoff mechanism of the visual excitation, including the phosphorylation of iodopsin. The rapid dark adaptation of cones compared with rods has been explained by the rapid regeneration of iodopsin from 11-cis retinal and opsin. One of the reasons for the rapid regeneration and susceptibility to chemicals of iodopsin compared with rhodopsin may be a unique structure near the chromophore-binding site of iodopsin.     

Conformational analysis of indole alkaloids corynantheine and dihydrocorynantheine by dynamic 1H NMR spectroscopy and computational methods: steric effects of ethyl vs vinyl group

1H NMR (400 MHz) spectra of the indole alkaloid dihydrocorynantheine recorded at room temperature show the presence of two conformers near coalescence. Low temperature 1H NMR allowed characterization of the conformational equilibrium, which involves rotation of the 3-methoxypropenoate side chain. Line-shape analysis yielded enthalpy of activation DeltaH(double dagger) = 71 +/- 6 kJ/mol, and entropy of activation DeltaS(double dagger) = 33 +/- 6 J/mol.K. The major and minor conformation contains the methyl ether group above and below the plane of the ring, respectively, as determined by low-temperature NOESY spectra, with free energy difference DeltaG degrees = 1.1 kJ/mol at -40 degrees C. In contrast to dihydrocorynantheine, the corresponding rotamers of corynantheine are in the fast exchange limit at room temperature. The activation parameters determined for corynantheine were DeltaH(double dagger) = 60 +/- 6 kJ/mol and DeltaS(double dagger) = 24 +/- 6 J/mol.K, with DeltaG degrees = 1.3 kJ/mol at -45 degrees C. The difference in the exchange rates of the rotamers of corynantheine and dihydrocorynantheine (respectively, 350 s(-1) and 9 s(-1) at 0 degrees C) reflects the difference in the steric bulk of the vinyl and the ethyl group. The conformational equilibria involving the side chain rotation as well as inversion of the bridgehead nitrogen in corynantheine and dihydrocorynantheine was studied by force-field (Amber and MMFF) and ab initio (density-functional theory at the B3LYP/6-31G level) computational methods, the results of which were in good agreement with the 1H NMR data. However, the calculations identified the rotamers as essentially isoenergetic, the experimental energy differences being to small to be reproduced exactly by the theory. Comparison of density-functional and force-field calculations with experimental results identified Amber as giving the most accurate results in the present case.     

Raman microspectroscopic study on polymerization and degradation processes of a diacetylene derivative at surface enhanced Raman scattering active substrates. 1. Reaction kinetics

Raman microspectroscopy was applied to study the polymerization kinetics of the Langmuir-Blodgett (LB) films of 10,12-pentacosadiynoic acid (DA) adsorbed on surface enhanced Raman scattering (SERS) active Ag island films. A two-dimensional (2D) Raman microscopic image measured at 1520 cm(-1) exhibits bright and dim spots with the diameter of several hundred nanometers. Raman microscopic spectra, measured by defocusing the excitation laser light (532 nm, diameter of ca. 10 mum) on the samples at room temperature, proved the occurrence of the surface processes consisting of the formation of polydiacetylene (PDA) in the blue phase, its conversion to the red phase, and subsequent bleaching. These reactions were negligible under the same condition for the DA-LB films prepared on a smooth (i.e., SERS-inactive) Ag film, indicating that the 532-nm-induced polymerization and the bleaching process are enhanced by the SERS-active substrates. At low temperatures below -50 degrees C, the Raman microscopic measurements proved the formation of the blue phase and its conversion to the red phase with much lower reaction rates compared to the corresponding rates at room temperature. The bleaching, however, was much suppressed at the low temperatures. The kinetic analyses of the formation of the blue phase and its conversion to the red phase were performed by using the intensity changes of the Raman bands due to the blue (1477 cm(-1)) and red (1517 cm(-1)) phases as a function of the irradiation time. The results strongly suggested the existence of at least two processes taking place simultaneously on the SERS-active substrates; that is, one of the processes is a sequential reaction, DA-monomers --> PDA in the blue phase --> PDA in the red phase, and the other is another sequential reaction, DA-monomers --> PDA in the red phase --> degradation species (probably amorphous carbon). Thus, even at the low temperatures, there occurs the surface reaction consisting of the formation of PDA and its degradation. The reaction can be ascribed to a process taking place at the highly SERS-active site, which gives the bright spot (so-called "hot spot") on the 2D Raman image, as proved by the confocal Raman microscopic measurement in the following paper.     

