In this paper we describe H/D isotope effects on the chemical shifts of intermolecular hydrogen-bonded complexes exhibiting low barriers for proton transfer, as a function position hydrogen bond proton. For purpose, low-temperature (100−150 K) 1H, 2H, and 15N NMR experiments were performed solutions various protonated deuterated acids AL (L = H, D) pyridine-15N (B) dissolved in 2:1 mixture CDClF2/CDF3. temperature range, regime slow exchange is reached, leading to resolved lines each species...

Abstract Liquid state 1 H and 19 F NMR experiments in the temperature range between 110 150 K have been performed on mixtures of tetrabutylammonium fluoride with HF dissolved a 1:2 mixture CDF 3 2 Cl. Under these conditions hydrogen bonded complexes − varying number molecules were observed slow proton bond exchange regime. At low concentrations well known bifluoride ion [FHF] is observed, exhibiting strong symmetric H‐bond. higher species [F(HF) ] , are formed to which we assign structure 4...

Abstract Hydrogen bond geometries and 1 H NMR chemical shifts of OHO hydrogen‐bonded systems have been analyzed using an improved valence order model. This model predicts that the heavy atom hydrogen coordinate q 2 = r + is a function proton ( ‐ ), where represent OH HO distances. In first part, it shown this correlation reproduces published equilibrium Zundel cation 5 O as well those water clusters in gas phase embedded fullerene C180. Using example hexamer, changing level calculation...

Ab initio calculations of the scalar coupling constants 1J15N-1H ≡ JNH and 2J15N···15N JNN N−H···N hydrogen bonds in anion [C⋮15N···L···15N⋮C]- (1), L = H, D, cyclic hydrogen-bonded formamidine dimer (HCNHNH2)2 (2) have been performed using density functional formalism as a function bond molecular geometries. The are discussed comparison with experimental calculated 1J19F-1H JFH 2J19F-19F JFF reported previously first set examples couplings across for clusters [F(HF)n]-, n 1−4 by...

Spin–spin coupling between all three nuclei of a hydrogen bridge is seen for the first time. The observation these couplings in fluoride/collidine complex (see figure) reveals covalent character bridge. Its geometry strongly affected by temperature dependent solvent electric field effects.

The low-temperature (1)H, (19)F, and (15)N NMR spectra of mixtures collidine-(15)N (2,4,6-trimethylpyridine-(15)N, Col) with HF have been measured using CDF(3)/CDF(2)Cl as a solvent in the temperature range 94-170 K. Below 140 K, slow proton hydrogen bond exchange regime is reached where four hydrogen-bonded complexes between collidine compositions 1:1, 2:3, 1:2, 1:3 could be observed assigned. For these complexes, chemical shifts scalar coupling constants across (19)F(1)H(19)F...

A novel series of hydrogen-bonded solid 1 : acid–base complexes 15N-labeled 2,4,6-trimethylpyridine (collidine) with carboxylic acids and their hydrogen bond deuterated analogs were synthesized studied by 1H magic angle spinning (MAS) 15N cross-polarization NMR without MAS. Not only zwitterionic the H-bond proton closer to nitrogen than oxygen but also molecular have been observed, where is located oxygen. For these complexes, isotropic chemical shifts shielding tensor elements measured (the...

The influence of solvent polarity on the properties hydrogen-bonded 1 : complexes 2,4,6-trimethylpyridine-15N with HF and DF, labeled below as FHN FDN, has been studied by multinuclear magnetic resonance spectroscopy in slow hydrogen bond exchange regime reached 190 K. Mixtures CDF3/CDClF2 were employed solvent, which is liquid down to 90 In order evaluate their polarity, static dielectric constants εo CHF3, CHClF2 binary mixture measured from 160 K A strong increase 14 at 38 103 observed...

1H, 2H, and 13C NMR spectra of enriched CH313COOH acid without in the presence tetra-n-butylammonium acetate have been measured around 110 K using a liquefied Freon mixture CDF3/CDF2Cl as solvent, function deuterium fraction mobile proton sites. For comparison, were also taken adduct CH313COOH·SbCl5 1 CH2Cl13COOH under similar conditions, well CH313COO- dissolved H2O D2O at low high pH 298 K. The temperatures employed allowed us to detect several well-known novel hydrogen-bonded complexes...

The tautomeric equilibrium in a Schiff base, N-(3,5-dibromosalicylidene)-methylamine 1, model for the hydrogen bonded structure of cofactor pyridoxal-5'-phosphate PLP which is located active site enzyme, was measured by means 1H and 15N NMR deuterium isotope effects on chemical shifts at variable temperature different organic solvents. position estimated using one-bond 1J(OHN) vicinal 3J(HαCNH) scalar coupling constants. Additionally, DFT calculations series bases,...

