Photoexcited triplet states of new UV absorbers, cinnamic acid 2-methylphenyl esters

Phosphorescence spectra of nonphosphorescent or very weakly phosphorescent new UV absorbers, 2-methylphenyl cinnamate (MePC), 2-methylphenyl 4-methoxycinnamate (MePMC) and 2-methylphenyl 4-ethoxycinnamate (MePEC) have been observed by using external heavy atom effects of ethyl iodide in ethanol at 77 K. The lowest excited triplet (T(1)) energies of these new UV absorbers are lower than those of a widely used UV-A absorber, 4-tert-butyl-4'-methoxydibenzoylmethane (BM-DBM), in both keto and enol forms. The intermolecular triplet-triplet energy transfer from photolabile BM-DBM to MePMC was observed by measuring the time-resolved phosphorescence spectra. Electron paramagnetic resonance spectra have been observed for the T(1) states of these new UV absorbers in ethanol at 77 K by using benzophenone as a triplet sensitizer. The observed T(1) lifetimes, zero-field splitting (ZFS) parameters and molecular orbital calculations of the ZFS parameters suggest that T(1) states of these new UV absorbers posses mainly (3)ππ* character. The deactivation processes of the lowest excited singlet (S(1)) states are predominantly fluorescence and internal conversion to the ground (G) states in MePMC and MePEC, while the main deactivation process of the S(1) state of MePC is internal conversion to the G state. The molar absorption coefficients of MePMC and MePEC in the UV-A and UV-B regions are larger than that of most widely used UV-B absorber, octyl methoxycinnamate.     

Romanowsky dyes and Romanowsky-Giemsa effect. 2. Eosin Y, erythrosin B, tetrachlorofluorescein, spectroscopic characterization of pure dyes, association of eosin Y

Analytically pure samples of the Romanowsky dyes eosin y, erythrosin b and tetrachlorofluorescein are prepared. DC of the dye samples shows no contaminations. We measured the absorption spectra of the dye dianions in alkaline aqueous solution and of the dye acids in 95% ethanol at very low dye concentrations. The molar extinction coefficients of the long wavelength absorption of the monomeric dye species are determined (Table 1). The extinction coefficients may be used for standardisation of dye samples. The absorption spectra of eosin y in aqueous solution are dependent on concentration. Using a new very sensitive method it was possible to identify two association equilibria from the concentration dependency of the spectra. Dimers are formed even in very dilute solutions, at higher concentrations tetramers. The dissociation constant of the dimers D in monomers M at 293 K, pH = 12, is K21 = 2,9 X 10(-5) M; of the tetramers Q in dimers D K42 = 2,4 X 10(-3) M. From the experimental spectra of eosin solutions at various concentrations, pH = 12, and the equilibrium constants K21, K42 the absorption spectra of the pure monomers, dimers and tetramers are calculated. M has one long wavelength absorption band, VM = 19300 cm-1, epsilon M = 1,03 X 10(5) M-1 cm-1; D also one absorption band, VD = 19300 cm-1, epsilon D = 1,74 X 10(5) M-1 cm-1; Q two absorption bands, VQ1 = 19100, VQ2 = 20200 cm-1, epsilon Q1 = 1,65 X 10(5), epsilon Q2 = 1,96 X 10(5) M-1 cm-1. The absorption spectrum of the dimers is discussed by quantum mechanics.     

Fluorescence of meso-tetrakis(4-(carboxy)phenyl)porphine covalently bound to oligonucleotides d(CG)5 and d(TA)5

