CN113087715B - Method for preparing porphyrin self-assembly nano structure by microemulsion method - Google Patents

Abstract

The invention discloses a method for preparing a porphyrin self-assembly nano structure by a microemulsion method. According to the method, tetraoctyl ammonium bromide is used for forming a microemulsion so as to help the nucleation and growth of zinc tetraphenylporphyrin, and porphyrin molecules are induced to be assembled under the action of an emulsifier, so that the self-assembled porphyrin nanostructure is prepared. Compared with the original porphyrin monomer, the positive charge TOAB can excite the internal oxidation-reduction property of porphyrin, and the synthesized porphyrin nanocrystal has stronger electrochemiluminescence property under the condition that oxygen is used as a coreaction reagent.

Description

Method for preparing porphyrin self-assembly nano structure by microemulsion method

Technical Field

The invention belongs to the field of electrochemiluminescence materials, and relates to a method for preparing a porphyrin self-assembly nano structure by a microemulsion method.

Background

Electrochemiluminescence (ECL) is a process in which a substance generated on an electrode undergoes a high-energy electron transfer reaction to form an excited state, returns to a ground state, and emits light. In other words, ECL is chemiluminescence triggered by an electrochemical method, has the advantages of time-space controllability of electrochemical reactions, simplicity and convenience in operation, and the like, has the characteristics of high sensitivity, wide linear range and the like of chemiluminescence analysis, is a combination of the electrochemical method and chemiluminescence, and is widely applied to many fields. ECL reactions typically require luminophores, also known as chemiluminescent reagents. Several classical ECL luminophores have been reported and extensively studied today, such as luminol, tris (2, 2-bipyridyl) ruthenium (II) (Ru (bpy) ₃ ²⁺ ) Quantum dots and porphyrins. However, ECL still suffers from drawbacks such as poor reproducibility of the electrochemical cycling of the individual luminophores, broad emission spectrum and loss of signal from ECL reagent leaving the detection zone. Therefore, further improvement of ECL signal is still of great significance. Research shows that the nano material can be used for constructing a novel ECL luminophor and applied to an ECL sensor to improve efficiency.

Porphyrins are macromolecular heterocyclic compounds with 18-pi electrons formed from a regular arrangement of four pyrroles interconnected by methine bridges (= CH-). Porphyrins have unique aromatic structures and beneficial properties (e.g., high molar absorption) and are key substances in biological processes (e.g., photosynthesis, oxygen transport, and biocatalysis), and thus, the electrochemical and photochemical properties of porphyrins have been of interest for decades. Porphyrin, a natural pigment derived from animals and plants, has excellent optical characteristics and rigid planar molecular structure, so that the porphyrin becomes an ideal base stone for synthesizing a photoactive nano material. In addition, the diversity of peripheral functional groups and central metals allows porphyrins to have a variety of properties and assembly modes, and more importantly, most porphyrin molecules can be used as good luminescent materials. However, the absorption range of the porphyrin monomer in the visible light region is relatively narrow, and the porphyrin monomer is easily corroded by light.

The J-aggregate formed by porphyrin has unique structure and photophysical properties, and has potential application prospect in nonlinear optics, nano photoconductors and photosystems. Studies indicate that fine adjustment of intermolecular arrangement and noncovalent interactions (such as hydrogen bonding, pi-pi stacking, hydrophilic or hydrophobic interactions, ligand coordination, etc.) can enhance the luminescent properties of porphyrins in self-assembled porphyrin structures.

Microemulsions (micro-emulsions) are thermodynamically stable colloidal dispersions of water and oil stabilized by surfactants and cosurfactants. Co-surfactants are typically required to reduce facial tension by three to four orders of magnitude, which is critical to forming a microemulsion. Generally, microemulsions may be composed of a variety of ingredients; however, the structure of the microemulsion may vary from spherical droplets to coarse agglomerates, depending on the composition of the microemulsion and the nature of the surfactant, the volume ratio and viscosity difference of the two phases, the nature, concentration and temperature of the surfactant, etc. being factors affecting the type of emulsion. Nowadays, the microemulsion method has become a common synthetic method for nano-crystallizing materials. A series of nanoparticles such as metal simple substance, metal sulfur, oxide and their composite material are prepared by microemulsion method. At present, no report of preparing porphyrin self-assembly nano structures by adopting a microemulsion method exists.

