Search results

1

Investigations of hydrogen bonding in the poly(urethane-urea)-based membrane materials by using FTIR spectroscopy

100%

Wolińska-Grabczyk A., Kaczmarczyk B., Jankowski A.

Polish Journal of Chemical Technology

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2008

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vol. 10

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issue 4

53-56

EN

FTIR analysis was used to study the hydrogen bonding in 4,4'-diaminodiphenylmethane-based segmented poly(urethane-urea)s varying in the length of the poly(tetramethylene oxide) (PTMO)-based soft segments. Experiments were designed to follow the IR absorption of both the NH and carbonyl regions as a function of temperature in order to directly investigate the extent and strength of the hydrogen bonds, and thereby to gain some information about the possible alteration of the initial phase-segregated morphology as a result of the applied thermal treatment.

2

Raman spectroscopic study of the hydration of short-chain poly(oxyethylene)s C 1EnC 1 (n=1−4)

100%

Georgiev M., Popova T., Nickolov Z., Goutev N., Georgiev G., Matsuura H.

Open Chemistry

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2004

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vol. 2

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issue 4

617-626

EN

The hypothesis that the degree of hydration of poly(oxyethylene) (POE) in aqueous solution depends on the mole ratio of water molecules to ether oxygen atoms in the molecule has been verified by studying the isotropic Raman spectra in the O−H stretching region for four short-chain POEs (C 1EnC 1 withn=1−4). Excellent coincidence of the O−H stretching Raman band for all four POEs studied in the range of mole ratio H2O/Oether from 25 to 0.6 was observed, thus confirming the assumption stated above. A conclusion that all ether oxygen atoms in the POE molecule participate in hydrogen bonding with water molecules has been made.

3

Determination of micelle aggregation numbers of alkyltrimethylammonium bromide and sodium dodecyl sulfate surfactants using time-resolved fluorescence quenching

100%

Pisárčik M., Devínsky F., Pupák M.

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issue 1

EN

The time-resolved fluorescence quenching method was applied to determine the micelle aggregation number of cationic single-chain surfactants dodecyltrimethylammonium bromide (DTAB), cetyltrimethylammonium bromide (CTAB) and anionic surfactant sodium dodecyl sulfate (SDS). The concentration dependence of micelle aggregation number was found to be linear for all investigated surfactants in the concentration range 2‒15 × the value of critical micelle concentration of the respective surfactant. The values of micelle aggregation number were found in the range 30‒77. Different trends in the linear concentration dependence of micelle aggregation number were observed for cationic surfactants and for the anionic surfactant SDS. A small slope value was found for cationic surfactants, while the SDS micelle aggregation number concentration dependence showed significantly a larger slope value. The aggregation number increase with the increasing SDS concentration results in the micellar growth. Results from a simple analysis based on computer models of cationic and anionic surfactant molecules with dodecyl chains supports, the formation of intramicellar hydrogen bonding between surfactant molecules in SDS micelle shell.

4

Hydrogen-bonded assembly and binding affinity of the multi-point acceptor and isophthalic acid

100%

Xu L., Zhu L., Wu S., Chen X., Teng Q.

Open Chemistry

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2006

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vol. 4

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issue 4

732-742

EN

Supermolecular complexes formed by oligophenyleneethynylene derivatives and isophthalic acid were studied using AM1 method to obtain binding energy. Electronic spectra and IR spectra of the complexes were calculated by INDO/CIS and AM1 methods based on AM1 geometries. Results indicated that the dimer could be formed by the monomers via hydrogen bonding because of the negative binding energy. Binding energy of the complexes was affected by electronegativity and steric effects of the substituents. The first UV absorptions and IR frequencies of N-H bonds of the complexes were both red-shifted compared with those of the monomers. The complexes could bind small molecules via hydrogen bonds, resulting in the change in UV absorptions and an increase in IR frequencies of N-H bonds.

5

A theoretical forecast of the hydrogen bond changes in the electronic excited state for BN and its derivatives

88%

Wang D., Hao C., Wang S., Dong H., Qiu J.

Open Physics

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2012

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vol. 10

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issue 1

116-123

EN

The relationship between electronic spectral shifts and hydrogen-bonding dynamics in electronically excited states of the hydrogen-bonded complex is put forward. Hydrogen bond strengthening will induce a redshift of the corresponding electronic spectra, while hydrogen bond weakening will cause a blueshift. Time-dependent density function theory (TDDFT) was used to study the excitation energies in both singlet and triplet electronically excited states of Benzonitrile (BN), 4-aminobenzonitrile (ABN), and 4-dimethylaminobenzonitrile (DMABN) in methanol solvents. Only the intermolecular hydrogen bond C≡N...H-O was involved in our system. A fairly accurate forecast of the hydrogen bond changes in lowlying electronically excited states were presented in light of a very thorough consideration of their related electronic spectra. The deduction we used to depict the trend of the hydrogen bond changes in excited states could help others understand hydrogen-bonding dynamics more effectively.

