Maximum Positive Charge Research Articles

Specific πδ+–πδ- interaction enables conjugated microporous polymers for highly selective capture of Pd(II)

The targeted capture of heavy metals from wastewater is urgently necessary in response to strategic demands of sustainable resource utilization, but it is severely hampered by the formation of specific adsorbent-adsorbate interactions. Herein, the conjugated microporous polymer CMP-1 with –C≡C– binding sites is introduced for the adsorption of PdCl42- in acid wastewater. The matched interaction between –C≡C– with vertical π bond and electron-rich Pd center with π58δ- exhibits exceptional PdCl42- selectivity in competitive systems with coexisting heavy metals. To regulate the electron density of π bond in –C≡C– to further reinforce the πδ+–πδ- interaction, p-FCMP and o-FCMP adsorbents are rationally designed through the substitution of electro-withdrawing F group at different positions. A joint experimental-simulation exploration reveals that the F-induced electron oriented migration in –C≡C– results in the decreased π-electron density, therefore enhancing the binding of PdCl42-. Notably, o-FCMP possesses the maximum positive charge density at –C≡C– binding sites, which greatly promotes the charge transfer between –C≡C– and PdCl42- for stronger bonding interaction, achieving an optimal adsorption capacity of 447.7 mg g−1 as well as enhanced selectivity. This work provides unique insights into the efficiently targeted removal of heavy metals.

Excited state and charge transfer dynamics in gas phase molecule of CH3NH3PbI3: first-principles study.

In this work, to probe the charge transfer mechanism of methylammonium lead triiodide (CH3NH3PbI3), we have used density functional theory (DFT) and time-dependent density functional theory (TDDFT). We investigate ground and excited states optimized geometry, UV-vis spectrum and vibrational frequencies of CH3NH3PbI3 molecule. It is observed that in an excited state, the structural change is mostly localized in PbI3 part of the molecule. Mulliken charge analysis shows that lead (Pb) atom acquires a maximum positive charge and all iodine atoms get a negative charge. In addition to this, all the hydrogen atoms donate their charge to iodine atoms. Therefore, electron transfer from lead (Pb) and hydrogen atoms to the iodine atoms can be considered as a significant charge transfer mechanism. Vibrational frequencies are obtained and assigned with the help of hessian calculations. Vibrational mode at 225cm-1 is identified as the NH3-I stretching.

The reactivity of cinnamic acid derivatives as lignin precursors

Objectives. Cinnamic acid derivatives belong to a large class of phenolic compounds, which are widely distributed in plants and have high potential for use in the medical and industrial fields. They have various useful practical properties, e.g., antioxidant, anti-inflammatory, antiplatelet, and anti-melanogenic properties. Hydroxycinnamic acids are of particular interest as phenylpropanoids, which are the starting compounds of lignin. The aim of this work was to study the electronic structure and analyze the reactivity of the simplest representatives of phenylpropanoids formed during the biosynthesis of the coumaric (p-hydroxycinnamic), caffeic (3,4-dihydroxycinnamic), ferulic (3-methoxy-4-hydroxycinnamic), sinapic (3,5-dimethoxy-4- hydroxycinnamic), and 3,4-dimethoxycinnamic acids. These acids are the biogenetic precursors of most other phenolic compounds (coumarins, melanins, lignins, and flavonoids) and are found in almost all higher plants.Methods.Calculations with full optimization of the geometric parameters were performed using the original Hartree–Fock theory and hybrid density functional method. All calculations were performed using the Firefly program.Results.A comparative quantum chemical calculation of the geometric parameters of hydroxycinnamic acid molecules was conducted via two methods, and the values of the charges on atoms according to Mulliken were determined. It was found that with the addition of hydroxyl and methoxy substituents at the meta and para positions relative to the carboxyl fragment, the electron density shifts toward the benzene ring, and the symmetry of the molecule decreases. Additionally, in these structures, there is π,π-conjugation of the carboxyl fragment of the –СН=СНСООН molecule with the aromatic ring, which significantly affects the geometric configuration of the molecule. The maximum positive charge is concentrated on the C9 atom, while the maximum negative charge is on the oxygen atoms belonging to the methoxy substituents and the hydroxyl group, which confirms the role of oxygen atoms in the chemical transformations of acids.Conclusions.Two different methods were used to calculate the geometric, electronic, and energy parameters and electrophilicity indices of the studied hydroxycinnamic acids in the gas phase. The obtained values were consistent (within the limits of error) with the experimental data as well as the results described in earlier works’ calculations by other methods.

