bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characterization of solvatochromic probes: simulation of merocyanine 540 absorption spectra in binary solvent mixtures and pure solvent systems
Authors: Bae S. Y. , Arnold B. R. 
Published: February 2004

AbstractAn empirical extension of the continuum model was used to reproduce the absorption spectrum of the optical probe merocyanine 540 in numerous solvents based on 27 probe‐specific parameters in conjunction with the dielectric constant and refractive index of the solvent. The calibrated absorption spectrum of this dye allowed the accurate determination of the dielectric constant and refractive index of the bulk solvent. This study incorporates several binary solvent mixtures in addition to several pure solvents of differing functionality, including protic and aprotic solvents. A single, generally applicable, set of probe‐specific parameters is presented. The accuracy of the determined solvent properties using this general set of probe parameters suggests that the influence of specific solvent–solute interactions on the absorption spectrum of this dye must be constant if not insignificant in the range of solvents studied, with the notable exception of water. Copyright © 2004 John Wiley & Sons, Ltd.
Radiation‐induced oxidation of substituted benzaldehydes: a pulse radiolysis study
Authors: Geeta S. , Rao B. S. M. , Mohan H. , Mittal J. P. 
Published: February 2004

AbstractThe reactions of the oxidizing radicals hydroxyl radical (.OH), azidyl radical $({\rm N}_3^\cdot)$ and sulfate radical anion $({\rm SO}_4^{-\cdot})$ with hydroxy‐, methoxy‐, chloro‐ and nitro‐substituted benzaldehydes were studied by pulse radiolysis. The rate constants for the .OH reaction [k ≈ (2.6–12.0) × 109 l mol−1 s−1] with these compounds are higher than those for the ${\rm N}_3^\cdot$ or ${\rm SO}_4^{-\cdot}$ reactions [k ≈ (0.01–4.2) × 109 l mol−1 s−1]. The .OH reaction shows a significant substituent effect which is reflected in the rate constants (k ≈ 12.0 × 109 dm3 mol−1 s−1 with hydroxybenzaldehyde and k ≈ 3.0 × 109 dm3 mol−1 s−1 with nitrobenzaldehyde). The transient species produced by the reaction of .OH with the m‐substituted benzaldehydes shows an absorption maximum at 370–400 nm, whereas the p‐substituted isomers exhibit two absorption peaks centred around 325 and 410 nm, except in the case of p‐nitrobenzaldehyde, which shows only a single peak at 330 nm. These spectra are identical with the spectra obtained for the $({\rm N}_3^\cdot)$ or ${\rm SO}_4^{-\cdot}$ reactions with substituted benzaldehydes. .OH adduct formation and subsequent decomposition to the corresponding phenoxyl radicals is the main reaction channel for the .OH‐induced oxidation of substituted benzaldehydes. One‐electron oxidation by $({\rm N}_3^\cdot)$ or ${\rm SO}_4^{-\cdot}$ of substituted benzaldehydes proceeds via an electron transfer process producing the corresponding radical cations. Copyright © 2004 John Wiley & Sons, Ltd.
Photophysics of Poly{2,2′‐bipyridine‐5,5′‐diylethynylene [2,5‐di(2‐ethylhexyl)oxy‐1,4‐phenylene[ethynylene}: a comparison with monomer and dimer model compounds
Authors: Grummt U.‐W. , Pautzsch Th. , Birckner E. , Utterodt A. , Neugebauer U. , Klemm E. 
Published: February 2004

AbstractThe title compound (P) was synthesized via Pd‐ and Cu‐catalyzed coupling reactions (Sonogashira reaction). Two model compounds prepared by similar synthetic routes, 1,4‐bis(2,2′‐bipyridin‐5′‐ylethynyl)‐2,5‐di(2‐ethylhexyl)oxybenzene (M), and 5,5′‐[1‐ethynyl‐4‐(2,2′‐bipyridin‐5′‐ylethynyl)‐2,5‐di(2‐ethylhexyl)oxybenzene]‐2,2′‐bipyridine (D), were included in the spectroscopic investigations for comparison. As a result of steady‐state and time‐resolved absorption and fluorescence investigations in solution and in solid films, we conclude that the π‐conjugation is restricted by torsional motions of the aromatic chain segments at ordinary temperature. It comprises about 2–3 repetition units in the S1 state as concluded from a comparison of the experimental radiative rate constant with that calculated from the Strickler–Berg relation. It is even less in the ground state. The theoretical limit obtained from DFT calculations is about twice as large for the ideal coplanar conformation. Whereas the π–π stacking interaction in pure polymer films is very weak in the ground state, it is significantly stronger in the S1 state, giving rise to excimer fluorescence. Energy migration along the polymer backbone is inefficient. Intermolecular energy migration and transfer to embedded acceptors becomes efficient in solid films. Copyright © 2004 John Wiley & Sons, Ltd.
Photochemistry of 9‐fluorenone oxime phenylglyoxylate: a combined TRIR, TREPR and ab initio study
Authors: Kolano Christoph , Bucher Götz , Wenk Hans Henning , Jäger Martin , Schade Olaf , Sander Wolfram 
Published: February 2004