6

NMR study of heterogeneity in pyridine-N-oxide...HCl crystal

75%

Balevicius V., Gacesa A., Plavec J.

Open Physics

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2004

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vol. 2

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issue 1

120-131

EN

An origin of narrow 1H NMR signals in pyridine-N-oxide (PyO)...HCl crystal has been investigated by means of MAS, SPEDAS, NOESY and COSY techniques. Spectra of crystalline samples are compared with those of solid phase obtained from liquid PyO...HCl solutions (in acetonitile/H2O) after the heterogeneous phase separation. It has been concluded that partially resolved peaks in 1H NMR spectra of solids are related with heterogeneity of spin system and presence of different H-bond clusters of water molecules. NOESY spectra show no cross-peaks even at very long mixing time (500 ms). This indicates there is no exchange process between spins causing different peaks, and thus the corresponding molecular aggregates are captured in “islands of mobility8 without any channels sufficient for exchange. Appearance of MAS side bands as “pseudo8 cross-peaks in 2D NMR spectra using MAS/COSY technique is reported. In the case of accidental coincidence of spinning frequency (ωMAS) with spectral distances between some diagonal signals, intensive non-diagonal peaks are observed at the corresponding cross-positions. A misleading conclusion concerning spin coupling is easy to avoid using various ωMAS.

7

DFT and neutron diffraction study of 1,6-anhydro-β-D-glucopyranose (levoglucosan)

75%

Sládkovic̆ová M., Mach P., Smrc̆ok L. u., Rundlöf H.

Open Chemistry

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2007

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vol. 5

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issue 1

55-70

EN

Geometries of 27 generated conformers of levoglucosan were optimized in vacuo at DFT level of theory combining several functionals with high quality basis sets. For the sake of comparison a reference molecular and crystal geometry obtained from 30 K single crystal neutron diffraction data was used. Analysis of the conformers’ geometries revealed that in all stable conformers intramolecular two-or three centre hydrogen bonds were formed. Relative energy of the conformer, which approximated the molecule in the crystal structure the most, was only ∼3 kcal/mol higher, than the energy of the most stable conformer in vacuo. The largest discrepancies between the geometries calculated in vacuo and experimental geometry concentrated in the vicinity of anomeric C1. These differences were reduced by involving O1 to intermolecular hydrogen bond using a simple model of the respective hydrogen bond in the crystal. [...]

8

Conformational Stability, TGA, and Molecular Docking Investigations of p-Coumaric Acid with Special Relevance to Anti-Cancer and Antibacterial Activity

75%

Sathish M., Meenakshi G., Xavier S., Sebastian S.

Acta Physica Polonica A

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2017

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vol. 131

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issue 6

1512-1518

EN

In this work an attempt is made to analysis of the possible different conformers of p-coumaric acid (PCA) by using density functional method. The total energy of four possible conformers were calculated by using B3LYP/6-311G(d,p) method. Computational result identifies that the most stable conformer of PCA is C2. The formation of inter- and intra-molecular hydrogen bonding between -OH and -COOH group gave the evidence for dimer formation for PCA molecule. The highest occupied-lowest unoccupied molecular orbital analysis shows that the negative electrostatic region situated over the -COOH group and positive electrostatic potential region are localized on ring system and all hydrogen. The PCA has been screened to anti-microbial activity and found to exhibit anti-bacterial effects. Molecular docking results suggest that PCA may exhibit inhibitory activity against lung cancer protein and may act as potential against lung cancer.

Refine search results

Investigations of hydrogen bonding in the poly(urethane-urea)-based membrane materials by using FTIR spectroscopy

Raman spectroscopic study of the hydration of short-chain poly(oxyethylene)s C 1EnC 1 (n=1−4)

Determination of micelle aggregation numbers of alkyltrimethylammonium bromide and sodium dodecyl sulfate surfactants using time-resolved fluorescence quenching

Hydrogen-bonded assembly and binding affinity of the multi-point acceptor and isophthalic acid

A theoretical forecast of the hydrogen bond changes in the electronic excited state for BN and its derivatives

NMR study of heterogeneity in pyridine-N-oxide...HCl crystal

DFT and neutron diffraction study of 1,6-anhydro-β-D-glucopyranose (levoglucosan)

Conformational Stability, TGA, and Molecular Docking Investigations of p-Coumaric Acid with Special Relevance to Anti-Cancer and Antibacterial Activity