Mixed Mode Of Interaction Research Articles

Cation-exchange/hydrophilic interaction mixed-mode liquid chromatographic method for analyzing the trigonelline class of bioactives in coffee beans

The coffee phytochemical trigonelline and its roasting products nicotinic acid and N-methylpyridinium represent an important class of bioactives that mediate the health benefits of coffee consumption. However, there is a paucity of methods for their simultaneous analysis in coffee beans, especially those affordable and reliable for widespread routine use. To improve this situation, an easy-to-use HPLC−UV method was developed in this study based on a reversed-phase/cation-exchange mixed-mode column showing unique chromatographic selectivity toward the polar and ionic analytes over the matrix components of coffee. The selectivity was achieved by using a decreasing acetonitrile gradient, which tuned the column to a cation-exchange/hydrophilic interaction (CEX/HILIC) mixed separation mode whilst minimizing its hydrophobic interaction capability. The method was assessed for figures of merit, giving limits of detection in coffee beans at around the 0.1 mg/100 g wet matter level, and verified for its applicability to a heterogeneous set of coffee bean samples differing in roasting degree and origin.

Click postsynthesis of microporous organic network@silica composites for reversed-phase/hydrophilic interaction mixed-mode chromatography.

Recently, the good physical and chemical properties, well-defined pore architectures, and designable topologies have made microporous organic networks (MONs) excellent potential candidates in high-performance liquid chromatography (HPLC). However, their superior hydrophobic structures restrict their application in the reversed-phase mode. To solve this obstacle and to expand the application of MONs in HPLC, we realized the thiol-yne "click" postsynthesis of a novel hydrophilic MON-2COOH@SiO2-MER (MER denotes mercaptosuccinic acid) microsphere for reversed-phase/hydrophilic interaction mixed-mode chromatography. SiO2 was initially decorated with MON-2COOH using 2,5-dibromoterephthalic acid and tetrakis(4-ethynylphenyl)methane as monomers, and MER was then grafted via thiol-yne click reaction to yield MON-2COOH@SiO2-MER microspheres (5μm) with a pore size of ~1.3nm. The -COOH groups in 2,5-dibromoterephthalic acid and the post-modified MER molecules considerably improved the hydrophilicity of pristine MON and enhanced the hydrophilic interactions between the stationary phase and analytes. The retention mechanisms of the MON-2COOH@SiO2-MER packed column were fully discussed with diverse hydrophobic and hydrophilic probes. Benefiting from the numerous -COOH recognition sites and benzene rings within MON-2COOH@SiO2-MER, the packed column exhibited good resolution for the separation of sulfonamides, deoxynucleosides, alkaloids, and endocrine-disrupting chemicals. A column efficiency of 27,556 plates per meter was obtained for the separation of gastrodin. The separation performance of the MON-2COOH@SiO2-MER packed column was also demonstrated by comparing with those of MON-2COOH@SiO2, commercial C18, ZIC-HILIC, and bare SiO2 columns. This work highlights the good potential of the thiol-yne click postsynthesis strategy to construct MON-based stationary phases for mixed-mode chromatography.

Preparation and characterization of glucose-based covalent organic polymer coated silica as stationary phase for high-performance liquid chromatography

Carbohydrate is a renewable, sustainable, hydrophilic, and biodegradable natural product, which is widely used in the field of adsorption. In this study, a glucose-based covalent organic polymer (COP) coated silica was fabricated by facile solvent knitting reaction between tetrabenzylglucose and silica-phenyl with anhydrous aluminum trichloride as catalyst, forming a core-shell stationary phase (donated as SiO2@COPBn-glu) for high performance liquid chromatography. The prepared SiO2@COPBn-glu was characterized by scanning electron microscopy, transmission electron microscopy, Fourier-transform infrared spectrometry, solid-state 13C nuclear magnetic resonance spectrometry, X-ray photoelectron spectroscopy, and N2 adsorption-desorption experiments. Owing to the coexistence of benzene units and alkyl, hydroxyl and ether groups in the skeleton of COPBn-glu shell, the developed chromatographic packing exhibited reversed-phase/hydrophilic interaction mixed-mode with multiple retention mechanisms, such as hydrophobic, π-π, hydrogen bonding, and electron donor-acceptor interactions. The results revealed that the SiO2@COPBn-glu column demonstrated excellent selectivity and retention behavior for both hydrophilic and hydrophobic compounds with good repeatability and stability. Meanwhile, the chromatographic performance of the prepared SiO2@COPBn-glu column was compared with a C18 column to assess the role of the coating COPBn-glu shell. Therefore, the development of the SiO2@COPBn-glu stationary phase expands the potential application of COPs in separation field.