Dynamics of structure and energy of horse carboxymyoglobin after photodissociation of carbon monoxide.

The energetics and structural volume changes after photodissociation of carboxymyoglobin are quantitatively investigated by laser-induced transient grating (TG) and photoacoustic calorimetric techniques. Various origins of the TG signal are distinguished: the phase grating signals due to temperature change, due to absorption spectrum change, and due to volume change. We found a new kinetics of approximately 700 ns (at room temperature), which was not observed by the flash photolysis technique. This kinetics should be attributed to the intermediate between the geminate pair and the fully dissociated state. The enthalpy of an intermediate species is determined to be 61 +/- 10 kJ/mol, which is smaller than the expected Fe-CO bond energy. The volume of MbCO slightly contracts (5 +/- 3 cm(3)/mol) during this process. CO is fully released from the protein by an exponential kinetics from 25 to -2 degrees C. During this escaping process, the volume expands by 14.7 +/- 2 cm(3)/mol at room temperature and 14 +/- 10 kJ/mol is released, which should represent the protein relaxation and the solvation of the CO (the enthalpy of this final state is 47 +/- 10 kJ/mol). A potential barrier between the intermediate and the fully dissociated state is DeltaH(*) = 41.3 kJ/mol and DeltaS(*) = 13.6 J mol(-1) K(-1). The TG experiment under a high wavenumber reveals that the volume expansion depends on the temperature from 25 to -2 degrees C. The volume changes and the energies of the intermediate species are discussed.     

A combined NMR, DFT, and X-ray investigation of some cinchona alkaloid O-ethers

Structures and conformational behavior of several cinchona alkaloid O-ethers in the solid state (X-ray), in solution (NMR and DFT), and in the gas phase (DFT) were investigated. In the crystal, O-phenylcinchonidine adopts the Open(3) conformation similar to cinchonidine, whereas the O-methyl ether derivatives of both cinchonidine and cinchonine are packed in the Closed(1) conformation. Dynamic equilibria in solutions of the alkaloids were revealed by combined experimental-theoretical spin simulation/iteration techniques for the first time. In the (1)H NMR spectra in CDCl3 and toluene-d8 at room temperature, Closed(1) conformation was observed for the O-silyl ethers as a separate set of signals. For O-methyl ether derivatives Closed(1) could be separated only at -30 degrees C in CDCl3 or toluene-d8 and for O-phenylcinchonidine at -70 degrees C in CDCl3/CD2Cl2. The ratio between the Closed(2) and Open(3) conformers was estimated by analyzing the vicinal coupling constant (3)J(H9,H8) at ambient and low temperatures. The observed conformational equilibria of O-(tert-butyldimethylsilyl)cinchonidine in CDCl 3 and toluene-d8 are in good agreement with the theoretically estimated equilibrium populations of the conformations according to Boltzmann statistics. The conformational equilibria of four cinchona alkaloid O-ether solutes in CDCl3 and toluene-d8 are discussed in the light of their relevance to the mechanism of 1-phenyl-1,2-propanedione (PPD) hydrogenation over cinchona alkaloid modified heterogeneous platinum catalysts. It was demonstrated that the conformation found to be abundant in the liquid phase has no direct correlation with the enantioselectivity of the PPD hydrogenation reaction.     

