阅读说明：本技术 三苯胺酚类化合物及其制备方法与其检测色氨酸的应用 (Triphenylamine phenolic compound, preparation method thereof and application thereof in tryptophan detection ) 是由 崔月芝 徐进振 陶芙蓉 张汉君 于 2021-08-05 设计创作，主要内容包括：本发明公开了三苯胺酚类化合物及其制备方法与其检测色氨酸的应用,其化学结构为其中,R-(1)为氢或烷基,R-(2)为或R-(3)为或R-(4)为氢或烷基,R-(5)为氢或烷基,R-(6)为氢或烷基,R-(7)为氢或烷基,本发明提供的三苯胺酚类化合物可以作为色氨酸专一性识别的荧光分子探针,对色氨酸的检测灵敏度高、抗干扰性强,可以用于色氨酸的痕量检测。(The invention discloses a triphenylamine phenol compound, a preparation method thereof and application thereof in detecting tryptophan, wherein the chemical structure of the compound is Wherein R is 1 Is hydrogen or alkyl, R 2 Is composed of Or R 3 Is composed of Or R 4 Is hydrogen or alkyl, R 5 Is hydrogen or alkyl, R 6 Is hydrogen or alkyl, R 7 The triphenylamine phenolic compound provided by the invention can be used as a fluorescent molecular probe for specifically identifying tryptophan, has high detection sensitivity and strong anti-interference performance on tryptophan, and can be used for trace detection of tryptophan.)

1. A triphenylamine phenol compound is characterized in that the chemical structure is shown as follows,

wherein R is₁Is hydrogen or alkyl, R₂Is composed ofR₃Is composed of R₄Is hydrogen or an alkaneRadical, R₅Is hydrogen or alkyl, R₆Is hydrogen or alkyl, R₇Is hydrogen or alkyl.

2. The triphenylamine phenol compound according to claim 1, wherein the alkyl group is a C1-C6 alkyl group;

or, R₁Is hydrogen;

or, R₂Is composed of

Or, R₃Is composed of

Preferably, the compound has the structural formula

3. The preparation method of the triphenylamine phenolic compound is characterized in that the triphenylamine phenolic compound is obtained by taking tris (4-aminophenyl) amine and an aldehyde compound as raw materials according to the following reaction route:

wherein R is₁Is hydrogen or alkyl, R₂Is composed ofR₃Is composed of R₄Is hydrogen or alkyl, R₅Is hydrogen or alkyl, R₆Is hydrogen or alkyl, R₇Is hydrogen or alkyl.

4. The method for producing a triphenylamine phenol compound according to claim 3, wherein the tris (4-aminophenyl) amine is obtained by Schiff base reaction with an aldehyde compound.

5. The method for preparing a triphenylamine phenol compound according to claim 3, wherein the temperature of the Schiff base reaction is 30 to 40 ℃;

or the molar ratio of the tri (4-aminophenyl) amine to the aldehyde compound is 1: 2.9-3.1;

or, the reaction solvent is methanol;

preferably, the purification process is: filtering, washing with ether and drying.

6. Use of the triphenylamine phenolic compound of claim 1 in the detection of tryptophan.

7. A fluorescent reagent for detecting tryptophan is characterized by comprising a fluorescent probe and a carrier, wherein the fluorescent probe is the triphenylamine phenol compound.

8. The fluorescent reagent for detecting tryptophan according to claim 7, wherein the carrier is a solvent.

9. A method for detecting tryptophan, which is characterized in that the triphenylamine phenol compound of claim 1 or the fluorescent reagent for detecting tryptophan of claim 7 is added into a solution to be detected containing tryptophan to obtain a detection solution, and the detection solution is subjected to fluorescence detection.

10. The method for detecting tryptophan according to claim 9, wherein the pH of the detection solution is 6 to 8;

or the detection wavelength is 400-410 nm.

