CN112881361A

CN112881361A - High-efficiency ionization reaction of compound with carboxylic group under surface plasmon catalysis

Info

Publication number: CN112881361A
Application number: CN202110033315.6A
Authority: CN
Inventors: 宋朋; 杨艳秋; 丁勇
Original assignee: Liaoning University
Current assignee: Liaoning University
Priority date: 2021-01-12
Filing date: 2021-01-12
Publication date: 2021-06-01

Abstract

The invention discloses a high-efficiency ionization reaction of a compound with a carboxylic group under the catalysis of surface plasmons. Dissolving a compound with a carboxylic acid group in ethanol, mixing the obtained ethanol solution of the compound with the carboxylic acid group with the SERS substrate, and irradiating by laser. Under laser irradiation, disulfide bonds of DTBA molecules are broken to form bimolecules similar to 4-MBA, and the bimolecules are adsorbed on the surfaces of AgNPs, so that bimolecular coupling greatly increases the possibility of the molecules combining with the Ag NPs, and the ionization reaction is stably and effectively carried out. Under the monitoring of Surface Enhanced Raman Spectroscopy (SERS), the generation of such high-efficiency ionization reaction provides a certain value for the development of further related reactions, and has wide application in pH sensors and intracellular pH monitoring.

Description

High-efficiency ionization reaction of compound with carboxylic group under surface plasmon catalysis

Technical Field

The invention belongs to the field of ionization reaction, and particularly relates to efficient ionization reaction of a compound with carboxylic acid groups under the catalysis of surface plasmons.

Background

In recent years, surface plasmon-driven surface-catalyzed chemical reactions have attracted considerable attention. The surface plasmon can collect a large amount of electromagnetic energy through Local Surface Plasmon Resonance (LSPR), and the electromagnetic energy is converted into reaction molecules to overcome an energy barrier in the reaction, so that the catalytic reaction is smoothly carried out. When light is incident on the nanoparticles made of noble metals, if the light is incidentIf the frequency of the daughter is matched to its vibration frequency, the nanoparticle will strongly absorb the photon energy and the LSPR phenomenon will occur. In this process, a large number of thermal electrons are generated due to the attenuation of the plasmon and a large amount of kinetic energy is provided to enable some chemical reactions, and holes occurring in pairs with electrons are used to accomplish a large number of oxidation reactions. Since 1974, Fleischmann et al adsorbed pyridine molecules on a roughened silver electrode surface and then performed raman spectroscopy analysis to obtain raman spectra of a monolayer of pyridine molecules for the first time. Van Duyneet et al, through a number of experiments and systematic theoretical calculations, believe that this is a surface enhancement effect caused by rough surfaces, known as Surface Enhanced Raman Scattering (SERS). Since then, SERS has become very popular in detection and analysis due to its rapid, simple sample requirements. The most representative of these are the oxidation of 4-aminothiophenol (PATP) and the reduction of p-nitrobenzothiophenol (PNTP), which can be catalyzed by surface plasmon into another molecule of p-mercaptoazobenzene (DMAB). This molecule had a distinct 1142cm in the Raman spectrum^-1，1390cm^-1，1432cm^-1Characteristic peak with high recognition degree. In 2011, Sun et al, theoretically and experimentally demonstrated that two PATP molecules form a DMAB molecule by surface plasmon coupling under SERS conditions. The important research results of the reaction have important reference significance for the subsequent understanding and development of Raman.

In recent years, SERS technology has been used to monitor a large number of organic thiol compounds, and few studies have been made on compounds having carboxylic acid groups. Among them, p-mercaptobenzoic acid (4-MBA) among carboxylic acid molecules has attracted much attention from researchers, and has been particularly spotlighted in the field of SERS, which has led to various applications of such molecules. It is well known that 4-MBA has a simple structure, only thiol and carboxyl groups are attached to the benzene ring, but the presence of these two groups makes it irreplaceable. In addition, in a non-acidic solution environment, a double bond binding site can be realized by two groups of a mercapto group and a carboxyl group, thereby allowing the reaction to proceed efficiently. 4-MBA is commonly used as a probe molecule to detect the enhanced properties of substrates in SERS. In addition, asA compound with a carboxyl group, which is very sensitive to the surrounding pH environment, and thus can also be used in pH sensors and ion detection, compared to the molecules commonly used in raman (PATP and PNTP). 4-MBA is taken as a widely used probe molecule, ionization reaction occurs in SERS, and in the process, proton hydrogen is lost and ionization balance is broken, so that new COO-groups are generated. The main step in some reactions in organic chemistry is the reaction of H⁺Is lost. Therefore, efficient ionization reactions of carboxylic acid molecules are beneficial. From a number of previous studies, 4-MBA is known to have some ionization, but the effect of this reaction is not very optimistic.