Spectral study on the binding of gadolinium ions with apoovotransferrin

The binding of Gd3+ ion to apoovotransferrin (apoOTf) was monitored by means of UV difference spectra in 0.01M Hepes, pH 7.4 at 25 degrees C. Used 2-p-toluidinylnaphthalene-6-sulfonate (TNS) as fluorescence probe the conformational changes of protein were studied while gadolinium ions bound to apoOTf. The results show that Gd3+ binding produces peaks at 244 and 294 nm that is the characteristic of binding at the apoOTf specific metal-binding sites. At 244 nm the molar absorptivity of Gd-apoOTf complex is (1.99+/-0.17)x10(4)cm(-1)M(-1). The apparent binding constants for the complexes of Gd3+ with apoovotransferrin are logK(1)=7.61+/-0.14 and logK(2)=4.96+/-0.26. A very large conformational change of apoovotransferrin appears when Gd3+ is bound to the N-terminal binding site. When Gd3+ is bound to C-terminal binding site there is less conformational change.     

DFT and IR spectroscopic analysis of p-tert-butylthiacalix[4]arene

Vibrational analysis of p-tert-butylthiacalix[4]arene based on an experimental mid and far IR spectra is described here. Density functional calculations of a most stable cone conformer related to crystalline solid FT-IR spectra in the temperature range up to 180 degrees C as well spectra of dilute solution have been used to obtain a better understanding of conformational state and a hydrogen bonding of p-tert-butylthiacalix[4]arene. Complete assignments were made for experimental FT-IR spectra of the cone conformer. Heating (up to 180 degrees C) of crystalline p-tert-butylthiacalix[4]arene did not change both conformational and cooperative H-bonding state of its molecules. A temperature spectral effect seems to be due to some relaxation of crystal packing mostly viewed on the OH bands.     

Anion conformation of low-viscosity room-temperature ionic liquid 1-ethyl-3-methylimidazolium bis(fluorosulfonyl) imide

Anion conformation of a low-viscosity room-temperature ionic liquid 1-ethyl-3-methylimidazolium bis(fluorosulfonyl) imide (EMI+FSI-) has been studied by Raman spectra and theoretical DFT calculations. Three strong Raman bands were found at 293, 328, and 360 cm(-1), which are ascribed to the FSI- ion. These Raman bands show significant temperature dependence, implying that two FSI- conformers coexist in equilibrium. This is supported by theoretical calculations that the FSI- ion is present as either C2 (trans) or C1 (cis) conformer; the former gives the global minimum, and the latter has a higher SCF energy of about 4 kJ mol(-1). Full geometry optimizations followed by normal frequency analyses show that the observed bands at 293, 328, and 360 cm(-1) are ascribed to the C2 conformer. The corresponding vibrations at 305, 320, and 353 cm(-1) were extracted according to deconvolution of the observed Raman bands in the range280-400 cm(-1 )and are ascribed to the C1 conformer. The enthalpy DeltaH degrees of conformational change from C2 to C1 was experimentally evaluated to be ca. 4.5 kJ mol(-1), which is in good agreement with the predicted value by theoretical calculations. The bis(trifluoromethanesulfonyl) imide anion (TFSI-) shows a conformational equilibrium between C1 and C2 analogues (DeltaH degrees = 3.5 kJ mol(-1)). However, the profile of the potential energy surface of the conformational change for FSI- (the F-S-N-S dihedral angle) is significantly different from that for TFSI- (the C-S-N-S dihedral angle).     

Temperature dependence of domain motions of calmodulin probed by NMR relaxation at multiple fields

Interdomain motions of Ca(2+)-ligated calmodulin were characterized by analyzing the nuclear magnetic resonance (15)N longitudinal relaxation rate R(1), transverse relaxation rate R(2), and steady-state {(1)H}-(15)N NOE of the backbone amide group at three different magnetic field strengths (18.8, 14.1, and 8.5 T) and four different temperatures (21, 27, 35, and 43 degrees C). Between 35 and 43 degrees C, a larger than expected change in the amplitude and the time scale of the interdomain motion for both N- and C-domains was observed. We attribute this to the shift in population of four residues (74-77) in the central linker from predominantly helical to random coil in this temperature range. This is consistent with the conformation of these residues in the calmodulin-peptide complex, where they are nonhelical. The doubling of the disordered region of the central helix (residues 78-81 at room temperature) when temperature is raised from 35 to 43 degrees C results in larger amplitude interdomain motion. Our analysis of the NMR relaxation data quantifies subtle changes in the interdomain dynamics and provides an additional tool to monitor conformational changes in multidomain proteins.     

