Do homochiral aggregates have an entropic advantage?

The present work seeks to illuminate the underlying principles which control the aggregation of chiral building blocks into larger aggregates by examining the role that entropy plays in this process. Entropic effects are first examined within the confines of a simple model system, and the results are then compared to experimental data on clusters of amino acids. The model system predicts that the formation of a specific structure is more likely to occur from an enantiopure solution because forming a particular structure from a racemic solution is hindered by significant entropic barriers. These predictions are in good agreement with the experimental results. In our examination of clusters of all of the amino acids, clusters which are unusually abundant are found only when enantiopure solutions are sampled. Furthermore, the majority of all clusters exhibit no preference for chiral composition, suggesting that entropic effects negate any changes in enthalpy. Although the experimental data are not comprehensive, our results strongly suggest that specificity in homochiral clusters is entropically advantageous compared to specificity in racemic clusters.     

Quantitative analyses of shape-selective intercalation of isomeric mixtures of muconates into [LiAl2(OH)6]Cl.yH2O layered double hydroxide

Quantitative investigation of the shape selectivity for the competitive intercalation reaction of isomeric mixtures in the interlayer of LDH was achieved by analyzing the solid phases synthesized by the reaction of [LiAl(2)(OH)(6)]Cl.yH(2)O with various compositional mixtures of (E,E)- and (Z,Z)-muconates. The apparent partition constant K' for the anion-exchange reaction between (E,E)- and (Z,Z)-muconates was quite dependent on the mole fraction of muconates in solution. The only single phase saturated with [LiAl(2)(OH)(6)](2)[(E,E)-C(6)H(4)O(4)].zH(2)O could be obtained in the range of the initial mole fraction of (E,E)-muconate larger than 0.6 in the starting solution, while mixed phases intercalated with (E,E)- and (Z,Z)-muconates could be obtained at lower mole fractions of (E,E)-muconate. The shape selectivity for the competitive reaction of two muconates on the [LiAl(2)(OH)(6)](+) lattice could be ascribed to thermodynamic processes, and the conditions under which that pure (E,E)-muconate was efficiently separated from isomeric mixtures of two muconates were successfully evaluated.     

Dual effect of oxidative stress on NF-kappakB activation in HeLa cells

Reactive oxygen species (ROS) has been implicated as an inducer of NF-kappaB activity in numbers of cell types where exposure of cells to ROS such as H(2)O(2) leads to NF-kappaB activation. In contrast, exposure to oxidative stress in certain cell types induced reduction of tumor necrosis factor (TNF)- induced NF-kappaB activation. And various thiol-modifying agents including gold compounds and cyclopentenone prostaglandins inhibit NF-kappaB activation by blocking IkappaB kinase (IKK). To understand such conflicting effect of oxidative stress on NF- kappakB activation, HeLa cells were incubated with H(2)O(2) or diamide and TNF-induced expression of NF-kappaB reporter gene was measured. NF-kappaB activation was significantly blocked by these oxidizing agents, and the inhibition was accompanied with reduced nuclear NF-kappaB and inappropriate cytosolic IkappaB degradation. H(2)O(2) and diamide also inhibited IKK activation in HeLa and RAW 264.7 cells stimulated with TNF and lipopolysaccharide, respectively, and directly blocked IKK activity in vitro. In cells treated with H(2)O(2) alone, nuclear NF-kappaB was induced after 2 h without detectable degradation of cytosolic IkappaBalphaa or activation of IKK. Our results suggest that ROS has a dual effect on NF-kappaB activation in the same HeLa cells: it inhibits acute IKK-mediated NF-kappakB activation induced by inflammatory signals, while longer-term exposure to ROS induces NF-kappaB activity through an IKK-independent pathway.     

