离子液体[bmim][BF4]对联苯甲酰光化学反应影响的瞬态吸收光谱

利用纳秒级激光光解瞬态吸收光谱研究了联苯甲酰(BZ)在离子液体1-丁基-3-甲基咪唑四氟硼酸盐([bmim][BF₄])与乙腈(MeCN)混合体系中的光化学反应行为. 考察了探针分子BZ存在下[bmim][BF₄]/MeCN比例对体系中化学反应动力学的影响. 实验发现: 在N₂饱和条件下, BZ溶液经激光辐照后产生的激发三线态³BZ^*遵循一级反应动力学规律衰减. 离子液体(IL)相对比例增加对³BZ^*瞬态吸收峰的位置和强度没有产生明显影响. 但离子液体体积分数V_IL的变化对[bmim][BF₄]/MeCN混合溶剂中光诱导电子转移的影响却非常显著, 总体上电子转移产生的自由基的表观生成速率常数k_gr随[bmim][BF₄]的V_IL增大而减小. 在[bmim]BF₄]比例足够大的情况下, ³BZ^*与三乙胺或四甲基对苯二胺之间的电子转移被抑制.     

Assessment ofBeauveria bassiana Nov. EO-1 strain,which produces a red pigment for microbial control

A new strain of the fungusBeauveria bassiana Nov. EO-1 (ATCC 74037), which produces a red pigment in solid and liquid culture, has been isolated from an infected whitefly. The red pigment was extracted and has been identified by mass spectrometry as oosporein, a potent dibenzoquinone mycotoxin. In order to assess the potential of this entomogenous fungi for microbial control purposes, a mycelium bead formulation was developed as a source for pathogenic conidial spores and oosporein production. The mycelium bead preparation was found to be a stable fungal carrier. Conidiation and germination studies have revealed the mycelium bead viability is 100% over a 1-yr period when stored at 4°C. Conidial spore production from the mycelium beads has been falling substantially per time from an initial value of 1.5 × 10⁸ spores per bead to 3 × 10⁵ spores per bead after a year storage at 4°C. However, the mycelium bead formulation continues to produce oosporein on agar media, at the same intensity throughout the 1 yr period. In in vitro and in vivo small scale greenhouse experimentsBeauveria bassiana Nov. EO-1 were compared with known entomogenous fungi,Beauveria sp. andPaceilomyces sp. Beauveria bassiana Nov. EO-1 was found to have a high pathogenicity against foliage insect pests (e.g., whiteflies and mealy bugs), and against soil insects (e.g., citrus root weevils). The utilization of a mycelium bead based on this strain,Beauveria bassiana Nov. EO-1, as a source of conidial spores and oosporein may have broad applications for the control of various insect pests.     

Oligoether derivatives of 1-phenoxyanthraquinone: Synthesis,photochromism, and complex formation with metal cations

1-Phenoxyanthraquinone isomeric conjugates with tetraethylene glycol were prepared. Their photochromic properties and complex formation in solutions were quantitatively studied by spectrophotometry, quantum yields of the arylotropic photoisomerism and stability constants of complexes between para–ana-quinoid isomers and metal cations. The photochemical migration of a phenyl group considerably affects the complex stability thus providing the possibility to regard the synthesized compounds as photocontrolled ionophores. The structure of some complexes was investigated by X-ray diffraction (XRD) analysis and quantum-chemical simulation.     

Synthesis,photophysical properties,and photochemical activity of the water-soluble dyad based on fullerene С<Subscript>60</Subscript> and chlorin <Emphasis Type="Italic">e</Emphasis><Subscript>6</Subscript> derivatives

Chlorin e₆ derivative and water-soluble dyad resulting from covalent bonding of polyanionic fullerene С₆₀ derivative to chlorin e₆ derivative were synthesized and studied for spectral properties and photochemical activity. A considerable change in the absorption spectra and pronounced fluorescence quenching for the chlorin moiety included in the dyad were identified. The singlet excited state of chlorin is quenched via electron transfer from the excited chlorin to the fullerene core. A comparison of the photochemical activities of the test compounds in aqueous solutions showed a tenfold increase in the photochemical activity of the chlorin–fullerene dyad compared with free chlorin per absorbed light quantum.     

ZUM PROBLEM DER PHOTODEHYDRIERUNG MIT CHINONEN. PHOTOCHEMISCHE UND BLITZSPEKTORSKOPISCHE UNTERSUCHUNGEN AN LÖSUNGEN VON DUROCHINON, DUROHYDROCHINON UND DIDUROCHINON

Abstract— Duroquinone shows no or only very slight dehydrogenation of solvents on flashing or irradiating (Λ > 330 nm) solutions in ethanol, isopropanol, tert .-butanol, cyclohexane or paraffin. Reversible reactions of excited duroquinone occur with its photochemical reaction products durohydroquinone and duroquinone dimer in preirradiated solutions. The results show the photochemical behaviour of duroquinone to be quite different from that of other quinones.     

