Joanna Gałęzowska

The influence of the intramolecular hydrogen bond on the 1,3-N,S- and 1,5-O,S-coordination of N-phosphoryl-N′-(R)-thioureas with Ni(II) and Pd(II)

Reaction of the potassium salts of N-phosphorylated thioureas of common formula R1–N(H)–C(S)–N(H)–P(O)(OiPr)2 (HA) with NiII and PdII cations leads to [MA2] chelate complexes (M = NiII, R1 = p-MeOC6H4, p-BrC6H4, t-Bu, c-Hex; M = PdII, R = iPr). In both the NiII and PdII complexes, the metal center is found in a square-planar N2S2 environment formed by the CS sulfur atoms and the P–N nitrogen atoms of two deprotonated ligands A−. The PdII atoms in [PdB2] complexes with deprotonated thioureas of common formula R2–C(S)–N(H)–P(O)(OiPr)2 (HB) (R2 = Et2N, morpholine-N-yl) are coordinated in a square-planar fashion by the CS sulfur atoms and the PO oxygen atoms of two anionic ligands. Molecular structures of four complexes [M(A-N,S)2] (M = NiII, R1 = p-MeOC6H4, p-BrC6H4, t-Bu; M = PdII, R1 = iPr) and the palladium(II) 1,5-O,S-chelate of formula [Pd(B-O,S)2] (R2 = morpholine-N-yl) were elucidated by X-ray diffraction.

Towards a new attenuating compound : A potentiometric, spectrophotometric and NMR equilibrium study on Fe(III), Al(III) and a new tetradentate mixed bisphosphonate-hydroxypyridinonate ligand

Coordination properties toward Fe(III) and Al(III) of a mixed bisphosphonate-hydroxypyridinonate ligand are presented. Potentiometric, spectrophotometric and NMR results allowed to conclude that Fe(III) and Al(III) coordination takes place on the pyridinone moiety. The high steric hindrance prevents the possibility of simultaneous coordination of both groups to the same metal ion. Quantum mechanical calculations confirm this finding allowing to determine the minimal length of the linker necessary for a stable conformation of complexes in which Fe(III) is coordinated both by pyridinone and bisphosphonate groups.

Cobalt Catalyst with a Proton‐Responsive Ligand for Water Oxidation

Herein, we report the synthesis, the thermochemical data, and the catalytic reactivity of a new mononuclear cobalt complex, which has four NH protons in the ligand sphere. The combination of the redox-active metal ion and NH units enabled the coupling of proton and electron-transfer steps, which we exploited in the electrocatalytic water oxidation.

Binding of β-lactam antibiotics to a bioinspired dizinc complex reminiscent of the active site of metallo-β-lactamases.

Metallo-β-lactamases (mβls) cause bacterial resistance toward a broad spectrum of β-lactam antibiotics by catalyzing the hydrolytic cleavage of the four-membered β-lactam ring, thus inactivating the drug. Minutiae of the mechanism of these enzymes are still not well understood, and reports about binding studies of the substrates to the enzymes as well as to synthetic model systems are rare. Here we report a new pyrazolate-based bioinspired dizinc complex (1) reminiscent of the active site of binuclear mβls. Since 1 does not mediate hydrolytic degradation of β-lactams, the binding of a series of common β-lactam antibiotics (benzylpenicillin, cephalotin, 6-aminopenicillanic acid, ampicillin) as well as the inhibitor sulbactam and the simplest β-lactam, 2-azetidinone, to the dizinc core of 1 could now be studied in detail by NMR and IR spectroscopy as well as mass spectrometry. X-ray crystallographic information was obtained for 1 and its complexes with 2-azetidinone (2) and sulbactam (3); the latter represents the first structurally characterized dizinc complex with a bound β-lactam drug. While 2-azetidinone was found deprotonated and bridging in the clamp of the two zinc ions in 2, in 3 and all other cases the substrates preferentially bind via their carboxylate group within the bimetallic pocket. The relevance of this binding mode for mβls and consequences for the design of functional model systems are discussed.

Physicochemical study of biomolecular interactions between lysosomotropic surfactants and bovine serum albumin

The interactions between two cationic lysosomotropic surfactants (2-dodecanoyloxyethyl)trimethylammonium bromide (DMM-11) and (2-dodecanoyloxypropyl)trimethylammonium bromide (DMPM-11) with bovine serum albumin (BSA) in Hepes buffer (pH=7.4) were systematically studied by surface tension, fluorescence and circular dichroism (CD) spectroscopy and isothermal titration calorimetry (ITC). Furthermore, the size of the micellar aggregates and the polydispersity indexes of both cationic surfactants were studied by dynamic light scattering technique (DLS). The hydrodynamic radii, micellar volumes and aggregation numbers were calculated using a method based on density functional theory (DFT). The results showed that, in both cases, the surface tension was modified upon addition of BSA, and the critical micelle concentration (CMC) values of DMM-11 and DMPM-11 were higher in the presence of BSA. The fluorescence intensity of BSA decreased significantly as the concentration of both cationic surfactants increased and this effect was attributed to the formation of surfactant-BSA complexes. Synchronous fluorescence spectrometry showed the binding-induced conformational changes in BSA. Finally, CD and DLS results revealed the occurrence of changes in the secondary structure of the protein in the presence of both surfactants. In conclusion, understanding the interactions between lysosomotropic surfactants and BSA is required to explore their potential applications in medicine.

