Theoretical Studies on the Chemical Structure of Carboxymethyl Chitosan

The density functional theory (DFT) calculations explored the structural optimization and the frequency of N-carboxymethyl chitosan (N-CMCS) and O-carboxymethyl chitosan (O-CMCS). For the isomers, the calculations comparatively were performed. The charge distribution and frontier molecular orbit were analyzed by using the natural bond orbital (NBO) method. The results showed: the two rotational isomers a and b can stably exist, with the stability order a>b; N-carboxymethyl chitosan reaction active sites are concentrated in -OH and -NHCH2COOH, while O-carboxymethyl chitosan reaction active sites are concentrated in -NH2 and -CH2COOH; The water-soluble mechanism of carboxymethyl chitosan was investigated deeply, on the one hand, the presence of carboxymethyl of carboxymethyl chitosan had a tendency to ionize H+, on the other hand the carboxymethyl increased the distance and weakened the hydrogen bonds between molecules, even though Einstein shift H-bond is formed in the carboxymethyl chitosan molecules.

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Study of the Stability and Chemical Reactivity of a Series of Tetrazole Pyrimidine Hybrids by the Density Functional Theory Method (DFT)

Oriental Journal Of Chemistry ◽

10.13005/ojc/370406 ◽

2021 ◽

Vol 37 (4) ◽

pp. 805-812

Author(s):

Ahissandonatien Ehouman ◽

Adjoumanirodrigue Kouakou ◽

Fatogoma Diarrassouba ◽

Hakim Abdel Aziz Ouattara ◽

Paulin Marius Niamien

Keyword(s):

Density Functional ◽

Theoretical Study ◽

Molecular Descriptors ◽

Chemical Reactivity ◽

Density Functional Theory Method ◽

Functional Theory ◽

Reactivity Descriptors ◽

The Density Functional Theory ◽

The Stability ◽

Global Reactivity Descriptors

Our theoretical study of stability and reactivity was carried out on six (06) molecules of a series of pyrimidine tetrazole hybrids (PTH) substituted with H, F, Cl, Br, OCH3 and CH3 atoms and groups of atoms using the density function theory (DFT). Analysis of the thermodynamic formation quantities confirmed the formation and existence of the series of molecules studied. Quantum chemical calculations at the B3LYP / 6-311G (d, p) level of theory determined molecular descriptors. Global reactivity descriptors were also determined and analyzed. Thus, the results showed that the compound PTH_1 is the most stable, and PTH_5 is the most reactive and nucleophilic. Similarly, the compound PTH_4 is the most electrophilic. The analysis of the local descriptors and the boundary molecular orbitals allowed us to identify the preferred atoms for electrophilic and nucleophilic attacks.

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Structural, elastic, electronic and thermal properties of InAs: A study of functional density

Revista Facultad de Ingeniería ◽

10.19053/01211129.v26.n46.2017.7320 ◽

2017 ◽

Vol 26 (46) ◽

Author(s):

Víctor Mendoza-Estrada ◽

Melissa Romero-Baños ◽

Viviana Dovale-Farelo ◽

William López-Pérez ◽

Álvaro González-García ◽

...

Keyword(s):

Thermal Properties ◽

Density Functional ◽

Experimental Studies ◽

Debye Model ◽

Band Gap Energy ◽

Functional Theory ◽

Zinc Blende ◽

The Density Functional Theory ◽

The Stability ◽

Experimental Values

In this research, first-principles calculations were carried out within the density functional theory (DFT) framework, using LDA and GGA, in order to study the structural, elastic, electronic and thermal properties of InAs in the zinc-blende structure. The results of the structural properties (a, B0, ) agree with the theoretical and experimental results reported by other authors. Additionally, the elastic properties, the elastic constants (C11, C12 and C44), the anisotropy coefficient (A) and the predicted speeds of the sound ( , , and ) are in agreement with the results reported by other authors. In contrast, the shear modulus (G), the Young's modulus (Y) and the Poisson's ratio (v) show some discrepancy with respect to the experimental values, although, the values obtained are reasonable. On the other hand, it is evident the tendency of the LDA and GGA approaches to underestimate the value of the band-gap energy in semiconductors. The thermal properties (V, , θD yCV) of InAs, calculated using the quasi-harmonic Debye model, are slightly sensitive as the temperature increases. According to the stability criteria and the negative value of the enthalpy of formation, InAs is mechanically and thermodynamically stable. Therefore, this work can be used as a future reference for theoretical and experimental studies based on InAs.

