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Hansen PE, Vakili M, Kamounah FS, Spanget-Larsen J. NH Stretching Frequencies of Intramolecularly Hydrogen-Bonded Systems: An Experimental and Theoretical Study. Molecules 2021; 26:molecules26247651. [PMID: 34946735 PMCID: PMC8706864 DOI: 10.3390/molecules26247651] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2021] [Revised: 12/10/2021] [Accepted: 12/13/2021] [Indexed: 11/25/2022] Open
Abstract
The vibrational NH stretching transitions in secondary amines with intramolecular NH···O hydrogen bonds were investigated by experimental and theoretical methods, considering a large number of compounds and covering a wide range of stretching wavenumbers. The assignment of the NH stretching transitions in the experimental IR spectra was, in several instances, supported by measurement of the corresponding ND wavenumbers and by correlation with the observed NH proton chemical shifts. The observed wavenumbers were correlated with theoretical wavenumbers predicted with B3LYP density functional theory, using the basis sets 6-311++G(d,p) and 6-31G(d) and considering the harmonic as well as the anharmonic VPT2 approximation. Excellent correlations were established between observed wavenumbers and calculated harmonic values. However, the correlations were non-linear, in contrast to the results of previous investigations of the corresponding OH···O systems. The anharmonic VPT2 wavenumbers were found to be linearly related to the corresponding harmonic values. The results provide correlation equations for the prediction of NH stretching bands on the basis of standard B3LYP/6-311++G(d,p) and B3LYP/6-31G(d) harmonic analyses, with standard deviations close to 38 cm−1. This is significant because the full anharmonic VPT2 analysis tends to be impractical for large molecules, requiring orders of magnitude more computing time than the harmonic analysis.
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Affiliation(s)
- Poul Erik Hansen
- Department of Science and Environment, Roskilde University, Universitetsvej 1, DK-4000 Roskilde, Denmark
- Correspondence: (P.E.H.); (J.S.-L.); Tel.: +45-4674-2432 (P.E.H.); +45-4674-2710 (J.S.-L.)
| | - Mohammad Vakili
- Department of Chemistry, Faculty of Science, Ferdowsi University of Mashhad, Mashhad 91775-1436, Iran;
| | - Fadhil S. Kamounah
- Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen, Denmark;
| | - Jens Spanget-Larsen
- Department of Science and Environment, Roskilde University, Universitetsvej 1, DK-4000 Roskilde, Denmark
- Correspondence: (P.E.H.); (J.S.-L.); Tel.: +45-4674-2432 (P.E.H.); +45-4674-2710 (J.S.-L.)
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2
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Perrin CL, Shrinidhi A, Burke KD. Isotopic-Perturbation NMR Study of Hydrogen-Bond Symmetry in Solution: Temperature Dependence and Comparison of OHO and ODO Hydrogen Bonds. J Am Chem Soc 2019; 141:17278-17286. [PMID: 31590490 DOI: 10.1021/jacs.9b08492] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Is a hydrogen bond symmetric, with the hydrogen centered between two donor atoms, or is it asymmetric, with the hydrogen closer to one but jumping to the other? The NMR method of isotopic perturbation has been used to distinguish these. Previous evidence from isotope shifts implies that a wide variety of dicarboxylate monanions are asymmetric, present as a rapidly equilibrating mixture of tautomers. However, calculations of hydrogen trajectories across an anharmonic potential-energy surface could reproduce the observed isotope shifts in a phthalate monoanion. Therefore, it was concluded that those isotope shifts are instead consistent with isotope-induced desymmetrization on a symmetric potential-energy surface. To distinguish between these two interpretations, the 18O-induced isotope effects on the 13C NMR chemical shifts of cyclohexene-1,2-dicarboxylate monoanion in chloroform-d and on the 19F NMR chemical shifts of difluoromaleate monoanion in D2O have been investigated. In both cases the isotope effects are larger at lower temperature and also with deuterium in the hydrogen bond. It is concluded that these behaviors are consistent with the perturbation of an equilibrium between asymmetric tautomers and inconsistent with isotope-induced desymmetrization on a symmetric potential-energy surface.
