Kinetics of the reaction of the hydrophobic ester 4-nitrophenyl decanoate with long-chain N-alkylimidazoles above and below their critical micelle concentration

1974 ◽  
Vol 27 (10) ◽  
pp. 2149 ◽  
Author(s):  
DG Oakenfull ◽  
DE Fenwick
Keyword(s):  
Critical Micelle Concentration ◽  
Chain Length ◽  
Mole Fraction ◽  
Rate Constants ◽  
Hydrophobic Interactions ◽  
Hydrocarbon Chain ◽  
Hydrocarbon Chain Length ◽  
Hydrocarbon Chains ◽  
Kinetics Of ◽  
Long Chain

The kinetics of the reaction of 4-nitrophenyl decanoate with a series of straight-chain N-alkylimidazoles have been studied at 25� in water and aqueous ethanol. In water, below the critical micelle concentration of the N-alkylimidazole, hydrophobic interaction between the hydrocarbon chains of the reactants caused substantial increases in the reaction rate (up to about 200-fold) compared with the rate of reaction of 4-nitrophenyl acetate with N-methylimidazole. The rate constants, though, differed from those previously reported which were measured with a higher initial concentration of ester. No increase in rate with increasing hydrocarbon chain length could be detected in the presence of a large concentration of ethanol (mole fraction of 0.31) but a rate increase did occur in the presence of a more moderate concentration of ethanol (mole fraction of 0.10), confirming that hydrophobic interactions persist in this mixed solvent. The long-chain ester reacts rapidly with N-alkylimidazole micelles. Association constants (K) for binding the ester to the micelles and rate constants for the reaction of the bound ester (km) were estimated by following the conventional treatment of the kinetics of micelle-catalysed reactions. The value of K was found to increase sharply with increasing hydrocarbon chain length of the micelle but km showed the opposite trend.

Conductometric study of hydrophobic interactions in aqueous solutions of double long-chain electrolytes

1973 ◽  
Vol 26 (12) ◽  
pp. 2649 ◽  
Author(s):  
DG Oakenfull ◽  
DE Fenwick
Keyword(s):  
Aqueous Solutions ◽  
Chain Length ◽  
Hydrophobic Interaction ◽  
Hydrophobic Interactions ◽  
Ion Pairs ◽  
Hydrocarbon Chain ◽  
Hydrocarbon Chain Length ◽  
Hydrocarbon Chains ◽  
Methylene Groups ◽  
Conductometric Study

We report measurements of the equivalent conductance (Λ) of aqueous solutions of a series of decyl- and hexadecyl-trimethylammonium carboxylates (acetate to undecanoate). In the decyl series, measurements were made on both sides of the critical micelle concentration (CMC). The CMC decreased when the hydrocarbon chain length of the carboxylate ion increased. In the hexadecyl series, measurements were confined to micellar solutions. ��� The results obtained below the CMC suggest that hydrophobic interaction between the hydrocarbon chains of decyltrimethylammonium undecanoate, decanoate, and nonanoate leads to the formation of ion- pairs. There was no evidence, however, for formation of ion-pairs by the shorter carboxylates. ��� By assuming that micellar ions obey the Onsager equation, we have derived a theoretical relationship between Λ and concentration above the CMC. An excellent fit of theoretical curve to experimental points can be obtained by adjusting the value of a single parameter. This parameter is {(m+1)/n}Kmic (where Kmic is the association constant for binding the carboxylate ion to the micelle and m/n is the ratio of tetra-alkylammonium ions to carboxylate ions in the micelle). ��� Plots of -RT ln[{(m+1)/n}Kmic] against the number of methylene groups on the carboxylate ion are linear for both series, which suggests that m/n is independent of the chain length of the carboxylate ion. Both lines have a slope equal to N�methy and Scheraga's estimate of the free energy of hydrophobic interaction between two methylene groups (-1.40 kJ/mol).

Hydrophobic interaction in deuterium oxide

1975 ◽  
Vol 28 (4) ◽  
pp. 715 ◽  
Author(s):  
DG Oakenfull ◽  
DE Fenwick
Keyword(s):  
Free Energy ◽  
Hydrophobic Interaction ◽  
Deuterium Oxide ◽  
Hydrocarbon Chain ◽  
Micellar Solutions ◽  
Hydrocarbon Chain Length ◽  
Hydrocarbon Chains ◽  
Methylene Groups ◽  
Free Energy Of Binding ◽  
Kinetics Of

Methods previously used to study hydrophobic interaction in ordinary water have been used to measure the free energy of hydrophobic interaction between hydrocarbon chains in deuterium oxide at 25�: ��� (1) Conductance measurements on micellar solutions of a series of hexadecyltrimethylammonium carboxylates give the effect of hydrocarbon chain length on the free energy of binding a counter-ion (carboxylate ion) to the micelle, and hence the free energy of hydrophobic interaction. ��� (2) Comparison of the kinetics of the reaction between decylamine and 4-nitrophenyl decanoate with the kinetics of the corresponding reaction without hydrophobic side chains (the reaction between ethylamine and 4-nitrophenyl acetate) gives the extent to which hydrophobic interaction stabilizes the transition state. This then provides another estimate of the free energy of hydrophobic interaction. ��� The free energy of hydrophobic interaction in D2O was found to be - 1.76 kJ mol-1, for each contact between two methylene groups, compared with -1.40 kJ mol-1 in H2O. Hydrophobic interaction is therefore stronger in D2O than in H2O.

