Low-temperature thermodynamics of Ln(Me2dtc)3(C12H8N2) (Me2dtc = dimethyldithiocarbamate, Ln = La, Pr, Nd, Sm)

The heat capacities of Ln(Me₂dtc)₃(C₁₂H₈N₂) (Ln = La, Pr, Nd, Sm, Me₂dtc = dimethyldithiocarbamate) have been measured by the adiabatic method within the temperature range 78–404 K. The temperature dependencies of the heat capacities, C _p,m [La(Me₂dtc)₃(C₁₂H₈N₂)] = 542.097 + 229.576 X ? 27.169 X ² + 14.596 X ³ ? 7.135 X ⁴ (J K^?1 mol^?1), C _p,m [Pr(Me₂dtc)₃(C₁₂H₈N₂)] = 500.252 + 314.114 X ? 17.596 X ² ? 0.131 X ³ + 16.627 X ⁴ (J K^?1 mol^?1), C _p,m [Nd(Me₂dtc)₃(C₁₂H₈N₂)] = 543.586 + 213.876 X ? 68.040 X ² + 1.173 X ³ + 2.563 X ⁴ (J K^?1 mol^?1) and C _p,m [Sm(Me₂dtc)₃(C₁₂H₈N₂)] = 528.650 + 216.408 X ? 16.492 X ² + 12.076 X ³ + 4.912 X ⁴ (J K^?1 mol^?1), were derived by the least-squares method from the experimental data. The heat capacities of Ce(Me₂dtc)₃(C₁₂H₈N₂) and Pm(Me₂dtc)₃(C₁₂H₈N₂) at 298.15 K were evaluated to be 617.99 and 610.09 J K^?1 mol^?1, respectively. Furthermore, the thermodynamic functions (entropy, enthalpy and Gibbs free energy) have been calculated using the obtained experimental heat capacity data.     

Thermal degradation of hydroxypropyl trimethyl ammonium chloride chitosan–Cd complexes

Thermal degradation of hydroxypropyl trimethyl ammonium chloride chitosan–Cd complexes (HTCC–Cd) was investigated by thermogravimetric analysis. The results indicate that the degradation of HTCC–Cd in nitrogen atmosphere was two-step reaction. For the first step of degradation, the initial temperature of mass loss (T ₀), the final temperature of mass loss (T _f), and the temperature of maximum mass loss (T _p) increase linearly with the rising of heating rate (B). T _o = 1.241B + 220.3, T _p = 1.111B + 245.8, and T _f = 1.335B + 358.2. Using different methods, the kinetic parameters of the two steps were investigated. The results show that the activation energies of the first step of degradation obtained using Friedman and Flynn–Wall–Ozawa methods are 1.684 × 10⁵ and 1.646 × 10⁵ J mol^?1, and the corresponding activation energies for the second step are 1.165 × 10⁵ J mol^?1 and 1.373 × 10⁵ kJ mol^?1. The results obtained from Phadnis–Deshpande methods indicate that the two degradation processes are both nucleation and growth process, and follow A₄ mechanism with intergral form g(X) = [?ln(1 ? X)]⁴.     

Synthesis and thermal behavior study of complexes of the type [Pd(μ-X)(4-eb-p-phen)]2 (X = Cl,Br, I,N3, NCO,SCN) and 4-eb-p-phen [bis(4-ethylbenzyl)p-phenylenediimine]

The Schiff base bis(4-ethylbenzyl) p-phenylenediimine, 4-eb-p-phen (1), and six new dimeric Pd(II) complexes of the type [Pd(μ-X)(4-eb-p-phen)]₂ {X = Cl (2), Br (3), I (4), N₃ (5), NCO (6), SCN (7)} have been synthesized and characterized by elemental analysis, IR spectroscopy, and ¹H and ¹³C{¹H}-NMR experiments. The thermal behavior of the complexes 2–7 has been investigated by means of thermogravimetry and differential thermal analysis. From the final decomposition temperatures, the thermal stability of the complexes can be ordered in the following sequence: 3 > 4 > 7 > 2 ≈ 5 > 6. The final products of the thermal decompositions were characterized as metallic palladium by X-ray powder diffraction (XRD).     

