Selective Na+/K+ Effects on the formation of alpha-cyclodextrin complexes with aromatic carboxylic acids: competition for the guest

Irina V. Terekhova, Anastasia O. Romanova, Roman S. Kumeev, Maxim V. Fedorov

Research output: Contribution to journalArticle

31 Citations (Scopus)

Abstract

We investigated the effects of K+ and Na+ ions on the formation of a-cyclodextrin complexes with ionized aromatic carboxylic acids. Using solution calorimetry and H-1 NMR, we performed the thermodynamic and structural investigation of a-cyclodextrin complex formation with benzoic and nicotinic acids in different aqueous solutions containing K and Na+ ions as well as in pure water. The experiments show that the addition of sodium ions to solution leads to a decrease in the binding constants of the carboxylic acids with a-cyclodextrin as compared to pure water and solutions containing potassium ions. From another side, the effect of potassium ions on the binding constants is insignificant as compared to pure water solution. We suggest that the selectivity of cation pairing with carboxylates is the origin of the difference between the effects of sodium and potassium ions on complex formation. The strong counterion pairing between the sodium cation and the carboxylate group shifts the equilibrium toward dissociation of the binding complexes. In turn, the weak counterion pairing between the potassium cation and the carboxylate group has no effect on the complex formation. We complemented the experiments with molecular modeling, which shows the molecular scale details of the formation of cation pairs with the carboxylate groups of the carboxylic acids. The fully atomistic molecular simulations show that sodium ions mainly form direct contact pairs with the carboxylate group. At the same time, potassium ions practically do not form direct contact pairs with the carboxylate groups and usually stay in the second solvation shell of carboxylate groups. That confirms our hypotheses that the selective formation of ion pairs is the main cause of the difference in the observed effects of sodium and potassium salts on the guest-host complex formation of a-cyclodextrin with aromatic carboxylic acids. We propose a molecular mechanism explaining the effects of salts, based on competition between the cations and a-cyclodextrin for binding with the ionized carboxylic acids.

LanguageEnglish
Pages12607-12613
Number of pages7
JournalJournal of Physical Chemistry B
Volume114
Issue number39
DOIs
Publication statusPublished - 7 Oct 2010

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Cyclodextrins
Carboxylic Acids
Carboxylic acids
carboxylic acids
carboxylates
Ions
Potassium
potassium
Cations
Positive ions
Sodium
ions
sodium
cations
Nicotinic Acids
Water
Salts
nicotinic acid
water
salts

Keywords

  • atom force-field
  • molecular dynamics
  • x-ray absorption
  • aqueous solutions
  • sodium chloride

Cite this

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title = "Selective Na+/K+ Effects on the formation of alpha-cyclodextrin complexes with aromatic carboxylic acids: competition for the guest",
abstract = "We investigated the effects of K+ and Na+ ions on the formation of a-cyclodextrin complexes with ionized aromatic carboxylic acids. Using solution calorimetry and H-1 NMR, we performed the thermodynamic and structural investigation of a-cyclodextrin complex formation with benzoic and nicotinic acids in different aqueous solutions containing K and Na+ ions as well as in pure water. The experiments show that the addition of sodium ions to solution leads to a decrease in the binding constants of the carboxylic acids with a-cyclodextrin as compared to pure water and solutions containing potassium ions. From another side, the effect of potassium ions on the binding constants is insignificant as compared to pure water solution. We suggest that the selectivity of cation pairing with carboxylates is the origin of the difference between the effects of sodium and potassium ions on complex formation. The strong counterion pairing between the sodium cation and the carboxylate group shifts the equilibrium toward dissociation of the binding complexes. In turn, the weak counterion pairing between the potassium cation and the carboxylate group has no effect on the complex formation. We complemented the experiments with molecular modeling, which shows the molecular scale details of the formation of cation pairs with the carboxylate groups of the carboxylic acids. The fully atomistic molecular simulations show that sodium ions mainly form direct contact pairs with the carboxylate group. At the same time, potassium ions practically do not form direct contact pairs with the carboxylate groups and usually stay in the second solvation shell of carboxylate groups. That confirms our hypotheses that the selective formation of ion pairs is the main cause of the difference in the observed effects of sodium and potassium salts on the guest-host complex formation of a-cyclodextrin with aromatic carboxylic acids. We propose a molecular mechanism explaining the effects of salts, based on competition between the cations and a-cyclodextrin for binding with the ionized carboxylic acids.",
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Selective Na+/K+ Effects on the formation of alpha-cyclodextrin complexes with aromatic carboxylic acids: competition for the guest. / Terekhova, Irina V.; Romanova, Anastasia O.; Kumeev, Roman S.; Fedorov, Maxim V.

