A new route to synthesize high degree polythiophene in a room temperature melt medium

Conducting polymers suffer from folds and kinks because of random nucleation and solvation of a free radical cation to yield a cross linked/disordered polymer and therefore a solvent free electrochemical polymerization in a room temperature melt medium is adopted to yield a high degree polymer with high electronic conductivity. Electropolymerization of thiophene was performed on platinum/ITO substrates using cyclic voltametry or galvenostatic mode in chloroaluminate room temperature melt medium to obtain a reddish brown free standing film which can be peeled off from the electrode surface after a minimum of 10 cycles. The conductivity was found to be around 102 S/cm. The degree of polymerization was calculated to be around 44 from IR studies. A layered structure supportive for high degree of polymerization was witnessed from potential step technique. From UV spectra the charge carriers were found to be bipolarons. The morphology of the film was found to be crystalline from SEM and XRD studies. Capacitative impedance properties for doped samples were interpreted from impedance spectroscopy.

The Effect of Tacticity on the Conformational Properties of Poly(1-olefin sulfone)s

The effect of tacticity on the conformational properties of poly(olefin sulfone)s was studied. Tactic polymers, prepared from racemic thiirane monomers using chiral inititators were compared with atactic polymers prepared by free radical co-polymerisation of the 1-olefin with sulfur dioxide. Analysis of the XRD patterns showed that the tactic polymers formed more ordered structures in the bulk with longer layer spacings, consistent with a model in which their side chains meet at the tips in contrast with the atactic polymers whose side chains interdigitate. 13C MAS nmr experiments suggest that as tacticity increases so too does the proportion of C-S bonds in the gauche conformation, however the proportion of S-C bonds in the trans conformation falls, in contrast to a reported molecular mechanics study. Finally, DSC measurements on the polymers with longer side chains showed the presence of two endotherms on heating, illustrating definite liquid crystalline behaviour.

Polymer-supported phosphoramidites: highly efficient and recyclable catalysts for asymmetric hydrogenation of dimethylitaconate and dehydroamino acids and esters

Several novel phosphoramidites have been prepared by reaction of the primary amines para-vinylaniline, ortho-anisidine, 2-methoxyphenyl(4-vinylbenzyl)amine, 8-aminoquinoline and 3-vinyl-8-aminoquinoline with (S)-1,1'-bi-2-naphthylchlorophosphite, in the presence of base. Rhodium(l) complexes of these phosphoramidites catalyse the asymmetric hydrogenation of dimethylitaconate and dehydroamino acids and esters giving ee values up to 95%. Soluble non-cross linked polymers of the para-vinylaniline and 3-vinyl-8-aminoquinoline-based phosphoramidites have been prepared by free radical co-polymerisation with styrene in the presence of AIBN as initiator. The corresponding [Rh(COD)](+) complexes serve as recyclable catalysts for the asymmetric hydrogenation dimethylitaconate and dehydroamino acids and esters to give ee values up to 80%. (C) 2003 Elsevier Science Ltd. All rights reserved.

Molecular detection of exercise-induced free radicals following ascorbate prophylaxis in type 1 diabetes mellitus: a randomised controlled trial

Aims/hypothesis: Patients with type 1 diabetes mellitus are more susceptible than healthy individuals to exercise-induced oxidative stress and vascular endothelial dysfunction, which has important implications for the progression of disease. Thus, in the present study, we designed a randomised double-blind, placebo-controlled trial to test the original hypothesis that oral prophylaxis with vitamin C attenuates rest and exercise-induced free radical-mediated lipid peroxidation in type 1 diabetes mellitus. Methods: All data were collected from hospitalised diabetic patients. The electron paramagnetic resonance spectroscopic detection of spin-trapped a-phenyl-tert-butylnitrone (PBN) adducts was combined with the use of supporting markers of lipid peroxidation and non-enzymatic antioxidants to assess exercise-induced oxidative stress in male patients with type 1 diabetes (HbA1c 7.9±1%, n=12) and healthy controls (HbA1c 4.6±0.5%, n=14). Following participant randomisation using numbers in a sealed envelope, venous blood samples were obtained at rest, after a maximal exercise challenge and before and 2 h after oral ingestion of 1 g ascorbate or placebo. Participants and lead investigators were blinded to the administration of either placebo or ascorbate treatments. Primary outcome was the difference in changes in free radicals following ascorbate ingestion. Resuts: Six diabetic patients and seven healthy control participants were randomised to each of the placebo and ascorbate groups. Diabetic patients (n=12) exhibited an elevated concentration of PBN adducts (p<0.05 vs healthy, n=14), which were confirmed as secondary, lipid-derived oxygen-centred alkoxyl (RO•) radicals (a nitrogen=1.37 mT and aßhydrogen=0.18 mT). Lipid hydroperoxides were also selectively elevated and associated with a depression of retinol and lycopene (p<0.05 vs healthy). Vitamin C supplementation increased plasma vitamin C concentration to a similar degree in both groups (p<0.05 vs pre-supplementation) and attenuated the exercise-induced oxidative stress response (p<0.05 vs healthy). There were no selective treatment differences between groups in the primary outcome variable. Conclusions/ interpretation: These findings are the first to suggest that oral vitamin C supplementation provides an effective prophylaxis against exercise-induced free radical-mediated lipid peroxidation in human diabetic blood.

