Hydrodynamic, molecular, and conformational characteristics of macromolecules of a random copolymer of N-Methyl-N-vinylacetamide and N-Methyl-N-vinylamine Hydrochloride

The development and optimization of processes involving polymeric molecules require determination and monitoring of key molecular characteristics of the polymer. Samples of poly-N-methyl-N-vinylacetamide were synthesized and fractionated. Partial hydrolysis of the homopolymer fractions was performed, and fractions of a random copolymer of N-methyl-N-vinylacetamide and N-methyl-N-vinylamine hydrochloride were obtained. The molecular weights and conformational parameters of the homo- and copolymers in 0.2 M aqueous NaCl were determined by methods of molecular hydrodynamics.     

Recombinant S-Adenosylhomocysteine Hydrolase from Thermotoga maritima: Cloning, Overexpression, Characterization, and Thermal Purification Studies

S-Adenosylhomocysteine hydrolase (SAHase) encoded by sahase gene is a determinant when catalyzing the reversible conversion of adenosine and homocysteine to S-adenosylhomocysteine in most living organisms. The sahase gene was isolated from the genome of the highly thermostable anaerobic bacteria Thermotoga maritima, and then it was cloned, characterized, overexpressed using Escherichia coli, and partially purified by thermal precipitation. The thermal purification of the recombinant SAHase resulted in changes in the circular dichroism spectra. As a result of this analysis, it was possible to determine the structural changes in the composition of the α-helix and β-sheet content of the recombinant enzyme after purification. Moreover, a predicted secondary structure and 3D structural model was rendered by comparative molecular modeling to further understand the molecular function of this protein including its attractive biotechnological use.     

The structure of trimethoxymethane in the gas phase,an electron diffraction,ab initio and molecular mechanics study

The structure of trimethoxymethane in the gas phase was studied by electron diffraction, ab initio molecular orbital calculations and molecular mechanics. The molecule was found to exist almost exclusively as an asymmetric all-staggered TGG conformer. The electron diffraction structural parameters (r_g distances, r_α angles) as obtained from geometrically consistent r_α-refinements are: r(C-O) central 1.382(6) Å, r(C-O) terminal 1.418(6) Å, r(C-H) 1.112(1) Å, ∠(O-C-O) in the gauche—gauche chain 115.0(1.0)°, in the gauche-anti chains 109.2(0.6)° ∠(C-O-C) 114.3(0.6)°, ∠(O-C-H)_Me 109.9(0.3)°, methyl torsion 68(6)°. The structure is adequately reproduced by molecular mechanics calculations applying Allinger's force field. The structures of methoxymethanes can be explained in terms of the anomeric effect. This is confirmed by ab initio calculations.     

Pulsed NMR of cis-polyisoprene solutions T1 and T2 relaxations,free volume,viscosity relationships

Previous pulsed NMR studies of polyisoprene have largely been concerned with entangled or crosslinked networks. This paper deals with (i) the relaxation of high molecular weight entangled; (ii) cross-linked; (iii) monodisperse low molecular weight; and (iv) high molecular weight polymer in the presence of tetrachloroethylene which, by increasing molecular mobility, can be expected to influence the NMR relaxation. For all four types of polyisoprene, the spin-lattice T₁, relaxation shows a minimum with position depending only on the free volume, as influenced by changes in temperature T and polymer concentration v₁,. For monodisperse polyisoprene of molecular weight 7200, insufficient to form an entangled network, the spin-spin relaxation decay constant T_2L is quantitatively related to the free volume ₁ by two parameters A′ and B″ when the free volume is altered by a change in temperature, or in polymer concentration (10–100/). This can also be expressed in the form where the parameter T_∞ at 100% concentration agrees with the value used to describe rheological properties. At other concentrations of polymer, T_∞ and B′ can be derived quantitatively from the coefficients of volume expansion of polymer and solvent. The variation of T_2L with molecular weight (T_2L ∝ M^?0.5) occurs via the A′ parameter. It is concluded that T_2L can be quantitatively related to the free volume available for molecular motion (as influenced by temperature and solvent concentration) as well as to molecular weight. Furthermore T_2L is simply related to viscosity n, over a wide range of temperatures and concentrations. T₂ can be used to analyse the molecular motions involved in theology.     