AbstractThe photochemistry of 9‐fluorenone oxime phenylglyoxylate (1) in tetrachloromethane was investigated by a variety of time‐resolved methods [STEP‐SCAN TRIR and time‐resolved EPR (TREPR)]. Photolysis of 1 yields the benzoyl radical, carbon dioxide and the fluorene‐9‐iminyl radical on pulsed irradiation (λ = 355 nm). All radicals have a lifetime in the range of microseconds and can be detected within the rise time of our time‐resolved equipment before undergoing recombination or reactions with the solvent. The benzoyl radical shows a strong absorption ($(\tilde \nu$C=O = 1824 cm−) in the IR spectrum. Upon purging the solution with oxygen, the benzoyl radical is quenched to yield the benzoylperoxy radical ($(\tilde \nu$C=O = 1814 cm−), which has a lifetime that is several microseconds longer than that of the benzoyl radical. Owing to the lack of a good IR chromophore, the fluorene‐9‐iminyl radical is not detected by IR spectroscopy. It can, however, be detected by TREPR spectroscopy, which allows the detection of a 1 : 1 : 1 triplet of the fluorene‐9‐iminyl radical at 3456 G and a 1 : 2 : 1 triplet of the benzoyl radical at 3460 G. Copyright © 2004 John Wiley & Sons, Ltd.
Diethyl ketone triperoxide: thermal decomposition reaction in chlorobenzene solution and its application as initiator of polymerization
Authors: Cañizo Adriana I. , Eyler Gladys N. , Morales Graciela , Cerna Jorge R. 
Published: February 2004

AbstractThe kinetics of the thermal decomposition reaction of diethyl ketone triperoxide (3,3,6,6,9,9‐hexaethyl‐1,2,4,5,7,8‐hexaoxacyclononane, DEKT) in chlorobenzene solution were studied in the temperature range 99.0–148.0°C and at initial concentrations of (1.65–4.97) × 10−2 M. The thermolysis of DEKT follows a first‐order kinetic law up to at least ca 80% triperoxide conversion. The activation parameter values for the initial O—O bond rupture in chlorobenzene (ΔH‡=134.6±1.7 kJ mol−1; ΔS‡ = 4.2 ± 3.8 J mol−1 K−1) and the reaction products observed support a stepwise reaction mechanism which includes as a first step the unimolecular homolytic cleavage of one peroxidic bond of the DEKT molecule giving rise to a biradical as intermediate. Additionally, the results obtained were compared with those obtained in toluene, toluene–styrene (50%, v/v) and chlorobenzene–styrene (50%, v/v) solution, showing that the decomposition reaction is strongly solvent dependant. Further, the biradical intermediate obtained in all cases was used to initiate styrene polymerization. It was demonstrated that DEKT can effectively act as initiator in styrene polymerization and its performance is similar to that presented by a multifunctional initiator giving rise to high molecular weight polystyrene at a high reaction rate. Copyright © 2004 John Wiley & Sons, Ltd.
Effect of pressure on sterically hindered reactions with late transition states
Authors: Gacem Badra , Jenner Gérard 
Published: February 2004

AbstractThe effect of high pressure is examined in two types of sterically congested reactions presenting late transition states: isopolar Diels–Alder cycloadditions of isoprene and quinones of various steric environment and conjugate additions of tert‐butylamine and acrylic compounds. In the Diels–Alder cycloadditions, pressure has no enhanced kinetic sensitivity in sterically demanding reactions compared with unhindered ones. This is due to the structural closeness of the transition state and product. At variance, in the conjugate addition of amines, the effect of pressure is magnified with increasing steric congestion at the reaction centres. This is ascribed to enhanced electrostriction with removal of steric hindrance to ionization. Copyright © 2004 John Wiley & Sons, Ltd.
Synthesis, x‐ray structure and spectroscopic and electronic properties of two new synthesized flavones
Authors: Cotelle Nicole , Vrielynck Laurence , Nowogrocki Guy , Cotelle Philippe , Vezin Hervé 
Published: February 2004

