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Solvent Polarity (solvent + polarity)
Kinds of Solvent Polarity Selected AbstractsInfluence of Decreasing Solvent Polarity (1,4-Dioxane/Water Mixtures) on the Acid,Base and Copper(II)-Binding Properties of Guanosine 5,-Diphosphate,HELVETICA CHIMICA ACTA, Issue 3 2005Emanuela The acidity constants of twofold protonated guanosine 5,-diphosphate, H2(GDP),, and the stability constants of the [Cu(H;GDP)] and [Cu(GDP)], complexes were determined in H2O as well as in 30 or 50% (v/v) 1,4-dioxane/H2O by potentiometric pH titrations (25°; I=0.1M, NaNO3). The results showed that in H2O one of the two protons of H2(GDP), is located mainly at the N(7) site and the other one at the terminal , -phosphate group. In contrast, for 50% 1,4-dioxane/H2O solutions, a micro acidity-constant evaluation evidenced that ca. 75% of the H2(GDP), species have both protons phosphate-bound, because the basicity of pyridine-type N sites decreases with decreasing solvent polarity whereas the one of phosphate groups increases. In the [Cu(H;GDP)] complex, the proton and the metal ion are in all three solvents overwhelmingly phosphate-bound, and the release of this proton is inhibited by decreasing polarity of the solvent. Based on previously determined straight-line plots of log,Kvs. pK (where R represents a non-interacting residue in simple diphosphate monoesters ROP(O,)(O)OP(O)(O,)2, RDP3,), which were now extended to mixed solvents (based on analogies), it is concluded that, in all three solvents, the [Cu(GDP)], complex is more stable than expected based on the basicity of the diphosphate residue. This increased stability is attributed to macrochelate formation of the phosphate-coordinated Cu2+ with N(7) of the guanine residue. The formation degree of this macrochelate amounts in aqueous solution to ca. 75% (being thus higher than that of the Cu2+ complex of adenosine 5,-diphosphate) and in 50% (v/v) 1,4-dioxane/H2O to ca. 60%, i.e., the formation degree of the macrochelate is only relatively little affected by the change in solvent, though it needs to be emphasized that the overall stability of the [Cu(GDP)], complex increases with decreasing solvent polarity. By including previously studied systems in the considerations, the biological implications are shortly discussed, and it is concluded that Nature has here a tool to alter the structure of complexes by shifting them on a protein surface from a polar to an apolar region and vice versa. [source] Multi-Input/Multi-Output Molecular Response System Based on the Dynamic Redox Behavior of 3,3,4,4-Tetraaryldihydro[5]helicene Derivatives: Reversible Formation/Destruction of Chiral Fluorophore and Modulation of Chiroptical Properties by Solvent PolarityCHEMISTRY - A EUROPEAN JOURNAL, Issue 37 2009Takanori Suzuki Prof. Abstract 3,3,4,4-Tetaaryldihydro[5]helicenes (1) and 1,1,-binaphthyl-2,2,-diylbis(diarylcarbenium)s (22+) can be reversibly interconverted upon electron transfer, which is accompanied by a vivid color change (electrochromism) as well as by the formation/cleavage of a CC bond ("dynamic redox behavior"). Because only the neutral donor 1 exhibits strong fluorescence, electrochemical input can further modify the fluorescent properties of the pair. Due to the configurational stability of the helicity in 1 and axial chirality in 22+, the redox reaction of optically pure material proceeds stereospecifically, which induces a chiroptical change such as circular dichroism (CD) as an additional output. The CD spectra of dications 22+ exhibit solvent dependency (chiro-solvatochromism), which is accompanied by solvatochromic behavior based on the ,,, interaction of the two cationic chromophores as well as coordinative interaction of the Lewis basic solvent to the Lewis acidic triarylcarbenium moieties. Thus, the present system is endowed with multi-input functionality for modifying multiple output signals. [source] Atom transfer radical polymerization of styrenic ionic liquid monomers and carbon dioxide absorption of the polymerized ionic liquidsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 7 2005Huadong Tang Abstract Polymeric forms of ionic liquids have many potential applications because of their high thermal stability and ionic nature. Two ionic liquid monomers, 1-(4-vinylbenzyl)-3-butyl imidazolium tetrafluoroborate (VBIT) and 1-(4-vinylbenzyl)-3- butyl imidazolium hexafluorophosphate (VBIH), were synthesized through the quaternization of N -butylimidazole with 4-vinylbenzylchloride and a subsequent anion- exchange reaction with sodium tetrafluoroborate or potassium hexafluorophosphate. Copper-mediated atom transfer radical polymerization was used to polymerize VBIT and VBIH. The effects of various initiator/catalyst systems, monomer concentrations, solvent polarities, and reaction temperatures on the polymerization were examined. The polymerization was well controlled and exhibited living characteristics when CuBr/1,1,4,7,10,10-hexamethyltriethylenetetramine or CuBr/2,2,-bipyridine was used as the catalyst and ethyl 2-bromoisobutyrate was used as the initiator. Characterizations by thermogravimetric analysis, differential scanning calorimetry, and X-ray diffraction showed that the resulting VBIT polymer, poly[1-(4-vinylbenzyl)-3-butyl imidazolium tetrafluoroborate] (PVBIT), was amorphous and had excellent thermal stability, with a glass-transition temperature of 84 °C. The polymerized ionic liquids could absorb CO2 as ionic liquids: PVBIT absorbed 0.30% (w/w) CO2 at room temperature and 0.78 atm. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1432,1443, 2005 [source] Oxido Pincer Ligands , Exploring the Coordination Chemistry of Bis(hydroxymethyl)pyridine Ligands for the Late Transition MetalsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 15 2009Axel Klein Abstract Coordination of the 2,6-bis(hydroxymethyl)pyridine-based oxido pincer ligands RR,pydimH2 [R = R, = H (pydimH2); R = R, = Me (pydipH2); R = 2-tolyl, R, = Me (pydotH2)] towards late transition metals CoII, NiII, CuII, ZnII, PdII and PtII allows the formation of molecular species (complexes), which exhibit three main structural motifs in the solid state. The two main species are pentacoordinate [(RR,pydimH2)MCl2] and hexacoordinate [(RR,pydimH2)2M]X2, both of which are stable in solution and can be interconverted by changing the solvent polarity. The disproportionation equilibrium [(RR,pydimH2)MCl2] [rlhar2] [(RR,pydimH2)2M]2+ + [MCl4]2, was studied by optical spectroscopy. The chiral ligand pydotH2 allows the formation of chiral complexes. In the square-planar complexes [(pydimH2)2MCl2] (M = PdII or PtII) the oxido donor functions of the ligands do not take part in the coordination.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Extended X-ray Absorption Fine Structure Study of Copper(I) and Copper(II) Complexes in Atom Transfer Radical PolymerizationEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 11 2003Tomislav Pintauer Abstract Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy has been used to investigate structural features of CuIBr and CuIIBr2 complexes with dNbpy, PMDETA, Me6TREN, tNtpy, and Me4CYCLAM in various solvents {dNbpy = 4,4,-bis(5-nonyl)-2,2,-bipyridine, PMDETA = N,N,N,,N,,,N,, -pentamethyldiethylenetriamine, Me6TREN = tris[2-(dimethylamino)ethyl]amine, tNtpy = 4,4,,4,,-tris(5-nonyl)-2,2,:6,,2,,-terpyridine, Me4CYCLAM = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane}. The structures of the CuI and CuII complexes were found to depend on the solvent polarity and the number of nitrogen atoms in the ligand. Generally, in non-polar media and with monomers typically used in ATRP, CuI complexes preferred a tetracoordinate geometry, and were either ionic as observed in [CuI(dNbpy)2]+[CuIBr2], (CuI,NAV = 2.00 Å, CuI,BrAV = 2.25 Å) and [CuI(Me4CYCLAM)]+[CuIBr2], (CuI,NAV = 2.06 Å, CuI,BrAV = 2.23 Å), or neutral as in [CuI(PMDETA)Br] (CuI,NAV = 2.12 Å, CuI,BrAV = 2.33 Å), and [CuI(tNtpy)Br] (CuI,NAV = 2.03 Å, CuI,BrAV = 2.29 Å). The EXAFS analysis of CuIIBr2 complexes indicated a preference for a coordination number of five, such as in [CuII(dNbpy)2Br]+[Br], (CuII,NAV = 2.03 Å, CuII,BrAV = 2.43 Å), [CuII(PMDETA)Br2] (CuII,NAV = 2.03 Å, CuII,Br1,AV = 2.44 Å, CuII,Br2,AV = 2.64 Å) and [CuII(Me6TREN)Br]+[Br], (CuII,NAV = 2.09 Å, CuII -BrAV = 2.39 Å), with the exception of the neutral tetracoordinate [CuII(dNbpy)Br2] (CuII,NAV = 2.02 Å, CuII,BrAV = 2.36 Å), which has been observed in non-polar media. Additionally, polar media were found to favor bromide dissociation in [CuII(Me6TREN)Br]+[Br], and [CuII(PMDETA)Br2], as indicated by a decrease in the Br and Cu coordination numbers at the Cu- and Br- K -edges, respectively. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Antioxidant capacity of rapeseed meal and rapeseed oils enriched with meal extractEUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 7 2010Aleksandra Szyd, owska-Czerniak Abstract Response surface methodology (RSM) was used to evaluate the quantitative effects of two independent variables: solvent polarity and temperature of the extraction process on the antioxidant capacity (AC) and total phenolics content (TPC) in meal rapeseed extracts. The mean AC and TPC results for meal ranged between 1181,9974,µmol TE/100,g and 73.8,814,mg sinapic acid/100,g of meal. The experimental results of AC and TPC were close to the predicted values calculated from the polynomial response surface models equations (R2,=,0.9758 and 0.9603, respectively). The effect of solvent polarity on AC and TPC in the examined extracts was about 3.6 and 2.6 times greater, respectively, than the effect of processing temperature. The predicted optimum solvent polarity of ,,=,78.3 and 63.8, and temperature of 89.4 and 74.2°C resulted in an AC of 10,014,µmol TE/100,g and TPC of 863,mg SAE/100,g meal, respectively. The phenolic profile of rapeseed meal was determined by an HPLC method. The main phenolics in rapeseed meal were sinapine and sinapic acid. Refined rapeseed oils were fortified with an extract , rich in polyphenols , obtained from rapeseed meal. The supplemented rapeseed oil had higher AC and TPC than the refined oil without addition of meal extracts. However, AC and TPC in the enriched oils decreased during storage. The TPC in the studied meal extracts and rapeseed oils correlated significantly (p<0.0000001) positively with their AC (R2,=,0.9387). Practical applications: Many bioactive compounds extracted from rapeseed meal provide health benefits and have antioxidative properties. Therefore, it seems worth to consider the application of antioxidants extracted from the rapeseed meal for the production of rapeseed oils with potent AC. Moreover, antioxidants extracted from the rapeseed meal were added to refined rapeseed oil in order to enhance its AC. AC was then tested by FRAP assay. FRAP method is based