In: Journal of Physical Chemistry B, Vol. 114, No. 39, 07.10.2010, p. 12607-12613.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Selective Na+/K+ Effects on the formation of alpha-cyclodextrin complexes with aromatic carboxylic acids: competition for the guest

AU - Terekhova, Irina V.

AU - Romanova, Anastasia O.

AU - Kumeev, Roman S.

AU - Fedorov, Maxim V.

PY - 2010/10/7

Y1 - 2010/10/7

N2 - We investigated the effects of K+ and Na+ ions on the formation of a-cyclodextrin complexes with ionized aromatic carboxylic acids. Using solution calorimetry and H-1 NMR, we performed the thermodynamic and structural investigation of a-cyclodextrin complex formation with benzoic and nicotinic acids in different aqueous solutions containing K and Na+ ions as well as in pure water. The experiments show that the addition of sodium ions to solution leads to a decrease in the binding constants of the carboxylic acids with a-cyclodextrin as compared to pure water and solutions containing potassium ions. From another side, the effect of potassium ions on the binding constants is insignificant as compared to pure water solution. We suggest that the selectivity of cation pairing with carboxylates is the origin of the difference between the effects of sodium and potassium ions on complex formation. The strong counterion pairing between the sodium cation and the carboxylate group shifts the equilibrium toward dissociation of the binding complexes. In turn, the weak counterion pairing between the potassium cation and the carboxylate group has no effect on the complex formation. We complemented the experiments with molecular modeling, which shows the molecular scale details of the formation of cation pairs with the carboxylate groups of the carboxylic acids. The fully atomistic molecular simulations show that sodium ions mainly form direct contact pairs with the carboxylate group. At the same time, potassium ions practically do not form direct contact pairs with the carboxylate groups and usually stay in the second solvation shell of carboxylate groups. That confirms our hypotheses that the selective formation of ion pairs is the main cause of the difference in the observed effects of sodium and potassium salts on the guest-host complex formation of a-cyclodextrin with aromatic carboxylic acids. We propose a molecular mechanism explaining the effects of salts, based on competition between the cations and a-cyclodextrin for binding with the ionized carboxylic acids.

AB - We investigated the effects of K+ and Na+ ions on the formation of a-cyclodextrin complexes with ionized aromatic carboxylic acids. Using solution calorimetry and H-1 NMR, we performed the thermodynamic and structural investigation of a-cyclodextrin complex formation with benzoic and nicotinic acids in different aqueous solutions containing K and Na+ ions as well as in pure water. The experiments show that the addition of sodium ions to solution leads to a decrease in the binding constants of the carboxylic acids with a-cyclodextrin as compared to pure water and solutions containing potassium ions. From another side, the effect of potassium ions on the binding constants is insignificant as compared to pure water solution. We suggest that the selectivity of cation pairing with carboxylates is the origin of the difference between the effects of sodium and potassium ions on complex formation. The strong counterion pairing between the sodium cation and the carboxylate group shifts the equilibrium toward dissociation of the binding complexes. In turn, the weak counterion pairing between the potassium cation and the carboxylate group has no effect on the complex formation. We complemented the experiments with molecular modeling, which shows the molecular scale details of the formation of cation pairs with the carboxylate groups of the carboxylic acids. The fully atomistic molecular simulations show that sodium ions mainly form direct contact pairs with the carboxylate group. At the same time, potassium ions practically do not form direct contact pairs with the carboxylate groups and usually stay in the second solvation shell of carboxylate groups. That confirms our hypotheses that the selective formation of ion pairs is the main cause of the difference in the observed effects of sodium and potassium salts on the guest-host complex formation of a-cyclodextrin with aromatic carboxylic acids. We propose a molecular mechanism explaining the effects of salts, based on competition between the cations and a-cyclodextrin for binding with the ionized carboxylic acids.

KW - atom force-field

KW - molecular dynamics

KW - x-ray absorption

KW - aqueous solutions

KW - sodium chloride

U2 - 10.1021/jp1063512

DO - 10.1021/jp1063512

M3 - Article

VL - 114

SP - 12607

EP - 12613

JO - Journal of Physical Chemistry B

T2 - Journal of Physical Chemistry B

JF - Journal of Physical Chemistry B

SN - 1520-6106

IS - 39

ER -