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Neutral Form (neutral + form)
Selected AbstractsElectropolymerization of a Bifunctional Ionic Liquid Monomer Yields an Electroactive Liquid-Crystalline PolymerADVANCED FUNCTIONAL MATERIALS, Issue 13 2010Sungwon Lee Abstract The preparation and polymerization of a bifunctional imidazolium-based ionic liquid (IL) monomer that incorporates both a vinyl group and a thiophene moiety is reported. Potentiodynamic electropolymerization of the monomer produces an optically birefringent polymer film that strongly adheres to the electrode surface. Fourier transform IR spectroscopy shows that polymerization occurs through both the vinyl and thienyl groups. Cylic voltammetry (CV) is used to determine the polymer oxidation potential (1.66,V) and electrochemical bandgap, Eg, of 2.45,eV. The polymer exhibits electrochromism, converting from yellow in the neutral form (,max,=,380,nm) to blue in the polaronic state at 0.6,V (,max,=,672,nm) and to blue-grey in the bipolaronic state at 1.2,V (,max,>,800,nm). Topographic atomic force microscopy (AFM) images reveal isolated (separated) fibrils. Grazing-incidence small-angle X-ray scattering (GISAXS) studies indicate a lamellar structure with a lattice spacing of 3.2,nm. Wide-angle X-ray diffraction (WAXD) studies further suggest that the polymerized thiophene sheets are oriented perpendicular to the polymerized vinylimidazolium. The electrical conductivity, as determined by four-probe dc conductivity measurements was found to be 0.53,S cm,1 in the neutral form and 2.36,S cm,1 in the iodine-doped state, values higher than typically observed for polyalkylthiophenes. The structural ordering is believed to contribute to the observed enhancement of the electrical conductivity. [source] Analysing Competence: Gender and Identity at WorkGENDER, WORK & ORGANISATION, Issue 5 2003Bronwen Rees Competence approaches are among the techniques that claim to measure the behaviour, skills, knowledge and understanding crucial to effective managerial performance. It is claimed that competence approaches empower and develop managers while enabling them to meet organizational objectives. Since the bases for the techniques are avowedly scientific, they are said to provide organizations with a gender neutral form of assessment. In this paper we construct a theoretical framework in terms of which these claims can be analysed and assessed. Using this framework, we examine the competence approach as it has been implemented in six organizations in relation to the claim to objectivity. [source] Proton affinity ladder for uridine and analogs: influence of the hydroxyl group on the sugar ring conformationJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 6 2005S. Mezzache Abstract A ladder of relative proton affinities (PA) for a series of modified uridines (e.g. araU, ddU, 5BrU, 5BrdU and 5IU) was established from competitive dissociations of proton-bound heterodimers using Cooks and co-workers' kinetic method. The studied heterodimers are constituted of a modified nucleoside and either an amino acid or a nucleoside with known PA value. These non-covalent heterodimers were prepared under electrospray conditions to be selected and dissociated into the ion-trap analyzer. These results allowed our PA ladder of uridine and deoxyuridine analogs substituted at the C-5 position in the uracil ring to be extended. From this scale, it was showed that the substitution of hydrogen atom at the C-2, position in the sugar ring by a hydroxyl group involves a decrease of about 7 kJ mol,1. The experimental values for U, 5MeU, dU, 5MedU, ddU and araU are consistent with those obtained by DFT calculations (B3P86/6,31+G*//B3LYP/6,31G*). Several neutral and protonated conformations of these compounds were considered, in particular the ring conformation of furanose and the orientation of the base with respect to the sugar ring. These calculated results showed the influence of sugar substituent on the conformation of the neutral form of theses nucleosides. However, the most stable protonated structure is the same for all the studied nucleosides except for araU, where the position of the anti 2,-OH group imposes a specific conformation. Copyright © 2005 John Wiley & Sons, Ltd. [source] Highly stable electrochromic polyamides based on N,N -bis(4-aminophenyl)- N,,N,-bis(4- tert -butylphenyl)-1,4-phenylenediamineJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 9 2009Sheng-Huei Hsiao Abstract A new triphenylamine-containing aromatic diamine monomer, N,N -bis(4-aminophenyl)- N,,N,-bis(4- tert -butylphenyl)-1,4-phenylenediamine, was synthesized by an established synthetic procedure from readily available reagents. A novel family of electroactive polyamides with di- tert -butyl-substituted N,N,N,,N,-tetraphenyl-1,4-phenylenediamine units were prepared via the phosphorylation polyamidation reactions of the newly synthesized diamine monomer with various aromatic or aliphatic dicarboxylic acids. All the polymers were amorphous with good solubility in many organic solvents, such as N -methyl-2-pyrrolidinone (NMP) and N,N -dimethylacetamide, and could be solution-cast into tough and flexible polymer films. The polyamides derived from aromatic dicarboxylic acids had useful levels of thermal stability, with glass-transition temperatures of 269,296 °C, 10% weight-loss temperatures in excess of 544 °C, and char yields at 800 °C in nitrogen higher than 62%. The dilute solutions of these polyamides in NMP exhibited strong absorption bands centered at 316,342 nm and photoluminescence maxima around 362,465 nm in the violet-blue region. The polyamides derived from aliphatic dicarboxylic acids were optically transparent in the visible region and fluoresced with a higher quantum yield compared with those derived from aromatic dicarboxylic acids. The hole-transporting and electrochromic properties were examined by electrochemical and spectro-electrochemical methods. Cyclic voltammograms of the polyamide films cast onto an indium-tin oxide-coated glass substrate exhibited two reversible oxidation redox couples at 0.57,0.60 V and 0.95,0.98 V versus Ag/AgCl in acetonitrile solution. The polyamide films revealed excellent elcterochemical and electrochromic stability, with a color change from a colorless or pale yellowish neutral form to green and blue oxidized forms at applied potentials ranging from 0.0 to 1.2 V. These anodically coloring polymeric materials showed interesting electrochromic properties, such as high coloration efficiency (CE = 216 cm2/C for the green coloring) and high contrast ratio of optical transmittance change (,T%) up to 64% at 424 nm and 59% at 983 nm for the green coloration, and 90% at 778 nm for the blue coloration. The electroactivity of the polymer remains intact even after cycling 500 times between its neutral and fully oxidized states. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2330,2343, 2009 [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] The Effect of pH on the Topography of Porphyrins in Lipid Membranes,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 2 2005Irena Bronshtein ABSTRACT The effect of the acidity of the environment on the topography and photophysics of sensitizer molecules in homogeneous solutions, and when embedded in a lipid microenvironment, was studied. Four hematoporphyrin (HP) analogs were studied, which have chemical "spacers" of varying lengths between the chromophoric tetrapyrrole and the carboxylate moiety. These derivatives have essentially the same chemical attributes and reactivity as the parent compound, HP IX, which is used in clinical procedures of photodynamic therapy. The binding constants of these HP derivatives to membrane model systems increase with the length of carboxylate chain in the pH range 3.0,6.6. This effect of chain length is attributed to an increase in the hydrophobicity of the molecule on elongation of the alkyl chains. A strong pH dependence of the quenching efficiency of the porphyrins' fluorescence by iodide ions was observed in aqueous solution and is attributed to a unique electrostatic interaction between the fluorophore and the quencher. The quenching efficiency in liposomes, relative to the quenching in buffer, as a function of pH, shows that porphyrins in the neutral form penetrate deeper inside the lipid bilayer and are less exposed to external quenching than when negatively charged at the carboxylic moiety. This vertical displacement in the membrane is also evidenced in the effect of pH on the photosensitized oxidation efficiency of a membrane-bound chemical target. Increasing the pH causes a significant decrease in the sensitization efficiency in liposomes. This