A recent study published in Scientific Reports investigated the interaction between graphene functionalized with easily ionizable lithium and biopolymer sodium alginate (SA).
Density functional theory (DFT) was employed to analyze the structural, electronic, and spectroscopic properties of these graphene/SA/Li composites for biomedical applications.
Study: Molecular modeling analysis for functionalized graphene/sodium alginate composite. Image Credit: Artbox/Shutterstock.com
Background
Two-dimensional (2D) nanomaterials such as graphene are promising for biomedical applications because of their unique physicochemical properties, including high surface area, enhanced stability, good biocompatibility, facile modification capabilities, and inherent multifunctionality.
Incorporating graphene into a composite material significantly improves its surface properties. Additionally, strategic doping of various atoms into the graphene structure can help optimize its properties for specific applications.
Elemental lithium is well-known as the only metal that can float on water. It is highly preferred in medications for preventing bipolar disorder due to its long-term stability, effectively hindering the return of both manic and depressive episodes. Thus, Li is a remarkable element for material functionalization.
Alternatively, sodium alginate is a natural, non-toxic, biocompatible biopolymer with high water absorption capabilities. Its ability to create strong hydrogels holds significant promise for various biomedical applications.
Thus, this study proposed using Li and SA to enhance the functionality and biocompatibility of graphene. The resulting composite's structural and functional properties were evaluated by DFT-based molecular modelling.
Computational Methods
The researchers used Gaussian 09 (G09) software for all modelling calculations. Firstly, the model molecules were optimized using DFT based on a hybrid exchange-correlation functional B3LYP. A split valence basis set 6-31G(d,p) was used to form the B3LYP/6-31G(d,p) model for the calculations.
The modeling process involved sequential functionalization, starting with graphene and then graphene-Li using various interaction schemes. Finally, the graphene-Li-SA composite was designed, and its structural, electronic, and spectroscopic properties were investigated.
After optimizing each structure, their important properties were analyzed, including total dipole moment (TDM) and molecular electrostatic potential.
Additionally, the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) energy gap (ΔE) was determined for each structure. A low ΔE and high TDMs generally suggest the high reactivity of a molecule.
Furthermore, infrared (IR) and Raman spectra were determined for the model molecules at the same level of theory.
Finally, the density of states (DOS) and projected density of states (PDOS) were plotted to comprehend their electronic properties.
Results and Discussion
The researchers used a model molecule comprising 24 carbon atoms as graphene and studied 13 different graphene-Li configurations.
Among these, graphene interacted weakly with two lithium atoms, exhibiting the highest reactivity in terms of TDM at 5.967 Debye and an ΔE of 0.748 eV. Notably, TDM and ΔE for pristine graphene were 0 Debye and 4.035 eV.
Electrostatic potential mapping demonstrated that graphene incorporated with lithium and three units of SA (graphene/3SA/Li) exhibited an increased potential density over its surface, specifically in areas close to alginate molecules. Other examined physical properties corroborated this.
Furthermore, the graphene/3SA/Li configuration experienced weak interaction at the two side carbons, demonstrating the highest reactivity with 15.509 Debye TDM and 0.280 eV ΔE.
The absolute hardness and softness of the composite were determined to assess the influence of adding Li atoms on the stability and reactivity of graphene/SA. The hardness and chemical potential of the graphene/SA/Li changed depending on the position of Li atoms. Thus, the interaction with Li made the graphene/SA more reactive.
Vibrational spectroscopy calculations confirmed the stability of the optimized molecules through the absence of negative frequencies in their spectra. In addition, the spectral characteristics of graphene demonstrated a shift towards lower wavenumbers (redshift) due to interaction with lithium and SA.
This was attributed to the change in ΔE values on interaction with Li and SA and could induce a shift in graphene's optical absorption.
Additionally, the PDOS plot for graphene/3SA/Li revealed an equal contribution from lithium, sodium, hydrogen, and oxygen in the highest HOMO orbitals, while the lowest contribution was from carbon.
Alternatively, in the LUMO orbitals, the highest contribution was from lithium, followed by sodium, hydrogen, and oxygen, with a lower contribution, while the lowest was from carbon.
Conclusion
Overall, the researchers successfully demonstrated the potential of functionalized graphene in biomedical applications through its interaction with easily ionizable elements like Li and the biopolymer SA.
The proposed modeling method involved first functionalizing graphene with Li and then introducing SA to enhance the composite’s biocompatibility. DFT at the B3LYP level was employed to investigate the structural, electrical, and spectral properties of graphene/Li/SA composite.
This computational analysis provided comprehensive insights into the functionalized graphene systems through parameters such as TDM, ΔE, molecular electrostatic potential, DOS, PDOS, and IR spectra.
It can aid in further development and optimization of graphene and other 2D materials for practical biomedical use.
Journal Reference
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