bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mechanistic change in the reactivity of substituted phenyl acetates over phenyl thiolacetates toward imidazole in aqueous phase
Authors: Rajarathnam D. , Jeyakumar T. , Nadar P. Ananthakrishna 
Published: February 2005

AbstractThe kinetics of aminolysis of several substituted phenyl acetates by imidazole is studied in aqueous medium at 20°C and an ionic strength of 0.1 M (KCl). By following the leaving groups spectrophotometrically (λmax = 272–401 nm), under excess free imidazole, pseudo‐first‐order rate constants (kobs) are obtained. For the esters with good nucleofuges, the reaction follows clean second‐order kinetics and the plots of (kobs−kH) against free imidazole concentration are linear at constant pH. The macroscopic nucleophilic substitution rate constants (kN) are obtained as the slopes of these plots and found to be pH independent. For the esters with poor nucleofuges, a rate dependence on more than first power of the free imidazole and a linear dependence of k'2 on free imidazole is observed. Accordingly, the microscopic rate constants for the assisted paths viz. kga and kgb have been disseminated besides for simple bimolecular attack. The Brönsted‐type plots and Hammett plots were constructed whose slope values are consistent with a stepwise mechanism through a bipolar tetrahedral addition intermediate whose formation or breakdown being rate determining for various paths. Comparison of this reaction of oxyesters with the earlier reported works on similar reaction of analogue thiolesters under identical reaction conditions showed remarkable mechanistic differences which are discussed in detail. The discussion is extended to include the details on previously studied ammonolysis of these two types of esters wherein thiolesters showed differed reactivity than that reported in the present study. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 211–221, 2005
Interactions in Nanosilica‐Polyurethane Composites Evidenced by Plate‐Plate Rheology and DMTA
Authors: Navarro‐Bañón Virtudes , Vega‐Baudrit José , Vázquez Patricia , Martín‐Martínez José Miguel 
Published: February 2005

AbstractFumed nanosilicas with different degree of silanization were used to obtain nanosilica‐polyurethane (TPU) composites to modify their rheological and mechanical properties. The higher the silanol content of the nanosilica, the higher the storage modulus and the thermal stability of the silica‐TPU composite. DMTA experiments confirmed that the TPU‐silica interactions increased by increasing the silanol content of the nanosilica.
Effect of the Amount of Calcium Carbonate as Filler on the Rheological and Adhesion Properties of a Water‐Based Polyurethane Dispersion
Authors: Muñoz‐Milán Ana Belén , Pérez‐Limiñana Ma Ángeles , Arán‐Aís Francisca , Torró‐Palau Ana , Orgilés‐Barceló A. César 
Published: February 2005

AbstractIn this study, the properties of water‐based adhesives based on a polyurethane ionomer (PUD) and a micronised CaCO3 as filler was analysed. Different amounts of a micronised CaCO3 (5‐25 wt%) were added to water‐based polyurethane (PUD) adhesive formulations in order to reduce its relatively high cost. The addition of a micronised calcium carbonate filler increased the viscosity, the storage and loss moduli of the PUD adhesives, and imparted pseudoplasticity and thixotropy, more noticeably for the adhesive with the highest calcium carbonate content. The creation of acid‐base interactions seemed to be responsible for the improvement in the rheological properties of the PUD adhesives containing CaCO3 as filler. On the other hand, the addition of CaCO3 filler might deteriorate the adhesion properties to PUD adhesives.
Poly(propylene)/PET/Undecyl Ammonium Montmorillonite Nanocomposites. Synthesis and Characterization
Authors: Velasco José Ignacio , Ardanuy Mónica , Miralles Lourdes , Ortiz Silvia , Maspoch Maria Lluisa , Sánchez‐Soto Miguel , Santana Orlando 
Published: February 2005

AbstractA natural bentonite rich in calcium montmorillonite (CaMMT) was initially purified and ion‐exchanged to obtain sodium montmorillonite (NaMMT). Both clays were organophillised by cationic exchange reaction with undecyl‐ammonium chloride, and characterized. Isotactic poly(propylene) (PP) was melt‐compounded with both the unmodified and the organophilic montmorillonites. The hybrids produced have been characterized structurally, thermally and mechanically. Maleic anhydride‐grafted PP (MAH‐g‐PP) was used as compatibilizer in some of the formulations. Homologous series of hybrids were also synthesized employing blends of PP/PET and compared with those of the pure PP to investigate possible beneficial effects due to the presence of small amounts of PET on the microstructure and properties of this kind of materials. The analysis of the results indicates some extension of both macromolecules intercalation and clay particles exfoliation in the hybrids prepared with the organophilic montmorillonite. The hybrids prepared with compatibilized PET/PP blends were found to have a better nanostructure.
Structure/Property Relationships for Polyamide 6 / Organoclay Nanocomposites in the Melt and in the Solid State
Authors: Karaman Vitaly M. , Privalko Valery P. , Privalko Eleonora G. , Lehmann Bjorn , Friedrich Klaus 
Published: February 2005

