Theoretical insight into the degradation of p-nitrophenol by OH radicals synergized with other active oxidants in aqueous solution.

The degradation of p-nitrophenol (p-NP) based on OH radicals (HO∙), HO2 radicals (HO2∙) and O2 in aqueous solution was investigated using theoretical computational methods. The complete degradation mechanisms of reaction between p-NP and HO∙ were explored by density functional theory (DFT) methods. The 4-nitrophenoxy radicals and 1,2-dihydroxy-4-nitrocylohexadienyl radicals are confirmed to be major intermediates of the HO∙-initiated reactions in aqueous phase, which consistent with experimental results. The chemical structures of some products (2,4-dihydroxycyclohexa-2,4-dien-1-one and 4-nitrocyclohexa-3,5-diene-1,2-dione) which were not identified in the experiment are determined. New favorable formation channels for some intermediates were found. The primary reactions initiated by HO∙ or HO2∙ with p-NP reveals that HO∙-initiated degradation is the dominant reaction. HO2∙ and O2 can enhance the degradation extent of p-NP in further reactions. Rate constants of the elementary reactions and overall rate constants were calculated. In addition, the HO∙-initiated primary reactions in a water box of 500 water molecules were studied using Monte Carlo simulation. All the OH-addition reactions are barrierless and highly feasible. The observed dynamic reaction process is similar to the DFT calculation prediction. Furthermore, the eco-toxicity evaluation shows that important products are harmless or harmful to aquatic organisms, and are much less toxic than p-NP.

Experimental and theoretical insights into photochemical transformation kinetics and mechanisms of aqueous propylparaben and risk assessment of its degradation products.

The kinetics and mechanisms of ultraviolet photochemical transformation of propylparaben (PPB) were studied. Specific kinetics scavenging experiments coupled with quantum yield determinations were used to distinguish the roles of various reactive species induced by self-sensitized and direct photolysis reactions, and the excited triplet state of PPB ((3) PPB*) was identified as the most important species to initiate the photochemical degradation of PPB in aquatic environments. The computational results of time-resolved absorption spectra proved that (3) PPB* is a highly reactive electron acceptor, and a head-to-tail hydrogen transfer mechanism probably occurs through electron coupled with proton transfer. Physical quenching by, or chemical reaction of (3) PPB* with, O2 was confirmed as a key step affecting the initial PPB transformation pathways and degradation mechanisms. The transformation products were identified and the toxicity evolutions of PPB solutions during photochemical degradation under aerobic and anaerobic conditions were compared. The results indicate that anaerobic conditions are more likely than aerobic conditions to lead to the elimination and detoxification of PPB but less likely to lead to PPB mineralization.

Radiolysis and photolysis studies on active transient species of berberine.

In this paper, the photochemical and photobiological characters of the active radicals of berberine (BBR) was investigated for finding an efficient and safe photosensitizer with highly active transient products using in Photodynamic therapy (PDT) study. The active species of BBR was generated and identified by using pulse radiolysis method. In neutral aqueous solution, BBR react with hydrated electron and hydroxyl radical, forming the radical anion and neutral radical of BBR, and the related reaction rates were determined as 3.5×10(10) and 6.7×10(9) M(-1) s(-1), respectively. Further, the capability of BBR to photosensitize DNA cleavage was testified by laser flash photolysis (LFP) method, the results demonstrated that BBR neutral radical could react with guanine mononucleotide (K=1.9×10(9) M(-1) s(-1)) via electron transfer to give the guanine neutral radical. Additionally BBR selective cleavage single and double strand DNA at guanine moiety was observed. Finally, combining with the thermodynamic calculation, the possible photodamage mechanism of dGMP and DNA induced by BBR was clarified.

Theoretical investigation on the mechanisms and kinetics of OH-initiated photooxidation of dimethyl phthalate (DMP) in atmosphere.

The atmospheric OH-initiated degradation mechanisms of dimethy phthalate (DMP) are analyzed at the MPWB1K/6-311++G(3df,2p)//MPWB1K/6-31+G(d,p) level of theory. The principal products detected experimentally are confirmed by this study while several major intermediates are reported for the first time. Additionally, the pathway scheme of hydroxylation reaction of DMP is proposed. The results about initial steps indicate that hydroxyl radical is most likely to be added to the ortho-carbon atom among additional reactions, while H atoms in methyl group are the most favorable to be abstracted by the OH radical. The rate constants of the elementary reactions over the temperature of 200-400 K were deduced using RRKM theory. The overall rate constant of the title reaction is 1.18×10(-12) cm(3) molecule(-1) s(-1) at 298 K and 760 Torr while H abstraction reactions predominate. According to the rate constants given at different temperatures, the Arrhenius equation is fitted. The atmospheric half life of DMP with respect to OH is estimated to be 6.8 days.

