EH Calculations Research Articles

Sentinel-2A and Landsat 8 OLI to model benthic habitat biodiversity index

Biodiversity of benthic habitats is among the highest of all ecological communities. This study was conducted to model benthic habitat biodiversity indices using a remote sensing approach in optically shallow waters in Karimunjawa Islands-Indonesia. These islands have a wide variety of benthic environments. Two multispectral imagers, namely Sentinel-2A and Landsat 8 OLI, were used. A series of statistical tests were applied in the empirical modeling using the pixel values of both images with in situ Shannon index (H), Simpson index (D), and Shannon's Equitability (EH) calculations. The modeling inputs were sunglint-corrected bands, water column-corrected bands, PCA-transformed bands, MNF bands, and occurrence texture bands. The results indicate that multispectral remote sensing images can be used to map benthic habitat biodiversity indices. However, the difference between the concepts of H, D, and EH calculations and the reflectance value recorded by the sensor remove the possibility of obtaining higher accuracy. H, D, and EH maps derived from Sentinel-2A had varying levels of accuracy, namely 46.8%, 59.1%, and 54.5%, respectively, while Landsat 8 OLI produced these three maps with 45.81%, 57.34%, and 53.81% accuracy.

The state of reduced glutathione in patients with impaired glycemic states and coronary heart disease

Antioxidative mechanisms prevent human body from the damaging action of free radicals and reactive oxygen species. Glutathione and related to it enzyme systems detoxicate H2O2 and hyperoxide and from there, reduced glutathione is a potential marker of oxidative stress level. Purpose: To investigete glutathione of erythrocytes in patients with prediabetes (IGT & IFG) and type 2 diabetes and concomitant coronary heart disease (CHD). Matherial and methods: We examined 25 patients with T2D and concomitant CHD and atherosclerosis (group 1), 20 patients with prediabetes (IGT & IFG) newly diagnosed and the same co-morbidity (group 2) and 47 almost healthy person (group 3). Examinations included clinical laboratory evaluation, fasting glicose, HbA1c. Total glutathione (GSHt) and oxidized glutathione (GSSG) were measered by use of glutathione reductase reaction. Redox potential (Eh) of glutathione was evaluated by use of Nernst equation. Results: Concentrations of GSHt and GSH were greater in group 2 to compare with groups 1 and 3 (by 4,2 times, p=0,012 and by 3,1 times, p=0,005 respectively). Increase of concentration of GSSG in group 1 may change extracellular redox condition. Calculation of Eh revealed its change to oxidized condition in group 1 to compare with group 2 (19,0 mV greater) and group 3 (15,4 mV greater). Conclusion: Antioxidant defense in red-cells is overactivated during prediabetes (IGT & IFG) with concomitant CHD and atherosclerosis while in patients with T2D was noticed depletion of compensatory mechanisms with increased GSSG and Eh. Reduction in 2GSH/GSSG suggests that intracellular antioxidant is lost; herewith cells become sensitive to oxidative stress.

Determination of the elastic properties of single microcapsules using micromanipulation and finite element modeling

Finite element modeling (FEM) has been used to simulate the compression of single elastic core–shell capsules between two parallel plates. FEM allows characterizing the compressions at deformations beyond the wall thickness, when both bending and stretching contribute to the force resisting compression. Due to the incorporation of bending effects, the force deformation profiles of capsules with the same elastic modulus E depend on the wall thickness to capsule radius ratio ( h/r). A model is presented that enables the (i) calculation of h/r from the individual compression force profiles at fractional deformations lower than 0.1, thus applicable for brittle capsules and for elastic–plastic capsules and (ii) calculation of Eh by comparison with FEM data at that h/r. Thus, the model allows the determination of E from compression data alone, as the wall thickness is also determined. The compression of melamine–formaldehyde capsules with a hexyl salicylate core using a micromanipulation technique is given as an example of the application of the model. The estimated wall thickness value, found to be independent of the capsule size, is in excellent agreement with transmission electron microscopy measurements.