Stereochemical analysis of d-glucopyranosyl-sulfoxides via a combined NMR,molecular modeling and X-ray crystallographic approach

(S)-α-Methoxyphenylacetic acid (MPAA) was used as an NMR shift reagent in combination with molecular modeling to predict the absolute configuration of a representative epimeric pair of glucopyranosyl sulfoxides. The correctness of this assignment was confirmed by X-ray crystallographic examination of one of the epimers, 3a1. The crystal structure of ethyl 2,3-di-O-acetyl-4,6-O-benzylidene-1-thio-β-d-glucopyranoside S-oxide monohydrate 3a1 was solved by direct methods and was shown to bear the (R)-configuration at the sulfinyl center in accordance with our prediction. Furthermore, the conformation of 3a1 in the solid state was found to be remarkably similar to that predicted by molecular mechanics calculations.     

Anti,anti acetals : Photoelectron spectroscopy of trans-1,8-dioxadecalins

The anti,anti acetals trans-1,8-dioxadecalin and trans-1,8-dioxa-4,5-dithiadecalin have been studied by photoelectron spectroscopy, and the electronic structure of the anti,anti acetal moiety was further elucidated by molecular orbital calculations on dimethoxymethane and visualized by stereoscopic drawings of the frontier orbitals.     

Synthesis,crystal structure,chromatographic seperation,and thermogravimetric investigation of a ONNO type asymmetric Schiff base and its trinuclear complexes

1,3-Propanediamine was put to react with 2-hydroxybenzaldehyde and 2-hydroxyacetophenone sequentially in aprotic medium. The crystalline product was examined by high performance liquid chromatography. The composition was 66% asymmetric Schiff base N(2-hydroxybenzylidene)-N′(2-hydroxyacetophenone)-1,3-propanediamine (SALLACH₂) and 33% bis-N,N′(2-hydroxyacetophenylidene)-1,3-propanediamine (LACH2). As the crystals were uniform and of appropriate size, the molecular model of the material was revealed by X-ray diffraction. It was seen that two molecules of SALLACH₂ and one molecule of LACH₂ formed the mixed crystals. The substance was separated to its components and the asymmetric Schiff base was purified with a silica column. The substance was characterized with elemental analysis, FT-IR, MS, ¹HNMR, and ¹³C NMR. In addition, six tri-nuclear complex with the nuclear structure of Ni^II-Ni^II-Ni^II, Ni^II-Cu^II-Ni^II, Ni^II-Mn^II-Ni^II were prepared from this Schiff base and stoichiometry was determined by elemental analysis, FT-IR and thermogravimetry. Finally, the molecular structures of two complexes were brought to light by XRD which highlights the asymmetry of the ligand more clearly.     

Combined ab initio,electron diffraction,molecular mechanics and vibrational investigations of 1,1 -dimethyl-trans-2-decalone

The conformational behavior of 1,1'dimethyl-trans-2-decalone was studied by combined ab initio, electron diffraction, molecular mechanics and vibrational procedures, and the molecule was found to exist in a distorted all-chair ground state with average C-C, C-H and CO bond distances of r_g = 1.543 Å ± 0.002, r_g = 1.122 Å ± 0.007, and r_g = 1.236 Å ± 0.012, respectively. The ab initio calculations were performed on an STO-3G minimal basis and are indicative of the growing usefulness of quantum-mechanical techniques in the study of medium-sized molecular systems.     

Raman,surface-enhanced Raman scattering and DFT study of para-nitro-aniline

Raman spectra of para-nitro-aniline (pNA), a molecule with high applicability potential in molecular electronics, were recorded in solid state and in ethanol solution. Complete assignment of the experimental spectra was made by using the B3LYP/6-31G(d) theoretical results. The calculated molecular electrostatic potential shows a high negative charge localized on the nitro group of pNA and the surface-enhanced Raman scattering (SERS) spectrum of pNA adsorbed to colloidal silver particles denote the molecule interaction with the silver surface mainly through the nitro group. However, theoretical results obtained by modeling the pNA–4Ag complex also suggest the adsorption of pNA through the amino group or a flattened orientation of pNA with respect to the silver surface.     