Chromatographic Regulation by the Building Blocks for Triazine Polymer-Based Core–Shell Stationary Phases

Two versions of reversed-phase/hydrophilic interaction mixed-mode core–shell stationary phases for high-performance liquid chromatography using porous organic polymers as the shell material were investigated. The stationary phase named SiO2@CTPCC-TPB using triazine-triphenylbenzene-based porous organic polymers as the shell material has been reported previously. To regulate chromatographic performance, heptazine–biphenyl moieties with fewer benzene rings and higher nitrogen content were used as organic building blocks to grow a porous shell on the surface of silica to acquire a core–shell stationary phase, namely, SiO2@CHPCy-DB. Various techniques were used to characterize the developed core–shell microsphere, and nonpolar/polar solutes were utilized as probes to investigate the chromatographic behavior of the stationary phase. The results revealed that SiO2@CHPCy-DB exhibited reversed-phase/hydrophilic interaction mixed-mode with multiple retention mechanisms. Meanwhile, the separation behavior of the two homemade columns and a commercial column was compared to assess the role of the building blocks in porous organic polymers in regulating and improving separation. The successful determination of drugs of abuse in urine via the SiO2@CHPCy-DB column indicated its potential for the determination of trace analytes in complex samples.

Monomer-mediated fabrication of microporous organic network@silica microsphere for reversed-phase/hydrophilic interaction mixed-mode chromatography

Microporous organic networks (MONs) are promising in high performance liquid chromatography (HPLC) with large specific surface area, good hydrophobicity and stability. However, their superhydrophobic structures restrict MONs-based HPLC only in reversed-phase mode. To decrease the hydrophobicity of pristine MONs and to expand their broad application in HPLC, here we described the monomer-mediated fabrication of core-shell MON-2COOH@SiO2 microspheres for reversed-phase liquid chromatography (RPLC)/hydrophilic interaction liquid chromatography (HILIC) mixed-mode chromatography for the first time. The –COOH groups were introduced into MONs’ skeleton to improve their hydrophilicity and to provide hydrophilic interaction sites. The MON-2COOH was grafted onto silica via a monomer mediated method to produce monodispersed core-shell microspheres. By adjusting the concentration of reactants, the thickness of MON-2COOH shell was easily manipulated. The packed MON-2COOH@SiO2 column showed high resolution and selectivity for separating both hydrophobic (alkylbenzenes, polycyclic aromatic hydrocarbons, anilines and phenols) and hydrophilic (nucleoside and nucleic bases) probes, highlighting the promise of MONs in mixed-mode HPLC. The MON-2COOH@SiO2 column also achieved good separation to sulfonamides, nonsteroidal anti-inflammatory drugs, flavonoids and phenylurea herbicides, and offered better resolution than commercial C18 and pristine SiO2 column. Multiple retention mechanisms were also found on MON-2COOH@SiO2 packed column, underlining the great potential of MONs in mixed-mode HPLC.

Structure and surface analysis of ibuprofen-organotin conjugate: Potential anti-cancer drug candidacy of the compound is proven by in-vitro DNA binding and cytotoxicity studies

An ibuprofen-organotin conjugate (TPTDI) was synthesized by reacting ibuprofen with triphenyltin hydroxide (fentin hydroxide) in dry ethanol under acidic conditions. Characterization data of the compound, obtained by spectroscopic techniques (FTIR, 1H NMR and 13C NMR), elemental analysis and its X-ray single crystal were found to corroborate the stoichiometry and structure of the title organotin (IV) ester. A detailed Hirshfeld surface analysis for the elucidation of possible intermolecular interactions indicated that the most important contributions to the crystal packing were from H…H (66.7%), H…C/C…H (27.9%) and H…O/O…H (5.3%) interactions. Hydrogen-bonding and van der Waals interactions were the dominant interactions in the crystal packing. TPTDI – DNA binding studies were done by DFT, molecular docking, UV–visible and fluorescence spectroscopies, cyclic voltammetry (CV) and by viscosity measurements at neutral pH (7.0) and at 37 °C. Theoretical and experimental investigations were found compatible and revealed significant reactivity of TPTDI with DNA via mixed mode of interaction. Binding parameters (ΔG, Kb and n) confirmed the reaction spontaneity and intercalation as prominent mode along with groove binding. In-vitro Huh-7 cancer cell line activity suggested TPTDI to be a potential anti-cancer drug candidate. Molecular, chemical and biological findings showed good correlations.

