bluuebunny/crossref_metadata_2025 huggingface dataset:
A Pseudohitchhiking Model of X vs. Autosomal Diversity
Authors: Betancourt Andrea J , Kim Yuseob , Orr H Allen
Published: December 2004

We study levels of X-linked vs. autosomal diversity using a model developed to analyze the hitchhiking effect. Repeated bouts of hitchhiking are thought to lower X-linked diversity for two reasons: first, because sojourn times of beneficial mutations are shorter on the X, and second, because adaptive substitutions may be more frequent on the X. We investigate whether each of these effects does, in fact, cause reduced X-linked diversity under hitchhiking. We study the strength of the hitchhiking effect on the X vs. autosomes when there is no recombination and under two different recombination schemes. When recombination occurs in both sexes, X-linked vs. autosomal diversity is reduced by hitchhiking under a broad range of conditions, but when there is no recombination in males, as in Drosophila, the required conditions are considerably more restrictive.
High-Resolution Fine Mapping and Fluorescence in Situ Hybridization Analysis of sun, a Locus Controlling Tomato Fruit Shape, Reveals a Region of the Tomato Genome Prone to DNA Rearrangements
Authors: van der Knaap E , Sanyal A , Jackson S A , Tanksley S D
Published: December 2004

The locus sun on the short arm of tomato chromosome 7 controls morphology of the fruit. Alleles from wild relatives impart a round shape, while alleles from certain cultivated varieties impart an oval shape typical of roma-type tomatoes. We fine mapped the locus in two populations and investigated the genome organization of the region spanning and flanking sun. The first high-resolution genetic map of the sun locus was constructed using a nearly isogenic F2 population derived from a cross between Lycopersicon pennellii introgression line IL7-4 and L. esculentum cv Sun1642. The mapping combined with results from pachytene FISH experiments demonstrated that the top of chromosome 7 is inverted in L. pennellii accession LA716. sun was located close to the chromosomal breakpoint and within the inversion, thereby precluding map-based cloning of the gene using this population. The fruit-shape locus was subsequently fine mapped in a population derived from a cross between L. esculentum Sun1642 and L. pimpinellifolium LA1589. Chromosome walking using clones identified from several large genomic insert libraries resulted in two noncontiguous contigs flanking sun. Fiber-FISH analysis showed that distance between the two contigs measured 68 kb in L. esculentum Sun1642 and 38 kb in L. pimpinellifolium LA1589, respectively. The sun locus mapped between the two contigs, suggesting that allelic variation at this locus may be due to an insertion/deletion event. The results demonstrate that sun is located in a highly dynamic region of the tomato genome.
Bile-Induced DNA Damage in Salmonella enterica
Authors: Prieto Ana I , Ramos-Morales Francisco , Casadesús Josep
Published: December 2004

In the absence of DNA adenine methylase, growth of Salmonella enterica serovar Typhimurium is inhibited by bile. Mutations in any of the mutH, mutL, and mutS genes suppress bile sensitivity in a Dam− background, indicating that an active MutHLS system renders Dam− mutants bile sensitive. However, inactivation of the MutHLS system does not cause bile sensitivity. An analogy with Escherichia coli, in which the MutHLS system sensitizes Dam− mutants to DNA-injuring agents, suggested that bile might cause DNA damage. In support of this hypothesis, we show that bile induces the SOS response in S. enterica and increases the frequency of point mutations and chromosomal rearrangements. Mutations in mutH, mutL, or mutS cause partial relief of virulence attenuation in a Dam− background (50- to 100-fold by the oral route and 10-fold intraperitoneally), suggesting that an active MutHLS system reduces the ability of Salmonella Dam− mutants to cope with DNA-damaging agents (bile and others) encountered during the infection process. The DNA-damaging ability of bile under laboratory conditions raises the possibility that the phenomenon may be relevant in vivo, since high bile concentrations are found in the gallbladder, the niche for chronic Salmonella infections.
DNA Methylation Affects Meiotic trans-sensing, Not Meiotic Silencing, in Neurospora
Authors: Pratt Robert J , Lee Dong W , Aramayo Rodolfo
Published: December 2004

During the early stages of meiosis in Neurospora, the symmetry of homologous chromosomal regions is carefully evaluated by actively trans-sensing their identity. If a DNA region cannot be detected on the opposite homologous chromosome, then this lack of “sensing” activates meiotic silencing, a post-transcriptional gene silencing-like mechanism that silences all genes in the genome with homology to the loop of unpaired DNA, whether they are paired or unpaired. In this work, we genetically dissected the meiotic trans-sensing step from meiotic silencing by demonstrating that DNA methylation affects sensing without interfering with silencing. We also determined that DNA sequence is an important parameter considered during meiotic trans-sensing. Altogether, these observations assign a previously undescribed role for DNA methylation in meiosis and, on the basis of studies in other systems, we speculate the existence of an intimate connection among meiotic trans-sensing, meiotic silencing, and meiotic recombination.
Inferring the Population Structure and Demography of Drosophila ananassae From Multilocus Data
Authors: Das Aparup , Mohanty Sujata , Stephan Wolfgang
Published: December 2004

