Electronic state dependence of the ion-molecule reaction CH(3)CN(+) + CH(3)CN → CH(4)CN(+) + CH(2)CN: threshold electron-secondary ion coincidence (TESICO) and direct ab initio molecular dynamics study

The ion-molecule reaction, CH(3)CN(+) + CH(3)CN → CH(3)CNH(+) + CH(2)CN, has been investigated using the threshold electron-secondary ion coincidence (TESICO) technique. Relative reaction cross sections for two microscopic reaction mechanisms, i.e., proton transfer (PT) from the acetonitrile ion CH(3)CN(+) to neutral acetonitrile CH(3)CN and hydrogen atom abstraction (HA) by CH(3)CN(+) from CH(3)CN, have been determined for two low-lying electronic states, (2)E and (2)A(1) of the CH(3)CN(+) primary ion. The cross section for PT of the (2)A(1) state was smaller than that of the (2)E state, whereas that of HA are almost the same in the two states. Ab initio calculations showed that the dissociation of the C-H(+) bond of CH(3)CN(+) is easier in the (2)E state than that in the (2)A(1) state. The direct ab initio molecular dynamics (MD) calculations showed that two mechanisms, direct proton transfer and complex formation, contribute the reaction dynamics.     

Effect of Head Size in Head‐Tail‐Type Polycations on their in vitro Performances as Nonviral Gene Vectors

Three kinds of head‐tail‐type block copolymers composed of polyamidoamine (PAMAM) dendron heads and poly(L ‐lysine) (PLL) tail blocks (PAMAM dendron‐PLL), having PAMAM dendrons with different generations (G2.5‐PLL, G3.5‐PLL and G4.5‐PLL) were synthesized. Some of the dendron heads were located at polyplex surface, and G2.5‐PLL and G3.5‐PLL could form small polyplexes (less than 150 nm in size). G2.5‐PLL and G3.5‐PLL polyplexes were taken up into the cells more effectively. PAMAM dendron‐PLL that had a larger dendron head could show a more‐effective buffering effect. The in vitro performance of the PAMAM dendron‐PLL polyplexes was controlled by the balance of cellular uptake and endosomal escape by a buffering effect.

     

Development of a fluorescent chelating ligand for gallium ion having a quinazoline structure with two Schiff base moieties

A novel chelating ligand, 2,4-[bis-(2,4-dihydroxybenzylidene)]-dihydrazinoquinazoline (DBHQ), was synthesized, and the fluorescence characteristics of its complex with metal ions were investigated.Thirty-five different metal ions were tested for the emission of fluorescence in the presence of DBHQ in aqueous solutions in a pH range of 3.0-10.5 (at a difference of 0.5 for each metal).It was observed that DBHQ fluoresces intensely at 470 nm with an excitation wavelength of 405 nm in the presence of Ga³⁺ or Al³⁺ in the pH range 3.0-4.0. The other metal ions did not show fluorescence with DBHQ. Although the presence of Cu²⁺, Co²⁺ and Fe³⁺ decreased the fluorescence intensity of DBHQ-Ga³⁺, the addition of a fluoride ion (NaF) recovered the fluorescence by masking the interfering ions. In addition, the fluoride ions were found to enhance the sensitive determination of Ga³⁺ because the fluorescence intensity of DBHQ-Ga³⁺ was further increased approximately 2.5-fold in the presence of F⁻ (? = 0.658) from that in the absence of F⁻ (? = 0.401). The fluoride ions also masked the Al³⁺ ions, which emit fluorescence on chelation with DBHQ. Therefore, a selective and sensitive detection of Ga³⁺ was achieved by using DBHQ in the presence of F⁻. The detection limit of Ga³⁺ was approximately 50 nmol L⁻¹ (3.5 ppb). The proposed method was applicable to determine Ga³⁺ in river water.     

Two regioisomers of condensed thioheterocyclic triazine synthesized from 6‐phenyl‐3‐thioxo‐2,3,4,5‐tetrahydro‐1,2,4‐triazin‐5‐one

In the crystal structure of 6‐phenyl‐3‐thioxo‐2,3,4,5‐tetrahydro‐1,2,4‐triazin‐5‐one, C₉H₇N₃OS, (I), the 1,2,4‐triazine moieties are connected by face‐to‐face contacts through two kinds of double hydrogen bonds (N—H...O and N—H...S), which form planar ribbons along the a axis. The ribbons are crosslinked through C—H...π interactions between the phenyl rings. The molecular structures of two regioisomeric compounds, namely 6‐phenyl‐2,3‐dihydro‐7H‐1,3‐thiazolo[3,2‐b][1,2,4]triazin‐7‐one, C₁₁H₉N₃OS, (II), and 3‐phenyl‐6,7‐dihydro‐4H‐1,3‐thiazolo[2,3‐c][1,2,4]triazin‐4‐one, C₁₁H₉N₃OS, (III), which were prepared by the condensation reaction of (I) with 1,2‐dibromoethane, have been characterized by X‐ray crystallography and spectroscopic studies. The crystal structures of (II) and (III) both show two crystallographically independent molecules. While the two compounds are isomers, the unit‐cell parameters and crystal packing are quite different and (II) has a chiral crystal structure.     