Release profiles of indometacin in <Emphasis Type="Italic">β</Emphasis>-cyclodextrin complexes from HPMC capsules

Powders containing indometacin complexed with β-cyclodextrin (1:1 ratio) obtained by two complexation methods (suspension/solution [with water removed by air stream, spray– and freeze–drying] and kneading techniques) were compared between them to observe the increase on the drug solubility and yield of the complexation process. The tests used for this comparison included the determination of the moisture content, true and bulk densities, angle of repose, Carr’s index and in vitro drug release (at pH 1.0) from HPMC capsules. In the dissolution tests the drug release was analyzed considering different parameters (similarity factor (f ₂), dissolution efficiency (DE) and the amounts released (M _t) at certain times (30, 60 and 180 min) by statistic analysis (α = 0.05)). The results obtained showed poor pharmaceutical properties for all mixtures and that the indometacin released from capsules containing inclusion complexes presented an increase on solubility when compared with reference formulation (lactose and microcrystalline cellulose instead of β-cyclodextrin). The release of indometacin showed no dependency on the amount of water used in the formation of the complexes being the differences observed mostly due to the characteristics of the particles, which were dependent on the complexation method. However the low yield of the complexation that occurred can be explained by the difference between the size of the drug molecule, the guest (diameter—7.5 Å, length—14.2 Å) and the size of the β-cyclodextrin cavity, the host (diameter—6.0–6.5 Å).     

Peroxidase-based oxidative polymerization of monolignols

Oxidative polymerization of the monolignols (sinapyl alcohol [SA] and coniferyl alcohol [CA]) has been performed using enzyme-based biocatalysts. The oxidation of SA, CA, or an SA/CA mixture has been carried out using peroxidase enzyme–assisted H₂O₂/t-BHP (oxidation reagent). The reaction provided radicals with high reactivity, in turn yielding a variety of polymeric structures. The efficiency of the oxidative polymerization system has been evaluated in terms of substrate conversion. Also, the polymeric products were characterized with the gel permeation chromatography technique (GPC). Accordingly, optimum experimental parameters have been set up (e.g. temperature, type of peroxidase enzyme, and oxidation reagent). Under optimum conditions, a maximum of 90% of the SA was transformed to polymeric products with MW = 3188 Da, Mn = 1115 Da, and PD = 2.8.     

Preparation of alginate coated chitosan hydrogel beads by thermosensitive internal gelation technique

Chitosan hydrogel beads were successfully prepared by the method of thermosensitive internal gelation technique. The prepared beads were spherical, smooth-surfaced and non-aggregated with a diameter of 1.7–2.1 mm. The diameters of beads can be controlled and have a correlation with the initial drop size, the concentration of CaCl₂, alginate and the time of solidification. The bead is comprised of three parts, which are chitosan/glycerophosphate (CS/GP) hydrogel core, chitosan-alginate (CS/SA) gel layer in the middle and calcium-alginate gelatin capsules in outer layer. Swelling studies indicate that the beads can be stable in simulated gastric fluid. But the beads shrink sharply when removed to simulated intestinal fluid. Drug release behavior showed that release of ornidazole in the beads is much slower than in the CS/GP hydrogel.     

Drug release behaviors of a pH/thermo-responsive porous hydrogel from poly(N-acryloylglycinate) and sodium alginate

A pH/thermo-responsive hydrogel with porous structure (HME), composed of poly(N-acryloylglycine methyl ester), poly(N-acryloylglycine ethyl ester) and sodium alginate (SA) was prepared for the controllable drug carrier. The resultants, CO₂ and CaCl₂ from the reaction of CaCO₃ particles and HCl act as pore-forming and crosslinking of SA, respectively. The porous HME was characterized by differential scanning calorimetry, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy and surface area and porosity analysis. The sheet, porous structure was clearly observed by the SEM measurement and the specific surface area of HME was evidently increased with an increase of CaCO₃ content. At pH 2.1 phosphate buffered saline (PBS), the release amount of caffeine at room temperature was only 7.2 % within 600 min, while this value approached to 65.3 % at pH 7.4 PBS. Additionally, the cumulative release at 37 °C is much higher than that at room temperature due to the thermo-sensitivity of HME. The experimental results indicated that porous HME has a potential to be used as the promising release-controlled drug carrier in the biomedical fields.     

Isothermal microcalorimetric investigation of the toxic action of the effective constituents of Podophyllum emodi Wall on Tetrahymena thermophila BF5

The effects of podophyllotoxin (PPT), etoposide (VP16), and teniposide (VM26) on the growth of Tetrahymena thermophila BF₅ (T.t.BF₅) was investigated by the TAM AIR isothermal microcalorimetric system. The extent and duration of toxic effects on T.t.BF₅ metabolism were evaluated by studying the growth rate constant (k), inhibitory ratio (I), maximum heat-output power (P _max), peak time of maximum heat-output power (t _p), and total heat production (Q _t). Experimental results showed that the value of t _p increased and the value of k and P _max decreased with the increasing compound concentrations. Furthermore, the growth rate constant k was linear with compound concentration. The corresponding I was obtained from different k values. According to the IC₁₀ (the concentration of inhibitor when the inhibitory ratio is 10 %), the relative toxicity of the three compounds was PPT (IC₁₀ = 49.6 μg mL^?1) > VP16 (IC₁₀ = 117.5 μg mL^?1) > VM26 (IC₁₀ = 359.1 μg mL^?1). The preliminary investigation of structure–activity relationships showed that the thienyl group was likely responsible for reducing the toxicity of the compounds.     