Technical Field

The invention belongs to the technical field of fluorescence detection, relates to fluorescence detection of amino acid, and particularly relates to triphenylamine phenol compounds, a preparation method thereof and application thereof in tryptophan detection.

Background

The information in this background section is only for enhancement of understanding of the general background of the invention and is not necessarily to be construed as an admission or any form of suggestion that this information forms the prior art that is already known to a person of ordinary skill in the art.

Chemical sensors are molecules that selectively bind a given ion to a biomolecular substance and when attached induce a measurable signal, primarily a chromophore or a change in the spectral properties of a fluorophore. Receptors for ions and biomolecular species in the receptor are in the binding site and the conversion occurs when the molecule attacks the guest molecule and actively dislocates the binding site. The inventors have found that, although some analytical methods (e.g. gas chromatography, gel-chromatography) using relatively high-end instruments are currently used to detect these low levels of biomolecules, they still suffer from some disadvantages, such as being time-consuming and expensive. Furthermore, reports of artificially synthesized molecular probes having high selectivity for tryptophan are still very insufficient, and thus there is a strong demand for inexpensive and simple detection of these biomolecules.

Disclosure of Invention

In order to solve the defects of the prior art, the invention aims to provide the triphenylamine phenolic compound, the preparation method thereof and the application thereof in detecting tryptophan.

In order to achieve the purpose, the technical scheme of the invention is as follows:

on one hand, the chemical structure of the triphenylamine phenolic compound is shown as follows,

wherein R is₁Is hydrogen or alkyl, R₂Is composed ofR₃Is composed of R₄Is hydrogen or alkyl, R₅Is hydrogen or alkyl, R₆Is hydrogen or alkyl, R₇Is hydrogen or alkyl.

On the other hand, the preparation method of the triphenylamine phenolic compound takes tri (4-aminophenyl) amine and aldehyde compounds as raw materials and is obtained according to the following reaction route:

wherein R is₁Is hydrogen or alkyl, R₂Is composed ofR₃Is composed of R₄Is hydrogen or alkyl, R₅Is hydrogen or alkyl, R₆Is hydrogen or alkyl, R₇Is hydrogen or alkyl.

In a third aspect, the application of the triphenylamine phenolic compound in tryptophan detection is provided.

In a fourth aspect, the fluorescent reagent for detecting tryptophan comprises a fluorescent probe and a carrier, wherein the fluorescent probe is the triphenylamine phenolic compound.

In a fifth aspect, in the method for detecting tryptophan, the triphenylamine phenolic compound or the fluorescent reagent for detecting tryptophan is added to a solution to be detected containing tryptophan to obtain a detection solution, and the detection solution is subjected to fluorescence detection.

The invention has the beneficial effects that:

1. after the triphenylamine phenolic compound provided by the invention is mixed with tryptophan, the fluorescence emission intensity is obviously improved, and the triphenylamine phenolic compound can be used as a fluorescent probe of the tryptophan in water.

2. The triphenylamine phenolic compound provided by the invention has selectivity on tryptophan superior to other amino acids, the detection limit is as low as 0.96bbs, and trace detection on tryptophan can be realized.

3. The triphenylamine phenol compound provided by the invention only needs to be synthesized by adopting tris (4-aminophenyl) amine and 2, 3-dihydroxy benzaldehyde in one step, the reaction raw materials are easy to obtain, the synthesis steps are simple, and the detection cost of p-tryptophan is favorably reduced.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and together with the description, serve to explain the invention and not to limit the invention.

