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951.
Visible‐Light‐Driven Hydrogen Evolution Using Planarized Conjugated Polymer Photocatalysts 下载免费PDF全文
Dr. Reiner Sebastian Sprick Dr. Baltasar Bonillo Rob Clowes Pierre Guiglion Nick J. Brownbill Dr. Benjamin J. Slater Dr. Frédéric Blanc Dr. Martijn A. Zwijnenburg Prof. Dave J. Adams Prof. Andrew I. Cooper 《Angewandte Chemie (International ed. in English)》2016,55(5):1792-1796
Linear poly(p‐phenylene)s are modestly active UV photocatalysts for hydrogen production in the presence of a sacrificial electron donor. Introduction of planarized fluorene, carbazole, dibenzo[b,d]thiophene or dibenzo[b,d]thiophene sulfone units greatly enhances the H2 evolution rate. The most active dibenzo[b,d]thiophene sulfone co‐polymer has a UV photocatalytic activity that rivals TiO2, but is much more active under visible light. The dibenzo[b,d]thiophene sulfone co‐polymer has an apparent quantum yield of 2.3 % at 420 nm, as compared to 0.1 % for platinized commercial pristine carbon nitride. 相似文献
952.
Cholesterol 5alpha-hydroperoxide, the major product of 1O2-oxidation of cholesterol, readily undergoes acid-catalyzed (Hock) cleavage of the C5-C6 bond to yield the 5,6-secosterol ketoaldehyde and the product of its intramolecular aldolization. These cholesterol oxidation products have long been thought to arise solely from ozonolysis of cholesterol, prompting the recent suggestion that ozone is produced in humans following their identification in arterial and brain tissue extracts. 相似文献
953.
954.
On the basis of a Gaussian quasichemical model of hydration, a model of non-van der Waals character, we explore the role of attractive methane-water interactions in the hydration of methane and in the potential of mean force between two methane molecules in water. We find that the hydration of methane is dominated by packing and a mean-field energetic contribution. Contributions beyond the mean-field term are unimportant in the hydration phenomena for a hydrophobic solute such as methane. Attractive solute-water interactions make a net repulsive contribution to these pair potentials of mean force. With no conditioning, the observed distributions of binding energies are super-Gaussian and can be effectively modeled by a Gumbel (extreme value) distribution. This further supports the view that the characteristic form of the unconditioned distribution in the high-epsilon tail is due to energetic interactions with a small number of molecules. Generalized extreme value distributions also effectively model the results with minimal conditioning, but in those cases the distributions are sufficiently narrow that the details of their shape are not significant. 相似文献
955.
On the dynamics of fragment isomerization in collision-induced dissociation of peptides 总被引:4,自引:0,他引:4
Polfer NC Bohrer BC Plasencia MD Paizs B Clemmer DE 《The journal of physical chemistry. A》2008,112(6):1286-1293
The structures of peptide collision-induced dissociation (CID) product ions are investigated using ion mobility/mass spectrometry techniques combined with theoretical methods. The cross-section results are consistent with a mixture of linear and cyclic structures for both b4 and a4 fragment ions. Direct evidence for cyclic structures is essential in rationalizing the appearance of fragments with scrambled (i.e., permutated) primary structures, as the cycle may not open up where it was initially formed. It is demonstrated here that cyclic and linear a4 structures can interconvert freely as a result of collisional activation, implying that isomerization takes place prior to dissociation. 相似文献
956.
