A structural bridge between alternant and non-alternant hydrocarbons

A simple set of trimethylene-substituted even, fully-pi-bonded, non-alternant monocycles is shown to have several key features in common with acyclic, even alternant polyenes at the Hückel level. These non-alternant molecules provide a bridge between alternant and non-alternant hydrocarbons. This topic might serve as a useful addition to Hückel theory courses targeted at senior undergraduate students.

On the application of knoevenagel condensation for the synthesis of benzylidene benzothiazine compounds and structural study

The synthesis and physico-chemical properties of new 6-acetylamino or 6-benzoyl-amino 2-benzylidene-4-methyl-4H-benzo[1,4]thiazin-3-ones and 6-benzoylamino or 6-nitro 2-benzylidene-4H-benzo[1,4]thiazin-3-ones are described. These benzylidene benzothiazine compounds were prepared by the Knoevenagel condensation with benzaldehydes. The configurations and conformations of benzylidene benzothiazine derivatives were optimised using the semi-empirical method AM1.

Synthesis of resorcinolic lipids bearing structural similarities to cytosporone A

Inspired by the structure and biological activities of resorcinolic lipids and, particularly cytosporone A- a potent inhibitor of plantule germination and growth, we have performed the synthesis of the analogs 3-heptyl-3-hydroxy-5,7-dimethoxy-2-benzofuran-1(3H)-one (1) and 3-heptyl-3-hydroxy-4,6-dimethoxy-2-benzofuran-1(3H)-one (2). The intermediates and products were submitted to allelopathic test using Lactuca sativa L. seeds. Target compound 1 showed an inhibitory effect on germination and growth of hypocotyl and radicle in milimolar range.

Structural and reactivity analyses of 2-benzylamino-1,4-naphthoquinone by X-ray characterization, electrochemical measurements, and dft single-molecule calculations

This study represents an integrated approach towards understanding the electronic and structural aspects of 2-benzylamino-1,4-naphthalenedione, a representative 2-amino-napfthoquinone. To this end, theoretical calculations performed at the B3PW91/6-31+G(d) level of density functional theory, electrochemical and X-ray structural investigation were employed. Two intramolecular H-bonds and other two intermolecular H-bonds were observed, including non-classical interactions. Cyclic voltammogram (CV) and differential pulse voltammetry (DPV) show two pairs of peaks, being each one a monoelectronic process.

Thermal and structural study of guava (Psidium guajava L) powders obtained by two dehydration methods

Two food products (powders) were obtained by hot-air drying or lyophilisation methods on the whole guava fruits. The powders were characterised by sensory and thermal analyses (TGA-DSC), infrared spectroscopy (IR), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Thermal, morphological and structural characterisations showed a similar behaviour for the two solids. TGA-DSC and IR showed the presence of pectin as the main constituent of solids. A semi-crystalline profile was evidenced by XRD, and lamellar/spherical morphologies were observed by SEM. Sensory analyses revealed an aroma highly related to guava. These value-added food products are an alternative to process guava and avoid loss during postharvest handling.

Encapsulation of naproxen in nanostructured system: structural characterization and in vitro release studies

Nanoparticles were produced by solvent emulsification evaporation method with the following characteristics: nanometric size (238 ± 3 nm), narrow polydispersity index (0.11), negative zeta potential (-15.1 mV), good yield of the process (73 ± 1.5%), excellent encapsulation efficiency (81.3 ± 4.2%) and spherical shape. X-rays diffraction demonstrated the loss of drug crystallinity after encapsulation; however, the profile of the diffractograms of the poly-ε-caprolactone (PCL) nanoparticles was kept. Differential scanning calorimetry thermograms, correspondingly, exhibited the loss of drug melting peak and the increasing of the melting point of the PCL nanoparticles, evidencing an interaction drug-polymer. Naproxen release was low and sustained obeying the Higuchi´s kinetic. The results show that nanoparticles are promising sustained release system to the naproxen.

Preparation of glasses and glass ceramics of heavy metal oxides containing silver: optical, structural and electrochemical properties

Silver containing heavy metal oxide glasses and glass ceramics of the system WO3-SbPO4-PbO-AgCl with different AgCl contents have been prepared and their thermal, structural and optical properties characterized. Glass ceramics containing metallic silver nanoparticles have been prepared by annealing glass samples at temperatures above the glass transition and analyzed by transmission electron microscopy and energy dispersive X-ray microanalysis. The presence of the metallic clusters has been also confirmed by the observation of a surface plasmon resonance band in the visible range. Cyclic voltammetric measurements indicated the presence of metallic silver into the glasses, even before to perform the thermal treatment.

Complete ¹H and 13C NMR structural assignments for a group of four goyazensolide-type furanoheliangolides

Four goyazensolide-type sesquiterpene lactones - lychnofolide, centratherin, goyazensolide and goyazensolide acetate - were thoroughly studied by NMR experimental techniques. ¹H NMR, 13C NMR {¹H}, COSY, HMQC, HMBC, J-res. and NOE experiments were performed to provide the needed structural information. Complete and unequivocal assignment, including the determination of all multiplicities, was obtained for each structure and the data collections are presented in tables.