Increased cerebral output of free radicals during hypoxia: implications for acute mountain sickness?

Bailey DM, Taudorf S, Berg RMG, Lundby C, McEneny J, Young IS, Evans KA, James PE, Shore A, Hullin DA, McCord JM, Pedersen BK, Moller K. Increased cerebral output of free radicals during hypoxia: implications for acute mountain sickness? Am J Physiol Regul Integr Comp Physiol 297: R1283-R1292, 2009. First published September 2, 2009; doi: 10.1152/ajpregu.00366.2009.-This study examined whether hypoxia causes free radical-mediated disruption of the blood-brain barrier (BBB) and impaired cerebral oxidative metabolism and whether this has any bearing on neurological symptoms ascribed to acute mountain sickness (AMS). Ten men provided internal jugular vein and radial artery blood samples during normoxia and 9-h passive exposure to hypoxia (12.9% O-2). Cerebral blood flow was determined by the Kety-Schmidt technique with net exchange calculated by the Fick principle. AMS and headache were determined with clinically validated questionnaires. Electron paramagnetic resonance spectroscopy and ozone-based chemiluminescence were employed for direct detection of spin-trapped free radicals and nitric oxide metabolites. Neuron-specific enolase (NSE), S100 beta, and 3-nitrotyrosine (3-NT) were determined by ELISA. Hypoxia increased the arterio-jugular venous concentration difference (a-v(D)) and net cerebral output of lipid-derived alkoxyl-alkyl free radicals and lipid hydroperoxides (P

Antioxidants in health and disease

Free radical production occurs continuously in all cells as part of normal cellular function. However, excess free radical production originating from endogenous or exogenous sources might play a role in many diseases. Antioxidants prevent free radical induced tissue damage by preventing the formation of radicals, scavenging them, or by promoting their decomposition. This article reviews the basic chemistry of free radical formation in the body, the consequences of free radical induced tissue damage, and the function of antioxidant defence systems, with particular reference to the development of atherosclerosis.

Further evidence for double-strand breaks originating from a paired radical precursor from studies of oxygen fixation processes

By using a fast reaction technique which employs H2S gas as a fast-reacting chemical repair agent, it is possible to measure the competition kinetics between chemical repair reactions and oxygen fixation reactions in model DNA and cellular systems. In plasmid pBR322 DNA irradiated with electrons, we have compared the oxygen fixation reactions of the free radical precursors that lead to the production of single-strand (SSBs) and double-strand breaks (DSBs). For the oxygen-dependent fixation of radical damage leading to SSBs, a second-order rate constant of 2.3 x 10(8) dm(3) mol(-1) s(-1) was obtained compared to 8.9 x 10(7) dm(3) mol(-1) s(-1) for DSBs. The difference is in general agreement with predictions from a multiple-radical model where the precursor of a DSB originates from two radicals. The fixation of this precursor by oxygen will require both radicals to be fixed for the DSB to be formed, which will have slower kinetics than that of single free-radical precursors of SSBs. (C) 1999 by Radiation Research Society.

Oxygen solubility in ionic liquids based on 1-alkyl-3-methylimidazolium cations

This work presents the results of oxygen solubility in ionic liquids based on 1-alkyl-3-methylimidazolium cations. Solubility measurements have been carried out in gasometric apparatus at 22, 50 and 90 degrees C under atmospheric pressure. We report the Henry's constants. In general the occurrence of carbon-fluorine bonds and carbon-hydrogen bonds in ionic liquids (ILs) which can create hydrogen bonds with dissolved oxygen, significantly affects the growth of value of solubility constant K-H. Additionally, the stability of ILs towards molecular oxygen was tested. All ILs used in this study were stable in the presence of oxygen and free-radical initiator.

