bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nonlinear optical spectroscopy of chiral molecules
Authors: Fischer Peer , Hache François 
Published: August 2005

AbstractWe review nonlinear optical processes that are specific to chiral molecules in solution and on surfaces. In contrast to conventional natural optical activity phenomena, which depend linearly on the electric field strength of the optical field, we discuss how optical processes that are nonlinear (quadratic, cubic, and quartic) functions of the electromagnetic field strength may probe optically active centers and chiral vibrations. We show that nonlinear techniques open entirely new ways of exploring chirality in chemical and biological systems: The cubic processes give rise to nonlinear circular dichroism and nonlinear optical rotation and make it possible to observe dynamic chiral processes at ultrafast time scales. The quadratic second‐harmonic and sum‐frequency‐generation phenomena and the quartic processes may arise entirely in the electric‐dipole approximation and do not require the use of circularly polarized light to detect chirality. They provide surface selectivity and their observables can be relatively much larger than in linear optical activity. These processes also give rise to the generation of light at a new color, and in liquids this frequency conversion only occurs if the solution is optically active. We survey recent chiral nonlinear optical experiments and give examples of their application to problems of biophysical interest. © 2005 Wiley‐Liss, Inc. Chirality 17:421–437, 2005.
Ab initio Studies of ClOx Reactions: Prediction of the Rate Constants of ClO+NO2 for the Forward and Reverse Processes
Authors: Zhu R. S. , Lin M. C. 
Published: August 2005

AbstractThe potential‐energy surface for the reaction of ClO with NO2 has been constructed at the CCSD(T)/6‐311+G(3df)//B3LYP/6‐311+G(3df) level of theory. Six ClNO3 isomers are located; these are ClONO2, pc‐ClOONO, pt‐ClOONO, OClNO2, pt‐OClONO, pc‐OClONO, with predicted energies relative to the reactants of −25.6, −0.5, 1.0, 1.9, 12.2 and 13.6 kcal mol−1, and heats of formation at 0 K of 7.8, 32.9, 34.4, 35.5, 45.6 and 47.0 kcal mol−1, respectively. Isomerizations among them are also discussed. The rate constants for the low‐energy pathways have been computed by statistical theory calculations. For the association reaction producing exclusively ClONO2, the predicted low‐ and high‐pressure‐limit rate constants in N2 for the temperature range of 200–600 K can be represented by: ${{\rm{k}}_1^0 }$(N2)=3.19×10−17 T−5.54 exp(−384 K/T) cm6 molecule−2 s−1 and ${{\rm{k}}_1^\infty }$=3.33×10−7 T−1.48 exp(−18 K/T) cm3 molecule−1 s−1. The predicted low‐ and high‐pressure‐limit rate constants for the decomposition of ClONO2 in N2 at 200–600 K can be expressed, respectively, by ${{\rm{k}}_{ - 1}^0 }$=6.08×1013 T−6.54 exp(−13813 K/T) cm3 molecule−1 s−1 and ${{\rm{k}}_{ - 1}^\infty }$=4.59×1023 T−2.43 exp(−13437 K/T) s−1. The predicted values compare satisfactorily with available experimental data. The reverse Cl+NO3 reaction was found to be independent of the pressure, giving exclusively ClO+NO2; the predicted rate constant can be expressed as k(Cl+NO3)=1.19×10−9 T−0.60 exp(58 K/T) cm3 molecule−1 s−1.
Hydrophobic–Hydrophilic Interactions of Water with Alkanethiolate Chains from First‐Principles Calculations
Authors: Silvestrelli Pier Luigi , Ancilotto Francesco , Toigo Flavio , Sbraccia Carlo , Ikeda Takashi , Boero Mauro 
Published: August 2005

