Polymerization of styrene using N-(p-tolyl)-N′,N′-diethyldithiocarbamoylacetamide as photoiniferter

N-(p-Tolyl)-N′,N′-diethyldithiocarbamoylacetamide was prepared and used as a new photoiniferter for polymerization of styrene in bulk under UV light. This photopolymerization showed some specific character, i.e., molecular weights of resulting polymers increase with reaction time and monomer conversion, respectively. The reversible reaction between growing radical and dormant species was confirmed by electron spin resonance using 2-methyl-2-nitrosopropane as a spin trapping agent. Thus, the end functionalized polymer, N,N-diethyldithiocarbamoyl-terminated polystyrene, reinitiated photopolymerization of methyl methacrylate and vinyl acetate to form block copolymers. The molecular weight distribution about 2.7 indicated that the polymerization is not a strictly living radical polymerization. © 1996 John Wiley & Sons, Inc.     

Electron-Nuclear Multiple Resonance on Stable and Transient Radicals

The physical principles underlying steady-state electron-nuclear double resonance (ENDOR) and electron-nuclear-nuclear triple resonance (TRIPLE) experiments on radicals in solution are discussed. The gain in spectral resolution achievable by these techniques, as compared with standard ESR, allows hyperfine coupling constants to be measured even for large and low-symmetry radicals. ENDOR/TRIPLE is applied to cation radicals related to bacterial photosynthesis. The measured hyperfine couplings are interpreted by means of the all-valence electron MO method RHF-INDO/SP. Information about the spatial structure of chromophores in the reaction centers of photosynthetic bacteria, Rb. sphaeroides and Rps. viridis, is obtained from an analysis of the spin density distribution and from minimization of the total energy. The results are compared with recently available structural data of the primary donor obtained from X-ray diffraction experiments. The spin density distribution in the primary donor cation radical P⁺₉₆₀, which consists of two bacteriochlorophyll b molecules, is discussed in terms of symmetry and perturbations from the protein environment.     

An Environmentally Benign,Highly Efficient Catalytic Reduction of p‐Nitrophenol using a Nano‐Sized Nickel Catalyst Supported on Silica‐Alumina

A green and effective method is reported for the reduction of p‐nitrophenol to p‐aminophenol using a nano‐sized nickel catalyst supported on silica‐alumina in the presence of hydrazine hydrate as an alternative source of hydrogen. It was found that nickel loaded on a silica‐alumina support is a very effective catalyst in the hydrogenation of p‐nitrophenol to p‐aminophenol. Thus it attained 100% conversion in only 69 seconds instead of 260 seconds for commercial Raney nickel. In addition, the possibility to reuse it more than one time with great efficiency gives it another advantage over commercial Rainey nickel which cannot be used more than once. This economical and environmentally friendly method provides a potentially new approach for the synthesis of the intermediate product of paracetamol in industry, which overcomes the drawbacks of the known reduction methods. The prepared catalysts were fully characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X‐ray (EDX), and electron spin resonance (ESR) tehniques.     

EPR Studies of V‐ATPase with Spin‐Labeled Inhibitors DCC and Archazolid: Interaction Dynamics with Proton Translocating Subunit c

Vacuolar‐type H⁺‐ATPases (V‐ATPases) have gained recent attention as highly promising anticancer drug targets, and therefore detailed structural analyses and studies of inhibitor interactions are very important research objectives. Spin labeling of the V‐ATPase holoenzyme from the tobacco hornworm Manduca sexta and V‐ATPase in isolated yeast (Saccharomyces cerevisiae) vacuoles was accomplished by two novel methods involving the covalent binding of a (2,2,6,6‐tetramethylpiperidin‐1‐yl)oxyl (TEMPO) derivative of N,N′‐dicyclohexylcarbodiimide (DCC) to the essential glutamate residue in the active site and the noncovalent interaction of a radical analogue of the highly potent inhibitor archazolid, a natural product from myxobacteria. Both complexes were evaluated in detail by electron paramagnetic resonance (EPR) spectroscopic studies and double electron–electron resonance (DEER) measurements, revealing insight into the inhibitor binding mode, dynamics, and stoichiometry as well as into the structure of the central functional subunit c of these medicinally important hetero‐multimeric proton‐translocating proteins. This study also demonstrates the usefulness of natural product derived spin labels as tools in medicinal chemistry.     

