Mono- and Dianion of a Bis(benzobuta)tetraazapentacene Derivative

A bis(benzobuta)tetraazapentacene derivative was reduced to its radical anion and its dianion, using potassium [18]crown-6 anthracenide in THF. Both reduced species were characterized by UV/Vis spectroscopy of the isolated species and by spectroelectrochemistry. Two distinct single-crystal structures of the dianion and an EPR spectrum of the radical anion were obtained. Contrary to other azaacenes, the lowest energy absorption in the UV/Vis spectrum of the dianion is redshifted in comparison to that of the neutral compound.     

Synthesis and characterization of novel ferrocenyl glycidyl ether polymer,ferrocenyl poly (epichlorohydrin) and ferrocenyl poly (glycidyl azide)

Poly (ferrocenyl glycidyl ether) was synthesized by polymerization of 2-[(4-ferrocenylbutoxy)methyl]oxirane (FcEpo) using toluene solution of methylaluminoxane as the catalyst. Copolymerization of 2-[(4-ferrocenylbutoxy)methyl]oxirane with epichlorohydrin was used for the synthesis of another ferrocenyl based poly (epichlorohydrin). Ferrocenyl based poly (glycidyl azide), GAP, was synthesized by treatment of sodium azide with this copolymer in DMF as solvent at room temperature. The synthesized ferrocenyl based polymers were characterized by FT-IR, ¹HNMR, UV–Vis, TGA, DSC and GPC analysis. The UV–Vis spectra of synthesized polymers show the absorption band of ferrocene moiety at about 450 nm. The TGA and DSC analysis show that poly (ferrocenyl glycidyl ether) has good thermal stability. The TGA analysis shows that the copolymerization of 2-[(4-ferrocenylbutoxy)methyl]oxirane with epichlorohydrin improved the thermal stability of the copolymer. The GPC analysis of poly (ferrocenyl glycidyl ether), ferrocenyl based poly (epichlorohydrin) and Ferrocenyl based poly (glycidyl azide) show the PDI between 1.14–1.17. The electrochemical behavior of synthesized polymers was investigated by cyclic voltammetry (CV) measurements. The CV curves of synthesized polymers show good electrochemical performance and there is one redox system with the single-electron reversible reaction that associated with ferrocene moiety in polymers structure. The anodic and cathodic peak currents increased with scan rate confirmed redox reactions in the system are kinetically fast diffusion-controlled reactions.     

The solvent cage effect: is there a spin barrier to recombination of transition metal radicals?

This investigation explored whether there is a spin barrier to recombination of first- and second-row transition metal-centered radicals in a radical cage pair. To answer this question, the recombination efficiencies of photochemically generated radical cage pairs (denoted as FcP) were measured in the presence and absence of an external heavy atom probe. Two methods were employed for measuring the cage effect. The first method was femtosecond pump-probe transient absorption spectroscopy, which directly measured FcP from reaction kinetics, and the second method (referred to herein as the "steady-state" method) obtained FcP from quantum yields for the radical trapping reaction with CCl4 as a function of solvent viscosity. Both methods generated radical cage pairs by photolysis (lambda = 515 nm for the pump probe method and lambda = 546 nm for the steady-state method) of Cp'2Mo2(CO)6 (Cp' = eta(5)-C5H4CH3). In addition, radical cage pairs generated from Cp'2Fe2(CO)4 and Cp*2TiCl2 (Cp* = eta(5)-C5(CH3)5) were studied by the steady-state method. The pump-probe method used p-dichlorobenzene as the heavy atom perturber, whereas the steady-state method used iodobenzene. For both methods and for all the radical caged pairs investigated, there were no observable heavy atom effects, from which it is concluded there is no spin barrier to recombination.     

