Chemical Structural Parameters Research Articles

Electrochemical Oxidation of Phenolic Compounds at Boron-Doped Diamond Anodes: Structure-Reactivity Relationships.

Electrochemical oxidation of phenolic compounds using boron-doped diamond (BDD) anodes has been shown as an effective approach to remove these contaminants from water. However, the understanding of the reaction mechanisms of substituted phenolic compounds at the BDD anode remains incomplete. In the present work, we investigated the electrochemical oxidation of 12 representative phenolic compounds (with varied substitution groups (e.g., -CH3, -OCH3, -NH2, -Cl, -OH, -COOH, -NO2, -CHO) and positions (-ortho, -meta, and -para)) at the BDD anode. Our analysis shows that unlike previous studies the two parameters, the Hammett constants of the substituents and the highest atomic charge on the aromatic ring, fail to adequately describe the reaction rate change when the chemical structures become complicated (i.e., with increased steric effects). Instead, a quantitative structure-property relationship (QSPR) was established with 26 molecular descriptors and using a partial least-squares regression approach. The QSPR analysis shows that the energy gap between the lowest unoccupied molecular orbital and the highest occupied molecular orbital, ELUMO - EHOMO, which reflects the chemical stability of a molecule, is the predominant molecular descriptor determining the reaction rate constant. Furthermore, the predicated rate constants agree well with the observed ones. The findings are consistent with previous studies of SnO2 anodes, suggesting that chemical structural parameters such as the molecular orbital energies are critical to consider when elucidating and predicating the electrochemical reactivity of phenolic compounds at these nonactive anodes.

Raman spectroscopy and TEM characterization of solid particulate matter emitted from soot generators and aircraft turbine engines

To obtain reliable mass concentrations of solid particulate matter (PM) in the exhaust emissions from engines using optical instruments, it is essential that the solid PM used for instrument calibration has similar optical properties to the solid PM emitted from the engines being tested. The solid PM emitted from combustion engines is predominantly soot. The optical properties of soot are dictated by its chemical structure, size, and morphology. In this work, the chemical bond structure, primary-particle diameters, aggregate sizes, and morphological parameters of the soot emitted from two laboratory soot generators, widely used for calibrating instruments, are compared to those of soot emitted from three aircraft turbine engines using Raman spectroscopy and transmission electron microscopy. The Raman spectral properties, size, and morphology of soot emitted from aircraft engines are distinctly different from the properties of soot emitted from the soot generators operating under globally near-stoichiometric and fuel-rich conditions. These differences can be attributed to the variations in the size and orientation of the graphitic crystallites, amorphous-carbon content, amount of polyacetylene compounds, deposition of organic material, and extent of oxidation. Conversely, general agreement is observed between the chemical structure, size, and morphology of soot emitted from aircraft engines and the soot emitted from the soot generators operating at globally fuel-lean conditions. The findings of this investigation can be useful for identifying suitable soot particles for the calibration of instruments to measure the mass concentration of solid PM emissions from engines, and for other types of soot.Copyright © 2017 Crown Copyright

PH-Sensitive Chitosan Hydrogel with Instant Gelation for Myocardial Regeneration

Recently in situ injectable hydrogels have received considerable attention to regenerate failure heart tissue after myocardial infarction (MI). But two criteria remain crucial: first, defining their chemical composition and structural parameters because they must be fabricated to withstand physiological condition while having high cell retention; second, providing the hydrogel with short gelation time to protect the cells from washout and extrusion in the injection site. In this study, two different pH-sensitive hydrogels with instant gelation in the presence of aqueous acetic acid (WH sample), and DMEM medium along with acetic acid (MH sample) were prepared. The morphology and structural and mechanical properties of the hydrogels were evaluated by SEM, FTIR and compressive strength test, respectively. Also, the equilibrium swelling ratio of each hydrogel and their degradation rate as a desirable property were also determined. MTT test confirmed that both hydrogels were biocompatible and non-toxic for human Bone Marrow Mesenchymal Stem Cells (hBMSCs) within 14 days as well as 31 and 36% cell growth during this time for WH and MH samples, respectively. The viability investigation of human Adipose Mesenchymal Stem Cells (hADSCs), tested by live/dead assay with Acridine Orange and Ethidium bromide staining, showed high cell survival and cell density increase during 1, 7, 14, 21 days. The overall results demonstrated that both in situ forming hydrogels are promising candidates for regeneration of the infarcted myocardium.

