Chelating Binding Mode Research Articles

Cover Feature: Photoswitching Affinity and Mechanism of Multivalent Lectin Ligands (Chem. Eur. J. 27/2022)

Photochemical cis–trans isomerization was used to switch a divalent lectin ligand between its two forms, which show contrasting binding properties to the plant lectin wheat germ agglutinin (WGA), as visualized by the yin-yang symbol. Whereas the E isomer (obtained under irradiation with green light) is able to bridge adjacent binding sites of WGA leading to a high-affinity chelating binding mode, the Z isomer (obtained under UV light irradiation) crosslinks two lectin molecules associated with a much lower binding affinity. More information can be found in the Research Article by V. Wittmann and co-authors (DOI: 10.1002/chem.202200267).

Photoswitching Affinity and Mechanism of Multivalent Lectin Ligands

Multivalent receptor–ligand binding is a key principle in a plethora of biological recognition processes. Immense binding affinities can be achieved with the correct spatial orientation of the ligands. Accordingly, the incorporation of photoswitches, which can be used to reversibly change the spatial orientation of molecules, into multivalent ligands is a means to alter the binding affinity and possibly also the binding mode of such ligands. We report a divalent ligand for the model lectin wheat germ agglutinin (WGA) containing an arylazopyrazole photoswitch. This switch, which has recently been introduced as an alternative to the more commonly used azobenzene moiety, is characterized by almost quantitative E/Z photoswitching in both directions, high quantum yields, and high thermal stability of the Z isomer. The ligand was designed in a way that only one of the isomers is able to bridge adjacent binding sites of WGA leading to a chelating binding mode. Photoswitching induces an unprecedentedly high change in lectin binding affinity as determined by isothermal titration calorimetry (ITC). Furthermore, additional dynamic light scattering (DLS) data suggest that the binding mode of the ligand changes from chelating binding of the E isomer to crosslinking binding of the Z isomer.

Structural Basis of Dystroglycan Function and the Pathogenesis of Muscular Dystrophy

Dystroglycan (DG) is a widely expressed high-affinity extracellular matrix receptor that requires extensive glycosylation and additional post-translational processing. In skeletal muscle, DG is part of the dystrophin-glycoprotein complex, which is embedded in the plasma membrane and establishes a continuous link between laminin-G-like (LG) domains of extracellular matrix-resident proteins (laminin, agrin, and perlecan) and the cytoskeleton. Extracellular matrix proteins that contain LG domains bind to α-DG via a novel heteropolysaccharide [-GlcA-β1,3-Xyl-α1,3-]n called matriglycan, which is synthesized by the bifunctional enzyme known as Like-acetylglucosaminyltransferase (LARGE). Abnormalities in the post-translational processing of DG lead to an absence or reduction of the matriglycan modification on α-DG, and thereby lead to various forms of glycosylation-deficient muscular dystrophy (secondary dystroglycanopathies). We have used a multidisciplinary approach to provide the first atomic-level insights into the structure of a unique protein-carbohydrate interaction that is essential for the binding of α-DG to the extracellular matrix and proper skeletal muscle function. We first purified LARGE and synthesized matriglycan chains of defined lengths in sufficient quantities to perform both biochemical and structural studies. Using NMR spectroscopy, we found that matriglycan bound to laminin-α2 LG4,5 with high affinity (KD=0.23 µM) and that this binding was calcium dependent. Next, we initiated a collaboration with Erhard Hohenester, who had previously crystallized laminin-α2 LG4,5. Dr. Hohenester soaked matriglycan into crystals of LG4,5 to produce a high-resolution crystal structure of LG4,5 bound to matriglycan. This analysis revealed that the LG4 domain is a Ca2+-dependent lectin with specificity for GlcA-β1,3-Xyl disaccharides, and that a single glucuronic acid-β1,3-xylose disaccharide repeat straddles a Ca2+ ion in the LG4 domain, with oxygen atoms from both sugars replacing Ca2+-bound water molecules. This chelating binding mode is unprecedented among animal lectins and accounts for the high affinity of this protein-carbohydrate interaction. Finally, we used two novel exoglycosidases to provide direct evidence that native α-DG contains unmodified matriglycan and numerous GlcA-Xyl repeats. The multiple tandem repeats in matriglycan are predicted to increase the apparent affinity of the protein for LG domains by favoring rapid rebinding after dissociation. Our results represent a major conceptual advancement regarding a functional carbohydrate and shed light on the mechanism of protein-carbohydrate interactions underlying dystroglycanopathies.

