Synergistic effect of Thiourea and HCl on Palladium (II) recovery: An investigation on Chemical structures and thermodynamic stability via DFT

This work duly investigates the recovery of Pd (II) chlorocomplexes from industrial wastewater. Chemical structures and thermodynamic stabilities of the complex formed are evaluated via density functional theory (DFT). By applying synergistic solutions of thiourea mixed with hydrochloric acid (HCl), the stripping reaction of Pd (II) in the loaded Aliquat 336 occurs and Pd (II) chlorocomplexes coordinated thiourea ligands are formed, thus 80.19% of Pd (II) chlorocomplexes can be recovered. The aim of this study is to gain a better understanding of the stripping mechanisms and the structure of the complexes formed via the synergistic system. Such an understanding is still limited since little research has been conducted in this field. Owing to their molecular geometry, ligand coordination and donor groups play a vital role in the reactivity of palladium (II) complex. Quantum models have been developed to evaluate the chemical structure and thermodynamics stability of ((NH₂)₂CS·PdCl₂) namely: (i) DFT with B3LYP/6-31g(d,p) and MP2/6-31g(d,p) basis set, (ii) MP2 with cc-pVTZ basis set and (iii) CCSD(T)/cc-pVTZ. Results demonstrate that the highest geometric stability exhibited is the structure of Pd-S bonding with 180° Cl-Pd-Cl. The distance (r) and angle (a) of the selected geometrical parameters for (NH₂)₂CS·PdCl₂ complex are reported. Additionally, FTIR and UV–vis spectroscopies have been conducted to analyze the sampling solutions. Further, the calculated vibrational frequencies and experimental spectroscopic results show good agreement with the optimized geometry.     

The influence of cyclodextrin complexation on proton transfer in piperidinomethyl-2-naphthol

Summary Piperidinomethyl-2-naphthol forms inclusion complexes with -cyclodextrin with an equilibrium constant of 265M ^–1 in aqueous solution. The proton transfer equilibrium between the neutral and the zwitterionic form is strongly influenced by the association.

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Der Einfluß der Komplexierung mit -Cyclodextrin auf das Protontransfer-Gleichgewicht in Piperidino-2-naphthol (Kurze Mitt.)

Zusammenfassung Piperidinomethyl-2-naphthol bildet Einschlußkomplexe mit -Cyclodextrin mit einer Gleichgewichtskonstante von 265M ^–1. Das Protontransfer-Gleichgewicht zwischen neutraler Form und zwitterionischer Struktur wird durch diese Assoziation stark beeinflußt.

     

Proton exchange reactions of C2–C4 alkanes sorbed in ZSM-5 zeolite

Photoelectrochemical cells with TiO₂ electrodes to convert sunlight and water into gaseous hydrogen and oxygen are a source of clean and renewable fuel. Despite their great potential, far-from-ideal performance and poor utilization of the solar spectrum have prevented them from becoming a widespread and practical technology. We review recent experimental work that uses dynamics measurements to study limitations of photoelectrochemical cells from a fundamental level and the use of TiO₂ nanotube arrays as a superior alternative to TiO₂ nanoparticles. Through a combination of nanoscale size control, doping, composite materials, and the incorporation of noble-metal nanoparticles, improved performance and light harvesting are demonstrated.     

An n-channel two-dimensional covalent organic framework

Co-condensation of metallophthalocyanine with an electron-deficient benzothiadiazole (BTDA) block leads to the formation of a two-dimensional covalent organic framework (2D-NiPc-BTDA COF) that assumes a belt shape and consists of AA stacking of 2D polymer sheets. Integration of BTDA blocks at the edges of a tetragonal metallophthalocyanine COF causes drastic changes in the carrier-transport mode and a switch from a hole-transporting skeleton to an electron-transporting framework. 2D-NiPc-BTDA COF exhibits broad and enhanced absorbance up to 1000 nm, shows panchromatic photoconductivity, is highly sensitive to near-infrared photons, and has excellent electron mobility as high as 0.6 cm(2) V(-1) s(-1).     

Comparative molecular field analysis of artemisinin derivatives: Ab initio versus semiempirical optimized structures

Based on the belief that structural optimization methods, producing structures more closely to the experimental ones, should give better, i.e. more relevant, steric fields and hence more predictive CoMFA models, comparative molecular field analyses of artemisinin derivatives were performed based on semiempirical AM1 and HF/3-21G optimized geometries. Using these optimized geometries, the CoMFA results derived from the HF/3-21G method are found to be usually but not drastically better than those from AM1. Additional calculations were performed to investigate the electrostatic field difference using the Gasteiger and Marsili charges, the electrostatic potential fit charges at the AM1 level, and the natural population analysis charges at the HF/3-21G level of theory. For the HF/3-21G optimized structures no difference in predictability was observed, whereas for AM1 optimized structures such differences were found. Interestingly, if ionic compounds are omitted, differences between the various HF/3-21G optimized structure models using these electrostatic fields were found.     