scholarly journals Structure and Interdigitation of Chain-Asymmetric Phosphatidylcholines and Milk Sphingomyelin in the Fluid Phase

Symmetry ◽  
2021 ◽  
Vol 13 (8) ◽  
pp. 1441
Author(s):  
Moritz P. K. Frewein ◽  
Milka Doktorova ◽  
Frederick A. Heberle ◽  
Haden L. Scott ◽  
Enrico F. Semeraro ◽  
...  
Keyword(s):  
Chain Length ◽  
Hydration Shell ◽  
Fluid Phase ◽  
Hydrocarbon Chain ◽  
Specific Model ◽  
Glycerol Backbone ◽  
Membrane Composition ◽  
Membrane Structures ◽  
Hydrocarbon Chain Length ◽  
Dynamics Simulations

We addressed the frequent occurrence of mixed-chain lipids in biological membranes and their impact on membrane structure by studying several chain-asymmetric phosphatidylcholines and the highly asymmetric milk sphingomyelin. Specifically, we report trans-membrane structures of the corresponding fluid lamellar phases using small-angle X-ray and neutron scattering, which were jointly analyzed in terms of a membrane composition-specific model, including a headgroup hydration shell. Focusing on terminal methyl groups at the bilayer center, we found a linear relation between hydrocarbon chain length mismatch and the methyl-overlap for phosphatidylcholines, and a non-negligible impact of the glycerol backbone-tilting, letting the sn1-chain penetrate deeper into the opposing leaflet by half a CH2 group. That is, penetration-depth differences due to the ester-linked hydrocarbons at the glycerol backbone, previously reported for gel phase structures, also extend to the more relevant physiological fluid phase, but are significantly reduced. Moreover, milk sphingomyelin was found to follow the same linear relationship suggesting a similar tilt of the sphingosine backbone. Complementarily performed molecular dynamics simulations revealed that there is always a part of the lipid tails bending back, even if there is a high interdigitation with the opposing chains. The extent of this back-bending was similar to that in chain symmetric bilayers. For both cases of adaptation to chain length mismatch, chain-asymmetry has a large impact on hydrocarbon chain ordering, inducing disorder in the longer of the two hydrocarbons.

scholarly journals Effect of Hydrocarbon Chain Length of Amphiphilic Ruthenium Dyes on Solid-State Dye-Sensitized Photovoltaics

Nano Letters ◽  
2005 ◽  
Vol 5 (7) ◽  
pp. 1315-1320 ◽  
Author(s):  
Lukas Schmidt-Mende ◽  
Jessica E. Kroeze ◽  
James R. Durrant ◽  
Md. K. Nazeeruddin ◽  
Michael Grätzel
Keyword(s):  
Solid State ◽  
Chain Length ◽  
Hydrocarbon Chain ◽  
Dye Sensitized ◽  
Hydrocarbon Chain Length ◽  
Ruthenium Dyes

Cation exchange in synthetic manganates: II. The structure of an alkylammonium-saturated phyllomanganate

Clay Minerals ◽  
1986 ◽  
Vol 21 (5) ◽  
pp. 957-964 ◽  
Author(s):  
E. Paterson ◽  
D.R. Clark ◽  
D. Russell ◽  
R. Swaffield
Keyword(s):  
Chain Length ◽  
Photoelectron Spectroscopy ◽  
Hydrocarbon Chain ◽  
Exchange Capacity ◽  
Basal Spacing ◽  
Water Molecules ◽  
Interlayer Water ◽  
X Ray ◽  
Alkyl Chains ◽  
Hydrocarbon Chain Length

AbstractA synthetic phyllomanganate saturated with a series of primary alkylammonium cations has been examined using XRD, chemical analysis and X-ray photoelectron spectroscopy. A linear relationship exists between the basal spacing of the saturated alkylammonium-manganate and the hydrocarbon chain length in the interlayer, and from the gradient it is concluded that the alkyl chains are perpendicular to the manganate sheet. This orientation is a function of both the charge density and the presence of a layer of water molecules immediately adjacent to the manganate basal surfaces. Evacuation results in the loss of this interlayer water and the structure of the organo-manganate is considerably disrupted. The extent to which the interlayer arrangement can be reinstated by rehydration is dependent on the chain length of the saturating organo-cation. For cations of chain length > C6 the C contents suggest that cation in excess of the exchange capacity is present in the interlayer, but the absence of any compensating anion and the release of amine on evacuation suggests that the excess C arises from the presence of free amine.

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