Properties of chloroformyl peroxynitrate, ClC(O)OONO(2)

The synthesis of ClC(O)OONO(2) is accomplished by photolysis of a mixture of Cl(2), NO(2), and CO in large excess of O(2) at about -70 degrees C. The product is isolated after repeated trap-to-trap condensation. The solid compound melts at -84 degrees C, and the extrapolated boiling point is 80 degrees C. ClC(O)OONO(2) is characterized by IR, Raman, (13)C NMR, and UV spectroscopy. According to the IR matrix spectra, the compound exists at room temperature only as a single conformer. The molecular structure of ClC(O)OONO(2) is determined by gas electron diffraction. The molecule possesses a gauche structure with a dihedral angle of phi(COON) = 86.7(19) degrees , and the C=O bond is oriented syn with respect to the O-O bond. The short O-O bond (1.418(6) A) and the long N-O bond (1.511(8) A) are consistent with the facile dissociation of ClC(O)OONO(2) into the radicals ClC(O)OO and NO(2). The experimental geometry of ClC(O)OONO(2) is reproduced reasonably well by B3LYP/6-311+G(2df) calculations, whereas the MP2 approximation predicts the N-O bond considerably too long and the dihedral angle too small.     

Convergent synthesis of the E'FGH ring fragment of ciguatoxin 1B via an acetylene cobalt complex strategy

A convergent synthesis of the E'FGH ring fragment 28 of ciguatoxin 1B, a principal toxin causing widespread seafood poisonings "ciguatera", has been accomplished through (i) coupling between the E' ring-acetylide 9 and the H ring-aldehyde 20, (ii) stereoselective F ring cyclization via an acetylene cobalt complex, (iii) conversion to a carbonyl function under high-pressure hydrogenation, and (iv) reductive hydroxyketone cyclization to construct the G ring. In the (1)H NMR analysis of 28 at room temperature, a considerable broadening phenomenon was observed due to the slow conformational changes of the FG ring, as reported for natural ciguatoxin 1B. When measured in pyridine at -20 degrees C, the spectra of 28 exhibited a 3.5:1 mixture of two conformational isomers (UP and DOWN conformers).     

Luminescent mu-ethynediyl and mu-butadiynediyl binuclear gold(I) complexes: observation of (3)(pi pi*) emissions from bridging C(n)(2-) units.

The synthesis and X-ray structural and spectroscopic characterization for LAuC triple bond CAuL x 4CHCl(3) and LAuC triple bond C--C triple bond CAuL x 2CH(2)Cl(2) (1 x 4CHCl(3) and 2 x 2CH(2)Cl(2), respectively; L = PCy(3), tricyclohexylphosphine) are reported. The bridging C(n)(2-) units are structurally characterized as acetylene or diacetylene units, with C triple bond C distances of 1.19(1) and 1.199(8) A for 1 x 4CHCl(3) and 2 x 2CH(2)Cl(2), respectively. An important consequence of bonding to Au(I) for the C(n)(2-) moieties is that the lowest-energy electronic excited states, which are essentially acetylenic (3)(pi pi*) in nature, acquire sufficient allowedness via Au spin-orbit coupling to appear prominently in both electronic absorption and emission spectra. The origin lines for both complexes are well-defined and are observed at 331 and 413 nm for 1 and 2, respectively. Sharp vibronic progressions corresponding to v(C triple bond C) are observed in both emission and absorption spectra. The acetylenic (3)(pi pi) excited state of 2 has a long lifetime (tau(0) = 10.8 mus) in dichloromethane at room temperature and is a powerful reductant (E degrees [Au(2)(+)/Au(2)] < or = -1.85 V vs SSCE).     

