Strong plasmon absorption in the near‐infrared (NIR) region renders gold nanorods (GNRs) amenable for biomedical applications, particularly for photothermal therapy. However, these nanostructures have not been explored for their imaging potential because of their weak emission profile. In this study, the weak fluorescence emission of GNRs is tuned to match that of the absorption of a photosensitizer (PS) molecule, and energy transfer from the GNR to PS enhances the emission profile of the GNR–PS combination. GNR complexes generally quench the fluorescence emission of nearby chromophores. However, herein, the complex retains or rather enhances the fluorescence through competition in energy transfer. Excitation‐dependent energy transfer has been explained experimentally and theoretically by using DFT calculations, the CIE chromaticity diagram, and power spectrum. The final GNR–PS complex modified for tumor specificity serves as an excellent organ‐specific theranostic probe for bioimaging and dual therapy both in vitro and in vivo. Principal component analysis designates photodynamic therapy a better candidate than that of photothermal therapy for long‐term efficacy in vivo.
Gold nanoclusters have the characteristics of small size, unique optical properties, and eco-friendly synthesis that make them promising candidates for biomedical applications, especially for bioimaging. However, their inherent photochemical activity and therapeutic efficiency are largely unknown and remain unexplored. Here, we report a simple one-step green synthesis procedure for the preparation of two tripeptide-stabilized silver-doped gold nanoclusters (TPGNCs) and their photodynamic therapeutic effect on cancer cells and simultaneous imaging. The custom-designed tripeptides were used for the preparation of silverdoped gold nanoclusters with enhanced fluorescence emission. These TPGNCs exhibited strong red fluorescence with high quantum yield, large Stokes shift, good photostability, and excellent biocompatibility toward normal cells. TPGNCs imparted minimum dark toxicity toward breast cancer cells. These TPGNCs exhibited appreciable photosensitization to generate ROS within the cancer cells triggering loss of mitochondrial membrane potential, leading to apoptotic cell death. The photosensitizing ability of TPGNCs will be a new avenue in the area of photoinduced cancer therapy with negligible side effects.
The design and development of a small molecule named NPB [3-{(4(2,3-dichlorophenyl)piperazin-1-yl}{2-hydroxyphenyl)methyl}-N-cyclopentylbenzamide], which specifically inhibited the phosphorylation of BAD at Ser99 in human carcinoma cells has been previously reported. Herein, the synthesis, characterization, and effect on cancer cell viability of NPB analogs, and the single-crystal X-ray crystallographic studies of an example compound (4r), which was grown via slow-solvent evaporation technique is reported. Screening for loss of viability in mammary carcinoma cells revealed that compounds such as 2[(4(2,3-dichlorophenyl)piperazin-1-yl][naphthalen-1-yl]methyl)phenol (4e), 5[(4(2,3-dichlorophenyl)piperazin-1-yl][2-hydroxyphenyl)methyl)uran-2-carbaldehyde (4f), 3[(2-hydroxyphenyl][4(p-tolyl)piperazin-1-yl)methyl)benzaldehyde (4i), and NPB inhibited the viability of MCF-7 cells with IC50 values of 5.90, 3.11, 7.68, and 6.5 µM, respectively. The loss of cell viability was enhanced by the NPB analogs synthesized by adding newer rings such as naphthalene and furan-2-carbaldehyde in place of N-cyclopentyl-benzamide of NPB. Furthermore, these compounds decreased Ser99 phosphorylation of hBAD. Additional in silico density functional theory calculations suggested possibilities for other analogs of NPB that may be more suitable for further development.
A series of acceptor and donor groups anchored to benzo[1,2-b:4,5-b′]dithiophene (BDT) molecule have been systematically investigated at the density functional theory (DFT) and time-dependent density functional theory (TDDFT) level to reveal structure-property relationships, charge transfer, and fluorescence lifetimes. The DFT optimization shows that the hetero atom in the ring induces the polarity from central ring to both ends of the thiophene ring, participating in the conjugation. The donor and acceptor groups were anchored at the terminals of the BDT at two different positions to fine-tune the properties according to the requirement and study the push-pull effect. All the models studied in this work retain their aromaticity as estimated from NICS(0) and NICS(1) aromaticity index in ground and excited states. The results show that the hardness, softness, HOMO-LUMO gaps, ionization potentials (IP), and electron affinities (EA) of the BDTs are significantly affected by the electron-withdrawing and electron-donating groups. The 1 H and 13 C NMR chemical shift values have been computed to quantify the push-pull effect. Further, the charge transfer properties in these BDTs were explored based on reorganization energies and diagnostic descriptors derived from hole-electron theory that present different electron excitation behavior. The relationship between the computed variables such as highest occupied molecular orbital, lowest unoccupied molecular orbital, oscillator strength, dipole moment, absorption, and fluorescence energy correlates the system with one another and also to extend the possible applications of the system in optical devices. Structure-property relationship of various BDTs reveal that, upon optical excitation, the resonance effect plays an important role changing the bonding character between the substituent and BDT unit, enabling efficient electron delocalization. The examination of TDDFT results indicates that among the various models studied in this work, nitro-substituted model is better candidate for optoelectronic properties with relatively large absorption wavelength and long fluorescence lifetime.
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