Role of Silica Nanoparticles on Structural, Optical and Morphological Properties of Poly(Vinyl Chloride-co-Vinyl Acetate-co-2- Hydroxypropyl Acrylate) Copolymer

Pure silica nanoparticles (SNPs) have been successfully obtained by thermal treatment of rice husk through a sol-gel surfactant free technique. Different concentrations of SNPs were embedded within the poly(vinyl chloride-co-vinyl acetate-co-2-hydroxypropyl acrylate) (PVVH) copolymer matrix via a solvent casting method. X-ray diffraction analysis (XRD) confirmed the amorphous nature for PVVH combined with an increase in the amorphous regions after addition of SNPs. Fourier transform infrared (FTIR) and ultraviolet/visible (UV/Vis.) spectroscopy revealed the induced changes in chemical structure and optical parameters (i.e. optical energy gap Eg, refractive index n) for PVVH/SNPs composites. Scanning electron microscopy (SEM) was performed to study the surface morphology and homogeneity of the prepared samples.

Novel Synthetic and Mechanistic Approach of TFA Catalysed Friedländer Synthesis of 2‐Acylquinolines from Symmetrical and Unsymmetrical 1,2‐Diketones with o‐Aminoarylketones

AbstractIn focussing on the reaction mechanism of Friedländer synthesis in the presence of acid catalysts, novel regioselective synthesis of 2‐acetylquinolines from reacting a symmetrical 1,2‐diketone, butan‐2,3‐dione with o‐aminoarylketones was reported. Similar condensation of o‐aminoarylketones with unsymmetrical 1,2‐diketone, pentan‐2,3‐dione leads to the formation of 2‐propanoylquinoline. The proposed reaction mechanism is scrutinized through density functional calculations at B3LYP/6‐311G (d,p) and M06‐2X/6‐311G (d,p) level of theory and also all the relative energy barriers and activation energies of the reaction steps are found to be minimum at above level of theory. Results from theoretical study have further strengthened by FT‐IR, FT‐NMR chemical shifts and structural parameters which were achieved with the same level of theory and the corresponding results were substantiate with experimental observations.

A Biodegradable Polyethylenimine-Based Vector Modified by Trifunctional Peptide R18 for Enhancing Gene Transfection Efficiency In Vivo.

Lack of capacity to cross the nucleus membrane seems to be one of the main reasons for the lower transfection efficiency of gene vectors observed in vivo study than in vitro. To solve this problem, a new non-viral gene vector was designed. First, a degradable polyethylenimine (PEI) derivate was synthesized by crosslinking low-molecular-weight (LMW) PEI with N-octyl-N-quaternary chitosan (OTMCS), and then adopting a designed trifunctional peptide (RGDC-TAT-NLS) with good tumor targeting, cell uptake and nucleus transport capabilities to modify OTMCS-PEI. The new gene vector was termed as OTMCS-PEI-R18 and characterized in terms of its chemical structure and biophysical parameters. Gene transfection efficiency and nucleus transport mechanism of this vector were also evaluated. The polymer showed controlled degradation and remarkable buffer capabilities with the particle size around 100–300 nm and the zeta potential ranged from 5 mV to 40 mV. Agraose gel electrophoresis showed that OTMCS-PEI-R18 could effectively condensed plasmid DNA at a ratio of 1.0. Besides, the polymer was stable in the presence of sodium heparin and could resist digestion by DNase I at a concentration of 63U DNase I/DNA. OTMCS-PEI-R18 also showed much lower cytotoxicity and better transfection rates compared to polymers OTMCS-PEI-R13, OTMCS-PEI and PEI 25 KDa in vitro and in vivo. Furthermore, OTMCS-PEI-R18/DNA complexes could accumulate in the nucleus well soon and not rely on mitosis absolutely due to the newly incorporated ligand peptide NLS with the specific nuclear delivery pathway indicating that the gene delivery system OTMCS-PEI-R18 could reinforce gene transfection efficiency in vivo.