Adsorption and aggregation properties of heterogemini surfactants containing a quaternary ammonium salt and a sugar moiety

A novel heterogemini surfactant comprising two hydrocarbon chains and two different hydrophilic groups such as a quaternary ammonium cation and gluconamide nonion N,N-dimethyl-N-[2-(N'-alkyl-N'-gluconamide)ethyl]-1-alkylammonium bromides (2CnAmGlu, where n represents hydrocarbon chain lengths of 8, 10, 12, and 14) was synthesized by reacting N,N-dimethylethylenediamine with alkyl bromide, followed by a reaction with 1,5-D(+)-gluconolactone. The adsorption properties of 2CnAmGlu were characterized by surface tension measurements made using the Wilhelmy plate method, and their aggregation properties were investigated by dynamic light scattering and cryogenic transmission electron microscopy techniques. The relationship between the hydrocarbon chain length and the logarithm of the critical micelle concentration (cmc) for 2CnAmGlu exhibited a linear decrease when the chain length was increased up to 12 and then a departure from linearity at n=14. The surface tension reached 24-26 mN m-1 at each cmc, indicating high efficiency in lowering the surface tension of water. Furthermore, it was found that the structure of the aggregate formed for 2CnAmGlu in solution was influenced by the hydrocarbon chain length; that is, for n=10 and 12, micelles with a hydrodynamic radius of 2-5 nm were formed, whereas vesicles were also observed for n=14.     

Extended applications of di-tert-butylsilylene-directed alpha-predominant galactosylation compatible with C2-participating groups toward the assembly of various glycosides

The high versatility of di-tert-butylsilylene(DTBS)-directed alpha-predominant galactosylation have been extended to the construction of difficult glycan sequences. First, to investigate the compatibility of the alpha-predominant reaction with various glycosylation systems a variety of 4,6-O-DTBS-tethered galactosaminyl or galactosyl donors were synthesized efficiently, which have C2-participating groups with a wide variety of leaving groups such as alkylsulfenyl, halide, trichloroacetimidate groups. The results of the detailed examination of the glycosylation reaction using the glycosyl donors showed the wide scope of the 4,6-DTBS-directed alpha-galactosylation. In the next step, the stereoselective construction of alpha-GalN-Ser/Thr sequences was examined by employing the DTBS-directed glycosylation. As a result, various types of serine and threonine derivatives were glycosylated alpha-selectively, producing alpha-GalN-Ser/Thr sequences in high yields. Moreover, the DTBS-directed galactosylation was successfully applied for the synthesis of alpha-tetrasaccharyl-Ser segment of glycophorin A.     

Total syntheses of zaragozic acids A and C by a carbonyl ylide cycloaddition strategy

A carbonyl ylide cycloaddition approach to the squalene synthase inhibitors zaragozic acids A and C is described. The carbonyl ylide precursor 8 was synthesized starting from di-tert-butyl D-tartrate (47) via an eleven-step sequence involving the regioselective reduction of the mono-MPM (MPM=4-methoxybenzyl) ether 48 with LiBH4 and the diastereoselective addition of sodium tert-butyl diazoacetate to alpha-keto ester 10. The reaction of alpha-diazo ester 8 with 3-butyn-2-one (40) in the presence of a catalytic amount of [Rh2(OAc)4] gave the desired cycloadduct 59 as a single diastereomer. The dihydroxylation of enone 59 followed by sequential transformations permitted the construction of the fully functionalized 2,8-dioxabicyclo[3.2.1]octane core 5. Alkene 79 derived from 5 serves as a common precursor to zaragozic acids A (1) and C (2), since the elongation of the C1 alkyl side chain can be attained by olefin cross-metathesis, especially under the influence of Blechert's catalyst (85).     

Ab initio MO analysis of interaction paths between radicals in ferromagnetic organic systems

Interaction path analyses for pi-conjugated organic systems were performed at the ab initio molecular orbital level to examine the relationship between inter-radical interactions and the high-spin stability of the system. It was found that the high-spin stability results from through-bond interactions between radicals, not from through-space interactions, in relation to the stabilization of a low-spin state due to the effects of electron correlation. L(ij)(min) value for estimating the mixing of nonbonding molecular orbitals well predicted the relationship between the through-bond interactions and the high-spin stability. Furthermore, molecular orbital calculations revealed that the all-trans type interaction path between radicals produces long-range exchange interactions, and the additivity of high-spin stability is observed by keeping short-range through-bond interaction paths.