Stability Constants of Complexes of Divalent and Rare Earth Metals with Substituted Salicynals

Summary.  5-Chloro-4-6-dimethyl-salicylaldehyde was synthesized from 4-chloro-3,5-dimethyl-phenol. A series of substituted salicynals were obtained by condensation of 5-chloro-4,6-dimethyl-salicylaldehyde with several amines. The amines were chosen such as to vary the basicity of salicynals by changing the substituents at one of the coordination sites. The stability constants of complexes of bivalent (Mg²⁺, Ca²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺) and trivalent (Y³⁺, La³⁺, Pr³⁺, Nd³⁺, Sm³⁺, Eu³⁺, Gd³⁺, Tb³⁺, Er³⁺, Yb³⁺) metal ions with these salicynals and the pK values corresponding to the dissociation of the phenolic proton and the association of a proton to the azomethine nitrogen were determined potentiometrically using the Calvin-Bjerrum technique as adopted by Irving and Rossotti at 303 K and a constant ionic strength of 0.1 M in a 75:25 (v/v) dioxan-water mixture in an inert atmosphere. The influence of substituents on the proton affinity of the ligands was examined on the basis of inductive and mesomeric effects. It is also shown that some of the complexes possess antibacterial, antitubercular, antifungal, and anticoagulant activity. Received August 5, 1999./Accepted November 11, 1999     

Stability Constants of Complexes of Divalent and Rare Earth Metals with Substituted Salicynals

 5-Chloro-4-6-dimethyl-salicylaldehyde was synthesized from 4-chloro-3,5-dimethyl-phenol. A series of substituted salicynals were obtained by condensation of 5-chloro-4,6-dimethyl-salicylaldehyde with several amines. The amines were chosen such as to vary the basicity of salicynals by changing the substituents at one of the coordination sites. The stability constants of complexes of bivalent (Mg²⁺, Ca²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺) and trivalent (Y³⁺, La³⁺, Pr³⁺, Nd³⁺, Sm³⁺, Eu³⁺, Gd³⁺, Tb³⁺, Er³⁺, Yb³⁺) metal ions with these salicynals and the pK values corresponding to the dissociation of the phenolic proton and the association of a proton to the azomethine nitrogen were determined potentiometrically using the Calvin-Bjerrum technique as adopted by Irving and Rossotti at 303 K and a constant ionic strength of 0.1 M in a 75:25 (v/v) dioxan-water mixture in an inert atmosphere. The influence of substituents on the proton affinity of the ligands was examined on the basis of inductive and mesomeric effects. It is also shown that some of the complexes possess antibacterial, antitubercular, antifungal, and anticoagulant activity.     

Solubility, dissolution rate and bioavailability enhancement of irbesartan by solid dispersion technique

The objective of present work was to enhance the solubility and bioavailability of poorly aqueous soluble drug Irbesartan (IBS). The solid dispersions were prepared by spray drying method using low viscosity grade HPMC E5LV. Prepared solid dispersions were characterized by dissolution study, fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and X-ray diffraction studies (XRD). Results of the SEM, DSC and XRD study showed the conversion of crystalline form of IBS to amorphous form. The dissolution rate was remarkably increased in case of solid dispersion compared to pure IBS. Solubility and stability of solid dispersion was increased due to surfactant and wetting property, slowing devitrification and having anti-plasticization effect of HPMC E5LV. In vivo studies were performed in healthy rabbits (New Zealand grey) and compared with plain IBS. Solid dispersions showed increase in relative bioavailability than the plain IBS suspension. In conclusion, the prepared solid dispersions showed remarkable increase in solubility, dissolution rate and hence bioavailability of poorly water soluble drug Irbesartan.     

Reactions of Podophyllotoxin with DDQ

Introduction 2, 3-Dichloro-5, 6-dicyanobenzoquinone (DDQ) can react with lignans of the mono- arylidene-butyrolactone1, aryltetralin2, dibenzylbutane3 and aryltetralin-butyrolactone4,5 series. We have studied the reactions of this reagent with podophyllotoxin 1, which is a well-known natural product on account of its long history of use in folk medicine and the biological activity of its many derivatives6. In particular, derivatives of 4-demethyl epipodophyllotoxin are used in cancer chemo…     

Difluorination at Boron Leads to the First Electrophilic Ligated Boryl Radical (NHC‐BF2.)

1,3‐Dimethylimidazol‐2‐ylidene difluoroborane (NHC‐BF₂H) was prepared in a one‐pot, two‐step reaction from the parent ligated borane (NHC‐BH₃). The derived difluoroboryl radical (NHC‐BF₂^.) was generated by laser flash photolysis experiments and characterized by UV spectroscopy and rate‐constant measurements. It is transient and reacts quickly with O₂. Unusually, it also reacts more rapidly with ethyl vinyl ether than with methyl acrylate. By this measure, it is the first electrophilic ligated boryl radical. Both NHC‐BH₃ and NHC‐BF₂H serve as co‐initiators in bulk photopolymerizations, converting both electron‐poor and electron‐rich monomers at roughly similar rates. However, the difluorinated coinitiator provides polymers with dramatically increased chain lengths from both monomers.