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At least 811 records · Page 45Linked to original sources
PubMed2006

Mechanism for interplay between electron and ionic fluxes in KhFek[Fe(CN)6]l.mH2O compounds.

This paper develops a framework for the interpretation of ionic insertion/deinsertion reactions in an aqueous environment taking place in transition-metal hexacyanoferrates of the general formula K(h)[Fe(2+) (CN)(6)](l).mH(2)O, also called Prussian Blue. Three different processes were fully separated in the electrochemistry of these films. It was clearly identified that one of these electrochemical processes involves the insertion/deinsertion of H(3)O(+) (hydrated protons) through the channels of the K(h)[Fe(2+) (CN)(6)](l).mH(2)O structure to reach the film electroneutrality during the electron transfer between Everitt's Salt and Prussian Blue. The other electrochemical processes involve K(+) or H(+) (proton) exchange through the water crystalline structure existing in the channels of the K(h)[Fe(2+)(CN)(6)](l).mH(2)O structure.

Journal Article↗
PubMed2006

On the interplay between CH...O and OH...O interactions in determining crystal packing and molecular conformation: an experimental and theoretical charge density study of the fungal secondary metabolite austdiol (C12H12O5).

The total experimental electron density rho(r), its Laplacian inverted delta(2)rho(r), the molecular dipole moment, the electrostatic potential phi(r), and the intermolecular interaction energies have been obtained from an extensive set of single-crystal X-ray diffracted intensities, collected at T = 70(1) K, for the fungal metabolite austdiol (1). The experimental results have been compared with theoretical densities from DFT calculations on the isolated molecule and with fully periodic calculations. The crystal structure of (1) consists of zigzag ribbons extended along one cell axis and formed by molecules connected by both OH...O and CH...O interactions, while in a perpendicular direction, adjacent molecules are linked by short CH...O intermolecular contacts. An extensive, quantitative study of all the intra- and intermolecular H...O interactions, based not only on geometrical criteria, but also on the topological analysis of rho(r), as well as on the evaluation of the pertinent energetics, allowed us (i) to assess the mutual role of OH...O and CH...O interactions in determining molecular conformation and crystal packing; (ii) to identify those CH...O contacts which are true hydrogen bonds (HBs); (iii) to determine the relative hydrogen bond strengths. An experimental, quantitative evidence is given that CH...O HBs are very similar to the conventional OH...O HBs, albeit generally weaker. The comparison between experimental and theoretical electric dipole moments indicates that a noticeable charge rearrangement occurs upon crystallization and shows the effects of the mutual cooperation of HBs in the crystal. The total intermolecular interaction energies and the electrostatic energy contribution obtained through different theoretical methods are reported and compared with the experimental results. It is found that the new approach proposed by Spackman, based on the use of the promolecular charge density to approximate the penetration contribution to intermolecular electrostatic energies, predicts the correct relative electrostatic interaction energies in most of the cases.

Aldehydes↗
PubMed2006

How the stabilization of INK4 tumor suppressor 3D structure evaluated by quantum chemical and molecular mechanics calculations corresponds well with experimental results: interplay of association enthalpy, entropy, and solvation effects.

The folding free energy of the INK4c tumor suppressor core, consisting of 10 helices, was determined as the sum of gas-phase interaction enthalpy, gas-phase interaction entropy, and dehydration and hydration free energy. The interaction energy and the hydration free energy were determined using the nonempirical density functional theory (DFT) method, augmented by a dispersion-energy correction term, the semiempirical density-functional tight-binding method covering the dispersion energy, and the density functional theory/conductor-like screening model (DFT/COSMO) procedure, whereas the interaction entropy was calculated with the empirical Cornell et al. force field. Alternatively, all contributions were evaluated consistently using empirical methods. All the values of the interaction energy of helix pairs are stabilizing, and the dominant stabilizing terms stem from the London dispersion energy and, in the case of charged systems, the electrostatic energy. The stabilization energy of the core, determined as the difference of the energy of the core and 10 separate helices, amounts to approximately 450 kcal/mol. Systematically, the difference in the hydration free energy of a helix pair and its separate components is smaller in magnitude than the interaction energy, and it is negative for some pairs while positive for others. The average total free energy of a core formation amounts to -29.6 kcal/mol (yielded by scaled quantum-chemical methods) and +13.9 kcal/mol (resulting from empirical methods). These values are considerably smaller than their single components, which are dominated by the interaction energy. The computationally predicted interval encloses the experimental value of the folding free energy (-2.8 kcal/mol).

Amino Acid Motifs↗
PubMed2006

Interplay of bonding and geometry of the adsorption complexes of light alkanes within cationic faujasites. Combined spectroscopic and computational study.

