Journal of Physical and Theoretical Chemistry
Volume:1 Issue: 1, Spring 2004

More recently medical chemistry research has been focused on proteins that drive and controlcell cycle progression. Among them, the cyclin dependent kinases (cdk’s) are a group ofserine/threonine kinases, which rule the transition between successive stages of the cell cycle. Theactivity of cdk’s is regulated by multiple mechanisms, including binding to cyclins, which is a broadclass of positive regulatory cdk-binding proteins. Among the chemical agents that act selectively ascdk inhibitors are flavonoids,flavopiridol is a semisynthetic flavonoid.Theoretical study is performedon flavopiridol using quantum chemical calculations. Interactions between flavopiridol withtransition metals were studied at HF/6-31G*, and HF/6-311G** levels of theory. Ab initio method at HF level of theory was used. Conformations, optimized parameters, bond length, were computed for metalated andisolated flavopiridol. Flavopiridol can be Metalated from its binding sites (oxo and hydroxyl groups) and theenergies of these compounds were computed.Abbreviations and notations: HF, Hartree-Fock; Cdk , Cyclin dependent kinases.

Ab initio calculations at HF/6-31G* level of theory for geometry optimization and MP2/6-31G*//HF/6-31G* for a single point total energy calculation are reported for the importantenergy-minimum conformations and transition-state geometries of 1, 3-diazacyclohepta-1, 2-diene (2) and 1, 3-diazacycloocta-1, 2-diene (3). The C2 symmetric twist-chair (2-TC)conformation of 2 is calculated to be 7.4 kJ mol-1 more stable than the twist-boat (2-TB, C2)conformer. Interconversion of 2-TC and 2-TB conformations takes place by a relatively highenergy(58.2 kJ mol-1) transition state. The unsymmetrical chair (3-C) conformation of 3 iscalculated to be 6.6 kJ mol-1 more stable than the C2 symmetric twist-boat (3-TB) form. Thetransition state linking 3-C and 3-TB conformations is 40 kJ mol-1 above 3-C. Racemization of2-TC and 3-C conformations occures by cis-rotation and requires 77.9 and 83.5 kJ mol-1,respectively.

We found that dibenzo-18-crown-6 (DB18C6) can be used as an ionophore to make a tin (II)-ionselectivemembrane electrode. The electrode exhibits a near Nernstian response for Sn2+ ions over aconcentration range from 1.0× 10-6 – 1.0× 10-2 M with a slope of 27.5 ± 0.6 mV per concentration decadein an acidic solution (pH=1). The limit of detection was 8.0× 10-7 M. It has a response time of < 20s andcan be used for at least 3 months without any divergence in potentials. The proposed membrane electroderevealed very good selectivity for Sn2+ ions over a wide variety of other cations and could be used inacidic media. It was used as indicator electrode in potentiometric determination of tin (II) ion in realsample.

The dependence on ionic strength of protonation of L-aspartic acid and its complexation withdioxouranium(VI) is reported in sodium perchlorate solution as a background salt. The measurementshave been performed at 25 ± 0.1 °C and various ionic strengths in the range 0.1 to 1.0 mol dm-3, using acombination of potentiometric and spectrophotometric techniques. The overall analysis of the present andthe previous data dealing with the determination of stability constants at different ionic strengths allowedus to obtain a general equation, by which a formation constant determined at a fixed ionic strength can becalculated, with a good approximation, at another ionic strength, if 0.1 ≤ ionic strength ≤ 1.0 mol dm-3sodium perchlorate.

A highly selective electrode for Bromide ion based on aza pyrilium derivative as an excellentionophore is described.The sensor exhibits a good linear response with a slope of ( 60±1 ) mV per decadeover the concentration range of ( 1×10-3 – 9×10-6 M ) , and a detection limit of ( 3×10-6 M ) of Bromideions .The electrode response is independent of pH in the range of(4.0 –9.5).Selectivity coefficientsdetermined by the matched potential method ( MPM ) . Indicate that the interference from inorganic andorganic anions is negligible. The proposed sensor shows a fast response time of approximately (20 s).Ithas been used as an indicator electrode in titration of Bromide with Ag +.

The relative stability of hydrogen-bonded of Molybdate-Phosphonic Acid (MPA) complex (1:2) ingas phase has been carried out using Density Functional Theory (DFT) methods. The methods are usedfor calculations are B3LYP, BP86 and B3PW91 that have been studied in two series of basis sets: D95**and 6-31+G(d,p) for hydrogen and oxygen atoms; LANL2DZ for Mo and Phosphorus. Predictedhydrogen-bond geometry and relative stability are discussed. Equilibrium geometry in the groundelectronic state energy has been calculated for 1:2 complex. The best results for energetics and geometryof the ground state was obtained with BP86 calculations.

In this work, a new spectrophotometric method for the determination of trace amount of Cobalt (ІІ) ionwas investigated and the stability constant of the related complex was evaluated 2.174 × 104. In the Cobalt(ІІ)-piroxicam complex, the maximum absorbance wavelength is 570 nm and the linearity of calibrationcurve was investigated (5-10 ppm). The relative standard deviation for seven replicate experiments is0.5292 percent. The accuracy is 0.15 percent and limit of detection is 1.19 ppm. The analytical sensitivityallows us to detect the concentration difference of 0.06 ppm with reliable level of confidence. The ligand tometal ratio was determined (1:1) by the continuous variation method. The above spectrophotometricmethod was optimized in terms of pH, temperature, time, ligand concentration and ionic strength. Thismethod is tolerant against several external matters, which means high selectivity.