Effect of Cetyltrimethyl Ammonium Bromide on Electrochemical Determination of Dexamethasone

The effect of surfactants on the electrochemical determination of dexamethasone at an edge plane pyrolytic graphite electrode (EPPGE), modified with single‐walled carbon nanotubes (SWNT) has been investigated. The unique electrocatalytic properties of SWNT along with the synergistic adsorption of CTAB on SWNT lead to sensitive voltammetric response of dexamethasone with the reduction peak at ca. ?1195 mV. The limit of detection and sensitivity of dexamethasone is estimated to be 9.1×10^?10 M and 0.727 µA µM^?1 respectively. The SWNT coated EPPGE had good stability and reproducibility. The analytical utility of the developed method was evaluated by applying it for sensing the drug in human body fluids and for the determination of dexamethasone content in several commercially available pharmaceutical preparations. A comparison of the observed results of proposed method with HPLC clearly indicates that the results of both the methods are in good agreement. The product obtained after the reduction of dexamethasone has also been characterized using ¹H NMR and carbonyl group at position 3 has been found to reduce. The method is instant, simple and accurate and can be easily applied for detecting cases of doping.     

Carboxymethylation of corn starch and characterization using asymmetrical flow field-flow fractionation coupled with multiangle light scattering

Asymmetrical flow field-flow fractionation (AsFlFFF) was coupled online with multiangle light scattering (MALS) to study the changes in the molecular weight and the size distribution of the corn starch during carboxymethylation. A corn starch was derivatized with sodium chloroacetate in alcoholic medium under alkaline condition to produce carboxymethyl starches (CMS) having various degrees of substitution (DS). The change in thermal characteristics and granule structure of the native corn starch and CMS were compared using Thermogravimetric analysis and scanning electron microscope. The ionic strength of the carrier liquid (water with 0.02% NaN₃) was optimized by adding 50 mM NaNO₃ to minimize the interactions among the starch molecules and between the starch molecules and the AsFlFFF membrane. A field-programmed AsFlFFF allowed determination of the molecular weight distribution (MWD) of starches within about 25 min. It was found that carboxymethylation of starch results in reduction in the molecular weight due to molecular degradation by the alkaline treatment. The weight-average molecular weight (M_w) was reduced down to about 4.4 × 10⁵ from about 7.2 × 10⁶ when DS was 0.14. It seems AsFlFFF coupled with MALS (AsFlFFF/MALS) is a useful tool for monitoring the changes taking place in the molecular weight and the size of starch during derivatization.     

3D nanogap interdigitated electrode array biosensors

Three-dimensional interdigitated electrodes (IDEs) have been investigated as sensing elements for biosensors. Electric field and current density were simulated in the vicinity of these electrodes as a function of the electrode width, gap, and height to determine the optimum geometry. Both the height and the gap between the electrodes were found to have significant effect on the magnitude and distribution of the electric field and current density near the electrode surface, while the width of the electrodes was found to have a smaller effect on field strength and current density. IDEs were fabricated based on these simulations and their performance tested by detecting C-reactive protein (CRP), a stress-related protein and an important biomarker for inflammation, cardiovascular disease risk indicator, and postsurgical recuperation. CRP-specific antibodies were immobilized on the electrode surface and the formation of an immunocomplex (IC) with CRP was monitored. Electrochemical impedance spectroscopy (EIS) was employed as the detection technique. EIS data at various concentrations (1 pg/mL to 10 μg/mL) of CRP spiked in buffer or diluted human serum was collected and fitted into an equivalent electrical circuit model. Change in resistance was found to be the parameter most sensitive to change in CRP concentration. The sensor response was linear from 0.1 ng/mL to 1 μg/mL in both buffer and 5% human serum samples. The CRP samples were validated using a commercially available ELISA for CRP detection. Hence, the viability of IDEs and EIS for the detection of serum biomarkers was established without using labeled or probe molecules.     

4‐Aminopyridinium 4‐aminobenzoate dihydrate and 4‐aminopyridinium nicotinate

In the title compounds, 4‐aminopyridinium 4‐aminobenzoate dihydrate, C₇H₆NO₂⁻·C₅H₇N₂⁺·2H₂O, (I), and 4‐aminopyridinium nicotinate, C₅H₇N₂⁺·C₆H₄NO₂⁻, (II), the aromatic N atoms of the 4‐aminopyridinium cations are protonated. In (I), the asymmetric unit is composed of two 4‐aminopyridinium cations, two 4‐aminobenzoate anions and four water molecules, and the compound crystallizes in a noncentrosymmetric space group. The two sets of independent molecules of (I) are related by a centre of symmetry which is not part of the space group. In (I), the protonated pyridinium ring H atoms are involved in bifurcated hydrogen bonding with carboxylate O atoms to form an R₁²(4) ring motif. The water molecules link the ions to form a two‐dimensional network along the (10) plane. In (II), an intramolecular bifurcated hydrogen bond generates an R₁²(4) ring motif and inter‐ion hydrogen bonding generates an R₄²(16) ring motif. The packing of adduct (II) is consolidated via N—H...O and N—H...N hydrogen bonds to form a two‐dimensional network along the (10) plane.     