2‐Nitro‐1,4‐diaminobenzene‐Functionalized Poly(vinyl amine)s as Water‐Soluble UV‐Vis‐Sensitive pH Sensors

Summary: Nucleophilic aromatic substitution of 2,6‐O‐dimethyl‐β‐cyclodextrin (β‐DMCD)‐complexed 4‐fluoro‐3‐nitroaniline derivatives with poly(vinyl amine) (PVAm) in water results in 2‐nitro‐1,4‐benzenediamine‐functionalized water‐soluble PVAms in one step. The 2‐nitro‐1,4‐benzenediamine moiety linked to the polymer is solvatochromic and undergoes protonation and deprotonation as function of pH as shown by UV‐Vis spectroscopy. The occurrence of an isosbestic point in the UV‐Vis spectrum is suitable to directly determine the pK_a value using the Henderson‐Hasselbalch equation. The influence of the methyl group substitution of the polymer and the 2‐nitro‐1,4‐benzenediamine moiety on the pK_a is discussed.

Structure of the 4‐N,N‐dimethyl‐2‐nitro‐1,4‐benzenediamine‐functionalized PVAm and its solution in water at varying pH.     

Theoretical Study of the Wavelength Selection for the Photocleavage of Coumarin-caged D-luciferin

The equilibrium structures and optical properties of the photolabile caged luciferin, (7-diethylaminocoumarin-4-yl)methyl caged D-luciferin (DEACM-caged D-luciferin), in aqueous solution were investigated via quantum chemical calculations. The probable conformers of DEACM-caged D-luciferin were determined by potential energy curve scans and structural optimizations. We identified 40 possible conformers of DEACM-caged D-luciferin in water by comparing the Gibbs free energy of the optimized structures. Despite the difference in their structures, the conformers were similar in terms of assignments, oscillator strengths and energies of the three low-lying excited states. From the concentrations of the conformers and their oscillator strengths, we obtained a theoretical UV/Vis spectrum of DEACM-caged D-luciferin that has two main bands of shape nearly identical to the experimental UV/Vis spectrum. The absorption bands with maxima ~ 384 and 339 nm were attributed to the electronic excitations of the caged group and the luciferin moiety, respectively, by analysis of the theoretical UV/Vis spectrum. Furthermore, the analysis showed that DEACM-caged D-luciferin is excited in the caged group only by light of wavelength ranging within 400–430 nm, which is in the long-wavelength tail of the 384 nm band. This should be tested to lower damage upon photocleavage.     

Synthesis,Characterization, Structural Description,Micellization Behavior,DNA Binding Study and Antioxidant Activity of 4, 5 and 6-Coordinated Copper(II) and Zinc(II) Complexes

Four mononuclear copper(II) and zinc(II) complexes were synthesized by the reaction of copper and zinc salts with 3,4-dichlorophenylactic acid, 2-bromophenylactic acid, biphenylacetic acid (O-donor ligand) and bipyridine (N-donor ligands) having the general formulae [(L)₂Cu(bp)(H₂O)] ( 1 ), [(BpA)₂Cu(bp)] ( 2 ), [(L)₂Zn(bp)(H₂O)] ( 3 ) and [(L*)₂Zn(bp)] ( 4 ) (L = 3,4-dichlorophenylacetate, L* = 2-bromophenylacetate bp = bipyridine, and BpA = biphenylacetate). Structures of all compounds were characterized through FT-IR spectroscopy and X-ray diffraction analysis. FT-IR spectra of all complexes confirmed the binding mode of Cu-O and Zn-O. XRD data revealed that complexes 1 – 3 exhibited distorted octahedral arrangement, whereas complex 4 has a distorted tetrahedral environment. Micellization behavior was examined with anionic surfactant (SDS) by conductance measurement as well as absorption spectral analysis. DNA binding study was assessed through viscosity measurement and UV/Vis spectrophotometry. DPPH free radical scavenging assay was measured by UV/Vis spectrophotometry. The results showed nice biological potential of all the complexes.     

Time-resolved spectroscopic studies of B(12) coenzymes: a comparison of the primary photolysis mechanism in methyl-, ethyl-, n-propyl-, and 5'-deoxyadenosylcobalamin.

