Photocatalytic degradation of nitrobenzenes with combustion synthesized nano-TiO2

The photocatalytic degradation of nitrobenzene and substituted nitrobenzenes under UV exposure was investigated with combustion synthesized nano-TiO2 and commercial TiO2 catalyst, Degussa P-25. The experimental data indicated that the photodegradation kinetics was first order. The photocatalytic degradation rates were considerably higher when catalyzed with combustion synthesized TiO2 compared to that of Degussa P-25. The degradation rate coefficients followed the order: 1-chloro,14-dinitrobenzene similar or equal to 4-nitrophenot > 2-nitrophenol > 1-chloro.4-nitrobenzene > 3-niti-ophenol > 2,4-dinitrophenol > 1-chloro,2-nitrobenzene > nitrobenzene > 1,3-dinitrobenzene. Plausible mechanisms and reasons for the observation of the above order are discussed.

Crystal structure of 8-methoxy-3-dibromoacetylcoumarin, C12H8Br2O4

C12H8BT2O4. monoclinic, P12(1)/cl (No. 14), a = 11.546(2) Angstrom, b = 6.885(4) Angstrom,= 15.949(3) Angstrom, beta = 101.75(2)degrees, V= 1241.3 Angstrom(3), Z = 4, p(m) = 2.040 g.cm(-3), R-all(F) = 0.039, wR(all)(F) = 0.043, T = 300 K.

Structure of 2',3'-O-isopropylideneguanosine dimethylsulfoxide solvate

CI3H17N5Os.C2H6OS, Mr=401.23, orthorhombic,P21212 p grown from Me2SO, a = 10.749 (2),b = 13.219 (2), c = 14.056 (2) A, V= 1997-23 A 3, Z =4, D_=1.40, D x=l.335Mgm -3, 2(CuKa)= 1.5418/~', g = 1.694 mm -~, F(000) = 848.00, T=293K, R =0.0538, wR =0.0634 for 2105 unique reflections with F > 3o(F). The asymmetric unit contains one nucleoside molecule with a disordered solvent Me2S_O molecule. The geometry about the C(4')-C(5') bond is gauche-gauche. The guanosine base is in the anti conformation with the furanose ring having C(3')-exo (E 3) puckering. The bases do not show any stacking in contrast to other guanosine-containing structures. The crystal structure is stabilized by N--H...N and N--H...O hydrogen bonding.

The structure of 3[beta],20[alpha]-bis(dimethylamino)pregn-5-en-18-ol

Abstract. C25H44N20 , M r= 388.6, orthorhombic, P21212 I, a = 6.185 (2), b = 18.123 (2), c = 20.852 (2) A, U= 2337.2 A 3, Z = 4, D x = 1.104 Mg m -a, 2(Cu Ka) = 1.5418 A,/~ = 0.47 mm -~, F(000) = 864, T= 293 K. Final R - 0.038 for 1791 reflections with I >_ 3a(I). Rings A and C are in chair conformation. Ring B is in an 8fl,9a-half-chair conformation. Ring D adopts a conformation in between 13fl,14a-half-chair and 13t-envelope. There is a quasitrans fusion of rings A and B, whilst ring systems B/C and C/D are trans fused about the bonds C(8)-C(9)and C(13)-C(14).

Syntheses, spectroscopy, structures, and conformations of .lambda.3-cyclotriphosphazanes: role of negative hyperconjugation

The reactions of As-chlorocyclotriphosphazane [EtNPCl], with phenols or trifluoroethanol yield the respective aryloxy- or trifluoroethoxy-containingX 3-cyclotriphosphazanes [EtNP(OR)]3 (R = C6H4Br-4 (2),C 6H5 (3C,6 H3-Mez-3,5 (4), C6H3Mez-2,6 (5), CH2CF3 (6)) as their cis-transisomericmixtures. The products have beencharacterized by IRand NMRspectroscopy. Thecrystalstructuresofboth thecis (2a) and trans(2b) isomer_softhep-bromophenoxy derivative have been determined by X-ray diffraction. Crystal data for 2a: triclinic, P1, a = 9.872(4) A, b = 13.438(6) A, c = 13.548(8) A, CY = 117.02(5)', 0 = 96.00(6)', y = 105.38(4)O, Z = 2, final R = 0.080. Crystal data for 2b: monoclinic, P21/n, a = 12.721(6) A, b = 13.468(7) A, c = 17.882(5) A, /3 = 101.62(3)O, Z = 4, final R = 0.066. The cis isomer exhibits a chair-triaxial conformation and the trans isomer a boat-triaxial conformation. Conformational preferences of X3-cyclotriphosphazanes have been probed by both MNDO and ab initio calculations on model systems [HNPXIp (X = H, F). In addition to vicinal lone pair repulsions, negative hyperconjugative interactions involving the nitrogen lone pairs and adjacent P-X Q* orbitals are found to be important (especially when X is an electronegative substituent) in determining the conformational preferences of X3-cyclotriphosphazanes. The calculations also show that the axial - equatorial conversion at phosphorus has a large activation barrier in these systems

