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Absorption Maxima (absorption + maximum)
Selected AbstractsEffects of Three Characteristic Amino Acid Residues of Pharaonis Phoborhodopsin on the Absorption Maximum ,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2000Kazumi Shimono ABSTRACT Phoborhodopsin (pR or sensory rhodopsin II, sRII) or pharaonis phoborhodopsin (ppR or pharaonis sensory rhodopsin II, psRII) has a unique absorption maximum (,max) compared with three other archaeal rhodopsins: ,max of pR or ppR at ca 500 nm and others at 560,590 nm. Alignment of amino acid sequences revealed three sites characteristic of the shorter wavelength,absorbing pigments. The amino acids of these three sites are conserved completely among archaeal rhodopsins having longer ,max, and are different from those of pR or ppR. We replaced these amino acids of ppR with amino acids corresponding to those of bacteriorhodopsin, Val-108 to Met, Gly-130 to Ser and Thr-204 to Ala. The ,max of V108M mutant was 502 nm with a slight redshift. G130S and T204A mutants had ,max of 503 and 508 nm, respectively. Thus, each site contributes only a small effect to the color tuning. We then constructed three double mutants and one triple mutant. The opsin-shifts of these mutants suggest that Val-108 and Thr-204 or Gly-130 are synergistic, and that Gly-130 and Thr-204 work additively. Even in the triple mutant, the ,max was 515 nm, an opsin-shift only ca 30% of the shift value from 500 to 560 nm. This means that there is another yet unidentified factor responsible for the color tuning. [source] Photochromic Properties of Perhydro- and Perfluorodithienylcyclopentene Molecular SwitchesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 10 2003Jaap J. D. de Jong Abstract Various substituted phenylthienyl perhydro- and perfluorocyclopentenes have been synthesized in order to compare their spectroscopic and photochromic properties. The difference in the electron densities of the central cyclopentene moieties in the perhydrocyclopentene and perfluorocyclopentene molecular switches has only a small effect on the absorption maxima of the electronic spectra, but causes some subtle changes in substituent and solvatochromic effects. The photochromic behaviour is remarkably similar, and both type of switches combine excellent quantum yields (0.6) with high degrees of photoconversion (> 0.85). The main difference is the lower photochemical and thermal stability of the perhydrocyclopentene molecular switches. It is concluded that in most studies the perhydrocyclopentenes are an excellent alternative for the perfluorocyclopentenes, while the perfluorocyclopentenes might be better suited for applications such as data storage, which depend critically on fatigue resistance and thermal stability. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Homologous expression of a bacterial phytochromeFEBS JOURNAL, Issue 8 2007The cyanobacterium Fremyella diplosiphon incorporates biliverdin as a genuine, functional chromophore Bacteriophytochromes constitute a light-sensing subgroup of sensory kinases with a chromophore-binding motif in the N-terminal half and a C-terminally located histidine kinase activity. The cyanobacterium Fremyella diplosiphon (also designated Calothrix sp.) expresses two sequentially very similar bacteriophytochromes, cyanobacterial phytochrome A (CphA) and cyanobacterial phytochrome B (CphB). Cyanobacterial phytochrome A has the canonical cysteine residue, by which covalent chromophore attachment is accomplished in the same manner as in plant phytochromes; however, its paralog cyanobacterial phytochrome B carries a leucine residue at that position. On the basis of in vitro experiments that showed, for both cyanobacterial phytochrome A and cyanobacterial phytochrome B, light-induced autophosphorylation and phosphate transfer to their cognate response regulator proteins RcpA and RcpB [Hübschmann T, Jorissen HJMM, Börner T, Gärtner W & deMarsac NT (2001) Eur J Biochem268, 3383,3389], we aimed at the identification of a chromophore that is incorporated in vivo into cyanobacterial phytochrome B within the cyanobacterial cell. The approach was based on the introduction of a copy of cphB into the cyanobacterium via triparental conjugation. The His-tagged purified, recombinant protein (CphBcy) showed photoreversible absorption bands similar to those of plant and bacterial phytochromes, but with remarkably red-shifted maxima [,max 700 and 748 nm, red-absorbing (Pr) and far red-absorbing (Pfr) forms of phytochrome, respectively]. A comparison of the absorption maxima with those of the heterologously generated apoprotein, assembled with phycocyanobilin (,max 686 and 734 nm) or with biliverdin IX, (,max 700 and 750 ± 2 nm), shows biliverdin IX, to be a genuine chromophore. The kinase activity of CphBcy and phosphotransfer to its cognate response regulator was found to be strictly Pr -dependent. As an N-terminally located cysteine was found as an alternative covalent binding site for several bacteriophytochrome photoreceptors that bind biliverdin and lack the canonical cysteine residue (e.g. Agrobacterium tumefaciens and Deinococcus radiodurans), this corresponding residue in heterologously expressed cyanobacterial phytochrome B was mutated into a serine (C24S); however, there was no change in its spectral properties. On the other hand, the mutation of His267, which is located directly after the canonical cysteine, into alanine (H267A), caused complete loss of the capability of cyanobacterial phytochrome B to form a chromoprotein. [source] Solution-Processed Organic Tandem Solar Cells,ADVANCED FUNCTIONAL MATERIALS, Issue 14 2006A. Hadipour Abstract A solution-processed polymer tandem cell fabricated by stacking two single cells in series is demonstrated. The two bulk-heterojunction subcells have complementary absorption maxima at ,max,,,850,nm and ,max,,,550,nm, respectively. A composite middle electrode is applied that serves both as a charge-recombination center and as a protecting layer for the first cell during spin-coating of the second cell. The subcells are electronically coupled in series, which leads to a high open-circuit voltage of 1.4,V, equal to the