Solvent-controlled E/Z isomerization vs. [2 + 2] photocycloaddition mediated by supramolecular polymerization

Control over the photochemical outcome of photochromic molecules in solution represents a major challenge, as photoexcitation often leads to multiple competing photochemical and/or supramolecular pathways resulting in complex product mixtures. Herein, we demonstrate precise and efficient control over the photochemical behaviour of cyanostilbenes in solution using a straightforward solvent-controlled approach based on supramolecular polymerization. To this end, we designed a π-extended cyanostilbene bolaamphiphile that exhibits tuneable solvent-dependent photochemical behaviour. Photoirradiation of the system in a monomeric state (in organic solvents) exclusively leads to a highly reversible and efficient E/Z photoisomerization, whereas a nearly quantitative [2 + 2] photocycloaddition into a single cyclobutane (anti head-to-tail) occurs in aqueous solutions. These results can be rationalized by a highly regular and preorganized antiparallel J-type arrangement of the cyanostilbene units that is driven by aqueous supramolecular polymerization. The presented concept demonstrates a novel approach towards solvent-selective and environmentally friendly photochemical transformations, which is expected to broaden the scope of supramolecular polymerization.

Controlled supramolecular polymerization is used to switch the photoresponsive behaviour of cyanostilbenes from a reversible E/Z photoisomerization in organic solvents to a highly efficient and selective [2 + 2] photocycloaddition in aqueous media.     

Studies on some enzymes of alginic acid biosynthesis in mucoid and nonmucoidAzotobacter chroococcum strains

Measurements of enzymes involved in alginate biosynthesis were straightforward in mucoid (alginate-positive)Azotobacter chroococcum ATCC 4412 crude extracts. At the stationary growth phase, where the production of the exopolysaccharide was greatest, the enzymes phosphomannose isomerase and GDP-mannose pyrophosphorylase increased markedly, whereas phosphomannomutase and GDP-mannose dehydrogenase kept the high activity levels measured in the acceleration growth phase. In nonmucoid (alginatenegative)A. chroococcum andA. vinelandii strains, the activities of phosphomannose isomerase and GDP-mannose pyrophosphorylase were rather low or, in some cases, undetectables. Except inA. chroococcum MCD1, which exhibited a low activity, phosphomanomutase was high in the nonmucoidAzotobacter strains, and GDP-mannose dehydrogenase reached a significant activity level in two out of four nonmucoid strains tested. The results suggest that derepression of phophomannose isomerase and GDP-mannose pyrophosphorylase is asine qua non condition for alginate formation byA. chroococcum.     

Synthesis of hollow bimetal particles based on silver and gold

A pioneering procedure is presented for the photochemical synthesis of aqueous solutions of hollow bimetal silver-gold nanoparticles in the presence of poly-N-vinylpyrrolidone. The structure and properties of synthesized nanocages were studied by the methods of high-resolution transmission electron microscopy, UV visible spectroscopy, and energy-dispersive X-ray structural analysis. The mechanism of the formation of AgAu nanocages was suggested on the basis of the experimental data.     

Photoreactivite de systemes hexatrieniques heterocycliques. Aryl-2 et 3 benzo[b]thiophene

The photochemical behavior of several benzo[b]thiophenes 1–4 in neutral solutions or in the presence of primary and tertiary amines has been examined. In most cases, the photoformation of adducts or dimers, rather than cyclisation, has been observed. An unusual photocyclisation of a saturated compound 12 obtained by photolysis of 3 in a primary amine was observed     

Molecular rydberg transitions in carbon monoxide: term value/ionization energy correlation of BF,CO and N2

The linear correlation between the term value and ionization energy for molecular Rydberg transitions is tested for the sequence of isoelectronic molecules BF, CO and N₂ based on a new measurement of the absorption spectrum of CO and data for BF and N₂. For the npσ series and npπ series converging on the first ionization potential, we find an excellent linear behavior (within 10 meV) corroborating (i) the correlation and (ii) the individual assignments. For Rydberg series leading to the A ²Π and B ²Σ⁺ states, where no data for BF are available, a comparison of term values for CO and N₂ is presented.     