Disclosure of Invention

The invention aims to provide a method for preparing a porphyrin self-assembly nano structure by a microemulsion method. The method utilizes microemulsion as a nano reactor to automatically assemble and synthesize porphyrin nano particles, controls the size of the porphyrin nano particles by the non-covalent interaction of the microemulsion in the process of limiting nucleation and growth, and synthesizes a novel self-assembled porphyrin nano structure.

The technical scheme for realizing the purpose of the invention is as follows:

a method for preparing porphyrin self-assembly nano-structure by a microemulsion method, wherein tetraoctyl ammonium bromide (TOAB) is used to form a microemulsion to help the nucleation and growth of zinc tetraphenylporphyrin (Zn (II) meso-tetraphenylphorphyrin chloride, znTPP), comprises the following steps:

chloroform (CHCl) of zinc tetraphenylporphyrin ₃ ) Adding the solution into tetraoctyl ammonium bromide aqueous solution, emulsifying the solution to form uniform microemulsion through ultrasonic treatment, heating the solution in a water bath to remove chloroform, continuously stirring the solution, inducing porphyrin molecules to be assembled under the action of an emulsifier, cooling, centrifuging, washing and drying the assembled porphyrin molecules to obtain the self-assembled porphyrin nanostructure (ZnTPP-TOAB).

Preferably, the concentration of the chloroform solution of zinc tetraphenylporphyrin is 10mg/mL.

Preferably, the concentration of the aqueous tetraoctylammonium bromide solution is 30mM.

Preferably, the ratio of the mass of zinc tetraphenylporphyrin to the molar amount of tetraoctylammonium bromide is 50: mmol of the active component.

Preferably, the sonication time is above 5 min.

Preferably, the temperature of the water bath heating is 65. + -. 5 ℃.

Preferably, the continuous stirring time is 24 hours or more.

Preferably, the centrifugation speed is 12000rpm.

Compared with the prior art, the invention has the following advantages:

(1) The oil phase is evaporated to increase the concentration of ZnTPP in the microemulsion drop, and the self-assembly of ZnTPP porphyrin into ordered nano-crystals is triggered through non-covalent interactions such as pi-pi accumulation, hydrophobic-hydrophobic interaction and the like, so that the ZnTPP nano-rods with high quality and high crystallinity are finally successfully synthesized.

(2) Ordered pi-pi accumulation and long-range delocalization in the porphyrin assembly body enable the prepared porphyrin self-assembly nano material to have a wider visible light absorption spectrum.

(3) Compared with commercial ZnTPP porphyrin powder, the porphyrin self-assembled nano material prepared by the invention has stronger electrochemiluminescence performance.

(4) The X-ray diffraction analysis shows that the main peak is between 5 and 30 degrees, and the shape of the XRD peak of ZnTPP-TOAB is sharp, which shows that the ZnTPP-TOAB has a good crystal structure.

Drawings

FIG. 1 is a scanning electron micrograph of (A) ZnTPP and (B) ZnTPP-TOAB.

FIG. 2 is a graph showing (A) the UV-visible absorption spectrum and (B) the IR spectrum of ZnTPP (curve a), TOAB (curve B) and ZnTPP-TOAB (curve c).

FIG. 3 is an X-ray diffraction spectrum of ZnTPP-TOAB.