Direct observation of a 14-electron ruthenacyclobutane relevant to olefin metathesis

The 14-electron ruthenium phosphonium alkylidene complex [(IH2Mes)Cl2Ru=CH(PCy3)][B(C6F5)4], 1b, a highly active olefin metathesis catalyst, reacts with stoichiometric quantities of ethylene at -50 degrees C in CD2Cl2 to generate the ruthenacyclobutane complex [(IH2Mes)Cl2RuCH2CH2CH2], 2, and [CH2=CH(PCy3)][B(C6F5)4] in quantitative yield by NMR spectroscopy. 1H and 13C NMR spectroscopies on 2 and 2-13C3 are consistent with a symmetrical C2v structure, providing the first experimental information concerning this crucial intermediate in ruthenium-mediated olefin metathesis. At -50 degrees C, exchange with free ethylene takes place on the chemical time scale. Complex 2 decomposes in solution upon warming to room temperature, generating propene and unknown ruthenium product(s).     

Nickel(II)-phenoxyl radical complexes: structure-radical stability relationship

Nickel(II) complexes of N3O-donor tripodal ligands, 2,4-di-tert-butyl-6-[([bis(2-pyridyl)methyl]amino)methyl]phenol (HtbuL), 2,4-di-tert-butyl-6-[([(6-methyl-2-pyridyl)methyl](2-pyridylmethyl)amino)methyl]phenol (HtbuLMepy), and 2,4-di-tert-butyl-6-[([bis(6-methyl-2-pyridyl)methyl]amino)methyl]phenol (HtbuL(Mepy)2), were prepared, and [Ni(tbuL)Cl(H2O)] (1), [Ni(tbuLMepy)Cl] (2), and [Ni(tbuL(Mepy)2)Cl] (3) were structurally characterized by the X-ray diffraction method. Complexes 1 and 3 have a mononuclear structure with a coordinated phenolate moiety, while 2 has a dinuclear structure bridged by two chloride ions. The geometry of the Ni(II) center was found to be octahedral for 1 and 2 and 5-coordinate trigonal bipyramidal for 3. Complexes 1-3 exhibited similar absorption spectra in CH3CN, indicating that they all have a mononuclear structure in solution. They were converted to the phenoxyl radicals upon oxidation with Ce(IV), giving a phenoxyl radical pi-pi transition band at 394-407 nm. ESR spectra at low temperature and resonance Raman spectra established that the radical species has a Ni(II)-phenoxyl radical bond. The cyclic voltammograms showed a quasi-reversible redox wave at E1/2=0.46-0.56 V (vs Ag/AgCl) corresponding to the formation of the phenoxyl radical, which displayed a first-order decay with a half-life of 45 min at room temperature for 1 and 26 and 5.9 min at -20 degrees C for 2 and 3, respectively. The radical stability increased with the donor ability of the N ligands.     

Recent bioorganic studies on rhodopsin and visual transduction

Rhodopsin, the pigment responsible for vision in animals, insect and fish is a typical G protein (guanyl-nucleotide binding protein) consisting of seven transmembrane alpha helices and their interconnecting extramembrane loops. In the case of bovine rhodopsin, the best studied of the visual pigments, the chromophore is 11-cis retinal attached to the terminal amino group of Lys296 through a protonated Schiff base linkage. Photoaffinity labeling with a 3-diazo-4-oxo-retinoid shows that C-3 of the ionone ring moiety is close to Trp265 in helix F (VI) in dark inactivated rhodopsin. Irradiation causes a cis to trans isomerization of the 11-cis double bond giving rise to the highly strained intermediate bathorhodopsin. This undergoes a series of thermal relaxation through lumi-, meta-I and meta-II intermediates after which the retinal chromophore is expelled from the opsin binding pocket. Photoaffinity labeling performed with 3-diazo-4-oxoretinal at -196 degrees C for batho-, -80 degrees C for lumi-, -40 degrees C for meta-I, and 0 degrees C for meta-II rhodopsin showed that in bathorhodopsin the ring is still close to Trp265. However, in lumi-, meta-I and meta-II intermediates crosslinking occurs unexpectedly at A169 in helix D (IV). This shows that large movements in the helical arrangements and a flip over of the ring moiety accompanies the transduction (or bleaching) process. These changes in retinal/opsin interactions are necessarily accompanied by movements of the extramembrane loops, which in turn lead to activation of the G protein residing in the cytoplasmic side. Of the numerous G protein coupled receptors, this is the first time that the outline of transduction pathway has been clarified.     

