Mass spectrometric characterization of phosphorylated peptides using MALDI in-source decay via redox reactions

Matrix-assisted laser desorption/ionization in-source decay (MALDI-ISD) has been used for characterization of a phosphorylated peptides and proteins because labile phosphate group is not lost during the MALDI-ISD process. The conventional MALDI-ISD is initiated by the hydrogen transfer from reducing matrix molecules to peptide backbone, leading to c'- and z'-series ions. In contrast, when an oxidizing chemical 5-nitrosalicylic acid (5-NSA) is served as the MALDI-ISD matrix, a- and x-series ions are specifically generated by hydrogen abstraction from peptide backbone to matrix molecule. The 5-NSA provides useful complementary information to the conventional MALDI-ISD for the analysis of amino acid sequencing and site localization of phosphorylation in peptides. The MALDI-ISD with reducing and oxidizing matrix could be a useful method for the de novo peptide sequencing.     

Sonolytic hydrolysis of peptides in aqueous solution upon addition of catechol

The sonolytic hydrolysis of peptides with addition of phenolic reagents to aqueous solutions is described. Sonolysis of an aqueous solution of peptides to which catechol (o-dihydroxybenzene) had been added resulted in hydrolytic products reflecting the amino acid sequence without any side reactions, while sonolysis without any additives resulted in oxidation analytes and degradation products caused by side reactions. Although the use of additives such as resorcinol (m-dihydroxybenzene), hydroquinone (p-dihydroxybenzene) and phenol was also effective in producing sequence related products, several degradation products were produced by side reactions. A characteristic of the sonolysis of peptides is that the N-terminal side of proline, Xxx-Pro, is more susceptible than other amino acid residues to the process. This characteristic of sonolysis is superior to that of acid hydrolysis in which cleavage at the C-terminal side of proline, Pro-Xxx is difficult, and where dehydration products result due to side reactions.     

Kinetics and mechanisms of the sonolytic destruction of non-volatile organic compounds: investigation of the sonochemical reaction zone using several OH* monitoring techniques

This study investigates the sonolytic degradation mechanism of non-volatile organic compounds and reaction sites for its degradation using various tools that allow OH* to be monitored, such as: the spin-trapping method of OH* detection using non-volatile nitrone trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), the hydrogen peroxide analytical methods and the p-chlorobenzoic acid (pCBA)-probe method. These methods can successfully monitor OH* produced during sonochemical processes, and identify the major reaction sites involving OH* of the three proposed reaction zones--within the cavity, in the bulk solution, and at the gas-liquid interfacial (shell) region. The patterns of hydrogen peroxide accumulation under the various conditions suggest that peroxides pre-form at the interfacial region, but the self-scavenging reaction by hydrogen peroxide simultaneously takes place in the same region. The simultaneously measured peroxide concentration, in the absence and presence of DMPO, and that of the DMPO-OH adduct indicated the peroxide production and DMPO-OH adduct formation reaction occur at the shell region. The sonolytic destruction efficiency of ultrasound coupled with Fe(II) has been also investigated. The coupled Fe(II)/ultrasound process was found to enhance the OH* production rate by 70% compared to the ultrasound process alone due to the reaction of Fe(II) with sonochemically produced hydrogen peroxide (Fenton's reaction). This accelerated reaction was also found to occur at the shell region rather than in the bulk solution. The enhancement effect of Fe(II)/ultrasound was also examined using pCBA as a probe. 2.8-fold and 3.6-fold increases of the pCBA degradation rate were observed at Fe(II) concentrations of 10 and 20 microM, respectively.     

模板法合成金属-分子-金属异质结及表面增强拉曼光谱研究

采用交流电沉积技术在阳极氧化铝(AAO)模板中沉积不同的金属纳米线, 以对巯基苯(1,4-BDT)为耦联分子, 通过自组装在模板内组装金属纳米粒子, 由此构建金属纳米线-分子-金属纳米粒子的异质结。以异质结内的分子为探针, 采用表面增强拉曼光谱(SERS)研究了异质结的增强行为,通过探针分子的SERS信号表达异质结的组成,并以异质结作为模型研究其SERS机理。研究结果表明该方法可成功构建异质结, 同一取向的异质结的SERS信号较随机取向的SERS信号强。     