The amino-reactive derivative of tetraphenylporphine meso-tetrakis[4-(carboxy)phenyl]porphine (TCPP) was synthesized, which is characterized by a high molar absorption coefficient (epsilon 416 = 36,500 M-1.cm-1). TCPP was covalently attached to oligonucleotides d(CG)5 [d(CG)5-TCPP] and d(TA)5 [d(TA)5-TCPP]. The spectral characteristics of these complexes were studied in 0.01 M phosphate buffer, pH 7 at 23 degrees C. UV-visible absorption spectra of these complexes have a clearly pronounced Soret band at (414 +/- 1) nm for d(CG)5-TCPP and at (412 +/- 1) nm for d(TA)5-TCPP. The fluorescence spectra of these complexes have maxima at (648 +/- 2) nm for d(CG)5-TCPP and at (658 +/- 2) nm for d(TA)5-TCPP. In this study we also determined fluorescence quantum yields q and fluorescence lifetimes tau [q = 0.099 +/- 0.011, tau = (9.0 +/- 0.3) ns for d(CG)5-TCPP and q = 0.080 +/- 0.011, tau = (8.7 +/- 0.3) ns for d(TA)5-TCPP]. A temperature rise from 5 to 50 degrees C produced only slight (within 23%) emission changes in both samples studied. Taking into account: a) high fluorescence yields (q), b) weak dependence of q on temperature, c) weak q dependence of q on the oligonucleotide type, we conclude that TCPP may be used as a sensitive fluorescence label in DNA studies.     

Additional characterization of the two oxygen-containing compounds formed by the interaction of phthalocyaninatoiron(II) and dioxygen. Reproducible synthesis of the species isomorphic with the α form of Fe(II)Pc

The two compounds obtained by the interaction in solution of Fe(lI)Pc with O₂, presently considered two crystalline modifications of the μ-oxo dimer of Fe(III)Pc, are further characterized by visible absorption, XPS and Mössbauer spectra. The results stress the difference between the solid state properties of the two Fe(III) compounds.The behaviour of Fe(II)Pc and the two oxidized compounds in some chlorinated and non-chlorinated solvents, at different temperatures in the presence and absence of O₂, is reported. It is seen that heating the two Fe(III) products in 1-chloronaphthalene, or dimethylformamide, in vacuum sealed tubes, gives as a final product βFe(II)Pc. However, the same procedure in chlorobenzene or nitrobenzene yields, in a reproducible way, the pure oxygen-containing species which is isomorphic with αFe(II)Pc. Until now this product was only obtained in a fortuitous manner.     

Synthesis, characterization and DNA-binding properties of four Zn(II) complexes with bis(pyrrol-2-yl-methyleneamine) ligands

A novel series of bis(pyrrol-2-yl-methyleneamine) ligands H2L(n) (n = 1-4) were synthesized via condensation of diamines with two equivalents of 2-formyl-pyrrole (2). Their Zn(II) complexes were characterized by elemental analyses, mass spectra and IR spectra. The crystal structures of [ZnL(1)]2 and [ZnL(4)]2 obtained from ethanol solution was determined by X-ray diffraction analysis, each of them possesses a double-stranded helical geometry. In addition, the DNA-binding properties of the compounds have been fully investigated by absorption, fluorescence and viscosity measurements.     

Synthesis of novel N-diazeniumdiolates based on hyperbranched polyethers

Novel N-diazeniumdiolate based on hyperbranched polyethers(HP-g-DACA/N(2)O(2)) were prepared through a two-step synthesized route. The alkyltrimethoxysilane containing secondary amine groups (DACA) was used to modify the hydroxyl end groups of hyperbranched polyethers (HP) to obtain the precursor hyperbranched diamine (HP-g-DACA). Then HP-g-DACA was reacted with NO at 80psi pressure to be converted into N-diazeniumdiolates. The structures were confirmed using (13)C NMR and IR spectra. UV-vis spectroscopy measurement indicated that the aqueous solution of obtained HP-g-DACA/N(2)O(2) had a characteristic absorption at 246nm. The final HP-g-DACA/N(2)O(2) product showed NO releasing within the prolonged periods of time, and the apparent half-life t(1/2) was more than 11min in phosphate buffer at 37 degrees C. The total amount of NO released from HP-g-DACA/N(2)O(2) could achieve to 0.43micromol/mg and was proportional to the modified degree of HP by DACA. In addition, the NO loading efficiency can be modulated by the modification degree of hyperbranched macromolecular end groups.     