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Affiliation(s)
- Charles L Perrin
- Department of Chemistry and Biochemistry , University of California-San Diego , La Jolla , California 92093-0358 , United States
| | - Annadka Shrinidhi
- Department of Chemistry and Biochemistry , University of California-San Diego , La Jolla , California 92093-0358 , United States
| | - Kathryn D Burke
- Department of Chemistry and Biochemistry , University of California-San Diego , La Jolla , California 92093-0358 , United States
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3
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Seyedkatouli S, Vakili M, Tayyari SF, Hansen PE, Kamounah FS. Molecular structure and intramolecular hydrogen bond strength of 3-methyl-4-amino-3-penten-2-one and its N Me and N-Ph substitutions by experimental and theoretical methods. J Mol Struct 2019. [DOI: 10.1016/j.molstruc.2019.02.007] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
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4
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Hansen PE, Spanget-Larsen J. NMR and IR Investigations of Strong Intramolecular Hydrogen Bonds. Molecules 2017; 22:E552. [PMID: 28353675 PMCID: PMC6154318 DOI: 10.3390/molecules22040552] [Citation(s) in RCA: 70] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2017] [Revised: 03/20/2017] [Accepted: 03/24/2017] [Indexed: 11/24/2022] Open
Abstract
For the purpose of this review, strong hydrogen bonds have been defined on the basis of experimental data, such as OH stretching wavenumbers, νOH, and OH chemical shifts, δOH (in the latter case, after correction for ring current effects). Limits for O-H···Y systems are taken as 2800 > νOH > 1800 cm-1, and 19 ppm > δOH > 15 ppm. Recent results as well as an account of theoretical advances are presented for a series of important classes of compounds such as β-diketone enols, β-thioxoketone enols, Mannich bases, proton sponges, quinoline N-oxides and diacid anions. The O···O distance has long been used as a parameter for hydrogen bond strength in O-H···O systems. On a broad scale, a correlation between OH stretching wavenumbers and O···O distances is observed, as demonstrated experimentally as well as theoretically, but for substituted β-diketone enols this correlation is relatively weak.
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Affiliation(s)
- Poul Erik Hansen
- Department of Science and Environment, Roskilde University, Universitetsvej 1, P.O. Box 260, DK-4000 Roskilde, Denmark.
| | - Jens Spanget-Larsen
- Department of Science and Environment, Roskilde University, Universitetsvej 1, P.O. Box 260, DK-4000 Roskilde, Denmark.
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5
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Bew SP, Stephenson GR, Rouden J, Godemert J, Seylani H, Martinez-Lozano LA. Gaining Insight Into Reactivity Differences Between Malonic Acid Half Thioesters (MAHT) and Malonic Acid Half Oxyesters (MAHO). Chemistry 2017; 23:4557-4569. [DOI: 10.1002/chem.201605148] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2016] [Indexed: 01/15/2023]
Affiliation(s)
- Sean P. Bew
- School of Chemistry; Norwich Research Park; University of East Anglia; NR4 7TJ UK
| | | | - Jacques Rouden
- Laboratoire de Chimie Moleculaire et thio-organique (LCMT); UMR CNRS 6507, Ensicaen; 6 Boulevard du Marechal Juin 14050 Caen France
| | - Jeremy Godemert
- School of Chemistry; Norwich Research Park; University of East Anglia; NR4 7TJ UK
| | - Haseena Seylani
- School of Chemistry; Norwich Research Park; University of East Anglia; NR4 7TJ UK
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6
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Ignaczak A, Porwański S, Szyszka M. Deeper insight into the properties of the newly synthesized macrocycles as drug receptors – some preliminary quantum chemical studies. NEW J CHEM 2017. [DOI: 10.1039/c6nj03089k] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We present the results of our experimental and theoretical studies on 1,10-N,N′-bis-(β-d-ureidocellobiosyl)-4,7,13-trioxa-1,10-diazacyclopentadecane, its complex with aspirin and the corresponding host–guest interactions.