吩噻嗪-1,4萘醌-乙二醇体系光化学过程的时间分辨ESR研究

用时间分辨ＥＳＲ方法研究了吩噻嗪（ＰＴＨ）－１，４－萘醌（ＮＱ）－乙二醇（ＲＨ）体系中的光化学过程．只观察到萘醌的中性半醌自由基ＮＱＨ．＊的全发射极化的ＣＩＤＥＰ（化学诱导动态极化）信号，并未观察到极化的萘醌负离子ＮＱ－·＊的ＣＩＤＥＰ信号，表明ＲＨ与三重态ＮＱ间的质子转移反应远比ＰＴＨ与ＮＱ间的电子转移反应为快．ＮＱＨ．＊的ＣＩＤＥＰ信号随ｐＨ值的变化表明体系中同时有极化自由基ＮＱＨ．＊与ＮＱＨ．＋＊２存在，并且其间有质子交换．     

吩噻嗪-1,4萘醌-乙二醇体系光化学过程的时间分辨ESR研究

用时间分辨ESR方法研究了吩噻嗪(PTH)-1,4-萘醌(NQ)-乙二醇(RH)体系中的光化学过程.只观察到萘醌的中性半醌自由基NQH^*的全发射极化的CIDEP(化学诱导动态极化)信号,并未观察到极化的萘醌负离子NQ·^-*的CIDEP信号,表明RH与三重态NQ间的质子转移反应远比PTH与NQ间的电子转移反应为快.NQH·^*的CIDEP信号随pH值的变化表明体系中同时有极化自由基NQH·^*与NQH·₂^+*存在,并且其间有质子交换.     

Sonochemical degradation of martius yellow dye in aqueous solution

The sonolytic degradation of the textile dye martius yellow, also known as either naphthol yellow or acid orange 24, was studied at various initial concentrations in water. The degradation of the dye followed first-order kinetics under the conditions examined. Based on gas chromatographic results and sonoluminescence measurements of sonicated aqueous solutions of the dye, it is concluded that pyrolysis does not play a significant role in its degradation. The chromatographic identification of hydroxy added species indicates that an OH radical induced reaction is the main degradation pathway of the dye. Considering the non-volatility and surface activity of the dye, the degradation of the dye most probably takes place at the bubble/solution interface. The quantitative and qualitative formation of the degradation intermediates and final products were monitored using HPLC and ESMS. The analytical results suggest that the sonolytic degradation of the dye proceeds via hydroxylation of the aryl ring and also by C-N bond cleavage of the chromophoric ring, either through OH radical attack or through another unidentified process. The identification of various intermediates and end products also imply that the degradation of martius yellow proceeds through multiple reaction pathways. Total organic carbon (TOC) analyses of the dye solutions at various times following sonication revealed that sonolysis was effective in the initial degradation of the parent dye but very slow in achieving mineralization. The slow rate of mineralization is likely to be due to the inability of many of the intermediate products such as, the carboxylic acids, to accumulate at the bubble (air/water) interface and undergo decomposition due to their high water solubility (low surface activity).     

Time‐dependent density functional theory study on the excited‐state hydrogen bonding strengthening of photoexcited 4‐amino‐1,8‐naphthalimide in hydrogen‐donating solvents

The time‐dependent density functional theory (TDDFT) method was performed to investigate the excited‐state hydrogen bonding dynamics of 4‐amino‐1,8‐naphthalimide (4ANI) as hydrogen bond acceptor in hydrogen donating methanol (MeOH) solvent. The ground‐state geometry optimizations, electronic transition energies and corresponding oscillation strengths of the low‐lying electronically excited states for the isolated 4ANi and hydrogen‐bonded 4ANi‐(MeOH)_1,4 complexes were calculated by the DFT and TDDFT methods, respectively. We demonstrated that the intermolecular hydrogen bond C═O···H–O and N–H···O–H in the hydrogen‐bonded 4ANi‐(MeOH)_1,4 is strengthened in the electronically excited state, because the electronic excitation energies of the hydrogen‐bonded complex are correspondingly decreased compared with that of the isolated 4ANi. The calculated results are consistent with the mechanism of the hydrogen bond strengthening in the electronically excited state, while contrast with mechanism of hydrogen bond cleavage. Furthermore, we believe that the transient hydrogen bond strengthening behavior in electronically excited state of fluorescent dye in hydrogen‐donating solvents exists in many other systems in solution. Copyright © 2013 John Wiley & Sons, Ltd.     