on the reduction of the ferric tripyridyltriazine (Fe3+ -TPTZ) complex to the ferrous tripyridyltriazine (Fe2+ -TPTZ), and it is simple, fast, low cost, and robust method. FRAP method does not require specialized equipment and can be performed using automated, semi-automatic, or manual methods. Therefore the proposed FRAP method can be employed by the fat industry laboratories to asses the AC of rapeseed oils and meal. [source] Medium Effect on the Reaction of N -Butyl-2,4,6-trinitroaniline with NaOH,EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 13 2007María Laura Salum Abstract The kinetics of the reaction of N -butyl-2,4,6-trinitroaniline (3) with NaOH have been studied in 10 and 60,% 1,4-dioxane/H2O at 25 °C. In both cases, several processes were observed. In 10,% 1,4-dioxane/H2O the only product formed was 2,4,6-trinitrophenol (4), whereas in 60,% 1,4-dioxane/H2O a mixture of 4 and 5,7-dinitro-2-propyl-1H -benzimidazole 3-oxide (5) was observed in ratios that depend on the HO, concentration. A mechanism involving the formation of , complexes through the addition of one or two HO, anions to unsubstituted ring positions is proposed for 2,4,6-trinitrophenol formation. The presence of these complexes was confirmed by NMR studies in 60,% [D8]1,4-dioxane/D2O. The mechanism suggested for the formation of the N -oxide includes the cyclization of an N -alkylidene-2-nitrosoaniline-type intermediate as the rate-determining step. The decrease in solvent polarity produces a decrease in the observed rate constant for the formation of 4 of about one order of magnitude making the cyclization reaction a competitive pathway. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Influence of Decreasing Solvent Polarity (1,4-Dioxane/Water Mixtures) on the Acid,Base and Copper(II)-Binding Properties of Guanosine 5,-Diphosphate,HELVETICA CHIMICA ACTA, Issue 3 2005Emanuela The acidity constants of twofold protonated guanosine 5,-diphosphate, H2(GDP),, and the stability constants of the [Cu(H;GDP)] and [Cu(GDP)], complexes were determined in H2O as well as in 30 or 50% (v/v) 1,4-dioxane/H2O by potentiometric pH titrations (25°; I=0.1M, NaNO3). The results showed that in H2O one of the two protons of H2(GDP), is located mainly at the N(7) site and the other one at the terminal , -phosphate group. In contrast, for 50% 1,4-dioxane/H2O solutions, a micro acidity-constant evaluation evidenced that ca. 75% of the H2(GDP), species have both protons phosphate-bound, because the basicity of pyridine-type N sites decreases with decreasing solvent polarity whereas the one of phosphate groups increases. In the [Cu(H;GDP)] complex, the proton and the metal ion are in all three solvents overwhelmingly phosphate-bound, and the release of this proton is inhibited by decreasing polarity of the solvent. Based on previously determined straight-line plots of log,Kvs. pK (where R represents a non-interacting residue in simple diphosphate monoesters ROP(O,)(O)OP(O)(O,)2, RDP3,), which were now extended to mixed solvents (based on analogies), it is concluded that, in all three solvents, the [Cu(GDP)], complex is more stable than expected based on the basicity of the diphosphate residue. This increased stability is attributed to macrochelate formation of the phosphate-coordinated Cu2+ with N(7) of the guanine residue. The formation degree of this macrochelate amounts in aqueous solution to ca. 75% (being thus higher than that of the Cu2+ complex of adenosine 5,-diphosphate) and in 50% (v/v) 1,4-dioxane/H2O to ca. 60%, i.e., the formation degree of the macrochelate is only relatively little affected by the change in solvent, though it needs to be emphasized that the overall stability of the [Cu(GDP)], complex increases with decreasing solvent polarity. By including previously studied systems in the considerations, the biological implications are shortly discussed, and it is concluded that Nature has here a tool to alter the structure of complexes by shifting them on a protein surface from a polar to an apolar region and vice versa. [source] Effect of the Media on the Quantum Yield of Singlet Oxygen (O2(1,g)) Production by 9H -Fluoren-9-one: Solvents and Solvent MixturesHELVETICA CHIMICA ACTA, Issue 2 2003Claudia We have investigated the effect of a series of 18 solvents and mixtures of solvents on the production of singlet molecular oxygen (O2(1,g), denoted as 1O2) by 9H -fluoren-9-one (FLU). The normalized empirical parameter E derived from ET(30) has been chosen as a measure of solvent polarity using Reichardt's betaine dyes. Quantum yields of 1O2 production (,,) decrease with increasing solvent polarity and protic character as a consequence of the decrease of the quantum yield of intersystem crossing (,ISC). Values of ,, of unity have been found in alkanes. In nonprotic solvents of increasing polarity, ,ISC and, therefore, ,, decrease due to solvent-induced changes in the energy levels of singlet and triplet excited states of FLU. This compound is a poor 1O2 sensitizer in protic solvents, because hydrogen bonding considerably increases the rate of internal conversion from the singlet excited state, thus diminishing ,, to values much lower than those in nonprotic solvents of similar polarity. In mixtures of cyclohexane and alcohols, preferential solvation of FLU by the protic solvent leads to a fast decrease of ,, upon addition of increasing amounts of the latter. [source] Ab initio QM/MM study of