Inferring the origin, population structure, and demographic history of a species is a major objective of population genetics. Although many organisms have been analyzed, the genetic structures of subdivided populations are not well understood. Here we analyze Drosophila ananassae, a highly substructured, cosmopolitan, and human-commensal species distributed in the tropical, subtropical, and mildly temperate regions of the world. We adopt a multilocus approach (with 10 neutral loci) using 16 population samples covering almost the entire species range (Asia, Australia, and America). Analyzed with our recently developed Bayesian method, 5 populations in Southeast Asia are found to be central, while the other 11 are peripheral. These 5 central populations were sampled from localities that belonged to a single landmass (“Sundaland”) during the late Pleistocene (∼18,000 years ago), when sea level was ∼120 m below the present level. The inferred migration routes of D. ananassae out of Sundaland seem to parallel those of humans in this region. Strong evidence for a population size expansion is seen particularly in the ancestral populations.
Oligosyndactylism Mice Have an Inversion of Chromosome 8
Authors: Wise Thomas L , Pravtcheva Dimitrina D
Published: December 2004

The radiation-induced mutation Oligosyndactylism (Os) is associated with limb and kidney defects in heterozygotes and with mitotic arrest and embryonic lethality in homozygotes. We reported that the cell cycle block in Os and in the 94-A/K transgene-induced mutations is due to disruption of the Anapc10 (Apc10/Doc1) gene. To understand the genetic basis of the limb and kidney abnormalities in Os mice we characterized the structural changes of chromosome 8 associated with this mutation. We demonstrate that the Os chromosome 8 has suffered two breaks that are 5 cM (∼10 Mb) apart and the internal fragment delineated by the breaks is in an inverted orientation on the mutant chromosome. While sequences in proximity to the distal break are present in an abnormal Os-specific Anapc10 hybrid transcript, transcription of these sequences in normal mice is low and difficult to detect. Transfer of the Os mutation onto an FVB/N background indicated that the absence of dominant effects in 94-A/K mice is not due to strain background effects on the mutation. Further analysis of this mutation will determine if a gene interrupted by the break or a long-range effect of the rearrangement on neighboring genes is responsible for the dominant effects of Os.
Deletion of a Disease Resistance Nucleotide-Binding-Site Leucine-Rich- Repeat-like Sequence Is Associated With the Loss of the Phytophthora Resistance Gene Rps4 in Soybean
Authors: Sandhu Devinder , Gao Hongyu , Cianzio Silvia , Bhattacharyya Madan K
Published: December 2004

Resistance of soybean against the oomycete pathogen Phytophthora sojae is conferred by a series of Rps genes. We have characterized a disease resistance gene-like sequence NBSRps4/6 that was introgressed into soybean lines along with Rps4 or Rps6. High-resolution genetic mapping established that NBSRps4/6 cosegregates with Rps4. Two mutants, M1 and M2, showing rearrangements in the NBSRps4/6 region were identified from analyses of 82 F1's and 201 selfed HARO4272 plants containing Rps4. Fingerprints of these mutants are identical to those of HARO4272 for 176 SSR markers representing the whole genome except the NBSRps4/6 region. Both mutants showed a gain of race specificities, distinct from the one encoded by Rps4. To investigate the possible mechanism of gain of Phytophthora resistance in M1, the novel race specificity was mapped. Surprisingly, the gene encoding this resistance mapped to the Rps3 region, indicating that this gene could be either allelic or linked to Rps3. Recombinant analyses have shown that deletion of NBSRps4/6 in M1 is associated with the loss of Rps4 function. The NBSRps4/6 sequence is highly transcribed in etiolated hypocotyls expressing the Phytophthora resistance. It is most likely that a copy of the NBSRps4/6 sequence is the Rps4 gene. Possible mechanisms of the deletion in the NBSRps4/6 region and introgression of two unlinked Rps genes into Harosoy are discussed.
The Changing Tails of a Novel Short Interspersed Element in Aedes aegypti
Authors: Tu Zhijian , Li Song , Mao Chunhong
Published: December 2004

A novel family of tRNA-related SINEs named gecko was discovered in the yellow fever mosquito, Aedes aegypti. Approximately 7200 copies of gecko were distributed in the A. aegypti genome with a significant bias toward A + T-rich regions. The 3′ end of gecko is similar in sequence and identical in secondary structure to the 3′ end of MosquI, a non-LTR retrotransposon in A. aegypti. Nine conserved substitutions and a deletion separate gecko into two groups. Group I includes all gecko that end with poly(dA) and a copy that ends with AGAT repeats. Group II comprises gecko elements that end with CCAA or CAAT repeats. Members within each group cannot be differentiated when the 3′ repeats are excluded in phylogenetic and sequence analyses, suggesting that the alterations of 3′ tails are recent. Imperfect poly(dA) tail was recorded in group I and partial replication of the 3′ tandem repeats was frequently observed in group II. Genomic evidence underscores the importance of slippage retrotransposition in the alteration and expansion of the tandem repeat during the evolution of gecko sequences, although we do not rule out postinsertion mechanisms that were previously invoked to explain the evolution of Alu-associated microsatellites. We propose that the 3′ tandem repeats and the poly(dA) tail may be generated by similar mechanisms during retrotransposition of both SINEs and non-LTR retrotransposons and thus the distinction between poly(dA) retrotransposons such as L1 and non-poly(dA) retrotransposons such as I factor may not be informative.
Population Genetics of the Developmental Gene optomotor-blind (omb) in Drosophila polymorpha
Authors: Brisson Jennifer A , Templeton Alan R , Duncan Ian
Published: December 2004