A Quantum Mechanically Guided View of Mg44Rh7.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

New Cu(i) and Ag(i) binuclear complexes containing the dppa ligand

New Cu(I) and Ag(I) binuclear complexes were prepared by reaction of [M(NCCH3)4][PF6] (M = Ag, Cu) with the bidentate phosphine ligands Ph2PNHPPh2 (dppa) and Ph2PCH2PPh2 (dppm). In the reaction of Cu(I) with dppa the phosphine is easily oxidized to give the octahedral species of [Cu(dppaO2)3][PF6], 1. In an inert atmosphere, the binuclear complexes [Cu2(dppa)2(NCCH3)3][PF6]2, 2, [Cu2(dppa)2(NCCH3)4][PF6]2, 3, [Ag2(dppa)2(NCCH3)2][PF6]2, 4, and [Ag2(dppm)2][PF6]2, 5, were formed and structurally characterized by X-ray diffraction (except for 5). The electrochemical studies showed that the most relevant property of the binuclear species was the ease of forming the metal upon reduction. EH and DFT calculations were performed in order to try and understand the structural features of the [M2(dppa)2(NCCH3)x]n+ complexes, including the 0.47 A increase in M⋯M distance upon going from 2 to 3.

The H⋯H interaction in the solid state structure of HMn(CO)5

HMn(CO)5 is an interesting complex which forms H⋯H bonded dimers in the crystal, with a separation of 2.292 A. In previous work, this interaction was explained on the basis of EH calculations and the geometry was partly reproduced by DFT calculations. HF and MP2 calculations were performed in several possible HMn(CO)5 dimers and led to the conclusion that the H⋯H bonded dimers interact more strongly than ones with a H⋯O close contact. The formation of the dimer was studied with the two H–Mn–Cax axes approaching linearly or at the experimental angle (155.8°), the first being more stable but exhibiting too short a H⋯H distance. In the geometry similar to the experimental one, the stabilization is −5.1 kcal mol−1, with the BSSE correction, and correlation effects contribute significantly to the formation of the dimer.

(Bipyridine)(terpyridine)(4-iodophenylcyanamide)ruthenium(II) complex: crystallography, electronic absorption spectroscopy, cyclic voltammetry and EPR measurements

The complex [Ru(bpy)(tpy)(Ipcyd)] + (where bpy: 2,2′-bipyridine, tpy: 2,2′:6′,2′′-terpyridine and Ipcyd: 4-iodophenylcyanamide anion) has been synthesized. An extensive characterization was carried out using IR, 1H and 13C NMR, ES-MS, UV–Vis, electrochemistry, EPR and X-ray single crystal diffraction analysis. Cyclic voltammogram shows an irreversible anodic peak around 0.7 V/ECS, the shape of the wave is typical of an electrochemical-chemical (EC) mechanism with an half-life time in the order of seconds for the generated species. Oxidation of the title compound has been investigated in order to explore its ability as a magnetic probe for further electronic studies on dinuclear complexes. The EPR spectrum at 100 K of the monooxidized species displays g ⊥=2.00 and g ∣∣=1.96 attributed to the presence of a radical coming from the phenylcyanamide oxidation, in relative good agreement with EH and ZINDO calculations.

A theoretical analysis of how geometrical distortions on Cu(μ-Cl) 2Cu dimers influence their electronic and magnetic properties

A structural classification of dimers, containing the Cu(μ-Cl) 2Cu core, based on data obtained from X-ray diffraction analysis reported in the literature has been performed. In these complexes, the local geometry around the copper metal center is generally a square pyramid, with a different degree of distortion towards a trigonal bipyramid. The global geometry of the dinuclear complex can be described in terms of the relative arrangement of the two square pyramids, giving rise to three types of geometries, termed: coplanar bases, parallel bases and perpendicular bases. Ideal models representing these geometries were defined and EH calculations were performed in each case, showing the different molecular orbitals involved in their corresponding frontier orbitals, together with their energy. EH calculations were also carried out for dimers embodying different type of structural distortions from the ideal models. The results obtained from those EH calculations have proven to be extremely useful for the proper interpretation and correlation of the magnetic data and dimer structure for those Cu(μ-Cl) 2Cu complexes reported in the literature.

