Molecular Structure Parameters Research Articles

Specific ion effects on the self-assembly of ionic surfactants: a molecular thermodynamic theory of micellization with dispersion forces.

The self-assembly of amphiphilic molecules is a key process in numerous biological and chemical systems. When salts are present, the formation and properties of molecular aggregates can be altered dramatically by the specific types of ions in the electrolyte solution. We present a molecular thermodynamic model for the micellization of ionic surfactants that incorporates quantum dispersion forces to account for specific ion effects explicitly through ionic polarizabilities and sizes. We assume that counterions are distributed in the diffuse region according to a modified Poisson-Boltzmann equation and can reach all the way to the micelle surface of charge. Stern layers of steric exclusion or distances of closest approach are not imposed externally; these are accounted for through the counterion radial distribution profiles due to the incorporation of dispersion potentials, resulting in a simple and straightforward treatment. There are no adjustable or fitted parameters in the model, which allows for a priori quantitative prediction of surfactant aggregation behavior based only on the initial composition of the system and the surfactant molecular structure. The theory is validated by accurately predicting the critical micelle concentration (CMC) for the well-studied sodium dodecyl sulfate (SDS) surfactant and its alkaline-counterion derivatives in mono- and divalent salts, as well as the molecular structure parameters of SDS micelles such as aggregation numbers and micelle surface potential.

Binuclear trans‐Bis(β‐iminoaryloxy)palladium(II) Complexes Doubly Linked with Pentamethylene Spacers: Structure‐Dependent Flapping Motion and Heterochiral Association Behavior of the Clothespin‐Shaped Molecules

The synthesis, structure, and solution-state behavior of clothespin-shaped binuclear trans-bis(β-iminoaryloxy)palladium(II) complexes doubly linked with pentamethylene spacers are described. Achiral syn and racemic anti isomers of complexes 1-3 were prepared by treating Pd(OAc)2 with the corresponding N,N'-bis(β-hydroxyarylmethylene)-1,5-pentanediamine and then subjecting the mixture to chromatographic separation. Optically pure (100 % ee) complexes, (+)-anti-1, (+)-anti-2, and (+)-anti-3, were obtained from the racemic mixture by employing a preparative HPLC system with a chiral column. The trans coordination and clothespin-shaped structures with syn and anti conformations of these complexes have been unequivocally established by X-ray diffraction studies. (1)H NMR analysis showed that (±)-anti-1, (±)-anti-2, syn-2, and (±)-anti-3 display a flapping motion by consecutive stacking association/dissociation between cofacial coordination planes in [D8]toluene, whereas syn-1 and syn-3 are static under the same conditions. The activation parameters for the flapping motion (ΔH(≠) and ΔS(≠)) were determined from variable-temperature NMR analyses as 50.4 kJ mol(-1) and 60.1 J mol(-1) K(-1) for (±)-anti-1, 31.0 kJ mol(-1) and -22.7 J mol(-1) K(-1) for (±)-anti-2, 29.6 kJ mol(-1) and -57.7 J mol(-1) K(-1) for syn-2, and 35.0 kJ mol(-1) and 0.5 J mol(-1) K(-1) for (±)-anti-3, respectively. The molecular structure and kinetic parameters demonstrate that all of the anti complexes flap with a twisting motion in [D8]toluene, although (±)-anti-1 bearing dilated Z-shaped blades moves more dynamically than I-shaped (±)-anti-2 or the smaller (±)-anti-3. Highly symmetrical syn-2 displays a much more static flapping motion, that is, in a see-saw-like manner. In CDCl3, (±)-anti-1 exhibits an extraordinary upfield shift of the (1)H NMR signals with increasing concentration, whereas solutions of (+)-anti-1 and the other syn/anti analogues 2 and 3 exhibit negligible or slight changes in the chemical shifts under the same conditions, which indicates that anti-1 undergoes a specific heterochiral association in the solution state. Equilibrium constants for the dimerizations of (±)- and (+)-anti-1 in CDCl3 at 293 K were estimated by curve-fitting analysis of the (1)H NMR chemical shift dependences on concentration as 26 M(-1) [KD(racemic)] and 3.2 M(-1) [KD(homo)], respectively. The heterochiral association constant [KD(hetero)] was estimated as 98 M(-1), based on the relationship KD(racemic) = 1/2 KD(homo) +1/4 KD(hetero). An inward stacking motif of interpenetrative dimer association is postulated as the mechanistic rationale for this rare case of heterochiral association.