Investigation of hydrogen desorption from CaSiH by means of calorimetric method

The present work deals with the study of the reaction of hydrogen desorption from the CaSiH_X hydride by means of the calorimetric method. The dehydrogenation of the CaSiH_X hydride was carried out at 548 K. For a calorimetric study, the installation composed of the differential heat-conducting Tian–Calvet type calorimeter connected with a conventional Sieverts-type apparatus was employed. Such installation permitted us to obtain simultaneously the P-X isotherms (P—equilibrium hydrogen pressure, X = H/CaSi) and variation of the partial molar enthalpies of the reaction of hydrogen desorption from CaSiH_X with the hydrogen concentration in the metallic matrix. It was ascertained that in the CaSi-H₂ system there was one region where values of the partial molar enthalpy of the reaction of hydrogen desorption from the CaSiH_X hydride remained constant. This means that formation of one hydride phase in the CaSi-H₂ system took place. The enthalpy and entropy values for the reaction of hydrogen desorption from the CaSiH_X in the plateau range are ΔH _des = 53.8 ± 1.2 kJ mol^?1 H₂ and ΔS _des = 94.2 ± 2.7 J mol^?1 H₂ K^?1 (ΔH _des and ΔS _des—the differential molar enthalpy and entropy desorption, respectively).     

Do halogen and methyl substituents have electronic effects on the structures of simple disilanes? An experimental and theoretical study of the molecular structures of the series X3SiSiMe3 (X = H, F, Cl and Br)

The gas-phase molecular structures of a series of halogen-substituted disilanes [X₃SiSiMe₃ (X = H, F, Cl and Br)], 1,1,1-trimethyldisilane (H₃SiSiMe₃), 1,1,1-trifluoro-2,2,2-trimethyldisilane (F₃SiSiMe₃), 1,1,1-trichloro-2,2,2-trimethyldisilane (Cl₃SiSiMe₃) and 1,1,1-tribromo-2,2,2-trimethyldisilane (Br₃SiSiMe₃), have been determined in the gas phase by electron diffraction. Ab initio calculations at the HF and MP2 level were used to support the experimental investigation using the SARACEN method. All of the investigated structures were determined to adopt a staggered structure with C _3v symmetry. The effect of substitution on the Si–Si bond and the Si–Si–X bond angle was investigated and these results were compared to results obtained from a recent study of halogen-substituted disilanes [X₃SiSiXMe₂ (X = F, Cl, Br and I)] to consider the effect of the methyl groups on the substituted disilanes.     

Thermodynamic properties of crystalline phosphate Ba0.5Zr2(PO4)3 over the temperature range from T → 0 to 610 K

The temperature dependence of the heat capacity of crystalline barium zirconium phosphate C _p ^o  = f(T) was measured over the temperature range 6–612 K. The experimental data obtained were used to calculate the standard thermodynamic functions C _p ^o (T), H°(T) ? H°(0), S°(T), G°(T) ? H°(0) over the temperature range from T → 0 to 610 K and standard entropy of formation at 298.15 K. The data on the low-temperature (6 ≤ T/K ≤ 50) heat capacity were used to determine the fractal dimension of Ba_0.5Zr₂(PO₄)₃. Conclusions concerning the topology of the structure of phosphate were drawn. Thermodynamic properties of M_0.5Zr₂(PO₄)₃ (M = Ca, Sr, Ba) were compared.     

Synthesis and characterization of palladium(II) complexes [PdX2(p-diben)] (X = Cl,Br, I,N3, or NCO; p-diben = N,N′-bis(4-dimethylaminobenzylidene)ethane-1,2-diamine): crystal structure of [Pd(N3)2(p-diben)]

Five new complexes of general formula [PdX₂(p-diben)], where p-diben = N,N′-bis(4-dimethylaminobenzylidene)ethane-1,2-diamine) (1) and X = Cl (2), Br (3), I (4), N₃ (5), or CNO (6), were synthesized and characterized by physicochemical and spectroscopic methods. The crystal structure of compound (5) was determined by single-crystal X-ray diffraction. Complexes 2–6 were characterized as N,N-chelated products. The crystal structure confirmed this formulation for [Pd(N₃)₂(p-diben)], besides showing the isomerism inversion of one of the C=N bonds, caused by Pd(II) coordination.     

