Stability-Indicating LC Method for the Determination of Olmesartan in Bulk Drug and in Pharmaceutical Dosage Form

A novel stability-indicating LC assay method was developed and validated for quantitative determination of olmesartan in bulk drugs and in pharmaceutical dosage form in the presence of degradation products generated from forced degradation studies. An isocratic, reversed phase LC method was developed to separate the drug from the degradation products, using an Ace5-C18 (250 mm × 4.6 mm, 5 μm) column, and 50 mM ammonium acetate (pH-5.5 by acetic acid) and acetonitrile (70:30 v/v) as a mobile phase. The detection was carried out at the wavelength of 235 nm. The olmesartan was subjected to stress conditions of hydrolysis (acid, base), oxidation, photolysis and thermal degradation. Degradation was observed for olmesartan in acid, base and in 30% H₂O₂ conditions. The drug was found to be stable in the other stress conditions attempted. The degradation products were well resolved from the main peak. The percentage recovery of olmesartan ranged from (99.89 to 100.95%) in pharmaceutical dosage form. The developed method was validated with respect to linearity, accuracy (recovery), precision, specificity and robustness. The forced degradation studies prove the stability-indicating power of the method.

     

A Stability-Indicating LC Method for Lumefantrine

A simple, rapid, and precise method is developed for the quantitative determination of lumefantrine (Lume) in active pharmaceutical ingredient (API). A chromatographic separation of Lume and its degradants were achieved with an X-Terra RP18, 250 × 4.6 mm, and 5 μ analytical column using buffer–acetonitrile (30:70 v/v). The buffer used in mobile phase contains 0.1 M sodium perchlorate monohydrate in double distilled water pH adjusted to 2.1 with trifluoroacetic acid. The instrumental settings are flow rate of 0.5 mL (L), column temperature at 35 °C, and detector wavelength of 235 nm using a photodiode array detector. Lume was exposed to thermal, photolytic, hydrolytic and oxidative stress conditions, and the stressed samples were analysed by the proposed method. Peak homogeneity data of Lume obtained by photodiode array detection, in the stressed sample chromatograms, demonstrated the specificity of the method for estimation in the presence of degradants. The described method shows excellent linearity over a range of 10–200 μg L⁻¹ for Lume. The correlation coefficient is 1. The relative standard deviation of peak area for six measurements is always less than 2% between days. The proposed method was found to be suitable and accurate for quantitative determination and stability study of Lume in API.

     

Synthesis of Oxygen‐Containing Spirobipyrrolidinium Salts for High Conductivity Room Temperature Ionic Liquids

Synthesis of ionic liquids (IL) based on oxygen‐containing spirobipyrrolidinium salts with BF₄, BF₃C₂F₅, and NTf₂ as counterions was undertaken. Their physical and electrochemical properties were evaluated for suitability for Room Temperature Ionic Liquids (RTIL) application. Reduction in melting point occurred upon exchange of C(2) by an O‐atom of spirobipyrrolidinium, without sacrificing the electrochemical stability; while introduction of alkyl groups between the N‐ and O‐atoms led to incorporation of asymmetry, and hence reduced the melting points, and viscosity.     

Effect of Matrix Treatment on Spectroscopic Properties of HCl Catalysed Sol-Gel Glasses Containing Coumarin Laser Dyes

Coumarin 1, Coumarin 2 and Coumarin 120 are embedded in transparent sol-gel glass samples prepared by sol-gel process using dip method. The sol-gel matrix is given dip treatment with Methanol /Distilled Water (50/50vol) for 1 to 16h before dipping into dye solution. The effect of dipping time of matrix in Methanol/ Distilled Water on spectroscopic properties of coumarin dye doped glass samples has been studied. The Optical Density (OD) at absorption maximum wavelength and Fluorescence Intensity (FI) at fluorescence maximum wavelength of all coumarin dyes increase with the time of dipping of the sol-gel sample. These absorption/fluorescence properties of coumarin dyes in sol-gel glass matrices are compared with its respective properties in methanolic solution in acidic environment. The cause of these changes in OD/FI with dipping time is discussed by taking into account the absorption / fluorescence of dye in acidified methanol.     

