bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cyclic Voltammetry of N,N-Dimethyl-p-Phenylenediamine and its HCl-Salt in Acetonitrile with Pyridine as Proton Acceptor
Authors: Nickel Ulrich , Garcia-Angel Maria de Gracia , Ramminger Ute , Weidinger Birgit 
Published: April 2006

Summary
The redox behaviour of N,N-dimethyl-p-phenylenediamine (PPD) and N,N-dimethyl-p-phenylenediamine · 2HCl (PPD · 2HCl) in acetonitrile was studied by means of cyclic voltammetry – both in the absence and in the presence of proton accepting pyridine. The oxidation occurs in two separate steps yielding first N,N-dimethyl-p-semiquinonediimine (SQDI+) and subsequently N,N-dimethyl-p-quinonediimine (QDI2+ or QDI+(H+)). In case of N,N-dimethyl-p-phenylenediamine the 1st oxidation step is fully reversible, while the 2nd oxidation step is slightly quasi-reversible. At 10°C the formal redox potentials of the PPD/SQDI+ and SQDI+/QDI2+ redox couples are −0.200 ± 0.005 V and 0.380 ± 0.010 V (versus Fc/Fc+), respectively. The synproportionation constant K
syn = [SQDI+]2/[PPD][QDI2+] is 2.1 × 1010. Adding pyridine to the reaction mixture leads to a shift of the 2nd anodic wave to less positive potentials. This shift is primarily due to proton transfer from QDI2+ to pyridine to form QDI+, which overall renders the oxidation easier. The corresponding cathodic peak, on the other hand, disappears as the reduction of QDI+ necessitates a proton. The formal oxidation potential of the redox couple SQDI+/QDI+(H+) is about 0.190 V and, therefore, the synproportionation constant K
syn = 1.7 × 106. N,N-dimethyl-p-phenylenediamine · 2HCl lacks completely the 1st anodic peak. The position of the anodic peak is given by the direct oxidation of PPDH+ to QDI2+(H+) and is similar to that of the SQDI+/QDI2+ redox couple. Upon adding pyridine the 2nd anodic peak shifts notably to less positive potentials and the redox process attributable to the PPD/SQDI+ redox couple is seen. As pyridine influences the potential of the Ag pseudo-reference electrode a reference electrode based on the ferrocene/ferrocenium redox couple was used.
Rational Design of Cation Hosts – Prediction of Cation Selectivity by Quantum Chemical Calculations
Authors: Galle Michael , Puchta Ralph , van Eikema Hommes Nico J. R. , van Eldik Rudi 
Published: April 2006

Summary
Structures of [M ⊂ 2.2.2]n+ obtained with MNDO, AM1, PM3, PM3/SPASS, and PM5, are evaluated against X-ray and DFT (B3LYP/LANL2DZp) geometries. DFT and X-ray structures agree well, followed by PM3/SPASS. The ion selectivity calculated with DFT and PM3/SPASS for a simple model reaction, agrees satisfactorily with the available complex-formation constants (log K
S). The applied theoretical treatment has a good predictive potential.
Cyclometallated Iridium(III) Complexes with 2-Phenylbenzimidazole Derivatives – Spectroscopic, Electrochemical and Electrochemiluminescence Studies
Authors: Kapturkiewicz A. , Nowacki J. , Borowicz P. 
Published: April 2006