Structure and Surface Analysis of Ibuprofen-Organotin Conjugate: Potential Anti-Cancer Drug Candidacy of the Compound is Proven by In-Vitro DNA Binding and Cytotoxicity Studies

An ibuprofen-organotin conjugate (TPTDI) was synthesized by reacting ibuprofen with triphenyltin hydroxide (fentin hydroxide) in dry ethanol under acidic conditions. Characterization data of the compound, obtained by spectroscopic techniques (FTIR, 1 H-NMR and 13 C-NMR), elemental analysis and its X-ray single crystal were found to corroborate the stoichiometry and structure of the title organotin (IV) ester. A detailed Hirshfeld surface analysis for the elucidation of possible intermolecular interactions indicated that the most important contributions to the crystal packing were from H…H (66.7%), H…C/C…H (27.9%) and H…O/O…H (5.3%) interactions. Hydrogen-bonding and van der Waals interactions were the dominant interactions in the crystal packing. TPTDI – DNA binding studies were done by DFT, molecular docking, UV-visible and fluorescence spectroscopies, cyclic voltammetry (CV) and by viscosity measurements at neutral pH (7.0) and at 37 o C. Theoretical and experimental investigations were found compatible and revealed significant reactivity of TPTDI with DNA via mixed mode of interaction. Binding parameters (∆G, K b and n) confirmed the reaction spontaneity and intercalation as prominent mode along with groove binding. In-vitro Huh-7 cancer cell line activity suggested TPTDI to be a potential anti-cancer drug candidate. Molecular, chemical and biological findings showed good correlations.

Controlled Fabrication of Silica@Covalent Triazine Polymer Core-Shell Spheres as a Reversed-Phase/Hydrophilic Interaction Mixed-Mode Chromatographic Stationary Phase.

The unique properties of covalent triazine-based organic framework/polymers, including large surface area, hydrophilic-lipophilic-balanced adsorption, and economical preparation, make it a promising candidate as a stationary phase for high-performance liquid chromatography. However, irregular shapes and wide size distributions of such particles hinder column packing, resulting in a low column efficiency or a high back pressure. Herein, we describe the fabrication of SiO2@ covalent triazine-based organic polymer (CTP) core-shell microspheres with a distinct sphere-coating-sphere appearance using aminosilica as the supporting substrate to grow the CTP shell. By adjusting the amount of reactants, the thickness of the CTP shell, which consists of triazine and 1,3,5-triphenylbenzene monomers, was easily controlled. The developed core-shell microspheres were characterized via scanning electron microscopy, energy dispersive X-ray spectroscopy, transmission electron microscopy, solid-state 13C nuclear magnetic resonance analysis, and N2 adsorption experiments. The synergism of the triazine and aromatic moieties on CTP provides the new stationary phase with multiple retention mechanisms, including hydrophobic, π-π, electron donor-acceptor, hydrogen-bonding interactions, and so forth. On the basis of these interactions, successful separation and higher shape selectivity were achieved among several analytes that vary in polarity under both reversed-phase and hydrophilic interaction liquid chromatography conditions. Therefore, SiO2@CTP microspheres combine the advantages of good column packing properties of the uniform monodisperse silica microspheres and the recognition performance of CTP, generating flexible selectivity and application prospect for both hydrophilic and hydrophobic analytes.

Synthesis, Crystal Structure, Hirshfeld Surface Analysis, DFT, and DNA-Binding Studies of (E)-2-(3-Hydroxy-4-Methoxybenzylidene)Hydrazinecarbothioamide.

(E)-2-(3-Hydroxy-4-methoxybenzylidene)hydrazinecarbothioamide 3 was synthesized by reacting thiosemicarbazide with 2-hydorxy-3-methoxybenzaldehyde in dry ethanol. The structure was elucidated by spectroscopic (FT-IR, 1H NMR, and 13C NMR) and single crystal X-ray diffraction techniques. A detailed analysis of the intermolecular interactions has been performed based on the Hirshfeld surfaces and their associated two-dimensional fingerprint plots. DFT, spectroscopic, and electrochemical DNA-binding analysis confirmed that the compound is reactive to bind with DNA. Viscometric studies suggested that compound 3 has a mixed mode of interaction and intercalated into the DNA base pairs predominantly along with the possibility of electrostatic interactions. Graphical Abstract.