Ethyl β‐{2‐[4‐(dimethylamino)phenyliminomethyl]‐1‐(phenylsulfonyl)indol‐3‐yl}acrylate

The title compound, C₂₈H₂₇N₃O₄S, crystallizes in the centrosymmetric space group P2₁/n, with one mol­ecule in the asymmetric unit. In the indole ring, the dihedral angle between the fused rings is 3.6 (1)°. The phenyl ring of the sulfonyl substituent makes a dihedral angle of 79.2 (1)° with the best plane of the indole moiety. The phenyl ring of the di­methyl­amino­phenyl group is orthogonal to the phenyl ring of the phenyl­sulfonyl group. The dihedral angle formed by the weighted least‐squares planes through the pyrrole ring and the phenyl ring of the di­methyl­amino­phenyl group is 7.8 (1)°. The molecular structure is stabilized by C—H?O and C—H?N interactions.     

A free-volume study on the phase modifications brought out by e-beam and microwave irradiations in PP/NBR and PVC/SAN blends

Partially miscible blends of PP/NBR and PVC/SAN with different compositions have been prepared by solvent casting and characterized by positron annihilation lifetime and differential scanning calorimetry. Phase modification in these systems has been brought about using e-beam and microwave irradiations. These changes have been studied through free-volume monitoring. The changes in free-volume parameters on e-beam and microwave irradiations on the two systems clearly show improved interaction between the blend constituents as a result of cross-linking through hydrogen bond formation. However, the free-volume data do not indicate whether the improvement in miscibility is due to changes at the interface or in the constituents of the blend. We have extended free-volume data to evaluate the hydrodynamic interaction parameter α, which is the measure of excess friction at the interface of the blend. Hydrodynamic interaction parameter shows that e-beam is a better interface stabilizer if the blends contain no polar group/groups and microwave irradiation is a better route to stabilize the interface in the case where the blend contains a polar group.     

Synthesis,characterization, antifungal,antibacterial, and antitumor activities of some tris(pentafluorophenyl)arsenic(V) derivatives

A series of tris(pentafluorophenyl) arsenic(V) derivatives of the type (C₆F₅)₃AsL₂, (C₆F₅)₃As(Cl)(L) [L =  OCOC₆H₄(o‐OH),  OCOC‐(OH)(C₆H₅)₂, and 2‐(6‐OCH₃C₁₀H₆)CH(CH₃) COO ], and cycloarsenates, (R = C₆H₅, p‐CF₃C₆H₄, and p‐OCH₃C₆H₄) have been isolated and characterized by elemental analysis and spectroscopic data (infrared; ¹H, ¹⁹F, and ¹³C NMR). These compounds were screened for their in vitro antifungal, antibacterial, and antitumor activities and were found to show moderate to significant activity. © 2010 Wiley Periodicals, Inc. Heteroatom Chem 21:181–187, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20593     

Di­cyclo­hexyl­ammonium 2,4‐di­chloro­phenoxy­acetate and (2,4‐di­chloro­phenoxy­acetato‐O,O′)bis­(tri­phenylphosphine‐P)silver(I)

The monoclinic cell of di­cyclo­hexyl­ammonium 2,4‐di­chloro­phenoxy­acetate contains four C₁₂H₂₄N⁺·C₅H₈Cl₂O₃^? ion pairs. The ammonium N atom is hydrogen bonded to the oxy­gen ends of two carboxyl groups to form a 12‐membered O—C—O?HNH?O—C—O?HNH ring. In (2,4‐di­chloro­phenoxy­lacetato)­bis­(tri­phenyl­phosphine)silver(I), [Ag(C₈H₅Cl₂O₃)(C₁₈H₁₅P)₂], the carboxyl CO₂ unit chelates to the Ag atom in an anisobidentate manner [Ag—O = 2.436 (2) and 2.517 (2) Å]; the Ag atom shows distorted tetrahedral geometry.     

Cobalt and magnesium ferrite nanoparticles: preparation using liquid foams as templates and their magnetic characteristics

An easy and convenient method for the synthesis of cobalt and magnesium ferrite nanoparticles is demonstrated using liquid foams as templates. The foam is formed from an aqueous mixture of an anionic surfactant and the desired metal ions, where the metal ions are electrostatically entrapped by the surfactant at the thin borders between the foam bubbles and their junctions. The hydrolysis is carried out using alkali resulting in the formation of desired nanoparticles, with the foam playing the role of a template. However, in the formation of ferrites with the formula MFe(2)O(4), where the metal ion and iron possess oxidation states of +2 and +3, respectively, forming a foam from a 1:2 mixture of the desired ionic solutions would lead to a foam composition at variance with the original solution mixture because of greater electrostatic binding of ions possessing a greater charge with the surfactant. In our procedure, we circumvent this problem by preparing the foam from a 1:2 mixture of M(2+) and Fe(2+) ions and then utilizing the in situ conversion of Fe(2+) to Fe(3+) under basic conditions inside the foam matrix to get the desired composition of the metal ions with the required oxidation states. The fact that we could prepare both CoFe(2)O(4) and MgFe(2)O(4) particles shows the vast scope of this method for making even multicomponent oxides. The magnetic nanoparticles thus obtained exhibit a good crystalline nature and are characterized by superparamagnetic properties. The magnetic features observed for CoFe(2)O(4) and MgFe(2)O(4) nanoparticles are well in accordance with the expected behaviors, with CoFe(2)O(4) particles showing higher blocking temperatures and larger coercivities. These features can easily be explained by the contribution of Co(2+) sites to the magnetocrystalline anisotropy and the absence of the same from the Mg(2+) ions.     

Bis(N,N‐di­methyl­thio­carbamoyl­thio)­acetic acid

Bis(N,N‐di­methyl­thio­carbamoyl­thio)­acetic acid, [(CH₃)₂NC(=S)S]₂CHC(=O)OH or C₈H₁₄N₂O₂S₄, exists as a centrosymmetric hydrogen‐bonded dimer [O?O 2.661 (3) Å].