Improved Synthesis of Chitosan -Bearing boldbeta-Cyclodextrin and Its Adsorption Behavior towards Bisphenol A and 4-Nonylphenol

The synthesis of chitosan-bearing -cyclodextrin (CDC) has been improved by use of an alternative condensing agent, 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMT-MM). CDC was obtained by the reaction of succinyl chitosan with a small amount of mono-6-amino-mono-6-deoxy--cyclodextrin (ACD) within a shorter reaction time. Under optimal conditions, the CD yields reached to 50%, which were almost the same as those in the reactions using 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride (EDC). The gelation time suggests that the crosslinking of chitosan and the immobilization of the ACD occur competitively. To test the potential of CDC for selective removal of pollutants, the adsorption of bisphenol A (BPA) and 4-nonylphenol (NP) from aqueous solution onto CDC was investigated. In the case of the equilibrium concentrations more than 10 mg/L, the amounts of both sorbents onto CDC were close to the estimated saturated value of the CDC (85 mg/g for BPA and 81 mg/g for NP).     

Study of pH-dependent zinc(II)-carboxamide interactions by zinc(II)-carboxamide-appended cyclen complexes (cyclen = 1,4,7,10-tetraazacyclododecane)

To elucidate intrinsic recognition of carboxamides by zinc(II) in carbonic anhydrase (CA) (as inhibitors) and carboxypeptidase A (CPA) (as substrates), a new series of Zn(2+)-carboxamide-appended cyclen complexes have been synthesized and characterized (cyclen = 1,4,7,10-tetraazacyclododecane). Two types of Zn(2+)-carboxamide interactions have been found. In the first case represented by a zinc(II) complex of carbamoylmethyl-1,4,7,10-tetraazacyclododecane (L(1)), the amide oxygen binds to zinc(II) at slightly acidic pH (to form ZnL(1)), and the deprotonated amide N(-) binds to zinc(II) at alkaline pH (to form ZnH(-1)L(1)) with pK(a) = 8.59 at 25 degrees C and I = 0.1 (NaNO(3)), as determined by potentiometric pH titrations, infrared spectral changes, and (13)C and (1)H NMR titrations. The X-ray crystal structure of ZnH(-1)L(3) (where L(3) = N-(4-nitrophenyl)carbamoylmethyl cyclen, pK(a) = 7.01 for ZnL(3) <==> ZnH(-1)L(3)) proved that the zinc(II) binds to the amidate N(-) (Zn-N(-) distance of 1.974(3) A) along with the four nitrogen atoms of cyclen (average Zn-N distance 2.136 A). Crystal data: monoclinic, space group P2(1)/n (No. 14) with a = 10.838(1) A, b = 17.210(2) A, c = 12.113(2) A, b = 107.38(1) degrees, V = 2156.2(5) A(3), Z = 4, R = 0.042, and R(w) = 0.038. These model studies provide the first chemical support that carboxamides are CA(-) inhibitors by occupying the active Zn(2+) site both in acidic and alkaline pH to prevent the occurrence of the catalytically active Zn(2+)-OH(-) species. In the second case represented by a zinc(II) complex of 1-(N-acetyl)aminoethylcyclen, ZnL(6), the pendant amide oxygen had little interaction with zinc(II) at acidic pH. At alkaline pH, the monodeprotonation yielded a zinc(II)-bound hydroxide species ZnL(6)(OH(-)) (pK(a) = 7.64) with the amide pendant remaining intact. The ZnL(6)(OH(-)) species showed the same nucleophilic activity as Zn(2+)-cyclen-OH(-). The second case may mimic the Zn(2+)-OH(-) mechanism of CPA, where the nucleophilic Zn(2+)-OH(-) species does not act as a base to deprotonate a proximate amide.     

Studies on uricosuric diuretics. III. Substituted 1,3-dioxolo[4,5-f]-1,2-benzisoxazole-6-carboxylic acids and 1,3-dioxolo[4,5-g]-1,2-benzisoxazole-7-carboxylic acids.

A series of substituted 1,3-dioxolo[4,5-f]-1,2-benzisoxazole-6-carboxylic acids 13 and 1,3-dioxolo[4,5-g]-1,2-benzisoxazole-7-carboxylic acids 14 were synthesized and evaluated for diuretic and uricosuric activities in rats. Most of the benzisoxazole derivatives 13 and 14 showed potent diuretic activities. Moderate uricosuric activities were also found in 14a, 14b, and 14f.     

Acid-promoted rearrangement of carbonate functionality anchored to the lower rim of a Calix

A unique calix[4]arene lower-rim intramolecular rearrangement, resulting in molecular asymmetry arising from the upper- and lower-rim substitution pattern, produces a new class of inherently chiral calix[4]arenes in a partial cone conformation. This was aided by molecular rigidification arising from pi-pi and C-H.pi interactions between bulky lower-rim substituents, with the corresponding circular dichroism spectra exhibiting the most intense bisignate Cotton effects yet observed for calix[4]arenes not bearing a chiral center.     

