Tri-fluoro-methane-sulfonate salt of 5,10,15,20-tetra-kis-(1-benzyl-pyridin-1-ium-4-yl)-21H,23H-porphyrin and its CaII complex.

The synthesis, crystallization and characterization of a tri-fluoro-methane-sulfonate salt of 5,10,15,20-tetra-kis-(1-benzyl-pyridin-1-ium-4-yl)-21H,23H-por-phy-rin, C68H54N8 4+·4CF3SO3 -·4H2O, 1·OTf, are reported in this work. The reaction between 5,10,15,20-tetra-kis-(pyridin-4-yl)-21H,23H-porphyrin and benzyl bromide in the presence of 0.1 equiv. of Ca(OH)2 in CH3CN under reflux with an N2 atmosphere and subsequent treatment with silver tri-fluoro-methane-sulfonate (AgOTf) salt produced a red-brown solution. This reaction mixture was filtered and the solvent was allowed to evaporate at room temperature for 3 d to give 1·OTf. Crystal structure determination by single-crystal X-ray diffraction (SCXD) revealed that 1·OTf crystallizes in the space group P21/c. The asymmetric unit contains half a porphyrin mol-ecule, two tri-fluoro-methane-sulfonate anions and two water mol-ecules of crystallization. The macrocycle of tetra-pyrrole moieties is planar and unexpectedly it has coordinated CaII ions in occupational disorder. This CaII ion has only 10% occupancy (C72H61.80Ca0.10F12N8O16S4). The pyridinium rings bonded to methyl-ene groups from porphyrin are located in two different arrangements in almost orthogonal positions between the plane formed by the porphyrin and the pyridinium rings. The crystal structure features cation⋯π inter-actions between the CaII atom and the π-system of the phenyl ring of neighboring mol-ecules. Both tri-fluoro-methane-sulfonate anions are found at the periphery of 1, forming hydrogen bonds with water mol-ecules.

Molecular two-point recognition of fructosyl valine and fructosyl glycyl histidine in water by fluorescent Zn(II)-terpyridine complexes bearing boronic acids.

Selective recognition of fructosyl amino acids in water by arylboronic acid-based receptors is a central field of modern supramolecular chemistry that impacts biological and medicinal chemistry. Fructosyl valine (FV) and fructosyl glycyl histidine (FGH) occur as N-terminal moieties of human glycated hemoglobin; therefore, the molecular design of biomimetic receptors is an attractive, but very challenging goal. Herein, we report three novel cationic Zn-terpyridine complexes bearing a fluorescent N-quinolinium nucleus covalently linked to three different isomers of strongly acidified phenylboronic acids (ortho-, 2Zn; meta-, 3Zn and para-, 4Zn) for the optical recognition of FV, FGH and comparative analytes (D-fructose, Gly, Val and His) in pure water at physiological pH. The complexes were designed to act as fluorescent receptors using a cooperative action of boric acid and a metal chelate. Complex 3Zn was found to display the most acidic -B(OH)2 group (pKa = 6.98) and exceptionally tight affinity for FV (K = 1.43 × 105 M-1) with a strong quenching analytical response in the micromolar concentration range. The addition of fructose and the other amino acids only induced moderate optical changes. On the basis of several spectroscopic tools (1H, 11B NMR, UV-Vis, and fluorescence titrations), ESI mass spectrometry, X-ray crystal structure, and DFT calculations, the interaction mode between 3Zn and FV is proposed in a 1 : 1 model through a cooperative two-point recognition involving a sp3 boronate-diol esterification with simultaneous coordination bonding of the carboxylate group of Val to the Zn atom. Fluorescence quenching is attributed to a static complexation photoinduced electron transfer mechanism as evidenced by lifetime experiments. The addition of FGH to 3Zn notably enhanced its emission intensity with micromolar affinity, but with a lower apparent binding constant than that observed for FV. FGH interacts with 3Zn through boronate-diol complexation and coordination of the imidazole ring of His. DFT-optimized structures of complexes 3Zn-FV and 3Zn-FGH show a picture of binding which shows that the Zn-complex has a suitable (B⋯Zn) distance to the two-point recognition with these analytes. Molecular recognition of fructosyl amino acids by transition-metal-based receptors has not been explored until now.

Water-soluble fluorescent chemosensor for sorbitol based on a dicationic diboronic receptor. Crystal structure and spectroscopic studies.

