Preparation of a weak anion exchange/hydrophobic interaction dual‐function mixed‐mode chromatography stationary phase for protein separation using click chemistry

In this study, 3‐diethylamino‐1‐propyne was covalently bonded to the azide‐silica by a click reaction to obtain a novel dual‐function mixed‐mode chromatography stationary phase for protein separation with a ligand containing tertiary amine and two ethyl groups capable of electrostatic and hydrophobic interaction functionalities, which can display hydrophobic interaction chromatography character in a high‐salt‐concentration mobile phase and weak anion exchange character in a low‐salt‐concentration mobile phase employed for protein separation. As a result, it can be employed to separate proteins with weak anion exchange and hydrophobic interaction modes, respectively. The resolution and selectivity of the stationary phase were evaluated in both hydrophobic interaction and ion exchange modes with standard proteins, respectively, which can be comparable to that of conventional weak anion exchange and hydrophobic interaction chromatography columns. Therefore, the synthesized weak anion exchange/hydrophobic interaction dual‐function mixed‐mode chromatography column can be used to replace two corresponding conventional weak anion exchange and hydrophobic interaction chromatography columns to separate proteins. Based on this mixed‐mode chromatography stationary phase, a new off‐line two‐dimensional liquid chromatography technology using only a single dual‐function mixed‐mode chromatography column was developed. Nine kinds of tested proteins can be separated completely using the developed method within 2.0 h.     

What Happens to Hydrophobic Interactions during Transfer from the Solution to the Gas Phase? The Case of Electrospray-Based Soft Ionization Methods

The disappearance of the hydrophobic effect in the gas phase due to the absence of an aqueous surrounding raises a long-standing question: can noncovalent complexes that are exclusively bound by hydrophobic interactions in solution be preserved in the gas phase? Some reports of successful detection by mass spectrometry of complexes largely stabilized by hydrophobic effect are questionable by the presence of electrostatic forces that hold them together in the gas phase. Here, we report on the MS-based analysis of model supramolecular complexes with a purely hydrophobic association in solution, β-cyclodextrin, and synthetic adamantyl-containing ligands with several binding sites. The stability of these complexes in the gas phase is investigated by quantum chemical methods (DFT-M06). Compared with the free interaction partners, the inclusion complex between β-cyclodextrin and adamantyl-containing ligand is shown to be stabilized in the gas phase by ΔG = 9.6 kcal mol^–1. The host–guest association is mainly enthalpy-driven due to strong dispersion interactions caused by a large nonpolar interface and a high steric complementarity of the binding partners. Interference from other types of noncovalent binding forces is virtually absent. The complexes are successfully detected via electrospray ionization mass spectrometry, although a high dissociation yield is also observed. We attribute this pronounced dissociation of the complexes to the collisional activation of ions in the atmospheric interface of mass spectrometer. The comparison of several electrospray-based ionization methods reveals that cold spray ionization provides the softest ion generation conditions for these complexes.     

Retention of Ionized Solutes in Reversed-Phase High Performance Liquid Chromatography

Abstract

The mechanism of retention in reversed-phase high performance liquid chromatography is affected by both solute-eluent interactions and the nature of the stationary phase. The hydrophobic expulsion of ionized solutes plays a major role in affecting solute behavior in the water-rich range of hydroorganic eluents. In the water-lean range of eluent composition, there is little hydrophobic expulsion, and specific interactions between the solute and surface can be observed. The nature of the surface affects the retention of a variety of ionized species, both large cations and anions. Octadecylsilane (ODS) bonded phases can exhibit two different binding sites: one exhibiting a weak interaction and the second a strong specific interaction with a solute. Styrenedivinylbenzene polymeric surfaces exhibit the potential for weak dispersion interactions, and in addition pi-bonding interactions with a solute. A variety of solutes have been injected in a water: methanol eluent system in order to assess solute-surface effects on reversed-phase supports.     

The Hydrophobic and Metal-Ion Coordinating Properties of α-Lipoic Acid—An Example of Intramolecular Equilibria in Metal-Ion Complexes

Hydrophobic interactions as structure determining factors for macromolecules are well-known in biochemistry. Considerably less recognized is the fact that these law-energy interactions may also determine the structure of low-molecular species. The same applies for weak ligand-metal ion interactions. That both these factors may lead to intramolecular, contraction-independent equilibria between isomeric metal-ion complexes is demostrated with α-lipoic acid as ligand. This cofactor affers metal ions two different binding sites: the carboxylate group and the disulfide linkage. The carboxylate group dominates the coordinating properties of this ligand towards the biologically important metal ions, but a disulfide-metal ion interaction is still possible and under sterically favourable conditions may becomevery important; this could also be true under enzymic conditions here the carboxyl group is no longer free but amide-liked to the protein. Furthermore, due to the valeric acid side chain, the lipoyl moiety is ideally suited to undergo hydrophobic ligand-ligand interactions in mixed-ligand complexes. Such hydrophobic interactions seem to be ideal to allwe migration, e.g., of the 14 Å long lipoyllysyl moiety, and also to caciliutate the correct ‘fixation’ at the surface of the enzyme.     

Cobalt(iii) complexes as functional ligands for metal (oxide) surfaces

Co(iii) polyamine complexes with either two or three labile coordination sites bind strongly to high surface area metal oxides such as goethite or aluminium trihydroxide, and have been shown to act as passivating agents for aluminium flake in aqueous media, in addition to providing a potential method for surface functionalisation.     