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Affiliation(s)
- Anna Ignaczak
- Department of Theoretical and Structural Chemistry
- Faculty of Chemistry
- University of Lodz
- Pomorska 163/165
- Poland
| | - Stanisław Porwański
- Department of Organic and Applied Chemistry
- Faculty of Chemistry
- University of Lodz
- 91-403 Łódź
- Poland
| | - Michalina Szyszka
- Department of Organic and Applied Chemistry
- Faculty of Chemistry
- University of Lodz
- 91-403 Łódź
- Poland
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7
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Noroozi Pesyan N, Rashidnejad H. Isotopic splitting patterns in the (13) C NMR spectra of some partially deuterated 1-aryl-2-(phenyldiazenyl)butane-1,3-dione and 4-hydroxy-3-(phenyldiazenyl)-2H-chromen-2-one: evidence for elucidation of tautomeric forms. MAGNETIC RESONANCE IN CHEMISTRY : MRC 2016; 54:358-364. [PMID: 26776053 DOI: 10.1002/mrc.4390] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/01/2015] [Revised: 10/20/2015] [Accepted: 10/29/2015] [Indexed: 06/05/2023]
Abstract
Nuclear magnetic resonance spectra of synthesized azo dyes derived from aniline derivatives in reaction with benzoylacetone and 4-hydroxycoumarin were studied in both CDCl3 and (CD3 )2 SO (two drops of D2 O were added into solutions of dyes). All dyes showed intramolecular hydrogen bonding. Dyes derived from o-nitro aniline in the reaction with benzoylacetone, and 4-hydroxycoumarin showed bifurcated intramolecular hydrogen bonds. The solvent-substrate proton exchange of dyes derived from benzoylacetone and 4-hydroxycoumarin was examined in the presence of two drops of D2 O. Among ten dye samples, two dyes derived from benzoylacetone did not show deuteration, three dyes showed partial deuteration and five dyes showed full deuteration under similar conditions. For the partially deuterated dyes the β-isotope effect in (13) C splitting was investigated and was used for the determination of the predominant tautomeric form.
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Affiliation(s)
- Nader Noroozi Pesyan
- Faculty of Chemistry, Department of Organic Chemistry, Urmia University, 57159, Urmia, Iran
| | - Hamid Rashidnejad
- Faculty of Chemistry, Department of Organic Chemistry, Urmia University, 57159, Urmia, Iran
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8
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Isotope effects on chemical shifts in the study of intramolecular hydrogen bonds. Molecules 2015; 20:2405-24. [PMID: 25647577 PMCID: PMC6272349 DOI: 10.3390/molecules20022405] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2014] [Revised: 12/17/2014] [Accepted: 01/05/2015] [Indexed: 11/16/2022] Open
Abstract
The paper deals with the use of isotope effects on chemical shifts in characterizing intramolecular hydrogen bonds. Both so-called resonance-assisted (RAHB) and non-RAHB systems are treated. The importance of RAHB will be discussed. Another very important issue is the borderline between “static” and tautomeric systems. Isotope effects on chemical shifts are particularly useful in such studies. All kinds of intramolecular hydrogen bonded systems will be treated, typical hydrogen bond donors: OH, NH, SH and NH+, typical acceptors C=O, C=N, C=S C=N−. The paper will be deal with both secondary and primary isotope effects on chemical shifts. These two types of isotope effects monitor the same hydrogen bond, but from different angles.
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9
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Platzer G, Okon M, McIntosh LP. pH-dependent random coil (1)H, (13)C, and (15)N chemical shifts of the ionizable amino acids: a guide for protein pK a measurements. JOURNAL OF BIOMOLECULAR NMR 2014; 60:109-129. [PMID: 25239571 DOI: 10.1007/s10858-014-9862-y] [Citation(s) in RCA: 149] [Impact Index Per Article: 14.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/29/2014] [Accepted: 09/09/2014] [Indexed: 06/03/2023]
Abstract
The pK a values and charge states of ionizable residues in polypeptides and proteins are frequently determined via NMR-monitored pH titrations. To aid the interpretation of the resulting titration data, we have measured the pH-dependent chemical shifts of nearly all the (1)H, (13)C, and (15)N nuclei in the seven common ionizable amino acids (X = Asp, Glu, His, Cys, Tyr, Lys, and Arg) within the context of a blocked tripeptide, acetyl-Gly-X-Gly-amide. Alanine amide and N-acetyl alanine were used as models of the N- and C-termini, respectively. Together, this study provides an essentially complete set of pH-dependent intra-residue and nearest-neighbor reference chemical shifts to help guide protein pK a measurements. These data should also facilitate pH-dependent corrections in algorithms used to predict the chemical shifts of random coil polypeptides. In parallel, deuterium isotope shifts for the side chain (15)N nuclei of His, Lys, and Arg in their positively-charged and neutral states were also measured. Along with previously published results for Asp, Glu, Cys, and Tyr, these deuterium isotope shifts can provide complementary experimental evidence for defining the ionization states of protein residues.
