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0Mechanisms of interactions of carbon nanoparticles with metal ions and biomacromolecules
S. Burikov1, A. Vervald1, K. Laptinskiy1'2, O. Sarmanova1, G. Chugreeva1, T. Dolenko1*
1- Department of Physics, Lomonosov Moscow State University, Leninskiye Gory 1/2, 119991 Moscow, Russia 2- Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, Leninsky Gory 1/2, 119991
Moscow, Russia
* tdolenko@mail.ru
Currently, researches concerning photoluminescent carbon nanoparticles are actively developed due to their wide prospects for use in biomedicine, nanosensory, optoelectronics, etc. One of the such nanomaterials are carbon quantum dots (CQD), which have chemical stability, nontoxicity, biocompatibility, intense stable photoluminescence (PL), sensitive to surrounding molecules and environmental parameters. Namely sensitivity of the PL of CQD to the environment is basis for the widespread use of nanoparticles as nanosensors and medical nanoagents. It is obvious that the effective use of CQD in various applications is impossible without knowledge of the mechanisms of formation of their PL. Therefore, the study of the interactions of surface groups of CQD with metal ions and biomacromolecules and the effect of these interactions on the PL of nanoparticles is an urgent task.
In this study, CQD synthesized by hydrothermal method from citric acid and ethylenediamine were the objects of research. The results of studying the interactions of CQD with molecules of various solvents, ions of solutions of metal salts and proteins are presented.
Using Raman laser spectroscopy, a general tendency has been established for all studied CQD to weaken hydrogen bonds in proton solvents. Numerical estimates of the energy of hydrogen bonds in various solvents have been obtained.
It was found that photoluminescence of CQD with carboxyl and hydroxyl surface groups significantly depends on the pH of the medium. The mechanism of the pH effect on the PL of such nanoparticles is caused by the (de)protonation of the carboxyl and hydroxyl groups on the surface of CQD.
Quenching of PL of CQD by the ions Fe3+, Cr3+, Al3+, Co2+, Cu2+, Pb2+, Zn2+, Ni2+, Mg2+ present in the medium was detected. Using the Stern-Volmer theory and measured PL decay kinetics, it was found that Cu2+, Zn2+, Ni2+, Mg2+ are characterized by a static type of quenching, while Fe3+, Cr3+, Al3+, Co2+, Pb2+ are characterized by a dynamic type of quenching. The molecular dynamics method was used to simulate the dynamics of molecular interactions in water with carboxyl, hydroxyl and amide groups and the specified metal ions. The analysis of the constructed functions of the radial distribution of ions of salts relative to the surface groups of CQD showed that metal cations and NO3" anions, when interacting with oppositely charged groups of CQD (deprotonated carboxyl group -COO- and superprotonated amide group -NH3+ respectively), are located at distances of 4.5, 7 and 9 A from them. Thus, there are 1, 2 or 3 hydrate layers with a certain network of hydrogen bonds between the surface groups of nanoparticles and metal cations. A high correlation has been established between the theoretical and experimental series in terms of the degree of quenching PL of CQD.
The results were obtained using laser Raman spectroscopy, photoluminescent spectroscopy, laser time-resolved spectroscopy, laser correlation spectroscopy, and IR absorption spectroscopy. Quantum chemical calculations and the method of molecular dynamics were used.
The research was carried out at the expense of the grant from the Russian Science Foundation № 22-12-00138, https://rscf.ru/en/project/22-12-00138/.