Theoretical investigations on the stereoselectivity of the proline catalyzed Mannich reaction in DMSO

The stereocontrol steps of the (S)-proline catalyzed Mannich reaction of cyclohexanone, formaldehyde, and aniline were theoretically investigated. The geometries of reactants, products, and transition states were optimized using density functional theory using the B3LYP functional with the 6-31++G(d,p) basis set. The energies of these compounds were then more accurately determined at the MP2 level, and the effect of DMSO as the solvent was included using a polarizable continuum model (PCM). The reaction was modeled from the previously proposed mechanism that cyclohexanone reacts with (S)-proline to generate an enamine, while formaldehyde reacts with aniline to produce an imine, and that the conformation around the C-N bond of the enamine 1 is crucial for the further enantioselective step. The formation of two conformations of the enamine via a proton transfer process was examined, revealing activation barriers for syn- and anti-enamine proton transfer of 10.2 and 17.9 kcal/mol, respectively. The transformation of syn- to anti-enamine through C-N bond rotation, however, was predicted to require only 4.2 kcal/mol, while the (S)- and (R)-intermediates could be obtained from subsequent reactions between enamine and imine with energy barriers of 8.5 and 12.4 kcal/mol, respectively. The difference between these barriers, but not the C-N rotation energy, becomes larger at the MP2 level and when DMSO as a solvent is included. This predicted enantioselective reaction, through the kinetic and thermodynamic favoring of the (S)-pathway, is in agreement with experimental results, which have reported the (S)-configuration as the major product.     

The electronic and molecular structure of carbon clusters: C8 and C10

Summary The equilibrium geometries of C₈ and C₁₀ have been determined from electronic structure calculations, using a variety of correlated methods and large basis sets of atomic natural orbitals. For C₈, a cyclic form withC _4h symmetry (¹ A _g) and a linear, cumulene-like form (³ _g ^– ) are isoenergetic candidates for the electronic ground state. For C₁₀, the ground-state equilibrium structure is definitely monocyclic. Three different cyclic structures have been considered here, i.e. cumulenicD _10h , distorted-cumulenicD _5h and acetylenicD _5h . These are all essentially isoenergetic, and are about 50 kcal/mol below the linear³ _g ^– state. The choice of basis sets and methods used has a strong impact on the predicted ground-state structures.Dedicated to Prof. Klaus Ruedenberg     

Glucose transformation to 5‐hydroxymethylfurfural in acidic ionic liquid: A quantum mechanical study

Isomerization and transformation of glucose and fructose to 5‐hydroxymethylfurfural (HMF) in both ionic liquids (ILs) and water has been studied by the reference interaction site model self‐consistent field spatial electron density distribution (RISM‐SCF‐SEDD) method coupled with ab initio electronic structure theory, namely coupled cluster single, double, and perturbative triple excitation (CCSD(T)). Glucose isomerization to fructose has been investigated via cyclic and open chain mechanisms. In water, the calculations support the cyclic mechanism of glucose isomerization; with the predicted activation free energy is 23.8 kcal mol^?1 at experimental condition. Conversely, open ring mechanism is more favorable in ILs with the energy barrier is 32.4 kcal mol^?1. Moreover, the transformation of fructose into HMF via cyclic mechanism is reasonable; the calculated activation barriers are 16.0 and 21.5 kcal mol^?1 in aqueous and ILs solutions, respectively. The solvent effects of ILs could be explained by the decomposition of free energies and radial distribution functions of solute‐solvent that are produced by RISM‐SCF‐SEDD. © 2015 Wiley Periodicals, Inc.     

Accurate torsional potentials in conjugated systems: ab initio and density functional calculations on 1,3-butadiene and monohalogenated butadienes

Accurate calculations of the torsional potentials for rotation around the carbon–carbon single bond of all conceivable monohalogenated 1,3-butadienes C₄ H ₅X, (X?∈?[F, Cl, Br]), are presented. The parent compound, 1,3-butadiene, is also included as a benchmark and reference case. Large-scale ab initio calculations were performed at the second-order Møller–Plesset perturbation theory (MP2) and the coupled cluster, CCSD(T), levels. Additionally, density functional methods were applied. In all compounds considered, the anti- or s-trans-conformation is the most stable. For all three halogens, the 2-halo-1,3-butadiene is the most stable isomer, followed by the cis-1-halo-1,3-butadiene. Depending on the position and the type of halogen, the original 1,3-butadiene torsional potential is modified in a different manner. The modifications are particularly visible in the region of the syn- or s-cis and the gauche structures and in the barrier heights.