Nucleophilic addition of benzenethiol to 1',2'-unsaturated nucleosides: 1'-C-phenylthio-2'-deoxynucleosides as anomeric radical precursors

The addition reaction of benzenethiol to the glycal portion of 1',2'-unsaturated uridine proceeds efficiently in the presence of Et(3)N. The mechanism involves nucleophilic attack of thiolate at the anomeric position in the rate-determining step, wherein conjugation between the nucleobase and the glycal portion is crucial. The derivative having a methyl group either at the 2'- or 6-position did not undergo this addition reaction, due to their sterically prohibited coplanarity. The 1',2'-unsaturated derivatives of thymine and adenine can also be used as substrates for this addition reaction. It was also shown that the resulting 1'-C-phenylthio-2'-deoxynucleosides serve as precursors for radical-mediated C-C bond formation at the anomeric position.     

Generalized Waiting Time Problems Associated with Pattern in Polya's Urn Scheme

Let X ₁, X ₂, ... be a sequence obtained by Polya's urn scheme. We consider a waiting time problem for the first occurrence of a pattern in the sequence X ₁, X ₂, ... , which is generalized by a notion score. The main part of our results is derived by the method of generalized probability generating functions. In Polya's urn scheme, the system of equations is composed of the infinite conditional probability generating functions, which can not be solved. Then, we present a new methodology to obtain the truncated probability generating function in a series up to an arbitrary order from the system of infinite equations. Numerical examples are also given in order to illustrate the feasibility of our results. Our results in this paper are not only new but also a first attempt to treat the system of infinite equations.     

On discrete distributions of orderk

Summary This paper gives some results on calculation of probabilities and moments of the discrete distributions of orderk. Further, a new distribution of orderk, which is called the logarithmic series distribution of orderk, is investigated. Finally, we discuss the meaning of theorder of the distributions. The Institute of Statistical Mathematics     

Separating ultrafilters on uncountable cardinals

A uniform ultrafilterU on κ is said to be λ-separating if distinct elements of the ultrapower never projectU to the same uniform ultrafilterV on λ. It is shown that, in the presence of CH, an ω-separating ultrafilterU on κ>ω is non-(ω, ω₁)-regular and, in fact, if κ < ℵ_ω thenU is λ-separating for all λ. Several large cardinal consequences of the existence of such an ultrafilterU are derived.     

Chemical ionization mass spectra of simple 1,3-dioxolanes and their sulphur analogues recorded with methane,isobutane, ammonia and acetone as reagent gas

The mass spectral behaviour of nine 1,3-dioxolanes, seven 1,3-dithiolanes and seven 1,3-oxathiolanes was studied under chemical ionization conditions with ammonia, isobutane, methane, acetone, acetone-d₆ or pentan-3-one as reagent gas. The proton affinity of the first members in each series was not large enough for ammonia to protonate them; instead, the ionization took place through unstable [M + NH₄]⁺ ions. Isobutane, which gave rise to abundant [M + H]⁺ ions in all cases, was the best reagent gas for the determination of the molecular mass. Methane chemical ionization caused extensive fragmentations either through ring cleavage or through the elimination of the largest substituent from ring positions 2 as a neutral hydrocarbon. The ketones used as reagent gas reacted to form adduct ions. In the case of dioxolanes and oxathiolanes, the [M + RCO]⁺ adduct ion decomposed through ring opening and then, as a consequence of intramolecular nucleophilic substitution, through the elimination of a neutral carbonyl compound. Resonance-stabilized dioxolanylium and oxathiolanylium ions were obtained for dioxolanes and oxathiolanes, respectively. This reaction was almost non-existent for the dithiolanes.     

Interaction of Antiseptic Compounds with Intercellular Lipids of Stratum Corneum

The interaction between three kinds of antiseptic compounds and components of intercellular lipids in the stratum corneum was characterized in terms of thermodynamics at pH 7.5 and 25°C, and the different mechanisms used to penetrate the stratum corneum were clarified. Anionic surfactants such as benzalkonium chloride and benzethonium chloride mainly bound to cholesterol (CH) and cholesterol sulfate with high affinity (10⁵–10⁶ M⁻¹) to extract endogenous CH from the stratum corneum and penetrated through the intercellular route. Chlorhexidine gluconate also bound to CH and accumulated in the stratum corneum without removing endogenous CH. An amphoteric surfactant of dodecyldiaminoethylglycine hydrochloride seemed to be incorporated into the lipid bilayer and bound to ceramide with its polar end close to the lipid polar heads by hydrophobic interaction. This revised version was published online in August 2006 with corrections to the Cover Date.     

Hydroxyl radical reactivity with nitrobenzene in subcritical and supercritical water

The bimolecular rate constants of the addition reaction between hydroxyl radical (*OH) and nitrobenzene (C(6)H(5)NO(2)) were measured in subcritical and supercritical water (SCW) at temperatures between ambient and 390 degrees C. The measured bimolecular rate constants showed distinctly non-Arrhenius behavior (i.e., essentially no increase with temperature) from ambient to 350 degrees C, but increased in the slightly subcritical and supercritical region between 350 and 390 degrees C. These data were modeled reasonably well over the entire temperature range with a three-step reaction mechanism, originally proposed by Ashton et al.(1) This model includes the formation of a pi-complex intermediate as the precursor of the nitrohydroxycyclohexadienyl radical.     

Binding of distamycin A to UV-damaged DNA

We have found that distamycin A can bind to DNA duplexes containing the (6-4) photoproduct, one of the major UV lesions in DNA, despite the changes, caused by photoproduct formation, in both the chemical structure of the base moiety and the local tertiary structure of the helix. A 20-mer duplex containing the target site, AATT.AATT, was designed, and then one of the TT sequences was changed to the (6-4) photoproduct. Distamycin binding to the photoproduct-containing duplex was detected by CD spectroscopy, whereas specific binding did not occur when the TT site was changed to a cyclobutane pyrimidine dimer, another type of UV lesion. Distamycin binding was analyzed in detail using 14-mer duplexes. Curve fitting of the CD titration data and induced CD difference spectra revealed that the binding stoichiometry changed from 1:1 to 2:1 with photoproduct formation. Melting curves of the drug-DNA complexes also supported this stoichiometry.     

Thermodynamic evaluation of antibacterial activity for inclusion complexes of amoxicillin with cyclodextrins

The antibacterial action of amoxicillin (AMPC) and the inclusion complexes of AMPC with α-, β- and γ-cyclodextrins (α-CD, β-CD and γ-CD, respectively) to Escherichia coli B (E. coli) was evaluated by isothermal titration microcalorimetry and by petri-dish bioassay method. The effects of the compounds on produced heat during the exponential phase of the E. coli growing were measured and the growing rate constants of the cells was calculated from the power-time (p-t) curve before and after the treatment with AMPC. Results from the both methods showed that the antibacterial activity became stronger in the following order: AMPC-βCD > AMPC-γCD ≈ AMPC-αCD > AMPC only.     

Review of molecular modification techniques for improved detection of biomolecules by mass spectrometry

After a soft ionizing method was established, MS (mass spectrometry) has become a more common tool in biochemistry because soft ionization made it possible to detect large molecules such as proteins. Many kinds of applications were established to further utilize MS for the identification or quantitation of biomolecules. In this review, we introduce recent applications with special focus on chemical modification techniques and chemical probes developed for the MS determination of biomolecules.