Showing papers by "Spanish National Research Council published in 1977"
TL;DR: In this article, the free radical-initiated copolymerization of N-phenyl maleimide (NPMI) with styrene (St), vinyl acetate (VAc) and methyl meth-acrylate (MMA) at 35°C in benzene solution initiated by AIBN was studied.
Abstract: Free radical-initiated copolymerization of N-phenyl maleimide (NPMI) with styrene (St), vinyl acetate (VAc) and methyl meth-acrylate (MMA) at 35°C in benzene solution initiated by AIBN was studied. The copolymerization of NPMI and St yields a “nearly equimolecular” alternating copolymer, irrespective of monomer feed. Reactivity ratios of NPMI with St, VAc, and MMA were determined by a curve-fitting method which has the advantage of delivering values not involving personal judgement. Q1 and e1 values of NPMI were also calculated. Tentative explanations have been proposed to Interpret the “nearly alternating” copolymerization between NPMI and St. In addition, thermal stabilities of copolymers were studied by using a programmed thermo-gravimetric analysis technique. Copolymers of St, VAc, and MMA show a considerable increase in thermal stability with increasing content of NPMI. The glass transition temperatures of copolymers of NPMI with MMA and St were measured by differential scanning calorimetry....
117 citations
TL;DR: Thiamphenicol and chlorampshenicol are good inhibitors of peptide bond formation in ribosomes and polysomes and their affinities are increased precisely when the peptidyl-tRNA is placed in the P-site preceeding the peptide Bond formation step, which is specifically blocked by the antibiotics.
Abstract: There is a single-site interaction of [methylene-14C]thiamphenicol and [methylene-14C]chloramphenicol with run-off ribosomes with dissociation constants Kd = 6.8 micronM and Kd = 4.6 micronM respectively. Similar affinities for the antibiotics are observed in polysomes totally deprived of nascent peptides, or bearing nascent peptides on the A-site. However, two types of interaction are observed in endogenous polysomes with some ribosomes bearing nascent peptides on the P-site and other in the A-site. The lower-affinity bindings (dissociation constants Kd = 6.4 micronM and Kd = 1.5 micronM for thiamphenicol and chloramphenicol respectively) are due to the ribosomes bearing nascent peptides on the A-site. The higher-affinity bindings (dissociation constants Kd = 2.3 micronM and Kd = 1.5 micronM for thiamphenicol and chloramphenicol, respectively) are due to the ribosomes bearing nascent peptides on the P-site. Therefore binding of nascent peptides to the A-site does not affect the affinities of thiamphenicol and chloramphenicol for the ribosome. On the other hand interaction of the nascent peptides with the P-site of the ribosomes increases the affinities of both antibiotics for the ribosome. Thiamphenicol and chloramphenicol are thus good inhibitors of peptide bond formation in ribosomes and polysomes. Their affinities are increased precisely when the peptidyl-tRNA is placed in the P-site preceeding the peptide bond formation step, which is specifically blocked by the antibiotics. There is a single-site interaction per ribosome for [35S]thiostrepton, which does not appear to be affected by the attachment to the ribosomes of mRNA, tRNA and nascent peptides either to the A or the P-site. [N-methyl-14C]Lincomycin, [N-methyl-14C]erythromycin, [G-3H]streptogramin B and [G-3H]-streptogramin A bind to run-off ribosomes and polysomes totally free from nascent peptides. However, these antibiotics do not interact with ribosomes bearing nascent peptides either in the A or the P-site and therefore are not active on preformed polysomes. Thus lincomycin and streptogramin A only interact with free ribosomes and 50-S subunits and block the early rounds of peptide bond formation prior to polysome formation. Erythromycin and streptogramin B do not inhibit either initiation or the first round of peptide bond formation. However, erythromycin and streptogramin B, prebound to the ribosome, block peptide elongation probably by steric hindrance with the growing oligopeptide chain when this reaches a certain critical length.
105 citations
TL;DR: The effects of ricin and abrin with PAP, alpha sarcin and enomycin on the EF l-dependent binding of aminoacyl-tRNA, formation of the EF 2-GTP-ribosome complex, peptidyl-t RNA translocation and EF 2and ribosome-dependent GTP hydrolysis using
88 citations
TL;DR: Treatment of newly eclosed adult milkweed bug females with precocene 2 prevents secretion of juvenile hormone by inhibition of postimaginal development of the corpus allatum.
