Temperature dependent gene expression induced by PNIPAM-based copolymers: potential of hyperthermia in gene transfer

The objective of this work was to obtain gene delivery vectors with high efficiency induced by application of local hyperthermia. As a building construct for the polyplex particles, block copolymers were used, in which one block represents poly(ethyleneimine) (PEI) and another block a statistical copolymer of poly(N-isopropylacryamide) (PNIPAM) and different hydrophilic monomers (acrylamide or vinylpyrrolidinone). The block copolymers were synthesizized by radical polymerization of the corresponding monomers directly onto PEI. The complexation of DNA with these copolymers led to small, charge neutral particles, which aggregated upon increasing the temperature from 37 degrees C to 42 degrees C. This aggregation was found to be responsible for the enhanced transfection efficiency of these formulations under hyperthermic conditions. Gene expression in cells treated by hyperthermia was found to be nearly 2 orders of magnitude higher in comparison to cells transfected at physiological temperature. The mechanism by which hyperthermia influences the gene transfection efficiency is proposed.     

Protection against oxidative protein damage induced by metal-catalyzed reaction or alkylperoxyl radicals: comparative effects of melatonin and other antioxidants

Melatonin is a well-known hydroxyl radical (*OH) scavenger that protects DNA and lipids from free radical attack. In this paper, we studied the ability of melatonin to prevent oxidative damage to bovine serum albumin (BSA) induced by two different paradigms: the metal-catalyzed oxidation (MCO) induced by Cu(2+)/H(2)O(2) and the alkoxyl and alkylperoxyl radicals formed by the azo initiator 2,2'-azobis(2-amidinopropane) hydrochloride (AAPH, 40 mM). The protective effects of melatonin were compared with 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (trolox), glutathione (GSH), ascorbate, 3,4',5-trihydroxy-trans-stilbene (resveratrol, 0.1 microM-4 mM) and mannitol (50 microM-100 mM). Melatonin efficiently prevented protein modification induced by both models, as assayed by polyacrylamide gel electrophoresis and carbonyl content. Both trolox and ascorbate had an obvious pro-oxidant effect in the Cu(2+)/H(2)O(2) model, whereas both prevented BSA damage induced by AAPH. In the MCO model, the efficacy of GSH in terms of protein protection was higher than melatonin at relatively high concentrations (250 microM-4 mM); however, at lower concentrations (50-250 microM), the efficacy of melatonin was superior to GSH. D-Mannitol (50 microM-100 mM) and resveratrol did not protect BSA from the site-specific damage induced by Cu(2+)/H(2)O(2). On the other hand, the relative protective efficiency in the AAPH model was melatonin approximately trolox>GSH>ascorbate.     

Methionine regulates copper/hydrogen peroxide oxidation products of Abeta.

Metal-catalysed oxidation (MCO) may play a causative role in the pathogenesis of Alzheimer's disease (AD). Amyloid beta peptide (Abeta), the major biomarker of AD, in the presence of copper ions reduces Cu(2+) to Cu(+) and catalyses the formation of H(2)O(2) that subsequently induces radicals through Fenton chemistry. Abeta is also subject to attack by free radicals, where the presence of Cu(2+) in conjunction with H(2)O(2) catalyses oxygenation, primarily at the methionine sulfur atom. This work investigates MCO of Abeta, to gain further insight into the role of oxidative stress in AD. By combining a fluorescence assay with gel electrophoresis to monitor MCO reactions of Abeta (1-28) in the presence and absence of methionine it was determined that methionine can both protect some residues against MCO and promote the oxidation of Tyr(10) specifically. Electrospray ionization mass spectrometric analysis of methionine MCO products indicated the formation of methionine sulfoxide, methionine sulfone and related hydroxylated products. Similar products could be formed from the oxidation of Met(35) of Abeta and may relate to changes in properties of the peptide following MCO.     