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Affiliation(s)
- Gerald Platzer
- Department of Biochemistry and Molecular Biology, Life Sciences Centre, 2350 Health Sciences Mall, University of British Columbia, Vancouver, BC, V6T 1Z3, Canada
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10
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Impact of metal cation complexation and protonation on tautomeric and resonance forms of the oxaalkyl Schiff bases derived from 5-substituted salicylaldehyde and 2-hydroxy-1-naphthlaldehyde. Struct Chem 2014. [DOI: 10.1007/s11224-014-0447-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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11
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Perrin CL, Burke KD. Variable-temperature study of hydrogen-bond symmetry in cyclohexene-1,2-dicarboxylate monoanion in chloroform-d. J Am Chem Soc 2014; 136:4355-62. [PMID: 24527684 DOI: 10.1021/ja500174y] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The symmetry of the hydrogen bond in hydrogen cyclohexene-1,2-dicarboxylate monoanion was determined in chloroform using the NMR method of isotopic perturbation. As the temperature decreases, the (18)O-induced (13)C chemical-shift separations increase not only at carboxyl carbons but also at ipso (alkene) carbons. The magnitude of the ipso increase is consistent with an (18)O isotope effect on carboxylic acid acidity. Therefore it is concluded that this monoanion is a mixture of tautomers in rapid equilibrium, rather than a single symmetric structure in which a chemical-shift separation arises from coupling between a desymmetrizing vibration and anharmonic isotope-dependent vibrations, which is expected to show the opposite temperature dependence.
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Affiliation(s)
- Charles L Perrin
- Department of Chemistry, University of California-San Diego , La Jolla, California 92093-0358, United States
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Pietrzak M, Grech E, Nowicka-Scheibe J, Hansen PE. Deuterium isotope effects on 13C chemical shifts of negatively charged NH…N systems. MAGNETIC RESONANCE IN CHEMISTRY : MRC 2013; 51:683-688. [PMID: 24038402 DOI: 10.1002/mrc.4000] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/05/2013] [Revised: 06/21/2013] [Accepted: 07/22/2013] [Indexed: 06/02/2023]
Abstract
Deuterium isotope effects on (13)C chemical shifts are investigated in anions of 1,8-bis(4-toluenesulphonamido)naphthalenes together with N,N-(naphthalene-1,8-diyl)bis(2,2,2-trifluoracetamide) all with bis(1,8-dimethylamino)napthaleneH(+) as counter ion. These compounds represent both "static" and equilibrium cases. NMR assignments of the former have been revised. The NH proton is deuteriated. The isotope effects on (13)C chemical shifts are rather unusual in these strongly hydrogen bonded systems between a NH and a negatively charged nitrogen atom. The formal four-bond effects are found to be negative indicating transmission via the hydrogen bond. In addition, unusual long range effects are seen. Structures, (1)H and (13)C NMR chemical shifts and changes in nuclear shieldings upon deuteriation are calculated using density functional theory methods.
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Affiliation(s)
- Mariusz Pietrzak
- Institute of Physical Chemistry, Polish Academy of Sciences, 01-224, Warsaw, Poland
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13
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Filarowski A, Hansen PE. Secondary Isotope Effects on 13C and 15N Chemical Shifts of Schiff Bases Revisited. ACTA ACUST UNITED AC 2013. [DOI: 10.1524/zpch.2013.0378] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Abstract
An analysis is presented of secondary deuterium isotope effects on 15N and 13C chemical shifts of the methylamine Schiff base of 4,6-dimethoxysalicylaldehyde. It is shown that for this compound existing as an equilibrium between an OH and a NH-form, the secondary isotope effects depend on the OH/NH ratio giving a function with a maximum and a minimum.
