Matrix IR studies on hydrogen-bonded complexes of hydrogen chloride and hydrogen bromide with ketene

Infrared spectra of matrices codeposited Ar/HX (X=Cl, Br) with Ar/H₂CCO mixtures have been examined. Isotopic substitutions (HX, DX, H₂CCO, D₂CCO) showed that ketene formed the 1:1 hydrogen-bonded complex with HX. The HX stretching modes were observed at 2684 cm⁻¹ in the H₂CCO–HCl complex and at 2384 cm⁻¹ in the H₂CCO–HBr complex. The ν₁ modes of the ketene submolecules were shifted to low frequency and the ν₉ modes to high frequency. It was proposed for the structure of the complex that the acid proton is bonded to the C=C pi electron system.     

1H/2H NMR studies of geometric H/D isotope effects on the coupled hydrogen bonds in porphycene derivatives

The 1H and 2H NMR spectra of porphycene (1), 2,3,6,7,12,13,16,17-octaethylporphycene (2), 2,7,12,17-tetra-n-propylporphycene (3), and 2,7,12,17-tetra-(tert-butyl)-3,6-13,16-dibenzo[cde;mno]porphycene (4) partially deuterated in the mobile proton sites are reported. These compounds exhibit two intramolecular NHN hydrogen bonds of increasing strength representing models of the concerted HH transfer in the parent compound, porphycene. The 1H chemical shifts of the mobile protons are correlated with the difference of the energies of the amino- and imino-N1s orbitals reported by Ghosh A.; Moulder J.; Br?ring M.; Vogel E. Angew. Chem., Int. Ed. 2001, 113, 445-448. The chemical shifts of 4 indicate a reduced contribution of the aromatic ring current as compared to the other compounds which is associated to the nonplanarity of this molecule. The primary H/D isotope effects on the chemical shifts give information about the primary, secondary, and vicinal geometric isotope effects of the two inner hydrogen bonds of porphycenes. The vicinal effects indicate a cooperative coupling of the two hydrogen bonds which may favor a concerted double proton-transfer mechanism.     

<Superscript>1</Superscript>H NMR study on microstructure of a novel acrylamide/methacrylic acid template copolymer in aqueous solution

A novel acrylamide/methacrylic acid template copolymer was prepared using polyallylammonium chloride (PAAC) as a template. This copolymer contains acrylamide (PAM), phenoxy acrylate (POA), and acylic acid (PAA) blocks. The investigation by high resolution nuclear magnetic resonance (¹H NMR) shows that intramolecular hydrogen bonds between the PAM and PAA blocks lead to compact molecular arrangement at quite low pH values, and the motion of the phenoxy side chain of the POA blocks is somewhat restricted. With the increase in pH value of the solution, the carboxylic acid of the PAA block gradually dissociates, which weakens hydrogen bonds between the PAM and PAA blocks. The decrease in D _w, self-diffusion coefficient of water, indicates the growth in aggregate size of the template copolymer. The cross peaks between amide protons and backbone protons shown in 2D nuclear overhauser spectroscopy (NOESY) spectra imply the existence of the intermolecular hydrogen bonding interaction between PAM and PAA blocks. After the carboxylic acid of the PAA block is completely dissociated in alkaline solution, the electrostatic repulsion of the carboxylic ion makes the molecular chain of the copolymer exhibit more outstretched. Consequently, the phenoxy groups (the side chain of the POA block) have more space to move.     

New deuterium isotope effects on C and F chemical shifts across intramolecular hydrogen bonds of non-resonance assisted systems

A series of thioanilides and corresponding anilides, some of which contain fluorinated phenyl rings, have been synthesized as model compounds. They all contain rather strong intramolecular hydrogen bonds, the strength of which varies. Deuterium isotope effects on ¹⁹F and ¹³C chemical shifts due to deuteriation at the NH proton show interesting new long-range isotope effects on chemical shifts that may be related to the existence of an intramolecular hydrogen bond and to transmission of the isotope effect due to an electric field effect. Deuterium isotope effects on chemical shifts report on variations in hydrogen bonding, for example, as a function of changes in substituents or temperature. Deuteriation leads to a strengthening of the hydrogen bond.     

