Phenolic derivatives and other chemical compounds from Cochlospermum regium

This study describes the chemical investigation of the ethyl acetate fraction obtained from the hydroethanolic extract of the xylopodium of Cochlospermum regium (Mart. & Schr.) Pilger, which has been associated with antimicrobial activity. Phytochemical investigation produced seven phenol derivatives: ellagic acid, gallic acid, dihydrokaempferol, dihydrokaempferol-3-O-β-glucopyranoside, dihydrokaempferol-3-O-β-(6"-galloyl)-glucopyranoside, pinoresinol, and excelsin. It also contained two triacylbenzenes, known as cochlospermines A and B. The hydroethanolic extract and its fractions exhibited antimicrobial activity (0.1 mg/mL) against Staphylococcus aureus and Pseudomonas aeruginosa. Gallic acid showed activity against S. aureus. Dihydrokaempferol-3-O-β-(6"-galloyl)-glucopyranoside is reported here for the first time in the literature.

Chemical constituents from red algae Bostrychia radicans (Rhodomelaceae): new amides and phenolic compounds

This study describes the isolation and structural determination of two amides, isolated for the first time: N,4-dihydroxy-N-(2'-hydroxyethyl)-benzamide (0.019%) and N,4-dihydroxy-N-(2'-hydroxyethyl)-benzeneacetamide (0.023%). These amides, produced by the red macroalgae Bostrychia radicans, had their structures assigned by NMR spectral data and MS analyses. In addition, this chemical study led to the isolation of cholesterol, heptadecane, squalene, trans-phytol, neophytadiene, tetradecanoic and hexadecanoic acids, methyl hexadecanoate and methyl 9-octadecenoate, 4-(methoxymethyl)-phenol, 4-hydroxybenzaldehyde, methyl 4-hydroxybenzeneacetate, methyl 2-hydroxy-3-(4-hydroxyphenyl)-propanoate, hydroquinone, methyl 4-hydroxymandelate, methyl 4-hydroxybenzoate, 4-hydroxybenzeneacetic acid and (4-hydroxyphenyl)-oxo-acetaldehyde. This is the first report concerning these compounds in B. radicans, contributing by illustrating the chemical diversity within the Rhodomelaceae family.

Revisão dos tratamentos químicos da fibra natural para mistura com poliolefinas

The use of natural fibers as reinforcement in polymer composites has been a focus of interest. However, these composites exhibit lower mechanical properties than those of pure polymers because of the low interfacial interactions between the hydrophobic polymer matrix and the hydrophilic fiber. To overcome this problem, different chemical treatments applied to the fibers have been reported. One of the most used treatments is mercerization, which can improve adhesion between the fiber and polymeric matrix. Another chemical treatment involves the use of acids (stearic and oleic acids). The chemically treated fibers used in composite materials showed improved mechanical properties.

Development and validation of a dissolution test for primaquine/polyethylene oxide matrix tablets

A simple, precise, specific, repeatable and discriminating dissolution test for primaquine (PQ) matrix tablets was developed and validated according to ICH and FDA guidelines. Two UV assaying methods were validated for determination of PQ released in 0.1 M hydrochloric acid and water media. Both methods were linear (R²>0.999), precise (R.S.D.<1.87%) and accurate (97.65-99.97%). Dissolution efficiency (69-88%) and equivalence of formulations (f2) was assessed in different media and apparatuses (basket/100 rpm and paddle/50 rpm) tested. Discriminating condition was 900 mL aqueous medium, basket at 100 rpm and sampling times at 1, 4 and 8 h. Repeatability (R.S.D.<2.71%) and intermediate precision (R.S.D.<2.06%) of dissolution method were satisfactory.

Acúmulo de cargas elétricas em propelente sólido compósito com matriz de polibutadieno líquido hidroxilado

Composite solid propellants prepared with HTPB prepolymer - Hydroxyl Terminated Polybutadiene, AP - Ammonium Perchlorate as oxidizer and aluminum particles as an additive metal, have characteristics of high electrical resistivity. The loading process of the polymer matrix did not obtain homogeneity, resulting in clusters, mainly of metal particles. The effect of clustering in the composite was studied and observed experimentally, and this effect was one of the factors explaining the phenomenon of electrical charging of the composite. This electrical potential, when discharged abruptly, can generate an electric spark with sufficient energy for sustained ignition of a solid rocket motor.

