Preparação, caracterização e estudos de biodegradação de blendas à base de PDLLA e PVP

Poly(D,L-lactide), PDLLA, is a polymer with potential applications in medical, environmental, and pharmaceutical areas. Despite its versatility, the hydrophobicity limits its applications. To overcome this problem, one strategy is the preparation of blends with hydrophilic polymers such as poly(vinylpyrrolidone), PVP. In this study, we report the preparation and characterization of blends based on PDLLA and PVP and the biodegradation studies by the Sturm test. It was observed that the components of the blends PDLLA/PVP are thermodynamically immiscible, however the biodegradation is faster than that of pure PDLLA.

Preparação de nanopartículas de prata e ouro: um método simples para a introdução da nanociência em laboratório de ensino

A new practical experiment involving silver and gold nanoparticle syntheses was introduced in an inorganic chemistry laboratory course for undergraduate students at the Institute of Chemistry, UNICAMP. The nanoparticles were synthesized by the reduction of silver nitrate and tetrachloroauric acid with sodium borohydride and sodium citrate in an aqueous medium. Stabilities of the suspensions were tested using several different reactants including sodium chloride, polyvinylpyrrolidone, polyvinyl alcohol and cistamine. Changes in optical properties were observed by electronic spectra and also by transmission electronic microscopy, which also yielded data for estimating particle size.

Preparação de derivados do lapachol em meio ácido e em meio básico: uma proposta de experimentos para a disciplina de Química Orgânica Experimental

In this educational paper we describe the extraction of lapachol from its natural source according to acid-base concepts in organic chemistry and the use of its derivatives β-lapachone and hydroxy-hydrolapachol to exemplify intramolecular cyclization, carbocation stability, Michael addition reaction and chromatography. The experiments were performed during three different undergraduate organic chemistry laboratory classes using low cost material, while avoiding color reagents for TLC visualization, as well as small-scale column chromatography to isolate the mixture of lapachol and β-lapachone.

Influência do método de preparação de eletrocatalisadores PtRu/C sobre a atividade catalítica frente à reação de oxidação de etanol em meio ácido

In this work the influence of variations in the borohydrate reduction method on the properties of PtRu/C electrocatalysts was investigated. The electrocatalysts were prepared using 1:1 ; 2:1; 5:1; 50:1 and 250:1 molar ratios of NaBH4 to metals. The reduction was also performed by dripping or by fast addition of the solution. The results showed that PtRu nanoparticles obtained by fast addition had the smallest crystallite sizes. It was also noted that the catalytic activity increased as the borohydrate:metal molar ratio increased. The PtRu/C electrocatalyst (50:1) obtained by fast addition presented the best catalytic activity for ethanol electro-oxidation.

Determinação espectrofotométrica de cloreto em cimento após preparo de amostra por piroidrólise

A method based on pyrohydrolysis was proposed for cement sample preparation and further chloride determination by spectrophotometry using flow injection analysis. Analytical parameters were evaluated and, under the selected conditions, the calibration curve was linear in the range of 0.2 to 10.0 µg mL-1 with r2 = 0.998. The limit of detection was5 µg g-1 of chloride and the relative standard deviation was less than 7%. The proposed pyrohydrolysis method is relatively simple and can be used for sample preparation for further spectrophotometric determination of low concentrations of chloride in cement.

Avaliação de tratamentos da amostra em microescala para a determinação de K, Mg, Na e Zn em carnes por técnicas de espectrometria atômica

This paper describes the development of methods in micro-scale for the determination of K, Mg, Na and Zn in meat by atomic spectrometry techniques. The limits of detection (LOD) for K and Na by microdigestion were 0.18 and 0.20 mg g-1, respectively whereas LOD for Mg and Zn by microsolubilization with TMAH were 2.40 and 18.4 µg g-1, respectively. The RSD values were lower than 6.0% and the CRMs analyzed showed values with 95% agreement. The proposed methods are simple, fast and use small amounts of sample (around 10 mg) yet do not require special equipment for sample preparation.

