Highly efficient and selective enrichment of phosphopeptides using porous anodic alumina membrane for MALDI-TOF MS analysis

Because of its good biocompatibility, high surface-to-volume ratio, and distinct surface electrical properties, porous anodic alumina (PAA) membrane has been used to selectively enrich phosphopeptides from a mixture of synthetic peptides and tryptic digest product of beta-casein by a direct MALDI-TOF MS analysis. As we reported previously, PAA membrane has strong incorporation ability to the phosphate anion. Herein, we describe the application of PAA membrane as a selective sampling absorbent for phosphopeptides. The PAA membrane could enrich phosphopeptides with high efficiency and selectivity; for example, the tryptic digest product of beta-casein at a concentration as low as 4 x 10(-9) M can be satisfactorily detected. Compared to that from the nonenriching peptide mixture, the MS signal of the phosphorylated peptides enriched by the PAA membrane is remarkably improved. In addition, acidic peptides have insignificant influence on the enriching process. Results show that the adsorption of phosphate anions on the PAA membrane plays a determining role in achieving highly selective enriching capacity toward phosphopeptides. The feasibility of PAA membranes as specific absorbents for phosphopeptides is also demonstrated.     

Characterization by tandem mass spectrometry of stable cysteine sulfenic acid in a cysteine switch peptide of matrix metalloproteinases

Cysteine sulfenic acid (Cys-SOH) is an elusive intermediate in reactive oxygen species-induced oxidation reactions of many proteins such as peroxiredoxins and tyrosine phosphatases. Cys-SOH is proposed to play a vital role in catalytic and signaling functions. The formation of cysteine sulfinic acid (Cys-SO(2)H) and cysteine sulfonic acid (Cys-SO(3)H) has been implicated in the activation of matrix metalloproteinase-7 (MMP-7) and oxidation of thiol to cysteine sulfinic acid has been associated with the autolytic cleavage of MMP-7. We have examined the formation of cysteine sulfenic acid in a synthetic peptide PRCGVPDVA, which is a cysteine switch domain of MMP-7 and other matrix metalloproteases. We have prepared the cysteine sulfenic acid containing peptide, PRC(SOH)GVPDVA, by reaction with hydroxyl radicals generated by the Fenton reaction (Fe(+2)/H(2)O(2)). We characterized this modified peptide by tandem mass spectrometry and accurate mass measurement experiments. In addition, we used 7-chloro-4-nitrobenzo-2-oxa-1,3-diazol (NBD-Cl) reagent to form an adduct with PRC(SOH)GVPDVA to provide additional evidence for the viability of PRC(SOH)GVPDVA in solution. We also characterized an intramolecular cysteine sulfinamide cross-link product PRC[S(O)N]GVPDVA based on tandem mass spectrometry and accurate mass measurement experiments. These results contribute to the understanding of a proteolytic cleavage mechanism that is traditionally associated with MMP activation.     

Analysis of food for toxic elements

The levels of the toxic elements Al, As, Cd, Hg, Pb and Sn are routinely monitored in food to protect the consumer. Increasingly, the chemical forms of As and Hg are also monitored. Analyses are performed to enforce regulatory standards and to accumulate background levels for assessing long-term exposure. The analytical procedures used for these activities evolve as requirements to determine lower levels arise and as both the types and sheer number of different foods that need to be analyzed increase. This review highlights recent work addressing improvements in the analysis of toxic elements in food. The topics covered include contamination control, analytical sample treatment and the common analytical techniques used for food analysis.     

Loop formation and stability of self-avoiding polymer chains

Using 3-dimensional Langevin dynamics simulations, we investigated the dynamics of loop formation of chains with excluded volume interactions, and the stability of the formed loop. The mean looping time τ _l scales with chain length N and corresponding scaling exponent α increases linearly with the capture radius scaled by the Kuhn length a/l due to the effect of finite chain length. We also showed that the probability density function of the looping time is well fitted by a single exponential. Finally, we found that the mean unlooping time τ _u hardly depends on chain length N for a given a/l and that the stability of a formed loop is enhanced with increasing a/l.     

