Cyano-bridged CuII-MV (M = Mo, W) bimetallic layered complexes exhibiting novel honeycomblike structures

Self-assembly of a new precursor [Cu(L)](ClO4)2 (1) (L = macrocyclic ligand) with octacyanometalates [M(CN)8]3- (M = Mo, W) produced two-dimensional cyano-bridged Cu(II)-M(V) bimetallic assemblies [Cu(L)]3n[M(CN)8]2n.6nH2O [M = Mo (2), W (3)] with novel honeycomblike structures, characterized by spectroscopic data, single-crystal X-ray diffraction studies, and magnetic measurements. The crystallographic determination reveals that compounds 2 and 3 are isostructural and crystallize in the triclinic system (P). The Cu atom in a distorted octahedral environment experiences a tetragonal elongation of apical nitrogen atoms exhibiting average Cu-Nax lengths of 2.566 Angstroms for 2 and 2.593 Angstroms for 3, which accounts for the Jahn-Teller effect of a Cu(II) ion. The Cu-NC angles are magnetically important, ranging from 135.7 to 159.2 degrees. Three types of L in the crystal lattice are observed, which are dependent on the relative positions of the pendant hydroxyl groups with respect to the CuN4 basal plane. The positions are correlated with hydrogen bonding of OH groups to neighboring atoms. The magnetic data indicate that ferromagnetic and antiferromagnetic interactions between Cu(II) and M(V) through the CN linkage coexist.     

Probing ruthenium-acetylide bonding interactions: synthesis, electrochemistry, and spectroscopic studies of acetylide-ruthenium complexes supported by tetradentate macrocyclic amine and diphosphine ligands

The synthesis and spectroscopic properties of trans-[RuL4(C[triple bond]CAr)2] (L4 = two 1,2-bis(dimethylphosphino)ethane, (dmpe)2; 1,5,9,13-tetramethyl-1,5,9,13-tetraazacyclohexadecane, 16-TMC; 1,12-dimethyl-3,4:9,10-dibenzo-1,12-diaza-5,8-dioxacyclopentadecane, N2O2) are described. Investigations into the effects of varying the [RuL4] core, acetylide ligands, and acetylide chain length for the [(-)C[triple bond]C(C6H4C[triple bond]C)(n-1)Ph] and [(-)C[triple bond]C(C6H4)(n-1)Ph] (n = 1-3) series upon the electronic and electrochemical characteristics of trans-[RuL4(C[triple bond]CAr)2](0/+) are presented. DFT and TD-DFT calculations have been performed on trans-[Ru(L')4(C[triple bond]CAr)2](0/+) (L' = PH3 and NH3) to examine the metal-acetylide pi-interaction and the nature of the associated electronic transition(s). It was observed that (1) the relationship between the transition energy and 1/n for trans-[Ru(dmpe)2{C[triple bond]C(C6H4C[triple bond]C)(n-1)Ph}2] (n = 1-3) is linear, and (2) the sum of the d(pi)(Ru(II)) --> pi*(C[triple bond]CAr) MLCT energy for trans-[Ru(16-TMC or N2O2)(C[triple bond]CAr)2] and the pi(C[triple bond]CAr) --> d(pi)(Ru(III)) LMCT energy for trans-[Ru(16-TMC or N2O2)(C[triple bond]CAr)2]+ corresponds to the intraligand pi pi* absorption energy for trans-[Ru(16-TMC or N2O2)(C[triple bond]CAr)2]. The crystal structure of trans-[Ru(dmpe)2{C[triple bond]C(C6H4C[triple bond]C)2Ph}2] shows that the two edges of the molecule are separated by 41.7 A. The electrochemical and spectroscopic properties of these complexes can be systematically tuned by modifying L4 and Ar to give E(1/2) values for oxidation of trans-[RuL4(C[triple bond]CAr)2] that span over 870 mV and lambda(max) values of trans-[RuL4(C[triple bond]CAr)2] that range from 19,230 to 31,750 cm(-1). The overall experimental findings suggest that the pi-back-bonding interaction in trans-[RuL4(C[triple bond]CAr)2] is weak and the [RuL4] moiety in these molecules may be considered to be playing a "dopant" role in a linear rigid pi-conjugated rod.     

