Alejandro Dorazco-González

Fluorescent anion sensing by bisquinolinium pyridine-2,6-dicarboxamide receptors in water

Dicationic N-methylated at quinolyl moieties derivatives of three isomers of N,N′-bis(quinolyl)pyridine-2,6-dicarboxamide, and respective N-methyl quinolinium benzamides as reference compounds, have been prepared and characterized by crystal structures, spectral and acid–base properties in water. First pKa values of dicarboxamides between 8.1 and 9.3 determined spectrophotometrically are unusually low for amides. Dicarboxamide derivatives of 3- (1) and 6-aminoquinoline (2) undergo efficient fluorescence quenching by halide, acetate, pyrophosphate and nucleotide anions but the derivative of 5-aminoquinoline (3) shows very small quenching effects. The shape of Stern–Volmer plots for dicarboxamides indicates the existence of ground state complexation with anions, which is absent for related benzamides. Association constants, KA, with anions were calculated from analysis of concentration profiles of the quenching effects on the fluorescence of 1 and 2. Quenching by nucleoside triphosphates is much more efficient than by inorganic anions. Efficient binding of even simple inorganic anions by neutral amide N–H donors in water is attributed to high acidity of amides and preorganized rigid structure of the receptors.

Directed self-assembly of mono and dinuclear copper(II) isophthalates into 1D polymeric structures. Design and an unusual cocrystallization

New examples of 1D coordination polymers containing mononuclear and dinuclear copper(II) complexes with a series of isophthalates have been designed, synthesized and characterized by single-crystal X-ray diffraction. The reaction between the aqua-complex [Cu(tmen)(H2O)x][ClO4]2 (tmen = N,N,N′,N′-tetramethylethylenediamine) and isophthalate 5-Xip (substituted in position 5, X = –H, –NO2) results in infinite chains with stoichiometry [Cu(tmen)(5-Xip)(H2O)]n. A charge-assisted hydrogen bond of type Cu–OH2⋯O organizes the 1D chains into 2D layers. On the other hand, the self-assembly of the complex [Cu(tmen)(H2O)x][ClO4]2 with a series of isophthalates 5-Xip dianion (X = –H, –NO2, –NH2, –OMe) in presence of 0.5 equiv. of KOH results in 1D chains with dinuclear complexes [Cu2(tmen)2(μ-OH)]+3 as building blocks. The absence of a water molecule coordinated to Cu(II) atom in the dinuclear chains generates different patterns into 2D. The reaction of the aqua-complex of Cu(II) with tetrafluoroisophthalate (TFip) gave a new Janus complex [Cu2(tmen)2(H2O)2(TFip)2]·[Cu(tmen)(TF-ip)]n·3(H2O), where two different supramolecular arrangements are present in the same single crystal (a dimeric structure and 1D polymeric structure).

Pharmacological evaluation of the anxiolytic-like effects of Lippia graveolens and bioactive compounds

Abstract Context: Lippia species (Verbenaceae) are widely used in Latin America and Africa as folk medicine for their tranquilizing properties. Objective: To evaluate the anxiolytic-like effects and safety of Lippia graveolens Kunth. by exploring its aqueous and organic leaf extracts and identifying the responsible chemical constituents. Material and methods: Aqueous and organic extracts (hexane, ethyl acetate and methanol) were pharmacologically evaluated at several doses. Chemical constituents were identified using MS, NMR and GC-MS analysis. The isolated compounds (3 mg/kg, i.p.), extracts (1, 3, 10 and 30 mg/kg, i.p.), and the reference drug diazepam (0.1 mg/kg, i.p.) were assessed in CD-1 mice using experimental behavioural models: open-field, cylinder, hole-board, plus-maze and sodium pentobarbital-induced hypnosis, as well as their acute toxicity (LD50). Results: After administration of the extracts and bioactive compounds, a significant anxiolytic-like response from 1 mg/kg, i.p. was observed, resembling the effect of diazepam. Major presence of thymol (33.40%) was observed in the hexane extract; whereas for the first time in this species a p-cymene + thymol mixture (9.78%), naringenin (0.18%) and cirsimaritin (1.16%) were obtained as bioactive constituents of the ethyl acetate crude extract. Acute toxicity was calculated to be LD50 = 1000 mg/kg for the crude hexane extract, lower in comparison to the other extracts analyzed (LD50 > 2000 mg/kg). Discussion and conclusion: Our results suggest that L. graveolens exerts anxiolytic-like activity involving many kinds of constituents, mainly of the terpenoid and flavonoid nature. These results reinforce the potential use of this species in the therapy of anxiety.

Interaction between aromatic rings as organizing tools and semi-coordination in Cu(II) compounds

In this paper, we present the use of the interaction between aromatic rings—usually called π–π interaction—as the main tool in the organization of coordination complexes in a crystal. To do so, we selected coordination compounds with aromatic rings pointing outside the molecules to favor their self-assembly through these interactions. Here, we report the molecular and crystal structures of three Cu(II) complexes: [Cu2(terpy)2(bz)2](ClO4)2 (1), [Cu2(terpy)2(tfipth)2] (2) and [Cu4(terpy)4(tfipth)2(ClO4)2](ClO4)2 (3), where terpy = 2,2′:6′,2′′ terpyridine, bz = benzoate and tfipth = tetrafluoro-isophthalate. In the three crystals, the interaction between aromatic rings organizes molecules in chains that closely pack with disordered anions or water molecules located in the space between the chains. A study of the Crystal Structure Database (CSD) indicates that the main interaction in terpy molecules is between a lateral ring and the central ring of different molecules and when terpy molecules point in opposite directions, they tend to form chains, suggesting that these interactions can be used as a design tool. The metal complexes were designed to obtain a square pyramidal structure around the metal ion, but we observed a contact between the non-coordinated O (carboxylate) and the Cu(II) ion. We studied the presence of this interaction and its nature with computational chemistry.

