Anion selectivity of a sapphyrin-modified silica gel HPLC support

On-column quantification of amino functionalities bonded to solid porous matrices packed within high performance liquid chromatography columns

Stationary phases (SPs) based on silica matrices functionalized with amino groups linked to their surface through alkyl chains of various length have found remarkable success in performing HILIC separations, showing really effective resolution towards a wide typology of compounds of biological interest, such as carbohydrates, nucleosides, purine and pyrimidine bases. Recently, we developed an operationally simple procedure, named DNBA-M, non-destructive for the analysed SP, designed to quantify the density of basic groups (typically amino groups) chemically bonded to the surface of porous solids. In the present study the DNBA-M procedure has been suitably modified to allow the quantification of any typology of amino groups present on silica matrices packed into HPLC columns. The new approach, named OC-DNBA-M, has been successfully validated through analysis of two HPLC columns packed with aminopropyl-silica matrices. Afterwards, it was also demonstrated as the OC-DNBA-M procedure may allow the effective and in-depth analysis of the structural composition characterizing SPs packed inside HPLC columns, in which amino-groups have been differently and only partially involved in following ureidic functionalizations. It was also proved how the analysed columns can be readily re-employed for the chromatographic applications for which they have been designed, without appreciable deterioration of the respective discrimination abilities.

Investigation of the retention characteristics of a 26-membered aromatic-aliphatic azamacrocycle bonded silica gel stationary phase for high performance liquid chromatography

A 26-membered aromatic-aliphatic azamacrocycle bonded silica gel stationary phase for high performance liquid chromatography was prepared and characterized.

Molecular recognition

The ‘marriage’ between porphyrin chemistry and the newly emerging molecular recognition science has opened up novel research opportunities leading to many biological and abiological applications. An overview of this fascinating research area is presented here.

Polyhydroxylated Sapphyrins: Multisite Non-metallic Catalysts for Activated Phosphodiester Hydrolysis

Enhanced hydrolysis rates for the cleavage of bis(4-nitrophenyl)phosphate (BNPP), a model phosphodiester, may be achieved by using appropriately designed ditopic receptors containing the known phosphate-binding nucleus, sapphyrin, attached covalently to suitably oriented polyhydroxyl subunits. Evidence for the interaction between sapphyrin and BNPP comes from solid-state X-ray diffraction analysis of a diprotonated dihydroxylated sapphyrin-BNPP complex and from solution-phase (31)P NMR spectroscopic binding studies. The sapphyrins described in this paper may have a role to play as oligonucleotide cleavage agents.

Dansylated aminopropyl controlled pore glass: a model for silica-liquid solvation

We have prepared a series of aminopropyl controlled pore glass (CPG) particles that have been labeled with a solvatochromic fluorescent probe molecule (dansyl). We report on the behavior of the attached dansyl reporter as a function of dansyl-to-amine molar ratio (i.e., dansyl loading), solvent dipolarity, and surface-residue end capping. In these experiments, we systematically adjust the dansyl loading by 10(5); a range much larger than ever explored. The dansylated CPG particles were also end capped with trimethylchlorosilane to derivatize most of the residual silanol and/or aminopropyl groups. The attached dansyl molecules can be surrounded by other dansyl molecules; they can be distributed within an ensemble of sites with differing physicochemical properties, and/or they can be distributed in sites that are restrictive to dansyl motion and/or solvent inaccessible. At high dansyl loadings, the majority of the dansyl groups are solvated by other dansyl moieties and solvent does not significantly alter the local microenvironment surrounding the average dansyl molecule (i.e., the cybotactic region) to any significant level. At intermediate dansyl loadings, the average distance between the dansyl groups increases and solvent is able to access/solvate/wet the dansyl groups and alter their cybotactic region to a greater extent. At the lowest dansyl loadings studied, the results suggest that these dansyl moieties are localized within solvent inaccessible/restrictive SiO2 sites (e.g., small pores).