excited state electron transfer between pyrene and 4,4,-bis(dimethylamino)-diphenylmethane with different solvent systems: Role of hydrogen bonding within solvent moleculesINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 4 2005Kakali Sen Abstract The exciplex is a charge transfer species formed in the process of electron transfer between an electron donor and an electron acceptor and hence is very sensitive to solvent polarity. In order to understand the role of solvent in exciplex formation between pyrene (PY) and 4,4,-bis(dimethylamino)diphenylmethane (DMDPM), we used two types of solvent approximations: an implicit solvent model and an explicit solvent model. The difference in energies between the excited and the meta-stable Frank,Condon state (,E) of the structures were assumed to correspond to the emission maximum of the exciplex in different solvents. The ,E values show the trend of stabilization of the exciplex with an increase in solvent polarity. This trend in stabilization is substantially more prominent in the explicit solvent model than that with the implicit solvent model. The ,E value obtained in methanol reflects equal stabilization compared to that in a more polar solvent, N,N-dimethylformamide. This extra stabilization of the exciplex may be explained on the basis of the H-bonding capability of the protic solvent, methanol. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 [source] Intramolecular electronic communication in a dimethylaminoazobenzene,fullerene C60 dyad: An experimental and TD-DFT studyJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 6 2010K. Senthil Kumar Abstract An electronically push,pull type dimethylaminoazobenzene,fullerene C60 hybrid was designed and synthesized by tailoring N,N -dimethylaniline as an electron donating auxochrome that intensified charge density on the ,-azonitrogen, and on N -methylfulleropyrrolidine (NMFP) as an electron acceptor at the 4 and 4, positions of the azobenzene moiety, respectively. The absorption and charge transfer behavior of the hybrid donor-bridge-acceptor dyad were studied experimentally and by performing TD-DFT calculations. The TD-DFT predicted charge transfer interactions of the dyad ranging from 747 to 601 nm were experimentally observed in the UV-vis spectra at 721 nm in toluene and dichloromethane. A 149 mV anodic shift in the first reduction potential of the NN group of the dyad in comparison with the model aminoazobenzene derivative further supported the phenomenon. Analysis of the charge transfer band through the orbital picture revealed charge displacement from the n(NN) (nonbonding) and , (NN) type orbitals centered on the donor part to the purely fullerene centered LUMOs and LUMO+n orbitals, delocalized over the entire molecule. The imposed electronic perturbations on the aminoazobenzene moiety upon coupling it with C60 were analyzed by comparing the TD-DFT predicted and experimentally observed electronic transition energies of the dyad with the model compounds, NMFP and (E)-N,N -dimethyl-4-(p-tolyldiazenyl)aniline (AZNME). The n(NN) , ,*(NN) and ,(NN) , ,*(NN) transitions of the dyad were bathochromically shifted with a significant charge transfer character. The shifting of ,(NN) , ,*(NN) excitation energy closer to the n , ,*(NN) in comparison with the model aminoazobenzene emphasized the predominant existence of charge separated quinonoid-like ground state electronic structure. Increasing solvent polarity introduced hyperchromic effect in the ,(NN) , ,*(NN) electronic transition at the expense of transitions involved with benzenic states, and the extent of intensity borrowing was quantified adopting the Gaussian deconvolution method. On a comparative scale, the predicted excitation energies were in reasonable agreement with the observed values, demonstrating the efficiency of TD-DFT in predicting the localized and the charge transfer nature of transitions involved with large electronically asymmetric molecules with HOMO and LUMO centered on different parts of the molecular framework. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010 [source] Principles of carbopeptoid folding: a molecular dynamics simulation studyJOURNAL OF PEPTIDE SCIENCE, Issue 2 2005Riccardo Baron Abstract The conformational spaces of five oligomers of tetrahydrofuran-based carbopeptoids in chloroform and dimethyl sulfoxide were investigated through nine molecular dynamics simulations. Prompted by nuclear magnetic resonance experiments that indicated various stable folds for some but not all of these carbopeptoids, their folding behaviour was investigated as a function of stereochemistry, chain length and solvent. The conformational distributions of these molecules were analysed in terms of occurrence of hydrogen bonds, backbone torsional-angle distributions, conformational clustering and solute configurational entropy. While a cis -linkage across the tetrahydrofuran ring favours right-handed helical structures, a trans -linkage results in a larger conformational variability. Intra-solute hydrogen bonding is reduced with increasing chain length and with increasing solvent polarity. Solute configurational entropies confirm the picture obtained: they are smaller for cis - than for trans -linked peptides, for chloroform than for dimethyl sulfoxide as solvent and for shorter peptide chains. The simulations provide an atomic picture of molecular conformational variability that is consistent