Secondary deuterium isotope effects on 13C and 15N chemical shifts are compared in a broader range of compounds and the above trend is confirmed. Changes in the dielectric constants of the medium with temperature are found to be rather unimportant for the change in equilibrium. Equilibrium isotope effects on chemical shifts are shown to be important. The magnitudes of the isotope effects are correlated both to intrinsic and equilibrium isotope effects. The latter correlate to the shape of the two-potential well, the energy difference and the difference in chemical shifts of the two tautomers.
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Honda H. ¹H-MAS-NMR chemical shifts in hydrogen-bonded complexes of chlorophenols (pentachlorophenol, 2,4,6-trichlorophenol, 2,6-dichlorophenol, 3,5-dichlorophenol, and p-chlorophenol) and amine, and H/D isotope effects on ¹H-MAS-NMR spectra. Molecules 2013; 18:4786-802. [PMID: 23609627 PMCID: PMC6270458 DOI: 10.3390/molecules18044786] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2013] [Revised: 04/12/2013] [Accepted: 04/18/2013] [Indexed: 11/17/2022] Open
Abstract
Chemical shifts (CS) of the ¹H nucleus in N···H···O type hydrogen bonds (H-bond) were observed in some complexes between chlorophenols [pentachlorophenol (PCP), 2,4,6-tricholorophenol (TCP), 2,6-dichlorophenol (26DCP), 3,5-dichlorophenol (35DCP), and p-chlorophenol (pCP)] and nitrogen-base (N-Base) by solid-state high-resolution ¹H-NMR with the magic-angle-spinning (MAS) method. Employing N-Bases with a wide range of pKa values (0.65-10.75), ¹H-MAS-NMR CS values of bridging H atoms in H-bonds were obtained as a function of the N-Base's pKa. The result showed that the CS values were increased with increasing pKa values in a range of DpKa < 0 [DpKa = pKa(N-Base)-pKa(chlorophenols)] and decreased when DpKa > 2: The maximum CS values was recorded in the PCP (pKa = 5.26)-4-methylpyridine (6.03), TCP (6.59)-imidazole (6.99), 26DCP (7.02)-2-amino-4-methylpyridine (7.38), 35DCP (8.04)-4-dimethylaminopyridine (9.61), and pCP (9.47)-4-dimethylaminopyridine (9.61) complexes. The largest CS value of 18.6 ppm was recorded in TCP-imidazole crystals. In addition, H/D isotope effects on ¹H-MAS-NMR spectra were observed in PCP-2-amino-3-methylpyridine. Based on the results of CS simulation using a B3LYP/6-311+G** function, it can be explained that a little changes of the N-H length in H-bond contribute to the H/D isotope shift of the ¹H-MAS-NMR peaks.
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Affiliation(s)
- Hisashi Honda
- Graduate School of Nanobioscience, Yokohama City University, Kanazawa-ku, Yokohama 236-0027, Japan.
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Perrin CL, Karri P, Moore C, Rheingold AL. Hydrogen-bond symmetry in difluoromaleate monoanion. J Am Chem Soc 2012; 134:7766-72. [PMID: 22519701 DOI: 10.1021/ja2117848] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The symmetry of the hydrogen bond in hydrogen difluoromaleate monoanion is probed by X-ray crystallography and by the NMR method of isotopic perturbation in water, in two aprotic organic solvents, and in an isotropic liquid crystal. The X-ray crystal structure of potassium hydrogen difluoromaleate shows a remarkably short O-O distance of 2.41 Å and equal O-H distances of 1.206 Å, consistent with a strong and symmetric hydrogen bond. Incorporation of (18)O into one carboxyl group allows investigation of the symmetry of the H-bond in solution by the method of isotopic perturbation. The (19)F NMR spectra of the mono-(18)O-substituted monoanion in water, CD(2)Cl(2), and CD(3)CN show an AB spin system, corresponding to fluorines in different environments. The difference is attributed to the perturbation of the acidity of a carboxylic acid by (18)O, not to the mere presence of the (18)O, because the mono-(18)O dianion shows equivalent fluorines. Therefore, it is concluded that the monoanion exists as an equilibrating pair of interconverting tautomers and not as a single symmetric structure not only in water but also in organic solvents. However, in the isotropic liquid crystal phase of 4-cyanophenyl 4-heptylbenzoate, tetrabutylammonium hydrogen difluoromaleate-(18)O shows equivalent fluorines, consistent with a single symmetric structure. These results support earlier studies, which suggested that the symmetry of hydrogen bonds can be determined by the local environment.
