Design, Synthesis And Spectra Study Of Reaction-Based Cyanide Receptors

Recognition and sensing of anions have received considerable attention for their important roles in biological, industrial, and environmental processes. In particular, cyanide ion is a detrimental anion causing poisoning in biology and the environment. Despite its toxic nature, its application in various areas as raw materials is inenitable, which releases cyanide ion into the environment as a toxic contaminant. Thus, there exists a need for an efficient sensing system for cyanide ion to monitor cyanide concentration from contaminant sources. However, the traditional cyanide receptors that relied on hydrogen-bonding have tenerally displayed weak selectivities relative to other anions. To overcome this limitation, reaction-based receptors for cyanide ion, which was taken advantage of its nucleophilic character, have been developed recently. In this dissertation, four types of reaction-based receptors for cyanide ion have been reported: colorimetric sensors based on amide, fluorescent sensors based on salicylaldehyde hydrazone, colorimetric sensors based on Schiff-base, and ratio fluorescent sensors based on amide. The reaction between cyanide and sensors would lead to signal changes, and the detailed investigations were done by UV-vis and fluorescent spectra.A series of simple nitroaniline-based benzamide compounds (2-1-2-5) for the'naked-eye'detection of cyanide in aqueous environment with high selectivity. Cyanide was detectable by nucleophilic attack toward the activated amide carbonyl function, and then followed by fast proton transfer of the acidic amide hydrogen to the developing alkoxide anion of these compounds. The proton transfer may trigger the latent chromogenic nitroaniline group into an active state (its anionic state), thus resulting in the enhancement of the push-pull character of the intramolecular charge transfer (ICT), which induces a large enhancement in absorption intensity and a marked color changes from colorless to yellow in DMSO:H2O=1:1(V/V) at room temperature. These compounds react with CN- in a 1:1 stoichiometric manner. Furthermore, the selectivity of this system for CN-over other anions is extremely high. In addition, the detection limit of 2-1 for CN- falls below the WHO detection level. Therefore, the chemosensor 2-1 appears to be a practical system for monitoring CN- concentrations in aqueous samples.The adduction of cyanide to imine group was discovered for the first time. This new type of stable chemosensors (3-1-3-3) bearing a salicylaldehyde hydrazone function were designed by intramolecular proton transfer. Cyanide was expected to be detectable by nucleophilic attack toward an imine functional group, which is activated by an intramolecular hydrogen bond. Fast proton transfer of the phenol hydrogen to the developing nitrogen anion would then bring about spectroscopic and color changes. These three cyanide sensors were carefully investigated by UV-vis and fluorescent spectra. The sensors shown specific selectivity to cyanide with a detection limit lower than 1.9μM in DMSO:H2O=1:1 (V/V) system. The 1:1 binding stoichiometry for each compound was proven by Job'plots and FTICR-MS.; and the mechanism were confirmed by 1H NMR. The imine proton and phenol proton of the sensors were dramatically shifted from low shield to high shield after addition of cyanide anions. The rational mechanism of fluorescent "off-on" that happened in sensors 3-1 and 3-3 were explained and an ab initio calculation of sensor 3-1 was also carried out to comfirm our explaination.Some structurally simple Schiff-based compounds (4-1-4-3) were synthesized based on the adduction mechanism which was discussed in last paragraph. The sensor 4-1 could distinguish CN- and AcO- with two different mechanisms as a tow channel sensor in DMSO:H2O=9:1 (V/V) system. The sensor could give two obvious spectral changes as signals out-put, as well as color changes, which could be detected by naked-eyes. After the adduct of CN-, the conjugation of the sensor 4-1 was disturbed and a blue-shift hence happened. On the other hand, AcO- is a good hydrongen-bond receptor as a basic anion which could interact with phenol proton of the sensor to induce the process of deprotonation. The deprotoned sensor enlarged its conjugation that led a red-shift. The associated constants of sensor 4-1 to CN- and AcO- were 106 M-1 and 7.8x104M-1,respectively. Competition experiment shown that the sensor could also detect CN- in the presence of other anions including AcO-.4-amide derivatives of 1,8-naphthalimide has been known to display a high fluorescent quantum yield and was influenced by polar solvents that led to an intramoleclar charge transfer, which could induce a ratio fluorescent change. In the present study, the amino group was modified as trifluoroacetamide (5-1) to facilitate the dissociation of their amide proton by CN- and F- with tow different mechanisms. The spectral research was carried out in acetonitrile to inhibit the dissociation of sensor 5-1. The adduction of CN- to trifluoroacetamide and the deprotonation by F- would induce the amide proton to dissociate, resulting in a ratio fluorescent change.