Deep data mining in a real space: separation of intertwined electronic responses in a lightly doped BaFe2As2

Electronic interactions present in material compositions close to the superconducting dome play a key role in the manifestation of high-Tc superconductivity. In many correlated electron systems, however, the parent or underdoped states exhibit strongly inhomogeneous electronic landscape at the nanoscale that may be associated with competing, coexisting, or intertwined chemical disorder, strain, magnetic, and structural order parameters. Here we demonstrate an approach based on a combination of scanning tunneling microscopy/spectroscopy and advanced statistical learning for an automatic separation and extraction of statistically significant electronic behaviors in the spin density wave regime of a lightly (∼1%) gold-doped BaFe2As2. We show that the decomposed STS spectral features have a direct relevance to fundamental physical properties of the system, such as SDW-induced gap, pseudogap-like state, and impurity resonance states.

Variation of the coal chemical structure and determination of the char molecular size at the early stage of rapid pyrolysis

Rapid pyrolysis (∼104K/s) experiments investigating lignite, bituminous coal and anthracite were conducted to study the effect of the thermal process on the coal structure. The interest was focused on the chemical structure variation occurring at the early stage of pyrolysis (0–500ms) and high temperature (1173–1773K), which includes the mass loss ratio, volatile content, element content and organic groups. A series of parameters was used to characterize the chemical structure, CH2/CH3 ratio, fraction of aromatic hydrogen and aromaticity (fa). The char’s molecular size was determined based on both ring condensation degree (R/C)u and equivalent diameter of the aromatic monomer (DC). This result demonstrated that these five chemical structural parameters (CSPs) increase with the pyrolysis time and temperature. The comparison of three types of coals reveals that the CSPs of lignite are lower and increase faster than those of bituminous coal and anthracite.

Influence of conformational parameters on physical properties of copolyimides containing pendant diphenylphosphine oxide units

Modification or designing new molecular architectures are the key strategies to obtain materials with improved/tunable properties able to address environmental restrictions and public needs. Herein, a series of copolyimides containing bulky diphenylphosphine oxide pendant units was synthesized and the physical properties were studied and correlated with the conformational parameters, such as Kuhn segments, Van der Waals and free volumes. It is shown that conformational rigidity determines the packing of macromolecules in glass state, and therefore the free volume, glass transition and dielectric permittivity. The Kuhn segment of the synthesized random copolyimides calculated by Monte Carlo method exhibited a nonlinear dependence on chemical composition. The use of correlations between the chemical structure and conformational parameters is the key to achieve polymers with tailored physicochemical characteristics by varying the comonomers’ ratio.

Grafting of cellulose acetate with ionic liquids for biofuel purification by a membrane process: Influence of the cation

A new strategy was developed for grafting ionic liquids (ILs) onto cellulose acetate in order to avoid IL extraction and improve its performance for ethyl tert-butyl ether (ETBE) biofuel purification by the pervaporation membrane process. This work extended the scope of IL-containing membranes to the challenging separation of organic liquid mixtures, in which these ILs were soluble. The ILs contained the same bromide anion and different cations with increasing polar feature. The membrane properties were strongly improved by IL grafting. Their analysis in terms of structure-property relationships revealed the influence of the IL content, chemical structure and chemical physical parameters α, β, π* in the Kamlet–Taft polarity scale. The ammonium IL led to the best normalized flux of 0.182kg/m2h for a reference thickness of 5μm, a permeate ethanol content of 100% and an outstanding infinite separation factor for the azeotropic mixture EtOH/ETBE at 50°C.