Disclosure of Invention

The purpose of the present invention is to search for an ionization reaction of a compound having a carboxylic acid group with the aid of a surface plasmon.

The technical scheme adopted by the invention is as follows: the method for the efficient ionization reaction of the compound with the carboxylic acid group under the catalysis of the surface plasmon comprises the following steps: dissolving a compound with a carboxylic acid group in ethanol, mixing the obtained ethanol solution of the compound with the carboxylic acid group with the SERS substrate, and irradiating by laser.

Preferably, in the efficient ionization reaction, the SERS substrate is Ag NPs.

Preferably, the preparation method of the Ag NPs comprises the following steps: dissolving silver nitrate in deionized water, heating, quickly adding a sodium citrate solution after the solution is boiled, and continuously reacting for 15-18min at 100-130 ℃ to obtain Ag NPs.

Preferably, in the above-mentioned high efficiency ionization reaction, the compound having a carboxylic acid group is DTBA.

Preferably, the concentration of the ethanol solution of DTBA in the high-efficiency ionization reaction is 10^-3～10^-7mol/L。

More preferably, the concentration of the ethanol solution of DTBA in the high-efficiency ionization reaction is 10^-5mol/L。

Preferably, the efficient ionization reaction is carried out at a volume ratio of 1:1 in an ethanol solution of DTBA to Ag NPs.

Preferably, the conditions of the high efficiency ionization reaction and the laser irradiation are that the laser intensity is 0.85-8.5 mW and the wavelength is 633 nm.

The invention has the advantages that

1. The invention prepares SERS substrate Ag NPs with enhancement effect by a simple method, and respectively realizes the ionization reaction of DTBA and 4-MBA molecules.

2. The core of the invention is that the bimolecular mechanism of DTBA effectively promotes the ionization reaction and realizes more efficient ionization.

3. The DTBA molecule with the bimolecular mechanism explored by the invention not only realizes more efficient ionization, but also has certain stability in reaction. Under the monitoring of SERS, the occurrence of the efficient and stable ionization reaction has a certain reference value for the progress of further related reactions.

4. The present invention seeks to find a broad application in pH sensors and intracellular pH monitoring due to the carboxylic acid group of the DTBA molecule, which results in some sensitivity to pH. The invention adopts SERS technology to monitor, and uses SEM, ultraviolet-visible absorption spectrum and the like to characterize the surface property, appearance and structure. The results show that 4-MBA molecules can undergo ionization reaction in the presence of Ag NPs. On the basis of 4-MBA molecular ionization reaction, probe molecule DTBA capable of generating more efficient ionization reaction is explored, and the properties, the morphology and the structure of the probe molecule DTBA are characterized by utilizing a scanning electron microscope, an ultraviolet-visible absorption spectrum and a Raman spectrum. The results indicate that more efficient ionization of DTBA molecules does occur under surface plasmon catalysis. The invention realizes the simple, rapid and effective ionization reaction of the DTBA molecules, and provides certain reference for the reactions such as plasmon catalytic reaction, decarboxylation and the like in the future. By comparing DTBA and 4-MBA parallel experiments, DTBA has better Raman activity, higher reaction efficiency and more stable reaction than 4-MBA molecules. The results suggest the mechanism: under laser irradiation, DTBA molecules are destroyed to form bimolecules similar to 4-MBA, and are adsorbed on the surface of Ag NPs. This bimolecular coupling greatly increases the possibility of binding to Ag NPs, allowing ionization reactions to proceed stably and efficiently. Furthermore, the molecule has a carboxylic acid group, which results in a certain sensitivity to pH.

5. Compared with the ionization of 4-MBA molecules, the DTBA molecules have more efficient ionization effect, can be accurately monitored by an SERS technology, and the mechanism of DTBA molecular reaction is determined. When 4-MBA molecules are dispersed on a metal substrate, only one molecule will bind to the corresponding substrate. Because of the dispersion and free distribution of hot spots, the probability of binding is not high, and naturally, the ionization reaction does not proceed sufficiently. Therefore, it remains a challenge to achieve strong and stable raman signals. DTBA molecules have a symmetrical structure with respect to 4-MBA molecules, and if disulfide bonds can be broken, it is expected that a pair of 4-MBAs molecules will be dispersed on Ag NPs, thereby allowing more hot spots to aggregate and achieving an efficient ionization reaction. The invention firstly explores DTBA molecules, and based on the similarity of the DTBA molecules and 4-MBA molecular structures, the DTBA molecules are presumed to have certain ionization reaction, and because disulfide bonds in the DTBA molecules are destroyed under laser irradiation, bimolecules similar to 4-MBA are formed and adsorbed on Ag NPs, the bimolecular coupling greatly increases the possibility of reaction, and the ionization action of the DTBA molecules is much stronger than that of the 4-MBA molecules, and the reaction is relatively uniform and stable. In addition, based on the structure of the molecule with carboxylic acid groups, it is assumed that it has some sensitivity to pH. The method of the invention not only can be widely applied to pH sensors and intracellular pH monitoring, but also can provide reference for further decarboxylation reactions and other related reactions.