AbstractThe interaction of water with alkanethiolate chains is studied from first principles. A detailed analysis is performed by optimizing the structure of small water clusters, one‐dimensional water chains, and ordered and disordered thin water layers adsorbed on hydroxyl(OH)‐ and methyl(CH3)‐terminated alkanethiol monolayers. The hydrophilic/hydrophobic character of these two different substrates is investigated by means of an energetic analysis combined with hydrogen‐bond counting. On the hydrophilic OH‐terminated alkanethiol surface, zigzag, one‐dimensional water chains and disordered thin water layers are the energetically favored structures. The ab initio results can be used to determine the optimal value of the empirical parameters characterizing a suitable force field to be used in classic molecular dynamics simulations.
Photophysical Characterization of Light‐Emitting Poly(indenofluorene)s
Authors: Keivanidis Panagiotis E. , Jacob Josemon , Oldridge Luke , Sonar Prashant , Carbonnier Benjamin , Baluschev Stanislav , Grimsdale Andrew C. , Müllen Klaus , Wegner Gerhard 
Published: August 2005

AbstractTime‐resolved photoluminescence spectroscopy experiments of three poly(2,8‐indenofluorene) derivatives bearing different pendant groups are presented. A comparison of the photophysical properties of dilute solutions and thin films provides information on the chemical purity of the materials. The photophysical properties of poly(2,8‐indenofluorene)s are correlated with the morphological characteristics of their corresponding films. Wide‐angle X‐ray scattering experiments reveal the order in these materials at the molecular level. The spectroscopic results confirm the positive impact of a new synthetic approach on the spectral purity of the poly(indenofluorene)s. It is concluded that complete side‐chain substitution of the bridgehead carbon atoms C‐6 and C‐12 in the indenofluorene unit, prior to indenofluorene ring formation, reduces the probability of keto formation. Due to the intrinsic chemical purity of the arylated derivative, identification of a long‐delayed spectral feature, other than the known keto band, is possible in the case of thin films. Controlled doping experiments on the arylated derivative with trace amounts of an indenofluorene‐monoketone provide quantitative information on the rates of two major photophysical processes, namely, singlet photoluminescence emission and singlet photoluminescence quenching. These results allow the determination of the minimum keto concentration that can affect the intrinsic photophysical properties of this polymer. The data suggest that photoluminescence quenching operates in the doped films according to the Stern–Volmer formalism.
A Colloidal Au Monolayer Modulates the Conformation and Orientation of a Protein at the Electrode/Solution Interface
Authors: Jiang Xiue , Zhang Lei , Jiang Junguang , Qu Xiaohu , Wang Erkang , Dong Shaojun 
Published: August 2005

AbstractThe orientation and conformation of adsorbed cytochrome c (cyt c) at the interface between an electrode modified with colloidal Au and a solution were studied by electrochemical, spectroscopic, and spectroelectrochemical techniques. The results indicate that the colloidal Au monolayer formed via preformation of an organic self‐assembled monolayer (SAM) can increase the electronic coupling between the SAM and cyt c in the same manner as bifunctional molecular bridges, one functional group of which is bound to the electrode surface while the other interacts with the protein surface. The approach of cyt c to the modified electrode/solution interface can be assisted by strong interactions of the intrinsic charge of colloidal particles with cyt c, while the heme pocket remains almost unchanged due to the screening effect of the negatively charged field created by the intrinsic charge. The conformational changes of cyt c induced by its adsorption at a bare glassy carbon electrode/solution interface and the effect of the electric field on the ligation state of the heme can be avoided at the colloidal‐Au‐modified electrode/solution interface. Finally, a possible model for the adsorption orientation of cyt c at the colloidal‐Au‐modified electrode/solution interface is proposed.
A Theoretical Description of Elastic Pillar Substrates in Biophysical Experiments
Authors: Mohrdieck Camilla , Wanner Alexander , Roos Wouter , Roth Alexander , Sackmann Erich , Spatz Joachim P. , Arzt Eduard 
Published: August 2005