Optical, surface charge state and photocatalysis study of ZnO with different exposure faces

A hydrothermal method was used to synthesize zinc oxide (ZnO) with different exposure faces. Only when the ratio of OH − / Zn2 + is 2/1, ZnO with different morphologies and exposure faces can be obtained by controlling the amount of the polyvinylpyrrolidone as a capping agent. Five samples with representative morphology and wurtzite crystal structure were selected from 28 different synthesis conditions. Their optical, surface charged, and photocatalytical properties are closely related to the exposed faces. The ultraviolet fluorescence emission is related to the nonpolar faces in the low index exposure face. All samples are n-type semiconductors and oxygen element is lacking compared to Zn. There is a great possibility that the oxygen vacancy is the oxygen defect that causes the visible fluorescence emission of the nanosheet. Samples are all positive-charged on the surface. The surface charge is not only related to the particle size but also directly affected by the polarity of exposed face and the missing atoms of the sample. The photocatalytic activity of ZnO with nanocolumn morphology is the best, due to high exposure ratio of the polar faces, maximum positive charge, and moderate particle size.

A Quantitative Structure-Activity Relationship Study on the Antimalarial Activities of 4-Aminoquinoline, Febrifugine and Artemisinin Compounds

Quantum chemical molecular descriptors representing different types of chemical reactivity were employed to investigate the antimalarial activities of 4-aminoquinoline, febrifugine, artemisinin and their derivatives. The quantitative structure-activity relationship results reveal that: (i) the antimalarial activities of 4-aminoquinoline compounds against the chloroquine-sensitive Plasmodium falciparum 3D7 strain are mainly affected by the electron flow and polarization interactions; (ii) The reactivity descriptors for the activities of febrifugine compounds against the chloroquine-resistant Plasmodium falciparum FCR-3 strain are the electron-acceptance chemical potential, the maximum nucleophilic and electrophilic local softness, the maximum positive charge of the hydrogen atom, etc.; (iii) The electron-donation chemical potential, the maximum negative charge, the inverse of the apolar surface area and the molar volume of artemisinin compounds are the most important descriptors for evaluating the activity against the chloroquine-resistant Plasmodium falciparum W-2 strain.

The capability of the pristine and (Sc, Ti) doped Be12O12 nanocluster to detect and adsorb of Mercaptopyridine molecule: A first principle study

The aims of this study is to investigate the potential and capability of the pristine and (Sc, Ti) doped beryllium oxide nanocluster (Be12O12) to detect, and adsorb Mercaptopyridine (MCP) molecule. For this purpose, we considered different configurations for adsorbing MCP drug on the surface of Be12O12 nanocluster. All considered configurations are optimized at the cam-B3LYP/Lanl2DZ level of theory, and then from optimized structures, we selected two stable models for adsorption of MCP from S and N sites on the surface Be12O12 nanocage. The calculated results indicate that the distance between nanocluster and drug from N site (d configuration) is lower than from S site (a configuration) and adsorption of MCP from N site is more favorable than S site. The adsorption energy, Gibbs free energy, enthalpy, atom in molecule (AIM) and reduced density gradient (RDG) results reveal that the interaction of MCP with Sc and Ti-doped Be12O12 nanocage is stronger than pristine model. The gap energy of Be12O12/MCP system is in range 1.76–5.55 eV. Comparison results indicate that the gap energy of the d configuration of MCP drug is lower than the a configuration. The natural bond orbital (NBO), HOMO-LUMO orbitals and electrostatic potential (ESP) plots results show that the maximum positive charge is located around nanocluster surface and the most negative charge is located around adsorption position and MCP drug surface. The results of nonlinear optical (NLO) demonstrate that with doping Ti atom the dipole moment, polarizability, and first hyperpolarizability of MCP/Be12O12 complex enhance significantly from original state and the optical properties of system increase significantly from the pristine model. The calculated results confirm that Ti-doped Be12O12 nanocage is a good candidate for delivering and making sensor for MCP molecule.

