Complexation of copper(II)-montmorillonite with a modified cyclodextrin

The uptake reaction of Cu(II)-montmorillonite with mono-(6--aminoethylamino-6-deoxy)--cyclodextrin (CDen) has been examined at 25°C. The CDen molecules in their neutral or cationic forms are taken up by forming complexes with the interlayer Cu(II) ions (Cu_int) and by displacing protons at the clay surface. At low uptakes of CDen, 11 complexes of CDen with Cu_int are intercalated as a monolayer of 13.7 Å in thickness, with their opening faces parallel to the interlayer surface. At higher contents, the CDen-Cu_int complexes are more voluminously packed to form two intercalated phases with larger spacings until a bilayer of 23.9 Å in thickness is formed. The uptake by the mode of ion exchange proceeds increasingly at the intermediate uptake stage. At higher levels, however, this additional uptake is decreased rapidly due to the increase in the pH of solution, resulting in a maximum in the curve of CDen uptake against CDen added.     

Rotational barriers in bisadducts of 1-cyano-1-methylethyl radicals with nitrones and nitroso compounds

The temperature-dependent ¹H NMR spectra have been measured for the bisadducts 2a and 3 of 1-cyano-1-methylethyl radicals with α-phenyl-N-benzylnitrone [N-(benzylidene)benzylamine N-oxide] and nitrosobenzene, respectively. A free energy of activation of ΔG^≠ = 62.8 ～ 64.4 kJ mol^?1 (15.0 ～ 15.4 kcal/mol) at 24 ～ 45 °C has been obtained for 2a by applying the Eyring equation to the rate constants at the coalescence points of the methyl signals. The line shapes due to four methyl signals exchanging between two sites of equal population have been simulated by the theoretical calculation to give an activation enthalpy of 52.3 kJ mol^?1 (12.5 kcal/mol) and the corresponding entropy of ?39.3 J K^?1 mol^?1 for 3. As the inversion barriers at pyramidal nitrogens of hydroxylamine derivatives should be lowered in N-phenyl derivatives because of conjugation, the rate process which is responsible for the observed temperature dependent NMR spectra can be assigned to restricted rotation around one of the skeletal C? N? O? C bonds. The relevance of the results to the conformations of nitroxides derived from the spin trapping method using α-phenyl-N-t-butylnitrone [N-(benzylidene)-t-butylamine N-oxide] and nitroso spin traps is discussed.     

Na adsorption on the Si111-(7 x 7) surface: from two-dimensional gas to nanocluster array

We have systematically investigated Na adsorption on the Si(111)-(7 x 7) surface at room temperature using scanning tunneling microscopy (STM). Below the critical coverage of 0.08 monolayer, we find intriguing contrast modulation instead of localized Na adsorbates, coupled with streaky noise in the STM images, which is accompanied by monotonic work function drop. Above the critical coverage, Na clusters emerge and form a self-assembled array. Combined with first-principles theoretical simulations, we conclude that the Na atoms on the (7 x 7) surface are, while strongly bound ( approximately 2.2 eV) to the surface, highly mobile in "basins" around the Si rest atoms, forming a two-dimensional gas phase at the initial coverage, and that the cluster at the higher coverage consists of six Na atoms together with three Si adatoms.     

Disuse atrophy alterations in normal and low temperature environments during hindlimb unloading in Syrian hamsters

This study examined whether a hypothermic environment reduces experimentally-induced atrophy of skeletal muscle, as judged by histochemical findings. The hind limbs of hamsters in a hypothermic group were suspended and flexed into plantar positions at the ankle joint, and housed for one week at 8 to 12 degree celsius in a temperature-controlled room, while the normothermic group was housed at 23 to 25 degree celsius. Hypothermia did not significantly alter the average caloric intake, and the animals from the hypothermic group lost a significant amount of body weight when compared with the normothermic group. The hypothermic group retained more muscle wet-weight and myofibers cross-sectional area in the soleus and gastrocnemius muscles compared with the normothermic group. Our results indicate that a hypothermic environment inhibits short-term muscle atrophy. This inhibition may be caused by the increased caloric intake combined with a state similar to hibernation in low-temperature environments.     

Some cytotoxicological aspects of ethyl and fluoroethyl alkanesulfonates in Escherichia coli: role of fluorine substitution

Several fluoroethyl derivatives of alkanesulfonates and N-nitrosourea were tested for cytotoxicity and mutagenicity in E. coli K12 AB1157. Cytotoxicity was potentiated by fluorine substitution in the alkyl moiety of the ethylating agents. Mutagenicity was strongly suppressed by fluorine substitution in the alkanesulfonates, but not in the N-nitrosourea. The capacity to induce the SOS repair network was suppressed, as was mutagenicity, in alkanesulfonates, but not in N-nitrosourea. The potentiating effect of fluorine on the cytotoxicity of alkanesulfonates seems to be due to an as yet unknown killing mechanism. An appreciable suppressive effect on the mutagenicity and the SOS induction is worth notice for the biological role of fluorine substitution in alkylating agents.     