trend is attributed to the vertical localization, and protonation of the carboxylic groups on lowering the pH leads to sinking of the sensitizer into the lipid bilayer and to a consequent generation of singlet oxygen at a deeper point. This increases the dwell time of singlet oxygen within the bilayer, which results in greater photodamage to a membrane-residing singlet oxygen target. [source] Infrared Study of Intercomponent Interactions in a Switchable Hydrogen-Bonded RotaxaneCHEMISTRY - A EUROPEAN JOURNAL, Issue 6 2008Dhiredj Abstract The macrocycle in rotaxane 1 is preferentially hydrogen bonded to the succinamide station in the neutral form, but can be moved to the naphthalimide station by one-electron reduction of the latter. The hydrogen bonding between the amide NH groups of the macrocycle and the CO groups in the binding stations in the thread was studied with IR spectroscopy in different solvents in both states. In addition, the solvent effect on the vibrational frequencies was analyzed; a correlation with the solvent acceptor number (AN) was observed. The conformational switching upon reduction could be detected by monitoring the hydrogen-bond-induced shifts of the ,(CO) frequencies of the CO groups of the succinamide and the reduced naphthalimide stations. The macrocycle was found to shield the encapsulated station from the solvent: wavenumbers of ,(CO) bands of the CO groups residing inside the macrocycle cavity remain unaffected by the solvent polarity. [source] Chiral NMR discrimination of amines: Analysis of secondary, tertiary, and prochiral amines using (18-crown-6)-2,3,11,12-tetracarboxylic acid,CHIRALITY, Issue 3-4 2008Ann E. Lovely Abstract Enantiomeric discrimination is observed in the 1H and 13C NMR spectra of secondary and tertiary amines in the presence of (,)-(18-crown-6)-2,3,11,12-tetracarboxylic acid (1). Nonequivalence of the resonances of prochiral nuclei in primary and secondary amines is also observed when they associate with 1. The amines are added in their neutral form and are protonated by the carboxylic acid groups of 1 to produce the corresponding ammonium and carboxylate ions. Secondary amines associate with 1 through two hydrogen bonds and an ion pair interaction. Tertiary amines can only form one hydrogen bond to accompany the ion pairing. Chiral discrimination in the 1H and 13C NMR spectra of a series of aryl-containing secondary amines is of sufficient magnitude to determine enantiomeric purities. The discrimination in the spectra of tertiary amines with 1 is smaller, but 13C NMR spectra provided enough distinction for the determination of enantiomeric purity. Chirality, 2008. © 2007 Wiley-Liss, Inc. [source] Studies toward a universal dye for textile fibresCOLORATION TECHNOLOGY, Issue 5 2004Potjanart Suwanruji A new organic dye was synthesised as part of an approach to producing a dye that could be applied to any of a variety of widely used fibre types. The dye synthesised is best described as a disperse-reactive dye and was obtained from a sequence of reactions that used an acid yellow dye as a starting compound. Dichlorotriazine was used as the reactive group in the target dye and the chemical structures of the new dye and its precursors were confirmed using 1H NMR, mass spectrometry and FTIR analyses. In the neutral form, the dye was suitable for polyester, nylon and wool fibres. When the pH was adjusted to 9 it dyed cotton, albeit in a pastel shade only. By adding N, N -dimethylethylenediamine to the dyebath, the dye could be applied to acrylic fabric at pH 5. The fastness of the dyed fibres was also evaluated. [source] The Role of One-Electron Reduction of Lipid Hydroperoxides in Causing DNA DamageCHEMISTRY - A EUROPEAN JOURNAL, Issue 40 2009Conor Crean Dr. Abstract The in vivo metabolism of plasma lipids generates lipid hydroperoxides that, upon one-electron reduction, give rise to a wide spectrum of genotoxic unsaturated aldehydes and epoxides. These metabolites react with cellular DNA to form a variety of pre-mutagenic DNA lesions. The mechanisms of action of the radical precursors of these genotoxic electrophiles are poorly understood. In this work we investigated the nature of DNA products formed by a one-electron reduction of (13S)-hydroperoxy-(9Z,11E)-octadecadienoic acid (13S -HPODE), a typical lipid molecule, and the reactions of the free radicals thus generated with neutral guanine radicals, G(,H).. A novel approach was devised to generate these intermediates in solution. The two-photon-induced ionization of 2-aminopurine (2AP) within the 2,-deoxyoligonucleotide 5,-d(CC[2AP]TCGCTACC) by intense nanosecond 308,nm excimer laser pulses was employed to simultaneously generate hydrated electrons and radical cations 2AP.