Experimental and Theoretical Investigation of Effects of Ethanol and Acetic Acid on Carcinogenic NDMA Formation in Simulated Gastric Fluid.

N-nitrosodimethylamine (NDMA), as a representative of endogenously formed N-nitroso compounds (NOCs), has become the focus of considerable research interest due to its unusually high carcinogenicity. In this study, effects of ethanol and acetic acid on the formation of NDMA from dimethylamine (DMA) and nitrite in simulated gastric fluid (SGF) were investigated. Experimental results showed that ethanol in the concentrations of 1-8% (v/v) and acetic acid in the concentrations of 0.01-8% (v/v) exhibit inhibitory and promotion effects on the formation of NDMA, respectively. Moreover, they are both in a dose-dependent manner with the largest inhibition/promotion rate reaching ∼70%. Further experimental investigations indicate that ethanol and acetic acid are both able to scavenge nitrite in SGF. It implies that there are interactions of ethanol and acetic acid with nitrite or nitrite-related nitrosating agents rather than DMA. Theoretical calculations confirm the above experimental results and demonstrate that ethanol and acetic acid can both react with nitrite-related nitrosating agents to produce ethyl nitrite (EtONO) and acetyl nitrite (AcONO), respectively. Furthermore, the reactivities of ethyl nitrite, acetyl nitrite, and dinitrogen trioxide reacting with DMA were found in the order of AcONO > N2O3 ≫ EtONO. This is probably the main reason why there are completely different effects of ethanol and acetic acid on NDMA formation. On the basis of the above results, two requirements for a potential inhibitor of NOCs formation in SGF were provided. The results obtained in this study will be helpful in better understanding the inhibition/promotion mechanisms of compounds on NDMA formation in SGF and searching for protective substances to prevent carcinogenic NOCs formation.

Determination of lead, cadmium, copper, and nickel in the tonghui river of beijing, china, by cloud point extraction-high resolution continuum source graphite furnace atomic absorption spectrometry.

Heavy metal contamination of water has become an important problem in recent years. Most hazardous heavy metals exist in environmental water in trace or ultra-trace amounts, which requires establishing highly sensitive analytical methods. In this research, quantitative analyses were performed using high-resolution continuum source graphite furnace atomic absorption spectrometry combined with cloud point extraction (CPE) to determine Pb, Cd, Cu, and Ni levels in environmental surface water. By optimizing the CPE conditions, the enrichment factors were 29 for Pb, Cd, and Cu and 25 for Ni. The limits of detection (LOD) were 0.080, 0.010, 0.035, and 0.014 µg L for Pb, Cd, Cu, and Ni, respectively. The sensitivity of the method is comparable with those reported in previous investigations using various methods and improves outcome by 2 to 3 orders of magnitude compared with the LODs of the current national standard methods of China. Our method was used to determine Pb, Cd, Cu, and Ni in 55 water samples collected from the Tonghui River, which is the principal river in the urban area of Beijing, China. The results indicated that the distributions of the four heavy metals in the Tonghui River were related with the environments. The levels of Pb and Ni exhibit increasing trends along the river from upstream to downstream possibly due to the existence of some chemical factories in the downstream area. Lead, Cd, Cu, and Ni averaged 13.9, 0.8, 46.8, and 38.5%, respectively, of the total amount of the determined heavy metals. The levels of the four heavy metals conformed to the Environmental Quality Standards for Surface Water (Grade I) of China. This work provides a reliable quantitative method to determine trace-amount heavy metals in water, which lays a foundation for establishing standards and regulations for environmental water protection.

Reactions of amine and peroxynitrite: evidence for hydroxylation as predominant reaction and new insight into the modulation of CO2.