Fluorimetric determination of amino acids and photochemical stability of their reaction products with ortho-phthalic aldehyde under irradiation by high-power pulsed laser

The opportunity of the highly sensitive determination of amino acids using the fluorescence of their derivatives that form in the reaction with aqueous solutions of ortho-phthalic aldehyde and nucleophilic agents, potassium cyanide, sodium sulfite, and N-acetyl-L-cysteine was studied as an example. The chemical stability of forming fluorescent compounds (substituted isoindoles) and their photochemical stability under the action of power pulsed laser radiation is higher, and the analytic characteristics of reagents are highly competive with a standard applied reagent for determining amino acids and a mixture ortho-phthalic aldehyde with 2-mercaptoethanol.     

UV-Vis, NMR, and time-resolved spectroscopy analysis of photoisomerization behavior of three- and six-azobenzene-bound tris(bipyridine)cobalt complexes

The photoisomerization properties of tris(bipyridine)cobalt complexes containing six or three azobenzene moieties, namely, [Co(II)(dmAB)3](BF4)2 [dmAB = 4,4'-bis[3'-(4'-tolylazo)phenyl]-2,2'-bipyridine], [Co(III)(dmAB)3](BF4)3, [Co(II)(mAB)3](BF4)2 [mAB = 4-[3' '-(4' '-tolylazo)phenyl]-2,2'-bipyridine], and [Co(III)(dmAB)3](BF4)3, derived from the effect of gathering azobenzenes in one molecule and the effect of the cobalt(II) or cobalt(III) ion were investigated using UV-vis absorption spectroscopy, femtosecond transient spectroscopy, and 1H NMR spectroscopy. In the photostationary state of these four complexes, nearly 50% of the trans-azobenzene moieties of the Co(II) complexes were converted to the cis isomer, and nearly 10% of the trans-azobenzene moieties of the Co(III) complexes isomerized to the cis isomer, implying that the cis isomer ratio in the photostationary state upon irradiation at 365 nm is controlled not by the number of azobenzene moieties in one molecule but rather by the oxidation state of the cobalt ions. The femtosecond transient absorption spectra of the ligands and the complexes suggested that the photoexcited states of the azobenzene moieties in the Co(III) complexes were strongly deactivated by electron transfer from the azobenzene moiety to the cobalt center to form an azobenzene radical cation and a Co(II) center. The cooperation among the photochemical structural changes of six azobenzene moieties in [Co(II)(dmAB)3](BF4)2 was investigated with 1H NMR spectroscopy. The time-course change in the 1H NMR signals of the methyl protons indicated that each azobenzene moiety in [Co(II)(dmAB)3](BF4)2 isomerized to a cis isomer with a random probability of 50% and without interactions among the azobenzene moieties.     

Structural peculiarities of a homologous series of iron(II) cage complexes with ribbed glyoximate,methylglyoximate, and dimethylglyoximate chelate fragments

The crystal and molecular structures of four representatives of the homologous series of iron(ii) clathrochelates FeBd₂Gm(BF)₂·1.5CHCl₃, FeBd₂Mm(BF)₂·CH₂Cl₂, FeBd₂Dm(BF)₂·CH₂Cl₂, and FeBd₂Dm(BF)₂·0.5C₆H₆·0.5iso-C₈H₁₈ whose frameworks contain two α-benzyldioximate (Bd) chelate rings and one acyclic α-dioximate fragment (Gm^2?, Mm^2?, and Dm^2? are glyoxime, methylglyoxime, and dimethylglyoxime dianions, respectively) were studied by X-ray diffraction. Two types, A and B, of independent macrobicycles were observed in the unit cell of the crystal FeBd₂Gm(BF)₂·1.5CHCl₃. The geometry of the FeN₆ coordination polyhedra of encapsulated iron(ii) ions is intermediate between a trigonal prism (TP) and a trigonal antiprism (TAP). The encapsulated iron(ii) ions occupy centers of the TP-TAP polyhedra. For the macrobicyclic derivatives of dimethylglyoxime, the distortion angles φ(average values 24.0 and 24.7°) are larger than for the glyoximate and methylglyoximate analogs (average values 20.7, 22.6, and 23.2°). The larger trigonal-prismatic distortion of the coordination polyhedron in type-B FeBd₂Gm(BF)₂ molecules as compared to type-A FeBd₂Gm(BF)₂ can be explained by a difference in their intermolecular interactions. The carbon-carbon distances in the glyoximate and methylglyoximate ribbed fragments of the clathrochelates FeBd₂Gm(BF)₂ and FeBd₂Mm(BF)₂ (average values 1.414 shorter than in the α-benzyldioximate chelate rings (about 1.45 FeBd₂Gm(BF)₂·1.5CHCl₃ and FeBd₂Dm(BF)₂·CH₂Cl₂ have laminated structures in which chains of the clathrochelate molecules are differently oriented relative to the axes of the unit cells. The crystals FeBd₂Mm(BF)₂·CH₂Cl₂ and FeBd₂Dm(BF)₂·0.5C₆H₆·0.5 iso-C₈H₁₈ have framework structures and their solvate molecules occupy voids between the dimeric associates and the macrobicyclic molecules, respectively.     