AbstractCommercial nanocomposites of polyamide 6 prepared by melt compounding with organoclays were characterized by complex viscosities and relaxation time spectra derived from storage and loss shear moduli measured in the melt state at 230°C, and by wide‐ and small‐angle X‐ray scattering, differential scanning calorimetry and stretching calorimetry in the solid state.In the melt state, the decrease of ∼ 25 % (compared to the pristine sample) in Newtonian viscosity at the lowest clay loading (2.5 %) suggested a lower equilibrium elasticity modulus of an entangled melt, as the small amounts of organoclay nanoparticles acted as specific “diluents” for the initial entanglement network. However, by increasing the clay loading this effect disappeared due to the importance of strong interactions at the nanoparticle/melt interface, leading to the formation of a fairly thick boundary interphase (BI) around the nanoparticles and ending up in the build‐up of an “infinite cluster” of clay nanoparticles coated with BI at the highest (albeit still unusually low) clay loading (7.5 %).In the solid state, organoclay nanoparticles proved to induce the crystallographic α → γ transformation of PA6 , while the matrix crystallinity in nanocomposites remained essentially unchanged. In the range of elastic (reversible) behavior below the apparent yield strains ϵ* , the highest Young's moduli E and the lowest linear thermal expansion coefficients αL were observed for dried nanocomposites, while the lowest E and the highest αL corresponded to the moisturized, pristine PA6. The endothermal process of shape distortion of the lamellar crystals was assumed to precede the onset of the exothermal process of lamellar fragmentation in the range of inelastic (irreversible) behaviour of PA6 above ϵ* . The energy balance of the inelastic behaviour of nanocomposites was dominated by the endothermal process of lamellar shape distortion.
Structure Analysis of PVC Nanocomposites
Authors: Kovarova Lucie , Kalendova Alena , Gerard Jean‐Francois , Malac Jiri , Simonik Josef , Weiss Zdenek 
Published: February 2005

AbstractIn this paper poly(vinyl chloride)/clay nanocomposites were prepared by melt intercalation using a single screw extruder. Problems with thermal stability of these nanocomposites during compounding were largely eliminated by pre‐treatment of the organoclay with plasticizer (dioctyl phthalate), which created a barrier between polymer and quaternary amine. These nanocomposite materials were analyzed with respect to their morphology. The intercalation, exfoliation, nano‐phase dispersion and orientation were investigated using Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and X‐ray diffraction (XRD). Moreover, different types of sample preparation for these techniques were tested as well. It was found that partially intercalated and disordered structure arose in poly (vinyl chloride) composites containing sodium type of montmorillonite, while a fine dispersion of partial to nearly full exfoliation of individual montmorillonite layers in poly (vinyl chloride) matrix was observed when this clay was organically modified. Finally, the influence of different mixing time (in extruder) on nano‐phase morphology was surveyed.
Preparation, Characterisation and Properties of Nanocomposites Based on Epoxy Resins – An Overview
Authors: Hartwig Andreas , Sebald Monika , Pütz Dirk , Aberle Lisa 
Published: February 2005

AbstractAn overview about the use of nanoparticles in epoxy resins is given. Deaggregated fumed silica, sol gel materials and other spheroidic nanoparticles improved the abrasion resistance and the mechanical properties of filled epoxides, and several properties can be improved by specific particles. Combustion properties, strength and permeation can be improved by organically modified layered silicates. The proper characterisation of the nanocomposites is still an art. TEM analysis of the cured materials and light scattering with 3D cross‐correlation for the liquid samples were sufficient methods for the characterisation of filled epoxides.
Predictive Models of Ethylene‐Vinyl Acetate (EVA) Copolymers with Powdered Zn Fillers
Authors: Balart Rafael , Parres Francisco , López Juan , García David 
Published: February 2005