Polymerisable squaramide receptors for anion binding and sensing

A novel series of polymerisable squaramides has been synthesised in high yields using simple chemical reactions, and evaluated in the binding of anionic species. These vinyl monomers can be used as functional building blocks in co-polymerisations with a plethora of co-monomers or cross-linkers, grace to their compatibility with free-radical polymerisation reactions. Aromatic substituted squaramides were found to be the strongest receptors, while binding of certain anions was accompanied by a strong colour change, attributed to the de-protonation of the squaramide. The best performing squaramide monomers were incorporated in molecularly imprinted polymers (MIPs) targeting a model anion and their capacities and selectivity were evaluated by rebinding experiments. Polymers prepared using the new squaramide monomers were compared to urea based co-polymers, and were found to contain up to 80% of the theoretical maximum number of binding sites, an exceptionally high value compared to previous reports. Strong polymer colour changes were observed upon rebinding of certain anions, equivalent to those witnessed in solution, paving the way for application of such materials in anion sensing devices.



Graphical abstract: Polymerisable squaramide receptors for anion binding and sensing

Levoglucosan formation mechanisms during cellulose pyrolysis

Levoglucosan is one important primary product during cellulose pyrolysis either as an intermediate or as a product. Three available mechanisms for levoglucosan formation have been studied theoretically in this paper, which are free-radical mechanism; glucose intermediate mechanism; and levoglucosan chain-end mechanism. All the elementary reactions included in the pathway of every mechanism were investigated; thermal properties including activation energy, Gibbs free energy, and enthalpy for every pathway were also calculated. It was concluded that free-radical mechanism has the highest energy barrier during the three levoglucosan formation mechanisms, glucose intermediate mechanism has lower energy barrier than free-radical mechanism, and levoglucosan chain-end mechanism is the most reasonable pathway because of the lowest energy barrier. By comparing with the activation energy obtained from the experimental results, it was also concluded that levoglucosan chain-end mechanism fits better with the experimental data for the formation of levoglucosan. © 2013 Elsevier B.V. All rights reserved.

Carreira Alkynylations with Paraformaldehyde. A Mild and Convenient Protocol for the Hydroxymethylation of Complex Base-SensitiveTerminal Acetylenes via Alkynylzinc Triflates

A new synthetic protocol for the hydroxymethylation of terminal acetylenes is described that involves stoichiometric Carreira alkynylation with solid paraformaldehyde (HO[CH₂O]_nH) in PhMe at 60 ^oC. Significantly, the method can be successfully applied on acetylenes that possess base-sensitive ester functionality and heterocyclic rings that readily undergo metallation. While N-methylephedrine (NME) is generally the best Zn(OTf)₂-coordinating ligand for promoting hydroxymethylation, TMEDA can serve as a replacement.

On the antioxidant properties of erythropoietin and its association with the oxidative-nitrosative stress response to hypoxia in humans

Aim: The aim of this study was to examine if erythropoietin (EPO) has the potential to act as a biological antioxidant and determine the underlying mechanisms.

Methods: The rate at which its recombinant form (rHuEPO) reacts with hydroxyl (HO center dot), 2,2-diphenyl-1-picrylhydrazyl (DPPH center dot) and peroxyl (ROO center dot) radicals was evaluated in-vitro. The relationship between the erythopoietic and oxidative-nitrosative stress response to poikilocapneic hypoxia was determined separately in-vivo by sampling arterial blood from eleven males in normoxia and following 12 h exposure to 13% oxygen. Electron paramagnetic resonance spectroscopy, ELISA and ozone-based chemiluminescence were employed for direct detection of ascorbate (A(center dot-)) and N-tert-butyl-a-phenylnitrone spin-trapped alkoxyl (PBN-OR) radicals, 3-nitrotyrosine (3-NT) and nitrite (NO2-).

Results: We found rHuEPO to be a potent scavenger of HO center dot (k(r) = 1.03-1.66 x 10(11) M-1 s(-1)) with the capacity to inhibit Fenton chemistry through catalytic iron chelation. Its ability to scavenge DPPH. and ROO center dot was also superior compared to other more conventional antioxidants. Hypoxia was associated with a rise in arterial EPO and free radical-mediated reduction in nitric oxide, indicative of oxidative-nitrosative stress. The latter was confirmed by an increased systemic formation of A(center dot-), PBN-OR, 3-NT and corresponding loss of NO2- (P <0.05 vs. normoxia). The erythropoietic and oxidative-nitrosative stress responses were consistently related (r =-0.52 to 0.68, P <0.05).

