Photochemical inactivation of trypsin

Abstract —The quantum yield for inactivation of aqueous trypsin fits the expression φ_f=Σ_rf_rφ‘_r, where f_r, is the fraction of incident light absorbed by residues of type r and the φ’_r are constants. The values φ‘_trp= 0.012, φ_tyr= 0.005 and φ’_eys= 0.10, obtained at pH 3 in the wavelength range 240–290 nm, are attributed to independent events by comparing with quantum yields of the initial photochemical products and permanent residue destruction. The proposed inactivating processes are photoionization of one essential tryptophyl residue, photolysis of one essential cystyl residue, and splitting of an essential cystyl residue induced by light absorption in a nearby tyrosyl residue. The initial photochemical process from pH 3–7 identified by flash photolysis is the ejection of electrons from approximately two tryptophyl residues, leading to the formation of the disulfide bridge electron adduct and the hydrated electron. It is proposed that one photoionized tryptophyl residue is permanently disrupted and the other is restored through a back reaction that leads to a damaged, active enzyme form. An enhanced inactivation quantum yield at flash photolysis light intensities is attributed to a biphotonic process. A model based on one-photon photoionization of tryptophan from a short-lived precursor of the fluorescent state and the biphotonic photoionization of tryptophan via the triplet state is consistent with the experimental results.     

吡啶萃取对烟煤热解过程焦油生成特性的影响

煤中含有以非共价键结合的可萃取物，煤的萃取物和萃余物热解反应性不同。本研究首先用醋酸消除煤中静电作用力，再以吡啶萃取消除氢键作用力，通过热重和固定床研究了煤萃取物和萃余物的热解特性。相对于原煤，萃取物（E1）的H/C原子比较高，而萃余物（R1）比原煤的孔径有所增大。热重实验表明，萃取物热分解温度低，失重率大；萃余物在485℃之前失重大于原煤，温度高于485℃小于原煤。固定床氮气热解表明，萃取物（E1）的焦油产率和气体比原煤高；萃余物（R1）的焦油产率低于原煤焦油产率。而氢气气氛下，萃取残渣的焦油产率明显高于原煤，这是由于吡啶萃余物具有更开放的孔结构，有利于加氢热解过程氢向孔内扩散，减少了缩聚反应。     

Improving the Selectivity of the Phosphoric Acid β-Elimination on a Biotinylated Phosphopeptide

This study aims at improving the MALDI-TOF detection of a phosphorylated peptide containing a cysteine residue by ??-elimination of H₃PO₄ hardly enriched by classical methods. The experimental conditions were optimized on this phosphopeptide (biot-pAdd) and its nonphosphorylated counterpart (biot-Add). The major side-reactions were H₂S elimination on the cysteine residues and H₂O elimination on the non phosphorylated serine residue of biot-Add. The former dilutes the MALDI-TOF signal for the desired species. The latter gives a product similar to what is obtained by H₃PO₄ elimination and should prompt to caution when working with a mixture between phosphorylated and non phosphorylated peptides. Modifications on the solvent, the reaction temperature and time, the nature, and concentration of the base were made. Major improvement of the selectivity of the reaction was observed in 30?% ACN, at room temperature for 4?h. However, these optimizations are specific to these sequences and should be performed anew for different peptides. The selectivity of the reaction towards H₃PO₄ elimination is improved, but the persistence of side-reactions renders a previous sample fractionation necessary. In these optimized conditions, the ionization enhancement is 3-fold and the detection limits for biot-pAdd are similar to biot-Add (100?fmol).     

The thermal decomposition of the carbonate reaction products

The complex thermal analysis was used in the investigations of the carbonate reaction products in the residue after Al leaching from calcium aluminate-12CaO·7Al₂O₃ and Selfdisintegrated Powder. The conversion of Al was calculated basing on a content of Al in the pregnant solution as well as in a residue obtained from the kinetic investigations. The third method of measurements of a conversion of Al was presented and discussed. Results show, that the proposed method can be used for conversion estimations with 95% of confidence level as well as for the detection of carbonate products and is useful for an interpretation of the new approach for kinetic mechanism of Al leaching.     