Functionalization/passivation of porous graphitic carbon with di-tert-amylperoxide

Porous graphitic carbon (PGC) particles were functionalized/passivated in situ in packed beds at elevated temperature with neat di-tert-amylperoxide (DTAP) in a column oven. The performance of these particles for high performance liquid chromatography (HPLC) was assayed before and after this chemistry with the following analytes: benzene, toluene, ethyl benzene, n-propyl benzene, n-butyl benzene, p-xylene, phenol, 4-methylphenol, phenetole, 3,5-xylenol, and anisole. After the first functionalization/passivation, the retention factors, k, of these compounds decreased by about 5% and the number of theoretical plates (N) increased by ca. 15%. These values of k then remained roughly constant after a second functionalization/passivation but a further increase in N was noticed. In addition, after each of the reactions, the peak asymmetries decreased by ca. 15%, for a total of ca. 30%. The columns were then subjected twice to methanol at 100°C for 5h at 1 mL/min. After these stability tests, the values of k remained roughly constant, the number of plates increased, which is favorable, and the asymmetries rose and then declined, where they remained below the initial values for the unfunctionalized columns. Functionalized and unfunctionalized particles were characterized by scanning electron microscopy and BET measurements, which showed no difference between the functionalized and unfunctionalized materials, and X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry (ToF-SIMS), where ToF-SIMS suggested some chemical differences between the functionalized and unfunctionalized materials. In particular ToF-SIMS suggested that the expected five-carbon fragments from DTAP exist at higher concentrations on DTAP-functionalized PGC. First principle calculations on model graphitic surfaces suggest that the first addition of a DTAP radical to the surface proceeds in an approximately isothermal or slightly favorable fashion, but that subsequent DTAP additions are then increasingly thermodynamically favorable. Thus, this analysis suggests that the direct functionalization/passivation of PGC with DTAP is plausible. Chemometric analyses of the chromatographic and ToF-SIMS data are also presented.     

Highly efficient dye-sensitized solar cells by TiCl4 surface modification of ZnO nano-flower thin film

Journal of Solid State Electrochemistry - In dye-sensitized solar cells (DSSCs), the semiconductor photo-anode film plays a significant role in enhancing the overall power conversion efficiency....     

DirichletL-function and power series for Hurwitz zeta function

For 0 < α < 1, letζ(s, α) be the Hurwitz zeta function and let ζ₁ (s, α) = ζ(s, α) -α? s. For a fixeds, we developζ ₁(s,α) as a power series in α in the complex circle ¦α¦ < 1. If $$\sum\limits_{\chi \left( {\bmod q} \right)} {L\left( {s,\chi } \right)L\left( {s',\bar \chi } \right)} = \frac{{\phi \left( q \right)}}{{q^{s + s'} }}\sum\limits_{k/q} \mu \left( {\frac{q}{k}} \right)\left( {\sum\limits_{a = 1}^k {\left( {\frac{k}{a}} \right)^{\operatorname{Re} s + \operatorname{Re} s'} + Q\left( {s,s',k} \right)} } \right)$$ , we obtain an asymptotic expansion for Q(k) =Q(s,s′,k) using the power series forζ ₁(s,α)     

Effects of physical aging,crystallinity, and orientation on the enzymatic degradation of poly(lactic acid)

The effects of physical aging, degree of crystallinity, and orientation of poly(lactic acid) (PLA) were studied using differential scanning calorimetry (DSC) and wide angle X-ray scattering (WAXS). The samples of PLA with 96% [L] and 4% [D] contents were prepared by injection molding. The physical aging of PLA strongly depended on time and temperature. The change of rate of physical aging was very fast initially and slowed down as time increased. The enzymatic degradation of PLA was carried out with proteinase K at 37°C at a pH value of 8.6 in a Tris/HCl buffer solution. The enzymatic degradation rate was found to decrease as a function of physical aging (i.e., excess enthalpy relaxation). The rate of enzymatic degradation of PLA decreased with the increase in crystallinity. A threshold was observed when the heat of fusion was less than 20 J/g. The weight loss of PLA with a low level of crystallinity had no apparent change during any period of testing time. The rates of enzymatic degradation of stretched and injection-molded specimens were comparable. © 1996 John Wiley & Sons, Inc.     

