Dynamics of flavin containing radical pairs in SDS micellar media probed by static and pulse magnetic field effect and pulse ADMR

ABSTRACT

The dynamics of the radical pairs generated from the electron transfer reaction from indole derivatives to flavin derivatives are studied by three techniques, time resolved magnetic field effect (TR-MARY) and pulse absorption detected magnetic resonance (ADMR), and absorption detected switching of external magnetic field techniques (AD-SEMF). The three techniques complementarily work for the precise analysis of the radical pair kinetics. The results by all three techniques reflect the difference of the hydrophobic nature of the radicals in the lifetime of RP in a micelle. Overcoming the difficulty of the determination of the short RP lifetime under the nearly quasi steady state due to slow and inhomogeneous decay kinetics of the precursor triplet excited state, AD-SEMF analysis enabled us to determine the kinetic parameters, which is consistent with the qualitatively observed by the other techniques.     

Magnetic field dependence of the deactivation rates of triplet azocumene in solution

The triplet sensitized photo-decomposition of azocumene into nitrogen and cumyl radicals is investigated by time resolved EPR and optical absorption spectroscopy. It is found that the cumyl radicals carry an initial spin polarization and are formed with a yield that depends on both the solution viscosity and the strength of an external magnetic field. The phenomenon is interpreted in terms of a depopulation-type triplet mechanism, i.e. a competition between decay into radicals and fast, triplet sublevel selective intersystem crossing (ISC) back to the azocumene ground state. Analysis of the data yields relative rate constants for the ISC processes and the cleavage reaction of triplet azocumene. The energetically lower zero field triplet substate is depopulated by ISC about seven times faster than the upper one and about two orders of magnitude faster than depopulation by cleavage occurs. Cleavage probably takes place on the nanosecond time scale, while the ISC must proceed on the picosecond scale, as at elevated viscosity it becomes faster than the rotational Brownian motion of the molecule.     

Magnetic field effects on the hydrogen abstraction reaction of triplet 4-methoxybenzophenone with thiophenol as studied by a picosecond laser flash photolysis technique

The hydrogen abstraction reaction of triplet 4-methoxybenzophenone with thiophenol at 265 K has been studied with a newly developed picosecond laser flash photolysis apparatus under magnetic fields of 0–1.7 T. The decay rate constant of the radical pair generated was found to increase from 3.42 × 10⁹ s^?1 to 4.15 × 10⁹ s^?1 with increasing the magnetic field from 0 to 1.7 T. The observed magnetic field effects can be explained by the Δg mechanism. Using the simple kinetics model with the Δg mechanism, the rate constant of the escape process from the pair (k _esc) and two rate constants for the T-S spin conversion process (k _T-S) at 0 and 1.7 T were found to be 1.97 × 10⁹ s^?1, 1.45 × 10⁹ s^?1, and 2.12 × 10⁹ s^?1, respectively. From the magnetic field dependence on k _T-S, the difference in the g values of the 4-methoxybenzophenone ketyl and phenylthiyl radicals was estimated to be 0.0087.     

Spin polarization in fullerene derivatives containing a nitroxide group. Observation of the intermediate photoexcited quartet state in radical triplet pair interaction

A series of C₆₀ fullerene derivatives containing a nitroxide group has been photoexcited by short LASER pulses in the microwave cavity of a cw-EPR spectrometer. Strongly spin polarized signals have been observed, in glassy matrix as well as in liquid solution, for both the ground electronic state and the excited quartet state. In the quartet state the excitation resides in the fullerene part and the molecule constitutes a triplet-radical pair with the partner covalently linked. The absorptive or emissive character of the transitions is explained in terms of the mechanism of radicaltriplet interaction producing spin polarization. Opposite initial sign and polarization patterns are observed for molecules with different spacer between nitroxide and fullerene. The time evolution of the relevant sublevel populations is fitted by a kinetic model taking into account quartet decay constants, quartet and doublet spin-lattice relaxation rates and branching ratios.     

Effect of electric fields on photoluminescence of 4-(dicyanomethylene)-2-methyl- 6-(p-dimethylaminostyryl)-4H-pyran

Electric-field-induced photoluminescent variation has been observed from the red-emitting dopant, 4-(di cyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM). The layered structure of Al/tris-(8-hydroxyquinoline) aluminum (Alq)/DCM-doped Alq (Alq:DCM)/indium tin oxide studied, exhibits relatively enhanced red emission when a voltage is applied such that the electric field runs directly from the Alq:DCM layer to the Alq layer, and relatively enhanced green emission in the opposite direction of the field . This phenomenon is attributed to field-enhanced aggregation and permeation of DCM molecules due to the polarity of the molecule. PACS 78.55.Kz; 68.55.Ln; 85.60.Jb; 78.66.Qn; 78.20.Jq     

