Thermochemical properties of the ammonia-water ionized dimer probed by ion-molecule reactions

The thermochemical properties of some small clusters such as the (H2O)2*+ dimer have already been investigated by both experimental and theoretical methods. The recent method to selectively prepare the ammonia-water ionized dimer [NH3, H2O]*+ (and not its proton transfer isomer [NH4+, OH*]) allowed us to study its chemical reactivity. This study focuses on the charge and proton transfer pathways: Ion-molecule reactions in the cell of an FT-ICR mass spectrometer were carried out with a range of organic compounds. Examination of the reactivity of the [NH3, H2O]*+ ionized dimer versus ionization energy and proton affinity of the neutral reagents shows a threshold in the reactivity in both instances. This leads to a bracketing of thermochemical properties related to the dimer. From these experiments and in agreement with ab initio calculations, the adiabatic recombination energy of the [NH3, H2O]*+ dimer was evaluated at -9.38 +/- 0.04 eV. The proton affinity bracketing required the reevaluation of two reference gas-phase basicity values. The results, in good agreement with the calculation, lead to an evaluation of the proton affinity of the [NH2*, H2O] dimer at 204.4 +/- 0.9 kcal mol(-1). These two experimental values are respectively related to the ionization energy of NH3*+ and to the proton affinity of NH2* by the difference in single water molecule solvation energies of ionized ammonia, of neutral ammonia, and of the NH2* radical.     

Determination of isoelectric points of acidic and basic proteins by capillary electrophoresis

The isoelectric point (pI) of a protein is of practical importance in many separation procedures, both analytical and preparative. The pI is defined as the pH where the net charge of the protein is zero. Therefore, by plotting the mobilities of the proteins against pH, the intercept at zero mobility should yield the pI value. Isoelectric points have traditionally been determined by isoelectric focusing. In this paper, the potential of capillary electrophoresis as an alternative technique for the determination of pI values of both acidic and basic proteins was investigated. The problem commonly encountered with adsorption of the positively charged proteins with the unprotonated silanol groups of the fused-silica wall is solved by applying a dynamic coating of a polycationic reagent to the wall. The advantages of this technique of determining the pI values are simplicity, speed and minimal sample requirement.     

Hydrated alumina surface treatment on a titanium dioxide pigment: changes at acidic and basic pH

Amphoteric, inorganic particles used as pigments and extenders in dried coatings are not completely inert, particularly when exposed to acidity similar to atmospheric pollution, or when in a water-borne paint suspension at alkaline pH. Changes to these materials may harm the integrity of the dried coating and thus its performance during weathering or affect the colloidal stability during storage within liquid paint. The effect on aqueous titanium dioxide pigment suspensions was examined under various pH conditions. A substantial amount of aluminum was dissolved, but little silicon or titanium. Dissolution occurred at both acid and alkali pH leaving a different balance of hydrated alumina phases and overall surface composition. Changes in particle surface were apparent in topography, colloidal properties and by thermogravimetry. Such changes show that other, more complicated, changes may be possible, particularly in an aqueous paint medium where there are many other ingredients in solution or suspension.     

Native horizontal ultrathin polyacrylamide gel electrophoresis of proteins under basic and acidic conditions.

The preparation of homogeneous ultrathin native polyacrylamide gels, using a basic as well as an acidic buffer system is described. The basic buffer system consists of Tris-HC1/Tris-glycine, the same buffer as in sodium dodecyl sulfate (SDS)-gel electrophoresis but without SDS. The acidic system uses potassium acetate, pH 4.3, as gel buffer and beta-alanine, pH 4.6, acetic acid as electrolytes. The gels are covalently bound on glass plates. Binding of acidic gels requires a special pretreatment of glass plates. The whole procedure is simple and extraordinarily fast: 100-120 min from the start of gel preparation to the end of electrophoresis. Coomassie staining is done in 40 min and silver staining in 90 min. The native gels are excellently suited for diffusion blotting. Further attractive properties of these gels are easy handling, simple drying and dimensional stability.     