Calcium handling in muscle fibres of mice and men: evolutionary adaptation in different species to optimize performance and save energy

Calcium handling in muscle fibres of mice and men: evolutionary adaptation in different species to optimize performance and save energy

Preparation, structure, and properties of solution-polymerized styrene-butadiene rubber with functionalized end-groups and its silica-filled composites

With anionic polymerization, the solution-polymerized styrene-butadiene rubber (SSBR) and solution-polymerized styrene-butadiene rubber with alkoxysilane-functionalization at two ends of macromolecular chains (A-SSBR) were synthesized by dilithium as initiator. The occurrences of end-group functionalization and condensation reaction were confirmed, but also the molecular structure parameters and end-functionalized efficiency of A-SSBR grafted alkoxysilane groups onto the ends of its macromolecular chains were calculated through the characterizations. By this novel structural modification, there were chemical bondings rather than conventional physical adsorption between silica and rubber matrix. This novel technology was beneficial to not only immobilizing the free chain ends to decrease the amount of macromolecular chains' free terminals, but also chemically bonding the rubber chains on the surfaces of silica particles to enhance the filler-polymer interaction significantly. Furthermore, the covering layer of end-functionalized macromolecular chains around the silica particles was conducive to reducing the silica agglomeration and improving the silica dispersion. The structures, morphologies, and properties of SiO2/SSBR and SiO2/A-SSBR composites prepared by co-coagulation and mechanical blending, were investigated. The results showed that SiO2/A-SSBR composites behaved better comprehensive performances including higher wet skid resistance and lower rolling resistance than SiO2/SSBR composites. Consequently, A-SSBR was an ideal material for the green tire treads.

A link between impact sensitivity of energetic compounds and their activation energies of thermal decomposition

A new relationship is introduced between impact sensitivity of energetic compounds and their activation energies of thermal decomposition. In this relationship, the impact sensitivity of an energetic compound with general formula CaHbNcOd is a function of its activation energy of thermal decomposition as well as the ratio of $$ \left( {\frac{{n_{\text{H}} }}{{n_{\text{O}} }}} \right) $$ and the contribution of specific molecular structural parameters. The new correlation can help us to elucidate the mechanism of initiation of energetic materials by impact. It can be used to predict the magnitude of impact sensitivity of new energetic materials. The new correlation has the root mean square and the average deviations of 2.22 and 1.79 J, respectively, for 40 energetic compounds with different molecular structures. The proposed new method is also tested for 11 energetic compounds, which have complex molecular structures, e.g., 4,10-dinitro-2,6,8,12-tetraoxa-4,10-diazaisowurtzitane and 1,3,7,9-tetranitrophenoxazine.

Quantum chemical calculations of conformation, vibrational spectroscopic, electronic, NBO and thermodynamic properties of 2,2-dichloro-N-(2,3-dichlorophenyl) acetamide and 2,2-dichloro-N-(2,3-dichlorophenyl) acetamide

The molecular structural parameters, thermodynamic properties and vibrational frequencies of the fundamental modes of 2,2-dichloro-N-(2,3-dichlorophenyl) acetamide (2,3CPA) and 2,2-dichloro-N-(2,4-dichlorophenyl) acetamide (2,4CPA) have been obtained using density functional theory (DFT) technique in the B3LYP approximation and 6-311G(d,p) basis set. Detailed vibrational assignments of the observed FTIR and FT Raman bands have been proposed on the basis of potential energy distribution (PED). Most of the modes have wavenumbers in the expected range. The molecular electrostatic potential has been mapped primarily for predicting sites and relative reactivities towards electrophilic and nucleophilic attack. The atomic charges, electronic exchange interaction and charge delocalization of the molecule have been studied by natural bond orbital (NBO) analysis. Absorption wavelengths and their assignments in UV–vis region have been predicted, based on time-dependent density functional theory (TD-DFT) calculations. The temperature dependence of thermodynamic properties has been analyzed. Global and local reactivity descriptors have been calculated in order to have a deep insight into the molecule for further applications.