AbstractArrays of elastic pillars are used in biophysical experiments as sensors for traction forces. The evaluation of the forces can be complicated if they are coupled to the pillar displacements over large distances. This is the case if many of the pillars are interconnected by elastic linkages as, for example, in fiber networks that are grown on top of pillars. To calculate the traction forces in such a network, we developed a set of nonlinear inhomogeneous equations relating the forces in the linking elements to the resulting pillar deflections. We chose a homogeneous, activated two‐dimensional network of cytoskeletal actin filaments to illustrate that a pillar substrate is generally not a force sensor but a force‐gradient sensor. In homogeneous networks the forces acting along the filaments can be approximated by analyzing only pillar deflections in the edge zones of the substrate and by integration over the corresponding force gradients.
Kinetics of the Initial Steps of G Protein‐Coupled Receptor‐Mediated Cellular Signaling Revealed by Single‐Molecule Imaging
Authors: Lill Yoriko , Martinez Karen L. , Lill Markus A. , Meyer Bruno H. , Vogel Horst , Hecht Bert 
Published: August 2005

AbstractWe report on an in vivo single‐molecule study of the signaling kinetics of G protein‐coupled receptors (GPCR) performed using the neurokinin 1 receptor (NK1R) as a representative member. The NK1R signaling cascade is triggered by the specific binding of a fluorescently labeled agonist, substance P (SP). The diffusion of single receptor–ligand complexes in plasma membrane of living HEK 293 cells is imaged using fast single‐molecule wide‐field fluorescence microscopy at 100 ms time resolution. Diffusion trajectories are obtained which show intra‐ and intertrace heterogeneity in the diffusion mode. To investigate universal patterns in the diffusion trajectories we take the ligand‐binding event as the common starting point. This synchronization allows us to observe changes in the character of the ligand–receptor‐complex diffusion. Specifically, we find that the diffusion of ligand–receptor complexes is slowed down significantly and becomes more constrained as a function of time during the first 1000 ms. The decelerated and more constrained diffusion is attributed to an increasing interaction of the GPCR with cellular structures after the ligand–receptor complex is formed.
DNA labeling in living cells
Authors: Martin Robert M. , Leonhardt Heinrich , Cardoso M. Cristina 
Published: August 2005

AbstractBackgroundLive cell fluorescence microscopy experiments often require visualization of the nucleus and the chromatin to determine the nuclear morphology or the localization of nuclear compartments.MethodsWe compared five different DNA dyes, TOPRO‐3, TOTO‐3, propidium iodide, Hoechst 33258, and DRAQ5, to test their usefulness in live cell experiments with continuous imaging and photobleaching in widefield epifluorescence and confocal laser scanning microscopy. In addition, we compared the DNA stainings with fluorescent histones as an independent fluorescent label to mark chromatin.ResultsFrom the dyes tested, only Hoechst and DRAQ5 could be used to stain DNA in living cells. However, DRAQ5 had several advantages, namely low photobleaching, labeling of the chromatin compartments comparable to that of H2B‐GFP fusion proteins, and deep red excitation/emission compatible with available genetically encoded fluorescent proteins such as C/G/YFP or mRFP.ConclusionsThe DNA dye DRAQ5 is well suited for chromatin visualization in living cells and can easily be combined with other fluorophores with blue to orange emission. © 2005 Wiley‐Liss, Inc.
Carbosilane Dendrons Functionalized at Their Focal Point
Authors: Andrés Román , de Jesús Ernesto , de la Mata F. Javier , Flores Juan C. , Gómez Rafael 
Published: August 2005