Enrichment and separation of acidic and basic proteins using the centrifugal ultrafiltration followed by nanoparticle-filled capillary electrophoresis

This report describes a method for enrichment and separation of acidic and basic proteins using the centrifugal ultrafiltration followed by nanoparticle-filled capillary electrophoresis. To improve stacking and separation efficiencies of proteins, the separation buffer containing 1.6% poly(diallyldimethylammonium chloride) was added with gold nanoparticles (AuNP), poly(ethylene oxide), cetyltrimethylammonium bromide, and poly(vinyl alcohol). As a result, the use of AuNP as additives exhibited better efficiency in separation, stacking, and analysis time. Even for large-volume samples (110 nL), the separation efficiencies of acidic and basic proteins remained greater than 10(4) and 10(5) plates/m, respectively. To further enhance detection sensitivity, protein samples were enriched using the centrifugal ultrafiltration, followed by our proposed stacking method. The detection sensitivity was improved up to 314-fold compared to normal hydrodynamic injection. Additionally, the limits of detection at a signal-to-noise of 3 for most proteins were down to nanomolar range. We have validated the application of our method by means of analyses of 50 nM lysozyme in saliva samples. The proposed method was also successfully applied to the analyses of egg-white proteins, which have large differences in molecular weight and pI.     

New physically adsorbed polymer coating for reproducible separations of basic and acidic proteins by capillary electrophoresis

In this work, a new physically adsorbed coating for capillary electrophoresis (CE) is presented. The coating is based on a N,N-dimethylacrylamide-ethylpyrrolidine methacrylate (DMA-EPyM) copolymer synthesized in our laboratory. The capillary coating is simple and easy to obtain as only requires flushing the capillary with a polymer aqueous solution for 2 min. It is shown that by using these coated capillaries the electrostatic adsorption of a group of basic proteins onto the capillary wall is significantly reduced allowing their analysis by CE. Moreover, the DMA-EPyM coating provides reproducible separations of the basic proteins with RSD values for migration times lower than 0.75% for the same day (n = 5) and lower than 3.90% for three different days (n = 15). Interestingly, the electrical charge of the coated capillary wall can be modulated by varying the pH of the running buffer which makes possible the analysis of basic and acidic proteins in the same capillary. The usefulness of this coating is further demonstrated via the reproducible separation of whey (i.e. acidic) proteins from raw milk. The coating protocol should be compatible with both CE in microchips and CE-MS of different types of proteins.     

双子表面活性剂及其保护的纳米金作为缓冲添加剂用于毛细管电泳蛋白质分离

报道了使用阳离子双子表面活性剂作为毛细管电泳的缓冲添加剂用于同时分离酸性和碱性蛋白质.在酸性的缓冲条件下,只需要使用低浓度的阳离子双子表面活性剂（0.1mmol/L18-s-18）作为缓冲液的添加剂,就可以有效地抑制酸性和碱性蛋白质在毛细管壁的吸附,从而得到高效的蛋白质分离.实验表明,较小的胶束尺寸（如s=5～8）比大的胶束尺寸（如s〈4或〉10）能更有效地抑制酸性蛋白质的吸附.改变双子表面活性剂的中间基的长度能够对蛋白质的电泳淌度进行一定的调节,从而对分离的选择性进行一定的优化.在最优的实验条件下,蛋白质迁移时间的日内和日间标准偏差（RSD）分别小于0.8%和2.2%,回收率为79%到100.4%.另外,还考察了双子表面活性剂保护的金纳米颗粒用作毛细管电泳缓冲添加剂在蛋白质分离中的应用.实验表明,在缓冲液中加入纳米金能够缩短分析时间,并能小幅度地提高分离效率.最后,使用该方法分析了一系列复杂生物样品,包括血浆、红细胞和鸡蛋清样品,均得到了满意的结果.     

