Resolution enhancement in hydrophobic interaction chromatography via electrostatic interactions

In this work, a new type of hydrophobic stationary phase that provide electrostatic interactions with analytes was developed by bonding β-phenylethylamine as a functional ligand to silica. This stationary phase can separate proteins with similar hydrophobicity that traditional hydrophobic resins cannot. Hen egg white was separated to examine the selectivity. The results show that the introduced electrostatic interactions are an important factor for the resolution enhancement and the new resin could have important applications in separation and purification of biological macromolecules.     

Putrescine homologues control silica morphogenesis by electrostatic interactions and the hydrophobic effect

A systematic model study on the role(s) of putrescine homologues on silicification is presented and it is proposed that electrostatic forces between additive and silicic acid, and the hydrophobic behaviour of the additives are both important in silicification.     

溶质在两种反相色谱柱中的动力学色谱行为

研究了不同流速下4种溶质在两种不同反相色谱柱上的色谱图及它们的动力学色谱性质,进一步验证了溶质相对保留值(RRT)与流动相流速之间存在良好的双对数线性关系,并对溶质在流速改变时洗脱顺序发生改变的现象从动力学因素上进行了合理的解释;同时还发现色谱填料的孔径及拓扑学构型不同将导致溶质在其上具有不同的动力学色谱参数及动力学色谱行为。     

HPLC behavior and hydrophobic parameters of some anilides

Summary The chromatographic behavior ofpara substituted anilides of 2,2-dimethylpropanoic, benzoic and α-phenyl acetic acid has been studied by reversed-phase high performance liquid chromatography. HPLC was performed on a C-18 column with various aqueous methanol mobile phases. The influence on the retention of anilide type and additional substituents in the molecule is discussed. Several chromatographic hydrophobicity parameters (CHP) have been calculated by linear correlation between logk of the investigated compounds and the concentration of methanol in the mobile phase. The chromatographic hydrophobicity parameters were compared with the logP values calculated by Rekker's fragmental method. The results show moderate correlations of CHP with logP. Thus, multiple linear regressions have been applied. It was found that besides logP even the electronic effects of individual polar groups capable of hydrogen bonding proced to be very important in hydrophobic characterization of the molecule.     

Self-assembled aggregates originated from the balance of hydrogen-bonding, electrostatic, and hydrophobic interactions

Rich phase behavior was observed in salt-free cationic and anionic (catanionic) mixtures of a double-tailed surfactant, di(2-ethylhexyl)phosphoric acid (abbreviated as DEHPA), and tetradecyldimethylamine oxide (C(14)DMAO) in water. At a fixed C(14)DMAO concentration, phase transition from L(1) phase to L(α) phase occurs with increasing amounts of DEHPA. Moreover, in the L(α) phase, with the increase in DEHPA concentration, a gradual transition process from vesicle phase (L(αv)) to stacked lamellar phase (L(αl)) was determined by cryo- and FF-TEM observations combining with (2)H NMR measurements. The rheological data show that the viscosity increases with DEHPA amounts for L(αv) phase samples because of the increase in vesicle density. At a certain molar ratio of DEHPA to C(14)DMAO, i.e., 80:250, the samples are with the highest viscoelasticity, indicating the existence of densely packed vesicles. While for L(αl) phase samples, with increasing DEHPA amount, a decrease of bilayer curvature was induced, leading to a decrease of viscosity obviously. Compared with general catanionic surfactant mxitures, in addition to the electrostatic interaction of ion pairs, the transition of the microstructures is also ascribed to the formation of the hydrogen bonding (-N(+)-O-H···O-N-) between C(14)DMAO molecules and protonated C(14)DMAOH(+), which induces the growth of aggregates and the decrease of aggregate curvatures.     

Effects of hydrophilic and hydrophobic counterions on the Coulombic interactions in perfluorosulfonate ionomers

Attenuated total reflectance FTIR spectroscopy was used to compare the influence of hydrophilic and hydrophobic counterions on the vibrational behavior of the sulfonate and perfluoroether groups in 1100 equivalent weight (EW) Nafion^® and 808 EW Dow perfluorosulfonate ionomer membranes. For dry, Na⁺-form membranes, the infrared band attributed to the —SO₃^? symmetric stretching vibration was found to shift to higher frequencies with an increase in the degree of neutralization. In contrast, neutralization with tetrabutlyammonium ions caused the —SO₃^? vibrational band to shift to lower frequencies with increasing neutralization. This behavior is attributed to a diminished polarization of the —SO₃^? groups by the hydrophobic and diffusely charged TBA⁺ cations, relative to the strong polarization observed with Na⁺ ions. Vibrational bands attributed to perfluoroether groups in close proximity to the sulfonate groups were also found to be influenced by Coulombic interactions within the clusters. The frequency shifts of these bands followed a trend that was virtually identical to that observed for the —SO₃^? symmetric stretch. This behavior is attributed to a combination of through-space, dipolar field effects, and through-bond inductive effects, from the neighboring ionic groups. In Nafion^®, the ether groups directly attached to the backbone are shielded from the Coulombic interactions within the clusters, while the ether groups within three bonds of the terminal ionic groups are very sensitive to the state of polarization of the sulfonate anion. ©1995 John Wiley & Sons, Inc.     

