Optical soliton perturbation in non-Kerr law media: Traveling wave solution

This paper analyses the dynamics of soliton propagation through optical fibers with non-Kerr law nonlinearities. The governing nonlinear Schrödinger equation is integrated in the presence of perturbation terms. The traveling wave hypothesis is used to carry out the integration. Domain restrictions on the soliton parameters are identified in the process. The five forms of nonlinearity that are studied are Kerr-law, power-law, parabolic-law, dual-power law and the log-law nonlinearity. Numerical simulations are presented for each of these nonlinear media.     

A generator of protein folding kinetics states for the diffusion–collision model

Two separate algorithms for calculating the intermediate states, using cellular automata, and the initial conditions in the rate matrix for the diffusion–collision model are introduced. They enable easy and fast calculations of the folding probabilities of the intermediate states, even for a very large number of microdomains. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 923–932, 2000     

Quantum-mechanical calculation of the van der Waals interaction between small metallic spheres

We give the first microscopic calculation of the leading terms in the van der Waals interaction energy between two very small metallic particles, treating their electronic excitations in the quantum-mechanical Infinite Barrier Model and the Random Phase Approximation. The results are very close to those obtained for the corresponding classical spheres, provided that we describe them by their effective radii calculated to satisfy the electrostatic zero-force sum-rule. We examine the higher order terms and the exact results at short distances in the plasmon-pole approximation, and discuss the convergence of the multipole expansions.     

HF in clusters of molecular hydrogen. I. Size evolution of quantum solvation by parahydrogen molecules

We present a theoretical study of the quantum solvation of the HF molecule by a small number of parahydrogen molecules, having n = 1-13 solvent particles. The minimum-energy cluster structures determined for n = 1-12 have all of the H(2) molecules in the first solvent shell. The first solvent shell closes at n = 12 and its geometry is icosahedral, with the HF molecule at the center. The quantum-mechanical ground-state properties of the clusters are calculated exactly using the diffusion Monte Carlo method. The zero-point energy of (p-H(2))(n)HF clusters is unusually large, amounting to 86% of the potential well depth for n > 7. The radial probability distribution functions (PDFs) confirm that the first solvent shell is complete for n = 12, and that the 13th p-H(2) molecule begins to fill the second solvent shell. The p-H(2) molecules execute large-amplitude motions and are highly mobile, making the solvent cage exceptionally fluxional. The anisotropy of the solvent, very pronounced for small clusters, decreases rapidly with increasing n, so that for n approximately 8-9 the solvent environment is practically isotropic. The analysis of the pair angular PDF reveals that for a given n, the parahydrogen solvent density around the HF is modulated in a pattern which clearly reflects the lowest-energy cluster configuration. The rigidity of the solvent clusters displays an interesting size dependence, increasing from n = 6 to 9, becoming floppier for n = 10, and increasing again up to n = 12, as the solvent shell is filled. The rigidity of the solvent cage appears to reach its maximum for n = 12, the point at which the first solvent shell is closed.     

Photoinduced gelation by stilbene oxalyl amide compounds

Oxalyl amide derivatives bearing 4-dodecyloxy-stilbene as a cis-trans photoisomerizing unit were synthesized. The trans derivative acted as a versatile gelator of various organic solvents, whereas the corresponding cis derivative showed a poor gelation ability or none at all. In diluted solution (c = 2.0 x10(-5) mol dm(-3), ethanol), the cis isomer was photochemically converted into the trans isomer within 4 min. Depending on the radiation wavelength, the trans isomer was stable or liable to photodecomposition. When exposed to irradiation, a concentrated solution of the cis isomer (c = 2.0 x 10(-2) mol dm(-3), ethanol) turned into a gel. The FT-Raman, FT-IR, and 1H NMR spectra demonstrated that the gelation process occurred because of a rapid cis --> trans photoisomerization followed by a self-assembly of the trans molecules. Apart from the formation of hydrogen bonding between the oxalyl amide parts of the molecules, confirmed by FT-IR spectroscopy, it was assumed that the pi-pi stacking between the trans-stilbene units of the molecule and a lipophilic interaction between long alkyl chains were the interactions responsible for gelation.     