Separation of acidic and basic proteins by capillary electrophoresis using gemini surfactants and gemini-capped nanoparticles as buffer additives

This paper demonstrated simultaneous separation of acidic and basic proteins using cationic gemini surfactants as buffer additives in capillary electrophoresis. We showed that even at a low concentration (0.1 mmol·L-1) of alkanediyl-α,ω-bis(dimethyloctadecylammonium bromide) (18-s-18), the wall adsorption of both acidic and basic proteins could be effectively suppressed under acidic conditions. Smaller micelle size (e.g., s=5-8) is more effective for the separation of acidic proteins than larger micelle siz...     

Investigation of deprotonation reactions on globular and denatured proteins at atmospheric pressure by ESSI-MS

Deprotonation reactions of multiply charged protein ions have been studied by introducing volatile reference bases at atmospheric pressure between an electrosonic spray ionization (ESSI) source and the inlet of a mass spectrometer. Apparent gas-phase basicities (GB(app)) of different charge states of protein ions were determined by a bracketing approach. The results obtained depend on the conformation of the protein ions in the gas phase, which is linked to the type of buffer used (denaturing or nondenaturing). In nondenaturing buffer, the GB(app) values are consistent with values predicted by the group of Kebarle using an electrostatic model (J. Mass Spectrom.2002, 38, 618) based on the crystal structures, but taking into account salt bridges between ionized basic and acidic sites on the protein surface. A new basicity order for the most basic sites was therefore obtained. An excellent agreement with the charge residue model (CRM) is obtained when comparing the observed and calculated maximum charge state. Decharging of the proteins in the electrosonic spray process could be also useful in the study on noncovalent complexes, by decreasing repulsive electrostatic interactions. A unified mechanism of the ESSI process is proposed.     

Electrophoretic separation of acidic and basic proteins in the presence of micromolar concentrations of an ionic liquid

We report on the use of an ionic-liquid (IL) as additive to an acidic background electrolyte (BGE) for capillary electrophoretic separation of the proteins human serum albumin, transferrin, trypsin inhibitor, hemoglobin, catalase, myoglobin and lysozyme. The method was carried out in a capillary zone electrophoresis mode because the concentration of the ionic liquid is far below its critical micelle concentration, and the proteins were detected by measurement of capacitively coupled contactless conductivity. The addition of the IL to the BGE in micromolar concentration improves (a) the detection sensitivity of the method, (b) the recovery of the protein due to the alleviated wall-adsorption of proteins, and (c) the resolution due to strong interaction between IL and protein. In fact, even microheterogeneous variants of trypsin inhibitor, hemoglobin and catalase could be resolved. Proteins were separated within typically 18?min at pH 2.5, with detection limits of 0.7 to 9.4???g mL^?1 (34.8?C141.1 nM). The method was specifically employed to analyze human serum samples.

Features of the interactions between the methyl-CpG motif and the arginine residues on the surface of MBD proteins

Recognition of the methylated regions of the DNA plays an important role in the epigenetic processes. We analyze the interactions between the methylated DNA and the methyl-CpG-binding proteins using two models. The first model was built from a methylated or non-methylated cytosine, a guanine and an arginine residue in the experimental arrangement. We applied the M06L density functional method with a small, polarized double-ζ basis set for the geometry optimizations, and the MP2 method with polarized triple-ζ basis set for the energy calculations. The second model was built from two methylcytosines, guanines, guanidinium groups plus an additional carboxyl group in the experimental arrangement. We applied the B3LYP method with a small, polarized double-ζ basis set for the geometry optimizations and thermal corrections. The single-point energies were obtained from dual-hybrid dRPA75 and dRPA@PBE0 calculations supplemented by a moderately large polarized triple-ζ basis set. The hydration effects were modeled by adding explicit water molecules. These calculations revealed that the hydrophobic interaction has the largest contribution to the Gibbs interaction energy and turns the arginine side chains into hydrogen bonding position. Our results show that the translation of the protein along the DNA double helix is sterically hindered by the contact of its arginine side chains with the methyl groups of the methyl cytosines. This supports a hopping mechanism for the searching movement of the protein along the DNA.

