Optimization of heat transfer properties on ferrofluid flow over a stretching sheet in the presence of static magnetic field

Journal of Thermal Analysis and Calorimetry - The main emphasis of the present research is to investigate the composite effects of magnetization force and rotational viscosity on two-dimensional...     

1,3‐Dipolar cycloadditions: Investigation of cycloadditions of c‐aryl‐n‐(4‐chlorophenyl) nitrones to n‐cinnamoyl piperidines

Investigation of cycloadditions of C‐aryl‐N‐(4‐chlorophenyl)nitrones to N‐cinnamoyl piperidines was carried out. Two diastereoisomeric and one regioisomeric cycloadducts, and in some cases ring‐opened compounds were characterized by spectroscopic and X‐ray data. Molecular modelling was carried out for conformational studies.     

Rigid-rod push-pull naphthalenediimide photosystems

Design, synthesis and evaluation of advanced rigid-rod pi-stack photosystems with asymmetric scaffolds are reported. The influence of push-pull rods on self-organization, photoinduced charge separation and photosynthetic activity is investigated and turns out to be surprisingly small overall.     

Hydrogen bonding of methanol in supercritical CO2: comparison between 1H NMR spectroscopic data and molecular simulation results

Molecular dynamics simulation results on hydrogen bonding in mixtures of methanol with CO2 at supercritical, liquid-like conditions are compared to 1H NMR spectroscopic data that have recently become available. The molecular models are parametrized using vapor-liquid equilibrium data only, which they reliably describe. A new molecular model for methanol of Lennard-Jones plus point charge type is presented. This molecular methanol model is investigated in terms of its capability to yield hydrogen-bonding statistics. Simple assumptions are made regarding the assignment of NMR chemical shifts to the different types of hydrogen-bonded species. Only two state-independent parameters are fitted to the large NMR data set on the basis of hydrogen-bonding statistics from molecular simulations. Excellent agreement between the molecular simulation results and the NMR data is found. This shows that the molecular models of the simple type studied here cannot only describe thermodynamic properties but also structural effects of hydrogen bonding in solutions.     

Excited-state dynamics of donor-acceptor bridged systems containing a boron-dipyrromethene chromophore: interplay between charge separation and reorientational motion

The excited-state dynamics of a series of electron donor-acceptor bridged systems (DABS) consisting of a boron-dipyrromethene chromophore covalently linked to a dinitro-substituted triptycene has been investigated using femtosecond time-resolved spectroscopy. The chromophores differ by the number of bromine atom substituents. The fluorescence lifetime of the DABS without any bromine atom is strongly reduced when going from toluene to polar solvents, this shortening being already present in chloroform. This effect is about 10 times weaker with a single bromine atom and negligible with two bromine atoms on the chromophore. The excited-state lifetime shortening is ascribed to a charge transfer from the excited chromophore to a nitrobenzene moiety, the driving force of this process depending on the number of bromine substituents. The occurrence of this process is further confirmed by the investigation of the excited-state dynamics of the chromophore alone in pure nitrobenzene. Surprisingly, no correlation between the charge separation time constant and the dielectric properties of the solvents could be observed. However, a good correlation between the charge separation time constant and the diffusional reorientation time of the chromophore alone, measured by fluorescence anisotropy, was found. Quantum chemistry calculations suggest that quasi-free rotation about the single bond linking the chromophore to the triptycene moiety permits a sufficient coupling of the donor and the acceptor to ensure efficient charge separation. The charge separation dynamics in these molecules is thus controlled by the reorientational motion of the donor relative to the acceptor.     

Studying Molecular Rearrangement of P1 Dye at a Passivating Alumina Surface Using Vibrational Sum-Frequency Generation Spectroscopy: Effect of Atomic-Level Roughness

The effect of roughness and thickness of alumina layers, mimicking the passivation layer commonly used in dye-sensitized photoelectrodes, on the molecular adsorption of P1 dye, 4-(bi(4-(2,2-dicyano-vinyl)-thiophene-2-yl]-phenyl]-aminobenzoic acid) has been studied using surface-sensitive vibrational sum frequency generation(VSFG) spectroscopy. The VSFG spectra reveal the formation of poorly ordered dye layers on relatively rough surfaces where XPS measures a higher dye loading. Furthermore, these poorly ordered dye molecules are responsible for the generation of trapped electronic states as probed by successive photoluminescence (PL) measurements. Surface sensitive VSFG spectroscopy in combination with XPS and PL measurements provide complementary spectral information on ordering of the adsorbed dyes, their density on the surface and electronic states of the adsorbed monolayer which are prerequisite for improving our understanding of molecularly functionalized photoelectrodes and their further development.     

Controlled Release of a Sparingly Water‐Soluble Anticancer Drug through pH‐Responsive Functionalized Gold‐Nanoparticle‐Decorated Liposomes

The binding and detachment of carboxyl‐modified gold nanoparticles from liposomes is used for controlled drug delivery. This study reveals that the binding and detachment of nanoparticles from liposomes depends on the degree of hydration of the liposomes. Liposomes with a lower hydration level undergo stronger electrostatic interactions with negatively charged gold nanoparticles, thus leading to a slower detachment of the carboxyl‐modified gold nanoparticles under gastric conditions. Therefore, under gastric conditions, gold‐nanoparticle‐decorated dipalmitoylphosphatidylcholine (DPPC) liposomes exhibit an at least ten‐times‐slower drug release compared to gold‐nanoparticle‐decorated 1,2‐dimyristoyl‐sn‐glycero‐3‐phosphocholine (DMPC) liposomes, although both liposomes in the bare state fail to pursue controlled release. Our study also reveals that one can modulate the drug‐release rate by simply varying the concentration of nanoparticles. This study highlights a novel strategy for the controlled release of drug molecules from liposomes.     

Kinetics and Mechanism of the Oxidative Regeneration of Carbonyl Compounds from Oximes by Pyridinium Fluorochromate

Oxidative deoximination of aldoximes and ketoximes by pyridium fluorochromate proceeds by nucleophilic attack of the chromate oxygen on the oxime carbon to give a cyclic intermediate in the rate-determining step.