Selective recognition of saccharides by phenylboronic dyes capable of functioning in aqueous conditions is a central topic of modern supramolecular chemistry that impacts analytical sciences and biological chemistry. Herein, a new dicationic diboronic acid structure 11 was synthesized, structurally described by single-crystal X-ray diffraction, and studied in-depth as fluorescent receptor for six saccharides in pure water at pH = 7.4. This dicationic receptor 11 has been designed particularly to respond to sorbitol and involves two convergent and strongly acidified phenyl boronic acids, with a pKa of 6.6, that operate as binding sites. The addition of sorbitol in the micromolar concentration range to receptor 11 induces strong fluorescence change, but in the presence of fructose, mannitol, glucose, lactose and sucrose, only moderate optical changes are observed. This change in emission is attributed to a static complexation photoinduced electron transfer mechanism as evidenced by lifetime experiments and different spectroscopic tools. The diboronic receptor has a high affinity/selectivity to sorbitol (K = 31 800 M-1) over other saccharides including common interfering species such as mannitol and fructose. The results based on 1H, 11B NMR spectroscopy, high-resolution mass spectrometry and density functional theory calculations, support that sorbitol is efficiently bound to 11 in a 1 : 1 mode involving a chelating diboronate-sorbitol complexation. Since the experimental B⋯B distance (5.3 Å) in 11 is very close to the calculated distance from the DFT-optimized complex with sorbitol, the efficient binding is attributed to strong acidification and preorganization of boronic acids. These results highlight the usefulness of a new diboronic acid receptor with a strong ability for fluorescent recognition of sorbitol in physiological conditions.

Fluorescence Sensing of Monosaccharides by Bis-boronic Acids Derived from Quinolinium Dicarboxamides: Structural and Spectroscopic Studies.

Three new diboronic acid-substituted bisquinolinium salts were synthesized, structurally described by single-crystal X-ray diffraction, and studied in-depth as fluorescent receptors for six monosaccharides and two open-chain polyols in water at physiological pH. The dicationic pyridine-2,6-dicarboxamide-based receptors contain two N-quinolinium rings as the fluorescent units covalently linked to three different isomers of phenylboronic acid (ortho, 2; meta, 3; and para, 4) as chelating binding sites for polyols. Additions of glucose/fructose in the micromolar concentration range to receptors 2 and 3 induce significant fluorescence changes, but in the presence of arabinose, galactose, mannose, and xylose, only modest optical changes are observed. This optical change is attributed to a static photoinduced electron transfer mechanism. The meta-diboronic receptor 3 exhibited a high affinity/selectivity toward glucose (K = 3800 M-1) over other monosaccharides including common interfering species such as fructose and mannitol. Based on multiple spectroscopic tools, electrospray ionization high-resolution mass spectrometry, crystal structures, and density functional theory calculations, the binding mode between 3 and glucose is proposed as a 1:1 complex with the glucofuranose form involving a cooperative chelating diboronate binding. These results demonstrate the usefulness of a new set of cationic fluorescent diboronic acid receptors with a strong ability for optical recognition of glucose in the sub-millimolar concentration range.

Efficient fluorescent recognition of ATP/GTP by a water-soluble bisquinolinium pyridine-2,6-dicarboxamide compound. Crystal structures, spectroscopic studies and interaction mode with DNA.

The new dicationic pyridine-2,6-dicarboxamide-based compound 1 bearing two N-alkylquinolinium units was synthesized, structurally determined by single-crystal X-ray diffraction, and studied in-depth as a fluorescent receptor for nucleotides and inorganic phosphorylated anions in pure water. The addition of nucleotides to 1 at pH = 7.0 quenches its blue emission with a selective affinity towards adenosine 5'-triphosphate (ATP) and guanosine 5'-tripohosphate (GTP) over other nucleotides such CTP, UTP, ADP, AMP, dicarboxylates and inorganic anions. On the basis of the spectroscopic tools (1H, 31P NMR, UV-vis, fluorescence), MS measurements and DFT calculations, receptor 1 binds ATP with high affinity (log K = 5.04) through the simultaneous formation of strong hydrogen bonds and π-π interactions between the adenosine fragment and quinolinium ring with binding energy calculated in 8.7 kcal mol-1. High affinity for ATP/GTP is attributed to the high acidity of amides and preorganized rigid structure of 1. Receptor 1 is an order of magnitude more selective for ATP than GTP. An efficient photoinduced electron transfer quenching mechanism with simultaneous receptor-ATP complexation in both the excited and ground states is proposed. Additionally, multiple spectroscopic studies and molecular dynamics simulations showed that 1 can intercalate into DNA base pairs.

Chemosensing of neurotransmitters with selectivity and naked eye detection of l-DOPA based on fluorescent Zn(ii)-terpyridine bearing boronic acid complexes.