The developmental gene optomotor-blind (omb) encodes a T-box-containing transcription factor that has multiple roles in Drosophila development. Previous genetic analyses established that omb plays a key role in establishing the abdominal pigmentation pattern of Drosophila melanogaster. In this report we examine patterns of omb nucleotide variation in D. polymorpha, a species that is highly polymorphic for the phenotype of abdominal pigmentation. Haplotypes at this locus fall into two classes that are separated by six mutational steps; five of these mutational events result in amino acid changes. Two lines of evidence are consistent with a role for omb in the abdominal pigmentation polymorphism of D. polymorpha. First, we find that haplotype classes of omb are correlated with abdominal pigmentation phenotypes, as are microsatellite repeat numbers in the region. Second, tests of selection reveal that the two haplotype classes have been maintained by balancing selection. Within each class there is a significantly low amount of diversity, indicative of previous selective sweeps. An analysis including D. polymorpha's closest relatives (members of the cardini group) provides evidence for directional selection across species. Selection at this locus is expected if omb contributes to variation in abdominal pigmentation, since this trait is likely of ecological importance.
Fitness Costs of Mutations Affecting the Systemic Acquired Resistance Pathway in Arabidopsis thaliana
Authors: Heidel Andrew J , Clarke Joseph D , Antonovics Janis , Dong Xinnian
Published: December 2004

This study investigated the fitness effects of four mutations (npr1, cpr1, cpr5, and cpr6) and two transgenic genotypes (NPR1-L and NPR1-H) affecting different points of the systemic acquired resistance (SAR) signaling pathway associated with pathogen defense in Arabidopsis thaliana. The npr1 mutation, which resulted in a failure to express SAR, had no effect on fitness under growth chamber conditions, but decreased fitness in the field. The expression of NPR1 positively correlated with the fitness in the field. Constitutive activation of SAR by cpr1, cpr5, and cpr6 generally decreased fitness in the field and under two nutrient levels in two growth chamber conditions. At low-nutrient levels, fitness differences between wild type and the constitutive mutants were unchanged or reduced (especially in cpr5). The reduced fitness of the constitutive mutants suggests that this pathway is costly, with the precise fitness consequences highly dependent on the environmental context.
In Vivo Activation of Protein Kinase A in Schizosaccharomyces pombe Requires Threonine Phosphorylation at Its Activation Loop and Is Dependent on PDK1
Authors: Tang Yi , McLeod Maureen
Published: December 2004

Phosphoinositide-dependent protein kinase 1 (PDK1) plays a central role in cellular signaling by phosphorylating members of the AGC family of kinases. This family includes protein kinase C (PKC), protein kinase B (PKB), p70/p90 ribosomal S6 kinases (RSK and S6K), and the catalytic subunit of cAMP-dependent protein kinase (PKA). Although PDK1 phosphorylates and activates PKC, PKB, and RSK in vivo, PDK1 regulation of PKA remains controversial. We isolated ksg1, the fission yeast ortholog of mammalian PDK1, as a suppressor of growth defects caused by loss of the stress-activated MAP kinase, Spc1. Here, we demonstrate that Ksg1 is required for activation of PKA. Cells containing the ksg1.12 thermolabile allele exhibit pleiotropic phenotypes, including the failure to arrest in G1 and an inability to conjugate. The ksg1.12 allele strongly suppresses defects associated with unregulated PKA. Pka1, the catalytic subunit of cAMP-dependent protein kinase, is phosphorylated in vivo at Thr-356, which is located in the activation loop of the kinase and corresponds to Thr-197 in mammalian PKA. Phosphorylation of Thr-356 is required for in vivo activation of Pka1 and is dependent upon Ksg1. These data provide experimental evidence that PKA is a physiological substrate for PDK1.
Genetic and Biochemical Interactions Among Yar1, Ltv1 and RpS3 Define Novel Links Between Environmental Stress and Ribosome Biogenesis in Saccharomyces cerevisiae
Authors: Loar Jesse W , Seiser Robert M , Sundberg Alexandra E , Sagerson Holly J , Ilias Nasreen , Zobel-Thropp Pamela , Craig Elizabeth A , Lycan Deborah E
Published: December 2004

In the yeast S. cerevisiae, ribosome assembly is linked to environmental conditions by the coordinate transcriptional regulation of genes required for ribosome biogenesis. In this study we show that two nonessential stress-responsive genes, YAR1 and LTV1, function in 40S subunit production. We provide genetic and biochemical evidence that Yar1, a small ankyrin-repeat protein, physically interacts with RpS3, a component of the 40S subunit, and with Ltv1, a protein recently identified as a substoichiometric component of a 43S preribosomal particle. We demonstrate that cells lacking YAR1 or LTV1 are hypersensitive to particular protein synthesis inhibitors and exhibit aberrant polysome profiles, with a reduced absolute number of 40S subunits and an excess of free 60S subunits. Surprisingly, both mutants are also hypersensitive to a variety of environmental stress conditions. Overexpression of RPS3 suppresses both the stress sensitivity and the ribosome biogenesis defect of Δyar1 mutants, but does not suppress either defect in Δltv1 mutants. We propose that YAR1 and LTV1 play distinct, nonessential roles in 40S subunit production. The stress-sensitive phenotypes of strains lacking these genes reveal a hitherto unknown link between ribosome biogenesis factors and environmental stress sensitivity.
Genetic Analysis of Yeast Yip1p Function Reveals a Requirement for Golgi-Localized Rab Proteins and Rab-Guanine Nucleotide Dissociation Inhibitor
Authors: Chen Catherine Z , Calero Monica , DeRegis Carol J , Heidtman Matthew , Barlowe Charles , Collins Ruth N
Published: December 2004

