Self-assembly of flexible supramolecular metallacyclic ensembles: structures and adsorption properties of their nanoporous crystalline frameworks

The syntheses, structures, and N2 adsorption properties of six new supramolecular metallacycles are reported. Flexible ditopic linkers, 1-4, with systematically varied lengths and conformational degrees of freedom were synthesized utilizing ester linkages. They were used in combination with (dppp)M(OTf)2, where M = Pt(II) and Pd(II), and cis-(Me3P)2Pt(OTf)2 to form flexible supramolecular metallacycles 5-10 in 88-98% isolated yields. Their structures were characterized via multinuclear NMR and X-ray crystallography. The metallacycles stack to form porous structures in the crystalline state. The pore dimensions depend on both the phosphorus ligands attached to the metals and the flexible linkers. Adsorption studies on the porous materials show that 5a, 6, 8, and 9 held 11.7, 16.5, 5.7, and 6.8 cm3/g STP of N2 at 77 K, respectively. A guest-exchange study with nitromethane and toluene reveals that the nanopore in 5 is flexible, a property which was transferred from the linker to the supramolecular structure in the solid state.     

BIPHOTONIC CHEMISTRY OF PHENANTHRENE UNDER 308 nm EXCIMER LASER IRRADIATION

Abstract— –The high intensity laser induced photochemistry of phenanthrene is complex and appears to be non-linear with respect to laser intensity. Photochemical products primarily involve the solvent (CH₂C1₂) and phenanthrene coupling. These species exhibit strong absorption and emission which are red-shifted from that of phenanthrene. In the presence of a-methyl styrene, styrene oligomers are formed, but no dimers, indicating that there are no a-methyl styrene cation radical reactions. In all cases of laser irradiation the solutions become acidic, which is ascribed to the deprotonation of the phenanthrene cation radical. Acid formation does not occur in the presence of a-methyl styrene under CW irradiation with a conventional Xe lamp. These differences are ascribed to photoionization from the singlet state for laser irradiation while under CW conditions triplet-triplet annihilation can produce the phenanthrene cation radical.     

Liquids and liquid mixtures: Deduction of the BGY equation considering the angular distribution function

The Born→Green→Yvon equation for molecular fluid has been deduced considering the orientational distribution functions. The isotropic and anisotropic parts of the distribution function have been separated. The expressions deduced can be used in the case of mixtures and for the non-central type of intermolecular potential energy.     

Steric guided change of electron transfer mechanism in benzene

In fluorescence quenching study via electron transfer (ET), the quenching rate constant (k(q)) values generally decrease with lowering of quencher concentration, since smaller concentration of quencher always leads to a red shift in the donor-acceptor (D-A) distance in ET [M. Tachiya, S. Murata, J. Phys. Chem. 96 (1992) 8441; S. Murata, M. Tachiya, J. Phys. Chem. 100 (1996) 4064; L. Burel, M. Mastafavi, S. Murata, M. Tachiya, J. Phys. Chem. A 103 (1999) 5882]. However, while doing a comparative study with different carbazole (CZ) derivatives-1,4-dicyanobenzene (DCB) systems in benzene (BZ), we observed a deviation from that normal behaviour. It was found that for all of them with lower quencher (DCB) concentration, k(q) values actually increase instead of the expected reduction. Exceptionally, for simple CZ (C12H9N) with decrease in concentration of DCB, k(q) values can even reach the order of energy transfer (10(11) s(-1)). Interestingly, it is not observed when toluene (TL) or xylene (XY) is used as solvent. To explain this unique observation, a sandwich type of molecular structure is predicted, where BZ sliding in between CZ and DCB brings them closer enough, imparting more through bond character to CZ-DCB interaction and hence a higher rate of ET (k(q)) is observed [L. Burel, M. Mastafavi, S. Murata, M. Tachiya, J. Phys. Chem. A. 103 (1999) 5882].     