Study on the relationship between structure and taste activity of the umami peptide of Stropharia rugosoannulata prepared by ultrasound

Through virtual screening, electronic tongue verification, and molecular docking technology, the structure-taste activity relationship of 47 kinds of umami peptides (octapeptide - undecapeptide) from Stropharia rugosoannulata prepared by simultaneous ultrasonic-assisted directional enzymatic hydrolysis was analyzed. The umami peptides of S.rugosoannulata can form hydrogen bond interaction and electrostatic interaction with umami receptors T1R1/T1R3. The amino acid residues at the peptides' N-terminal and C-terminal play a vital role in binding with the receptors to form a stable complex. D, E, and R are the primary amino acids in the peptides that easily bind to T1R1/T1R3. The basic amino acid in the peptides is more easily bound to T1R1, and the acidic amino acid is more easily bound to T1R3. The active amino acid sites of the receptors to which the peptides bind account for 42%−65% of the total active amino acid residues in the receptors. ASP147 and ASP219 are the critical amino acid residues for T1R1 to recognize the umami peptides, and ARG64, GLU45, and GLU48 are the critical amino acid residues for T1R3 to recognize the umami peptides. The increase in the variety and quantity of umami peptides is the main reason for improving the umami taste of the substrate prepared by synchronous ultrasound-assisted directional enzymatic hydrolysis. This study provides a theoretical basis for understanding simultaneous ultrasound-assisted directional enzymatic hydrolysis for preparing umami peptides from S.rugosoannulata, enhancing the flavor of umami, and the relationship between peptide structure and taste activity.     

Ultrasonication promotes extraction of antioxidant peptides from oxhide gelatin by modifying collagen molecule structure

This study primarily explored the internal mechanism underlying the ultrasonication-induced release of antioxidant peptides. An oxhide gelatin solution was treated ultrasonically (power = 200, 300, and 400 W), followed by enzymatic hydrolysis and structural and morphological analysis. The results showed that ultrasonication increased not only the degree of hydrolysis (DH) and protein recovery rate of the oxhide gelatin but also the ABTS radical scavenging, DPPH radical scavenging, ferrous chelating, and ferric reducing activities of its hydrolysate. The oxhide gelatin hydrolysate treated with 300-W ultrasonication had the maximum antioxidant activities. Ultrasonication inhibited hydrogen bond formation, reduced the crosslinking between collagen molecules, transformed part of the folded structure into a helical structure, and lowered the thermal stability of collagen molecules. The micromorphological analysis revealed that ultrasonication caused the gelatin surface to become loose and develop cracks, and as the power of the ultrasonication increased, the repetition interval distance (dÅ) also increased. Moreover, ultrasonication improved the solubilization, surface hydrophobicity, and interface characteristics and increased the content of basic and aromatic amino acids in the hydrolysate. In conclusion, ultrasonication modifies the protein structure, which increases the enzyme’s accessibility to the peptide bonds and further enhances antioxidant peptide release. These findings provide new insights into the application of ultrasonication in the release of antioxidant peptides.     

Thermodynamic and kinetic analysis of the reaction between biological catecholamines and chlorinated methylperoxy radicals

The antiradical potency of catecholamines (dopamine, epinephrine, norepinephrine, L-DOPA), metabolites of dopamine (homovanillic acid, 3-methoxytyramine and 3,4-dihydroxyphenylacetic acid) and catechol towards substituted methylperoxy radicals is investigated. The thermodynamic parameters, together with the kinetic approach, are used to determine the most probable mechanism of action. The natural bond orbital and quantum theory of atoms in molecules are utilised to explain the highest reactivity of trichloromethylperoxy radical. The preferred mechanism is dependent both on the thermodynamic and kinetic parameters . The number of chlorine atoms on radical, the presence of intra-molecular hydrogen bond and number of hydroxy groups attached to the aromatic ring significantly influence the mechanism. The results suggest that sequential proton loss electron transfer (SPLET) is the most probable for reaction with methylperoxy and hydrogen atom transfer (HAT) for reaction with trichloromethylperoxy radicals, with a gradual transition between SPLET and HAT for other two radicals. Due to the significant deprotonation of molecules containing the carboxyl group, the respective anions are also investigated. The HAT and SPLET mechanisms are highly competitive in reaction with MP radical, while the dominant mechanism towards chlorinated radicals is HAT. The reactions in methanol and benzene are also discussed.     

Sonochemical and sonophotocatalytic degradation of malachite green: the effect of carbon tetrachloride on reaction rates

A comparative study between the sonolytic, photocatalytic and sonophotocatalytic oxidation processes of aqueous solutions of malachite green was carried out in the presence of carbon tetrachloride, under a low power ultrasonic field (<15 W) and using titanium dioxide as a photocatalyst. The effect of a number of parameters such as ultrasonic intensity, TiO2 crystalline structure and the presence of CCl4 were studied using an inexpensive reactor. Enhanced rates of sonolytic degradation of malachite green in the presence of CCl4 were demonstrated. On the other hand, the simultaneous use of sonolysis and photocatalysis in the presence of CCl4 does not improve the degradation rate of malachite green in comparison with the one obtained using only sonolysis, but it makes possible a faster oxidative degradation of some reaction intermediaries. Finally, in air saturated solutions both processes, the sonolytic and the photocatalytic one, follow a first-order rate law.     

