ESR studies of Mo?Mg oxide catalysts

For 0.1–0.5 wt.% Mo–Mg oxide samples with high concentration of⁹⁵Mo isotopes two types of Mo⁵⁺ have been identified. Their role in the formation of O ₂ ^– anion-radicals in low-temperature oxygen adsorption on reduced samples has been established.

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, ⁹⁵Mo, Mo⁵⁺ Mo–Mg (0,1–0,5 .% Mo) - O ₂ ^– .

     

Interaction of carboxyl-containing polymers with deoxypeganine

Polymeric complexes of deoxypeganine hydrochloride with a number of carboxyl-containing polymers have been synthesized and investigated. It has been found that in the interaction of polymers with deoxypeganine both hydrogen bonds and electrostatic bonds arise.Translated from Khimiya Prirodnykh Soedinenii, Vol. 33, No. 1, pp. 87–90, January–February, 1997.     

Computational study of the aminolysis of 2-benzoxazolinone

Three possible mechanisms (zwitterionic, neutral stepwise, and neutral concerted) of the ring-opening reaction of 2-benzoxazolinone (BO) upon aminolysis with methylamine were studied at the B3LYP/6-31G* level. In the gas phase, the neutral concerted mechanism is shown to be most favorable, which proceeds via a rate-determining barrier of 28-29 kcal/mol. The transition state, CTS, associated with this barrier is a four-centered one, where 1,2-addition of the N[bond]H of methylamine to the C[bond]O of BO ring occurs. The rate-determining barrier of the neutral stepwise pathway is found to be ca. 42 kcal/mol. The inclusion of solvent effects by a polarizable continuum model (PCM) does not change the conclusions based on the gas-phase study; the barrier at CTS is reduced to 20, 20, and 22 kcal/mol in water, ethanol, and acetonitrile, respectively.     

Theoretical study of isomerization by a 1,2-hydrogen shift in HAB molecules and HAB+ ions with 10 valence electrons

The potential-energy surfaces (PES's) of HAB molecules and HAB⁺ ions with the diatomic cores AB=CN^–, BO^–, BeF^–, N₂, CO, BF, CP^–, BS^–, NP, CS, BCl, SiN^–, AlO^–, SiO, AlF, SiP^–, AlS^–, P₂, SiS, and AlCl, which contain 10 valence electrons, have been calculated by the nonempirical MO-LCAO-SCF method with subsequent consideration of electron correlation in the framework of the third-order Møller—Plesset (MP3) method, and the isomerization realized by a 1,2-hydrogen shift in them has been studied. The similarities and differences in the form of the PES's corresponding to the migration of Li⁺ (which was previously investigated) and the migration of H⁺ around AB have been traced, and the geometric characteristics and relative energies of the isomers, as well as the heights of the activation barriers between them, have been compared. An attempt has been made to relate the differences in the properties to differences in the electronic structure of HAB and LiAB.Institute of New Chemical Problems, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 32, No. 2, pp. 3–11, March–April, 1991.     

Metal-peroxo versus metal-oxo oxidants in non-heme iron-catalyzed olefin oxidations: computational and experimental studies on the effect of water

Computational and experimental studies show that Fe(BPMEN)-catalyzed olefin oxidation has two (FeIII-OOH and FeV=O) oxidant species, which act with comparable activation barriers. The presence of water favors formation of an HO-FeV=O oxidant via water-assisted O-OH bond cleavage and leads to both epoxide and cis-diol products. In the absence of water, the oxidant is the FeIII-OOH [or (MeCN)FeIII-OOH], and oxidation mainly leads to epoxide. This conclusion differs from that derived from DFT investigations of iron-porphyrin-catalyzed olefin epoxidation, where the FeIII-OOH pathway is deemed too high in energy to be plausible. The difference between these two systems may lie in the more flexible coordination environment of the non-heme iron complex, which has an available adjacent coordination site that contributes to the activation of the peroxide in both wa and nwa pathways.     