Yip1p is the first identified Rab-interacting membrane protein and the founder member of the YIP1 family, with both orthologs and paralogs found in all eukaryotic genomes. The exact role of Yip1p is unclear; YIP1 is an essential gene and defective alleles severely disrupt membrane transport and inhibit ER vesicle budding. Yip1p has the ability to physically interact with Rab proteins and the nature of this interaction has led to suggestions that Yip1p may function in the process by which Rab proteins translocate between cytosol and membranes. In this study we have investigated the physiological requirements for Yip1p action. Yip1p function requires Rab-GDI and Rab proteins, and several mutations that abrogate Yip1p function lack Rab-interacting capability. We have previously shown that Yip1p in detergent extracts has the capability to physically interact with Rab proteins in a promiscuous manner; however, a genetic analysis that covers every yeast Rab reveals that the Rab requirement in vivo is exclusively confined to a subset of Rab proteins that are localized to the Golgi apparatus.
The Effect of Sequence Divergence on Recombination Between Direct Repeats in Arabidopsis
Authors: Opperman Roy , Emmanuel Eyal , Levy Avraham A
Published: December 2004

It is well established that sequence divergence has an inhibitory effect on homologous recombination. However, a detailed analysis of this relationship is missing for most higher eukaryotes. We have measured the rate of somatic recombination between direct repeats as a function of the number, type, and position of divergent nucleotides in Arabidopsis. We show that a minor divergence level of 0.16% (one mutation in otherwise identical 618 bp) has a profound effect, decreasing the recombination rate approximately threefold. A further increase in the divergence level affects the recombination rate to a smaller extent until a “divergence saturation” effect is reached at relatively low levels of divergence (∼0.5%). The type of mismatched nucleotide does not affect recombination rates. The decrease in the rate of recombination caused by a single mismatch was not affected by the position of the mismatch along the repeat. This suggests that most recombination intermediate tracts contain a mismatch and thus are as long as the full length of the 618-bp repeats. Finally, we could deduce an antirecombination efficiency of ∼66% for the first mismatch in the repeat. Altogether, this work shows some degree of conservation across kingdoms when compared to previous reports in yeast; it also provides new insight into the effect of sequence divergence on homologous recombination.
Competing Crossover Pathways Act During Meiosis in Saccharomyces cerevisiae
Authors: Argueso Juan Lucas , Wanat Jennifer , Gemici Zekeriyya , Alani Eric
Published: December 2004

In Saccharomyces cerevisiae the MSH4-MSH5, MLH1-MLH3, and MUS81-MMS4 complexes act to promote crossing over during meiosis. MSH4-MSH5, but not MUS81-MMS4, promotes crossovers that display interference. A role for MLH1-MLH3 in crossover control is less clear partly because mlh1Δ mutants retain crossover interference yet display a decrease in crossing over that is only slightly less severe than that seen in msh4Δ and msh5Δ mutants. We analyzed the effects of msh5Δ, mlh1Δ, and mms4Δ single, double, and triple mutants on meiotic crossing over at four consecutive genetic intervals on chromosome XV using newly developed computer software. mlh1Δ mms4Δ double mutants displayed the largest decrease in crossing over (13- to 15-fold) of all mutant combinations, yet these strains displayed relatively high spore viability (42%). In contrast, msh5Δ mms4Δ and msh5Δ mms4Δ mlh1Δ mutants displayed smaller decreases in crossing over (4- to 6-fold); however, spore viability (18–19%) was lower in these strains than in mlh1Δ mms4Δ strains. These data suggest that meiotic crossing over can occur in yeast through three distinct crossover pathways. In one pathway, MUS81-MMS4 promotes interference-independent crossing over; in a second pathway, both MSH4-MSH5 and MLH1-MLH3 promote interference-dependent crossovers. A third pathway, which appears to be repressed by MSH4-MSH5, yields deleterious crossovers.
Patterns of Sequence Divergence in 5′ Intergenic Spacers and Linked Coding Regions in 10 Species of Pathogenic Bacteria Reveal Distinct Recombinational Histories
Authors: Hughes Austin L , Friedman Robert
Published: December 2004

We compared the pattern of nucleotide difference in 8034 genes and in their 5′ intergenic spacers between conspecific pairs of genomes from 10 species of pathogenic bacteria. Certain genes or spacers showed much greater sequence divergence between the genotypes compared to others; such divergent regions plausibly originated by recombinational events by which a gene and/or spacers was donated from a divergent genome. Different patterns of divergence in genes and spacers identified different recombinational patterns. For example, in Chlamydophila pneumoniae, there were examples of both unusually divergent spacers and unusually divergent genes, but there were no cases in which a gene and its spacer were both unusually divergent. This pattern suggests that, in C. pneumoniae, recombination events have broken up the linkage between genes and 5′ spacers. By contrast, in Streptococcus agalactiae, there were a number of cases in which both spacer and gene were unusually divergent, indicating that a number of large-scale recombination events that included both genes and 5′ spacers have occurred; there was evidence of at least two large-scale recombination events in the genomic region including the pur genes in S. agalactiae.
Does Chromosome Size Affect Map Distance and Genetic Interference in Budding Yeast?
Authors: Turney Dana , de los Santos Teresa , Hollingsworth Nancy M
Published: December 2004

The hypothesis that chromosome size affects the rate and distribution of meiotic crossovers in budding yeast was tested. Map distance and interference were measured in the same genetic intervals present on either small (340 and 508 kb) or large (917 and 1085 kb) chromosomes, respectively. No differences were observed.
Spontaneous Mutations in Diploid Saccharomyces cerevisiae
Authors: Joseph Sarah B , Hall David W
Published: December 2004

