Although there have been many reports on the preparation and applica- tions of various polymer nanofibers with the electrospinning technique, the under- standing of synthetic parameters in electrospinning remains limited. In this article, we investigate experimentally the influence of solvents on the morphology of the poly(vinyl pyrrolidone) (PVP) micro/nanofibers prepared by electrospinning PVP solution in dif- ferent solvents, including ethanol, dichloromethane (MC) and N,N-dimethylformamide (DMF). Using 4 wt % PVP solutions, the PVP fibers prepared from MC and DMF solvents had a shape like a bead-on-a-string. In contrast, smooth PVP nanofibers were obtained with ethanol as a solvent although the size distribution of the fibers was somewhat broadened. In an effort to prepare PVP nanofibers with small diameters and narrow size distributions, we developed a strategy of using mixed solvents. The exper- imental results showed that when the ratio of DMF to ethanol was 50:50 (w/w), regular cylindrical PVP nanofibers with a diameter of 20 nm were successfully prepared. The formation of these thinnest nanofibers could be attributed to the combined effects of ethanol and DMF solvents that optimize the solution viscosity and charge density of the polymer jet. In addition, an interesting helical-shaped fiber was obtained from 20 wt % PVP solution in a 50:50 (w/w) mixed ethanol/DMF solvent. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3721-3726, 2004

Influence of solvents on the formation of ultrathin uniform poly(vinyl pyrrolidone) nanofibers with electrospinning

A new film of Triton X-100 to incorporate hemoglobin for biosensor fabrication is presented in this paper. In this film, hemoglobin displays a pair of redox peaks in pH 6.0 NaAc–HAc buffer solution with a formal potential of −0.257 V (versus SCE) and shows a thin-layer behavior. Without electron mediator or promoter, the modified electrode has an electrocatalytic activity to the reduction of hydrogen peroxide (H2O2), which shows a linear dependence on the H2O2 concentration ranging from 1.0 × 10−6 to 1.0 × 10−4 mol/L. The detection limit of 3.0 × 10−7 mol/L is estimated when the signal-to-noise ratio is 3. The K M app value of hemoglobin in Triton X-100 film has been determined to be 4.27 mmol/L. Ascorbate, uric acid, dopamine, catechol, cystine and epinephrine will not interfere with the sensitive determination of H2O2.

A third-generation hydrogen peroxide biosensor fabricated with hemoglobin and Triton X-100

In line with the enhancement of antimalarial activities of the current clinical artemisinins against parasites cultured under CO, the artemisinins are unaffected in vitro by carboxyhemoglobin (CO-Hb-Fe(II)) or CO-heme-Fe(II), but are competitively decomposed by Hb-Fe(II) or heme-Fe(II). In the latter case, the heme studies are greatly facilitated by solubilization of the heme in aqueous medium by use of arginine. None of the Hb species has an appreciable effect on artemisone, or on other aminoartemisinins, and antimalarial activities are either less affected or remain essentially unchanged against parasites cultured under standard microaerophilic conditions or under CO. The findings not only indicate that artemisinins do not require Hb-Fe(II) or heme-Fe(II) for promotion of antimalarial activity, but are also important in relation to the therapy of severe/complicated or cerebral malaria.

Interaction of Artemisinins with Oxyhemoglobin Hb–FeII, Hb–FeII, CarboxyHb–FeII, Heme–FeII, and Carboxyheme FeII: Significance for Mode of Action and Implications for Therapy of Cerebral Malaria

A well-defined amphiphilic diblock copolymer, poly [ N -(2-methacryloyloxyethyl) pyrrolidone]- block -poly [glycidyl methacrylate] (PNMP- b -PGMA), was applied to immobilize hemoglobin (Hb) in a simple procedure. The characterization of PNMP- b -PGMA/Hb film was demonstrated by ultraviolet–visible (UV–vis) spectra, atomic force microscopy (AFM), and electrochemical impedance spectroscopy (EIS). The electrochemical behaviors of Hb in PNMP- b -PGMA film have been investigated and a pair of well-defined and nearly reversible cyclic voltammetric peaks for the protein heme Fe(III)/Fe(II) redox couples were observed at about −0.409 V (vs. SCE) in pH 7.0 phosphate buffer solution (PBS). The results showed that the PNMP- b -PGMA film improved the protein loading with the retention of bioactivity and greatly promoted the direct electron transfer between Hb and electrode surface. This PNMP- b -PGMA/Hb film modified electrode also exhibited high electrocatalytic effects towards reduction of nitric oxide (NO). These results indicated the potential applicability of the films as new types of third-generation biosensors or bioreactors based on direct electrochemistry of the proteins.

Direct electrochemistry and electrocatalysis of hemoglobin immobilized in an amphiphilic diblock copolymer film

The complex and indeterminant composition of NOM makes characterization of its redox properties challenging. Approaches that have been taken to address this challenge include chemical probe reactions, potentiometric titrations, chronocoulometry, and voltammetry. In this study, we revisit the use of direct voltammetric methods in aprotic solvents by applying an expanded and refined suite of methods to a large set of NOM samples and model compounds (54 NOM samples from 10 different sources, 7 NOM model compounds, and 2 fresh extracts of plant materials that are high in redox-active quinonoid model compounds dissolved in DMSO). Refinements in the methods of fitting the data obtained by staircase cyclic voltammetry (SCV) provided improved definition of peaks, and square wave voltammetry (SWV), performed under the same conditions as SCV, provided even more reliable identification and quantitation of peaks. Further evidence is provided that DMSO improves the electrode response by unfolding some of the tertiary structure of NOM polymers, thereby allowing greater contact between redox active functional groups and the electrode surface. We averaged experimental peak potentials for all NOM compounds and calculated potentials in water. Average values for Epa1, Epc1, and Ep1 in DMSO were -0.866 ± 0.069, -1.35 ± 0.071, and -0.831 ± 0.051 V vs. Ag/Ag+, and -0.128, -0.613, and -0.0930 V vs. SHE in water. In addition to peak potentials, the breadth of SCV peaks was quantified as a way to characterize the degree to which the redox activity of NOM is due to a continuum of contributing functional groups. The average breadth values were 1.63 ± 0.24, 1.28 ± 0.34, and 0.648 ± 0.15 V for Epa1, Epc1, and Ep1 respectively. Comparative analysis of the overall dataset-from SCV and SWV on all NOMs and model compounds-revealed that NOM redox properties vary over a narrower range than expected based on model compound properties. This lack of diversity in redox properties of NOM is similar to conclusions from other recent work on the molecular structure of NOM, all of which could be the result of selectivity in the common extraction methods used to obtain the materials.

/pdf/electrochemical-characterization-of-natural-organic-matter-4r6ev9t8ar.pdf

Electrochemical characterization of natural organic matter by direct voltammetry in an aprotic solvent

Enhanced electron-transfer reactivity of cytochrome b5 by dimethylsulfoxide and N, N'-dimethylformamide

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Enhanced electron-transfer reactivity of cytochrome b5 by dimethylsulfoxide and N, N'-dimethylformamide