Artificial brain structure-based modeling to predict the photo-thermal conversion performance of graphene nanoplatelets nanofluid using experimental data

Journal of Thermal Analysis and Calorimetry - Radiation is one of the means of thermal energy and heat transfer. Therefore, investigating and determining materials’ abilities to absorb energy...     

Using Taguchi experimental design to reveal the impact of parameters affecting the abrasion resistance of sol–gel based UV curable nanocomposite films on polycarbonate

This work aims at studying the abrasion resistance of differently formulated organic–inorganic hybrid coatings prepared by sol–gel method. The organic phase contained UV curable urethane acrylate oligomers and monomers having different functionalities. The inorganic phase was composed of tetraethyl orthosilicate (TEOS) and 3-methacryloxy propyltrimethoxy silane (MEMO). Through a Taguchi experimental design, the impact of influencing parameters such as molar ratio of precursors, hydrolysis ratio (R), post-curing temperature, post-curing time and weight percentage of inorganic to organic part were investigated. Very high transparency of hybrid coatings indicated that nano sized inorganic phase had formed. MEMO could facilitate the connection of two phases, preventing macro phase separation. However, high levels of MEMO lead to ‘defect structure’ in silica network as well as to decreased transparency and mechanical properties. The optimum condition in which highly transparent films with great abrasion resistance occurred was observed at equimolar ratio of water to alkoxide and TEOS: MEMO ratio being unity. Statistical analysis revealed that thermal post-curing was not significantly important.     

Hyperconjugative interactions are the main responsible for the anomeric effect: a direct relationship between the hyperconjugative anomeric effect,global hardness and zero-point energy

The correlations between the global hardness (η), hyperconjugative anomeric effect, Pauli exchange-type repulsions, electrostatic model associated with dipole–dipole interaction and structural parameters in 2-fluorotetrahydropyran, -thiopyran, -selenopyran (1–3) and their chloro- (4–6) and bromo-analogs (7–9) were investigated by means of the conventional and range-corrected functionals and natural bond orbital (NBO) interpretation. By deletion of the HC-exo-AE and HC-endo-AE, the equatorial conformations of compounds 1–9 become more stable than their corresponding axial forms, revealing that anomeric relationships in compounds 1–9 have the hyperconjugative anomeric effect origins while the electrostatic model associated with dipole–dipole interaction does not play a determining role on the variations of the anomeric relationships in these compounds. The anomeric relationships in compounds 1–3 have no Pauli exchange-type repulsions origin, but it has a significant impact on the conformational preferences in compounds 4–6 and 7–9. A canonical molecular orbital interpretation was conducted to investigate the correlations between the linear combinations of natural bond orbitals in the HOMOs, LUMOs and the global hardness (η) values. There is a direct relationship between the hyperconjugative anomeric effect, global hardness (η) and zero-point energies in compounds 1–3, 4–6 and 7–9. The harder axial conformations with the greater hyperconjugative anomeric effect and zero-point energy values are more stable than their corresponding equatorial forms.     

NBO,NMR Analysis,and Hybrid DFT Study of Structural and Configurational Properties of Di-tert-butyl-, bis(trimethysilyl)-, Bis(trimethgermyl)-, and Bis(trimethylstannyl)- cyclopenta-1,3-dienes

Abstract

The alkyl 1,2-shift in di-tert-butylcyclopenta-1,3-diene (1) and the metallotropic 1,2-shifts in bis(trimethylsilyl)cyclopenta-1,3-diene (2), bis(trimethylgermyl)cyclopenta-1,3-diene (3), and bis(trimethylstannyl)cyclopenta-1,3-diene (4) have been investigated by means of natural bond orbital (NBO), nuclear magnetic resonance (NMR) analysis, and hybrid density functional theory based methods. The B3LYP/DZVP results showed that the M(CH₃)₃ group [M = C (1), Si (2), Ge (3), and Sn (4)] migration barrier heights around cyclopentadienyl rings decrease from di-tert-butylcyclopenta-1,3-diene to its stannane derivative. Also, based on the results obtained, the stabilities of the 5,5-isomers in comparison to the 1,5- and 2,5-isomers increase from di-tert-butylcyclopenta-1,3-diene to its stannane derivative. The results suggest that in these compounds the metallotropic shifts are controlled by the stabilization energies associated with σ→π* electron delocalizations and the increase of the σ_C5-M→π*_C1-C2 electron delocalizations facilitates the M(CH₃)₃ group migrations around cyclopentadienyl rings. Based on the aromatic stabilization energy (ASE) values calculated, the aromaticity increases from the 5,5-isomers of di-tert-butylcyclopenta-1,3-diene to its stannane derivative but the variation of the nucleus-independent chemical shift, NICS(0) and NICS(1), values calculated are not in accordance with the ASE values calculated and the σ_C5-M→π*_C1-C2

electron delocalizations. The correlations between the sigmatropic shift barrier heights, σ→π* electron delocalizations, ASE, and NICS values were investigated.

