Design,syntheses And Applications Of Red Fluorescent BODIPY Probes For Targeting Mitochondria

Mitochondria are the central role of cell metabolism and signal transmission.Mitochondria in cells are in a constant flow state,changing their number and distribution according to the energy demand or metabolic pressure in the cell.In addition to providing energy molecules such as ATP and NADH for cell physiological processes,mitochondria are closely involved in the coordinated storage of cellular Ca²⁺ions,the regulation of metabolism and apoptosis,and the balance regulation of important physiological processes such as cell signal transduction.Once the equilibrium of internal environmental of mitochondria is destroyed,and the function of mitochondria is impaired,resulting in insufficient ATP required by cells,a surge of ROS,and cell damage.Finally,abnormal or lack of tissue function leads to a series of related diseases.Therefore,monitoring the changes of mitochondria in cells will help us better understand the relationship between mitochondrial dysfunction and diseases.Monitoring the morphological changes of mitochondria in time and space is of great significance for the diagnosis,prevention and treatment of various diseases related to mitochondrial dysfunction.Fluorescent probes can selectively illuminate cell mitochondria and are powerful tools for monitoring morphological changes and studying these processes.Many small molecule fluorescent dyes such as Rhodamine123,JC-1 and Mito-Tracker Red（MTR）and other commercial dyes have been used for mitochondrial imaging.However,they generally have many shortcomings such as poor water solubility,small Stokes shift,short fluorescence lifetime,short emission wavelength,and accompanying concentration quenching（ACQ）effect,which limit their biological applications.At the same time,in order to observe the dynamic changes within a certain period of time,the probe must have light stability under the continuous irradiation of the fluorescence microscope.BODIPY as a fluorescent probe has many advantages,such as strong molar absorption coefficient,good biocompatibility,relatively stable chemical properties,and high quantum yield（close to 100%）.Because there are multiple reaction sites on the core,the structure is easy to modify,and the optical properties are easy to adjust.However,water solubility and short emission wavelength are the two major obstacles that limit the use of BODIPY derivatives in physiological applications.In order to better solve the above-mentioned problems,we have prepared a series of BODIPY derivatives,studied their structure-activity relationship,and provided reference for the development and development of mitochondrial fluorescent probes.This paper is divided into five chapters,as follows:Chapter 1.This chapter mainly clarifies the importance of mitochondria and their relationship with diseases.At the same time,it summarizes the fluorescence mechanism of fluorescence and the development of fluorescence.Finally,it introduces the design,classification and uptake mechanism of mitochondrial probes.Chapter 2.We mainly modify BODIPY with OEG of different chain lengths to increase the hydrophilicity of the probes,and TPP groups were employed as the target mitochondrial group to construct a series of molecules with different hydrophilicity.The experimental results prove that even when the units of ethylene glycol were increased to 5 units,the probe is still quenched in the aqueous medium and maintains good dispersibility in the state of nanoparticles.When the length of ethylene glycol is1-3 units,the state of the nanoparticles of the compound is unstable and will coagulate quickly.Because Mito-BDP 1-3 possessed a certain lipid-water partition coefficient,good biocompatibility,and low phototoxicity,it can be used to accurately target for mitochondria imaging.Since the chain length Mito-BDP 5 is in a nano-state with good dispersibility in aqueous matrix,we constructed pure organic nanoparticle without encapsulation by a polymer,surfactants or amphiphilic compounds,which were applied in tumor tissues.Imaging（PTI）and Photoacoustic Imaging（PAI）.In view of the strong phototoxicity and photothermal conversion efficiency of Mito-BDP5,it is expected to be a reagent for multi-modal imaging to guide cancer therapy to achieve complex and universal"integrated"therapeutic functions.Chapter 3.Based on above study,the parent core of BODIPY modified with neutral water soluble OEG groups cannot overcome the quenching in aqueous matrix.Considering that the mitochondrial membrane potential is negative,so we modified it with quaternary ammonium cations to increase the hydrophilicity of the probe.We designed two mitochondrial targeted fluorescent probes,Mito-BDP 760 and Mito-BDP 630.They not only emit red fluorescence,but also have low cytotoxicity,excellent light stability and chemical stability.However,Mito-BDP 760 is not suitable for mitochondrial imaging due to the presence of ACQ in the aqueous solution.Therefore,the water solubility of the dye must be considered when constructing mitochondrial targeting probes.In contrast,Mito-BDP 630 has potential applications in mitochondrial imaging in physiological environments.Chapter 4.In virtue of the group of pyridine salt not only increased the water solubility of BODIPY,but also enhanced the ability of targeted mitochondria,TPP groups were no longer required to target mitochondria.Furthermore,their synthetic routes were extremely simple and their yield of products were high.Therefore,a series of pyridine salt-modified BODIPY derivatives were strategically constructed by3,5 positions condensation.By changing the position of the pyridine salt,the solvation effect of the probe molecule was reduced,and its accumulation in the mitochondria was increased.The pyridine salt-modified probes such as mMPy-BDP,oMePy-BDP and pMePy-BDP could not aggregate and their fluorescence does not quench aqueous matrix,and still maintain excellent optical properties.It has good photobleaching resistance,low cytotoxicity and phototoxicity,and can specifically accumulate in mitochondria.Consequently,we could synthesize more excellent probes more efficiently by using a simple process.Chapter 5.Summary and perspectives.