Pavel Řezanka

Application of gold nanoparticles in separation sciences

The review article is devoted mainly to the description of applications of gold nanoparticles (GNPs) in separation sciences, especially in electromigration and chromatographic techniques. The applications of GNPs in particular separation methods, CE, microchip CE, MEKC, CEC, HPLC and GC, are classified according to the molecular size of the analytes from low-molecular-mass compounds via medium sized substances to biopolymers (proteins and nucleic acids). A very recent and promising utilization of GNPs for sample preparation, preconcentration and preseparation of selected analytes from complex matrices is presented as well. Moreover, in two introductory sections, typical preparation procedures of the GNPs and their modifications are presented and physico-chemical and analytical methods employed for characterization of the native and modified GNPs are briefly introduced.

Application of cyclodextrins in chiral capillary electrophoresis

CE represents a very powerful separation tool in the area of chiral separations. CD‐mediated chiral CE is a continuously flourishing technique within the frame of the electromigration methods. In this review, a brief overview of the synthetic procedures leading to modified CDs is provided first. Next, selected aspects related to the utilization of CDs in chiral CE are discussed specifically in the view of recently published data. Advantages of CDs and basic principles of chiral CE are remained. The topic of the determination of binding constants is touched. Particular attention is paid to the effort aiming at better understanding of the molecular level of the enantiorecognition between CDs and the analyte in the solution. Powerful approaches extensively utilized in this field are NMR, molecular modeling, and computer simulations. Then, a summary of applications of CDs in the CE enantioseparations is given, covering years 2008–2013. Finally, the general trend of modified CDs use in separation science is statistically evaluated.

Open-tubular capillary electrochromatography with bare gold nanoparticles-based stationary phase applied to separation of trypsin digested native and glycated proteins.

In this work, open-tubular capillary electrochromatography (OT-CEC) method with bare gold nanoparticles (GNPs)-based stationary phase has been developed and applied for separation of tryptic peptide fragments of native and glycated proteins, bovine serum albumin (BSA), and human transferrin (HTF). The GNPs-based stationary phase was prepared by immobilization of bare GNPs, freshly reduced from tetrachloroaurate(III) ions by citrate reduction, on the sol-gel pretreated inner wall of the fused silica capillary. The separation efficiency, peak capacity, and peptide recovery of this open-tubular capillary column were investigated by varying the experimental parameters such as type and concentration of the buffering constituent and pH of the background electrolyte (BGE), temperature, and separation voltage. The best separations of the above tryptic peptides were achieved in the BGE composed of aqueous 100 mmol/L sodium phosphate buffer, pH 2.5, at separation voltage 10 kV per 47-cm long, 50 μm inside diameter capillary thermostated at 25°C. OT-CEC with bare GNPs stationary phase is shown to be a suitable technique for separation of complex peptide mixtures arising from tryptic digestion of native and glycated BSA and HTF, and for investigation of glycation (nonenzymatic glycosylation) of these proteins.

Application of bare gold nanoparticles in open-tubular CEC separations of polyaromatic hydrocarbons and peptides.

In this study, bare gold nanoparticles (GNPs) immobilized in the sol-gel-pretreated fused-silica (FS) capillary as a stationary phase for open-tubular capillary electrochromatography (OT-CEC) are for the first time shown to be able to separate both hydrophobic polyaromatic hydrocarbons (PAHs) as well as hydrophilic cationic antimicrobial peptides. Model mixture of four PAHs, naphthalene, fluorene, phenanthrene, and anthracene, was resolved by OT-CEC in the GNP-modified FS capillaries using the hydro-organic background electrolyte (BGE) composed of 20 mmol/L sodium phosphate buffer, pH 7, modified with ACN at 8:2 v/v ratio. On the other hand, three synthetic analogues of an antimicrobial peptide mastoparan PDD-B, basic tetradecapeptides INWKKLGKKILGAL-NH(2), INSLKLGKKILGAL-NH(2) and NWLRLGRRILGAL-NH(2), were separated in aqueous acidic BGEs, pH 2.1-3.1, composed of weak acids (formic and acetic) or amphoteric amino or imino acids (aspartic or iminodiacetic), utilizing the advantage of a slow reversed (anodic) EOF and slightly positive charge of the GNP-modified FS capillary suppressing the adsorption of cationic peptides on the inner capillary wall and improving their resolution.

Impact of substituent position in monosubstituted α-cyclodextrins on enantioselectivity in capillary electrophoresis

In this study, our three recently synthesized regiospecifically monosubstituted carboxymethyl-α-cyclodextrins (CMACDs) were successfully applied for the enantiomeric separation of several biologically important low-molecular weight compounds by capillary electrophoresis. The enantioselectivity of the individual monosubstituted CMACDs added into the background electrolyte (BGE) was studied and compared with the mixture of three monosubstituted CMACDs and with native α-cyclodextrin at pH of the BGE ranging from 2.5 to 11. Our experiments revealed a significant influence of the position of the carboxymethyl group on the α-cyclodextrin skeleton on the enantioselectivity for all the studied analytes. Interestingly, the least common 3(I)-O regioisomer was revealed as the most effective chiral selector.