Prediction of low‐rank coal pyrolysis behavior by chemical percolation devolatilization model

The chemical percolation devolatilization (CPD) model was proposed to predict the pyrolysis behavior of fast‐heated coal based on the chemical structure of low‐rank coal sample. The coal‐dependent chemical structure parameters were taken directly from solid state 13C nuclear magnetic resonance (NMR) analysis, with the exception of one empirical coefficient initial fraction of char bridges (c0). The Fourier transform infrared spectroscopic analysis was also employed to describe the pyrolysis characteristics of parent coal. The predictions of amount and characteristics of volatiles, tar and char from CPD model indicated that the crosslinking mechanism plays an important role for the pyrolysis of low‐rank coal. In order to deeply understand the structure and chemical bonds of coal sample, the average chemical structure of low‐rank coal was built by ACD/Labs software of ChemSketch. The 13C NMR spectrum of established average coal structure fitted well with that of parent coal sample. © 2016 American Institute of Chemical Engineers Environ Prog, 35: 1215–1220, 2016

2D 31P solid state NMR spectroscopy, electronic structure and thermochemistry of PbP7

Phase pure polycrystalline PbP7 was prepared from the elements via a lead flux. Crystalline pieces with edge-lengths up to 1mm were obtained. The assignment of the previously published 31P solid state NMR spectrum to the seven distinct crystallographic sites was accomplished by radio-frequency driven dipolar recoupling (RFDR) experiments. As commonly found in other solid polyphosphides there is no obvious correlation between the 31P chemical shift and structural parameters. PbP7 decomposes incongruently under release of phosphorus forming liquid lead as remainder. The thermal decomposition starts at T>550K with a vapor pressure almost similar to that of red phosphorus. Electronic structure calculations reveal PbP7 as a semiconductor according to the Zintl description and clearly shows the stereo-active Pb-6s2 lone pairs in the electron localization function ELF.

MAGNETIC CORE SHELL STRUCTURES: from 0D to 1D assembling.

Material research and development studies are focused on different techniques of bringing out nanomaterials with desired characteristics and properties. From the point of view of materials development, nowadays scientists are strongly focused on obtaining materials with predefined characteristics and properties. The morphology control seems to be a determinant factor and increasing attention is devoted to this aspect. At this moment it is possible to engineer the material's features by using different methods and materials combination for both medical and industrial applications. In the applications of chemistry and synthesis, biology, mechanics, optics solar cells and microelectronics tailoring the adjustable parameters of stoichiometry, chemical structure, shape and segregation are evaluated and opens new fields. Because of the magnetic features of nanoparticles and durable particle size, less than 100 nm, this study is aiming to describe their uses in practical applications. That's why the whole hydrodynamic magnetic core shell topic will be reviewed on this paper. Additionally, the properties acting in general sight in solid-state physics are utilized for material selection and for defining issue connecting the core, shell structure and their producing properties. Here, in the study of core/shell nanoparticle various physical and chemical synthesis routes and the effect of electrospun method are briefly discussed. Starting from a real void of the scientific literature, the existent data related to the 1D magnetic electrospun materials are reviewed. The perspectives in the medical, environmental or energetic sector is great and bring some real advantages related to the 0D core@shell structures because both mechanical and biological properties are dependent on the morphology of the materials.

Redefinition of thalénite-(Y) and discreditation of fluorthalénite-(Y): A re-investigation of type material from the Österby pegmatite, Dalarna, Sweden, and from additional localities

