Library

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    The relationship between permeant size and permeability in lipid bilayer membranes (1994)
    Springer
    The journal of membrane biology 140 (1994), S. 111-122 
    Details
    ISSN: 1432-1424
    Keywords: Permeability ; Transport ; Bilayers ; Size dependence ; Partition coefficients ; Diffusion coefficients
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Permeability coefficients (P m ) across planar egg lecithin/decane bilayers and bulk hydrocarbon/water partition coefficients (K w→hc) have been measured for 24 solutes with molecular volumes, V, varying by a factor of 22 and P m values varying by a factor of 107 to explore the chemical nature of the bilayer barrier and the effects of permeant size on permeability. A proper bulk solvent which correctly mimics the microenvironment of the barrier domain was sought. Changes in P m /Kw→hc were then ascribed to size-dependent partitioning and/or size-dependent diffusivity. The diffusion coefficient-size dependency was described by D barrier = D 0 /V n . When n-decane was used as a reference solvent, the correlation between log P m /K w→hc and log V was poor (r = 0.56) with most of the lipophilic (hydrophilic) permeants lying below (above) the regression line. Correlations improved significantly (r = 0.87 and 0.90, respectively) with more polarizable solvents, 1-hexadecene and 1,9-decadiene. Values of the size selectivity parameter n were sensitive to the reference solvent (n = 0.8 ± 0.3, 1.2 ± 0.1 and 1.4 ± 0.2, respectively, for decane, hexadecene, and decadiene). Decadiene was selected as the most suitable reference solvent. The value for n in bilayer transport is higher than that for bulk diffusion in decane (n = 0.74±0.10), confirming the steep dependence of bilayer permeability on molecular size. Statistical mechanical theory recently developed by the authors suggests that a component of this steep size dependence may reside in size-dependent solute partitioning into the ordered chain region of bilayers. This theory, combined with the above diffusion model, yielded the relationship, P m /K W→hc=D 0 exp(™αV)V n . A fit of the experimental data to this model gave the best fit (r=0.93) with α = 0.0053±0.0021 and n=0.8 ± 0.3, suggesting that both diffusion and partitioning mechanisms may play a role in determining the size dependence of lipid bilayer permeabilities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00232899
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Phospholipid surface density determines the partitioning and permeability of acetic acid in DMPC:cholesterol bilayers (1995)
    Springer
    The journal of membrane biology 148 (1995), S. 157-167 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Relationships between the permeability coefficient (PHA) and partition coefficient (K m/w) of acetic acid and the surface density of DMPC:cholesterol bilayers have been investigated. Permeability coefficients were measured in large unilamellar vesicles by NMR line broadening. Bilayer surface density, σ, was varied over a range of 0.5–0.9 by changing cholesterol concentration and temperature. The temperature dependence of PHA for acetic acid exhibits Arrhenius behavior with an average apparent activation energy (E a ) of 22±3 kcal/mole over a cholesterol mole fraction range of 0.00–0.40. This value is much greater than the enthalpy change for acetic acid partitioning between bulk decane and water (ΔH° = 4.8±0.8 kcal/mole) and the calculated E a (= 8.0 kcal/mole) assuming a “bulk phase” permeability model which includes the enthalpy of transfer from water to decane and the temperature dependence of acetic acid's diffusion coefficient in decane. These results suggest that dehydration, previously considered to be a dominant component, is a minor factor in determining E a . Values of 1n PHA decrease linearly with the normalized phospholipid surface density with a slope of κ = -12.4±1.1 (r = 0.90). Correction of PHA for those temperature effects considered to be independent of lipid chain order (i.e., enthalpy of transfer from water to decane and activation energy for diffusion in bulk hydrocarbon) yielded an improved correlation (κ = -11.7±0.5 (r = 0.96)). The temperature dependence of Km/w is substantially smaller than that for PHA and dependent on cholesterol composition. Values of 1n Km/w decrease linearly with the surface density with a slope of κ = -4.6±0.3 (r = 0.95), which is 2.7-fold smaller than the slope of the plot of 1n PHA vs. σ. Thus, chain ordering is a major determinant for molecular partitioning into and transport across lipid bilayers, regardless of whether it is varied by lipid composition or temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00207271