Anion binding properties of 5,5′-dicarboxamido-dipyrrolylmethanes

A series of 5,5'-dicarboxamido-dipyrrolylmethanes have been synthesized and in some cases crystallographically characterized. Proton NMR titrations have revealed that these compounds, that contain only four neutral hydrogen bond donors and are acyclic, selectively bind anions in very competitive solvent media such as DMSO-d6/water mixtures.

Green Chemistry for Preparation of Oligopyrrole Macrocycles Precursors: Novel Methodology for Dipyrromethanes and Tripyrromethanes Synthesis in Water

A novel methodology for preparation of linear oligopyrroles is presented. Synthetic protocol uses water as a solvent for acid catalysed condensation of an aldehyde or ketone with unsubstituted pyrrole. While the most procedures for the above-mentioned compounds are performed in organic solvents, or large excess of pyrrole (used as solvent), we present here a novel, mild and efficient procedure for selective preparation of linear oligopyrroles in aqueous environment. Preparation of dipyrromethanes 3 and tripyrromethanes 4 was optimised by varying the molar ratio and concentrations of starting compounds (aldehyde to pyrrole) and acid catalyst. The high initial concentration of aldehyde and pyrrole leads to the preferential formation of 3, where the driving force for the product formation is precipitation of 3 from water solution; the reaction proceeds at room temperature within a couple of minutes in excellent yields. On the other hand, low concentration of starting compounds led to preferential formation of tripyrromethanes 4. Formation of 3 and 4 can also be controlled by the initial ratio of aldehyde and pyrrole, where generally the ratios over 1:6 gave mostly 3. Application of this synthetic protocol for ketones revealed that only 3 are formed, regardless of the ratio of starting compounds, which is interpreted as a result of lower reactivity of ketones in this particular condensation reaction.

Influencing electroosmotic flow and selectivity in open tubular electrochromatography by tetrakis(pentafluorophenyl)porphyrin as capillary wall modifier

A physically adsorbed and covalently bonded porphyrin derivative, 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin, H2TPFPP, has been used as a fused-silica capillary wall modifier in open tubular capillary electrochromatography (OT-CEC), and its influence on the electroosmotic flow (EOF) velocity and on the selectivity of OT-CEC separations of a set of model aromatic carboxylic acids has been tested. Whereas most of the coatings of this category bring about an increase in selectivity with a concomitant slow down of the EOF, H2TPFPP coating, depending on pH of the background electrolyte used, resulted both in decreasing of EOF at pH 8.5 by 5% and in increasing of EOF by 10-43% at pH 6 and 5, respectively. The separation efficiency and the resolution of aromatic carboxylic acids separation in coated capillaries, namely in that one with covalent coating, were better than in the bare fused-silica capillary. The perspectives of H2TPFPP as capillary wall modifier are visualized in introducing well defined electroosmotic properties of materials used for miniaturized separation channels preparation in chip-based electromigration devices.

Retention of anions on silica-based metalloporphyrin stationary phases

The silica-based Fe(III)-protoporphyrin and Zn-tetraphenylporphyrin stationary phases were examined for the HPLC separation of anions. The retention of nine common inorganic anions as well as benzoate anion (BA) and its hydroxy analogues (HBA) was examined using tartrate, acetate, and succinate eluents. The retention factors of inorganic anions on the FeProP stationary phase were in the order Cl- < NO3- < ClO4- < I- < SCN- and for organic anions benzoate < p-hydroxybenzoate < m-hydoxybenzoate < o-hydroxybenzoate. The retention factors of organic anions examined for a ZnTPP column were in the order p-HBA < m-HBA < BA < o-HBA.

Sapphyrins: versatile anion binding agents

Sapphyrin was the first expanded porphyrin to be reported in the literature and remains among the most extensively studied. Much of the interest in this macrocycle reflects its ability to bind anions, a phenomenon that has been examined in solution and in the solid state by a wide range of experimental techniques. In this Account, we summarize these studies while also outlining strategies that may be used to synthesize sapphyrins.

