Search

Ketene-forming elimination from C4H3(O)CH2C(O)OC6H3-2-X-4-NO2 (1) promoted by R2NH in MeCN has been studied. The reactions produced elimination products and exhibited second-order kinetics with Bronsted β = 0.51, and |βlg| = 0.47–0.53, indicating that the reaction proceeds by the E2 mechanism via an E2-central transition state. Comparison of β, |βlg|, ΔH≠, and ΔS≠ values for R2NH-promoted eliminations from ArCH2C(O)OC6H3-2-X-4-NO2 reveals that the transition-state structures for Ar = furyl and thienyl are similar and more symmetrical than that for Ar = Ph. This outcome has been attributed to the greater double bond stabilizing ability of the former than that of the latter.

Elimination reactions of (E)-2,4,6-(NO2 ) 3C6H2CHNOC(O)C6H4X (3) promoted by R2NH/R2NH2 + in 70 mol% MeCN (aq) have been studied. The reactions produced elimination products and exhibited second-order kinetics. The β and |βlg| values remained nearly the same for all leaving groups and bases. The results can be described by the negligible pxy interaction coefficient, pxy = ∂β/∂pK lg = ∂βlg/∂pK BH ≈ 0, which provides a strong support for the (E1cb)irr mechanism. For eliminations from (E)-ArCHNOC(O)C6H4X (1, 3) and (E)-2,4,6-(NO2)3C6H2CHNOAr′ (2, 3), the change of the β-aryl group (Ar) from 2,4-dinitrophenyl (1) to 2,4,6-trinitrophenyl (3) increased the rate by 270-fold without appreciable change in the transition state structure. On the other hand, the leaving group (OAr′) variation from benzoate (3) to 4-nitrophenoxy (2) induced a change in reaction mechanism from (E1cb)irr to E2. These results have been attributed to the cyclic transition state for the nitrile-forming eliminations involving the benzoate leaving group.

Nucleophilic substitution reactions of 5-XC4H2 (S)C(O)OC6H3 -2-Y-4-NO2 (1) promoted by 4-Z-C6H4O −/4-Z-C6H4OH in 20 mol % dimethyl sulfoxide (DMSO)(aq) have been studied kinetically. The reactions exhibited second-order kinetics with βacyl = −2.52 to −2.83, ρ(x) = 2.81–3.16, βnuc = 0.88–0.04 and βlg = −0.94, respectively. The results have been interpreted with an addition–elimination mechanism in which the nucleophilic attack occurs in the rate-determining step. Comparison with existing data reveals that the rate-determining step changes from the second to the first step by the change in the nucleophile from R2NH/R2NH2 + to 4-Z-C6H4O −/4-Z-C6H4OH.

the effect of the β-aryl group on the ketene-formingelimination was assessed.Key Words : Elimination, E2 and E1cb Mechanism, β–Aryl Group effectIntroductionExtensive studies of the structure-reactivity relationshipsin the ketene-forming elimination reactions have led to thequalitative understanding of the relationship between thereactant structure and the mechanism.

value increased with a stronger electron-withdrawing 5-thienyl substituent, the Hammett plots arelinear except for X = MeO, and Yukawa-Tsuno plots are linear with ρ = 0.79-1.32 and r = 0.28-0.93,respectively. The ρ value increased and r value decreased with a stronger nucleophile, indicating an increase inthe electron density at the C=O bond and a decrease in the resonance demand. These results have beeninterpreted with enhanced N-C bond formation in the transition state with the reactivity increase. Key Words : Aminolysis, Bronsted-type plot, Hammett plot, Yukawa-Tsuno plot IntroductionExtensive studies of the structure-reactivity relationshipsin the acyl transfer reactions from XC

Elimination reactions of (E)-2,4-(NO2)2C6H2CH=NOC6H3-2-X-4-NO2 (1a-e) promoted by R3N/R3NH + in 70 mol % MeCN(aq) have been studied kinetically. The reactions are second-order and exhibit Bronsted β = 0.800.84 and |βlg| = 0.39-0.42, respectively. For all leaving groups and bases employed in this study, the β and |βlg| values remained almost the same. The results can be described by a negligible pxy interaction coefficient, pxy = ∂β/pKlg = ∂βlg/pKBH ≈ 0, which describes the interaction between the base catalyst and the leaving group. The negligible pxy interaction coefficient is consistent with the (E1cb)irr mechanism. Change of the base-solvent system from R3N/MeCN to R3N/R3NH + -70 mol % MeCN(aq) changed the reaction mechanism from E2 to (E1cb)irr. Noteworthy was the relative insensitivity of the transition state structure to the reaction mechanism change.

