scispace - formally typeset
Search or ask a question

Showing papers by "Instituto Politécnico Nacional published in 1973"


Journal ArticleDOI
TL;DR: The property of the local anesthetic to bind hydrophobically to the lipid membrane enables the positively charged group of tetracaine to complete favourably with the polyvalent cation for the lecithin phosphates.

69 citations


Journal ArticleDOI
TL;DR: It was demonstrated that UBF can monitor reversal of charge phenomena such as that obtained by the interaction of phosphatidylcholine + dicetyl phosphate liposomes (anionic colloid) with poly-L-lysine (cationic colloid), and the use of UBF as a probe of respiration-dependent energy-linked reactions in submitochondrial particles is presented.
Abstract: In order to understand the localization of dyes and the nature of their responses in membranes and particularly in those involved in energy-conservation processes, the influence of micelles of neutral and ionic surfactants on the pKa of solubilized fluorophoric (umbelliferone) and chromophoric (bromthymol blue and methyl red) indicator dyes is studied. It is shown that the pKa of the indicator adsorbed onto micelles shifted towards the acid extreme with cationic micelles, to the alkaline side with anionic micelles while it was not significantly modified by the neutral ones. Maximal displacements were observed with Methyl Red where the difference in pKa between anionic and cationic micelles was as large as 3 pH units. Phospholipid liquid crystals (Liposomes) of phosphatidylcholine with and without adsorbed long-chain ions introduced in order to confer to it a net surface charge induced displacements of the pKa of UBF analogous to those detected in the presence of detergent micelles. It was demonstrated that UBF can monitor reversal of charge phenomena such as that obtained by the interaction of phosphatidylcholine + dicetyl phosphate liposomes (anionic colloid) with poly-L-lysine (cationic colloid). The partition of the indicator dyes between micellar and aqueous phases was determined by gel filtration revealing thequasi exclusive presence of the dyes in the micellar phase. Fluorescence polarization measurement of solubilized UBF in either ionic micelles or submitochondrial particles indicate that the dye tumbling rate is as rapid as in pure water suggesting that the dye is mobile in an interfacial environment where it can experience modifications due to changes in surface potential. The use of UBF as a probe of respiration-dependent energy-linked reactions in submitochondrial particles is presented. The available data on the use of indicator dyes in mitochondrial, chloroplast and bacterial chromatophore membranes is reevaluated, on the basis of the evidence of the extreme sensitivity of these probes to surface charge. The implications of these results and considerations are discussed in terms of the importance of the surface potential in the primary event of the energy-coupling process in oxidative and photosynthetic phosphorylation.

66 citations


Journal ArticleDOI
TL;DR: In this article, the importance of softening local behavior (decreasing bending moment for increasing flexural deformation) in the inelastic analysis of reinforced concrete beams and frames has been presented.
Abstract: The importance of softening local behavior (decreasing bending moment for increasing flexural deformation) in the inelastic analysis of reinforced concrete beams and frames has been presented elsewhere. Further studies led to a fairly general theory of the implications of flexural softening on the overall stability. However, the bifurcation of equilibrium paths, which can be caused by softening even in the absence of any geometric effects, seems to have escaped attention. This note aims at illuminating this phenomenon that parallels the well-known phenomenon that may occur in structures with stable local behavior when geometry changes affect significantly the equilibrium equations.

55 citations


Journal ArticleDOI
TL;DR: Experiments performed in black lipid films show that indeed the ionophore makes the membrane permeable to Pr 3+ , thus supporting the interpretation of the PMR data.

45 citations


Journal ArticleDOI
TL;DR: In this article, Fowler's hypothesis was extended to deal with the problem of internal photoemission, which leads to the empirical relation between the quantum efficiency and photon energy, which is currently used to interpret hole photo-emission experiments.
Abstract: Fowler's hypothesis commonly used to interpret results of photoemission into the vacuum has been extended to deal with the problem of internal photoemission. This leads to the empirical relation $Y\ensuremath{\propto}{(E\ensuremath{-}{E}_{t})}^{2}$ between the quantum efficiency $Y$ and the photon energy $E$, currently used to interpret hole photoemission experiments. ${E}_{t}$ is the threshold energy for photoemission. Various cases of internal electron and hole photoemission between metals and semiconductors are discussed.