Conclusion: These findings demonstrate that EPO has the capacity to act as a biological antioxidant and provide a mechanistic basis for its reported cytoprotective benefits within the clinical setting.

Caracterização e transformação de Lenhosulfonatos de Eucalyptus globulus

Os lenhosulfonatos representam um sub-produto formado durante o cozimento ao sulfito ácido, sendo queimados para a regeneração da base e recuperação de energia. No entanto, os lenhosulfonatos são também considerados uma importante matéria-prima para a produção de vários produtos de valor acrescentado. Os objectivos principais deste trabalho foram contribuir para uma melhor compreensão sobre a caracterização química e estrutural dos lenhosulfonatos do Eucalyptus globulus, assim como, para complementar a informação disponível sobre a síntese e a caracterização estrutural e térmica de materiais poliméricos obtidos a partir de compostos modelo dos produtos de oxidação dos lenhosulfonatos. O licor de cozimento ao sulfito foi analisado em termos do teor de cinzas, extractáveis, compostos voláteis, açúcares e lenhosulfonatos. O teor de cinzas e açúcares no licor de cozimento é muito elevado, tendo sido necessário purificar o mesmo (2,8-13,8 % e 3,2-9,1 %, respectivamente). A análise dos açúcares mostrou uma quantidade considerável de pentoses, sendo o açúcar predominante a xilose. Os lenhosulfonatos foram purificados, isolados e caracterizados por química molhada (titulação potenciométrica e oxidação com permanganato), análise elementar, espectroscopia de ultravioleta/visível (UV/Vis), espectroscopia de infravermelho de transformada de Fourier (FTIR), espectroscopia de ressonância magnética nuclear de protão (RMN de 1H) e carbono (RMN de 13C), espectrometria de massa de ionização por electrospray (ESI-MS), cromatografia de permeação em gel (GPC), termogavimetria (TGA) e calorimetria diferencial de varrimento (DSC). Os lenhosulfonatos são constituídos principalmente por unidades S, são parcialmente sulfonados e possuem um peso molecular relativamente baixo (Mw = 1250-2400 Da). A ruptura das ligações β-O-4 e α-O-4 da lenhina do Eucalyptus globulus após cozimento ao sulfito ácido originam olígomeros de baixo peso molecular cuja estrutura foi elucidada por RMN 1D/2D e ESI-MS. A degradação térmica dos lenhosulfonatos apresentou dois máximos de degradação a 188-190ºC e a 315-380ºC. As curvas de DSC mostraram um pico endotérmico para temperaturas inferiores a 130ºC e um pico exotérmico a 300-500ºC. Os lenhosulfonatos foram despolimerizados na presença de oxigénio molecular em meio alcalino. Os produtos de oxidação principais foram o aldeído siríngico, a vanilina, o ácido vanílico e o ácido siríngico. A adição do catalisador (sal de cobre) promoveu a oxidação dos lenhosulfonatos aumentando o rendimento dos aldeídos aromáticos (< 50%). A presença de açúcares nos lenhosulfonatos teve um efeito negativo no rendimento dos produtos de oxidação principais. Alguns compostos modelo dos produtos de oxidação dos lenhosulfonatos foram polimerizados por poliadição (catiónica e radicalar) e policondensação. Os monómeros e os polímeros foram caracterizados por espectroscopia de infravermelho de transformada de Fourier e reflectância total atenuada (FTIR-ATR), RMN em solução e no estado sólido, UV/Vis no estado sólido, GPC, difracção de raios-X (XRD), TGA e DSC. Os compostos modelo estudados foram os estirenos metoxi-substituídos (p-metoxiestireno e 3,4-dimetoxiestireno) e os ácidos hidroxi aromáticos metoxi-substituídos (ácido vanílico e ácido siríngico). O 3,4-dimetoxiestireno foi ainda copolimerizado com o éter isobutil vinílico e os seus copolímeros foram desmetilados, assim como, o poli(p-metoxiestireno) e o poli(3,4-dimetoxiestireno). A polimerização catiónica do p-metoxiestireno e 3,4-dimetoxiestireno é mais rápida e mais completa do que a polimerização radicalar produzindo polímeros com pesos moleculares elevados. O poli(p-metoxiestireno) (Mw = 235000 Da) possui um peso molecular maior do que o poli(3,4-dimetoxiestireno) (Mw = 18800 Da). A estabilidade térmica e a temperatura de transição vítrea diminuiram com a presença do segundo grupo metoxilo. A desmetilação dos homopolímeros foi bem sucedida, tendo sido corroborada por FTIR-ATR e RMN. A policondensação do ácido siríngico foi dificultada pela presença do segundo grupo metoxilo, tendo sido necessário adicionar uma maior quantidade do agente de condensação devido a factores estéricos. O poli(ácido vanílico) e poli(ácido siríngico) são insolúveis na maior parte dos solventes orgânicos, sendo parcialmente solúveis em clorofórmio, ácido triflúoracético, 1,1,2,2- tetracloroetano, dimetilsulfóxido, tetrahidrofurano, N,N’-dimetilformamida e 1,1,1,3,3,3-hexaflúor-2-propanol. A estabilidade térmica diminuiu com a presença do segundo grupo metoxilo e os dois polímeros não exibiram temperatura de transição vítrea. O poli(ácido vanílico) e poli(ácido siríngico) apresentaram uma estrutura muito cristalina (grau de cristalinidade 70% e 50%, respectivamente). O segundo grupo metoxilo aumentou o valor da absorvância, mas a forma do espectro de UV/Vis foi similar. A polimerização catiónica do éter isobutil vinílico resultou na produção de um polímero muito viscoso com peso molecular elevado (Mw = 20400 Da). A degradação térmica do polímero ocorreu em várias gamas de temperatura e foi completa (0% de resíduo a 800ºC). A copolimerização catiónica do 3,4-dimetoxiestireno com o éter isobutil vinílico foi realizada com proporções diferentes 80:20, 50:50 e 20:80. Os copolímeros apresentaram uma viscosidade elevada e um peso molecular baixo (Mw = 2000-4000 Da) que aumentou com a quantidade de éter isobutil vinílico. A degradação térmica dos copolímeros ocorreu também em várias gamas de temperatura, sendo a sua degradação completa (0,9-1,5% de resíduo a 800ºC). A desmetilação dos copolímeros não foi bem sucedida, tendo sido confirmada por FTIR-ATR e RMN.