Vibrational spectroscopic study of o-, m- and p-hydroxybenzylideneaminoantipyrines

Three structurally similar antipyrine derivatives of o-hydroxybenzylideneaminoantipyrine (o-HBAP), m-hydroxybenzylideneaminoantipyrine (m-HBAP) and p-hydroxybenzylideneaminoantipyrine (p-HBAP) were characterized by FT-IR, FT-Raman experimental techniques and density functional theoretical (DFT) calculations. The comparisons between the calculated and experimental results covering molecular structures, assignments of fundamental vibrational modes and thermodynamic properties were investigated. The optimized molecular geometries agree well with the corresponding experimental values by comparing with the XRD data. The comparisons and assignments of the vibrational frequencies indicate that the experimental spectra also coincide satisfactorily with those of theoretically simulated spectrograms except the hydrogen-bond coupling infrared vibrations, and compounds can be distinguished by the IR and Raman spectra due to the differences of the hydroxyl-substituted positions and molecular packing, and the strong Raman scattering activities of the compounds are tightly relative to the molecular conjugative moieties linked through the Schiff base imines. The thermodynamic functions and their correlations with temperatures were also obtained from the theoretical harmonic frequencies.     

DFT,AIM, and NBO study of the interaction of simple and sulfur-doped graphenes with molecular halogens,CH3OH,CH3SH,H2O,and H2S

Graphene is an important material in adsorption processes because of its high surface. In this work, the interactions between graphene (G), S-doped graphene (SG), and 2S-doped graphene (2SG) with eight small molecules including molecular halogens, CH₃OH, CH₃SH, H₂O, and H₂S were studied using density functional theory calculations. The adsorption energies showed that the SG was the best adsorbent, fluorine was the best adsorbate, and all molecular halogens were adsorbed on graphenes better than the other molecules. Most adsorption processes in the gas phase were exothermic with small positive ΔG _ads. Moreover, the solvent effect on the adsorption process was examined and all ΔH _ads and ΔG _ads values for adsorption processes tended to be more negative in all solvents. Therefore, most adsorption processes in the solvents were thermodynamically favorable. The second order perturbation energies obtained from NBO calculations confirmed that the interactions between molecular halogens and our molecules had more strength than those of other molecules. The Laplacian of ρ values obtained from the AIM calculations indicated that the type of interaction in all our complexes was one of closed shell interaction. The MO results and DOS plots also revealed that sulfur doping could increase the conductivity of graphene and this conductivity was enhanced more when they interacted with molecular halogens.     

Impact of regio-isomeric monochlorinated end groups on packing mode,miscibility, and photovoltaic performance of asymmetric selenophene-fused M-series acceptors

Optimal bulk-heterojunction (BHJ) morphology is crucial for efficient charge transport and good photovoltaic performance in organic solar cells (OSCs). Yet, the correlation between chemical structures of nonfullerene acceptors (NFAs) and molecular interaction in the BHJ blends remains opaque. Herein, we study three isomeric NFAs referred to as MQ1-x (x = β, γ, or δ) that shared an asymmetric selenophene-fused heteroheptacene backbone end-capped by two monochlorinated end groups. Remarkably, miscibility between the polymer donor of PM6 and MQ1-x successively elevates as the chlorine atoms move from β-, to γ-, to δ-position of terminals. Combined with the varied molecular crystallinity of these NFAs, diverse BHJ morphologies are observed in their blend films. As a result, the MQ1-δ-based devices present the highest PCE of 12.08% owing to the efficient charge dissociation and transport induced by the compact molecular packing and optimal BHJ morphology. Our investigation provides a new insight in the material design that has a good balance in molecular packing and film morphology for high-performance OSCs.     