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Affiliation(s)
- Charles L Perrin
- Department of Chemistry, University of California-San Diego, La Jolla, California 92093-0358, USA.
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Abstract
In a symmetric hydrogen bond (H-bond), the hydrogen atom is perfectly centered between the two donor atoms. The energy diagram for hydrogen motion is thus a single-well potential, rather than the double-well potential of a more typical H-bond, in which the hydrogen is covalently bonded to one atom and H-bonded to the other. Examples of symmetric H-bonds are often found in crystal structures, and they exhibit the distinctive feature of unusually short length: for example, the O-O distance in symmetric OHO H-bonds is found to be less than 2.5 Å. In comparison, the O-O distance in a typical asymmetric H-bond, such as ROH···OR(2), ranges from about 2.7 to 3.0 Å. In this Account, we briefly review and update our use of the method of isotopic perturbation to search for a symmetric, centered, or single-well-potential H-bond in solution. Such low-barrier H-bonds are thought to be unusually strong, owing perhaps to the resonance stabilization of two identical resonance forms [A-H···B ↔ A···H-B]. This presumptive bond strength has been invoked to explain some enzyme-catalyzed reactions. Yet in solution, a wide variety of OHO, OHN, and NHN H-bonds have all been found to be asymmetric, in double-well potentials. Examples include the monoanion of (±)-2,3-di-tert-butylsuccinic acid and a protonated tetramethylnaphthalenediamine, even though these two ions are often considered prototypes of species with strong H-bonds. In fact, all of the purported examples of strong, symmetric H-bonds have been found to exist in solution as pairs of asymmetric tautomers, in contrast to their symmetry in some crystals. The asymmetry can be attributed to the disorder of the local solvation environment, which leads to an equilibrium among solvatomers (that is, isomers that differ in solvation). If the disorder of the local environment is sufficient to break symmetry, then symmetry itself is not sufficient to stabilize the H-bond, and symmetric H-bonds do not have an enhanced stability or an unusual strength. Nor are short H-bonds unusually strong. We discuss previous evidence for "short, strong, low-barrier" H-bonds and show it to be based on ambiguous comparisons. The role of such H-bonds in enzyme-catalyzed reactions is then ascribed not to any unusual strength of the H-bond itself but to relief of "strain."
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Affiliation(s)
- Charles L. Perrin
- Department of Chemistry & Biochemistry, University of California—San Diego, La Jolla, California 92093-0358, United States
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17
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Nakano R, Honda H, Kimura T, Kyo SS, Ishimaru S, Miyake R, Nakata E, Takamizawa S, Noro S. Anomalous H/D Isotope Effect on 35Cl NQR Frequencies and H/D Isotope Effect on 1H MAS NMR Spectra in Pyrrolidinium p-Chlorobenzoate. BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 2010. [DOI: 10.1246/bcsj.20090300] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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18
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Deuterium isotope effects on 13C and 15N chemical shifts of intramolecularly hydrogen-bonded enaminocarbonyl derivatives of Meldrum’s and Tetronic acid. J Mol Struct 2010. [DOI: 10.1016/j.molstruc.2010.03.059] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Kövér KE, Szilágyi L, Batta G, Uhrín D, Jiménez-Barbero J. Biomolecular Recognition by Oligosaccharides and Glycopeptides: The NMR Point of View. COMPREHENSIVE NATURAL PRODUCTS II 2010:197-246. [DOI: 10.1016/b978-008045382-8.00193-3] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/27/2023]
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Abstract
Abstract
A series of 5-acyl-3-methylrhodanines have been synthesized. The structures of those are described using 1H and 13C NMR, deuterium isotope effects on 13C chemical shifts and DFT calculations. The compounds exist as exocyclic enols with intramolecular hydrogen bonds to the C = ONCH3 oxygen. No signs of enhanced mesoionic character were found.