Efficient preparation and improved sensitivity of molecularly imprinted polymers using room temperature ionic liquids

Synthesis of trans-aconitic acid molecularly imprinted polymers in [bmim][BF4] and [bmim][PF6] under photochemical (5 degrees C, AIBN) and thermal (60 degrees C, AIBN) conditions gave polymer micro-spheres (<200 nm), under bulk and precipitation polymerisation conditions, and higher selectivity indices (100% improvement) relative to the more traditional precipitation polymerisation (CH3CN, high solvent volumes) approach.     

Molecular Structure,Vibrational Spectra,and Hydrogen Bonding of the Ionic Liquid 1‐Ethyl‐3‐methyl‐1H‐imidazolium Tetrafluoroborate

The IR and Raman spectra and conformations of the ionic liquid 1‐ethyl‐3‐methyl‐1H‐imidazolium tetrafluoroborate, [EMIM] [BF₄] ( 6 ), were analyzed within the framework of scaled quantum mechanics (SQM). It was shown that SQM successfully reproduced the spectra of the ionic liquid. The computations revealed that normal modes of the EMIM⁺?BF ion pair closely resemble those of the isolated ions EMIM⁺ and BF , except for the antisymmetric BF stretching vibrations of the anion, and the out‐of‐plane and stretching vibrations of the H? C(2) moiety of the cation. The most plausible explanation for the pronounced changes of the latter vibrations upon ion‐pair formation is the H‐bonding between H? C(2) and BF . However, these weak H‐bonds are of minor importance compared with the Coulomb interactions between the ions that keep them closely associated even in dilute CD₂Cl₂ solutions. According to the ‘gas‐phase’ computations, in these associates, the BF anion is positioned over the imidazolium ring of the EMIM⁺ cation and has short contacts not only with the H? C(2) of the latter, but also with a proton of the Me? N(3) group.     

Cloning of a new allelic variant of aSaccharomyces diastaticus glucoamylase gene and its introduction into industrial yeasts

A new allelic variant of theSTA2 gene, designated asSTA2 ^K, coding for a secreted glucoamylase, was cloned. Differences were revealed both in the structural gene and in the promoter region, as compared to otherSTA genes. The most peculiar structural features ofSTA2 ^K are 1. a 1.1-kb natural deletion in its promoter located 189 nucleotides upstream of the translation start codon; and2. an Asn→ Asp single amino acid change within the putative active site of the encoded glucoamylase. Neither the presence of glucose in the medium nor the host cell's mating type constellation affected the expression level ofSTA2 ^K inS. cerevisiae. Self-replicating yeast plasmids containingSTA2 ^K were constructed and used to transform a laboratory yeast strain and various brewing strains. Pilot brewing tests with glucoamylase-secreting transformants of a brewing strain produced superattenuated beers at accelerated fermentation rates.     

Preparation and Properties of Hybrid Nanostructures of Zinc Tetraphenylporphyrinate and an Amphiphilic Copolymer of <Emphasis Type="Italic">N</Emphasis>-Vinylpyrrolidone in a Neutral Aqueous Buffer Solution

Water-soluble forms of a hydrophobic dye, zinc tetraphenylporphyrinate, are obtained via its solubilization by polymer particles of the micellar type formed by a copolymer of N-vinylpyrrolidone with triethylene glycol dimethacrylate. Hydrodynamic radii R_h and the size distribution of such particles in neutral aqueous buffer solutions are determined via dynamic light scattering. The electrochemical activity of the encapsulated dye is found, and its photochemical properties (absorption and fluorescence) are studied.     