Stoichiometry of lanthanide(III) complexes with tripodal aminophosphonic ligands – a new solution to an old problem

The Eu3+ and Gd3+ complexes with an N-(methylene-2-pyridine)-N,N-di(methylenephosphonate) ligand (H4NP2py), an analogue of nitrilotri(methylphosphonic) acid (H6NTP), were synthesized and structurally characterized by X-ray single crystal diffraction. The determined crystal structures ([C(NH2)3]5[Ln(NP2py)2]·12H2O) are the first example of a monomeric Ln3+ complex encapsulated by two tripodal aminophosphonic ligands. Each of the NP2py anions coordinates to Ln3+ through two oxygen atoms from each monodentate phosphonic group, amine nitrogen and pyridine nitrogen atoms, filling thus 8 coordination sites of Ln3+. The luminescence properties of [C(NH2)3]5[Eu(NP2py)2]·12H2O crystals were studied and compared with those of Eu–NP2py complexes in solution. Speciation analysis of Ln–NP2py complexes (Ln : NP2py = 1 : 2), performed by luminescence and potentiometric methods, showed that both [Ln(NP2py)]− and [Ln(NP2py)2]5− species may exist in solution. However, the formation of the latter one occurs in alkaline solutions at pH as high as 8. By implementing the Specific Ion Interaction Theory (SIT) it was possible to calculate the thermodynamic stability constants of the [Eu(NP2py)]− and [Eu(NP2py)2]5− complexes. The corresponding log β0Eul and values are 16.3 ± 0.11 and 19.5 ± 0.15, respectively.

Aminobisphosphonates based on cyclohexane backbone as coordinating agents for metal ions. Thermodynamic, spectroscopic and biological studies

Single and double amino-bisphosphonates were synthesized and tested for coordination capabilities towards Ca2+, Mg2+, Cu2+ and Ni2+ metal ions by means of potentiometry, UV-vis spectroscopy, mass spectrometry (ESI-MS) and isothermal titration calorimetry (ITC), as well as for cytotoxic activity by MTT [(3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide)] assay. Half minimal inhibitory concentrations (IC50) were determined with respect to two cell lines (human melanoma A375 and human colorectal adenocarcinoma HT29). Basing the structure of compounds on a cyclohexane ring allowed for a slight reduction of high hydrophilic character of the studied bisphosphonates (BPs). The ligands efficiently bind the examined metal ions forming complex equilibria with diversified stoichiometry of equimolar, polynuclear species and biscomplexes. Both ligands as well as their Ca2+ and Mg2+ complexes show selective antiproliferative activity toward the studied cancer cell lines. Given the thermodynamic and biological data, it can be assumed that ligands are good candidates for linking compounds that may be used in the design of new drug delivery systems. In this approach, one bisphosphonate moiety acts as a bone-targeting molecule, while another molecule can be readily attached to the second donor function (primary amine or bisphosphonate).

Reaction of 3-Amino-1,2,4-Triazole with Diethyl Phosphite and Triethyl Orthoformate: Acid-Base Properties and Antiosteoporotic Activities of the Products

The reaction of diethyl phosphite with triethyl orthoformate and a primary amine followed by hydrolysis is presented, and the reaction was suitable for the preparation of (aminomethylene)bisphosphonates. 3-Amino-1,2,4-triazole was chosen as an interesting substrate for this reaction because it possesses multiple groups that can serve as the amino component in the reaction—namely, the side-chain and triazole amines. This substrate readily forms 1,2,4-triazolyl-3-yl-aminomethylenebisphosphonic acid (compound 1) as a major product, along with N-ethylated bisphosphonates as side products. The in vitro antiproliferative effects of the synthesized aminomethylenebisphosphonic acids against J774E macrophages were determined. These compounds exhibit similar activity to zoledronic acid and higher activity than incadronic acid.

Thermodynamics of the Interactions of Aminobisphosphonates and Their Calcium Complexes with Bovine Serum Albumin

Binding of bisphosphonates (BPs) to plasma proteins was investigated in the 1990s as a pharmacokinetic issue in order to fully understand bio‐distribution of BP drugs which are successfully used for the treatment of several bone‐related diseases. It has been hypothesized that binding to these proteins occurs with low to moderate affinity despite of unfavorable hydrophilicity of BPs, and Ca2+ was identified as a strong catalyst of this binding. However, these studies mainly consisted in the separation and quantification of bound and unbound drug or protein fractions using chromatographic techniques without an outcome on the molecular level. Presented thermodynamic studies analyze the interactions of three N‐BPs as well as their Ca2+ complexes with bovine serum albumine (BSA) by means of isothermal calorimetry. The studies reveal spontaneous enthalpy favored interactions of N‐BPs (amino‐containing BPs) with BSA, which are enhanced by the presence of Ca2+ ions up to ~15‐fold, strongly depending on N‐BP. Those are low affinity binding events, comparable to Ca2+‐N‐BP interactions, which most likely occur at Ca2+ binding site(s). It is a first example of estimation of thermodynamic forces of interactions of free and calcium‐bound N‐BPs with albumin.