Structural Basis of Dystroglycan Function and the Pathogenesis of Muscular Dystrophy

(DG) is a widely expressed high‐affinity extracellular matrix receptor that requires extensive glycosylation and additional post‐translational processing. In skeletal muscle, DG is part of the dystrophin‐glycoprotein complex, which establishes a continuous link between laminin‐G‐like (LG) domains of extracellular matrix‐resident proteins (laminin, agrin, and perlecan) and the cytoskeleton. Extracellular matrix proteins that contain LG domains bind to α‐DG via a novel heteropolysaccharide [‐GlcA‐β1,3‐Xyl‐α1,3‐]n called matriglycan, which is synthesized by the bifunctional enzyme known as Like‐acetylglucosaminyltransferase (LARGE). We have used a multidisciplinary approach to provide the first atomic‐level insights into the structure of a unique protein‐carbohydrate interaction that is essential for the binding of α‐DG to the extracellular matrix. We first purified LARGE and synthesized matriglycan chains of defined lengths in sufficient quantities to perform both biochemical and structural studies. Using NMR spectroscopy, we found that matriglycan bound to laminin‐α2 LG4,5 with high affinity (Kd=0.23 μM) and that this binding was calcium dependent. Next, we initiated a collaboration with Erhard Hohenester, who had previously crystallized laminin‐α2 LG4,5. We provided Dr. Hohenester with enough matriglycan to soak into crystals of LG4,5 and to produce a high‐resolution crystal structure of LG4,5 bound to matriglycan. This analysis revealed that the LG4 domain is a Ca2+‐dependent lectin with specificity for GlcA‐β1,3‐Xyl disaccharides, and that a single glucuronic acid‐β1,3‐xylose disaccharide repeat straddles a Ca2+ ion in the LG4 domain, with oxygen atoms from both sugars replacing Ca2+‐bound water molecules. This chelating binding mode is unprecedented among animal lectins and accounts for the high affinity of this protein‐carbohydrate interaction as measured by NMR. Finally, we used two novel exoglycosidases to provide direct evidence that native α‐DG contains unmodified matriglycan and numerous GlcA‐Xyl repeats. The multiple tandem repeats in matriglycan are predicted to increase the apparent affinity of the protein for LG domains by favoring rapid rebinding after dissociation. Abnormalities in the post‐translational processing of DG lead to an absence or reduction of the matriglycan modification on α‐DG, and thereby lead to various forms of muscular dystrophy (secondary dystroglycanopathies). Our results represent a major conceptual advancement regarding a functional carbohydrate and shed light on the mechanism of protein‐carbohydrate interactions.Support or Funding InformationDr. Campbell is an investigator of the Howard Hughes Medical Institute. This work was supported in part by a Paul D. Wellstone Muscular Dystrophy Cooperative Research Center grant.

Precipitation-free high-affinity multivalent binding by inline lectin ligands.