Molecular Changes in Asphaltenes within H2 Plasma

In the present work, the chemical changes in asphaltenes, solid residues, when they are treated with hydrogen plasma were analyzed. H2 plasma was characterized by the presence of electrons, H+ and H2+ ions, at kinetic energies as low as 30 eV. These species can interact with the asphaltenes to produce changes in the chemical structure by different mechanisms such as bond cleavage, recombination, and condensation. Asphaltene samples were exposed to different treatment times (up to 120 min). The plasma was characterized by optical emission spectroscopy (OES) as well as by the different products created in the reactions of asphaltenes. The presence of C+, CH+, C2+, NH+, and V+ was confirmed. Spectroscopic techniques such as Fourier transform infrared spectroscopy (FT-IR), matrix-assisted laser desorption ionization-time of flight-mass spectrometry (MALDI-TOF-MS), nuclear magnetic resonance spectroscopy (1H NMR and 13C NMR), and X-ray diffractometry (XRD) were used to characterize the chemical composition of asphaltenes at the different treatment times. Chemical changes were analyzed from the molecular structural parameters calculated by the above-mentioned spectroscopic techniques. Possible changes in the asphaltene cluster structures were analyzed using XRD. This work explores the application of plasma technologies to modify the chemical composition of asphaltenes and obtain valuable chemical products resulting from a plasma treatment process.

The interaction between organic phosphate ester and p53: An integrated experimental and in silico approach

Concerns have been raised in regards to the environmental impact of the more used organophosphate flame retardants (OPFRs). In this study, to better understand the relationship between molecular structural features of OPFRs and binding affinity for the tumor suppressor p53, an integrated experimental and in silico approach was used. From docking analysis, hydrogen bonding and hydrophobic interactions were found to be the dominant interactions, which implied the binding affinities of the compounds. The binding constants of 5 OPFRs were determined by surface plasmon resonance technology (SPR). Based on the observed interactions, appropriate molecular structural parameters were adopted to develop a quantitative structure-activity relationship (QSAR) model. The developed QSAR model had good robustness, predictive ability and mechanism interpretability. The interactions between the OPFRs and p53 (Ebinding) and the partition ability of the OPFRs into the bio-phase are main factors governing the binding affinities.

Molecular structure and excited states for BN under strong electric field

The ground states of BN molecule under different strong electric fields ranging from -0.06 a.u. to 0.06 a.u. are optimized using density functional method B3LYP at 6-311++g(d.p) level. Optimized parameters, dipole moment, charge distribution. HOMO energy, LUMO energy, energy gaps, infrared spectrum are obtained. The result shows that with the increasing of the external electric field, the correlation between molecular structure parameters and the electric field intensity becomes obvious and presents the asymmetry. In addition, TDDFT method at the same level is used to study the influence of external electric field on BN molecular excitation energy and oscillator strength, and the result shows that the electron transition spectrum is blue-shifted with the increase of the external electric field, but the intensity of the vibrator has a more complicated change, showing that the spectral intensity is affected by the electric field.

QSAR Studies of Some Thiazolo[4,5-b]pyridines as Novel Antioxidant Agents: Enhancement of Activity by Some Molecular Structure Parameters

The antioxidant activity of novel N3 and C6 substituted 5,7-dimethyl-3H-thiazolo[4,5-b]pyridine-2-one derivatives was evaluated in vitro by the method of scavenging effect on 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals. The correlation analysis between the antioxidant activity and different subsets molecular descriptors was carried out for 19 compounds. The regression models derived with QSAR-analysis display the significant influence of topological structure, atom and bond type counts, physicochemical properties, and quantum-chemical structure parameters on the free radical scavenging effect of the compounds. Визначено антиоксидантну активність синтезованих похідних 5,7-диметил-тіазоло[4,5-b]піридин-2-ону, що містять замісники різної природи у 3-му та 6-му положеннях базового гетероциклу. Антиоксидантну активність сполук досліджували in vitro, визначаючи зменшення концентрації вільного радикалу 2,2-дифеніл-1-пікрилгідразилу. Для виборки з 19 похідних було проведено кореляційний аналіз залежності їх антиоксидантної активності від різних типів молекулярних дескрипторів. Аналіз рівнянь регресії, одержаних на основі проведеного QSAR аналізу, свідчить про суттєвий вплив топологічної будови молекул, кількостей атомів та зв’язків різних типів, фізико-хімічних властивостей речовин та квантово-хімічних параметрів їх структури на величини радикалпоглинаючої активності досліджуваних сполук.