Taatjes CA Osborn DL Selby TM Meloni G Fan H Pratt ST 《The journal of physical chemistry. A》2008,112(39):9336-9343
The absolute photoionization cross-section of the methyl radical has been measured using two completely independent methods. The CH3 photoionization cross-section was determined relative to that of acetone and methyl vinyl ketone at photon energies of 10.2 and 11.0 eV by using a pulsed laser-photolysis/time-resolved synchrotron photoionization mass spectrometry method. The time-resolved depletion of the acetone or methyl vinyl ketone precursor and the production of methyl radicals following 193 nm photolysis are monitored simultaneously by using time-resolved synchrotron photoionization mass spectrometry. Comparison of the initial methyl signal with the decrease in precursor signal, in combination with previously measured absolute photoionization cross-sections of the precursors, yields the absolute photoionization cross-section of the methyl radical; sigma(CH3)(10.2 eV) = (5.7 +/- 0.9) x 10(-18) cm(2) and sigma(CH3)(11.0 eV) = (6.0 +/- 2.0) x 10(-18) cm(2). The photoionization cross-section for vinyl radical determined by photolysis of methyl vinyl ketone is in good agreement with previous measurements. The methyl radical photoionization cross-section was also independently measured relative to that of the iodine atom by comparison of ionization signals from CH3 and I fragments following 266 nm photolysis of methyl iodide in a molecular-beam ion-imaging apparatus. These measurements gave a cross-section of (5.4 +/- 2.0) x 10(-18) cm(2) at 10.460 eV, (5.5 +/- 2.0) x 10(-18) cm(2) at 10.466 eV, and (4.9 +/- 2.0) x 10(-18) cm(2) at 10.471 eV. The measurements allow relative photoionization efficiency spectra of methyl radical to be placed on an absolute scale and will facilitate quantitative measurements of methyl concentrations by photoionization mass spectrometry. 相似文献
957.
Gary S. Groenewold Dr. Michael J. Van Stipdonk Prof. Wibe A. de Jong Dr. Jos Oomens Dr. Garold L. Gresham Dr. Michael E. McIlwain Dr. Da Gao Dr. Bertrand Siboulet Dr. Lucas Visscher Prof. Michael Kullman Nick Polfer Prof. 《Chemphyschem》2008,9(9):1278-1285
UO2+–solvent complexes having the general formula [UO2(ROH)]+ (R=H, CH3, C2H5, and n‐C3H7) are formed using electrospray ionization and stored in a Fourier transform ion cyclotron resonance mass spectrometer, where they are isolated by mass‐to‐charge ratio, and then photofragmented using a free‐electron laser scanning through the 10 μm region of the infrared spectrum. Asymmetric O=U=O stretching frequencies (ν3) are measured over a very small range [from ~953 cm?1 for H2O to ~944 cm?1 for n‐propanol (n‐PrOH)] for all four complexes, indicating that the nature of the alkyl group does not greatly affect the metal centre. The ν3 values generally decrease with increasing nucleophilicity of the solvent, except for the methanol (MeOH)‐containing complex, which has a measured ν3 value equal to that of the n‐PrOH‐containing complex. The ν3 frequency values for these U(V) complexes are about 20 cm?1 lower than those measured for isoelectronic U(VI) ion‐pair species containing analogous alkoxides. ν3 values for the U(V) complexes are comparable to those for the anionic [UO2(NO3)3]? complex, and 40–70 cm?1 lower than previously reported values for ligated uranyl(VI) dication complexes. The lower frequency is attributed to weakening of the O?U?O bonds by repulsion related to reduction of the U metal centre, which increases electron density in the antibonding π* orbitals of the uranyl moiety. Computational modelling of the ν3 frequencies using the B3LYP and PBE functionals is in good agreement with the IRMPD measurements, in that the calculated values fall in a very small range and are within a few cm?1 of measurements. The values generated using the LDA functional are slightly higher and substantially overestimate the trends. Subtleties in the trend in ν3 frequencies for the H2O–MeOH–EtOH–n‐PrOH series are not reproduced by the calculations, specifically for the MeOH complex, which has a lower than expected value. 相似文献
958.
