scholarly journals Quantum chemical study on the interaction of arginine with silica surface

2021 ◽  
Vol 12 (4) ◽  
pp. 358-364
Author(s):  
A. A. Kravchenko ◽  
◽  
E. M. Demianenko ◽  
A. G. Grebenyuk ◽  
M. I. Terets ◽  
...  
Keyword(s):  
Aqueous Solution ◽  
Hydrogen Atom ◽  
Oxygen Atom ◽  
Silica Surface ◽  
Silanol Group ◽  
Basis Set ◽  
Carboxyl Group ◽  
Amino Group ◽  
Silanol Groups ◽  
Guanidine Group

The structure and energy characteristics of structures formed during arginine adsorption on silica surface from aqueous solution were studied by the density functional theory (B3LYP) method using a valence-split basis set 6-31++G(d,p) within the continuous solvent model (PCM) and supermolecular approximation. The equilibrium structural and energy parameters of the protonated arginine molecule in the gas phase dependent on the location of the hydrogen atom are considered including those of two possible zwitterions. The structure of the arginine ion Н2А+, which is formed when a proton attaches to a molecule or zwitterion of a given amino acid, has been elucidated. To determine the deprotonation constant of the carboxyl group in an acidic medium, the complexes of the arginine molecule (AH32+) in the state with undissociated and deprotonated carboxyl groups are considered. The simulation of the acid medium was performed by taking into account the interaction with two hydrated HCl ion pairs, which provided the protonation of the a-amino group and the nitrogen atom of amino group within the guanidine group. In the study on the interaction of an arginine molecule with silica surface in an aqueous medium, complexes containing a Si8O12(OH)7O– ion with a deprotonated silanol group, six water molecules, and an arginine molecule with a deprotonated carboxyl group were considered. It has been found that the arginine molecule is most likely to be adsorbed on slica surface with formation of hydrogen bonds between the hydrogen atoms of the a-amino group and the oxygen atom of the deprotonated silanol group. In this case, the formation of a hydrogen bond between the oxygen atom of the carboxyl group and the hydrogen atom of the neighboring silanol group is possible. Slightly less likely is adsorption of arginine molecules due to interaction of the guanidine group with silanol groups of the surface. According to the calculated data, the adsorption of the zwitterionic form of the arginine molecule from the aqueous solution is equally likely to occur due to interaction of silanol groups of silica surface with both the carboxyl group and the guanidine group.

Effect of amino group protonation on the carboxyl group in aqueous glycine observed by O 1s X-ray emission spectroscopy

2018 ◽  
Vol 20 (36) ◽  
pp. 23214-23221 ◽  
Author(s):  
Y. Horikawa ◽  
T. Tokushima ◽  
O. Takahashi ◽  
Y. Harada ◽  
A. Hiraya ◽  
...  
Keyword(s):  
Aqueous Solution ◽  
Amino Acid ◽  
Electronic Structures ◽  
Emission Spectroscopy ◽  
Selective Excitation ◽  
Carboxyl Group ◽  
Amino Group ◽  
X Ray ◽  
Excitation Conditions ◽  
Amino Acid Glycine

The valence electronic structures of the amino acid glycine in aqueous solution were investigated in detail through X-ray emission spectroscopy at O 1s excitation under selective excitation conditions of the CO site in the carboxyl group.

scholarly journals Interaction of N-acetylneuraminic acid with surface silicon in aqueous solution with carbohydrates

Surface ◽  
2020 ◽  
Vol 12(27) ◽  
pp. 36-52
Author(s):  
L. M. Ushakova ◽  
◽  
E. M. Demianenko ◽  
M. I. Terets ◽  
V. V. Lobanov ◽  
...  
Keyword(s):  
Aqueous Solution ◽  
Density Functional ◽  
Silica Surface ◽  
Mutual Influence ◽  
Density Functional Theory Method ◽  
Basis Set ◽  
Water Molecules ◽  
Acid Molecule ◽  
Acetylneuraminic Acid ◽  
Carbohydrate Molecule

