Conjugation in hydrogen-bonded systems

Novakovskaya, Yu. V.

doi:10.1007/s11224-012-0029-8

Cited by 15 publications

(2 citation statements)

References 10 publications

(20 reference statements)

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“…125°, and ca. 144° for the g 1 , g 2 , and g 3 conformers, respectively, it may be assumed that the six- and seven-membered rings are mostly stabilized through electrostatic C–H δ+ ···O δ− hydrogen bond interactions. − …”

Section: Resultsmentioning

confidence: 99%

Conformational Analysis and Electronic Interactions of Some 4′-Substituted-2-ethylthio-phenylacetates

et al. 2015

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The conformational analysis of various 4'-substituted-2-ethylthio-phenylacetate compounds bearing the substituents NO2 (1), Cl (2), H (3), Me (4), and OMe (5) was performed using infrared (IR) spectroscopic analysis of the carbonyl stretching band (νCO) supported by B3LYP/6-31G(d,p), NBO, QTAIM, and SM5.42R calculations for compounds 1, 3, and 5. The IR spectra in n-hexane indicate the presence of three components, whose intensities decrease upon increasing frequency. In solvents with high permittivity, while the low intensity component at higher frequency disappears, the relative intensity of the component at the intermediate frequency changes with respect to the lower frequency component with differing trends for the various derivatives. It can be observed that the intensity does not vary for compounds 1 and 2, which bear an electron-withdrawing substituent at 4', while it increases in intensity for compounds 3-5. The computational results predict the presence of three gauche conformers, defined by the orientation of the C-S bond with respect to the carbonyl group, whose intensities and νCO frequencies are in agreement with the experimental results. In solvents with increasing permittivity, the SM5.42R solvation model results reproduce the experimental trend observed for the two components in the low frequency region, while it overestimates the amount of the higher frequency conformer. NBO analysis suggests that all the conformers are stabilized to the same extent in the gauche conformation via σC-S → π*CO and πCO → σ*C-S orbital interactions. The different stability can be attributed to the geometrical arrangement of the C(O)-CH2-S-CH2-CH3 moiety, which assumes a six-membered chair-like geometry in the g1 conformer, a six-membered twisted-chair-like geometry in the g2 conformer, and a seven-membered chair-like ring in the g3 conformer. Quantum theory of atoms in molecules (QTAIM) indicates that the ring geometries were formed and stabilized from short contacts between the oppositely charged carbonyl oxygen and the methylene/methyl hydrogen atoms, which interact through unusual intramolecular electrostatic hydrogen bonding that satisfies the Popelier criteria.

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Section: Resultsmentioning

confidence: 99%

Conformational Analysis and Electronic Interactions of Some 4′-Substituted-2-ethylthio-phenylacetates

et al. 2015

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“…Furthermore, water molecules, similar to other typical H-bond forming particles, are known to demonstrate collective properties when bound to each other, and the most pronounced collective effects are observed when the molecules are involved in closed H-bonded sequences (rings), within which covalent and hydrogen bonds are alternating, for example, (H)O–H···(H)O–H···(H)O–H···. We suggested to refer to such sequences as conjugated because such alternation provides spatial possibilities for the actual conjugation of bonds due to the substantial π-kind contribution to typical H-bonding . Examining the orientation of water molecules around a sodium ion, it can be noticed that due to the predominant ion–dipole interactions, both O–H bonds of each water molecule are oriented from the ion (at a certain tilt angle) and form H-bonds with additional water molecules so that the former ones can be scarcely involved in the aforementioned closed conjugated H-bond sequences.…”

Section: Introductionmentioning

confidence: 99%

Flexibility and Regularity of the Hydration Structures of Ions by an Example of Na⁺: Nonempirical Insight

Novakovskaya

2022

J. Phys. Chem. A

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The stationary nonempirical simulations of [Na(H2O) n ]+ clusters with n in the range of 28–51 carried out at the density functional level with a hybrid B3LYP functional and the Born-Oppenheimer molecular dynamics modeling of the size-selected clusters reveal the interrelated structural and energetic peculiarities of the sodium ion hydration structures. Surface, bulk, and transient structures are distinguished by different locations of the sodium nucleus (close to either the spatial center of the structure or one of its side faces) and a consistently changing coordination number (which typically equals five or six). The differences and correlations between the stationary and averaged dynamically changing configurations are quantified. The ⟨r NaO⟩, mean Na–O distances for the first-shell water molecules, are found to depend both on the spatial character of the structure and the local coordination of sodium. The ⟨r NaO⟩ values are compared to different experimental estimates, and the virtual discrepancy of the latter is explained based on the results of cluster simulations. Different coordination neighborhoods of the sodium ion are predicted depending on its local fraction in actual specimens.

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Self‐Assembly of PEGylated Diphenylalanines into Photoluminescent Fibrillary Aggregates

et al. 2019

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Diphenylalanine (FF) represents one of the most studied selfassembling peptides. As a consequence of non-covalent interactions (aromatic stacking and hydrogen bonds), FF is able to generate different nanoarchitectures, proposed in the last years as innovative tools for several applications. The identification of the relationship between the chemical building block composition and the supramolecular structure of final material is the objective of intense research. Different FF analogues were synthetized and studied. At the state of art, in the high number of FF derivatives, PEGylation has not been studied yet, notwithstanding its role has been demonstrated for longer poly-phenylalanine peptides. Herein, we describe the synthesis and the supramolecular behavior of two PEGylated-FF derivatives, PEG2-FF and PEG6-FF, in which the zwitterionic FF has been derivatized at the N-terminus with two or six ethoxylic moieties, respectively. Spectroscopic methodologies (fluorescence, circular dichroism, Fourier transform infrared) allowed the identification of their secondary structure and the calculation of the critical aggregation concentration. PEGylation of the dipeptide induces a modification of the conformational organization from nanotubes with hexagonal symmetry to βsheet rich fibrils. This structural organization confers photoluminescence features to the supramolecular structures.[a] Dr.

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Conjugation in hydrogen-bonded systems

Cited by 15 publications

References 10 publications

Conformational Analysis and Electronic Interactions of Some 4′-Substituted-2-ethylthio-phenylacetates

Conformational Analysis and Electronic Interactions of Some 4′-Substituted-2-ethylthio-phenylacetates

Flexibility and Regularity of the Hydration Structures of Ions by an Example of Na⁺: Nonempirical Insight

Self‐Assembly of PEGylated Diphenylalanines into Photoluminescent Fibrillary Aggregates

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Conjugation in hydrogen-bonded systems

Cited by 15 publications

References 10 publications

Conformational Analysis and Electronic Interactions of Some 4′-Substituted-2-ethylthio-phenylacetates

Conformational Analysis and Electronic Interactions of Some 4′-Substituted-2-ethylthio-phenylacetates

Flexibility and Regularity of the Hydration Structures of Ions by an Example of Na+: Nonempirical Insight

Self‐Assembly of PEGylated Diphenylalanines into Photoluminescent Fibrillary Aggregates

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Flexibility and Regularity of the Hydration Structures of Ions by an Example of Na⁺: Nonempirical Insight