1H NMR studies of proton transfer equilibria in hydrogen bonds – the role of the entropy

2001 ◽  
Vol 79 (9) ◽  
pp. 1376-1380
Author(s):  
Roland Langner ◽  
Georg Zundel
Keyword(s):  
Hydrogen Bonds ◽  
Proton Transfer ◽  
Methanesulfonic Acid ◽  
Negative Interaction ◽  
Nmr Studies ◽  
Left Hand ◽  
H Nmr ◽  
Proton Transfers ◽  
Proton Potential ◽  
Dimethylphosphinic Acid

The influence of the entropy on the proton transfer equilibria AH···B [Formula: see text]A–···H+B in the dimethylphosphinic acid (DMP)-N-base and in the methanesulfonic acid (MSA)-N-oxide hydrogen bonds is studied by 1H NMR spectroscopy as a function of the ΔpKa, i.e., the pKa of the base minus the pKa of the acid. It is shown that with increasing ΔpKa the proton transfers to the N-oxide acceptor. In the DMP + N-base family of systems, first the double-minimum proton potentials (ΔH = 0) occurs and only with further increasing ΔpKa do the POH···N [Formula: see text] PO–···H+N equilibria become symmetrical (ΔG = 0). ΔG and ΔH are connected by the Gibbs–Helmholtz equation, ΔG = ΔH –TΔS. Hence, the reason of this effect is the large negative interaction entropy term (ΔSI) arising from the large order around the polar structure, which shifts the equilibria strongly to the left-hand side. With the MSA-N-oxide hydrogen bonds a single-minimum proton potential was found. The minimum shifts with increasing ΔpKa from the donor to the acceptor of the O···H+···N hydrogen bonds. It is shown that with increasing ΔpKa the proton potential becomes on average symmetrical, whereas the proton is still largely on the left-hand side. This result is also explained by the large negative interaction entropy due to the order of the environment if the proton is at the acceptor B.Key words: entropy, hydrogen bonds, infrared, spectroscopy, proton transfer.

PCILO study of hydrogen bond and proton transfer in systems 1-methylthymine-acetamide and 1-methylthymine-acetic acid

1981 ◽  
Vol 46 (4) ◽  
pp. 957-962 ◽  
Author(s):  
Milan Remko
Keyword(s):  
Hydrogen Bond ◽  
Acetic Acid ◽  
Hydrogen Bonds ◽  
Proton Transfer ◽  
Quantum Chemical ◽  
Potential Functions ◽  
Double Proton Transfer ◽  
Proton Potential ◽  
Pcilo Method

Complexes containing two hydrogen bonds of the systems 1-methylthymine-acetamide and 1-methylthymine-acetic acid have been studied by the quantum-chemical PCILO method. In accordance with experiment our PCILO calculations have shown that acetic acid forms stronger hydrogen bonds than acetamide with 1-methylthymine. Further the PCILO method has been used to study of double proton transfer in O-H...O and N-H...O bonds of the complexes 1-methylthymine-acetamide and 1-methylthymine-acetic acid. Using equilibrium O...O and N...O distances, the PCILO calculations have given one-minimum proton potential functions. The proton transfer has not been observed. At somewhat longer N...O and O...O distances (0.30 nm) the PCILO calculations indicate a second minimum as a shoulder.

1H NMR studies of proton transfer in Schiff base and carboxylic acid systems

1990 ◽  
Vol 68 (10) ◽  
pp. 1909-1916 ◽  
Author(s):  
Hoa Le-Thanh ◽  
D. Vocelle
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Hydrogen Bond ◽  
Schiff Base ◽  
Proton Transfer ◽  
Carboxylic Acids ◽  
Proton Nuclear Magnetic Resonance ◽  
Nmr Studies ◽  
H Nmr ◽  
Mineral Acids ◽  
Rapid Equilibrium

When the unconjugated Schiff base, isobutylidene isopropylamine (2), reacts with acids such as the mineral acids HCl, HBr, and HI, or the carboxylic acids trichloroacetic, monochloroacetic, and propionic acid, in CDCl3, several complexes are formed. In this study, 1H NMR allows us to differentiate between several possibilities. With the mineral acids, only 1:1 structures are seen and the chemical shift of the [Formula: see text] proton varies according to the strength of the hydrogen bond between the protonated Schiff base and its counterion. With the carboxylic acids, 1:1 and 1:2 structures are present in rapid equilibrium. In the presence of an excess of acid, protonation of the Schiff base increases considerably. Extrapolation of the results is given in terms of the molecular mechanism of vision. Keywords: protonation, proton nuclear magnetic resonance, proton transfer, rhodopsins, Schiff base.

