Organocatalytic asymmetric thio-Michael addition of arylmethyl mercaptans to cyclic enones by a primary amino acid

A simple primary amino acid was found to be an efficient catalyst for thio-Michael addition of benzyl mercaptan to cyclic enones.     

Synthesis and evaluation of 1-arylsulfonyl-3-piperazinone derivatives as factor Xa inhibitors V. A series of new derivatives containing a spiro[imidazo[1,2-a]pyrazine-2(3H),4'-piperidin]-5(1H)-one scaffold

We have already reported unique compounds containing a N,O-spiro acetal structure as an orally active factor Xa (FXa) inhibitor. This time, we described a N,N-spiro acetal structure as an analogue of the N,O-spiro acetal structure for an orally active FXa inhibitor. The synthesis of these analogues could be achieved in a similar fashion to the N,O-spiro acetal synthesis. Consequently, FXa inhibitory activity was increased and more active compounds could be found (M58163: IC50 = 0.61 nM, M58169: IC50 = 0.58 nM). Additionally, the absolute configuration could be determined by X-ray crystallography analysis (M58169: (R)-config.).     

Liquid crystal and crystal structure of octahomotetraoxacalix[4]arenes

Octahomotetraoxacalix[4]arenes bearing long alkyl chains on their lower rim were prepared. Ester 4a existed in a 1,2-alternate conformation in its crystal structure, which was examined by single-crystal X-ray diffraction analysis. To prepare liquid crystalline materials possessing calixarene moieties by self-assembling, carboxylic acid derivatives 5 were synthesized. Among them, 5c, the octadecyloxy derivative, showed smectic liquid crystal phase. Homooxacalixarenes 5 also formed liquid crystal phases with longer layer distances when two equivalent moles of 1,2-ethylenediamine were added as a linker. These phases were investigated with X-ray diffraction, differential scanning calorimetry, and polarized optical microscopy.     

Cyclic monoterpenes trapped in a polyaromatic capsule: unusual selectivity,isomerization, and volatility suppression

Cyclic monoterpenes (CMTs) are intractable natural products with high volatility and strong odors so that there has been no molecular receptor capable of selectively and tightly trapping CMTs in both solution and the solid state. We herein report that a polyaromatic capsule acts as a functional nanoflask for CMTs with the following five features: (i) the capsule can selectively bind menthone from mixtures with other saturated CMTs in water. In contrast, (ii) treatment of the capsule with mixtures of menthone and π-conjugated CMTs gives rise to ternary host–guest complexes with high pair-selectivity. Notably, (iii) the encapsulated menthone displays unusual isomerization from a typical chair conformer to otherwise unstable conformers upon heating. (iv) The selective binding of volatilized CMTs is demonstrated by the capsule even in the solid state at atmospheric pressure. Furthermore, (v) the volatilities of CMTs are significantly suppressed at elevated temperatures by the capsule upon encapsulation in solution as well as in the solid state.

A polyaromatic capsule demonstrated its unique host functions toward cyclic monoterpenes, i.e., selective binding in water, pair-selective encapsulation, unusual isomerization, selective binding in the solid state, and remarkable volatility suppression.     

Collective motions of myosin head derived from backbone molecular dynamics and combination with X‐ray solution scattering data

Collective modes of myosin head, S1, were derived from molecular dynamics trajectories of a simplified protein model, backbone model. Because the model requires only the positions of C_α‐atoms, large proteins are tractable, even when the amino acid sequence and the side‐chain orientations are unknown. The S1 is a large molecule and only the C_α‐atomic positions have been experimentally determined. In the simulation, large flipping motions of the extended α‐helical C‐terminal tail of S1 were found only in the largest and second largest amplitude collective modes, which were approximately perpendicular to each other. A few collective modes other than the first and second largest ones largely deformed the actin binding site of S1. The pair‐distance distribution, obtained from the X‐ray solution scattering, suggests a large conformational change of S1, isolated in solution without binding to actin filament, during the ATP hydrolysis. The modeling of the large conformational change was done with using the collective modes, and showed that the second mode mainly contributed to the large conformational change. The modeling procedure, introduced here, can be easily generalized for various experimental data, and applicable to the collective modes obtained from an all‐atom simulation. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1983–1994, 2001     