+. The latter radicals either in cationic or neutral forms, rapidly oxidize the nearby G base to form G(,H).. In deoxygenated buffer solutions (pH,7.5), the hydrated electrons rapidly reduce 13S -HPODE and the highly unstable alkoxyl radicals formed undergo a prompt ,-scission to pentyl radicals that readily combine with G(,H).. Two novel guanine products in these oligonucleotides, 8-pentyl- and N2 -pentylguanine, were identified. It is shown that the DNA secondary structure significantly affects the ratio of 8-pentyl- and N2 -pentylguanine lesions that changes from 0.9:1 in single-stranded, to 1:0.2 in double-stranded oligonucleotides. The alkylation of guanine by alkyl radicals derived from lipid hydroperoxides might contribute to the genotoxic modification of cellular DNA under hypoxic conditions. Thus, further research is warranted on the detection of pentylguanine lesions and other alkylguanines in vivo. [source] Application of the Perimeter Model to the Assignment of the Electronic Absorption Spectra of Gold(III) Hexaphyrins with [4n+2] and [4n] ,-Electron SystemsCHEMISTRY - A EUROPEAN JOURNAL, Issue 15 2009Atsuya Muranaka Dr. Abstract Expanded porphyrins: The electronic excited states of two forms of meso -hexakis(pentafluorophenyl)-substituted gold(III) hexaphyrin(1.1.1.1.1.1), such as that depicted, have been investigated by density functional calculations and magnetic circular dichroism spectroscopy to assign their low-energy excited singlet states. The electronic excited states of two forms of meso -hexakis(pentafluorophenyl)-substituted gold(III) hexaphyrin(1.1.1.1.1.1) have been investigated by density functional calculations and magnetic circular dichroism (MCD) spectroscopy, in order to assign their low-energy excited singlet states. We found that the perimeter model can be successfully applied to the interpretation of the electronic states. In the case of the neutral forms (Au2 -N, Au-N), the absorption bands observed in the NIR and visible region can be assigned to ,,,* transitions referred to as the L and B bands, respectively, analogous to the Q and Soret bands of regular porphyrins. In marked contrast with the neutral forms, the absorption bands of the reduced forms (Au2 -R and Au-R) are attributed to ,,,* transitions involving six frontier molecular , orbitals. By applying the 4N -electron perimeter model, the six orbitals are labeled as h,, h+, s,, s+, l,, and l+, while the observed absorption bands can be assigned to the S, N1, N2, P1, and P2 transitions, in order of increasing energy. [source] Ultrafast Photoisomerization of Photoactive Yellow Protein Chromophore Analogues in Solution: Influence of the Protonation StateCHEMPHYSCHEM, Issue 8 2006Agathe Espagne Dr. Abstract We investigate solvent viscosity and polarity effects on the photoisomerization of the protonated and deprotonated forms of two analogues of the photoactive yellow protein (PYP) chromophore. These are trans- p -hydroxybenzylidene acetone and trans- p -hydroxyphenyl cinnamate, studied in solutions of different polarity and viscosity at room temperature, by means of femtosecond fluorescence up-conversion. The fluorescence lifetimes of the protonated forms are found to be barely sensitive to solvent viscosity, and to increase with increasing solvent polarity. In contrast, the fluorescence decays of the deprotonated forms are significantly slowed down in viscous media and accelerated in polar solvents. These results elucidate the dramatic influence of the protonation state of the PYP chromophore analogues on their photoinduced dynamics. The viscosity and polarity effects are, respectively, interpreted in terms of different isomerization coordinates and charge redistribution in S1. A trans-to-cis isomerization mechanism involving mainly the ethylenic double-bond torsion and/or solvation is proposed for the anionic forms, whereas "concerted" intramolecular motions are proposed for the neutral forms. [source] | |||||||||||||