Kinetics of Hydroperoxide Epoxidation of 1-Octene in the Presence of MoB2

We have studied the kinetics of the process of epoxidation of 1-octene by tert-butyl hydroperoxide in the presence of molybdenum boride MoB₂. We have studied the effect of the concentrations of starting materials and reaction products on the process. We suggest a kinetic scheme and we calculate the kinetic parameters of the process.     

Alignment of molecules in pulsed resonant laser fields

We investigate by numerical simulations the dynamics of alignment of linear molecules in resonant pulsed laser fields and its dependence on pulse length, field strength, and molecular parameters. We propose an analytical short-time approximation for the time-dependent wave packets. We provide a theoretical basis for the occurrence of saturation in the rotational pumping. We present a formula to predict the time at which the maximum alignment occurs. We discuss the magnitude of the laser-induced alignment and we relate it to a theoretical upper limit.     

Power-law intermittency of single emitters

We summarize experimental observations of fluorescence intermittency of single semiconductor nanocrystals and single molecules. We review the main models proposed earlier to explain the broad power-law distributions of on- and off-blinking times. We argue that a self-trapping model with a distribution of trapping distances can account for most, if not all, observations to date. We propose possible scenarios for photo-ionization, the switching to states with long on-times and the influence of disorder and surfaces on the trapping dynamics.     

Alkaline erosion of CR 39 polymer surfaces

We have investigated the mechanism of erosion of CR 39 polymer in alkaline environments. We observed the kinetics of absorption of water and methanol into both unirradiated and γ-irradiated samples. We use a capillary model to interpret our results.We etched our samples in both KOH solutions, and KOH solutions doped with methanol. Etch rate was desensitizing to γ-irradiation when KOH concentration approached saturation, but KOH solutions doped with methanol were not desensitizing, unlike with nuclear tracks. We account for this difference.     

The potential and flux landscape theory of evolution

We established the potential and flux landscape theory for evolution. We found explicitly the conventional Wright's gradient adaptive landscape based on the mean fitness is inadequate to describe the general evolutionary dynamics. We show the intrinsic potential as being Lyapunov function(monotonically decreasing in time) does exist and can define the adaptive landscape for general evolution dynamics for studying global stability. The driving force determining the dynamics can be decomposed into gradient of potential landscape and curl probability flux. Non-zero flux causes detailed balance breaking and measures how far the evolution from equilibrium state. The gradient of intrinsic potential and curl flux are perpendicular to each other in zero fluctuation limit resembling electric and magnetic forces on electrons. We quantified intrinsic energy, entropy and free energy of evolution and constructed non-equilibrium thermodynamics. The intrinsic non-equilibrium free energy is a Lyapunov function. Both intrinsic potential and free energy can be used to quantify the global stability and robustness of evolution. We investigated an example of three allele evolutionary dynamics with frequency dependent selection (detailed balance broken). We uncovered the underlying single, triple, and limit cycle attractor landscapes. We found quantitative criterions for stability through landscape topography. We also quantified evolution pathways and found paths do not follow potential gradient and are irreversible due to non-zero flux. We generalized the original Fisher's fundamental theorem to the general (i.e., frequency dependent selection) regime of evolution by linking the adaptive rate with not only genetic variance related to the potential but also the flux. We show there is an optimum potential where curl flux resulting from biotic interactions of individuals within a species or between species can sustain an endless evolution even if the physical environment is unchanged. We offer a theoretical basis for explaining the corresponding Red Queen hypothesis proposed by Van Valen. Our work provides a theoretical foundation for evolutionary dynamics.     

Monte Carlo analyses of multiple backscattering of gamma rays

We have written a Monte Carlo code to simulate the experimental results of a previously reported study. We were able to analyse the energy distributions of photons that reached the detector system after suffering several successive Compton scatterings in the target. We have also investigated how the number of multiply backscattered events depends on the target thickness and the energy of the primary photons.     

Calculation of ionization of helium by relativistic heavy ions with a relativistic CTMC-method

We have used a relativistic classical trajectory Monte Carlo (CTMC)-method to calculate cross sections for single and double ionization of helium by relativistic heavy ions. We compare our results with experimentally obtained cross sections. We comment on the limits of the validity of relativistic classical calculations.     