(1-PYRENYL)METHYL CARBAMATES FOR FLUORESCENT "CAGED" AMINO ACIDS AND PEPTIDES

A highly fluorescent 1-pyrenylmethyloxycarbonyl amino acid (Pmoc-amino acid) is obtained in moderate yield by the reaction of (1-pyrenylmethyl)-4-nitrophenylcarbonate with an amino acid in the presence of sodium carbonate. The condensation of Pmoc-amino acid with an amino acid gives Pmoc-peptide in the presence of 1-ethyl-3-(3-dimethylaminepropyl)carbodiimide and 1-hydroxyben-zotriazole. The amino acid is recovered from an H₂O-dioxane (2:3) solution of Pmoc-amino acid by irradiation through a Pyrex filter with a medium pressure Hg lamp or at 340 nm. Although the quantum yield of the photolysis is rather low (ca 0.01), the photolysis proceeds fast and efficiently due to the large absorption coefficient of Pmoc-amino acid at around 340 nm. Thus, the use of Pmoc-amino acid as a “caged” amino acid is promising.     

Elucidation of the stereochemistry of Tl+ in oxide glasses by electron spin resonance spectroscopy

The relation has been elucidated between the stereochemistry of Tl⁺ and the chemical composition of host oxide glasses by measuring the ESR of paramagnetic Tl²⁺ induced with γ-irradiation at 77 K. The spectra have been analyzed by using a new solution of the spin-Hamiltonian developed by the authors. The results indicate: (1) there are two sites for Tl⁺ in a wide variety of oxide glasses (site I and site II). Tl⁺ in site I has a heavily distorted ligand field (lone pair electrons of Tl⁺ occupy a s-p(-d) hybridized non-bonding orbital extruding in one direction). The geometry of the Tl⁺-complex in site II is nearly spherically-symmetric (lone pair electrons locate in an anti-bonding sigma orbital to which the Tl 6s atomic orbital mainly participates); (2) site I appears in the glasses where both the bridging and non-bridging oxygens coexist. Site II is observed in the other glasses; (3) a drastric change in lineshape of Tl²⁺ induced with 77 K irradiation was observed upon thermal annealing. A structural model for this change was proposed; the Tl²⁺ with an excess plus charge is stabilized by the cooperative motion of the alkali ion pairing with Tl²⁺ and intervening non-bridging oxygens, the alkali being repelled and the oxygens being attracted.     

Lignified materials as potential medicinal resources. III. Diversity of biological activity and possible molecular species involved

Diverse biological activities of hot-water and alkali extracts of lignified materials were reviewed and the molecular species involved are discussed. Materials tested included pine cone of Pinus parviflora SIEB. et Zucc., wood chips of slash pine, Douglas fir, and tallow wood, and two basidiocarps, in addition to their partially degraded preparations and commercial lignins. As a tentative conclusion, the lignin structure of these extracts might be responsible for the potent stimulation of granulocytic cell iodination, inhibition of viral infection and/or proliferation in vitro, and inactivation of viral ribonucleic acid (RNA)-dependent RNA polymerase and (adenosine diphosphate-ribose)n glycohydrolase. Other activities displayed by some of these extracts, such as antibacterial and antitumor activities, induction of hemolytic plaque-forming-cells in mice, and stimulation of deoxyribonucleic acid synthesis of isolated splenocytes, remain to be investigated.     

Tandem base-promoted ring opening/brook rearrangement/allylic alkylation of O-silyl cyanohydrins of beta-silyl-alpha,beta-epoxyaldehydes

[reaction: see text]. Metalated O-silyl cyanohydrins of beta-silyl-alpha,beta-epoxyaldehyde have been found to serve as functionalized homoenolate equivalents by a tandem sequence involving a base-promoted ring opening of the epoxide, Brook rearrangement, and alkylation of the resulting allylic anion.     

Stereoselective construction of eight-membered oxygen heterocycles by Brook rearrangement-mediated [3 + 4] annulation

[reaction: see text] A newly developed strategy for eight-membered oxygen heterocycle construction via [3 + 4] annulation is described. The method involves the combination of beta-substituted acryloylsilanes and enolates of 6-oxacyclohept-2-en-1-one. A unique feature of this annulative approach is its capacity to generate eight-membered ring systems containing useful functionalities for further synthetic elaboration from readily available three- and four-carbon components.