45 citations


Journal ArticleDOI
TL;DR: The surface-charge dependence of this phenomenon indicates the persistence of the asymmetric lipid distribution in the bilayer after its formation from two different monolayers.

43 citations


Journal ArticleDOI
01 May 1973-Virology
TL;DR: The results suggest that the primary site of CaMV-DNA replication may be the host-cell nucleus, but that the viroplasm is a major site for virus replication.

34 citations


Journal ArticleDOI
TL;DR: In this paper, the authors considered the variation of mobile dislocation density during plastic deformation by treating a dislocation model of the statistical distribution of internal stresses, based on the idea that for a given applied stress, only certain dislocations in regions with low internal back stresses are free to move and contribute to plastic flow.

32 citations



Journal ArticleDOI
TL;DR: In this article, the authors proposed a finite element with linear moment distributions and linearized yield criteria to determine lower bounds to the collapse load of thin plates as solutions of linear programs, which can yield accurate bounds with considerably shorter computer times and relatively small number of elements.
Abstract: Finite elements having linear moment distributions and use of linearized yield criteria allow one to determine lower bounds to the collapse load of thin plates as solutions of linear programs. The method is quite general and rigorously meets the requirement of the lower bound theorem of limit analysis for concentrated or line load distributions. Ways of treating distributed surface loads are also discussed and tested. Actual bounds are computed for a variety of plate problems governed by Tresca yield criterion and compared with previous solution obtained from higher order stress elements and non-linear optimization techniques. The comparison shows that the present method can yield accurate bounds with considerably shorter computer times and relatively small number of elements. Additional tests show that numerical convergence to the limit loads is assured by suitable refinement of the mesh pattern.

28 citations


Journal ArticleDOI
TL;DR: In this article, it was shown that the observed spin-polarization of the photo-and field-emitted electrons is largely determined by spin-exchange collisions in the surface sheet.



Journal ArticleDOI
TL;DR: The relationships among more than 200 species of higher fungi of eastern and western United States and Mexico are discussed.
Abstract: The relationships among more than 200 species of higher fungi of eastern and western United States and Mexico are discussed. Four types of relationships between both mycofloras are established: (1)...

Journal ArticleDOI
TL;DR: The results are interpreted as evidence for a rapid axonal transport of neurophysin from its site of synthesis in the cell bodies of the hypothalamus to the posterior pituitary.
Abstract: 1. An immunohistochemical study has been made of the hypothalamo-neurohypophyseal system of the dog, 20h after crushing the pituitary stalk. 2. By use of a cross-species-reactive neurophysin antiserum it was shown that neurophysin is a component of the axons which originate in the supraoptic and paraventricular nuclei and terminate around blood vessels in the posterior pituitary. 3. Neurophysin specific fluorescence accumulated in axons proximal to the constriction but was absent from the axons immediately distal to the site of injury. 4. In dogs left for six days it was shown by radioimmunoassay that the amount of neurophysin in the hypothalamus and stalk proximal to the constriction increased twofold while that remaining in the posterior pituitary and stalk distal to the constriction decreased five-fold over the same period. 5. The results are interpreted as evidence for a rapid axonal transport of neurophysin from its site of synthesis in the cell bodies of the hypothalamus to the posterior pituitary.


Journal ArticleDOI
TL;DR: In this paper, homolytic benzylation of 4-substituted pyridines gives 1,2-diphenylethane and a benzyl-4-substantituted Pyridine in a ratio determined by the nature of the 4substituents.