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Influence of a Transmembrane Protein on the Permeability of Small Molecules Across Lipid Membranes (2000)
    Springer
    The journal of membrane biology 173 (2000), S. 187-201 
    Details
    ISSN: 1432-1424
    Keywords: Key words: Permeability — Gramicidin A — Partition coefficients — Lipid bilayers — Membrane transport — Linear free-energy relationships
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract. The influence of the nonchannel conformation of the transmembrane protein gramicidin A on the permeability coefficients of neutral and ionized α-X-p-methyl-hippuric acid analogues (XMHA) (X = H, OCH3, CN, OH, COOH, and CONH2) across egg-lecithin membranes has been investigated in vesicle efflux experiments. Although 10 mol% gramicidin A increases lipid chain ordering, it enhances the transport of neutral XMHA analogues up to 8-fold, with more hydrophilic permeants exhibiting the greatest increase. Substituent contributions to the free energies of transfer of both neutral and anionic XMHA analogues from water into the bilayer barrier domain were calculated. Linear free-energy relationships were established between these values and those for solute partitioning from water into decadiene, chlorobutane, butyl ether, and octanol to assess barrier hydrophobicity. The barrier domain is similar for both neutral and ionized permeants and substantially more hydrophobic than octanol, thus establishing its location as being beyond the hydrated headgroup region and eliminating transient water pores as the transport pathway for these permeants, as the hydrated interface or water pores would be expected to be more hydrophilic than octanol. The addition of 10 mol% gramicidin A alters the barrier domain from a decadiene-like solvent to one possessing a greater hydrogen-bond accepting capacity. The permeability coefficients for ionized XMHAs increase with Na+ or K+ concentration, exhibiting saturability at high ion concentrations. This behavior can be quantitatively rationalized by Gouy-Chapman theory, though ion-pairing cannot be conclusively ruled out. The finding that transmembrane proteins alter barrier selectivity, favoring polar permeant transport, constitutes an important step toward understanding permeability in biomembranes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002320001019
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    The Barrier Domain for Solute Permeation Varies With Lipid Bilayer Phase Structure (1998)
    Springer
    The journal of membrane biology 165 (1998), S. 77-90 
    Details
    ISSN: 1432-1424
    Keywords: Key words: Permeability — Partition coefficients — Lipid bilayers — Group contributions — Linear free energy relationships
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract. The chemical selectivities of the transport barriers in lipid bilayers varying in composition and phase structure (gel-phase DPPC and DHPC bilayers and liquid-crystalline DPPC/CHOL/50:50 mol% bilayers) have been investigated by determining functional group contributions to transport of a series of α-substituted p-toluic acid analogs obtained in vesicle efflux experiments. Linear free energy relationships are established between the free energies of transfer for this series of compounds from water to the barrier domain and corresponding values for their transfer from water into six model bulk solvents (hexadecane, hexadecene, decadiene, chlorobutane, butyl ether, and octanol) determined in partitioning experiments to compare the barrier microenvironment to that in these model solvents. The barrier microenvironment in all bilayers studied is substantially more hydrophobic than octanol, thus establishing the location of the barrier beyond the hydrated headgroup interfacial region, as the interface is expected to be more hydrophilic than octanol. The chemical nature of the barrier domain microenvironment varies with bilayer phase structure. The barrier regions in non-interdigitated DPPC and interdigitated DHPC gel-phase bilayers exhibit some degree of hydrogen-bond acceptor capacity as may occur if these domains lie in the vicinity of the ester/ether linkages between the headgroups and the acyl chains. Intercalation of 50 mol% cholesterol into DPPC bilayers, which induces a phase transition to a liquid-crystalline phase, substantially increases the apparent barrier domain hydrophobicity relative to gel-phase bilayers to a nonhydrogen bonding, hydrocarbonlike environment resembling hexadecene. This result, combined with similar observations in liquid-crystalline egg-PC bilayers (J. Pharm. Sci. (1994), 83:1511–1518), supports the notion that the transition from the gel-phase to liquid-crystalline phase shifts the barrier domain further into the bilayer interior (i.e., deeper within the ordered chain region).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002329900422