AbstractMetallic Zn filler was used to increase the electrical properties of ethylene‐vinyl acetate copolymer (EVA). Other properties were also modified such as mechanical and thermal behavior. It is possible to predict the behaviour of EVA‐Zn system by using different models.
Dynamic Mechanical Behavior of PP/PET/MAPP Blends Filled with Glass Beads
Authors: Rodríguez‐Pérez M.A. , Velasco J.I. , González‐Peña J.I. , Ruiz‐Herrero J.L. , Arencon D. , de Saja J.A. 
Published: February 2005

AbstractPP/PET/MAPP blends have been filled with 50 wt% of glass beads. The orientation of the PP crystalline phase, the crystallization behavior and the dynamic mechanical response of these materials have been analyzed. The dynamic mechanical response is strongly affected by the presence of the glass beads, being possible to detect the effect of PET and MAPP on the storage modulus and loss factor values. Moreover, the alpha relaxation of the composites is visibly affected by thermal treatments.
Rainbow trout has two genes for growth hormone
Authors: Agellon L. B. , Davies S. L. , Lin C.‐M. , Chen T. T. , Powers D. A. 
Published: February 2005

AbstractWe report the primary structures of two mRNA species (GH1 and GH2), each predicted from the cloned cDNA and genomic gene sequences, that encode growth hormone in rainbow trout (Salmo gairdneri). Both GH1 and GH2 mRNA contain open reading frames comprising 630 nucleotides and encode 210 amino acid residues, of which 11 are variant. The translated regions of mRNA are flanked by a short 5′‐untranslated sequence, which is highly conserved, and a relatively long 3′‐untranslated sequence, which is highly divergent. The differences at the 3′‐untranslated regions suggest that the GH1 and GH2 mRNA originate from different loci. RNA blot analysis of trout pituitary RNA using an oligonucleotide probe specific for the GH2 sequence indicates that the cloned gene is expressed. The GH1 and GH2 mRNA likely are transcribed from two distinct loci, which were duplicated during tetraploidization of the salmonid genome between 50 and 100 million years ago.
Protein phosphorylation in meiotically competent and incompetent mouse oocytes
Authors: Bornslaeger Elayne A. , Mattei Peter M. , Schultz Richard M. 
Published: February 2005

AbstractSpecific changes in the two dimensional gel electrophoretic pattern of mouse oocyte phosphoproteins precede germinal vesicle breakdown (GVBD). We report that changes in the relative abundance of phosphoamino acids occurred prior to GVBD. We also report data that further strengthen the close association of the changes in phosphoprotein patterns with resumption of meiosis. The calmodulin antagonist W7, which transiently inhibits GVBD, inhibited partially at least two of the maturation‐associated phosphoprotein changes, the dephosphorylation of a 60,000 Mr 24,000 and 28,000 occurred; all these changes occurred, however, in oocytes from juvenile mice that were competent to resume meiosis. The microinjection of the heat‐stable inhibitor of cyclic adenosine monophosphate (cAMP)‐dependent protein kinase (PKI), which induces GVBD in fully grown oocytes, did not induce GVBD in meiotically incompetent oocytes. Microinjected PKI did not induce the increased protein phosphorylations associated with maturation, but it did induce the dephosphorylation of the 60,000 Mr phosphoprotein. These results provide molecular markers for commitment to resume meiosis in GV‐intact oocytes and indicate a potential basis for meiotic incompetence.
Changes in polyadenylation of lactate dehydrogenase‐X mRNA during spermatogenesis in mice
Authors: Fujimoto Hirokazu , Erickson Robert P. , Toné Shigenobu 
Published: February 2005

AbstractThe expression of the mRNA for mouse testicular lactate dehydrogenase (LDH‐X) was examined by Northern analyses of meiotic and postmeiotic spermatogenic cell populations. Silver grains accumulated in cells inside the second layer from the periphery of the seminiferous tubule, confirming previous findings that LDH‐X mRNA first appears in the spermatocyte and continues to accumulate until the late spermatid stage. Northern analyses showed that meiotic and postmeiotic cells contained 1.2 and 1.3 kb classes of hybridizing mRNA, respectively. RNase H digestion of oligo(dT)‐hybridized RNA and poly(U)‐Sepharose column chromatography with differential elution by formamide revealed that the difference in size of the two classes of mRNAs was due to the poly(A) tail length of the LDH‐X mRNA. When the distribution of the LDH‐X mRNA was examined across polysome gradients, both mRNAs were partially associated with polysomes. These results suggest that the changes in the polyadenylation of LDH‐X mRNA were associated with the meiotic division during spermatogenesis in the mouse. They raise the possibility that the stable accumulation of the LDH‐X mRNAs in the postmeiotic cells is enhanced by poly(A) tails of increased length.
Sexing the human fetus and identification of polyploid nuclei by DNA–DNA in situ hybridisation in interphase nuclei
Authors: West John D. , Gosden Christine M. , Gosden John R. , West Katrine M. , Davidson Zoe , Davidson Catherine , Nicolaides Kypros H. 
Published: February 2005