Biological catecholamines such as l-DOPA and dopamine play vital physiological roles in the brain and are chemical indicators of human diseases. A new range of fluorescent Zn(ii)-terpyridine complexes are described and studied in-depth as chemosensors for catecholamine-based neurotransmitters and nucleosides in pure water. The new Zn-terpyridine-based chemosensors contain a cationic N-isoquinolinium nucleus as the optical indicator covalently linked to three different isomers of strongly acidified phenylboronic acids (ortho-, 2.Zn; meta-, 3.Zn and para-, 4.Zn, substituted derivatives) as catechol binding sites. The addition of l-DOPA, dopamine, epinephrine, l-tyrosine and nucleosides to Zn(ii)-boronic acid chemosensors at physiological pH quenches their blue emission with a pronounced selectivity and an unprecedented high affinity towards l-DOPA (log K = 6.01). This efficient response by l-DOPA was also observed in the presence of coexisting species in blood plasma and urine with a detection limit of 3.0 µmol L-1. A photoinduced electron transfer quenching mechanism with simultaneous chemosensor-l-DOPA complexation in both the excited and ground states is proposed. The fluorescence experimental observations show that the 2.Zn·eosin-Y adduct can be used as a selective naked-eye chemosensing ensemble for l-DOPA with a fast turn-on fluorescent response and color change from blue to green under UV light at the micromolar level. On the basis of multiple spectroscopic techniques (1H, 11B NMR, UV-Vis, and fluorescence), MS-ESI experiments, crystal structures, and DFT calculations, the binding mode between Zn(ii)-chemosensors and l-DOPA is proposed in a 1 : 1 model through a cooperative two-point recognition involving the reversible esterification of the boronic acid moiety with the aromatic diol fragment of l-DOPA together with the coordination of the carboxylate anion to the Zn(ii) atom with strong electrostatic contribution.

Chemosensing of Guanosine Triphosphate Based on a Fluorescent Dinuclear Zn(II)-Dipicolylamine Complex in Water.

Guanosine triphosphate (GTP) is a key biomarker of multiple cellular processes and human diseases. The new fluorescent dinuclear complex [Zn2(L)(S)][OTf]4, 1 (asymmetric ligand, L = 5,8-Bis{[bis(2-pyridylmethyl)amino] methyl}quinoline, S = solvent, and OTf = triflate anion) was synthesized and studied in-depth as a chemosensor for nucleoside polyphosphates and inorganic anions in pure water. Additions at neutral pH of nucleoside triphosphates, guanosine diphosphate, guanosine monophosphate, and pyrophosphate (PPi) to 1 quench its blue emission (λem = 410 nm) with a pronounced selectivity toward GTP over other anions, including adenosine triphosphate (ATP), uridine triphosphate (UTP), and cytidine triphosphate (CTP). The efficient quenching response by the addition of GTP was observed in the presence of coexisting species in blood plasma and urine with a detection limit of 9.2 µmol L-1. GTP also shows much tighter binding to the receptor 1 on a submicromolar level. On the basis of multiple spectroscopic tools (1H, 31P NMR, UV-vis, and fluorescence) and DFT calculations, the binding mode is proposed through three-point recognition involving the simultaneous coordination of the N7 atom of the guanosine motif and two phosphate groups to the two Zn(II) atoms. Spectroscopic studies, MS-ESI, and DFT suggested that GTP bound to 1 in 1:1 and 2:2 models with high overall binding constants of log ß1 (1:1) = 6.05 ± 0.01 and log ß2 = 10.91 ± 0.03, respectively. The optical change and selectivity are attributed to the efficient binding of GTP to 1 by the combination of a strong electrostatic contribution and synergic effects of coordination bonds. Such GTP selectivity of an asymmetric metal-based receptor in water is still rare.

Bifunctional colorimetric chemosensing of fluoride and cyanide ions by nickel-POCOP pincer receptors.

Three Ni(ii)-POCOP pincer complexes [NiCl{C6H2-4-OH-2,6-(OPPh2)2}], 1; [NiCl{C6H2-4-OH-2,6-(OPtBu2)2}], 2 and [NiCl{C6H2-4-OH-2,6-(OPiPr2)2}], 3 were studied as bifunctional molecular sensors for inorganic anions and acetate. In CH3CN, fluoride generates a bathochromic shift with a colorimetric change for 1-3 with a simultaneous fluorescence turn on, this optical effect is based on deprotonation of the para-hydroxy group of the POCOP ligand. On the other hand, in a neutral aqueous solution of 80 vol% CH3CN, additions of cyanide produce a distinct change of color by forming very stable complexes with the nickel-based receptors 1-3 with log Ka in the range of 4.38-5.03 M-1 and pronounced selectivity over other common anions such as iodide, phosphate, and acetate. Additionally, bromide shows a modest spectral change and affinity, but lower than those observed for cyanide. On the basis of 1H NMR experiments, UV-vis titrations, ESI-MS experiments, and the crystal structure of the neutral bromo complex of 1, it is proposed that the colorimetric change involves an exchange of chloride by CN- on the Ni(ii) atom. The Ni(ii)-based sensor 1 allows the fluorescent selective detection of fluoride with a limit of 5.66 µmol L-1 and colorimetric sensing of cyanide in aqueous medium in the micromolar concentration range.