Magnetic field effects on the yields of dyes in sensitized transformation of diphenylamine in micellar systems

A strong influence (an increase in the rate of formation of the diphenylbenzidine dication by up to three times) of an external magnetic field on the yields of colored products was observed when micellar solutions of benzophenone and diphenylamine derivatives were UV irradiated in the presence of acids. A mechanism of the phenomenon was suggested. The mechanism by based on the concept of the simultaneous occurrence of two processes, (1) geminate recombination of ketyl and aminyl radicals with the formation of triarylmethane dye and (2) bulk recombination of two radical cations produced in the protonation of aminyl radicals with the formation of the diphenylbenzidine dication. Magnetic field is a factor determining the rate of the triplet-singlet conversion of radical pairs formed in the photoreduction of the ketone by amine and, therefore, the ratio between the stationary concentrations of aminyl radicals and radical cations. The influence of the structure of ketones, the ratio between the reagents and surfactant, and the pH value on the dye yield and the scale of magnetic-spin effects were analyzed.     

Conformational analysis of 2,3-dihydro-3-O-(1,4-naphthoquinon-2-yl)-2-oxo-1,4-naphthoquinone derivatives by the density functional method and IR spectroscopy

We have used the PBE/3z, B3LYP/6-31G, B3LYP/6-31G(d), and B3LYP/6-311G(d) methods to study the conformational mobility of 2,3-dihydro-3-O-(1,4-naphthoquinon-2-yl)-2-oxo-1,4-naphthoquinones (1–4). We have shown that more than 99% of these compounds exist as the major tautomeric form, while differences in the structure of the Q_2H (2,3-dihydro-2-oxo-1,4-naphthoquinones) and Q_1,4 (1,4-naphthoquinon-2-yl) moieties lead to qualitative differences in the internal rotation potentials of the ethyl substituents V(θ_Et−1) and V(θ_Et−2), and consequently each of compounds 1−4 exists as six different rotameric forms. For diquinone 3, we have calculated the dependences of the frequencies (ν) and intensities (A) of the normal vibrations on the torsional angles θ_Et−1 and θ_Et−2, and also on the changes in the geometry of the ether bond. We have found that the values of ν and A for the bands in the carbonyl region of the IR spectrum change little on going from one rotameric form to another, and also for the in-plane bends of the ether bond, and change considerably for the out-of-plane bends of the ether bond. However, for T ≤ 300 K, there is no qualitative change in the overall contour, and it can be interpreted based on a simple additive model. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 5, pp. 573–581, September–October, 2006.     

Calculation of frequencies of normal vibrations and interpretation of IR spectra for 2,3-dihydro-3-O-(1,4-naphthoquinon-2-yl)-2-oxo-1,4-naphthoquinone derivatives

We have used B3LYP/6-31(d) density functional theory to calculate the frequencies and modes of the normal vibrations of 2-oxo-2,3-dihydro-and 2-methoxy-1,4-naphthoquinones. Based on these calculations within an additive model, we have assigned the carbonyl bands in the IR spectra of 2,3-dihydro-3-O-(1,4-naphthoquinon-2-yl)-2-oxo-1,4-naphthoquinones (diquinones 1–4). We have carried out a direct calculation of the vibrational spectra for diquinones 1–4 using PBE and B3LYP correlation functionals. We have shown that the calculation of the vibrational spectra of the diquinones based on an additive model on the whole is quite consistent with the results of direct calculations and the experimental spectra. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 6, pp. 713–720, November–December, 2006.     

Magnetic-field dependent optically detected ESR in the photoexcited triplet states of bridged Zr(IV) metallocenes