     

Structural control of surface layer proteins at electrified interfaces investigated by in situ Fourier transform infrared spectroscopy

In situ Fourier Transform Infrared (FTIR) Spectroscopy complemented by Electrochemical Quartz Microbalance (EQMB) investigations allowed a detailed insight into the influence of the electrode potential on competing adsorption processes and bonding mechanisms of buffer ions and S-layer protein molecules of Lysinibacillus sphaericus CCM2177 at an electrified liquid/gold interface. The S-layer proteins adsorb on gold polarized positively of the point of zero charge by displacing perchlorate anions in the Helmholtz plane by their carboxylate groups. This is indicated by an increase of the peptide and carboxylate infrared absorption signals accompanied by a decrease of the perchlorate signal. S-layers interlinked laterally with Ca(2+) ions, positive of the point of zero charge, resulted in the formation of a crystalline layer participating in the Helmholtz layer. In contrast to the absence of the Ca(2+)-linkers, S-layers remain structurally intact also in the negative polarization domain where the Helmholtz layer is solely sustained by mainly solvated cations without participation of the negatively charged protein carboxylate functions.     

Chromatographic methods for the analysis of basic neurotransmitters and their acidic metabolites.

Chromatographic techniques for the determination of trace amounts of neurotransmitters were reviewed. The two techniques found to be most useful were GC-MS and the reversed-phase mode of HPLC with an electrochemical or fluorescent detector. For structure determination or unequivocal peak identification, GC-MS is the method of choice. In addition the limits of detection of GC-MS were better than those obtained by HPLC. However for routine analyses, HPLC is now being used in studies of mental illness and other diseases. Good resolution, reproducibility and sensitivity can be obtained without the derivatisation steps required for GC-MS, and catecholamines, serotonin, and their acidic metabolites can be concomitantly determined in one analysis.     

Influence of intense pulsed laser irradiation on optical and morphological properties of gold nanoparticle aggregates produced by surface acid-base reactions

Gold nanoparticles were surface modified with an ionizable and pH-sensitive monolayer of thiobarbituric acid (TBA). By variation of the pH value of the solution, nanoparticle aggregates can be produced in a controlled way. The aggregates thus prepared were irradiated with an intense pulsed laser at 532 nm. The products in solution were examined by transmission electron microscopy (TEM) and optical absorption spectroscopy. The TEM images of the products revealed that the nanoparticle aggregates dissociate upon laser irradiation and form much smaller gold nanoparticles. The optical absorption spectra measured simultaneously show the gradual disappearance of the absorbance band of the aggregates at around 680 nm. Additionally, a blue shift (from 534 to 524 nm) of the resonance absorbance corresponding to isolated nanoparticles has been observed. All the observations suggest that the colloidal solution becomes more stable after laser irradiation. Both the reduced nanoparticle size and the stabilizing TBA ligands present on the particle surface contribute to the acquired stability of the colloidal solutions.     

Catalytic reactions at the surface of solid calcium and potassium amides

Summary It was shown that isomerization of alkenes with displacement of the double bond and hydrogen exchange in ] hydrocarbons both belong to the class of acid-base reactions; they are catalyzed by amide ions in ammoniacal solutions and by solid amides under heterogeneous conditions.     

极性有机物在零价态过渡金属表面的配位化学反应

咪唑、腈、酯类等极性有机物吸附在铜、铂、银、汞等过渡金属表面时,氮原子或氧原子上的孤对电子插入金属原子的外层价轨道,在表面生成零价态金属原子的配合物。由于电子的迁移,使金属原子及有机物中相应的化学键同时被活化。这一现象被作者称为"表面吸附层的配位双活化效应"。在有氧存在时,零价态金属原子极易与上述有机物发生化学反应,导致了N-H键、C≡N键或C-O键的破裂,生成超薄化学吸附层覆盖在金属表面。