Peroxynitrite is related to numerous diseases including cardiovascular diseases, inflammation, and cancer. In order to expand the understanding for the toxicology of peroxynitrite in biological system, the reactions of amine (morpholine as a probe) with peroxynitrite and the modulation of CO2 were investigated by using DFT methods. The results strongly indicate that the hydroxylation of amine by peroxynitrous acid ONOOH, which was previously overlooked by most studies, is predominant relative to the widely reported nitration and nitrosation in the absence of CO2. The product N-hydroxylamine is proposed to be mainly generated via nonradical pathway (two-electron oxidation). The modulation of CO2 exhibits two main functions: (1) inhibition of hydroxylation due to the promoted consumption of peroxynitrite via fast reaction of CO2 with ONOO¯ to form ONOOCO2¯; (2) dual effect (catalysis and inhibition) of CO2 toward nitration and nitrosation. As a new insight, amine does react with CO2 and produce inert amine carbamate R2NCOO¯. This reaction has the potential to compete with the reaction of CO2 and ONOO¯, which leads to inhibition of nitration and nitrosation. The concentration of CO2 could be a critical factor determining the final effect, catalysis or inhibition. As a new finding, HCO3¯ is probably an effective catalyst for the reaction of amine and CO2. Moreover, further studies on how the different types of the amine might affect the outcome of the reactions would be an interesting topic.

[Progress in study of biomolecular damages by Raman spectroscopy].

Raman spectroscopy is an analytical techniques based on Raman scattering, which gives information of molecular vibration and rotation. Raman spectroscopy has been widely employed in the investigations of the structure of biomolacules, because it has many advantages over the common chemical analysis. Raman spectroscopy is non-destructive to the samples. Moreover, it requires simple sample preparation and small sample amount. Raman spectroscopy can be used not only for fast detections of damages of biological macromolecules, such as proteins, nucleic acids and lipids, but also for diagnosis and surgical treatments of cancer. By comparing the Raman spectra of normal tissue and cancer tissue, the differences in the characteristic absorption peaks between the two kinds of tissues can be confirmed, which provides significant information for final diagnosis of cancer and determination of the resection extent of tumor. This paper reviewed the researches on biomolecular damages by Raman spectral inspections. It described the applications of Raman spectral techniques, such as surface-enhanced Raman spectroscopy, Fourier transform Raman and UV resonance Raman spectroscopy, in the detection of protein secondary structures, membrane lipids and DNA damages. A prospect of the development of Raman spectroscopy in the future was given.

[Determination of trace lead in environmental water by cloud point extraction-high resolution continuum source graphite furnace atomic absorption spectrometry].

Comparison investigations were performed for the enrichment method of lead in environmental waters, including coprecipitation, ion exchange and cloud point extraction (CPE). CPE was selected as the optimal enrichment method because of its less consumption of water sample, higher enrichment factor and simpler procedure than the other enrichment methods. Pb contents in the water samples from Tonghui River in Beijing were determined by high resolution continuum source graphite furnace atomic absorption spectrometry coupled with CPE enrichment. The results indicate that the limit of detection of the method is 0.08 microg x L(-1), the relative standard deviation (RSD) is 1.3% to 4.5% (n = 6), the recovery of Pb contents is 93% to 108%, and the enrichment factor of CPE method is 29. The Pb contents in the 13 water samples from Tonghui River all conform to the Environmental Quality Standards for Surface Water (Grade I). Moreover, the Pb content in the whole river exhibits a decreasing trend from Tongzhou district to Chaoyang district.

[Determination of Pb, Cd and Cr in food by high resolution continuum source graphite furnace atomic absorption spectrometry].

The contents of lead, cadmium and chromium were determined for 22 kinds of foods including cereals, vegetables, beverage, sea foods and dairy products by using high resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GFAAS). The methods for sample preparation, digestion, and quantitative analysis were established, by which satisfying analytical precision (RSD = 1.3%-4.9%) and recovery (95.1%-104.6%) were achieved. The results indicated that the contents of lead in tea leaves and chromium in shellfish were much higher than those in the other foods; the contents of cadmium in millet, leek and shellfish were relatively higher than the others. This work established reliable methods for quantitative analysis of heavy metals in foods, which provided experimental references for the constitution of food quality and safety standards. Meanwhile, the distributions of heavy metals in foods given by this work can be expected to enhance the consumers' consciousness of food safety.

[Rapid detection of 6-benzylaminopurine residues in sprout beans by surface-enhanced raman spectroscopy].