Electrochemical evaluation of total antioxidant capacity of beverages using a purine-biosensor

In this paper, it was evaluated the total antioxidant capacity (TAC) of beverages using an electrochemical biosensor. The biosensor consisted on the purine base (guanine or adenine) electro-immobilization on a glassy carbon electrode surface (GCE). Purine base damage was induced by the hydroxyl radical generated by Fenton-type reaction. Five antioxidants were applied to counteract the deleterious effects of the hydroxyl radical. The antioxidants used were ascorbic acid, gallic acid, caffeic acid, coumaric acid and resveratrol. These antioxidants have the ability to scavenger the hydroxyl radical and protect the guanine and adenine immobilized on the GCE surface. The interaction carried out between the purinebase immobilized and the free radical in the absence and presence of antioxidants was evaluated by means of changes in the guanine and adenine anodic peak obtained by square wave voltammetry (SWV). The results demonstrated that the purine-biosensors are suitable for rapid assessment of TAC in beverages.

The kinetics and induced decomposition on the thermal decomposition of hydroperoxides /

This project is focussed on the thermsLl decomposition of t-butyl hydroperoxide and sec-butyl hydroperoxide at 120°C to 160°C in three alcohol solvents. These are methanol, ethajiol and isopropyl alcohol. The aim of the project was to examine the process of induced decomposition. Thermal decomposition of t-hutyl hydroperoxide and sec-butyl hydroperoxide indicate that these reactions have first-order kinetics with activation energies on the order of 20 to 28 K cal/mole, Styrene was used as a free radical trap to inhibit the induced decomposition. The results permitted calculation of how much induced decomposition occurred in its absence. The experimental resvilts indicate that the induced decomposition is important for t-butyl hydroperoxide in alcohol solvents, as shown by both the reaction rate suid product studies. But sec-butyl hydroperoxide results show that the concerted mechanism for the interaction of two sec-butylperoxy radicals occurs in addition to the induced decomposition. Di-sodium E.D,T.A. was added to reduce possible effects of trace transition metal ion .impurities. The result of this experiment were not as expected. The rate of hydroperoxide decomposition was about the same but was zero-order in hydroperoxide concentration.