Total synthesis of clavosolide A

For the total synthesis of (−)-clavosolide A described herein, a Schmidt glycosidation reaction was used to attach the sugar moiety at an early stage in the synthesis to the 4-hydroxy group of the substituted tetrahydropyran unit of the molecule, which itself was built following a Ti(III)-mediated method developed by us earlier, and at the end, it was the Yamaguchi reaction that was successfully employed for the cyclodimerization of the two halves of the molecule leading to its total synthesis.     

Recent advancements in the anticancer potentials of first row transition metal complexes

The frequently severe effects of currently utilized platinum-based complexes have prompted researchers to develop less toxic transition metal based anticancer drugs. Transition metal complexes have recently gained considerable attention as promising anticancer agents due to their efficient drug design and fast optimisation. Some transition metal complexes displayed better anticancer activity than cis-platin. This led to the transition metal complexes for clinical application of chemotherapeutic drugs for cancer therapy. Cytotoxicity of the complexes has been evaluated on the basis of their IC₅₀ values. In this review, we have focussed on recent findings about the anticancer mechanism of action of first row transition metal complexes during the last ten years.     

Speciation of Arsenic in Environmental and Biological Samples

A novel arsine generator glass assembly is constructed and reported for the spectrophotometric determination and speciation of arsenic in real samples. In an arsine generator, sodium borohydride is added dropwise to the acidic sample solution and arsine thus formed is reacted with silver diethyldithiocarbamate (Ag‐DDTC) ‐ Tritron‐X (TX‐100) solution in pyridine to form a red coloured complex. The complex showed the absorption maximum at λ_max 540 nm. The molar absorptivity of the method was found to be (1.55) × 10⁴ L mole^?1 cm^?1 at this wavelength. The presence of non‐ionic surfactant, i.e. TX‐100 in the Ag‐DDTC solution, makes the method ≈ 3 times more sensitive than the conventional Ag‐DDTC method. Beer's law is obeyed in the concentration range of 0.05–2.80 mg L^?1 of arsenic. The detection limit of the method was calculated to be 20 μg L^?1 As. Speciation of arsenite from other forms of arsenic in sample solutions was carried out by extraction of arsenite with Pb‐DDTC in chloroform, followed by spectrophotometric determination. After arsenite separation the sample is used for the arsenate determination. Total arsenic was determined by acid decomposition of the same sample. The speciation data were found to be comparable (±2%) with ICP‐MS, with better precision (< 1%). The method has been successfully applied for the speciation of arsenic in drinking water and dust samples of arsenic affecting the Rajnandgaon district of Chhattisgarh, India, and urine and blood samples of patients with arsenical diseases. Concentration of total arsenic in tube‐well water of this area was 3–6 times more than the permissible limit. Dust samples contained less amounts of arsenic than the ground water.     

Effect of TiO2 on electron paramagnetic resonance, optical transmission and dc conductivity of vanadyl doped sodium borate glasses

Glass systems with composition xTiO2.(30 - x)Na2O.70B2O3 (series I) and xTiO2.(70 - x)B2O3.30Na2O (series II) containing 2 mol% V2O5 have been prepared (0 < or = x < or = 7, mol%) by normal melt-quenching. The electron paramagnetic resonance (EPR) spectra of VO2+ ions have been recorded in the X-band (approximately 9.13 GHz) at room temperature. Spin Hamiltonian parameters, gparallel, gperpendicular, Aparallel, Aperpendicular, the dipolar hyperfine coupling parameter (P) and the Fermi contact interaction parameter (K) have been calculated. The increase in Deltagparallel/Deltagperpendicular with increase in TiO2 content in series I shows that the octahedral symmetry of V4+O6 complex is reduced, whereas in series II the octahedral symmetry is improved with increase in x. The decrease in P, in both the series, indicates that the 3dxy orbit expands with increase in mol% of TiO2. The molecular orbital coefficients, alpha2 and gamma2 have been calculated by recording the optical transmission spectra in the range 500-850 nm. alpha2 and gamma2 increase with increase in x in both the series, which indicates that, the covalency of the vanadium oxygen bonds decreases. The dc conductivity sigma, decreases and activation energy, W increases with increase in TiO2:Na2O ratio whereas with increase in TiO2:B2O3 ratio the variation in sigma and W is within experimental error.     

Surface thermodynamics of Efavirenz and a blend of Efavirenz with cellulose acetate propionate by inverse gas chromatography

The purpose of this paper is to study the effect of an excipient on the surface energetics of Efavirenz (EFV) drug. The net retention volumes, V_N, for n‐alkanes and polar solutes on the two columns, namely, EFV drug and a blend of EFV with cellulose acetate propionate have been measured by inverse gas chromatography. The dispersive surface free energy, , Lewis acid parameter, K_a, and Lewis base parameter, K_b, have been determined using V_N values. The values are decreased linearly with increase of temperature for pure EFV as well as for the blend. Furthermore, the values of EFV are higher than in the blend, for example, values at T = 318.15 K for EFV, and for the blend are 28.09 ± 6.02 mJ/m² and 28.30 ± 2.31 mJ/m², respectively. The specific component of surface free energy has been obtained by the Schultz method as well as by the Dong et al. method. The values have been used to calculate Lewis acid‐base parameters for the EFV as well as the blend. The K_a values for the EFV and the blend are almost similar, where as the K_b values are higher in EFV than in the blend. Similar trend in K_a and K_b has been observed in both methods studied. Copyright © 2015 John Wiley & Sons, Ltd.     

A classification of time scales and analysis of the general delays on time scales with applications

In this paper, we present five classes/categories of time scales. Then, on each class, we introduce and analyze delays that not only lead to new types of delay systems on time scales but also reveal the limitations of the known results in the literature. To show the importance and significance of our analysis, several examples are illustrated. We conclude our paper with some interesting open problems. Copyright © 2015 John Wiley & Sons, Ltd.     

Largest Placement of One Convex Polygon Inside Another

We show that the largest similar copy of a convex polygon P with m edges inside a convex polygon Q with n edges can be computed in O(mn ² log n) time. We also show that the combinatorial complexity of the space of all similar copies of P inside Q is O(mn ² ) , and that it can also be computed in O(mn ² log n) time. Received December 11, 1995, and in revised form March 3, 1997.