Kinetic studies of retinol addition radicals

Retinol neutral radicals (RS-retinol˙), generated from the reaction of retinol with 4-pyridylthiyl and 2-pyridylthiyl radicals in argon-saturated methanol, undergo β-elimination, which can be monitored via the slow secondary absorption rise at 380 nm attributed to the rearrangement of the unstable retinol neutral addition radicals to the more stable addition radicals. Rate constants for the β-elimination reactions (k(β)) of 4-PyrS-retinol˙ were measured at different temperatures and the Arrhenius equation for the reaction is described by log (k(β)/s(-1)) = (12.7 ± 0.2) - (54.3 ± 1.3)/θ, where θ = 2.3RT kJ mol(-1). The reactivities of retinol addition radicals (RS-retinol˙), generated from the reaction of retinol with various thiyl radicals, towards oxygen have also been investigated in methanol. In the presence of oxygen, the decay of RS-retinol˙ fits to biexponential kinetics and both observed rate constants for the RS-retinol˙ decay are oxygen-concentration dependent. This suggests that at least two thiyl addition radicals, formed from the reaction of RS˙ with retinol, undergo oxygen addition reactions. In light of the estimated rate constants for oxygen addition to RS-retinol˙ and RS-CAR˙ (CAR: carotenoid), the antioxidant-prooxidant properties of retinol are discussed.     

Cloud Point Phenomenon in Amphiphilic Drug Promethazine Hydrochloride+Electrolyte Systems

Herein we report clouding phenomenon occurring in amphiphilic drug promethazine hydrochloride (PMT) in the presence of electrolytes. The CP of 50 mM drug solution, prepared in 10 mM sodium phosphate buffer, was found to decrease with increasing pH due to deprotonation of drug molecules at high pH. Addition of inorganic salts (KF, KCl and KBr) to drug solutions at fixed pH (6.7) and drug concentration (50 mM) caused an increase in CP. The results have been discussed on the desorption/adsorption of counterions to the headgroups. Cations also increased the CP by affecting the water structure with their effectiveness being in the order: Li⁺<Na⁺<K⁺<NH₄ ⁺. In the presence of NaCl, increase in drug concentration increased the CP while increase in pH showed an opposite trend.     

Phase Separation Phenomenon in Non-ionic Surfactant TX-114 Micellar Solutions: Effect of Added Surfactants and Polymers

Clouding (or phase separation) in non-ionic surfactants is a well-known phenomenon. Clouding is to be avoided in some applications whereas in others it is preferred. Herein the results of CP (cloud point—the temperature at which solution separates into two phases) measurements of the non-ionic surfactant Triton X-114 (TX-114) in the presence of surfactants and polymers are presented. Cationic and nonionic surfactants, in the absence and presence of the quaternary salt tetrabutylammonium bromide (TBAB), increase the CP of TX-114. Anionic surfactants, in the absence of TBAB, increase the CP; in the presence of TBAB, these surfactants decrease the CP. Polymers of PEG and PVP series have been found to decrease the CP. The results are discussed by taking into consideration the nature of the added surfactants and polymers.     

Effects of pharmaceutical excipients on cloud points of amphiphilic drugs

The clouding behavior, i.e., formation of phase separation at elevated temperature (the temperature being known as cloud point (CP)), of three amphiphilic drugs, amitriptyline (AMT), clomipramine (CLP) and imipramine (IMP) hydrochlorides in the presence of various additives, like cationic surfactants (conventional and gemini), nonionic surfactants, bile salts, anionic hydrotropes, sodium salts of fatty acids and cyclodextrin has been investigated. These additives are generally used as drug delivery systems. The drugs used are tricyclic antidepressants. All the surfactants increase the CP of mixed micelles formed by cationic (conventional and gemini) and nonionic surfactants. Hydrotropes, bile salts and fatty acid salts, when added in low concentrations, increase the CP, whereas at high concentrations, they decrease it. β-Cyclodextrin behaves as simple sugar and decreases the CP of the drug solutions.     

Synthesis,Characterization, and Screening for Antiamoebic Activity of Palladium(II), Platinum(II), and Ruthenium(II) Complexes with NS‐Donor Ligands

Reaction of [PdCl₂(DMSO)₂], [PtCl₂(DMSO)₂], and [RuCl₂(η⁴‐C₈H₁₂)(MeCN)₂] with S‐acetyl N^β‐acetyldithiocarbazate (=2‐acetylhydrazinecarbodithioic acid anhydrosulfide with ethanethioic acid; aadt; 1 ), S‐methyl N^β‐[(5‐nitrothiophene‐2‐yl)methylene]dithiocarbazate (=S‐methyl 2‐[(5‐nitrothiophene‐2‐yl)methylene]hydrazinecarbodithioate; mntdt; 2 ), and S‐benzyl N^β‐[(5‐nitrothiophene‐2‐yl)methylene]dithiocarbazate (=S‐benzyl 2‐[(5‐nitrothiophene‐2‐yl)methylene]hydrazinecarbodithioate; bntdt; 3 ) led to new complexes [PdCl₂(L)], [PtCl₂(L)], and [RuCl₂(η⁴‐C₈H₁₂)(L)] (L=ligands 1 – 3 ). All these compounds were characterized by elemental analysis, IR, ¹H‐ and ¹³C‐NMR and UV/VIS spectra and thermogravimetric analysis. Ligand 1 coordinates through the thioxo S‐atom and the carbazate N(β) atom, whereas in ligands 2 and 3 the thioxo S‐atom and the azomethine N‐atom are coordinated to the metal ion. Screening of antiamoebic activity of these compounds was performed in vitro against the HK‐9 strain of E. histolytica. All the complexes were more active than their respective ligands; compound 3a showed the most promising activity.