Imobilização de lacase de Aspergillus sp. em quitosana e sua aplicação na bioconversão de fenóis em reatores de leito fixo

The immobilization of laccase on chitosan by cross-linking and application of the immobilized laccase in the bioconversion of phenolic compounds in batch and fixed bed reactors were studied. The process for immobilization of enzyme was optimized using a rotational central composite design. The optimized conditions to generate immobilized laccase with maximal activity were determined to be a glutaraldehyde concentration of 1.0% (v/v), a pH of 6.0, an immobilization time of 5.0 hours and an enzyme concentration of 5.2 g L-1. In packed bed reactors, the activity of the immobilized enzyme is maintained for a longer time in the bioconversion of 2,6-dimethoxyphenol than in the bioconversion of syringaldazine.

Phenolic composition and antioxidant properties of Brazilian honeys

The antioxidant activities and polyphenolic levels of "assa peixe," "cambara," and "morrão de candeia" Brazilian honeys were investigated. Phenolic extracts of 11 honeys were evaluated spectrophotometrically to determine their total phenolic and flavonoid contents, and their antioxidant activities were measured using DPPH, ABTS, and FRAP assays. High-performance liquid chromatography coupled with diode array detection was applied to determine the phenolic composition of the honey extracts. The presence of fourteen phenolic compounds was established (eleven phenolic acids and three flavonoids), as well as HMF and abscisic acid. Principal component analysis was applied to classify the honey samples according to their floral origins.

Simultaneous determination of four phenolic compounds in extracts of aerial parts of Ipomoea pes-caprae (L.) R. Br. (Convolvulaceae) by HPLC-UV

Among other applications, Ipomoea pes-caprae is popularly used to treat jellyfish stings, supporting the development of a product for dermatological use. Hydroethanolic spray-dried extract was chosen for the further development of phytomedicines, and a stability-indicative HPLC-UV method was developed and validated for the determination of isoquercitrin and isochlorogenic acids A, B and C. The method was developed using a C18 column (250 x 4.6 mm, 5 µm) with an acetonitrile:water mobile phase at pH 3.0 in a gradient run. The four constituents and other unidentified components of the extract were appropriately resolved without interference of degradation products after stress tests (acid, alkali, neutral, oxidant, photolysis). The method showed linearity in the isoquercitrin concentration range from 5.0-50.0 µg mL-1, with adequate precision (RSD% < 2.5% for the intra- and inter-day studies), accuracy (recovery of 100.0 ± 2.0%), and robustness. Both the herbal drug and spray-dried extract of I. pes-caprae were subjected to stability studies in accelerated and long-term conditions over four months. The samples maintained their characteristics and marker contents (< 10% of variation).

EVALUATION OF A BUFFERED SOLID PHASE DISPERSION PROCEDURE ADAPTED FOR PESTICIDE ANALYSES IN THE SOIL MATRIX

An evaluation of the pesticides extracted from the soil matrix was conducted using a citrate-buffered solid phase dispersion sample preparation method (QuEChERS). The identification and quantitation of pesticide compounds was performed using gas chromatography-mass spectrometry. Because of the occurrence of the matrix effect in 87% of the analyzed pesticides, the quantification was performed using matrix-matched calibration. The method's quantification limits were between 0.01 and 0.5 mg kg-1. Repeatability and intermediate precision, expressed as a relative standard deviation percentage, were less than 20%. The recoveries in general ranged between 62% and 99%, with a relative standard deviation < 20%. All the responses were linear, with a correlation coefficient (r) ≥0.99.

OBTENÇÃO DE COMPÓSITOS HÍBRIDOS BASEADOS EM HIDROGÉIS E CIMENTO PORTLAND

In this study, a novel hybrid composite based on biodegradable hydrogel and Portland cement with promising technological properties was reported. In the first step, a full 23 with central point factorial design was utilized to obtain the enhanced polyacrylamide-carboxymethylcellulose hydrogel compositions. A mathematical model was devised, indicating that the 3 main variables were significant and the AAm and MBAAm variables positively contributed to the mode and showing that the CMC variable had the opposite contribution. In the second step, these compositions were mixed with Portland cement to obtain the hybrid composites. The presence of cement improved the mechanical properties of polymeric matrices, and electronic microscopic micrographics revealed that the hydrogels were well adhered to the cement phase and no phase separation between hydrogel and cement was detected. Finally, using the energy dispersive X-ray technique, the elements Na, Mg, Al, Si, S, K, Ca and Fe were detected in the polymeric matrix, consistent with the hybrid composite formation.