Aspects of nonviral gene therapy: Correlation of molecular parameters with lipoplex structure and transfection efficacy in pyridinium-based cationic lipids

This study seeks correlations between the molecular structures of cationic and neutral lipids, the lipid phase behavior of the mixed-lipid lipoplexes they form with plasmid DNA, and the transfection efficacy of the lipoplexes. Synthetic cationic pyridinium lipids were co-formulated (1:1) with the cationic lipid 1,2-dimyristoyl-sn-glycero-3-ethylphosphocholine (EPC), and these lipids were co-formulated (3:2) with the neutral lipids 1,2-dioleoyl-sn-glycero-3-phosphatidylethanolamine (DOPE) or cholesterol. All lipoplex formulations exhibited plasmid DNA binding and a level of protection from DNase I degradation. Composition-dependent transfection (beta-galactosidase and GFP) and cytotoxicity was observed in Chinese hamster ovarian-K1 cells. The most active formulations containing the pyridinium lipids were less cytotoxic but of comparable activity to a Lipofectamine 2000™ control. Molecular structure parameters and partition coefficients were calculated for all lipids using fragment additive methods. The derived shape parameter values correctly correlated with observed hexagonal lipid phase behavior of lipoplexes as derived from small-angle X-ray scattering experiments. A transfection index applicable to hexagonal phase lipoplexes derived from calculated parameters of the lipid mixture (partition coefficient, shape parameter, lipoplex packing) produced a direct correlation with transfection efficiency.

Novel surfactants incorporated with 1,3,5-triethanolhexahydro-1,3,5-triazine moiety as corrosion inhibitors for carbon steel in hydrochloric acid: Electrochemical and quantum chemical investigations

The main objective of this work was to examine the corrosion inhibition ability of three novel surfactant molecules synthesized from 1,3,5-triethanolhexahydro-1,3,5-triazine, which named (I, II and III). The chemical structure of these surfactants was confirmed by FT-IR and 1H NMR spectroscopy. Also the surface active properties for the synthesized compounds were calculated. The effect of these surfactants on carbon steel in a solution of 1M HCl was studied using mass-loss and electrochemical measurements. Protection efficiencies were found to be 93.1%, 90.7%, and 87% for III, II, and I, respectively. The order of increasing inhibition efficiency was correlated with increasing the number of ethylene oxide units. Potentiodynamic polarization curves indicated that the prepared surfactants acted as mixed type inhibitors. Adsorption of the inhibitor obeys the Langmuir isotherm. Quantum chemical calculations based on ab initio method were performed on I, II and III. The molecular structural parameters, such as the frontier molecular orbital energy HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital), the charge distribution and the fraction of electrons (ΔN) transfer from inhibitor to carbon steel were calculated and discussed.

Structural characteristics of coal functional groups using quantum chemistry for quantification of infrared spectra

The extinction coefficient differs for different functional groups making the quantitative analysis of their infrared spectra problematic. Although the coefficients of some functional groups have been researched previously, they are inaccurate because of deviations in techniques used and linear fitting. The distribution and structural characteristics of functional groups from coal infrared spectra is therefore inaccurate. In this study, quantum chemistry methods are used for the quantification of coal infrared spectra based on the Beer–Lambert law. The effect of the extinction coefficients of different functional groups is eliminated. The experimental infrared intensities, unit absorption intensities and their ratios are obtained to calculate the percentage composition of coal functional groups and molecular structure parameters. Accurate distribution and structural characteristics of coal functional groups are obtained. A linear relationship between the distribution of some functional groups and structural parameters is obtained. Multiple structural parameters are used to determine the grade and maturity of coal samples. The ethylene in coal oxidation experiments below 200°C is consistent with the hydrocarbon-generating potential parameters. These results will improve the accuracy of the quantitative analysis of infrared spectra for determining coal structural features and provide an index for the utilization and prevention of the spontaneous combustion of coal.