Drawings

FIG. 1 shows a Raman spectrum (a) of DTBA powder and a Raman spectrum (b) of 4-MBA powder.

Fig. 2 is an SEM image of silver nanoparticles.

FIG. 3 is an SEM image of DTBA-Ag NPs.

FIG. 4 is a diagram showing UV-vis absorption spectra of DTBA-Ag NPs (a) and 4-MBA-Ag NPs (b).

FIG. 5 is 10^-4UV-vis absorption spectra of mol/L DTBA solution mixed with Ag NPs of different concentrations.

FIG. 6 shows a Raman spectrum (a) of DTBA powder and a SERS spectrum (b) of DTBA-Ag NPs.

FIG. 7 is a SERS spectrum of DTBA-Ag NPs;

wherein, a) the start of laser irradiation; b) after 60 s; c) and (4) completely ionizing.

FIG. 8 is a 3D SERS spectrum of DTBA-Ag NPs (A) and 4-MBA-Ag NPs (B) systems respectively varying with concentration.

FIG. 9 is a 3D surface scan of 4-MBA-Ag NPs.

FIG. 10 is a 3D map of DTBA-Ag NPs.

FIG. 11 is a pH dependent 3D SERS spectrum of DTBA-Ag NPs.

FIG. 12 is a diagram showing the mechanism of ionization reaction.

Detailed Description

For better understanding of the technical solution of the present invention, specific examples are described in further detail, but the solution is not limited thereto.

Example 1

Preparation of (I) SERS substrate-Ag NPs

Adding 100ml of deionized water into 18mg of silver nitrate, stirring and dissolving, heating, quickly adding 2ml of 1% sodium citrate solution when the solution is boiled, continuing to react for 15-18min at 100 ℃, and stopping the reaction to obtain the SERS substrate-Ag NPs.

(II) ionization reaction of 4-MBA under surface plasmon catalysis

4-MBA (p-mercaptobenzoic acid) is respectively connected with a mercapto group and a carboxyl group at the para position of a benzene ring, and the structural formula is as follows:

the ionization reaction method comprises the following steps: using absolute ethyl alcohol as solvent, and its preparation concentration is 10^-3～10^-7A 4-MBA ethanol solution of mol/L. Mixing the 4-MBA ethanol solution with the prepared Ag NPs according to the volume ratio of 1:1, and irradiating under laser (the laser intensity is 1.7mW, and the wavelength is 633 nm).

(III) ionization reaction of DTBA molecules under catalysis of surface plasmons

The structural formula of the DTBA (4,4' -dithiodibenzoic acid) molecule is as follows:

the ionization reaction method comprises the following steps: using absolute ethyl alcohol as solvent, and its preparation concentration is 10^-3～10^-7A mol/L DTBA ethanol solution. Mixing the DTBA ethanol solution with the prepared Ag NPs according to the volume ratio of 1:1, and irradiating under laser (the laser intensity is 1.7mW, and the wavelength is 633 nm).

(IV) characterization

1. FIG. 1 shows a Raman spectrum (a) of DTBA powder and a Raman spectrum (b) of 4-MBA powder. As can be seen from FIG. 1, the Raman peaks of these two molecules are very similar, especially at 1000-^-1The intermediate frequency range of (c). Structurally, the DTBA molecule corresponds to the loss of H from each of the two 4-MBA molecules⁺Then linked by a disulfide bond, i.e., equivalent to 1 DTBA molecule consisting of two 4-MBA molecules, both of which have similar structures. This is demonstrated in figure 1 by the similarity of the raman characteristic peaks of dtba (a) and 4-mba (b). Curve b in FIG. 1 is 2564cm^-1There is shown a clear raman peak due to the-SH characteristic vibrational peak, indicating the presence of an-SH group in the 4-MBA molecule. Figure 1 not only shows the similarity of the two molecular structures, but also analyzes the molecular structures and also ensures the purity of the two drugs.