Electron migration in DNA matrix: an electron transfer reaction

This paper brings an active and provocative area of current research. It describes the investigation of electron transfer (ET) chemistry in general and ET reactions results in DNA in particular. Two DNA intercalating molecules were used: Ethidium Bromide as the donor (D) and Methyl-Viologen as the acceptor (A), the former intercalated between DNA bases and the latter in its surface. Using the Perrin model and fluorescence quenching measurements the distance of electron migration, herein considered to be the linear spacing between donor and acceptor molecule along the DNA molecule, was obtained. A value of 22.6 (± 1.1) angstroms for the distance and a number of 6.6 base pairs between donor and acceptor were found. In current literature the values found were 26 angstroms and almost 8 base pairs. DNA electron transfer is considered to be mediated by through-space interactions between the p-electron-containing base pairs.

Determination of hydroquinone in a square wave voltammetry procedure using a graphite-polyurethane composite electrode

In order to a better characterization of a graphite-polyurethane composite intended to be used as a voltammetric sensor, the performance in a square wave voltammetric procedure was investigated. Using hydroquinone (HQ) as a probe, the electrode showed to be useful in square wave voltammetry with limit of detection of 0.28 µmol L-1, with recoveries between 99.1 and 101.5%. The results of the proposed method agreed with HPLC ones within 95% confidence level.

Determination of phenolic compounds and evaluation of antioxidant capacity of Campomanesia adamantium leaves

Five flavanones and three chalcones were isolated from Campomanesia adamantium Berg. (Myrtaceae) leaves. The contents of these compounds were determined by HPLC. The phenolic contents were also determined. The monitoring of the antioxidant activity was carried out by inhibition of peroxidation using the linoleic acid system and radical-scavenging (DPPH). The plants were collected from 4 distinct cities of the Mato Grosso do Sul State, Brazil. The different samples exhibited a range of 4.67-232.35 mg/g chalcones and 15.62-50.71 mg/g flavanones and phenolic contents of the 7.24-21.19 mg/g gallic acid. All extracts showed high antioxidant activity with a wide range of the radical-scavenging (DPPH) from 52.0 to 92.2 % and inhibition oxidation of linoleic acid from 14.6 to 94.2%.

Matrix- based logic for avoiding paradoxes and its paraconsistent alternative

The present article shows that there are consistent and decidable many- valued systems of propositional logic which satisfy two or all the three criteria for non- trivial inconsistent theories by da Costa (1974). The weaker one of these paraconsistent system is also able to avoid a series of paradoxes which come up when classical logic is applied to empirical sciences. These paraconsistent systems are based on a 6- valued system of propositional logic for avoiding difficulties in several domains of empirical science (Weingartner (2009)).

Bonding of Composite Resin to Alumina and Zirconia Ceramics with Special Emphasis on Surface Conditioning and Use of Coupling Agents

Dental oxide ceramics have been inspired by their biocompability and mechanical properties which have made durable all-ceramic structures possible. Clinical longevity of the prosthetic structures is dependent on effective bonding with luting cements. As the initial shear bond strength values can be comparable with several materials and procedures, long-term durability is affected by ageing. Aims of the current study were: to measure the shear bond strength of resin composite-to-ceramics and to evaluate the longevity of the bond; to analyze factors affecting the bond, with special emphasis on: the form of silicatization of the ceramic surface; form of silanization; type of resin primer and the effect of the type of the resin composite luting cement; the effect of ageing in water was studied regarding its effect to the endurance of the bond. Ceramic substrates were alumina and yttrium stabilized zirconia. Ceramic conditioning methods included tribochemical silicatization and use of two silane couplings agents. A commercial silane primer was used as a control silane. Various combinations of conditioning methods, primers and resin cements were tested. Bond strengths were measured by shear bond strength method. The longevity of the bond was generally studied by thermocycling the materials in water. Additionally, in one of the studies thermal cycling was compared with long-term water storaging. Results were analysed statistically with ANOVA and Weibull analysis. Tribochemical treatment utilizing air pressure of 150 kPa resulted shear bond strengths of 11.2 MPa to 18.4 MPa and air pressure of 450 kPa 18.2 MPa to 30.5 MPa, respectively. Thermocycling of 8000 cycles or four years water storaging both decreased shear bond strength values to a range of 3.8 MPa to 7.2 MPa whereas initial situation varied from 16.8. Mpa to 23.0 MPa. The silane used in studies had no statistical significance. The use of primers without 10-MDP resulted spontaneous debonding during thermocycling or shear bond strengths below 5 MPa. As conclusion, the results showed superior long-term bonding with primers containing 10-MDP. Silicatization with silanizing showed improved initial shear bond strength values which considerably decreased with ageing in water. Thermal cycling and water storing for up to four years played the major role in reduction of bond strength, which could be due to thermal fatigue of the bonding interface and hydrolytic degradation of the silane coupled interface.