ABSTRACT
The effect of external electric field (EEF) of 5.14, 25.70, and 51.40 MV/cm upon Cys-Asn-Ser, Glu-Arg-Leu, Glu-Cys-Glc, Ser-Asp-Leu, Ser-Glu-Met tripeptide inner salts was simulated involving HyperChem 8.0 software together with the AM1 method for optimization of the molecules' conformation. The reaction to EEF is diverse and specific to particular peptides. EEF stimulated an increase in the positive charge density on the hydrogen atoms of the N(+)H3, peptide bond NH, NH2, and COOH groups as well decrease in the negative charge density on the oxygen atoms of the peptide bond carbonyl groups. Thus, EEF could control behavior and action of tripeptides, such as an increase in their catalytic activity.
Subject(s)
Oligopeptides/chemistry , Amino Acid Sequence , Catalysis , Electrochemistry , Hydrogen Bonding , Molecular ConformationABSTRACT
Several aromatic compounds derived from benzene by its annelation (naphthalene, anthracene, phenanthrene, pyrene) and exocyclic substitution (e.g., nitrobenzene, dinitrobenzenes, trinitrobenzene, chlorobenzene, N,N-dimethylaniline, and others) and endocyclic substitution (pyridine, quinoline, isoquinoline) efficiently sorbed on multi-walled carbon nanotubes (MWCNTs). Equilibrium constants for the sorption process have been determined. Computations of the energy of formation were performed for surface complexes of those arenes on single-walled carbon nanotubes (SWCNTs). Formation energies of those complexes were correlated against the experimental equilibrium constants. The latter were also correlated against calculated LUMO energy of the arenes. Solely, limited tendencies to the linearity could be observed. The analysis of the results of the correlations indicated that the arenes acting as the charge acceptors formed stronger complexes than arenes with a high electron density in the molecular orbital, for instance, N, N-dimethylaniline. The area of the arene--SWCNT contact was very essential for the complexation. The proximity of the HOMO orbital of SWCNT and LUMO of the arene was another essential factor. Bulky substituents in the arene molecules obscured their efficient contact with SWCNT.
Subject(s)
Chemistry, Organic/methods , Nanotechnology/methods , Nanotubes, Carbon/chemistry , Nanotubes/chemistry , Aniline Compounds/chemistry , Benzene/chemistry , Kinetics , Microscopy, Electron, Transmission , Models, Chemical , Nanostructures/chemistry , Spectrophotometry , Spectrophotometry, Ultraviolet/methods , Surface Properties , Temperature , Time FactorsABSTRACT
Closed-end single-walled carbon nanotubes were wetted in aqueous solutions of monosaccharides, forming weak surface complexes, as proven by the estimation of the content of monosaccharides in complexes isolated from aqueous solutions. The complexation was confirmed by micro-Raman spectroscopy. The Gaussian 03 (Molecular Mechanics UFF method) computations of total energy of the single-walled carbon nanotube-monosaccharides inclusion and surface complexes showed that inclusion complexes should be more stable than corresponding surface complexes. Computed total energies for particular complexes pointed to a lack of preferences for the formation of complexes with either alpha- or beta-tautomers and either pyranoses or furanoses. The forms preferred in the formation of the surface complexes usually differ from these favored in the formation of the inclusion complexes.
Subject(s)
Models, Chemical , Models, Molecular , Monosaccharides/chemistry , Nanotubes, Carbon/chemistry , Nanotubes, Carbon/ultrastructure , Water/chemistry , Binding Sites , Computer Simulation , Crystallization/methods , Macromolecular Substances/analysis , Macromolecular Substances/chemistry , Molecular Conformation , Solutions , Surface PropertiesABSTRACT
As proven by the UV-VIS, micro-Raman spectroscopies, differential scanning calorimetry, beta-carotene, lycopene, retinoic acid, and retinol adsorbed on the surface of single-walled carbon nanotubes (SWCNT) form electron donor-acceptor (EDA) complexes. The rate of the adsorption of carotenoids is estimated as the rate of decrease in their concentration in solution followed the exponential curve equation. The rate of the adsorption decreased with the chain length of the guest capable sorption on the surface and steric effect of the terminals in the beta-carotene was also essential. Also, increase in the polarity of the functional groups expressed, for instance, in Taft sigma* substituent constants had its impact. The HyperChem 7 followed by Gaussian 03 computations revealed that the inclusion SWCNT-carotenoid complexes were more stable than corresponding surface complexes. In the surface complexes carotenoids acted as donors in respect to SWCNT whereas in the inclusion complexes they were acceptors.