Application of Response Surface Methodology To Formulation Optimization of Rapamycin Loaded Magnetic Fe3O4/Carboxymethylchitosan Nanoparticles

In this paper, a new drug delivery system was designed using magnetic Fe₃O₄/carboxymethylchitosan nanoparticles (Fe₃O₄/CMCS NPs) as carrier and rapamycin (Rapa) as the antitumor drug. The process and formulation variables of Fe₃O₄/CMCS-Rapa NPs were optimized using response surface methodology (RSM) with a three-level, three-factor Box-Behnken design (BBD). The independent variables were the mass ratio of Fe₃O₄/CMCS: Rapa, W/O phase ratio and stirring rate; dependent variables were drug loading content and entrapment efficiency. Mathematical equations and response surface plots were used to relate the dependent and independent variables. The optimized formulation was characterized by TEM, FT-IR, and in vitro drug release. Results for mean particle size, drug loading content, entrapment efficiency and in vitro drug release of Fe₃O₄/CMCS-Rapa were found to be of 30 ± 2 nm, 6.32% ± 3.36%, 62.9% ± 2.30%, and 65.35% ± 2.46% at pH 7.4 after 70 h, respectively; also, they possess magnetism with a saturation magnetization of 67.1 emu/g, negligible coercivity and remanence at room temperature. Also the effect of magnetic targeted nanoparticles on the proliferation of human hepatoma cell line HepG2 in vitro was investigated. The results from MTT assays showed that the Fe₃O₄/CMCS-Rapa nanoparticles could effectively inhibit the proliferation of HepG2 cells, which displayed time or concentration-dependent manner. All these results indicated that the nanoparticles had the potential to be used as a novel drug carrier system.     

Thermokinetics simulation for multi-walled carbon nanotubes with sodium alginate by advanced kinetics and technology solutions

To accomplish an effective analysis of adsorption, the strong acid dye from aqueous solution of sodium alginate (SA) and multi-walled carbon nanotubes (MWCNTs) composite gel beads were used as important parameters. Differential scanning calorimetry (DSC) was used to measure the heat of breakdown reaction. The experimental conditions were set at 0.5, 1, 2, 4, and 8 °C min^?1, and the temperature range was 30–300 °C. The heating rates and the temperature range were set as follows: Four kinds of proportion in this experiment contained 2 SA % w/v (SA), 0.03, 0.09, 0.18, 0.36 % w/v (MWCNTs), and 10 % w/v calcium chloride, respectively. Four samples, 5, 6, 7, 8, and 9 mg, were used to detect the experimental data. It contributed to understanding the reaction for the distinctive MWCNTs. With the thermokinetic data by isoconversional approach obtained from advanced kinetics and technology solutions (AKTS), the related thermal safety information can be obtained from the thermal reaction of MWCNTs. Valuable parameters, such as activation energy (E _a) and heat of decomposition, can be applied in operation, including adsorption and desorption processes. After DSC tests, and under the four compositions of SA/MWCNTs, at different heating rates of 0.5, 1, 2, 4, and 8 °C min^?1, primarily we found that when the heating rate was increased, exothermic onset temperature would increase gradually. After analyzing E _a value by isoconversional kinetics, we learned that in four different adsorption compositions, SA/MWCNTs_0.03 (161.20 kJ mol^?1) was the minimum. Among them, the highest value was SA/MWCNTs_0.18 (220.48 kJ mol^?1). However, in this study, for SA/MWCNTs compositions we found that E _a value will drop in the final material SA/MWCNTs_0.36. Accordingly, if the ratio of SA and calcium chloride was fixed, then different compositions of the MWCNTs would affect adsorption efficiency of SA/MWCNTs and E _a variation.     

Thermoresponsive N-vinyl caprolactam grafted sodium alginate hydrogel beads for the controlled release of an anticancer drug