Synergistic effect and mechanisms of ultrasound and AlOOH suspension on Al hydrolysis for hydrogen production

Ultrasound can accelerate and change the reaction process and is widely used in the field of hydrogen production and storage. In this study, ultrasound (US) and AlOOH suspension (AH) are used to promote hydrogen production from Al hydrolysis. The results indicate that both US and AH greatly shorten the induction time and enhance the hydrogen production rate and yield. The promoting effect of US and AH on Al hydrolysis originates from the acoustic cavitation effect and catalytic effect, respectively. When AH is used in combination with US, Al hydrolysis has the best hydrogen production performance and the hydrogen yield can reach 96.6 % within 1.2 h, because there is a synergistic effect on Al hydrolysis between AH and US. Mechanism analyses reveal that the micro-jets and local high temperature environment arising from acoustic cavitation improve the catalytic activity of AlOOH, while the suspended AlOOH particles enhance the cavitation effect of US. This work provides a novel and feasible method to promote hydrogen production from Al hydrolysis.     

Sonolysis and radiolysis of glyceraldehyde in deaerated aqueous solution

The objective of this work was to contribute to the mechanism of the sonolytic and radiolytic reactions leading in deaerated aqueous solutions of sugars to products by radical-radical combination. For this purpose glyceraldehyde, the first homologue of the series of aldoses, was investigated. Primary glyceraldehyde radicals are produced by abstraction of carbon-bonded hydrogen atoms by sonolytic or radiolytic H and OH radicals. Secondary glyceraldehyde radicals are derived from primary radicals by elimination of water. Both kinds of radicals were found to participate in dimer production.     

Magnetic field effects on the reaction of the photoexcited triplet of 2-methyl-1,4-naphthoquinone in SDS micellar solution containing the 4-(lauroylamino)-TEMPO radical

A study has ben made of magnetic field effects (MFEs) on the reaction of the photoexcited triplet of 2-methyl-1,4-naphthoquinone (MNQ) in SDS micellar solution containing the 4-lauroylamino-TEMPO radical (L-R^?) under magnetic fields below 1.75 T by a nanosecond laser flash photolysis technique. The triplet MNQ mainly underwent the hydrogen abstraction from an SDS molecule to give a radical pair. The lifetime of the radical pair increased with increasing magnetic field from 0 to 0.62 T. The escaped radical yield also increased from 0 to 1.75 T. The qualitative features of these MFEs were similar to those observed for the photo-reduction of MNQ in SDS micellar solution without L-R^?, and these MFEs can be explained by the relaxation mechanism. However, it was found that L-R^? affected the MFEs for this reaction in two ways: first, L-R^? reacted with the triplet MNQ through H abstraction and/or electron transfer, and second, the spin relaxation of the radical pair was enhanced through the spin-spin interactions of the individual radical with L-R^?.     

Pulse-shift measurement: a direct observation of radical pair dynamics in a micelle

The hydrogen abstraction reactions of benzophenone in a micellar solution in the absence and presence of 1,4-cyclohexadiene are compared with time-resolved electron spin resonance (ESR) and optically detected (OD) ESR. “Pulse shift” measurement by OD-ESR, which observes the effect of a resonant microwave pulse at different delay times after laser excitation, reveals that the lifetime of the radical pair becomes much shorter in the presence of 1,4-cyclohexadiene. This explains the change of chemically induced dynamic electron polarization from spin-correlated radical pair polarization in the absence of 1,4-cyclohexadiene to conventional, E^*/A polarization in its presence. The rate constants determined by this technique indicate that the escaping rate of cyclohexadienyl radical is ten times larger than those of alkyl and benzophenone ketyl radicals.     