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    A Quantitative Model for the Dependence of Solute Permeability on Peptide and Cholesterol Content in Biomembranes (2000)
    Springer
    The journal of membrane biology 177 (2000), S. 137-148 
    Details
    ISSN: 1432-1424
    Keywords: Key words: Permeability coefficients — Gramicidin A — Cholesterol — Lipid bilayers — Solubility parameters — Fluorescence anisotropy — Regular solution theory
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract. The influence of varying concentrations of a transmembrane peptide, gramicidin A (gA), and cholesterol (Chol) on the passive permeation of p-methylhippuric acid (MHA) and α-carbamoyl-p-methylhippuric acid (CMHA) across egg-lecithin membranes (EPC) has been investigated in vesicle efflux experiments. Incorporation of 0.25 volume fraction of gA in its nonchannel conformation increased the permeability coefficient (P m ) for CMHA by a factor of 6.0 ± 1.8 but did not alter P m for MHA, a more lipophilic permeant. In contrast, incorporation of 0.26 volume fraction Chol with no added protein decreased the P m values for both CMHA and MHA by similar factors of 4.2 ± 1.1 and 3.5 ± 1.2, respectively. A quantitative structure-transport model has been developed to account for the dependence of P m on the membrane concentrations of gA and Chol in terms of induced changes in both membrane chain ordering and hydrophobicity. Chain ordering is assumed to affect P m for both permeants similarly since they are comparable in molecular size, while changes in P m ratios in the presence of gA or Chol are attributed to alterations in membrane hydrophobicity. Changes in lipid chain ordering were detected by monitoring membrane fluidity using fluorescence anisotropy of 1-[4-(trimethylamino)phenyl]-6-phenylhexa-1,3,5-triene incorporated into the membranes. The influence of additives on membrane hydrophobicity, which governs P m ratios through effects on solute partitioning into the barrier domain, were rationalized within the framework of regular solution theory using solubility parameters as a measure of membrane hydrophobicity. Fits of the P m ratios using the theoretical model yielded solubility parameters for gA and Chol in EPC membranes of 13.2 and 7.7 (cal/ml)1/2, respectively, suggesting that gA decreases the barrier domain hydrophobicity while Chol has a minimal effect on barrier hydrophobicity. After correcting for barrier domain hydrophobicity, permeability decrements due to membrane ordering induced by gA or Chol were found to exhibit a strong correlation with membrane order as predicted by free-surface-area theory, regardless of whether gA or Chol is used as the ordering agent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002320001107
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 6
    Electronic Resource
    Electronic Resource
    Infrared laser dissociation of CF"2CFCl in a molecular beam: Spectroscopy and energy distribution, and relaxation of CFCl radical
    Amsterdam : Elsevier
    Chemical Physics Letters 147 (1988), S. 183-188 
    Details
    ISSN: 0009-2614
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0009-2614(88)85080-2
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 7
    Electronic Resource
    Electronic Resource
    Intermolecular state couplings in the presence of a radiation field. I. Non-resonant V-V transitions
    Amsterdam : Elsevier
    Chemical Physics 144 (1990), S. 189-200 
    Details
    ISSN: 0301-0104
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0301-0104(90)80084-B
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 8
    Electronic Resource
    Electronic Resource
    Vibrational relaxation of NH"2X^2B"1(O, v"2, O) radicals
    Amsterdam : Elsevier
    Chemical Physics 101 (1986), S. 157-163 
    Details
    ISSN: 0301-0104
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/0301-0104(86)87031-8
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 9
    Electronic Resource
    Electronic Resource
    State-selected reaction and relaxation of CH with H"2
    Amsterdam : Elsevier
    Chemical Physics 130 (1989), S. 299-305 
    Details
    ISSN: 0301-0104
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0301-0104(89)87059-4
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...