Enhanced stabilization of aerosol-OT surfactant monolayer upon interaction with small amounts of bovine serum albumin at the air-water interface

An investigation is made of the influence from small amounts of the protein bovine serum albumin (BSA) on the lateral organization of low molecular weight surfactant sodium bis-2-ethylhexyl sulfosuccinate (AOT) at the air-water interface. Surface pressure (pi - A), surface potential (deltaV - A) and Brewster angle microscopy (BAM) experiments were carried out, with particular emphasis on the monolayer stability under successive compression-expansion cycles. AOT monolayer is not stable at the air-water interface, which means that the majority of AOT molecules go into the aqueous subphase as monomers and/or normal micelles. When a waiting time elapses between spreading and compression, the surfactant monolayer tends to reorganize partially at the air-water interface, with a monolayer expansion being observed for waiting times as large as 12 h. The incorporation of very small amount of BSA (10(-9)M) at the interface, also inferred from BAM, increases the monolayer stability as revealed by pi - A and deltaV - A results. For a waiting time of circa 3 h, the mixed monolayer reaches its maximum stability. This must be related to protein (and/or protein-surfactant complexes) adsorbed onto the AOT monolayer, thus altering the BSA conformation to accommodate its hydrophobic/hydrophilic residues. Furthermore, the effects from such small amounts of BSA in the monolayer formation and stabilization mean that the AOT monolayer responds cooperatively to BSA.     

Horseradish peroxidase extraction and purification by aqueous two-phase partition

The effect of poly(ethyleneglycol) (PEG) molecular weight, system pH, and sodium chloride concentration on the partitioning behavior of horseradish peroxidase fromArmomcia rusticana root extract was investigated in poly(ethyleneglycol)/sodium phosphate systems. PEG molecular weight strongly affects the enzyme partition coefficient, whereas pH variation from 5.5 to 8.0 has little effect. The addition of sodium chloride (8% w/w) to a PEG 1540/phosphate system, pH 7.0, raises the peroxidase partition coefficient 13.5-fold without important changes in that of total horseradish root proteins. Moreover, these conditions allow direct homogenization of theA. rusticana roots with the selected aqueous two-phase system with the clear top phase containing over 90% of the enzyme and the purification factor being 4.8.     

Photochromic polymers: effects of structure and environment on photoresponsiveness

In this review paper the photoresponsiveness of photochromic macromolecules under different structural and environmental conditions is discussed with reference to results from the authors' laboratories. Polypeptides, in particular poly(L -glutamic acid) and poly(L -lysine), with spirobenzopyrane side chains show photoinduced conformational variations which are amplified by addition of organic acids or bases to hexafluoro-2-propanol (HFP) solutions. Thus combination of light and environment effects allows modulation of order–disorder conformational transitions. Such photoindiced conformational changes are not observed in the case of macromolecules with a hydrocarbon main chain and azobenzene or stilbene side chains, obtained by polymerization of acrylic monomers. However, even in these systems structural variations affect the dependence of optical properties on irradiation. Moreover, the combination of organic solvents and water shows that polymer solubility can be modulated by light.     

Upper and lower bounds to polarizabilities and van der Waals forces I. General theory

Upper and lower bounds to polarizabilities, and long-range interactions of atoms and molecules are derived using operator inequalities. The formulae for the dispersion and the three-body non-additive forces are given in terms of the S(k), related by sum rules to properties of the separated systems. Some known approximations are obtained but with additional information about their nature, as well as several new inequalities. Their interest is that they give explicit and rigorous bounds involving quantities available from experimental data.     

Layer-by-layer self-assembled chitosan/poly(thiophene-3-acetic acid) and organophosphorus hydrolase multilayers

The aim of this study is to immobilize an enzyme, namely, organophosphorus hydrolase (OPH), and to detect the presence of paraoxon, which is an organophosphorus compound, using the layer-by-layer (LbL) deposition technique. To lift the OPH from the solid substrate, a pair of polyelectrolytes (positively charged chitosan (CS) and negatively charged poly(thiophene-3-acetic acid) (PTAA)) were combined. These species were made charged by altering the pH of the solutions. LbL involved alternate adsorption of the oppositely charged polyions from dilute aqueous solutions onto a hydrophilic quartz slide. This polyion cushion was held together by the electrostatic attraction between CS and PTAA. The growing process was monitored by fluorescence spectroscopy. OPH was then adsorbed onto the five-bilayer CS/PTAA system. This five-bilayer macromolecular structure compared to the solid substrate rendered stability to the enzyme by giving functional integrity in addition to the ability to react with paraoxon solutions. The ultimate goal is to use such a system to detect the presence of organophosphorus compounds with speed and sensitivity using the absorption and fluorescence detection methodologies.     

Improved hollow-fibre membranes for dye-affinity chromatography

Hollow-fibre membranes with different degrees of surface hydrophilicity were obtained by grafting mixtures of glycidyl methacrylate (GMA) and dimethyl acrylamide (DMAA) in various proportions, and Cibacron Blue F3G-A was attached to them through ammonia or glucamine spacers. Membrane hydrophilicity increased with the amount of dimethyl acrylamide in the grafted polymer. As the hydrophilicity increased the permeability decreased from 352 mL/cm2 min MPa for membranes grafted with GMA with ammonia spacer to 12.7 mL/cm2 min MPa for membranes grafted with GMA/DMAA 1/3 with glucamine spacer. Membranes grafted with GMA/DMAA 1/3 with ammonia spacer showed the best performance for BSA and lysozyme adsorption: maximum capacity was 15.3 +/- 2.2 mg BSA/mL membrane and 58.3 +/- 6.6 mg lysozyme/mL membrane while dissociation constants were 0.27 +/- 0.16 and 0.13 +/- 0.12 mg/mL, respectively. Over 80% of adsorbed proteins could be eluted with 2 M NaCl + 20% isopropanol in 20 mM sodium phosphate buffer, pH 7.0.     