OH-initiated oxidation mechanisms and kinetics of 2,4,4'-Tribrominated diphenyl ether.

2,4,4'-Tribromodiphenyl ether (BDE-28) was selected as a typical congener of polybrominated diphenyl ethers (PBDEs) to examine its fate both in the atmosphere and in water solution. All the calculations were obtained at the ground state. The mechanism result shows that the oxidations between BDE-28 and OH radicals are highly feasible especially at the less-brominated phenyl ring. Hydroxylated dibrominated diphenyl ethers (OH-PBDEs) are formed through direct bromine-substitution reactions (P1∼P3) or secondary reactions of OH-adducts (P4∼P8). Polybrominated dibenzo-p-dioxins (PBDDs) resulting from o-OH-PBDEs are favored products compared with polybrominated dibenzofurans (PBDFs) generated by bromophenols and their radicals. The complete degradation of OH adducts in the presence of O2/NO, which generates unsaturated ketones and aldehydes, is less feasible compared with the H-abstraction pathways by O2. Aqueous solution reduces the feasibility between BDE-28 and the OH radical. The rate constant of BDE-28 and the OH radical is determined to be 1.79 × 10(-12) cm(3) molecule(-1) s(-1) with an atmospheric lifetime of 6.7 days.

Advanced oxidation kinetics and mechanism of preservative propylparaben degradation in aqueous suspension of TiO2 and risk assessment of its degradation products.

The absolute kinetic rate constants of propylparaben (PPB) in water with different free radicals were investigated, and it was found that both hydroxyl radicals (HO(•)) and hydrated electrons could rapidly react with PPB. The advanced oxidation kinetics and mechanisms of PPB were investigated using photocatalytic process as a model technology, and the degradation was found to be a pseudo-first-order model. Oxidative species, particularly HO(•), were the most important reactive oxygen species mediating photocatalytic degradation of PPB, and PPB degradation was found to be significantly affected by pH because it was controlled by the radical reaction mechanism and was postulated to occur primarily via HO(•)-addition or H-abstraction reactions on the basis of pulse radiolysis measurements and observed reaction products. To investigate potential risk of PPB to humans and aqueous organisms, the estrogenic assays and bioassays were performed using 100 µM PPB solution degraded by photocatalysis at specific intervals. The estrogenic activity decreased as PPB was degraded, while the acute toxicity at three trophic levels first increased slowly and then decreased rapidly as the total organic carbon decreased during photocatalytic degradation.

Interaction mechanism between berberine and the enzyme lysozyme.

In the present paper, the interaction between model protein lysozyme (Lys) and antitumorigenic berberine (BBR) was investigated by spectroscopic methods, for finding an efficient and safe photosensitizer with highly active transient products using in photodynamic therapy study. The fluorescence data shows that the binding of BBR could change the environment of the tryptophan (Trp) residues of Lys, and form a new complex. Static quenching is the main fluorescence quenching mechanism between Lys and BBR, and there is one binding site in Lys for BBR and the type of binding force between them was determined to be hydrophobic interaction. Furthermore, the possible interaction mechanism between BBR and Lys under the photoexcitation was studied by laser flash photolysis method, the results demonstrated that BBR neutral radicals (BBR(-H)) react with Trp (K=3.4×10(9)M(-1)s(-1)) via electron transfer to give the radical cation (Trp/NH(+)) and neutral radical of Trp (TrpN). Additionally BBR selectively oxidize the Trp residues of Lys was also observed by comparing the transient absorption spectra of their reaction products. Through thermodynamic calculation, the reaction mechanisms between (3)BBR and Trp or Lys were determined to be electron transfer process.

Role of primary reaction initiated by 254 nm UV light in the degradation of p-nitrophenol attacked by hydroxyl radicals.

The degradation kinetics of p-nitrophenol (p-NP) exposed to 254/185 nm UV light were studied in two modes, i.e., 254 nm UV light intensity enhanced mode and normal mode. It was observed that the extra 254 nm UV light source accelerated the degradation process both in the presence and the absence of oxygen. Considering that hydroxyl radical (*OH) is the dominant factor that causes the degradation of p-NP, the enhanced degradation that occurred in the presence of the extra light source was attributed to the synergistic effect between *OH attack and the primary reactions initiated by 254 nm UV light. The synergistic effect has been confirmed by 266 nm laser flash photolysis (LFP) experiments. It is demonstrated that the phenoxy radical generated from the photoionization of p-NP is capable of reacting with *OH. On the basis of these results, it should be noted that UV light could cause more severe damage to p-NP attacked by *OH in aqueous solution.