AbstractTwo new flavones (1 and 2) in which one or two di‐tert‐butylhydroxyphenyl groups replace the B‐ring of flavonoids, respectively, were synthesized according to the Baker–Vankataraman method. Their crystal structures were determined by x‐ray diffraction methods and compared with those obtained by theoretical calculations using join Monte Carlo conformational search analysis and geometry optimization ab initio formalism. NMR NOE data, ESR spectra and electronic properties were obtained in order to understand their implication in the enhancement of low‐density lipoprotein (LDL) resistance to oxidation. The oxidative modification of LDL has been alleged to play an important role in the development of human atherosclerosis and neurodegenerative diseases. Copyright © 2004 John Wiley & Sons, Ltd.
Comparative study of the catalytic behaviour of Ru(III) and Ru(VI) on the oxidation of alcohols by hexacyanoferrate(III)
Authors: Mucientes A. E. , Gabaldón R. E. , Poblete F. J. , Villarreal S. 
Published: February 2004

AbstractThe oxidation reactions of 2‐methyl‐2,4‐pentanediol upon treatment with alkaline hexacyanoferrate(III) using Ru(III) or Ru(VI) as catalysts are governed by two quasi‐identical experimental rate equations, which show that both catalysts are equally effective for the oxidation of alcohols by ${\rm Fe(CN)}_6^{3-}$. The reaction mechanism proposed involves the oxidation of 2‐methyl‐2,4‐pentanediol by the catalyst, a process that occurs through the formation of a substrate–catalyst complex. The decomposition of this complex yields Ru(IV) and a protonated ketone (owing to a hydride transfer from the α‐C—H bond of the alcohol to the oxoligand of ruthenium) in the case of Ru(VI), but a ketyl radical and Ru(II) (hydrogen transfer) for Ru(III). The role of the co‐oxidant, ${\rm Fe(CN)}_6^{3-}$, is to regenerate the catalyst. For both oxidation reactions, the rate constants of complex decomposition and catalyst regeneration have been determined. Copyright © 2004 John Wiley & Sons, Ltd.
The gas‐phase reactivity of epichlorohydrin with hydroxide
Authors: Merrill G. N. 
Published: February 2004

AbstractThe reaction of hydroxide with epichlorohydrin in the gas phase was investigated with ab initio calculations. Three mechanisms were examined, each corresponding to nucleophilic attack at a different carbon atom of the substrate. It was determined that through attack at the ring methylene position was favored, whereas attacks at the alkyl methylene or ring methine positions were found to have larger activation energies. These results are consistent with experimental results found in the literature. Copyright © 2004 John Wiley & Sons, Ltd.
Mechanism of Ir(III)‐catalysed and Hg(II)‐co‐catalysed oxidation of reducing sugars by N‐bromoacetamide in acidic medium
Authors: Singh Ashok Kumar , Rahmani Shahla , Singh Bharat , Singh Ramesh Kumar , Singh Manju 
Published: February 2004

AbstractThe kinetics of Ir(III)‐catalysed and Hg(II)‐co‐catalysed oxidation of D‐glucose (Glu) and D‐fructose (Fru) by N‐bromoacetamide (NBA) were studied in acidic medium. The reactions follow identical kinetics, being zero order in each sugar concentration. The experimental results show a first‐order dependence on NBA and Ir(III) at low concentrations, but tending towards zeroth order at higher concentrations. A negative effect of variation of [H+], [Cl−] and [NHA] was observed whereas the ionic strength (I) of the medium has no influence on oxidation rate. The important feature of the reaction is that it follows a second‐order dependence on mercury(II) ion concentration at low concentrations, but it tends towards first order at higher concentrations. Various activation parameters were calculated and recorded. The corresponding acids were identified as the main oxidation products of the reaction. On the basis of the experimental findings, a suitable mechanism consistent with the observed kinetics was proposed. A comparative study was also made between the kinetic results of the present investigation and those of Ru(III)‐ and Pd(II)‐catalysed oxidations of reducing sugars. Copyright © 2004 John Wiley & Sons, Ltd.
NMR spectroscopic and molecular modelling study of the solution structure and the complexational behavior of maleonitrile tetrathia crown ethers with silver(I)
Authors: Holzberger Anja , Holdt Hans‐Jürgen , Kleinpeter Erich 
Published: February 2004

