Calculations of the electrostatic free energy contributions to the binding free energy of sulfonamides to carbonic anhydrase

The interactions between biologically important enzymes and drugs are of great interest. In order to address some aspects of these interactions we have initiated a program to investigate enzymedrug interactions. Specifically, the interactions between one of the isozymes of carbonic anhydrase and a family of drugs known as sulfonamides have been studied using computational methods. In particular the electrostatic free energy of binding of carbonic anhydrase II with acetazolamide, methazolamide,p-chlorobenzenesulfonamide,p-aminobenzenesulfonamide and three new compounds (MK1, MK2, and MK3) has been computed using finite-difference Poisson-Boltzmann (FDPB) [1] method and the semimacroscopic version [2, 3] of the protein dipole Langevin dipole (PDLD) method [4]. Both methods, FDPB and PDLD, give similar results for the electrostatic free energy of binding even though different charges and different treatments were used for the protein. The calculated electrostatic binding free energies are in reasonable agreement with the experimental data. The potential and the limitation of electrostatic models for studies of binding energies are discussed.     

Trapping effect of eugenol on hydroxyl radicals induced by L-DOPA in vitro

Many researchers have stated that eugenol might inhibit lipid peroxidation at the stage of initiation, propagation, or both, and many attempts have been made to elucidate the mechanism of its antioxidant activity. Nevertheless, details of its mechanism are still obscure. This study was carried out to investigate the trapping effect of eugenol on hydroxyl radical generated from L-3,4-dihydroxyphenylalanine (DOPA) in MiliQ water and the generation mechanism of the hydroxyl radical by this system which uses no metallic factor. This was studied by adding L-DOPA and 5,5-dimethyl-1-pyrroline N-oxide (DMPO) to phosphate buffered saline (PBS) or MiliQ water, and the generation of hydroxyl radical was detected on an ESR spectrum. By this method, the effect of antioxidants was detected as a modification of ESR spectra. We found that the eugenol trapped hydroxyl radicals directly, because it had no iron chelating action, did not trap L-DOPA semiquinone radical and inhibited hydroxyl radicals with or without iron ion.     

Polyether-bridged sexithiophene as a complexation-gated molecular wire for intramolecular photoinduced electron transfer

The porphyrin-sexithiophene-fullerene triad 2, where the two central thiophene units of the sexithiophene spacer are bridged with a crown-ether-like polyether chain, undergoes efficient intramolecular electron transfer from the photoexcited porphyrin moiety to the fullerene through the sexithiophene. However, complexation with a sodium cation in the crown ether ring causes complete suppression of electron transfer as a result of a drastic conformational change of the sexithiophene backbone. Furthermore, decomplexation resumes the photoinduced electron transfer. This on/off switching phenomenon indicates that the polyether-bridged sexithiophene can function as a complexation-gated molecular wire.     

A new theoretical approach to the empirical resonance energies of the aromatic hydrocarbons

In the framework of the Hückel MO approximation, the differences in total binding energy between a given molecule and the corresponding distorted Kekulé-type structure are calculated for a variety of benzenoid hydrocarbons. The total binding energy is assumed to be given by the sum of the -electron and -electron binding energies. It is shown that there is a good linear relationship between the calculated differences in total binding energy and the -electron delocalization energies (DE) as obtained by using the simple Hückel MO method. This provides a physical basis for the use of the -electron DE as a theoretical index to the empirical resonance energy (RE). Further, by examining the changes in -electron binding energy between a given molecule and the corresponding distorted Kekulé-type structure, it is concluded that in benzenoid hydrocarbons the main contributor to the RE is not the -electron DE but the compressional energy of bonds.     

Preparation and characterization of polypropylene/mesoporous silica nanocomposites with confined polypropylene

Polypropylene (PP)/Ti-MCM-41 nanocomposites were prepared by isospecific propylene polymerization with Ti-MCM-41/Al(i-C₄H₉)₃ catalyst. The cross polarization/magic angle spinning (CP/MAS) ¹³C NMR spectrum of the composite was similar to that of the conventional isotactic PP, and the decrease in the pore volume of Ti-MCM-41 in the nanocomposites, as measured by N₂ adsorption, was consistent with the value calculated from the weight loss in the thermogravimetric analysis (TGA) curve; both these facts attest to propylene polymerization within the mesopores of Ti-MCM-41. Alkali treatment followed by extraction with o-dichlorobenzene allows us to extract the confined PP out of the Ti-MCM-41 mesopores. Although the PP/Ti-MCM-41 nanocomposites do not exhibit a crystalline melting point, the same PP when extracted from the mesopores showed a clear melting point at 154.7 °C; this indicates that the crystallization of PP confined in mesopores is strongly hindered. For the PP polymerized within the confinement, the molecular weight (M_w) and molecular weight distribution (M_w/M_n) were 84,000 and 4.3, respectively; these values were considerably smaller than those of the PP polymerized concurrently outside the Ti-MCM-41 mesopores (M_w = 200,000–450,000, M_w/M_n = 40–75). Therefore, the confinement also has a marked effect on the molecular weight of the PP. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3324–3332, 2003     