Single crystals of amylose with a low degree of polymerization

Single crystals of amylose with a low degree of polymerization were prepared from dilute solution in water or mixtures of water and ethanol. Depending on the concentration of ethanol used, three different polymorphs resulted. From pure water amylose B was obtained and, respectively, from 15% (v/v) ethanol, amylose A, and from 40% (v/v) ethanol, V amylose. The crystals were studied by electron diffraction after quench-freezing and the crystallographic parameters were compared with those already reported in the literature.     

Coordination chemistry of F430. Axial ligation equilibrium between square-planar and bis-aquo species in aqueous solution

X-ray absorption spectroscopic characterization of axial ligand coordination to factor F430, the nickel-tetrapyrrole cofactor of the S-methyl-coenzyme M (CH3SCoM) methyl reductase enzyme from methanogenic bacteria, is presented. The nickel of isolated F430 is hexacoordinate at 10 K in aqueous solution (as is the enzyme-bound cofactor), whereas the epimerized and ring-oxidized derivatives of F430 have four-coordinate nickel. Reduction of the ring-oxidized derivative, F560, with dithionite yields F430 in its native configuration, with axial ligands indistinguishable from those present when the cofactor is obtained directly from the holoenzyme. Thus, we conclude that the axial ligands to F430 in aqueous solution are water molecules. Analysis of the nickel extended x-ray absorption fine structure is consistent with this conclusion. Resonance Raman spectra obtained at room temperature contain features characteristic of both 4- and 6-coordinate forms of the cofactor. We have found that the resonance Raman, optical, and x-ray absorption spectra of aqueous solutions of F430 are temperature-dependent due to a ligand-binding equilibrium involving the square-planar and 6-coordinate bis-aquo forms of the cofactor. At low temperatures (less than 250 K) the 6-coordinate form predominates, whereas higher temperature solutions contain both 4- and 6-coordinate species in a dynamic equilibrium. Similar behavior is observed in other weakly coordinating solvents such as methanol and ethanol. The 4-coordinate form is predominant in solvents with strong electron-withdrawing substituents such as 2,2,2-trifluoroethanol and 2-mercaptoethanol. The relevance of this facile ligand exchange to the active site structure and enzymatic mechanism of the parent enzyme is discussed.     

A mass spectrometric analysis of sensitizer solution used for dye-sensitized solar cell

We report a mass spectrometric study of ruthenium(II) sensitizer ((C₄H₉)₄N)₂[Ru(4-carboxy-4′-carboxylate-2,2′bipyridine)₂(NCS)₂] (N719) in various organic and aqueous solvents. At the equilibrium different species were found, depending on solution properties. After stoichiometry confirmation through high-resolution mass spectra and isotopic pattern analysis, the formation of these complexes was found to strongly depend from the polarity and the ionic strength of solvent medium. Mass spectra obtained in acetonitrile/tert-butanol (1:1) mixture, used for the absorption of N719 on TiO₂, suggests that the main species involved in the adsorption process is the dicarboxylate form of N719 with one (C₄H₉)₄N as counter ion. The photovoltaic data of the N719 sensitizer adsorbed on TiO₂ films exhibited a remarkable power conversion efficiency, 11.20% at 1 sun.     

短梗霉黑色素的分离纯化及结构的初步分析

采用热碱提取、水煮酸沉法从短梗霉发酵液中提取得到黑色素粗品,再经DMSO萃取、酸性甲醇(pH=2)沉淀得到不含多糖和蛋白的短梗霉黑色素。此黑色素不溶于水及常规有机溶剂,可溶于碱性溶液和DMSO;离子交换色谱分析表明黑色素组分均一,出峰时间26±0.5 m in;紫外光谱谱图最大吸收峰为215 nm左右,未见蛋白(280 nm)与核酸(260 nm)的特征吸收峰;红外光谱谱图具有黑色素3μm和6μm的特征吸收峰,并含大量的羟基、氨基,与核磁共振和液质联机谱图结合分析推出短梗霉黑色素可能含有酚羟基、羧基和吲哚等官能团,主要结构骨架为5,6-二羟基吲哚-羧酸和多巴醌,推断该黑色素为酪氨酸酶控制合成的真黑素。     