Role of hydrophobic and electrostatic interactions for initial enteric virus retention by MF membranes

Membranes are of increasing interest for the removal of human enteric viruses from wastewater, especially when the goal of treatment is reuse. Limited work has been undertaken on fundamental issues such as aggregation and the role of electrostatic and hydrophobic interactions, as opposed to the sieving of viruses by membranes. One apparently critical factor would be the iso-electric point (pI) of a virus. As an example of a worst-case model virus, the retention of bacteriophage MS-2 was investigated using hydrophobic (GVHP) and hydrophilic (GVWP) 0.22 μm MF membranes at different pH levels and with different salts. High retention levels were measured at the iso-electric point of MS-2, pH 3.9 (5 log retention) and pH 7 (4.3 log retention) in the presence of salts and with a hydrophobic membrane. When retention was compared on a hydrophilic membrane, it was clear that hydrophobic interactions dominated virus retention, and this was improved by salt, presumably causing reduction of the Gouy double-layer when MS-2 was charged (pH 7). This paper shows that knowledge of the adsorption characteristics of viruses and the suspending conditions are important to predict removal of viruses by hydrophobic MF membranes, and discusses some of the practical implications of these important hydrophobic interactions.     

Comparison of the chromatographic behavior of tricyclic neuroleptics on calixarene-bonded, monolithic and conventional RP-HPLC columns

The effect of different chromatographic conditions, such as buffer concentration and type of organic modifier, on the retention behavior of nine tricyclic neuroleptics on three different RP-HPLC columns was investigated. Two recently developed columns, calixarene-bonded (CALTREX) AIII) and monolithic (Chromolith) Performance RP-18e) columns, were compared with a conventional RP-C18 HPLC column (LiChrospher). The results showed how the mobile phase conditions had different effects on the analyte retention on these three columns. For example, the elution order of some analytes and the initiation of separation of the geometric isomers of the three analytes--which have E/Z-isomers (cis/trans-isomers)--could be altered by changing the conditions and the column type. Under identical conditions, a calixarene-bonded phase was the best for this separation, a monolithic phase gave comparable results and the conventional RP-column was the least effective. Concerning the geometric isomers separation, the Chromolith Performance RP-18e was superior.     

Nanofibers resulting from cooperative electrostatic and hydrophobic interactions between peptides and polyelectrolytes of opposite charge

We investigated whether cationic peptides that contain hydrophobic side chains were able to stabilize themselves via hydrophobic interactions between neighboring peptide molecules upon electrostatic binding to oppositely charged polyelectrolytes. The interaction mechanism was examined through a model system consisting of the anionic polyelectrolyte alginate and the cationic decapeptide ozarelix. The interaction resulted in the formation of highly ordered complexes that were noticeable upon visual inspection. These complexes were then investigated by microscopic techniques and shown to exhibit a branched network structure. Cryogenic-temperature transmission electron microscopy (cryo-TEM) and negative staining TEM revealed that the molecular interactions between alginate and ozarelix led to the formation of nanofibers. The rodlike nanofibers had a diameter distribution of 4-8 nm. Isothermal titration calorimetry was used to determine the thermodynamic parameters of the alginate-ozarelix interaction. The binding constant was found to be on the order of 10(6) M(-1), indicating a high binding affinity. The interaction of the peptide with the polyelectrolyte triggered profound changes in the conformation of ozarelix, which was confirmed by UV spectroscopy and circular dichroism. On the basis of these experimental results, a theoretical modeling study of the alginate-ozarelix interaction was conducted to gain a better molecular-level understanding of the complex structure. It revealed that, upon binding of ozarelix to alginate, new intermolecular and intramolecular aromatic interactions between the ozarelix molecules occurred. These interactions changed the conformation of the peptide, a modification in which the aromatic side chains played a major role. Our results indicate that the cationic peptides interact with the polyanions via electrostatic interactions, but are additionally stabilized via hydrophobic interactions. This binding mode may serve as a powerful tool to extend the duration of drug release in hydrogel drug delivery systems.     