with the available experimental data. Copyright © 2004 European Peptide Society and John Wiley & Sons, Ltd. [source] Synthesis of N -alkoxybenzimidoyl azides and their reactions in electrophilic mediaJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 3 2010Debra D. Dolliver Abstract A new general route to N -alkoxybenzimidoyl azides [ArC(N3)=NOR] from a reaction of N -alkoxybenzimidoyl bromide [ArC(Br)=NOR] with sodium azide in DMSO is described. These reactions result in the Z -geometric configuration. These compounds show a moderate degree of thermal stability as assessed by differential scanning calorimetry, and lack reactivity in traditional 1,3-dipolar cycloaddition ,click' reactions. Upon exposure to electrophilic compounds (trifluoroacetic acid or acetyl chloride), these azide compounds can react by two pathways: a Schmidt-type rearrangement to form an N -alkoxyurea or an isomerization,cyclization reaction pathway to form an N -alkoxytetrazole. The route of the reaction has no dependence on solvent polarity and appears to depend upon the electrophile (H+vs. CH3CO+): reaction of the azide with trifluoroacetic acid results predominantly in the urea; reaction with acetyl chloride results solely in the tetrazole. Calculations indicate that the urea product is thermodynamically favored over the tetrazole product. They also indicate that both reaction conditions result in an equilibration between the starting azide and the tetrazole with the tetrazole being the major component in this equilibrium mixture. The fact that the azide also undergoes a Schmidt-type rearrangement to form an N -alkoxyurea when treated with trifluoroacetic acid appears to indicate that the barrier for aromatic ring migration is lower in the protonated azide produced on reaction with trifluoroacetic acid than in the acetylated azide produced on reaction with acetyl chloride. Copyright © 2009 John Wiley & Sons, Ltd. [source] 3H -1,2-Dithiole-3-thione derivatives as novel solvatochromic dyesJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 11 2008Alejandro M. Fracaroli Abstract The UV,Vis spectrum of 5-(1-butylthio)-3H -1,2-dithiole-3-thione (1a) and that of the chromium pentacarbonyl complex of 5-methyl-3H -1,2-dithiole-3-thione (3) present significant changes with the solvent polarity. The two absorption bands shown by the compounds in the region above 300,nm were identified by theoretical calculations. For Compound 1a these are n,,* and ,,* transitions and for Compound 3 the longest wavelength absorption corresponds to a charge transfer band and shows a remarkably negative solvatochromism. Not only has the wavelength of maximum absorption changed with the solvent but also the ratio of the absorbances at the two wavelengths. The effect of solvents was correlated with solvatochromic parameters such as ,* and ,. The spectrum of 5-(1-butylthio)-3H -1,2-dithiole-3-one (2) was also measured in different solvents but in this case the changes observed are less significant than for the other two compounds. The spectra of 1a and 3 were also determined in the presence of anionic (SDS), cationic (CTAB), and neutral surfactants (Brig-35) and it is shown that these compounds can be used as probes for the polarity of the binding sites of organized assemblies. Copyright © 2008 John Wiley & Sons, Ltd. [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] Correlations and predictions of solvent effects on reactivity: some limitations of multi-parameter equations and comparisons with similarity models based on one solvent parameterJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 6 2006T. William Bentley Abstract Three recent publications on multi-parameter correlations of solvent effects on solvolytic reactivity are re-examined, by considering ,similarity' and/or ,analogy'. Systematic errors due to compensation effects and to comparisons between dissimilar processes are found. Models for solvent nucleophilicity involving dissimilar spectroscopic processes (e.g. , or B parameters) give insensitive measures of low nucleophilicity. From qualitative considerations based on structural similarities, it is predicted that the sensitivities to changes to solvent polarity for solvolyses of chloroalkanes should be in the order: 1-adamantyl (3),>,2-methyl-2-adamantyl (1),>,t -butyl (2). The predictions are confirmed quantitatively by simple linear free-energy relationships and similarity models, involving correlations with YCl (based on solvolyses of 1-chloroadamantane) or ET(30) (based on solvatochromism). Multi-parameter correlations, indicating that solvolyses of 1 show a low sensitivity to both solvent polarity and electrophilicity, and also a negative sensitivity to solvent nucleophilicity, are shown to be unreliable. Large errors are also evident in recent KOMPH2 calculations. Conclusions are supported by comparing several multi-parameter treatments of solvolyses of 4-methoxyneophyl tosylate, for which there is a reliable set of kinetic data and a generally accepted mechanism. Copyright © 2006 John Wiley & Sons, Ltd. [source] Fluorescence and photoisomerization studies of p -nitrophenyl-substituted ethenylindolesJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 1 2006Anil K. Singh Abstract The synthesis, electronic absorption, fluorescence (,f, ,ex, ,f, ,f) and photoisomerization (,t,c, photostationary state composition) properties of 3-(4-nitrophenylethenyl- E)-NH-indole (1), 