Efficient syntheses of 2-chloro-2'-deoxyadenosine (cladribine) from 2'-deoxyguanosine(1)

We report efficient syntheses of the clinical agent cladribine (2-chloro-2'-deoxyadenosine, CldAdo), which is the drug of choice against hairy-cell leukemia and other neoplasms, from 2'-deoxyguanosine. Treatment of 3',5'-di-O-acetyl- or benzoyl-2'-deoxyguanosine (1) with 2,4,6-triisopropyl- or 4-methylbenzenesulfonyl chloride gave high yields of the 6-O-arylsulfonyl derivatives 2 or 2'b. Deoxychlorination at C6 of 1 also proceeded to give the 2-amino-6-chloropurine derivative 5 in excellent yields. The nonaqueous diazotization/chloro dediazoniation (acetyl chloride/benzyltriethylammonium nitrite) of 2, 2'b, and 5 gave the 2-chloropurine derivatives 3, 3'b, and 6, respectively. The selective ammonolysis at C6 (arylsulfonate with 3 or chloride with 6) and accompanying deprotection of the sugar moiety gave CldAdo (64-75% overall yield from 1).     

Quantum dynamics of coupled translational and rotational motions of H2 inside C60

We report rigorous quantum calculations of the translation-rotation (T-R) eigenstates of the H2 molecule in C60. The resulting level structure can be explained in terms of a few dominant features. These include the coupling between the orbital and the rotational angular momenta of H2 to give the total angular momentum lambda, and the splitting of the sevenfold degeneracy of T-R levels with lambda=3 by the nonsphericity of C60, according to the rules of the icosahedral I h group.     

Solid-state reaction mechanisms in monomer-dimer interconversions of p-bromonitrosobenzene. Single-crystal-to-single-crystal photodissociation and formation of new non-van der Waals close contacts

Thermal and photochemical reactions and the phase transition mechanisms of solid-state monomer-dimer interconversions of p-bromonitrosobenzene were studied on the basis of kinetics data and single-crystal-to-single-crystal transformations. From the crystal structure and packing of p-bromobenzeneazodioxide and the previously determined structure of the freshly sublimed monomer, we have explained both consecutive steps in thermal dimerization. While the first reaction (formation of the metastable dimer) with first-order kinetics affords diminishing of the (2 2 0) critical crystal plane that intersects atoms of the nitroso groups, the second phase transformation step includes four critical planes, which show sigmoid kinetics. In the new phase growth, these crystal planes developed in two (Cartesian) dimensions as vectors perpendicular to ab and ac planes, which is in agreement with the dimensionality previously determined on the basis of the Avrami-Erofeyev analysis (with m = 2.01). Photochromic dissociation of the azodioxide at 100 K was followed by structure determination of the single-crystal-to-single-crystal transformation. A new metastable monomer was discovered, in which, despite bond breaking, the nitrogen atoms of the neighboring monomers remained very close to each other (2.30 A), i.e., 23.3% closer than is the sum of two N-atom van der Waals radii. Such an extraordinary close contact was also observed between N and O atoms. This tight packing can explain why the return to dimerization after the low temperature photodissociation occurs so rapidly at a temperature as low as 170 K.     

Membrane switch hypothesis. 2. Domain structure of phagocytes in horses with recurrent airway obstruction

The mechanism of recurrent airway obstruction (RAO) in horses was investigated by measuring the membrane domain structure and oxy-redoxy activity in phagocytes isolated from bronchoalveolar lavage fluid (BAL) and from the blood of healthy and RAO horses by electron paramagnetic resonance (EPR). Differences in the activity of intracellular antioxidant enzymes CAT, GPx, and SOD measured in phagocytes of RAO horses in comparison to healthy horses showed that the phagocytes were affected by oxidative stress. In comparison with polymorphonuclear leukocytes (phagocytes) from the blood of healthy horses the reduction mechanisms in BAL were faster and coincided with the merging of disordered membrane domains, while in horses with RAO the reduction and membrane domain structure remained unchanged. We assume that the merging of lipid domains observed in phagocytes from BAL of healthy horses could promote cluster formation of membrane proteins or ligands, which could trigger the activation process in phagocytes of healthy horses and consequently the physiological response that probably did not happen in phagocytes of RAO horses.     

Recognition of homo-polynucleotides containing adenine by a phenanthridinium bis-uracil conjugate in aqueous media

Among novel bis-nucleobase-phenanthridinium conjugates bis-uracil analogue stabilized significantly more effective poly-dA-poly-dT and poly-AH(+)-poly-AH(+) than adenine analogue and reference compound . For the alternating poly-dAdT-poly-dAdT however, the binding preference is lost, pointing to the importance of specific interactions of uracils of with homopolynucleotides containing consecutive adenines.