The Extraction of Divalent Manganese,Cobalt, Copper,Zinc, and Cadmium from Hydrochloric Acid Solutions by Tri-n-octylamine

Abstract

The distribution of divalent manganese, cobalt, copper, zinc, and cadmium between hydrochloric acid solutions and solutions of tri-n-octylamine (TOA, R₃N) in benzene has been investigated under different conditions. It is found that the extraction of these divalent metals by TOA proceeds as MCl₂(aq) + 2R₃NHCl(org) ? (R₃NH)₂MCl₄(org). The electronic, electron spin resonance, and infrared spectral results indicate that all the complexes formed in the organic phases are in a tetrahedral arrangement. Further, the stability constants of the aqueous chloro complexes of divalent manganese, cobalt, copper, and zinc are determined on the basis of the equilibrium equation.     

Reactivity Analysis of New Multivalent Electrophilic Probes for Affinity Labeling of Carbohydrate Binding Proteins

We have designed and synthesized six different multivalent electrophiles as carbohydrate affinity labeling probes. Evaluation of the reactivity of the electrophiles against peanut agglutinin (PNA) and Ricinus communis agglutinin (RCA) showed that p- and m-aryl sulfonyl fluoride are effective protein reactive groups that label carbohydrate binding lectins in a ligand-dependent fashion at a nanomolar probe concentration. Analysis of the selectivity of affinity labeling in the presence of excess BSA as a nonspecific protein indicated that m-arylsulfonyl fluoride is a more selective protein-reactive group, albeit with attenuated reactivity. Further analysis showed that the labeling efficiency of the multivalent electrophilic probes can be improved by employing reaction conditions involving 25 °C instead of typically employed 4 °C. Both isomers of arylsulfonyl fluoride groups together represent promising affinity labels for target identification studies that could serve as more efficient alternatives to photoreactive groups.     

Effects of Fe2+/Fe3+ Binding to Human Frataxin and Its D122Y Variant,as Revealed by Site-Directed Spin Labeling (SDSL) EPR Complemented by Fluorescence and Circular Dichroism Spectroscopies

Frataxin is a highly conserved protein whose deficiency results in the neurodegenerative disease Friederich’s ataxia. Frataxin’s actual physiological function has been debated for a long time without reaching a general agreement; however, it is commonly accepted that the protein is involved in the biosynthetic iron-sulphur cluster (ISC) machinery, and several authors have pointed out that it also participates in iron homeostasis. In this work, we use site-directed spin labeling coupled to electron paramagnetic resonance (SDSL EPR) to add new information on the effects of ferric and ferrous iron binding on the properties of human frataxin in vitro. Using SDSL EPR and relating the results to fluorescence experiments commonly performed to study iron binding to FXN, we produced evidence that ferric iron causes reversible aggregation without preferred interfaces in a concentration-dependent fashion, starting at relatively low concentrations (micromolar range), whereas ferrous iron binds without inducing aggregation. Moreover, our experiments show that the ferrous binding does not lead to changes of protein conformation. The data reported in this study reveal that the currently reported binding stoichiometries should be taken with caution. The use of a spin label resistant to reduction, as well as the comparison of the binding effect of Fe²⁺ in wild type and in the pathological D122Y variant of frataxin, allowed us to characterize the Fe²⁺ binding properties of different protein sites and highlight the effect of the D122Y substitution on the surrounding residues. We suggest that both Fe²⁺ and Fe³⁺ might play a relevant role in the context of the proposed FXN physiological functions.     