FIG. 1 is a nuclear magnetic hydrogen spectrum of TNB prepared by an example of the present invention;

FIG. 2 is a nuclear magnetic carbon spectrum of TNB prepared by an example of the present invention;

FIG. 3 is a nuclear magnetic hydrogen spectrum of TCN prepared by an example of the present invention;

FIG. 4 is a nuclear magnetic carbon spectrum of TCN prepared according to an example of the present invention;

FIG. 5 shows the UV absorption spectrum of TNB (a), TNN (b) reacted with tryptophan prepared in the example of the present invention;

FIG. 6 is a graph showing the fluorescence emission characteristics of compounds prepared in the examples of the present invention, (a) is a fluorescence emission curve of TNB, (b) is a fluorescence histogram of TNB, and the detection wavelength of TNB + Trp is 353nm, the detection wavelength of TNB is 323nm, the detection wavelength of Trp is 330nm, and the detection wavelength of a mixture of TNB and other amino acids is 330nm, and (c) is a fluorescence emission curve of TNN;

FIG. 7 is a graph showing the stability characteristics of TNB reacted with tryptophan prepared according to the example of the present invention;

FIG. 8 is a graph depicting the effect of pH on TNB detection of tryptophan in an example of the present invention, (a) a graph depicting the recoverability of the probe, (b) the fluorescence emission intensity of TNB and tryptophan reactants at different pH values, excitation wavelength: 275nm, and a detection wavelength of 353 nm;

FIG. 9 is a performance characterization diagram of TNB detection of tryptophan in the present example, (a) the UV-visible spectrum of TNB probe and tryptophan (0-3 equivalents), (b) the fluorescence emission spectrum of TNB probe and tryptophan (0-3 equivalents), (c) the TNB detection limit of tryptophan;

FIG. 10 is a diagram illustrating anti-interference characteristics of Tryptophan detection by TNB in an embodiment of the present invention, wherein the detection wavelength of TNB + Other amino acid + Trp is 353 nm; the detection wavelength of the TNB + Other amino acid is 330 nm;

FIG. 11 is a nuclear magnetic spectrum of a mechanism study of TNB detection of tryptophan in an embodiment of the present invention, wherein (a) the nuclear magnetic spectrum of TNB, TNB and tryptophan¹H NMR spectrum of (b) TNN, TNN and tryptophan¹H NMR spectrum;

FIG. 12 is a diagram showing the mechanism of TNB and tryptophan proton transfer in an embodiment of the present invention.

Detailed Description

It is to be understood that the following detailed description is exemplary and is intended to provide further explanation of the invention as claimed. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the invention. As used herein, the singular is intended to include the plural unless the context clearly dictates otherwise, and it should be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of features, steps, operations, devices, components, and/or combinations thereof.

Aiming at the problem that few molecular probes with high selectivity on tryptophan exist, the invention provides a triphenylamine phenolic compound, a preparation method thereof and application thereof in tryptophan detection.

In a typical embodiment of the present invention, there is provided a triphenylamine phenol compound having a chemical structure as shown below,

wherein R is₁Is hydrogen or alkyl, R₂Is composed ofR₃Is composed of R₄Is hydrogen or alkyl, R₅Is hydrogen or alkyl, R₆Is hydrogen or alkyl, R₇Is hydrogen or alkyl.

R₁In the case of alkyl, the position may be at the 4-, 5-or 6-position.

R₄In the case of alkyl, the position may be at the 2-, 3-or 4-position.

R₅In the case of alkyl, the position may be at the 4-, 5-or 6-position.

R₆In the case of alkyl, the position may be at the 2-, 3-or 4-position.

R₇In the case of alkyl, the position may be at the 4-, 5-or 6-position.

In some embodiments of this embodiment, the alkyl group is a C1-C6 alkyl group. Such as methyl, ethyl, propyl, n-butyl, isobutyl, pentyl, hexyl and the like.

In some embodiments of this embodiment, R₁Is hydrogen.

In some embodiments of this embodiment, R₂Is composed of

In some embodiments of this embodiment, R₃Is composed of

In some embodiments of this embodiment, the compound is of the formula

Another embodiment of the present invention provides a preparation method of triphenylamine phenolic compounds, which is obtained by using tris (4-aminophenyl) amine and aldehyde compounds as raw materials according to the following reaction route:

wherein R is₁Is hydrogen or alkyl, R₂Is composed ofR₃Is composed of R₄Is hydrogen or alkyl, R₅Is hydrogen or alkyl, R₆Is hydrogen or alkyl, R₇Is hydrogen or alkyl.

