Vacuum-UV-photolysis of aqueous solutions of citric and gallic acids

The vacuum-UV- (VUV-) photolysis of water is one of the advanced oxidation processes (AOP) based on the production of hydroxyl radicals (HO) that can be applied to the degradation of organic pollutants in aqueous systems. The kinetics of the VUV-photolyses of aqueous solutions of citric acid (1) or gallic acid (2) were investigated in the presence or absence of dissolved molecular oxygen (O₂) and under different pH conditions. In the case of 1, the rate of consumption of the substrate was faster at pH 3.4 than in alkaline solution (pH 11), whereas, in the case of 2, the variation of pH (2.5–7.5) did not affect the course of the reaction. Unexpectedly, the rates of depletion of both 1 and 2 decreased in the absence of O₂, this effect being much more pronounced in the case of 2. In order to explain these results, possible reaction pathways for the degradation of 1 and 2 are proposed, and the roles of the oxidizing (HO) and reducing (H and e_aq⁻) species produced by the VUV-photolysis of water are discussed.     

Iridium derivatives of fluorinated aromatics by C-H activation: isolation of classical and non-classical hydrides

A reaction of trans-[Ir(H)(5)(PiPr(3))(2)] (1) with 2,3,5,6-tetrafluoropyridine, pentafluorobenzene or 1,3-difluorobenzene in the presence of neohexene affords the square-pyramidal C-H activation products cis-trans-[Ir(4-C(5)NF(4))(H)(2)(PiPr(3))(2)] (2), cis-trans-[Ir(C(6)F(5))(H)(2)(PiPr(3))(2)] (4) and cis-trans-[Ir(2-C(6)H(3)F(2))(H)(2)(PiPr(3))(2)] (6). Irradiation of complex 1 with 2,3,5,6-tetrafluoropyridine or pentafluorobenzene gave the hydrides cis-trans-[Ir(4-C(5)NF(4))(H)(2)(H(2))(PiPr(3))(2)] (3) or cis-trans-[Ir(C(6)F(5))(H)(2)(H(2))(PiPr(3))(2)] (5). The presence of non-classical bound H(2) moieties has been demonstrated by the measurement of T(1) times at different temperatures. For 3 the H-H distance in the H(2) ligand can be estimated to be 0.82 A. The dihydride compounds 2, 4 and 6 react with CO to yield the complexes cis-trans-[Ir(Ar)(H)(2)(CO)(PiPr(3))(2)] (7: Ar = 4-C(5)NF(4), 8: Ar = C(6)F(5), 9: Ar = 2-C(6)H(3)F(2)). A reaction of 2 or 3 with an excess of ethylene leads to the formation of ethane and the Ir(i) ethylene complex trans-[Ir(4-C(5)NF(4))(eta(2)-C(2)H(4))(PiPr(3))(2)] (10). Treatment of 10 with CO furnishes the Ir(i) complex trans-[Ir(4-C(5)NF(4))(CO)(PiPr(3))(2)] (11).     

Ultrafast ring-closure reaction of photochromic indolylfulgimides studied with UV-pump-IR-probe spectroscopy

The ring-opening and ring-closure reactions of a photochromic indolylfulgimide are investigated with femtosecond vibrational spectroscopy. Spectral signatures due to excited-state decay and vibrational cooling are seen in the mid-IR region. For the ring-opening reaction triggered with visible pulses, a lifetime of the excited electronic state of 4 ps was obtained in polar solution. In a nonpolar solvent, this time constant is reduced to 2 ps. The ring-closure reaction induced with UV pulses displays an excited-state lifetime and thus a building of the photoproduct of roughly 0.5 ps. For all processes, the subsequent cooling occurs on a 15-ps time scale lasting up to approximately 50 ps. The time-resolved IR measurements do not support the existence of any long-living intermediate states.     

Routes to unique palladium A-frame complexes with a bridging fluoro-ligand

Treatment of a toluene solution of [PdMe(2)(Cy(2)PCH(2)PCy(2))](1) with pentafluoropyridine in the presence of traces of water affords the generation of the A-frame complexes [(PdMe)(2){mu-kappa(2)(P,P)Cy(2)PCH(2)PCy(2)}(2)(mu-F)][SiMeF(4)]() and [(PdMe)(2){mu-kappa(2)(P,P)Cy(2)PCH(2)PCy(2)}(2)(mu-F)][OC(5)NF(4)](2b). If the reaction is performed in an NMR tube equipped with a PFA inliner, complex 2b is produced, only. Treatment of 1 with pentafluoropyridine in the presence of an excess water yields the pyridyloxy complex [PdMe(OC(5)NF(4))(Cy(2)PCH(2)PCy(2))](3). Compound [(PdMe)(2){mu-kappa(2)(P,P)Cy(2)PCH(2)PCy(2)}(2)(mu-F)][FHF](2c) bearing a bifluoride anion instead of SiMeF(4)(-) or OC(5)NF(4)(-) can be generated by reaction of 1 with substoichiometric amounts of Et(3)N.3HF. The analogous complex [(PdMe)(2){mu-kappa(2)(P,P)Ph(2)PCH(2)PPh(2)}(2)(mu-F)][FHF] (5c) has been synthesized by addition of Ph(2)PCH(2)PPh(2) to a solution of [PdMe(2)(Me(2)NCH(2)CH(2)NMe(2))](4) in THF and subsequent treatment of the reaction mixture with Et(3)N.3HF. The structure of the A-frame complex 5c has been determined by X-ray crystallography.     