Relationship between electric spark sensitivity and activation energy of the thermal decomposition of nitramines for safety measures in industrial processes

This study presents a new simple correlation between electric spark sensitivity of nitramines and their activation energies of thermolysis, which are important for safety measures in industrial processes. The new correlation can help to elucidate the mechanism of initiation of energetic materials by electric spark. It can be used to predict the magnitude of electric spark sensitivity of new nitramines, which is difficult to measure. The methodology assumes that electric spark sensitivity of a nitramine with general formula CaHbNcOd can be expressed as a function of its activation energy of thermal decomposition as well as optimized elemental composition and the contribution of specific molecular structural parameters. The new correlation has the root mean square and the average deviations of 1.37 and 1.09 J, respectively, for 21 nitramines with different molecular structures. The proposed new method is also tested for 16 nitramines so that there is no experimental data of electrostatic sensitivity for them.

A novel method for risk assessment of electrostatic sensitivity of nitroaromatics through their activation energies of thermal decomposition

This study presents a novel relationship between electric spark sensitivity of nitroaromatic energetic compounds and their activation energies of thermal decomposition. The new correlation can help to elucidate the mechanism of initiation of energetic materials by electric spark. It can be used to predict the magnitude of electric spark sensitivity of new nitroaromatics, which is difficult to measure. The methodology assumes that electric spark sensitivity of a nitroaromatic energetic compound with general formula CaHbNcOd can be expressed as a function of its activation energy of thermal decomposition as well as optimized elemental composition and the contribution of specific molecular structural parameters. The new correlation has the root mean square and the average deviations of 1.43 and 1.17 J, respectively, for 22 nitroaromatic energetic compounds with different molecular structures. The proposed new method is also tested for eight nitroaromatic energetic compounds, which have complex molecular structures, e.g., 1,3,7,9-tetranitrophenoxazine, 2,4,6-tris(2,4,6-trinitrophenyl)-1,3,5-triazine, and 1-(2,4,6-trinitrophenyl)-5,7-dinitrobenzotriazole.

Investigation of the azo-hydrazone tautomeric equilibrium in an azo dye involving the naphthalene moiety by UV–vis spectroscopy and quantum chemistry

Photophysical properties of the azo-hydrazone tautomerism of Eriochrome Blue Black B (1-(1-hydroxy-2-naphthylazo)-2-naphthol-4-sulphonic acid) in DMF, MeCN and water were investigated using UV–visible spectroscopy and quantum chemical calculations. The optimized molecular structure parameters, relative energies, mole fractions, electronic absorption spectra and HOMO–LUMO energies for possible stable tautomeric forms of EBB were theoretically calculated by using hybrid density functional theory, (B3LYP) methods with 6-31G(d) basis set level and polarizable continuum model (PCM) for solvation effect. The effects of varying pH-, dye concentration-, solvent-, temperature-, and time-dependences on the UV–vis spectra of Eriochrome Blue Black B were also investigated experimentally. The calculations showed that the dye exhibited acid–base, azo-hydrazone and aggregate equilibria in DMF solution, while the most probably preferred form in MeCN solution was azo form. Thermodynamic parameters of dimerization reaction in DMF solution proved that entropy was the driving force of this reaction.

A New General Correlation for Predicting Impact Sensitivity of Energetic Compounds

AbstractThis paper describes an improved simple model for prediction of impact sensitivity of different classes of energetic compounds containing nitropyridines, nitroimidazoles, nitropyrazoles, nitrofurazanes, nitrotriazoles, nitropyrimidines, polynitroarenes, benzofuroxans, polynitroarenes with α‐CH, nitramines, nitroaliphatics, nitroaliphatic containing other functional groups, and nitrate energetic compounds. The model is based on some molecular structural parameters. It is applied for 90 explosives, which have different molecular structures. The predicted results are compared with outputs of complex neural network approach as one of the best available methods. Root mean squares (rms) of deviations of different energetic compounds are 24 and 49 cm, corresponding to 5.88 and 12.01 J with 2.5 kg dropping mass, for new and neural network methods, respectively. The novel model also predicts good results for eight new synthesized and miscellaneous explosives with respect to experimental data.