Abstract: Treatment of newly eclosed adult milkweed bug (Oncopeltus fasciatus) females with precocene 2 prevents secretion of juvenile hormone by inhibition of postimaginal development of the corpus allatum. Ovarian development which is dependent upon juvenile hormone is prevented or reversed, depending upon the timing of precocene treatment. Juvenile hormone secretion is shown to be related to the development of the corpus allatum.
86 citations
TL;DR: The effect of mutations in the cistrons coding for the phage structural proteins has been studied, suggesting a single route for the assembly of phage phi29.
Abstract: The effect on phage morphogenesis of sus mutations in the cistrons coding for nonstructural proteins has been studied. Mutants in three cistrons analyzed that are involved in phage DNA synthesis, as well as in cistron 16 which codes for a late nonstructural protein, produce prolate capsids which are more rounded at the corners than complete phage heads and have an internal core; they contain the head proteins, the upper collar protein and protein p7, not present in mature phage particles. Mutants in cistron 7 do not produce capsids nor other phage-related structures; this result and the presence of p7 in phage capsids suggest an essential role in capsid assembly for this protein. The protein product of cistron 13 is probably needed for a stable DNA encapsulation since mutants in this cistron produce mainly DNA-free complete phage particles and only about 10% of uninfective DNA-containing complete phage. Cistron 15 codes for a late, partially dispensable, nonstructural protein which is present in the DNA-free capsids produced after infection with the delayed-lysis mutant sus14(1242), used as the wild-type control, or with mutants in cistrons 9, 11, 12 and 13. Proteins p15 and p16 are probably involved in the encapsulation of viral DNA in a prohead.
65 citations
TL;DR: In this paper, the principal reflectivities of uniaxial and baoxial substances were compared to the mean values of random, maximum and minimum reflectivities measured on particulate samples.
Abstract: SUMMARY
Theoretical and empirical formulae are given which relate the principal reflectivities of uniaxial and biaxial substances to the mean values of random, maximum and minimum reflectivities measured on particulate samples. Instead of using values of Ra and Ra − Rc determined along the principal directions, a method is described for determining respectively: (a) coal rank through the mean random vitrinite reflectivity, and (b) the bireflectance using the difference between the mean random maximum and minimum reflectivities measured on particulate samples, irrespective of uniaxial or biaxial character.
52 citations
TL;DR: A comparative study of the proteins released by treatment in the two types of particles suggests the involvement in the peptidyl transferase center of the ribosome of one or more of the floolwing proteins: L21, L24, L27, L28 and L36.
Abstract: Protein-deficient particles have been obtained by treating rat liver 80-S ribosomes or their 60-S subunits with 1 M NH4Cl in the presence of 50% ethanol at 0 degrees C (Po-cores) and 37 degrees C (P37-cores). The Po-cores from 80-S ribosomes are totally inactive in polyphenylalanine synthesis but fully active in the 'fragment assay' to test peptidyl transferase activity. The polymerizing activity of the cores is restored up to 40--50% of control activity by incubation in the presence of the split proteins. Three proteins are totally lost in the treatment, namely proteins L12, L40/41 ans S25. A series of up to nine different spots in the region of the L40/41 proteins are detected when the split fraction is analyzed by two-dimensional electrophoresis. This series of spots is, however, reduced to only two proteins when the second dimension is carried out in the presence of sodium dodecylsulphate. 80-S ribosome-derived P37-cores are about 80% active in the 'fragment reaction' while 60-S-subunit-derived particles are inactive in this assay. The inhibitory effect of a number of antibiotics is differentially affected by the treatment suggesting different localization of their binding sites. A comparative study of the proteins released by treatment in the two types of particles suggests the involvement in the peptidyl transferase center of the ribosome of one or more of the floolwing proteins: L21, L24, L27, L28 and L36.
49 citations
TL;DR: In this article, the absolute vibrational Raman intensities and depolarization ratios for the fundamental and some overtone and combination bands of CH 4, CH 3 D, CH 2 D 2, CHD 3, and CD 4 are reported.