Synthesis, characterization, and properties of poly(2- and 3-aminophenol) and poly(2- and 3-aminophenol)-Cu(II) materials

Summary Poly(2-aminophenol) and poly(3-aminophenol) were synthesized from the respective monomers by using CuCl₂ × 2H₂O and ammonium persulfate as oxidizing agents in HCl(aq). The materials were characterized by FT-IR, X- ray electron spectroscopy (XPS), electron spin resonance (ESR) and nuclear magnetic resonance (NMR) spectroscopy, elemental analysis, thermal stability, and electrical conductivity. The poly(2-aminophenol) presented a higher copper(II) content than that of poly(3-aminophenol), moreover as shown by ESR measurements, Cu appears homogeneously dispersed in the former, poly(2-amino phenol), while it seems not to be the case in the latter. The electrical conductivity did not depend on the conditions of synthesis as well as of the hydroxyl groups position. The results indicate that the polymers have several branched rings and their thermal stability increased by the presence of the copper ions into the polymer matrix. Received: 7 August 2002/Revised version: 8 November 2002/ Accepted: 12 November 2002 Correspondence to B. L. Rivas     

Constituents of Amomum tsao-ko and their radical scavenging and antioxidant activities

Constituents of the fruit of Amomum tsao-ko were investigated following a preliminary screening of the antioxidant activity of several extracts of the fruit of this plant that showed that the dichloromethane extract and the ethyl acetatesoluble and water-soluble fractions of the 70% aqueous acetone extract had higher activity than α-tocopherol and butylated hydroxytoluene (BHT). Eleven compounds were isolated from the ethyl acetate-soluble fraction, and their structures were elucidated as (+)-hannokinol (1), meso-hannokinol (2), (+)-epicatechin (3), (−)-catechin (4), β-sitosterol (5), β-sitosterol 3-O-glucoside (6), 2,6-dimethoxyphenol (7), protocatechualdehyde (8), protocatechuic acid (9), vanillic acid (10), and p-hydroxybenzoic acid (11) based on mass and various nuclear magnetic resonance (NMR) spectroscopic techniques. This is the first isolation of epicatechin and catechin from the genus Amomum. The radical scavenging activity of the isolated compounds was evaluated using 1,1-diphenyl-2-picrylhydrazyl (DPPH) and colorimetric and electron spin resonance (ESR) analyses. The antioxidant activity of the compounds was also determined based on the oxidative stability index (OSI). The catechins and catechol derivatives showed strong activities in both the DPPH radical scavenging activity and antioxidant activity assays.     

Studies on melt spinning. VI. Simulation of draw resonance using Newtonian and power law viscosities

Draw resonance, a periodic variation of spin line diameter in unstable melt spinning, was measured for its wave form under 34 different spinning conditions for PET and PP. In and attempt to simulate the measured wave form, the equations of continuity and momentum for the isothermal melt spinning of power law fluids were solved for their limit cycle solutions expressed in the time variations in the cross-sectional area at the take-up. Power law exponent p and draw down ratio ψ_w uniquely define the solution. Theoretical curves were superposed on the experimental amplitude-versus-ψ_w diagram and oscillation period-versus-ψ_w diagram to assign p value to each experimental point. Excellent agreement between theory and experiment was obtained with PET in that p values were nearly independent of ψ_w and of the diagram used in the determination of the p value, amplitude diagram, or oscillation period diagram. Motion pictures (16mm) of the side profiles of the pulsing spinline showed good agreement with the theoretical side profiles constructed from the corresponding limit cycle solution. It was proposed that the stability of melt spinning has no direct equivalence to the spinnability of fluids.     

Preparation and characterization of thin films of the poly(p‐phenylene vinylene) semiconducting polymer

Conjugated polymers have been the subject of many studies because of their widespread applications in electronic and optoelectronic devices. Poly(p‐phenylene vinylene) is a leading semiconducting polymer in optical applications. This work is focused on the development of thin films of poly(p‐phenylene vinylene) by spin coating and their characterization with Fourier transform infrared spectroscopy, X‐ray diffraction, and scanning electron microscopy to understand their changes. An empirical model has been developed to show the effect of the variables—the spin speed, polymer concentration, and spin time—on the film thickness. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of valence electron spin polarization on the physical properties of CuCl2‐filled poly(vinylidene fluoride) as a microwave modulator