Application of solid phase microextraction in the determination of paralytic shellfish poisoning toxins

A SPME-HPLC-post-column fluorescent derivatization method for the direct determination of saxitoxin (STX), the most potent paralytic shellfish poisoning (PSP) toxin, in water has been developed. Commercially available SPME devices with 50 microm Carbowax templated resin (CW/TPR) coating was found to be able to pre-concentrate STX from aqueous media. A special pre-conditioning treatment of soaking the SPME coating in 0.1 M NaOH solution significantly improved the extraction efficiency. The optimal pH for the SPME process is 8.1 and the equilibration time is 40 min. The partition coefficient, K, of the distribution of STX between the SPME coating and the aqueous media was measured to be 2.99 +/- 0.04 x 10(3). Extracted toxin on the SPME stationary phase was difficult to be desorbed by the HPLC mobile phase under dynamic desorption mode. A static ion-pairing desorption technique using a desorption solvent mixture of 20 mM sodium 1-heptanesulfonate in 30% aqueous acetonitrile acidified with 50 mM sulfuric acid was developed to overcome this problem. The method detection limit and repeatability achieved by this SPME-HPLC method were 0.11 ng ml(-1) and 3.7%, respectively, with a sample volume of just 5 ml of water. This analytical method is adequate for the monitoring of the PSP toxin in fresh/drinking waters. However, serious interference was observed when this technique was applied to saline water samples. This is probably due to competition of sodium ions with the cationic STX for absorption into the SPME stationary phase.     

Time-resolved resonance Raman and density functional theory study of the deprotonation reaction of the triplet state of p-hydroxyacetophenone in water solution

[reaction; see text] Picosecond and nanosecond time-resolved resonance Raman (TR(3)) spectroscopy was employed to investigate the deprotonation/ionization reaction of p-hydroxyacetophenone (HA) after ultraviolet photolysis in water solution. The TR(3) spectra in conjunction with density functional theory (DFT) calculations were used to characterize the structure and dynamics of the excited-state HA deprotonation to form HA anions in near neutral water solvent. DFT calculations based on a solute-solvent intermolecular H-bonded complex model containing up to three water molecules were used to evaluate the H-bond interactions and their influence on the deprotonation reaction and the structures of the intermediates. The deprotonation reaction was found to occur on the triplet manifold with a planar H-bonded HA triplet complex as the precursor species. The HA triplet species is generated within several picoseconds and then decays with a approximately 10 ns time constant to produce the HA triplet anion species after 267 nm photolysis of HA in water solution. The triplet anion species was observed to decay with a time constant of about 90 ns into the ground-state anion species that was found to have a lifetime of about 200 ns. The DFT calculations on the H-bonded complexes of the anion triplet and ground-states species suggest that these anion species are H-bonded complexes with planar quinonoidal structures containing two water molecules H-bonded, respectively, with oxygen lone pairs of the carbonyl and deprotonated hydroxyl moieties. A deactivation scheme of the photoexcited HA in regard to the deprotonation reaction in neutral water solutions was proposed. With the above dynamic and structural information available, we briefly discuss the possible implications of the model HA photochemistry in water solutions for the photodeprotection reactions of related p-HP phototrigger compounds in aqueous solutions.     

Ionic-liquid-supported peptide synthesis demonstrated by the synthesis of Leu(5)-enkephalin

A new strategy for the synthesis of oligopeptides was developed using an ionic liquid as a soluble support. The efficiency of this ionic liquid-phase approach was demonstrated by the synthesis of a bioactive pentapeptide, Leu(5)-enkephalin, in good yield and reasonable purity. The structures and purities of the reaction intermediates in each step were verified easily by routine spectroscopic analysis, and no chromatographic procedures were needed during the synthesis.     

Assay of free ferulic acid and total ferulic acid for quality assessment of Angelica sinensis