The aim of the work is to study interaction of N-acetylneuraminic acid (NANA) with the surface of ultrafine silica (UFS) with the participation of glucose and sucrose in aqueous solution at the supramolecular level by density functional theory method (exchange-correlation functional B3LYP, basis set of 6-31G (d, p). The adsorption of N-acetylneuraminic acid, as well as individual carbohydrates (glucose and sucrose) on the hydrated surface of UFS in aqueous solution, was considered as a process of replacement of water molecules on the surface of silica by adsorbate molecules. This work considers two schemes of carbohydrate molecule influence on adsorption of N-acetylneuraminic acid. According to the first scheme the interaction of the NANA molecule occurs with the silica-monosaccharide complex, according to the second scheme, the silica cluster interacts with the NANA-monosaccharide complex, where silica binds to the complex through the carbohydrate molecule. The analysis of the calculated geometric and energy characteristics show that adsorption on the surface of silica, with hydration taken into account, is thermodynamically probable for the sucrose. The glucose molecule has a positive value (+9.8 and +2.7 kJ / mol) is an unfavorable process in terms of thermodynamics regardless of the hydrating water cluster size. The N-acetylneuraminic acid molecule has a value of -1.3 kJ / mol for the reaction with five water molecules and +0.9 kJ / mol with eight water molecules. It was found that the presence of sucrose on the silica surface in the aqueous solution weakens the hydration energy (i.e. it is easier to replace the cluster of water with the N-acetylneuraminic acid molecule from the surface of the modified adsorbent), which in turn promotes NANA adsorption on the silica surface. Therefore, scheme 1 is thermodynamically more likely than scheme 2. This indicates that there is a mutual influence of substances in a mixture of NANA with carbohydrates on the interaction with silica in comparison with the interaction of substances with silica alone.

Using of modified-bentonite as low-cost sorbent for removal of methylene blue dye from aqueous solution

2020 ◽  
Vol 27 (2) ◽  
pp. 45-54
Author(s):  
Saraa Muwafaq Ibrahim ◽  
Ziad T. Abd Ali
Keyword(s):  
Aqueous Solution ◽  
Methylene Blue ◽  
Silanol Group ◽  
Infrared Spectrometry ◽  
Blue Dye ◽  
Ammonium Bromide ◽  
Vibration Band ◽  
Order Kinetic ◽  
Methylene Blue Dye ◽  
Modified Bentonite

Batch experiments have been studied to remove methylene blue dye (MB) from aqueous solution using modified bentonite. The modified bentonite was synthesized by replacing exchangeable calcium cations in natural bentonite with cationic surfactant cetyl trimethyl ammonium bromide (CTAB). The characteristics of modified bentonite were studied using different analysis such as Scanning electronic microscopy (SEM), Fourier transform infrared spectrometry (FTIR) and surface area. Where SEM shows the natural bentonite has a porous structure, a rough and uneven appearance with scattered and different block structure sizes, while the modified bentonite surface morphology was smooth and supplemented by a limited number of holes. On other hand, (FTIR) analysis that proved NH group aliphatic and aromatic group of MB and silanol group are responsible for the sorption of contaminate. The organic matter peaks at 2848 and 2930 cm-1 in the spectra of modified bentonite which are sharper than those of the natural bentonite were assigned to the CH2 scissor vibration band and the symmetrical CH3 stretching absorption band, respectively, also the 2930 cm-1 peak is assigned to CH stretching band. The batch study was provided the maximum removal efficiency (99.99 % MB) with a sorption capacity of 129.87 mg/g at specified conditions (100 mg/L, 25℃, pH 11 and 250rpm). The sorption isotherm data fitted well with the Freundlich isotherm model. The kinetic studies were revealed that the sorption follows a pseudo-second-order kinetic model which indicates chemisorption between sorbent and sorbate molecules.

Structural Study of a new Compound Based on Acid 1,4-Cyclohexanedicarboxylic (1,4-CDC)

2010 ◽  
Vol 6 (1) ◽  
pp. 891-896
Author(s):  
Manel Halouani ◽  
M. Dammak ◽  
N. Audebrand ◽  
L. Ktari
Keyword(s):  
Aqueous Solution ◽  
Water Molecules ◽  
Carboxyl Group ◽  
X Ray Diffraction ◽  
Compound I ◽  
Unit Cell Parameters ◽  
Monoclinic System ◽  
X Ray ◽  
Cell Parameters ◽  
Cyclohexanedicarboxylic Acid

One nickel 1,4-cyclohexanedicarboxylate coordination polymers, Ni2 [(O10C6H4)(COO)2].2H2O  (I), was hydrothermally synthesized from an aqueous solution of Ni (NO3)2.6H2O, (1,4-CDC) (1,4-CDC = 1,4-cyclohexanedicarboxylic acid) and tetramethylammonium nitrate. Compound (I) crystallizes in the monoclinic system with the C2/m space group. The unit cell parameters are a = 20.1160 (16) Å, b = 9.9387 (10) Å, c = 6.3672 (6) Å, β = 97.007 (3) (°), V= 1263.5 (2) (Å3) and Dx= 1.751g/cm3. The refinement converged into R= 0.036 and RW = 0.092. The structure, determined by single crystal X-ray diffraction, consists of two nickel atoms Ni (1) and Ni (2). Lots of ways of which is surrounded by six oxygen atoms, a carboxyl group and two water molecules.