In some examples of this embodiment, the tris (4-aminophenyl) amine and the aldehyde compound are obtained by schiff base reaction. The Schiff base reaction refers to the reaction that primary amine and carbonyl are condensed to generate carbon-nitrogen double bonds.

In one or more embodiments, the temperature of the schiff base reaction is 30 to 40 ℃. Under this temperature, can guarantee that reaction efficiency is higher, reaction temperature is lower moreover, is favorable to manufacturing cost's reduction.

In some examples of this embodiment, the molar ratio of tris (4-aminophenyl) amine to aldehyde compound is 1:2.9 to 3.1. Can ensure the complete reaction of the primary amine group and the aldehyde group.

The reaction solvent may be methanol, ethanol, tetrahydrofuran, chloroform, dichloromethane, dimethylsulphoxide, N-dimethylformamide, etc. In some embodiments of this embodiment, the reaction solvent is methanol. Researches show that the product triphenylamine phenolic compound is insoluble in methanol, and the raw material is easily soluble in methanol, so that the methanol is adopted as the reaction solvent, the purification process of the product can be greatly simplified, and the cost is further reduced.

In one or more embodiments, the purification process is: filtering, washing with ether and drying.

In a third embodiment of the invention, the application of the triphenylamine phenolic compound in the detection of tryptophan is provided.

The fourth embodiment of the invention provides a fluorescent reagent for detecting tryptophan, which comprises a fluorescent probe and a carrier, wherein the fluorescent probe is the triphenylamine phenolic compound.

The carrier can be a solvent, such as tetrahydrofuran, dimethyl sulfoxide, N-dimethylformamide and the like, can dissolve the triphenylamine phenolic compound, and can be mutually soluble with water, so that the triphenylamine phenolic compound can be more uniformly dispersed in a water sample to be detected, and the water sample to be detected can be detected.

In a fifth embodiment of the present invention, a method for detecting tryptophan is provided, wherein the triphenylamine phenolic compound or the fluorescent reagent for detecting tryptophan is added to a solution to be detected containing tryptophan to obtain a detection solution, and the detection solution is subjected to fluorescence detection.

In some embodiments of this embodiment, the pH of the detection solution is between 6 and 8. The research shows that the pH is the fluorescence signal of the detection method. When the pH value is 6-8, especially 6.9-7.1, the fluorescence signal is more obvious.

In some examples of this embodiment, the detection wavelength is 400 to 410 nm.

In order to make the technical solutions of the present invention more clearly understood by those skilled in the art, the technical solutions of the present invention will be described in detail below with reference to specific embodiments.

Examples

(1) Synthesis of 1,1, 3-dicyclohexyl-5- (9-ethyl-9H-carbazol-3-yl) methylene) pyrimidine-2, 4,6- (1H,3H, 5H) -Trione (TNB).

The method comprises the following steps of weighing 5mmol of tri (4-aminophenyl) amine by using an electronic analytical balance, adding the weighed material into a three-neck flask containing methanol (15mL), weighing 15mmol of 2, 3-dihydroxy benzaldehyde by using the electronic analytical balance again, placing the three-neck flask into a low-temperature constant-temperature stirring reaction bath, stirring, heating to 35 ℃ in a reflux state, continuously reacting for 12 hours, taking out the three-neck flask, and cooling at room temperature until solid precipitates. And (3) carrying out reduced pressure filtration by using a circulating water type vacuum pump to obtain TNB, purifying the obtained TNB by using anhydrous ether to obtain the TNB without impurities, and drying in a vacuum oven at the temperature of 60 ℃ for 14 hours. Yield: 98 percent. Color: deep red. Melting point; 244 ℃.¹H NMR (400MHz, DMSO-d6) δ 13.29(s,3H),9.17(s,3H),8.94(s,3H),7.44(d, J ═ 8.5Hz, 6H),7.15(d, J ═ 8.6Hz,6H), 7.10-7.05 (m,3H), 6.95-6.90 (m,3H),6.78(t, J ═ 7.8Hz,3H), and the nuclear magnetic spectrum is shown in fig. 1-2.