Design,synthesis of novel quinazolin-4-one derivatives and biological evaluation against human MCF-7 breast cancer cell line

A new series of 6,8-dibromo-2-(4-chlorophenyl)quinazolin-4(3H)-one derivatives VI–XIII were synthesized. Their chemical structures were confirmed by spectral and elemental analysis. The cytotoxic effect of the newly synthesized compounds was tested in vitro against human breast cancer cell line (MCF-7). Most of the tested compounds have shown promising cytotoxic activity. Compounds X and XIIIb exerted a powerful cytotoxic effect against MCF-7 with a very low IC50 (0.0015 and 0.0047 µmol/ml), while compounds VI, VII, VIII, XIIb, XI, XIIIc and IX exerted a moderate cytotoxic effect (IC50 0.01523, 0.0213, 0.031, 0.0478, 0.049, 0.068 and 0.079 µmol/ml respectively), compared to doxorubicin (0.0025 µmol/ml). Exploring their apoptotic effect; interestingly,all compounds activated apoptotic cascade in MCF-7. Compounds VI, XIIIb, XIIb, XI, XIIa, VII, V and VIII showed potent effect even much more than doxorubicin by 12.87–5.91 folds, while compounds XIIIc, IX, XIIIa, XIIc and X showed moderate increase in CASP3 activity by 4.96–3.22 folds relative to untreated cells more or less similar to doxorubicin (5.57 folds).     

An experimental and density functional study of the Sb–C bond activation and organo-Rh bond formation from the spontaneous decay of [RhCl3(SbPh3)3]

The reaction of RhCl₃ with SbPh₃ that produces mer-[RhCl₃(SbPh₃)₃] 1 and trans,mer-[RhCl₂(Ph)(SbPh₃)₃] 2 [A. Cavaglioni, R. Cini, J. Chem. Soc., Dalton Trans. (1997) 1149 (and references cited therein)], as well as the transformation of 1 to 2, was studied in details using the UV–Vis spectroscopy and density functional approaches. We elucidated the mechanism of Sb–C(Ph) bond activation and Rh–C(Ph) bond formation during these processes. Experimental studies show that the first step of the reaction of RhCl₃ with SbPh₃ is the formation of 1, which later rearranges to complex 2 via a concerted mechanism. The transition state associated with this transformation includes the Rh(III) center (hepta-coordinate) that interacts with three Cl^? ligands, two Sb-centers of SbPh₃ ligands, and one Sb–Ph bond of the third SbPh₃ ligand. The Cl^? ligand, trans to Sb, bridges Rh and Sb atom from the third SbPh₃ ligand. A possible pathway involving rhodium(I) intermediate species was also taken into account. The calculated geometry parameters of models of complexes 1 and 2 are in good agreement with the available X-ray data. Presented relative energies of the studied reactions are in good agreement with the relative yields of 1 and 2.     

Ultra-low-frequency dust-electromagnetic modes in self-gravitating magnetized dusty plasmas

Obliquely propagating altra-low-frequency dust-electromagnetic waves in a self-gravitating, warm, magnetized, two fluid dusty plasma system have been investigated. Two special cases, namely, dust-Alfvén mode propagating parallel to the external magnetic field and dustmagnetosonic mode propagating perpendicular to the external magnetic field have also been considered. It has been shown that effects of self-gravitational field, dust fluid temperature, and obliqueness significantly modify the dispersion properties of these ultra-low-frequency dust-electromagnetic modes. It is also found that in parallel propagating dust-Alfvén mode these effects play no role, but in obliquely propagating dust-Alfvén mode or perpendicular propagating dust-magnetosonic mode the effect of self-gravitational field plays destabilizing role whereas the effect of dust/ion fluid temperature plays stabilizing role.     

A dodecanuclear Zn cluster sandwiched by polyoxometalate ligands

A dodecazinc silicotungstate K(20)Na(2)[Zn(6)(OH)(7)(H(2)O)(Si(2)W(18)O(66))](2)·34H(2)O (1) has been synthesized and characterized by X-ray crystallography, elemental analysis, infrared, UV-vis spectroscopy, cyclic voltammetry, acid-base titration, and DFT calculations. The twelve zinc atoms between the two [Si(2)W(18)O(66)](16-) frameworks make this complex more stable hydrolytically than the heteropolytungstate ligands, [Si(2)W(18)O(66)](16-), themselves. The structurally unique central Zn(12) core is formed by the fusion of two [Zn(6)(OH)(7)(H(2)O)](5+) units through two edge-sharing Zn6 atoms. DFT B3LYP calculations give HOMO-LUMO and (HOMO - 1)-LUMO energy gaps of ～3.65 and 3.91 eV, respectively, as compared to the band gap in ZnO of 3.35 eV.