Dimeric Fe (II, III) complex of quinoneoxime as functional model of PAP enzyme: Mössbauer, magneto-structural and DNA cleavage studies

Purple acid phosphatase, (PAP), is known to contain dinuclear Fe₂ ^?+?2,?+?3 site with characteristic Fe^?+?3 ← Tyr ligand to metal charge transfer in coordination. Phthiocoloxime (3-methyl-2-hydroxy-1,4-naphthoquinone-1-oxime) ligand L, mimics (His/Tyr) ligation with controlled and unique charge transfers resulting in valence tautomeric coordination with mixed valent diiron site in model compound Fe-1: [μ-OH-Fe₂ ^?+?2,?+?3 (o-NQ_CH3ox) (o-NSQ_CH3ox)₂ (CAT) H₂O]. Fe-2: [Fe^?+?3(o-NQ_CH3ox) (p-NQ_CH3ox)₂]₂ a molecularly associated dimer of phthiocoloxime synthesized for comparison of charge transfer. ⁵⁷Fe Mössbauer studies was used to quantitize unusual valences due to ligand in dimeric Fe-1 and Fe-2 complexes which are supported by EPR and SQUID studies. ⁵⁷Fe Mössbauer spectra for Fe-1 at 300 K indicates the presence of two quadrupole split asymmetric doublets due to the differences in local coordination geometries of [Fe^?+?3]_A and [Fe^?+?2]_B sites. The hyperfine interaction parameters are δ _A = 0.152, (ΔE _Q)_A = 0.598 mm/s with overlapping doublet at δ _B = 0.410 and (ΔE _Q)_B = 0.468 mm/s. Due to molecular association tendency of ligand, dimer Fe-2 possesses 100% Fe^?+?3(h.s.) hexacoordinated configuration with isomer shift δ = 0.408 mm/s. Slightly distorted octahedral symmetry created by NQ_CH3ox ligand surrounding Fe^?+?3(h.s.) state generates small field gradient indicated by quadrupole split ΔE _Q = 0.213 mm/s. Decrease of isomer shifts together with variation of quadrupole splits with temperature in Fe-1 dimer compared to Fe-2 is result of charge transfers in [Fe₂ ^?+?2,?+?3 SQ] complexes. EPR spectrum of Fe-1 shows two strong signals at g ₁ = 4.17 and g ₂ = 2.01 indicative of S = 3/2 spin state with an intermediate spin of Fe^?+?3(h.s.) configuration. SQUID data of $\chi _m^{{\rm corr}} \mbox{.T}$ were best fitted by using HDVV spin pair model S = 2, 3/2 resulting in antiferromagnetic exchange (J = ?13.5 cm^???1 with an agreement factor of R = 1.89 × 10^???5). The lower J value of antiferromagnetic exchange leads to Fe⁺³μ-(OH) Fe^?+?2 bridging in Fe-1 dimer instead of μ-oxo bridge. The intermolecular association through H-bonds may lead to weakly coupled antiferromagnetic interaction between two Fe-2 molecules having Fe^?+?3(h.s.) centers. Using S = 5/2, 5/2 spin pair model we obtained best-fitted parameters such as J = ?12.4 cm^???1, g = 2.3 with R = 3.58 × 10^???5. Synthetic strategy results in non-equivalent iron sites in Fe-1 dimer analogues to PAP enzyme hence its reconstitution results in pUC-19 DNA cleavage activity, as physiological functionality of APase. It is compared with nuclease activity of Fe-2 RAPase.     

High pressure effect on structural and mechanical properties of some LnO (Ln=Sm, Eu, Yb) compounds

The structural and mechanical properties of LnO (Ln=Sm, Eu, Yb) compounds have been investigated using a modified interionic potential theory, which includes the effect of Coulomb screening. We predicted a structural phase transition from NaCl (B₁)- to CsCl (B₂)-type structure and elastic properties in LnO compounds at very high pressure. The anomalous properties of these compounds have been correlated in terms of the hybridisation of f-electrons of the rare earth ion with conduction band and strong mixing of f-states of lanthanides with the p-orbital of neighbouring chalcogen ion. For EuO, the calculated transition pressure, bulk modulus and lattice parameter are close to the experimental data. The nature of bonds between the ions is predicted by simulating the ion-ion (Ln-Ln and Ln-O) distances at high pressure. The second order elastic constants along with shear modulus and Young's modulus, elastic anisotropy and Poisson's ratio are also presented for these oxides.