49 citations
TL;DR: In this paper, conditions for the validity of the Adler-Bardeen theorem for non-Abelian gauge theories are obtained based on the derivation of Slavnov-Taylor identities modified by the presence of anomalous terms and a renormalization-group-like equation for the anomaly coefficient.
Abstract: Conditions for the validity of (a weak version of) the Adler-Bardeen theorem for non-Abelian gauge theories are obtained. Its validity ensures that those theories in which the coefficient of the triangle anomaly vanishes at the one-loop level are anomaly free and therefore they are renormalizable and unitary. This result is based on the derivation of Slavnov-Taylor identities modified by the presence of anomalous terms and on a renormalization-group-like equation for the anomaly coefficient. In the derivation, the dimensional regularization scheme has been followed.
47 citations
45 citations
TL;DR: In this article, the effect of spatial dispersion on the electrodynamics of surfaces is studied for a phenomenological model which describes the surface scattering of the elementary excitations in terms of a parameter p, the specular surface being the case p = 1.
Abstract: The effect of spatial dispersion on the electrodynamics of surfaces is studied for a phenomenological model which describes the surface scattering of the elementary excitations in terms of a parameter p, the specular surface being the case p = 1. Surface impedance, reflectivity and surface mode dispersion relation are obtained for arbitrary p without resorting to additional boundary conditions. It is thus shown that the problem is sufficiently defined if the model, including the effect of the surface, is specified. Various forms of additional boundary conditions used in the literature are discussed and characterized as models corresponding to particular values of p. The different roles of the longitudinal and transverse dielectric constants are discussed in physical terms.
TL;DR: The subsolidus phase relations of the ZrO2-rich region of the system Er2O3-ZrO 2 were studied by high temperature X-ray diffractometry and thermal expansion measurements.
Abstract: The subsolidus phase relations of the ZrO2-rich region of the system Er2O3-ZrO2 were studied by high temperature X-ray diffractometry and thermal expansion measurements. Compositions in the entire system were examined by X-ray diffraction at room temperature. The range of existence of the solid solutions based on ZrO2 and Er2O3 was determined by the precision lattice parameter method. Two hexagonal compounds were found: the first is formed at 40 mol% Er2O3 and decomposes above 1500°C into a fluorite-type cubic solid solution; the second is formed at 70 mol% Er2O3 and decomposes above 1700°C into a C-type cubic solid solution.
TL;DR: In this paper, a mechanism for the formation of the stretching and librational bands of the OH groups in ir spectra of various apatites is discussed, and it is deduced that hydrogen bonds between the HO groups and the nearest O's of PO3−4 ions exist, and that they are responsible for the observed frequencies of the HO bands.
TL;DR: An increased affinity of [G-3H]streptogramin B in the presence of streptograms A can explain the synergistic effects of mixtures of strePTogramins A and B at the ribosome level.
Abstract: Quantitative binding studies of [G-3H]streptogramin A and [G-3H]streptogramin B with high-salt-washed ribosomes were carried out in the presence of a minimum of 10% (v/v) ethanol because of the antibiotic insolubility in water. It was observed that the presence of streptogramin A increases the affinity of [G-3H]streptogramin B for the ribosome. Thus the dissociation constant for [G-3H]-streptogramin B interaction with the ribosome is Kd=13.3 nM in the presence of streptogramin A and Kd=59 nM in its absence. Furthermore the values for the dissociation constants for [G-3H]-streptogramin B interaction in the presence of 50% (v/v) ethanol, were Kd=0.13 micronM in the presence of streptogramin A and Kd=0.70 micronM in its absence. This increased affinity of [G-3H]streptogramin B in the presence of streptogramin A can explain the synergistic effects of mixtures of streptogramins A and B at the ribosome level.
TL;DR: In this article, four different enzymes, A, B, C, and D, have a sequential timing of induction during the early larval development and show a different elution pattern after chromatography on DEAE-cellulose and a different sensitivity to protease inhibitors.
TL;DR: In this article, the formation of pyrochlore structure compound Gd 2 Hf 2 O 7 (a = 10,498 A) was found, which undergoes an order-disorder transformation at very high temperature to yield a fluorite-type structure.
TL;DR: The suppression of herbs, especially grasses, in heathlands can be explained, at least partially, by the allelopathic effects of E. scoparia L. upon its environment.