Synthesis of Novel Tritopic Hydrazone Ligands: Spectroscopy,Biological Activity,DFT, and Molecular Docking Studies

Polytopic organic ligands with hydrazone moiety are at the forefront of new drug research among many others due to their unique and versatile functionality and ease of strategic ligand design. Quantum chemical calculations of these polyfunctional ligands can be carried out in silico to determine the thermodynamic parameters. In this study two new tritopic dihydrazide ligands, N’2, N’6-bis[(1E)-1-(thiophen-2-yl) ethylidene] pyridine-2,6-dicarbohydrazide (L1) and N’2, N’6-bis[(1E)-1-(1H-pyrrol-2-yl) ethylidene] pyridine-2,6-dicarbohydrazide (L2) were successfully prepared by the condensation reaction of pyridine-2,6-dicarboxylic hydrazide with 2-acetylthiophene and 2-acetylpyrrole. The FT-IR, ¹H, and ¹³C NMR, as well as mass spectra of both L1 and L2, were recorded and analyzed. Quantum chemical calculations were performed at the DFT/B3LYP/cc-pvdz/6-311G+(d,p) level of theory to study the molecular geometry, vibrational frequencies, and thermodynamic properties including changes of ∆H, ∆S, and ∆G for both the ligands. The optimized vibrational frequency and (¹H and ¹³C) NMR obtained by B3LYP/cc-pvdz/6-311G+(d,p) showed good agreement with experimental FT-IR and NMR data. Frontier molecular orbital (FMO) calculations were also conducted to find the HOMO, LUMO, and HOMO–LUMO gaps of the two synthesized compounds. To investigate the biological activities of the ligands, L1 and L2 were tested using in vitro bioassays against some Gram-negative and Gram-positive bacteria and fungus strains. In addition, molecular docking was used to study the molecular behavior of L1 and L2 against tyrosinase from Bacillus megaterium. The outcomes revealed that both L1 and L2 can suppress microbial growth of bacteria and fungi with variable potency. The antibacterial activity results demonstrated the compound L2 to be potentially effective against Bacillus megaterium with inhibition zones of 12 mm while the molecular docking study showed the binding energies for L1 and L2 to be −7.7 and −8.8 kcal mol⁻¹, respectively, with tyrosinase from Bacillus megaterium.     

Rotary friction,dipole moments,conformation and rigidity of polybutylisocyanate molecules in solution

Experimental data on the dependence of the rotatory diffusion coefficients and dipole moments on molecular weight and the theory of hydrodynamic properties and of the size of wormlike chains were used for determining the main conformational characteristics of the polyisocyanate chain S is the number of molecular units in a segment, λ is the length of the projection of the monomer unit on the axis of the molecule, and μ_o is the dipole moment of the monomer unit. The values of S and λ agree with those found previously by hydrodynamic methods. It was shown that the flat cis-structure of the polyisocyanate chain corresponds to values of λ = 2 × 10^?8cm andμ_o = 1·8D. Analysis of experimental data indicates that dimensions of “geometrical” and “electrical” segments in the PBIC chain are identical.     

Proximate Composition,Antioxidant Properties,and Hepatoprotective Activity of Three Species of Shellfish of the Pacific Coast of Russia

The objective of the present study was to investigate the proximate composition, antiradical properties and hepatoprotective activity of three species of shellfish, Corbicula japonica, Spisula sachalinensis, and Anadara broughtonii, from the coastal areas of Far East Russia. Biologically active peptides such as taurine (3.74 g/100 g protein) and ornithine (2.12 g/100 g protein) have been found in the tissues of A. broughtonii. C. japonica contains a high amount of ornithine (5.57 g/100 g protein) and taurine (0.85 g/100 g protein). The maximum DPPH and ABTS radical scavenging activity (36.0 µg ascorbic acid/g protein and 0.68 µmol/Trolox equiv/g protein, respectively) was determined for the tissue of C. japonica. The protein and peptide molecular weight distribution of the shellfish tissue water extracts was investigated using HPLC. It was found that the amount of low molecular weight proteins and peptides were significantly and positively correlated with radical scavenging activity (Pearson’s correlation coefficient = 0.96), while the amount of high molecular weight proteins negatively correlated with radical scavenging activity (Pearson’s correlation coefficient = −0.86). Hepatoprotective activity, measured by the survival rate of HepG2 hepatocytes after cotreatment with t-BHP, was detected for C. japonica. The highest protection (95.3 ± 2.4%) was achieved by the cold water extract of C. japonica at the concentration of 200 mg/mL. Moreover, oral administration of hot water extract of C. japonica to rats before the treatment with CCl₄ exhibited a markedly protective effect by lowering serum levels of ALT and AST, inhibiting the changes in biochemical parameters of functional state of rat liver, including MDA, SOD, GSH and GST.     