An ultrafast transient absorption study of the primary photolysis of ethyl- and n-propylcobalamin in water is presented. Data have been obtained for two distinct excitation wavelengths, 400 nm at the edge of the UV gamma-band absorption, and 520 nm in the strong visible alphabeta-band absorption. These data are compared with results reported earlier for the B(12) coenzymes, methyl- and adenosylcobalamin. The data obtained for ethylcobalamin and n-propylcobalamin following excitation at 400 nm demonstrate the formation of one major photoproduct on a picosecond time scale. This photoproduct is spectroscopically identifiable as a cob(II)alamin species. Excitation of methyl-, ethyl-, and n-propylcobalamin at 520 nm in the low-lying alphabeta absorption band results in bond homolysis proceeding via a bound cob(III)alamin MLCT state. For all of the cobalamins studied here competition between geminate recombination of caged radical pairs and cage escape occurs on a time scale of 500 to 700 ps. The rate constants for geminate recombination in aqueous solution fall within a factor of 2 between 0.76 and 1.4 ns(-1). Intrinsic cage escape occurs on time scales ranging from 相似文献   

Synthesis and characterization of fluorine functionalized graphene oxide dispersed quinoline-based polyimide composites having low-k and UV shielding properties

Polyimide nanocomposites having low-k and UV shielding properties have been developed using fluorine functionalized graphene oxide and bis(quinoline amine) based polyimide. The polyimide was synthesized using bis(quinoline amine) and pyromellitic dianhydride at appropriate experimental conditions, and its molecular structure was confirmed through various spectral analysis such as FTIR and NMR. The polyimide (PI) composites were prepared using bis(quinoline amine), pyromellitic dianhydride, and separately filled with 1, 5, 10 wt% of fluorinated graphene oxide (FGO) through in situ polymerization. The polymer composites were characterized using thermo gravimetric analysis (TGA), X-ray powder diffraction (XRD), and scanning electron microscopy (SEM). In addition, the water contact angle, dielectric behavior, and UV–Vis shielding behavior of FGO/PI composites were evaluated. The value of the water contact angle of the polyimide was increased with increment of FGO in the polyimide matrix. The highest water contact angle of polyimide composites observed 108° was obtained for 15 wt% FGO reinforced polyimide composite. The value of the dielectric constant for neat, 1, 5, and 15 wt% FGO reinforced polyimide composites was obtained as 4.5, 3.7, 2.6, and 2.0, respectively. It is also observed from by UV–Vis spectroscopy analysis that the FGO reinforced polyimide composites have good UV shielding behavior.     

Schiff base substitute polyphenol and its metal complexes derived from o‐vanillin with 2,3‐diaminopyridine: synthesis,characterization, thermal,and conductivity properties

Poly‐2,3‐bis[(2‐hydroxy‐3‐methoxyphenyl)methylene]diamino pyridine (PHMPMDAP) that a new Schiff base polymer has been synthesized and characterized by spectroscopy, elemental, and thermal analyses techniques. This azomethine polymer was found to form complexes readily with Cu(II), Zn(II), Co(II), Pb(II), and Fe(II). From IR and UV‐Vis studies, the phenolic oxygen and imine nitrogen of the ligand were found to be the coordination sites. Thermogravimetric analysis (TGA) data indicate the polymer to be more stable than the monomer. The structure of the polymer obtained was confirmed by FT‐IR, UV‐Vis, ¹³C‐NMR, and ¹H‐NMR. Characterization was undertaken by TGA, size exclusion chromatography (SEC), and solubility tests. Also, electrical conductivities of PHMPMDAP and polymer–metal complexes are measured by four probe technique. Copyright © 2008 John Wiley & Sons, Ltd.     