Multivalent ligand–protein interactions are a key concept in biology mediating, for example, signalling and adhesion. Multivalent ligands often have tremendously increased binding affinities. However, they also can cause crosslinking of receptor molecules leading to precipitation of ligand–receptor complexes. Plaque formation due to precipitation is a known characteristic of numerous fatal diseases limiting a potential medical application of multivalent ligands with a precipitating binding mode. Here, we present a new design of high-potency multivalent ligands featuring an inline arrangement of ligand epitopes with exceptionally high binding affinities in the low nanomolar range. At the same time, we show with a multi-methodological approach that precipitation of the receptor is prevented. We distinguish distinct binding modes of the ligands, in particular we elucidate a unique chelating binding mode, where four receptor binding sites are simultaneously bridged by one multivalent ligand molecule. The new design concept of inline multivalent ligands, which we established for the well-investigated model lectin wheat germ agglutinin, has great potential for the development of high-potency multivalent inhibitors as future therapeutics.

Cobalt(II) complexes with the non-steroidal anti-inflammatory drug diclofenac and nitrogen-donor ligands

The interaction of the non-steroidal anti-inflammatory drug sodium diclofenac with CoCl2 in the absence or presence of the nitrogen-donor ligands 2,2′-bipyridine, 1,10-phenanthroline, 2,2′-bipyridylamine, pyridine or imidazole resulted in the formation of six mononuclear Co(II) complexes. The complexes were characterized by diverse physicochemical and spectroscopic techniques and single-crystal X-ray crystallography revealing a monodentate or a bidentate chelating binding mode of the diclofenac ligands. The scavenging activity of the complexes was evaluated in vitro against the free radicals of 1,1-diphenyl-2-picrylhydrazyl, 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and hydroxyl; the complexes present significant scavenging activity of ABTS and hydroxyl radicals. The interaction of the complexes with calf-thymus (CT) DNA and bovine serum albumin (BSA) was also investigated; the complexes can bind tightly to CT DNA via intercalation and can bind to BSA tightly and reversibly.

Zinc-oxaprozin compounds: Synthesis, structure and biological activity

Four novel zinc complexes, namely [Zn(oxa)2(MeOH)4] (1), [Zn(oxa)2(H2O)(bipy)]·MeOH·2.5H2O (2·MeOH·2.5H2O), [Zn(oxa)2(bipyam)]·1.25MeOH (3·1.25MeOH) and [Zn(oxa)2(phen)] (4), with the non-steroidal anti-inflammatory drug oxaprozin (Hoxa) and a N,N′-donor heterocyclic ligand, such as 2,2′‑bipyridylamine (bipyam), 1,10‑phenanthroline (phen) or 2,2′‑bipyridine (bipy), were characterized with physicochemical techniques, various spectroscopies and single-crystal X-ray crystallography. In these coordination compounds, the oxaprozin ligands are coordinated to zinc ion in a monodentate or a bidentate chelating binding mode. The antioxidant activity of the complexes was evaluated via their ability to scavenge in vitro 1,1‑diphenyl‑2‑picrylhydrazyl, hydroxyl and 2,2′‑azinobis‑(3‑ethylbenzothiazoline‑6‑sulfonic acid) radicals. The complexes bind to calf-thymus DNA via intercalation as suggested via a series of studies employing UV–vis spectroscopy, DNA-viscosity measurements and competition with ethidium bromide. The complexes may bind to serum albumins tightly and reversibly in order to get transferred through the bloodstream.

Cyclometalated Palladium NHC Complexes Bearing PEG Chains for Suzuki–Miyaura Cross-Coupling in Water

We present the synthesis and characterization of four new polyethylene glycol (PEG) substituted palladium complexes bearing a cyclometalated 2-phenylimidazole ligand and an N-heterocyclic carbene (NHC) ligand. A solid-state structure reveals the chelating binding mode and the coiling of the PEG chain in the auxiliary ligand. The PEG substitution significantly increased the solubility of the complexes in several solvents, enabling the efficient Suzuki–Miyaura cross-coupling reaction of aryl chlorides in an aqueous medium. Under optimized reaction conditions, sterically demanding biphenyl compounds with up to three ortho substituents were accessible in good to excellent yields.

