Magnetic field effect on photoinduced electron transfer between [Cu(phen)2]2+ and DNA

The magnetic field effect (MFE) on the photoinduced electron transfer (PET) reaction between the [Cu(phen)2]2+ complex and DNA has been studied in homogeneous buffer medium and in reverse micelles. The copper complex on photoexcitation can oxidize DNA in a deoxygenated environment. A prominent MFE is found even in a homogeneous aqueous medium for the triplet born radicals. The process of partial intercalation of [Cu(phen)2]2+ complex within DNA is responsible for such a rare observation. In reverse micelles, the MFE is not very much prominent because of the large separation distance between the component radicals of the geminate radical ion pairs generated through PET.     

An efficient, high yielding protocol for the synthesis of functionalized quinolines via the tandem addition/annulation reaction of o-aminoaryl ketones with α-methylene ketones

A mild and efficient method has been developed for the condensation of 2-aminoaryl ketones with α-methylene ketones in the presence of a catalytic amount of reusable catalyst CeCl₃·7H₂O (25 mol %) at ambient temperature to afford the corresponding poly-substituted quinolines in high yields under mild conditions.     

Mixed protonic-electronic conduction and dielectric response in layered vanadyl phosphate nanocomposites

The layered vanadyl phosphate, VOPO(4)2H(2)O, is employed to prepare nanosized conducting polypyrrole by redox intercalation method. Transport and dielectric properties of various compositions have been investigated by impedance technique over a temperature range of 300-120 K. Grain boundary conductivity is larger than the bulk conductivity. The conductivity reveals a discontinuity at about 212-235 K. The conductivity is predominantly ionic at high temperature and electronic at low temperature. The dielectric spectra reveal a peak in the frequency range up to 2 MHz for higher concentration of intercalated polypyrrole. The activation energy of conductivity relaxation is different from that of total conductivity derived from the impedance plot.     

Thermal Analysis of Polypropylene Hydroperoxide

Studies on the low temperature oxidation of polyolefins have been the subject matter of several investigations because of interest in understanding the aging and weathering of polymers. One of the key steps in such an oxtdatton is the formation of hydroperoxide. Estimation of the hydroperoxide in oxidized samples, which is conventionally done by iodometric titrations, is quite important to gain knowledge about the kinetics and mechanism of the process. The present investigation is the first report of the thermal analysis of polypropylene hydroperoxide samples from two angles: (1) the thermal behavior of its decomposition and (2) whether such an analysis leads to knowledge of the concentration of hydroperoxide in the sample.     

Note New Organic Polymers. 5. Synthesis of Poly(2-Vinyl-3-Substituted-4-Quinazolone)s

Heterocyclic polymers are well known for their outstanding thermal stability [I]. Sillion et al. [2, 31 reported that polyquinazolones prepared from 6,6′-bi(3,1-benzoxazin-4-one) substituted in the 2-position by a methyl or phenyl group and aromatic diamines are soluble in m-cresol and possess good thermal stability. The present paper deals with the synthesis of polyquinazolones from poly [l-(2-carboxyanilinocarbonyl)ethylene]. See Figs. 1 and 2.     

Solvation dynamics in ionic liquid swollen p123 triblock copolymer micelle: a femtosecond excitation wavelength dependence study

Femtosecond solvation dynamics of coumarin 480 (C480) in a mixed micelle is reported. The mixed micelle consists of a triblock copolymer (PEO)20-(PPO) 70-(PEO)20 (Pluronic P123) and an ionic liquid (IL), 1-pentyl-3-methylimidazolium tetrafluoroborate ([pmim][BF4]). At a low concentration (0.3 M), the sparingly water soluble IL ([pmim][BF4]) penetrates the hydrophobic PPO core of the P123 micelles. Thus emission maximum of C480 in the core (accessed at lambdaex=375 nm) in 0.3 M IL is red-shifted by 8 nm from that in its absence and the red edge excitation shift (REES) is large (19+/-1 nm). At a high concentration (0.9 M), the ionic liquid [pmim][BF4] invades both the core and corona region and the mixed micelle exhibits very small REES (3+/-1 nm). Anisotropy decay and solvation dynamics in different regions of the mixed micelle are studied by variation of excitation wavelength (lambda ex). In P123 micelle, the average rotational time () is 2800 ps in the core (at lambdaex=375 nm) and 1350 ps in the corona region (at lambdaex=435 nm). In 0.3 M [pmim][BF4], tau rot at the core of the mixed micelle decreases to 1950 ps while that in the corona remains unaffected. In 0.9 M IL, both the core and corona (lambda ex=375 and 435 nm) exhibit similar and short approximately 600 ps. In 0.3 M IL, solvation dynamics in the core region (lambdaex=375 nm) of P123 micelle is about 2 times faster than in its absence. In 0.3 M IL, solvation dynamics in the corona region (lambdaex=435 nm) is approximately 100 times faster than that in the core. In 0.9 M IL, the solvation dynamics in the core and in the corona is, respectively, approximately 9 times and 4 times faster than that in 0.3 M IL.     