Optical and scintillation properties of Pr-doped Li-glass for neutron detection in inertial confinement fusion process

Optical and scintillation properties of Pr-doped Li-glass, 20Al(PO₃)₃-80LiF:Pr 3%, have been studied for applications in neutron detection systems. Based on optical transmission and reflectivity, the absorption coefficient and refractive index were calculated from the Beer Lambert law. The absorption edge was apparently shifted to the longer wavelength from 160 nm to 240 nm due to 4f → 5d transitions of Pr ions. The strong absorption peaks of praseodymium 4f → 4f transitions were observed from 420 nm to 500 nm and around 590 nm. The radio-luminescence spectrum excited by ²⁴¹Am 5.5 MeV α source was measured. Strong emission peaks were observed around 250 nm. The α-ray excited pulse height spectrum and decay kinetics were also examined. Light yield was estimated to be 400 ± 40 photons/5.5 MeV α and the main component of the decay time was evaluated to be about 12 ns. Furthermore, the pulse height spectrum of the glass excited by ²⁵²Cf neutrons was also measured, and the light yield was estimated to be 140 ± 10 photons/neutron.     

Efficient overall water splitting under visible-light irradiation on (Ga(1-x)Zn(x))(N(1-x)O(x)) dispersed with Rh-Cr mixed-oxide nanoparticles: Effect of reaction conditions on photocatalytic activity

The photocatalytic activity of (Ga(1-x)Zn(x))(N(1-x)O(x)) loaded with Rh-Cr mixed-oxide (Rh(2-y)Cr(y)O3) nanoparticles for overall water splitting under visible-light irradiation (lambda > 400 nm) is investigated with respect to reaction pH and gas pressure. The photocatalytic performance of the catalyst is found to be strongly dependent on the pH of the reactant solution but largely independent of gas pressure. The present photocatalyst exhibits stable and high photocatalytic activity in an aqueous solution of pH 4.5 for 72 h. The photocatalytic performance is much lower at pH 3.0 and pH 6.2, attributable to corrosion of the cocatalyst and hydrolysis of the catalyst. The dispersion of Rh(2-y)Cr(y)O3 as a cocatalyst on the (Ga(1-x)Zn(x))(N(1-x)O(x)) surface promotes hydrogen evolution, which is considered to be the rate-determining step for overall water splitting on this catalyst.     

Modulation of luminescence intensity of lanthanide complexes by photoinduced electron transfer and its application to a long-lived protease probe

Luminescent lanthanide complexes (Tb(3+), Eu(3+), etc.) have excellent properties for biological applications, including extraordinarily long lifetimes and large Stokes shifts. However, there have been few reports of lanthanide-based functional probes, because of the difficulty in designing suitable complexes with a luminescent on/off switch. Here, we have synthesized a series of complexes which consist of three moieties: a lanthanide chelate, an antenna, and a luminescence off/on switch. The antenna is an aromatic ring which absorbs light and transmits its energy to the metal, and the switch is a benzene derivative with a different HOMO level. If the HOMO level is higher than a certain threshold, the complex emits no luminescence at all, which indicates that the lanthanide luminescence can be modulated by photoinduced electron transfer (PeT) from the switch to the sensitizer. This approach to control lanthanide luminescence makes possible the rational design of functional lanthanide complexes, in which the luminescence property is altered by a biological reaction. To exemplify the utility of our approach to the design of lanthanide complexes with a switch, we have developed a novel protease probe, which undergoes a significant change in luminescence intensity upon enzymatic cleavage of the substrate peptide. This probe, combined with time-resolved measurements, was confirmed in model experiments to be useful for the screening of inhibitors, as well as for clinical diagnosis.