Molecular level understanding of the role of aldehyde in vegetable‐aldehyde–collagen cross‐linking reaction

The role of formaldehyde (HCHO) in vegetable‐aldehyde–collagen cross‐linking reaction was investigated at the B3LYP/6‐31+G(d) level, where lysine (LYS) was used as model of collagen and catechin (EC) as model of condensed vegetable tannin. Atomic charge and Frontier molecular orbital analysis show that intermediates formed by HCHO reacting with LYS or EC, that is, M_LYS, M_EC‐6, and M_EC‐8, still have both nucleophilic and electrophilic sites, which are elements to form ternary cross‐linking in vegetable‐aldehyde–collagen system. The analysis of energy gap between HOMO (highest occupied molecular orbit) and LUMO (lowest unoccupied molecular orbit) indicate that the intermediate of HCHO–LYS residues (M_LYS) can further react with free HCHO to form product P‐N(CH₂OH)₂ (P‐N‐represents amino acid residue; N represents nitrogen atom on side chain), but the reaction of intermediate M_LYS with free EC is difficult to take place. So, the probability of forming ternary cross‐linking structure of amino acid residue–HCHO–EC is small, if HCHO is added before vegetable tannin in vegetable‐aldehyde–collagen system. However, the reactions of EC–HCHO intermediates (M_EC‐6 and M_EC‐8) with free amino acids, HCHO–amino acid residue intermediate (M_LYS), as well as with other EC–HCHO intermediates (M_EC‐6 and M_EC‐8), are very easy to take place. The reaction enthalpy also shows that the cross‐linking tendency is favorable in thermodynamics. So, it can be deduced that covalent cross‐linking among amino side chain of collagen and vegetable tannin may take place when aldehyde is added after vegetable tannin. In this way, a multiple point cross‐linking reaction occurs to create a high stabilization of collagen. © 2011 Wiley Periodicals, Inc.     

Observation of phosphorylation site-specific dissociation of singly protonated phosphopeptides

In ultraviolet photodissociation of phosphopeptide ions with a basic residue (arginine, lysine, or histidine) at the N-terminus, intense a_n − 97 peaks were observed. These ions were formed by cleavage at phosphorylated residues only. For multiply phosphorylated peptides, this site-specific cleavage occurred at every phosphorylated residue. H/D exchange studies showed that a_n − 97 was formed by H₃PO₄ loss from a_n+1 radical cations. The site-specificity of phosphate loss observed here is in contrast to the nonspecific phosphate loss from b_n and y_n reported previously. Characteristics of the reaction and its potential utility for phosphopeptide analysis are discussed.     

Sulfuric acid breakdown of fluorite in the presence of silica

We study the reaction of CaF₂ with concentrated sulfuric acid in the presence of silica at 120 and 140°C using fluorite mineral, fluorite concentrate, and mica-fluorite ore samples. When steam is fed to the reaction mixture, fluorosilicic acid is formed and then distilled off, materially influencing the fluoride ion recovery. Addition of quartz makes the reaction to proceed in the kinetic area and increases the fluoride ion recovery, while the presence of mica-bound SiO₂ displaces the reaction to the diffusion area and decreases the fluoride ion recovery. We have found that rare alkali metals are concentrated as hexafluorosilicates in the insoluble residue during the sulfuric acid breakdown of fluorite in the presence of SiO₂.     