3-(4-nitrophenylethenyl- E)- N -ethylindole (2) and 3-(4-nitrophenyl ethenyl- E)- N -benzenesulfonylindole (3) in organic solvents of varying polarity are reported. The absorption maximum of these compounds undergoes a moderate red shift with increasing solvent polarity. However, the fluorescence maximum becomes highly red shifted with increasing solvent polarity. Whereas 1 and 2 show broad fluorescence bands, 3 exhibits dual fluorescence. Further, 1 and 2 fluoresce much more efficiently than 3. Correlation of the Stokes shift with solvent polarity parameters such as ,f and ET(30) and excited-state dipole moment indicate a highly polar excited state for 1,3. Time-resolved fluorescence studies show that the fluorescence decays are single- and multi-exponential type, depending on the solvent polarity. Further, 1 and 2 do not show photoisomerization on irradiation. However, 3 is photoactive and shows efficient photoisomerization in non-polar heptane. The sensitivity (,) of the photoreaction is determined in various solvent in terms of the Hammett plot, which showed that the excited states involved are electron deficient in nature and consequently stabilized more by an electron sufficient polar solvent and electron donating substituent. These results led us to suggest the existence of three types of excited states, namely the locally excited state, the intramolecular charge-transfer excited state and the conformationally relaxed intramolecular charge-transfer excited state in the photoprocesses of these compounds. Copyright © 2005 John Wiley & Sons, Ltd. [source] Asymmetric anionic polymerization of 7-cyano-7-ethoxycarbonyl-1,4-benzoquinone methideJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 21 2009Noboru Nakagaki An optically active polymer having configurational chirality in the main chain was synthesized from a prochiral monomer, 7-cyano-7-ethoxycarbonyl-1,4-benzoquinone methide (1), by asymmetric anionic polymerization using various chiral anionic initiators. The effects of the chiral ligand and solvent polarity on the specific rotations of the resulting polymers were investigated. The polymerization of 1 using iPrPhOLi/(,)-PhBox complex initiator in a mixture solution of dichloromethane/toluene ratio of 30/70 (in vol %) at ,78 °C afforded an optically active polymer with a large positive specific rotation ([,]435 = +90.4°). [source] Effect of the solvent polarity on the living ligated anionic polymerization of tert -butyl methacrylate and copolymerization with methyl methacrylateJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 10 2001C. Zune Abstract An anionic polymerization of t -butyl methacrylate and a copolymerization with methyl methacrylate were initiated with an organolithium ligated with 10 equiv of LiCl. As a rule, the complexation of the active species by LiCl masked the effect that the polarity of the solvent might have on the molecular structure of the chains. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1774,1785, 2001 [source] Heteroarm Star Polystyrene- block -Poly(4-vinylpyridine): Multiple Morphologies in Dilute SolutionsMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 22 2008Chia-Hung Lin Abstract Synthesis and solution morphologies of four new heteroarm star polystyrene- block -poly(4-vinylpyridine) were studied. As the water content increased, a morphological transformation of heteroarm PS4 -P4VP4 from spheres to cylinders, vesicles, and large compound vesicles was observed. The morphology of PS4 -P4VP4 in the solvent mixture of DMF/water or 1,4-dioxane/water was spherical, but changed to large compound micelles in THF/water. As the P4VP molar ratio decreased, the morphology changed from spherical mixed with cylindrical to vesicles, giant vesicles, and then to LCMs. The present study demonstrated the formation of multiple morphologies through manipulating solvent polarity and block ratio in dilute solution. [source] Luminescent Monomer and Poly(methacrylate) Containing 1,3,4-Oxadiazole and Stilbene Units: Synthesis and Optical PropertiesMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 14 2004John A. Mikroyannidis Abstract Summary: A monomer M as well as a poly(methacrylate) P carrying the same chromophore, that consists of 1,3,4-oxadiazole and stilbene units, were efficiently synthesized. They dissolved in common organic solvents such as THF, chloroform, dichloromethane, 1,1,2,2-tetrachloroethane and chlorobenzene. P showed a Tg value of 145,°C. Both M and P were stable up to approximately 300,°C and afforded anaerobic char yield of about 40% at 800,°C. Their optical properties were comparable. They emitted intense violet-blue light in THF solution with a PL maximum at 413 nm and a PL quantum yield of 0.29 for M and 0.73 for P. Thin films of them displayed optical band gap of 3.03 eV and blue-light emission with a PL maximum around 440 nm. The PL curves of both samples were progressively red-shifted with increasing the solvent polarity. The influence of the annealing on the PL emission spectrum of M and P thin films was investigated. [source] Chlorin,Bacteriochlorin Energy-transfer Dyads as Prototypes for Near-infrared Molecular Imaging Probes: Controlling Charge-transfer and Fluorescence Properties in Polar MediaPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2009Hooi Ling Kee The photophysical properties of two energy-transfer dyads that are potential candidates for near-infrared (NIR) imaging probes are investigated