Two new 5-deoxyflavones from Albizia odoratissima

Two new 5-deoxyflavones, 7,8-dimethoxy-3',4'-methylenedioxyflavone (1) and 7,2',4'-trimethoxyflavone (2) together with a known flavone, 7,4'-dimethoxy-3'-hydroxyflavone (3) were isolated from the rootbark of Albizia odoratissima. The structures of these new compounds were elucidated by electrospray ionization mass spectrometry (ESI-MS) and 1D and 2D-NMR spectral studies including (1)H-(1)H correlation spectroscopy (COSY), heteronuclear single quantum coherence (HSQC), heteronuclear multiple bond connectivity (HMBC) and nuclear Overhauser enhancement spectroscopy (NOESY).     

Investigation by infrared absorption of the by-products of the cyanoethylation of cotton cellulose

The soluble cyanoethyl ether of cellulose, prepared by reaction in the presence of NaOH catalyst to high degrees of substitution (DS = 2.95), can be precipitated by various organic media and contains more nitrogen than can be accounted for by simple addition of acrylonitrile at each cellulose hydroxyl group. Infrared absorption spectra of such samples and of the reacted residues show various types of vibrational absorption bands, characteristic of amino groups. At advanced stages of the reaction the characteristic broad unresolved band of cellulose extending from 1200–950 cm.^?1 largely disappears, leaving only a few weaker bands which likely overlap those due to C–N stretching. Comparison is made of the spectra of the partially cyanoethylated cellulose and the polyacrylonitrile which forms in the stock acrylonitrile, to characterize the products. It is inferred that the highly cyanoethylated cellulose, partly dissolved in the acrylonitrile, further degrades and changes under a complex mechanism to various forms of amines. The yellow to orange color of the samples is assumed to be due to these by-products. The thermogravimetric analysis reveals that these products are more heat-resistant than the cyanoethylated cellulose.     

Thiourea as a transfer agent in the radical polymerization of methyl methacrylate in aqueous solution at 42

Chain transfer involving thiourea in radical polymerization of methyl methacrylate in acidic aqueous media has been studied by polymer endgroup analysis using the dye-partition technique. Thiourea has feeble reactivity in chain transfer, the transfer constant with respect to poly (methyl methacrylate) radicals being 1.21 × 10^?4 at 42°. This chain transfer study led to the development of a new method for studying the tautomeric equilibrium between the thione and thiol forms of thiourea. The equilibrium is pH dependent and the equilibrium constant at 42° is 232. The ratios of the equilibrium concentrations of the thiol to thione forms of thiourea at various pH's have been calculated. The thiol form is responsible for the chain transfer reactivity; it predominates in strongly acidic media and is almost absent above pH 3.5. This new method may be used for studying the thione-thiol tautomerism of other thiourea derivates.     

Estimation of iron in fruit samples by substoichiometric extraction with malonic anilide

A radiochemical solvent extraction method for the determination of iron(III) employing the chelating extractant malonic anilide (MA), synthesized in our laboratory, has been described. Effects of different parameters on the extraction of iron(III) from 2M hydrochloric acid into a mixed organic solvent (methyl isobutyl ketone (TIBK) and diethyl ether) have been studied in detail. The method was applied for the estimation of iron content in several fruits using the principle of substoiciometric isotope dilution analysis.     

Enzymatic kinetic resolution of racemic 4-tetrahydropyranols by Candida rugosa lipase

Enzymatic kinetic resolution of (±)-hydroxytetrahydropyrans has been achieved for the first time by means of lipase-mediated transesterification to afford optically active (2S,4R)-tetrahydropyranyl acetates and (2R,4S)-tetrahydropyranols in excellent yields with high enantioselectivity. Absolute configurations of the tetrahydropyranyl acetates were assigned as (S) by chemical correlation.     

Preferred conformers in n-propanol: A PCILO study

Preferred conformers around the central C-C and C-O bonds in n-propanol have been determined using the quantum-mechanical PCILO method and compared with those observed experimentally by microwave spectroscopy. The agreement between theory and experiment is excellent, thus minimizing time consuming searches for microwave transitions corresponding to the preferred conformers.