(2) Synthesis of (Z) -N1-benzylidene-N4, N4-bis (4- (Z) -benzylideneamino) phenyl) benzene-1, 4-diamine (TNN).

Benzaldehyde (5mmol) was weighed out and added to a three-necked flask containing methanol (15mL), and then 2, 3-dihydroxybenzaldehyde 15mmol was weighed out and placed in the three-necked flask so that the solute in the mixed solution could undergo condensation reaction. Stirring in a low-temperature constant-temperature stirring reaction bath at 40 ℃, and continuously stirringStirring for 12 hours to obtain a crude product TNN, cooling the crude product TNN at room temperature until solid precipitates, carrying out reduced pressure filtration by a circulating water type vacuum pump to obtain the TNN without impurities, and further purifying the TNN in an anhydrous ether solvent to obtain the TNN without impurities. And (3) putting the TNN into a vacuum oven at 50 ℃ for drying treatment. Yield: 98 percent. Color: yellow. Melting point; 226 ℃ is prepared.¹H NMR (400MHz, DMSO-d6), δ 8.68(s,3H),7.93(dd, J ═ 6.5,2.9Hz,6H),7.56 to 7.49(m,9H),7.32(d, J ═ 8.3Hz,6H),7.11(d, J ═ 8.3Hz,6H), and the nuclear magnetic spectrum is shown in fig. 3 to 4.

The performance of TNB and TNN was tested as follows.

1. Solubility in water

The dissolving performance of 7 common solvents (tetrahydrofuran, chloroform, dichloromethane, N-dimethylformamide, dimethyl sulfoxide, tetrachloromethane and water) on TNB and TNN is tested, and the dissolving speed in the solvent at 25 ℃ is observed by naked eyes. Weighing two compounds with the same mass, respectively adding the two compounds into 7 solvents with the same volume, wherein the two compounds are soluble when being rapidly dissolved, and are insoluble when not being completely dissolved, and the two compounds are insoluble when being still insoluble by means of ultrasound, heating and the like. The results of the study are shown in Table 1.

TABLE 1 solubility comparison of TNB and TNN in common solvents (25 ℃ C.)

It can be seen that both compounds are soluble in 7 solvents, but in contrast, TNN compounds are less soluble than TNB, because TNN compounds do not contain hydrogen bonds, and are slightly less soluble according to the principle of similar solubility.

2. Optical Properties

2.1 UV-visible absorption Properties

First, respectively configure 1 × 10^-5Tetrahydrofuran solution of TNB and TNN compounds in mol/L and 1X 10^-3After the deionized water solution of the tryptophan is fully dissolved, 500 mu L of deionized water solution of the tryptophan is added into TNB and TNNAnd (3) putting the two compounds into a 5mL volumetric flask, then fixing the volume of the solution to 5mL, and shaking the solution repeatedly by using an instrument to fully and uniformly mix the solution to obtain the fluorescent substance solution of the two compounds and tryptophan. The prepared solution was then measured in an ultraviolet spectrophotometer, and the results are shown in fig. 5.

Fig. 5(a) is three absorption spectra for TNB. The peaks with absorption wavelengths of 405nm and 275nm are respectively the Intramolecular Charge Transfer (ICT) peak and the pi-pi of benzene^*Transition peak, small shoulder at 405nm band. When tryptophan was added to TNB, the positions of the 405nm and 275nm peaks were essentially unchanged, but the small shoulder of TNB in the 405nm band disappeared and the peak shape became smooth. When TNB was mixed with tryptophan for one hour, a new peak appeared, because TNB and tryptophan also reacted to give a tryptophan absorption peak.

