HO Hydrogen Bond Research Articles

Preparation and characterization of copper(II) coordination compounds with linear chain fatty acids with 7–12 carbon atoms and pyridine. Crystal structure of Cu(O 2CC 8H 17) 2(py) 2(H 2O)

Mononuclear compounds of the composition CuX 2(py) 2(H 2O) and binuclear of the composition Cu 2X 4(py) 2 (py = pyridine, X = heptanoate, octanoate, nonanoate, decanoate or dedecanoate) were prepared, analysed and characterized by vibrational spectroscopy and thermogravimetry. Generally, the complexes are unstable, the mononuclear being even less stable than binuclear, losing pyridine in air at room temperature. The X-ray crystal structure of the mononuclear adduct of copper(II) nonanoate with pyridine, Cu(O 2CC 8H 17) 2(py) 2(H 2O), was determined by X-ray diffraction. The copper(II) ion is in a square pyramidal environment with two pyridine nitrogen atoms and two oxygen atoms from unidentate nonaoato ligands forming the basal plane of the pyramid and a water molecule coordinated at the apex. The carboxylate oxygen O(2) is not coordinated to copper, but is bound to water from a neighbouring molecule by the OHO(2) hydrogen bond of 2.691 (5) Å.

Enthalpy of hydrogen bond formation in a protein-ligand binding reaction.

Parallel measurements of the thermodynamics (free-energy, enthalpy, entropy and heat-capacity changes) of ligand binding to FK506 binding protein (FKBP-12) in H2O and D2O have been performed in an effort to probe the energetic contributions of single protein-ligand hydrogen bonds formed in the binding reactions. Changing tyrosine-82 to phenylalanine in FKBP-12 abolishes protein-ligand hydrogen bond interactions in the FKBP-12 complexes with tacrolimus or rapamycin and leads to a large apparent enthalpic stabilization of binding in both H2O and D2O. High-resolution crystallographic analysis reveals that two water molecules bound to the tyrosine-82 hydroxyl group in unliganded FKBP-12 are displaced upon formation of the protein-ligand complexes. A thermodynamic analysis is presented that suggests that the removal of polar atoms from water contributes a highly unfavorable enthalpy change to the formation of C=O...HO hydrogen bonds as they occur in the processes of protein folding and ligand binding. Despite the less favorable enthalpy change, the entropic advantage of displacing two water molecules upon binding leads to a slightly more favorable free-energy change of binding in the reactions with wild-type FKBP-12.

Ab initioSCF investigation of the intramolecular hydrogen bonding in ?-aminohexanoic acid

Ab initioRHF results (geometry data and potential barriers) are reported for the 14 symmetry unique local minima in the potential energy surface of ϵ-aminohexanoic acid, which contain an intramolecular N HO hydrogen bond. Comparison of characteristic data with those of the homologs with fewer carbon atoms shows that δ-aminopentanoic acid forms the most stable hydrogen bonds. In contrast to these homologs, the COOH group is not limited to anti-periplanar orientation in the H-bonded conformers of ϵ-aminohexanoic acid: In four such conformers, it occurs in syn-clinal orientation. © 1994 John Wiley & Sons, Inc.

Crystal and molecular structure of 4-p-hydroxyphenyl-2,2,4-trimethylthiachroman-1,1-dioxide

The title compound1 crystallizes as colorless polyhedra in the monoclinic polar space groupCc, witha=8.107(2),b=21.577(3),c=9.542(2)A,β=103.58(2)°, by contrast with its thioether precursor3, crystals of which have the trigonal space groupR¯3. The structure comprises infinite chains of molecules linked head-to-tail by S=O⋯HO hydrogen bonds of length 2.723(2)A, with H⋯O contact 1.97(4)A and O-H⋯O 177(3)°; H⋯O=S 146(1)°.

Structure and oxidation-reduction conversions of quinhydrone complexes

1. Chloro-, bromo-, and methyl-substituted p-benzoquinones and hydroquinones in the crystalline phase form quinhydrone complexes that contain a π bond and a network of O...HO hydrogen bonds. The hydrogen bond causes significant stabilization of the excited level of the complex that reaches 10,500 cm−1. 2. In the crystalline phase the activation energy of the redox reactions of the complexes is close to the energy of the CT complexes.