sum of each subcell. The layer thickness of the first (bottom) cell is tuned to maximize the optical absorption of the second (top) cell. The performance of the tandem cell is presently limited by the relatively low photocurrent generation in the small-bandgap polymer of the top cell. The combination of our tandem architecture with more efficient small-bandgap materials will enable the realization of highly efficient organic solar cells in the near future. [source] Synthesis of some novel bis(hetaryl)azo disperse dyes and investigation of their absorption spectraHETEROATOM CHEMISTRY, Issue 6 2007Zeynel Sefero 3-Amino-2-cyano-4,6-disubstituted-thieno{2,3-b}pyridines and 3-aminopyridine were diazotized and coupled with 2-phenylindole, 2-methylindole, and 1-methyl-2-phenylindole, respectively. These dyes were characterized by UV-Visible, FT-IR, 1H NMR, and mass spectroscopic techniques. Solvent effects on the visible absorption spectra of the dyes were evaluated. The color of the dyes is discussed with respect to the nature of the heterocyclic ring and substituent present therein. In addition, effects of temperature, concentration, as well as acid and base on the visible absorption maxima of the dyes are reported. © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:622,630, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20361 [source] QM/MM calculation of solvent effects on absorption spectra of guanineJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 1 2010Maja Parac Abstract Electronic spectra of guanine in the gas phase and in water were studied by quantum mechanical/molecular mechanical (QM/MM) methods. Geometries for the excited-state calculations were extracted from ground-state molecular dynamics (MD) simulations using the self-consistent-charge density functional tight binding (SCC-DFTB) method for the QM region and the TIP3P force field for the water environment. Theoretical absorption spectra were generated from excitation energies and oscillator strengths calculated for 50 to 500 MD snapshots of guanine in the gas phase (QM) and in solution (QM/MM). The excited-state calculations used time-dependent density functional theory (TDDFT) and the DFT-based multireference configuration interaction (DFT/MRCI) method of Grimme and Waletzke, in combination with two basis sets. Our investigation covered keto-N7H and keto-N9H guanine, with particular focus on solvent effects in the low-energy spectrum of the keto-N9H tautomer. When compared with the vertical excitation energies of gas-phase guanine at the optimized DFT (B3LYP/TZVP) geometry, the maxima in the computed solution spectra are shifted by several tenths of an eV. Three effects contribute: the use of SCC-DFTB-based rather than B3LYP-based geometries in the MD snapshots (red shift of ca. 0.1 eV), explicit inclusion of nuclear motion through the MD snapshots (red shift of ca. 0.1 eV), and intrinsic solvent effects (differences in the absorption maxima in the computed gas-phase and solution spectra, typically ca. 0.1,0.3 eV). A detailed analysis of the results indicates that the intrinsic solvent effects arise both from solvent-induced structural changes and from electrostatic solute,solvent interactions, the latter being dominant. © 2009 Wiley Periodicals, Inc. J Comput Chem 2010 [source] Accurate evaluation of the absorption maxima of retinal proteins based on a hybrid QM/MM methodJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 14 2006Azuma Matsuura Abstract Here we improved our hybrid QM/MM methodology (Houjou et al. J Phys Chem B 2001, 105, 867) for evaluating the absorption maxima of photoreceptor proteins. The renewed method was applied to evaluation of the absorption maxima of several retinal proteins and photoactive yellow protein. The calculated absorption maxima were in good agreement with the corresponding experimental data with a computational error of <10 nm. In addition, our calculations reproduced the experimental gas-phase absorption maxima of model chromophores (protonated all-trans retinal Schiff base and deprotonated thiophenyl- p -coumarate) with the same accuracy. It is expected that our methodology allows for definitive interpretation of the spectral tuning mechanism of retinal proteins. © 2006 Wiley Periodicals, Inc. J Comput Chem, 2006 [source] Photochromism of dihydroindolizines part VII: multiaddressable photophysical properties of new photochromic dihydroindolizines bearing substituted benzo[i]phenanthridine as a fluorescing moiety,JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 8 2007Saleh Abdel-Mgeed Ahmed Abstract Sixteen benzo[i]phenanthridine derivatives 8a-p were prepared via photocyclization of cis-trans substituted 4-styrylquinolines in low-to-moderate yields. The chemical structure of the photocyclized benzo[i]phenanthridine derivatives was unambiguously elucidated by means of both spectral and analytical tools. The photochromic (PC) dihydroindolizines (DHIs) 8a-p based on benzo[i]phenanthridines were prepared in 19,57% yields via nucleophilic addition of benzo[i]phenanthridines 4a-p to spirocyclopropenes 5. The 1D, 2D, NOESY NMR spectra, mass spectrometry, and elemental analysis were used for characterization of the chemical structures of the newly synthesized DHIs 8a-p. Developing and tuning of the photophysical properties of the synthesized compounds by substituents in the base part have been achieved. The absorption maxima (,max) and the half-lives (t1/2) of the colored zwitterionic forms 7a-p were detected in all cases by flash-photolysis measurements due to the fast 1,5-electrocyclization back to the DHI system. Irradiation of DHI 8a-p in'CH2Cl2 solution with polychromatic light leads to the formation of green to green,blue colored betaines 7a-p after cooling with liquid nitrogen. The kinetics of the fast bleaching process of betaines 7a-p to DHIs 8a-p, studied by flash photolysis as well as low temperature FT-UV/VIS, were found to take place in the millisecond range (432,2675,ms) in dichloromethane solution and fitted well a first-order thermal back reaction. The fluorescence spectra as well as the fluorescence quantum yield were studied. Noticeable bathochromic and hypsochromic shifts in the emission