Simplerealizations of generalized measurements in quantum mechanics

This paper discusses the approach to the analysis of measurements in quantum mechanics which is based on a set of "detection operators" forming a resolution of identity. The expectation value of each of these operators furnishes the counting rate at a detector for any object state that is prepared. "Predictable measurements" are those for which there is a representation in which only one element of each diagonal matrix representing each operator is not zero. A set of commuting detection operators defines the class of "spectral measurements", which may be either predictable or not. An even more general definition of measurement may be given by abandoning the requirement of commutativity of the detection operators. In this case one cannot define an observable which corresponds to a single self-adjoint operator, which violates the standard theory of quantum mechanical measurement. Simple experimental realizations of each of these classes of measurement are suggested.     

Immobilization of uricase in layer-by-layer films used in amperometric biosensors for uric acid

The layer-by-layer technique was exploited to immobilize the enzyme uricase onto indium tin oxide substrates coated with a layer of Prussian Blue. Uricase layers were alternated with either poly(ethylene imine) or poly(diallyldimethylammoniumchloride), and the resulting films were used as amperometric biosensors for uric acid. Biosensors with optimum performance had a limit of detection of 0.15 μA μmol l⁻¹ cm⁻² with a linear response between 0.1 and 0.6 μM of uric acid, which is sufficient for use in clinical tests. Bioactivity was preserved for weeks, and there was negligible influence from interferents, as detection was carried out at 0.0 V vs saturated calomel electrode. This paper is dedicated to the memory of Francisco C. Nart.     

Regioselective photocyclization of (e)‐2‐(2,3,6‐trichlorostyryl)‐benzothiazole and synthesis of 3,4‐dichloro‐ and 4‐chlorobenzothiazolo[3,2‐α]quinolinium chlorides: A synthetic and theoretical study

A high degree of regioselectivity is observed in the photochemically induced cyclization of (E)‐2‐(2,3,6‐trichlorostyryl)benzothiazole ( 1a ). According to the proposed mechanism, this compound was expected to afford two products, 3,4‐dichloro‐ and 1,4‐dichlorobenzothiazolo[3,2‐α]quinolinium chlorides ( 4a and 4a' , respectively). However, this reaction produced 3,4‐dichlorobenzazolo[3,2‐α]quinolinium chloride ( 4a ) as the sole product. On the other hand, irradiation of (E)‐2‐(2,3,5‐trichlorostyryl)benzothiazole ( 1b ) failed to produce the expected 1,3‐dichlorobenzothiazolo[3,2‐α]quinolinium chloride ( 4b ). Furthermore, (E)‐2,3‐difluorostrylbenzothiazole ( 1c ) also failed to give the corresponding 1‐fluorobenzothiazolo[3,2‐α]quinolinium fluoride ( 4c ). Interestingly, the irradiation of 2,6‐dichlorostyrylbenzothialole ( 1d ) produced 4‐chlorobenzothiazolo[3,2‐α]quinolinium chloride ( 4d ) in excellent yield. This paper presents the results of these investigations and a mechanistic rationale for the outcome of this reaction based on steric arguments and theoretical studies using a combination of molecular mechanics (MM+) and semiempirical quantum mechanical calculations (PM3/RHF/CI). Two‐dimensional high field nmr methods were employed to make complete assignments of the proton and carbon spectra of all new compounds.     

A kinetic study of the reaction of N,N-dimethylanilines with 2,2-diphenyl-1-picrylhydrazyl radical: a concerted proton-electron transfer?

The reactivity of the 2,2-diphenyl-1-picrylhydrazyl radical (dpph*) toward the N-methyl C-H bond of a number of 4-X-substituted- N, N-dimethylanilines (X = OMe, OPh, CH 3, H) has been investigated in MeCN, in the absence and in the presence of Mg(ClO 4) 2, by product, and kinetic analysis. The reaction was found to lead to the N-demethylation of the N, N-dimethylaniline with a rate quite sensitive to the electron donating power of the substituent (rho (+) = -2.03). With appropriately deuterated N, N-dimethylanilines, the intermolecular and intramolecular deuterium kinetic isotope effects (DKIEs) were measured with the following results. Intramolecular DKIE [( k H/ k D) intra] was found to always be similar to intermolecular DKIE [( k H/ k D) inter]. These results suggest a single-step hydrogen transfer mechanism from the N-C-H bond to dpph* which might take the form of a concerted proton-electron transfer (CPET). An electron transfer (ET) step from the aniline to dpph* leading to an anilinium radical cation, followed by a proton transfer step that produces an alpha-amino carbon radical, appears very unlikely. Accordingly, a rate-determining ET step would require no DKIE or at least different inter and intramolecular isotope effects. On the other hand, an equilibrium-controlled ET is not compatible with the small slope value (-0.22 kcal (-1) K (-1)) of the log k H/Delta G degrees plot. Furthermore, the reactivity increases by changing the solvent to the less polar toluene whereas the reverse would be expected for an ET mechanism. In the presence of Mg (2+), a strong rate acceleration was observed, but the pattern of the results remained substantially unchanged: inter and intramolecular DKIEs were again very similar as well as the substituent effects. This suggests that the same mechanism (CPET) is operating in the presence and in the absence of Mg (2+). The significant rate accelerating effect by Mg (2+) is likely due to a favorable interaction of the Mg (2+) ion with the partial negatively charged alpha-methyl carbon in the polar transition state for the hydrogen transfer process.