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Computational Evidence Suggests That 1-chloroethanol May Be an Intermediate in the Thermal Decomposition of 2-chloroethanol into Acetaldehyde and HCl

10.26434/chemrxiv.7608857.v1 ◽

2019 ◽

Author(s):

Zoi Salta ◽

Agnie M. Kosmas ◽

Oscar Ventura ◽

Vincenzo Barone

Keyword(s):

Aqueous Solution ◽

Water Molecule ◽

Gas Phase ◽

Density Functional ◽

Water Molecules ◽

Functional Theory ◽

Direct Transformation ◽

The Density Functional Theory ◽

Successive Step ◽

The One

The dehalogenation of 2-chloroethanol (2ClEtOH) in gas phase with and without participation of catalytic water molecules has been investigated using methods rooted into the density functional theory. The well-known HCl elimination leading to vinyl alcohol (VA) was compared to the alternative elimination route towards oxirane and shown to be kinetically and thermodynamically more favorable. However, the isomerization of VA to acetaldehyde in the gas phase, in the absence of water, was shown to be kinetically and thermodynamically less favorable than the recombination of VA and HCl to form the isomeric 1-chloroethanol (1ClEtOH) species. This species is more stable than 2ClEtOH by about 6 kcal mol-1, and the reaction barrier is 22 kcal mol-1 vs 55 kcal mol-1 for the direct transformation of VA to acetaldehyde. In a successive step, 1ClEtOH can decompose directly to acetaldehyde and HCl with a lower barrier (29 kcal mol-1) than that of VA to the same products (55 kcal mol-1). The calculations were repeated using a single ancillary water molecule (W) in the complexes 2ClEtOH_W and 1ClEtOH_W. The latter adduct is now more stable than 2ClEtOH_W by about 8 kcal mol-1, implying that the water molecule increased the already higher stability of 1ClEtOH in the gas phase. However, this catalytic water molecule lowers dramatically the barrier for the interconversion of VA to acetaldehyde (from 55 to 6 kcal mol-1). This barrier is now smaller than the one for the conversion to 1ClEtOH (which also decreases, but not so much, from 22 to 12 kcal mol-1). Thus, it is concluded that while 1ClEtOH may be a plausible intermediate in the gas phase dehalogenation of 2ClEtOH, it is unlikely that it plays a major role in water complexes (or, by inference, aqueous solution). It is also shown that neither in the gas phase nor in the cluster with one water molecule, the oxirane path is competitive with the VA alcohol path.

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Electronic and structural study of hexagonal TiC nanowires: ab initio study

BIBECHANA ◽

10.3126/bibechana.v16i0.20865 ◽

2018 ◽

Vol 16 ◽

pp. 7-14 ◽

Cited By ~ 1

Author(s):

Puspa Raj Adhikari ◽

Om Prakash Upadhyay ◽

Gopi Chandra Kaphle ◽

Anurag Srivastava

Keyword(s):

Density Functional ◽

Small Diameter ◽

Hexagonal Structure ◽

Density Of State ◽

Electronic Density ◽

Functional Theory ◽

The Density Functional Theory ◽

The One ◽

The Impact ◽

Bulk Structures

Nanowire are the one-dimensional nanostructure with the diameter order of one to few hundred nanometre. These structure shows unique properties other than their bulk structures. In this article, a qualitative first principle discussion of TiC nanowire is reported, indicating the impact of DFT based GGA relativistic corrections on its electronic properties. Here, we analyse the Titanium Carbide (TiC) nanowire of hexagonal structure periodic in Z-direction with the density functional theory (DFT). The GGA with RBBE Correlation analysis of this material shows the metallic characteristics in its bulk but the electronic density of state shows that the hybridization state are different from their bulk when the material is analysed in nanostructure form. Three structures of hexagonal TiC nanowire directed in (1,1,1) plane were analysed to explore diameter (4-18) Å dependent comparative study of electronic, stabilizing and optical property which shows unique different result counterparts to its bulk. Hexagonal TiC nanowire were found to be semiconducting with narrow band gap (0.21-0.34) eV in small diameter while metallic in higher diameter. They are comparable stables as their bulk for higher structure. Similarly, for the same investigation, the structures are cross checked by surface atom passivation to verify the reliability of the result that we found.BIBECHANA 16 (2019) 7-14

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Density Functional Theory Calculations of Properties of the Grain Boundaries in Aluminum

MRS Proceedings ◽

10.1557/opl.2011.531 ◽

2011 ◽

Vol 1297 ◽

Cited By ~ 2

Author(s):

Marek Muzyk ◽

Krzysztof J. Kurzydlowski

Keyword(s):

Density Functional Theory ◽

Grain Boundaries ◽

Density Functional ◽

Quantitative Description ◽

Aluminum Matrix ◽

Density Functional Theory Calculations ◽

Functional Theory ◽

Nano Crystalline ◽

The Density Functional Theory ◽

The Stability

ABSTRACTThe Density Functional Theory has been used to analyze an inter-granular segregation of Cu and Mg. The stability of Cu and Mg atoms in the aluminum matrix, intermetallic phases and symmetric twist grain boundaries has been compared. The quantitative description of solubility of Cu and Mg atoms in the nano-crystalline aluminum has been proposed. The calculations have been carried out to investigate the properties of symmetric twist boundaries in aluminum with and without Cu/Mg atoms. The phenomena of are discussed and its effect on the stability of precipitates containing these elements.