We performed a 1012-generation mutation-accumulation (MA) experiment in the yeast, Saccharomyces cerevisiae. The MA lines exhibited a significant reduction in mean fitness and a significant increase in variance in fitness. We found that 5.75% of the fitness-altering mutations accumulated were beneficial. This finding contradicts the widely held belief that nearly all fitness-altering mutations are deleterious. The mutation rate was estimated as 6.3 × 10−5 mutations per haploid genome per generation and the average heterozygous fitness effect of a mutation as 0.061. These estimates are compatible with previous estimates in yeast.
End-Joining Repair of Double-Strand Breaks in Drosophila melanogaster Is Largely DNA Ligase IV Independent
Authors: McVey Mitch , Radut Dora , Sekelsky Jeff J
Published: December 2004

Repair of DNA double-strand breaks can occur by either nonhomologous end joining or homologous recombination. Most nonhomologous end joining requires a specialized ligase, DNA ligase IV (Lig4). In Drosophila melanogaster, double-strand breaks created by excision of a P element are usually repaired by a homologous recombination pathway called synthesis-dependent strand annealing (SDSA). SDSA requires strand invasion mediated by DmRad51, the product of the spn-A gene. In spn-A mutants, repair proceeds through a nonconservative pathway involving the annealing of microhomologies found within the 17-nt overhangs produced by P excision. We report here that end joining of P-element breaks in the absence of DmRad51 does not require Drosophila LIG4. In wild-type flies, SDSA is sometimes incomplete, and repair is finished by an end-joining pathway that also appears to be independent of LIG4. Loss of LIG4 does not increase sensitivity to ionizing radiation in late-stage larvae, but lig4 spn-A double mutants do show heightened sensitivity relative to spn-A single mutants. Together, our results suggest that a LIG4-independent end-joining pathway is responsible for the majority of double-strand break repair in the absence of homologous recombination in flies.
Fine Mapping of a Grain-Weight Quantitative Trait Locus in the Pericentromeric Region of Rice Chromosome 3
Authors: Li Jiming , Thomson Michael , McCouch Susan R
Published: December 2004

As the basis for fine mapping of a grain-weight QTL, gw3.1, a set of near isogenic lines (NILs), was developed from an Oryza sativa, cv. Jefferson × O. rufipogon (IRGC105491) population based on five generations of backcrossing and seven generations of selfing. Despite the use of an interspecific cross for mapping and the pericentromeric location of the QTL, we observed no suppression of recombination and have been able to narrow down the location of the gene underlying this QTL to a 93.8-kb region. The locus was associated with transgressive variation for grain size and grain weight in this population and features prominently in many other inter- and intraspecific crosses of rice. The phenotype was difficult to evaluate due to the large amount of variance in size and weight among grains on a panicle and between grains on primary and secondary panicles, underscoring the value of using multiple approaches to phenotyping, including extreme sampling and NIL group-mean comparisons. The fact that a QTL for kernel size has also been identified in a homeologous region of maize chromosome 1 suggests that this locus, in which the dominant O. rufipogon allele confers small seed size, may be associated with domestication in cereals.
One‐ and Two‐Dimensionally Structured Polymer Networks in Liquid Crystals for Switchable Diffractive Optical Applications
Authors: Kossyrev P. , Sousa M. E. , Crawford G.
Published: December 2004

We have created one‐ and two‐dimensionally structured polymer networks dispersed in a liquid‐crystal solvent using a holographic exposure technique. These structures have potential for electrically switchable, reverse‐mode, polarization selective and non‐selective diffractive optical elements. Using a simple phenomenological model to describe our diffraction measurements in conjunction with microscopic studies, we are able to estimate the structured polymer wall thickness as a function of monomer concentration.
Cd1–xMnxS Diluted Magnetic Semiconductors as Nanostructured Guest Species in Mesoporous Thin‐Film Silica Host Media
Authors: Kouzema A. V. , Fröba M. , Chen L. , Klar P. J. , Heimbrodt W.
Published: December 2004

Recently, we demonstrated the possibility of synthesizing ordered nanowires of diluted magnetic II/VI semiconductors inside the channels of mesoporous silica host structures. Here, we expand this procedure from mesoporous powders to mesoporous thin films. Diluted magnetic semiconductors Cd1–xMnxS were synthesized within the pores of mesoporous thin‐film silica host structures by a wet‐impregnation technique using an aqueous solution of the respective metal acetates, followed by drying steps and a conversion to sulfide by thermal H2S treatment. The presence of Cd1–xMnxS nanoparticles inside the pores was proved by powder X‐ray diffraction, infrared and Raman spectroscopy, and transmission electron microscopy. Photoluminescence excitation measurements clearly demonstrate the quantum size effect of the incorporated nanostructured guest species. The quality of the nanoparticles incorporated into the mesoporous films is comparable to that of those inside the mesoporous powders.
In Search of High‐Performance Platinum(II) Phosphorescent Materials for the Fabrication of Red Electroluminescent Devices
Authors: Kavitha J. , Chang S.‐Y. , Chi Y. , Yu J.‐K. , Hu Y.‐H. , Chou P.‐T. , Peng S.‐M. , Lee G.‐H. , Tao Y.‐T. , Chien C.‐H. , Carty A. J.
Published: December 2004