Aggregation of alpha-synuclein induced by the Cu,Zn-superoxide dismutase and hydrogen peroxide system

Alpha-synuclein is a major component of the abnormal protein aggregation in Lewy bodies of Parkinson's disease (PD) and senile plaques of Alzheimer's disease (AD). Previous studies have shown that the aggregation of alpha-synuclein was induced by copper (II) and H(2)O(2) system. Since copper ions could be released from oxidatively damaged Cu,Zn-superoxide dismutase (SOD), we investigated the role of Cu,Zn-SOD in the aggregation of alpha-synuclein. When alpha-synuclein was incubated with both Cu,Zn-SOD and H(2)O(2), alpha-synuclein was induced to be aggregated. This process was inhibited by radical scavengers and spin trapping agents such as 5,5'-dimethyl 1-pyrolline N-oxide and tert-butyl-alpha-phenylnitrone. Copper chelators, diethyldithiocarbamate and penicillamine, also inhibited the Cu,Zn-SOD/H(2)O(2) system-induced alpha-synuclein aggregation. These results suggest that the aggregation of alpha-synuclein is mediated by the Cu,Zn-SOD/H(2)O(2) system via the generation of hydroxyl radical by the free radical-generating function of the enzyme. The Cu,Zn-SOD/H(2)O(2)-induced alpha-synuclein aggregates displayed strong thioflavin-S reactivity, reminiscent of amyloid. These results suggest that the Cu,Zn-SOD/H(2)O(2) system might be related to abnormal aggregation of alpha-synuclein, which may be involved in the pathogenesis of PD and related disorders.     

Anti- and pro-oxidant effects of urate in copper-induced low-density lipoprotein oxidation.

We reported earlier that urate may behave as a pro-oxidant in Cu2+-induced oxidation of diluted plasma. Thus, its effect on Cu2+-induced oxidation of isolated low-density lipoprotein (LDL) was investigated by monitoring the formation of malondialdehyde and conjugated dienes and the consumption of urate and carotenoids. We show that urate is antioxidant at high concentration but pro-oxidant at low concentration. Depending on Cu2+ concentration, the switch between the pro- and antioxidant behavior of urate occurs at different urate concentrations. At high Cu2+ concentration, in the presence of urate, superoxide dismutase and ferricytochrome c protect LDL from oxidation but no protection is observed at low Cu2+ concentration. The use of Cu2+ or Cu+ chelators demonstrates that both copper redox states are required. We suggest that two mechanisms occur depending on the Cu2+ concentration. Urate may reduce Cu2+ to Cu+, which in turn contributes to formation. The Cu2+ reduction is likely to produce the urate radical (UH.-). It is proposed that at high Cu2+ concentration, the reaction of UH.- radical with generates products or intermediates, which trigger LDL oxidation. At low Cu2+ concentration, we suggest that the Cu+ ions formed reduce lipid hydroperoxides to alkoxyl radicals, thereby facilitating the peroxidizing chain reaction. It is anticipated that these two mechanisms are the consequence of complex LDL-urate-Cu2+ interactions. It is also shown that urate is pro-oxidant towards slightly preoxidized LDL, whatever its concentration. We reiterate the conclusion that the use of antioxidants may be a two-edged sword.     

Metal-catalyzed oxidation induces carbonylation of peroxisomal proteins and loss of enzymatic activities

Peroxisomes are involved in oxidative metabolic reactions and have the capacity to generate large amounts of reactive oxygen species that could damage biomolecules including their own resident proteins. The purpose of this study was to determine whether peroxisomal proteins are susceptible to oxidation and whether oxidative damage affects their enzymatic activity. Peroxisomal proteins were subjected to metal-catalyzed oxidation (MCO) with CuCl(2)/ascorbate and derivatized with 2,4-dinitrophenylhydrazine which allowed for spectrophotometric quantification of carbonylation. Immunochemical detection of carbonylated peroxisomal proteins, resolved by gel electrophoresis and detected with anti-DNP antibodies, revealed five oxidatively modified proteins with the following molecular weights: 80, 66, 62, 55, and 50 kDa. The proteins at 66, 62, and 55 kDa were identified as malate synthase (MS), isocitrate lyase, and catalase (CAT), respectively. MS and CAT were estimated to contain 2-3 mol of carbonyl/mol of protein as a result of MCO. Enzymatic assays revealed varying degrees of activity loss. Isocitrate lyase and malate synthase showed significant loss of activity while catalase and malate dehydrogenase were less inhibited by carbonylation. Our findings show that peroxisomal proteins are vulnerable to MCO damage and thus may also be affected by in vivo exposure to reactive oxygen species.     