Temperature-induced nucleation of poly(p-phenylene vinylene-co-2,5-dioctyloxy-m-phenylene vinylene) crystallization by HiPco single-walled carbon nanotubes

Hybrid systems of the conjugated organic polymer poly(p-phenylene vinylene-co-2,5-dioctyloxy-m-phenylene vinylene)(PmPV) and HiPco single-walled carbon nanotubes (SWNTs) are explored using spectroscopic and thermal techniques to determine specific interactions. Vibrational spectroscopy indicates a weak interaction, and this is further elucidated using differential scanning calorimetry (DSC), confocal laser scanning microscopy, temperature-dependent Raman spectroscopy, and temperature-dependent infrared spectroscopy of the raw materials and the composite. An endothermic transition is observed in the DSC of both the polymer and the 0.1% HiPco composite in the region of 50 degrees C. Also observed in the DSC of the composite is a double-peaked endotherm at -39 and -49 degrees C, which does not appear in the polymer. The Raman spectroscopy of the polymer upon increasing the temperature to 60 degrees C shows a diminished cis-vinylene mode at 1575 cm(-1), with an increase in relative intensity of the trans-vinylene mode at 1630 cm(-1). Partially irreversible change in isomerization suggests increased order in the polymer. This change in the polymer is also manifest in the Raman composite spectrum upon increase of the temperature to 60 degrees C, where the spectrum becomes abruptly dominated by nanotubes. Raman spectroscopy of the composite shows no change at -35 degrees C; however, infrared absorption measurements suggest that the transition at -35 degrees C derives from the polymer side chains. Here the composite at -35 degrees C shows a change in the absorbance of the polymer side chain aryl-oxide linkage at 1250 cm(-1) and alkyl-oxide stretch at 1050 cm(-1). Infrared spectra thus suggest that the transitions in the lower temperature region around -35 degrees C are side chain-induced, while Raman spectra suggest that the transition at 60 degrees C is backbone-induced. Furthermore, temperature cycling induces an irreversible decrease in the mean fluorescence intensity of the polymer, coupled with a further reduction in the mean fluorescence intensity of the composite. This suggests that an increase in crystallization of the composite is supported and enhanced by an increase in ordering of the polymer. Implications are discussed.     

Low atmospheric temperature dependence on photodegradation of wood

This paper deals with the photodegradation of wood in low atmospheric temperature region (-40 to 50 degrees C), and discusses the changes in color and IR spectra. The color and IR spectra of wood hardly changed with photo-irradiation at -40 degrees C but did at -20 degrees C. Therefore, it is thought that the photo-energy causes the scission of chemical bonds or the production of radicals; however, heat energy is needed to yellow of wood (i.e., to produce quinone). In case of softwoods, the absorption of the carbonyl band consisted of two sub-bands, and the carbonyl band at around 1710 cm(-1) increased at lower temperature than that at around 1760 cm(-1) by light-irradiation. Such IR measurement due to lignin degradation means that the photodegradation of softwoods is faster than that of hardwoods. The color change by exposure to light in the low temperature was also caused by the degradation of lignin.     

Volume-demanding cis-trans isomerization of 1,2-diaryl olefins in the solid state

Volume-demanding cis-trans photoisomerization of the aromatic substituted alkenes 1-3 in the solid state at room temperature and at 50 degrees C is presented. Alkene 3 did not undergo the cis-trans isomerization in the solid state either at room temperature or at 50 degrees C. The importance of the presence of void space near the reaction center to facilitate the large volume change during cis-trans photoisomerization is discussed.