The study of enantioselectivity of all regioisomers of mono‐carboxymethyl‐β‐cyclodextrin used as chiral selectors in CE

This work documents the influence of the position of single carboxymethyl group on the β-cyclodextrin skeleton on the enantioselectivity. These synthesized monosubstituted carboxymethyl cyclodextrin (CD) derivatives, native β-cyclodextrin, and commercially available carboxymethyl-β-cyclodextrin with degree of substitution approximately 3 were used as additives into the BGE consisting of phosphate buffer at 20 mmol/L concentration, pH 2.5, and several biologically significant low-molecular-mass chiral compounds were enantioseparated by CE. The results indicate that different substituent location on β-cyclodextrin skeleton has a significant influence on the enantioseparation of the investigated enantiomers. The enantioselectivity of 2(I)-O-regioisomer was better than with native β-cyclodextrin. Comparable results to native β-cyclodextrin were obtained for 6(I)-O- regioisomer and the enantioselectivity of 3(I)-O-regioisomer was even worse than with native β-cyclodextrin. Commercially available derivative of CD provides better resolutions than the monosubstituted carboxymethyl CD derivatives for most of the investigated analytes.

Nonaqueous Capillary Electrophoretic Enantioseparation of Water Insoluble Tröger's Base Derivatives Using β-Cyclodextrin as Chiral Selector

Racemic mixtures of six Trögers base derivatives were separated by chiral nonaqueous capillary electrophoresis. The separation protocol was optimized first for suitable solvents. Then the applicability of various salts dissolved in organic solvents and their mixtures was evaluated. As chiral selectors β-cyclodextrin and heptakis(2,6-di-O-methyl)-β-cyclodextrin at various concentrations were used. The best enantioselectivity for the studied analytes was obtained utilizing formamide as organic nonaqueous solvent containing a mixture of sodium citrate and tris(hydroxymethyl)aminomethane acetate as electrolytes, and β-cyclodextrin as chiral additive. The experimental results demonstrated the feasibility of nonaqueous capillary electrophoresis for enantioseparation of Trögers base derivatives. This technique represents a suitable alternative to more commonly used capillary electrophoresis in aqueous environment.

The influence of the substituent position in monocarboxymethyl‐γ‐cyclodextrins on enantioselectivity in capillary electrophoresis

Three newly synthesized chiral selectors, namely, 2(I)-O-, 3(I)-O-, and 6(I)-O-carboxymethyl-γ-cyclodextrin, native γ-cyclodextrin, and commercially available carboxymethylated γ-cyclodextrin with degree of substitution of 3-6 were used as additives in a background electrolyte composed of phosphate buffer at 20 mmol/L concentration and pH 2.5. This system was used for the analysis of several biologically significant low-molecular-mass chiral compounds by capillary electrophoresis. The results confirmed that the position of carboxymethyl group influences the enantioseparation efficiency of all the studied analytes. The 2(I)-O- and 3(I)-O- regioisomers provide a significantly better resolution than native γ-cyclodextrin, while the 6(I)-O-regioisomer gives only a slightly better enantioseparation than native γ-cyclodextrin. The application of γ-cyclodextrin possessing higher number of carboxymethyl groups led to the best resolution for the majority of the compounds analyzed.

Enantioseparation of Tröger's base derivatives by capillary electrophoresis using cyclodextrins as chiral selectors.

The enantioseparation of seven Trögers base derivatives (TBs) was carried out by capillary electrophoresis using α-, β-, and γ-cyclodextrins as chiral selectors and phosphate at 20 mmol/l concentration, pH 2.5, as background electrolyte. The method was optimized with respect to the concentration of chosen chiral selectors (0-50 mmol/l) and the amount of organic solvent (acetonitrile, 0-25 % (v/v)) in the electrolyte. The results indicate that all the studied variables, i.e., type of chiral selector, its concentration, and the amount of the added organic solvent, have a significant impact on the enantioseparation of the studied TBs. The best results for the majority of the separated TBs were obtained utilizing β-cyclodextrin at 5 mmol/l concentration and with various amounts of acetonitrile added ranging from 5 to 15% (v/v) in the background electrolyte. For the two smallest studied TBs, γ-cyclodextrin with 10% (v/v) acetonitrile also provided good resolution.

Influence of surface properties on the deposition of a polyaniline film and detection of tumor markers

The deposition of polyaniline (PANI) onto the surface of plasticized poly(vinyl chloride) (PVC) membranes requires optimizing the membrane composition. Controlling the ratio between the plasticizer and PVC enables the hydrophilic surface to be prepared and a homogeneous PANI film to be deposited through chemical polymerization. Our studies showed that such modified PVC membranes can be used for the potentiometric detection of three tumor markers (TMs) that are metabolites of catecholamines and serves as a screening test for neuroblastoma. Furthermore, the interactions of PANI with these TMs were proved by a capillary electrophoresis method in which a capillary covered with PANI was used.