Maqsood Ahmad Malik

Tetrazoles as carboxylic acid isosteres: chemistry and biology

Tetrazoles are often used as metabolism-resistant isosteric replacements for carboxylic acids in SAR-driven medicinal chemistry analogue syntheses. Tetrazoles have not been found in nature; with rare exceptions, these compounds do not exhibit appreciable biological activity, but they are at the same time resistant to biological degradation. This property makes it possible to use tetrazoles as isosteric substituents of various functional groups in the development of biologically active substances. The tetrazole motif has been used in various drug pharmacophores as a suitable replacement of carboxylic acid moiety and different methods have been used for the synthesis of tetrazoles using different reaction conditions. This review tries to give a vivid look on the different synthetic methods, using catalysts or different reagents for the synthesis of tetrazoles. The biological importance of tetrazoles has also been highlighted.

Synthesis, Structure Optimization and Antifungal Screening of Novel Tetrazole Ring Bearing Acyl-Hydrazones

Azoles are generally fungistatic, and resistance to fluconazole is emerging in several fungal pathogens. In an attempt to find novel azole antifungal agents with improved activity, a series of tetrazole ring bearing acylhydrazone derivatives were synthesized and screened for their in vitro antifungal activity. The mechanism of their antifungal activity was assessed by studying their effect on the plasma membrane using flow cytometry and determination of the levels of ergosterol, a fungal-specific sterol. Propidium iodide rapidly penetrated a majority of yeast cells when they were treated with the synthesized compounds at concentrations just above MIC, implying that fungicidal activity resulted from extensive lesions of the plasma membrane. Target compounds also caused a considerable reduction in the amount of ergosterol. The results also showed that the presence and position of different substituents on the phenyl ring of the acylhydrazone pendant seem to play a role on the antifungal activity as well as in deciding the fungistatic and fungicidal nature of the compounds.

Nanotoxicity: Dimensional and Morphological Concerns

Nanotechnology deals with the construction of new materials, devices, and different technological systems with a wide range of potential applications at the atomic and molecular level. Nanomaterials have attracted great attention for numerous applications in chemical, biological, and industrial world because of their fascinating physicochemical properties. Nanomaterials and nanodevices are being produced intentionally, unintentionally, and manufactured or engineered by different methods and released into the environment without any safety test. Nantoxicity has become the subject of concern in nanoscience and nanotechnology because of the increasing toxic effects of nanomaterials on the living organisms. Nanomaterials can move freely as compared to the large-sized particles; therefore, they can be more toxic than bulky materials. This review article delineates the toxic effects of different types of nanomaterials on the living organisms through different sources, like water, air, contact with skin, and the methods of determinations of these toxic effects.

Extraction of metal ions by ELM Separation Technology

The removal of toxic heavy metal ions is of great concern in the environmental field. Emulsion liquid membrane (ELM) technology has been proposed for the separation processes to enhance the extraction process and reduce the solvent and carrier requirement in comparison with other conventional solvent extractions techniques. Emulsion liquid membrane is an unsupported liquid membrane in which the membrane phase of an emulsion is dispersed into the feed phase to be treated. ELM technique is an accessible and easy way for the removal of different chemicals, metal ions, organic compounds, biomolecules, pollutants from aqueous feed phase and the transport them into desired receiving phases. This review article delineates the role of different parameters on the extraction process in ELM separation processes. These parameters strongly influence the percentage removal of metal ions and emulsion leakage. The optimum membrane properties can enhance the recovery of the desired phase and improves the stability of the ELM by minimizing the swelling and leakage of the membrane. The future direction of ELM technology can be the use of room temperature ionic liquids (RTILs) as stabilizers, carriers and can replace the conventional volatile toxic organic solvents.

Submicellar catalytic effect of cetyltrimethylammonium bromide in the oxidation of ethylenediaminetetraacetic acid by MnO4

The effects of cetyltrimethylammonium bromide (CTAB), sodiumdodecyl sulphate (SDS) and Triton X-100 (TX-100) on the oxidative degradation of ethylenediaminetetraacetic acid (EDTA) by MnO4(-) have been studied spectrophotometrically at 525 and 420 nm, respectively. It was found that cationic surfactant catalyse the reaction rate while anionic and non-ionic have no effect. The premicellar environment of CTAB strongly catalyses the reaction rate which may be due to the favorable electrostatic binding of both reactants (MnO4(-) and EDTA) with the positive head groups of the CTAB aggregates. The influence of different parameters such as [MnO4(-)], [EDTA], [H(+)] and [surfactants] were also considered. The reaction follows the first- and fractional-order kinetics with respect to [MnO4(-)] and [EDTA]. The proposed mechanism and the derived rate law are consistent with the observed kinetics.