Proton-transfer equilibria in phenol−carboxylate hydrogen bonds. Implications for the mechanism of light-induced proton activation in bacteriorhodopsin

Proton transfer equilibria in OH…O −– −O…HO hydrogen bonds between phenols and acetate are studied by IR spectroscopy. These hydrogen bonds show large proton polarizability. It is concluded that the proton activation in bacteriorhodopsin could be performed by a local electric field acting on a tyrosine-aspartate hydrogen bond.

Hydrogen Bonding and Protonation Site in N,N‐Diethylnicotinamide

AbstractThe hydrogen bonded complexes between N,N‐diethylnicotinamide and proton donors such as phenol derivatives or hydrochlorid acid have been studied by infrared spectrometry. The thermodynamic parameters, the ΔνOH values and the shift of the νCO band to lower frequencies indicate that with phenol derivatives (pKa=10.2 ‐7.7 ), normal CO…HO hydrogen bonds are formed. The spectra show that the adduct with HCI is a proton transfer complex and that the protonation occurs at the nitrogen atom of the pyridine ring.

The hydroxyl group protonation rates of α, β and γ-cyclodextrins in dimethyl sulphoxide

The mobility k of the hydroxylic protons of α, β and γ-cyclodextrins are in the order k OH(6)>k OH(2)>k OH(3)′), thus revealing an instramolecular HO(2)…HO(3′) hydrogen-bond in which the OH(2) hydroxyl group is the donor.

Thio-hydroxoanionen des Germaniums: Darstellung, Struktur und Eigenschaften von Na2GeS2(OH)2 · 5 H2O / Thio-hydroxo Anions of Germanium: Preparation, Structure and Properties of Na2GeS2(OH)2 · 5 H2O

Abstract Pure thio-hydroxo-germanates can be prepared from aqueous solutions by reactions of stoichiometric amounts of either sodium sulfide and GeO2, or NaOH and GeS2. The preparation of colourless crystalline Na2GeS2(OH)2 · 5 H2O is reported. The compound is characterized by a single-crystal X-ray structure analysis. It is orthorhombic, space group Pbcn, with a = 10.752(2), b= 13.787(2), c = 14.150(2) Å. The structure contains novel monomeric GeS2(OH)2 2- anions with Ge-S bond distances of 2.150(1) and 2.145(1) Å and with Ge-O lengths of 1.809(3) and 1.815(3) Å. An extensive S ··· HO-and O -HO-hydrogen bond system connects the anions with the octahedrally coordinated Na+ ions. The vibrational spectra are reported. The symmetric GeS2 andGeO2 stretching vibrations in the anion are observed at 415 and 618 cm-1.

Intramolecular, negatively charged, easily polarizable hydrogen bonds in monosalts of diols. Infrared and nuclear magnetic resonance studies

Monotetraethylammonium salt solutions of o-bis(hydroxymethyl)benzene (compound 1), of 2,5-dimethylhexane-2,5-diol (compound 2), of 2,4-dimethyl-pentane-2,4-diol (compound 3), and of 2,3-dimethylbutane-2,3-diol (compound 4) were studied by n.m.r. and i.r. spectroscopies. In the mono salts, intramolecular OH…O–⇌–O…HO hydrogen bonds are formed quantitatively. Very intense continua in the i.r. spectra demonstrate that these hydrogen bonds are easily polarizable. With compounds 1 and 2 these continua extend from 3000 cm–1 over the whole region studied. Comparison with theory shows that these hydrogen bonds are of medium length, and that typical double-minimum proton potentials are present in these hydrogen bonds. This confirms the n.m.r. result that the proton is delocalized in these hydrogen bonds. In the series of compounds 2–4, owing to sterical conditions, these intramolecular hydrogen bonds become weaker, the intensity of the continua decreases a little, and at smaller wavenumbers it vanishes to a large extent.

