Microcalorimetric and chromatographic investigations of the binding of some pyridine derivatives to cyclodextrins

An UPLC-MS/MS Method for Simultaneous Determination of Tropicamide and Phenylephrine in Rabbit Ocular Tissues and Plasma

Purpose: Mixed eye drops containing 0.5% tropicamide and 0.5% phenylephrine are commercially available for cycloplegic refraction. Determining the pharmacokinetics (PK) and distribution of tropicamide and phenylephrine simultaneously in ocular tissues is an important but challenging issue. Herein, we developed a sensitive and selective ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method for simultaneous determination of tropicamide and phenylephrine concentrations in rabbit ocular tissues and plasma. Methods: The two analytes were extracted with ethyl acetate using etofesalamide as an internal standard and separated using a chromatographic C₈ column with isocratic elution. Mass spectrometry analysis was performed with positive electrospray ionization and data were acquired in a multiple reaction monitoring mode. Results: We validated this method over a concentration range of 5-1,600 ng/mL for tropicamide and 1-320 ng/mL for phenylephrine in ocular tissues, as well as 0.5-64 ng/mL for both compounds in plasma. Inter- and intraday precisions in all samples were both <12.9% and the accuracy was within 92.1%-108.4%. The highest concentration of tropicamide was found in aqueous humor (C_max: 29430 ng/g), while was in cornea for phenylephrine (C_max: 3465 ng/g). All the ocular tissues concentrations were much higher than those of blood. Conclusion: This UPLC-MS/MS method allowed us to determine the PK and distribution of tropicamide and phenylephrine in rabbit ocular tissue, which may be helpful in the future development and application of mydriatic agents.

A manganese porphyrin–α-cyclodextrin conjugate as an artificial enzyme for the catalytic epoxidation of polybutadiene

A manganese porphyrin–α-cyclodextrin conjugate was designed as an artificial clamp-like enzyme to catalyze the epoxidation of cis-polybutadiene with trans-epoxide preference.

Preparation and Characterization of N-Octyl Pyridine Tetrafluoroborate

Ionic liquids combine a set of proper ties like non-flammability, non-volatility, high ionic density and intrinsically high ionic conductivity; they also behave as good solvents for various chemical and electrochemical processes. These attributes make them appealing as alternative materials to replace conventional solvents, wherefore the interest in ionic liquid based materials for diverse electrochemical devices has boosted in the last few decades. The halogenated hydrocarbon and pyridine are used in the preparation of room temperature ionic liquid intermediates bromided N-octyl pyridine OPB, and the intermediate infrared spectrometer are used in chemical structure characterization, so it is determined that the product is the room temperature ionic intermediates OPB. Infrared spectrometer for the structure characterization is used, it is proved that OP-BF4 room temperature ionic liquid has been gotten. Both solvent polarity and acid alkali have an influence on ultraviolet spectrum diagram displacement of room temperature ionic liquid. If the ultraviolet spectrum diagram of ionic liquids and other solvent mixed solution is studied, it is necessary to indicate which solvent is used.

Ground-state and excited-state multiple proton transfer via a hydrogen-bonded water wire for 3-hydroxypyridine

The multiple proton transfer reactions of 3-hydroxypyridine-(H₂O)₃ have been demonstrated, and a perfect proton transfer cycle has been revealed in the ground and excited states.

Effect of 2-hydroxypropyl-β-cyclodextrin on solubility of sparingly soluble drug derivatives of anthranilic acid

Guest-host complex formation of three drug derivatives of anthranilic acid, mefenamic acid, niflumic acid, and flufenamic acid with 2-hydroxypropyl-β-cyclodextrin (2HP-β-CD) in aqueous solutions was investigated using “Phase solubility study” with UV-vis spectrophotometry. Solubility of sparingly soluble drugs has been improved by addition of 2HP-β-CD at two temperatures 298.15 K and 310.15 K and two pH values 2 and 7. The influence of different 2HP-β-CD concentration on solubility of drugs at different pH and temperatures has been investigated. The 2HP-β-CD-drug complex stability constants (K_s), and dissociations constants (K_d), as well as the thermodynamic parameters of reaction, i.e., the free energy change (ΔG), the enthalpy change (ΔH) and the entropy change (ΔS), were determined. The experimental data indicated formation of 1:1 inclusion complexes, which were found effective binders increasing the solubility of drugs.

