Solvent-induced shift of the lowest singlet π → π* charge-transfer excited state of p-nitroaniline in water: an application of the TDDFT/EFP1 method

The combined time-dependent density functional theory effective fragment potential method (TDDFT/EFP1) is applied to a study of the solvent-induced shift of the lowest singlet π → π* charge-transfer excited state of p-nitroaniline (pNA) from the gas to the condensed phase in water. Molecular dynamics simulations of pNA with 150 EFP1 water molecules are used to model the condensed-phase and generate a simulated spectrum of the lowest singlet charge-transfer excitation. The TDDFT/EFP1 method successfully reproduces the experimental condensed-phase π → π* vertical excitation energy and solvent-induced red shift of pNA in water. The largest contribution to the red shift comes from Coulomb interactions, between pNA and water, and solute relaxation. The solvent shift contributions reflect the increase in zwitterionic character of pNA upon solvation.     

Thermal management of GaInNAs/GaAs VECSELs

Different methods used to reduce temperature increase within the active region of vertical-external-cavity surface-emitting lasers (VECSELs) are described and compared with the aid of the self-consistent thermal finite-element method. Simulations have been carried out for the GaInNAs/GaAs multiple-quantum-well (MQW) VECSEL operating at room temperature at 1.31 μm. Main results are presented in form of ‘thermal maps’ which can be simply used to determine maximal temperature of different structures at specified pumping conditions. It has been found that these maps are also appropriate for some other GaAs-based VECSELs and can be very helpful especially during structure designing. Moreover, convective and thermal radiation heat transfer from laser walls has been investigated.     

Particle capture by radiation drag around a highly luminous compact stars

In the present work, we explored the effect of the radiation on the effective impact parameter for capture in a fully general relativistic manner. To summarize our results, evidently due to the radiation drag (the Poynting–Robertson effect), critical impact parameter of point particle gets larger by the factor of two, thus, the effective cross section of the luminous relativistic star becomes 4 times larger than that of the star without radiation emission. In addition, the finite size effect of the star adds up to this growth of the effective cross section.     

On the Convolution of a Finite Number of Analytic Functions Involving a Generalized Srivastava–Attiya Operator

The present paper gives several subordination results involving a generalized Srivastava–Attiya operator (defined below). Among the results presented in this paper include also a sufficiency condition for the convexity of the convolution of certain functions and a sharp result relating to the convolution structure. We also mention various useful special cases of the main results including those which are related to the Zeta function.     

Rigid Plastic Plates under a Concentrated Moving Load∗

A rigid-plastic rectangular plate subjected to a moving transverse load is analyzed. The load is too large for the plate to be supported under static conditions. The present study indicates that there is a critical value for the moving load, above which the crossing cannot be made, irrespective of its speed. The relation between the moving load and its speed is given for values less than ciritical, as well as the distribution of displacement for a simply supported rectangular plate.     

Reaction kinetics study of short DNA strands using a maximum entropy method and nonlinear curve fitting

It is important to understand the formation of double-strand DNA (dsDNA) in a salt solution because it is one of the key reactions in life. A short cDNA strand pair was designed, and each single-strand DNA (ssDNA) was attached to a fluorescent dye that was either a donor or an acceptor of fluorescence resonance energy transfer. The fluorescence intensity was expected to change as time passed as the complementary pairs of ssDNAs formed dsDNAs. The concentration of dsDNA was theoretically calculated, and the measured data were consistent with theoretical results. The analysis of the nonlinear fitting method and the maximum entropy method detected that the reaction curve contains two major types of kinetics that likely represent the formation of dsDNA and mismatching.     

Synthesis and pharmacological effects of the enantiomers of the N-phenethyl analogues of the ortho and para e- and f-oxide-bridged phenylmorphans

The N-phenethyl analogues of (1R*,4aR*,9aS*)-2-phenethyl-1,3,4,9a-tetrahydro-2H-1,4a-propanobenzofuro[2,3-c]pyridin-6-ol and 8-ol and (1R*,4aR*,9aR*)-2-phenethyl-1,3,4,9a-tetrahydro-2H-1,4a-propanobenzofuro[2.3-c]pyridin-6-ol and 8-ol, the ortho- (43) and para-hydroxy e- (20), and f-oxide-bridged 5-phenylmorphans (53 and 26) were prepared in racemic and enantiomerically pure forms from a common precursor, the quaternary salt 12. Optical resolutions were accomplished by salt formation with suitable enantiomerically pure chiral acids or by preparative HPLC on a chiral support. The N-phenethyl (-)- para-e enantiomer (1S,4aS,9aR-(-)-20) was found to be a mu-opioid agonist with morphine-like antinociceptive activity in a mouse assay. In contrast, the N-phenethyl (-)-ortho-f enantiomer (1R,4aR,9aR-(-)-53) had good affinity for the mu-opioid receptor (K(i) = 7 nM) and was found to be a mu-antagonist both in the [(35)S]GTP-gamma-S assay and in vivo. The molecular structures of these rigid enantiomers were energy minimized with density functional theory at the level B3LYP/6-31G* level, and then overlaid on a known potent mu-agonist. This superposition study suggests that the agonist activity of the oxide-bridged 5-phenylmorphans can be attributed to formation of a seven membered ring that is hypothesized to facilitate a proton transfer from the protonated nitrogen to a proton acceptor in the mu-opioid receptor.     

The optical properties of Yb3+ ions in LiTaO3:Nd,Yb crystals

3+ ions excited by energy transfer from Nd³⁺ ions in LiTaO₃:Nd, Yb crystals are presented. The emission band of Yb³⁺ ions is broad, due to the strong phonon-coupling and to the relative large Stark-splitting of the ground ²F_7/2 multiplet. The emission cross-section was evaluated by the reciprocity method, and a value of 0.53×10^-20 cm² was obtained. The gain coefficients derived for the inversion parameters in the range 0.05 to 0.5 indicate positive gain in the 985–1070 nm range. Received: 17 March 1997/Revised version: 10 June 1997     

Radiationless deactivation of hybridization-sensitive DNA probe

In this study we attempt to determine the deactivation mechanism of a hybridization-sensitive DNA probe by using steady state absorption and fluorescence spectroscopy. Thiazole orange or 2,2′-Methylenebis(N-alkylbenzothiazole) is covalently linked to a single nucleotide in the DNA probe. Radiationless deactivation of the fluorophores is mainly determined by photo-induced isomerization of the methine bridge. Experiments done using solutes of differing molecular weight (sucrose, glucose and glycerin) to provide solutions of similar viscosity reveals the importance of solution viscosity and fluorophore conformation on radiationless deactivation. The quantum yield of the fluorophore in high viscous solutions can be explained by a simple diffusion model. This linear relationship is broken when a dimer conformation of the fluorophore starts to form, which in turn influences the emission intensity of the fluorophore.