Inactivation of enzymes and an enzyme inhibitor by oxidative modification with chlorinated amines and metal-catalyzed oxidation systems.

Oxidative inactivation of various key enzymes and alpha-1-proteinase inhibitor (alpha-1-PI) was studied by treatment with N-chloramines and the metal-catalyzed oxidation (MCO)-systems ascorbate/Fe(III) and ascorbate/Cu(II). Chlorinated amines completely inhibited alpha-1-PI, fructose-1,6-bis phosphatase (Fru-P2ase) and glyceraldehyde phosphate dehydrogenase (GAPD) at a low molar excess, and glucose-6-phosphate dehydrogenase (G6PD) at a high molar excess, but did not impair beta-N-acetylglucosaminidase (beta-NAG), alkaline phosphatase (AP) or lactate dehydrogenase (LDH). MCO-systems affected the activities of Fru-P2ase, GAPD, AP, LDH and G6PD, but not those of beta-NAG or alpha-1-PI. EDTA prevented inactivation of Fru-P2ase, G6PD and LDH by ascorbate/Cu(II) and of Fru-P2ase by ascorbate/Fe(III) suggesting a site-specific oxidation catalyzed by a protein-bound metal ion. In conclusion, N-chloramines and MCO-systems exhibited different properties with regard to oxidative inactivation, sulfhydryl-enzymes were susceptible to both systems, but other enzymes were only susceptible to one or neither system.     

Cu(0) as the reaction additive in purge-free ATRP-assisted DNA detection

We report here the use of Cu(0) as a reducing reagent to eliminate dissolved oxygen-induced ATRP catalyst oxidation and radical chain termination. It eliminates the need for an inert environment as in a conventional ATRP reaction and allows DNA detection to be conducted in a purge-free fashion. 2-Hydroxyethylmethacrylate (HEMA) is the model monomer in our study, and Cu(I)/2,2'-dipyridyl-based complexes are used as the reaction catalyst. The amount of polymer chains grafted on the substrate upon reaction termination is quantified by measuring the final film thicknesses using ellipsometry. Synthesis of PHEMA films atop both small molecules and ssDNA in the presence of a limited amount of air at room temperature is achieved by adding Cu(0) as the reducing reagent. No compromised DNA detection sensitivity is noticed, though a 10:1 ratio of Cu(0):Cu(I) is required to achieve optimal polymer growth. Successful employment of Cu(0) as the reducing agent eliminates the cumbersome purging process in ATRP and renders the ATRP-assisted DNA sensing method more portable, simpler, and more time-efficient.     

Synthesis of tentacle-type magnetic beads as immobilized metal-chelate affinity support for cytochrome c adsorption

