Ion-specific swelling behavior of uncharged poly(acrylic acid) gel

The ion-specific swelling behavior of poly(acrylic acid) (PAA) gel prepared by -ray irradiation was investigated as a function of salt concentration in the presence of 0.01 M HCl. The anion specificity for the swelling ratio was similar to that for many kinds of hydrogels, i.e., Cl^–<Br^–<NO₃ ^–<I^–, while the cation specificity proved to be rather unusual, i.e., Mg²⁺<Ca²⁺<Li⁺<Na⁺<K⁺<Cs⁺. In order to find any differences in the hydration of uncharged PAA from that of other polymers having typical polar groups, the hydrogen-bonding hydrations on the relevant polar groups were compared for small molecule analogues with an ab initio molecular orbital calculation. According to the results, the marked deswelling of PAA gel in the presence of strongly hydrated cations was ascribed to the unfavorable hydration to the acidic proton of PAA due to the reduced availability of water oxygen as well as to the destabilization of hydrophobic hydration developing around the uncharged PAA.     

Determination of dissociation constants of sparingly soluble phenothiazine derivatives by second-derivative spectrophotometry

The dissociation constants (pK_a) for sparingly soluble phenothiazines (promazine, chlorpromazine, trifluoropromazine) in water were measured by second-derivative spectrophotometry. The intense background signals in the absorption spectra due to the turbidity caused by the precipitation of insoluble free base of the phenothiazine derivatives were eliminated in the second-derivative spectra, and the solubilities of the phenothiazine derivatives could be easily determined from the peak-to-trough lengths (D values) of the second-derivative signals. The pK_a values were calculated from the pH dependence of the D values. The pK_a values obtained agreed well with reported values and the standard deviations for 6–10 determinations were ? 0.02. The solubilities of the free bases of the phenothiazines were also determined.     

Production and excited state dynamics of the photorearranged isomer of benzyl chloride and its methyl derivatives studied by stepwise two-color laser excitation transient absorption and time-resolved thermal lensing techniques

Production and photoexcited dynamics of reaction intermediates with photolyses of benzyl chloride (BzCl) and methyl-substituted benzyl chlorides (MeBzCls) were studied by using stepwise two-color laser excitation transient absorption (TC-TA) and two-color laser excitation time-resolved thermal lensing (TC-TRTL) measurements. With photoexcitation of BzCl the formation of transient photorearranged isomer was suggested in the previous paper [Res. Chem. Intermed. 2001, 27, 137]. Such an isomer formation for MeBzCls was also observed in a 248 nm excitation. It was found that further photoexcitation of the isomers with the 308 nm light caused photodissociation to yield the corresponding benzyl radicals. The reaction quantum yield and the molar absorptivity of the photorearranged isomer of BzCl were estimated. The heat of reaction for the photodissociation of the isomer was successfully determined with the TC-TRTL measurement. These experimental results were consistent with MO calculations.     

Synthesis and reactions of a monosubstituted dithiirane 1-oxide, 3-(9-triptycyl)dithiirane 1-oxide

A 3-monosubstituted dithiirane 1-oxide, 3-(9-triptycyl)dithiirane 1-oxide, was prepared for the first time, by the reaction of (9-triptycyl)diazomethane and S₈O. The dithiirane 1-oxide was obtained as cis- and trans-isomers, and the structure of the trans-isomer was verified by X-ray crystallography. The cis-isomer isomerized gradually to the trans-isomer in solution. The divalent sulfur atom of the cis- and trans-dithiirane 1-oxides were removed on treatment with triphenylphosphine to give the corresponding Z- and E-sulfines, respectively. The reaction of the trans-dithiirane 1-oxide with (Ph₃P)₂Pt(C₂H₄) provided the (sulfenato-thiolato)Pt^II complex, and that with Lawesson's reagent yielded the 1,3,4,2-trithiaphospholane and 1,2,4,5,3-tetrathiaphosphorinane derivatives.     

Regio- and stereocontrolled Diels-Alder reaction tethered by Asp-Thr dipeptide

The Asp-Thr tethered Diels-Alder reaction of 1a was accomplished to provide 2a exclusively in a regio- and stereoselective manner.     

Cerebroside Langmuir monolayers originated from the echinoderms: II. Binary systems of cerebrosides and steroids