Summary
Simple synthetic procedure (reactions between iridium trichloride hydrate with a series of fluorine substituted 2-phenyl-N-methyl-benzimidazole derivatives L) leads to the cyclometallated Ir(III) complexes IrL2(acac) and IrL2(pic) where acac = acetylacetonate and pic = α-picolinate anions, respectively. All the investigated complexes exhibit strong absorption in the UV region, due to the spin allowed intra-ligand (IL) transitions, and moderately intense bands in the visible region, due to the metal-to-ligand-charge-transfer (MLCT) transitions. The complexes exhibit also strong luminescence in the deoxygenated 1:1 acetonitrile/dioxane solutions at 298 K as well as in the butyronitrile glasses at 77 K. In both experimental conditions the structured emissions (with the 0–0 transition within the 480–510 nm range of UV-Vis radiation) have been observed. Cyclic voltammetry investigations point out to reversible character of the electrochemical reactions leading to stable IrL2(acac)+ or IrL2(pic)+ cations and IrL2(pic)− anions. The corresponding IrL2(acac)− species have been found to be unstable under the applied experimental conditions (1:1 acetonitrile/dioxane solutions containing 0.1 M (C4H9)4NPF6 as the supporting electrolyte) most probably due to the irreversible electrochemical reduction of the acac− ligand. Appropriate combination of the electrochemical and luminescence properties found for the investigated complexes allows for the electron transfer generation of the excited 3∗IrL2(pic) and 3∗IrL2(acac) species. Triple-potential-step technique was used to create electrochemiluminescence (ECL) emission by annihilation of the electrochemically generated IrL2(acac)+ or IrL2(pic)+ cations and 4,4’-dicyano-biphenyl radical anion. Very high ECL emission efficiencies (close to the excited 3∗IrL2(acac) and 3∗IrL2(pic) luminescence yields) have been found.
ESR-Investigations on the Dynamic Solvent Effects of Degenerate Electron Exchange Reactions. Part I: Cyanobenzenes
Authors: Mladenova Boryana , Kattnig Daniel R. , Grampp Günter 
Published: April 2006

Summary
The rates of degenerate electron exchange (electron self-exchange) of various cyanobenzenes have been measured by EPR line broadening technique in nine different solvents at room temperature. The molecules studied comprise besides benzene-1,2-dicarbonitrile, benzene-1,4-dicarbonitrile and benzene-1,2,4,5-tetracarbonitrile, the two isomeric tricyanobenzenes, benzene-1,2,3-tricarbonitrile and benzene-1,2,4-tricarbonitrile, the anion radicals of which have not been characterized before.
The experimentally observed rates vary from 4.5 × 108 to 44.0 × 108 M−1 s−1 and show the pronounced dependence on the longitudinal relaxation times, τL, of the solvents. The solvent dynamical effect so manifested is confirmed with remarkable clarity using solvents spanning a wide range of τL-values, which comprise acetonitrile (0.2 ps) and o-dichlorobenzene (6.0 ps) at its extremes. The rate constants are compared with Marcus theory using the continuum model (CM) and the mean spherical approximation (MSA) for the outer sphere reorganization energies and Nelson’s method for the inner sphere reorganization energies. Furthermore, an estimation of the resonance splitting energies, V
RP, is given based on the experimental rates.
Building of an Experimental Cline With Arabidopsis thaliana to Estimate Herbicide Fitness Cost
Authors: Roux Fabrice , Giancola Sandra , Durand Stéphanie , Reboud Xavier 
Published: April 2006

Abstract
Various management strategies aim at maintaining pesticide resistance frequency under a threshold value by taking advantage of the benefit of the fitness penalty (the cost) expressed by the resistance allele outside the treated area or during the pesticide selection “off years.” One method to estimate a fitness cost is to analyze the resistance allele frequency along transects across treated and untreated areas. On the basis of the shape of the cline, this method gives the relative contributions of both gene flow and the fitness difference between genotypes in the treated and untreated areas. Taking advantage of the properties of such migration–selection balance, an artificial cline was built up to optimize the conditions where the fitness cost of two herbicide-resistant mutants (acetolactate synthase and auxin-induced target genes) in the model species Arabidopsis thaliana could be more accurately measured. The analysis of the microevolutionary dynamics in these experimental populations indicated mean fitness costs of ∼15 and 92% for the csr1-1 and axr2-1 resistances, respectively. In addition, negative frequency dependence for the fitness cost was also detected for the axr2-1 resistance. The advantages and disadvantages of the cline approach are discussed in regard to other methods of cost estimation. This comparison highlights the powerful ability of an experimental cline to measure low fitness costs and detect sensibility to frequency-dependent variations.
Disentangling Reasons for Low Y Chromosome Variation in the Greater White-Toothed Shrew (Crocidura russula)
Authors: Lawson Handley Lori J , Berset-Brändli Laura , Perrin Nicolas 
Published: April 2006