Magnetic poly(2-hydroxyethylmethacrylate) (mPHEMA) beads with an average diameter of 100-140 microm were produced by suspension polymerization in the presence of magnetite particles (i.e. Fe3O4). Specific surface area and average pore size of the magnetic beads was found to be 50 m2/g and 819 nm, respectively. Ester groups in the mPHEMA structure were converted to imine groups by reacting with poly(ethyleneimine) (PEI) in the presence of NaH. Amino (-NH2) content of PEI-attached mPHEMA beads was determined as 102 mg PEI/g. Then, Cu2+ ions were chelated on the magnetic beads in the range of 20-793 micromol Cu2+/g. Cytochrome c (cyt c) adsorption was performed on the metal chelating beads from aqueous solutions containing different amounts of cyt c at different pHs, Cu2+ loadings and temperatures. Cyt c adsorption on the mPHEMA/PEI beads was 4.6 mg/g. Cu2+ chelation increased the cyt c adsorption significantly (40.1 mg/g). Adsorption capacity increased with Cu2+ loading and then reached a saturation value. Cyt c adsorption decreased with increasing temperature. Cyt c molecules could be reversibly adsorbed and eluted ten times with the magnetic adsorbents without noticeable loss in their cyt c adsorption capacity. The applicability of two kinetic models including pseudo-first order and pseudo-second order model was estimated on the basis of comparative analysis of the corresponding rate parameters, equilibrium capacity and correlation coefficients. Results suggest that chemisorption processes could be the rate-limiting step in the adsorption process. In the last part of this article, cyt c adsorption experiments were performed in a magnetically stabilized fluidized bed (MSFB) system at optimum conditions determined from the batch experiments. The adsorption capacity decreased significantly from 46.8 to 15.4 mg/g polymer with the increase of the flow-rate from 0.5 to 4.0 ml/min. The resulting magnetic chelator beads possessed excellent long-term storage stability.     

Iron and dioxygen chemistry is an important route to initiation of biological free radical oxidations: an electron paramagnetic resonance spin trapping study

Iron can be a detrimental catalyst in biological free radical oxidations. Because of the high physiological ratio of [O2]/[H2O2] (> or = 10(3)), we hypothesize that the Fenton reaction with pre-existing H2O2 is only a minor initiator of free radical oxidations and that the major initiators of biological free radical oxidations are the oxidizing species formed by the reaction of Fe2+ with dioxygen. We have employed electron paramagnetic resonance spin trapping to examine this hypothesis. Free radical oxidation of: 1) chemical (ethanol, dimethyl sulfoxide); 2) biochemical (glucose, glyceraldehyde); and 3) cellular (L1210 murine leukemia cells) targets were examined when subjected to an aerobic Fenton (Fe2+ + H2O2 + O2) or an aerobic (Fe2+ + O2) system. As anticipated, the Fenton reaction initiates radical formation in all the above targets. Without pre-existing H2O2, however, Fe2+ and O2 also induce substantial target radical formation. Under various experimental ratios of [O2]/[H2O2] (1-100 with [O2] approximately 250 microM), we compared the radical yield from the Fenton reaction vs. the radical yield from Fe2+ + O2 reactions. When [O2]/[H2O2] < 10, the Fenton reaction dominates target molecule radical formation; however, production of target-molecule radicals via the Fenton reaction is minor when [O2]/[H2O2] > or = 100. Interestingly, when L1210 cells are the oxidation targets, Fe2+ + O2 is observed to be responsible for formation of nearly all of the cell-derived radicals detected, no matter the ratio of [O2]/[H2O2]. Our data demonstrate that when [O2]/[H2O2] > or = 100, Fe2+ + O2 chemistry is an important route to initiation of detrimental biological free radical oxidations.     

Oxidative modification of neurofilament-L by the Cu,Zn-superoxide dismutase and hydrogen peroxide system

Neurofilament-L (NF-L) is a major element of neuronal cytoskeletons and known to be important for their survival in vivo. Since oxidative stress might play a critical role in the pathogenesis of neurodegenerative diseases, we investigated the role of Cu,Zn-superoxide dismutase (SOD) in the modification of NF-L. When disassembled NF-L was incubated with Cu,Zn-SOD and H2O2, the aggregation of protein was proportional to the concentration of hydrogen peroxide. Cu,Zn-SOD/H2O2-mediated modification of NF-L was significantly inhibited by radical scavenger, spin trap agents and copper chelators. Dityrosine crosslink formation was obtained in Cu,Zn-SOD/H2O2-mediated NF-L aggregates. Antioxidant molecules, carnosine and anserine significantly inhibited the aggregation of NF-L and the formation of dityrosine. This study suggests that copper-mediated NF-L modification may be closely related to oxidative reactions which play a critical role in neurodegenerative diseases.     