Synthesis and biological activity of sulfur compounds showing structural analogy with combretastatin A-4

We extended our previous exploration of sulfur bridges as bioisosteric replacements for atoms forming the bridge between the aromatic rings of combretastatin A-4. Employing coupling reactions between 5-iodo-1,2,3-trimethoxybenzene and substituted thiols, followed by oxidation to sulfones with m-CPBA, different locations for attaching the sulfur atom to ring A through the synthesis of nine compounds were examined. Antitubulin activity was performed with electrophoretically homogenous bovine brain tubulin, and activity occurred with the 1,2,3-trimethoxy-4-[(4-methoxyphenyl)thio]benzene (12), while the other compounds were inactive. The compounds were also tested for leishmanicidal activity using promastigote forms of Leishmania braziliensis (MHOM/BR175/M2904), and the greatest activity was observed with 1,2,3-trimethoxy-4-(phenylthio)benzene (10) and 1,2,3-trimethoxy-4-[(4-methoxyphenyl) sulfinyl]benzene (15).

A new approach to evaluate immobilization of β-galactosidase on Eupergit® C: structural, kinetic, and thermal characterization

This study aimed to evaluate β-galactosidase immobilization. For this purpose, the ionic strength of the buffer, reaction time, amount of the immobilization support, and pH were evaluated by a central composite design. Assay 8, which consisted of 1.5 mol L-1 phosphate buffer (pH 7.5) and a reaction time of 2 h, produced the maximum yield. Eupergit® C (400 mg) was subsequently used as an immobilization support. Immobilization kinetics wereinvestigated, and a significant increase in the yield was obtained after immobilization compared with that obtained from assay 8 (22.0 U mL-1 vs. 15.6 U mL-1). The enzyme efficiency of actuation was evaluated using o-nitrophenyl-β-D-galactopyranoside and lactose, with lactose providing better results. The reuse of β-galactosidase was evaluated, and more than 50% of the initial enzyme activity was maintained after five cycles of use. Enzyme characterization revealed that immobilization improved some aspects of the thermostability of β-galactosidase.

SYNTHESIS AND CHARACTERIZATION OF HDTMA-ORGANOCLAYS: INSIGHTS INTO THEIR STRUCTURAL PROPERTIES

This study aims to synthesize and characterize organoclays developed from an Argentinian montmorillonite (Bent) using hexadecyltrimethylammonium bromide (HDTMA-Br) as the intercalation agent. Subsequently, an adsorption mechanism is proposed. The obtained organoclays were more hydrophobic than the starting clay. Surfactant molecules were adsorbed initially through cation exchange in sites placed in the interlayer space of the clay. Adsorption in such sites continued until the interlayer space was saturated. Depending on the surfactant loading introduced during the intercalation process, different organizations of surfactant in the interlayer were obtained. Further adsorption of surfactant occurred in the mesopores generated by tactoids in the "house of cards" organization. This process kept surfactant molecules relatively free and out of the interlayer space.

Structural bioinformatics study of cyclin-dependent kinases complexed with inhibitors

The present work describes molecular models for the binary complexes CDK9, CDK5 and CDK1 complexed with Flavopiridol and Roscovitine. These structural models indicate that the inhibitors strongly bind to the ATP-binding pocket of CDKs and the structural comparison with the complexes CDK2:Flavopiridol and CDK2:Roscovitine correlates the structural differences with differences in inhibition of these CDKs by the inhibitors. These structures open the possibility of testing new inhibitor families, in addition to new substituents for the already known lead structures such as flavones and adenine derivatives.

Synthesis, structural and morphological characterization of CeO2-ZnO nanosized powder systems from Pechini's method

This work reports on the investigation of nanosized CeO2-ZnO systems prepared by Pechini's method. The structural and morphological characterization of CeO2-ZnO systems as well as the characterization of CeO2 and ZnO separately, showed that the employed method result in powders with spheroidal particles whose size are in the range 30 - 200 nm, which is appropriate to provide homogeneous suspensions. The ZnO present in the prepared mixed oxides seems to increase particle size distribution and to influence the arrangement of the particles after powder dispersion.

Analysis of the structural and electronic properties of 1-(5-Hydroxymethyl - 4 -[ 5 - (5-oxo-5-piperidin-1-yl-penta-1,3dienyl)-benzo[1,3]dioxol-2-yl] -tetrahydro-furan-2-yl)-5-methyl-1H-pyrimidine-2,4dione molecule

The structural and electronic properties of 1-(5-Hydroxymethyl - 4 -[ 5 - (5-oxo-5-piperidin- 1 -yl-penta- 1,3 -dienyl)-benzo [1,3] dioxol- 2 -yl]-tetrahydro -furan-2 -yl)-5-methy l-1Hpyrimidine-2,4dione (AHE) molecule have been investigated theoretically by performing density functional theory (DFT), and semi empirical molecular orbital calculations. The geometry of the molecule is optimized at the level of Austin Model 1 (AM1), and the electronic properties and relative energies of the molecules have been calculated by density functional theory in the ground state. The resultant dipole moment of the AHE molecule is about 2.6 and 2.3 Debyes by AM1 and DFT methods respectively, This property of AHE makes it an active molecule with its environment, that is AHE molecule may interacts with its environment strongly in solution.

Estimation of standard enthalpy of formation of alkanes in gaseous state by calculating size, structural and electronic parameters in the molecules

A quantitative analysis is made on the correlation ship of thermodynamic property, i.e., standard enthalpy of formation (ΔH fº) with Kier's molecular connectivity index(¹Xv),vander waal's volume (Vw) electrotopological state index (E) and refractotopological state index (R) in gaseous state of alkanes. The regression analysis reveals a significant linear correlation of standard enthalpy of formation (ΔH fº) with ¹Xv, Vw, E and R. The equations obtained by regression analysis may be used to estimate standard enthalpy of formation (ΔH fº) of alkanes in gaseous state.