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  • 1
    Electronic Resource
    Electronic Resource
    Influence of membrane heterogeneity on kinetics of nonelectrolyte tracer flows (1976)
    Springer
    The journal of membrane biology 29 (1976), S. 255-264 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary In a composite membrane with heterogeneous channels, prevention of net volume flow with hydrostatic pressure differences and/or impermeant osmotic solutes may induce positive isotope interaction (coupling of isotope flows) consequent to circulation of volume flow. The permeability coefficient for net flow will then exceed the tracer permeability coefficient. A permeant osmotic solute will induce either positive or negative isotope interaction, according to whether membrane heterogeneity is more marked for the test solute or the osmotic solute, respectively. Thus membrane heterogeneity may account for phenomena commonly attributed to “single file diffusion” or “exchange diffusion”. For sufficiently small flows the general flux ratio relationship for homogeneous membranes will continue to apply.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01868965
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  • 2
    Electronic Resource
    Electronic Resource
    Inhibitory and stimulatory effects of amiloride analogues on sodium transport in frog skin (1979)
    Springer
    The journal of membrane biology 46 (1979), S. 155-169 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Effects of amiloride analogues on Na transport were studied in isolated skins of the frogRana ridibunda. The pattern of structure-activity relationship of these compounds showed that both the −NH2 group at position 5 and Cl at position 6 of the pyrazine ring of the amiloride molecule were important for their biological activity. The paramount role of the groups at position 5 was further demonstrated by the striking properties of an analogue resulting from dimethylation of that −NH2 group. A stimulation of Na transport, opposite to the effect of amiloride itself, was observed in this instance. The increase in Na transport could already be seen at 10−6 m and was equivalent to the measured increase in Na influx, reversible, dose-dependent, and additive to the natriferic action of oxytocin. Such characteristics resemble those reported with “external” agents like propranolol and La3+. Furthermore, mutual inhibition was observed between the stimulatory effects of this analogue and those of propranolol or La3+. These results suggest that the analogue may be considered as another “external” agent acting at sites of the external membrane distinct from those activated by cAMP but similar to the Ca sites described by Herrera and Curran (Herrera, F.C., Curran, P.F. 1963.J. Gen. Physiol. 46:999).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01961378
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  • 3
    Electronic Resource
    Electronic Resource
    Tracer flow, permeability, and partial conductance (1975)
    Springer
    The journal of membrane biology 20 (1975), S. 341-346 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary It is often not possible to evaluate a permeability coefficient for net flowP from the small flows produced by physiological gradients of concentration or electrical potential. The common use of a tracer permeability coefficientP x for this purpose, under the assumption thatP x =P, requires that the species be transported passively, and that there be no significant coupling between its flow and that of other chemical species, and between the flows of its tracer and abundant isotopes (isotope interaction). These conditions are often not satisfied. However, for passive transport in the absence of coupling of flows of different chemical species the measurement of tracer flow at two values of electrical potential difference evaluates (P x /P) and thusP. In the presence of coupling of flows of different chemical species, although these measurements no longer evaluateP, they evaluate the partial conductanceG. A graphical method of evaluating (P x /P),P andG is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01870642
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  • 4
    Electronic Resource
    Electronic Resource
    Kinetics of tracer flows and isotope interaction in an ion exchange membrane (1974)
    Springer
    The journal of membrane biology 19 (1974), S. 93-104 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The thermodynamic formulation of isotope interaction (coupling of abundant and tracer isotope flows) has been tested in a highly permselective anion exchange membrane in the absence of significant electroosmosis. A previous study of Cl− permeation has now been extended to include permeation of I−, Acetate, and SO 4 2− in different bath concentrations, with the use of both electrical and chemical driving forces. The flux ratios were “abnormal” according to the usual criteria for simple passive flow, but were closely predicted by the theoretical expression incorporating the influence of isotope interaction. In the absence of coupled flows of other chemical species the extent of isotope interaction can be determined either from the flux ratio or from the measurement of a single unidirectional flux at two settings of the electrochemical potential difference. Direct evidence of negative isotope interaction was presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01869972
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  • 5
    Electronic Resource
    Electronic Resource
    Structure-activity relationship of amiloride analogs as blockers of epithelial Na channels: I. Pyrazine-ring modifications (1985)
    Springer
    The journal of membrane biology 83 (1985), S. 45-56 
    Details
    ISSN: 1432-1424
