H nuclear magnetic resonance spectroscopy analysis for simultaneous determination of levodopa, carbidopa and methyldopa in human serum and pharmaceutical formulations

A method utilizing NMR spectroscopy has been developed to confirm the identity and quantity of levodopa, carbidopa and methyldopa in human serum and pharmaceutical preparations. The method is based on 500 MHz proton NMR spectra of individual catecholamine molecules. Qualitative and quantitative analyses are based on resonance characteristics of the functional groups present in their structures and the integral ratio of selected signals belonging to different compounds with respect to those of an internal standard, respectively. Experiments are performed to validate the quantitative NMR method, and the linearity and reproducibility of the proposed method are verified. The detection limit of the proposed method was estimated as 4.2, 1.7 and 1.6  μg ml⁻¹ for levodopa, carbidopa and methyldopa, respectively. The recovery studies performed on human serum samples ranged from about 82-96% with relative standard deviations of <4%. The method was also applied successfully to the determination of each active compound in real pharmaceutical samples, and compared with the results obtained by the reference methods. The method is rapid, precise, accurate, and suitable for routine analyses.     

Synthesis and Crystal Structure of N,N~′-Bis(p-nitrophenyl)-2,2~′-(p-phenylene-dioxy)diacetamide DMF Monohydrate

1 INTRODUCTION Many crown ethers have been synthesized[1, 2] and widely used[3～5]. The amide-type acyclic poly- ethers with versatile molecular structures offer many advantages over the traditional crown ethers, such as their potential activity for ion-selective electrodes[6] and the extraction of metal ions[7], so they have attracted much scientific attention[8～10]. In an effort to investigate the effect of skeleton of acyclic polyether on the extractability of metal ions, and to find …     

N-PHOSPHORYL AMINO ACIDS AND PEPTIDES: PART I. THE CRYSTAL AND MOLECULAR STRUCTURE OF N-(O,O-DIISOPROPYL PHOSPHORYL)-TRANS-4-HYDROXY-D,L-PROLINE

Abstract

The crystal and molecular structure of N-(O,O-diisopropyl phosphoryl)-trans-4-hydroxy-D,L-proline has been determined by X-ray diffraction analysis and is compared with proline or hydroxyproline residue in a peptide chain described in the literature. The compound crystallized in orthorhombic system with space group P2₁2₁2₁, a=6.934(2), b=8.694(3), c=26.727(7) Å, V=1611.3(8) ų, Z=4, Dx=1.22 g/cm³. The structure was solved by direct method and refined by anisotropic least squares to a discrepancy index R=0.072. In the compound, the nitrogen atom is trigonal and its remaining 2p orbital is conjugated with the P?Oπ system; the conformation of the phosphorimidate function is favoured by the trans orientation of the P=O bond with respect to the N-C4 bond. In the pyrrolidine ring moeity, the C2-C1-N-C4 atoms are nearly copolnar and the C3 atom is out of the plane by about 0.47 Å.     

A transfer principle for inequalities in vector lattices

A transfer principle from inequalities with inner products to inequalities containing positive semidefinite symmetric bilinear operators with values in a vector lattices is proved. Some applications are also given.     

Unified analysis for stabilized methods of low-order mixed finite elements for stationary Navier-Stokes equations

A unified analysis is presented for the stabilized methods including the pres-sure projection method and the pressure gradient local projection method of conforming and nonconforming low-order mixed fi...     

Efficient 2-aryl benzothiazole formation from acetophenones,anilines, and elemental sulfur by iodine-catalyzed oxidative C(CO)-C(alkyl) bond cleavage

A novel and efficient iodine-catalyzed one-pot reaction of aromatic amines, acetophenones, and elemental sulfur for the synthesis of 2-aryl benzothiazoles is described. The process involves sequential C?S and C-N bond formation followed by C(CO)?C bond cleavage from readily accessible starting materials. A wide range of functional groups is tolerated under oxidant and metal-free condition and moderate to good product yields are obtained.     

Polymorphism in a benzo[b][1,4]diazepine derivative: Crystal structure,phase behavior and selective influence of solvents

Ethyl 4-[(Z)-3-ethoxy-2,3-dioxopropylidene]-4,5-dihydro-1H-benzo[b][1,4]diazepine-2-carboxylate forms two polymorphic modifications α and β, which differ in molecular conformations, as well as in the dimension of H-bonded supramolecular motifs in crystals that are a 1D chain or a 0D dimer, respectively. The formation of polymorphs can be controlled by choice of the solvent used. Crystallization from a solution in a polar protic solvent, ethanol, results in the thermodynamically favorable α-form, while using a low-polarity solvent, chloroform, and melt crystallization lead to the metastable β-form.     

Stabilization of solutions of dissipative Hamiltonian systems

We study the stabilization of solutions of damped Hamiltonian systems. We give sufficient conditions for convergence of these solutions, decay estimate and examples of applications.     

Identification of the 13/2+ isomer in 199At

The 13/2⁺ isomeric state in the ¹⁹⁹At nucleus has been identified at an excitation energy of 573 keV and its half-life measured to be 580(130) ns using the recoil-decay tagging technique. Received: 19 September 2000 / Accepted: 1 November 2000