Synthesis of Renewable Poly(limonene): A Kinetic Modeling Study to Improve the Polymerization

Abstract Despite its potential in the production of polymers from renewable sources, D-limonene faces difficulties in its polymerization, resulting in low monomer conversion and molar mass. In order to investigate the non-ideality inherent kinetics, this work explores different modeling strategies for D-limonene radical polymerization, using benzoyl peroxide as initiator. The starting model considered the classical approach for conventional radical polymerization. This model was then corrected by including reaction orders different from the unit. After an analysis and choice of the best model, computer simulations were compared with experimental results from literature, validating the chosen approach. It was found that the process is drastically influenced by chain transfer reactions, presenting a non-ideal behavior. Finally, an analysis of distinct reaction conditions provided information on monomer conversion, molar mass and polymer dispersity, which could guide future research in the synthesis optimization. Higher molar mass poly(limonene) were obtained by simultaneously reducing the monomer and initiator concentrations.

Optical properties of polyvinyl alcohol membrane with n-HAp for bio-medical applications

Composite membrane as a flexible materials have found diverse applications in industrial and biomedical simultaneously, the recent studies have shown intrinsic improvement for membrane properties by inclusion of nanoparticles as a fillers with high portion ratio in inorganic polymers, the combination between two parts polymer and filler is as a result of collection the advantage of two component systems parts together. In this work, samples of polyvinyl alcohol (PVA)-nanoHaydroxyapatite (nHAp) composites were prepared by using casting method. The effects of addition of (nHAp) with different concentration on the optical properties of (PVA- nHAp) composite membrane have been studied by using wavelength range (220-820) nm. The absorption spectra, transmittance spectra, absorption coefficient, energy gap, refractive index, optical conductivity and extinction coefficient have been determined. The results show that the optical constants change with the increase of nHPA concentrations.

Associação entre fatores de risco cardiovascular e indicadores antropométricos de obesidade em universitários de São Luís, Maranhão, Brasil / The association between cardiovascular risk factors and anthropometric obesity indicators in university students in São Luís in the State of Maranhão, Brazil

O presente artigo tem por objetivo avaliar associação entre fatores de risco cardiovascular (FRCV) e indicadores antropométricos em amostra de base populacional de universitários de São Luís/MA. Estudo transversal com 968 universitários, mediana de 22 anos. Glicemia, triglicerídeos (TGL), HDL-c, tabagismo, consumo de álcool, sedentarismo, síndrome metabólica (SM–critérios do Joint Interim Statement) e resistência insulínica (RI), foram associados e correlacionados com os indicadores antropométricos Índice de Massa Corporal (IMC), Circunferência da Cintura (CC), Relação Cintura Quadril (RCQ) e Relação Cintura Altura (RCA). Encontraram-se associações entre TGL, HAS, SM e maiores valores de todas as variáveis antropométricas. RI associou-se a maiores valores IMC e RCA em homens e mulheres. Baixo HDL-c foi associado a maiores valores de todas as variáveis antropométricas em mulheres. Consumo de álcool associou-se a valores mais elevados de IMC e CC em mulheres e RCQ e RCA em homens. Fumo associou-se a maiores valores de RCA em ambos os sexos. Sedentarismo foi associado a maiores valores de RCQ apenas em homens. As correlações mais altas foram estabelecidas para mulheres entre TGL e IMC, CC, RCQ e RCA. Os indicadores que mais se associaram aos FRCV foram IMC, CC e RCA em mulheres e RCQ e RCA em homens.

The article aims to evaluate the relation between cardiovascular risk factors (CVRF) and anthropometric indicators in a sample of university students from São Luís-MA, Brazil. It is a cross-sectional study conducted with 968 university students, with median age of 22. Glycemia, triglycerides, HDL-c, smoking, alcohol consumption, physical inactivity, metabolic syndrome (Joint Interim Statement criteria) and insulin resistance (IR), were associated and correlated with anthropometric indicators such as BMI, WC, WHR and WHtR. Associations were found between TGL, SH, SM and higher values of all anthropometric variables. The RI was associated with higher BMI values and WHtR in men and women. The low HDL-c was associated with higher values of all anthropometric variables in women. Consumption of alcohol was associated with higher values of BMI and WC in women and WHR in men and WHtR. Smoking was associated with higher values of WHtR in both sexes. Physical inactivity was associated with higher values of WHR in men only. The highest correlations were established for women between TGL and BMI CC, WHR and WHtR. The indicators most associated with CVRF were BMI, WC and WHtR in females and WHR and WHtR in men.

One-pot synthesis of graphene-chitosan nanocomposite modified carbon paste electrode for selective determination of dopamine

Background A simple, rapid, low-cost and environmentally friendly method was developed to determine dopamine (DA) in the presence of ascorbic (AA) and uric acid (UA) based on a novel technique to prepare a graphene-chitosan (GR-CS) nanocomposite and modify it on the surface of carbon paste electrode (CPE). For our design, CS acts as a media to disperse and stabilize GR, and then GR plays a key role to selective and sensitive determination of DA. Results Under physiological conditions, the linear range for dopamine was determined from 1 × 10- 4 to 2 × 10- 7 mol/L with a good correlation coefficient of 0.9961 in the presence of 1000-fold interference of AA and UA. The detection limit was estimated to be 9.82 × 10- 8 mol/L (S/N = 3). In order to study the stability and reproducibility, GR/CS/CPE underwent successive measurements in 10 times and then tested once a d for 30 d. The result exhibited 98.25% and 91.62% activities compared with the original peak current after 10-time measurements and 30-d storage. Conclusion The GR/CS/CPE has wide linear concentration range, low detection limit, and good reproducibility and stability, which suggests that our investigations provide a promising alternative for clinic DA determination.

Biosynthesis of selenium nanoparticles using Klebsiella pneumoniae and their recovery by a simple sterilization process

The use of biologically derived metal nanoparticles for various proposes is going to be an issue of considerable importance; thus, appropriate methods should be developed and tested for the biological synthesis and recovery of these nanoparticles from bacterial cells. In this research study, a strain of Klebsiella pneumoniae was tested for its ability to synthesize elemental selenium nanoparticles from selenium chloride. A broth of Klebsiella pneumoniae culture containing selenium nanoparticles was subjected to sterilization at 121ºC and 17 psi for 20 minutes. Released selenium nanoparticles ranged in size from 100 to 550 nm, with an average size of 245 nm. Our study also showed that no chemical changes occurred in selenium nanoparticles during the wet heat sterilization process. Therefore, the wet heat sterilization process can be used successfully to recover elemental selenium from bacterial cells.