spectra by changing the substituents in the base part were monitored. Interestingly, the photo-fatigue resistance of some studied betaines 7a-p showed a higher t30 -value than the standard one (dicyanopyridazine DHI). Large solvatochromic effects on the absorption maxima (,max) as well as a substantial increase in the half-lives (t1/2) with solvent polarity of betaines 7a-p were also observed. The multiaddressable PC properties of DHIs 8a-p will help these compounds to find applications. Copyright © 2007 John Wiley & Sons, Ltd. [source] Solvatochromism of carbenium,arene EDA (electrondonor,acceptor) complexes and their behaviour on silicaJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 5 2001Stefan Spange Abstract Spectral characteristics of two different types of electron donor,acceptor (EDA) complexes with charged components (arene,carbenium and anion,, acceptor) are presented. The UV,Vis absorption maxima of the charge-transfer (CT) band (,max,CT) of the EDA complexes were measured in various solvents and after adsorption on silica. Tropylium, triarylmethylium and diarylmethylium ions in combination with aromatic , donors, e.g. pyrene, acenaphthene and methoxy-substituted benzene derivatives and also the tetraethylammonium iodide,1,3,5-trinitrobenzene complex have been investigated by means of a special UV,Vis technique in transparent slurries of silica nanoparticles in 1,2-dichloroethane. Multiple linear regression analyses of the ,max,CT values of the EDA complexes in various solvents and on silica with the Kamlet,Taft solvent parameters and structure,reactivity terms of the complex components, e.g. the oxidation potential of the arene component or the Hammett substituent constant, ,p+, of the arylmethyl component, show their related properties to the solution complexes. The influence of the electron-pair donating capacity of a solvent on ,max,CT of carbenium/arene complexes was compared with the property of the silica surface in order to link EDA complexes. For the diarylmethyl carbenium ion,pyrene complexes on silica, the presence of a ,-like structure is discussed. Copyright © 2001 John Wiley & Sons, Ltd. [source] Synthesis and characterization of cyclopentadithiophene-based low bandgap copolymers containing electron-deficient benzoselenadiazole derivatives for photovoltaic devicesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 6 2010In Hwan Jung Abstract We have synthesized two cyclopentadithiophene (CDT)-based low bandgap copolymers, poly[(4,4-bis(2-ethyl-hexyl)-4H -cyclopenta[2,1- b:3,4- b,]dithiophene-2,6-diyl)- alt -(benzo[c][1,2,5]selenadiazole-4,7-diyl)] (PCBSe) and poly[(4,4-bis(2-ethyl-hexyl)-4H -cyclopenta[2,1- b:3,4- b,]dithiophene-2,6-diyl)- alt -(4,7-dithiophen-2-yl-benzo[c][1,2,5]selenadiazole-5,5,-diyl)] (PCT2BSe), for use in photovoltaic applications. Through the internal charge transfer interaction between the electron-donating CDT unit and the electron-accepting benzoselenadiazole, we realized exceedingly low bandgap polymers with bandgaps of 1.37,1.46 eV. The UV,vis absorption maxima of PCT2BSe were subjected to larger hypsochromic shifts than those of PCBSe, because of the distorted electron donor,acceptor (D,A) structures of the PCT2BSe backbone. These results were supported by the calculations of the D,A complex using the ab initio Hartree-Fock method with a split-valence 6-31G* basis set. However, PCT2BSe exhibited a better molar absorption coefficient in the visible region, which can lead to more efficient absorption of sunlight. As a result, PCT2BSe blended with [6,6]-phenyl-C61 -butyric acid methyl ester (PC61BM) exhibited a better photovoltaic performance than PCBSe because of the larger spectral overlap integral with respect to the solar spectrum. Furthermore, when the polymers were blended with PC71BM, PCT2BSe showed the best performance, with an open circuit voltage of 0.55 V, a short-circuit current of 6.63 mA/cm2, and a power conversion efficiency of 1.34% under air mass 1.5 global illumination conditions. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1423,1432, 2010 [source] Synthesis and properties of conjugated polymers containing 3,9- and 2,9-linked carbazole units in the main chainJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 14 2009Kosaku Tamura Abstract Novel conjugated polymers containing 3,9- or 2,9-linked carbazole units in the main chain were synthesized by the polycondensation of ethynyl- and iodo-substituted 9-arylenecarbazolylene monomers, and their optical and electrical properties were studied. Polymers with weight-average molecular weights of 3400,12,000 were obtained in 76,99% yields by the Sonogashira coupling polycondensation in piperidine or tetrahydrofuran (THF)/piperidine at 30 °C for 48 h. All the 3,9-linked polymers absorbed light around 300 nm. The para -phenylene-linked polymer also absorbed light around 350 nm, while meta -phenylene-linked one did not. The 3,9-linked polymers absorbed light at a wavelength longer than the 2,9-linked one. The polymers emitted blue fluorescence with high quantum yields (0.21,0.78) upon excitation at the absorption maxima. The polymers were oxidized around 0.6 V, and reduced around 0.5 V. Poly(1) showed the dark conductivity of 3.7 × 10,11 S/cm (103 V/cm). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3506,3517, 2009 [source] Photophysical and electrochemical characterization of new poly(arylene vinylene) copolymers containing quinoline or bisquinoline segmentsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 13 2009John A. Mikroyannidis Abstract Four new fluorescent conjugated vinylene-copolymers incorporating quinoline or bisquinoline segments along the backbone were synthesized by Heck coupling. Three of them were fluorenevinylene-copolymers and contained quinoline (PQFV, PQFVT) or bisquinoline segments (PBQFV). One of them (PBQPV) was phenylenevinylene-copolymer and contained bisquinoline segments. All the copolymers were soluble in common organic solvents and had relatively low glass transition temperature (Tg = 50,56 °C for fluorenevinylenes and Tg < 25 °C for phenylenevinylene). In THF solutions, the quinoline-containing copolymers showed absorption maxima at 411,420 nm while the bisquinoline-containing ones exhibited maxima at 357,361 nm. The emission maxima of solutions were 465,490 nm. The copolymers showed high quantum yields up to 64%. The films exhibited absorption and emission maxima in the range of 371,437 nm and 480,521 nm, respectively. All copolymers revealed reversible reduction with electron affinity of 2.66,3.53 eV and irreversible oxidation scans with ionization potential of 5.39,5.53 eV. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3370,3379, 2009 [source] Soluble dithienothiophene polymers: Effect of link patternJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 11 2009Shiming Zhang Abstract Soluble conjugated polymers based on 3,5-didecanyldithieno[3,2- b:2,,3,- d]thiophene,single-bond (1), double-bond (2), and triple-bond linked (3),were synthesized by palladium(0)-catalyzed Stille coupling reaction and oxidation polymerization. The thermal, absorption, emission, and electrochemical properties of these polymers were examined; the effect of the link pattern was studied. All polymers exhibit decomposition temperatures over 295 °C and glass-transition temperatures in the range of 137,202 °C. The absorption spectra of 1, 2, and 3 in thin films exhibit absorption maxima at 381, 584, and 444 nm, respectively. Polymer 1 exhibits intense green emission located at 510 nm in film, whereas polymers 2 and 3 are nonemissive both in solution and in film due to H-aggregate. Cyclic voltammograms of polymers 1, 2, and 3 display irreversible oxidation waves with onset oxidation potentials at 1.73, 0.78, and 1.03 V versus Ag+/Ag, respectively. Theory calculation on model compounds suggests that the dihedral angle decreases in the order of 1 > 3 > 2. On reducing the dihedral angle, the polymer exhibits a longer absorption maximum, a smaller bandgap, a less oxidizing potential and fluorescence quench, due to more coplanar and more ,-electron delocalized backbone structure. Polymer solar cells were fabricated based on the blend of polymer 2 and methanofullerene [6,6]-phenyl C61-butyric acid methyl ester (PCBM). The power conversion efficiency of 0.45% was achieved under AM 1.5, 100 mW cm,2 using polymer 2:PCBM (1:2, w/w) as active layer. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2843,2852, 2009 [source] Field-effect transistors based on PPV derivatives as a semiconducting layerJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 1 2009Woo-Hyung Lee Abstract A series of modified thiophene groups containing PPV-based semiconducting materials, poly[(2,5-bis(octyloxy)-1,4-phenylenevinylene)-alt-(2,2,bithienylenevinylene)] (PPBT), poly[(2,5-bis(octyloxy)-1,4-phenylenevinylene)-alt-(5,5-thiostilylenevinylene)] (PPTVT), have been synthesized through a Horner coupling reaction. From the FTIR and 1H NMR spectroscopy, the configuration of the vinylene groups in the polymers was all trans (E) geometry. The weight-average molecular weights (Mw) of PPBT and PPTVT were found to be 11,700 and 11,800, with polydispersity indices of 2.51 and 2.53, respectively. PPBT and PPTVT thin films exhibit UV,visible absorption maxima at 538 and 558 nm, respectively, and the strong absorption shoulder peaks at 578 and 602 nm, respectively. Solution processed field-effect transistors (FET) fabricated using all the polymers showed p -type OTFT characteristics. The field-effect mobility of the PPTVT was obtained up to 2.3 × 10,3 cm2 V,1 s,1, an on/off ratio of 1.0 × 105 with ambient air stability. Studies of the atomic force microscopy (AFM) and X-ray diffraction (XRD) analysis of the polymer thin films revealed that all the polymers were amorphous structure. The greater planarity and rigidity of PPTVT compared to PPBT results in elongation of conjugation length and better ,,, stacking of polymer chains in amorphous region, which leads to improved FET performance. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 111,120, 2009 [source] Synthesis of silicon-bridged polythiophene derivatives and their applications to EL device materialsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2007Joji Ohshita Abstract Palladium-catalyzed oxidative homo-coupling of 2,6-bis(tributylstannyl)dithienosiloles with CuCl2 afforded poly(dithienosilole-2,6-diyl)s as novel polythiophene derivatives with intra-chain silicon bridges, which exhibited red-shifted UV absorption maxima by about 100 nm from those of the corresponding silole-free polythiophenes. Alternate copolymers also were prepared by palladium-catalyzed cross-coupling reactions of 2,6-dibromodithienosiloles with distannylthiophene or bithophene. These polymer films were applied to single and double-layered organic electroluminescence devices. It was found that some of the resulting polymers exhibited electroluminescence properties and emitted red light in EL devices with the structure of ITO/polymer/Mg-Ag. Introducing an electron-transporting Alq3 layer between the polymer film and the Mg-Ag cathode led to a remarkable improvement in the devices performance. An application of the copolymer to a field effect transistor was also studied. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4588,4596, 2007 [source] Novel aromatic polyamides and polyimides functionalized with 4- tert -butyltriphenylamine groupsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 15 2006Sheng-Huei Hsiao Abstract A new triphenylamine-containing diamine monomer, 4,4,-diamino-4,- tert -butyltriphenylamine, was successfully synthesized by the cesium fluoride-mediated N,N -diarylation of 4- tert -butylaniline with 4-fluoronitrobenzene, followed by the reduction of the nitro group. The obtained diamine monomer was reacted with various aromatic dicarboxylic acids and tetracarboxylic dianhydrides to produce two series of novel triphenylamine-based polyamides and polyimides with pendent tert -butyl substituents. Most of the polymers were readily soluble in polar organic solvents, such as N -methyl-2-pyrrolidone and N,N -dimethylacetamide (DMAc), and could be solution cast into tough and flexible polymer films. These polymers showed high glass transition temperatures between 282 and 320 °C, and they were fairly stable up to a temperature above 450 °C (for polyamides) or 500 °C (for polyimides). These polymers exhibited UV absorption maxima around 308 to 361 nm. The photoluminescence spectra of the polyamides in DMAc exhibited a peak emission wavelength in the blue at 421,433 nm. Cyclic voltammograms of polyamides and polyimides showed an oxidation wave at 1.0,1.1 V versus Ag/AgCl in an acetonitrile solution. All the polyamides and polyimides exhibited excellent reversibility of electrochromic characteristics by continuous several cyclic scans between 0.0 and 1.1,1.3 V, with a color change from the original pale yellowish neutral form to the green or blue oxidized forms. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4579,4592, 2006 [source] Solvent effects on sunscreen active ingredients using Raman spectroscopyJOURNAL OF RAMAN SPECTROSCOPY, Issue 10 2003L. Beyere Abstract We present Raman spectra of five sunscreen active ingredients in 10 solvents. Shifts in the UV absorption maxima and the CO Raman mode wavenumber are observed for some of the sunscreens as a function of solvent. Correlations between the observed wavenumber shifts and solvent properties indicate that hydrogen bonding is a key interaction between sunscreen active ingredients and solvent. Interestingly, the relative Raman intensities are also sensitive to the hydrogen-bonding and polarizability properties of the solvent, reflecting differential stabilization of the sunscreen's resonance structures. These results suggest an ,expanded polarizability' view of the solvent's effect on the solute. The observed wavenumber and relative intensity changes were also utilized to identify the active agents present in commercial sunscreen preparations from their in situ Raman spectra. Copyright © 2003 John Wiley & Sons, Ltd. [source] Structural Effects on the Electronic Absorption Properties of 5,6-Dihydroxyindole Oligomers: The Potential of an Integrated Experimental and DFT Approach to Model Eumelanin Optical Properties,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 3 2008Marco D'Ischia Elucidation of the relationships between structural features and UV,visible absorption properties of 5,6-dihydroxyindole oligomers is an essential step towards an understanding of the unique optical properties of eumelanins. Herein, we report the first combined experimental and density functional theory (DFT) investigation of the 5,6-dihydroxyindole oligomers so far isolated. 2,2,-Biindolyl 2 and the 2,4,-biindolyl 3 absorb at longer wavelengths relative to 2,7,-biindolyl 4 and their spectra were well predicted by DFT analysis. The absorption bands of 2,4,:2,,4,,- and 2,4,:2,,7,,-triindolyls 5 and 6 also fall at different wavelengths and can be interpreted by DFT simulations as being due to a combination of two main separate transitions. Tetramer 7, in which two 2,4,-biindolyl units are linked through a 2,3,-connection, exhibits a broad chromophore extending over the entire UV range without well defined absorption maxima. Within the dimer,tetramer range examined, three key points emerge: (1) an increase in oligomer chain length does not result in any regular and predictable bathochromic shift; (2) a marked broadening of the absorption bands occurs when going from the monomer to the tetramer structure; and (3) the mode of coupling of the indole units is a crucial, hitherto unrecognized, structural parameter affecting the electronic absorption properties of 5,6-dihydroxyindole oligomers. It is concluded that use of experimentally characterized oligomeric scaffolds as a basis for DFT calculations is a most promising approach to building reliable structural models for studies of eumelanins optical properties. [source] Barley polyamine oxidase: characterisation and analysis of the cofactor and the N-terminal amino acid sequencePHYTOCHEMICAL ANALYSIS, Issue 3 2001Anna Radová Abstract This paper reports the first purification method developed for the isolation of an homogeneous polyamine oxidase (PAO) from etiolated barley seedlings. The crude enzyme preparation was obtained after initial precipitation of the extract with protamine sulphate and ammonium sulphate. The enzyme was further purified to a final homogeneity (by the criteria of isoelectric focusing and SDS,PAGE) using techniques of low pressure chromatography followed by two FPLC steps. The purified yellow enzyme showed visible absorption maxima of a flavoprotein at 380 and 450,nm: the presence of FAD as the cofactor was further confirmed by measuring the fluorescence spectra. Barley PAO is an acidic protein (pI 5.4) containing 3% of neutral sugars: its molecular mass determined by SDS,PAGE was 56,kDa, whilst gel permeation chromatography revealed the higher value of 76 kDa. The N-terminal amino acid sequence of barley PAO shows a high degree of similarity to that of maize PAO and to several other flavoprotein oxidases. The polyamines spermine and spermidine were the only two substrates of the enzyme with Km values 4,×,10,5 and 3,×,10,5,M and pH optima of 5.0 and 6.0, respectively. Barley polyamine oxidase is markedly inhibited by acridine dyes and hydrazines. Weak inhibition was observed with substrate analogues, aminoaldehydes, metal chelating agents and several other compounds. Copyright © 2001 John Wiley & Sons, Ltd. [source] In vitro and in vivo comparison of two different light sources for topical photodynamic therapyBRITISH JOURNAL OF DERMATOLOGY, Issue 4 2006P. Babilas Summary Background, Photodynamic therapy (PDT) with 5-aminolaevulinic acid (ALA) is an effective and safe treatment option for the treatment of actinic keratosis (AK). Incoherent lamps are often used, matching the absorption maxima of ALA. Objectives, A comparative trial was performed to evaluate the efficacy of recently developed light-emitting diodes (LEDs). Methods, Human epidermal keratinocytes were incubated for 24 h with ALA (100, 200, 300, 400 or 500 ,mol L,1) and irradiated consecutively using either an incoherent halogen lamp (,em = 580,750 nm; 24 J cm,2; 40 mW cm,2) or an LED system (,em = 633 ± 3 nm; 3, 6, 12 or 24 J cm,2; 40 mW cm,2). Topical ALA-PDT was performed on 40 patients with AK (n = 584) in a symmetrical distribution suitable for two-sided comparison. After incubation with ALA (20% in cream base) irradiation was performed with the incoherent