Metal-catalyzed oxidation reactions and mass spectrometry: the roles of ascorbate and different oxidizing agents in determining Cu-protein-binding sites

Further study has been made of metal-catalyzed oxidation (MCO) reactions and mass spectrometry as a method to determine the binding site of copper in metalloproteins. The role of ascorbate and a variety of oxidizing agents, including O2, H2O2, and S2O8(2-), have been investigated using Cu/Zn superoxide dismutase (SOD) as a model system. Ascorbate is found to play two competing roles in the MCO reactions. It reduces Cu(II), which initiates and maintains the generation of reactive oxygen species, and it scavenges radicals, which helps to localize oxidation products to amino acids near the metal center. An ascorbate concentration of 100 mM is found to be optimal with regard to localizing oxidation products to only the Cu-binding residues (His44, His46, His61, and His118) of Cu/Zn SOD. This concentration of ascorbate is very similar to the optimum concentration found in our previous studies of different Cu-binding proteins. Another notable result from this study is the observation that S2O8(2-) is more effective as an oxidant than O2 or H2O2 in the MCO reactions. Because S2O8(2-) is more stable in solution than H2O2, using it as an oxidizing agent results in much less nonspecific oxidation to the protein. The overall results of this study suggest that general MCO reaction conditions may exist for determining the metal-binding site of a wide range of Cu-binding proteins.     

The hydrogen peroxide/copper ion system, but not other metal-catalyzed oxidation systems, produces protein-bound dityrosine

Dityrosine formation leads to the cross-linking of proteins intra- or intermolecularly. The formation of dityrosine in lens proteins oxidized by metal-catalyzed oxidation (MCO) systems was estimated by chemical and immunochemical methods. Among the four MCO systems examined (H(2)O(2)/Cu, H(2)O(2)/Fe-ethylenediaminetetraacetic acid (Fe-EDTA), ascorbate/Cu, ascorbate/Fe-EDTA), the treatment with H(2)O(2)/Cu preferentially caused dityrosine formation in the lens proteins. The success of oxidative protein modification with all the MCO systems was confirmed by carbonyl formation estimated using 2,4-dinitrophenylhydrazine. The loss of tyrosine by the MCO systems was partly due to the formation of protein-bound 3,4-dihydroxyphenylalanine. The formation of dityrosine specific to H(2)O(2)/Cu was confirmed by using poly-(Glu, Ala, Tyr) and N-acetyl-tyrosine as a substrate. The dissolved oxygen concentration in the H(2)O(2)/Cu system hardly affected the amount of dityrosine formation, suggesting that dityrosine generation by the H(2)O(2)/Cu system is independent of oxygen concentration. Moreover, the combination of copper ion with H(2)O(2) is the most effective system for dityrosine formation among various metal ions examined. The addition of reducing agents, glutathione or ascorbic acid, into the H(2)O(2)/Cu system suppressed the generation of the dityrosine moiety, suggesting effective quench of tyrosyl radicals by the reducing agents.     

Thiourea protects against copper-induced oxidative damage by formation of a redox-inactive thiourea-copper complex

Although thiourea has been used widely to study the role of hydroxyl radicals in metal-mediated biological damage, it is not a specific hydroxyl radical scavenger and may also exert antioxidant effects unrelated to hydroxyl radical scavenging. Thus, we investigated the effects of thiourea on copper-induced oxidative damage to bovine serum albumin (1 mg/ml) in three different copper-containing systems: Cu(II)/ascorbate, Cu(II)/H₂O₂, and Cu(II)/H₂O₂/ascorbate [Cu(II), 0.1 mM; ascorbate, 1 mM; H₂O₂, 1 mM]. Oxidative damage to albumin was measured as protein carbonyl formation. Thiourea (0.1–10 mM) provided marked and dose-dependent protection against protein oxidation in all three copper-containing systems. In contrast, only minor protection was observed with dimethyl sulfoxide and mannitol, even at concentrations as high as 100 mM. Strong protection was also observed with dimethylthiourea, but not with urea or dimethylurea. Thiourea also significantly inhibited copper-catalyzed oxidation of ascorbate, and competed effectively with histidine and 1,10-phenanthroline for binding of cuprous, but not cupric, copper, as demonstrated by both UV-visible and low temperature electron spin resonance measurements. We conclude that the protection by thiourea against copper-mediated protein oxidation is not through scavenging of hydroxyl radicals, but rather through the chelation of cuprous copper and the formation of a redox-inactive thiourea-copper complex.     

