Effect of adsorbed water on the electrorheology of silica suspensions

Monodisperse silica particles were formed by hydrolyzing tetraethylorthosilicate in an ethanol solution and the silica suspensions dispersed in a silicone oil were prepared by a different procedure. The effects of adsorbed water on the electrorheological (ER) behavior were studied under oscillatory shear. The amounts of adsorbed water and surface silanol groups were determined by thermogravimetric analysis. The magnitude of the complex viscosity, |η^*|, increases with the application of electric fields. The physically adsorbed water is primarily responsible for the ER effect. However, the fluids containing large amounts of adsorbed water do not always show excellent ER performance. The surface silanol groups have an important role in promoting the ER effect. Not only the amount but also the situation of silanol groups determines the ER activity of adsorbed water.     

Synthesis and γ-radiolysis of 2′-deoxy-5-fluorouridine and 5-fluorouridine derivatives

Seventeen compounds having a variety of substituents at the 3- and 5′-positions of 2′-deoxy-5-fluorouridine (5-FUdR) and 5-fluorouridine (5-FUR) were synthesized, and their γ-radiolysis in aqueous solutions were studied. The compounds having thioureido (RNHCSNH, R ? H, PhCH₂, acyl) and thiocarbonylamino (XCSNH, X ? PhCH₂S, PhO) groups at the 3-position of 5-FUdR were efficiently cleaved to give 5-FUdR with high G values upon γ-irradiation of their aqueous solutions. The active species for these cleavage reactions were hydrated electron (e^? _aq), H^? and HO^?. However, the compounds having a dimethylsulfoxyimino group at 3-position of 5-FUdR and 5-FUR afforded 5-FUdR and 5-FUR only under the radiolysis conditions where e^? _aq becomes a principal active species. The compound having a 2-benzoylthiazoylthiocarbonylamino group at the 3-position of 5-FUdR showed the highest reactivity toward HO^.. The mechanisms of these γ-radiolysis reactions are discussed. The examination of anticellular activities of γ-irradiated compounds having a thiocarbonylamino group at the 3-position of 5-FUdR toward murine Sarcoma 180 cells revealed that these compounds may be utilized as a candidate for a radiation-induced drug (RID).     

A fluorescent-labeled oligopeptide for monitoring PKA-mediated phosphorylation

A fluorescent-labeled oligopeptide (DACM-CLRRASLK-fluorescein), containing a consensus amino acid sequence (RRXSL) of cyclic AMP (cAMP) dependent protein kinase A (PKA) substrate-proteins, was designed. The fluorescent peptide was a good substrate of PKA, and the phosphorylation of its serin residue caused an intensive change in fluorescent intensity. We expect that the peptide will be useful as a fluorescent indicator for monitoring PKA activity in living cells.     

Normal mode analysis of oligomeric proteins: Reduction of the memory requirement by consideration of rigid geometry and molecular symmetry

A method is presented to reduce the memory requirement of normal mode analysis applied to systems containing two or more large proteins when these systems exhibit symmetry properties. We use a rigid geometry model (i.e., only the dihedral angles of the polypeptide chain are considered as variables). This model allows a reduction by a factor of 8 on average of the number of variables with a concomitant freezing of the high-frequency modes. The symmetry properties of the system are used to reduce further the number of variables that must be considered in the computation. Application of group theory leads to a factorization of the matrices of interest (the coefficient and the Hessian matrices) into independent blocks along the diagonal. The initial, reducible representation is thus transformed into a number of irreducible representations of smaller dimensions. In the case of the C₂ symmetry group, the method leads to a reduction of the size of the matrices that must be manipulated during the computation (coefficient matrix, Hessian matrix, and eigenvectors matrix) by a factor of 256 compared with the usual normal mode analysis in Cartesian coordinate space. The method is particularly well adapted to the study of the dynamics of oligomeric proteins because these proteins often display symmetry properties (e.g., virus coat proteins, immunoglobulins, hemoglobin, etc.). In favorable cases, in conjunction with X-ray diffuse scattering data, the study of systems showing allosteric properties might be considered. © 1994 by John Wiley & Sons, Inc.     

γ-Radiolysis of 5-fluorouracil and 5-fluorouridine derivatives having sulfur-containing substituents

γ-Radiolysis reactions of eight 5-fluorouracil (5-FU) derivatives having sulfonyl group-containing substituents at the 1-position and five 5-fluorouridine (5-FUR) derivatives having thioureido group-containing substituents were studied under the conditions where hydrated electron (e_aq^?) and hydroxyl radical (HO·) become the principal reactive species. The 5-FU and 5-FUR derivatives were radiolyzed to give 5-FU and 5-FUR, respectively. The efficiency of the reactions depended upon the nature of reactive species and also upon the nature of substituents. The reactivity features of the γ-radiolysis reactions are discussed.     

The fifth overtones of the C-H stretching vibrations and the bond lengths in some heterocyclic compounds

The fifth overtones of the C-H stretching vibrations of pyridine, pyrazine, thiophene, 3-methylthiophene, furan and pyrrole in the liquid state have been observed by a thermal lens technique. It was found that their frequency shifts from that of benzene are proportional to the decrease in the relevant C-H bond length.     

Proximity Effects in Acid and Base-Catalysed Ether Formation

When heated with sodium ethoxide in ethanol 7-methylidenebicyclo[3.3.1]nonan-3-endo-ol (endo- 1 ) is converted into 1-methyl-2-oxa-adamantane ( 3 ). This reaction involves nucleophilic addition of a hydroxy group to an unactivated olefinic bond. Formation of the cyclic ether 3 also takes place when endo- 1 is heated in aqueous ethanol. This electrophilic addition is strongly catalysed by weak acids and suppressed by weak bases. These unusual reactions proceed more slowly with 7-methylbicyclo[3.3.1]non-6-en-3-endo-ol (endo- 2 ) and can be ascribed to a proximity effect. This follows from the IR . and NMR . spectra of endo- 1 and endo- 2 which show strong intramolecular hydrogen (OH-π) bonding. The unsaturated endo- and exo-alcohols 1 and 2 , respectively, undergo only exo-complexation with silver ion.     

Polytheonamides A and B, highly cytotoxic, linear polypeptides with unprecedented structural features, from the marine sponge, Theonella swinhoei

Polytheonamides A and B are highly cytotoxic polypeptides with 48 amino acid residues isolated from the marine sponge, Theonella swinhoei. The structure of polytheonamide B was determined by spectral and chemical methods, especially extensive 2D NMR experiments, which resulted in the unprecedented polypeptide structure; the N-terminal glycine blocked with a 5,5-dimethyl-2-oxo-hexanoyl group, the presence of eight tert-leucine, three beta-hydroxyvaline, six gamma-N-methylasparagine, two gamma-N-methyl-beta-hydroxyasparagine, and beta,beta-dimethymethionine sulfoxide residues. More significantly, it has the sequence of alternating D- and L-amino acids. Polytheonamide A is an epimer of polytheonamide B differing only in the stereochemistry of the sulfoxide of the 44(th) residue.