Photoreactivity of cyanoacetylene trapped in water ice: an infrared, isotopic and theoretical study

Photoreactivity of cyanoacetylene with water was successively studied in cryogenic matrixes and in the solid phase at lambda > 120 nm. These studies were performed using FTIR spectroscopy, isotopic experiments and DFT calculations at the B3LYP/6-31G level of theory. The photolysis of cyanoacetylene complexed with water in an argon cryogenic matrix led to the formation of two products. The first one corresponds to the cyanoketene and the second to the HCN:C2O complex. Trapped in water ice and submitted to UV photolysis, the cyanoacetylene molecule shows great photoreactivity. Indeed, besides the cyanoketene and cyanhydric acid, we characterized and identified the formation of other compounds issued from the addition of water to the CC triple bond of cyanoacetylene.     

A laser flash photolysis study of curcumin in dioxane-water mixtures.

Curcumin [bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione] was studied by means of UV-VIS absorption spectroscopy and nanosecond laser flash photolysis in 1,4-dioxane-water mixtures in a series of dioxane-water volume ratios. The transient characteristics were found to be dependent on the amount of water. In pure dioxane the triplet state of the molecule in its enolic form was detected (lambda(max) = 720 nm, tau = 3.2 micros), whereas upon water addition, the diketo form was found to prevail, because of the perturbation of intramolecular H-bonded structure. This led to hydrogen abstraction from dioxane by curcumin triplet state and the formation of the corresponding ketyl radical (lambda(max) = 490 nm, tau approximately 10 micros). Laser flash photolysis measurements, carried out in solvents of different polarity and proticity (benzene, cyclohexane and various alcohols), allowed the transient assignments to be confirmed, supporting our interpretation.     

Chelating Complexes of Diethylzinc and ZnCl2 with 2,2‐Bipyridine and 1,6,7,12,13,18‐Hexaazatrinaphthylene (HATN) as Ligands

The 1,6,7,12,13,18‐hexaazatrinaphthylene (HATN) complex [(Et₂Zn)₃(μ₃‐HATN)] was synthesized and characterized by IR spectroscopy, UV/Vis spectroscopy, elemental analysis and ESI‐MS spectrometry. Attempts to prepare ZnCl₂ complexes of HATN leads only to the mononuclear [(Cl₂Zn)(HATN)] derivative, characterized by X‐ray diffraction, IR‐ and UV/Vis‐spectroscopy as well as ESI‐MS spectrometry. The bright red 2,2′‐bipyridine (bipy) complex [(Et₂Zn)(bipy)] ( 1 ) was synthesized and characterized by X‐ray diffraction and NMR spectroscopy. The UV/Vis‐spectra of the HATN‐complexes show absorptions in regions of far longer wavelengths than the corresponding 2,2′‐bipyridine or 1,10‐phenantroline complexes. Consequently the π*‐LUMO of HATN ( 5 ) is lower in energy than the π*‐LUMO of 2,2′‐bipyridine ( 2 ) or 1,10‐phenanthroline (phen).     

Synthesis,spectral and quantum mechanical studies and molecular docking studies of Schiff base (E)2-hydroxy-5-(((4-(N-pyrimidin-2-yl)sulfamoyl)phenyl)imino)methyl benzoic acid from 5-formyl salicylic acid and sulfadiazine

A new Schiff base (E)2-hydroxy-5-(((4-(N-pyrimidin-2-yl)sulfamoyl)phenyl)imino)methyl benzoic acid (5FSADA) compound was synthesized by condensation of 5-formyl salicylic acid and sulfadiazine, and the product formed was characterized using FTIR and UV–Visible spectroscopy. The geometry was optimized using DFT. The FTIR were computed from DFT and is compared with experimental spectra, followed by detailed vibrational assignment, which shows that the experimental and simulated data is in close agreement. The UV–Vis spectrum calculated using TD-DFT, IEFPCM solvation model with DMSO as solvent. Wave function based properties like localized orbital locator, electron localization function and non-covalent interactions has been studied extensively. The physical properties (ADMET) of the compound 5FSADA indicated that the compound has excellent drug likeness and PASS studies showed that it has anti-infective properties, which is confirmed by a docking score of −9.0 ​kcal/mol.     