Microwave-assisted hydrothermal treatment of corncob using tin(IV) chloride as catalyst for furfural production

The hydrothermal treatment of pentose-rich corncob under microwave irradiation was performed using SnCl₄ as catalyst for furfural production in this study. The influences of the catalyst amount, reaction temperature and reaction time on the compositions of the hydrolysate and solid residue were discussed comparatively. The solid residue obtained was characterized by FTIR, XRD and SEM. The results showed that the cell wall structure of the treated corncob was destroyed to a certain extent under the function of catalysts during the treatment, and most of the hemicelluloses were released from the cell wall and entered the hydrolysate as hemicellulose-derived sugars, followed by the selective dehydration to furfural. When the temperature reached the preset value of 190 °C under microwave irradiation, the highest furfural yield of 9.0 wt% (based on the dry weight of corncob) was achieved from the one-step conversion of corncob under the microwave-assisted hydrothermal treatment with a 1 % amount of SnCl₄ (based on the dry weight of corncob) and a solid-to-liquor ratio of 1:20.     

Reaction of 4-acetoxy-1,4-benzoxazin-3-one with DNA. A possible chemical mechanism for the antifungal and mutagenic activities

A reaction of 4-acetoxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one with DNA and nucleotides was described. The N⁴ position of the benzoxazinone reacted with the C₈ position of the guanine residue of DNA and guanylic acid.     

Influence of caged bicyclic phosphate and CaCO3 nanoparticles on char-forming property of PU rigid foams

Char-forming property of PU rigid foams, which can be assessed by char residue (%) when PU is burned at certain temperature, was studied by TG and DTG. The results showed that pure PU rigid foam had low char residue of only 17%, while 33% of char residue was achieved when PU rigid foam was modified by adding 8 wt% of 1-oxo-2,6,7-trioxa-1-phosphabicyclo[2,2,2] octane (PEPA), which is a caged bicyclic phosphate. The experiment results of FTIR and XPS showed that the PEPA modified PU rigid foam could be dehydrogenated and dehydrated at temperature between 380 and 450 °C, resulting in the increase of char residue of PU rigid foam. Further study also revealed that the addition of CaCO₃ nanoparticles could enhance the char stability when the PEPA modified PU rigid foam was being burned. The mechanism was investigated and it was found that the enhanced char stability could be attributed to the limited permeation of oxygen caused by the formation of calcium phosphate and calcium pyrophosphate by the reaction of PEPA and CaCO₃ at high temperature, which were covered on or buried in the char layer.     

Pyrrolidylsubstituted Azadipyrromethene with Fully Chelated Boron Atom

A difluorosubstituted aza-boron–dipyrromethene derivative with fully chelated boron atom was synthesized by the reaction of BF₃ · Et₂O with 3,3,5,5-tetraarylazadipyrromethene, which was easily prepared from 1,3-diaryl-4-nitro-butan-1-one and ammonium acetate. One fluorine atom of the dye was substituted by pyrrolidine residue. This resulted in a significant bathochromic effect. Ultraviolet absorption and fluorescence emission spectra were recorded, and quantum yields of the obtained compounds were calculated.     

Oxidatively-mediated in silico epimerization of a highly amyloidogenic segment in the human calcitonin hormone (hCT15-19)

In order to study the effects of peptide exposure to oxidative attack, we chose a model reaction in which the hydroxyl radical discretely abstracts a hydrogen atom from the α-carbon of each residue of a highly amyloidogenic region in the human calcitonin hormone, hCT_15-19. Based on a combined Molecular Mechanics / Quantum Mechanics approach, the extended and folded L- and D-configuration and radical intermediate hCT_15-19 peptides were optimized to obtain their compactness, secondary structure and relative thermodynamic data. The results suggest that the epimerization of residues is generally an exergonic process that can explain the cumulative nature of molecular aging. Moreover, the configurational inversion induced conformational changes can cause protein dysfunction. The epimerization of the central residue to the D-configuration induced a hairpin structure in hCT_15-19, concomitant with a possible oligomerization of human calcitonin into Aβ(1–42)-like amyloid fibrils present in patients suffering from Alzheimer’s disease.     