Infrared and optical spectra, differential thermal analysis, dc electrical resistivity, magnetic susceptibility, electron spin resonance, and microwave response of CuCl₂‐filled poly(vinylidene fluoride) (PVDF) films, over the filler mass fraction range 0.05 ≤ W ≤ 0.4, were measured. The infrared spectra evidenced the presence of β‐phase, for all of the filler levels with main deformations of 20% (for W = 0.25) and 30% (for other filler levels) head‐to‐head and tail‐to‐tail units, which were considered as polaron and bipolaron defects. Optical activity was mainly influenced by PVDF structure. Differential thermal analysis revealed dipole relaxation and premelting endothermic peaks. A quasi–one‐dimensional interpolaron hopping was thought to proceed in the direct current electric conduction, with a hopping distance less than the distance between two successive head‐to‐head sites. A temperature‐independent Pauli paramagnetic behavior was observed, confirming the presence of induced energy bands due to CuCl₂ filling. Most of the observed electron spin resonance signals were antisymmetric, with superimposed repels due to the hyperfine interactions characterizing PVDF. The obtained linear dependence of the isotropic hyperfine coupling constant (ΔA` ), for Cu(II), on average g‐factor, implied that ΔA` is a measure of the valence electron spin polarization. An octahedral or distorted octahedral configuration was suggested for Cu(II). The present system is a good microwave modulator. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 771–781, 1999     

Synthesis,structural studies,and antimicrobial activity of polymeric copper(II) tetrathiocyanato diargentate(I) complexes with some acylhydrazones

Copper(II) complexes of the type Cu[Ag(SCN)₂]₂·L (where L is acetophenone benzoyl hydrazone, acetophenone isonicotinoyl hydrazone, acetophenone salicyloyl hydrazone, acetophenone anthraniloyl hydrazone, p‐hydroxyl acetophenone benzoylhydrazone, p‐hydroxyl acetophenone isonicotinoyl hydrazone, p‐hydroxyl acetophenone salicyloyl hydrazone, or p‐hydroxyl acetophenone anthraniloyl hydrazone) were synthesized and characterized. All the complexes were polymeric and insoluble in common organic solvent and were nonelectrolytes. The ligands were coordinated through >C?O and >C?N? groups. All the SCN groups present in the complexes acted as bridges between two metal centers, resulting in a polymeric structure of the Lewis acid Cu[Ag(SCN)₂]₂ as well as its complexes. Electronic and electron spin resonance spectra suggested a square planar geometry for the Lewis acid and an elongated tetragonally distorted octahedral geometry for all the complexes. The powder X‐ray diffraction parameters for acetophenone salicyloyl hydrazone and p‐hydroxyl acetophenone anthraniloyl hydrazone complexes corresponded to orthorhombic and tetragonal crystal lattices, respectively. The complexes showed a fair degree of antifungal activity against Rizoctonia sp., Aspergillus sp., and Stemphylium sp. and moderate antibacterial activity against Clostridium sp. (Gram‐positive) and Pseudomonas sp. (Gram‐negative). The complexes were more active than the parent ligands. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Understanding the role of d-Allulose and soy protein addition in pectin gels

d -Allulose (a monosaccharide and C3 epimer of fructose), one of the common rare sugars is getting attention due to its low caloric values. In this study, d -Allulose was used as a replacement of sucrose at different ratios (d -Allulose/Sucrose: 35/0, 20/15, 10/25, 0/35) to formulate pectin-based soft confectionery gels. Soy protein isolate was also added to increase the protein content. Physical properties, such as hardness, moisture content, pH, and color, were measured for the gels. Higher hardness values were obtained for the soy protein containing gels due to pectin–soy protein interaction (p < 0.05). Also, higher moisture content was observed in soy protein containing gels (p < 0.05). In addition, nuclear magnetic resonance T₂ relaxation times were measured at low field (~0.5 T) to determine how the water distribution in the samples changed and to observe how d -Allulose affected the polymer–water interactions. The study also showed that the presence of d -Allulose increased the crystallization tendency (% crystallinity of 7.9) of the pectin gels. X-ray diffraction results showed the d -allulose peaks at 33.76 and 48.68^oθ. Morphologies of the gels were also examined by scanning electron microscope. Sugar type and soy protein isolate addition were found to have significant impact on the gel formulations.     

