Microdialysis sampling and high-performance liquid chromatography with chemiluminescence detection for in-vivo on-line determination and study of the pharmacokinetics of levodopa in blood

A simple, reliable, and reproducible method for in-vivo on-line separation and determination of levodopa has been based on microdialysis then high-performance liquid chromatography with chemiluminescence detection. The perfusate is perfused at a flow rate of 5 L min^–1. The concentration of levodopa in the dialysate is determined on line with a chemiluminescence system. The dialysate sample volume is approximately 20 L. The response of the system is linearly related to the concentration of levodopa in the range 1×10^–8 to 1×10^–6 g mL^–1 (r²=0.9995) with a detection limit (3) of 3×10^–9 g mL^–1 and sample throughput of 12 h^–1; RSD is 2.8% (n=11). The method has been successfully used to study the pharmacokinetics of levodopa in vivo; the values of the pharmacokinetics parameters C_max, AUC_0–t and T_max were 16.60, 20.92 ng mL^–1, and 90 min, respectively.     

Synthesis and Spectroscopic Characterization of Two Different Types of Heterobimetallic Glycolate Complexes of Niobium(V)

An entirely new class of heterobimetallic homoleptic glycolate complexes of the type Nb(OGO)₃{Ta(OGO)₂} [where G=CMe₂CH₂CH₂CMe₂ (G¹) (3); CMe₂CH₂ CHMe(G²) (4); CHMeCHMe (G³) (5); CH₂CMe₂CH₂ (G⁴) (6); CMe₂CMe₂(G⁵) (7); CH₂CHMeCH₂ (G⁶) (8); CH₂CEt₂CH₂ (G⁷) (9); CH₂CMe(Prⁿ)CH₂ (G⁸) (10)] have been prepared by the reactions of Nb(OGO)₂(OGOH) [G=G¹ (1a); G² (1b); G³ (1c); G⁴ (1d); G⁵ (1e); G⁶ (1f); G⁷ (1g); G⁸ (1h)] with Ta(OGO)₂ (OPrⁱ) (G=G¹ (2a); G² (2b); G³ (2c); G⁴ (2d); G⁵ (2e) G⁶ (2f); G⁷ (2g); G⁸ (2h). In addition to the novel derivatives (2)–(10), our earlier investigations on heterobimetallic glycolate-alkoxide derivatives have been extended to derivatives of the type Nb(OGO) [where M=A1 n=3, G=G³ (11);G⁴ (12); G⁶ (13) G⁷ (14); G^s (15); G⁹=CH₂CH₂CH₂ (16) and M=Ti (n=4, G=G⁴) (17), Zr(n=4,G=G⁴) (18)], which are conveniently prepared by the reactions of metalloligands Nb(OGO)₂(OGOH) [G=G³ (1c); G⁴ (1d); G⁶ (1f); G⁷ (1g); G⁸ (1h); G⁹ (1i)] with different metal alkoxides. All of these new complexes have been characterized by elemental analyses, molecular weight determinations, and spectroscopic (I.r. and ¹H, ²⁷Al-n.m.r.) studies. Structural features of the new derivatives have been elucidated on the basis of molecular weight and spectroscopic data.     

Simultaneous determination of rosiglitazone and metformin in plasma by gradient liquid chromatography with UV detection

A novel, fast and simple liquid chromatographic method was developed and validated for the simultaneous determination of rosiglitazone and metformin in human plasma. The analysis was performed on a phenyl column (250 mm × 4.6 mm i.d., 5 μm) using a gradient method starting with mobile phase composed of acetonitrile:5 mM acetate buffer pH 5.5 (75:25, v/v). The flow rate was 1 mL min⁻¹. UV detection was performed at 245 nm and verapamil was used as internal standard. The total run time was less than 10 min. Sample preparation included a simple protein precipitation step with acetonitrile. Validation experiments were performed to demonstrate stability, specificity, sensitivity, linearity, accuracy, precision and robustness. The limit of quantification was 100 ng mL⁻¹ for rosiglitazone and 250 ng mL⁻¹ for metformin. The extraction recoveries were 100.02-105.0% for rosiglitazone and 105.64-103.88% for metformin. The method was applied with success to plasma samples obtained from diabetic patients undergoing treatment with rosiglitazone and metformin.     