Structural Diversity Observed in Two-dimensional Square Lattice Metal–Organic Frameworks Assembled from Zn(II) and 3-(4-Pyridyl)benzoate

The reaction of 3-(4-pyridyl)benzoate (34pbz) under solvothermal and solvent evaporation conditions produced several two-dimensional (2D) square lattice metal–organic frameworks compounds, {[Zn(34pbz)2]·DMF}n (1), {[Zn(34pbz)2]·DMF}n (2), and {[Zn(34pbz)2]·2DMF·CH3OH·1/2H2O}n (3). Although the frameworks of 1, 2, and 3 have identical elemental composition, these networks differ in the binding mode of the carboxylate moiety to the metal center. In compound 1 the carboxylate moiety assumes a monodentate binding mode, while in 2 and 3 it assumes a chelating binding mode. Compounds 1 and 3 crystallize in space group P21/c with different unit cell parameters, while compound 2 crystallizes in the tetragonal crystal system. In all three crystal structures, networks are formed by connecting mononuclear Zn(II) units with 34pbz linkers forming a square grid network. The solvent accessible void volumes in 1 (21%) and 2 (18%) are comparable, while compound 3 has a void volume of 42%, which is extremely large for a 2D...

Synthesis, crystal structures, spectral, thermal and antimicrobial properties of new Zn(II) 5-iodo- and 5-bromosalicylates

Two new analogous zinc(II) complexes containing 5-iodo- and 5-bromosalicylate ligands, respectively, were prepared in single-crystal form and characterized by IR spectroscopy, thermal analysis and elemental analysis. The solid-state structures of prepared complexes were determined by single crystal X-ray crystallography. Both complexes are isostructural and their crystal structures composed of neutral molecules [Zn(5-Xsal)2(H2O)2] (where X = Br, I, sal = salicylato). Central Zn(II) atom is in both complexes coordinated by six oxygen atoms, four of which are from two chelate bonded 5-halosalicylates and remaining two from coordinated water molecules. The found chelate binding mode is in line with the Δ values calculated from IR spectral data. Antimicrobial activity of prepared complexes was studied against selected bacteria, yeast and filamentous fungi. Obtained results indicate that 5-iodosalicylate complex is more antimicrobially active than its 5-bromo substituted analogue.

Regioselective Termination Reagents for Ring-Opening Alkyne Metathesis Polymerization.

Alkyne cross-metathesis of molybdenum carbyne complex [TolC≡Mo(OCCH3(CF3)2)3]·DME with 2 equiv of functional ynamines or ynamides yields the primary cross-metathesis product with high regioselectivity (>98%) along with a molybdenum metallacyclobutadiene complex. NMR and X-ray crystal structure analysis reveals that ynamides derived from 1-(phenylethynyl)pyrrolidin-2-one selectively cleave the propagating molybdenum species in the ring-opening alkyne metathesis polymerization (ROAMP) of ring-strained 3,8-dihexyloxy-5,6-dihydro-11,12-didehydrodibenzo[a,e][8]annulene and irreversibly deactivate the diamagnetic molybdenum metallacyclobutadiene complex through a multidentate chelate binding mode. The chain termination of living ROAMP with substituted ethynylpyrrolidin-2-ones selectively transfers a functional end-group to the polymer chain, giving access to telechelic polymers. This regioselective carbyne transfer strategy gives access to amphiphilic block copolymers through synthetic cascades of ROAMP followed by ring-opening polymerization of strained ε-caprolactone.

Construction of one dimensional Co(II) and Zn(II) coordination polymers based on expanded N,N′-donor ligands