Sonolytic and sonophotolytic degradation of Carbamazepine: Kinetic and mechanisms

An in-depth investigation on the ultrasonic decomposition of Carbamazepine (CBZ), one of the most regularly identified drugs in the environment, was conducted. The effects of diverse variables were evaluated, such as frequency, power, solution pH, initial CBZ concentration and varied inorganic anions. Reaction order was determined on the basis of analyzing reaction kinetics of CBZ degradation. The sonophotolysis and photolysis of CBZ was also examined in this contribution. The influence of water composition on the sonolytic and sonophotolytic elimination of CBZ was analyzed. Additionally, 21 intermediates were identified during sonolytic degradation of CBZ based on LC/ESI-MS/MS analysis, among which two escaped from the detection in previous studies. Possible decay pathways were proposed accordingly. The epoxidation, cleavage of double bond, hydration, hydroxylation, ring contraction and intramolecular cyclization were believed to be involved in sonochemical degradation of CBZ.     

Analysis of sonolytic degradation products of azo dye Orange G using liquid chromatography-diode array detection-mass spectrometry

In this paper, seven new sonolytic degradation products of Orange G were found and identified using powerful analytical techniques such as liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS), tandem mass spectrometry (MS/MS), and liquid chromatography with diode-array detection (LC-DAD). Each technique provided complementary information for the degradation products identification. In order to resolve the MS and MS/MS spectra obtained, the separation conditions were optimized. Among them, Orange G was unambiguously identified based on its abundant [M-H](-) ion, [M+H](+) ion, ultra-violet and visible spectra, retention time, and tandem mass spectrometric analysis compared with an authentic standard. The seven new degradation products were tentatively identified based on ultra-violet and visible spectra, [M-H](-) ions, and tandem mass spectrometry. The neutral losses of SO(2), SO(3), N(2) and H(2)O for MS/MS spectra which appear to be characteristic of the negative ion mode were observed. Based on this by-product identification, a possible multi-step degradation scheme is proposed. The analysis results of degradation products reveal that the degradation mechanism proceeds via reductive cleavage of the azo linkage, as well as intermolecular dehydration and desulfonation due to the powerful oxidizing hydroxyl radicals as well as hydrogen radical.     

Sonolysis of aqueous 4-nitrophenol at low and high pH

The sonolysis of 4-nitrophenol in argon-saturated aqueous solution has been studied at 321 kHz. In order to evaluate separately the effect of OH radicals that are formed in the cavitational bubble and part of which react in the aqueous phase with this substrate, radiolytic studies in N2O-saturated solutions were carried out for comparison. A detailed product study of the sonolysis of 4-nitrophenol solutions shows that at pH 10, where 4-nitrophenol is deprotonated (pKa = 7.1), its sonolytic degradation is fully accounted for by OH-radical-induced reactions in the aqueous phase. At this pH, the sonolytic yield of H2O2 resulting from OH radical recombination in the solution, measured as a function of the 4-nitrophenol concentration, is reduced in line with the scavenging capacity of the 4-nitrophenolate. In contrast, at pH 4 the formation of H2O2 is already fully suppressed when the solution is 7 x 10(-4) mol dm-3 in 4-nitrophenol, and oxidative-pyrolytic degradation predominates, as exemplified by the large yields of CO and CO2 which are accompanied by a large H2 yield. The basis of this difference in behavior is a hydrophobic enrichment of 4-nitrophenol (which is undissociated at pH 4) at the interface of the cavitational bubble by a factor of about 80. The pH dependence of the yields of the pyrolytic products reflects the hydrolytic equilibrium concentration of 4-nitrophenol. The paper also demonstrates that the complexity of this sonochemical system precludes its use a gauge to determine the temperature in the interior of the cavitational bubble.     

OH-radical formation by ultrasound in aqueous solution--Part II: Terephthalate and Fricke dosimetry and the influence of various conditions on the sonolytic yield

Terephthalate and Fricke dosimetry have been carried out to determine the sonolytic energy yields of the OH free radical and of its recombination product H2O2 in aqueous solutions under various operating conditions (nature of operating gas, power, frequency, temperature). For example, in the sonolysis of Ar-saturated terephthalate solutions at room temperature, a frequency of 321 kHz, and a power of 170 W kg-1, the total yield [G(.OH) + 2 G(H2O2)], equals 16 x 10(-10) mol J-1. This represents the total of .OH that reach the liquid phase from gas phase of the cavitating bubble. The higher the solute concentration, the lower the H2O2 production as more of the OH free radicals are scavenged, in competition with their recombination. Fricke dosimetry, in the absence and presence of Cu2+ ions, shows that the yield of H atom reaching the liquid phase is much lower, with G(H.) of the order of 3 x 10(-10) mol J-1. These sonolytic yields are smaller in solutions that are at the point of gas saturation, and increase to an optimum as the initial sonication-induced degassing and effervescence subsides. The probing of the sonic field has shown that the rate of sonolytic free-radical formation may vary across the sonicated volume depending on frequency and power input.