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Perrin CL, Lau JS, Kim YJ, Karri P, Moore C, Rheingold AL. Asymmetry of the “Strongest” OHO Hydrogen Bond, in the Monoanion of (±)-α,α′-Di-tert-butylsuccinate. J Am Chem Soc 2009; 131:13548-54. [DOI: 10.1021/ja905806h] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Charles L. Perrin
- Department of Chemistry, University of California—San Diego, La Jolla, California 92093-0358
| | - Jonathan S. Lau
- Department of Chemistry, University of California—San Diego, La Jolla, California 92093-0358
| | - Yeong-Joon Kim
- Department of Chemistry, University of California—San Diego, La Jolla, California 92093-0358
| | - Phaneendrasai Karri
- Department of Chemistry, University of California—San Diego, La Jolla, California 92093-0358
| | - Curtis Moore
- Department of Chemistry, University of California—San Diego, La Jolla, California 92093-0358
| | - Arnold L. Rheingold
- Department of Chemistry, University of California—San Diego, La Jolla, California 92093-0358
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Abstract
A classic question regarding hydrogen bonds (H-bonds) concerns their symmetry. Is the hydrogen centered or is it closer to one donor and jumping between them? These possibilities correspond to single- and double-well potentials, respectively. The NMR method of isotopic perturbation can answer this question. It is illustrated with 3-hydroxy-2-phenylpropenal and then applied to dicarboxylate monoanions. The 18O-induced 13C NMR splittings signify that their intramolecular H-bonds are asymmetric and that each species is a pair of tautomers, not a single symmetric structure, even though maleate and phthalate are symmetric in crystals. The asymmetry is seen across a wide range of solvents and a wide variety of monoanions, including 2,3-di-tert-butylsuccinate and zwitterionic phthalates. Asymmetry is also seen in monoprotonated 1,8-bis(dimethylamino)naphthalenediamines, N,N'-diaryl-6-aminofulvene-2-aldimines, and 6-hydroxy-2-formylfulvene. The asymmetry is attributed to the disorder of the local environment, establishing an equilibrium between solvatomers. The broader implications of these results regarding the role of solvation in breaking symmetry are discussed. It was prudent to confirm a secondary deuterium isotope effect (IE) on amine basicity by NMR titration of a mixture of PhCH2NH2 and PhCHDNH2. The IE is of stereoelectronic origin. It is proposed that symmetric H-bonds can be observed in crystals but not in solution because a disordered environment induces asymmetry, whereas a crystal can guarantee a symmetric environment. The implications for the controversial role of low-barrier H-bonds in enzyme-catalyzed reactions are discussed.
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Affiliation(s)
- Charles L. Perrin
- 1Department of Chemistry, University of California, San Diego, La Jolla, CA 92093-0358, USA
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23
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Hansen PE. Deuterium isotope effects on 13C chemical shifts of nitromalonamide. MAGNETIC RESONANCE IN CHEMISTRY : MRC 2008; 46:726-729. [PMID: 18470887 DOI: 10.1002/mrc.2237] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
The OH chemical shift of the enol form of nitromalonamide is found at 18.9 ppm both in DMSO-d(6) and in DMF-d(7) indicating a very strong hydrogen bond. The OH chemical shift is insensitive to temperature changes. Contrary to the large OH chemical shift, a small two-bond deuterium isotope effect of 0.135 ppm due to deuteration at the OH position is found at the enolic carbon. This is confirmed by density functional theory calculations. The observed effects are interpreted as due to an equilibrium between identical enolic forms. These show a strong OH...O hydrogen bond as well as a NH...O-N=O hydrogen bond.
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Affiliation(s)
- Poul Erik Hansen
- Department of Science, Systems and Models, Roskilde University, Roskilde, Denmark.
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