The transition state was shifted toward theE1cb corner by an electron-withdrawing β-aryl substituentand toward the E1 intermediate and the product by astronger base in the reaction coordinate diagram. On theother hand, when the leaving group was changed from 2,4-dinitrophenoxide to picrate, the ρ value decreased but the βvalue increased. The results are in conflict with the predic-tion of the reaction coordinate diagram because both ρ and βvalues should be decreased with a better leaving group. Theunusual changes in the transition-state structure noted withthe leaving group variation have been interpreted as result-ing from a large difference in the anion-stabilizing ability ofthe leaving groups. However, the validity of this interpreta-tion remains to be verified. To determine whether a change in mechanism could berealized by introducing an even more electron-withdrawingβ-aryl substituent, we have now studied the reactions of ( E)-2,4-dinitrobenzaldehyde O-aryloxime with R

Nitrile-forming eliminations from (1) promoted by in 70 mol % MeCN(aq) have been studied kinetically. When X = , the reactions exhibited second-order kinetics as well as Brnsted = 0.63 and = 0.34-0.46, and an E2 mechanism is evident. As the leaving group was made poorer (X = H, Cl, and ), Brnsted value increased from 0.63 to 0.85-0.89 without much change in the value E2, indicating that structure of the transition state changed to an E1cb-like with extensive bond cleavage, significant negative charge development at the -carbon, and limited -OAr bond cleavage.

E-mail: chk@inha.ac.krReceived December 22, 2010, Accepted January 27, 2011Key Words : Cyclodextrin, Mesoporous silica, Sugar, Stimuli-responsive, Controlled releaseStimuli-responsive silica nanoparticles with porous channelshave great potential for useful application in the area of drugand gene delivery because of their unique responsivenessand high stability.

A combination of a strong electron-withdrawing β-aryl group and anion-solvating protic solvent was required for the mecha-nistic change.We were interested in learning if a change to the E1cB mechanism could be realized in aprotic solvent by making the β-aryl group even more electron-withdrawing. To explore such possibility, we have now studied the reactions of (

The polymerization reaction of 4-[(n-butylsulfinyl)methyl]-4'-(chloromethyl)benzene (1a) with t-BuONa in CH 2 Cl 2 /monomethylformamide (MMF) (4/6) was studied kinetically. The reaction proceeds in two steps; the formation of a p-quinodimethane intermediate (M) followed by the polymerization of M. Results of kinetic studies and H-D exchange experiments reveal that the 1,6-elimination proceeds by the (Elcb)i rr mechanism. The rate of the disappearance of M was increased by the carbanion and S 2 O 8 2- , inhibited by TEMPO and unaltered by the addition of HCl. From these results, a free radical polymerization mechanism is proposed.

The gel electrolytes were prepared with sulfuric acid and phosphoric acid, where hydrophilic fumed silica was used as a gelling agent. The influences of gel electrolyte on performance of the valve regulated lead acid (VRLA) batteries were investigated employing capacity tests, electrochemical impedance spectroscopy and scanning electron microscopy. The initial capacities of the sulfuric gel VRLA batteries were higher than that of phosphoric gel VRLA batteries. The sulfuric gel VRLA battery using 1.210 specific gravity of sulfuric acid with hydrophilic fumed silica exhibited the highest capacity of 0.828Ah. In the impedance measurements, the ohmic and charge transfer resistances for the phosphoric gel VRLA batteries were higher than that of sulfuric gel batteries. The morphology of electrodes of phosphoric gel VRLA batteries were more deteriorated in the SEM image.

Ketene-forming eliminations from C4H3(S)CH2C(0)0-C6H3-2-X-4-N02 (1) promoted by R 2 NH in MeCN have been studied kinetically. The reactions are second-order and exhibit Bronsted β=0.51-0.62 and lβlgl= 0.47-0.53. Hence, an E2 mechanism is evident. The Bronsted β increased from 0.33 to 0.53 and |βlg| remained nearly the same by the change of the base-solvent from Bz(i-Pr)NH/Bz(i-Pr)NH 2 + in 70 mol% MeCN(aq) to Bz(i-Pr)NH-MeCN, indicating a change to a more symmetrical transition state with similar extents of Cβ-H and C α -OAr bond cleavage. When the /?-aryl group was changed from thienyl to phenyl in MeCN, the /? value increased from 0.53 to 0.73 and lβ lg l decreased from 0.53 to 0.43. This indicates that the transition state became skewed toward more Cβ-H bond breaking with less C α -OAr bond cleavage. Noteworthy is the greater double bond stabilizing ability of the thienyl group in the ketene-forming transition state.