Photosensitive Azopolymer Brushes via Atom Transfer Radical Polymerization for Protein Sensing

Novel photosensitive azopolymer brushes were synthesized via surface initiated atom transfer radical polymerization using initiator self‐assembled on Au surface. The chemical structures of azobenzene derivatives were confirmed by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (NMR). The surface morphology of azopolymers via atom transfer radical polymerization (ATRP) for different time was investigated by atomic force microscopy (AFM). Additionally, the photoisomerization of azopolymer was measured by ultraviolet‐visible spectroscopy (UV‐Vis). The results indicate that such azopolymers can undergo trans‐cis‐trans photoisomerization efficiently by photo‐irradiation with UV light. Furthermore, this photoisomerization property could also induce the reversible adsorption of bovine serum albumin (BSA) adsorption on azopolymer brush surfaces. This adsorption kinetics of the reversible process can be measured by surface plasmon resonance (SPR) spectroscopy in situ. It suggests that the protein biochips could be regenerated safely by UV irradiation rather than by being rinsed with chemical reagents.     

Stepwise Reduction of 9,10‐Bis(dimesitylboryl)anthracene

Stepwise reduction of 9,10‐bis(dimesitylboryl)anthracene afforded an radical anion and a dianion, accompanied by stepwise changes of the aromaticity of the anthracene moiety. The radical has a planar semiquinoidal structure, while the dianion has a puckered quinoidal structure. The alteration of the geometries of the 9,10‐bis(dimesitylboryl)anthracene upon reduction is rationalized by the nature of the bonding. These results have been confirmed by cyclic voltammetry, X‐ray crystallography, NMR, EPR, and UV‐vis‐NIR spectroscopy, as well as DFT calculations.     

New generation of organosilyl radicals by photochemically induced homolytic cleavage of silicon-boron bonds

Unlike bis(diethylamino)organosilylboranes, bis(diisopropylamino)organosilylboranes, which have UV absorption at longer wavelength than 300 nm, undergo photolysis to afford pairs of an organosilyl radical and a bis(diisopropylamino)boryl radical by homolytic scission of the silicon-boron bonds. Generation of organosilyl radical and organoboryl radical was confirmed by trapping experiments using TEMPO (2,2,6,6-tetramethylpiperidine N-oxyl). The organosilyl radical thus generated induces not only silylation of mono-olefins and silylative cyclization of dienes but also polymerization to afford polymers bearing organosilyl termini. On the other hand, the bis(diisopropylamino)boryl radical generated is not incorporated into the olefin adducts.     

Reactions of OH and NO radicals with 1,1-dichloroethylene in argon matrices. FTIR and theoretical studies

HONO/1,1-dichloroethylene/Ar matrices were subjected to UV radiation (lambda > 340 nm) from a medium pressure mercury lamp. The products of the photolysis were studied experimentally by means of FTIR spectroscopy and theoretically using the ab initio MP2 method. Two conformers of 2-nitroso-2,2-dichloroethanol molecule have been identified as the final products of the double addition reaction of the OH, NO radicals to 1,1-dichloroethylene. The additional reactive species observed in the matrix is tentatively identified as an 1,1-dichloro-2-hydroxyethyl radical, an intermediate formed by single addition of OH to 1,1-dichloroethylene. The three photoproducts have been identified and observed for the first time. The identities of the products have been justified by comparison with the experiments with deuterated DONO and by performing concentration and annealing studies as well as by reference to the spectral data of related molecules. The results of the quantum mechanical calculations confirmed both the assignment of the new molecules and mechanism of the reaction observed in our experiment.     

"LIVING" FREE RADICAL SYNTHESIS OF NOVEL RODCOIL DIBLOCK COPOLYMERS WITH POLYSTYRENE AND MESOGEN-JACKETED LIQUID CRYSTAL POLYMER SEGMENTS*

The synthesis of rod-coil diblock copolymers was achieved for the firsttime by TEMPO-mediated "living" free radical polymerization of styrene and 2,5-bis[(4-methoxyphenyl)oxycarbonyl]styrene(MPCS). The block architecture of the two diblockcopolymers thus prepared, MPCS-b-St(5400/2400) and MPCS-b-St(10800/8700), was con-firmed by GPC, DSC studies and the formation of multimolecular micelles.     