A FT-IR spectroscopic study of methane, ethane, and propane adsorption on magnesium and calcium forms of zeolite Y reveals different vibrational properties of the adsorbed molecules depending on the exchanged cation. This is attributed to different adsorption conformations of the hydrocarbons. Two-fold eta(2) coordination of light alkanes is realized for MgY, whereas in case of CaY zeolite quite different adsorption modes are found, involving more C-H bonds in the interaction with the cation. The topological analysis of the electron density distribution function of the adsorption complexes shows that when a hydrocarbon coordinates to the exchanged Mg(2+) ions, van der Waals bonds between H atoms of the alkane and basic zeolitic oxygens significantly contribute to the overall adsorption energy, whereas in case of CaY zeolite such interactions play only an indirect role. It is found that, due to the much smaller ionic radius of the Mg(2+) ion as compared to that of Ca(2+), the former ions are significantly shielded with the surrounding oxygens of the zeolitic cation site. This results in a small electrostatic contribution to the stabilization of the adsorbed molecules. In contrast, for CaY zeolite the stabilization of alkanes in the electrostatic field of the partially shielded Ca(2+) cation significantly contributes to the adsorption energy. This is in agreement with the experimentally observed lower overall absorption of C-H stretching vibrations of alkanes loaded to MgY as compared to those for CaY zeolite. The preferred conformation of the adsorbed alkanes is controlled by the bonding within the adsorption complexes that, in turn, strongly depends on the size and location of the cations in the zeolite cavity.

Journal Article↗
PubMed2006

Electronic interplay on illuminated aqueous carbon nanohorn-porphyrin ensembles.

Tetracationic water-soluble porphyrin (H(2)P(4+)) has been immobilized by pi-pi stacking interactions onto the skeleton of carbon nanohorns (CNH), without disrupting their pi-electronic network. The stable aqueous solution of the CNH-H(2)P(4+) nanoensemble was examined by both electron microscopy and spectroscopic techniques. The efficient fluorescence quenching of the H(2)P(4+) moiety in the CNH-H(2)P(4+) nanoensemble was probed by steady-state as well as time-resolved fluorescence emission spectroscopy, suggesting charge separation from the photoexcited H(2)P(4+) to CNH. In the presence of methyl viologen dication (MV(2+)) and a hole trap, accumulation of the reduced species of methyl viologen was observed by the photoillumination of CNH-H(2)P(4+), suggesting that the electron migration from the initially formed charge-separated state takes place. Transient absorption spectroscopy gave further insights on the transient species such as the charge-separated state (CNH(*-))-(H(2)P(4+))(*+), which was consumed in the presence of MV(2+) and hole shifter, leaving the reduced methyl viologen.

Letter↗
PubMed2007

The behavior of exciplex decay processes and interplay of radiationless transition and preliminary reorganization mechanisms of electron transfer in loose and tight pairs of reactants.

Exciplex emission spectra and rate constants of their decay via internal conversion and intersystem crossing are studied and discussed in terms of conventional radiationless transition approach. Exciplexes of 9-cyanophenanthrene with 1,2,3-trimethoxybenzene and 1,3,5-trimethoxybenzene were studied in heptane, toluene, butyl acetate, dichloromethane, butyronitrile, and acetonitrile. A better description of spectra and rate constants is obtained using 0-0 transition energy and Gauss broadening of vibrational bands rather than the free energy of electron transfer and reorganization energy. The coincidence of parameters describing exciplex emission spectra and dependence of exciplex decay rate constants on energy gap gives the evidence of radiationless quantum transition mechanism rather than thermally activated medium reorganization mechanism of charge recombination in exciplexes and excited charge transfer complexes (contact radical ion pairs) as well as in solvent separated radical ion pairs. Radiationless quantum transition mechanism is shown to provide an appropriate description also for the main features of exergonic excited-state charge separation reactions if fast mutual transformations of loose and tight pairs of reactants are considered. In particular, very fast electron transfer (ET) in tight pairs of reactants with strong electronic coupling of locally excited and charge transfer states can prevent the observation of an inverted region in bimolecular excited-state charge separation even for highly exergonic reactions.

Journal Article↗
PubMed2005

Interplay between cubic and hexagonal phases in block copolymer solutions.