Deuterium isotope effects on hydrophobic interactions: the importance of dispersion interactions in the hydrophobic phase

Hydrogen/deuterium isotope effects on hydrophobic binding were examined by means of reversed-phase chromatographic separation of protiated and deuterated isotopologue pairs for a set of 10 nonpolar and low-polarity compounds with 10 stationary phases having alkyl and aryl groups bonded to the silica surface. It was found that protiated compounds bind to nonpolar moieties attached to silica more strongly than deuterated ones, demonstrating that the CH/CD bonds of the solutes are weakened or have less restricted motions when bound in the stationary phase compared with the aqueous solvent (mobile phase). The interactions responsible for binding have been further characterized by studies of the effects of changes in mobile phase composition, temperature dependence of binding, and QSRR (quantitative structure-chromatographic retention relationship) analysis, demonstrating the importance of enthalpic effects in binding and differentiation between the isotopologues. To explain our results showing the active role of the hydrophobic (stationary) phase we propose a plausible model that includes specific contributions from aromatic edge-to-face attractive interactions and attractive interactions of aliphatic groups with the pi clouds of aromatic groups present as the solute or in the stationary phase.     

Agarose gels in HPLC separation of biopolymers

Agarose gels of high concentration (above 6–8%) are both highly permeable to macromolecules and very rigid, particularly after cross-linking. Gel spheres of agarose can therefore be used with advantage as matrices for HPLC. Owing to the well-known good chromatographic properties of agarose gels they have been used for 20 years as packing materials in various conventional low-pressure chromatographic techniques. The way is now open to use these methods in the HPLC mode with attendant improvements in run times and resolution. Agarose based HPLC matrices will be commercially available.     

The dynamic chromatographic behavior of tri-o-thymotide on HPLC chiral stationary phases

The interconverting stereoisomers of tri-o-thymotide have been separated by HPLC on chiral stationary phases and the temperature dependence of the dynamic chromatographic patterns has been interpreted in terms of exchange between enantiomeric propeller and helical conformations. Computed low energy structures and CD spectra were used in absolute configuration assignment.     

Comparison of the chromatographic behavior of monolithic capillary columns in capillary electrochromatography and nano-high-performance liquid chromatography

Porous monoliths based on N,N-dimethylacrylamide (DMAA) or methacrylamide (MAA) were prepared inside fused silica capillaries as stationary phases for nano-chromatography. The columns were characterized in terms of flow rate and backpressure and showed, e.g. differences as a function of the salt concentration added to the polymerization mixture. When the columns were investigated for the separation of uncharged (polar hydroxylated aromatic compounds) and charged (amino acids) analytes under pressure driven conditions (pLC), differences to the previously observed behavior under voltage driven conditions (CEC) were observed. Whereas the non-charged analytes showed similar behavior in both cases--thus, corroborating the previous assumption of a mainly chromatographic separation mode driven by hydrophilic interactions in CEC--the charged amino acids did not. Assuming that the separation was governed by chromatographic phenomena in the pLC mode and by both chromatographic and electrophoretic effects in the CEC mode, the experiments allowed deconvoluting the two contributions. In particular, the charged amino acids appeared to interact with the stationary phases mainly by electrostatic interactions modified by some hydrophilic effects.     

Keen competition between electrostatic and argentophilic interactions in the formation and behavior of molecular rings

The macrocyclic structures and behavior on the reaction of AgX (X = NO₃ and CF₃SO₃) with bis(nicotinoyl)-4,4′-(9-fluorenylidene)diphenolates (L) have been carried out. Discrete oblong rings and linked rings were constructed via the keen competition between the inter-ring argentophilic (Ag···Ag) interaction and the electrostatic interaction between Ag(I) and its anion, and the interconversion of the two species was attempted by means of anion exchange.     

Effects of electrostatic interactions on the photocyclization reactivity of diaza-1,2-diarylethylenes

Electrostatic repulsion of nonbonded nitrogen atoms is recognized as the responsible factor for the diminished photocyclization reactivity of those initial conformations of diaza-1,2-diarylethylenes having short NN distances.     

三聚氰胺在双色谱柱串联模式下的色谱保留研究

研究了亲水相互作用色谱柱串联C_(18)柱上三聚氰胺的色谱保留,并应用牛奶基质中三聚氰胺的高效分离。将HILIC柱与C_(18)柱串联,研究不同色谱柱串联顺序及色谱分离条件下三聚氰胺的保留情况,结果表明:当流动相为乙腈-乙酸铵(10mmol/L)=85∶15(v/v)、柱温30℃、流速0.75mL/min、检测波长220nm、HILIC柱在前C_(18)柱在后串联时,三聚氰胺分离效果最佳。在最佳的色谱条件下,对市售牛奶进行测定,未检测出三聚氰胺,加标回收率在81.1%～119%,三聚氰胺在双柱模式下分析效果良好。