New method for rapid and quantitative analysis of 6-benzylaminopurine (6-BA) residues in sprout beans was studied by using FAST-SPE and portable surface-enhanced Raman spectroscopy (SERS). With homemade sprout bean samples as blank control, 6-BA solutions extracted from inserted-treatment samples showed typical characteristic Raman peaks at 1002 cm(-1) tested by SERS, and normalized 1002 cm(-1) intensities had a good linear relationship with gradient concentrations of 6-BA insert-standard solutions. The high concentration linear range was 0.5-14 microg x mL(-1), and the low one was 0. 1-2 microg x mL(-1). The quantitative detection limit was down to 0.02 mg x kg(-1) that was below the maximum allowable residues (MAL) of 0. 2 mg kg(-1) in related National Standard. The recoveries were 82.3%-95.1% and the RSD was below 5%. This method with portable equipment and simple pre-treatment showed good reproducibility, short test time-consuming and easy operating, and thus it would provide efficient and sensitive solutions for large-scale on-site and rapid detections.

Carbon dioxide in the nitrosation of amine: catalyst or inhibitor?

Nitrosamines are a class of carcinogenic, mutagenic, and teratogenic compounds generally produced from the nitrosation of amine. This paper investigates the mechanism for the formation of nitrosodimethylamine (NDMA) from the nitrosation of dimethylamine (DMA) by four common nitrosating agents (NO(2)(-), ONOO(-), N(2)O(3), and ONCl) in the absence and presence of CO(2) using the DFT method. New insights are provided into the mechanism, emphasizing that the interactions of CO(2) with amine and nitrosating agents are both potentially important in influencing the role of CO(2) (catalyst or inhibitor). The role of CO(2) as catalyst or inhibitor mainly depends on the nitrosating agents involved. That is, CO(2) shows the catalytic effect when the weak nitrosating agent NO(2)(-) or ONOO(-) is involved, whereas it is an inhibitor in the nitrosation induced by the strong nitrosating agent N(2)O(3) or ONCl. To conclude, CO(2) serves as a "double-edged sword" in the nitrosation of amine. The findings will be helpful to expand our understanding of the pathophysiological and environmental significance of CO(2) and to develop efficient methods to prevent the formation of carcinogenic nitrosamines.

[Determination of aluminum in wheat flour food by microwave digestion-high resolution continuum source graphite furnace atomic absorption spectrometry].

The contents of aluminum (Al) in four kinds of wheat flour food (noodle, dumpling wrapper, twisted cruller and soda biscuit) were determined by high resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GFAAS) combined with microwave digestion. The samples were completely digested by the mixture of HNO3 and H2O2 in closed polytetrafluoroethylene (PTFE) vessels. The conditions for microwave digestion, pyrolysis temperature and atomization temperature were optimized. The optimum experimental conditions were determined as follows. The microwave digestion was performed with HNO3/H2O2 7:1 (volume ratio), microwave power 1000 W and 190 degrees C for 40 minutes. The optimum pyrolysis temperature was 1350 degrees C and the optimum atomization temperature was 2400 degrees C. Magnesium nitrate solution with the concentration of 1 g x L(-1) was used as the matrix modifier. The correlation coefficient for the standard curve was 0.9999, the relative standard deviation (RSD) was from 1.7% to 2.4%, and the recovery for the samples was from 98.16% to 102.67%. The assay method for the determination of Al in wheat flour food established in this study has referential importance for the constituent of the correlated food standards.

[Progress in study of biomacromolecular damages by infrared spectroscopy].

Infrared spectroscopy (IR) is employed as an important tool in the investigation of biological macromolecules because of its high sensitivity and nondestructivity to samples. When proteins, lipids or nucleic acids are damaged, the position, shape and intensity of their IR characteristic absorption peaks will be significantly changed. This provides evidences for the determination of the damages of biomolecules, which further shed light on the clarification of the occurrence, development and early prevention of some diseases. In the present paper, the applications of IR to the detection of biomolecular damages are reviewed. Various IR techniques are introduced, including Fourier transform infrared spectroscopy (FTIR), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), Fourier transform infrared spectroscopy microscope and so on. A general review was performed for the application of IR technique to the qualitative and quantitative analysis of secondary structure of protein, fluidity of membrane lipid, interaction of drugs with DNA and so on. The existing problems of IR were pointed out and the prospect of IR technique in the field of biomedicine was discussed. It is expected that, in the future the researches involving IR techniques will be focused on the application in early diagnosis of diseases, instrumental combinations and quantitative techniques.

[Pretreatment methods of urine proteomics in children with primary nephrotic syndrome].