Open-tubular electrochromatography of organic phosphates on a sapphyrin-modified capillary

Sapphyrin coating of the inner wall of the capillary results in a distinct interaction of the phosphate residue-possessing compounds as proven by a seven-membered model mixture of nucleoside mono- and diphosphates and ATP. Modification of the inner surface of the capillary not only alters the endoosmotic flow (as would have been expected) but brings about an electrochromatographic effect based on the interaction of tested phosphate moiety-bearing solutes with the immobilized sapphyrin layer. Elution of the sample can be achieved by using either 25 mM borate-acetate buffer in which monophosphates are not only separated from each other, but also selectively separated from di- and triphosphates (ATP). With the other two buffer systems tested, i.e. borate-phosphate and Tris-HCl, better selectivity (though smaller interaction with the capillary coating) was observed. The coating is relatively stable (can be used for 20 subsequent runs at least), simple to materialize, and in spite of a strong UV absorbancy of sapphyrin at the wavelength used (254 nm), decreases the limit of detection by no more than one order of magnitude as compared to the untreated capillary. Resolution factors (calculated to the preceding peak) are in most cases better in the electrochromatographic separation mode as compared to the separation in the untreated capillary, which reflects both the decrease in the electroosmotic flow and the interaction with the capillary wall coating.

Interaction of Rh(I) with meso-arylsapphyrins and -rubyrins: first structural characterization of bimetallic hetero-rubyrin complex

The ligational behavior of meso-arylsapphyrins and rubyrins toward Rh(I) is investigated. Sapphyrins form monometallic complexes with coordination of one imine and amine type nitrogens of the bipyrrole unit in an eta2 fashion. The Rh(I) coordination is completed by the presence of two ancillary carbon monoxide ligands. Rubyrins form both monometallic and bimetallic complexes. Two types of bimetallic complexes have been isolated. In the first type, both rhodium atoms are projected above the mean rubyrin plane, while in the second type, one rhodium atom is projected above and the other below the mean plane. Detailed 1H and 2D NMR spectral analyses along with IR and UV-visible spectra of the complexes confirm the proposed binding modes for the rhodium complexes. Furthermore, the single-crystal X-ray analysis of one of the bimetallic complexes of rubyrin shows a bowl-shaped symmetric structure where both Rh(I) atoms are projected above the mean rubyrin plane at an angle of 71.73 degrees. The geometry around each rhodium center is approximately square planar [N1-Rh1-N2, 80.38(9) degrees; C15-Rh1-C16, 86.95(14) degrees; N1-Rh1-C15, 97.13(12) degrees; and N2-RH1-C16, 94.97(12) degrees ]. The omicronbserved distance of 4.313 A between the two rhodium centers reveals very little interaction between the two rhodium atoms. This type of metal binding is accompanied by a 180 degrees ring flip of the heterocyclic ring connecting the two bipyrrole units. In dioxarubyrin, where one of the pyrrole rings of the bipyrrole unit is inverted, Rh(I) binds at the periphery to the pyrrole nitrogen, leaving the rubyrin cavity empty. The absence of one amino and one imino nitrogen on the dipyrromethene subunits in the sapphyrins and rubyrins described here forces Rh(I) to bind to bipyrrole nitrogens.

Analytical Application of Oligopyrrole Macrocycles

Progress of modern analytical chemistry is closely related with advancement in other fields such as organic chemistry and biochemistry. Successful solution of current scientific problems is inconceivable without close cooperation of different chemical disciplines. As an example of such hot and very intricate theme research in the field of molecular recognition of biologically active compounds can serve, where numerous methods of analytical chemistry, organic chemistry and biochemistry can suitably be utilized, elaborated and brought into consonance. This multidisciplinary overlap logically leads to the advent of new scientific fields with their own tools, methodologies and subjects of exploration - bioanalytical chemistry and nanotechnology. This review covers different aspects of analytical application of oligopyrrole macrocycles (mainly porphyrins and sapphyrins). These compounds are widely used in analytical chemistry due to their outstanding optical properties. In our contribution oligopyrrole macrocycles are considered as signaling and structural parts of chemical receptors and selectors in various applications. Introduction of different moieties into meso-position of macrocyclic rings allows to obtain e.g., sterically well-organized receptors for recognition of biologically important analytes, new chromatographic materials, and powerful tools in electrochemical research. Finally, future trends in the field are outlined briefly.