AbstractY chromosome variation is determined by several confounding factors including mutation rate, effective population size, demography, and selection. Disentangling these factors is essential to better understand the evolutionary properties of the Y chromosome. We analyzed genetic variation on the Y chromosome, X chromosome, and mtDNA of the greater white-toothed shrew, a species with low variance in male reproductive success and limited sex-biased dispersal, which enables us to control to some extent for life-history effects. We also compared ancestral (Moroccan) to derived (European) populations to investigate the role of demographic history in determining Y variation. Recent colonization of Europe by a small number of founders (combined with low mutation rates) is largely responsible for low diversity observed on the European Y and X chromosomes compared to mtDNA. After accounting for mutation rate, copy number, and demography, the Y chromosome still displays a deficit in variation relative to the X in both populations. This is possibly influenced by directional selection, but the slightly higher variance in male reproductive success is also likely to play a role, even though the difference is small compared to that in highly polygynous species. This study illustrates that demography and life-history effects should be scrutinized before inferring strong selective pressure as a reason for low diversity on the Y chromosome.
A New Method of Estimating the Pollen Dispersal Curve Independently of Effective Density
Authors: Robledo-Arnuncio Juan J , Austerlitz Frédéric , Smouse Peter E 
Published: April 2006

AbstractWe introduce a novel indirect method of estimating the pollen dispersal curve from mother–offspring genotypic data. Unlike an earlier indirect approach (TwoGener), this method is based on a normalized measure of correlated paternity between female pairs whose expectation does not explicitly depend on the unknown effective male population density (de). We investigate the statistical properties of the new method, by comparison with those of TwoGener, considering the sensitivity to reductions of de, relative to census density, resulting from unequal male fecundity and asynchronous flowering. Our main results are: (i) it is possible to obtain reliable estimates of the average distance of pollen dispersal, δ, from indirect methods, even under nonuniform male fecundity and variable flowering phenology; (ii) the new method yields more accurate and more precise δ-estimates than TwoGener under a wide range of sampling and flowering scenarios; and (iii) TwoGener can be used to obtain approximate de estimates, if needed for other purposes. Our results also show that accurately estimating the shape of the tail of the pollen dispersal function by means of indirect methods remains a very difficult challenge.
Assessing the Relative Ages of Admixture in the Bovine Hybrid Zones of Africa and the Near East Using X Chromosome Haplotype Mosaicism
Authors: Freeman Abigail R , Hoggart Clive J , Hanotte O , Bradley Daniel G 
Published: April 2006

AbstractHistorical hybridization events between the two subspecies of cattle, Bos taurus and B. indicus, have occurred in several regions of the world, while other populations have remained nonadmixed. We typed closely linked X chromosome microsatellites in cattle populations with differing histories of admixture from Africa, Europe, the Near East, and India. Haplotype breakdown will occur as admixed populations age, and longer ancestral haplotypes will remain intact in more recently admixed populations compared to older ones. We genotyped male animals from these populations, obtaining unambiguous haplotypes, and measured levels of linkage disequilibrium (LD) and ancestral mosaicism. Extensive LD, likely to be the result of ongoing admixture, was discovered in hybrid cattle populations from the perimeter of the tsetse zone in West Africa. A Bayesian method to assign microsatellite allele ancestry was used to designate the likely origin of each chromosomal segment and assess the relative ages of admixture in the populations. A gradient of the age of admixture in the African continent emerged, where older admixture has produced more fragmented haplotypes in the south, and longer intact haplotypes, indicating more recent hybridization, feature in the northwest.
Evaluation of DNA Pooling for the Estimation of Microsatellite Allele Frequencies: A Case Study Using Striped Bass (Morone saxatilis)
Authors: Skalski Garrick T , Couch Charlene R , Garber Amber F , Weir Bruce S , Sullivan Craig V 
Published: April 2006

