2.?Experimental Section2.1. Chemicals and MaterialsZnCl2, Zn(NO3)2?6H2O, L-histidine, 1,10-phenanthroline, 3-mercaptopropionic acid, and Na2S?9H2O, all of ACS purity, were purchased from Sigma-Aldrich (St. Louis, MO, USA). Stock solutions were prepared using ACS water immediately before use. pH values were measured using an inoLab Level 3 instrument (Wissenschaftlich-TechnischeWerkstatten GmbH; Weilheim, Germany). Deionised water underwent demineralization by reverse osmosis using an Aqua Osmotic 02 system (Aqua Osmotic, Tisnov, Czech Republic) and was subsequently purified using a Millipore RG system MiliQ water, 18 M��, (Millipore Corp., Billerica, MA, USA).2.1.1. Preparation of Zinc Nitrate HexahydrateStock solution of zinc nitrate (1 mM) was prepared by dissolving of zinc nitrate hexahydrate (0.

297 g) in water (1 L).2.1.2. Preparation of Zn(phen)(his)Cl2ZnCl2 (0.136 g) was dissolved in water (10 mL). A suspension of histidine (0.155 g) and 1,10-phenanthroline (0.2 g) in water (90 mL) was added to the ZnCl2 solution under constant stirring. The reaction mixture was placed in an ultrasonic bath for 30 min and dissolution of reaction components occurred. After that, the reaction mixture was stirred overnight. The resulting colourless solution was used for measurements.2.1.3. Preparation of Zn(his)Cl2Preparation of the complex was the same as for Zn(phen)(his)Cl2, but only histidine was added to the ZnCl2 solution. A colourless solution was obtained.2.1.4. Preparation of ZnS Quantum Dots (QDs)ZnS MPA (MPA = 3-mercaptopropionic acid) QDs were prepared using the slightly modified method published in [18,19,37].

Zinc nitrate hexahydrate Zn(NO3)2?6H2O (0.03 g, 0.1 mM) was dissolved in ACS water (25 mL). 3-Mercaptopropionic acid (35 ��L, 0.4 mM) was added slowly to the stirring solution. Afterwards, the pH was adjusted to 9.1 with 1 M NH3 (1.5 mL). Sodium sulphide nonahydrate Na2S?9H2O (0.024 g, 0.1 mM) in ACS water (22 mL) was poured into the first solution under vigorous stirring. The obtained colourless solution was then stirred for 1 h.2.2. UV/VIS ��SpectrophotometryAbsorption spectra were GSK-3 recorded using a SPECORD 210 spectrophotometer (Analytik Jena, Jena, Germany) in the range 200�C400 nm and in steps of 1 nm. Quartz cuvettes with 1 cm optical path (Hellma, Essex, UK) were used. The cell with cuvette was thermostated to 20 ��C with a Julabo thermostat (Labortechnik, Wasserburg, Germany).

Absorption spectra were recorded after 60 min of interaction and were evaluated using the WinASPECT program, version 2.2.7.0.Spectral Analysis of ZincZinc forms a red chelate complex with 2-(5-bromo-2-pyridylazo)-5-(N-propyl-N-sulfo-propylamino) phenol (Nitro-PAPS) with an absorption maximum at �� = 560 nm. The colour intensity is proportional to the total zinc concentration in the sample. A volume of 800 ��L of reagent (Greiner, Frickenhausen, Germany), 0.