Metal catalyzed oxidation of tyrosine residues by different oxidation systems of copper/hydrogen peroxide

Metal-catalysed oxidation (MCO) reactions result in the formation of reactive oxygen species (ROS) in biological systems. These ROS cause oxidative stress that contributes to a number of pathological processes leading to a variety of diseases. Tyrosine is one residue that is very susceptible to oxidative modification and the formation of dityrosine (DT) and 3,4-dihydroxyphenylalanine (DOPA) have been widely reported in a number of diseases. However, the mechanisms of MCO of tyrosine in biological systems are poorly understood and require further investigation. In this study we investigated the mechanism of DT and DOPA formation by MCO using N-acetyl tyrosine ethyl ester as a model for tyrosine in proteins and peptides. The results showed that DT formation could be observed upon Cu2+/H2O2 oxidation at pH 7.4. Our results indicate that it is unlikely to be via Fenton chemistry since Cu+/H2O2 oxidative conditions did not lead to the formation of DT.     

Amplification of antioxidant activity of catechin by polycondensation with acetaldehyde

Catechin exhibits numerous biological and pharmacological effects attributed to antioxidant action. The synthetic poly(catechin)s condensed through acetaldehyde with different molecular weights were assessed in terms of antioxidant activity and enzyme inhibitory activity on the basis of a catechin repeating unit and compared with monomeric catechin. The poly(catechin)s showed great amplification of superoxide scavenging activity, xanthine oxidase (XO) inhibitory activity, and inhibition effects on human low-density lipoprotein oxidation initiated by 2,2'-azobis(2-amidinopropane)dihydrochloride (AAPH) as a radical generator on the catechin unit level, compared to monomeric catechin: these activities were proportional to their molecular weights. The reducing power of the polymer was lower than that of monomeric catechin, which decreased with increasing the molecular weight. The polymer also protected endothelial cells from oxidative injury induced by AAPH, with a greater effect expressed on a catechin unit basis than that of the monomer. These results demonstrate that the poly(catechin)s are more potent antioxidant agents and enzyme inhibitors.     

Enzymatic synthesis and antioxidant properties of poly(rutin)

Rutin, quercetin-3-rutinoside, is one of the most famous glycosides of flavonoid and widely present in many plants. In this study, we performed an oxidative polymerization of rutin using Myceliophthora laccase as catalyst in a mixture of methanol and buffer to produce a flavonoid polymer and evaluated antioxidant properties of the resultant polymer. Under selected conditions, the polymer with molecular weight of several thousands was obtained in good yields. The resulting polymer was readily soluble in water, DMF, and DMSO, although rutin monomer showed very low water solubility. UV measurement showed that the polymer had broad transition peaks around 255 and 350 nm in water, which were red-shifted in an alkaline solution. Electron spin resonance (ESR) measurement showed the presence of a radical in the polymer. The polymer showed greatly improved superoxide scavenging activity and inhibition effects on human low-density lipoprotein (LDL) oxidation initiated by 2,2'-azobis(2-amidinopropane)dihydrochloride (AAPH), compared with the rutin monomer. The polymer also protected endothelial cells from oxidative injury induced by AAPH as a radical generator with a much greater effect than the rutin monomer.     

