Tunable Aggregation And Chemical Sensing Of Bornic Acid Based Organic Dyes

Chemical sensing is one of the most important parts of supramolecular chemistry,and the development of sensitive and selective chemosensors for some biologically relevant species are of intense current interest since these species play important roles in our living system and environment,but it is still a large challenge to realize recognition for these species with high sensing performance.As a new emerging area in chemical sensing,sensing using supramolecular aggregates exhibits unique advantages over that using conventional small-molecule chemical sensors,in terms of high sensitivity and selectivity,and the simplicity of the sensory building blocks.For this purpose,sensing for glycosyl biogenic small molecules based on induced supramolecular aggregation,disaggregation and transformation of the aggregates of boronic acid functionalized organic dyes were invested in this thesis.There are five chapters in this thesis:In the first chapter the basic knowledge of boronic acid with diol was briefly introduced,as well as some research for carbohydrate sensing based on boronic acid receptors.H-and J-aggregation,of organic dyes including perylene and cyanine dyes were then introduced,including their influencing factors.Research in chemical sensing using supramolecular aggregates was also introduced.In chapter 2,we report a new strategy for an enhance performance of fluorescent sensing of bio-relevant species that often bind with natural receptors via multiple interactions with opcrative multivalency.We propose to make the fluorescent sensory molecules to exist in H-aggregates so that their emission are quenched leaving a much lower background,and upon binding to a biologically relevant species the aggregates are switched to the other forms in which the fluorescent species are better protected to lead to a much stronger emission signal.At the same time the aggregated fluorescent dyes could allow a multiple interactions with the sensing species that require more than one binding site.The much lower background,stronger binding and stronger signal would therefore lead to a much better sensing performance as improved selectivity would also result from the signal amplification.To support this working principle,we designed a near-IR cyanine dye bearing two boronic acid groups(Cy-BA)for ATP,in which boronic acids in the dye bind to the cis-diol moiety in ATP.In aqueous solutions in the presence of cationic dodecyltrimethylammonium bromide(DTAB)at a concentration below its critical aggregation concentration(CAC),Cy-BA molecules exist in H-aggregates being thereby practically nonfluorescent.Upon mixing with ATP in the presence of DTAB,a dramatic enhancement in the near-IR fluorescence of Cy-BA was observed,because of the formation of vesicles in which fluorescent dye molecule,binding to ATP via boronic acid/cis-diol motif while the formed negatively charged boronates and the triple phosphate anions in ATP interacting with the cationic polar head of DTAB,is now well dispersed and protected.This new sensing scheme,despite the reversible dynamic nature of the boronic acid/cis-diol interaction and the weak selectivity of this interaction and the electrostatic interaction,allows a highly sensitive(LOD 90 nM)and selective detection of ATP.In chapter 3,we present a novel sensing strategy to develop probes for biologically relevant species by induced transformation of organic dye aggregates from one to another.Based on this strategy,the representative complex biomolecule,NADH,was successfully detected by a near-IR cyanine dye(IR-DBA)possessing two boronic acid groups.Upon binding with the two cis-diols moiety in NADH,the aggregates of IR-DB A transformed from J-to H-type,revealing a highly selective and sensitive sensing for NADH at an LOD of 21 nM.The aggregates of the cyanine dyes as the interacting species could afford enhanced interactions with NADH,and upon these interactions,the J-aggregates were transformed into H-type that again maybe involved signal amplification,enhancing the selectivity and sensitivity for NADH sensing.This work provides a novel approach to increase the sensitivity and selectivity for complicated biologically relevant species sensing using supramolecular aggregates of simple organic dyes.In chapter 4,we report an induced helical aggregation of achiral cationic perylene-3,4-dicarboximide(1)that contains a phenylboronic acid group,together with UMP that bears a cis-diol moiety being able to interact with boronic acid and an imide group known to coordinate with Hg2+.In chosed solvents 1 exists in monomer form and remains even in the presence of either UMP or Hg2+.Helical aggregation only takes place when 1 is mixed with both UMP and Hg2,which we showed to result from the formation of a building block of the form 1-U-Hg2+-U-1 consisting of five components.Strong exciton-coupled CD signals were observed at the absorption window of the achiral dye chromophore,featuring the tranferring of the molecular chirality of UMP to the supramolecular aggregates of P-helicity.Synergism was shown to occur upon the aggregation of the building block of the form 1-U-Hg2+-U-1,since substantially enhanced affinity and binding selectivity were observed for UMP or Hg2+,despite the otherwise weak and less selective interactions of 1/UMP and UMP/Hg2+.In supporting this synergism,the g-factor of the aggregates was found to be 1.4 × 10-2 that represents a high value in its kind.We thus show a strategy of in situ construction of building blcok from multiple components among which the interactions can be weak and less selective,therefore substantially easing the design and syntheses of the forming components yet diverse functions can be expected from their supramolecular aggregates.In the last chapter,an amphipathic perylene dicarboximide derivative(PBI-MBA),with a phenylboronic acid group in one side and a positive charge in another,was designed and synthesized.Simultaneously introducing phenylboronic acid and positive charge into PBI-MBA molecule,not only improve the solubility of the compound but also bring in more binding sites.The amphiphilic dye PBI-MBA was well dispersed in methanol as monomers but formed H-aggregates in water.An appropriate methanol/water ratio was selected,and the pH value of the solution was adjusted to alkaline led to boric acid ionized with a negative charge,based on the cooperation of hydrophobic effect,?-? stacking and electrostatic interaction,PBI-MBA was promoted into H-dimer.The dimer,containing multiple binding sites,such as boric acid and the positively charged quaternary ammonium salt,matched with the ribose and negatively charged phosphate sites in NADH.The results go as we expected,NADH could induce PBI-MBA dimer aggregated into H-type aggregates,which caused the obvious changes of the spectra and colors of the solution,realizing the recognition of NADH.Synergistic effect and signal amplification in the induced aggregation process enhanced the binding constants of boric acid with cis-dio1,and improved the sensitivity for NADH detection.The highly matching of the spatial position of the binding sites makes PBI-MBA dimer show high selectivity for NADH recognition.