AbstractThe Si–Ph bond of PhSi[(CH2)3SiMe2Bz]3 (5) is cleaved with triflic acid to give TfOSi[(CH2)3SiMe2Bz]3, which, in turn, reacts with triethylammonium chloride or potassium cyclopentadienide to give, respectively, ClSi[(CH2)3SiMe2Bz]3 (8) and (C5H5)Si[(CH2)3SiMe2Bz]3 (10). This strategy can be applied to the post‐growth incorporation of nucleophiles to the focal point of carbosilane dendritic wedges. In this way, cyclopentadiene‐functionalized dendritic wedges of second and third generation C5H5‐Gn‐[(CH2)3SiMe2Bz]x (n = 2, x = 9, 11; n = 3, x = 27, 12) have been obtained starting from Ph‐Gn‐[(CH2)3SiMe2Bz]x (6, 7). The metallocenes [{(BzMe2SiCH2CH2CH2)3SiC5H4}2MCl2] (M = Ti, 14; Zr, 15) have also been obtained from 10 and their catalytic behavior in ethylene and propylene polymerization, using MAO as a cocatalyst, has been studied and compared to that of related non‐dendritic complexes. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Bifunctional Bioorganometallic Iridium(III)–Platinum(II) Complexes Incorporating Both Intercalative and Covalent DNA Binding Capabilities
Authors: Gençaslan Susan , Sheldrick William S. 
Published: August 2005

AbstractThe DNA binding of bifunctional IrIII–PtII complexes containing [(η5‐Cp*)Ir(dppz)]2+ and [Pt(terpy)]2+ or trans‐[PtL2L′]2+ fragments (L = NH3, L′ = DMF; L = H2O, L′ = NH3) bridged by flexible κS:κN(amino)‐coordinated methionine‐containing peptides has been studied by UV/Vis and CD spectroscopy. Stable intercalative binding of the IrIII fragment of the complexes [{(η5‐Cp*)Ir(dppz)}(μ‐peptide‐κS:κN){Pt(terpy)}](CF3SO3)4 (5) (peptide = H‐Gly‐Gly‐Phe‐Met‐OH; H‐Gly‐OH = glycine, H‐Phe‐OH = L‐phenylalanine, H‐Met‐OH = L‐methionine) and 6 [peptide = H‐(Ala)4‐Met‐OH; H‐Ala‐OH = L‐alanine] is indicated by their steady decrease in absorbance at maxima between 350 and 390 nm on titration with CT DNA and by the bathochromic shifts of these maxima. Binding constants Kb of 1.4(4) × 106 M–1 for both 5 and 6 and site sizes s of 2.8(1) and 2.2(1), respectively, are in accordance with this monofunctional mode. Both peptide chain length and the site(s) of the labile PtII substituents DMF or H2O play an important role in determining the degree of intercalation of the IrIII fragment and the extent of helix distortion caused by simultaneous covalent binding of PtII centres for the DNA interaction of the complexes [{(η5‐Cp*)Ir(dppz)}(μ‐peptide‐κS:κN){trans‐(PtL2L′)}]4+ 7–10. Whereas both 9 and 10 (L = H2O, L′ = NH3; peptide = H‐Gly‐Met‐OH or H‐Gly‐Gly‐Met‐OH) exhibit a high degree of bifunctional binding [9, Kb = 1.1(5) × 106 M–1, s = 1.3(1); 10, Kb = 1.4(7) × 106 M–1, s = 2.1(1)], CD spectroscopy indicates that a more pronounced reorganisation of the DNA helix is required for the former complex with its shorter peptide. Effective intercalation is also observed for 8 (L = NH3, L′ = DMF; peptide = H‐Gly‐Gly‐Met‐OH) but not for 7 with the analogous PtII fragment but a shorter bridging peptide (H‐Gly‐Met‐OH). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Polycyclic aromatic hydrocarbons in vegetable oils from canned foods
Authors: Moret Sabrina , Purcaro Giorgia , Conte Lanfranco S. 
Published: August 2005

AbstractA rapid method previously set up for polycyclic aromatic hydrocarbons (PAH) determination in vegetable oils was used to carry out a survey on 62 samples of vegetable oils from canned vegetables and fish and oil‐based sauces. Of the oil samples from vegetable products, 15% exceeded the 2‐ppb level for benzo(a)pyrene. The highest PAH concentration was found in the oil from a grilled mushroom sample, which presented 11.3 ppb of BaP and 47.1 ppb of total heavy PAH. Regarding the canned fish, none of the analyzed samples exceeded the limit for BaP. The highest contamination level was found in an olive oil sample from canned tuna: 1.9 ppb of BaP and 11.3 ppb of total heavy PAH. The high PAH concentrations found in some oil samples from vegetable products could be due to the contribution from contaminants in the vegetables.
Effect of channel structure on preparation of a water‐in‐oil emulsion by polymer microchannels
Authors: Liu Haijie , Nakajima Mitsutoshi , Nishi Taiji , Kimura Toshinori 
Published: August 2005

