A Spectrofluorimetric Sequential Injection Method for the Determination of Penicillamine Using Fluorescamine in the Presence of β-cyclodextrins

A simple, robust and sensitive sequential injection spectrofluorimetric method for the determination of penicillamine (PA) in pharmaceutical formulations is developed. The method is based on the formation of a highly fluorescent derivative when penicillamine is reacted with fluorescamine (FL) in borate buffer of pH 9.3. The derivative produced is monitored at an emission wavelength of 495 nm using an excitation wavelength of 355 nm. The optimum conditions for the determination of PA with FL were: 3 mM FL, pH 9.3, 5 mM methyl-β-cyclodextrin, sample volume of 75 μL and reagent volume of 75 μL. Furthermore, the effect of various media on the fluorescence intensity of the PA–FL derivative was studied and methyl-β-cyclodextrin was found to give the largest enhancement. A linear dynamic range for the determination of PA of 5–80 ppm was obtained with a sampling frequency of 50 h⁻¹ and a relative standard deviation of less than 2.5%. The method was applied to the determination of PA in pharmaceutical formulations with reasonable recoveries ranging from 101.0–103.1%, indicating that no interference is observed from concomitants usually present in dosage forms.     

Potentiometric Titration of Trace Concentrations of Penicillamine Using Ion Selective Electrodes

Abstract

Penicillamine (PA) has shown promise as a therapeutic agent in the treatment of rheumatoid arthritis (RA), and a sensitive analytical procedure applicable to physiological fluids is needed. PA is a metal chelating agent which forms very strong complexes with heavy metal ions (e.g., Hg²⁺, Cu²⁺, Pb²⁺). This characteristic has been applied to the analytical problem presented. The method developed is based on potentiometric titration of the ligand with a metal ion solution utilizing for endpoint detection an indicator electrode selective for this metal ion. The procedure described used lead (II) as the titrant and a lead (II) selective electrode. Demonstrated precision was ±2.0% when 7.5 μg PA was determined in 50 ml solution.     

Chiral separation with ligand-exchange micellar electrokinetic chromatography using a D-penicillamine-copper(II) ternary complex as chiral selector

D-Penicillamine is demonstrated for the first time as a chiral ligand for the enantioseparation of dansyl amino acids based on ligand-exchange micellar electrokinetic chromatography (LE-MEKC). Copper(II) was used as the central ion in the ternary complex. The effect of surfactant on the resolution was significant. A concentration of 20 mM sodium dodecyl sulfate (SDS) was shown to be necessary for the separation. Other important parameters, such as the concentration ratio of D-penicillamine (D-PEN) to Cu2+, the kind of metal central ion, the type and pH value of buffer, were also investigated. N-Acetyl-D-penicillamine and L-valine (Val), with similar structure to D-penicillamine, were applied as their copper(II) complexes as chiral selector and the chiral recognition mechanism is briefly discussed. Under optimum experimental conditions, i.e., 20 mM NH4OAc, pH 6.5, a 2:1 concentration ratio of D-penicillamine to Cu(II), 4 mM CuSO4 and 8 mM D-penicillamine, the chiral separation of eight pairs of different dansyl amino acid enantiomers was accomplished with resolution ranging from 1.1 to 5.9. When L-PEN was used instead of D-PEN, reversal of the migration order was observed.     

Synthesis of (S)-naproxen-benzotriazole and its application as chiral derivatizing reagent for microwave-assisted synthesis and indirect high performance liquid chromatographic separation of diastereomers of penicillamine, cysteine and homocysteine

(S)-Naproxen-benzotriazole was synthesized by the reaction of (S)-naproxen with 1H-benzotriazole using coupling reagent dicyclohexyl carbodiimide and 4-dimethylamino pyridine (DCC/DMAP). It was used as chiral derivatizing reagent for microwave irradiated synthesis of diastereomers of penicillamine, cysteine and homocysteine. The diastereomers were separated by reversed phase high performance liquid chromatography using gradient elution of triethylammonium phosphate (pH 3.5)-acetonitrile (30-65% within 30 min). The method was validated for accuracy, precision, and limit of detection.     

Nanomolar Determination of Penicillamine by Using a Novel Cobalt/Polyaniline/Carbon Paste Nanocomposite Electrode

The fabrication of cobalt/polyaniline nanocomposite was performed using a simple chemical method. It was characterized by using TEM and FTIR techniques. The nanocomposite was applied as a modifier in a carbon paste electrode for selective determination of penicillamine. Penicillamine reacts with emeraldine polyaniline by using 1,4, Michael addition reaction. It can decrease the voltammetric peak current of emeraldine polyaniline. The effects of pH and potential sweep rate on the response of the electrode were investigated. Differential pulse voltammetry was applied for quantitative determination. Dynamic linear ranges were obtained in the ranges of 1.0×10^?8–1.0×10^?7 mol L^?1 and 1.0×10^?9–1.0×10^?8 mol L^?1.     