CoMn2O4 spinel from a MOF: synthesis, structure and magnetic studies

A hydrothermal reaction of Mn(OAc)(2)center dot 4H(2)O, Co(OAc)(2)center dot 4H(2)O and 1,2,4 benzenetricarboxylic acid at 220 degrees C for 24 h gives rise to a mixed metal MOF compound, CoMn2(C6H3(COO)(3))(2)], I. The structure is formed by the connectivity between octahedral CoO6 and trigonal prism MnO6 units connected through their vertices forming a Kagome layer, which are pillared by the trimellitate. Magnetic susceptibility studies on the MOF compound indicate a canted anti-ferromagnetic behavior, due to the large antisymmetric DM interaction between the M2+ ions (M = Mn, Co). Thermal decomposition studies indicate that the MOF compound forms a tetragonal mixed-metal spinel phase, CoMn2O4, with particle sizes in the nano regime at 400 degrees C. The particle size of the CoMn2O4 can be controlled by varying the decomposition temperature of the parent MOF compound. Magnetic studies of the CoMn2O4 compound suggests that the coercivity and the ferrimagnetic ordering temperatures are dependent on the particle size.

Structural variants of hyperbranched polyesters

Hyperbranched polyesters based on 3,5-dihydroxybenzoic acid and its derivatives were prepared by self-condensation of the corresponding ester under standard trans-esterification conditions. The spacer segment length that connects the branching points was systematically varied by starting from the appropriate ethyl 3,5-bis(omega-hydroxyoligo(ethyleneoxy))benzoate. The thermal properties of the hyperbranched polyesters were studied using DSC, and they have been compared with those of the linear analogues prepared from the corresponding p-hydroxybenzoic acid derivatives and also with the molecularly ''kinked'' analogues prepared from the meta isomers. These hyperbranched polyesters were also terminally functionalized by using a potentially mesogenic 4-butoxybiphenylcarboxylic acid derivative in an attempt to prepare novel hyperbranched liquid crystalline polyesters. This was achieved by copolymerization of the AB(2) monomer with the mesogenic A-type capping unit. These polymers were found to be amorphous and did not exhibit any liquid crystalline phases, probably due to the random distribution of the mesogenic segments on the polymer framework, making it difficult to both crystallize and form mesophases.

Structure of 4,6-Diacetylresorcinol

C10H10O4, M(r) = 194.19, monoclinic, P2(1)/c, a = 7.089 (1), b = 11.361 (1), c = 11.656 (1) angstrom, beta = 100.45 (3)-degrees, V = 922.92 (1) angstrom 3, Z = 4, D(m) = 1.410 (5), D(x) = 1.397 Mg m-3, lambda(Cu K-alpha) = 1.5418 angstrom, mu(Cu K-alpha) = 0.89 mm-1, T = 300 K, F(000) = 408, final R = 0.057 for 1701 observed reflections. The molecule is almost planar, with O(9) and O(12) of the acetyl groups deviating by 0.074 (1) and 0.071 (2) angstrom from the mean plane of the benzene ring. The bond lengths and bond angles of the benzene ring are normal. There are intramolecular hydrogen bonds between O(9) and H(14) and between O(12) and H(13); there are no intermolecular hydrogen bonds. The molecules are packed in layers parallel to the ac plane and are held together essentially by van der Waals interactions.