Accurate measurement of the exciton diffusion length in a conjugated polymer using a heterostructure with a side-chain cross-linked fullerene layer

Exciton diffusion and photoluminescence quenching in conjugated polymer/fullerene heterostructures are studied by time-resolved photoluminescence. It is observed that heterostructures consisting of a spin-coated poly(p-phenylene vinylene) (PPV)-based derivative and evaporated C60 are ill-defined because of diffusion of C60 into the polymer, leading to an overestimation of the exciton diffusion length. This artifact is resolved by the use of a novel, thermally side-chain polymerizing and cross-linking fullerene derivative (F2D) containing two diacetylene moieties, forming a completely immobilized electron acceptor layer. With this heterostructure test system, an exciton diffusion length of 5 +/- 1 nm is derived for this PPV derivative from time-integrated luminescence quenching data.     

Phenomenological analysis of elongational flow birefringence in semidilute solutions of hydroxypropylcellulose

The relaxation time of a polymer chain in an elongational flow field was investigated for hydroxypropylcellulose (HPC) semidilute solution systems by two methods: phenomenological analysis of elongational flow-induced birefringence, and dynamic light scattering (DLS) and rheological measurements. To understand the relaxation time of an entangled semiflexible polymer solution in an elongational flow field, scaling analysis of the elongational flow-induced birefringence curve was performed. The results of both temperature and concentration scaling analyses showed that birefringence curves at different temperatures and at several HPC concentrations were described well by a universal birefringence–strain rate curve. This scaling behavior was compared with the "fuzzy cylinder" model. The critical strain rate corresponded to the correlation time of the slow relaxation mode determined by DLS measurement and the relaxation spectrum obtained by dynamic viscoelasticity measurement. The elongational flow-induced birefringence observed in an HPC semidilute solution was concluded to be attributed to the orientation of the HPC segment in the entangled molecular system, because the dominant relaxation mode is found to be the concentration fluctuation of an entangled molecular cluster in a quiescent state.     

Structure and mechanical properties of poly(l-lactide)/layered silicate nanocomposites

Poly(ε-caprolactone) (PCL) masterbatches with the intercalated and the exfoliated morphology were prepared by ring opening polymerization of ε-caprolactone in the presence of organomodified montmorillonite (MMT) Cloisite 30B. Poly(l-lactide) (PLLA) nanocomposites with Cloisite 30B or PCL masterbatches were prepared by melt blending. The effects of the silicate type, MMT content and the nanocomposite morphology on thermal and mechanical properties of PLLA nanocomposites were examined. The montmorillonite particles in PLLA/Cloisite 30B and PLLA/intercalated masterbatch nanocomposites were intercalated. In contrary to expectations, the exfoliated silicate layers of exfoliated masterbatch were not transferred into the PLLA matrix. Due to a low miscibility of PCL and PLLA, MMT remained in the phase-separated masterbatch domains. The stress-strain characteristics of PLLA nanocomposites, Young modulus E, yield stress σ_y and yield strain ε_y, decreased with increasing MMT concentration, which is associated with the increase in PCL content. The expected stiffening effect of MMT was low due to a low aspect ratio of its particles and was obscured by both plastifying effects of PCL and low PLLA crystallinity. Interestingly, in contrast to the neat PLLA, ductility was enhanced in all PLLA/Cloisite 30B materials and in PLLA/masterbatch nanocomposites with low MMT concentrations.     

