Naslov
Weak intramolecular interactions in bis(L- threoninato)copper(II) compared to bis(L-allo- threoninato)copper(II)

Autori
Marković, Marijana ; Ramek, Michael ; Loher, Claudia ; Sabolović, Jasmina

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
3rd Symposium on Weak Molecular Interactions - Book of Abstracts / Teobald Kupka - Opole, 2017, 46-47

Skup
3rd Symposium on Weak Molecular Interactions

Mjesto i datum
Opole, Poljska, 27.03.2017. - 29.03.2017

Vrsta sudjelovanja
Ostalo

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
conformational analysis ; hydrogen bond ; B3LYP ; MP2 ; LanL2DZ ; MDF10

Sažetak
L-threonine (L-Thr) is one of two essential α- amino acids with a hydroxyl group in the side chain. It is also one of two essential α-amino acids with a chiral side chain (the second one is L-isoleucine). Its diastereomer, L-allo- threonine (L-aThr), is rarely present in nature. In L-Thr, Cα and Cβ are L- and D- chiral, respectively. In L-aThr, both of these atoms are L-chiral. Bis(L- threoninato)copper(II), Cu(L-Thr)2, is part of the exchangeable pool of copper(II) in human blood plasma, whereas the bis(L-allo- threoninato)copper(II), Cu(L-aThr)2, does not regularly appear in the living organisms. One L-Thr, as well as L-aThr, can bind to Cu(II) via amino nitrogen (Nam), carboxylato oxygen (O), and hydroxy oxygen (Oh) atoms, in three coordination modes, as presented in Figure 1: 1. a glycine-like (via Nam and O atoms) – marked with G 2. an amino-hydroxy (via Nam and Oh atoms) – marked with No 3. a carboxy-hydroxy (via O and Oh atoms) – marked with Oo, yielding six possible coordination modes in Cu(L-Thr)2 and in Cu(L-aThr)2. Fig.1. Three coordination modes of binding of L-Thr to Cu(II) Information on the actual coordination modes to Cu(II) in Cu(L-Thr)2 and Cu(L-aThr)2 complex in aqueous solution are available from the experimental data, such as visible absorption and circular dichroism measurements. According to them, at physiological pH value, 7.4, both L-Thr and L- aThr ligands coordinate to Cu(II) in a glycine- like coordination mode. At higher pH values increasing up to ~ 9.4, coordination via Nam and Oh atoms to Cu(II) was observed in Cu(L- Thr)2, whereas only one Nam coordinated in Cu(L-aThr)2.1, 2 To examine the relative stabilities of these coordination modes and possible conformations of both systems in the gas phase, quantum chemical B3LYP/LanL2DZ{;D95v+ (d)}; conformational analyses were performed.3 They resulted in 196 and 267 gas-phase Cu(L- Thr)2 and Cu(L-aThr)2 conformers, respectively.3 The glycine-like mode is calculated as the most stable for both complexes.3 Intramolecular hydrogen bonds, as the most dominant weak molecular interaction in both copper compounds, generally create an important effect on molecular stability and relative energy of the two systems. For example, the position of the hydroxyl group in the physiological Cu(L-Thr)2 complex causes the described restriction of its conformational space, compared to Cu(L-aThr)2. To model the solvent effects, calculations with the polarizable continuum model (PCM) were performed.3 As initial structures, the five lowest-energy gas-phase conformers for each of the coordination modes were optimized by using B3LYP/LanL2DZ{;D95v+(d)}; in the aqueous medium using PCM.3 As a result, we found generally that the most stable gas-phase conformers are also the most stable ones in aqueous solution.3 The versatility of gas-phase and aqueous Cu(L- Thr)2 and Cu(L-aThr)2 minima obtained will be presented. As a conclusion, our data may explain why Cu(L-aThr)2 is not present in the body. Acknowledgement: M.M. is grateful for the financial support of “Scholarship of the Scholarship Foundation of the Republic of Austria for Postdocs” given via Österreichische Austauschdienst. This work has been supported by the Croatian Science Foundation under the Project No. IP-2014-09-3500. Computational resources were provided by the Graz University of Technology and by the Isabella cluster (isabella.srce.hr) at the Zagreb University Computing Centre. References: [1] P. Grenouillet, R. P. Martin, A. Rossi, M. Ptak, Biochim. Biophys. Acta, 322, 185 (1973). [2] V. Noethig-Laslo, N. Paulić, Monatsh. Chem. Chem. Mon., 128, 1101 (1997). [3] M. Marković, M. Ramek, C. Loher, J. Sabolović, Inorg. Chem., 55, 7694 (2016).

Izvorni jezik
Engleski

Znanstvena područja
Fizika, Kemija

POVEZANOST RADA