13C isotope effects on 1H chemical shifts: NMR spectral analysis of 13C‐labelled D‐glucose and some 13C‐labelled amino acids

The one‐ and two‐bond ¹³C isotope shifts, typically ?1.5 to ?2.5 ppb and ?0.7 ppb respectively, in non‐cyclic aliphatic systems and up to ?4.4 ppb and ?1.0 ppb in glucose cause effects that need to be taken into account in the adaptive NMR spectral library‐based quantification of the isotopomer mixtures. In this work, NMR spectral analyses of some ¹³C‐labelled amino acids, D ‐glucose and other small compounds were performed in order to obtain rules for prediction of the ¹³C isotope effects on ¹H chemical shifts. It is proposed that using the additivity rules, the isotope effects can be predicted with a sufficient accuracy for amino acid isotopomer applications. For glucose the effects were found strongly non‐additive. The complete spectral analysis of fully ¹³C‐labelled D ‐glucose made it also possible to assign the exocyclic proton signals of the glucose. Copyright © 2009 John Wiley & Sons, Ltd.     

Quantitative 2H NMR spectroscopy. 1. Thermodynamic H/D isotope effects in N,N-dimethylformamide and cyclopentadiene molecules

A new method for quantification of the relative distribution of deuterium in molecules is proposed. The technique is based on the lineshape analysis in the ²H NMR spectra obtained at the natural abundance level of deuterium with allowance for inhomogeneity of the magnetic field. The equilibrium thermodynamic H/D isotope effects for hindered rotation about the C—N bond in the N,N-dimethylformamide molecule and for prototropic exchange in the cyclopentadiene molecule were determined. The results obtained agree with those of DFT calculations of the vibrational energies.     

Diastereoisomerism of thiol complexes of arsenic acids and pseudoasymmetry of arsenic: a 1H and 13C NMR study

Diastereoisomeric complexes of methylphenylarsinic acid and (L)-glutathione could be partially separated by HPLC, but the separated compounds rapidly racemized, presumably by pyramidal inversion at the arsenic atom. Hydrolysis of the diastereoisomeric complexes yielded methylphenylarsinous acid as a pair of enantiomers revealed by a 1H NMR study with an asymmetric lanthanide shift reagent. Methylphenylarsinous acid was also synthesized as an enantiomeric pair, shown by an asymmetric shift reagent experiment, by the hydrolysis of iodomethylphenylarsine. 1H and 13C NMR spectroscopy were used to demonstrate that complexing of phenylarsonic acid with (R,S)-3-mercapto-1,2-propanediol and with (R,S)-1-mercapto-2-propanol yielded, in each case, a pair of enantiomers, PhAs[(R)-ligand)]2, PhAs[(S)-ligand)]2, in which the homomorphic ligands were diastereotopic, and a pair of diastereoisomers, PhAs[(R)-ligand][(S)-ligand], which differed from each other in the configuration about the pseudoasymmetric arsenic atom.     

Competition between π–π stacking and hydrogen bonding in (1:2) picrates of 1,5-diamino-3-oxapentane, 1,8-diamino-3,6-dioxaoctane and 1,5-diamino-3-azapentane—solid state studies

Crystallographic studies of (2:1) salts of picric acid with 1,5-diamino-3-oxapentane (1OPICR), 1,8-diamino-3,6-dioxaoctane (2OPICR) and 1,5-diamino-3-azapentane (1NPICR) showed significant conformational change of the picrate ion due to numerous electrostatic, H-bonding and π–π stacking interactions present in the crystal lattice. In particular, intermolecular N–HO H-bonds were found to cause significant twisting of the o-NO₂ groups from the plane of the benzene ring, whereas overlapping of the picrate ions due to electrostatic interactions and π–π stacking caused flattening of the molecule. Analysis of the geometry of 74 picrate ions found in the Cambridge Crystallographic Database, in their various crystallochemical environments, showed that competition between essentially weak but numerous intermolecular interactions of different types led to systematic changes in geometric parameters within the picrate ion. In particular, relations found between the C1–C2–N–O (C1–C6–N–O) torsion angle and the endocyclic C1–C2–C3 (C1–C6–C5) valence angle can be explained on the basis of competition between resonance effects of the o-NO₂ group and π–π stacking.     