Hydrochloric acid leaching of a pre-reduced Brazilian ilmenite concentrate in an autoclave

As a part of the Project on Integrated utilization of the Fe–Ti–V ore from Campo Alegre de Lourdes (Bahia), the present work have as its main objective to investigate the hydrochloric acid leaching of a pre-reduced ilmenitic concentrate, with the purpose of obtaining synthetic rutile. Initially, the crude ore was submitted to the following steps: partial reduction, grinding, sizing and magnetic separation at low and high intensity (the last one shown to be of low effectiveness). In order to guide the thermogravimetric analysis of the ilmenite during pyrometallurgical treatments, oxidation–reduction diagrams of the Fe–Ti–H–O system were constructed. Tests of those treatments were conducted in a STANTON thermobalance to determine the best operational conditions. Of fundamental importance were the calculation and construction of Eh–pH diagrams for the system Fe–Ti–Cl–H 2O at elevated temperatures, in the development of the hydrochloric acid leaching processes studied. It was verified, through these diagrams, that a reaction medium of high acidity and moderately reductive potential is necessary to get iron into solution, in the Fe 2+ form, and titanium as a solid oxide (TiO 2). Eh–pH diagrams for the system Fe–Cl–H 2O, at elevated concentrations were also produced, through which it became possible to explain the results of the processes developed by previous researchers. Tests on hydrochloric acid leaching were carried out in a Parr autoclave, model 4562. It was observed that in the hydrochloric acid leaching on the pretreated ilmenitic concentrate, the effect of the oxidation as a pre-treatment step before reduction is not significant. The best results for iron extraction (about 97.5%) and titanium content in the residue (about 47.5%) were obtained with hydrochloric acid leaching of the reduced ilmenitic concentrate at 100°C with 4 M HCl solution.

A Method for Calculating Thermal Radiation Properties of Multilayer Films from Optical Constants

A calculation method for the incident angle dependence of the solar absorptance αS and the temperature dependence of the total hemispherical emittance eH of multilayer films is proposed. The method is based on calculation of αS and eH from optical constants in the wavelength region from 0.25 to 100 μm for thin polymer films and deposited metal. In this paper we provide values of αS in the incident angle region from 0 to 90° and eH in the temperature range from 173.15 to 373.15 K for two-layer samples of aluminum-deposited polyimide film. The results obtained for αS and eH by the present method are compared with experimental results measured by both spectroscopic and calorimetric methods. The calculated results of αS and eH agree well with the experimental results.

Gold(I)−Gold(III) Interactions in Polynuclear Sulfur-Centered Complexes. Synthesis and Structural Characterization of [S(Au2dppf){Au(C6F5)3}] and [{S(Au2dppf)}2{Au(C6F5)2}]OTf (dppf = 1,1‘-Bis(diphenylphosphino)ferrocene)

The reactions of [S(Au2dppf)] (dppf = 1,1‘-bis(diphenylphosphino)ferrocene) with the gold(III) precursors [Au(C6F5)3(OEt2)] and [Au(C6F5)2(OEt2)2]OTf afford the mixed-valence complexes [S(Au2dppf){Au(C6F5)3}] (1) and [{S(Au2dppf)}2{Au(C6F5)2}]OTf (2). The crystal structures of these derivatives have been determined and show short gold(I)−gold(III) contacts of 3.404(1) A in 1 and 3.2195(8) and 3.3661(10) A in 2. DFT calculations, including correlation and relativistic corrections, show that in these compounds where sulfur bridges three gold atoms it prefers to become pyramidal rather than planar, and Au(I)−Au(III) distances are indicative of a possible weak interaction. EH calculations suggest that such interaction is similar in origin to the well-studied Au(I)−Au(I) weak interactions and that it may occur in some real compounds.