M-P versus M=M bonds as protonation sites in the organophosphide-bridged complexes [M2Cp2(mu-PR2)(mu-PR'2)(CO)2], (M = Mo, W; R, R' = Ph, Et, Cy)

The unsaturated complexes [W2Cp2(mu-PR2)(mu-PR'2)(CO)2] (Cp = eta5-C5H5; R = R' = Ph, Et; R = Et, R' = Ph) react with HBF4.OEt2 at 243 K in dichloromethane solution to give the corresponding complexes [W2Cp2(H)(mu-PR2)(mu-PR'2)(CO)2]BF4, which contain a terminal hydride ligand. The latter rearrange at room temperature to give [W2Cp2(mu-H)(mu-PR2)(mu-PR'2)(CO)2]BF4, which display a bridging hydride and carbonyl ligands arranged parallel to each other (W-W = 2.7589(8) A when R = R' = Ph). This explains why the removal of a proton from the latter gives first the unstable isomer cis-[W2Cp2(mu-PPh2)2(CO)2]. The molybdenum complex [Mo2Cp2(mu-PPh2)2(CO)2] behaves similarly, and thus the thermally unstable new complexes [Mo2Cp2(H)(mu-PPh2)2(CO)2]BF4 and cis-[Mo2Cp2(mu-PPh2)2(CO)2] could be characterized. In contrast, related dimolybdenum complexes having electron-rich phosphide ligands behave differently. Thus, the complexes [Mo2Cp2(mu-PR2)2(CO)2] (R = Cy, Et) react with HBF4.OEt2 to give first the agostic type phosphine-bridged complexes [Mo2Cp2(mu-PR2)(mu-kappa2-HPR2)(CO)2]BF4 (Mo-Mo = 2.748(4) A for R = Cy). These complexes experience intramolecular exchange of the agostic H atom between the two inequivalent P positions and at room-temperature reach a proton-catalyzed equilibrium with their hydride-bridged tautomers [ratio agostic/hydride = 10 (R = Cy), 30 (R = Et)]. The mixed-phosphide complex [Mo2Cp2(mu-PCy2)(mu-PPh2)(CO)2] behaves similarly, except that protonation now occurs specifically at the dicyclohexylphosphide ligand [ratio agostic/hydride = 0.5]. The reaction of the agostic complex [Mo2Cp2(mu-PCy2)(mu-kappa2-HPCy2)(CO)2]BF4 with CN(t)Bu gave mono- or disubstituted hydride derivatives [Mo2Cp2(mu-H)(mu-PCy2)2(CO)2-x(CNtBu)x]BF4 (Mo-Mo = 2.7901(7) A for x = 1). The photochemical removal of a CO ligand from the agostic complex also gives a hydride derivative, the triply bonded complex [Mo2Cp2(H)(mu-PCy2)2(CO)]BF4 (Mo-Mo = 2.537(2) A). Protonation of [Mo2Cp2(mu-PCy2)2(mu-CO)] gives the hydroxycarbyne derivative [Mo2Cp2(mu-COH)(mu-PCy2)2]BF4, which does not transform into its hydride isomer.     

Photochemistry of planar four-co-ordinate palladium(II) complexes—III. Photosynthesis and crystal structure of [Pd2(PPr3n2(NCS)(SCN)2(μ-CN)]

U.V. irradiation of MeOH and CH₃CN solutions of trans-[Pd(PPr₃ⁿ)₂(NCS)₂] causes a stepwise photochemical reaction. When the solvent is CH₃CN the photoproduct can be conveniently isolated in a crystalline form. This compound has been shown, by X-ray analysis, to be a cyano bridged palladium(II) complex.     

Fluoride abstraction and reversible photochemical reduction of cationic uranyl(VI) phosphine oxide complexes

The syntheses, structural and spectroscopic characterization, fluoride abstraction reactions, and photochemical reactivity of cationic uranyl(VI) phosphine oxide complexes are described. [UO2(OPPh3)4][X]2 (1a, X = OTf; 1b, X = BF4) and [UO2(dppmo)2(OPPh3)][X]2 (2a, X = OTf; 2b, X = BF(4)) are prepared from the corresponding uranyl(VI) chloride precursor and 2 equiv each of AgX and phosphine oxide. The BF4- compounds 1b and 2b are prone to fluoride abstraction reactions in methanol, leading to dinuclear fluoride-bridged uranyl(VI) complexes. Fluoride abstraction of 2b in methanol generates two structural isomers of the fluoride-bridged uranyl(VI) dimer [(UO2(dppmo)2)2(mu-F)][BF4]3 (4), both of which have been structurally characterized. In the major isomer 4C, the four dppmo ligands are all chelating, while in the minor isomer 4B, two of the dppmo ligands bridge adjacent uranyl(VI) centers. Photolysis of 2b in methanol proceeds through 4 to form the uranium(IV) fluoride complex [UO2F2(dppmo)3][BF4]2 (5), involving another fluoride abstraction step. X-ray crystallography shows 5 to be a rare example of a structurally characterized uranium(IV) complex possessing terminal U-F bonds. Complex 5 reverts to 4 in solution upon exposure to air.