AbstractThe flexibility and complex formation of two maleonitrile tetrathia crown ethers were studied in solution using 1H and 13C NMR spectroscopy and molecular modelling. Both the stoichiometry and the stability of the complexes that these crown ethers form with Ag(I) were determined by NMR titration measurements. Spin–lattice relaxation time measurements provided information concerning the donor atoms involved in complex formation and also the intramolecular mobility of the free and complexed ligands. Molecular modelling was also used to gain further insight into the conformational space of the free ligands and their silver(I) complexes. Copyright © 2004 John Wiley & Sons, Ltd.
Simultaneous Sv and TS measurements on Young-of-the-Year (YOY) freshwater fish using three frequencies
Authors: Guillard J , Lebourges-Dhaussy A , Brehmer P 
Published: February 2004

Abstract
In autumn, the fish population above the thermocline in Lake Annecy mainly comprises young perch (Perca fluviatilis) of the year. The fish are distributed in schools during the day and as scattered individual fish targets at night. Measurements of volume-backscattering strength and target strengths (TS) were carried out in a synchronous way using three echosounders operating at three frequencies (70, 120, and 129 kHz), with different characteristics (split beam, dual beam, beam shape, pulse length, etc.). Target-strength values show variability from one elementary sampling unit to another and from one device to another, but the mean global TS values are similar, independently of the frequency. The volume-backscattering strengths measured on precise schools by the three acoustic devices give significantly similar results. Acoustic measurements on YOY perch are completely independent of the frequency and the characteristics of the echosounders.
Fitting growth models to length frequency data
Authors: Laslett Geoff M. , Eveson J. Paige , Polacheck Tom 
Published: February 2004

Abstract
A novel two-stage procedure for fitting growth curves to length frequency data collected from commercial fisheries is described. The method is suitable for species in which cohorts are spawned over a limited time period, and samples of length frequency data are collected regularly (e.g. in weekly, fortnightly, or monthly time intervals) over an extended time period. In the first stage of analysis, Gaussian mixtures are fitted separately to the data for each time interval, and summary statistics (component means and standard errors) are extracted. In the second stage, parametric growth models, such as the von Bertalanffy seasonal growth curve, are fitted to the summary data. The error structure in this second stage of analysis incorporates random between-year effects, random within-year age-group effects, random within-year time-interval effects, random within-year age-group and time-interval interactions, and sampling errors. This complex error structure incorporating unbalanced crossed and nested random effects acknowledges that commercial fishing is not an exercise in random sampling, and allows for the inevitable additional sources of random variation in such an enterprise. The method is applied to South Australian southern bluefin tuna length frequency data collected from 1964 to 1989, and leads to the conclusion that juvenile tuna grew faster in the 1980s than in the 1960s, with the 1970s being a decade of highly variable growth.
Evolutionary Dynamics of the DNA-Binding Domains in Putative R2R3-MYB Genes Identified from Rice SubspeciesindicaandjaponicaGenomes
Authors: Jia Li , Clegg Michael T. , Jiang Tao 
Published: February 2004

AbstractThe molecular evolution of the R2R3-MYB gene family is of great interest because it is one of the most important transcription factor gene families in the plant kingdom. Comparative analyses of a gene family may reveal important adaptive changes at the protein level and thereby provide insights that relate structure to function. We have performed a range of comparative and bioinformatics analyses on R2R3-MYB genes identified from the rice (Oryza sativa subsp. japonica and indica) and Arabidopsis genome sequences. The study provides an initial framework to investigate how different evolutionary lineages in a gene family evolve new functions. Our results reveal a remarkable excess of non-synonymous substitutions, an indication of adaptive selection on protein structure that occurred during the evolution of both helix1 and helix2 of rice R2R3-MYB DNA-binding domains. These flexible α-helix regions associated with high frequencies of excess non-synonymous substitutions may play critical roles in the characteristic packing of R2R3-MYB DNA-binding domains and thereby modify the protein-DNA interaction process resulting in the recognition of novel DNA-binding sites. Furthermore, a co-evolutionary pattern is found between the second α-helix of the R2 domain and the second α-helix of the R3 domain by examining all the possible α-helix pairings in both the R2 and R3 domains. This points to the functional importance of pairing interactions between related secondary structures.
Identification and Functional Analysis of a Locus for Improvement of Lodging Resistance in Rice
Authors: Kashiwagi Takayuki , Ishimaru Ken 
Published: February 2004