Temperature-controlled properties of DNA complexes with poly(ethylenimine)-graft-poly(N-isopropylacrylamide)

End-functionalized poly(N-isopropylacrylamide) (PNIPA) was synthesized by living free radical polymerization and conventional free radical polymerization and was used to prepare graft copolymers with poly(ethylenimine) (PEI). The copolymers exhibited lower critical solution temperature (LCST) behavior between 30 and 32 degrees C and formed complexes with plasmid DNA. The LCST of the copolymers in the DNA complexes increased slightly to approximately 34-35 degrees C. Cytotoxicity of the copolymers was evaluated by measuring lactate dehydrogenase (LDH) release from cells. The copolymers exhibited temperature-dependent toxicity, with higher levels of LDH release observed at temperatures above the LCST. Cellular uptake and transfection activity of the DNA complexes with the PEI-g-PNIPA copolymers were lower than those of the control PEI/DNA complexes at temperature below the LCST but increased to the PEI/DNA levels at temperatures above the LCST.     

The influence of medium components on Cu(2+)-dependent oxidation of low-density lipoproteins and its sensitivity to superoxide dismutase.

The extent of in vitro Cu(2+)-dependent oxidation of low-density lipoproteins (LDL) has been reported to vary widely depending upon reaction conditions. In this study, the effect of proteins and amino acids on Cu(2+)-induced LDL oxidation was examined. Treatment of LDL with 5 microM CuSO4 for 18 h in either phosphate-buffered saline (PBS) or Ham's F-10 medium resulted in extensive oxidation as determined by the content of thiobarbituric acid reactive substances (TBARS) and by increased lipoprotein electronegativity. In PBS, oxidation was entirely blocked by histidine and the tripeptide, gly-his-lys (GHK). Oxidation was also prevented by bovine serum albumin, but superoxide dismutase (SOD) provided only 20% protection. Both proteins bound similar amounts of Cu2+, but albumin appeared to be a more effective peroxyl radical trap as evidenced by its ability to prevent LDL oxidation induced by 2,2'-azo-bis(2-amidinopropane hydrochloride). In F-10 medium, SOD had marked inhibitory effects, in contrast to PBS. The addition of disulfides to PBS markedly enhanced the ability of SOD to inhibit oxidation. These results indicate that medium components which affect Cu2+ availability influence LDL oxidation and suggest that albumin is ideally suited as a plasma antioxidant to prevent oxidative modification of LDL. Furthermore, in certain instances, the inhibitory effects of SOD may be attributable to effects such as Cu2+ binding rather than dismutation of superoxide.     

8.9% Single‐Stack Inverted Polymer Solar Cells with Electron‐Rich Polymer Nanolayer‐Modified Inorganic Electron‐Collecting Buffer Layers

Enhanced power conversion efficiency (PCE) is reported in inverted polymer solar cells when an electron‐rich polymer nanolayer (poly(ethyleneimine) (PEI)) is placed on the surface of an electron‐collecting buffer layer (ZnO). The active layer is made with bulk heterojunction films of poly[[4,8‐bis[(2‐ethylhexyl)oxy]benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl][3‐fluoro‐2‐[(2‐ethylhexyl)carbonyl]thieno[3,4‐b]thiophenediyl]] (PTB7) and [6,6]‐phenyl‐C₇₁‐butyric acid methyl ester (PC₇₁BM). The thickness of the PEI nanolayer is controlled to be 2 nm to minimize its insulating effect, which is confirmed by X‐ray photoelectron spectroscopy and optical absorption measurements. The Kelvin probe and ultraviolet photoelectron spectroscopy measurements demonstrate that the enhanced PCE by introducing the PEI nanolayer is attributed to the lowered conduction band energy of the ZnO layer via the formation of an interfacial dipole layer at the interfaces between the ZnO layer and the PEI nanolayer. The PEI nanolayer also improves the surface roughness of the ZnO layer so that the device series resistance can be noticeably decreased. As a result, all solar cell parameters including short circuit current density, open circuit voltage, fill factor, and shunt resistance are improved, leading to the PCE increase up to ≈8.9%, which is close to the best PCE reported using conjugated polymer electrolyte films.