Improved expression by cytomegalovirus promoter/enhancer and behavior of vascular endothelial growth factor gene after myocardial injection of naked DNA

Direct injection of the vascular endothelial growth factor (VEGF) gene plasmid DNA into the myocardium was shown to induce development of new blood vessels to increase the circulation in the heart of patients with coronary artery diseases. However, such angiogenic gene therapy (via naked DNA) was limited by low level of gene expression. Furthermore, the temporal and spatial characteristics of VEGF gene transfer in the heart are not known. In this study, we demonstrated that a plasmid vector, containing the human cytomegalovirus immediate early (HCMV IE) promoter and enhancer, induces greater expression of gene in the rat heart monitored by gene fused to the chloramphenicol acetyl transferase (CAT) reporter, than four different viral and cellular promoters. Interestingly, expression of VEGF121 protein showed an earlier peak, a shorter duration, and a wider distribution than that of CAT only. Therefore, a plasmid vector with an HCMV IE promoter/enhancer provides clear advantages over other previously developed plasmids. Furthermore, expression profile of VEGF121 gene may provide useful information in the design of angiogenic gene therapy in the heart.     

Reaction kinetics and critical phenomena: rates of some first order gas evolution reactions in binary solvents with a consolute point

We have measured the rate of carbon dioxide evolution in the aniline catalyzed decomposition of acetone dicarboxylic acid in a mixture of isobutyric acid + water near its consolute point. Within a temperature interval of 1 degrees C, which included the critical solution temperature, the first-order rate constant oscillated in magnitude by about 10% as it passed through three complete cycles of slowing down followed by speeding up. Whereas we can find no ready explanation for the speeding up, we suggest that, because the mixture contained no inert components, the slowing down should belong to the Griffiths-Wheeler class of strong critical effects [Phys. Rev. A 1970, 2, 1047]. As a check on this conclusion, we have measured the rate of the SN1 decomposition of benzene diazonium tetrafluoroborate in 2-butoxyethanol + water near the lower critical solution temperature and also the rate of the acid-catalyzed decomposition of ethyl diazoacetate in isobutyric acid + water near the upper critical solution temperature. Both of these reactions evolve nitrogen. In the first reaction, 2-butoxyethanol is inert, whereas in the second, isobutyric acid is inert. In both cases, because there was one inert component, we regarded the response of the rate constant to temperature in the critical region to be representative of the Griffiths-Wheeler class of weak critical effects. Within our accuracy of measurement of about 2% in the rate constant and about 1 mK in the temperature, we could detect no effect of the critical point on the rates of either of these reactions, suggesting that a weak effect may be too small to be seen with our experimental apparatus. The successful observation of a critical effect in the rate of decomposition of acetone dicarboxylic acid proves, however, that kinetic critical phenomena are observable in heterogeneous reactions.     

Modeling drop shape on contaminated surfaces or surfaces with physical structures

Surface contaminants are commonly found on films. They get transferred to the surface from incompletely cured silicone liners on the films or owing to migration of additives to the surface from within the film. During the process of ink jet printing (a noncontact printing process), surface contamination affects the shape of the drops (causing the formation of fingers and crescents) and hence image quality. This study uses modeling methods to examine how such surface contamination affects the drops shapes. Subsequently, it models the effect of surface structures (pits) on the drop shape. This study explores how image quality can be controlled in the presence of surface contamination and surface structures.     

Catalytic combustion of chlorobenzene over V2O5/TiO2 catalysts prepared by the precipitation-deposition method

Catalytic combustion of chlorobenzene over supported vanadium oxides has been investigated. TiO₂ was prepared by the sol-gel method from titanium isopropoxide. The supported vanadium oxide catalysts have been prepared by precipitation-deposition and impregnation method and characterized by XRD, FT-Raman and TPR. In the VO_x/TiO₂catalysts prepared using the impregnation method, when vanadium loading reaches 3 wt.%, the activity shows a maximum. However, in the VO_x/TiO₂catalysts prepared by precipitation-deposition, when vanadium loading reaches 7 wt.%, the activity shows a maximum. This result suggests that the precipitation-deposition can yield a higher metal loading on the support and a high dispersion compared to the impregnation method. This revised version was published online in August 2006 with corrections to the Cover Date.     

Design of molecular two-photon probes for in vivo imaging. 2H-Benzo[h]chromene-2-one derivatives

2H-Benzo[h]chromene-2-one derivatives showing appreciable water solubility, significant two-photon cross sections, high photostability, cell permeability, low toxicity, and ability to be converted to a protein TP probe have been developed by incorporating all of the needed functions within a small molecule.