AbstractUsing type material from the Österby pegmatite in Dalarna, Sweden, the chemical composition and structural parameters of thalénite-(Y) [ideally Y3Si3O10(OH)] were examined by wavelength dispersive spectroscopy electron microprobe (WDS EMP) analysis and single-crystal X-ray diffraction. High contrast back-scatter electron images of the Österby material show at least two generations of thalénite-(Y). The formula of the primary thalénite-(Y) normalized to 11 anions is (Y2.58Dy0.11Yb0.09Gd0.06Er0.06Ho0.02Sm0.02Tb0.02Lu0.02Nd0.01Tm0.01)Σ3.00Si3.01O10F0.97OH0.03. The secondary thalénite-(Y), replacing the primary material, is weakly enhanced in Y and depleted in the lightest and the heaviest rare-earth elements, yielding the formula (Y2.63Dy0.12Yb0.06Gd0.06Er0.05Ho0.02Sm0.02Tb0.02Tm0.01Nd0.01Lu0.01)Σ3.00Si3.01O10F0.98OH0.02. Structural data for thalénite-(Y) from Österby clearly indicate the monoclinic space group P21/n, with a = 7.3464(4), b = 11.1726(5), c = 10.4180(5) Å, β = 97.318(4)°, V = 848.13(7) Å3, Z = 4, which is consistent with previous investigations. The structure was refined from single-crystal X-ray diffraction data to R1 = 0.0371 for 1503 unique observed reflections, and the final chemical composition obtained from the refinement, (Y2.64Dy0.36)Σ3.00F0.987[Si3O10], Z = 4, is in good agreement with the empirical formula resulting from electron microprobe (EMP) analysis. Both techniques reveal a strong dominance of F over OH, which means that the type material actually corresponds to the fluorine analogue. Moreover, new EMP analyses of samples of thalénite-(Y) from an additional seven localities (Åskagen and Reunavare in Sweden; White Cloud and Snow Flake in Colorado, USA; the Guy Hazel claim in Arizona, USA; Suishoyama and Souri in Japan) clearly show the prevalence of F over OH as well. Based on these observations, the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association has recommended a redefinition of the chemical composition of thalénite-(Y) to represent the F-dominant species with the ideal formula Y3Si3O10F, as it has historical priority. Consequently, the later described fluorthalénite-(Y) has to be discredited.

Investigation of structural parameters and self-aggregation of Algerian asphaltenes in organic solvents

Elemental analysis, Fourier transform infrared (FTIR), 1H-NMR, fluorescence spectroscopy, and surface tension methods have been used to characterize the molecular structure and the aggregation behaviors of two asphaltenic fractions derived, respectively, from an Algerian petroleum well and a corresponding storage tank deposit. Elemental analysis, FTIR, 1H-NMR, and fluorescence spectroscopy were used to investigate the chemical composition and structural parameters of asphaltenes, while the surface tension method was used to measure the critical micelle concentration (CMC) in organic solvents with different solubility parameters and polarities in order to characterize the asphaltenes’ aggregation behaviors. Results show that the unstable asphaltenes fraction extracted from the storage tank deposit possesses a higher polarity (higher heteroatoms content) and a lower aromaticity than stable asphaltenes from the petroleum well. The CMC results indicate that asphaltenes with high polarity and low aromaticity have a high solubility in polar solvents such as nitrobenzene, whereas asphaltenes with low polarity and high aromaticity are more soluble in solvents with weak polarity, like toluene. It is concluded that the difference of structure of asphaltene samples and polarity of solvents can lead to difference of aggregation behaviors.

Kinetic model of hydropyrolysis based on the CPD model

A kinetic model of hydropyrolysis was developed based on the Chemical Percolation Devolatilization (CPD) network devolatilization model, considering the hydrogenation reactions of active species and fragments produced during the decomposition of the coal structure with hydrogen. Light gas compositions were calculated and the yields of oxygen-containing species were corrected. The calculation results show that the model well predicts the yields of volatile matter and methane for the coals that are in the scope of application of the correlation of the chemical structure parameters, with the value of β ranging from 0.0035 to 0.004atm−1, where β is a coefficient related to the ratio of the reaction rate of hydrogenation to that of crosslinking. The model successfully predicts the influence of coal type, final temperature and pressure on the hydropyrolysis yield and gas compositions. Further studies are needed to validate the model and determine the value and influencing factors of β.

Aromatic versus heteroradialene character in extended thiophloroglucinol ligands and their trinuclear nickel(II) complexes.

Extended phloroglucinol ligands and complexes are best described as nonaromatic heteroradialenes. Herein, the electronic structures of extended thiophloroglucinol ligands and their Ni(II) 3 complexes are evaluated by comparison to their phloroglucinol analogs by means of NMR, FTIR, UV/Vis, and structural parameters. To provide a full set of compounds for this comparison of S versus O substitution, a new triplesalen ligand, its Ni(II) 3 complex, and a new thiophloroglucinol were synthesized. (1) H and (15) N NMR chemical shifts and coupling constants prove that the thiophloroglucinol ligands exist as the N-protonated and not the O-protonated tautomer. (13) C and (15) N NMR chemical shifts and structural parameters further demonstrated that the extended thiophloroglucinol ligands must be described with a predominant thione-enamine (heteroradialene) character despite the participation of a CS double bond. In the Ni(II) 3 complexes, this heteroradialene character is reduced but still predominant.