Four new 1-D coordination polymers [Zn(acac)2(L1)] n (1), [Co(acac)2(L1)]n (2), [Co(acac)2(L2)]n (3) and [Co(acac)2(L3)]n (4) were afforded by the complexation reaction of appropriate zinc and cobalt metal salts, acetylacetone co-ligand as well as three linear electron rich and bi-functional N,N′-bipyridyl-base ligands of N,N′-bis(pyridin-4-ylmethylene)naphthalene-1,5-diamine (L1), N,N′-bis(pyridin-4-ylmethylene) phenylene-1,4-diamine (L2) and N,N′-bis(pyridin-4-ylmethylene)hydrazine (L3). The structures of these compounds were characterized by FT-IR spectroscopy, elemental analysis, X-ray powder and single crystal X-ray diffractions. X-ray crystallography analyses revealed that these compounds have 1-D linear chain structures a containing {N2O4} metal coordination environment in which the N-donor Lx (x=1–3) bridges occupy trans positions. The acetylacetone (acac) ancillary ligands control the coordination number of the metal cation and adopt chelating binding mode on octahedral metal center. Furthermore, 1-D chains are held together with their neighboring ones by C–H⋯O, C–H⋯π and π-π stacking intermolecular interactions to stabilize 2-D supramolecular networks. The two former cases 1 and 2, containing same L1 spacer ligand generate isomorphous structures. Theoretical calculations invoking electronic properties, frontier molecular orbital description and the strength of interactions between metal ion and coordinated atoms via second order perturbation energies were carried out using natural bond orbital analysis (NBO). Finally, thermal stability of compound 2–4 was examined by thermogravimetric (TGA) analysis.

Structural basis of laminin binding to the LARGE glycans on dystroglycan.

Dystroglycan is a highly glycosylated extracellular matrix receptor with essential functions in skeletal muscle and the nervous system. Reduced matrix binding by α-dystroglycan (α-DG) due to perturbed glycosylation is a pathological feature of several forms of muscular dystrophy. Like-acetylglucosaminyltransferase (LARGE) synthesizes the matrix-binding heteropolysaccharide [-glucuronic acid-β1,3-xylose-α1,3-]n. Using a dual exoglycosidase digestion, we confirm that this polysaccharide is present on native α-DG from skeletal muscle. The atomic details of matrix binding were revealed by a high-resolution crystal structure of laminin G-like (LG) domains 4-5 of laminin α2 bound to a LARGE-synthesized oligosaccharide. A single glucuronic acid-β1,3-xylose disaccharide repeat straddles a Ca2+ ion in the LG4 domain, with oxygen atoms from both sugars replacing Ca2+-bound water molecules. The chelating binding mode accounts for the high affinity of this protein-carbohydrate interaction. These results reveal a novel mechanism of carbohydrate recognition and provide a structural framework for elucidating the mechanisms underlying muscular dystrophy.

Thiourea-based spacers in potent divalent inhibitors of Pseudomonas aeruginosa virulence lectin LecA.

A new divalent highly potent inhibitor of the Pseudomonas aeruginosa lectin and virulence factor LecA was prepared. It contains two thiourea linkages which were found to be in the Z,Z isomeric form. This brings the spacer into an elongated conformation required to bridge the two binding sites, which results in the chelating binding mode responsible for the high potency.

Synthesis of N-methyl alkylaminomethane-1,1-diphosphonic acids and evaluation of their complex-formation abilities towards copper(II)

A series of N-methyl alkylaminomethane-1,1-diphosphonic acids (3a–g) with a common tertiary nitrogen atom (CH3–N–R) bearing linear or branched alkyl, cycloheptyl or phenylalkyl R substituents was synthesized in the reaction of diethylphosphonate with triethyl orthoformate and secondary amine followed by hydrolysis, and by the Eschweiler–Clarke methylation of the alkylaminomethane-1,1-diphosphonic acids with formic acid and formaldehyde. Complex-formation abilities of 3a–g towards copper(II) in solution were studied by means of pH-potentiometry, ESI-MS spectrometry, UV–Vis and EPR methods.Evaluation of stability constants for the Cu(II) complexes of 3a–g has revealed their dependence on a combination of steric and electronic effects imposed by R substituents. It has been demonstrated that compounds with linear or branched alkyl on the N atom (3a, 3d, 3e) form the most stable complexes with Cu(II), the least stable are complexes of 3f, which can be attributed to the steric effect imposed by cycloheptyl ring attached directly to the N atom. In addition to the main [Cu(HL)2] complexes, with well-known {O, O} chelating binding mode, [Cu(HL)L] and [CuL2] species with the {O, N} donor set, protonated dinuclear [Cu2HxL3] (x=4, 5, 6) species have been detected in all studied systems. The nitrogen coordination in the [Cu(HL)L] and [CuL2] complex has been confirmed by Vis and EPR spectra.

