Based On The New Structure Difluoroborane Fluorescence / Chemiluminescence Probe Design Synthesis And Biological Applications

Small-molecule fluorescent probes are widely used in the field of biological detection and recognition because of their high sensitivity and selectivity. Although have shown some superiorities, the traditional fluorescent probes also have some points that need to be improved. Probes derivatized from cyanines exhibit long emission wavelength, which is non-invasive and with deep penetration in biological imaging. In addition, the auto-fluorescence of this long emission range is effectively avoided. However, the relatively small stokes shift and photobleaching, as well as low quantum yields limit their biological application. Fluorescent probes from rhodamines, fluoresceins, and coumarins show good quantum yield and water solubility. But the emission in visible and ultraviolet range makes them be susceptible to interference from auto-fluorescence of complicated biological matrix. BODIPY-based probes exhibit high quantum yield and good photostability, but their water solubility is not so good. Therefore, taking the factors of abovementioned probes into consideration, it is urgent to design and propose some new probes with good characteristics which can perform well in biological samples. Normally, the designing of a fluorescent probe is divided into five aspects. First, increase the fluorescence quantum yields to increase the detection sensitivity. Second, enlarge stokes shift to efficiently avoid self-absorption and spectral interference. Third, push the emission to far-visible and near- infrared region to improve the penetration ability for biotissues and meanwhile, decrease the interference from biological matrix to obtain good signal to noise ratio. Fourth, good stability in the presence of radiation. Fifth, good water solubility, good cell membrane permeability, and low toxicity for organism.Chemiluminescence analysis has developed fast in recent years as it has high sensitivity, good rapidity, and good simplicity. The energy produced from a chemical reaction initiates the electron transition from its ground state to an excited state, which then goes back to ground state to release energy in the from of light emission. The process is advantageous because of no need of light source, low background signal, and high sensitivity. The current chemiluminescent probes are still needed to be improved because of their relatively low quantum yields, short wavelength emission and restricted selectivity. Therefore, designing and synthesizing of new chemiluminescent probes suitable for biological analysis and imaging will widen and broaden the practical application of optical probes.The acid-alkaline equilibrium and redox equilibrium are the two among the indispensable processes that dominate the normal physiological function of cells. Therefore, it is urgent to uncover the mechanisms in relation to the reservation or regulation of these two processes. Under normal physiological conditions extracellular hydrogen ion (H⁺) concentration is maintained within very narrow limits. Deviation by 0.10-0.20 pH units in either direction can cause cardiopulmonary and neurologic problems, and more extreme variations can be fatal. unregulated production of reactive oxygen species (ROS) results in oxidative stress, and subsequent buildup of free radical damage to proteins, lipids, and nucleic acids is connected to serious human diseases and aging. These two processes are complex and reversible, and are fairly relevant to the redox chemistry and acid-alkaline chemistry, providing motivation for developing new ways to trace their dynamic and transitional variation in vivo, especially in the living cells. In this regard, fluorescence imaging for pH variation and chemilumncent probe for ROS are potentially powerful approach to probe various stages of acid-alkaline equilibrium and redox equilibrium.The aim of our work is to map the spatial and temporal changes or distribution of H⁺ or ROS in biological systems based on the new fluorescent or chemiluminescent probes. Inspired by this, we have designed and synthesized two difluoro-boron (BF₂) based fluorescent probes for cellular pH. Moreover, a chemiluminescent probe derivatized from BF₂ was synthesized and was used to detect superoxide anion radical (O₂^·-). In particular, we carried out four aspects of investigation:First, recent progress on fluorescent and chemiluminescent probes in biological analysis was reviewed. The structural characteristics, physical and chemical properties, and application in optical detection of BF₂ derivatized compounds were introduced.Second, a BF₂ derivatized fluorescent probe for cellular pH was designed and synthesized. The probe was reversible and can be used as a naked eye chemosensor. With a pH responsive group of–SH, the probe responded sensitively to pH variation from 4.0 to 8.0 at excitation wavelength of 465 nm and emission wavelength of 608 nm. The probe showed good photostability and cell membrane permeability, as well as low cytotoxicity. The probe was successfully applied to the imaging of pH in human HG2 cells with good sensitivity and selectivity.Third, a BF₂ derivatized fluorescent probe for cellular pH was designed and synthesized. with a pH responsive group of pyridine, the probe responded sensitively to pH variation from3.0 to 6.0 at excitation wavelength of 530nm and emission wavelength of 572nm. The probe showed good photostability and cell membrane permeability, as well as low cytotoxicity. The probe was successfully applied to the imaging of pH in human HG2 cells with good sensitivity and selectivity.Fourth, a chemiluminescent probe for O₂^·- was synthesized. The probe consists of a BF₂ core and two MCLA reacting parts. Reacting with O₂^·- resulted in a transitional excited compound with emission wavelength at about 645 nm, which lies in far-visible region.