2D-QSAR and 3D-QSAR simulations for the reaction rate constants of organic compounds in ozone-hydrogen peroxide oxidation

Synergistic oxidation of ozone (O3) and hydrogen peroxide (H2O2) is an effective water treatment for the elimination of organic pollutants. In this study, 23 organic compounds were conducted to study the reaction rate constants during O3-H2O2 oxidation. Then, two- and three-dimensional quantitative structure-activity relationship (QSAR) models were established to investigate the factors influencing the reaction rate constants by using multiple linear regression method and comparative molecular similarity index analysis (CoMSIA) method, respectively. Both of the two models showed good performance on predicting the reaction rate constants, the associated statistical indices of 2D-QSAR and 3D-QSAR models were R2 = 0.898 and 0.952, q2 = 0.841 and 0.951, Qext2 = 0.968 and 0.970, respectively. But varied in the influence factors, as for the 2D-QSAR model, three quantum chemical parameters, included dipole moment, the largest change of charge in each atom during the nucleophilic attack, the maximum positive partial charge on a hydrogen atom linked with a carbon atom affected the reaction rate. While in the 3D-QSAR model, the electrostatic field played the most important role in evaluating the reaction rate with the contribution of 35.8%, followed by hydrogen bond acceptor and hydrophobic fields with the contribution of 24.9% and 23.2%, respectively. These two models provided predictive tools to study the influencing factors for the degradation of organics and might potentially be applied for estimating the removal properties of unknown organics in O3-H2O2 oxidation process.

A quantitative structure–activity relationship approach for assessing toxicity of mixture of organic compounds

Four types of reactivity indices were employed to construct quantitative structure–activity relationships for the assessment of toxicity of organic chemical mixtures. Results of analysis indicated that the maximum positive charge of the hydrogen atom and the inverse of the apolar surface area are the most important descriptors for the toxicity of mixture of benzene and its derivatives to Vibrio fischeri. The toxicity of mixture of aromatic compounds to green alga Scenedesmus obliquus is mainly affected by the electron flow and electrostatic interactions. The electron-acceptance chemical potential and the maximum positive charge of the hydrogen atom are found to be the most important descriptors for the joint toxicity of aromatic compounds.

Halogenation Reactions of Phosphiniminocyclotrithiazenes: Search for New Inorganic Heterocycles

Though the chemistry of tetrasulfur tetranitride is very well developed and studied, that of phosphiniminocyclotrithiazenes is not. Reactions of symmetrically substituted R3PN-S3N3 [R = Ph, OC4H8N, MeNC4H8N, and C5H10N] with halogens and halogen sources (SO2Cl2, PhICl2, Br2, and I2) gave rise to various products. In case of R = Ph, the ring-retained product, while for others, ring-degraded products were obtained. A novel cyclotrithiazene heterocycle, [Ph3PN]2S3N3+I3− containing a tetracoordinated sulfur atom with two phosphinimino substituents was obtained, which was further established by IR, NMR (1H-, 13C-, and 31P-) and elemental analysis. Cyclic voltammetric studies indicated the redox behavior as well as the presence of triiodide. Theoretical calculations clearly indicate the residence of maximum positive charge (close to unity) on the tetracoordinated sulfur atom.

A QSPR study on the solvent-induced frequency shifts of acetone and dimethyl sulfoxide in organic solvents

In this study, solvent-induced frequency shifts (SIFS) in the infrared spectrum of acetone and dimethyl sulfoxide in organic solvents were investigated by using four types of quantum-chemical reactivity descriptors. The results showed that the SIFS of acetone is mainly affected by the electron-acceptance chemical potential and the maximum nucleophilic condensed local softness of organic solvents, which represent the electron flow and the polarization between acetone and solvent molecules. On the other hand, the SIFS of dimethyl sulfoxide changes with the maximum positive charge of hydrogen atom and the inverse of apolar surface area of solvent molecules, showing that the electrostatic and hydrophilic interactions are main mechanisms between dimethyl sulfoxide and solvent molecules. The introduction of the four-element theory model-based quantitative structure–property relationship approach improved the assessing quality and provided a basis for interpreting the solute–solvent interactions.