Zinc Complexes with the N-Donor-Functionalized Cyclopentadienyl Ligand C5Me4(CH2)2NMe2

The amino-functionalized zincocene [ZnCpN2] (4; CpN = C5Me4(CH2)2NMe2), which is the first mononuclear zincocene with two donor-functionalized cyclopentadienyl ligands, was prepared through treatment of KCpN with ZnCl2 in a 2/1 ratio. X-ray crystallography reveals the chelating binding mode of each CpN ligand via an η1-coordinated Cp ring and the amino group. The structural dynamics of 4 in solution were examined by variable-temperature 1H NMR spectroscopy, and decoalescence of the NMR signals was found at low temperatures. Reacting 4 with [ZnR2] (R = Et, Cp*) yields the monocyclopentadienyl and mixed-ring donor-functionalized complexes [ZnEtCpN] (5) and [ZnCp*CpN] (6). In contrast to the reaction of KCpN with ZnCl2 in a 2/1 ratio, which yields the zincocene 4, the reaction in a 1/1 ratio results exclusively in the formation of the chlorido-bridged dimer [Zn(μ-Cl)CpN]2 (7). This compound is comparable to [Zn(μ-Cl)Cp*(THF)]2 (8), which crystallizes from a THF solution of equimolar amounts of [ZnCp*2] (1) and ZnCl2.

Photocytotoxic Oxidovanadium(IV) Complexes of Polypyridyl Ligands Showing DNA‐Cleavage Activity in Near‐IR Light

AbstractOxidovanadium(IV) complexes [VO(pyphen)(L)]Cl2 (1, 2) and [VO(pydppz)(L)]Cl2 (3, 4), where L is 1,10‐phenanthroline (phen in 1 and 3) and dipyrido[3,2‐a:2′,3′‐c]phenazine (dppz in 2 and 4) are prepared and characterized. The crystal structure of [VO(pyphen)(phen)](ClO4)2 (1a) shows a six‐coordinate VN5O geometry with a VO2+ moiety in which the polypyridyl ligand binds in a meridional fashion and the phen ligand displays a chelating binding mode with an N‐donor site trans to the oxidovanadyl group. The complexes show a d–d band within 720–750 nm in DMF. The one‐electron paramagnetic complexes are 1:2 electrolytes in DMF. The complexes exhibit an irreversible VIV/VIII redox response near –0.85 V vs. SCE in DMF/0.1 M TBAP. The complexes bind to calf thymus (ct) DNA giving Kb values within 7.5 × 104 to 1.1 × 106 M–1. The complexes show poor chemical nuclease activity in the dark and exhibit significant DNA‐photocleaving activity in near‐IR light of 705 and 785 nm forming ·OH radicals. Complexes 2–4 show remarkable photocytotoxicity in HeLa cancer cells. FACS analysis of the HeLa cells treated with complex 4 shows cell death as highlighted by the sub G1 peak. Propidium iodide staining data indicate apoptosis as the primary mode of cell death.