as a function of solvent polarity. The dyads (FbC-FbB and ZnC-FbB) contain either a free base (Fb) or zinc (Zn) chlorin (C) as the energy donor and a free base bacteriochlorin (B) as the energy acceptor. The dyads were studied in toluene, chlorobenzene, 1,2-dichlorobenzene, acetone, acetonitrile and dimethylsulfoxide (DMSO). In both dyads, energy transfer from the chlorin to bacteriochlorin occurs with a rate constant of ,(5,10 ps),1 and a yield of >99% in nonpolar and polar media. In toluene, the fluorescence yields (,f = 0.19) and singlet excited-state lifetimes (,,5.5 ns) are comparable to those of the benchmark bacteriochlorin. The fluorescence yield and excited-state lifetime decrease as the solvent polarity increases, with quenching by intramolecular electron (or hole) transfer being greater for FbC-FbB than for ZnC-FbB in a given solvent. For example, the ,f and , values for FbC-FbB in acetone are 0.055 and 1.5 ns and in DMSO are 0.019 and 0.28 ns, whereas those for ZnC-FbB in acetone are 0.12 and 4.5 ns and in DMSO are 0.072 and 2.4 ns. The difference in fluorescence properties of the two dyads in a given polar solvent is due to the relative energies of the lowest energy charge-transfer states, as assessed by ground-state redox potentials and supported by molecular-orbital energies derived from density functional theory calculations. Controlling the extent of excited-state quenching in polar media will allow the favorable photophysical properties of the chlorin,bacteriochlorin dyads to be exploited in vivo. These properties include very large Stokes shifts (85 nm for FbC-FbB, 110 nm for ZnC-FbB) between the red-region absorption of the chlorin and the NIR fluorescence of the bacteriochlorin (,f = 760 nm), long bacteriochlorin excited-state lifetime (,5.5 ns), and narrow (,20 nm) absorption and fluorescence bands. The latter will facilitate selective excitation/detection and multiprobe applications using both intensity- and lifetime-imaging techniques. [source] A Photodissociation Reaction: Experimental and Computational Study of 2-Hydroxy-2,2-dimethylacetophenone,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2006X. Allonas ABSTRACT The photophysical parameters controlling the cleavage process of 2-hydroxy-2,2-dimethylacetophenone (HDMA) were investigated in detail. Time-resolved picosecond absorption experiments show that the formation of the triplet state occurs within 20 ps after excitation and decays within hundreds of picoseconds depending on the solvent polarity. Molecular modeling reveals that three stable conformations exist in the ground state, the most stable one exhibiting an intramolecular hydrogen bond that modifies the electronic properties of the molecule. This explains quite well the steady-state absorption properties. The conformation of the most stable triplet state is twisted by 180° with respect to the ground state. Computation of the potential energy surface along the molecular coordinate for the dissociation reaction evidences an electronic state crossing yielding a final ,,* state, in perfect agreement with the state correlation diagram. Optimization of the transition state allows the calculation of the activation energy and the use of the transition-state theory leads to an estimate of 100 ps for the cleavage process in the gas phase. Single-point energy calculations using a solvent model predict an increase of the dissociation rate constant with the increase of the solvent polarity, in good agreement with the value deduced from kinetic measurements. [source] The Effect of Molecular Environment on the Photoisomerization of Urocanic Acid,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 2 2004Richard A. Wallis ABSTRACT Urocanic acid, imidazole propenoic acid, is a metabolic product of histidine, which accumulates in skin and is excreted in sweat. It absorbs UV radiation at wavelengths shorter than 340 nm, and its principal photochemical reaction is a trans-cis isomerization about the propenyl double bond. This isomerization to the biologically active cis isomer is implicated in the photo-induced suppression of the immune system of skin. The kinetics of the trans,cis photoisomerization of urocanic acid has been determined in a number of solvents, spanning a range of polarities. The initial rates of isomerization and the photostationary trans-cis compositions, in all solvents except water, correlate linearly with solvent polarity. This indicates that the isomerization proceeds through a polar intermediate that is stabilized by coulombic interactions with the molecular environment. [source] Organometallic dyes: Part 1.APPLIED ORGANOMETALLIC CHEMISTRY, Issue 11 2001Synthesis of orange to cyan dyes based on donor, acceptor chromogenes using ferrocene as the donor group, conjugated Abstract A novel series of organometallic donor,conjugated,acceptor dyes derived from ferrocene as the donor group have been synthesized via the Knoevenagel reaction of ferrocene carboxaldehyde and various active methylene compounds to give a range of dyes ranging from orange to blue,green in color. The most bathochromic dye is that derived from dialkyl thiobarbituric acid and the least is that derived from the tetralone. The dyes showed an unusual negative solvatochromism as the solvent polarity increased. All dyes synthesized are expected to have some non-linear optical properties, as evidenced from the pronounced solvatochromism. Copyright ©,2001 