Fig. 5(b) is three absorption spectra for TNN. As can be seen from FIG. 5(b), the absorption spectra of TNN and the mixture of TNN and tryptophan, and the absorption spectrum of the mixture after one hour of standing, are substantially unchanged, indicating that there is no chemical reaction between TNN and tryptophan. The comparison shows that the new absorption peak generated in FIG. 5(a) is due to the reaction of the tryptophan hydroxyl group with the hydroxyl group on TNB and the formation of a new chemical bond, and the pi-pi conjugation effect between the heterocycle on tryptophan and the TNB benzene ring.

2.2 fluorescence emission Properties

As shown in fig. 6(a) and (b), the fluorescence emission intensity spectrum of the TNB mixed with the fluorescence emission spectra of different amino acids (alanine (Ala), leucine (Leu), isoleucine (Ile), phenylalanine (Phe), tryptophan (Trp), methionine (Met), glycine (Gly), serine (Ser), arginine (Arg), histidine (His), threonine (Thr), cysteine (Cys), aspartic acid (Asp), glutamic acid (Glu)) in the mixed solution of THF and water. When TNB is mixed with tryptophan, the fluorescence emission intensity increases immediately compared with other amino acids, while the fluorescence intensity of other amino acids hardly changes. Therefore, TNB has unique selectivity for tryptophan and tryptophan can be detected simply and rapidly. As shown in FIG. 6(c), in the mixed solution of THF and water, a slight increase in the fluorescence emission intensity of TNN and tryptophan occurred, causing an increase in the emission intensity, probably due to the fluorescence emission intensity of tryptophan itself. Since TNB differs from TNN in the presence or absence of hydroxyl groups, the fluorescence emission spectrum of TNN reflects that phenolic hydroxyl groups are likely to be the main cause of the increase in fluorescence emission intensity after TNB is mixed with tryptophan. The specific reasons may be that, with the addition of tryptophan, the fluorescence emission intensity of TNB at 405nm is rapidly increased, TNB has a flexible structure to form a cavity with a complementary shape, the cavity can selectively accommodate tryptophan through the proton transfer of phenolic hydroxyl and amino, and the free rotation of two host-guest objects is limited through pi-pi stacking to form a host-guest complex, so that the fluorescence emission intensity is greatly increased.

2.3 fluorescent stability assay of TNB plus Trp

THF-H to TNB₂The O solution (volume ratio 99:1) was continuously excited for 1800 seconds, and the change of fluorescence intensity with excitation time was measured, and the result is shown in FIG. 7. The experimental results show that the fluorescence emission intensity is always at a relatively high position, the stability of the fluorescence emission intensity is very good along with the time, and most importantly, the fluorescence emission intensity is only reduced by 3 percent within 30 minutes, so that the Trp can be completely detected. The reason for this is that the flexible TNB molecule has a plurality of phenolic hydroxyl groups, so that proton transfer between host and guest molecules can occur, and at the same time, Trp can be selectively accommodated to form a stable host-guest complex, which makes the fluorescence of TNB particularly stable, so that TNB is completely suitable for detection as an excellent sensor for Trp according to the specificity and stability of TNB.