2. Fig. 2 is an SEM image of silver nanoparticles (Ag NPs). As can be seen from fig. 2, the synthesized Ag NPs exist mainly in a spherical shape, and appear in a somewhat rod shape. It can be seen that its surface is rough, increasing the number of "hot spots" of the plasmon-driven chemical reaction, and further enhancing the intensity of plasmon resonance. The desired SERS substrate is known to be successfully synthesized.

3. FIG. 3 is an SEM image of DTBA-Ag NPs. As can be seen from FIG. 3, not only the DTBA molecules are present, but also a plurality of spherical silver particles are embedded on the surface and at the gaps, and the Ag NPs are smaller compared with the DTBA molecules. The key point is that the Ag NPs and DTBA molecules do not exist in a self-dispersed state, but are attached together, and the phenomenon can be preliminarily guessed that the Ag NPs and the DTBA molecules have better interaction.

4. FIG. 4 is a diagram showing UV-vis absorption spectra of DTBA-Ag NPs (a) and 4-MBA-Ag NPs (b). Ag NPs were added to the cuvette (the amounts of both Ag NPs were controlled to be 70. mu.L, respectively), and then each was added at a concentration of 10^-4Putting the ethanol solution of DTBA in mol/L or the ethanol solution of 4-MBA into a cuvette, fully mixing, and carrying out ultraviolet test. As can be seen from FIG. 4, the absorption peaks appearing at around 430nm of the DTBA-Ag NPs are attributed to the characteristic absorption peaks of the Ag NPs, the DTBA-Ag NPs are red-shifted compared with the 4-MBA-Ag NPs system, more importantly, a new absorption peak appears near 580nm, the absorption peaks in the DTBA-Ag NPs system appear more obviously and the intensity of the Ag NPs is reduced more, and the ionization reaction between the DTBA and the Ag NPs is judged to be stronger than the interaction between the 4-MBA and the Ag NPs.

5. FIG. 5 shows the concentration of 10^-4UV-vis absorption spectra of mol/L DTBA solution mixed with Ag NPs of different concentrations. Adding Ag NPs with different volumes into the cuvette respectively, and then adding the Ag NPs with the concentration of 10^-4And (3) putting the mol/L DTBA solution into a cuvette, fully mixing and carrying out ultraviolet testing. As can be seen from fig. 5, the intensity of the new absorption peak appearing around 587nm gradually increases with the increase in the content of Ag NPs, and the new absorption peak appears more and more clearly. This procedure not only demonstrated sufficient interaction between DTBA and Ag NPs, but indirectly demonstrated the enhanced effect of Ag NPs on DTBA molecule production.

6. FIG. 6 is a Raman spectrum of DTBA powder (a) and a SERS spectrum of DTBA-Ag NPs (b). In the corresponding Raman spectra of the DTBA powder, it can be clearly seen at 1075 and 1587cm^-1Are provided with prominent Raman peaks respectively corresponding to v_8aAnd v₁₂The vibration of the aromatic ring indicates that the molecule has a benzene ring structure. In contrast to the Raman spectrum corresponding to DTBA powder, in the SERS spectrum of DTBA-Ag NPs, it can be seen that the Raman spectrum is 1380cm^-1A new absorption peak appears, which is attributed to the characteristic vibrational peak of COO-, demonstrating that the DTBA molecule undergoes an ionization reaction. It can be noted that DAfter the TBA molecules interact with the Ag NPs, the characteristic peak of the ring is slightly changed, but the basic structure of the benzene ring is not changed.

7. FIG. 7 is a SERS spectrum of DTBA-Ag NPs at the beginning (a), 60s later (b) and complete ionization (c) of laser irradiation (laser wavelength 633 nm). The ionization reaction of DTBA occurs easily, but its high efficiency must be observed at a suitable power and wavelength. However, in order to analyze the reaction process, very weak plasmon intensity is required. As can be seen from fig. 7, the a curve shows the reaction at low plasmon, the b curve shows the SERS spectrum of DTBA when the plasmon intensity is increased after 60s, and the c curve shows the sufficient ionization spectrum of DTBA when the plasmon intensity is strong. Fig. 7 clearly shows the ionization reaction of DTBA molecules depending on plasmon intensity. The DTBA molecule itself can be clearly observed under weak plasmons, a in fig. 7. When the intensity of the plasmon increases, an intermediate state, b in fig. 7, can be seen in which the product after DTBA ionization and the reactant before ionization exist. Finally, when the plasmon intensity is increased to some extent, it can be seen that almost all the substances are ionized products, c in fig. 7. The results show that the high-intensity surface plasmon requires laser with proper wavelength and laser power, so that the reaction is more fully performed.