Stability and acidity contributions of heteropolymetalates: a theoretical study of the Keggin and Dawson ions

The Dawson-type anion [X ( n) 2M 18O 62] 2(8 − n) −, is derived from the Keggin anion [X ( n) M 12O 40] (8 − n) − (X=Si, Ge, P, S) by fusing two trivalant shells, producing an oval shaped closed framework. The central oxoanions, contributing an overall charge to the clathratic cluster, retain tetrahedral coordination. Generally, the Dawson heteropolyoxometalates are more thermally stable and catalytically more active than the corresponding Keggin ions. In this work, the comparisons among the Keggin and Dawson ions are addressed in terms of relative stability, hardness and acidity. These predictions are based on the theoretical results obtained from the extended Hückel, EH calculations. This analysis of the Dawson structure presently represents the most significant modelling work on large oxyanions. Absolute comparisons between the EH and density functional are not available for Dawson structures. The correlations between these methods have been shown valid for the Keggin ions and are expected to be similar for the Dawson ions. The substitution chemistry of the central oxoanions is similar to that of the Keggin clusters in both the stability and acidity.

Metal‐Catalyzed Oxidations, 4. The Reaction of Molybdenumperoxo Complexes with Brønsted and Lewis Acids

AbstractNMR studies of the reaction of complexes of the type (L‐L)MoO(O2)2 (L – L= bidentate ligand) with strong Brønsted and Lewis acids prove that protons are transferred preferentially to an η2‐peroxo and not to the oxo ligand. This behavior in proton transfer reactions is one critical point of the catalytic activity of such complexes in olefin epoxidation. EH calculations on the model complex (NH3)2MoO(O2)2 support the spectroscopic investigations.

Electron transfer and electronic structure of KCuFeS 2

The electron transfer that occurs in the insertion of potassium in CuFeS 2 has been analyzed by two different techniques. The binding energies of the core electrons of CuFeS 2, KCuFeS 2 and K x CuFeS 2 ( x ≈ 0) has been studied by XPS experiments, while the band structure of these phases has been investigated by tight-binding EH calculations. Both experimental and numerical results strongly support the belief that the insertion reaction induces a redox process in the starting CuFeS 2, by which the Fe 3+ ions are reduced to Fe 2+. Upon removal of the potassium ions, the Fe 2+ ions are oxidized to Fe 3+. Copper atoms do not participate in the redox reaction.

Molecular mechanical and quantum chemical study on the species involved in the hydrolysis of cis-diamminedichloroplatinum(II) and substituted bis(ethylenediamine)dichloroplatinum(II) complexes Part I. Reactants and products

Cisplatin and its substituted ethylenediamine derivatives, cis-PtCl 2(R 2en) (en=ethylenediamine, R=H, Ph (phenyl), 2-, 3- and 4-PhOH) have been studied with respect to the first step of their hydrolysis reaction. The geometry of the reactants and products was determined by molecular mechanics (MM). The MM optimized structures were used to calculate by the extended Hückel method the charge distribution and relative electronic energies. The MM and EH calculations were carried out with different ligand conformations. Due to increased non-bonded repulsion, with increasing ligand buikiness, the square planar arrangement is the preferred geometry also by the MM results. This additional (to the electronic) stabilization of the square planar arrangement around Pt(II) is unfavorable for the aquation process. The thermodynamic stabilities correlate with the rate of hydrolysis of meso-, (+)- and (−)-[1,2-bis(2-hydroxyphenyl)ethylenediamine]dichloroplatinum(II) (3-PtCl 2). The slower rate of hydrolysis of the meso diastereoisomer as compared with that of the d, l species of 3-PtCl 2 is explained by the presence of a 5th Pt-O contact in the meso diastereoisomer which hinders the entrance of the water molecule and makes the hydrolysis slower.

A comparative MO study of three dichlorodiamminedihydroxo Pt(IV) isomers

The electronic structure of the ground state of the title complexes is investigated by means of Xα-MSW and EH calculations. The facile isomerization of the all- trans complex to the corresponding cis, trans, cis is explained in terms of total energy and atomic d level stabilization, as they emerge from the MO calculations. Furthermore, a qualitative prediction is made of the antitumor activity of the compounds provided that this is a consequence of their reduction to cis-dichlorodiammine Pt(II) by reductive elimination of their HO ligands.