Alpha‐Synuclein Binds to the Inner Membrane of Mitochondria in an α‐Helical Conformation

The human alpha‐Synuclein (αS) protein is of significant interest because of its association with Parkinson's disease and related neurodegenerative disorders. The intrinsically disordered protein (140 amino acids) is characterized by the absence of a well‐defined structure in solution. It displays remarkable conformational flexibility upon macromolecular interactions, and can associate with mitochondrial membranes. Site‐directed spin‐labeling in combination with electron paramagnetic resonance spectroscopy enabled us to study the local binding properties of αS on artificial membranes (mimicking the inner and outer mitochondrial membranes), and to evaluate the importance of cardiolipin in this interaction. With pulsed, twofrequency, double‐electron electron paramagnetic resonance (DEER) approaches, we examined, to the best of our knowledge for the first time, the conformation of αS bound to isolated mitochondria.     

Structural change in diamond by hydrogen plasma treatment at room temperature

The structural change of diamond induced by hydrogen plasma exposure at room temperature, and its thermal stability, were investigated using electron spin resonance (ESR), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) techniques. ESR observation revealed that it gave rise to a highly defective structure (spin concentration of 10²⁰ cm^{− 3}), which is very similar to the structure of hydrogenated amorphous carbon (a-C : H) confirmed by XPS and FTIR. Post-annealing was also carried out to clarify the thermal stability of the defects. The number of spin centers decreased with increasing annealing temperature, and eventually, the defective structure changed to a graphitic one by annealing at 800 °C.     

Distribution in correlation times for rotational diffusion of spin probes in polymers

Electron spin resonance spectra of poly(vinyl acetate) (PVAc) and plasticised PVAc doped with nitroxide spin probes show a double-peak feature at temperatures immediately below T_{50 G}. This can be explained on the basis that probe tumbling occurs with a distribution of correlation times τ_R arising from a distribution of free volume within the polymeric matrix. The two-component e.s.r. spectra arise because the distribution in τ_R of the probes straddles the value (c. 3 × 10^?9 s) which marks the change-over from fast- to slow-motion spectra. The implications of the existence of a distribution of τ_R values for calculations based on the assumption of a single value are examined. It is concluded that when probe tumbling is slow the error in τ_R could be significant, but for rapid tumbling (motionally narrowed spectra) the error is likely to be insignificant.     

Orthogonal Translation Meets Electron Transfer: In Vivo Labeling of Cytochrome c for Probing Local Electric Fields

Cytochrome c (cyt c), a redox protein involved in diverse fundamental biological processes, is among the most traditional model proteins for analyzing biological electron transfer and protein dynamics both in solution and at membranes. Studying the role of electric fields in energy transduction mediated by cyt c relies upon appropriate reporter groups. Up to now these had to be introduced into cyt c by in vitro chemical modification. Here, we have overcome this restriction by incorporating the noncanonical amino acid p‐cyanophenylalanine (pCNF) into cyt c in vivo. UV and CD spectroscopy indicate preservation of the overall protein fold, stability, and heme coordination, whereas a small shift of the redox potential was observed by cyclic voltammetry. The C≡N stretching mode of the incorporated pCNF detected in the IR spectra reveals a surprising difference, which is related to the oxidation state of the heme iron, thus indicating high sensitivity to changes in the electrostatics of cyt c.     

Copolymerization of methyl methacrylate and allyl acetate Part I. Rate of reaction

Free radical bulk copolymerization of methyl methacrylate (MMA) and allyl acetate (AAc) has been investigated using electron spin resonance (ESR) and FT–near infrared (FTNIR) spectroscopy. Data are used to evaluate the rate constants. The mole fraction of AAc plays an important role in the copolymerization of these two monomers. AAc not only delays the Trommsdorff effect but also increases the onset of percentage total conversion at which the Trommsdorff region begins. With AAc fraction 0.5 and higher, no Trommsdorff effect was observed. Inclusion of AAc into copolymer structure mainly occurs in the Trommsdorf region or when the AAc fraction in the comonomer feed is dominant. This is associated with a drop in the concentration of propagating radicals. However, ESR spectra indicate that the MMA propagating radical is predominant during the reaction. In the comonomer mixtures where a Trommsdorff region can be observed, the addition of AAc does not produce any significant change in k_p and k_t in the steady state region. Major changes in k_p and k_t are observed after the gel point and glassy state, respectively. © 2001 Society of Chemical Industry