We report on the magnetic-field-dependent optically detected magnetic resonance (ODMR) spectra for polycrystalline samples of the bridged Zr(IV) metallocenes, Me₂Si<(Cp₂)ZrCl₂ ( (dimethylsilylbis(cyclopentadienyl)zirconium-dichloride) and Me₂C<(Cp₂)ZrCl₂ (iso-propylidenebis(cyclopentadienyl)zirconium-dichloride). ODMR spectra at zero magnetic field were recorded by frequency sweeping a microwave source from 0.1 to 10 GHz with the sample contained in a microwave helix. ODMR spectra at finite magnetic fields were recorded with the sample contained in either a helix or a slotted-tube resonator with a fixed microwave frequency and sweeping the magnetic field. For all experiments, the sample and microwave probes were contained in an immersion dewar cryostat, and the temperature was held at about 2 K. All three zero field ODMR transitions (2|E|, and |D| − |E| and |D|+|E|) were observed in the frequency-swept ODMR spectra recorded at zero and small magnetic fields. The zero-field frequency-swept spectra allowed the determination ofD andE values uniquely. For frequency-swept small-field ODMR spectra recorded at successively higher magnetic fields, each of the ODMR line intensities was observed to increase with increasing magnetic field. This intensity increase was observed for all three ODMR lines, reflecting an increase in the total intensity rather than simply a change in the polarization of the triplet sublevels. The latter would result in a change in the relative intensities of the ODMR lines but would not change simultaneously the intensities of all three lines. The ODMR line intensities increase in proportion toB ⁿ, wheren<1. This field dependence is weaker than the expected proportionalB ² dependence from the Zeeman effect, which likely originates from the magnetic field dependence of the spin relaxation rates between the triplet sublevels. Magnetic-field-swept ODMR spectra recorded at fixed microwave frequencies in the X-band frequency range (9.8 GHz) do not show all three expected classic Pake powder pattern line shape profiles, exhibited by the molecules with their magneticZ, Y, andX axes parallel to the external magnetic field. In particular, the intensity for molecular magneticY-axes parallel to the external magnetic field is completely suppressed. In addition, an external magnetic field dependence in field-swept ODMR spectra was observed, which results in a linear decrease of the ODMR intensity with increasing strength of the external magnetic field over and above that would be expected in a polycrystalline spectrum. The data are analyzed by simulation of the continuous-wave ESR spectrum with the eigenvalues and eigenvectors of the spin Hamiltonian matrix characterizing the triplet state exhibiting the ODMR spectrum, in conjunction with homotopy, as a function of the orientations of the magnetic axes of the various molecules in a polycrystalline sample. This approach is useful to interpret the experimentally observed ODMR transition frequencies andg-values but does not take the amplitudes in the ODMR spectrum. The corrections required to modify the continuous-wave ESR spectral amplitudes that reproduce the observed ODMR amplitudes are effects associated with the ODMR processes.     

Polyethylene glycol (PEG-400) promoted one-pot,five-component synthesis of (E)-ethyl2-(2-((E)-2-(1-(4-methyl-2-(phenylamino)thiazol-5yl)ethylidene)hydrazinyl)-4-oxothiazol-5(4H)-ylidene)acetates

Molecular Diversity - A facile, inexpensive and eco-friendly synthesis of functionalised...     

(2-(4-甲基-2-羟基苯基)苯并噻唑)锌的分子结构和光谱学性能

合成并研究了(2-(4-甲基-2-羟基苯基)苯并噻唑)锌(Zn(4-MeBTZ)2)的分子结构、热稳定性和光谱学特性.Zn(4-MeBTZ)2的单晶数据如下:三斜晶系,P-1空间群,晶胞参数为α=8.989 9(11)(A)b=12.161 7(15)(A),c=12.8719(16)(A),α=63.492(2)°,...     

Discovery of 5-methyl-2-(4-((4-(methylsulfonyl)benzyl)oxy)phenyl)-4-(piperazin-1-yl)pyrimidine derivatives as novel GRP119 agonists for the treatment of diabetes and obesity

A series of fused-pyrimidine derivatives were prepared and evaluated for their agonistic activities against human GPR119. Compound 9i showed high potent agonistic activity against HEK293T cells over-expressing human GPR119 and improved glucose tolerance in dose-dependent manner, as well as promoted insulin secretion. In a DIO mice model, 9i also ameliorated the obese-related symptoms by decreasing the body weights without markedly changing food intake, normalized some serum biomarkers, such as ALT, AST, ALP, GLU, CHOL, HDL, and LDL, and exerted therapeutic activity on fat deposition in liver tissue. We consider 9i to have utility as a GPR119 agonists for the treatment of type 2 diabetes mellitus and obese-related symptoms.     

“Unusual” lines observed in low-frequency cw ENDOR of photoexcited triplet state molecules: the primary donor triplet in photosynthetic reaction centers as an example

The origin of frequently observed “negative” (opposite phase) ENDOR lines in the low-frequency region of triplet state ENDOR spectra is explained in terms of microwave hole burning and RF modulation phenomena. From this, a new method of detecting burnt side holes in EPR spectra is derived which is based on cw ENDOR instrumentation. The method uses the modulation satellites that are induced by a longitudinal RF field component and appear around any EPR line, including burnt holes (“negative” lines). The longitudinal RF field was generated by a coil oriented parallel to the external field, but a longitudinal component of the RF field also exists in most conventional ENDOR spectrometers because of slight misalignments of the ENDOR coil generating the transversal RF field. The lines it induces in the low-frequency part of ENDOR spectra are generally considered as artifacts. It is shown, however, that RF induced modulation satellites provide valuable information concerning the lines distant from the spectral position in the EPR spectrum chosen for ENDOR observation. This allows one to record the pattern of side holes burnt by microwave saturation through forbidden transitions that carries information about ENDOR frequencies comparable to what can be extracted from ESEEM experiments. Such comparability is demonstrated for examples of nitrogen ENDOR of photoexcited triplet states of the primary donor in photosynthetic reaction centers and related compounds.     