Abstract
Using striped bass (Morone saxatilis) and six multiplexed microsatellite markers, we evaluated procedures for estimating allele frequencies by pooling DNA from multiple individuals, a method suggested as cost-effective relative to individual genotyping. Using moment-based estimators, we estimated allele frequencies in experimental DNA pools and found that the three primary laboratory steps, DNA quantitation and pooling, PCR amplification, and electrophoresis, accounted for 23, 48, and 29%, respectively, of the technical variance of estimates in pools containing DNA from 2–24 individuals. Exact allele-frequency estimates could be made for pools of sizes 2–8, depending on the locus, by using an integer-valued estimator. Larger pools of size 12 and 24 tended to yield biased estimates; however, replicates of these estimates detected allele frequency differences among pools with different allelic compositions. We also derive an unbiased estimator of Hardy–Weinberg disequilibrium coefficients that uses multiple DNA pools and analyze the cost-efficiency of DNA pooling. DNA pooling yields the most potential cost savings when a large number of loci are employed using a large number of individuals, a situation becoming increasingly common as microsatellite loci are developed in increasing numbers of taxa.
Remarkable Site Specificity of Local Transposition Into the Hsp70 Promoter of Drosophila melanogaster
Authors: Shilova Victoria Y , Garbuz David G , Myasyankina Elena N , Chen Bing , Evgen'ev Michael B , Feder Martin E , Zatsepina Olga G 
Published: April 2006

Abstract
Heat-shock genes have numerous features that ought to predispose them to insertional mutagenesis via transposition. To elucidate the evolvability of heat-shock genes via transposition, we have exploited a local transposition technique and Drosophila melanogaster strains with EPgy2 insertions near the Hsp70 gene cluster at 87A7 to produce numerous novel EPgy2 insertions into these Hsp70 genes. More than 50% of 45 independent insertions were made into two adjacent nucleotides in the proximal promoter at positions −96 and −97, and no insertions were into a coding or 3′-flanking sequence. All inserted transposons were in inverse orientation to the starting transposon. The frequent insertion into nucleotides −96 and −97 is consistent with the DNase hypersensitivity, absence of nucleosomes, flanking GAGA-factor-binding sites, and nucleotide sequence of this region. These experimental insertions recapitulated many of the phenotypes of natural transposition into Hsp70: reduced mRNA expression, less Hsp70 protein, and decreased inducible thermotolerance. The results suggest that the distinctive features of heat-shock promoters, which underlie the massive and rapid expression of heat-shock genes upon heat shock, also are a source of evolutionary variation on which natural selection can act.
Characterization and Mapping of a Shattering Mutant in Rice That Corresponds to a Block of Domestication Genes
Authors: Ji Hyeon-So , Chu Sang-Ho , Jiang Wenzhu , Cho Young-Il , Hahn Jang-Ho , Eun Moo-Young , McCouch Susan R , Koh Hee-Jong 
Published: April 2006

Abstract
Easy shattering reduces yield due to grain loss during harvest in cereals. Shattering is also a hindrance in breeding programs that use wild accessions because the shattering habit is often linked to desirable traits. We characterized a shattering mutant line of rice, Hsh, which was derived from a nonshattering japonica variety, Hwacheong, by N-methyl-N-nitrosourea (MNU) treatment. The breaking tensile strength (BTS) of the grain pedicel was measured using a digital force gauge to evaluate the degree of shattering of rice varieties at 5, 10, 15, 20, 25, 30, 35, and 40 days after heading (DAH). The BTS of Hwacheong did not decrease with increasing DAH, maintaining a level of 180–240 gf, while that of Hsh decreased greatly during 10–20 DAH and finally stabilized at 50 gf. Optical microscopy revealed that Hsh had a well-developed abscission layer similar to the wild rice Oryza nivara (accession IRGC105706), while Hwacheong did not produce an abscission layer, indicating that the shattering of Hsh was caused by differentiation of the abscission layer. On the basis of the BTS value and morphology of the abscission layer of F1 plants and segregation data in F2 populations, it was concluded that the easy shattering of Hsh was controlled by the single recessive gene sh-h. The gene sh-h was determined to be located on rice chromosome 7 by bulked segregant analysis. Using 14 SSR markers on rice chromosome 7, the gene sh-h was mapped between the flanking markers RM8262 and RM7161 at distances of 1.6 and 2.0 cM, respectively. An SSR marker Rc17 cosegregated with the gene sh-h. The locus sh-h for shattering was tightly linked to the Rc locus conferring red pericarp, as well as a QTL qSDs-7-1 for seed dormancy, implying that this region might represent a domestication block in the evolutionary pathway of rice.
Dominant Mutants of the Saccharomyces cerevisiae ASF1 Histone Chaperone Bypass the Need for CAF-1 in Transcriptional Silencing by Altering Histone and Sir Protein Recruitment
Authors: Tamburini Beth A , Carson Joshua J , Linger Jeffrey G , Tyler Jessica K 
Published: April 2006

