Competitive capacitive biosensing technique (CCBT): A novel technique for monitoring low molecular mass analytes using glucose assay as a model study

A novel technique for monitoring of low molecular mass analytes using a flow-injection capacitive biosensor is presented. The method is based on the ability of a small molecular mass analyte to displace a large analyte–carrier conjugate from the binding sites of an immobilized biorecognition element with weak affinity to both compounds. A model study was performed on glucose as the small molecular mass analyte. In the absence of glucose, binding of a glucose polymer or a glycoconjugate to concanavalin A results in a capacitance decrease. Upon introduction of glucose, it displaces a part of the bound glucose polymer or glycoconjugate leading to a partial restoration of capacitance. Experimental results show that the change in capacitance depends linearly on glucose concentration within the range from 1.0 × 10⁻⁵ to 1.0 × 10⁻¹ M, corresponding to 1.8 μg ml⁻¹ to 18 mg ml⁻¹ in a logarithmic plot, with a detection limit of 1.0 × 10⁻⁶ (0.18 μg ml⁻¹) under optimized conditions. In addition, by modifying the molecular mass of the glucose polymer, amount of biorecognition element, and buffer composition, we were able to tune the analyte-sensing range. The developed technique has the benefits of expanded dynamic range, high sensitivity, and excellent reusability.     

Organic thermal stabilizers for rigid poly(vinyl chloride). Part XII: N-phenyl-3-substituted-5-pyrazolone derivatives

N-phenyl-3-substituted-5-pyrazolone derivatives have been examined as thermal stabilizers or co-stabilizers for rigid PVC in air, at 180 °C. Their high stabilizing efficiency is detected by their high induction period values (T_s) when compared with some of the common reference stabilizers used industrially, such as dibasic lead carbonate, calcium-zinc soap and n-octyl tin mercaptide. Blending these derivatives with some of the reference stabilizers in different ratios had a synergistic effect on both the induction period and the dehydrochlorination rate.A probable mechanism for the stabilizing mode of N-phenyl-3-substituted-5-pyrazolone derivatives has been proposed. The stabilizing efficiency is attributed at least partially to the ability of the organic stabilizer to be incorporated in the polymeric chains, thus disrupting the chain degradation.     

Friezes

The construction of friezes is motivated by the theory of cluster algebras. It gives, for each acyclic quiver, a family of integer sequences, one for each vertex. We conjecture that these sequences satisfy linear recursions if and only if the underlying graph is a Dynkin or an Euclidean (affine) graph. We prove the “only if” part, and show that the “if” part holds true for all non-exceptional Euclidean graphs, leaving a finite number of finite number of cases to be checked. Coming back to cluster algebras, the methods involved allow us to give formulas for the cluster variables in case Am and ; the novelty is that these formulas use 2 by 2 matrices over the semiring of Laurent polynomials generated by the initial variables (which explains simultaneously positivity and the Laurent phenomenon). One tool involved consists of the SL₂-tilings of the plane, which are particular cases of T-systems of Mathematical Physics.     

Three-dimensional thermal shock problem of generalized thermoelastic half-space

A three-dimensional model of the generalized thermoelasticity with one relaxation time is established. The resulting non-dimensional coupled equations together with the Laplace and double Fourier transforms techniques are applied to a specific problem of a half space subjected to thermal shock and traction free surface. The inverses of Fourier transforms and Laplace transforms are obtained numerically by using the complex inversion formula of the transform together with Fourier expansion techniques. Numerical results for the temperature, thermal stress, strain and displacement distributions are represented graphically.     

Vibrational Spectroscopic Analysis of L,D-Dipeptides

Raman and infrared spectra of Boc-D-Leu-L-Leu-OMe, Boc-L-Ile-D-aIle-OMe and its N-deuterated derivative have been obtained. Normal mode frequencies on the models of these dipeptides have been calculated and the conformationally sensitive amide I, II, III and V modes are compared with the experimentally observed frequencies. The calculated frequencies are in good agreement with the observed frequencies. It is observed that the amide frequencies in these dipeptides are not very sensitive to their backbone conformation. This is in contrast to the well established conformational dependence of the amide modes in peptides, polypeptides and proteins. The normal mode calculations on these peptides also show absence of mixing in amide I and II modes, and hence lack of appreciable splitting in these modes due to transition dipole coupling.

     

A physicochemical study of Schiff base metal complexes derived from α-benzylmonoxime

Summary Metal complexes of general formula [M(DDE)·nH₂O]· nH₂O and [M(DDB)·nH₂O] [where M = Co^II, Ni^II, Cu^II, Pd^II and UO ₂ ²⁺ ; n = 0–4; DDE and DDB are the anion of bis(1,2-diphenyl-1-hydroxyimino-2-ethylidine)-1,2-diaminoethane and bis(l,2-diphenyl-l-hydroxy-imino-2-ethylidine)-1,4-diaminobenzene, respectively] were prepared and characterized by i.r. electromagnetic and n.m.r. spectroscopy and magnetic measurements.     

Free radicals in γ-irradiated poly-α-methylstyrene

Electron spin resonance (ESR) spectra were observed at ?160°C and at room temperature for γ-irradiated poly-α-methylstyrene. The spectrum observed at room temperature has been attributed to the radical species while that at ?160°C results from the same radical and superposition of the spectrum due to the radical ?H₂-C(CH₃)(C₆H₅)-. The radicals which are stable at room temperature could be used to graft vinyl acetate.     

p-Benzoquinone-tin polycondensates as stabilisers for polybutadiene rubber against photo-degradation

p-Benzoquinone-tin derivatives, obtained by polycondensation of the quinone and SnCl₄ in the absence of solvent, have been investigated as uv stabilisers for polybutadiene rubber. Intrinsic viscosity measurements have shown the greater efficiency of these products relative to phenyl salicylate which is commonly used in industry. The stabilising efficiency increases as the tin content of the stabiliser increases. A mechanism based on the involvement of both the quinone part of the stabiliser and the SnSn bonds in scavenging the radical species formed, as well as blocking the radical sites on the polymeric chains, has been developed. Moreover, it has been shown that prior oxidation of the stabilisers of higher tin content can afford complete protection of rubber from degradation by uv irradiation.     

Selective nitrosation of guanazine: preparation of azidoaminotriazole and nitrosoguanazine anion-Cu(II) complexes

Guanazine (3,4,5-triamino-1,2,4-triazole) is selectively nitrosated on C-NH₂ to produce nitrosoguanazine (3-nitrosamino-4,5-diamino-1,2,4-triazole). The nitrosoguanazine is used to prepare 5-azido-3-amino-1,2,4-triazole and nitrosoguanazine anion-Cu(II) complexes.