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Influences of Fe Doping on the Electronic Structure of Mg(0001) Surface and Hydrogenation Mechanism in Fe-Doped Mg(0001) Surface

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.873.114 ◽

2013 ◽

Vol 873 ◽

pp. 114-120 ◽

Cited By ~ 3

Author(s):

Zhi Wen Wang ◽

Xin Jun Guo ◽

Hong Xia Zhang ◽

Li Li

Keyword(s):

Density Functional ◽

Hydrogen Molecule ◽

Functional Theory ◽

Practical Applications ◽

Atom Diffusion ◽

Charge Density Difference ◽

The Density Functional Theory ◽

Diffusion Paths ◽

The Stability ◽

Dissociation Path

First-principles calculations within the density functional theory (DFT) have been carried out to study the interaction of hydrogen molecule with Fe-doped Mg (0001) surfaces. First we have calculated the stability of the Fe atom on the Mg surface, On the basis of the energetic criteria, Fe atom prefer to substitute one of the Mg atoms from the second layer. In the second step, we have studied the interaction between hydrogen molecule and the Fe-doped Mg (0001) surface. The results show that for Fe atoms doped Mg (0001) surface in the second layer, enhances the chemisorption interaction between H2molecule and Fe atom, but also benefits H atom diffusion into Mg bulk with relatively more diffusion paths compared with that of clean Mg surface. Charge density difference plots provided some ideas about why certain alloying elements on the surface reduce the energy barrier of H2molecule dissociation on Fe-doped Mg (0001) surface. We can see that Fe as catalyst for the hydrogenation/dehydrogenation of Mg alloy samples and provide more dissociation path for H2molecule and diffusion paths for H atom, The present results not only beneficial for clarify the experimentally observed fast hydrogenation kinetics for Fe-capped Mg materials but also help to design new types of hydrogen storage materials for practical applications in the auto industry.

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Aromaticity in pericondensed cyclopenta-fused polycyclic aromatic hydrocarbons determined by density functional theory nucleus-independent chemical shifts and the Y-rule — Implications in oil asphaltene stability

Canadian Journal of Chemistry ◽

10.1139/v09-052 ◽

2009 ◽

Vol 87 (10) ◽

pp. 1280-1295 ◽

Cited By ~ 20

Author(s):

Yosadara Ruiz-Morales

Keyword(s):

Density Functional Theory ◽

Thermodynamic Stability ◽

Density Functional ◽

Chemical Shifts ◽

Functional Theory ◽

Electronic Distribution ◽

Polycyclic Aromatic ◽

Minimum Number ◽

The Stability ◽

The One

The characterization of the stability of the fused aromatic region (FAR) in oil asphaltenes in terms of kinetic and thermodynamic stability is primary. Such an understanding is important if we are to get the optimal use from the heavy fraction of any crude oil. The FAR region is composed of pericondensed cyclopenta-fused polycyclic aromatic hydrocarbon compounds (CPPAHs) with N, S, and O heteroatoms. The Clar model, which states that the most important representation of a PAH is one having the maximum number of disjoint π-sextets, depicted by inscribed circles, and a minimum number of fixed double bonds, captures the essence of the kinetic and thermodynamic stability arguments. This model is readily employed for complex aromatics of the sort to be considered for asphaltenes. In the present research we prove that the aromaticity of CPPAHs can be assessed by using the qualitative easy-to-apply Y-rule. In the literature, it is proven that the Y-rule is applicable to elucidate the aromaticity of benzenoid PAHs and it has been validated for pericondensed benzenoid PAHs but not for pericondensed CPPAHs. Here, we verify that it is applicable for CPPAHs. The applicability of the Y-rule has been theoretically proven by comparing the π-electronic distribution obtained with it with the one obtained from nucleus-independent chemical shift (NICS) calculations at the density functional theory (DFT) level. The importance of doing this is that due to the polydispersity in the composition of the oil asphaltenes, and to understand their aromatic core structure, it is necessary to be able to asses the aromaticity of many cyclopenta-fused PAHs (possibly more than 500), of different sizes (up to 15 rings between hexagons and pentagons), and different spatial rearrangements in a quick but realistic and effective way. To try to do this with NICS will be very time consuming and computationally expensive, especially in the case of big systems.