Synthesis and Characterization of Novel Template Complexes

Novel neutral polynuclear Ni^II chelates of L ‐cysteine (L ‐cyst) or D ‐penicillamine (D ‐pen) with dicyandiamide (dcda) were synthesized and characterized using elemental analysis, UV, CD, reflectance, and IR spectroscopy and/or thermogravimetric and X‐ray analysis. The obtained dinuclear compounds add important information about the chemistry of nickel(II) ions, which form types of bonds that cannot be obtained with other metal ions such as Co^II. These dinuclear nickel compounds contain four‐membered rings with two sulfur and two nickel atoms. Electronic transitions were elucidated from reflectance, CD and absorbance spectroscopy and confirm a distorted square planar arrangement of the nickel ions. Because the same structure with Co^II ions could not be obtained directly, dimethylglyoxime was added to a suspension of the template complex with D ‐pen in water to separate the nickel ions. The separation of the ligand was confirmed by elemental analysis, IR, and ¹H NMR spectroscopy. It reacted with Co^II to give a different mononuclear crystalline complex that was studied by X‐ray single crystal diffraction. The crystals are orthorhombically with space group C222₁, a = 0.11769(4) pm, b = 0.13632(4) pm, c = 0.25239(8) pm, V = 0.0040490(2) pm³, and Z = 8.     

Precisely Regulated and Efficient Locking of Linear Peptides into Stable Multicyclic Topologies through a One‐Pot Reaction

We report the discovery of a small phenyl molecule with four isosteric thiolate‐reactive groups of sequentially varied reactivity. This molecule was exploited in combination with cysteine/penicillamine thiolates of different nucleophilic reactivity for precisely regulated and efficient locking (PROP‐locking) of linear peptides into multicyclic topologies through a one‐pot reaction. The PROP‐locking relies on multistep and sequential thiolate/fluorine nucleophilic substitutions, which is not only rapid but highly specific, thus enabling rapid locking of peptides with high amino acid diversities without protecting groups. Several tricyclic peptide templates and bioactive peptides were designed and synthesized using the PROP‐locking strategy. We believe that tricyclic peptides precisely locked through stable thioether bonds should be promising structurally constrained scaffolds for developing potential therapeutics and target ligands.     

Enhancement of the chemiluminescence of penicillamine and ephedrine after derivatization with aldehydes using tris(bipyridyl)ruthenium(II) peroxydisulfate system and its analytical application

A novel sequential injection (SI) method was developed for the determination of penicillamine (PA) and ephedrine (EP) based on the reaction of these drugs with tris(bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺) and peroxydisulfate (S₂O₈²⁻) in the presence of light. Derivatization of PA and EP with aldehydes has resulted in a significant enhancement of the chemiluminescence emission signal by at least 25 times for PA and 12 times for EP, leading to better sensitivities and lower detection limits for both drugs. The instrumental setup utilized a syringe pump and a multiposition valve to aspirate the reagents, (Ru(bpy)₃²⁺ and S₂O₈²⁻), and a peristaltic pump to propel the sample. The experimental conditions affecting the derivatization reaction and the chemiluminescence reaction were systematically optimized using the univariate approach. Under the optimum conditions linear calibration curves between 0.2–24 μg mL⁻¹ for PA and 0.2–20 μg mL⁻¹ for EP were obtained. The detection limits were 0.1 μg mL⁻¹ for PA and 0.03 μg mL⁻¹ for EP. The procedure was applied to the analysis of PA and EP in pharmaceutical products and was found to be free from interferences from concomitants usually present in these preparations.     

Electrochemical behavior of uric acid at a penicillamine self-assembled gold electrode

The fabrication and electrochemical characteristics of a penicillamine (PCA) self-assembled monolayer modified gold electrode were investigated. The electrode can enhance the electrochemical response of uric acid (UA), and the electrochemical reaction of UA on the PCA electrode has been studied by cyclic voltammetry and differential pulse voltammetry. Some electrochemical parameters, such as diffusion coefficient, standard rate constant, electron transfer coefficient and proton transfer number have been determined for the electrochemical behavior on the PCA self-assembled monolayer electrode. The electrode reaction of UA is an irreversible process, which is controlled by the diffusion of UA with two electrons and two protons transfer at the PCA/Au electrode. In phosphate buffer (pH 5.0), the peak current is proportional to the concentration of UA in the range of 6.0 × 10⁻⁵–7.0 × 10⁻⁴ mol L⁻¹ and 2.0 × 10⁻⁵–7.0 × 10⁻⁴ mol L⁻¹ for the cyclic voltammetry and differential pulse voltammetry methods with the detection limits of 5.0 × 10⁻⁶ and 3.0 × 10⁻⁶ mol L⁻¹, respectively. The method can be applied to determine UA concentration in real samples.