Study on complex formation of biologically active pyridine derivatives with cyclodextrins by capillary electrophoresis

The capillary electrophoretic separation of the pyridine derivatives pyridoxine, pyridoxal, nicotinamide, nicotinic acid and isonicotinic acid in phosphate buffer using cyclodextrins as buffer additives was studied at pH 2.0 and 3.5. Superior separation was achieved at pH 2.0. Addition of alpha- and beta-cyclodextrin and the respective 2-hydroxypropyl derivatives as well as carboxymethyl-alpha-cyclodextrin to the running buffer did not significantly improve the resolution of the compounds. The interactions of alpha- and beta-cyclodextrin as well as their hydroxypropyl derivatives with the pyridine derivatives were investigated by capillary electrophoresis at pH 2.0. No complex formation was observed between the cyclodextrins and pyridoxine, pyridoxal and nicotinamide. alpha-Cyclodextrin and 2-hydroxypropyl-alpha-cyclodextrin form weak 1:1 complexes with nicotinic and isonicotinic acids in aqueous media at 298.15K, while beta-cyclodextrin and its hydroxypropyl derivative did not form complexes. The apparent stability constants (K) of the complexes calculated from the electrophoretic mobility data ranged between 3 and 33 kg/mol. The negative values of enthalpy and entropy of complex formation obtained from the graphical plot of the van't Hoff equation indicate an important role of van der Waals and electrostatic interactions in the binding of nicotinic acid with alpha-cyclodextrin.

Chromatographic determination of the association constant between 8-methoxypsoralen and modified β-cyclodextrin: protective effect of hydroxypropyl-β-cyclodextrin on 8-methoxypsoralen toxicity in human keratinocytes

The retention of 8-methoxypsoralen (8-MOP) on an immobilised hydroxypropyl-beta-cyclodextrin (HP-beta-CD) column was analysed in HPLC by the determination of its Langmuir distribution isotherm. A such method was used to confirm the potential drug complexing role of this cyclodextrin. The 8-MOP/HP-beta-CD association constant (K) was equal to 29.5 and 18.7 M-1, respectively, at a temperature equal to 5 and 25 degrees C, respectively. These association constant values were used to determine the cytotoxicity profile of human keratinocyte cell line (HaCaT) in relation to the complex concentration. It was showed through these data that HP-beta-CD had a cytoprotective since a reverse effect of HP-beta-CD on 8-MOP cytotoxicity was observed.

High-performance liquid chromatographic determination of phenylephrine and tropicamide in human aqueous humor

A high-performance liquid chromatographic method for the simultaneous determination of phenylephrine and tropicamide in human aqueous humor was developed. After centrifugation, an aliquot of the supernatant was injected onto the column and the eluent was monitored at 280 nm then 254 nm after 5 min. Separation was performed on a CN column with 0.01 M Pic B8 (octane sulfonic acid)-acetonitrile (65:35, v/v) as mobile phase. The standard curves were linear in the detection range. The precision of the method (expressed by relative standard deviation) and the accuracy (mean error in per cent) were <5% for both intra- and interassays.

Analytical applications of enhanced drug luminescence

Luminescence emission from drugs is strongly dependent on their physicochemical environment. Several biomedically and environmentally important compounds and pharmaceuticals exhibit sufficient intrinsic luminescence properties to allow their determination by high-performance liquid chromatography (HPLC) with fluorimetric, chemiluminescence or room temperature phosphorimetric detection. In the case of weakly fluorescing compounds it is possible to use the dependence of the emitted radiation on the molecular environment at the moment of measurement. The composition of the eluent, i.e. solvents, added salts and buffers, pH and ionic strength, oxygen content and temperature, are of the highest importance for the luminescence detection of drugs in solution (e.g. in liquid chromatography) or adsorbed onto solid surfaces (e.g. in thin-layer chromatography). Post-column or post-plate acid-base manipulation and the use of specific reagents may remarkably enhance the observed luminescence of several molecules. The term "enhancement" of luminescence comprises various sample treatments leading to an increase of the emitted radiation. These treatments include the addition of non-fluorescent compounds to, or the creation of organized media (surfactants, cyclodextrins, heavy atoms) in, the sample to be measured. They may also involve changes in molecular environment, pH, the application of excessive drying conditions, the removal of oxygen, the protection of adsorbed compounds against non-radiative decay mechanisms by means of specific spraying or dipping conditions, amongst others. The use of organized media in luminescence spectroscopy is growing. Many of the recent studies have involved micelles for enhancing the fluorescence, room temperature phosphorescence and chemiluminescence of several chemicals. Cyclodextrins are increasingly used for various analytical applications. Liquid paraffin, triethanolamine, dodecane, Triton X-100 and Fomblin Y-Vac are commonly used fluorescence enhancers in chromatographic assays. Examples of these systems in drug analysis are presented.