Structure of N-nitroso-r-2,c-7-diphenylhexahydro-1,4-diazepin-5-one

C17H17N3O2, M(r) = 295.34, orthorhombic, P2(1)2(1)2(1), a = 7.659 (1), b = 12.741 (1), c = 15.095 (1) angstrom, V = 1473.19 (2) angstrom 3, Z = 4, D(m) = 1.33, D(x) = 1.32 Mg m-3, lambda(Cu K-alpha) = 1.5418 angstrom, mu = 0.68 mm-1, F(000) = 624, T = 295 K, R = 0.031 for 1549 unique observed reflections with I > 2.5-sigma(I). The seven-membered heterocyclic ring adopts a boat conformation flattened at the nitroso end of the ring. The substituent phenyl rings occupy pseudo-axial positions and the nitroso group is coplanar with the C(2), N(1), C(7) plane of the central ring. The crystal structure is stabilized by intermolecular N-H...O and weak C-H...O hydrogen bonds.

1H and 13C NMR spectral studies of conformation of some N-(2-pyridinyl)-3-pyridinecarboxamides

The 1H and 13C NMR spectra of N-(2-pyridinyl)-, N-(4-methyl2-pyridinyl)-, and N-(6-methyl-2-pyridinyl)-3-pyridine-carboxamides (1�3, respectively) and 3-pyridinecarboxamide (4) in different solvents have been analysed using COSY, HETCOR, chemical shift and coupling constant correlations. The conformations of 1�4 have been obtained by utilizing the NMR spectra, NOE experiments and MINDO/3 calculations. In dilute solutions, the 2-pyridyl ring is coplanar with the amide group while the 3-pyridyl ring is apparently not. Compounds 1�3 dimerize through cooperative hydrogen bonding in concentrated CDCl3 solution (approximately 0.1 M) and the structure of the dimer resembles some of the DNA base-pairs. Hydrogen bonding between N---H and the solvent molecules hinders dimerization in (CD3)2CO and CD3CN.

[n]peristylanes and [n]oxa[n]peristylanes (n = 3-6): A theoretical study

Theoretical studies at the HF and Becke3LYP levels using 6-31G* basis sets were carried out on a series of [n]peristylanes and [n]oxa[n]peristylanes (n = 3-6) to understand their structure and energetics. The structures of the [3]- and [4]peristylanes (1, 2) and their era-derivatives (5, 6) were calculated to have the anticipated high symmetry, C-nv. In contrast, a C-s structure (9) at HF/6-31G* and another (25) at the Becke3LYP/6-31G* level were calculated for the [5]oxa[5]peristylane. The energy difference between them is extremely small even though there are major differences in the structures indicating every soft potential energy surface: On the other hand, the potential energy surface of [6]oxa[6]peristylane is not as soft. Similar structures were also calculated for the top rings. Calculations on the seco-compounds 11-14 and 15-19 (Table 4) indicate that there is no unusual strain involved in the formation of 27 from 19. The Li+ interaction energies of the [n]oxa[n]peristylanes are 61.7 (n = 3), 72.8 (n = 4), 84.2 (n = 5) and 91.7 (n = 6) kcal mol(-1) at the Becke3LYP/6-3IG* level. Dramatic differences between the C-C bond lengths obtained from the solid state X-ray diffraction studies and those from the calculations for the [n]oxa[n]peristylanes were also observed.

Probing the limits of steric constraints in the oligomerization of copper(I) complexes: structures of two sterically congested oligomers

Oligomeric copper(I) clusters are formed by the insertion reaction of copper(I) aryloxides into heterocumulenes. The effect of varying the steric demands of the heterocumulene and the aryloxy group on the nuclearity of the oligomers formed has been probed. Reactions with copper(I)2-methoxyphenoxide and copper(I)2-methylphenoxide with PhNCS result in the formation of hexameric complexes hexakis[N-phenylimino(aryloxy)methanethiolato copper(I)] 3 and 4 respectively. Single crystal X-ray data confirmed the structure of 3. Similar insertion reactions of CS2 with the copper(I) aryloxides formed by 2,6-di-tert-butyl-4-methylphenol and 2,6-dimethylphenol result in oligomeric copper(I) complexes 7 and 8 having the (aryloxy)thioxanthate ligand. Complex 7 was confirmed to be a tetramer from single crystal X-ray crystallography. Reactions carried out with 2-mercaptopyrimidine, which has ligating properties similar to N-alkylimino(aryloxy)methanethiolate, result in the formation of an insoluble polymeric complex 11. The fluorescence spectra of oligomeric complexes are helpful in determining their nuclearity. Ir has been shown that a decrease in the steric requirements of either the heterocumulene or aryloxy parts of the ligand can compensate for steric constraints acid facilitate oligomerization. (C) 1999 Elsevier Science Ltd. All rights reserved.