A geometrical parametrization of C1′-C5′ RNA ribose chemical shifts calculated by density functional theory

It has been recently shown that NMR chemical shifts can be used to determine the structures of proteins. In order to begin to extend this type of approach to nucleic acids, we present an equation that relates the structural parameters and the (13)C chemical shifts of the ribose group. The parameters in the equation were determined by maximizing the agreement between the DFT-derived chemical shifts and those predicted through the equation for a database of ribose structures. Our results indicate that this type of approach represents a promising way of establishing quantitative and computationally efficient analytical relationships between chemical shifts and structural parameters in nucleic acids.

Quantum chemical analysis of the thermodynamics of 2D cluster formation of 2-hydroxycarboxylic acids at the air/water interface

In the framework of the quantum chemical semiempirical PM3 method, the thermodynamic and structural parameters of formation and clusterization were calculated for 2-hydroxycarboxylic acids with the general formula CnH2n+1CHOHCOOH (n = 5–15). Dimers and tetramers were formed on the basis of optimized monomer structures. It was shown that the alkyl chains in the considered associates orientate themselves with the following values of the tilt angles with respect to the p- and q-directions of the interface: δ = 7.2–21.2° and φ = 9.8–21.1° depending on the monomer structure of the cluster. Comparing the Gibbs energy values of clusterization for small aggregates, a possible scheme of 2D clusterization is proposed based on the formation of linear aggregates constructed by dimers with ‘parallel’ orientation of the functional groups for 2-hydroxycarboxylic acid monomers with n ≤ 16 carbon atoms in the alkyl chain. The following parameters of the unit cell for the most energetically preferred structure of 2D film 3 were found: a = 4.85 Å, b = 5.41 Å, and the angle between them θ = 95°. The molecular tilt angle of 2-hydroxycarboxylic acids with respect to the air/water interface was calculated to be t = 21.7°. The spontaneous clusterization threshold is 14 carbon atoms in the 2-hydroxycarboxylic acid chain at the air/water interface for a monolayer built on the basis of monomer 3 in good agreement with the existing experimental data.

On the inclusion of alkanes into the monolayer of aliphatic alcohols at the water/alkane vapor interface: a quantum chemical approach

In the framework of the quantum chemical semiempirical PM3 method thermodynamic and structural parameters of the formation and clusterization of aliphatic alcohols C(n)H(2n+1)OH (n(OH) = 8-16) at 298 K at the water/alkane vapor C(n)H(2n+2), (n(CH(3)) = 6-16) interface were calculated. The dependencies of enthalpy, entropy and Gibbs' energy of clusterization per one monomer molecule of 2D films on the alkyl chain length of corresponding alcohols and alkanes, the molar fraction of alkanes in the monolayers and the immersion degree of alcohol molecules into the water phase were shown to be linear or stepwise. The threshold of spontaneous clusterization of aliphatic alcohols at the water/alkane vapor interface was 10-11 carbon atoms at 298 K which is in line with experimental data at the air/water interface. It is shown that the presence of alkane vapor does not influence the process of alcohol monolayer formation. The structure of these monolayers is analogous to those obtained at the air/water interface in agreement with experimental data. The inclusion of alkane molecules into the amphiphilic monolayer at the water/alkane vapor interface is possible for amphiphiles with the spontaneous clusterization threshold at the air/water interface (n(s)(0)) of at least 16 methylene units in the alkyl chain, and it does not depend on the molar fraction of alkanes in the corresponding monolayer. The inclusion of alkanes from the vapor phase into the amphiphilic monolayer also requires that the difference between the alkyl chain lengths of alcohols and alkanes is not larger than n(s)(0) - 15 and n(s)(0) - 14 for the 2D film 1 and 2D film 2, respectively.