1,4-bis[2-(4-pyridyl)ethenyl]-benzene衍生物热致变色研究

本文制备了三种在1,4-bis[2-(4-pyridyl)ethenyl]-benzene(bp-eb)上接枝不同烷基链长度的热致变色材料DC8、DC12、DC16. 在365 nm激发光下,随着温度升高,它们呈现出荧光颜色的改变,这种改变来自于晶体态与无定形态之间的转变. 此外,DC16也呈现出光致变色的性质. 通过差示扫描量热法测试得到的相转变温度高于实验过程中荧光颜色改变时的温度. 因此,这种变色行为来自于光与热共同作用的结果. 乙醇可以使粉末变回起始的晶体状态,从而使荧光颜色恢复,实现热致变色行为的可逆. 本研究对理解热致变色分子的结构-性质关系,指导热致变色分子设计具有重要意义.     

Magnetic properties of the new organic superconductor λ-(BETS)2GaCl4

This papr discusses the results of the first investigation of the magnetic properties of the organic superconductor λ-(BETS)₂GaCl₄. It is shown that the transition to the superconducting state begins at T _c≈7 K, which is considerably lower than the value T _c≈10 K determined from resistive measurements. The estimated value of the critical current density turns out to be two orders of magnitude lower than in superconductors of the family κ-(ET)₂ X. Zh. éksp. Teor. Fiz. 112, 760–762 (August 1997)     

Structure of 2-(2-(anthracen-9-ylmethylene)hydrazinyl)-4-(3-methyl-3-phenylcyclobutyl)thiazole by combined X-Ray crystallographic and molecular modelling studies

A single crystal of 2-(2-(anthracen-9-ylmethylene)hydrazinyl)-4-(3-methyl-3-phenylcyclobutyl)thiazole (C₂₉H₂₅N₃S) containing anthracene, thiazole and cyclobutane rings has been synthesised. The synthesised crystal structure was characterised using IR, ¹H-NMR and ¹³C-NMR spectroscopic and X-Ray analysis techniques. In the crystal, neighbouring molecules formed chains along [110] by interconnecting with N–H···N hydrogen bonding and π–π interactions. The geometrical parameters of the title compound were optimised by Gaussian 09 software in the gas phase and Quantum-Espresso software under Periodic Boundary Conditions (PBC) in the solid phase. Theoretically, IR, NMR spectra, Mulliken, NPA and AIM atomic charges, Hirshfeld surface and frontier molecular orbitals (FMOs) of the title compound were examined. Using the Hirshfeld surface and two-dimensional (2D) fingerprint graphics, the presence of intermolecular interactions in the crystal packing were analysed. The energies of these interactions and their distribution on the crystal structure were shown graphically. In general, it was seen that theoretical calculations were consistent with X-Ray results.     

Magnetic Field-Effect on Photoluminescence of Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) Nanoparticles in a Poly[vinyl butyral] Matrix

Abstract

In this work the magnetic field effects (MFE) on the photoluminescence of MEH-PPV film and nanoparticles were obtained using the MFE technique with continuous-wave photoexcitation. The analysis of the MFE dependence for the MEH-PPV film gave a HWHM (half-width at half maximum) ～ 65?mT and a total MFE value about 102.8% at 200?mT whereas the MFE dependence of the MEH-PPV nanoparticles showed significant broadening, with their HWHM ～ 280?mT and a total MFE value of 99% at 550?mT. By a simple theoretical model based on rate equations, the mechanism of the negative magnetic field effect was explained. The observed negative effect was the result of the dominant singlet exciton formation rate in the MEH-PPV nanoparticles. For explaining this negative effect the enhanced triplet-triplet annihilation due to confinement of triplet excitons in the nanoparticles and singlet molecular oxygen-triplet exciton annihilation were proposed.     

Magnetic excitations in the spin-1 anisotropic Heisenberg antiferromagnetic chain system NiCl(2)-4SC(NH(2))(2)

NiCl(2)-4SC(NH(2))(2) (DTN) is a quantum S=1 chain system with strong easy-pane anisotropy and a new candidate for the Bose-Einstein condensation of the spin degrees of freedom. ESR studies of magnetic excitations in DTN in fields up to 25 T are presented. Based on analysis of the single-magnon excitation mode in the high-field spin-polarized phase and previous experimental results [Phys. Rev. Lett. 96, 077204 (2006)10.1103/PhysRevLett.96.077204], a revised set of spin-Hamiltonian parameters is obtained. Our results yield D=8.9 K, J(c) = 2.2 K, and J(a,b) = 0.18 K for the anisotropy, intrachain, and interchain exchange interactions, respectively. These values are used to calculate the antiferromagnetic phase boundary, magnetization, and the frequency-field dependence of two-magnon bound-state excitations predicted by theory and observed in DTN for the first time. Excellent quantitative agreement with experimental data is obtained.