Center for Magnetic Resonance

A.A. Belyaev, D.V. Krupenya, E.V. Grachova, V.V. Gurzhiy, A.S. Melnikov, P.Yu. Serdobintsev, E.S. Sinitsyna, E.G. Vlakh, T.B. Tennikova, S.P. Tunik

“Supramolecular AuI–CuI Complexes as New Luminescent Labels for Covalent Bioconjugation”

Bioconjugate Chem, 2016, 27, 143-150
DOI:10.1021/acs.bioconjchem.5b00563

Two new supramolecular organometallic complexes, namely, [Au₆Cu₂(C₂C₆H₄CHO)₆(PPh₂C₆H₄PPh₂)₃](PF₆)₂ and [Au₆Cu₂(C₂C₆H₄NCS)₆(PPh₂C₆H₄PPh₂)₃](PF₆)₂, with highly reactive aldehyde and isothiocyanate groups have been synthesized and characterized using X-ray crystallography, ESI mass spectrometry, and NMR spectroscopy. The compounds obtained demonstrated bright emission in solution with the excited-state lifetime in microsecond domain both under single- and two-photon excitation. The luminescent complexes were found to be suitable for bioconjugation in aqueous media. In particular, they are able to form the covalent conjugates with proteins of different molecular size (soybean trypsin inhibitor, human serum albumin, rabbit anti-HSA antibodies). The conjugates demonstrated a high level of the phosphorescent emission from the covalently bound label, excellent solubility, and high stability in physiological media. The highest quantum yield, storage stability, and luminance were detected for bioconjugates formed by covalent attachment of the aldehyde-bearing supramolecular AuI–CuI complex. The measured biological activity of one of the labeled model proteins clearly showed that introduced label did not prevent the biorecognition and specific protein–protein complex formation that was extremely important for the application of the conjugates in biomolecular detection and imaging.

E.S. Yandanova, D.M. Ivanov, M.L. Kuznetsov, A.G. Starikov, G.L. Starova, V.Yu. Kukushkin

“Recognition of S···Cl Chalcogen Bonding in Metal-Bound Alkylthiocyanates”

Chem. Commun., 2016, 52, 5565
DOI:10.1021/acs.cgd.6b00346

Reaction of K₂[PtCl₄] with excess AlkSCN in water gives the alkylthiocyanate complexes trans-[PtCl₂(AlkSCN)₂] (Alk = Et 1, nPr 2; 80–85%). These species were studied, in particular, by X-ray crystallography. In the solid state, both 1 and 2 exhibit the previously unreported S···Cl chalcogen bonding, which consolidates the complexes into networks and leads to layered structures. Theoretical density functional theory calculations and Bader’s atoms in molecules analysis demonstrated two types of intermolecular interactions in tetramer (1)4, viz. the S···Cl chalcogen and the H···Cl hydrogen bonds. Despite that each particular S···Cl or H···Cl bonding is weak with the estimated energy of 1–2 kcal/mol, altogether they play a crucial role in the stabilization of the S₂Cl₂ fragment in (1)4, the basis set of superposition error corrected interaction energy being −12.8 kcal/mol per monomer complex molecule. The chalcogen bonding and the rhomboidal structure of the S₂Cl₂ fragment can be interpreted in terms of electrostatic arguments as a result of the interaction between the belt of negative electrostatic potential around the Cl atoms and the sulfur σ-holes. The natural bond orbital analysis revealed that both LP(S) → LP*(Pt)/σ*(Pt–N)/σ*(Pt–Cl) and LP(Cl) → σ*(S–C) types of hyperconjugative charge transfers are important in the chalcogen bonding.