1,10-Phenanthroline Analogue Pyridazine-Based N-Heterocyclic Carbene Ligands

Synthesis of a planar, π-conjugated pyridazine-based biscarbene is reported. Starting from 3,6-dimethylpyridazine, the bisimidazolium salt 1*2HPF6 was prepared in a four-step synthesis by chlorination, amination, formylation, and cyclization. The free carbene 1 can be generated in situ by addition of base. Despite the rigid annelated tricycle, the carbene ligand turns out to be highly flexible upon coordination of transition-metal complexes. With silver(I) oxide or copper(I) oxide binuclear carbene complexes with a bridging coordination mode of the ligand are obtained. Transmetalation of both complexes to the respective gold complex is described. The bridging coordination mode of the carbene ligand is similar to that of 2,2′-bipyridine. Reaction of the bisimidazolium salt 1*2HPF6 with potassium acetate and [RhCl(COD)]2 leads to a mononuclear rhodium complex with the chelating binding mode of 1, resembling strongly the coordination properties of 1,10-phenanthroline.

Zinc(II) and cadmium(II) complexes based on 4-(3,5-diphenyl-1 H-pyrazol-1-yl)-6-(piperidin-1-yl)pyrimidine (L): Synthesis, structure, luminescence. Double lone pair–π interactions in the structure of ZnL 2Cl 2

A series of zinc(II) and cadmium(II) complexes with 4-(3,5-diphenyl-1 H-pyrazol-1-yl)-6-(piperidin-1-yl)pyrimidine (L), ZnLCl 2, CdLCl 2, ZnL 2Cl 2, CdL 2Cl 2, CdL 2Cl 2·0.5Me 2CO·1.5H 2O and CdL 2Cl 2·0.5CHCl 3·0.5H 2O, have been synthesized. The compounds ZnLCl 2 and CdLCl 2 were obtained in a M:L = 1:1 molar ratio in EtOH solutions, while ZnL 2Cl 2 and CdL 2Cl 2 were isolated in a M:L = 1:3 molar ratio in EtOH/Me 2CO mixtures. Surprisingly, attempts to crystallize CdLCl 2 from EtOH/Me 2CO mixture afforded single crystals of a compound, having 1:2 metal-to-ligand stoichiometry, CdL 2Cl 2·0.5Me 2CO·1.5H 2O, instead of a complex with 1:1 stoichiometry. At the same time, crystallization of CdL 2Cl 2 from Me 2CO/CHCl 3 mixture afforded CdL 2Cl 2·0.5CHCl 3·0.5H 2O single crystals. According to X-ray crystal structure data, ZnLCl 2, ZnL 2Cl 2, CdL 2Cl 2·0.5Me 2CO·1.5H 2O and CdL 2Cl 2·0.5CHCl 3·0.5H 2O complexes have molecular mononuclear structures. The molecules of L adopt bidentate chelating binding mode being coordinated to the metal ions through N 2 atom of the pyrazole and N 3 atom of the pyrimidine rings. The coordination core of zinc atom in ZnLCl 2 complex is a distorted ZnN 2Cl 2 tetrahedron. The coordination cores of metal atoms in the structures of ZnL 2Cl 2, CdL 2Cl 2·0.5Me 2CO·1.5H 2O and CdL 2Cl 2·0.5CHCl 3·0.5H 2O are the distorted cis-MN 4Cl 2 (M = Zn, Cd) octahedra. In the structure of ZnL 2Cl 2 double lone pair(N(piperidine))–π(pyrimidine) interactions were observed. The photoluminescent properties of L, ZnLCl 2, CdLCl 2, ZnL 2Cl 2 and CdL 2Cl 2 were studied in the solid state under the same experimental conditions. These compounds were found to display bright blue luminescence. Highest relative intensity of emission was detected for ZnL 2Cl 2.

AFM investigation of Pseudomonas aeruginosa lectin LecA (PA-IL) filaments induced by multivalent glycoclusters

Atomic force microscopy reveals that Pseudomonas aeruginosa LecA (PA-IL) and a tetra-galactosylated 1,3-alternate calix[4]arene-based glycocluster self-assemble according to an aggregative chelate binding mode to create monodimensional filaments. Lectin oligomers are identified along the filaments and defects in chelate binding generate branches and bifurcations. A molecular model with alternate 90° orientation of LecA tetramers is proposed to describe the organisation of lectins and glycoclusters in the filaments.