Aleksan G. Shahkhatuni

National Academy of Sciences of Armenia

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Astghik A. Shahkhatuni

Institute of Fine Organic Chemistry of Scientific - Technological Center of Organic and Pharmaceutical Chemistry

Henry A. Panosyan

National Academy of Sciences of Armenia

Aleksandr B. Sahakyan

MRC Weatherall Institute of Molecular Medicine

Arpine S. Harutyunyan

National Academy of Sciences of Armenia

H. S. Attaryan

Institute of Fine Organic Chemistry of Scientific - Technological Center of Organic and Pharmaceutical Chemistry

Valentine P. Ananikov

N.D. Zelinsky Institute of Organic Chemistry

Ashkharuhi G. Aleksanyan

Institute of Fine Organic Chemistry of Scientific - Technological Center of Organic and Pharmaceutical Chemistry

S. S. Mamyan

National Academy of Sciences of Armenia

Robert M. Hakobyan

Institute of Fine Organic Chemistry of Scientific - Technological Center of Organic and Pharmaceutical Chemistry

Alexander Pines

University of California, Berkeley

Cooperative Institutions

National Academy of Sciences of Armenia

Institute of Fine Organic Chemistry of Scientific - Technological Center of Organic and Pharmaceutical Chemistry

Yerevan State University

National Academy of Sciences

Scientific Center of Zoology and Hydroecology

University of California, Berkeley

Lawrence Berkeley National Laboratory

National Polytechnic University of Armenia

N.D. Zelinsky Institute of Organic Chemistry

Russian Academy of Sciences

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Long range deuterium isotope effects on ¹³C NMR chemical shifts of 2-alkanones in CD₃OD solutions of imidazolium acetate ionic liquids

RSC Advances (2021)

Astghik A. Shahkhatuni Aleksan G. Shahkhatuni Arpine S. Harutyunyan

Long range deuterium isotope effects on the carbon spectral pattern in 2-hexanone reveal the existence and distribution of H/D isotopomers.

Deuterium NMR

Kinetic isotope effect

10.1039/d1ra07232c

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Citations (2)

Structural Molecular Biology — The New Perspective for Regional Science

Springer eBooks (2002)

Aleksan G. Shahkhatuni

10.1007/978-94-010-0367-4_32

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Citations (0)

Torsion sensitivity in NMR of aligned molecules: study on various substituted biphenyls

Magnetic Resonance in Chemistry (2007)

Aleksandr B. Sahakyan Aleksan G. Shahkhatuni Astghik A. Shahkhatuni Henry A. Panosyan

To estimate the torsion sensitivity of dipolar coupling, biphenylic molecules were chosen as probes due to their relatively simple structure and the surprisingly high ambiguity of the only flexible parameter-the interring torsion angle. Solution structures of 4,4'-dibromobiphenyl and 4,4'-diiodobiphenyl are reported for the first time in two liquid crystals I52 and ZLI 1695. The comparison of NMR structures of various para-substituted biphenyls (BPs), calculated by the additive potential maximum entropy (APME) approach, shows that the small spread of torsion angle values in case of different solvents and para-substituents is in good agreement with theoretical expectations from hybrid density functional theory (DFT) methods. Furthermore, the real structural changes of interring torsion and the prevalence of solvent effects over para-halosubstitution can be correctly revealed from these small fluctuations.

Dihedral angle

Proton NMR

10.1002/mrc.2142

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Citations (3)

Dielectric permittivity and temperature effects on spin–spin couplings studied on acetonitrile

Magnetic Resonance in Chemistry (2007)

Aleksandr B. Sahakyan Astghik A. Shahkhatuni Aleksan G. Shahkhatuni Henry A. Panosyan

Abstract Dielectric permittivity (ε) and temperature effects on indirect spin–spin coupling constants were studied using acetonitrile as a probe molecule. Experiments were accompanied by hybrid DFT (density functional theory) studies, where the solvent was modeled using the polarization continuum model. Owing to its numerous types of J ‐couplings, acetonitrile is a very convenient molecule against which various basis sets can be tested or the best basis set can be selected for a given study. The results show reasonable agreement between calculated and experimental values. According to our data, scalar spin–spin coupling constants undergo substantial shifts at lower values of the dielectric constant. Thus J ‐coupling values are not transferable between measurements made at differing ε–conditions, and the assumption of the ε‐independence of the J ‐coupling can lead to crucial mistakes in experiments using low‐ε media. Dielectric permittivity also causes small geometric fluctuations within the molecule, which themselves can affect J ‐coupling values. Examinations of the results computed with frozen and relaxed geometries show that geometry mediation mostly affects the spin‐dipole term of the J ‐coupling; hence, for accurate evaluation of the latter, frozen geometries are not acceptable. Another interesting fact revealed is the connection between the solvent dielectric properties and the temperature‐dependence slopes of J ‐couplings in corresponding media. Copyright © 2008 John Wiley & Sons, Ltd.