Journal ArticleDOI
TL;DR: In this paper, the authors make an attempt at showing the importance of the formation of tetravalent titanium ions during the spontaneous passivation of titanium in acidic solutions, and they start by studying the anodic behaviour of titanium, in order to work out a basis for the evaluation of specimens of different origin.
Abstract: Despite numerous investigations into the corrosion behaviour of Ti and its alloys there are numerous discrepancies in literature with respect to the type of the tetravalent ion formed during the dissolution of titanium in aerated acid solutions; the same applies to the thermodynamical data concerning a possible redox reaction between titanium ions having different valencies. It is for this reason that the authors make an attempt at showing the importance of the formation of tetravalent titanium ions during the spontaneous passivation of titanium in acidic solutions. In this context they start by studying the anodic behaviour of titanium, in order to work out a basis for the evaluation of specimens of different origin. The studies are carried out in aerated and deoxygenated sulfuric acid, with and without external polarization. The anodic behaviour is then interpreted in terms of the mixed potential theory. Eine Untersuchung des Verhaltens von Titan in sauren Losungen. Teil I: Anodisches Verhalten und Verhalten ohne ausere Polarisation Trotz zahlreicher Untersuchungen uber das Korrosionsverhalten von Ti und dessen Legierungen gibt es in der Literatur noch zahlreiche Unstimmigkeiten bezuglich der Art des vierwertigen Ions, das bei der Auflosung von Titan in belufteten sauren Losungen entsteht; gleiches gilt fur die thermodynamischen Werte einer moglichen Redox-Reaktion zwischen Titanionen verschiedener Wertigkeit. Aus diesem Grunde wird versucht, die Bedeutung der Bildung von Ionen des vierwertigen Titans bei der spontanen Passivierung von Titan in sauren Losungen zu zeigen. Dabei wird zunachst das anodische Verhalten von Titan untersucht, um eine Grundlage fur die Beurteilung des Verhaltens von Proben verschiedener Herkunft zu erarbeiten. Die Untersuchungen werden in belufteter und entlufteter Schwefelsaure durchgefuhrt, und zwar mit und ohne ausere Polarisation. Das anodische Verhalten wird dann auf der Grundlage der Theorie der Mischpotentiale interpretiert.


Journal ArticleDOI
TL;DR: The structure of the ester of 2-hydroxy-4-methoxy-6-methylbenzoic acid with 6-acetoxy-7-hydroxymethylpolyphenyl-3-propenyl was assigned to wortmin, a new member of the sclerotiorin group of metabolites, produced by Penicillium wortmanni Klocker as mentioned in this paper.
Abstract: The structure of ester of 2-hydroxy-4-methoxy-6-methylbenzoic acid with 6-acetoxy-7-hydroxy-7-methyl-3-propenyl-3,4,5,6,7,8-hexahydro-1H-benzo[e]pyran-8-one (1) is assigned to wortmin, a new member of the sclerotiorin group of metabolites, produced by Penicillium wortmanni Klocker.

Journal ArticleDOI
TL;DR: An unstable ring resonator has been studied, both theoretically and experimentally; quasi-traveling-wave operation is obtained with a high ratio of the powers of the two opposite rotating waves and with diffraction-limited output beams as mentioned in this paper.
Abstract: An unstable ring resonator has been studied, both theoretically and experimentally; quasi-traveling-wave operation is obtained with a high ratio of the powers of the two opposite rotating waves and with diffraction-limited output beams.

Journal ArticleDOI
TL;DR: The mass spectra of fifteen 1,2-benzisothiazoles are reported; their fragmentation patterns have been investigated by labelling experiments, high resolution mass measurements and defocused metastable ion detection as discussed by the authors.
Abstract: The mass spectra of fifteen 1,2-benzisothiazoles are reported; their fragmentation patterns have been investigated by labelling experiments, high resolution mass measurements and defocused metastable ion detection. The parent compound of the series, 1,2-benzisothiazole, eliminates HCN after partial inter-ring hydrogen scrambling. The extent of scrambling has been determined for normal daughter ions produced at different electron beam energies and also for metastable daughter ions, and is compared with the data reported for benzothiazole. Some 3-substituted derivatives show unusual fragmentation patterns. The mechanisms of these processes are under further investigation.

