Physico-Chemical nanomaterials science

Binding of iron(II) clathrochelate functionalized by sulfoalkyl groups to albumins

Chornenka N.V.1, Vakarov S.V.1, Losytskyy M.Y.2, Meier-Menches S.3, Gerner C.3, Arion V.3, Gumienna-Kontecka E.4, Voloshin Y.5, Kovalska V.B.2

1 V.I. Vernadsky Institute of General and Inorganic Chemistry NASU, Kyiv.
e-mail:nina.v.chornenka@gmail.com

2 Institute of Molecular Biology and Genetics, NASU, Kyiv.
3 University of Vienna, Vienna, Austria.
4 Faculty of Chemistry, University of Wroclaw, Wroclaw, Poland.
5 Nesmeyanov Institute of Organoelement Compounds RAS, Moscow, Russia.

Macrobicyclic metal complexes iron(II) clathrochelates were recently discovered as prospective CD (circular dichroism) reporters for sensing of proteins. Ribbed functional substituents of such cage molecules are responsible for their binding to proteins. The presence of alkyl or aryl carboxy ribbed substituent was required for assembling of clathrochelate to protein and induction of CD signal.
Here iron(II) clathrochelate bearing two terminal sulfoalkyl groups was firstly characterized  for its binding to albumins by CD and ESI-MS spectroscopy. 
Cyclic voltammograms of this clathrochelate contain the single quasireversible Fe2+/+ reduction wave in the cathodic potential range (-1.2 V) and two irreversible oxidation waves in the anodic potential range, assigned to a metal-centered Fe2+/3+ process (0.92 V) and to oxidation of sulfoalkyl groups (1.05 V).
Disulfoalkyl-terminated iron(II) clathrochelate induces noticeable CD response in visible spectral range (350–600 nm) in presence of albumins: bovine and human serum albumins (BSA, HSA) – with intensity 12; 16.4 mdeg respectively.  This evidences about assembling of clathochelate to proteins.
 It is discovered that the interaction of HSA with mentioned clathrochelate resulted in clear mass signals mainly corresponding to mono- (1338 Da), bis- (+2×1057 Da) and tris-adducts (+3×998 Da). Bis- and tris-adducts of HSA with complex corresponded to the addition of two or three discrete molecules to HSA. 
Thus iron(II) clathrochelate functionalized with terminal sulfoalkyl groups is able to bind to albumins giving pronounced CD signal.  This substituent could be used for design of clathrochelate based protein-sensitive CD reporters.
 
The project leading to these results has received funding from the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Qurie grant agreement No 778245).