Studies on the biosynthesis of terrecyclic acid A II confirmation of the cyclization mechanism and hydrogen shifts using [2-2H3]acetate and [213C2H3]acetate

Feeding experiments with [2-³H₃]acetate and [2-¹³C²H₃]acetate in $\text{Aspergillus terreus}$ Thom No. 14 indicated that the hydrogen at C-2 in terrecyclic acid A is incorporated without migration from the precursor acetic acid; the results favour our group's earlier speculation for the cyclization to the tricyclic skeleton in the biosynthetic scheme.     

Determination of selenium in sediments by hydride generation atomic absorption spectrometry. Elimination of interferences

Summary The hydride generation/atomic absorption spectrometry (AAS) with an automated flow system is useful for the routine analysis of selenium in environmental samples. This method is, however, subject to interferences from transition metal ions and other hydride forming ions. The conditions to minimize the interferences were established: the concentration of hydrochloric acid 6 mol/l; the concentration of tetrahydroborate 0.5%. Iron(III) chloride released the depression of selenium signals by metal ions such as copper(II) and bismuth(III). Selenium in several standard reference materials including sediment samples was determined by the present method and by fluorimetry with 2,3-diaminonaphthalene. The results obtained by the two methods agreed with an acceptable precision. This means that hydride generation/AAS offers good precision and accuracy in the determination of selenium in sediment samples as well as DAN fluorimetry. However, the former is much simpler in operation. The method was applied to the determination of selenium in estuarine sediments collected in Nagoya harbor and Ise Bay. The results can be used to assess the pollution state of these places.

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Selenbestimmung in Sedimenten durch AAS mit Hydriderzeugung. Eliminierung von Störungen

     

Vinyl polymerization. 275. Polymerization of vinyl monomers photosensitized by tetramethyltetrazene

A study of the photopolymerization of vinyl monomers in the presence of tetramethyltetrazene (TMT) was made. TMT was found to act as an effective sensitizer. In the photopolymerization of vinyl monomers such as methyl methacrylate or styrene the rate of polymerization was expressed by the equation: R_p = k[TMT]^1/2[monomer]. The chain-transfer constant of TMT under ultraviolet irradiation was estimated to be 3.8 × 10^?2 for the above monomers. A linear correlation was found to exist between the reactivity of dimethylamino radical toward the vinyl monomers and e values for the corresponding monomers.     

Mapping analyses of Fe-diffused mc-Si using M?ssbauer microscope and photoluminescence

Twenty CK chondrites collected in the Antarctica Continent were characterized by inductively-coupled plasma mass spectrometry (ICP-MS), prompt gamma ray analysis (PGA), instrumental neutron activation analysis (INAA), X-ray diffractometry (XRD) and ⁵⁷Fe-M?ssbauer spectroscopy. As a result of elemental analysis, it was revealed that 18.2~26.4 mass% of iron was included in the each chondrite. M?ssbauer spectrum of LEW86258, classified as a typical CK chondrite, was found to be composed of two paramagnetic doublets and two magnetic sextets. M?ssbauer spectra were assigned to the absorption due to forsterite (Mg_1.36Fe_0.64SiO₄) and magnetite (Fe₃O₄), as also confirmed by XRD. XRD study of LAP03834, reclassified from CK to R chondrite, revealed the presence of crystalline phase due to forsterite. These results indicate that LAP03834 and related chondrites, i.e., MET01149, LAP03923 and MAC02453, should be reclassified as R or LL chondrite.     

Note Water Vapor Sorption by the Polyelectrolyte Complex of Poly (Acrylic Acid) and Poly (4-Vinyl-N-Ethylpyridinium Bromide)

A great number of studies of polyelectrolyte complexes have been carried out by various investigators; most of them concentrated on the reaction between oppositely charged polyelectrolytes [1-3]. The structure and properties of the resultant complexes have been investigated to a lesser extent, and the understanding of this new class of polymer materials is still insufficient. Thus, we have been investigating the sorption of water vapor by the complexes and the morphological changes caused by this sorption [4,5].