2-Deoxyribose Radicals in the Gas Phase and Aqueous Solution. Transient Intermediates of Hydrogen Atom Abstraction from 2-Deoxyribofuranose

2005 ◽  
Vol 70 (11) ◽  
pp. 1769-1786 ◽  
Author(s):  
Luc A. Vannier ◽  
Chunxiang Yao ◽  
František Tureček
Keyword(s):  
Aqueous Solution ◽  
Hydrogen Atom ◽  
Gas Phase ◽  
Computational Study ◽  
Hydrogen Atom Abstraction ◽  
Oh Radical ◽  
Free Energies ◽  
Intramolecular Hydrogen ◽  
Solvation Free Energies ◽  
Transient Intermediates

A computational study at correlated levels of theory is reported to address the structures and energetics of transient radicals produced by hydrogen atom abstraction from C-1, C-2, C-3, C-4, C-5, O-1, O-3, and O-5 positions in 2-deoxyribofuranose in the gas phase and in aqueous solution. In general, the carbon-centered radicals are found to be thermodynamically and kinetically more stable than the oxygen-centered ones. The most stable gas-phase radical, 2-deoxyribofuranos-5-yl (5), is produced by H-atom abstraction from C-5 and stabilized by an intramolecular hydrogen bond between the O-5 hydroxy group and O-1. The order of radical stabilities is altered in aqueous solution due to different solvation free energies. These prefer conformers that lack intramolecular hydrogen bonds and expose O-H bonds to the solvent. Carbon-centered deoxyribose radicals can undergo competitive dissociations by loss of H atoms, OH radical, or by ring cleavages that all require threshold dissociation or transition state energies >100 kJ mol-1. This points to largely non-specific dissociations of 2-deoxyribose radicals when produced by exothermic hydrogen atom abstraction from the saccharide molecule. Oxygen-centered 2-deoxyribose radicals show only marginal thermodynamic and kinetic stability and are expected to readily fragment upon formation.

Quest for the ideal olefin metathesis catalyst

2008 ◽  
Vol 80 (1) ◽  
pp. 31-43 ◽  
Author(s):  
Anna Michrowska ◽  
Karol Grela
Keyword(s):  
Oxygen Atom ◽  
Quaternary Ammonium ◽  
Olefin Metathesis ◽  
Amino Group ◽  
Sulfonated Polystyrene ◽  
Grubbs Catalyst ◽  
Metathesis Catalyst ◽  
Metathesis Catalysts ◽  
Novel Strategy ◽  
The Ideal

Attempts were made to create a catalyst that approaches Gladysz's vision of an "ideal catalyst". Modifications of the Hoveyda-Grubbs catalyst were carried out with the aim to increase its activity and broaden the scope of its applicability to challenging metathesis reactions. This was done by introduction of an electron-withdrawing substituent on the isopropoxybenzylidene group in order to diminish the donor properties of the oxygen atom. The resulting stable and easily accessible nitro-substituted Hoveyda-Grubbs catalyst has found a number of successful applications in various research and industrial laboratories. Also, a new concept for noncovalent immobilization of a ruthenium olefin metathesis catalyst is presented. The 2-isopropoxybenzylidene ligand of Hoveyda-Grubbs carbene is further modified by an additional amino group, and immobilization is achieved by treatment with sulfonated polystyrene, forming the corresponding ammonium salt. In this novel strategy for the immobilization of ruthenium-based metathesis catalysts, the amino group plays a dual role, being first an active anchor for immobilization and secondly, after protonation, activating the catalysts by electron-donating to -withdrawing switch. The same concept has been used in the preparation of a quaternary ammonium catalyst for aqueous olefin metathesis.

The Effect of Support Pretreatment with Ammonia on Pd/SiO2 Catalyst

2018 ◽  
Vol 922 ◽  
pp. 125-129
Author(s):  
Ji Soo Kwon ◽  
Jae Ho Baek ◽  
Hak Sung Lee ◽  
Man Sig Lee
Keyword(s):  
Silanol Group ◽  
N2 Adsorption ◽  
Ammonia Water ◽  
Co Chemisorption ◽  
Silanol Groups ◽  
Pd Dispersion ◽  
Highly Dispersed ◽  
High Metal ◽  
Ft Ir ◽  
Effect Of Support

We have reported the effect of support pretreatment with ammonia on Pd/SiO2 catalyst in this study. SiO2 was pretreated with ammonia water to increase the Pd dispersion before the preparation of Pd/SiO2 catalysts. The effect of support pretreatment with ammonia on Pd/SiO2 catalyst was investigated by XRD, FT-IR, N2-adsorption and FE-TEM. The Pd supported on pretreated SiO2 were characterized by XRD, CO-chemisorption and FE-TEM. The pretreatment of SiO2 with ammonia water lead to decrease of silanol groups (Si-OH) up to temperature 200 °C. This decline of silanol groups on the SiO2 affects highly dispersed Pd/SiO2 as 6.52 %. The result showed that the decrease of silanol group on the SiO2 was favorable for the Pd dispersion. It is reason that absence of the silanol groups contribute to the high metal reducibility.

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