John Wiley & Sons, Ltd. [source] Study on polymerization of the pharmaceutical substances isohexenylnaphthazarinsBIOMEDICAL CHROMATOGRAPHY, Issue 8 2004A. N. Assimopoulou Abstract Polymerization of naturally occurring isohexenylnaphthazarins (IHN), such as alkannin, shikonin (A/S) and their derivatives, which are potent pharmaceutical substances, signi,cantly affects their use in pharmaceuticals, cosmetics and as food colorants, because it leads to reduction of the lustre of their red coloration, a decrease in their solubility and reduces the active monomeric IHN derivatives. In the present study, the in,uence of several crucial variables (processing and storage) was experimentally investigated on IHN polymerization by size exclusion chromatography (SEC). Temperature and solvent polarity increased signi,cantly the concentration of hydroxynaphthoquinone (HNQ) polymers, while air and light exposure conditions did not signi,cantly affect IHN polymerization. Low temperatures are proposed for all processes of industrial production of pharmaceutical preparations containing IHN and HNQ. An optimization of the industrial conditions used for the preparation of pharmaceutical and cosmetic preparations containing IHN, maximizing the active monomeric IHN fraction, was performed. Copyright © 2003 John Wiley & Sons, Ltd. [source] Fluorescence enhancement of warfarin induced by interaction with ,-cyclodextrinBIOTECHNOLOGY PROGRESS, Issue 4 2009Jacob M. Vasquez Abstract Warfarin is the most common agent used for control and prevention of venous as well as arterial thromboembolism (blood clots). In aqueous media, warfarin forms inclusion complexes with a family of cyclic oligosaccharides, ,, ,, ,-cyclodextrins (CD). The formation of these complexes results in enhancement of the fluorescence of warfarin. Such spectroscopic changes offer a venue for the development of bioanalytical methodologies for warfarin quantification in biological liquids. We characterized the photophysical properties of warfarin in solvents with varying polarity and viscosity. The fluorescence quantum yield of warfarin correlated: (1) strongly with the solvent viscosity (R = 0.979) and (2) weakly with the solvent polarity (R = 0.118). These findings indicate that it is the change of the viscosity, rather than polarity, of the microenvironment that causes the fluorescence enhancement of warfarin upon binding to ,-CD. Utilizing the observed fluorescence enhancement in fluorescence titration measurements, the binding constants of warfarin to ,-CD were obtained (2.6 × 102 M,1,3.7 × 102 M,1). Using multivariable linear analysis, we extracted the stoichiometry of warfarin-,-CD interaction (1:1). © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009 [source] Light-Driven Charge Separation in Isoxazolidine,Perylene Bisimide DyadsCHEMISTRY - A EUROPEAN JOURNAL, Issue 46 2009Heinz Langhals Prof. Abstract A series of arrays for light-driven charge separation is presented, in which perylene tetracarboxylic bisimide is the light-absorbing chromophore and electron acceptor, whereas isoxazolidines are colourless electron donors, the electron-releasing properties of which are increased with respect to the amino group by means of the ,-effect. Charge separation (CS) in toluene over a distance ranging from ,10 to ,16,Å, with efficiencies of ,95 to ,50,% and CS lifetimes from 300,ps to 15,ns, are demonstrated. In dichloromethane the charge recombination reaction is faster than charge separation, preventing accumulation of the CS state. The effects of solvent polarity and molecular structure are discussed in the frame of current theories. [source] Synthesis and Photoinduced Electron-Transfer Properties of Phthalocyanine,[60]Fullerene ConjugatesCHEMISTRY - A EUROPEAN JOURNAL, Issue 12 2008Maurizio Quintiliani Dr. Abstract A series of three novel ZnPc,C60 conjugates (Pc=phthalocyanine) 1,a,c bearing different spacers (single, double, and triple bond) between the two electroactive moieties was synthesized and compared to that of ZnPc,C60 conjugate 2, in which the two electroactive moieties are linked directly. The synthetic strategy, towards the preparation of 1,a,c, involved palladium-catalyzed cross-coupling reactions over a monoiodophthalocyanine precursor 4 to introduce the corresponding spacer, and subsequent dipolar cycloaddition reaction to C60. Detailed photophysical investigations of 1,a,c and 2 prompted an intramolecular electron transfer that evolves from the photoexcited ZnPc to the electron-accepting C60. In particular, with the help of femtosecond laser photolysis charge separation was indeed confirmed as the major deactivation channel. Complementary time-dependent density functional calculations supported the spectral assignment, namely, the spectral identity of the ZnPc.+ radical cation and the C60., radical anion as seen in the differential absorption spectra. The lifetimes of the correspondingly formed radical ion-pair states depend markedly on the solvent polarity: they increase as polarity decreases. Similarly, although to a lesser extent, the nature of the linker impacts the lifetime of the radical ion-pair states. In general, the lifetimes of these states tend to be shortest in the system that lacks any spacer at all (2), whereas the longest lifetimes were found in the system that carries the triple-bond spacer (1,a). [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] | |||||||||||||||||||||||||||||||