The rational design and syntheses of Pt(iqdz)2 (1) and Pt(pydz)2 (2) bearing isoquinolinyl indazole (iqdz)H or pyridyl indazole (pydz)H groups on the coordinating ligands are reported. Single‐crystal X‐ray diffraction studies of 1 reveal a square planar geometry, in which two iqdz ligands adopt a trans‐configuration. Short N…H contacts (∼2.21 Å) are detected between the ortho‐hydrogen atom of isoquinoline and the adjacent N atom of the indazole fragment, making the overall molecular geometry analogous to that of the platinum(II) porphyrinato complexes. The lowest absorption bands for both complexes reveal strong state mixings between singlet and triplet (metal‐to‐ligand charge transfer and intra‐ligand) manifolds. This, in combination with the introduction of a camphor‐like structure to avoid the stacking effect, leads to phosphorescence with unprecedented brightness both in solution and in the solid state. Organic light‐emitting diode (OLED) devices fabricated using 1 as a dopant emitter have been achieved in a multilayer configuration. The results constitute the first highly efficient PtII‐based red OLED.
Seed‐Assisted Synthesis of BaCrO4 Nanoparticles and Nanostructures in Water‐in‐Oil Microemulsions
Authors: Johnson C. J. , Li M. , Mann S.
Published: December 2004

Isooctane dispersions of discrete isometric BaCrO4 nanoparticles or self‐assembled linear chains of prismatic BaCrO4 nanoparticles were added as surfactant‐coated seed crystals/nanostructures to Na2CrO4/NaAOT/Ba(AOT)2/isooctane microemulsion reaction solutions prepared at w = 10 with molar ratios favoring the de novo synthesis of either nanoparticle chains ([Ba2+]/ [CrO42–] = 1:1) or isolated nanoparticles ([Ba2+]/[CrO42–] = 1:5.5). Addition of BaCrO4 nanoparticles or chains under particle‐ or chain‐producing conditions, respectively, resulted in preferential growth of the seeds with retention of particle morphology and nanostructure architecture. In contrast, addition of linear chains to microemulsion reaction solutions under particle‐producing conditions resulted in disruption of the seed nanostructure and overgrowth of the released prismatic nanoparticles to produce discrete oval‐shaped or cuboidal nanocrystals depending on the seed concentration used. Discrete faceted nanoparticles were also produced by seed‐assisted synthesis when isometric nanoparticles were added at relatively high concentrations to chain‐producing microemulsion reaction solutions; however, decreasing the seed population resulted in intact self‐assembled linear chains and superlattices that consisted of interlinked prismatic nanoparticles with end‐capped pseudo‐hexagonal morphology. Growth of the seeds and their assembly/disassembly was consistent with a model of coupled synthesis and self‐organization based on the strength of electrostatic interactions at the surfactant‐crystal interface. The results suggest that microemulsion‐based processes could be of general importance for controlling the secondary growth of pre‐organized nanoparticle‐based superstructures, as well as the morphological refinement of their constituent building blocks.
Shape‐memory behaviors of sensitizing radiation‐crosslinked polycaprolactone with polyfunctional poly(ester acrylate)
Authors: Zhu G. M. , Xu Q. Y. , Liang G. Z. , Zhou H. F.
Published: December 2004

The sensitizing effects of polyfunctional poly(ester acrylate) on the radiation crosslinking of polycaprolactone (PCL) were studied. The influences of the use of the polyfunctional material, the number of functional groups, and the radiation dose on the radiation crosslinking, dynamic mechanical properties, and shape‐memory behaviors of PCL, respectively, were investigated. The radiation crosslinking of PCL, under the conditions in which the polyfunctional material was applied, did not follow the classic Charlesby–Pinner equation but instead followed the Chen–Liu–Tang relation. The efficiency of the radiation crosslinking of PCL was distinctly improved with the polyfunctional material. The greater the usage and functional group number were, the greater gel content and the more distinctive the radiation‐crosslinking effects were. This also indicated that the polyfunctional material directly participated in the crosslinking reaction. Dynamic mechanical analysis indicated that enhanced radiation crosslinking better raised the heat deformation temperature of PCL and presented a higher and wider rubbery‐state plateau; it also produced greater strength at temperatures higher than the melting temperature and provided greater force for recovering the deformation than pure PCL. The shape‐memory results revealed that sensitizing crosslinked PCL presented 100% recoverable deformation and a quicker recovery rate. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 634–639, 2005
Development of discrete nanopores. II. Comparison between layered films and blends of polyolefins
Authors: Lee Jonghwi , Macosko Christopher W. , Bates Frank S.
Published: December 2004

Discrete nanopores develop in the interfacial regions of polyolefin blends and layered films under tension. They originate from crazelike structures in the early development stage, which later undergo disruption processes with an increase in strain. The disruption processes appear to be triggered by the existence of adjacent ductile polyolefins and their micromechanical deformations. The degree of nanopore development significantly varies among blends and layered systems, depending on several material parameters, such as the interfacial strength. Discrete nanopores are observed more often in metallocene systems and blends than in Ziegler–Natta systems and layered films. Macroscopically, with the development of discrete nanopores, metallocene systems show higher strain to break and significant shear yielding under tension. The disruption mechanism can be used to prepare nanoporous materials or to improve the mechanical performances of polyolefins. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 708–718, 2005
Hydrolytic depolymerization of poly(ethylene terephthalate) under microwave irradiation
Authors: Liu Lixin , Zhang Dong , An Lijia , Zhang Huayang , Tian Yiguang
Published: December 2004

