Chemical Papers

An inexpensive, simple, sensitive and validated approach is developed for estimation of fingolimod through production of colored charge transfer complexes of fingolimod with different electron acceptor reagents, including a reaction of fingolimod as n-donor with 7,7,8,8-tetracyanoquinodimethane, tetrachloro 1,4-benzoquinone and tetracyanoethylene and as n-acceptors, yielding colored and stable anions which were measured spectrophotometrically. The range that obeyed Beer’s law is 50–300 µg mL−1 for fingolimod with all the studied reagents. The various parameters that affect the reaction were studied and optimized. The results were statistically compared with a reported method showing equal precision and accuracy. The researched approaches were utilized to determine the cited drug in its pharmaceutical form and spiked human plasma with accepted accuracy and precision.

A rapid kinetic method for the simultaneous determination of levodopa, dopamine, and dobutamine was examined and developed. It was based on a consecutive reaction of a reduction of Cu(II) to Cu(I) by catecholamines, followed by the complexation of Cu(I) with neocuproine to form a yellow product in an acetic acid-acetate buffer. Spectrophotometric data were recorded at 453 nm (wavelength at the yellow complex absorption maximum) for 300 s. Linear calibrations were obtained in the concentration ranges of (0.08–1.44) × 10−5 mol L−1, (0.08–1.44) × 10−5 mol L−1, and (0.16–1.44) × 10−5 mol L−1 for levodopa, dopamine, and dobutamine, respectively. A variety of multivariate calibration models was developed for simultaneous analysis of the three analytes; while most models produced satisfactory prediction results for synthetic samples, the hybrid linear analysis method was arguably the best-performing (relative prediction error, RPET = 6.6 %). The proposed method was applied to an analysis of spiked rabbit serum samples and the results showed good agreement with the high performance liquid chromatography measurements.

In this paper, a novel synthetic method for 4-N-substituted 6-bromopyrido[2,3-d]pyrimidines was reported. Starting from 2-aminonicotinonitrile, following by bromination of aromatic ring, condensation, cyclization, and Dimroth rearrangement, a series of 21 new pyrido[2,3-d]pyrimidine derivatives was prepared in high yields (up to 98%). In the last two steps, microwave irradiation was used. The structures of synthesized compounds were determined by NMR, IR, and HRMS techniques. The results showed that application of microwave irradiation has a beneficial effect for the preparation of desired products, as it is simple and efficient method for improving the yields and reducing the formation of undesirable by-products.

Dung dịch mangan ba giá hòa tan có thể được sử dụng làm điện phân cho pin dòng chảy redox mangan (MRFB), nhờ vào chi phí thấp, thân thiện với môi trường và nhiều trạng thái sạc. Tuy nhiên, sự ổn định kém của dung dịch mangan ba giá hòa tan và nồng độ mangan ba giá thấp là những nhược điểm của điện phân. Để tối ưu hóa độ ổn định và độ dẫn điện của dung dịch mangan ba giá hòa tan, nồng độ axit sulfuric, một trong những yếu tố ảnh hưởng chính, cần được cải thiện đầu tiên. Công nghệ điện phân tế bào hai ngăn đã được áp dụng thành công trong công trình này. Hơn nữa, để cải thiện nồng độ Mn3+, một số yếu tố chính, chẳng hạn như nồng độ MnSO4, mật độ dòng điện, thời gian điện phân và nhiệt độ, cần được điều chỉnh thêm. Các kết quả cho thấy nồng độ mangan ba giá được sản xuất này (≧ 0.3 M trong 6 M H2SO4; ≧ 0.4 M trong 5 M H2SO4; ≧ 0.5 M trong 4 M H2SO4) cao hơn nhiều so với các báo cáo trước đây. Sản phẩm rắn của sulfát mangan(III) cũng được chuẩn bị lần đầu tiên. Đối với sự hình thành mangan ba giá hòa tan, 5 mol/L H2SO4 là độ axit tối ưu và 10.9 mA/cm2 là mật độ dòng điện tốt nhất ở 273 K trong 3 giờ. Một số thông số động học điện hóa cũng đã được tính toán (điện giải là 5 M H2SO4 và 0.4 M MnSO4), chẳng hạn như hệ số khuếch tán của Mn2+ là 5.3057 × 10−6 cm2/s, hệ số truyền của phản ứng điện cực là 0.3782, và mật độ dòng điện trao đổi là 1.5662 × 10−4 A/cm2. Kết quả CV đã chứng minh rằng quá trình redox của Mn(III)/Mn(II) là quá trình nửa hồi phục.

The interaction study of water-soluble galactomannan polysaccharide guar gum (GG) and biosurfactant bile salt may have implications in lipid digestion and food formulations. In this work, we have tried to bring almost all fundamental aspects of the interaction of guar gum and bile salt sodium deoxycholate (NaDC), and the physicochemical properties allied with their association. The critical aggregation concentration (CAC), aggregation number (Nagg), and critical micellar concentration (CMC) of GG/NaDC mixed system were calculated using fluorescence parameters of pyrene molecule and conventional conductivity data. The thermodynamic parameters of GG/NaDC system were calculated, and the association was found to be a spontaneous and feasible process. At various regions of their interaction, zeta potential and dynamic light scattering studies have been done to gain a better understanding of their interaction.

A number of poly(lactic acid-co-glycolic acid)/polyurethane (PLGA/PU) blend films with various PU mole contents were prepared by casting the polymer blend solution in chloroform. The surface morphologies of the PLGA/PU blend films were studied by scanning electron microscopy (SEM). The thermal, mechanical and chemical properties of the PLGA/PU blend films were investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), tensile tests and surface contact angle tests. The results revealed that the introduction of PU could markedly modify the properties of PLGA films.

A new binary chiral selector system effective for the enantioselective extraction of racemic mandelic acid is presented. While L-dipentyl tartrate and β-cyclodextrin had a very low enantioselectivity as single selectors, a preferential extraction of D-mandelic acid to the organic phase was found in the binary selector system. Using decanol as organic solvent and pH of a phoshate buffer equal to 2.3, the distribution coefficients of D-and L-mandelic acids as high as 14.9 and 7.0, respectively, and the enantioselectivity value of 2.1 were found at optimum concentration of β-cyclodextrin.

A photocatalytic film reactor with a titanium dioxide film was used for oxidation of gaseous ethanol at 253.7 nm. The influences of partial pressures of oxygen and water vapour in different carrier gases were studied. The rate of photocatalytic oxidation of ethanol was significantly affected by the content of oxygen but water vapour had no effect. It was suggested that the photocatalytic transformation of ethanol follows a direct oxidation mechanism where the interaction of ethanol with positive hole gives first cationic free radical of ethanol, which is converted by multipathway reactions with oxygen to acetaldehyde, ethyl formate, and ethyl acetate.