Mononuclear manganese carboxylate complexes: Synthesis and structural studies

Several manganese carboxylates complexes having Pz^iPr2H (3,5-diisopropylpyrazole), Tp^Ph,Me (hydrotris(3-phenyl,5-methyl-pyrazol-1-yl)borate), Tp^ipr2 (hydrotris(3,5-diisopropyl-pyrazol-1-yl)borate) as supporting ligands have been synthesised and structurally characterized. Single-crystal X-ray diffraction studies suggest that the manganese center in complexes (Pz^iPr2H)₄Mn(NO₂–OBz)₂ (5) and (Pz^iPr2H)₄Mn(F–OBz)₂ (6) have same coordination environment and geometry whereas the complex [Tp^Ph,MeMn(OAc)Pz^Ph,MeH] (7) has a five coordinate manganese center. In all these complexes, the carboxylate groups are coordinated as monodentate and the uncoordinated oxygen atom of the carboxylate groups form intramolecular hydrogen bonds with the NH group of the corresponding coordinated pyrazole (Pz^iPr2H/Pz^Ph,MeH). The complexes 5–8 and 10 were tested for their superoxide dismutase activity and it was found that only complex 7 has SOD activity as its structure is very similar to the active site structure of the native Mn–SOD enzyme. The SOD activity studies on these carboxylate complexes suggest that any model compound with analogous active site structure and intramolecular hydrogen bonding may be a suitable mimic for the Mn–SOD enzyme.     

Linear balls and the multiplicity conjecture

A linear ball is a simplicial complex whose geometric realization is homeomorphic to a ball and whose Stanley–Reisner ring has a linear resolution. It turns out that the Stanley–Reisner ring of the sphere which is the boundary complex of a linear ball satisfies the multiplicity conjecture. A class of shellable spheres arising naturally from commutative algebra whose Stanley–Reisner rings satisfy the multiplicity conjecture will be presented.     

Mathematical models for drug delivery to chronic patients

Mathematically, analysis of drug delivery kinetics involves two moving boundary problems: diffusion front and eroding front. In this paper, we have models for drug delivery for the sites which can be enclosed by spherical shaped matrices covered by membranes and these problems are helpful for designing the drug delivery devices to deliver the drug inside from outside and a corresponding device supplying drug from inside. Once the time required for treatment and rate of drug delivery is known from medical diagnosis, this analysis can design a device releasing the drug/active agent over a long period of time. The purpose of such drug delivery is to achieve more effective therapies while eliminating the effect of over dosing and maintaining drug levels within the desired levels. The device may work on optimal use of drug and increase the patient’s convenience. The proposed models provide design for eroding tumor or chemotherapy to cancerous regions. The results have been obtained for steady state release rate, zero order release time and life time of the device and discussed. It has been observed that zero order time and life time increase by introducing a membrane of uniform thickness.     

Complexation of fluoroquinolone antibiotics with human serum albumin: A fluorescence quenching study

Mechanism of interaction and detailed physico-chemical characterization of the binding of four fluoroquinolones: levofloxacin, sparfloxacin, ciprofloxacin HCl and enrofloxacin with human serum albumin has been studied at physiological pH (7.4) using fluorescence spectroscopic technique. The stoichiometry of interaction was found to be 1:1 for all the drugs used. The association constants for the interaction were of the order of 10⁴ in most cases. At low drug:protein ratios, a significant fraction of the added drug was bound. The predominant interactions involved are hydrogen bonding and Van der Waal’s interactions in the case of levofloxacin, hydrophobic interactions in the case of ciprofloxacin hydrochloride and enrofloxacin and hydrogen bonding, hydrophobic and electrostatic interactions in the case of sparfloxacin.The drug binding region did not coincide with that of the hydrophobic probe, 1-anilinonaphthalene-8-sulfonate (ANS). From the displacement of site-specific probes and site-marker drugs, it was concluded that ciprofloxacin hydrochloride is site II-specific while enrofloxacin is a site I-specific drug. Levofloxacin binds at both site I and site II with equal affinity. Sparfloxacin had higher affinity for site II than site I. It is also possible that sparfloxacin binds at the interface between site I and site II. Stern-Volmer analysis of the data showed that the quenching mechanism is predominantly collisional for the binding of ciprofloxacin HCl and enrofloxacin while both static and collisional quenching mechanisms are operative in the case of levofloxacin and sparfloxacin. High magnitude of the rate constant for quenching showed that the process is not entirely diffusion controlled. Circular dichroism (CD) spectroscopic studies showed that the presence of drugs did not cause any major changes in the secondary structure of HSA.     

A theoretical study of structural, elastic and thermal properties of heavy lanthanide monoantimonides

The structural, elastic and thermal properties of three heavy monoantimonides of holmium, erbium and thulium (LnSb, Ln=Ho, Er and Tm) have been investigated theoretically by using an interionic potential theory consisting of long-range Coulomb, short-range repulsive and van der Waal’s (vdW) interactions. These compounds exhibit first-order crystallographic phase transition from their initial NaCl-type structure to CsCl-type structure at pressures 27, 33.2 and 29.8 GPa for HoSb, ErSb and TmSb, respectively. The values of elastic constants and Debye temperatures as a function of pressure are also reported. The elastic properties such as Young modulus (E), Shear modulus (G), Poisson ratio (υ) and anisotropic ratio (A) in an NaCl-type structure are also predicted.     

Nickel-catalyzed synthesis of five-membered heterocycles

In recent decades, a large number of reports related to the synthesis of N-, O- and S-containing heterocycles have appeared owing to a wide variety of their biological activity. The investigation of methods for the chemical synthesis is a growing area of interest due to increasing environmental issues. The use of catalysts in organic reactions has gained extensive interest. Metal and nonmetal catalysts provided a new improved alternative to traditional methods in modern synthetic chemistry. The aim of present review is to focus on the applications of nickel for the synthesis of five-membered heterocylces.