OBJECTIVE: To optimize a pretreatment method of urine proteomics in children with primary nephrotic syndrome. METHODS: Urine from children with primary nephrotic syndrome was treated in different pH and isolated by cold acetone precipitation for different durations. Then the amounts and kinds of proteins were compared by quantify, SDS-polyacrylamide gel electrophoresis (SDS-PAGE) and two-dimensional electrophoresis (2-DE) in order to optimize a way to deal with urine protein. RESULTS: Most proteins were obtained at pH 2.7. The amounts of protein precipitated by acetone for 0.5 hr was obviously less than those precipitated for 1 and 2 hrs (P<0.05), while there was no significant difference between the amount of protein precipitated for 1 and for 2 hrs. Protein precipitated by cold acetone for 1 hr at pH 2.7 was selected as the best pretreatment method. Satisfactory 2-DE maps can be acquired. CONCLUSIONS: Urine protein can be best obtained at pH 2.7 and precipitated by cold acetone for 1 hr.

Preparation of 4,7-diphenyl-1,10-phenanthroline-2,9-dicarboxylic acid catalyzed by iron(III)porphyrins with (diacetoxyiodo)benzene.

Using iron(III)porphyrins in combination with (diacetoxyiodo)benzene allows for the conversion of 2,9-bis(bromomethyl)-4,7-diphenyl-1,10-phenanthroline into 4,7-diphenyl-1,10-phenanthroline-2,9-dicarboxylic acid. This method provides a cost-effective and environmentally-friendly oxidation procedure using less toxic PhI(OAc)2 and biologically relevant iron(III)porphyrins. The catalytic activity of five kinds of iron-metallated functional porphyrins were investigated using different oxidants, including air, H2O2, PhI(OAc)2, PhIO and NaClO. Our results showed that the use of T(p-NO2)PPFeCl with PhI(OAc)2 as the oxidant in the presence of water displays remarkable activity for the desired oxidation reaction. The generality of this method was examined by synthesizing the carboxylic acids of pyridines and quinolines.

Anodic oxidation of catechols in the presence of alpha-oxoketene N,N-acetals with a tetrahydropyrimidine ring: selective alpha-arylation reaction.

The electrochemical oxidation of catechols leads to the formation of o-benzoquinones. This property has been applied to effectively synthesize alpha-arylated products of alpha-oxoketene N,N-acetals with a tetrahydropyrimidine ring.

Theoretical investigation of N-nitrosodimethylamine formation from nitrosation of trimethylamine.

Tertiary amines have been demonstrated to be capable of undergoing nitrosative cleavage to produce carcinogenic N-nitrosamines. The reaction mechanism of the nitrosation of trimethylamine (TMA) to produce N-nitrosodimethylamine (NDMA) was investigated at the CBS-QB3 level of theory. The formation of NDMA from TMA was proposed to be initiated by the formation of an iminium ion, Me(2)N(+) horizontal lineCH(2). Two different mechanisms (NOH elimination mechanism and oxidation abstraction mechanism) leading to Me(2)N(+) horizontal lineCH(2) were investigated, and the oxidation abstraction mechanism was found to be mainly operative. This result indicates that the oxidation abstraction mechanism plays an important role in the nitrosation of both N,N-dialkyl aromatic and tertiary aliphatic amines. Starting from the iminium ion, two experimentally proposed mechanisms (pathways 1 and 2) and one new mechanism (pathway 3) were examined. Pathway 1 proposes that the iminium ion undergoes hydrolysis to give dimethylamine (DMA), which then can be further nitrosated to NDMA; pathway 2 proposes that the iminium ion reacts with NO(2)(-) and forms a neutral intermediate, which then collapses to NDMA. In pathway 3, the iminium ion reacts with N(2)O(3) to give NDMA. Calculation results indicate that in aqueous solution pathway 1 is more feasible than pathways 2 and 3; moreover, the transformation from the iminium ion to NDMA is the rate-determining step. This work will be helpful to elucidate the formation mechanisms of the carcinogenic N-nitrosamines from the nitrosation of tertiary amines.

One-pot electrochemical synthesis of fused indole derivatives containing active hydroxyl groups in aqueous medium.