The phase behavior of a symmetric styrene-isoprene (SI) diblock copolymer in a styrene-selective solvent, diethylphthalate, was investigated by in situ small-angle X-ray scattering on isotropic and shear-oriented solutions and by rheology and birefringence. A remarkable new feature in this phase diagram is the coexistence of both body-centered cubic (bcc) and hexagonally close-packed (hcp) sphere phases, in a region between close-packed spheres (cps) and hexagonally packed cylinders (hex) over the concentration range phi approximately 0.33-0.45. By focusing on the transitions among these various ordered phases during heating and cooling cycles, we observed a strong hysteresis: supercooled cylinders persisted upon cooling. The stability of these supercooled cylinders is quite dependent on concentration, and for phi > or = 0.40, the supercooled cylinders do not revert to spheres even after quiescent annealing for 1 month. The spontaneous formation of spheres due to the dissociation of cylinders is kinetically hindered in this case, and the system is apparently not amenable to any pretransitional fluctuations of cylinders prior to the cylinder-to-sphere transition. This contrasts with the case of cylinders transforming to spheres upon heating in the melt. The application of large amplitude shear to the supercooled cylinders is effective in restoring the equilibrium sphere phases.

Journal Article↗
PubMed2006

Controlling two-dimensional tethered vesicle motion using an electric field: interplay of electrophoresis and electro-osmosis.

We recently introduced methods to tether phospholipid vesicles or proteoliposomes onto a fluid-supported lipid bilayer using DNA hybridization (Yoshina-Ishii, C.; Miller, G. P.; Kraft, M. L.; Kool, E. T.; Boxer, S. G. J. Am. Chem. Soc. 2005, 127, 1356-1357). These intact tethered vesicles diffuse in two dimensions parallel to the supporting membrane surface. In this article, we report the dynamic response of individual tethered vesicles to an electric field applied parallel to the bilayer surface. Vesicles respond to the field by moving in the direction of electro-osmotic flow, and this can be used to reversibly concentrate tethered vesicles against a barrier. By adding increasing amounts of negatively charged phosphatidylserine to the supporting bilayer to increase electro-osmosis, the electrophoretic mobility of the tethered vesicles can be increased. The electro-osmotic contribution can be modeled well by a sphere connected to a cylindrical anchor in a viscous membrane with charged headgroups. The electrophoretic force on the negatively charged tethered vesicles opposes the electro-osmotic force. By increasing the amount of negative charge on the tethered vesicle, drift in the direction of electro-osmotic flow can be slowed; at high negative charge on the tethered vesicle, motion can be forced in the direction of electrophoresis. The balance between these forces can be visualized on a patterned supporting bilayer containing negatively charged lipids that reorganize in an externally applied electric field to create a gradient of charge within a corralled region. The charge gradient at the surface creates a gradient of electro-osmotic flow, and vesicles carrying similar amounts of negative charge can be focused to a region perpendicular to the applied field where electrophoresis is balanced by electro-osmosis, away from the corral boundary. Electric fields are effective tools to direct tethered vesicles and concentrate them and to measure the tethered vesicle's electrostatic properties.

Electrochemistry↗
PubMed2000

Interplay of Twisting and Folding in Overcrowded Heteromerous Bistricyclic Aromatic Enes.

Fluorenylidenexanthenes 5-7 were synthesized by 2-fold extrusion diazo-thione couplings. 7 exhibited yellow crystals and purple (560 nm) solutions. (1)H NMR of 5 and 7 indicated subtle equilibria twisted (t) right harpoon over left harpoon anti-folded (a) major/minor conformations. (13)C DNMR of 6 gave DeltaG(c)(double dagger)(enantiomerization/inversion) = 26.5 kJ/mol and DeltaG(c)(double dagger)(E,Z-topomerization) = 82.0 kJ/mol. PM3 calculations of 5 revealed minima a, t, ts (twisted/syn-folded), DeltaDeltaH(f) degrees = 0.0, 14.1, 15.6 kJ/mol, and transition states [t-ts], [a-ts], [t( perpendicular)], [a-a], DeltaDeltaH(f) degrees = 16.3, 17.4, 82.2, 99.3 kJ/mol.

Journal Article↗
PubMed2004

Model systems for flavoenzyme activity: interplay of hydrogen bonding and aromatic stacking in cofactor redox modulation.

[structure: see text] A model system has been developed to study the synergy between aromatic stacking and hydrogen bonding in the binding of a flavin derivative. The results show that the identity of both the hydrogen bonding and pi-stacking units strongly determine the overall receptor affinity for flavin in both the oxidized and radical anion forms.

Flavin Mononucleotide↗
PubMed2000

Discourse before gender: an event-related brain potential study on the interplay of semantic and syntactic information during spoken language understanding.