Chitosan and Aloe Vera: Two Gifts of Nature

The present review discusses the preparation of chitosan, chemical composition, and constituents of aloe vera, their physiochemical characteristics, and their applications, particularly their wound healing properties. Since chitosan and aloe vera are two natural polymers having the required properties for wound healing these have been used since antiquity as wound healers and are since then considered as the natures two gifts to mankind. Chitosan based wound dressings have been prepared and at the same time some reports about the preparation of aloe vera based wound dressings are there, however till now no wound dressing based on both chitosan and aloe vera together has been reported and therefore, an effort has been made to review the literature, dealing with properties, processing, and applications, with an emphasis on wound healing.

Preparation of silver nanoparticles using tryptophan and its formation mechanism.

A non-toxic route was used for the preparation of silver nanoparticles using tryptophan (Trp) as reducing/stabilizing agent in the presence of cetyltrimethyl ammonium bromide (CTAB). Role of water soluble neutral polymer poly(vinylpyrrolidone) (PVP) has been studied on the growth of yellow colour silver nanoparticle formation. The synthesized nanostructures were characterized by UV-Visible absorption spectroscopy, transmission electron microscopy (TEM) by observing the size and distribution of silver nanoparticles. As the reaction proceeded, particles grew up to about 10 and 20 nm in the presence and absence of PVP, respectively, as determined by TEM. The formed nanoparticles showed the highest absorption plasmon band at 425 nm. Rate of silver sol formation increases with the [Trp], [CTAB] and [PVP], reaching a limiting value and then decreases with the increase in concentrations of these reagents. It was observed that nanoparticles are spherical, aggregated and poly dispersed in the absence and presence of PVP, respectively. On the basis of kinetic data, a suitable mechanism is proposed and discussed for the silver sol formation.

A kinetic study of silver nanoparticles formation from paracetamol and silver(I) in aqueous and micellar media

UV-vis spectrophotometeric, transmission electron microscopy (TEM) and viscometric techniques were used for the formation, characterization and kinetics of silver sol formation using silver nitrate as source of silver, paracetamol as reducing agent and cetyltrimethylammonium bromide (CTAB) as the stabilizer in absence and presence of poly(vinyl alcohol) (PVA). The sigmoidal curve of absorbance versus the reaction time suggests an autocatalytic reaction path. Transmission electron microscopy (TEM) results show that the silver nanoparticles are all spherical, highly dispersed and aggregated in aqueous solution. In the formation of silver nanoparticles, alkaline solution is required. The presence of PVA inhibits the rate of silver nanoparticles formation. Effects of [Ag(+)], [paracetamol], [CTAB], [NaOH] and [PVA] on the silver sol formation rate were analyzed.

Oxidation of tyrosine by permanganate in presence of cetyltrimethylammonium bromide

In this paper we report the effect of cetyltrimethylammonium bromide, CTAB on the oxidative degradation of tyrosine by permanganate. The reaction rate bears a first-order dependence on the [MnO(4)(-)] under pseudo-first-order conditions (large excess of [tyrosine] for at least 10 times over [MnO(4)(-)]) in presence of 10.0x10(-4)moldm(-3) CTAB. The effect of total [CTAB] on the reaction rate was determined. When [CTAB] was less than its critical micelle concentration (CMC) the rate constants (k(psi)) values decreased from 18.5x10(-4) to 7.2x10(-4)s(-1). As the [CTAB] was greater than the CMC, the k(psi) values increase from 7.2x10(-4) to 15.8x10(-4)s(-1)at room temperature. The premicellar environment of CTAB strongly inhibits the reaction rate where as increase in rate constant ascribed to the incorporation of tyrosine and MnO(4)(-) in to the Stern layer of CTAB micelles. The reaction has acid-dependent and acid-independent paths and, in the former case, the zero-order kinetics with respect to [H(2)SO(4)] shifted to fractional-order at higher [H(2)SO(4)]. Experiments have been done to confirm the nature of Mn(IV) formed during the reduction of permanganate by tyrosine. The mechanism with the observed kinetics has been proposed and discussed. The presence of -OH group is responsible for the higher reactivity of tyrosine which easily transfers the proton to MnO(4)(-).

ESTIMATION OF EXCESS MOLAR VOLUMES, THEORETICAL VISCOSITIES, AND ULTRASONIC SPEEDS OF BINARY LIQUID MIXTURES AT DIFFERENT TEMPERATURES

Excess molar volumes, , have been derived by using viscosity data for the binary mixtures of styrene (STY) with dimethylsulfoxide (DMSO), acetone (ACT), chlorobenzene (CB), and ethanol (EA) at different temperatures. From the literature data of viscosities, entropies, (ΔS*, and enthalpies, (ΔH*, of activation of viscous flow have been determined. Moreover, theoretical values of viscosities and ultrasonic speeds of the binary mixtures were calculated using different empirical relations and theories. The results were discussed in terms of deviations in experimentally and theoretically calculated values. The sign and magnitude of these parameters were found to be sensitive towards interactions prevailing in the studied systems. The predicted properties show good accuracy in comparison with the experimentally derived properties.