甘氨酸镧（Ⅲ）配合物与牛血清白蛋白的相互作用研究

红外光谱和X射线衍射分析表明甘氨酸与镧(Ⅲ)作用形成配合物。利用同步荧光光谱和荧光光谱探究了牛血清白蛋白(BSA)和甘氨酸镧(Ⅲ)配合物之间的相互作用。结果可知甘氨酸镧(Ⅲ)配合物与牛血清白蛋白的荧光猝灭为静态猝灭,根据双对数方程处理荧光猝灭数据得到了甘氨酸镧(Ⅲ)配合物与牛血清白蛋白在不同温度下的结合常数Kb和结合位点数n。热力学数据表明配合物与BSA作用主要是疏水作用力。利用同步荧光光谱法研究了甘氨酸镧(Ⅲ)配合物对于牛血清白蛋白的构象影响。     

Shear-responsive peptide/siRNA complexes as lung-targeting gene vectors

Particles administrated intravenously will pass through the pulmonary capillary network before being distributed to the body. Therefore, fabrication of vectors sensitive to blood shear and active with blood components should be a practical approach to develop lung-targeting gene carriers self-regulated by circulatory system. In this work, we designed a series of cationic peptides with the same charge density but varying hydrophobicity and capacity to form hydrogen bonds, and investigated their ability to form complexes with siRNA, the behaviours of peptide/siRNA complexes in the presence of serum under shear, and the lung-targeting efficacy of the complexes regulated by blood. The hydrophobic interaction controls the complexation between peptide and siRNA, while the hydrogen bonds are responsible for the binding of peptides to the serum components in blood. In vivo tests show that all the peptide/siRNA complexes can accumulate in lung. However, only the complexes that exhibit weak interaction with serum components and can be broken down by shear avoid the inflammation and death caused by pulmonary embolism. Moreover, the peptide with strong hydrophobicity can retain siRNA in lung without early release of the cargo. Our study provides a step toward the development of adaptive gene carriers under the regulation of circulatory system.     

Enzymes in Organic Synthesis: Application to the Problems of Carbohydrate Recognition (Part 2)

Recognition of carbohydrates by proteins and nucleic acids is highly specific, but the dissociation constants are relatively high (generally in the mM to high μM range) because of the lack of hydrophobic groups in the carbohydrates. The high specificity of this weak binding often comes from many hydrogen bonds and the coordination of metal ions as bridge between sugars and receptors. Though weak hydrophobic interactions between sugars and proteins have also been identified, the unique shape of a complex carbohydrate under the influence of anomeric and exo anomeric effects (the glycosidic torsion angles are therefore often not flexible but are typically somewhat restricted) and the topographic orientation of the hydroxyl and charged groups contribute most significantly to the recognition process. Studies on the structure–function relationship of a complex carbohydrate therefore require deliberate manipulation of its shape and functional groups, and synthesis of oligosaccharide analogs from modified monosaccharides is often useful to address the problem. The availability of various monosaccharides and their analogs for the synthesis of complex carbohydrates together with the information resulting from structural studies (such a NMR or X-ray studies on sugar–protein complexes) will certainly provide a basic understanding of complex carbohydrate recognition. An ultimate goal is to develop simple and easy-to-make non-carbohydrate molecules that resemble the active structure involved in carbohydrate–receptor interaction or the transition-state of an enzyme-catalyzed transformation (for example, glycosidase or glycosyltransferase reactions) and have the approprite bioavailability to be used to control the carbohydrate function in a specific manner. In part one of this review we described various enzymatic approaches to the synthesis of monosaccharides, analogs, and related structures. We describe in this part enzymatic and chemoenzymatic approaches to the synthesis of oligosaccarides and analogs, including those involved in E-selectin recognition, and strategies to inhibit glycosidases and glycosyltransferases.     

Molecular dynamics simulation study of water adsorption on hydroxylated graphite surfaces

In this paper, we present results from molecular dynamic simulations devoted to the characterization of the interaction between water molecules and hydroxylated graphite surfaces considered as models for surfaces of soot emitted by aircraft. The hydroxylated graphite surfaces are modeled by anchoring several OH groups on an infinite graphite plane. The molecular dynamics simulations are based on a classical potential issued from quantum chemical calculations. They are performed at three temperatures (100, 200, and 250 K) to provide a view of the structure and dynamics of water clusters on the model soot surface. These simulations show that the water-OH sites interaction is quite weak compared to the water-water interaction. This leads to the clustering of the water molecules above the surface, and the corresponding water aggregate can only be trapped by the OH sites when the temperature is sufficiently low, or when the density of OH sites is sufficiently high.     

pH-potentiometirc study of polyion complexes between chitosan and poly(vinyl sulfate) or dodecylbenzene sulfonate

Polyion complexes of three chitosans with poly(vinyl sulfate) (PVS) and dodecylbenzene sulfonate (DBS) were examined by a potentiometric study that was to separately measure the pH of sample solutions individually prepared. Apparent formation constants (Ki) of ion association between the protonated amines of chitosan and the sulfates of PVS or the sulfonates of DBS were determined. The effects of pH, coexistent salt concentration, and molecular weight on the values of Ki were investigated in order to reveal the properties of the complexation. The values of Ki for chitosan-PVS were quite larger than that for chitosan-DBS. The deducing effect of the coexistent salt was strong against chitosan-PVS, but was weak against chitosan-DBS. Thus, chitosan-PVS complexes possessed a strong electrostatic binding, and chitosan-DBS complexes included a hydrophobic interaction. For chitosan-PVS complexes the effect of the coexistent salt was weaker for a high molecular weight of chitosan than for a low molecular weight.