AbstractMonodisperse water‐in‐oil emulsions were successfully prepared using a polymer microchannel (PMC) with hydrophobic properties and high anti‐alkalinity and fabricated by the molding injection method. We investigated the effect of the channel structure on the droplet preparation characteristics, including the average droplet diameter, the coefficient of variation (CV), the pressure range for stable droplet formation, and the critical flow velocity of the dispersed phase. Various PMC with different structures were fabricated and used for emulsification. The results indicated that the average droplet diameter and the CV did not change remarkably and that the critical flow velocity of the dispersed phase was increased slightly when we used PMC with different small rectangular‐shaped convexes in the channel. However, the pressure range for stable droplet formation widened, the CV decreased, and the critical flow velocity of the dispersed phase increased significantly with a decrease of the PMC equivalent diameter and an increase of the PMC length, which revealed greater stability and productivity of the emulsion droplets.
Isolation and evaluation of antioxidants from leaves of a Tunisian cultivar olive tree
Authors: Bouaziz Mohamed , Sayadi Sami 
Published: August 2005

AbstractQuantitative and qualitative determinations of phenolic compounds were carried out on Chemlali olive leaves, a by‐product of olive tree pruning. The evolution of the amount of the major phenolic compound was monitored from July 2003 to March 2004. Quantitative analysis was performed by high‐performance liquid chromatography (HPLC), which revealed that oleuropein was always the major compound. Its concentration reached 6.8 g per 100 g of fresh olive leaves, while monomeric phenols were the minor compounds. Beside oleuropein, six flavonoids (luteolin 7‐O‐glucoside, luteolin 7‐O‐rutinoside, apigenin 7‐O‐glucoside, rutin, luteolin and apigenin) were identified. The identification was based on separation by HPLC equipped with a diode array detector, followed by liquid chromatography‐mass spectrometry analysis. A relative high amount of purified hydroxytyrosol (2.3 g per 100 g of fresh olive leaves) was obtained in short time by a simple hydrolysis reaction of Olea europaea leaf extract and by purification using a C‐18 silica gel column. The antioxidant activities of the extracts and the purified compounds were evaluated by measuring the radical‐scavenging effect on 1,1‐diphenyl‐2‐picrylhydrazyl and by using the β‐carotene linoleate model assay. Hydroxytyrosol and hydrolysate products have the highest antioxidant activities.
Pyridine‐Based Oligonitriles as Pincer Ligands for Palladium(II), Copper(II), Cobalt(II), and Nickel(II) Ions
Authors: Behrens Henrik , Fröhlich Roland , Würthwein Ernst‐Ulrich 
Published: August 2005

AbstractNucleophilic ring opening of the 1‐oxa‐3,5‐diazinium salts 2 and 3 by propylamine furnishes the new polydentate, branched, pincer‐type ligands 4 and 5, respectively, in 34 and 57 % yield. The 1‐oxa‐3,5‐diazinium salts 2 and 3 were prepared from pyridine‐2,6‐dicarbonyl dichloride (1) by treatment with dimethylcyanamide and diisopropylcyanamide in the presence of antimony pentachloride and tin tetrachloride, respectively. The structure of 4, which is characterised by a strongly twisted N‐acyloligonitrile arm, was determined by X‐ray crystallography. The ligand 4, with its short and long arms, forms chelate complexes 4–·Pd(OAc)+ and 4·CuCl2 when treated with palladium(II) acetate and copper(II) chloride, respectively. 4–·Pd(OAc)+ shows remarkable catalytic activity in Suzuki–Miyaura cross‐coupling reactions. The pincer‐type ligand 5 gives the chelate complexes 5·Co(ClO4)2·DMF, 5·CoCl2 and 5·Ni(ClO4)2·DMF upon treatment with the respective metal salts. These three complexes show octahedral configuration, with DMF or chloride occuping the sixth coordination site. For the CoII complexes a cis configuration is oberserved for 5·CoCl2 and a trans configuration for 5·Co(ClO4)2·DMF. In all cases 5 acts as a pentadentate ligand. All metal complexes were characterised by X‐ray diffraction. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Synthesis of 3‐ and 4‐Hydroxy‐2‐aminocyclohexanecarboxylic Acids by Iodocyclization
Authors: Szakonyi Zsolt , Gyónfalvi Szilvia , Forró Enikö , Hetényi Anasztázia , De Kimpe Norbert , Fülöp Ferenc 
Published: August 2005