An novel and convenient electrochemical approach was developed for the synthesis of indole derivatives from catechols and alpha-oxoheterocyclic ketene N,O-acetals. This method provides an environmentally benign access to fused indole derivatives containing active hydroxyls and carbonyl under mild reaction conditions.

Theoretical investigation of N-nitrosodimethylamine formation from dimethylamine nitrosation catalyzed by carbonyl compounds.

The carbonyl-compound-catalyzed nitrosation of amines to form carcinogenic nitrosamines under nonacidic condition is different from the classic nitrosation via acidification of nitrite anion. The mechanistic pathways of N-nitrosodimethylamine (NDMA) formation by the reactions of dimethylamine (DMA) with the nitrite anion catalyzed by carbonyl compounds have been investigated using the DFT/B3LYP method at the 6-311+G(d,p) level. The computational results show that the energy barriers of the nucleophilic addition reaction, which were calculated as 27-40 kcal/mol, increase significantly with methylation but vary slightly with chloromethylation on the carbonyl group. Comparison of energy barriers of this nucleophilic addition reaction and the electrophilic substitution reaction indicates that the former is the rate-determining step, from which the order of the catalytic activity is obtained as formaldehyde > chloral > acetaldehyde > acetone. Furthermore, analysis of electronic and steric effects on catalytic activity reveals that electron-withdrawing substituents decrease the energy barrier but electron-donating substituents and steric hindrance will block this catalytic reaction. Based on this discovery, fluoral is proposed as a good catalyst for the nitrosation of DMA by nitrite anion, which has a calculated energy barrier of about 26 kcal/mol. The results obtained in this work will help elucidate the mechanisms of formation of nitrosamines.

Design, synthesis and anti-HIV integrase evaluation of 4-oxo-4H-quinolizine-3-carboxylic acid derivatives.

4-Oxo-4H-quinolizine-3-carboxylic acid derivatives bearing sulfamido, carboxylamido, benzimidazole and benzothiazole substituents have been designed and synthesized. The structures of these new compounds were confirmed by (1)H-NMR, (13)C- NMR, IR and ESI (or HRMS) spectra. Compounds were screened for possible HIV integrase inhibitory activity.

Structure-based Discovery of Novel CK2α-Binding Cyclic Peptides with Anti-cancer Activity.

Protein kinase CK2 is considered as an emerging target in cancer therapy, and recent efforts have been made to develop its ATP-competitive inhibitors, but achieving selectivity with respect to related kinases remains challenging because of the highly conserved ATP-binding pocket of kinases. Non-ATP competitive inhibitors might solve this challenge; one such strategy is to identify compounds that target the CK2α/CK2ß interface as CK2 holoenzyme antagonists. Here we improved the binding affinity to CK2α and cell-based anti-cancer activity of a CK2ß-derived cyclic peptide (Pc) by combining structure-based computational design with experimental evaluation. By analyzing molecular dynamics simulations of Pc bound to CK2α, a series of Pc-derived peptides was rationally designed and synthesized to evaluate their binding affinity to CK2α, as well as anti-proliferative and pro-apoptotic effects against HepG2 cancer cell line. One amino acid substitutions on Pc, I192F, exhibited over 10-fold improvement in the predicted binding affinity to CK2α when compared to Pc, and a cell-permeable version, I192F-Tat, also demonstrated more potent anti-proliferative and pro-apoptotic effects against HepG2 compared to Pc. A second modification of Pc, H193W, also led to more potent cell-based activity, despite having weaker binding affinity (∼5×) to CK2α. The discovery of the I192F and H193W peptides provides new insights for further optimization of CK2 antagonist candidates as anti-cancer leads.

Metabolism of benzo[a]pyrene in peroxynitrite/Fe(III) porphyrin system.

The peroxynitrite/porphyrin biomimetic system was established to investigate the effects of peroxynitrite on benzo[a]pyrene (B[a]P) metabolism. Three model systems consisting of different iron porphyrins were compared, and the results showed that the peroxynitrite/T(p-Cl)PPFeCl system was the highest catalytic efficiency in the metabolism of B[a]P. We analyzed the B[a]P metabolites produced from this system by RP-HPLC method and firstly identified the formation of nitrobenzo[a]pyrenes which are the special metabolites of B[a]P induced by peroxynitrite.