The Free Energies of Hydration of Gaseous Ions

Hush, NS

doi:10.1071/ch9480480

Cited by 14 publications

(16 citation statements)

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“…On the other hand, compared to WT HCN4 channels, C479T channels showed marked elevations in permeability to large organic cations, particularly DMA + and TMA + ions, as well as Li + ions, which have the largest hydrated radius (i.e. 3.8 Å) of the alkali series of cations and are unlikely to be dehydrated due to their very negative free energy of hydration (ΔG H = −120.1 kcal/mol) [52]. These observations suggest that replacement of C479 with threonine enlarged the pore diameter.…”

Section: Discussionmentioning

confidence: 99%

P-Loop Residues Critical for Selectivity in K+ Channels Fail to Confer Selectivity to Rabbit HCN4 Channels

D’Avanzo

Pekhletski

Backx³

2009

PLoS ONE

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HCN channels are thought to be structurally similar to Kv channels, but show much lower selectivity for K+. The ∼3.3 Å selectivity filter of K+ channels is formed by the pore-lining sequence XT(V/I)GYG, with X usually T, and is held stable by key residues in the P-loop. Differences in the P-loop sequence of HCN channels (eg. the pore-lining sequence L478C479IGYG) suggest these residues could account for differences in selectivity between these channel families. Despite being expressed, L478T/C479T HCN4 channels did not produce current. Since threonine in the second position is highly conserved in K+ channels, we also studied C479T channels. Based on permeability ratios (PX/PK), C479T HCN4 channels (K+(1)>Rb+(0.85)>Cs+(0.59)>Li+(0.50)≥Na+(0.49)) were less selective than WT rabbit HCN4 (K+(1)>Rb+(0.48)>Cs+(0.31)≥Na+(0.29)>Li+(0.03)), indicating that the TIGYG sequence is insufficient to confer K+ selectivity to HCN channels. C479T HCN4 channels had an increased permeability to large organic cations than WT HCN4 channels, as well as increased unitary K+ conductance, and altered channel gating. Collectively, these results suggest that HCN4 channels have larger pores than K+ channels and replacement of the cysteine at position 479 with threonine further increases pore size. Furthermore, selected mutations in other regions linked previously to pore stability in K+ channels (ie. S475D, S475E and F471W/K472W) were also unable to confer K+ selectivity to C479T HCN4 channels. Our findings establish the presence of the TIGYG pore-lining sequence does not confer K+ selectivity to rabbit HCN4 channels, and suggests that differences in selectivity of HCN4 versus K+ channels originate from differences outside the P-loop region.

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Section: Discussionmentioning

confidence: 99%

P-Loop Residues Critical for Selectivity in K+ Channels Fail to Confer Selectivity to Rabbit HCN4 Channels

D’Avanzo

Pekhletski

Backx³

2009

PLoS ONE

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“…This is different from the distance dependence of e ett , since it relates specifically to the size of the fields generated by the ions. As already noted, equation 76, with e = e solv , exaggerates the screening of the ion's field by the solvent; this has been treated operationally by assuming ionic radii in solution are larger than crystallographic radii (Glueckauf, 1964;Hush, 1948;Grahame, 1950Grahame, , 1953. However it is the large electric fields in solvent near an ion which are the more probable causes for the discrepancies.…”

Section: Non-linearity Of Electrical Responsementioning

confidence: 99%

Theoretical perspectives on ion-channel electrostatics: continuum and microscopic approaches

Partenskii¹,

Jordan

1992

Quart. Rev. Biophys.

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Peter Läuger introduced me (P.C.J.) to the field of ion-channel electrostatics while I was a sabbatical visitor at Konstanz in 1978–79. Läuger pointed out that the relative conductance of hydrophobic ions through phosphatidyl choline (PC) and glyceryl monooleate (GMO) membranes differed by a factor of about 100 (Hladky & Haydon, 1973), quite consistent with the difference in the water-membrane potential differences in the two systems (Pickar & Benz, 1978). However, cation conductance through gramicidin channels spanning these membranes only differs by a factor of 2–3 (Bamberg et al. 1976). Why? It is the pursuit of an answer to this question which led me into my researches in this field.

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“…18,[184][185][186][187][188][189][190][191][192][193] Unlike the solvation free energies obtained using the cluster pair or TATB approximations, the solvation free energies obtained from these types of experiments contain, in addition to the free energy required to couple the solute to the bulk solvent, a free energy term that depends on the surface potentials of the two phases that are brought into contact with one another. (As discussed in the first paragraph of the present article, the solvation free energies resulting from these types of experiments are usually referred to as real solvation free energies to distinguish them from absolute, or Gibbs, solvation free energies, which do not contain the contribution due to the potential of the phase.)…”

Section: Previous Estimates Of the Absolute Solvation Free Energy Of mentioning

confidence: 99%

Single-Ion Solvation Free Energies and the Normal Hydrogen Electrode Potential in Methanol, Acetonitrile, and Dimethyl Sulfoxide

2006

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The division of thermodynamic solvation free energies of electrolytes into ionic constituents is conventionally accomplished by using the single-ion solvation free energy of one reference ion, conventionally the proton, to set the single-ion scales. Thus the determination of the free energy of solvation of the proton in various solvents is a fundamental issue of central importance in solution chemistry. In the present article, relative solvation free energies of ions and ion-solvent clusters in methanol, acetonitrile, and dimethyl sulfoxide (DMSO) have been determined using a combination of experimental and theoretical gas-phase free energies of formation, solution-phase reduction potentials and acid dissociation constants, and gas-phase clustering free energies. Applying the cluster pair approximation to differences between these relative solvation free energies leads to values of −263.5, −260.2, and −273.3 kcal/mol for the absolute solvation free energy of the proton in methanol, acetonitrile, and DMSO, respectively. The final absolute proton solvation free energies are used to assign absolute values for the normal hydrogen electrode potential and the solvation free energies of other single ions in the above solvents.

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The Free Energies of Hydration of Gaseous Ions

Cited by 14 publications

References 1 publication

P-Loop Residues Critical for Selectivity in K+ Channels Fail to Confer Selectivity to Rabbit HCN4 Channels

P-Loop Residues Critical for Selectivity in K+ Channels Fail to Confer Selectivity to Rabbit HCN4 Channels

Theoretical perspectives on ion-channel electrostatics: continuum and microscopic approaches

Single-Ion Solvation Free Energies and the Normal Hydrogen Electrode Potential in Methanol, Acetonitrile, and Dimethyl Sulfoxide

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