Aroylthiourea derivatives of ciprofloxacin drug as DNA binder: Theoretical, spectroscopic and electrochemical studies along with cytotoxicity assessment

Aroylthiourea derivatives of ciprofloxacin drug — [1-cyclopropyl-6-fluoro-7-(4-((4-methoxybenzoyl)carbamothioyl)piperazin-1-yl)-4-oxo-1,4-dihydroquinoline-3-carboxylic acid] ATU-1, [1-cyclopropyl-7-(4-((2,4-dibromobenzoyl)carbamothioyl)piperazin-1-yl)-6-fluoro-4-oxo-1,4-dihydroquinoline-3-carboxylic acid] ATU-2, and [1-cyclopropyl-7-(4-((3,5-dinitrobenzoyl)carbamothioyl)piperazin-1-yl)-6-fluoro-4-oxo-1,4-dihydroquinoline-3-carboxylic acid] ATU-3 were synthesized, characterized and investigated for DNA binding at stomach pH (4.7) and at 37 °C. All findings by using DFT, molecular docking, spectroscopic (UV-, fluorescence; FL-), cyclic voltammetric (CV) and viscometric techniques revealed that these compounds have the potency to bind with DNA via a mixed mode of interaction. The binding affinity of ATU-1 was evaluated comparatively greater with Kb × 104/M−1 (docking; 5.55, UV-; 7.93, FL-; 5.62, CV; 6.06), ΔG/kJmol−1(docking; −27.07, UV-; −29.07, FL-; −28.18, CV; −28.38) and n (FL-; 1.20, CV; 2.72). Stern-Volmer quenching constant (Ksv) further pointed towards comparatively greater binding affinity of ATU-1 for DNA, while bimolecular quenching constant (Kq) values showed the involvement of static quenching mechanism in the compound — DNA interaction. Comparatively lesser IC50 (7.1 μM) value obtained from biological work on Huh-7 cancer cell line further confirmed the greater anticancer potential of ATU-1 than that of ATU-2&3.

A reversed-phase/hydrophilic bifunctional interaction mixed-mode monolithic column with biphenyl and quaternary ammonium stationary phases for capillary electrochromatography.

A novel organic polymer monolithic column with reversed-phase/hydrophilic (RPLC/HILIC) bifunctional interaction mixed-mode was successfully synthesized with the monomers 4-vinylbiphenyl and vinylbenzyl trimethylammonium chloride and the cross-linker ethylene dimethacrylate by in situ copolymerization in a binary porogenic solvent consisting of cyclohexanol and dodecanol for capillary electrochromatography. The stationary phases formed by styrene-based monomers can allow powerful π-π, hydrophobic and hydrophilic interactions, which is beneficial for the chromatographic separation with high resolution and high column efficiency. One mixed-mode monolithic column can work as two individual mode columns based on the combination of binary RPLC and HILIC separation mechanisms. Vanillin substances and neutral and alkaline compounds can be separated perfectly on the monolithic column in different chromatographic modes which can be switched by changing the content of the organic modifier in the running phase. For benzene, the highest column efficiency was 3.49 × 105 plates per m (theoretical plates, N). The relative standard deviations of retention time of different test analytes for intra-day (n = 5), inter-day (n = 5), column-to-column (n = 3) and batch-to-batch (n = 3) reproducibility were all less than 5.0%. All these results demonstrate that the monolithic column with RPLC/HILIC mixed-mode has great application potential.

Controllable preparation of a reverse-phase/hydrophilic interaction mixed-mode chromatographic stationary phase with adjustable selectivity

A mixed-mode stationary phase prepared by grafting block copolymers via ATRP could adjust separation selectivity by simply tuning the ratios of copolymer chains.

Layer-by-layer self-assembly of polyelectrolyte multilayers on silica spheres as reversed-phase/hydrophilic interaction mixed-mode stationary phases for high performance liquid chromatography

In this study, a series of stationary phases, comprising silica spheres and polyelectrolyte multilayers (PEMs) as the core and surface coating, respectively, were prepared via a layer-by-layer self-assembly approach for use in high-performance liquid chromatography. PEMs coatings were formed by the alternate deposition of positively charged poly(allylamine hydrochloride) and negatively charged poly(ethylene-alt-maleate) anions which were synthesized by esterification between poly(ethylene-alt-maleic anhydride) and n-alkyl alcohols (CnH2n+1OH, n=4, 8, 10, 12). The chromatographic performance and retention mechanism of the new stationary phases were evaluated in simultaneous reversed-phase/hydrophilic interaction mixed-mode chromatography using different solute probes, such as alkyl benzene, p-hydroxybenzoic acid and its esters, anilines, phenols, and pyrimidines. The separation performance of the new stationary phases was optimized by tuning the n-alkyl chain length of poly(ethylene-alt-maleate) and bilayer numbers of PEMs. These results indicated that the new stationary phases demonstrate promise for the simultaneous separation of complex hydrophobic and hydrophilic samples with high selectivity.