This article covers the depolymerization of poly(ethylene terephthalate) (PET) under microwave irradiation in neutral water. The reaction was carried out in a sealed reaction vessel in which the pressure (or temperature) was controlled. The hydrolytic product contained terephthalic acid, ethylene glycol, and diethylene glycol characterized by IR spectrometry and gas chromatography. The undepolymerized PET was identified by gel permeation chromatography. Both the yield of terephthalic acid and the degree of PET depolymerization were seriously influenced by pressure (or temperature), the weight ratio of water to PET, and the reaction time. The applied irradiation power had little influence on the degree of PET depolymerization. With a pressure of 20 bar (temperature = 220°C), a reaction time of 90–120 min, and a weight ratio of water to PET of 10:1, the PET resin was depolymerized completely. The molecular weight and the molecular weight distribution indicated that the hydrolytic depolymerization of PET obeyed the regular chain‐scission mechanism to some extent. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 719–723, 2005
Influence of swelling solutions on the behavior of cholesteric networks
Authors: Wang Xiaohua , Wang Linge , Huang Yong
Published: December 2004

The swelling behavior of an ethyl‐cyanoethyl cellulose/crosslinked poly(acrylic acid) cholesteric network in different swelling solutions was studied. The swelling behavior of the cholesteric network was reversible in acid or neutral solutions and was irreversible in basic solutions. The cholesteric network retained the cholesteric structure during the swelling process in NaCl aqueous solutions, and the swelling behavior was incompletely reversible. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 724–729, 2005
Electromagnetic radiation shielding by composites of conducting polymers and wood
Authors: Sapurina Irina , Kazantseva Natalia E. , Ryvkina Natalia G. , Prokeš Jan , Sáha Petr , Stejskal Jaroslav
Published: December 2004

Polyaniline or polypyrrole composites with fir or oak wood have been prepared by in situ polymerization of the corresponding monomers in an aqueous suspension of wood sawdust. The percolation threshold of compressed coated particles is located below 5 wt % of the conducting component and, above this limit, the conductivity of most composites was higher than 10−3 S cm−1. The conductivity of composites containing ca 30 wt % of conducting polymer was of the order of 10−1 S cm−1, an order of magnitude lower than that of the corresponding homopolymers, polyaniline and polypyrrole. The conductivity stability has been tested at 175°C. The polypyrrole‐based composites generally lasted for a longer time than pyrrole homopolymers, also on account of the improved mechanical integrity of the samples provided by the presence of wood. The reverse order was found with polyaniline composites. The dielectric properties of the composites were determined in the range of 100 MHz–3 GHz, indicating that thick layers of composite material, ∼ 100 mm, are needed for the screening of the electromagnetic radiation below −10 dB level in this frequency range. Nevertheless, considering the potential production cost of composites and their low weight, such composite materials could be of practical interest in the shielding of electromagnetic interference. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 807–814, 2005
The kinetics of B‐a and P‐a type copolybenzoxazine via the ring opening process
Authors: Su Yi‐Che , Yei Ding‐Ru , Chang Feng‐Chih
Published: December 2004

The structure of benzoxazines is similar to that of phenolic resin through thermal self‐curing of the heterocyclic ring opening reaction that neither requires catalyst nor releases any condensation byproduct. These polybenzoxazine resins have several outstanding properties such as high thermal stability and high glass transition temperature. To better understand the curing kinetics of this copolybenzoxazine thermosetting resin, dynamic and isothermal differential scanning calorimetry measurements were performed. Three models, the Kissinger method, the Flynn–Wall–Osawa method, and the Kamal method, were used to describe the curing process. Dynamic kinetic activation energies based on Kissinger and Flynn–Wall–Osawa methods are 72.11 and 84.06 KJ/mol, respectively. The Kamal method based on an autocatalytic model results in a total order of reaction between 2.66 and 3.03, depending on curing temperature. Its activation energy and Arrhenius preexponential are 50.3 KJ/mol and 7959, respectively. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 730–737, 2005
Preparation and porous structure characterization of 4,4′‐diphenylmethane dimethacrylate/divinylbenzene polymeric particles
Authors: Maciejewska Małgorzata , Gawdzik Barbara
Published: December 2004

Copolymers of isobutyl 4,4′‐diphenylmethane dimethacrylate and divinylbenzene in the form of microspheres were obtained. For their preparation, the following techniques of heterogeneous polymerization were used: suspension polymerization, suspension–emulsion polymerization, and precipitation polymerization. Among the obtained microspheres, those synthesized by suspenson–emulsion polymerization were of a size suitable for high‐performance liquid chromatography, whereas the product of suspension polymerization could be used as a packing material for gas chromatography. Their porous structure was studied in details. The influence of the polymerization technique on the particle size and morphology was examined. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 863–870, 2005
Relationship between the separation performances and free volume distributions of polyimide/Ag3O4 composite membranes
Authors: Shi Baoli , Feng Chunsheng , Wu Yonglie
Published: December 2004

First, water, methanol, ethanol, acetone, and methyl t‐butyl ether were used as molecular probes to measure the free volume distribution of a type of polyimide membrane material (HQDEA–DMMDA). The methods were equilibrium swelling and separation membrane technologies. From the Kirchheim theory of free volume distribution, a Gaussian distribution function was determined. The Gaussian distribution function was confirmed with tensile testing and wide‐angle X‐ray diffraction of the polyimide films. Second, polyimide/Ag3O4 composite hollow‐fiber membranes were prepared by dry/wet phase inversion. The separation performances of the composite membranes were characterized with a methanol/methyl t‐butyl ether mixture. The change in the separation performances was explained by the free volume distribution function very well. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 871–879, 2005
Phosphazene cyclomatrix network polymers: Some aspects of the synthesis, characterization, and flame‐retardant mechanisms of polymer
Authors: Zhang Teng , Cai Qing , Wu De‐Zhen , Jin Ri‐Guang
Published: December 2004