AbstractSamples of human adult lymphocytes, fetal lymphocytes, amniotic fluid cells, and chorionic villus cells were sexed independently by cytogenetics and DNA–DNA in situ hybridisation to a tritiated Y probe. For the in situ hybridisation analysis, the presence of Y bodies (hybridisation bodies) in 100 interphase nuclei were scored after autoradiography. In all, 82/83 samples were sexed in this way (one technical failure) and 78/82 were sexed by both in situ hybridisation and cytogenetics. There was complete agreement between the two methods. There was a considerable variation (40–100%) in the percentage of interphase nuclei with a hybridisation body among the male samples, but very few nuclei from female samples showed significant hybridisation. In situ hybridisation could be used to sex the conceptus when males but not females are at risk for various X‐linked genetic disorders and may also be useful for detecting 45,X/46,XY mosaicism or polyploid/diploid mosaicism. This would be particularly useful for direct preparations of chorionic villus samples, which often prove difficult to analyse cytogenetically but offer the best means of avoiding maternal contamination. Some interphase nuclei had more than one hybridisation body, and this was most commonly found among amniotic fluid cells. Comparison of sizes of nuclei with one or two hybridisation bodies strongly suggested that most of the amniotic fluid cell nuclei with two hybridisation bodies were tetraploid.
The use of DNA probes in preimplantation and prenatal diagnosis
Authors: West John D. 
Published: February 2005

AbstractDNA probes are now widely used for prenatal diagnosis, but the prospect of preimplantation diagnosis of genetic disorders requires the development of sensitive genetic tests that can be performed on small numbers of cells removed from a preimplantation‐stage pre‐embryo. The sensitivity of molecular tests can now be increased by specifically amplifying the target DNA with the polymerase chain reaction. In situ hybridisation with chromosome‐specific DNA probes to repeated sequences also permits the detection of particular numerical chromosome aberrations or the distinction of male and female pre‐embryos when only a few interphase nuclei are available. We have used in situ hybridisation to a Y chromosome‐specific DNA probe to sex preimplantation‐stage pre‐embryos and to sex fetuses from samples of chorionic villus cells, amniotic fluid cells, and fetal blood. These two approaches (amplification of target DNA and in situ hybridisation) provide suitable tests for improving prenatal diagnosis particularly when few cells are available and they offer the possibility of tests suitable for preimplantation diagnosis.
Expression of two actin genes during larval development in the sea urchin Strongylocentrotus purpuratus
Authors: Cameron R. Andrew , Britten Roy J. , Davidson Eric H. 
Published: February 2005

AbstractWe report the first measurements of cell number, total RNA, and transcript accumulations for two actin genes during larval development of the sea urchin Strongylocentrotus purpuratus. At 5 weeks of feeding, when development of laboratory‐raised larvae is completed, the cell number has increased about 100‐fold with respect to the pluteus‐stage embryo to about 150,000 ± 50,000, and the total RNA has increased 46‐fold to about 130 ng per larva. The transcripts of the Cylla cytoskeletal actin gene, which is expressed in adult tissues, continue to accumulate throughout larval development. A contrasting pattern of transcript accumulation is observed for Cyllla, a different cytoskeletal actin gene that in the embryo is expressed only in aboral ectoderm. These transcripts increase in number early in larval development, when the larval epidermis is differentiating, and then decline in quantity. It is known that at metamorphosis the larval epidermis is largely histolyzed and that the Cyllla gene is not expressed in the juvenile or adult.
Expression and struture of the CyIIIb actin gene of the sea urchin Strongylocentrotus purpuratus
Authors: Flytzanis Constantin N. , Bogosian Elizabeth A. , Niemeyer Christina C. 
Published: February 2005