Photolysis of gamma-(alpha-carboxy-2-nitrobenzyl)-L-glutamic acid investigated in the mcrosecond time scale by time-resolved FTIR

The photolytic release of substrates from caged substrates has proven to be an excellent method to generate concentration jumps for kinetic measurements in the microsecond time scale. In this report we use time-resolved FTIR in the step-scan mode to probe the photolysis mechanism of one such caged compound, namely gamma-(alpha-carboxy-2-nitrobenzyl)glutamate, and to obtain a direct measure of the rate of photorelease of the substrate glutamate. The time-resolved difference FTIR spectra exhibit specific signals that can be assigned to the reactant caged glutamate, photolytically released product glutamate, as well as to the aci-nitro intermediate, the key intermediate of the photolysis reaction. Therefore these signals allow the characterization of the kinetics of formation and decay of the intermediate and products. This is the first such report that provides a direct determination of the rate of formation of the photolysis product from a caged compound in the microsecond time scale. Furthermore, the results presented provide a good basis for further time-resolved FTIR studies of molecular reaction mechanisms, such as ligand protein interactions, in the microsecond time scale through the photolytic release of substrates from caged compounds.     

Photochemistry of an azido-functionalized cryptand: controlling the reactivity of an extremely long-lived singlet aryl nitrene by complexation to alkali cations

Photolysis of the cryptand 1, bearing an intraannular azido substituent, results in a complex photochemistry. Low-temperature photolysis yields the triplet nitrene (3)2, which has been characterized by EPR spectroscopy. Small differences in ZFS parameters are detected between the uncomplexed nitrene-functionalized ligand (in EtOH: D' = 0.93 cm(-1)) and its sodium (NaBr@(3)2 in EtOH: D' = 0.88 cm(-1)) and potassium (KBr@(3)2 in MTHF: D' = 0.89 cm(-1)) complexes. If the photolysis of the free ligand is conducted at ambient temperature, a derivative of o-aminobenzaldehyde 4 is found to be the main product, which is formed by reaction of the o-iminoquinone methide 9 with water. The latter can be detected by UV/vis spectroscopy. Its lifetime is tau = 254 s in acetonitrile solution at ambient temperature. In the presence of diethylamine, the methyleneazepine derivative 5 is formed, which is indicative of didehydroazepine formation (7). Room-temperature photolysis of acetonitrile solutions of the sodium or potassium complexes also results in formation of the o-aminobenzaldehyde derivative. In the presence of diethylamine, however, no methyleneazepine 5 is found. Formation of the aniline derivative 8 instead points to free radical processes. Laser flash photolysis (LFP) of acetonitrile solutions of 1 leads to the detection of a short-lived (tau = 1.4 mus, lambda(max) = 445 nm plus weak absorption at lambda > 500 nm) intermediate A, which decays to transient B (tau = 8 ms, lambda(max) = 295 and ca. 350-400 nm). LFP of acetonitrile solutions of complexes NaBr@1 and KBr@1 gives similar transient spectra. In the presence of sodium and potassium cations, the lifetime of the short-lived transient A is reduced (Na(+): A', tau = 200 ns; K(+): A", tau = 160 ns). Transients A' and A" decay to long-lived transients B' + C' (B" + C"). Based on the results of our product studies, a comparison with the low-temperature results, and quantum mechanical calculations, the transients A, A', and A" are identified as singlet nitrenes (1)2, NaBr@(1)2, and KBr@(1)2, while the long-lived transients B, B', and B" are assigned to didehydroazepines 7, NaBr@7, and KBr@7. Transients C' and C" can be assigned to aminyl radicals NaBr@16 and KBr@16.