A facile entry into a new class of spiroheterocycles: synthesis of dispiro[oxindolechromanone/flavanone/tetralone]pyrroloisoquinoline ring systems

A series of novel dispiroheterocyclic systems have been synthesized by the cycloaddition of a new azomethine ylide generated by the decarboxylative route from tetrahydroisoquinoline-3-carboxylic acid and isatin with various dipolarophiles containing exocyclic double bond such as 3-arylidene-4-chromanone, 3-arylidene-4-flavanone and 2-arylidenetetrahydro-1-naphthalenone in moderate to good yield. The regio and stereochemistry of the title compounds was established by single crystal X-ray structure and spectroscopic techniques. (C) 2002 Elsevier Science Ltd. All rights reserved.

Dicopper(II) complexes showing DNA hydrolase activity and monomeric adduct formation with bis(4-nitrophenyl)phosphate

Ferromagnetic dicopper(II) complexes [Cu(2)(mu-O(2)CCH(3))(mu-OH)(L)(2)(mu-L(1))](PF(6))(2), where L = 1,10-phenanthroline (phen), L(1) = H(2)O in 1 and L = dipyrido[3,2-d:2',3'-f]quinoxaline (dpq), L(1) = CH(3)CN in 2, are prepared and structurally characterized. Crystals of 1 and 2 belong to the monoclinic space group of P2(1)/n and P2(1)/m, respectively. The copper(II) centers display distorted square-pyramidal geometry having a phenanthroline base and two oxygen atoms of the bridging hydroxo and acetate group in the basal plane. The fifth coordination site has weak axially bound bridging solvent molecule H(2)O in 1 and CH(3)CN in 2. The Cu center dot center dot center dot Cu distances are 3.034 and 3.046 angstrom in 1 and 2, respectively. The complexes show efficient hydrolytic cleavage of supercoiled pUC19 DNA as evidenced from the mechanistic studies that include T4 DNA ligase experiments. The binuclear complexes form monomeric copper(II) adducts [Cu(L)(2)(BNPP)](PF(6)) (L = phen, 3; dpq, 4) with bis(4-nitrophenyl)phosphate (BNPP) as a model phosphodiester. The crystal structures of 3 and 4 reveal distorted trigonal bipyramidal geometry in which BNPP binds through the oxygen atom of the phosphate. The kinetic data of the DNA cleavage reactions of the binuclear complexes under pseudo- and true-Michaelis-Menten conditions indicate remarkable enhancement in the DNA hydrolysis rate in comparison to the control data. (C) 2011 Elsevier B.V. All rights reserved.

Solubilities of Pb+2, Bi+3, Sb+3 and Cu+1 sulphides in (NaCl KCl Na2S) melts

Solubilities of common metal sulfides have been determined in the (NaCl+KCl) eutectic melt with and without Na2S. A novel gas-phase equilibrium technique has been used for PbS, Bi2S3, and So2S3, and an improved liquid phase equilibrium technique for Cu2S, which eliminates the errors due to physical entrapment of the sulfide phase and segregation on quenching, enabling precise measurements to be made. Solubilities in the (NaCl+KCl) eutectic melt were determined as a function of temperature in the rante 700° to 950°C, and were found to be small. The partial molar heats of mixing of the sulfides in the eutectic melt have been calculated from the solubility measurements, to be 13.3, 31.4, 37.1, and 49.0 kcal for PbSs), Sb2S2(l), and Cu2S(s), respectively. Sodium sulfide addition was observed to enhance these solubilities, the effect being largest for Cu2S followed by Sb2S3, Bi2S3, and PbS. This effect is explained qualitatively. It was observed that PbS and Sb2S3 obey Henry's law up to saturation in (NaCl+KCl+Na2S) melts.