Thermochemical production of hydrogen

Copper oxychloride, Cu₂OCl₂, was synthesized from CuCl, or CuCl₂·2H₂O in a tubular furnace in a dry air atmosphere between 325 and 400?°C. Thermal gravimetric and gas analysis of the reaction products were used to follow the decomposition of Cu₂OCl₂ in both dry air and argon environments. The thermograms show the release of chlorine and oxygen gases, the volatilization of CuCl, and a residue, identified as CuO, of ~17 to 25% which varies as the conditions of the run. A mechanism of reaction able to describe the experimental results has been proposed and used to explain other published data.     

Friessche Verschiebung vonortho- undpara-Methoxyphenylacetaten. Die Bildung von Ketoestern

During theFries rearrangement ofo- andp-methoxy phenyl acetates with AlCl₃ in nitromethane at 20°C substitution occurs mainly in thep-position of the phenolic residue to yieldp-acylphenols. Larger quantities ofo-acylphenols are obtained only, if thisp-position is already substituted. Witho-methoxy phenyl acetates the substitution of the acid residue to yield ketoesters is observed as a side reaction. Those ketoesters are obtained as main products if TiCl₄ is taken as a catalyst.

     

Time-resolved photodissociation study of singly protonated peptides with a histidine residue generated by matrix-assisted laser desorption ionization: Dissociation rate constant and internal temperature

Product ion yields in post-source decay and time-resolved photodissociation at 193 and 266 nm were measured for some peptide ions with a histidine residue ([HF₆+H]⁺, [F₆H+H]⁺, and [F₃HF₃+H]⁺) formed by matrix-assisted laser desorption ionization (MALDI). Compared with similar data for peptide ions without any basic residue reported previously, significant reduction in dissociation efficiency was observed. Internal temperatures (T) of the peptide ions and their dissociation kinetic parameters—the critical energy (E ₀) and entropy (ΔS ^‡)—were determined by the method reported previously. Slight decreases in E ₀, ΔS ^‡, and T were responsible for the histidine effect-reduction in dissociation rate constant. Regardless of the presence of the residue, ΔS ^‡ was far more negative than previous quantum chemical results. Based on this, we propose the existence of transition structures in which the nitrogen atoms in the histidine residue or at the N-terminus coordinate to the reaction centers. Reduction in T in the presence of a histidine residue could not be explained based on popular models for ion formation in MALDI, such as the gas-phase proton transfer model.     

稻杆的热溶剂提质及多级分离

采用1-甲基萘(1-MN)为溶剂,在不同温度下(250、300、350 ℃)对稻秆进行热溶剂提质及多级分离,获得3种主要固体产物:低分子量萃取物(soluble)、高分子量萃取物(deposit)和萃取残渣(residue),以及少量气体产物和液体产物。对各组分的元素组成、化学结构、物理化学特性等进行了详细分析,并采用ICP-MS测定了其碱金属和碱土金属(AAEM)含量。结果发现,低分子量萃取物收率随着温度的升高而增大,350 ℃时碳基收率达到33.48%。3种固体产物的碳含量和氧含量随着温度的升高而分别升高和降低,350 ℃时soluble、deposit的碳含量分别高达82.36%、80.59%,氧含量分别低至9.50%、12.03%,稻杆原样中高达86.99%的氧以H₂O或CO₂的形式释放。soluble几乎无灰,deposit的灰含量也低于1.50%。3种固体产物的高位发热量显著高于稻杆原样。FT-IR结果表明,稻杆热溶剂处理过程中除发生了脱水反应、脱羧基反应外,还有明显的芳香化反应。soluble和deposit的Na、Mg和K含量极低,而且随温度的升高其含量逐渐降低。总之,热溶剂提质及多级分离法实现了温和条件下的生物质脱水脱氧提质,并获得低灰低氧含量、高碳含量和发热量的多种产物,此方法有较好的应用前景。     

Thermal degradation of copolymers of butadiene and acrylonitrile

Ten copolymers of butadiene and acrylonitrile have been prepared covering the composition range 100-25 mole % butadiene; reactivity ratios are r_butadiene = 0?50, r_{acrylonitrile} = 0?07. The thermal analysis techniques (TVA, TGA and DSC) have been applied to determine the general features of the thermal degradation of these copolymers. The fractions of products comprising permanent gases, products volatile at 20°, chain fragment material and residue have been separated and analysed. The constituent parts of the overall reaction have been discussed and the whole represented in the form of an integrated reaction mechanism.     