Novel phosphazene cyclomatrix network polymers were synthesized via nucleophilic displacement of activated nitro groups of tri(4‐nitrophenoxy)tri(phenoxy)cyclotriphosphazene and hexa(p‐nitrophenoxy)cyclotriphosphazene with the hydroxyls of bisphenol A. Both the monomers and polymers were characterized by Fourier transform infrared (FTIR) and 1H‐NMR spectroscopy, and their structures were identified. The thermal and flame‐retardant properties of the polymers were investigated with thermogravimetric analysis in air, pyrolysis, and combustion experiments. Both solid and gaseous degradation products were collected in a pyrolysis process and analyzed with FTIR spectroscopy, gas chromatography/mass spectrometry, and scanning electron microscopy. The results demonstrated that the cyclomatrix phosphazene polymer would have excellent thermal stability and flame‐retardant properties if it could form a crosslinked phosphorous oxynitride structure during pyrolysis or combustion. A flame‐retardant mechanism of “intumescent” was proposed to elucidate the pyrolysis and combustion process. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 880–889, 2005
Complexation of titanium alkoxides with pentenoic acid and allylacetoacetate and their hydrolysis and addition reactions with H‐silanes
Authors: Kayan Asgar , Hoebbel Dagobert , Schmidt Helmut
Published: December 2004

Complexation reactions of titanium tetraethoxide [Ti(OEt)4] and titanium tetra‐n‐butoxide [Ti(OBun)4] with 3‐pentenoic acid (PA) and allylacetoacetate (AAA), in a 1 : 1M ratio, were studied in ethanol solution at room temperature. 13C‐NMR and FTIR spectra showed that all PA and AAA completely reacted with both titanium alkoxides. Hydridosilane compounds such as triethoxysilane and triethylsilane were added to titanium chelate complexes in a 1 : 1M ratio. The investigation of products by 13C‐ and 29Si‐NMR and FTIR showed additions of SiH to the CC double bond. The hydrolysis of titanium–PA and AAA complexes, by water in 1 : 4 ratios, resulted in released PA in an amount of 10% and AAA of 20%. The stability of hydrolyzed products was investigated by 13C‐NMR, 29Si‐NMR, and FTIR. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 790–796, 2005
A Short and Concise Asymmetric Synthesis of Hamigeran B
Authors: Trost Barry M. , Pissot‐Soldermann Carole , Chen Irwin
Published: December 2004

The interesting biological properties of the hamigerans wherein hamigeran B is a potent antiviral agent with low cytotoxicity to host cells make these deceptively simple looking structures challenging synthetic targets. A strategy to hamigeran B evolved wherein the three contiguous stereocenters are established ultimately from a Pd catalyzed asymmetric allylic alkylation (AAA). The latter involves an asymmetric allylation of a non‐stabilized ketone enolate in 77 % yield and 93 % ee. By using this process, (S)‐5‐allyl‐2‐isopropyl‐5‐methyl‐1‐trifluoromethanesulfonyloxycyclopentene becomes available in four steps from 2‐methylcyclopentanone. Introduction of the aryl unit by cross‐coupling proceeded intermolecularly but failed intramolecularly. On the other hand, reductive removal of the triflate permitted a Heck reaction to effect intramolecular introduction of the aryl ring. The unusual conformational properties of this molecular architecture are revealed by the regioselectivity of the β‐hydrogen elimination in the Heck reaction and the diastereoselectivity of the reduction establishing the stereochemistry of the carbon bearing the isopropyl group. The successful route consists of 15 steps from 2‐methylcyclopentanone and dimethylorcinol illustrating the efficiency of the route based upon the Pd AAA.
A Phase I trial of fixed dose rate gemcitabine and capecitabine in metastatic renal cell carcinoma
Authors: Rini Brian I. , Weinberg Vivian , Small Eric J.
Published: December 2004

BACKGROUND

Metastatic renal cell carcinoma (RCC) has modest response rates to chemotherapy with gemcitabine and 5‐fluorouracil (5‐FU). Fixed dose rate gemcitabine infusion leads to enhanced intracellular accumulation of drug and possible augmented clinical effect. To determine the toxicity of this combination therapy in metastatic RCC, a Phase I trial was conducted.

METHODS

Patients with metastatic RCC were enrolled in a Phase I dose escalation trial. Patients received fixed dose rate gemcitabine on Days 1, 8, and 15 in combination with capecitabine, an oral 5‐FU analog, given on Days 1–21 of a 28‐day cycle.

RESULTS

Nine patients were enrolled at one of two dose levels. The initial dose level produced dose‐limiting toxicity (DLT), including prominent palmar‐plantar erythrodysesthesia (hand‐foot syndrome). A modified second dose level also resulted in DLT, precluding further study. No central nervous system (CNS) toxicity was observed in three patients with CNS metastases. Two patients demonstrated an objective partial response.

CONCLUSIONS

Fixed dose rate gemcitabine in combination with capecitabine produced unacceptable toxicity in patients with advanced RCC. Further development of this schedule in RCC cannot be recommended. Cancer 2005. © 2004 American Cancer Society.