Ab initio calculation of vibrational frequencies and Raman spectra of barium peroxide glass including comparison of tetrahedral BaO4 with GeO4 and SiO4

We have calculated the vibrational frequencies of clusters of atoms from the first principles by using the density-functional theory in the local density approximation (LDA). We are also able to calculate the electronic binding energy for all of the clusters of atoms from the optimized structure. We have made clusters of BanOm (n, m=1-6) and have determined the bond lengths, vibrational frequencies as well as intensities in each case. We find that the peroxide cluster BaO2 occurs with the O-O vibrational frequency of 836.3 cm(-1). We also find that a glass network occurs in the material which explains the vibrational frequency of 67 cm(-1). The calculated values agree with those measured from the Raman spectra of barium peroxide and Ba-B-oxide glass. We have calculated the vibrational frequencies of BaO4, GeO4 and SiO4 each in tetrahedral configuration and find that the vibrational frequencies in these systems depend on the inverse square root of the atomic mass.     

Temperature dependence of the fluorescence properties of curcumin

Steady-state and time-resolved techniques were employed to study the nonradiative process of curcumin dissolved in ethanol and 1-propanol in a wide range of temperatures. We found that the nonradiative rate constants at temperatures between 175-250 K qualitatively follow the same trend as the dielectric relaxation times of both neat solvents. We attribute the nonradiative process to solvent-controlled proton transfer. We also found a kinetic isotope effect on the nonradiative process rate constant of ~2. We propose a model in which the excited-state proton transfer breaks the planar hexagonal structure of the keto-enol center of the molecule. This, in turn, enhances the nonradiative process driven by the twist angle between the two phenol moieties.     

Study of Oxidation-Reduction Properties and NO-Donor Ability of Dienediamines in the Indole, Pyrrole, and Thiophene Series

We have conducted an electrochemical study of the oxidation-reduction properties of synthesized dienediamines: derivatives of indole, pyrrole, and thiophene. We have established that reduction of the indicated compounds occurs with successive transfer of two electrons, the first transfer being reversible. We consider the effect of structural factors and the nature of the heterocycle on the ease of reduction of the given compounds. We present the results of an initial study of the NO-donor ability of the compounds upon oxidation.     

Polarization propagator calculation of spectroscopic properties of molecules

We propose 10 desirable features or criteria for general purpose methods to be applied to the calculation of a range of spectroscopic properties. We discuss the second-order polarization propagator approximation (SOPPA ) in light of these criteria by giving the actual computational expression used as well as a few numerical examples taken from the theory of NMR spectra (magnetic shieldings and spin-spin coupling constants). We demonstrate that SOPPA comes close to fulfilling these criteria.     

Study of the Mechanism of Hexane Isomerization under Micropulse Conditions

We have developed a highly informative micropulse method for isomerization of n-hexane. We have found that the primary reaction products on Pd/HM, Pd/HY, and Pd/HTsVM [analog of HZSM] catalysts are only 2- and 3-methylpentanes. We propose mechanisms for their formation. The reaction is considered to be unimolecular.     

Drops and shells of liquid crystal

We review the state of the art concerning drops and shells of liquid crystal. We especially focus on the defect structures observed with liquid crystals with different degrees of order under different boundary conditions and on the transitions between these structures. We conclude with an overview where we emphasize those areas that are still unexplored.     

Electrostatics of DNA complexes with cationic lipid membranes

We present the exact solutions of the linear Poisson-Boltzmann equation for several problems relevant to electrostatics of DNA complexes with cationic lipids. We calculate the electrostatic potential and electrostatic energy for lamellar and inverted hexagonal phases, concentrating on the effects of dielectric boundaries. We compare our results for the complex energy with the known results of numerical solution of the nonlinear Poisson-Boltzmann equation. Using the solution for the lamellar phase, we calculate the compressibility modulus and compare our findings with the experimental data available. Also, we treat charge-charge interactions across, along, and between two low-dielectric membranes. We obtain an estimate for the strength of electrostatic interactions of one-dimensional DNA smectic layers across the lipid membrane. We discuss in the end some aspects of two-dimensional DNA condensation and DNA-DNA attraction in the DNA-lipid lamellar phase in the presence of di- and trivalent cations. We analyze the equilibrium DNA-DNA separations in lamellar complexes using the recently developed theory of electrostatic interactions of DNA helical charge motifs.     

Tautomerism of uracil,cytosine, isocytosine,and some of their thio-derivatives

We present an ab initio study of tautomerism in uracil, cytosine, isocytosine, and some of their derivatives, mainly those due to thio substitution. We advance gas phase enthalpies for the tautomerization processes. We observe that the substitution of atoms not directly involved in the tautomerism has no appreciable effect on the enthalpy values. On the other hand, thio substitution of the oxygen involved in the tautomerism produces a general and small shift favoring the thiol isomer in aromatic complexes. We compare the theoretical predictions with the experimental evidence available and find them to agree.     