Study on the mechanism of photo-degradation of p-nitrophenol exposed to 254 nm UV light.

The degradation mechanism of p-nitrophenol (p-NP) exposed to 254 nm UV light was studied in the presence and the absence of oxygen respectively via both steady-state photolysis and time-resolved laser flash photolysis (LFP) experiments. It has been confirmed that p-NP can be photo-ionized to produce its radical cation (p-NP(+)) and hydrated electron (e(aq)(-)) with a quantum yield of 0.52. In neutral solution p-NP(+) will be quickly deprotonated to form its phenoxyl radical (p-NP) which will react with oxygen to promote the breakage of benzene ring of p-NP. The degradation efficiency of p-NP exposed to 254 nm UV is as low as commonly reported. However, oxygen could improve the photo-degradation efficiency, which is due to the reaction of oxygen with p-NP. The reaction between oxygen and p-NP has been experimentally confirmed both in LFP and in pulse radiolysis.

MFalpha signal peptide enhances the expression of cellulase eg1 gene in yeast.

Ethanol production from lignocellulose by recombinant yeast with high level expression of heterologous cellulase genes has been a major anticipation. The native secretion signal sequence of the cellulase endoglucanase I (eg1) gene was replaced by Saccharomyces cerevisiae mating factor alpha prepro-leader sequence (MFalpha). The transformants containing native secretion signal (Y(1)) and MFalpha secretion signal (Y(2)) were characterized with respect to gene expression and growth on cellulose substrate. Increased enzyme activity and cellulose utilization were observed. The enzyme activity of Y(2) was 0.084 U/ml, 61.5% higher than Y(1) (0.052 U/ml). The sufficiency parameter (S value) was raised from 0.6 to 0.84. MFalpha signal peptide was more efficient than the native signal peptide of eg1 gene, suggesting that signal peptide replacement is an efficient way to enhance the cellulase expression level in yeast, for cellulose-derived ethanol production.

Characterization of the transient species generated by the photoionization of Berberine: a laser flash photolysis study.

Using 266 nm laser flash photolysis it has been demonstrated that Berberine (BBR) in aqueous solution is ionized via a mono-photonic process giving a hydrated electron, anion radical that formed by hydrated electron react with steady state of BBR, and neutral radical that formed from rapid deprotonation of the radical cation of BBR. The quantum yield of photoionization is determined to be 0.03 at room temperature with KI solution used as a reference. Furthermore utilizing pH changing method and the SO(4.)(-) radical oxidation method, the assignment of radical cation of BBR was further confirmed, the pK(a) value of it was calculated, and the related set up rate constant was also determined.

The examination of berberine excited state by laser flash photolysis.

The property of the excited triplet state of berberine (BBR) was investigated by using time-resolved laser flash photolysis of 355 nm in acetonitrile. The transient absorption spectra of the excited triplet BBR were obtained in acetonitrile, which have an absorption maximum at 420 nm. And the ratio of excitation to ionization of BBR in acetonitrile solvent was calculated. The self-decay and self-quenching rate constants, and the absorption coefficient of (3)BBR* were investigated and the excited state quantum yield was determined. Furthermore utilizing the benzophenone (BEN) as a triplet sensitizer, and the beta-carotene (Car) as an excited energy transfer acceptor, the assignment of (3)BBR* was further confirmed and the related energy transfer rate constants were also determined.

Protective effect of melatonin on photo-damage to lysozyme.

The behavior of melatonin in the riboflavin-sensitized photo-oxidation of lysozyme was monitored. Melatonin was found to prevent aggregation of protein and the decrease of enzyme activity induced by photo-oxidation. Electron spin resonance experiments showed that photo-oxidation of lysozyme in the presence of riboflavin resulted in formation of protein radicals, and melatonin was highly effective in reducing the formation of protein radicals. Direct evidence of melatonin's ability for quenching the triplet state of riboflavin and singlet oxygen was presented. A mechanism of the protective effect of melatonin on photo-oxidation of protein was proposed and the physiological relevance was discussed.

Transient and steady-state photolysis of p-nitroaniline in aqueous solution.