A series of thermoresponsive sodium alginate-g-poly(vinyl caprolactam) (NaAlg-g-PNVCL) beads were prepared as drug delivery matrices of 5-flurouracil (5-FU) crosslinked by glutaraldehyde (GA) in the hydrochloric acid catalyst. Graft copolymers of sodium alginate with vinyl caprolactam were synthesized using azobisisobutyronitrile as an initiator, and characterized by Fourier infrared spectroscopy, differential scanning calrimetry and X-ray diffraction for analysis of the amorphous nature drug in the beads, and by scanning electron microscopy for the spherical nature of the beads. Preparation condition of the beads was optimized by considering the percentage of encapsulation efficiency, swelling behavior of beads and their release data. Effects of variables such as GA concentration, drug/polymer ratio and catalyst concentration on the release of 5-FU were carried out at two different temperatures (25 and 37 °C) in simulated intestinal fluid for 12 h. It was observed that, drug release from the beads decreased with increasing drug/polymer (d/p) ratio, extent of crosslinking agent and catalyst concentration. The swelling degree of graft copolymer beads was found to be increased with decreasing of environmental temperature. In vitro release studies were performed at 25 and 37 °C for 12 h, and showed that thermoresponsive graft copolymer beads had higher drug release behavior at 25 °C than that at 37 °C, following Fickian diffusion transport mechanism with slight deviation.     

麦饭石含量对载药复合凝胶小球释药性能的影响

以瓜尔胶-g-聚丙烯酸/麦饭石复合水凝胶(GG-g-PAA/MS)和海藻酸钠(SA)为原料,双氯芬酸钠(DS)为模拟药物,采用离子凝胶法制备了载药复合凝胶小球,考察了pH敏感性以及MS含量对复合凝胶小球的包封率、载药率、溶胀性和药物释放行为的影响.结果表明:凝胶小球具有明显的pH敏感性,在不同pH介质中溶胀率和释放速率...     

Electrical properties study of multi-walled carbon nanotubes/hybrid-glass nanocomposites

Electrical properties of multi-walled carbon nanotubes (MWNTs)/hybrid-glass nanocomposites prepared by the fast-sol–gel reaction were investigated in light of percolation theory. A good correlation was found between the experimental results and the theory. We obtained a percolation threshold ? _c  = 0.22 wt%, and a critical exponent of t = 1.73. These values are reported for the first time for a silica-based system. The highest conductivity measured on the MWNT/hybrid-glass nanocomposites was σ ≈ 10^?3(Ω cm)^?1 for 2 wt% carbon nanotube (CNT) loading. The electrical conductivity was at least 12 orders of magnitude higher than that of pure silica. Electrostatic force microscopy and conductive-mode atomic force microscopy studies demonstrated conductivity at the micro-level, which was attributed to the CNT dispersed in the matrix. It appears that the dispersion in our MWNT/hybrid-glass system yields a particularly low percolation threshold compared with that of a MWNT/silica-glass system. Materials with electrical conductivities described in this work can be exploited for anti-static coating.     

Determination of Alendronate Sodium by Box-Behnken Statistical Design

Spectrophotometric and LC methods have been developed and validated for the analysis of alendronate sodium in tablet dosage forms. Methods were based on reaction of the primary amino group of alendronate with ninhydrin reagent in methanolic solution of sodium bicarbonate. The condensed product exhibited UV absorption maximum at 569 nm whereas neither the reagents nor the analyte had any UV absorption. A Box-Behnken statistical design was employed to study the effect of independent variables, ninhydrin (X ₁ ), NaHCO₃ (X ₂ ) and drug concentration (X ₃ ) on dependent variable, absorption via spectrophotometer. From the point prediction tool of design software, it was observed that ninhydrin (0.26%) and NaHCO₃ (0.048 mol L^?1) produced maximum absorption. These optimized parameters were then selected for method validation. The methods obeyed Beer’s law over a selected concentration range with good correlation co-efficient (>0.99). The limit of detection and limit of quantification were 4.5 and 13.75 μg mL^?1 by spectroscopy, and 87 and 263 ng mL^?1 by LC, respectively. Accuracy, precision and % recovery were satisfactory for the proposed method. The method was highly feasible and reproducible for determination of alendronate sodium in bulk powder and pharmaceutical dosage form.     

Production of octyl levulinate biolubricant over modified H-ZSM-5: Optimization by response surface methodology

The present study highlighted the use of modified H-ZSM-5 (Meso-HZ-5) as heterogeneous catalyst for the synthesis of octyl levulinate biolubricant by catalytic esterification of biomass derived renewable levulinic acid (LA) with n-octanol. The process variables such as catalyst loading (X₁), n-octanol to LA molar ratio (X₂) and reaction temperature (X₃) were optimized through response surface methodology (RSM), using Box-Behnken model. Analysis of variance was performed to determine the adequacy and significance of the quadratic model. The yield of octyl levulinate was obtained to be 99% at optimum process parameters. The developed quadratic model was found to be adequate and statistically accurate with correlation value (R²) of 0.9971 to predict the yield of octyl levulinate biolubricant. The study was also extended on the validation of theoretical and experimental data, including catalyst reusability.