Atomistic simulation of the homogeneous nucleation and of the growth of N2 crystallites

We report on a computer simulation study of the early stages of the crystallization of molecular nitrogen. First, we study how homogeneous nucleation takes place in supercooled liquid N(2) for a moderate degree of supercooling. Using the umbrella sampling technique, we determine the free energy barrier of formation for a critical nucleus of N(2). We show that, in accord with Ostwald's rule of stages, the structure of the critical nucleus is predominantly that of a metastable polymorph (alpha-N(2) for the state point investigated). We then monitor the evolution of several critical nuclei through a series of unbiased molecular dynamics trajectories. The growth of N(2) crystallites is accompanied by a structural evolution toward the stable polymorph beta-N(2). The microscopic mechanism underlying this evolution qualitatively differs from that reported previously. We do not observe any dissolution or reorganization of the alpha-like core of the nucleus. On the contrary, we show that alpha-like and beta-like blocks coexist in postcritical nuclei. We relate the structural evolution to a greater adsorption rate of beta-like molecules on the surface and show that this transition actually starts well within the precritical regime. We also carefully investigate the effect of the system size on the height of the free energy barrier of nucleation and on the structure and size of the critical nucleus.     

Synthesis of N-Pyridylmethylidene-2-aminopyridines and their Methyl-substituted Derivatives in the Presence of Molecular Sieves

We have studied condensation of 2-, 3-, 4-pyridinealdehydes and 6-methylpyridine-2-aldehyde with 2-aminopyridine and its 3-, 4-, and 6-methyl derivatives in benzene in the presence of molecular sieves. The reactions occur even at room temperature to form the corresponding pyridyl-pyridyl azomethines, and also aminals. We have determined the optimal conditions for carrying out the processes with the aim of obtaining both types of products. We consider the characteristics of the mass spectra for the synthesized aldimines. We present the X-ray diffraction results for the two aminals.     

Role of Rydberg states in the photochemical dynamics of ethylene

We use the ab initio multiple spawning method with potential energy surfaces and nonadiabatic coupling vectors computed from multistate multireference perturbation theory (MSPT2) to follow the dynamics of ethylene after photoexcitation. We introduce an analytic formulation for the nonadiabatic coupling vector in the context of MSPT2 calculations. We explicitly include the low-lying 3s Rydberg state which has been neglected in previous ab initio molecular dynamics studies of this process. We find that although the 3s Rydberg state lies below the optically bright ππ* state, little population gets trapped on this state. Instead, the 3s Rydberg state is largely a spectator in the photodynamics, with little effect on the quenching mechanism or excited state lifetime. We predict the time-resolved photoelectron spectrum for ethylene and point out the signature of Rydberg state involvement that should be easily observed.     

Voltametric behaviour of solutions of γ-irradiated KCl

We have studied the voltametric behaviour of solutions of γ-irradiated alkali halides. We identify the existence of hydrated electrons and we believe we have observed the phenomenon of aquoluminescence.     

Single vesicle observations of the cardiolipin-cytochrome C interaction: induction of membrane morphology changes

We present a novel platform for investigating the composition-specific interactions of proteins (or other biologically relevant molecules) with model membranes composed of compositionally distinct domains. We focus on the interaction between a mitochondrial-specific lipid, cardiolipin (CL), and a peripheral membrane protein, cytochrome c (cyt c). We engineer vesicles with compositions such that they phase separate into coexisting liquid phases and the lipid of interest, CL, preferentially localizes into one of the domains (the liquid disordered (L(d)) phase). The presence of CL-rich and CL-depleted domains within the same vesicle provides a built-in control experiment to simultaneously observe the behavior of two membrane compositions under identical conditions. We find that cyt c binds strongly to CL-rich domains and observe fascinating morphological transitions within these regions of membrane. CL-rich domains start to form small buds and eventually fold up into a collapsed state. We also observe that cyt c can induce a strong attraction between the CL-rich domains of adjacent vesicles as demonstrated by the development of large osculating regions between these domains. Qualitatively similar behavior is observed when other polycationic proteins or polymers of a similar size and net charge are used instead of cyt c. We argue that these striking phenomena can be simply understood by consideration of colloidal forces between the protein and the membrane. We discuss the possible biological implications of our observations in relation to the structure and function of mitochondria.