Mesoporous silica functionalized with diethylenetriamine moieties for metal removal and thermodynamics of cation–basic center interactions

The inorganic–organic hybrid material was synthesized by co-condensation of tetraethylorthosilicate and the organosilane N-[3-(trimethoxysilyl)propyl]diethylenetriamine. Spectroscopic analysis of the hybrid material by FTIR showed bands at 2937 and 2839 cm⁻¹ related to ν(CH); ²⁹Si NMR spectrum gave signals at −108, −99, −68 and −59 ppm, Q⁴, Q³, T⁴ and T² species related to the silica backbone structure. The well-defined peaks obtained in the ¹³C NMR spectrum in the 10–58 ppm region confirmed the attachment of organic functional groups as pendant chains bonded into the porous silica. Particle morphology evaluated by a scanning electron microscopic (SEM) study showed the formation of spherical particles in the nanometer range. The X-ray diffraction pattern showed a peak at a 2θ of 2.3°, demonstrating the mesoporous characteristic of the synthesized material. Adsorption evaluated by batch equilibrium processes gave the maximum adsorption of 2.2 and 2.8 mmol g⁻¹ for copper and nickel, respectively. From these values a stoichiometry of 2:1 for cation/ligand was established, considering the amount of 1.2 mmol of pendant groups per gram of the hybrid material. Thermodynamic parameters related to the adsorption of metal ions, evaluated using the calorimetric titration technique presented a negative Gibbs free energy value, in agreement with the spontaneity of cation removal on the basic center in the mesoporous silica at the solid/liquid interface.     

Reactions of reducing radicals with 2- and 3-nitroanilines in aqueous solutions: a pulse radiolysis study

Reactions of 2- and 3-nitro anilines (2- and 3-NA) with e_aq⁻, H-atoms and one-electron reductants have been studied using pulse radiolysis in aqueous solutions. Reactions of e_aq⁻ were found to be quite fast with both 2-NA and 3-NA resulting in their corresponding semi-reduced species which are reducing in nature. Reduction potentials for 2-NA/2-Na^•′ have been estimated to be approx. −0.56 Vvs. NHE and that for 3-NA/3-NA^•− was found to be between −0.185 V and −0.45 Vvs. NHE. Semi-reduced 2-NA has main absorption peak at 300 nm with a shoulder in the 350 nm region and a broad weak band in the 470–500 nm region, whereas semi-reduced 3-NA possesses an absorption peak at 520 nm. Reducing radicals such as (CH₃)₂ C^•OH and CO₂^•− reacted with 2-NA, producing semi-reduced species, whereas reactions of these radicals with 3-NA produced their corresponding radical-adduct species.     

A quasi-tetrahedral Cu4 cluster and a helical-chain copper (II) complex with single syn-anti carboxylate bridges: crystal structure and magnetic properties

A tridentate Schiff base carboxylate ligand, derived from the condensation of pyridine 2-carboxaldehyde with anthranilic acid, reacts with copper trifluoroacetate salt to give rise to the helical chain complex [Cu(C(13)H(9)N(2)O(2))(F(3)CCO(2))](n)() (1) and with copper nitrate to give rise to the tetranuclear complex [[Cu(4)(C(13)H(9)N(2)O(2))(4)(H(2)O)(4)].3.5NO(3).0.5N(3)] (2) with the addition of azide salt. The structures of these complexes have been solved by X-ray crystallography. The Cu(II) ions are in a distorted square-pyramidal environment in complex 1. They are sequentially bridged by carboxylate groups in the syn-anti conformation, resulting in the formation of an infinite helix like chain along the crystallographic c-axis. The crystal structure of complex 2 consists of tetranuclear [Cu(4)(L)(4)(H(2)O)(4)](4+) (L = C(13)H(9)N(2)O(2)(-)) cations and isolated NO(3)(-) and N(3)(-) anions in the ratio 1:3.5:0.5, respectively, involving bridging carboxylate groups in the syn-anti conformation. For 1 the carboxylato-Cu(II) coordination is apical-basal, while for 2 it is basal-basal. From the magnetic susceptibility measurements the complex 1 is found to exhibit very weak antiferromagnetic interaction whereas a weak ferromagnetic coupling has been established for complex 2. The magnetic behavior can be satisfactorily explained on the basis of the structural data for these and related complexes.     

Kinetics and mechanism of the aminolysis of aryl phenyl chlorothiophosphates with anilines

Kinetic studies of the reactions of aryl phenyl chlorothiophosphates (1) and aryl 4-chlorophenyl chlorothiophosphates (2) with substituted anilines in acetonitrile at 55.0 degrees C are reported. The negative values of the cross-interaction constant rhoXY (rhoXY = -0.22 and -0.50 for 1 and 2, respectively) between substituents in the nucleophile (X) and substrate (Y) indicate that the reactions proceed by concerted SN2 mechanism. The primary kinetic isotope effects (kH/kD = 1.11-1.13 and 1.10-1.46 for 1 and 2, respectively) involving deuterated aniline nucleophiles are obtained. Front- and back-side nucleophilic attack on the substrates is proposed mainly on the basis of the primary kinetic isotope effects. A hydrogen-bonded, four-center-type transition state is suggested for a front-side attack, while the trigonal bipyramidal pentacoordinate transition state is suggested for a back-side attack. The MO theoretical calculations of the model reactions of dimethyl chlorothiophosphate (1') and dimethyl chlorophosphate (3') with ammonia are carried out. Considering the specific solvation effect, the front-side nucleophilic attack can occur competitively with the back-side attack in the reaction of 1'.