lamp (100 J cm,2; 160 mW cm,2) on one side and the LED system (40 J cm,2; 80 mW cm,2) on the opposite side followed by re-evaluation up to 6 months. Results, No significant differences between the LED system (3, 6, 12 or 24 J cm,2) and the incoherent light source (24 J cm,2) regarding cytotoxicity was found in vitro. The complete remission rate yielded in the in vivo investigation was also not significantly different at 6 weeks (P = 0·95), 3 months (P = 0·75) and 6 months (P = 0·61) following therapy. Six weeks following therapy complete remission rates of 84·3% (LED system) and 82·8% (incoherent lamp) were achieved. There was also no significant difference between both light sources regarding pain during light treatment (P = 0·67), patient satisfaction (P = 1·0) or cosmesis (P = 1·0) following therapy. Conclusions, These results show the efficacy of an LED system for ALA-PDT both in vitro and in vivo. ALA-PDT with the LED system showed a noninferiority regarding the clinical outcome in the treatment of AK compared with the incoherent lamp. [source] Designing Simple Tridentate Ligands for Highly Luminescent Europium ComplexesCHEMISTRY - A EUROPEAN JOURNAL, Issue 41 2009Abstract A series of tridentate benzimidazole-substituted pyridine-2-carboxylic acids have been prepared with a halogen, methyl or alkoxy group in the 6-position of the benzimidazole ring, which additionally contains a solubilising N -alkyl chain. The ligands form neutral homoleptic nine-coordinate lanthanum, europium and terbium complexes as established from X-ray crystallographic analysis of eight structures. The coordination polyhedron around the lanthanide ion is close to a tricapped trigonal prism with ligands arranged in an up,up,down fashion. The coordinated ligands serve as light-harvesting chromophores in the complexes with absorption maxima in the range 321,341,nm (,=(4.9,6.0)×104,M,1,cm,1) and triplet-state energies between 21,300 and 18,800,cm,1; the largest redshifts occur for bromine and electron-donor alkoxy substituents. The ligands efficiently sensitise europium luminescence with overall quantum yields () and observed lifetimes (,obs) reaching 71,% and 3.00,ms, respectively, in the solid state and 52,% and 2.81,ms, respectively, in CH2Cl2 at room temperature. The radiative lifetimes of the Eu(5D0) level amount to ,rad=3.6,4.6,ms and the sensitisation efficiency ,sens=(,rad/,obs) is close to unity for most of the complexes in the solid state and equal to approximately 80,% in solution. The photophysical parameters of the complexes correlate with the triplet energy of the ligands, which in turn is determined by the nature of the benzimidazole substituent. Facile modification of the ligands makes them promising for the development of brightly emissive europium-containing materials. [source] Tetrahedral Oligothiophenes; Synthesis, X-ray Analysis, and Optoelectronic Properties of Highly Symmetrical, 3D-Branched OligothiophenesCHEMISTRY - AN ASIAN JOURNAL, Issue 12 2008Kouzou Matsumoto Dr. Abstract Tetrakis(bithienyl)methane and tetrakis(terthienyl)methane have been synthesized from tetrakis(2-thienyl)methane by use of Suzuki,Miyaura coupling as a key reaction. Their trimethylsilyl (TMS) derivatives are also synthesized. X-ray analysis reveals that each oligothiophene moiety tends to adopt anti -conformations and show relatively small torsion angles between the adjacent thiophene rings. While the longest absorption maxima of these tetrakis(oligothienyl)methanes exhibit only a slight bathochromic shift compared to the corresponding linear oligothiophene derivative, tetrakis(bithienyl)methane and its TMS derivative exhibit an appreciable red-shift in their fluorescence spectra. The intramolecular interaction between thienyl groups of tetrakis(2-thienyl)methane is supported by DFT calculation. [source] Excited State Intramolecular Proton Transfer of New Diphenyl- ethylene Derivatives Bearing Imino Group: A Combination of Experimental and Theoretical InvestigationCHINESE JOURNAL OF CHEMISTRY, Issue 7 2010Fang Gao Abstract In this paper, we described the synthesis and characterization of new diphenylethylene bearing imino group. We concentrated particularly on the investigation of the possibility of the excited state intramolecular charge transfer (ESIPT) of the new dyes experimentally and theoretically. The absorption and fluorescence spectroscopy of the dyes were determined in various solvents. The results showed that the maximal absorption wavelength of 2-[(4,- N,N -dimethylamino-diphenylethylene-4-ylimino)methyl]phenol (C1) and 4-[(4,- N,N -dimethylamino-diphenylethylene-4-ylimino)methyl]phenol (C2) exhibited almost independence on the solvent polarity. While as contrast, the maximal fluorescence wavelength of the dyes showed somewhat dependence on the solvent polarity. In particular, C1 displayed well-separated dual fluorescence spectroscopy. The second fluorescence peak was characterized with an "abnormal" fluorescence emission wavelength in aprotic solvents with large Stokes shift (ca. 140 nm in THF), which was much more than normal Stokes shift (ca. 30 nm in THF). This emission spectroscopy could be assigned to ESIPT emission. On the other hand, the ESIPT fluorescence of C1 was much reduced or lost in the protic solvents. While, only normal fluorescence emission was detected in various solvents. Although the absorption maxima of C1 exhibited about 10 nm red-shift with respect to those of C2, the normal fluorescence maxima of C1 and C2 were almost identical in various solvents. These results suggested that C1 could undergo ESIPT, but C2 was not able to proceed ESIPT. The molecular geometry optimization of phototautomers in the ground electronic state (S0) was carried out with HF method (Hartree-Fock) and at DFT level (Density Functional Theory) using B3LYP both, while the CIS was employed to optimize the geometries of the first singlet excited state (S1) of the phototautomers of C1 and C2 respectively. The properties of the ground state and the excited state of the phototautomers of C1 and C2, including the geometrical parameter, the energy, the frontier orbits, the Mulliken charge and the dipole moment change were performed and compared completely. The