2.4 Effect of pH on TNB detection of Tryptophan

The method comprises the steps of preparing a mixed solution of TNB and tryptophane with the pH value of 1-14 by utilizing concentrated hydrochloric acid solution, sodium hydroxide solid and deionized water, and measuring fluorescence emission intensity under each pH value by using a fluorescence spectrometer. As shown in fig. 8(a), under neutral conditions at pH 7, TNB and tryptophan reactants had significant fluorescence emission at 405 nm. And adding NaOH solution into the mixture after the mutual reaction of the probe molecules TNB and tryptophan, and finding that the fluorescence emission intensity peak of the solution after the TNB and tryptophan are mixed almost completely disappears. However, the fluorescence emission intensity of the mixed solution of TNB and tryptophan is very obviously enhanced after adding hydrochloric acid solution to neutralize hydroxide in the mixture, probably because the reaction of TNB and tryptophan is not favored under alkaline conditions, and after acid-base neutralization, the reaction of TNB and tryptophan is recovered. FIG. 8(b) shows fluorescence emission intensity of TNB and tryptophan after mixing under different pH conditions, and it can be seen that TNB and tryptophan are not easily reacted under the conditions of strong acid and strong base. The fluorescence emission intensity of the probe TNB mixed with tryptophan can only reach the maximum under neutral conditions, so that the pH value of the detection environment should be neutral in the first place although a plurality of factors need to be considered in the application.

2.5 Tryptophan assay Performance of TNB

First, respectively configure 1 × 10^-5After the tetrahydrofuran solution of the TNB compound and the deionized water solution of tryptophan are dissolved sufficiently, 50 mu L of the aqueous solution of the TNB compound are respectively added into 20 volumetric flasks of 5mL prepared in advance, and then 0-6000 mu L of the aqueous solution of tryptophan with the concentration of 300 mu L as the gradient and the concentration of 2g/L of the aqueous solution of tryptophan are respectively added into each flask. Then the solution is fixed to 5mL, and the solution is fully and uniformly mixed by repeatedly shaking the solution by an instrument to obtain 1 × 10^-7A fluorescent substance solution in mol/L. Then, the prepared solution is placed under an ultraviolet spectrophotometer for measurement, and the test conditions are as follows: the excitation wavelength is 275nm, and the excitation and emission slits are 2.5nm and 5 nm. As shown in FIG. 9(a), the molar concentration ratio of the reaction of TNB and tryptophan was determined by UV titration experiment, and it was found that when tryptophan was present at 3 equivalents (3X 10)^-5mol/L), the UV absorption peak hardly changes at all. The reason may be that the probe TNB is a three-branched structure with each branch being identical, and therefore three equivalents of tryptophan are required for complete reaction. As shown in FIG. 9(b), the fluorescence emission intensity reached a maximum value after the addition of 3 equivalents of tryptophan, while there was hardly any change in the fluorescence intensity when the molar amount of tryptophan was continuously increased,it was also confirmed that the molar ratio of the two was 1: 3. TNB was studied for various concentrations of tryptophan (0-3X 10) by changes in fluorescence emission intensity under optimal conditions for fluorescence^-5M), as can be seen from FIG. 9(b), TNB probe showed weak fluorescence emission intensity at 340nm, almost no fluorescence, and when tryptophan was added, the fluorescence emission intensity gradually increased with the increase of the tryptophan concentration, and the recovery efficiency of fluorescence was [ (F-F)₀)/F₀](wherein F₀And F represents the fluorescence intensity of TNB in the absence and presence of tryptophan analyte, respectively) has a good linear relationship with tryptophan concentration in this range from 0 to 3X 10^-5M (fig. 9 (c)). The linear regression equation for tryptophan detection can be obtained by calculation as Y10.67X +1.2258, from R²The linear equation has excellent linear correlation (R) as can be known from the numerical values of²0.9988), wherein Y represents the fluorescence recovery efficiency of TNB and X represents the concentration of tryptophan. The linear equation shows that the probe is sensitive enough to detect the physiological tryptophan concentration (0-3X 10) with the limit of detection (LOD)^-5mol/L) (S/N3, the concentration required to generate a net signal equal to three times the background standard deviation) has a detection limit of 0.96bbs under experimental conditions.

The fluorescence spectrometer was used to investigate whether probe TNB interferes with the detection of Trp in the presence of other amino acids (tryptophan, leucine, alanine, isoleucine, phenylalanine, methionine, glycine, tryptophan, arginine, histidine, serine, threonine, cysteine, glutamic acid, aspartic acid) (3.0 equivalents). As shown in FIG. 10, the TNB solution has little change in fluorescence intensity when different amino acids are added, and the fluorescence intensity is greatly enhanced when Trp is added to the mixed solution of TNB and other amino acids. The occurrence of the phenomenon can show that the probe TNB has high specific selectivity for identifying tryptophan and has excellent anti-interference capability without being influenced by other amino acids.