8. FIG. 8 is a 3D SERS spectrum of DTBA-Ag NPs (A) and 4-MBA-Ag NPs (B) systems respectively varying with concentration. The intensity of the plasmons may also be affected by the concentration. Therefore, suitable concentration conditions are discussed herein. As can be seen from FIG. 8, in both systems, the reaction concentration was 10^-5At mol/L, the ionization reaction can proceed more sufficiently, however, the higher the reaction concentration is, the stronger the plasmon intensity is not. On the contrary, it can be seen that when the concentration of the carboxylic acid molecule is 10^-3At mol/L, it can be seen that the concentration is 1700cm^-1A characteristic raman peak appeared nearby, which was attributed to the stretching vibration peak of C ═ O, indicating that this reaction did not proceed sufficiently at this concentration. Meanwhile, it can be seen that in the DTBA-Ag NPs system, the ionization effect is obviously better than that of the reaction of the 4-MBA-Ag NPs system. Thus, the entire SERS isIn the test, the selection concentration is 10^-5The mol/L solution was used as the reaction solution.

9. FIG. 9 is a 3D surface scan of 4-MBA-Ag NPs. As can be seen in FIG. 9, the 4-MBA molecule is 1380cm^-1The existence of a COO-characteristic vibration peak can prove that the molecule is subjected to ionization reaction, but the SERS signal peak is not very strong. The signal peaks exhibited by the 4-MBA-Ag NPs were not very strong over the entire swept area, and the peaks were relatively dispersed over the entire swept area of the 4-MBA molecule, indicating that the 4-MBA molecule was not susceptible to ionization.

10. FIG. 10 is a 3D map of DTBA-Ag NPs. As can be seen from FIG. 10, the molecule DTBA was found at 1380cm^-1Is very strong and the signal peak displayed over the entire sweep area is very strong. Furthermore, it can be seen that in the ionization reaction of DTBA molecule, at 1075cm^-1And 1587cm^-1The characteristic peak at (a) is also very strong. In addition, the raman signal present in DTBA molecules is not only strong but also very uniform and well ordered. As can be understood from a comparison of fig. 10 and 9, when laser light is irradiated onto the carboxylic acid molecules, the connection between the bimolecular 4-MBAs-like molecules and the Ag NPs greatly increases the possibility of their interaction and promotes efficient occurrence of ionization reactions. The mechanism provides a certain reference for the research of the reaction of the carboxylic acid compounds.

11. FIG. 11 is a pH dependent 3D SERS spectrum of DTBA-Ag NPs. As is clear from fig. 11, the SERS signal peak intensity of the DTBA molecule increases with increasing pH of the solution. Large amount of H in acid environment⁺The presence of (A) can hinder the reaction, since H⁺A large number of electrons are trapped and the intensity of the plasmon is reduced. However, in an alkaline environment, a large number of OH groups^-The presence of the group will provide some assistance in the progress of the ionization reaction, indicating that an alkaline environment is favorable for the ionization reaction to occur. Furthermore, in an alkaline environment, sulfur atoms and COO-are simultaneously bonded to the surface of Ag NPs, and the increase of the number of bonding points is also very advantageous for this reaction. Due to the sensitive response of carboxylic acid molecules to pH changes, carboxylic acid molecules have wide application in pH sensors and intracellular pH monitoring.

Claims

1. The method is characterized in that the method comprises the following steps: dissolving a compound with a carboxylic acid group in ethanol, mixing the obtained ethanol solution of the compound with the carboxylic acid group with the SERS substrate, and irradiating by laser.

2. The high efficiency ionization reaction of claim 1, wherein the SERS substrate is Ag NPs.

3. The efficient ionization reaction of claim 2, wherein the Ag NPs are prepared by the following steps: dissolving silver nitrate in deionized water, heating, quickly adding a sodium citrate solution after the solution is boiled, and continuously reacting for 15-18min at 100-130 ℃ to obtain Ag NPs.

4. The high efficiency ionization reaction of claim 2, wherein the carboxylic acid group bearing compound is DTBA.

5. The efficient ionization reaction of claim 4, wherein the concentration of the ethanol solution of DTBA is 10^-3～10^-7mol/L。

6. The efficient ionization reaction of claim 5, wherein the concentration of the ethanol solution of DTBA is 10^- ⁵mol/L。

7. The efficient ionization reaction of claim 5, wherein the ratio of the ethanol solution of DTBA to Ag NPs is 1:1 by volume.

8. The efficient ionization reaction according to claim 4, wherein the laser irradiation is performed under conditions of a laser intensity of 0.85 to 8.5mW and a wavelength of 633 nm.