Substituent effects on the photophysical properties of pterin derivatives in acidic and alkaline aqueous solutions

Pterins are heterocyclic compounds with important biological functions, and most of them may exist in two acid-base forms in the pH range between 3 and 13 in aqueous solution. In this work, the photophysical properties of acid and basic forms of six compounds of the pterin family (6-hydroxymethylpterin [HPT], 6-methylpterin [MPT], 6,7-dimethylpterin [DPT], rhamnopterin [RPT], N-methylfolic acid [MFA], and pteroic acid [PA]) have been studied. The effects of the chemical nature of the substituents at position 6 of the pterin moiety and the effects of the pH on the absorption and emission properties are analyzed. The fluorescence characteristics (spectra, quantum yields, lifetimes) of these compounds have been investigated using the single-photon-counting technique. Results obtained for pterin derivatives containing small substituents with 1 carbon atom (HPT, MPT, DPT) and short hydrocarbon chain (4 carbon atoms) (RPT) are different from those found for pterin derivatives containing a p-aminobenzoic acid (PABA) moiety in the substituent (MFA and PA). Fluorescence quantum yields (Phi(F)) of the first group of compounds are relatively high (>/=0.4), whereas MFA and PA exhibit very small Phi(F) values (相似文献   

Nanoporous Materials Can Tune the Critical Point of a Pure Substance

Molecular simulations and NMR relaxometry experiments demonstrate that pure benzene or xylene confined in isoreticular metal–organic frameworks (IRMOFs) exhibit true vapor–liquid phase equilibria where the effective critical point may be reduced by tuning the structure of the MOF. Our results are consistent with vapor and liquid phases extending over many MOF unit cells. These results are counterintuitive since the MOF pore diameters are approximately the same length scale as the adsorbate molecules. As applications of these materials in catalysis, separations, and gas storage rely on the ability to tune the properties of adsorbed molecules, we anticipate that the ability to systematically control the critical point, thereby preparing spatially inhomogeneous local adsorbate densities, could add a new design tool for MOF applications.     

Two-dimensional electrophoresis of membrane proteins

One third of all genes of various organisms encode membrane proteins, emphasizing their crucial cellular role. However, due to their high hydrophobicity, membrane proteins demonstrate low solubility and a high tendency for aggregation. Indeed, conventional two-dimensional gel electrophoresis (2-DE), a powerful electrophoretic method for the separation of complex protein samples that applies isoelectric focusing (IEF) in the first dimension and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) in the second dimension, has a strong bias against membrane proteins. This review describes two-dimensional electrophoretic techniques that can be used to separate membrane proteins. Alternative methods for performing conventional 2-DE are highlighted; these involve replacing the IEF with electrophoresis using cationic detergents, namely 16-benzyldimethyl-n-hexadecylammonium chloride (16-BAC) and cetyl trimethyl ammonium bromide (CTAB), or the anionic detergent SDS. Finally, the separation of native membrane protein complexes through the application of blue and clear native gel electrophoresis (BN/CN-PAGE) is reviewed, as well as the free-flow electrophoresis (FFE) of membranes.     

Unusual heme-histidine bond in the active site of a chaperone

The heme chaperone CcmE is essential for the delivery of heme to c-type cytochromes. It forms an unusual transient, yet covalent, bond between an essential histidine, H130, and heme. We report on the discovery of the chemical structure of this bond solved by NMR, where the heme vinyl is cross-linked at the beta carbon to the Ndelta1 of H130. As this type of heme linkage has not been described previously in any cytochrome or hemoprotein, it represents a novel type of heme-histidine complex.     

HPLC-MS-MS法测定水体中残留的氨基甲酸酯类农药

应用高效液相色谱-串联质谱(HPLC-MS-MS)联用技术,建立了检测水体中氨基甲酸酯类农药残留的方法。水样经氨基柱固相萃取,二氯甲烷洗脱,梯度流动相洗脱,电喷雾正离子(ESI+)模式采集、选择反应性监测模式(SRM)对定性、定量离子进行MS/MS测定。5种氨基甲酸酯类农药在5～200ng/L范围内线性关系良好,回收率为80%～92%,相对标准偏差均小于10%,方法检出限分别为:异丙威和仲丁威为1.4ng/L,克百威和甲萘威为1.5ng/L,恶虫威为1.6ng/L。该方法适用于水体中氨基甲酸酯类农药残留的检测。     

Observation of Photoelectron Circular Dichroism Using a Nanosecond Laser

Photoelectron circular dichroism (PECD) is a fascinating phenomenon both from a fundamental science aspect but also due to its emerging role as a highly sensitive analytic tool for chiral recognition in the gas phase. PECD has been studied with single-photon as well as multi-photon ionization. The latter has been investigated in the short pulse limit with femtosecond laser pulses, where ionization can be thought of as an instantaneous process. In this contribution, we demonstrate that multi-photon PECD still can be observed when using an ultra-violet nanosecond pulse to ionize chiral showcase fenchone molecules. Compared to femtosecond ionization, the magnitude of PECD is similar, but the lifetime of intermediate molecular states imprints itself in the photoelectron spectra. Being able to use an industrial nanosecond laser to investigate PECD furthermore reduces the technical requirements to apply PECD in analytical chemistry.