Using 15N solid-state NMR, we have studied protonation and H-bonded states of the cofactor pyridoxal 5′-phosphate (PLP) linked as an internal aldimine in alanine racemase (AlaR), aspartate aminotransferase (AspAT), poly-l-lysine. Protonation pyridine nitrogen PLP coupled proton transfer from phenolic oxygen (enolimine form) to (ketoenamine is often considered be a prerequisite initial step (transimination) enzyme-catalyzed reaction. Indeed, using NMR H-bond correlations AspAT, observe strong...

Hydrogen bond patterns of crystals phosphinic, phosphonic, and phosphoric acids their cocrystals with phosphine oxides were studied using 31P NMR single-crystal X-ray diffraction. Two main factors govern these favor or prevent the formation cocrystals. The first one is a high proton-accepting ability P═O moiety in acids. As result, this effectively competes other proton acceptors for hydrogen bonding. For example, stronger acceptor than C═O carboxylic second factor inclination both to form...

Matrix effects on the optimized geometries and electronic properties of acid−base complexes XHB, with HX = HF, HCl, HBr, HCN B NH3, have been modeled using ab initio methods (6-31G** 6-311++G** basis sets) in two different ways. Model A corresponds to Onsager SCRF model, model a homogeneous electric field F 2qe0/re2 2.88 × 105q V/cm varying strength generated by distant charges +qe0 −qe0 opposite sign placed at distances re 100 Å. In both models, minima reaction coordinate proton transfer...

ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTHydrogen/Deuterium-Isotope Effects on NMR Chemical Shifts and Symmetry of Homoconjugated Hydrogen-Bonded Ions in Polar SolutionParwin Schah-Mohammedi, Ilja G. Shenderovich, Carsten Detering, Hans-Heinrich Limbach, Peter M. Tolstoy, Sergei N. Smirnov, Gleb S. Denisov, Nikolai GolubevView Author Information Institut für Chemie der Freien Universität Berlin Takustrasse 3, D-14195, Berlin, Germany Institute Physics, St. Petersburg State...

Using liquid state 1H, 2H and 19F NMR spectroscopy in the temperature range 110–130 K we have studied hydrogen-bonded anions (FH)2F− (FH)3F− their partially fully deuterated analogs dissolved low-freezing freon mixture CDF3/CDF2Cl, presence of (C4H9)4N+ as counter cation. The spin multiplets three isotopologs HH, HD, DD (FH)2F−, four HHH, HHD, HDD, DDD been resolved assigned. Thus, were able to determine zero-, one- two-bond H/D isotope effects on hydrogen fluorine chemical shifts well...

In this paper, equations are proposed which relate various NMR parameters of OHN hydrogen-bonded pyridine-acid complexes to their bond valences in turn correlated with hydrogen-bond geometries. As the valence model is strictly valid only for weak hydrogen bonds appropriate empirical correction factors take into account anharmonic zero-point energy vibrations. The different and ODN depend on whether a double or single well potential realized strong regime. One factor was determined from known...

The 1H and 15N NMR spectra of several 15N-labeled pyridoxal-5'-phosphate model systems have been measured at low temperature in various aprotic protic solvents different polarity, i.e., dichloromethane-d2, acetonitrile-d3, tetrahydrofuran-d8, freon mixture CDF3/CDClF2, methanol. In particular, the 5'-triisopropyl-silyl ether N-(pyridoxylidene)-tolylamine (1a), N-(pyridoxylidene)-methylamine (2a), Schiff base with 15N-2-methylaspartic acid (3a) their complexes proton donors such as...

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTFormation of Charge Relay Chains between Acetic Acid and Pyridine Observed by Low-Temperature Nuclear Magnetic ResonanceNikolai S. Golubev, Sergei N. Smirnov, Vladimir A. Gindin, Gleb Denisov, Hans Benedict, Hans-Heinrich LimbachCite this: J. Am. Chem. Soc. 1994, 116, 26, 12055–12056Publication Date (Print):December 1, 1994Publication History Published online1 May 2002Published inissue 1 December...

Using 15N NMR spectroscopy and hydrogen bond correlations, we have localized a mechanistically critical proton in aspartate aminotransferase microcrystals aqueous solution. It is H-bond between carboxylate O of Asp222 the pyridine nitrogen pyridoxal-5'-phosphate. At neutral pH water, are unprotonated, but they share enzyme. shown that such binuclear base typical for acid−base interactions aprotic polar solvents. Active site H-bonds to assist protonation enzyme, which considered prerequisite...