Copper L X-ray spectra measured by a high resolution ion-induced X-ray spectrometer

High resolution L X-ray emission spectra of Cu have been measured by 0.75 MeV/u H, He, and F, 0.73 MeV/u Ar, 0.64 MeV/u Si, and 0.073 MeV/u Si ion impacts with a crystal spectrometer. The X-ray transition energies in the Cu target for Lι, Lη, L_1,2, Lβ₁, and Lβ_3,4 diagram lines induced by H ion impact are determined, which are in good agreement with those given in the reference by Bearden (Rev. Mod. Phys. 39, 78, 1967). The X-ray spectra produced by F, Si, and Ar ions have complicated structures due to multiple L and M shell vacancy production. The L_1,2 and Lβ₁ emission spectra for H and He ions are compared with the calculated ones based on the multiconfiguration Dirac-Fock method. The origin of the broadening of the L_1,2 line to the lower energy for H ion impact is attributed to one 2p plus one 3d electron vacancy production.     

Relative reactivities of cyclic ethers in cationic copolymerizations: Effects of ring strain and basicity

The relative reactivities of α-monosubstituted cyclic ethers having rings of three to six members toward a cation were estimated from their copolymerizations with 3,3-bis-(chloromethyl)oxetane (M₁) catalyzed by boron trifluoride etherate in methylene chloride at 0°C. It was found that the reactivity of these cyclic ethers was dominated by both the ring strain and the basicity. The following empirical equation was derived to represent the relative reactivity of cyclic ethers: log (1/r₁) = ?0.086ΔRS ? 0.31ΔB + 0.57, where ΔRS and ΔB are constants, characteristic of ring strain and basicity of the cyclic ethers and determined from the differences in free energy of polymerization of the corresponding cycloalkanes and in basicity between M₁ and M₂ monomers, respectively. A good linear correlation was observed between the reactivities calculated from this equation and those obtained from the experiments.     

Bimetallic clusters Pt6Au: geometric and electronic structures within density functional theory

Within density functional theory at the general gradient approximation for exchange and correlation (BPW91) and the relativistic 19-electron Los Alamos National Laboratory effective core pseudopotentials and basis sets (3s3p2d), the geometric and electronic structures of Pt(6)Au bimetallic clusters have been studied in detail in comparison with Pt(7). A total of 38 conformations for Pt(6)Au are located. The most stable conformation for Pt(6)Au is a sextet with an edge- and face-capped trigonal bipyramid, in which the Au atom caps an edge of the trigonal bipyramid. Pt(6)Au, in general, prefers a three-dimensional geometry and high spin electronic state with multireference character. The electronic impact of the doping of Au in Pt clusters on the overall chemical activity of the doped bimetallic cluster is not as significant as that of the doping of Pt in Au clusters; however, the doping of Au lowers the chemical activity, thus enhancing the chemoselectivity in the gas phase, of PtAu bimetallic clusters.     

A convenient synthesis of dihydrocoumarins from phenols and cinnamic acid derivatives

A facile procedure for synthesis of dihydrocoumarin derivatives was described. Although the yield of the products in the reaction of phenols with acrylates in trifluoroacetic acid in the presence of Pd(OAc)₂ giving coumarins was found to be very low, dihydrocoumarin derivatives were obtained in good to high yields in the absence of Pd(OAc)₂ when ethyl cinnamates bearing electron-donating groups were employed in this reaction.     

Enhancement of electrochemical activity by small-sizing the vinylferrocene-immobilized polystyrene latex particles

Voltammetry of vinylferrocene (VFc)-immobilized polystyrene(PS)-based latex particles was carried out in aqueous suspensions by changing the size of latex particles in order to investigate the dependence of the electroactivity of the particles on their size. The anodic peak current was controlled by diffusion of the latex. The voltammetric peak currents increased with an increase in the diameter of PS latex particles for a given analytical concentration of the particles, exhibiting the dependence on 1.5 powers of the diameter of the particles. The increase can be explained in terms of combination of the uniform distribution of VFc in the particle, the partial charge transfer, and the Stokes-Einstein equation for diffusion coefficients. The oxidation of VFc occurs in the restricted domain (0.07 microm) from a contact point of the particle with the electrode. The overall reaction mechanism is diffusion of the particle to the electrode, partial oxidation to VFc+, release of VFc+ from the particle to the solution, and reduction of the released VFc+.     

An amphotericin B-ergosterol covalent conjugate with powerful membrane permeabilizing activity

Amphotericin B-sterol conjugates were synthesized and examined for their membrane permeabilizing activity. Ergosterol and cholesterol, each connected with amphotericin B via an ethylenecarbamate or hexamethylenecarbamate linker, were examined by K(+) flux assays using liposomes and by single-channel recording across phospholipid membrane. Among four conjugates tested, AmB-ergosterol bearing an ethylenecarbamate linker exhibited the most powerful activity, which substantially exceeded that of the cholesterol homolog. Single-channel recording clearly exhibited that the ergosterol conjugate elicited channel current with the conductance of 28 pS, which was comparable with those by AmB, and revealed a higher channel open probability than the cholesterol conjugate. These results imply that direct interaction between amphotericin B and ergosterol is reproduced by their conjugate, which may serve as a model compound for understanding the drug's selective toxicity.