Both transient photolysis and steady-state photo-degradation experiments were performed to gain insight into the kinetics and mechanisms of degradation of p-nitroaniline (p-NA) in aqueous solutions. Monophotonic photo-ionization of p-NA was characterized by 266 nm Laser Flash Photolysis (LFP). The quantum yield of e(aq)(-) was calculated. Radical cations and neutral radicals of p-NA were identified, respectively. The LFP of p-NA with H(2)O(2) in aqueous solutions was investigated for the first time. For steady-state photo-degradation, degradation of p-NA was observed at diverse irradiation conditions under 254 nm UV light. Direct photo-degradation of p-NA by 254 nm UV light in aqueous solution was very difficult. Once H(2)O(2) was added into the experimental system, degradation of p-NA was enhanced remarkably. In the absence of O(2), degradation rate increased rapidly along with the irradiation time and reached 80% at 10 min. p-NA could be totally removed after 15 min in UV/H(2)O(2) process. In the presence of O(2) and H(2)O(2), degradation rate increased linearly along with the irradiation time and reached 80% at 7.5 min. p-NA could be totally removed after 10 min. The mechanisms behind the photo-degradation of p-NA were discussed.

Nanotoxicity of TiO(2) nanoparticles to erythrocyte in vitro.

Titanium dioxide (TiO(2)) has been considered as non-toxic mineral particles widely used in the fields like cosmetics, food and drug. When the scale come to nanometer, TiO(2) nanoparticles (nano-TiO(2)) exhibits multiple specific characteristics coupled with unknown risks on health. The purpose of this study was to systematically research the influence of nano-TiO(2) on erythrocyte. The results indicated that the erythrocytes treated with nano-TiO(2) underwent abnormal sedimentation, hemagglutination and dose dependent hemolysis, totally differing from those treated with micro-TiO(2). The ghost cells were firstly investigated by using ultra-thin cell section in the case under nano-TiO(2). The mechanism of such adverse effects is (1) the attachment around erythrocyte change the surface native properties and ultimately lead to hemoagglutination; (2) the content leak to the outside of erythrocyte through the breakage induced by both the nano-TiO(2) trans-membrane and the oxidative stress under nano-TiO(2). Our findings imply that nano-TiO(2) may have potential toxicity to human being health.

Down-regulation of osteopontin suppresses growth and metastasis of hepatocellular carcinoma via induction of apoptosis.

BACKGROUND & AIMS: Expression of osteopontin correlates with tumor progression and metastasis. The mechanisms by which osteopontin promotes tumor cell survival remain unclear. Here we used short-hairpin RNA-mediated gene silencing to investigate the antitumor effects by osteopontin depletion in hepatocellular carcinoma (HCC). METHODS: We applied polyethylenimine nanoparticles to deliver a short-hairpin RNA for depletion of osteopontin expression in HCC cells. Tumorigenicity and metastatic potentials of HCC cells were studied in vitro and in nude mice. Nuclear factor-kappaB (NF-kappaB) activation was analyzed by gel shift assay and luciferase analysis. The expressions of integrins were examined by real-time reverse-transcription polymerase chain reaction. Apoptosis was examined by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling assay and mitochondrial membrane potential analysis. RESULTS: Down-regulation of osteopontin inhibited HCC cell growth, anchorage-independent growth, adhesion with fibronectin and invasion through extracellular matrix in vitro, and suppressed tumorigenicity and lung metastasis in nude mice. Osteopontin silencing resulted in suppression of alphav, beta1, and beta3 integrin expressions, blockade of NF-kappaB activation, inhibition of Bcl-2/Bcl-xL and XIAP expressions, increase of Bax expression, and induction of a mitochondria-mediated apoptosis. Furthermore, down-regulation of osteopontin inhibited drug-induced NF-kappaB activation and sensitized HCC cells to chemotherapeutic agents in vitro, which led to complete regression of HCC xenografts in nude mice. CONCLUSIONS: Osteopontin may facilitate tumorigenesis and metastasis through prevention of tumor cells from apoptosis. RNA interference-mediated depletion of osteopontin may be a promising strategy for the treatment of HCC by sensitizing the chemotherapeutic drugs.

Effects of ionic liquid [bmim][PF6] on absorption spectra and reaction kinetics of the duroquinone triplet state in acetonitrile.

The transient absorption spectra and photoinduced electron-transfer process of duroquinone (DQ) in mixed binary solutions of ionic liquid (IL) [bmim][PF6] and acetonitrile (MeCN) have been investigated by laser photolysis at an excitation wavelength of 355 nm. A spectral blue shift of 3DQ* was observed in the IL/MeCN mixtures compared to MeCN. At lower VIL(volume fraction of IL), the interaction between DQ and the solvent is dominant, and the decay rate constant (kobs) of 3DQ* increases steadily with the increasing of VIL; to the contrary, at higher VIL, the network structures due to the hydrogen bond and viscosity are dominant, and the decay rate constant decreases obviously with increasing VIL. A critical point (turnover) was observed at VIL = approximately 0.30. The dependence of the observed growth rate (kgr) of the photoinduced electron-transfer (PET) products on VIL is complex and shows a special change; kgr first decreases with increasing VIL, then increases, and finally decreases slowly with further increasing of VIL. It is speculated that the PET process in the mixture can be affected by factors including the local structure and the reorganization energy of the solvent and salt and cage effects. The change of local structure of [bmim][PF6]/MeCN is supported by following the steady-state fluorescence behavior of the mixture, in combination with the molecular dynamics simulation of the thermodynamic property. The results revealed that the degree of self-aggregation of monomeric cations (bmim+) to associated forms increases with increasing VIL. This is in good agreement with the laser photolysis results for the same solutions.