Synthesis and cross-coupling reaction of alkenyl[(2-hydroxymethyl)phenyl]dimethylsilanes

Highly stable alkenyl[2-(hydroxymethyl)phenyl]dimethylsilanes are prepared by stereo- and regioselective hydrosilylation of alkynes catalyzed either by a platinum or ruthenium catalyst using protected [2-(hydroxymethyl)phenyl]dimethylsilanes. Cyclic silyl ether, 1,1-dimethyl-2-oxa-1-silaindan, also serves as a starting material for the alkenylsilanes by the ring-opening reaction with alkenyl Grignard reagents. The resulting alkenylsilanes undergo cross-coupling reaction with various aryl and alkenyl iodides under reaction conditions employing K₂CO₃ as a base at 35–50 °C in highly regio- and stereospecific manners. The reaction tolerates a diverse range of functional groups including silyl protections. The silicon residue is readily recovered and reused on a gram-scale synthesis. Intramolecular coordination of a proximal hydroxyl group is considered to efficiently form pentacoordinate silicates having a transferable group possibly at an axial position and, thus, responsible for the cross-coupling reaction under conditions significantly milder than those reported for the silicon-based reactions.     

Biotinylation of Peptides/Proteins Using Biocytin Hydrazide

Biocytin hydrazide is widely used to biotinylate the carbohydrate moieties of glycoproteins. In this study, however, biocytin hydrazide was found to be able to directly biotinylate peptides and proteins. This phenomenon may cause false identification of non‐glycopeptides/non‐glycoproteins as glycopeptides/glycoproteins. Here, we report a systematic investigation of the reaction of peptides/proteins with biocytin hydrazide. Matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry is used to analyze the biotinylation reaction between peptides/proteins and biocytin hydrazide. Peptides/proteins were reacted with biocytin hydrazide in diverse solvent systems with different biocytin hydrazide concentrations for up to 96 h at temperatures ranging from 4 °C to 65 °C. Singly biotinylated or multiply biotinylated peptides/proteins are observed. The efficiency of the biotinylation reaction increases with higher temperature, higher biocytin hydrazide concentration, or longer reaction time. The influence of buffer pH on the biotinylation reaction of peptides/proteins is less pronounced. The biotinylation efficiency is optimum at neutral pH. Data suggests that the peptides are biotinylated as efficiently as proteins. The observation that peptides/proteins condense only with biocytin hydrazide, 2‐iminobiotin hydrazide, adipic dihydrazide and phenyl hydrazine but not with biocytin HCl and 2‐iminobiotin, indicates that the biotinylation reaction of peptides/proteins occurs with the hydrazide moiety but not with biotin moiety of the biotinylated reagent. The postsource decay data of biotinylated P₁₄R indicates that biocytin hydrazide condenses with the guanidino group of arginine's side chain of P₁₄R, indicating that besides N‐terminal and lysine residue of peptides/proteins, arginine residue is capable of reacting with biocytin hydrazide.     

Direct Oxidation of Propylene with Molecular Oxygen Over Ti-Modified Sulfated Zirconia Catalyst, 2. In Situ Diffuse Reflectance FT-IR Study

During the reaction of propylene with O₂, in situ Diffuse Reflectance FT-IR measurements were performed over Ti-modified SZ and SZ catalysts. Without O₂, the main bands characteristic of (branched) hydrocarbons, formed by oligomerization leading to, finally, carbonaceous residue, appeared within the range of 3900-2750 cm^-1, which was affected by the bands of surface OH groups. Investigation of these IR bands showed the role of molecular oxygen not only to limit the formation of carbonaceous species on the catalyst surface, but also to form oxygenates and these findings were in good agreement with the results of catalytic reaction.