GRAPHICAL ABSTRACT     

Experimental and theoretical studies of diethyl 2-(<Emphasis Type="Italic">ter</Emphasis>-butylimino)-2,5-dihydro-5-oxo-1-phenyl-1H-pyrrole-3,4-dicarboxylate using DFT calculations

In this study, diethyl 2-(ter-butylimino)-2,5-dihydro-5-oxo-1-phenyl-1H-pyrrole-3,4-dicarboxylate compound 1 is synthesized and characterized by FT-IR, ¹H and ¹³C NMR spectroscopy. The DFT calculations are carried out for compound 1 by B3LYP and PBE1PBE methods. The bond lengths, bond angles, dihedral angles, charge density on the atoms of 1 are calculated. A comparison of the DFT calculations indicate that the B3LYP method with the 6-311G++(d,p) basis set can give accurate results. The ¹³C NMR and ¹H NMR chemical shifts of 1 are calculated and compared with the available experimental data on the molecules. The nuclear independent chemical shift (NICS) calculations are utilized for the pyrrole ring in compound 1.     

Conformational Behaviors of 2-Substituted Cyclohexanone Oximes: An AB Initio,Hybrid Dft Study,and NBO Interpretation

Abstract

The impacts of the generalized anomeric effect (GAE) and gauche effect (GE) associated with donor–acceptor electron delocalizations and dipole–dipole interactions on the conformational properties of 2-methoxy- (1), 2-methylthio- (2), 2-methylseleno- (3), 2-fluoro- (4), 2-chloro- (5), and 2-bromocyclohexanone oxime (6) have been studied by means of hybrid density functional theory (B3LYP/6–311+G**) and ab initio molecular orbital (HF/6–311+G**)-based methods and natural bond orbital (NBO) interpretation. Both methods used showed that the above compounds exist predominantly in the axial chair conformation and the axial conformation stability increased from 2-methoxy- (1) to 2-methylselenocyclohexanone oxime (3) and also from 2-fluoro- (4) to 2-bromocyclohexanone oxime (6). The NBO analysis showed that the GAE increases from compound 1 to compound 3 and also from compound 4 to compound 6. GE does not have significant impact on the conformational behaviors of compounds 1–6 and GAE succeeds in accounting qualitatively for the increase of the axial preferences in both series of compounds.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements for the following free supplemental resource: Table S1.

Supporting Information Available. The structures optimized and thermodynamic functions of the axial and equatorial conformations of compounds 1–6. This material is available free of charge via the Internet.     

Structural characterization of tellurite glasses doped with transition metal oxides using Raman spectra and ab initio calculations

Systems of iron tellurite glasses were prepared by melt quenching with compositions of [85%TeO2+5%Fe2O3+10%TMO], where transition metal oxides (TMO) are TiO2, V2O5, MnO, CoO, NiO and CuO. Furthermore, the main structural units of these samples have been characterized by means of Raman spectra (150-1200 cm(-1)) as well as wavenumber predictions by means of Gaussian 98 ab initio calculations for the proposed site symmetries of TeO4(4-) triagonal bipyramid (C2v) and Te2O7(6-) bridged tetrahedra (Cs and C1). Aided by normal coordinate analysis, calculated vibrational frequencies, Raman scattering activities, force constants in internal coordinates and potential energy distributions (PEDs), revised vibrational assignments for the fundamental modes have been proposed. The main structural features are correlated to the dominant units of triagonal bipyramid (tbp) or bridged tetrahedral (TeO3+1 binds to TeO3 through TeOTe bridge; corner sharing). Moreover, the Raman spectra of the investigated tellurites reflect a structural change from tbp (coordination number is four) to triagonal pyramidal (coordination number is three).     

Mechanically controlled, morphologically determined sol–gel derived UV curable hybrid nanocomposites: SAXS and DMTA studies

This work reports preparation of organic–inorganic hybrid materials by sol–gel method. To this end, UV cured urethane acrylate and different functional monomers were used as organic network together with tetraethyl orthosilicate (TEOS) as inorganic network former and 3-methacryloxy propyltrimethoxy silane (MEMO) as network modifier. The effect of sol–gel precursor’s ratio on morphological properties of hybrid network was studied by small angle X-ray scattering (SAXS). Dynamic mechanical thermal analysis (DMTA) was performed to investigate the mechanical behavior of hybrid films. Whilst hybrids with low content of TEOS and high amounts of MEMO represented a “structural defect”, it was found that by increasing TEOS/MEMO ratio, the silica domain size decreased, showing a mass fractal behavior. This was attributed to a more compact structure of silica and a stronger hybrid network. The changes observed in compactness of hybrid films directly affected the glass transition temperature. By increasing the inorganic phase, more restriction in segmental motion of the polymeric phase occurred. Upon increasing TEOS/MEMO ratio a broader tan δ peak deduced from DMTA graphs was observed, indicating greater phase separation and higher heterogeneity.     

Chemical and biological treatment of waste water with a novel silver/ordered mesoporous alumina nanocomposite

One of the serious problems in the present century is chemical and biological pollution of the environment. Nanocomposites are multiphase solid materials that have been used as adsorbent of pollutants such as dyes, pesticides, anions and etc. in the last decades. In this study, a novel nanocomposite including silver nanoparticles and ordered mesoporous alumina (OMA) has been synthesized and used for the removal of dyes pollutants (methyl orange, bromothymol blue and reactive yellow) from aqueous solution. The characterization of synthesized nanocomposite has been performed by TEM, N₂ adsorption/desorption, XRD and energy dispersive X-ray spectroscopy analysis. The adsorption kinetic and equilibrium data have been obtained by UV–vis spectroscopy. The results show that the silver/OMA nanocomposite (Ag/OMA nanocomposite) is good adsorbent for the removal of anionic dyes from aqueous solution, and also this nanocomposite has a biocidal action against both Gram-negative and Gram-positive bacteria.