Mullen KM Johnstone KD Webb M Bampos N Sanders JK Gunter MJ 《Organic & biomolecular chemistry》2008,6(2):278-286
The thermodynamically controlled self-assembly of rotaxane and pseudorotaxane systems consisting of (i) a naphthodiimide thread unit terminated at one end with a pyridine ligand, and covalently linked at the other to a gel-phase polystyrene resin support, (ii) a dinaphtho-crown ether shuttle unit, and (iii) a ruthenium carbonyl metalloporphyrin stopper unit, is investigated by high resolution magic angle spinning proton (HR MAS 1H) NMR spectroscopy. The effects of variable concentration of the solution-phase components, the temperature, and added Li+ and Na+ ions are described, and the limitations of the technique are addressed. The dynamic behaviour is compared directly to the solution-phase analogues, where a bulky stopper group is substituted for the polystyrene resin bead. 相似文献
959.
Parigoridi IE Corban GJ Hadjikakou SK Hadjiliadis N Kourkoumelis N Kostakis G Psycharis V Raptopoulou CP Kubicki M 《Dalton transactions (Cambridge, England : 2003)》2008,(38):5159-5165
The reaction of 2-pyrimidone hydrochloride ([C(4)H(5)N(2)O](+)[Cl](-) or [PMOH(2)](+)[Cl](-)) with diiodine in a dichloromethane-methanol solution resulted in the formation of ([C(4)H(5)N(2)O](+))(2)[I(2)Cl(2)](2-) (1) complex. The compound was characterized by elemental analysis, FT-IR, DTA-TG and conductivity titrations. The crystal structure of 1 was also determined by X-ray diffraction at 294(1) K. Compound 1 is monoclinic, space group P2(1)/n, consisting of two cationic [PMOH(2)](+) species and a [I(2)Cl(2)](2-) counter dianion. The cation is in its keto form. Direct reaction of thiazolidine-2-thione (tzdtH), with diiodine in dichloromethane solution, on the other hand, led to the formation of a crystalline solid which contained two complexes of formulae [(tzdtH)(2)I](+)[I(3)](-).2I(2) (2) and [(tzdtH)I(2)](2).I(2) (2a) in a ratio of 90 to 10%. Complex 2a was characterized by X-ray analysis at 180(2) K. Compound is monoclinic, space group C2/c and contains two units of [(tzdtH)I(2)] "spoke" structures. Compound 1, as well as the known species iodonium salt [(tzdtH)(2)I](+)[I(3)](-).2I(2) (2) and the charge transfer (CT) iodine complexes of formulae [(bztzdtH)I(2)] (3) and [(bztzdtH)I(2)].I(2) (4) (bztzdtH = 2-mercaptobenzothiazole) with "spoke" and extended "spoke" structures respectively, were tested for their oxidizing activity towards 3,5-di-tert-butylcatechol to 3,5-di-tert-butyl-o-benzoquinone. 相似文献
960.
Blom MN Compagnon I Polfer NC Helden Gv Meijer G Suhai S Paizs B Oomens J 《The journal of physical chemistry. A》2007,111(31):7309-7316
How many solvent molecules are required to solvate an amino acid? This apparently simple question, which relates to the number of solvent molecules necessary to change the amino acid from its gas-phase neutral structure to the zwitterionic solvated structure, remains unanswered to date. Here we present experimental and theoretical (density functional theory: B3LYP/6-31+G**) infrared spectra for tryptophan-watern complexes where n = 1-6, which suggest that the zwitterionic structure becomes competitive in energy at the high end of the series. Compelling evidence for a gradual transition to zwitterionic structures comes from tryptophan-methanol complexes up to n = 9. Starting from n = 5, the infrared spectra show increasing intensity in the diagnostic asymmetric COO- stretch and in the weaker NH3+ bending modes as the cluster size increases. Moreover, convergence toward the Fourier transform infrared spectrum of a solution of tryptophan in methanol is clearly observed. For small solvent complexes (n = 1-4), the microsolvation by methanol and water is shown to behave very similarly. A detailed comparison of the experimental and the theoretical spectra allows us to determine both the preferred solvent binding sites on the amino acid and the evolution of conformational structures of tryptophan as the number of attached solvent molecules increases. 相似文献