AbstractThe developmental pattern of expression of the Strongylocentrotus purpuratus Cylllb actin gene was determined by RNA blot hybridizations carried out with a gene‐specific probe and total embryonic RNA isolated from various stages of development. The results indicate that the Cylllb mRNA is not detected in the maternal pool, and, although the gene is activated at the early stages (about 10 hr postfertilization), considerable amounts of mRNA do not accumulate until well into the pluteus stage 3 days later. These results suggest either a post‐transcriptional regulatory mechanism that governs early embryonic expression of the Cylllb actin or a late embryonic transcriptional enhancement of this gene. We present here the complete nucleotide sequence of the Cylllb gene, which lies within the 10,361 base pairs of the sequenced region. The entire transcription unit is 7,455 nt long and shares structural similarities with the other cytoskeletal‐type actin genes from this sea urchi. Sequence comparisons of Cylllb to the Cyllla actin gene, to which it is linked, reveals extensive homology even in the introns. The deduced amino acid sequence of the Cylllb actin shows five amino acid substitutions compared with the Cyllla actin and nine when compared with the Cyl, the endodermal embryonic cytoskeletal‐type actin. Five out of these nine amino acid differences occur within a small peptide (position 257 to 267). The 5′ flanking sequence of the Cylllb gene shows a remarkable homology (∼75–80%) with the Cyllla upstream region up to the position −200 and a lack of any obvious similarity further upstream. This observation suggests that the two genes possibly share some common regulatory factors.
Differential regulation of protein biosynthesis at translational level in the fat body cells of adult Locusta migratoria
Authors: Glinka A. V. , Triseleva T. A. 
Published: February 2005

AbstractVitellogenin (Vg) and lipophorin (Lp) are synthesized by the fat body of adult locust (Locusta migratoria) females. We have shown by an immunohistochemical technique that both proteins are produced in the same cells of the fat body. The rate of Vg synthesis was measured with the use of double immunoprecipitation of labeled proteins at oviposition and 24 h later. It was found that the rate of Vg synthesis declined significantly by the time of oviposition; however, 24 h later, it was raised to the highest possible level. The rate of Lp synthesis remained constant at both indicated points. The similar postlaying increase in the Vg synthesis rate was observed in the fat bodies of females treated by α‐amanitin immediately after oviposition. The data provide evidence that Vg biosynthesis in L. migratoria is regulated by selective periodical repression and derepression of Vg mRNAs in the fat body cells but not by total inhibition and stimulation of protein‐synthesizing machinery.
Flow cytometric analysis of rodent epididymal spermatozoal chromatin condensation and loss of free sulfhydryl groups
Authors: Evenson D. P. , Baer R. K. , Jost L. K. 
Published: February 2005

AbstractFlow cytometric measurements were made on acridine orange (AO) and 7‐diethylamino‐3‐(4′‐maleimidylphenyl)‐4‐methylcoumarin (CPM)‐stained epididymal‐ and vas deferens‐derived spermatozoal nuclei to follow the course of chromatin condensation and oxidation of free sulfhydryl groups, respectively, during passage through mouse and rat posttesticular reproductive tracts. Alterations of mouse and rat spermatozoal chromatin during transition from a testicular elongated spermatids to epididymal caput spermatozoc resulted in a threefold loss of DNA stainability with AO. Passage of spermatozoa from the caput to corpus epididymis was accompanied by an approximate 15% loss of DNA stainability, which was maintained at that level throughout passage into the vas deferens. AO stainability of epididymal spermatozoal nuclei was generally independent of –SH group stainability. CPM stanability of rat spermatozoal nuclei free –SH groups was 83%, 18%, and 11% of caput spermatozoal values for corpus, cauda epididymis, and vas deferens, respectively. Comparable values for mice were 69%, 20%, and 18%. CPM stainability was relatively homogeneous for these mouse and rat reproductive tract regions, except mouse corpus epididymis spermatozoal nuclei stained very heterogeneously. Rat spermatozoa detained by ligature up to 7 days in the caput, corpus, and cauda epididymi had CPM staining values equal to or below those of normal vas spermatozoa, indicating that disulfide (S‐S) bonding is intrinsic to the spermatozoa and is independent of the epididymal environment. These data suggest that chromatin condensation and loss of spermatozoal DNA stainability during passage from the testis to the vas deferens are independent of S‐S bonding. Furthermore, the results are in agreement with previous findings suggesting that autoxidation of SH groups occurs independently of movement through the epididymis.