Chiral molecular polygons based on the Pt-alkynyl linkage: Self-assembly, characterization, and functionalization

Treatment of 2,2′-diacetoxy-1,1′-binaphthyl-6,6′-bis(ethyne), L-H₂, with one equiv of trans-Pt(PEt₃)₂Cl₂ led to a mixture of different sizes of chiral metallocycles [trans-(PEt₃)₂Pt(L)]_n (n = 3-8, 1-6). Each of the chiral molecular polygons 1-6 was purified by silica-gel column chromatography and characterized by ¹H, ¹³C{¹H}, and ³¹P{¹H} NMR spectroscopy, MS, IR, UV-Vis, and circular dichroism (CD) spectroscopies, size exclusion chromatography, and microanalysis. Chiral molecular square 2 was also characterized by single-crystal X-ray diffraction. The acetyl groups of 2 were readily deprotected under mild conditions to generate 2a which possesses exposed chiral dihydroxy functional groups. The dihydroxy groups were functionalized with n-octadecyl chains or Fréchet-type dendrons to generate dendritic molecules built on a chiral molecular square core. This work shows the potential of generating interesting functional supramolecular systems based on Pt-alkynyl chiral molecular polygons.     

1,2,3-triazole derivative: Synthesis,characterization, DFT,molecular docking study and antibacterial-antileishmanial activities

In this study, 4-((1-(4-chlorobenzyl)-1H-1,2,3-triazole-4-yl)methoxy)-3-methoxybenzaldehyde (I) was synthesized and molecular structure of compound I was confirmed by FTIR and NMR (¹H and ¹³C NMR) spectroscopic methods. The geometric structure of compound I was optimized by DFT/B3LYP method using 6–311++G(d, p) basis set. The molecular docking study was carried out against six different proteins. The antibacterial and antileishmanial activities of compound I were tested by microdilution broth with Alamar blue method and minimum inhibitor concentrations (MIC) were determined. According to the test results, it was found to be effective against eleven types of bacteria at different concentrations (MIC: 312–5000 ​μg/mL). In addition, compound I was not effective against leishmania species at the concentrations that were examined.     

Microwave spectrum,structure, dipole moment and internal rotation of ethyl fluorosilane

Microwave spectra of the trans and gauche isomers of ethyl fluorosilane and their eleven isotopically substituted species have been measured. The r_s structures of the two isomers were determined from the observed moments of inertia. The molecular structures found for the two isomers in the present study are compared with those of analogous molecules. Dipole moments of the two isomers were determined by Stark-effect measurements and are also compared with those of analogous molecules. The energy difference between the trans and gauche isomers was obtained from the relative intensity measurements of the spectra and the barrier to internal rotation of the methyl group for the gauche isomer was obtained from the A—E splittings of the spectra in the first excited methyl torsional state. The V₃ value was 2775 ± 25 cal mol^?1.     

Design, synthesis, insecticidal evaluation and molecular docking studies of cis-nitenpyram analogues bearing diglycine esters

Based on the strategies of receptor structure-guided neonicotinoid design, a series of novel cis-nitenpyram analogues bearing diglycine esters were designed and synthesized. Preliminary bioassays indicated that the insecticidal spectra of the target compounds were expanded compared with our previous work, while all the target compounds presented excellent insecticidal activities against Nilaparvata lugens and Aphis medicagini at 100 mg/L. Among these analogues, 6b showed 100% mortality against Nilaparvata lugens (LC 50 = 0.163 mg/L) and 90% against Aphis medicagini at 4 mg/L. SARs suggested that the insecticidal potency of our designed cis-nitenpyram analogues was dual-controlled by the size and species of the ester groups. The molecular docking simulations revealed that the structural uniqueness of these analogues may lead to a unique molecular recognition and binding mode compared with the previously designed compounds. Introduction of the peptide bond gave rise to more significant hydrogen bonds between the nitenpyram analogues bonding with the amino acid residues of insect nAChRs. The docking results explained the SARs observed in vitro, and shed light on the novel insecticidal mechanism of these cis-nitenpyram analogues.