Diffusion of hydrogen isotopes and their mutual perturbation in Ti0.33V0.67HxDy (x+y≈0.9) studied by H and H NMR

Ti_0.33V_0.67H_xD_y (x+y≈0.9) alloys have been studied by means of X-ray powder diffraction (XRD), differential scanning calorimetry (DSC) and ¹H and ²H NMR. The crystal structures are body-centered-cubic (bcc) dominantly, being mixed with a face-centered-cubic (fcc) phase. A phase transition similar to that from the δ_D phase to the α_D phase in the V-D system is observed in all the samples except for the protide. H and D are considered to occupy tetrahedral sites. The temperature and frequency dependence of spin-lattice relaxation times T₁ of ¹H and ²H has been analyzed by Bloembergen-Purcell-Pound equations with a distribution of correlation times, and parameters of hydrogen diffusion are estimated. The mean activation energy for D diffusion (E_D) is higher than that for H diffusion (E_H). E_H is constant while E_D increases slightly with the [D]/[H] ratio. The distribution of the correlation times increases as the [D]/[H] ratio decreases.     

Influence of number of calibration standards within a defined range on pharmacokinetic disposition—case studies with omeprazole and clopidogrel carboxylic acid

While the practice of using a smaller number of non‐zero standards (typically seven to eight) has not been entertained in routine bioanalytical work, it is important to innovate and be pragmatic about minimizing the number of calibration standards to promote cost‐effective and speedy assessment. In this exercise, two important compounds, omeprazole and clopidogrel carboxylic acid, were considered. Additionally, both analytes offered a 1000‐fold calibration curve range with eight non‐zero standards to permit a systematic evaluation. Accordingly various scenarios of post‐hoc analysis of the calibration data were formulated which included step‐wise reduction of the number of calibration standards from a maximum of n = 8 to a minimum of n = 3. In all the scenarios evaluated in this exercise, a calibration curve was reconstructed and both quality control samples and in vivo pharmacokinetics were calculated in each instance. Based on the data generated in this exercise, a minimum of three non‐zero calibration standards were adequate to predict the quality control samples with the predefined accuracy and precision estimates for both omeprazole and clopidogrel carboxylic acid. Additionally, the in vivo pharmacokinetic characterization of the chosen compounds was not hampered by the reduction of calibration standards (from n = 8 to n = 3). Hence, consideration for reducing number of calibration standards in bioanalytical work may provide a viable alternative in several situations such as formulation screening strategies, routine therapeutic drug monitoring and sparse sample analyses. Copyright © 2009 John Wiley & Sons, Ltd.     

Gold(III)‐Induced Oxidation of Amino Acids and Malonic Acid: Reaction Pathways Studied by NMR Spectroscopy with Isotope Labelling

Reactions of Au(III) with biomolecules are of interest in relation to understanding the mechanism of action of therapeutic gold compounds. NMR investigations of ¹³C and ¹⁵N isotopically‐labelled glycine and alanine show that Au(III) induces deamination and subsequent decarboxylation of both amino acids with the same mechanism. For comparison, reactions of Au(III) with sarcosine and the dicarboxylic acid malonic acid were also investigated. The major intermediates and products have been identified.     

Syntheses and characterization of triorganotin complexes: X-ray crystallographic study of triorganotin pyridinedicarboxylates with trinuclear, 1D polymeric chain and 2D network structures

A series of new triorganotin(IV) pyridinedicarboxylates [(C₂H₅)₃NH][(Me₃Sn)₃(2,6-pdc)₂(H₂O)₂] (1), [(C₂H₅)₃NH][(Ph₃Sn)₃(2,6-pdc)₂(H₂O)₂] (2), [(C₂H₅)₃NH]{[(PhCH₂)₃Sn]₃(2,6-pdc)₂(H₂O)₂} (3), [Me₃Sn(3,5-pdc)]_n (4), [Ph₃Sn(3,5-pdc)]_n (5), [(PhCH₂)₃Sn(3,5-pdc)]_n (6), [(Me₃Sn)₂(2,5-pdc)]_n (7), [(Ph₃Sn)₂(2,5-pdc)]_n (8) and {[(PhCH₂)₃Sn]₂(2,5-pdc)}_n (9) were synthesized by the reaction of trimethyltin(IV), triphenyltin(IV) or tribenzyltin(IV) chloride with 2,6(3,5 or 2,5)-H₂pdc (pdc = pyridinedicarboxylate) when triethylamine was added. Complexes 1-9 have been characterized by elemental, IR, ¹H, ¹³C and ¹¹⁹Sn NMR analyses. Among them complexes 1, 5 and 7 have also been characterized by X-ray crystallographic diffraction analyses. Complex 1 has a trinuclear structure and forms a 2D supramolecular structure due to the coordinated water molecules via hydrogen bonds to the pendant O atoms of the carboxyl groups and the N atoms derived of the pyridine ring. Complex 5 forms a 1D polymeric chain by the intermolecular Sn?N (N atom derived of pyridine ring) interactions. Complex 7 has a network structure where 2,5-pyridinedicarboxylate acts as a tetradentate ligand coordinated to trimethyltin(IV) ions.     