Journal ArticleDOI
TL;DR: In this article, Flemingin- E and F have been isolated from inflorescences of Flemingia congesta, together with two other chalcones, which are allylic alcohols with an additional OH group in the side chain.

Book ChapterDOI
01 Jan 1973
TL;DR: In this article, the authors define reactive functional groups as chemical functions enabling a polymer to chemically react with, or to exert a definite chemical action on one or more components of a surrounding medium, either in artificial or biological systems.
Abstract: Considerable interest is being focused at present on synthetic polymers bearing reactive functional groups. By “reactive functional groups” I mean chemical functions enabling the polymer to chemically react with, or to exert a definite chemical action on one or more components of a surrounding medium, either in artificial or in biological systems. This definition is not absolute, since any chemical group may undergo chemical reactions. However, a polymer containing “reactive chemical groups” is usually prepared to be, and expected to act as a reactive substance and not merely as inert material.


Journal ArticleDOI
TL;DR: In this paper, a novel type of interannular coupling (6JH,F = 1.0 to 1.3 Hz) has been observed in some fluorodinitrodiphenyl ethers between the fluorine(s) on one ring ortho to the ether linkage and a proton on the other ring.
Abstract: A novel type of interannular coupling (6JH,F = 1.0 to 1.3 Hz) has been observed in some fluorodinitrodiphenyl ethers between the fluorine(s) on one ring ortho to the ether linkage and a proton ortho to it on the other ring. 1H and 19F chemical shift and coupling constant data support the previous conclusion that these ethers preferentially adopt a twist (propeller) conformation. On account of the geometrical disposition of the six bonds between the interacting nuclei and the latter's spatial proximity in this conformation, direct coupling through-space is indicated. Concerted libration around the ether bonds brings about magnetic equivalence of the o-fluoro substituents on one ring and causes equal coupling to be observed to the o-proton on the other ring. The possiblity that the coupling is mediated by an intervening π-cloud is suggested as an alternate mechanism for indirect coupling. The observed interannular transmission of spin information provides evidence in favor of a recent proposal made concerning the mode of action of the thyroid hormones.

Journal ArticleDOI
TL;DR: A procedure has been developed whereby the components of the nitrate reductase complex from the membrane of Escherichia coli can be extracted by means of a nonionic detergent and separated from each other as discrete elements in an active form.
Abstract: A procedure has been developed whereby the components of the nitrate reductase complex from the membrane of Escherichia coli can be extracted by means of a nonionic detergent and separated from each other as discrete elements in an active form. It is not yet clear whether these are the dissociated enzymatic elements or whether they are fragments containing other membrane proteins. In any case, they appeared nearly lipid-free and still active.

Journal ArticleDOI
TL;DR: In this article, the retentions in cationic sites are linearly correlated with those in anionic sites, but the slope of the line is different for the hydrated and anhydrous salts and for cis and trans salts.

Journal ArticleDOI
TL;DR: In this article, calcium, present within supported Ag apparently as distinct oxide phase inclusions, is shown to be a necessary ingredient to cause yield of ethylene oxide enhancement due to pre-irradiation of said catalyst with γ rays in the presence of air.

Journal ArticleDOI
TL;DR: In this article, a Veneziano-type expression for the magnetic transition form factor was proposed for the ε-transition form factor of the ϵ-Delta, and the agreement with present experimental data up to 2.34$ was obtained.
Abstract: A Veneziano-type expression is proposed for the magnetic-transition form factor of the $\ensuremath{\Delta}(1236)$. The agreement with present experimental data up to $\ensuremath{-}t=2.34$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^{2}$ is found to be quite satisfactory.