The spectral properties, namely the circular dichroism, electric absorption and luminescence properties, of A-and A-[Ru(II)(1,10-phenanthroline)2benzodipyrido[b:3,2-h:2',3'-j]phenazine]2+ ([Ru(phen) 2 BDPPZ] 2+ ) in the presence and absence of single stranded poly(dA) and poly(dT) were compared in this work. In the presence of single stranded DNAs, hypochromism in the absorption spectrum and significant changes in the circular dichroism spectrum in the ligand absorption band were apparent, indicating the strong interaction of the [Ru(phen) 2 BDPPZ] 2+ complex with the single stranded DNAs. The luminescence intensity of the Ru(II) complex decreased stoichiometrically with increasing concentrations of the single stranded DNAs. All of these spectral changes were independent of the configuration of the Ru(II) complex and the nature of the DNA bases. Therefore, it is conceivable that both enantiomers of the [Ru(phen) 2 BDPPZ] 2+ complex interact electrostatically with the negatively charged phosphate groups of DNA. However, the spectral properties of [Ru(II)(1,10-phenanthroline)3]2+ were not altered even in the presence of single stranded DNAs. Therefore, the size of the ligand involved in the interaction of the metal complex with the phosphate group of DNA may play an important role, even when the nature of the interaction is electrostatic.

Human hepatitis B virus (HBV) is a pathogen related to the development of liver diseases including chronic hepatitis, cirrhosis, and hepatocellular carcinoma (HCC). However, the efficient methods to suppress HBV replication have not been developed yet. Therefore, we have used RNA interference (RNAi) as a potential tool for the suppression of HBV replication. Here, we designed a 21 nt small intefering dsRNA (siRNA) against hepatitis B virus X (HBx) RNA with 3' overhanging ends derived from T7 promoter. It has been reported that HBV X protein plays an important role in HBV gene expression and viral replication. The suppression of HBx gene expression by the 21 nt siRNA was investigated by Northern blot analysis and chloramphenicol acetyl transferase (CAT) assay. The level of HBx mRNA was decreased by siRNA in a dose-dependent manner. We also found that the 21 nt siRNA inhibited the HBV replication in hepatocellular carcinoma cell.

Elimination reactions of have been studied under various conditions. When X was moderately electron-withdrawing, Y = H, and base-solvent was NH-MeCN, the reaction proceeded by the E2 mechanism via an E1cb-like transition state. Concave downward curve was noted in the Hammett plots. When X = 4-, Y = Cl, , and the base-solvent was in 70 mol % MeCN(aq), the reaction proceeded by the E2 mechanism. The mechanism changed to a competing E2 and E1cb when X = 4- and Y = H, MeO, and to the E1cb when X = 2,4-(, and Y = . From these results, a plausible pathway of the change of the mechanism from E2 to the E1cb extreme is proposed.

There has been significantprogress in both areas. However, the rate accelerationsreported to date for synthetic catalysts of RNA cleavage are,in general, far below those obtained for enzyme catalysts;and, there are a number of important unresolved questionsabout the mechanisms; the spon taneous and buffer-catalyzedcleavage reactions which have been set out with great clarityin a previous review.

Hydrolysis reactions of S-phenyl-S-vinyl-N-p-tosylsulfilimine (VSI) and its derivatives at various pH have been investigated kinetically. The hydrolysis reactions produced phenylvinylsulfoxide and p-toluene sulfonamide as the products. The reactions are first order and Hammett ρ values for pH 1.0, 6.0, and 11.0 are 0.82, 0.45, and 0.57, respectively. This reaction is not catalyzed by general base. The plot of k vs pH shows that there are three different regions of the rate constants ( kt) in the profile.; At pH 10, the rate constants are directly proportional to the concentrations of hydronium and hydroxide ion catalyzed reactions, respectively. The rate constant remains nearly the same at 2 10.0, the reaction proceeds by the addition of hydroxide ion to sulfur directly. In the range of pH 2.0-10.0, the addition of water to sulfur of sulfilimine appears to be the rate controlling step.

Enynals bearing an olefinic pendant were successfully cyclized via Huisgen-type [3+2] cycloaddition to the tetracyclic Pt-carbene complexes which would undergo insertion into a C-H bond of the -position to afford the fused cyclopropane intermediates. Their tandem rearrangement afforded diverse types of spiranes depending on the tethered alkenes of the enynals.