1H, 13C and 31P NMR spectral analysis of monoalkyl (α‐anilinobenzyl)phosphonates and their dipalladium(II) metallocyclic complexes

A ¹H, ¹³C and ³¹P NMR study of monoethyl (HL1) and monobutyl (HL2) esters of (α‐anilinobenzyl)phosphonic acid and their metallocyclic dipalladium complexes (Pd₂L₄,L = L1, L2) in DMSO‐d₆ was performed, based on 1D and 2D homo‐ and heteronuclear experiments including ¹H,¹³C,³¹P,APT,¹H–¹H COSY, ¹H–¹³C COSY, gs‐HMQC and gs‐HMBC NMR techniques. The results obtained are discussed with respect to those for some palladium(II) complexes reported for various anilinobenzylphosphonate derivatives. Copyright © 2002 John Wiley & Sons, Ltd.     

Stereoelectronic and inductive effects on 1H and 13C NMR chemical shifts of some cis-1,3-disubstituted cyclohexanes

This work presents the substituent effects on the 1H and 13C NMR chemical shifts in the cis-isomer of 3-Y-cyclohexanols (Y = Cl, Br, I, CH3, N(CH3)2 and OCH3) and 3-Y-1-methoxycyclohexanes (Y = F, Cl, Br, I, CH3, N(CH3)2 and OCH3). It was observed that the H-3 chemical shift, due to the substituent alpha-effect, increases with the increase of substituent electronegativity when Y is from the second row of the periodic table of elements, (CH3 *sigma(C3--H3a) interaction energy. This interaction energy, for the halogenated compounds, decreases with an increase in size of the halogen, and this is a possible reason for the largest measured chemical shift for H-3 of the iodo-derivatives. The beta-effect of the analyzed compounds showed that the chemical shift of hydrogens at C-2 and C-4 increases with the decrease of n(Y) --> *sigma(C2-C3) and n(Y) --> *sigma(C3-C4) interaction energies, respectively, showing a behavior similar to H-3. The alpha-effect on 13C chemical shifts correlates well with substituent electronegativity, while the beta-effect is inversely related to electronegativity in halogenated compounds. NBO analysis indicated that the substituent inductive effect is the predominant effect on 13C NMR chemical shift changes for the alpha-carbon. It was also observed that C-2 and C-4 chemical shifts for compounds with N(CH3)2, OCH3 and F are more shielded in comparison to the compounds having a halogen, most probably because of the larger interaction of the lone pair of more electronegative atoms (n(N) > n(O) > n(F)) with *sigma(C2-C3), *sigma(C3-C4) and *sigma(C3-H3a) in comparison with the same type of interaction with the lone pair of the other halogens.     

1H and 13C NMR signal assignments of carboxyl‐linked glucosides of bile acids

Complete ¹H and ¹³C resonance assignments were carried out for a new type of carboxyl‐linked glucosides of chenodeoxycholic (3α,7α‐dihydroxy‐5β‐cholan‐24‐oic) and hyodeoxycholic (3α,6α‐dihydroxy‐5β‐cholan‐24‐oic) acids by using several homonuclear (¹H–¹H) and heteronuclear (¹H–¹³C) 2D NMR techniques. Differences in the ¹H and ¹³C resonances between the α‐ and β‐anomers of the ester glucosides of bile acids were clarified for the first time. A comparison of the ¹H and ¹³C signal shifts induced by β‐D ‐glucosidation at the 24‐carboxyl and 3α‐hydroxyl groups in the parent 5β‐cholanoic acid was also made. Copyright © 2003 John Wiley & Sons, Ltd.     

