Synthesis Of Organic Compounds With Boronic Acid And Different Fluorophores And Study On Their Properties

Saccharides play a critical role in a variety of biological processes, such as offering energy for human bodies, which can be found easily in nature. Meanwhile, saccharides recognition and detection are very important in medical area, cell-biology and food industry. Developing chemosensor for saccharides recognition selectively attracts a lot of chemistry workers. Sugar sensors commonly consist of receptor, linker and reporter. Recent years, boronic acid compounds are widely used for saccharides recognition, because boronic acids can readily and reversibly form cyclic boronate esters with 1,2- or 1,3- hydroxy groups of saccharides via two covalent bonds to switch a photoelectron transfer process , which largely changed the fluorescence intensity of chromophore. So, boronic acid-based fluorescent chemosensors are widely developed.Based on the mechanism of PET ( photoinduced electron transfer ), we synthesized two boronic acid compounds using p-tolylboronic acid, 8-Hydroxyquinoline, 1-Naphthaldehyde and so on. One is 1-[ N -(2-phosphoryl)- N -(boronobenzyl)] benzyl naphthalene(NPBBN), the other is N-(boronobenzyl)-8-hydroxyquinolinium bromide ( BHQB ) , these two compounds are both water soluble. We also detected their properties respectively, in order to construct novel and effective sugar sensors.Compound NPBBN contains boronic acid as the receptor and naphthalene as the reporter. At the beginning, we studied the relationship between the fluorescence intensity and the pH value of the aqueous solution. Firstly, we prepared compound NPBBN solution (1×10-4M) buffered at different pH values and D-fructose solution (1M). Compared with the NPBBN system without D-fructose, in the range of near physiological pH values, the fluorescence intensity of that in the presence of D-fructose changed a lot. It's because the boronic acid in receptor formed a stable five-membered cyclic boronate ester with the saccharide , which resulted in the electronic cloud density of fluorophore decreased. Therefore, the fluorescence intensity was increased obviously. According to experiment above, we chose pH=6.86 as the proper condition to further the following detection. Then we tested the recognition of compound NPBBN for different saccharides. We prepared the NPBBN aqueous solution (1×10-4M) with pH=6.86 buffer, and we chose three different sugar containing diol structure. From the test we found that, in the same circumstance, compound NPBBN system has various recognition abilities for these saccharides. The selective order is D-fructose(Ka=207) > D-galactose(Ka=41)> D-glucose( Ka=11 ) ,which demonstrated that this system tend to combine with fructofuranose rather than galactopyranose and glucopyranose . Therefore the NPBBN compound system we designed can be applied to sugar recognition for different monosaccharides selectively. Furthermore, we introduced CTAB (cetyltrimethyammonium bromide), which is a kind of cation surfactant , with the aim to improve the response of single NPBBN system .Compared the two systems that is in the absence and presence of CTAB , we discovered that the fluorescence intensity of the mixed aqueous solution system with NPBBN and CTAB remarkably increased. The reason of this change is that CTAB can be self-organized to micelle in aqueous solution, the hydrophilic head groups bearing positive charge attracted the phosphate radicals bearing negative charge of compound NPBBN. Then a lot of NPBBN molecular aggregated on the micelle surface, in other words, the local concentration of compound NPBBN was enhanced. So, the fluorescence intensity depending on the fluorophore concentration of this mixed system was obviously increased.Compound BHQB contains boronic acid as the receptor and 8-Hydroxyquinoline as the reporter. We still chose pH=6.86 buffer to prepare the samples in our experiments. We prepared BHQB aqueous solution (1×10-4M) and D-fructose (1M) solution. At first we examined the excitation wave and emission wave, according to the fluorescence spectra, we can see that the excitation wavelength of BHQB is about 372nm, and meanwhile there are two emission wavelengths about 430nm and 520nm. This might show that there are two states of compound BHQB in solution. One is free boronic acid containing the B which is sp2 hybridigation, the other is boronic acid containing the B which is sp3 hybridigation due to combination with hydroxyl groups in aqueous solution. They are in equilibrium state and can be transformed into each other. In order to figure out the corresponding state of the two emission wavelengths, we checked the emission spectra and absorption spectra of BHQB system adding D-fructose and the result is conformable. The boronic acid receptor of compound BHQB binding with the hydroxy of D-fructose formed boronate esters, which induced the elector from quinolinium ring transfer to B atom. So the fluorescence was quenched resulting in the enhancement of fluorescence intensity, which was reflected by the increase of 430nm emission wavelength. The formation of boronate esters lowered the concentration of free boronic acid and broke the equilibrium. The boronic acid with B of sp3 hybridigation transformed into free boronic acid with B of sp2 hybridigation , which was reflected by the decrease of 510nm emission wavelength.In conclusion, there are two compounds containing boronic acid and different fluorophores were synthetized and their properties were studied. Compounds NPBBN and BHQB are both water soluble, gives signals adding mono saccharides in the near physiological pH buffer solution. All these merits make them ideal sugar sensors for detection in vitro and in vivo.