2.6 mechanism study of Tryptophan detection by TNB

Using DMSO-d₆Preparation of TNB solutions as solventsAnd (3) testing the nuclear magnetic resonance spectra of the solution, the TNB and the tryptophan mixed solution (the TNB solution is mixed with 3 equivalents of tryptophan deionized water solution and reacts for twenty-four hours in a vacuum environment at 35 ℃, then the temperature of a vacuum drying oven is increased to 60 ℃, trace water in the solution is evaporated to obtain the moisture-free TNB and tryptophan mixed solution for detection), and the nuclear magnetic resonance spectra are shown in figure 11 (a). As shown in fig. 11(a), the TNB solution has two hydroxyl peaks near the chemical shift δ of 9.0, and the other characteristic peak is a methylene peak at δ of 13.5. Observing the nuclear magnetic spectrum of the mixed solution of TNB and tryptophan, the hydroxyl peak near the chemical shift delta of 9.0 disappears, which is probably that the acidic phenolic hydroxyl group of the probe TNB and the basic amino group of tryptophan have proton transfer reaction, so that the phenolic hydroxyl group loses the hydrogen proton and becomes negatively charged, and the tryptophan amino group obtains the hydrogen proton and is transferred to positively charged, as shown in FIG. 12. The methylene proton moves to high field (δ ═ 11) due to its position close to the adduct negative charge (phenoxide anion), and the deprotonated compound TNB forms a stable host-guest complex with tryptophan due to the presence of the electron donor — N ═ CH. This proton transfer mechanism is also reported in the literature. In addition, several new peaks appearing at δ 2.50 to 3.50 are characteristic peaks of tryptophan. The appearance of these characteristic peaks for tryptophan, because tryptophan is not soluble in DMSO, indicates that tryptophan reacted with TNB to form a product that is soluble in DMSO.

In order to prove that tryptophan reacts with phenolic hydroxyl of TNB, a compound TNN which does not contain phenolic hydroxyl and has a similar structure with TNB is designed and synthesized, 3 equivalents of tryptophan is added into DMSO solution of TNN, the mixture reacts for twenty-four hours in a vacuum environment at 35 ℃, then the temperature of a vacuum drying oven is increased to 60 ℃, trace water in the solution is evaporated to obtain a mixed solution of TNN and tryptophan which does not contain moisture, insoluble substances are removed through filtration, and the mixed solution is measured and measured¹H NMR spectra, with DMSO solutions of TNN¹The H NMR spectra were compared, as shown in FIG. 11 (b). It can be seen that the nuclear magnetic spectrum of the TNN solution after tryptophan was added was almost identical to that of the TNN solution without tryptophan. This indicates that TNN does not react with tryptophan and that free tryptophan is not soluble in DMSOIs removed by filtration and, consequently, both solutions are eventually in effect DMSO solutions of TNN, so they have the same nuclear magnetic spectrum. This phenomenon confirms that the phenolic hydroxyl group in TNB plays a crucial role in the reaction with tryptophan.

Summary of the invention

After the TNB and the tryptophan are mixed, the fluorescence emission intensity is obviously improved. The fluorescence intensity is increased by 5 times due to the combined accumulation of tryptophan and TNB triggered by hydroxyl groups of the TNB, so that the TNB with weak fluorescence is converted into a high-fluorescence host-guest complex. The selectivity of TNB for tryptophan is superior to other amino acids, the detection limit is as low as 0.96bbs, the detection in trace amount is completely satisfied, and the existence of non-covalent interaction in the ligand is very sensitive to the microenvironment for selective tryptophan detection.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.