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The difference in stability between 5′R and 5′S diastereomers of 5′,8-cyclopurine-2′-deoxynucleosides. DFT study in gaseous and aqueous phase

Open Chemistry ◽

10.2478/s11532-009-0104-1 ◽

2010 ◽

Vol 8 (1) ◽

pp. 134-141 ◽

Cited By ~ 1

Author(s):

Boleslaw Karwowski

Keyword(s):

Density Functional ◽

Bond Cleavage ◽

Basis Set ◽

Small Range ◽

Functional Theory ◽

The Density Functional Theory ◽

Formic Acid Hydrolysis ◽

The Difference ◽

The Stability ◽

First Time

AbstractOxidatively generated damage to DNA frequently appears in the human genome as an effect of aerobic metabolism or as the result of exposure to exogenous oxidizing agents. Due to these facts it has been decided to calculate the stability of 5′,8-cyclo-2′-deoxyadenosine/guanosine (cdA, cdG) in their 5′R and 5′S diastereomeric forms. For all points of quantum mechanics studies presented, the density functional theory (DFT) with B3LYP parameters on 6-311++G** basis set level was used. The calculations showed a significant negative enthalpy for glycosidic bond cleavage reaction for cationic forms and slightly negative for neutral ones. The preliminary study of the discussed process has shown the nature of stepwise nucleophilic substitution DN*AD type mechanism. Surprisingly, the different values in free energy, between short-lived oxacarbenium ion intermediates, have been found to lie over a relatively small range, around 1 and 2.8 kcal mol−1. For anions, the decomposition enthalpies were found as positive in aqueous phases. These theoretical results are supported by the formic acid hydrolysis experiments of both diastereomers of cdA, for the first time. (5′S)cdA exhibited higher stability than (5′R)cdA.

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First-principle study of the electronic structure and optical property of Nb-doped anatase TiO2

International Journal of Modern Physics B ◽

10.1142/s021797921450091x ◽

2014 ◽

Vol 28 (17) ◽

pp. 1450091

Author(s):

Q. Y. Hou ◽

Q. L. Liu ◽

C. W. Zhao ◽

Y. Zhang

Keyword(s):

Electronic Structure ◽

Optical Property ◽

Band Gap ◽

Absorption Edge ◽

Short Wavelength ◽

Density Functional ◽

Functional Theory ◽

Long Wavelength ◽

The Density Functional Theory ◽

The Stability

The absorption edge shifted to long wavelength direction and short wavelength direction of two opposite experimental conclusions have been reported, when the band-gap and absorption spectra of Nb -doped anatase TiO 2 were studied. In order to solve this contradiction, the electronic structure and the optical property of Nb heavy doped anatase TiO 2 have been studied by the first-principles plane-wave ultrasoft pseudopotential method based on the density functional theory with +U method modification. The calculated results indicate that the higher the Nb -doping is, the higher the total energy is, the worse the stability is, the higher the formation energy is, the more difficult the doping is, the wider the optical band-gap is, the more obvious the absorption edge shifting to short wavelength direction is, the lower the absorptivity and the reflectivity is, which is in agreement with the experimental results. The reasonable interpretation of the contradiction has been reported in this paper, too.

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Gold Nanoclusters Grown on MoS2 Nanosheets by Pulsed Laser Deposition: An Enhanced Hydrogen Evolution Reaction

Molecules ◽

10.3390/molecules26247503 ◽

2021 ◽

Vol 26 (24) ◽

pp. 7503

Author(s):

Yuting Jing ◽

Ruijing Wang ◽

Qiang Wang ◽

Xuefeng Wang

Keyword(s):

Active Sites ◽

Density Functional ◽

Au Nanoparticles ◽

Gold Nanoclusters ◽

Density Functional Theory Calculations ◽

Laser Deposition ◽

Mos2 Nanosheets ◽

Functional Theory ◽

The Density Functional Theory ◽

A Current

Au nanoparticles were decorated on a 2H MoS2 surface to form an Au/MoS2 composite by pulse laser deposition. Improved HER activity of Au/MoS2 is evidenced by a positively shifted overpotential (−77 mV) at a current density of −10 mA cm−2 compared with pure MoS2 nanosheets. Experimental evidence shows that the interface between Au and MoS2 provides more sites to combine protons to form an active H atom. The density functional theory calculations found that new Au active sites on the Au and MoS2 interface with improved conductivity of the whole system are essential for enhancing HER activity of Au/MoS2.

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