Synthesis, Molecular Structure, Metabolic Stability and QSAR Studies of a Novel Series of Anticancer N-Acylbenzenesulfonamides.

A series of novel N-acyl-4-chloro-5-methyl-2-(R1-methylthio)benzenesulfonamides 18–47 have been synthesized by the reaction of N-[4-chloro-5-methyl-2-(R1-methylthio)benzenesulfonyl]cyanamide potassium salts with appropriate carboxylic acids. Some of them showed anticancer activity toward the human cancer cell lines MCF-7, HCT-116 and HeLa, with the growth percentages (GPs) in the range from 7% to 46%. Quantitative structure-activity relationship (QSAR) studies on the cytotoxic activity of N-acylsulfonamides toward MCF-7, HCT-116 and HeLa were performed by using topological, ring and charge descriptors based on the stepwise multiple linear regression technique (MLR). The QSAR studies revealed three predictive and statistically significant models for the investigated compounds. The results obtained with these models indicated that the anticancer activity of N-acylsulfonamides depends on topological distances, number of ring system, maximum positive charge and number of atom-centered fragments. The metabolic stability of the selected compounds had been evaluated on pooled human liver microsomes and NADPH, both R1 and R2 substituents of the N-acylsulfonamides simultaneously affected them.

Synthesis and DFT studies of structural and some spectral parameters of nickel(II) complex with 2-(2-hydroxybenzoyl)-N-(1-adamantyl) hydrazine carbothioamide

An efficient synthesis of the novel 2-(2-hydroxybenzoyl)-N-(1-adamantyl) hydrazine carbothioamide and its Ni(II) complex are described. Quantum chemical calculations including molecular geometry and vibrational frequencies were carried out for the structures to explain stability and geometry using both density functional (DFT/B3LYP) with 6-311+G(d,p) and LANL2DZ basis sets. 1H-NMR chemical shifts were also studied using a gauge-including atomic orbital approach (GIAO), and were found to be in good agreement with the experimental values. The Mulliken charges and HOMO–LUMO orbital energies were calculated and analyzed. The calculated HOMO–LUMO energies show that the charge transfer occurs within the molecule. The maximum positive atomic charge was obtained for C11 and the presence of a large negative charge on O (46) and O (45) for the ligand suggested the bonding of the Ni(II) ion with oxygen atoms. The chemical structures of the compounds were established by elemental analysis, FT-IR, 1H-NMR, 13C-NMR, UV–Vis spectra, magnetic moments, and thermal analyses. The electronic spectra and magnetic measurement studies revealed that the structure of complex is octahedral. Additionally, the cytotoxic effects of the obtained ligand and its complex were determined by using PC3 prostate cancer cell cultures. The results indicated that the ligand showed distinctly better activity than the complex.

Dual Role of Biochars as Adsorbents for Aluminum: The Effects of Oxygen-Containing Organic Components and the Scattering of Silicate Particles

The adsorption of aluminum by biochars produced at different temperatures from rice straw (RS) and cattle manure (CM) was studied to determine the dual roles of biochar for aluminum adsorption. The compositional structures and surface charges of the biochars and ashes with and without Al loading were analyzed by Fourier-transform infrared spectroscopy, ζ-potential, scanning electron microscopy, and X-ray diffraction. The Al adsorption isotherms were fit well by the Langmuir model. The adsorption of Al to the biochars produced at 400 and 700 °C was much greater than the adsorption to the precursory materials and ashes. We found that the organic components and silicate particles within the biochars served as dual adsorptive sites for Al. The complexation of Al with organic hydroxyl and carboxyl groups and the surface adsorption and coprecipitation of Al with silicate particles (as KAlSi3O8) both contributed to the Al adsorption of the biochars. After the biochars were loaded with Al, the ζ-potentials of the biochars and ashes increased as a function of pH. The positive charge was maximized at pH 4.5, which is similar to the pH at which the maximum positive charge occurs for silica. The charge reversal was caused by the Stern-layer adsorption of hydrolyzed aluminum species (i.e., Al(OH)(2+) and Al(OH)2(+)) on the silicate surfaces via hydrogen bonds.