Activity of Chinese Danggui (DG), the processed root of Angelica sinensis (Oliv.) Diels, is linked to the ferulic acid content but the stability of ferulic acid during extraction for medicinal use is not known. The stabilities of ferulic acid and coniferyl ferulate were evaluated in the extracts of DG using a variety of extraction solvents. These included various combinations and proportions of methanol, water, formic acid, 1 M aqueous hydrochloric acid and 2% sodium hydrogen carbonate (NaHCO3) in water. Coniferyl ferulate was found liable to hydrolyze into ferulic acid in neutral, strongly acidic and basic solvents, where heat and water could facilitate this hydrolysis. However, the hydrolysis was relatively resisted in weakly organic acid. Based on the stability evaluation, two new terms, namely: free ferulic acid and total ferulic acid, were suggested and defined. Free ferulic acid refers to the natural content of ferulic acid in herbs. Total ferulic acid means the sum of free ferulic acid plus the amount of related hydrolyzed components. Meanwhile, the high-performance liquid chromatographic (HPLC) method was developed to assay free ferulic acid and total ferulic acid in DG using methanol-formic acid (95:5) and methanol-2% NaHCO3 in water (95:5) as extraction solvents, respectively. Ten DG samples were investigated on their contents of free and total ferulic acid. The results indicated that the amount variety of free ferulic acid was larger than that of their counterparts, and the ratio of total ferulic acid to free ferulic acid was 4.07 +/- 2.73 (mean +/- SD, n = 10). The chemical assay of DG using total ferulic acid content would be a better choice to assess the herbal quality and was recommended.     

Lewis acid mediated reactions of aldehydes with styrene derivatives: synthesis of 1,3-dihalo-1,3-diarylpropanes and 3-chloro-1,3-diarylpropanols

[reaction: see text] The reactions of aryl aldehydes with styrene derivatives, mediated by various boron Lewis acids, were investigated. 1,3-Dihalo-1,3-diarylpropanes were obtained in high yields with boron trihalides, while 3-chloro-1,3-diarylpropanols were obtained in good to excellent yields with phenylboron dichloride. Reactions involving nonenolizable aliphatic aldehydes, trans-cinnamaldehyde, and beta-substituted styrenes were also investigated for the first time.     

De novo asymmetric syntheses of D- and L-talose via an iterative dihydroxylation of dienoates

[reaction: see text] A short and highly efficient route to D- and L-talo-gamma-lactones has been developed. The key transformation was the sequential osmium-catalyzed bis-dihydroxylation reaction of substituted 2,4-dienoates. When the first dihydroxylation reaction is performed on (2Z,4E)-dienoates with use of the Sharpless AD-mix procedure, a regio- and enantioselective dihydroxylation resulted along with an in situ lactonization. A subsequent dihydroxylation, using OsO4/NMO in MeOH conditions, resulted in an exceedingly diastereo- and enantioselective synthesis of talo-gamma-lactone.     

Ab initio and variational transition state approach to beta-C3N4 formation: kinetics for the reaction of CH3NH2 with H

The CH3NH2 molecule has been considered as either an important intermediate in methane and ammonia mixtures or a precursor in methylamine and hydrogen mixtures in the synthesis of carbon nitride thin films. The fast Hydrogen (H) abstraction from CH3NH2 is an important process involved in the formation of HCN or CNH in the chemical vapor deposition (CVD) of carbon nitride thin films. The energetic and kinetic characteristics of the H abstraction reaction from CH3NH2 by atomic H used in CVD of beta-C3N4 were studied using ab initio direct dynamics methods for the first time. Two primary processes were identified for this reaction: H abstraction from the CH3 group and H abstraction from the NH2 group. On the basis of ab initio data, the rate constants of each channel have been deduced by canonical variational transition state theory with small-curvature tunneling correction over a wide temperature range of 200 to approximately 3000 K. The theoretical results were compared with available experimental data.     

Solvation thermodynamics: theory and applications

Potential distribution and coupling parameter theories are combined to interrelate previous solvation thermodynamic results and derive several new expressions for the solvent reorganization energy at both constant volume and constant pressure. We further demonstrate that the usual decomposition of the chemical potential into noncompensating energetic and entropic contributions may be extended to obtain a Gaussian fluctuation approximation for the chemical potential plus an exact cumulant expansion for the remainder. These exact expressions are further related to approximate first-order thermodynamic perturbation theory predictions and used to obtain a coupling-parameter integral expression for the sum of all higher-order terms in the perturbation series. The results are compared with the experimental global solvation thermodynamic functions for xenon dissolved in n-hexane and water (under ambient conditions). These comparisons imply that the constant-volume solvent reorganization energy has a magnitude of at most approximately kT in both experimental solutions. The results are used to extract numerical values of the solute-solvent mean interaction energy and associated fluctuation entropy directly from experimental solvation thermodynamic measurements.