A study is presented on the effects of discourse-semantic and lexical-syntactic information during spoken sentence processing. Event-related brain potentials (ERPs) were registered while subjects listened to discourses that ended in a sentence with a temporary syntactic ambiguity. The prior discourse-semantic information biased toward one analysis of the temporary ambiguity, whereas the lexical-syntactic information allowed only for the alternative analysis. The ERP results show that discourse-semantic information can momentarily take precedence over syntactic information, even if this violates grammatical gender agreement rules.

Adult↗
PubMed2000

Brief Strategic Family Therapy: twenty-five years of interplay among theory, research and practice in adolescent behavior problems and drug abuse.

This article describes a systematic program of research that focuses on Brief Strategic Family Therapy (BSFT) and the adaptations that were developed based on BSFT principles. The culture-specific origins of BSFT are reviewed, as well as its broader applications to the field of family therapy. Research is reviewed demonstrating that BSFT is a promising family-based approach to treating Hispanic youth behavior problems and drug abuse. Treatment innovations are described that address the combination of intergenerational and cultural differences that occur among youths and their Hispanic parents. Programmatic work is described that challenges basic principles of family therapy by expanding BSFT to a One Person modality and a strategic engagement procedure. Both of these novel approaches are intended to add tools to therapists' repertoire in working with difficult-to-engage families. A preview discussion of results is presented from a randomized clinical trial that is an application of an ecosystemic prevention version of BSFT. The implications of the work of the Center for Family Studies are discussed in the context of the broader service system. Ultimately, this article articulates a way of thinking about adolescent problem behavior, its social interactional determinants, and a range of theoretically consistent family-centered strategies that attempt to change social ecological processes that impact adolescent developmental trajectories.

Adolescent↗
PubMed2001

Flavonoids and urate antioxidant interplay in plasma oxidative stress.

Flavonoids are naturally occurring plant compounds with antioxidant properties. Their consumption has been associated with the protective effects of certain diets against some of the complications of atherosclerosis. Low-density lipoprotein (LDL) oxidative modification is currently thought to be a significant event in the atherogenic process. Most of the experiments concerning the inhibition of LDL oxidation used isolated LDL. We used diluted human whole plasma to study the influence of flavonoids on lipid peroxidation (LPO) promoted by copper, and their interaction with uric acid, one of the most important plasma antioxidants. Lipid peroxidation was evaluated by the formation of thiobarbituric acid reactive substances (TBARS) and of free malondialdehyde (MDA). The comparative capability of the assayed flavonoids on copper (II) reduction was tested using the neocuproine colorimetric test. In our assay system, urate disappears and free MDA and TBARS formation increase during the incubation of plasma with copper. Most of the tested flavonoids inhibited copper-induced LPO. The inhibition of LPO by flavonoids correlated positively with their capability to reduce copper (II). The urate consumption during the incubation of plasma with copper was inhibited by myricetin, quercetin and kaempferol. The inhibition of urate degradation by flavonoids correlated positively with the inhibition of LPO. Urate inhibited the copper-induced LPO in a concentration-dependent mode. Luteolin, rutin, catechin and quercetin had an antioxidant synergy with urate. Our results show that some flavonoids could protect endogenous urate from oxidative degradation, and demonstrate an antioxidant synergy between urate and some of the flavonoids.

Adult↗
PubMed2001

Emotion-perception interplay in the visual cortex: "the eyes follow the heart".

Emotive aspects of stimuli have been shown to modulate perceptual thresholds. Lately, studies using functional Magnetic Resonance Imaging (fMRI) showed that emotive aspects of visual stimuli activated not only canonical limbic regions, but also sensory areas in the cerebral cortex. However, it is still arguable to what extent such emotive, related activation in sensory areas of the cortex are affected by physical characteristic or attribute difference of stimuli. To manipulate valence of stimuli while keeping visual features largely unchanged, we took advantage of the Expressional Transfiguration (ET) of faces. In addition, to explore the sensitivity of high level visual regions, we compared repeated with unrepeated (i.e. different) stimuli presentations (fMR adaptation). Thus, the dynamics of brain responses was determined according to the relative signal reduction during "repeated" relative to "different" presentations ("adaptation ratio"). Our results showed, for the first time, that emotional valence produced significant differences in fMR adaptation, but not in overall levels of activation of lateral occipital complex (LOC). We then asked whether this emotion modulation on sensory cortex could be related to previous personal experience that attached negative attributes of stimuli. To clarify this, we investigated Posttraumatic Stress Disorder (PTSD) and non-PTSD veterans. PTSD is characterized by recurrent revival of trauma-related sensations. Such phenomena have been attributed to a disturbed processing of trauma-related stimuli, either at the perceptual level or at the cognitive level. We assumed that PTSD veterans would differ from non-PTSD veterans (who have similar combat experience) in their high order visual cortex responses to combat-related visual stimuli that are associated with their traumatic experience. An fMRI study measured the cerebral activation of subjects while viewing pictures with and without combat content, in "repeated" or "different" presentation conditions. The emotive effect on the visual cortex was found, again, only in the fMR-adaptation paradigm. Visual cortical regions showed significant differences between PTSD and non-PTSD veterans only in "repeated" presentations of trauma-related stimuli (i.e. combat). In these regions, PTSD veterans showed less decrease in signal with repeated presentations of the same combat-related stimuli. This finding points to the possibility that traumatic experience modulates brain activity at the level of sensory cortex itself.