Structural role of hydrogen bond networks in amino acid–acid systems. (I) The network with highly polarizable OHO hydrogen bonds in sarcosine–methanesulfonic acid (2:1) crystal

The sarcosine–methanesulfonic acid (2:1) crystal was selected for examination of two problems: relations between different components of the amino acid–acid hydrogen bond network and a role of very strong and highly polarizable OHO hydrogen bond in the main structural units of the crystal: sarcosinium–sarcosine dimers (complexes). Our observations are based on phase transitions of the crystal monitored by DSC, X-ray diffraction and temperature evolutions of selected bands of IR spectra. Our experimental and DFT results provide information on the potential energy profile of the OHO proton and its evolution with temperature. The OO distance of the primary hydrogen bond remains almost unchanged and its proton is strongly delocalized and sensitive on neighbour NHO hydrogen bond. We propose a possible mechanism of the phase transitions and coupling between νCO vibrations of the carboxyl group and moving of the proton in neighbour OHO hydrogen bridge.     

Inverse Ubbelohde effect in the short hydrogen bond of photosystem II: Relation between H/D isotope effect and symmetry in potential energy profile

The short hydrogen bond between tyrosine Y_z and D1‐His190 of photosystem II (PSII) was investigated using multicomponent quantum mechanics, where the quantum fluctuation of a hydrogen nucleus was incorporated into electronic structure calculation. Our computation demonstrated that the deuteration for hydrogen in the short hydrogen bond of PSII led to the reduction of the O…N distance. It indicated an inverse Ubbelohde effect typically recognized in strong and symmetric hydrogen‐bonding clusters such as FHF^– and . We confirmed that the relation between the geometric isotope effect and the symmetry of the potential energy profile of FHF^– was reasonably agreed with that of PSII. According to this agreement, the short hydrogen bond in PSII can be regarded as a short strong hydrogen bond. © 2016 Wiley Periodicals, Inc.     

Solvent isotope effects on the complexation and exchange kinetics of Tl(I), K and Na with 18-crown-6 by competitive NMR spectroscopy: Competition between homo- and heterobimolecular cations exchange

The thermodynamic properties of complexation and exchange kinetics of thallium by 18-crown-6 have been studied by thallium NMR spectroscopy. Effects of solvent isotope, counterion (ClO₄⁻ and NO₃⁻) and presence of competitive cations, such as Na⁺ and K⁺, on the exchange characteristics of the system have been considered. The obvious relationships between the effects of D₂O-H₂O solvent isotope on the thermodynamic properties and activation parameters of complexation have been investigated. In the absence of competitor cations, the mechanism of thallium exchange is unimolecular decomplexation and in the presence of competitor cations, homobimolecular cation exchange is the predominant mechanism at low concentrations of the ligand. At higher concentrations of the ligand, the measured rate constants show that the complexation/decomplexation process obeys a heterobimolecular cation interchange mechanism. The rate constants ratios (k_D2O/k_H2O < 1) for unimolecular mechanisms also show an inverse solvent isotope effect.     

99Tc NMR as a promising technique for structural investigation of biomolecules: theoretical studies on the solvent and thermal effects of phenylbenzothiazole complex

The phenylbenzothiazole compounds show antitumor properties and are highly selective. In this paper, the ⁹⁹Tc chemical shifts based on the (^99mTc)(CO)₃(NNO) complex conjugated to the antitumor agent 2‐(4′‐aminophenyl)benzothiazole are reported. Thermal and solvent effects were studied computationally by quantum‐chemical methods, using the density functional theory (DFT) (DFT level BPW91/aug‐cc‐pVTZ for the Tc and BPW91/IGLO‐II for the other atoms) to compute the NMR parameters for the complex. We have calculated the ⁹⁹Tc NMR chemical shifts of the complex in gas phase and solution using different solvation models (polarizable continuum model and explicit solvation). To evaluate the thermal effect, molecular dynamics simulations were carried, using the atom‐centered density matrix propagation method at the DFT level (BP86/LanL2dz). The results highlight that the ⁹⁹Tc NMR spectroscopy can be a promising technique for structural investigation of biomolecules, at the molecular level, in different environments. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis, Characterization and Crystal Structure of [Na2(APZC)2(μ-H2O)2(μ3-H2O)]n

The synthesis and spectroscopic properties of a Na^＋ complex with ligand 3-aminopyrazine-2-carboxylic acid were described. The resulting complex was characterized by elemental analysis, IR, UV-Vis, NMR spectroscopy and single crystal X-ray diffraction method. The title compound crystallizes in the triclinic system with space group . The crystalline structure of this compound consists of supramolecular architectures involving strong intramolecular N—H…O in pyrazine molecules and intermolecular O—H…N, O—H…O, and N—H…N hydrogen bonds between substituted pyrazine and water molecules.