Abstract: The phytochemical action of Erica scoparia L. upon its environment was studied. The toxicity of biogenic heath products on red clover seedlings was demonstrated by biological tests. Ten phenolic hydrosoluble compounds were identified; p-Hydroxybenzoic, vanillic, syringic, caffeic, ferulic, p-coumaric, protocatechuic, genetisic, and 2-hydroxyphenyl acetic acid, as well as 2,4-dihydroxyphenyl acetonitrile. The suppression of herbs, especially grasses, in heathlands can be explained, at least partially, by the allelopathic effects of E. scoparia L.
TL;DR: Sediment types and depositional environments are correlatable in the Strait of Sicily: coarse calcareous sand layers, interbedded with mud and sandy lutite (fining-and coarsening-upward sequences), prevail on shallow banks; homogeneous mud occurs in the neritic and bathyal environments and also in some basins; moderate-to well-stratified units (sandy gravity-flow deposits alternating with hemipelagic and turbiditic mud) increase as hemipelagous mud decreases with increasing depth as discussed by the authors.
Abstract: Sediment types and depositional environments are correlatable in the Strait of Sicily: coarse calcareous sand layers, interbedded with mud and sandy lutite (fining- and coarsening-upward sequences), prevail on shallow banks; homogeneous mud occurs in the neritic and bathyal environments and also in some basins; and moderate- to well-stratified units (sandy gravity-flow deposits alternating with hemipelagic and turbiditic mud) increase as hemipelagic mud decreases with increasing depth. Bioturbation also is closely depth related. This type of lithofacies determination is a potentially useful technique to interpret the depositional environment of marine sequences in the rock record.
TL;DR: In this paper, alternating direction implicit (A.D.I) methods are derived for solving fourth order parabolic equations with variable coefficients in one, two, and three space dimensions.
TL;DR: From the roots of Ferula loscosii the coumarins umbelliprenin, coladin and coladonin and the new natural isovaleryl derivative of the latter have been isolated.
TL;DR: In this article, an empirical model for calculating the torsional angles for flexible 6-membered rings is presented in terms of three independent parameters, two geometrical and one pseudorotation angle.
TL;DR: A 5-day-old male child presenting some features of Wolf syndrome is studied, and the analysis of his karyotype showed a ring chromosome of B group, which was present in most of the cells examined.
Abstract: A 5-day-old male child presenting some features of Wolf syndrome is studied. The analysis of his karyotype by usual techniques showed a ring chromosome of B group. This chromosome was present in most of the cells examined. By GTG banding it was identified as a No.4 chromosome, the karyotype being: 46,XY,r(4),(p15→q35). The analysis was completed by familial cytogenetic and dermatoglyphic studies.
TL;DR: In this paper, the electronic states at the (111)-surface of Cu in the energy region around EF were calculated based on the empirical pseudopotential method, where a proper position of an abrupt potential barrier ensures overall charge neutrality.
TL;DR: In this paper, the 13 C NMR chemical shifts of ent -beyer-15-ene and one hydroxy and four acetoxy derivatives are reported, and the substituent effects of the acetoxy groups upon the saturated and olefinic carbon atoms are discussed.
TL;DR: In this article, the 1 H and 19 F NMR spectra of the keto-enol was used to study the reaction of 1 with water and alcohols, and the equilibrium of the starting ketoenol forms with the corresponding hydrate and hemiketals.
TL;DR: In this paper, the role of surface scattering of electrons in dispersive conducting media is studied in a semiclassical approximation using a phenomenological specularity parameter p (0 ~ p ~ 1).
Abstract: 2014 For dispersive conducting media the role of surface scattering of electrons is studied in a semiclassical approximation using a phenomenological specularity parameter p (0 ~ p ~ 1). The problem of unphysical charge accumulation at the surface, which often appears in treatments in terms of p, is explicitly discussed and avoided. The P-mode surface plasmon dispersion relation in the quasistatic limit (c ~ oo) is obtained for arbitrary p and 03BA (propagation vector). This permits a study of the effect of surface scattering on surface plasmon damping and also of the different roles of the longitudinal and transverse dielectric functions. This is illustrated with an application in terms of simple interpolation formulae for the dielectric functions. LE JOURNAL DE PHYSIQUE TOME 38, JUILLET 1977,