Adult↗
PubMed2001

Schistosome glycoconjugates in host-parasite interplay.

Schistosomes are digenetic trematodes which cause schistosomiasis, also known as bilharzia, one of the main parasitic infections in man. In tropical and subtropical areas an estimated 200 million people are infected and suffer from the debilitating effects of this chronic disease. Schistosomes live in the blood vessels and strongly modulate the immune response of their host to be able to survive the hostile environment that they are exposed to. It has become increasingly clear that glycoconjugates of schistosome larvae, adult worms and eggs play an important role in the evasion mechanisms that schistosomes utilise to withstand the immunological measures of the host. Upon infection, the host mounts innate as well as adaptive immune responses to antigenic glycan elements, setting the immunological scene characteristic for schistosomiasis. In this review we summarise the structural data now available on schistosome glycans and provide data and ideas regarding the role that these glycans play in the various aspects of the glycobiology and immunology of schistosomiasis.

Animals↗
PubMed2003

Exploiting a minimal system to study the epigenetic control of DNA replication: the interplay between transcription and replication.

In order to analyze epigenetic factors involved in the regulation of DNA replication in higher eukaryotic cells, minimal systems have to be established. We have recently constructed a non-viral episomal vector system which replicates episomally in mammalian cells and is stably maintained in the cell in the absence of selection. The potential functional elements contained in this construct are an expression cassette upstream of a chromosomal S/MAR sequence and the SV40 origin of replication. In this report we describe that an active transcription upstream of the S/MAR running into this sequence is required and probably sufficient for episomal replication. We propose a model for the activation of replication in this system which may be the basis for further analysis of replication control in other systems.

Animals↗
PubMed2003

The interplay among risk factors for suicidal ideation and suicide: the role of depression, poor health, and loved ones' messages of support and criticism.

When individuals who receive social support are in poor physical or mental health and are criticized or made to feel unwanted, they may perceive themselves as a burden. Poor physical health and depression were hypothesized to exacerbate the harmful effects on suicidal ideation of receiving critical negative messages and of receiving social support. These hypotheses were tested using secondary analyses of data from a sample of 533 unemployed married individuals who were assessed shortly after job loss, and 6 months later. The results of our analyses supported the hypotheses and demonstrated that for participants with poor health or high level of depressive symptoms an increase in critical messages and social support (from Time 1 to Time 2) predicted increased suicidal ideation. This relationship was not observed for non-depressed participants in good health. The results are discussed in terms of their implications for suicide prevention.

Aged↗
PubMed2004

Long-term quality-of-life outcomes among adults living with HIV in the HAART era: the interplay of changes in clinical factors and symptom profile.

Changes in quality-of-life perceptions and their relations to clinical status for 41 adult outpatients living with HIV/AIDS were assessed over a 4-year period. Clinical variables and quality-of-life (Medical Outcomes Study Short-Form-36) ratings were measured in three waves (T1, 1997; T2, 1999; T3, 2001). Mean T1-T3 CD4 increase was 196 cells/microL (p < .0001), corresponding to a mean viral load reduction of 1.4 log10 copies/mL (p < .0001) and an increase in proportions with "undetectable" viral load status from 32% to 61% (p < .01). The T1-T2 increase in overall mean number of symptoms (including both disease-related symptom complex and treatment side effects) was mitigated by T2-T3 symptom reduction. Quality-of-life dimensions were generally stable or slightly improved over time for the overall sample, a finding that contrasts with pre-highly active antiretroviral therapy longitudinal research. Mental aspects of quality of life remained consistently lower than reference norms. Results of multiple regression suggested that quality of life was less sensitive to immunologic/virologic changes compared to responsiveness to symptom changes, consistent with cross-sectional inverse relations between symptom burden and quality of life. CD4 repletion offset negative effects of symptoms for some aspects of quality of life. The long-term course of quality of life was somewhat predicted by viral load suppression due to the conjoint influence of symptoms and CD4 count.

Adult↗