AbstractStarting from cis‐7‐azabicyclo[4.2.0]oct‐4‐en‐8‐one, novel routes have been developed for the synthesis of 2‐amino‐4‐hydroxycyclohexanecarboxylic acid and its 3‐hydroxy‐substituted analog via iodooxazine, iodooxazoline or iodolactone intermediates. After CAL‐B‐catalyzed enzymatic transformation of the starting β‐lactam, the iodolactone method was applied to the synthesis of 3‐hydroxy‐substituted β‐amino acid enantiomers. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Variability of EEG synchronization prior to and during observation and execution of a sequential finger movement
Authors: Calmels Claire , Holmes Paul , Jarry Gilbert , Hars Magaly , Lopez Emilie , Paillard Aurore , Stam Cornelis J. 
Published: August 2005

AbstractThe aim of this study was to test the validity of mirror neuron activity in humans through analysis of electroencephalographic (EEG) functional connectivity during an action not directed towards an object. We investigated changes in EEG interchannel synchronization prior to and during action execution and also prior to and during observation of the same action. Twelve participants observed a simple finger movement sequence. In a second testing session they physically executed the movement. EEGs were recorded from 19 active sites across the cortex. Activity was considered in four frequency bands (7–10 Hz, 10–13 Hz, 13–20 Hz, and 20–30 Hz) using a new measure: synchronization likelihood. This technique considers rapid changes in signal synchronization and spatiotemporal patterns of coherence. The results revealed no statistically significant difference in synchronization likelihood between the observation and execution data. We found an increase in synchronization over a broad frequency range during task processing and suggest that this may reflect interregional cortical coupling of intricately and hierarchically interconnected networks that are active in a similar way during both observation and execution of a movement. While EEG may be insensitive to differences present during the observation and execution of a movement, the results of the present study shed some light on the general mechanisms of cognitive integration. Hum Brain Mapp, 2005. © 2005 Wiley‐Liss, Inc.
Convergence of behaviour change models for AIDS risk reduction in sub‐Saharan Africa
Authors: Odutolu Oluwole 
Published: August 2005

AbstractThere is increasing programme focus on the impact of HIV and AIDS and the advances in biomedical research that are taking central stage even in sub‐Saharan Africa. Perhaps out of frustration, communication and behaviour change efforts are receiving lesser attention. But as long as heterosexual intercourse remains the predominant means of transmission of HIV in sub‐Saharan Africa, there is the inherent danger of more people getting infected thus mopping up the gains from other approaches. This paper therefore argues for evidence based behaviour change interventions in sub‐Saharan Africa, revisits the behaviour change theories and their relevance to the African situation. It proposes an integration of models based on the convergence of three existing theories of social learning, diffusion of innovation and social networks and the author's understanding of some African culture. The beauty of the model is based on the fact that ‘social norms are best understood and influenced at the level of social networks’; existing chains of communication and the naturalness of exchange of information. A case is made for application of the ‘model’ to precipitate sexual behaviour change and HIV reduction in sub‐Saharan Africa. Copyright © 2005 John Wiley & Sons, Ltd.