Use of Pincer Compounds as Metal-Based Receptors for Chemosensing of Relevant Analytes

Abstract This chapter provides an overview of the latest advances on the use of d8 metal-based pincer complexes for optical chemosensing/recognition of relevant analytes, made post-2007. The field is active and constantly growing, however, there are still many potential applications focused on molecular recognition studies that remain largely unexplored in comparison to historical applications, such as catalysis for organic transformations, and to a lesser extent, as luminescent biomarkers for proteins and phosphorescent compounds for new materials. The present work provides a structural approach describing luminescent and chromogenic sensing properties of divalent pincer complexes of Pt, Pd, and Ni containing terpyridine (N^N^N), rigid mer-tridentate (N^C^N), and bisphosphinite (P^C^P) chelating-ligands for the recognition of inorganic/organic anions, biologically relevant anionic species such as nucleotides and proteins, pollutant transition metals, and chemical compounds. Moreover, their potential implications for diverse scientific fields are also discussed. Metal-based pincer compounds with outstanding photophysical properties and potential binding sites for specific guests have emerged through the past few years as a new and interesting approach to breaking the limit of affinity and sensing of typical molecular sensors in competitive media as polar organic solvents and aqueous media.

Anion and sugar recognition by 2,6-pyridinedicarboxamide bis-boronic acid derivatives

Abstract Two 2,6-pyridinedicarboxamide derivatives containing arylboronic acid fragments were prepared and fully characterized including X-ray crystal diffraction analysis of a pinacol ester. These compounds are potential bifunctional receptors for sugars and anions. Acid dissociation and stability constants for complexation of both receptors with glucose and fructose were determined by potentiometric titrations in aqueous DMSO. Also, binding of alizarin red S indicator was studied spectrophotometrically and a highly sensitive detection of fructose by an indicator displacement assay was proposed. Complexation with anions was studied by 1H NMR titrations in DMSO-d6. Binding of acetate anion occurs only via hydrogen bonding to OH groups of boronic acid fragments and does not affect signals of NH protons but chloride anion induces large shift of the signals of NH protons and small shifts of the signals of OH groups. This behavior makes possible anion discrimination based on preference in the type of binding site rather than simply on anion basicity as is typical for majority of neutral hydrogen bonding anion receptors.

Crystal structure of 3-benzamido-1-(4-nitro­benz­yl)quinolinium tri­fluoro­methane­sulfonate

In the title salt, each cation shows a moderate distortion between the planes of the amide groups and the quinolinium rings. The trifluoromethanesulfonate anions are linked to organic cations via N—H⋯O hydrogen-bonding interactions involving the NH amide groups. In the crystal, weak C—H⋯O hydrogen bonds and π-stacking interactions between the quinolinium and phenyl rings link the organic cations into chains.

Crystal structure of bis­(μ2-tetra­bromo­phthalato-κ2O1:O2)bis[aqua(N,N,N′,N′-tetra­methyl­ethane-1,2-di­amine-κ2N,N′)copper(II)]

In the title complex, [Cu2(C8Br4O4)2(C6H16N2)2(H2O)2], the CuII cation is chelated by a tetramethylethane-1,2-diamine ligand and coordinated by a water molecule as well as bridged by two tetrabromophthalate anions in a distorted O3N2 trigonal–bipyramidal geometry. The two symmetry-related tetrabromophthalate anions bridge the two CuII cations, forming a centrosymmetric dinuclear complex in which the Cu⋯Cu separation is 5.054 (2) Å. Intramolecular classic O—H⋯O hydrogen bonds and weak C—H⋯O hydrogen bonds occur in the dinuclear molecule. In the crystal, the molecules are linked by weak C—H⋯Br and C—H⋯O interactions into supramolecular chains propagating along the b-axis direction.

Crystal structure of N,N′-bis­[(pyridin-4-yl)meth­yl]naphthalene di­imide

In the centrosymmetric title compound, C26H16N4O4 {systematic name: 6,13-bis[(pyridin-4-yl)methyl]-6,13-diazatetracyclo[6.6.2.04,16011,15]hexadeca-1,3,8,10,15-pantaene-5,7,12,14-tetrone}, the central ring system is essentially planar [maximum deviation = 0.0234 (8) Å] and approximately perpendicular to the terminal pyridine ring [dihedral angle = 84.38 (3)°]. The molecules displays a trans conformation with the (pyridin-4-yl)methyl groups on both sides of the central naphthalene diimide plane. In the crystal, molecules are linked by π–π stacking between parallel pyridine rings [centroid–centroid distances = 3.7014 (8) and 3.8553 (8) Å] and weak C—H⋯O hydrogen bonds, forming a three-dimensional supramolecular architecture.