The bimolecular sensitization of nitric oxide release from weak interacting ruthenium units

This work reports on the bimolecular sensitization of nitric oxide release from cis-[Ru(bpy)₂(iso)NO](PF₆)₃ (1) (iso = isoquinoline and bpy = 2,2′-bipyridine) by irradiating the MLCT transition of the chloro analog cis-[Ru(bpy)₂(iso)Cl]PF₆ (2)_. The compounds displayed peaks in the ESI-MS spectra at m/z 749.1 and m/z 578.1 ascribed, respectively, to ([1(NO⁰)−2PF₆·CH₃OH]²⁺) and ([2−PF₆]⁺). In the cyclic voltammograms, the nitrosyl complex presented two redox waves related to the NO ligand at 0.48 and −0.37 V (versus Ag/AgCl, NO^+/0/−1 processes), while the sensitizer showed two reversible waves at 0.79 and −1.46 V (versus Ag/AgCl, Ru^2+/3+ and bpy ^0/−1, respectively). The most important feature of this system is that the nitrosyl compound does not have significant absorption in the visible region, while the sensitizer has an intense band centered at 496 nm. The irradiation of an equimolar mixture of the two compounds in an ethanol:water solution (v:v) with light of λ > 500 nm leads to NO release, as probed by amperometric measurements. The variational method was applied, showing that the two compounds self-assembly in solution with a 1:1 stoichiometry. Fluorescence spectra acquired at 77 K provided the E_0-0 for the system and, from the thermodynamic cycle it was estimated that the photoinduced electron transfer between the species has a ΔG value of −1.59 eV.     

Light absorption, electron paramagnetic resonance and resonance Raman characteristics of nitridochromium(V) protoporphyrin-IX and its reconstituted hemoproteins.

A surprisingly stable complex of the photolyzed product of azidochromium(III)protoporphyrin-IX was prepared and examined by light absorption, electron paramagnetic resonance (EPR) and resonance Raman spectroscopies. The characteristic EPR spectrum for this complex was consistent with a nitridochromium(V)-porphyrin complex which was two oxidation equivalents above the resting Cr(III) complex. The Cr(V)-N stretching mode was observed at 1010 cm-1 by resonance Raman spectroscopy. A simple diatomic harmonic oscillation model gave a force constant of 6.7 mdyn/A for the Cr(V)-N bond, in the region characteristic for the metal-nitrogen triple bond. Nitridochromium(V) protoporphyrin-IX reconstituted myoglobin and cytochrome c peroxidase were prepared for the first time. The nitridochromium(V)-porphyrins in these apo-proteins were unstable in contrast with the protein-free chromium(V)porphyrin. Upon irradiation of the azide complexes of the chromium(III) protoporphyrin-IX reconstituted myoglobin and cytochrome c peroxidase with ultraviolet light aerobically at room temperature, the characteristic optical and EPR spectra for nitridochromium(V) derivatives were observed. The optical spectra of these photo-induced products were different from those of the nitridochromium(V) protoporphyrin-IX reconstituted hemoproteins. The electrochemical structures of the unusual metalloporphyrin seemed to be modulated by the heme surrounding amino acid residues.     

Two-dimensional nuclear Overhauser enhancement investigation of the solution structure and dynamics of the DNA octamer [d(GGTATACC)]2

The resonances of nearly all 70 of the non-exchangeable protons of the duplex [d(GGTATACC)]2 in aqueous solution are assigned by proton two-dimensional nuclear Overhauser enhancement (2D NOE) spectra obtained in pure absorption phase at 500 MHz. Experimental and theoretical 2D NOE spectra are compared at each mixing time (100, 175, 250 and 400 ms) using two B-DNA structures: a standard B-form and an energy-minimized form. The GG and CC ends of the octamer duplex are well represented by the regular B-DNA structure. But large discrepancies from these models are observed for the 'TATA' box. All 2D NOE data are consistent with nanosecond correlation times, as indicated by non-selective proton spin-lattice relaxation times, but small variations in the correlation time are observed, suggesting that there are some local differences in mobility within the octamer duplex structure in solution.     

