Effects of type of adsorption isotherms on parallel diffusion of sulfonated dyes into porous cellulose membrane

Transport phenomenon of three sulfonated azo dyes, C.I. Acid Red 88, C.I. Direct Yellow 12, and C.I. Direct Blue 15 into water-swollen cellulose membranes has been analyzed on the basis of parallel transport theory by surface and pore diffusion. Langmuir equation was applied into the mass balance equation to estimate dye concentration in the pores. The results were compared with the results obtained by applying Freundlich equation in our previous papers. The surface diffusivity (D _s) and the pore diffusivity (D _p) for the parallel diffusion model obtained by applying Langmuir equation agreed with those obtained by applying Freudlich equation. The theoretical concentration profiles for parallel diffusion calculated usingD _s andD _p coincided accurately with the experimental data when we applied either Langmuir or Freundlich equations.     

Designer ribozymes: programming the tRNA specificity into flexizyme

Fx3 is an artificial ribozyme with the ability to aminoacylate various tRNAs with phenylalanine and its nonnatural derivatives. Herein we report a simple strategy to build tRNA specificity into the generic Fx3, by appending to its 3'-end a tRNA-specific sequence (TSS), which is complementary to the acceptor stem of the cognate tRNA. This new designer ribozyme, referred to as Fx10, is able to recognize its cognate tRNA via a 10-base-pair interaction that is formed after the invasion of the tRNA acceptor stem by the TSS. We have demonstrated that Fx10 can aminoacylate its cognate tRNA with a high degree of specificity and also discriminate against the noncognate tRNAs. Because the tRNA specificity can be easily programmed into Fx10, it is a custom-made catalyst to generate nonnatural aminoacyl-tRNAs.     

Formation and stabilization model of the 42-mer Abeta radical: implications for the long-lasting oxidative stress in Alzheimer's disease

Amyloid fibrils mainly consist of 40-mer and 42-mer peptides (Abeta40, Abeta42). Abeta42 is believed to play a crucial role in the pathogenesis of Alzheimer's disease because its aggregative ability and neurotoxicity are considerably greater than those of Abeta40. The neurotoxicity of Abeta peptides involving the generation of free radicals is closely related to the S-oxidized radical cation of Met-35. However, the cation's origin and mechanism of stabilization remain unclear. Recently, structural models of fibrillar Abeta42 and Abeta40 based on systematic proline replacement have been proposed by our group [Morimoto, A.; et al. J. Biol. Chem. 2004, 279, 52781] and Wetzel's group [Williams, A. D.; et al. J. Mol. Biol. 2004, 335, 833], respectively. A major difference between these models is that our model of Abeta42 has a C-terminal beta-sheet region. Our biophysical study on Abeta42 using electron spin resonance (ESR) suggests that the S-oxidized radical cation of Met-35 could be generated by the reduction of the tyrosyl radical at Tyr-10 through a turn structure at positions 22 and 23, and stabilized by a C-terminal carboxylate anion through an intramolecular beta-sheet at positions 35-37 and 40-42 to form a C-terminal core that would lead to aggregation. A time-course analysis of the generation of radicals using ESR suggests that stabilization of the radicals by aggregation might be a main reason for the long-lasting oxidative stress of Abeta42. In contrast, the S-oxidized radical cation of Abeta40 is too short-lived to induce potent neurotoxicity because no such stabilization of radicals occurs in Abeta40.     

Steroid Cyclophanes as Artificial Cell-surface Receptors. Molecular Recognition and its Consequence in Signal Transduction Behavior

Steroid cyclophanes, bearing four bile acid moieties covalently placed on a tetraazaparacyclophane skeleton, were designed and synthesized as artificial cell-surface receptors. Guest-binding behavior of the steroid cyclophanes embedded in a bilayer membrane formed with a synthetic peptide lipid was clarified by means of fluorescence and circular dichroism spectroscopy. We found that the steroid cyclophane effectively bound aromatic guests in both bilayer membranes and aqueous solution. In addition, copper(II) ions acted as a guest species for the steroid cyclophane and a competitive inhibitor toward a NADH-dependent lactate dehydrogenase (LDH). On these grounds, we constituted a supramolecular assembly as an artificial signaling system in combination with the steroid cyclophane, a cationic peptide lipid, and LDH. As a consequence, the steroid cyclophane acted as an effective artificial cell-surface receptor being capable of transmitting an external signal to the enzyme in collaboration with copper(II) ions as a signal transmitter.     

Copper-catalyzed coupling of aryl halides and nitrite salts: a mild Ullmann-type synthesis of aromatic nitro compounds

Nitration of aromatic halides proceeded smoothly in the presence of catalytic amounts of Cu bronze and N,N′-dimethylethylenediamine. Sodium nitrite-18-crown-6, or tetra-n-butylammonium nitrite (n-Bu₄NNO₂) turned out to be efficient nitrating agents. The aromatic nitro compounds were synthesized under essentially neutral conditions.     

Right Alternative Unital Bimodules over the Matrix Algebras of Order $ \geq 3 $

Siberian Mathematical Journal - We address the unital right alternative bimodules over the matrix algebras  $ {\mathrm{M}}_{n}(\Phi) $ of order $ n\geq 3 $ , prove that each of these...     

Effect of solvent on the cation-sensitive fluorescence of polyanions bearing 4′-acryloylbenzo-18-crown-6 Units

Changes in the fluorescence intensity of polyanions bearing 4-acryloylbenzo-18-crown-6 units on the addition of cations were studied in a mixed solvent of methanol and water at 30°C. The sensitivity of the change in fluorescence intensities of the polymers toward cations was strongly enhanced compared to that of the corresponding model compound. When alkali metal cations were added, the fluorescence intensity of the polymers decreased in the orders Li⁺>Na⁺>Cs⁺>Rb⁺>K⁺ in a methanol-water (19) mixture and Li⁺>Na⁺>Rb⁺>K⁺Cs⁺ in a methanol-water (91) mixture. Alkaline earth metal cations and alkylamine hydrochlorides decreased the fluorescence intensity of the polymers in a methanol-water (19) mixture. The cation-dependent decrease in the fluorescence intensity of the polymers was affected by the water fraction in a mixed solvent of methanol and water.