Structure and reactivity of aromatic .sigma.-complexes (cyclohexadienylium ions): a correlated experimental and theoretical study

Steric and electronic properties for a series of u-complexes have been examined by experimental and theoretical techniques. Crystal structures for three 2,4,6-tripyrrolidinocyclohexadienylium salts 3a, 3b, and 4a and for l-methyl-2,4,6- tripyrrolidinobenzene 5 are reported. With respect to the cyclohexadienylium ring, the H,H u-complexes, 3, display a planar conformation whereas u-complexes 4 and 6 are bent. Steric interactions force the larger substituents of the tetrahedral carbon atom in 4 and 6 into the pseudoaxial position. The results of EH, MNDO, and 3-21G calculations are in agreement with the crystal structure determinations for 0-complexes 3,4, and 6. Calculations performed for other u-complexes indicate that the ring conformation for a-complexes with small substituents in the 2- and 6-positions should be planar even in cases with different substituents on the tetrahedral carbon atom; with larger substituents, a bent conformation is favored with the larger substituent at C1 axial. The activation energy for planarization of the bent structure is fairly high, and it is even higher for inversion. For stereoelectronic reasons, only the ligand in the axial position of bent u-complexes can dissociate during rearomatization. Thus the stability and reactivity of a-complexes are strongly dependent on their conformation. The large differences in pK, values of planar and nonplanar momplexes, as well as the unexpectedly high stability of phloroglucinophane a-complexes, can be explained by the high inversion energy for the formation of the u-complexes with the proton as the leaving group in the axial position.

A reinvestigation of the isomerization of alkyne dicobalt hexacarbonyl complexes by the perpendicular-to-parallel twist of the alkyne: Influence of the induced carbonyl reorientations

The isomerization of the (CH 2H 2)Co 2(CO) 6 complex by the perpendicular-to-parallel twist of the alkyne has been reinvestigated. The large monotonous increase of the energy found earlier by EH calculations turns out not to be due to the twisting process itself but rather to the fact that no allowance was made for relaxation of the carbonyl orientations; upon reorientation of the carbonyls into a trigonal bipyramid geometry about the cobalt centers the increase in energy disappears almost completely. A Mulliken population analysis does not reveal the expected analogy between the reaction with the isomerization of tetrahedrane into cyclobutadiene. Calculations on intermediate structures along a twisting reaction path in which the carbonyls undergo a continuous reorientation induced by the acetylene twist, lead to a state correlation diagram in which a level crossing is observed, allowing the reaction to be classified as symmetry forbidden. The same diagram indicates, however, that there is an upper limit for the activation energy of this isomerization of 117 kJ/mol, a value which can be regarded as within the range of allowed reactions. This result is considered in the light of the available kinetic data on various substitution reactions of (alkyne)Co 2(CO) 6 complexes.

Synthesis and Properties of a New Kind of One-Dimensional Conductors 15. Extended HÜCKEL Calculations on the Energy Band Structures of Triply Bridged Polymers

Abstract The structural principle of previous papers of this series, namely coordination polymers of the type (MX4L)∞ in which unities MX4 are linearly bridged by ligands L to one-dimensional chains, is extended to the type (M2L6)·. Here each transition metal atom M is triply bridged by ligands L. EH calculations are executed on two samples: Fe2 (III) (pyrazolate)6 and Fe2 (0) (CO)6. These calculations yield partly filled energy bands, but the structures seem to be sensitive to Peierls distortions. The influence of irreversible doping is discussed.

Counterintuitive orbital mixing in semiempirical and ab initio molecular orbital calculations

In both extended Hiickel and limited basis set ab initio SCF molecular orbital calculations an intriguing phenomenon occurs, especially in calculations on transition metal complexes. Some of the lower orbitals, which are made up primarily of ligand 2s combinations, mix into themselves the metal virtual orbitals, 4s and 4p, in an out-of-phase manner, opposite to what one would have predicted from a simple perturbation analysis. We call this counterintuitive orbital mixing (COM). The conse- quences of COM are lowered metal to ligand overlap populations and negative Mulliken gross atomic populations of the virtual orbitals. We analyze the prerequisites for occurrence of COM in both semiempirical and SCF methods and propose a modified Wolfsberg-Helmholz formula for reducing the magnitude of the effect in EH calculations.