188Re-labeled MPEG-modified superparamagnetic nanogels: preparation and targeting application in rabbits.

Polyacrylamide-coated magnetic nanogels were synthesized via photochemical method in surfactants and initiators free aqueous system at room temperature. After Hoffmann elimination of carbonyl and further modification with methoxy poly(ethylene glycol) (MPEG), the MPEG-modified superparamagnetic nanogels (MSN) with better hydrophilicity and biocompatibility were obtained. The MSN were characterized by FTIR, XRD, SEM and PCS. Covalently linked with 188Re complex, the 188Re-labeled MSN were prepared and intravenously injected into the left ears of the anesthetized rabbits in control group (without external magnetic field) or in targeting group (in presence of external magnetic field). The average radioactivity distribution of organs in control group was detected and the magnetic targeting feature was investigated in targeting group.

Fast repair of oxidative DNA damage by phenylpropanoid glycosides and their analogues.

The repair activities and reaction mechanisms of phenylpropanoid glycosides (PPGs) and their analogues, isolated from Chinese folk medicinal herbs, towards oxidative DNA damage were studied with pulse radiolytic technique. On pulse irradiation of nitrogen-saturated 4 mM poly C aqueous solution containing one of the tested polyphenols, 40 mM K2S2O8 and 200 mM t-BuOH, the transient absorption spectrum of the oxidative radical of poly C decays with the concurrent formation of the phenoxyl radical of the tested polyphenols within several tens of microseconds after the electron pulse irradiation. The result indicated that there was a repair reaction between oxidative radical of poly C and the tested polyphenols. The repair activities also were observed for the tested polyphenols towards the radical cations of single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA). The rate constants were determined to be 3.7-6.4 x 10(9), 4.8-5.5 x 10(8) and 8.8-10.3 x 10(8) M(-1).sec(-1) for the repair reactions of oxidative radical of poly C and radical cations of ssDNA and dsDNA, respectively. The result of this study together with those of our previous studies demonstrates that PPGs and their analogues can fast repair not only the damage of deoxynucleoside and deoxynucleotide but also the damage of integral DNA, with the latter being closer to a cellular condition.

[Synthesis and screening of polyethylenimine as a carrier for gene transfer into cultured human tumor cells].

BACKGROUND & OBJECTIVE: Choosing suitable gene carrier is very important in gene therapy. Recently, polyethylenimine (PEI), a new polycation compound, is particularly attractive due to its high transduction efficiency and low toxicity. This study was to synthesize a series of PEI nanogels of different particle diameters by photochemistry, investigate the relation between the transfection efficiency and particle diameter, and screen ideal gene carrier. METHODS: PEI nanogels were synthesized by photochemistry. The particle diameter was detected by photo correlation spectroscopy (PCS). The spherical morphology of the nanogels was characterized by scanning electron microscopy (SEM), and confirmed by atomic force microscopy (AFM). Using PEI/DNA complex as a plasmid vector, the enhanced green fluorescence protein (EGFP) gene was transferred into Bel7402 and A549 cells. Gene expression was quantitatively evaluated by fluorescent microscopy and flow cytometry (FCM). RESULTS: The diameter of synthesized PEI nanogels was in the range of 80-200 nm, and most of them were globular. The delivery rate reached the maximum when using 4 microg PEI (86.9 nm) to transfer 2 microg EGFP: the delivery rates were (32.75+/-1.01)% for Bel7402 cells and (29.81+/-1.84)% for A549 cells when detected by fluorescent microscopy, and were (32.40+/-1.41)% for Bel7402 cells and (30.00+/-1.86)% for A549 cell when detected by FCM. There was no significant difference between PEI and LipofectamineTM 2000 in the transfection efficiency (P > 0.05). CONCLUSIONS: PEI nanogels synthesized by photochemistry are effective nonviral vectors for gene delivery into human tumor cells in vitro. The transfection efficiency of 86.9 nm PEI is the highest.