Molecular Energetics of Alkyl Pyrrolecarboxylates: Calorimetric and Computational Study

The pyrrole subunit plays an important role in material science as the building block of polypyrroles, an important representative class of conducting polymers, which found widely applications in the area of new materials due to their chemical, thermal, and electrical properties associated with their easiness and low cost of production, making them especially promising for commercial applications. The energetic characterization of this kind of molecules provides information concerning stability, reactivity, and biodegrability of chemical compounds in environment being, for example, helpful in choosing the most adequate method for their elimination by converting the waste into harmless compounds or even decreasing the production of toxic substances in industrial processes. This work reports a combination of calorimetric and computational determinations of several alkyl pyrrolecarboxylates (alkyl = methyl or ethyl) whose main purpose is the calculation of their standard (p° = 0.1 MPa) molar enthalpies of formation, in the gaseous phase, at T = 298.15 K. Experimentally, for methyl 1-pyrrolecarboxylate (M1PC), methyl 2-pyrrolecarboxylate (M2PC), and ethyl 2-pyrrolecarboxylate (E2PC), these values were derived from the standard (p° = 0.1 MPa) molar enthalpies of formation, in the condensed phase, ΔfHm° (cr,l), at T = 298.15 K, obtained by static bomb combustion calorimetry, and from the standard molar enthalpies of phase transition, Δcr,l(g)Hm°, at T = 298.15 K, determined by high-temperature Calvet microcalorimetry. Standard ab initio molecular calculations, at the G3(MP2)//B3LYP level, were performed, and the standard enthalpies of formation of these three compounds were estimated. A very good agreement between the calculated and the experimental data was obtained. Thereby, we have extended these calculations to other alkyl pyrrolecarboxylates, namely, ethyl 1-pyrrolecarboxylate (E1PC), methyl 3-pyrrolecarboxylate (M3PC), and ethyl 3-pyrrolecarboxylate (E3PC), whose study was not performed experimentally. The computational analysis, at the B3LYP/6-31G(d) level of theory, of the six molecules allowed a detailed inspection and a better knowledge about their molecular structure and geometrical parameters.

Electrogenerated Conductive Polymers from Triphenylamine End-Capped Dendrimers

Electroactive end-capped dendritic macromolecules were designed and synthesized. Their structures contain triphenylamine moieties as part of the core or dendrons. The electrogenerated films produced with these monomers behaved as conductive dendritic polymers that can be reversible charged, both in the core and in the peripheral units. The design of dendrimer structures with the introduction of systematic changes allows to establish relationships between their electro-optical properties with molecular structural parameters. The films of polymeric material hold good electrical conductivity, reversible electrochemical processes and chemical stability. The results indicate that the use of conjugated and rigid structures in dendritic macromolecules is an important factor in order to obtain electropolymeric films. This work provides a model to design starburst dendrimers capable to form electrochemically active polymers with potential applications in electronic and optoelectronic devices.

Synthesis, spectroscopic and structural characterization of 5-benzoyl-4-phenyl-2-methylthio-1H-pyrimidine with theoretical calculations using density functional theory

In this paper, we will report a combined experimental and theoretical investigation of the molecular structure and spectroscopic parameters (FT-IR, 1H NMR, 13C NMR) of 5-benzoyl-4-phenyl-2-methylthio-1H-pyrimidine. The compound crystallizes in the triclinic space group P-1 with Z=2. The molecular geometry was also optimized using density functional theory (DFT/B3LYP) method with the 6-311G(d,p) and 6-311++G(d,p) basis sets in ground state and compared with the experimental data. All the assignments of the theoretical frequencies were performed by potential energy distributions using VEDA 4 program. Information about the size, shape, charge density distribution and site of chemical reactivity of the molecules has been obtained by mapping electron density isosurface with electrostatic potential (ESP). Also, non-linear optical properties of the title compound were performed at B3LYP/6-311++G(d,p) level. The theoretical results showed an excellent agreement with the experimental values.