Juruin: an antifungal peptide from the venom of the Amazonian Pink Toe spider, Avicularia juruensis, which contains the inhibitory cystine knot motif

The aim of this study was to screen the venom of the theraposid spider Avicularia juruensis for the identification of antimicrobial peptides (AMPs) which could be further used as prototypes for drug development. Eleven AMPs, named juruentoxins, with molecular weight ranging from 3.5 to 4.5 kDa, were identified by mass spectrometry after the soluble venom was separated by high performance liquid chromatography. Juruentoxins have a putative inhibitory cystine knot (ICK) motif, generally found in neurotoxins, which are also resistant to proteolysis. One juruentoxin that has 38 amino acid residues and three disulfide bonds were characterized, to which we proposed the name Juruin. Based on liquid growth inhibition assays, it has potent antifungal activity in the micromolar range. Importantly, Juruin lacks haemolytic activity on human erythrocytes at the antimicrobial concentrations. Based on the amino acid sequence, it is highly identical to the insecticidal peptides from the theraposid spiders Selenocosmia huwena, Chilobrachys jingzhao, and Haplopelma schmidti from China, indicating they belong to a group of conserved toxins which are likely to inhibit voltage-gated ion channels. Juruin is a cationic AMP, and Lys22 and Lys23 show maximum positive charge localization that might be important for receptor recognition. Although it shows marked sequence similarity to neurotoxic peptides, Juruin is a novel exciting molecule with potent antifungal activity, which could be used as a novel template for development of drugs against clinical resistant fungi strains.

Quantum-chemical descriptors and the assessment of surface activity in coal flotation

The activity of reagents in coal flotation may be assessed on the basis of quantum-chemical descriptors. Semiempirical calculations indicate that hard electrophilic centers in the coal surface correspond to carbon atoms with maximum positive charge. The oxygen atoms are nucleophilic centers of complex terephthalates, which are characterized by maximum negative charges and therefore able to form donoracceptor complexes with electrophilic sections of the coal surface. The reaction corresponds to a charge-controlled mechanism.

Material Research on High-Quality Passivation Layers with Controlled Fixed Charge for Crystalline Silicon Solar Cells

We evaluated the three types of composition spread passivation layer, i.e., Al2O3–HfO2, HfO2–Y2O3, and Al2O3–Y2O3 systems, by combinatorial pulsed laser deposition to evaluate and control the fixed charge, while interface states were kept constant with a SiO2 interlayer. The flat-band voltage of the capacitance–voltage (C–V) curves was shifted widely from positive to negative by changing the composition. The calculated fixed charge in the Y2O3 was positive while those in the HfO2 and Al2O3 were negative. In the Al2O3–Y2O3 system, the fixed charge was significantly varied between -2.7 and 1.3×1012 cm-2 with composition spread. The maximum negative charge was found in the Al2O3 layer with a slight amount of Y2O3, while the maximum positive charge was realized with almost pure Y2O3. The fixed charge modifications were also found in the Al2O3–HfO2 and HfO2–Y2O3 systems. Additional oxidation after layer deposition also modified the fixed charge properties. The largest negative fixed charge of -3.1×1012 cm-2 was found in approximately HfO2:Y2O3=1:1 after the annealing process, while the largest positive charge of 1.3×1012 cm-2 was found for Y2O3 with Al2O3 incorporation. The passivation layers with controlled fixed charge can be promising materials for the high-quality passivation layer in crystalline silicon solar cells.

Interaction between electric double layers of kaolinite and Fe/Al oxides in suspensions

Interaction of the diffuse layers of electric double layer between negatively charged kaolinite particle and positively charged particles of goethite, gibbsite, hematite or γ-Al 2O 3 is investigated in this article through the comparison of zeta potential between single kaolinite system and the binary-system containing kaolinite and Fe/Al oxides. The overlapping of the diffuse layers on kaolinite and Fe/Al oxides decreases the effective negative charge density on kaolinite and thus increases the zeta potential of the binary-system containing kaolinite and Fe/Al oxides. The interaction of the diffuse layers increases with the increase in the ratio of kaolinite to Fe/Al oxides and decreases with the rise of system pH. The interaction also relates to the charge characteristics on the Fe/Al oxides. Gibbsite which posses comparative maximum positive charge density leads to the strongest interaction of the diffuse layers between the oxide and kaolinite as followed by goethite, and hematite, and the γ-Al 2O 3 with the least positive charge density results in the weakest interaction of the diffuse layers. The outcome of the present investigation is likely to be useful reference for the interpretation of the interaction of the diffuse layers in authentic variable charge soils.