Preparation of Organic-Silica Hybrid Monolith with Anion Exchange/Hydrophilic Interaction Mixed-Mode Via Epoxy–Amine Ring-Opening Polymerization Using Polyethylenimine as Functional Monomer

Polyethylenimine (PEI) and 2,4,6,8-tetramethyl-2,4,6,8-tetrakis(propyl glycidyl ether)cyclotetrasiloxane (POSS–epoxy) were used as precursors for the preparation of organic-silica hybrid monolithic columns (PEI–POSS monolith) via epoxy–amine ring-opening polymerization (ROP). The high density of amine groups in PEI provides rich chromatographic interaction sites for the polar or acidic analytes in hydrophilic interaction (HILIC) and weak anion exchange (WAX) mechanisms. The column preparation conditions, such as the porogens, solvent and reaction temperature, were systematically investigated according to the morphology, permeability and column efficiency. The separation mechanisms of HILIC and WAX were evaluated with neutral polar compounds and halogen benzoic acids. Owing to the existence of reactive amine groups on the matrix surface, the PEI–POSS monolith is also an ideal starting material for the preparation of HILIC or strong anionic exchange (SAX) stationary phases by modification. The modification of PEI–POSS monoliths with iodomethane or bromoacetic acid via the nucleophilic substitution reaction could achieve the retention mechanisms of SAX or zwitterionic HILIC, respectively.

Imidazolium embedded C8 based stationary phase for simultaneous reversed-phase/hydrophilic interaction mixed-mode chromatography

A new imidazolium embedded C8 based stationary phase (SIL-MPS-VOL) was facilely prepared by two steps and characterized by Fourier transform infrared spectrometry and thermogravimetric analysis. Due to the introduction of quaternary imidazolium group to the traditional C8 stationary phase, the developed SIL-MPS-VOL column demonstrated both reversed-phase liquid chromatography (RPLC) and hydrophilic interaction liquid chromatography (HILIC) retention mechanisms. A series of hydrophobic and hydrophilic test samples, including benzene homologues, anilines, positional isomers, nucleosides and nucleotides, were used to evaluate the developed SIL-MPS-VOL stationary phase. A rapid separation time, high separation efficiency and planar selectivity were achieved, compared with the commercially available C8 column. Moreover, the developed stationary phase was further used to detect and separate of melamine in powdered infant formula and high polar component of secondary metabolites of Trichoderma, and improved separation efficiency was achieved, indicating the potential merits of the developed SIL-MPS-VOL stationary phase for simultaneous separation of complex hydrophobic and hydrophilic samples with high selectivity.

Development and application of separation materials for mixed-mode chromatography

Mixed-mode chromatography has received more and more attention due to its unique chromatographic characteristics recently. In this review, a summary of the development and applications of mixed-mode chromatography is presented. According to the types of hydrophilic interaction/ion-exchange mixed-mode chromatography (HILIC/IEX), reversed-phase/hydrophilic interaction mixed-mode chromatography (RPLC/HILIC) and reversed-phase/ion-exchange mixed-mode chromatography (RPLC/IEX), the preparation and applications of each type are introduced. Compared with single mode chromatography, the selectivity as well as the sample loading capacity of the mixed-mode chromatography can be improved. The researches mostly focus on the design of mixed-mode stationary phases and the applications especially to bio-analysis. The mixed-mode chromatography will be a potent approach for the analysis and separation of complex samples, and it will also be an effective and complementary tool in practical separation work.

Flavonoid–DNA binding studies and thermodynamic parameters

Interactional studies of new flavonoid derivatives (Fl) with chicken blood ds.DNA were investigated spectrophotometrically in DMSO–H 2O (9:1 v/v) at various temperatures. Spectral parameters suggest considerable binding between the flavonoid derivatives studied and ds.DNA. The binding constant values lie in the enhanced-binding range. Thermodynamic parameters obtained from UV studies also point to strong spontaneous binding of Fl with ds.DNA. Viscometric studies complimented the UV results where a small linear increase in relative viscosity of the DNA solution was observed with added optimal flavonoid concentration. An overall mixed mode of interaction (intercalative plus groove binding) is proposed between DNA and flavonoids. Conclusively, investigated flavonoid derivatives are found to be strong DNA binders and seem to be promising drug candidates like their natural analogues.