Abstract
Transcriptional silencing involves the formation of specialized repressive chromatin structures. Previous studies have shown that the histone H3–H4 chaperone known as chromatin assembly factor 1 (CAF-1) contributes to transcriptional silencing in yeast, although the molecular basis for this was unknown. In this work we have identified mutations in the nonconserved C terminus of antisilencing function 1 (Asf1) that result in enhanced silencing of HMR and telomere-proximal reporters, overcoming the requirement for CAF-1 in transcriptional silencing. We show that CAF-1 mutants have a drastic reduction in DNA-bound histone H3 levels, resulting in reduced recruitment of Sir2 and Sir4 to the silent loci. C-terminal mutants of another histone H3–H4 chaperone Asf1 restore the H3 levels and Sir protein recruitment to the silent loci in CAF-1 mutants, probably as a consequence of the weakened interaction between these Asf1 mutants and histone H3. As such, these studies have identified the nature of the molecular defect in the silent chromatin structure that results from inactivation of the histone chaperone CAF-1.
Genetic Control of X Chromosome Inactivation in Mice: Definition of theXceCandidate Interval
Authors: Chadwick Lisa Helbling , Pertz Lisa M , Broman Karl W , Bartolomei Marisa S , Willard Huntington F 
Published: April 2006

AbstractIn early mammalian development, one of the two X chromosomes is silenced in each female cell as a result of X chromosome inactivation, the mammalian dosage compensation mechanism. In the mouse epiblast, the choice of which chromosome is inactivated is essentially random, but can be biased by alleles at the X-linked X controlling element (Xce). Although this locus was first described nearly four decades ago, the identity and precise genomic localization of Xce remains elusive. Within the X inactivation center region of the X chromosome, previous linkage disequilibrium studies comparing strains of known Xce genotypes have suggested that Xce is physically distinct from Xist, although this has not yet been established by genetic mapping or progeny testing. In this report, we used quantitative trait locus (QTL) mapping strategies to define the minimal Xce candidate interval. Subsequent analysis of recombinant chromosomes allowed for the establishment of a maximum 1.85-Mb candidate region for the Xce locus. Finally, we use QTL approaches in an effort to identify additional modifiers of the X chromosome choice, as we have previously demonstrated that choice in Xce heterozygous females is significantly influenced by genetic variation present on autosomes (Chadwick and Willard 2005). We did not identify any autosomal loci with significant associations and thus show conclusively that Xce is the only major locus to influence X inactivation patterns in the crosses analyzed. This study provides a foundation for future analyses into the genetic control of X chromosome inactivation and defines a 1.85-Mb interval encompassing all the major elements of the Xce locus.
Differential Roles of Transcriptional Mediator Complex Subunits Crsp34/Med27, Crsp150/Med14 and Trap100/Med24 During Zebrafish Retinal Development
Authors: Dürr Katrin , Holzschuh Jochen , Filippi Alida , Ettl Anne-Kathrin , Ryu Soojin , Shepherd Iain T , Driever Wolfgang 
Published: April 2006

Abstract
The transcriptional mediator complex has emerged as an important component of transcriptional regulation, yet it is largely unknown whether its subunits have differential functions in development. We demonstrate that the zebrafish mutation m885 disrupts a subunit of the mediator complex, Crsp34/Med27. To explore the role of the mediator in the control of retinal differentiation, we employed two additional mutations disrupting the mediator subunits Trap100/Med24 and Crsp150/Med14. Our analysis shows that loss of Crsp34/Med27 decreases amacrine cell number, but increases the number of rod photoreceptor cells. In contrast, loss of Trap100/Med24 decreases rod photoreceptor cells. Loss of Crsp150/Med14, on the other hand, only slightly reduces dopaminergic amacrine cells, which are absent from both crsp34m885 and trap100lessen mutant embryos. Our data provide evidence for differential requirements for Crsp34/Med27 in developmental processes. In addition, our data point to divergent functions of the mediator subunits Crsp34/Med27, Trap100/Med24, and Crsp150/Med14 and, thus, suggest that subunit composition of the mediator contributes to the control of differentiation in the vertebrate CNS.