Coupling constant

10.1002/mrc.2137

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Electric Field Effects on One-Bond Indirect Spin−Spin Coupling Constants and Possible Biomolecular Perspectives

The Journal of Physical Chemistry A (2008)

Aleksandr B. Sahakyan Aleksan G. Shahkhatuni Astghik A. Shahkhatuni Henry A. Panosyan

Electric field (EF) induced changes of one-bond indirect spin−spin coupling constants are investigated on a wide range of molecules including peptide models. EFs were both externally applied and internally calculated without external EF application by the hybrid density functional theory method. Reliable agreement with experimental data has been obtained for calculated one-bond J-couplings. The role of the EF sign and direction, internal and induced components, hydrogen bonding, internuclear distance and hyperconjugative interactions on the one-bond J-coupling vs EF interconnection is analyzed. A linear dependence of 1J on EF projection along the bond is obtained, if the bound atoms possess different enough electron densities and an EF determined by the electronic polarization exists along the bond. Accentuating the 1JNH couplings as possible EF sensitive parameters, a systematic study is done in two sets of molecules with a large variation of the native internal EF value. The most EF affected component of the 1JNH coupling constant is the spin-dipole term of Ramsey's formulation; however, in the total J-coupling formation, the EF influence on the Fermi contact term is the most significant. The induced EF projection along the bond is 6.7 times weaker in magnitude than the simulated external uniform field. The absolute EF dependence of the one-bond J-coupling involves only the internal field, which is the sum of the induced field (if the external field exists) and the internuclear field determined by the native polarization. That linear and universal dependence joins the corresponding couplings in a diverse set of molecules under various electrostatic conditions. Many types of the one-bond J-couplings can be potentially measured in biomolecules, and the study of their relation with the electrostatic properties at the corresponding sites opens a new avenue to the full exploitation of the NMR measurable parameters with novel and exciting applications.

Coupling constant

Fermi contact interaction

10.1021/jp800670y

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Revealing the specific solute–solvent interactions via the measurements of the NMR spin–spin coupling constants

Journal of Molecular Structure (2014)

Astghik A. Shahkhatuni Aleksan G. Shahkhatuni N. S. Minasyan Henry A. Panosyan Aleksandr B. Sahakyan

Coupling constant

Halogen bond

10.1016/j.molstruc.2014.11.058

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Citations (4)

NMR Studies of ¹³C-Iodomethane: Different Behavior in Thermotropic and Lyotropic Liquid Crystals

The Journal of Physical Chemistry A (2004)

Aleksan G. Shahkhatuni Astghik A. Shahkhatuni Henry A. Panosyan Gregory H. J. Park Rachel W. Martin

High-resolution NMR spectra of 13C-iodomethane dissolved in thermotropic and lyotropic liquid crystalline solvents have been used to measure 1H−1H and 13C−1H dipolar couplings. The ratio of these two couplings, which is a function of the H−C−H bond angle in 13C-iodomethane, is, in general, different from that expected from the known molecular structure; solvent−solute interactions in liquid crystalline solutions are responsible for this difference. In thermotropic liquid crystalline solutions, the apparent bond angle deviation (Δθa) increases with decreasing molecular ordering. In contrast, in lyotropic liquid crystals, no significant spectral aberration has been observed. These results indicate a fundamental physicochemical difference between the intermolecular interactions that prevail in thermotropic and lyotropic liquid crystals.

Thermotropic crystal

Lyotropic

Lyotropic liquid crystal

Solvophobic

10.1021/jp047330g

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Citations (13)

Assessment of solvent effects: do weak alignment media affect the structure of the solute?

Magnetic Resonance in Chemistry (2007)

Astghik A. Shahkhatuni Aleksan G. Shahkhatuni Henry A. Panosyan Aleksandr B. Sahakyan In‐Ja L. Byeon

Abstract Alignment media used for measuring residual dipolar couplings, such as solutions of filamentous phages, phospholipid mixtures, polyacrylamide gels and various lyotropic liquid crystalline systems were investigated with respect to solvent effects on molecular structure. Structural parameters of the small rigid model compound 13 C‐acetonitrile were calculated from dipolar couplings and variations from expectation values were used for assessment of solvent effects. Only minor solvent effects were observed for most of the media employed and the measured structural data are in good agreement with microwave data and theoretical predictions. Copyright © 2007 John Wiley & Sons, Ltd.

Lyotropic

Residual dipolar coupling

10.1002/mrc.2004

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Citations (7)

Determination of the Three‐Dimensional Structure for Weakly Aligned Biomolecules by NMR Spectroscopy

ChemInform (2003)

Astghik A. Shahkhatuni Aleksan G. Shahkhatuni

Abstract For Abstract see ChemInform Abstract in Full Text.

Biomolecule

10.1002/chin.200322298

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