Synthesis, micellar properties, DNA binding and antimicrobial studies of some surfactant-cobalt(III) complexes

A new class of surfactant-cobalt(III) complex ions of the type, cis-[Co(X)(2)(C(14)H(29)NH(2))Cl](2+) (where X=ethylenediamine (en), or 2,2'-bipyridyl (bpy), or 1,10-phenanthroline (phen)) and cis-[Co(trien)(C(14)H(29)NH(2))Cl](2+) (trien=triethylenetetramine) were synthesized and characterized by IR, NMR, UV-visible electronic absorption spectra, elemental analysis and metal analysis. The critical micelle concentration (CMC) values of these surfactant-cobalt(III) complexes in aqueous solution were obtained from conductance measurements. Specific conductivity data (at 298, 308, 318 and 328 K) served for the evaluation of the temperature-dependent CMC and the thermodynamics of micellization (DeltaG(0)(m), DeltaH(0)(m) and DeltaS(0)(m)). Interactions between calf thymus DNA and the surfactant-cobalt(III) complexes in aqueous solution have been investigated by electronic absorption spectroscopy, emission spectroscopy and viscosity measurements. The electrostatic interactions, van der Waals interactions and/or partial intercalative binding have been observed in these systems. The surfactant-cobalt(III) complexes were screened for their antibacterial and antifungal activities against various microorganisms. The results were compared with the standard drugs, Ciprofloxacin and Fluconazole respectively.     

Multiquantum EPR spectroscopy of spin-labeled arrestin K267C at 35 GHz

Three- and five-quantum absorption and dispersion multiquantum electron paramagnetic resonance spectra of a spin-labeled protein have been obtained for the first time at Q-band (35 GHz). Spectra of arrestin spin-labeled at site 267 were recorded at room temperature as a function of microwave power. The separation of irradiating microwave frequencies, Deltaf, was 10 kHz, and a newly-designed multiquantum Q-band electron paramagnetic resonance bridge was utilized, operating in a superheterodyne detection mode. The sample volume was 30 nL using a 3-loop-2-gap resonator. Most spectra were obtained at a 300 microM concentration in single, 2-min scans, but spectra were also successfully obtained at 30 microM, corresponding to one picomole of protein. Enhanced sensitivity to T(1) and T(2) was evident in the spectra, and linewidths varied considerably across the spectra. The pure absorption displays are beneficial relative to field modulation methods for spectral characterization. The presence of two states of the nitroxide spin-label with different relaxation times is evident, particularly in the dispersion spectra, which are expected to exhibit enhanced sensitivity to lineshape variation relative to absorption. Feasibility has been established for the use of this technique for site-directed spin-labeling studies of biologically relevant samples, particularly the study of protein structure and dynamics.     

Somatic Antigens of Streptococcus Group E: II. Separation and a Partial Physicochemical Characterization1

Antigenic extracts of Streptococcus group E (SGE) were subjected to fractional ethanol precipitation, block (preparative) electrophoresis, and gel filtration for the purpose of separating the type antigen from the group antigen. Ethanol precipitation was ineffective in separating the substances. Block electrophoresis yielded serologically pure group antigen and a mixture of type and group antigen. Serologically pure type antigen was obtained by gel filtration. In some cases, pure group antigen was also recovered; in others, it was contaminated with type antigen. Gel filtration column effluents of antigenic extracts of SGE serotypes, I, II, III, IV, V and "untypable" isolates, collected from the region in which type antigen was eluted, were studied by paper chromatography and infrared spectrophotometry in an effort to develop a nonserological means of detecting type antigen. Hydrolysates of type antigens or suspect type antigens of serotypes I through V contained l-rhamnose, d-glucose, and several unidentified substances. d-Galactose also was present in hydrolysates of serotypes III and V. Untypable isolates and negative controls contained traces of d-glucose only. The data suggested that serotypes I through V contained a type antigen and that the untypable isolates were devoid of type antigen. Infrared absorbance spectra seemed to support the paper chromatography data.     