Swelling of <Emphasis Type="Italic">N</Emphasis>-vinylcaprolactam-dodecyl methacrylate gel in {heptane + toluene} mixtures

A copolymer gel has been synthesized from N-vinylcaprolactam and dodecyl methacrylate in ethanol using the free radical cross-linking polymerization method. Characterizations of the gel were performed by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and thermal gravimetric analysis (TGA) techniques. Swelling behavior of the gel was investigated in heptane, toluene, and their binary mixtures with different compositions. Swelling value in toluene is higher than that in heptane and swelling value increases with the increasing initial content of toluene in the binary mixture with heptane. The swelling values are correlated by the first- and second-order differential equations, and the best model correlating the experimental results is a second-order one. Diffusion coefficients have also been calculated for heptane and toluene at each concentration by power-law and first-order equations. While the diffusion mechanism of the gel in heptane is a Fickian one, the gel swelled in toluene exhibits a non-Fickian character. Diffusion mechanisms of the gels in binary mixtures are much more complicated. Because of the higher swelling degree in toluene compared to that in heptane, selectivity of the gel in different {heptane + toluene} mixtures with selectivity close to 1 has also been taken into consideration.     

Flame retardant finishing of cotton fleece: part VII. Polycarboxylic acids with different numbers of functional group

In our previous research, multifunctional carboxylic acids have been used as flame retardants to reduce the flammability of cotton fleece so that the garment made of cotton fleece can pass the US mandatory requirement specified by the government regulation “Standard for the Flammability of Clothing Textiles” (16 CFR 1610). In this research, we studied and compared the effectiveness of the polycarboxylic acids having different numbers of carboxylic groups as the durable flame retardants for cotton fleece. The cotton fabrics were treated with 1,2,3,4-butanetetracarboxylic acid (BTCA), citric acid (CA), succinic acid (SUA) and malic acid (MLA). We compared the reactivity of those polycarboxylic acids to esterify cotton cellulose and their effectiveness to reduce the flammability of the cotton fleece. The data indicated that the polycarboxylic acids with higher functionalities (BTCA and CA) form more esterlinkages on cotton and are more durable to home launderings than that treated with their bifunctional counter parts (SUA and MLA, respectively). In addition, the cotton fabrics treated with BTCA and CA have higher dimensional stability and higher strength loss. All those differences can be attributed to the fact that only those acids with three or more carboxylic groups, i.e., BTCA and CA, are able to crosslink cotton cellulose whereas the bifunctional acids (SUA and MLA) only form single esterlinkage with cotton.     

Phosphorous,nitrogen, and molybdenum ternary co-doped TiO2: preparation and photocatalytic activities under visible light

P, N, and Mo ternary co-doped nano TiO₂ photocatalysts ((P, N, Mo)-TiO₂) were prepared by a single step sol–gel method, which show much enhanced photocatalytic activities over Mo-TiO₂, (P, N)-TiO₂, un-doped TiO₂ and Degussa P25 under visible light irradiation. The degradation rate of 0.72Mo–P-TiO₂ is as high as 65.3%, which is about 6.7 times of that of Degussa P25. Possible reasons for the improvement of photocatalytic activities were analyzed.     

Solvent Effects on the Structure-Activity Relationship of Phenytoin-like Anticonvulsant Drugs

The absorption spectra of nine compounds structurally related to phenytoin (5,5-diphenylhydantoin) were recorded in twelve solvents over the range of 200 to 400 nm. The effects of solvent dipolarity/polarizability and solvent/solute hydrogen bonding interactions were analyzed by means of the linear solvation energy relationship (LSER) concept proposed by Kamlet and Taft. The lipophilic activity of the investigated hydantoins was estimated by calculation of their log ₁₀ P values. The calculated values of log ₁₀ P were correlated with the ratio of the contributions of specific and non-specific solute/solvent interactions. The correlation equations were combined with the corresponding ED₅₀ values to generate new equations that demonstrate exact relationship between solute/solvent interactions and the structure-activity parameters.     

Fatty acid profile of <Emphasis Type="Italic">Trichosanthes kirilowii</Emphasis> Maxim. seed oil

Fatty acid profile data for refined cold-pressed Trichosanthes kirilowii Maxim. seed oil, in comparison to other commercially available oils — olive, rapeseed and camellia, are presented. Trichosanthes kirilowii Maxim. seed oil has high oleic and linoleic acid content and high polyunsaturated acid content. Squalene elutes as a distinct peak in the GC chromatograph. For a positive identification, MS detection was used. In the samples analyzed, squalene occurred in the range of 57.4–68.2 mg g⁻¹.