How are hydrogen bonds modified by metal binding?

Abstract

How are hydrogen bonds modified by metal binding?Husberg, Charlotte; Ryde, Ulf General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal Take down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. AbstractWe have used density-functional theory calculations to investigate how the hydrogenbond strength is modified when a ligand is bound to a metal, using over 60 model systems involving six metals and eight ligands frequently encountered in metalloproteins. We study how the hydrogen-bond geometry and energy vary with the nature of metal, the oxidation state, the coordination number, the ligand involved in the hydrogen bond, other first-sphere ligands, and different hydrogen-bond probe molecules. The results show that in general, the hydrogen-bond strength is increased for neutral ligands and decreased for negatively charged ligands. The size of the effect is mainly determined by the net charge of the metal complex and all effects are typically decreased when the model is solvated. In water solution, the hydrogen-bond strength can increase by up to 37 kJ/mol for neutral ligands, and that of negatively charged ligands can both increase (for complexes with a negative net charge) or decrease (for positively charged complexes). If the net charge of the complex does not change, there is normally little difference between different metals or different types of complexes. The only exception is observed for sulphur-containing ligands (Met and Cys) and if the ligand is redox active (e.g. high-valent Fe-O complexes).Key Words: hydrogen bonds, metalloproteins, quantum-mechanical calculations, densityfunctional theory, dispersion correction, solvation. 2 IntroductionHydrogen bonds play an important role in all types of biochemical systems, strongly affecting catalysis, ligand binding, and enzyme function, for example [1]. They have been thoroughly studied by a variety of experimental and theoretical methods [2,3,4,5,6,7,8,9,10,11,12,13,14,15] so that the strengths of the common hydrogen bonds in biological systems are accurately known.However, it is well-known that metal sites affect the properties of bound ligands. For example, the pK a value of water in aqueous metal complexes is reduced from 15.7 for bulk water, to 12.8 for Ca 2+ and to 2.2 for Fe 3+ [16]. Therefore, it is also likely that metal ions also change the strength and structure of hydrogen bonds inv...

Redox-state sensing by hydrogen bonds in the CuA center of cytochrome c oxidase

“…This result contradicts recent QM calculations in the blue copper protein azurin, [31] which suggest a weaker sulfur-hydrogen bond in the oxidized state. The difference might be attributed to either an increased flexibility in the reduced protein (which is not the case, based on NMR studies [21]) or, more likely, to a lowered stability of the reduced protein, as reported in unfolding studies [32].…”

Hydrogen Bonding between Metal‐Ion Complexes and Noncoordinated Water: Electrostatic Potentials and Interaction Energies

“…Coordination of a water molecule to a metal ion greatly influences its hydrogen bonding. Analysis of crystal structures from the Cambridge Structural Database (CSD) and ab initio calculations show that the hydrogen bonding between coordinated and noncoordinated water molecules is much stronger than that between two noncoordinated waters . Similarly, the interaction of benzene with coordinated water is stronger than with noncoordinated water .…”

“…Analysis of crystal structures from the Cambridge StructuralD atabase (CSD) and ab initio calculations show that the hydrogen bonding between coordinated and noncoordinated water molecules is much stronger than that between two noncoordinated waters. [9,10] Similarly, the interaction of benzene with coordinated water is stronger than with noncoordinated water. [11] These effectsare considera-bly increased when the metal complexes are charged, fore xample,[Zn(H 2 O) 6 ] 2 + versus [ZnCl 2 (H 2 O) 4 ].…”

Water Confined in the Local Field of Ions

“…Bulk water becomes depleted in highly concentrated ionic solutions; therefore, the first hydration shells of cations and anions begin to overlap, thus placing the water molecule under simultaneous influence of both charges (positive and negative). Under these circumstances, alkali ons attract and localize the lone pairs of oxygen and strengthen the OÀH···X À Hb, constituting the cooperative effect of cations and anions M + ···OÀH···X À (in which M = Li, Na, K, Cs and X = F, Cl, Br, I), which was already demonstrated by high-level ab initio [19] and density functional theory [20] simulation studies, and is herein shown experimentally for the first time ( Figure 2). Therefore, ordering of alkali-perturbed solutions demonstrates the cooperative trend in which the more densely charged M + ion strengthens the M + ···OÀH···Cl À Hb, bringing them closer to WWHb (i.e.…”