Hydrogen bonds and proton transfer in imidazole oligomers and (imidazole)2H(+) system: quantum-chemical calculations

1980 ◽  
Vol 45 (12) ◽  
pp. 3482-3487 ◽  
Author(s):  
Milan Remko
Keyword(s):  
Hydrogen Bond ◽  
Hydrogen Bonds ◽  
Proton Transfer ◽  
Quantum Chemical ◽  
Equilibrium Distance ◽  
Hydrogen Bond Energy ◽  
Proton Potential ◽  
Pcilo Method ◽  
System Quantum ◽  
Semi Empirical

The semi-empirical PCILO method has been applied to study of hydrogen bonds and proton transfer in linear n-mers of imidazole (n = 3). The calculated hydrogen bond energy in the dimer is 30.64 kJ mol-1. In imidazole trimer interaction energy of the "second" hydrogen bond increased to 32.02 kJ mol-1. One-minimum functions only have been found by calculations of the proton potential functions in imidazole dimer and trimer for the equilibrium distances RN...N. For somewhat longer distances RN...N = 0.30 nm a second minimum was observed as shoulder. On the contrary, for the (imidazole)2H(+) system the proton potential curve has two minima for the equilibrium distance RN...N = 0.252 nm, the second minimum is more stable by 3.97 kJ mol-1.

scholarly journals 5-(7-Methanesulfonyl-2-morpholin-4-yl-6,7-dihydro-5H-pyrrolo[2,3-d]pyrimidin-4-yl)-pyrimidin-2-ylamine mesylate

IUCrData ◽  
2017 ◽  
Vol 2 (9) ◽  
Author(s):  
Masahide Aoki ◽  
Takahiro Ichige ◽  
Junichi Shiina ◽  
Satoshi Tanida ◽  
Koji Shiraki ◽  
...  
Keyword(s):  
Hydrogen Bond ◽  
Hydrogen Bonds ◽  
Proton Transfer ◽  
Title Compound ◽  
Methanesulfonic Acid ◽  
Compound C

In the title compound, C15H20N7O3S+·CH3O3S−(CH5132799 mesylate), two molecular entities form a salt with proton transfer from methanesulfonic acid to the aminopyrimidine moiety of CH5132799. In the crystal, methanesulfonate is retained by bifurcated O...H—N hydrogen bonds and an N+—H...O−charge-assisted hydrogen bond.

scholarly journals A hemicryptophane with a triple-stranded helical structure

2018 ◽  
Vol 14 ◽  
pp. 1885-1889 ◽  
Author(s):  
Augustin Long ◽  
Olivier Perraud ◽  
Erwann Jeanneau ◽  
Christophe Aronica ◽  
Jean-Pierre Dutasta ◽  
...  
Keyword(s):  
Molecular Structure ◽  
Hydrogen Bonds ◽  
Helical Structure ◽  
Aromatic Rings ◽  
Nmr Studies ◽  
Intramolecular Hydrogen Bonds ◽  
X Ray ◽  
H Nmr ◽  
Amine Groups ◽  
Intramolecular Hydrogen

A hemicryptophane cage bearing amine and amide functions in its three linkers was synthesized in five steps. The X-ray molecular structure of the cage shows a triple-stranded helical arrangement of the linkers stabilized by intramolecular hydrogen bonds between amide and amine groups. The chirality of the cyclotriveratrylene unit controls the propeller arrangement of the three aromatic rings in the opposite part of the cage. 1H NMR studies suggest that this structure is retained in solution.

1H NMR Conformational Studies in Water of Angiotensin II Analogues Modified at the N- and C-Termini: Interactions of the Aromatic Side Chains and Folding of the N-Terminal Domain

1994 ◽  
Vol 59 (11) ◽  
pp. 2523-2532 ◽  
Author(s):  
John Hondrelis ◽  
John Matsoukas ◽  
George Agelis ◽  
Paul Cordopatis ◽  
Ning Zhou ◽  
...  
Keyword(s):  
Shielding Effect ◽  
Resonance Spectroscopy ◽  
Nmr Studies ◽  
Previous Suggestion ◽  
Aminoisobutyric Acid ◽  
H Nmr ◽  
Neutral Ph ◽  
Angiotensin Ii Analogues ◽  
Proton Resonances ◽  
Cosy Nmr

The conformation of [Sar1]angiotensin II in water at neutral pH has been examined by proton magnetic resonance spectroscopy at 400 MHz and in particular by comparing its 1H NMR spectral data with those of analogues modified at positions 1,4 and 6, namely [Sar1,Cha8]ANGII, [Des Asp1,Cha8]ANGII, [Aib1,Tyr(Me)4]ANGII, [Aib1,Tyr(Me)4,Ile8]ANGII, [N-MeAib1,Tyr(Me)4]ANGII, [N-MeAib1,Tyr(Me)4,Ile8]ANGII, ANGIII and [Sar1,Ile8]ANGII. Assignment of all proton resonances in these analogues was made possible by 2D COSY NMR experiments. The H-2 and H-4 protons for the histidine ring in [Sar1]ANGII, ANGII and ANGIII were shielded compared with the same protons in [Sar1,Ile8]ANGII, [Sar1,Cha8]ANGII and [Des Asp1,Cha8]ANGII; this shielding effect was not disturbed upon methylation of the tyrosine hydroxyl and/or replacement of residue 1 (sarcosine or aspartic acid) with aminoisobutyric acid (Aib) or N-methyl aminoisobutyric acid (N-MeAib). These data are consistent with our previous suggestion based on NMR studies in neutral DMSO that a characteristic folded conformation for ANGII previously observed in non-polar solvents can also be detected in water at neutral pH, but to a lesser degree.

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