Structurally symmetrical, easily polarizable hydrogen bonds between side chains in proteins and proton‐conducting mechanisms. III

Abstract(L‐Cys)n, (L‐Lys)n, and (L‐Glu)n were studied by ir spectroscopy in terms of their degree of deprotonation or protonation. It is shown that structurally symmetrical, easily polarizable SH ⃛S− ⇌ −S ⃛HS, N+H ⃛N ⇌ N ⃛H+N, and OH ⃛O− ⇌ −O ⃛HO hydrogen bonds are formed between the side chains. The different wave number distributions of the ir continua caused by these hydrogen bonds show that the barrier in the double‐minimum proton potential decreases in the series of these hydrogen bonds. The stability of these hydrogen bonds against hydration increases in this series. The OH ⃛O− ⇌ −O ⃛HO bonds are not broken by small amounts of water. With (L‐Cys)n the formation of easily polarizable hydrogen bonds and a β‐structure–coil transition are strongly interdependent. As a result of this coupling effect, the β‐structure–coil transition becomes cooperative. With (L‐Glu)n, the formation of the polarizable hydrogen bonds and the observed conformational change are independent processes. The (L‐Glu)n conformation changes from α‐helix to coil only if more than 80% of the residues are deprotonated. Finally, on the basis of the various types of easily polarizable hydrogen bonds, charge shifts in active centers of enzymes and the proton‐conducting mechanism through hydrophobic regions of biological membranes are discussed.

Hydrogen bonding and charge transfer: Interaction of OH radical with rare gas atoms

Hydroxyl radical in solid Ne at 4.2 K is known to rotate freely, vibrationally relax slowly, and have an essentially unperturbed structure. However, the HO structure and dynamics are profoundly affected by solvation in the heavier rare gases Ar, Kr, and Xe. One Ar atom nearest neighbor increases the OH (A 2Σ+) vibrational relaxation rate by a factor of ?103, and A 2Σ+↔X 2Π spectra consistant with a linear–linear transition in hydrogen bonded ArHO are observed. The Ar–HO (A 2Σ+) well depth is D0?675 cm−1 with ωe?203 cm−1 and ωexe?13.1 in solid Ar host; the Kr–HO (A 2Σ+) well depth is ?1000 cm−1. The Ar–HO hydrogen bond length is shorter by Δre=1.15±0.1 Å in the excited state. The OH (A 2Σ+) (0,0) emission band shifts from 3090 in Ne to 4400 Å in Xe. The theory of hydrogen bond formation in both ground and excited states is discussed, with particular reference to the contribution of charge transfer in various environments. Comparison is made with the spectra of hydrogen halides, and the physical origin of rotation–translation coupling theory is discussed. The role of charge transfer complexes in the gas phase quenching of free radical luminescence by rare gas atoms is also considered.

NMR detection of intermolecular hydrogen bonding in 1-(β-hydroxyethoxy)-2,4-dinitrobenzene

Abstract The rate of hydroxylic proton exchange of 1-(β-hydroxyethoxy)-2,4-dinitrobenzene ( 1 ) in acetonitrile solution is retarded by the formation of intermolecular -NO 2 ⋯HO-hydrogen bonds. This retardation in rate is sufficient to allow the observation of spin-spin coupling ( J H-O-C-H ) between the hydroxylic and methylene protons.

Infrared Frequency and Dissociation Constant of the Carboxylate Group

THE hexuronic acids of polyuronides such as the alginates and chondroitin sulphates vary in their acid dissociation constants (pKa) and in their abilities to react with periodate1. Both phenomena could be explained by the formation of a hydrogen bond between the carboxylate group and a hydroxyl group at C2 or C3 of the uronic acid1. Hanrahan2 inferred that the increase in frequency (ν) of the antisymmetric stretching vibration of the ionized carboxylate group in the mono-ions of dicarboxylic acids is due to the formation of CO−2 … HO hydrogen bonds. A similar increase in ν was found by Nakamoto3 when the carboxylate group underwent monodentate coordination by metal ions.