Preparação, caracterização e aplicação de fases estacionárias tipo C8 modificadas por óxidos metálicos para cromatografia líquida

This work describes three C8-stationary phases for high performance liquid chromatography based on silica metallized with ZrO2, TiO2 or Al2O3 layers, having poly(methyloctylsiloxane) immobilized onto their surfaces. The stationary phases were characterized using XRF, XAS, FTIR, SEM and elemental analysis to determine the physical characteristics of the oxide and polysiloxane layers formed on the surfaces and chromatographically to evaluate the separation parameters. The results show the changes on the silica surface and allowed proposing a structure for the oxide layer, being observed tetrahedral and octahedral structures, what is completely new in the literature. The formation of a homogeneous layer of metallic oxide (TiO2 and ZrO2) was observed on the silica. The C8-titanized and C8-aluminized stationary phases presented good chromatographic performances, with good values of asymmetry and efficiency. All stationary phase presented few loss of the polymeric layer after the HPLC, indicating that this layer is well attached on the metalized support.

Preparação e caracterização do complexo de inclusão do óleo essencial de Croton zehntneri com β-ciclodextrina

Croton zehntneri, a plant native to northeastern Brazil, is widely used in folk medicine to treat gastrointestinal problems and has rich essential oil content. The essential oil of C. Zehntneri was analyzed by GC-MS, and its inclusion complex with β-cyclodextrin (β-CD) was characterized by both vibrational spectroscopy and differential scanning calorimetry (DSC). Estragol was the major component identified in the essential oil by the study. IR spectra indicated an interaction of β-CD with essential oil from C. zehntneri, a finding corroborated by the stability constant and scanning calorimetry. Microencapsulation within β-CD has the potential to mask sensory attributes and increase aqueous solubility of oils, thereby improving their applicability as drugs.

Membranas de condução mista iônica e eletrônica (miec): composições, preparação e desempenho

This paper presents a review of different chemical compositions that are used in the production of mixed ionic-electronic conducting membranes with the perovskite structure. In these dense membranes, oxygen from the air is permeated through ionic and electronic processes, and high oxygen permeation fluxes are observed at high temperatures (800-900 ºC). Various membranes were compared for their performance and properties after being synthesized by different methods.

Nanocompósitos entre nanotubos de carbono e nanopartículas de platina: preparação, caracterização e aplicação em eletro-oxidação de álcoois

The synthesis and characterization of different platinum nanoparticle/carbon nanotube nanocomposite samples are described along with the application of these nanocomposites as electrocatalysts for alcohol oxidation. Samples were prepared by a biphasic system in which platinum nanoparticles (Pt-NPs) are synthesized in situ in contact with a carbon nanotube (CNT) dispersion. Variables including platinum precursor/CNT ratio, previous chemical treatment of carbon nanotubes, and presence or absence of a capping agent were evaluated and correlated with the characteristic of the synthesized materials. Samples were characterized by Raman spectroscopy, X-ray diffraction, thermogravimetric analysis and transmission electron microscopy. Glassy carbon electrodes were modified by the nanocomposite samples and evaluated as electrocatalysts for alcohol oxidation. Current densities of 56.1 and 79.8/104.7 mA cm-2 were determined for the oxidation of methanol and ethanol, respectively.

Efeito da variação de parâmetros reacionais na preparação de grafeno via oxidação e redução do grafite

This work shows the influence of several reactional parameters for obtaining graphene through successive steps of oxidation and exfoliation of bulk graphite (resulting in graphene oxide), followed by chemical reduction. The results showed that changes in temperature, reaction time, reducing agent and source of primary graphite lead to different surface compositions and stability in dispersion of graphene oxide. Also, the use of different reducing agents promoted different degrees of restoration of C=C bonds in the bidimensional structure of graphene.

CONSTRUÇÃO DE UM DISPOSITIVO DE PRESSURIZAÇÃO A VÁCUO PARA A PREPARAÇÃO DE FASES ESTACIONÁRIAS MONOLÍTICAS VIA PROCESSO SOL-GEL

The filling of capillaries via the sol-gel process is growing. Therefore, this technical note focuses on disseminating knowledge acquired in the Group of Analytical Chemistry and Chemometrics over seven years working with monolithic stationary phase preparation in fused silica capillaries. We believe that the detailed information presented in this technical note concerning the construction of an alternative high pressurization device, used to fill capillary columns via the sol-gel process, which has promising potential for applications involving capillary electrochromatography and liquid chromatography in nano scale, may be enlightening and motivating for groups interested in developing research activities within this theme.