data were analyzed further based on our experimental results. Furthermore, the absorption and fluorescence spectra were calculated in theory and compared with the measured ones. The rate constant of internal proton transfer (9.831×1011 s,1) of C1 was much lower than that of salicylidene methylamine (C3, 2.045×1015 s,1), which was a typical Schiff base compound and was well demonstrated to undergo ESIPT easily under photoexcitation. [source] Indirect laser-induced fluorescence detection for capillary electrophoresis using a frequency-doubled diode laserELECTROPHORESIS, Issue 3 2003Natalia Ragozina Abstract A blue (452 nm) frequency-doubled diode laser with a quasi-cw optical output power of 10 ,W is used for indirect laser-induced fluorescence detection in combination with the capillary electrophoretic separation of inorganic anions. As fluorescing probe ion the anion of 8-hydroxypyrene-1,3,6-trisulfonic acid (HPTS) was selected having an absorption maximum of 454 nm in alkaline medium. Employing a capillary coated with linear acrylamide, baseline separation of eight inorganic anions was possible within 5 min. With a separation buffer containing 50 ,mol·L -1 HPTS and 10 mmol·L -1 lysine the limits of detection for sulfate, nitrite, nitrate, azide, thiocyanate, and chlorate were between 0.9 and 4.7 ,mol·L -1. Separation of chloride and sulfate was achieved by adding 0.25 mmol·L -1 calcium hydroxide to the separation buffer. Inorganic anions in several mineral and tap water samples have been determined with the technique developed and results are compared to data obtained by ion chromatography in combination with conductivity detection after conductivity suppression. [source] Oxidation of oleuropein studied by EPR and spectrophotometryEUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 2 2008Evaggelia D. Tzika Abstract The autoxidation at alkaline pH and enzymatic oxidation by mushroom tyrosinase of oleuropein, the dominant biophenol present in the fruits and leaves of Olea europea, was followed by both electron paramagnetic resonance (EPR) and absorption spectroscopy. For comparison, the same oxidation processes were applied to 4-methylcatechol, a simple polyphenol present in olive mill wastewaters. EPR spectra of stable o -semiquinone radicals produced during autoxidation at pH,12 and short-lived o -semiquinone free radicals produced during autoxidation at pH,9.0 or tyrosinase action and stabilized by chelation with a diamagnetic metal ion (Mg2+) were recorded for both polyphenols, and the corresponding hyperfine splitting constants were determined. The UV-Vis spectral characteristics of the oxidation of polyphenols were highly dependent on the type of polyphenol, oxidant type and the pH of the reaction. The kinetic behavior of tyrosinase in the presence of oleuropein and 4-methylcatechol was followed by recording spectral changes at 400,nm (absorption maximum) over time. The tysosinase activity with oleuropein showed a pronounced pH optimum at pH,6.5 and a minor one around pH,8. From the data analysis of the initial rate at pH,6.5, the kinetic parameters Km = 0.34,±,0.03,mM and Vmax = 0.029,±,0.002 ,A400,min,1 were determined for oleuropein. [source] Dye-Sensitized Solar Cells Based on a Novel Fluorescent Dye with a Pyridine Ring and a Pyridinium Dye with the Pyridinium Ring Forming Strong Interactions with Nanocrystalline TiO2 FilmsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 1 2010Yousuke Ooyama Abstract As new-type donor,acceptor ,-conjugated dyes capable of forming a strong interaction between the electron-acceptor moiety of the sensitizers and a TiO2 surface, fluorescent dye OH11 and pyridinum dye OH12 with a pyridine and pyridinium ring as the electron-accepting group, respectively, have been designed and synthesized as photosensitizers for use in dye-sensitized solar cells (DSSCs). The fluorescent dye OH11 exhibits an absorption band at around 410 nm and a fluorescence band at around 530 nm. On the other hand, the pyridinum dye OH12 shows an absorption maximum at around 560 nm, assigned to a strong intramolecular charge-transfer excitation from the dibutylamino group to the pyridinium ring. The short-circuit photocurrent densities of the DSSCs prepared by using OH11 and OH12 are 4.33 and 1.74mA cm,2, and the solar energy-to-electricity conversion yields are 1.33 and 0.51,%, respectively, under simulated solar light [AM (air mass) 1.5, 100 mW,cm,2]. The open-circuit photovoltage for OH11 (525 mV) is higher than that of OH12 (444 mV). The effects of the configuration of the dyes on the TiO2 surface and of their chemical structures on the photovoltaic performances are discussed on the basis of semi-empirical molecular orbital calculations (AM1 and INDO/S), spectral analyses and cyclic voltammetry. [source] Systematic Studies on Photoluminescence of Oligo(arylene-ethynylene)s: Tunability of Excited States and Derivatization as Luminescent Labeling Probes for ProteinsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 14 2006Yong-Gang Zhi Abstract Functionalized oligo(phenylene-ethynylene)s (OPEs) with different conjugation lengths, p -X(C6H4C,C)nSiMe3 (n = 1,4; X = NH2, NMe2, H) were synthesized by Sonogashira coupling of (phenylene-ethynylene)s and 1-iodo-4-(trimethylsilylethynyl)benzene, followed by desilylation of the p -substituted (trimethylsilylethynyl)benzenes with potassium hydroxide. The photoluminescent properties for the OPE series with different chain lengths and their solvatochromic responses were examined. The absorption maxima were red-shifted with increasing numbers of ,(C6H4C,C), units (n), and a linear plot of the absorption energy maxima vs. 1/n was obtained for each series. The emission spectra in dichloromethane showed a broad and structureless band, the energies of which (in wavenumbers) also fit linearly with 1/n. Both the absorption and emission wavelength maxima of the NH2 - and NMe2 -substituted OPEs exhibited significant solvent dependence, whereas the parent OPEs (X = H) showed only minor shifts of the ,max values in different solvents. Substituent effects upon the photoluminescent characteristics of the OPEs and the tunability of the excited states were examined with the p -X(C6H4C,C)nSiMe3 (n = 2, 3; X = NH2, NMe2, H, SMe, OMe, OH, and F) series. The H- and F-substituted counterparts exhibited high-energy vibronically structured emissions attributed to the 3(,,*) excited states of the (arylene-ethynylene) backbone. For compounds bearing NH2 and NMe2 groups, a broad red-shifted emission with a remarkable Stokes shift from the respective absorption maximum was observed, which can be assigned to an n , ,* transition. The n , ,* assignment was supported by MO calculations on the model compounds p -X(C6H4C,C)2SiH3 (X = NH2, H). Functionalization of the oligo(arylene-ethynylene)s with the N -hydroxysuccinimidyl (NHS) moiety enabled covalent attachment of the fluorophore to HSA protein molecules. A series of fluorescent labels, namely p -X(C6H4C,C)nC6H4NHS, (n = 1, X = NH2, NMe2, SMe, OMe, OH, F; n = 2, X = NH2, NMe2) and p -Me2NC6H4C,C(C4H2S)C,CC6H4NHS were synthesized, and their conjugates with HSA (human serum albumin) were characterized by MALDI-TOF mass spectrometry, UV/Vis absorption spectroscopy, and gel electrophoresis. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] UV-B INDUCTION OF UV-B PROTECTION IN ULVA PERTUSA (CHLOROPHYTA),JOURNAL OF PHYCOLOGY, Issue 3 2005Young-Seok Han The green macroalga Ulva pertusa Kjellman produced UV-B absorbing compounds with a prominent absorption maximum at 294 nm in response only to UV-B, and the amounts induced were proportional to the UV-B doses. Under a 12:12-h light:dark regime, the production of UV-absorbing compounds occurred only during the exposure periods with little turnover in the dark. There was significant reduction in growth in parallel with the production of UV-B absorbing compounds. The polychromatic action spectrum for the induction of UV-B absorbing compounds in U. pertusa exhibits a major peak at 292 nm with a smaller peak at 311.5 nm. No significant induction was detected above 354.5 nm, and radiation below 285 nm caused significant reduction in the levels of UV-B absorbing compounds. After UV-B irradiation at 1.0 W·m,2 for 9 h, the optimal photosynthetic quantum yield of the samples with UV-B absorbing compounds slightly increased relative to the initial value, whereas that of thalli lacking the compounds declined to 30%,34% of the initial followed by subsequent recovery in dim light of up to 84%,85% of the initial value. There was a positive and significant relationship between the amount of UV-B absorbing compounds with antioxidant activity as determined by the ,,,-diphenyl-,-picrylhydrazyl scavenging assay. In addition to mat-forming characteristics and light-driven photorepair, the existence and antioxidant capacity of UV-B absorbing compounds may confer U. pertusa a greater selective advantage over other macroalgae, thereby enabling them to thrive in the presence of intense UV-B radiation. [source] Soluble dithienothiophene polymers: Effect of link patternJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 11 2009Shiming Zhang Abstract Soluble conjugated polymers based on 3,5-didecanyldithieno[3,2- b:2,,3,- d]thiophene,single-bond (1), double-bond (2), and triple-bond linked (3),were synthesized by palladium(0)-catalyzed Stille coupling reaction and oxidation polymerization. The thermal, absorption, emission, and electrochemical properties of these polymers were examined; the effect of the link pattern was studied. All polymers exhibit decomposition temperatures over 295 °C and glass-transition temperatures in the range of 137,202 °C. The absorption spectra of 1, 2, and 3 in thin films exhibit absorption maxima at 381, 584, and 444 nm, respectively. Polymer 1 exhibits intense green emission located at 510 nm in film, whereas polymers 2 and 3 are nonemissive both in solution and in film due to H-aggregate. Cyclic voltammograms of polymers 1, 2, and 3 display irreversible oxidation waves with onset oxidation potentials at 1.73, 0.78, and 1.03 V versus Ag+/Ag, respectively. Theory calculation on model compounds suggests that the dihedral angle decreases in the order of 1 > 3 > 2. On reducing the dihedral angle, the polymer exhibits a longer absorption maximum, a smaller bandgap, a less oxidizing potential and fluorescence quench, due to more coplanar and more ,-electron delocalized backbone structure. Polymer solar cells were fabricated based on the blend of polymer 2 and methanofullerene [6,6]-phenyl C61-butyric acid methyl ester (PCBM). The power conversion efficiency of 0.45% was achieved under AM 1.5, 100 mW cm,2 using polymer 2:PCBM (1:2, w/w) as active layer. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2843,2852, 2009 [source] Hyperbranched copolymer containing triphenylamine and divinyl bipyridyl units for fluorescent chemosensorsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 1 2009Jichang Feng Abstract A fluorescent hyperbranched copolymer (HTP) and a linear copolymer (PTP) as a reference sample to HTP both containing triphenylamine and divinyl bipyridyl units were synthesized via Heck coupling reaction from 5,5,-Divinyl-2,2,-bipyridyl with tris(4-bromophenyl)amine and with 4,4,-dibromotriphenylamie, respectively. The chemical structure of HTP was confirmed by FTIR, 1H NMR, and 13C NMR. The polymer HTP had a number-average molecular weight of 1895 and a weight-average molecular weight of 2315, and good solubility in conventional organic solvents, such as THF, DMF, and chloroform, and exhibited good thermal stability. The UV,vis absorption and photoluminescence (PL) spectra exhibited absorption maximum at 428 nm and emissive maximum at 531 nm for the HTP solution. The spectroscopic results of HTP and PTP indicated that hyperbranched conjugated structure increases the effective conjugation length, as compared with corresponding linear conjugated structure. The fluorescence of the polymer in solution can be quenched by various transition metal ions. The effect of backbone structure of the conjugated polymer-based chemosensors on the sensitivity and selectivity in metal ions sensing have been investigated, and the quenching effect of HTP is more sensitive toward transition metal than linear copolymer PTP. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 222,230, 2009 [source] | |||||||||||||||||||||||||||||||