Two-component Langmuir monolayers formed on a subphase of 0.5M sodium chloride solution were investigated for two different cerebrosides (LMC-1 and LMC-2) with steroids of cholesterol (Ch) and cholesteryl sodium sulfate (Ch-S); i.e. LMC-1/Ch, LMC-1/Ch-S, LMC-2/Ch, and LMC-2/Ch-S were examined in terms of surface pressure (pi), the surface potential (DeltaV) and the dipole moment (mu( perpendicular)) as a function of surface area (A) by employing the Langmuir method, the ionizing electrode method, and the fluorescence microscopy. Surface potentials (DeltaV) of steroids were analyzed using the three-layer model proposed by Demchak and Fort. The miscibility of cerebrosides and steroids in the insoluble monolayers was examined by plotting the variation of the molecular area and the surface potential as a function of the steroid molar fraction (X(steroid)) based upon the additivity rule. From the A-X(steroid) and DeltaV(m)-X(steroid) plots, partial molecular surface area (PMA) and apparent partial molecular surface potential (APSP) were determined at the different surface pressures. The PMA and APSP with the mole fraction were discussed for the miscible system. Judging from the two-dimensional phase diagrams, they can be classified into two types. The first is a completely immiscible type; the combination of cerebrosides with cholesterol. The second is a negative azeotropic type, where cerebrosides and cholesteryl sodium sulfate are completely miscible both in the expanded state and in the condensed state. In addition, a regular surface mixture (the Joos equation for the analysis of the collapse pressure of two-component monolayers) allowed calculation of the interaction parameter (xi) and the interaction energy (-Delta epsilon) between the cerebrosides and Ch-S. The miscibility of cerebroside and steroid components in the monolayer state was also supported by fluorescence microscopy.     

Experimental and theoretical studies on ferromagnetically coupled metal complexes with imino nitroxides

Copper(II), zinc(II), and nickel(II) complexes with tridentate imino nitroxyl diradicals, [CuCl(bisimpy)(MeOH)](PF(6)) (1), [ZnCl(2)(bisimpy)] (2), and [NiCl(bisimpy)(H(2)O)(2)]Cl x 2H(2)O (3) (bisimpy = 2,6-bis(1'-oxyl-4',4',5',5'-tetramethyl-4',5'-dihydro-1'H-imidazol-2'-yl)pyridine), were prepared, and their magnetic properties were studied. In 1, the Cu(II) ion has a square pyramidal coordination geometry, of which the equatorial coordination sites are occupied by three nitrogen atoms from the bisimpy and a chloride ion. The coordination geometry of the Zn(II) ion in 2 can be described as a trigonal bipyramid, with two chloride ions and a bisimpy. In 3, the Ni(II) ion has a distorted octahedral coordination geometry, of which four coordination sites are coordinated by the bisimpy and chloride ion, and two water molecules occupy the remaining cis positions. Magnetic susceptibility and EPR measurements revealed that in 1 and 3 the Cu(II) and Ni(II) ions with imino nitroxyl diradicals were ferromagnetically coupled, with the coupling constants J (H = -2J(ij) summation operator S(i)S(j)) of +165(1) and 109(2) cm(-1), respectively, and the intraligand ferromagnetic interactions in 1-3 were very weak. DFT molecular orbital calculations were performed on the diradical ligand, 1, and 2 to study the spin density distribution before and after coordination to the metal ions.     

Some chemical transformations of 7a-cyanohexahydro-1H-pyrrolizine into 7a-substituted hexahydro-1H-pyrrolizines

Chemical transformations of 7a-cyanohexahydro-1H-pyrrolizine ( 2 ) into 7a-substituted hexahydro-1H-pyrrolizines are described. In the reaction of 2 with lithium aluminum hydride, the orientation of the lone pair of the bridgehead nitrogen against C-CN bond can be regarded as significant.     

Crystal growth in syndiotactic poly(vinyl alcohol) hydrogels

Aqueous solutions of syndiotacticity-rich poly(vinyl alcohol) (s-PVA) form gels easily. The optimum condition of growth of the calcium tartrate crystal formed by diffusing calcium chloride into hydrogels containing tartaric acid was studied with use ofs- PVA of a syndiotacticity of 56 % and a degree of polymerization of 1460. The crystal grew in the gel of the concentrations of 2 % s-PVA and of 0.5 N tartaric acid at pH=4. The relation between the formation of Liesegang rings and shear modulus of a gel was studied by diffusing silver nitrate into gels containing potassium chromate. The distance between rings decreased with increasing shear modulus of a gel in the range from 670 to 7500 dyne/cm². The Liesegang rings were not formed for the shear modulus gel for 280 and 16200 dyne/cm₂.     

Enhanced microfiltration of γ-globulin solution upon treatment of NaCl addition and/or DNase digestion

Microfiltration of a γ-globulin solution has been investigated through the virus removal membranes having different pore sizes (i.e. r=15, 35 and 75 nm) and a dialysis membrane (r=3.4 nm), which were all made of the same regenerated cellulose material. The addition of NaCl in the γ-globulin feed solution was effective to enhance the flux and transmission through the membranes having a pore size ranging from 15 to 75 nm. DNase treatment of a γ-globulin solution with Micrococcal nuclease enhanced the flux and transmission of γ-globulin through the membranes either with or without NaCl. The membranes having a pore size of 35 nm showed dramatically enhanced flux in the microfiltration of a γ-globulin solution containing NaCl and/or being treated with Micrococcal nuclease. This can be explained as a DNase treatment and NaCl addition in the protein solution dissociate protein aggregates of DNA–γ-globulin complex, which plugs the pores in the microfiltration membranes.