Prediction of retention factors in micellar electrokinetic chromatography from theoretically derived molecular descriptors

An artificial neural network (ANN) was constructed and trained for the prediction of the retention factors of some benzene derivatives and heterocyclic compounds in micellar electrokinetic chromatography (MEKC) based on quantitative structure-property relationship. The inputs of this network are theoretically derived descriptors, which were chosen by the stepwise multiple linear regressions features selection technique. These descriptors are; molecular surface area, Kier shape index, dipole moment and maximum positive charge on the Carbon atom which were used as inputs for constructed 4:2:1 ANN. By comparing of the results obtained from multiple linear regression and ANN models, it can be seen that statistical parameters (Fisher ratio, correlation coefficient and standard error of the model) of the ANN model are better than that regression model, which indicates that nonlinear model can simulate the relationship between the structural descriptors and the MEKC retention of the investigated molecules more accurately. Also the cross-validation test was used for the evaluation of the predictive power of the ANN model. The statistical parameters obtained were Q2 = 0.57 and PRESS = 0.55, which reveals the credibility of ANN model.

A QSAR Study of the Brain/Blood Partition Coefficients on the Basis of pKa Values

AbstractA database including histamine receptor antagonists and agonists and neutral compounds, physicochemical properties and the equilibrium brain/blood concentration ratios (logBB) were analysed by using linear regression. The correlation between logBB and physicochemical properties has been remarkably improved by grouping the compounds according to their pKa values. For compounds with pKa≥8.5 logBB increases with the maximum atomic positive charge, polarity characterized by the sum of substructural partial charges and decreases with the maximum H‐bond acceptor and the H‐bond donor (n=16, r2=0.864, s=0.316, Q2=0.783). For compounds with a pKa in the range of 6.8≤pKa<8.5 logBB increases with molecular size/bulk (polarizability α) and decreases with polarity and the H‐bond acceptor (n=11, r2=0.892, s=0.246, Q=0.652). For compounds with pKa<6.8 and neutral compounds logBB increases with polarizability and and decreases with the H‐bond acceptor (n=28, r2=0.869, s=0.162, Q2=0.820). logBB of the compounds with high pKa can be also described by logP defined as the difference between logP values measured in 1‐octanol water and those measured in alkane water well, whilst logBB of the neutral compounds and the compounds with low pKa values can be also described by logP(1‐octanol/water) very well, and it seems to be neither logP nor logP can describe logBB of the compounds with intermediate pKa values. These show that the compounds in three groups have different interaction mechanism in brain.

Direct Correlation of the Crystal Structure of Proteins with the Maximum Positive and Negative Charge States of Gaseous Protein Ions Produced by Electrospray Ionization

Electrospray mass spectrometric studies in native folded forms of several proteins in aqueous solution have been performed in the positive and negative ion modes. The mass spectra of the proteins show peaks corresponding to multiple charge states of the gaseous protein ions. The results have been analyzed using the known crystal structures of these proteins. Crystal structure analysis shows that among the surface exposed residues some are involved in hydrogen-bonding or salt-bridge interactions while some are free. The maximum positive charge state of the gaseous protein ions was directly related to the number of free surface exposed basic groups whereas the maximum negative charge state was related to the number of free surface exposed acidic groups of the proteins. The surface exposed basic groups, which are involved in hydrogen bonding, have lower propensity to contribute to the positive charge of the protein. Similarly, the surface exposed acidic groups involved in salt bridges have lower propensity to contribute to the negative charge of the protein. Analysis of the crystal structure to determine the maximum charge state of protein in the electrospray mass spectrum was also used to interpret the reported mass spectra of several proteins. The results show that both the positive and the negative ion mass spectra of the proteins could be interpreted by simple consideration of the crystal structure of the folded proteins. Moreover, unfolding of the protein was shown to increase the positive charge-state because of the availability of larger number of free basic groups at the surface of the unfolded protein.