Abstract
We identified a new locus responsible for increased pushing resistance of the lower part of rice (Oryza sativa) and analyzed its physiological function to understand how to improve lodging resistance in rice. Quantitative trait loci (QTLs) controlling pushing resistance of the lower part were analyzed in a population of backcross inbred lines of japonica Nipponbare × indica Kasalath plants cut out at 40 cm to exclude the effect of the weight of the upper parts. Five QTLs for pushing resistance were detected; only one QTL from Kasalath on chromosome 5 (prl5) had a positive effect. The likelihood odds ratio curve of prl5 echoed that for lodging resistance by typhoon. We selected three near-isogenic lines (NILs) in which the chromosomal region of prl5 was substituted with that of Kasalath in the Nipponbare background. The dry weights and densities and the contents of accumulated carbohydrate in stems below 40 cm (lower stems) in each NIL were significantly higher than those of Nipponbare. There was no difference between Nipponbare and the NILs in yield, root characteristics, or the weights of the upper parts. Pushing resistance of the lower part and lodging resistance in the NILs were up to twice as high as in Nipponbare. These results suggest that prl5 might affect the characteristics of the lower stems of the NILs, thus increasing lodging resistance.
Osmotically Induced Cell Swelling versus Cell Shrinking Elicits Specific Changes in Phospholipid Signals in Tobacco Pollen Tubes
Authors: Zonia Laura , Munnik Teun 
Published: February 2004

Abstract
Pollen tube cell volume changes rapidly in response to perturbation of the extracellular osmotic potential. This report shows that specific phospholipid signals are differentially stimulated or attenuated during osmotic perturbations. Hypo-osmotic stress induces rapid increases in phosphatidic acid (PA). This response occurs starting at the addition of 25% (v/v) water to the pollen tube cultures and peaks at 100% (v/v) water. Increased levels of PA were detected within 30 s and reached maximum by 15 to 30 min after treatment. The pollen tube apical region undergoes a 46% increase in cell volume after addition of 100% water (v/v), and there is an average 7-fold increase in PA. This PA increase appears to be generated by phospholipase D because concurrent transphosphatidylation of n-butanol results in an average 8-fold increase in phosphatidylbutanol. Hypo-osmotic stress also induces an average 2-fold decrease in phosphatidylinositol phosphate; however, there are no detectable changes in the levels of phosphatidylinositol bisphosphates. In contrast, salt-induced hyperosmotic stress from 50 to 400 mm NaCl inhibits phospholipase D activity, reduces the levels of PA, and induces increases in the levels of phosphatidylinositol bisphosphate isomers. The pollen tube apical region undergoes a 41% decrease in cell volume at 400 mm NaCl, and there is an average 2-fold increase in phosphatidylinositol 3,5-bisphosphate and 1.4-fold increase in phosphatidylinositol 4,5-bisphosphate. The phosphatidylinositol 3,5-bisphosphate increase is detected within 30 s and reaches maximum by 15 to 30 min after treatment. In summary, these results demonstrate that hypo-osmotic versus hyperosmotic perturbation and the resultant cell swelling or shrinking differentially activate specific phospholipid signaling pathways in tobacco (Nicotiana tabacum) pollen tubes.
Iron-Regulated Expression of a Cytosolic Ascorbate Peroxidase Encoded by the APX1 Gene in Arabidopsis Seedlings
Authors: Fourcroy Pierre , Vansuyt Gérard , Kushnir Sergei , Inzé Dirk , Briat Jean-François 
Published: February 2004

Abstract
Iron (Fe) is an essential element for living organisms. However, under aerobic conditions, its use is complicated because of its high insolubility and its potential toxicity through reactivity with reduced forms of oxygen. In plants, Fe overload can lead to intracellular concentrations beyond the storage and detoxification capacities of cells. Such a displacement toward a pro-oxidant state can activate antioxidant defenses, including Fe-mediated expression of ascorbate peroxidase genes. In this work, we demonstrate that Fe overload specifically induces the AtAPX1 gene encoding a cytosolic ascorbate peroxidase in Arabidopsis leaves. The strong constitutive expression of the AtAPX1 gene in roots is unaffected by Fe and depends on the first 5′-untranslated region intron. Presence of an AtAPX1 expressed sequence tag in the Arabidopsis database, longer in its 5′ region than what could be predicted from the published AtAPX1transcription initiation site, leads to define a new transcription initiation region for this gene. A minimal promoter sequence enabling Fe-induced expression of the AtAPX1 gene is defined by following expression of various AtAPX1::β-glucuronidase constructs in transformed Arabidopsis plantlets. This 118-bp minimal promoter sequence contains an Fe-dependent regulatory sequence-like cis-element known to be necessary for maize (Zea mays) and Arabidopsis ferritin gene derepression in response to Fe overload. Site-directed mutagenesis of this element within the AtAPX1 promoter sequence does not abolish the Fe-dependent activation of a reporter gene, indicating that it is likely not involved in the Fe-regulated expression of the AtAPX1 gene.