Liquid transport properties of porcine tracheal epithelium.

Because of its possible importance to the etiology of cystic fibrosis lung disease, the ion and water transport properties of tracheal epithelium were studied. Net liquid flux (J(V)) across porcine tracheal epithelium was measured in vitro using blue dextran as a volume probe. Luminal instillation of isosmotic sucrose solution (280 mM) induced a small net secretion of liquid (7.0 +/- 1.7 nl x cm(-2) x s(-1)), whereas luminal hyposmotic sucrose solutions (220 or 100 mM) induced substantial and significant (P < 0.05) liquid absorption (34.5 +/- 12 and 38.1 +/- 7.3 nl x cm(-2) x s(-1), respectively). When the luminal solution was normal (isosmotic) Krebs buffer, liquid was absorbed at 10.2 +/- 1.1 nl x cm(-2) x s(-1). Absorptive J(V) was abolished by 100 microM amiloride in the luminal solution and significantly reduced when the luminal solution was Na(+)-free Krebs solution. Absorptive J(V) was not significantly affected by 300 microM 5-nitro-2-(3-phenylpropylamino)benzoate or 100 microM diphenylamine-2-carboxylic acid, both cystic fibrosis transmembrane conductance regulator protein (CFTR) inhibitors, in the instillate but was significantly reduced by 60% when the luminal solution was Cl(-)-free Krebs solution. We conclude that water freely permeates porcine tracheal epithelium and that absorption of liquid is normally driven by active transcellular Na(+) transport and does not require the CFTR.     

Study of the influence of metal ions on tRNA(Phe) thermal unfolding equilibria by UV spectroscopy and multivariate curve resolution

The influence of metal ions (Na(+), Mg(2+) and Cd(2+)) on the thermal unfolding of phenylalanine transfer ribonucleic acid (tRNA(Phe)) was studied by UV spectroscopy-monitored melting experiments. Absorbance data were obtained during the unfolding process in the range 220-340 nm and later analyzed by a multivariate curve resolution approach (MCR-ALS) based on factor analysis. This procedure determines the number of spectroscopically distinct conformations present during the unfolding process and reveals their concentration profiles and pure spectra, without any initial assumption having to be made about the number of steps in the unfolding pathway. From the concentration profiles and pure spectra, information such as T(m) values can be recovered. The results were compared with those obtained previously in spectroscopic and calorimetric unfolding experiments, showing that the multivariate approach recovers information that complements that obtained in traditional spectroscopic melting experiments.     

Determination of the degree of acetylation of chitosan by UV spectrophotometry using dual standards

Determination of the degree of acetylation of chitosan by UV spectrophotometry using dual standards is investigated. The UV absorbance of a pure chitosan solution is contributed additively by the N-acetylglucosamine and glucosamine residues; the absorbance divided by the total molar concentration of the residues (A/c(t)) is linearly related to the degree of acetylation (DA). Using acetyl glucosamine and glucosamine hydrochloride as standards in 0.1M hydrochloric acid solution, the equation obtained by linear regression is A/c(t)=3.3615 DA+0.0218, R(2)=0.9958. The DA of the analytical sample (m milligram of chitosan in V liters solution) can be calculated by.     

Evidence for a μ-oxi-diiron(III) species from Mössbauer spectroscopy

Mössbauer spectra of frozen aqueous solutions that were formed by dissolving pyridinium μ-oxo- bis(trichloroferrate(III))pyridine in watet provide direct evidence for the existence of a μ-oxo-bis- (ferrate(III)) species. Thus the μ-oxo-bis(ferrate(III)) bridge remains intact in aqueous solution. This species should be of use in modelling two iron proteins such as haemerythrin.