    Keywords: amiloride ; blocking kinetics ; structure-activity relationship ; Na channels ; frog skin ; fluctuation analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The overall on-and off-rate constants for blocking epithelial Na channels by amiloride analogs were estimated by noise analysis of frog skin epithelium. The substituents at position-5 and −6 of the pyrazine ring of amiloride were varied in order to obtain the structure/rate constant relationship. (1) The off-rate constant increases with halo-substitutions at position-6 in the order Cl〈Br〈I〈F〈H. Substitution of Cl by H lowers the standard free energy of activation of the off-step by 2.3 kcal mol−1. The on-rate constant is not affected. Apparently the substituent at ring position-6 controls the duration of attachment in the blocking position. pK a considerations show that the duration is longer when the 6-substituent is more negatively polarized. We suggest that this substituent binds to the receptor by virtue of its electronegativity. (2) In contrast, replacement of the adjacent 5-amino group (electron donor) by H or Cl affects both the on-rate and the off-rate. The dual effect may be explained by a decrease of the electronic charge at more remote parts of the molecule (on-rate decrease), as well as at the 6-position (off-rate increase). Apparently the 5-amino group stabilizes the blocking position by increasing the electron density on the 6-ligand.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01868737
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  • 6
    Electronic Resource
    Electronic Resource
    Structure-activity relationship of amiloride analogs as blockers of epithelial Na channels: II. Side-chain modifications (1987)
    Springer
    The journal of membrane biology 95 (1987), S. 171-185 
    Details
    ISSN: 1432-1424
    Keywords: amiloride ; analogs ; blocking kinetics ; structure-activity relationship ; Na channels ; frog skin ; fluctuation analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The overall on- and off-rate constants for blockage of epithelial Na channels by amiloride analogs were estimated by noise analysis of the stationary Na current traversing frog skin epithelium. The (2-position) side chain structure of amiloride was varied in order to obtain structure/rate constant relationships. (1) Hydrophobic chain elongations (benzamil and related compounds of high blocking potency) increase the stability of the blocking complex (lowered off-rate), explained by attachment of the added phenyl moiety to a hydrophobic area near the site of side chain interaction with the channel protein. (2) Some other chain modifications show that the on-rate, which is smaller than a diffusion-limited rate, varies with side chain structure. In several cases this effect is not attributable to steric hindrance on encounter, and implies that the side chain interacts briefly with the channel protein (encounter complex) before the main blocking position of the molecule is attained. The encounter complex must be labile since the overall rate constants of blockage are not concentration-dependent. (3) In two cases, changes at the 2-position side chain and at other ring ligands, with known effects on the blocking rate constants, could be combined in one analog. The rate constants of blocking by the resulting compounds indicate that the structural changes have additive effects in terms of activation energies. (4) Along with other observations (voltage dependence of the rate constants and competition with the transported Na ion), these results suggest a blocking process of at least two steps. It appears that initially the 2-position side chain invades the outward-facing channel entrance, establishing a labile complex. Then the molecule is either released completely (no block) or the 6-ligand of the pyrazine ring gains access to its receptor counterpart, thus establishing the blocking complex, the lifetime of which is strongly determined by the electronegativity of the 6-ligand.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01869162
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  • 7
    Electronic Resource
    Electronic Resource
    The kinetic relationships and activation energy of Bi-based superconducting phase formation
    Amsterdam : Elsevier
    Physica C: Superconductivity and its applications 229 (1994), S. 124-128 
    Details
    ISSN: 0921-4534
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0921-4534(94)90820-6
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  • 8
    Electronic Resource
    Electronic Resource
    Photodynamic therapy in the treatment of malignant tumours: An analysis of 540 cases
    Amsterdam : Elsevier
    Journal of Photochemistry and Photobiology B: Biology 6 (1990), S. 149-155 
    Details
    ISSN: 1011-1344
    Keywords: Haematoporphyrin derivative ; cancer ; laser. ; malignant tumours ; photodynamic therapy
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/1011-1344(90)85084-A
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  • 9
    Electronic Resource
    Electronic Resource
    Evolution of island–pit surface morphologies of InAs epilayers grown on GaAs (001) substrates (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 3700-3705 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on a study of the morphological evolution of InAs layers grown on GaAs (001) substrates by molecular-beam epitaxy under In-rich conditions. The surface morphology of the InAs layers is characterized by a feature of island–pit combinations. We show that the vertical sizes of the islands and pits can grow simultaneously beyond the average layer thickness, up to several hundred nanometers. The composition of the islands is found to be ternary InxGa1−xAs rather than the expected binary InAs due to intermixing of the layer and substrate materials. We determine that this intermixing is caused by dissociation of the exposed GaAs at the pits, followed by migration of excess Ga atoms and their incorporation into the islands. The density of the island–pit combinations keeps nearly constant for different layer thicknesses. Eventually, as the layer grows beyond a certain thickness, the pits are filled up by the expanding islands, forming a nearly pure island morphology at the growth front. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1354637
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  • 10
    Electronic Resource
    Electronic Resource
    Relaxed Ge0.9Si0.1 alloy layers with low threading dislocation densities grown on low-temperature Si buffers (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 3160-3162 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Relaxed GexSi1−x epilayers with high Ge fractions but low threading dislocation densities have been successfully grown on Si (001) substrate by employing a stepped-up strategy and a set of low-temperature GeySi1−y buffers. We show that even if the Ge fraction rises up to 90%, the threading dislocation density can be kept lower than 5×106 cm−2 in the top layers, while the total thickness of the structure is no more than 1.7 μm. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.121579
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