A New Strategy for the Synthesis of alpha-Difluoromethyl-Substituted alpha-Hydroxy and alpha-Amino Acids

A new method for the preparation of alpha-chlorodifluoromethyl-, alpha-bromodifluoromethyl-, and alpha-difluoromethyl-substituted alpha-hydroxy and alpha-amino acid esters 11, 19-21 is described. The key step of the synthesis is the regioselective alkylation of ketones 5, 7-9 and imines 16-18 with C-nucleophiles. The ketones 7-9 are readily available from 3,3,3-trifluorolactate 1 by a five-step procedure. Subsequent removal of the protecting groups from 19-21 provides the corresponding free amino acids 25, 26, 28.     

A Structural Investigation of La2(GeO4)O and Alkaline-Earth-Doped La9.33(GeO4)6O2

The structures of the oxyorthogermanate La₂(GeO₄)O and the apatite-structured La_9.33(GeO₄)₆O₂ have been refined from powder neutron diffraction data. La₂(GeO₄)O crystallizes in a monoclinic unit cell (P2₁/c) and is cation stoichiometric in contrast to previous reports. La_9.33(GeO₄)₆O₂ crystallizes in a hexagonal unit cell (P6₃/m) and the powder diffraction data show anisotropic peak broadening that is observed in electron diffraction patterns as incommensurate diffuse spots at hkq reciprocal planes (with q=1.6-1.7) and can be attributed to a correlated disorder in the “apatite channels”. This compound was doped up to a nominal composition close to M₂La₈(GeO₄)₆O₂ with M=Ca, Sr, Ba. The dopant ions preferentially occupy the 4f sites as the number of La vacancies decreases. The measured ionic conductivity of La_9.33(GeO₄)₆O₂ is about 3 orders of magnitude larger than for La₂(GeO₄)O at high temperatures and decreases with increasing dopant content from the highest value of about 0.16 S cm⁻¹ at 1160 K.     

A model for surfactant distribution in latex coatings

The presence of surfactants in dried latex films can adversely affect the adhesive, water-resistant, and gloss properties, so investigating the surfactant distribution in latex coatings is of prime industrial relevance. Here we present a model that predicts the distribution of surfactant in a latex coating during the solvent evaporation stage. The conservation equation for surfactant during solvent evaporation is solved in the limit of infinite particle Peclet numbers, a dimensionless quantity giving the measure of relative magnitudes of evaporative to diffusive fluxes. A parametric analysis using the model reveals that the surfactant adsorption isotherm is the determining physical parameter. The model always predicts surfactant excesses at the top surface and either excess or depletion at the bottom surface depending on the isotherm. Uniform distributions are predicted for low surfactant Peclet numbers. Attenuated total reflection Fourier transform infrared spectroscopic probes on film surfaces conform to the behavior predicted by the model.     

Use of the molybdenum-thiocyanate-rhodamine 6G ternary complex for spectrophotometric molybdenum determination without extraction

A modified thiocyanate method without extraction by using rhodamine 6G as a secondary ligand was developed. Molybdenum in 1.0×10⁻² M HCl, after the addition of ascorbic acid, was heated for 10 min in a 90 °C water bath for reduction. Suitable amounts of glycerine, Triton X-100, rhodamine 6G solutions and 2+1 (v/v) 9 M H₂SO₄+3 M KHSO₄ were added in this order. This solution was allowed to cool to room temperature and the absorbance at 570 nm was measured against a reagent blank 45 min after the addition of thiocyanate solution and the second aliquot of Triton X-100 solution. The complex was stable for at least 4 h, the order of reagent addition was important, and thiocyanate should be in large excess. Beer’s law was obeyed over the range 0.9×10⁻⁶ to 1.1×10⁻⁵ M Mo with the molar absorptivity being 1.1×10⁵ l mol⁻¹ cm⁻¹. The R.S.D. for the determination of 0.7 mg Mo l⁻¹ was 1.83% (n=8). Possible interferences of various cations and anions on molybdenum determination were studied. The proposed method was applied to the determination of molybdenum in a dental alloy, Wiron 99.