PREPARAÇÃO E CARACTERIZAÇÃO DE MEMBRANAS DE CELULOSE REGENERADA A PARTIR DA CELULOSE EXTRAÍDA DE RESÍDUOS AGROINDUSTRIAIS PARA APLICAÇÃO EM PROCESSOS DE SEPARAÇÃO

The aim of this study was to produce membranes using the adapted cuprammonium method. The cellulose utilized was obtained from recycled agroindustrial residues: sugarcane bagasse, corn stover and soybean hulls. The levels of Cu (II) ions in regenerated cellulose membranes produced with cellulose from bagasse, corn stover and soybean hulls were 0.0236 wt%, 0.0255 wt% and 0.0268 wt%, respectively. These levels were approximately 15 times lower than those observed in previous studies (0.3634 wt%). Cellular viability data show that membranes produced from bagasse cellulose do not present toxicity to the cellular cultures studied. These results demonstrate an evolution in production of regenerated cellulose membranes from agroindustrial residues mainly due to a decrease in the Cu (II) ions level, showing the possibility of application of these systems with improved membranes processing.

NOVO SORVENTE DE HIDROFOBICIDADE REDUZIDA PARA EXTRAÇÃO EM FASE SÓLIDA: PREPARAÇÃO E CARACTERIZAÇÃO

C18 chemically bonded sorbents have been the main materials used in solid phase extraction (SPE). However, due their high hydrophobicity some hydrophobic solutes are strongly retained leading to the consumption of larger quantities of organic solvent for efficient recoveries. This work presents a sorbent with lower hydrophobicity but similar selectivity to the C18 sorbent, prepared by thermal immobilization of poly(dimethylsiloxane-co-alkylmethylsiloxane) (PDAS) on silica. PDAS has organic chains with methyl groups alternating with octadecyl or hexadecyl groups in its monomeric unities. For the Si(PDAS) sorbent presented, the polymeric layer was physically adsorbed on the silica surface with 12% carbon load. Although the coating of silica with the polymeric layer was incomplete, the PDAS provided better protection for the silica surface groups, promoting mostly hydrophobic interactions between analytes and the sorbent. Sorption isotherm studies revealed that the retention of hydrophobic solutes on Si(PDAS) was less intense than on conventional sorbents, confirming the lower hydrophobicity of the lab-made sorbent. Additional advantages of Si(PDAS) include simplicity and low cost of preparation, making this material a potential sorbent for the analysis of highly hydrophobic solutes.

APROVEITAMENTO DE RESÍDUO DE BIODIESEL PARA PREPARAÇÃO DE CARVÕES ÁCIDOS COM ELEVADA ATIVIDADE CATALÍTICA NA REAÇÃO DE ETERIFICAÇÃO DO GLICEROL

Environmentally friendly acid carbon (CG) catalysts, containing a high amount of sulfonated and oxygenated groups, were prepared from glycerin, a biodiesel waste. CGs were produced by glycerin carbonization in the presence of H2SO4 at 1:3 m:m ratio in a closed autoclave at 180ºC for different times: 0.25; 1; 3 and 6 hours (CG-0.25h; CG-1h; CG-3h and CG-6h, respectively). The catalyst properties for all carbons were evaluated in the glycerol etherification reaction with tert-butyl alcohol (TBA). The yield for mono-tert-butyl glycerol (MTBG), di-tert-butyl glycerol (DTBG) and tri-tert-butyl-glycerol (TTBG) was high and very similar for all CGs, of about 43% and 20% for the MTBG and DTBG + TTBG, respectively. Furthermore, the activity of these catalysts were close to those obtained using a commercial resin, Amberlyst-15, of about 50% and 27% for MTBG and DTBG + TTBG, respectively.