FIG. 4 shows (A) ZnTPP/GCE (a) and ZnTPP-TOAB/GCE (b) in O ₂ Saturated 10mmol L ^-1 ECL potential scan curve in pH 7.4HEPES electrolyte; (B) ECL-time response curve of ZnTPP-TOAB/GCE in aqueous solution, potential scanning range is-1.6-0V, and scanning speed is 50mV s ^-1 。

FIG. 5 shows (A) TOAB/GCE, (B) ZnTPP/GCE and (C) ZnTPP-TOAB/GCE in N ₂ Saturation of (a) and O ₂ CV curve in saturated (b) 10mM HEPES electrolyte containing 0.3M KCl, scan rate: 50mV s ^-1 。

FIG. 6 shows ZnTPP-TOAB/GCE on N ₂ Saturation (a), air saturation (b) and O ₂ ECL-voltage response curves in saturated (c) 10mM HEPES buffer solution with 0.3M KCl at pH 7.4.

Detailed Description

In order to facilitate understanding of the present invention, the present invention will be described in further detail with reference to the following examples and accompanying drawings.

The invention synthesizes a new self-assembled porphyrin nano structure by limiting non-covalent interaction in the nucleation and growth processes through microemulsion. The microemulsion-assisted self-assembly technology synthesizes novel ZnTPP-TOAB nanocrystals. Compared with the original porphyrin monomer, the TOAB with positive charge can excite the internal oxidation-reduction property of porphyrin, and the synthesized porphyrin nanocrystal has strong electrochemiluminescence property under the condition that oxygen is used as a coreaction reagent. And (3) sealing and storing the obtained product at the temperature of 25 +/-5 ℃, and then performing characterization on an ultraviolet-visible absorption spectrum, an infrared spectrum, an SEM (scanning electron microscope) and an XRD (X-ray diffraction spectrum).

In the following examples, the measurement method of the electrochemiluminescence property of the material is as follows:

a glassy carbon electrode of 3mm diameter was drop coated with 0.3 and 0.05 μm γ -Al in sequence ₂ O ₃ Polishing the chamois leather of the saturated aqueous solution, then carrying out ultrasonic cleaning by using ultrapure water and ethanol in sequence, and finally blowing and drying by using nitrogen. mu.L of ZnTPP-TOAB solution (1 mg-mL) ^-1 ) And (4) dripping the solution on the surface of GCE, and drying at room temperature to obtain the modified electrode ZnTPP-TOAB/GCE. Example ZnTPP-TOAB/GCE was investigated in the presence of 0.3mmol L ^-1 10mmol L of KCl ^-1 (pH 7.4) HEPES electrolyte in O ₂ ECL behavior in saturated regime.

In the following examples, the electrochemical properties of the materials were determined as follows:

first, 1.0mg of the porphyrin-based assembly structure (i.e., znTPP-TOAB) was dispersed in 1mL of deionized water and sonicated for 5 minutes to fully disperse the material. The GCE was mechanically polished with 0.3 and 0.05 μm alumina powder, then ultrasonically cleaned in ethanol and double distilled water, respectively, the GCE was rinsed with pure water, and dried under a nitrogen stream. And coating the 20 mu LZnTPP-TOAB solution on the surface of the glassy carbon electrode, and air-drying at room temperature to obtain a modified electrode, which is recorded as ZnTPP-TOAB/GCE. For the control experiment, znTPP dispersions (1 mg mL) were also used separately according to the same procedure ^-1 ) And TOAB (1 mg mL) ^-1 ) The solution was prepared ZnTPP/GCE and TOAB/GCE. In the absence and presence of oxygen, different modified electrodes were compared at 0.3mol L ^{- 1} CV curve in KCl in 10mM HEPES solution. Electrochemical testing used a CHI660D electrochemical workstation, and the auxiliary electrode and the reference electrode were a 2mm platinum wire and a saturated calomel electrode, respectively.

Example 1

1. The method for preparing the porphyrin self-assembly nano structure by the microemulsion method comprises the following steps:

step one, dissolving 5mg zinc tetraphenylporphyrin in 0.5mL chloroform, carrying out ultrasonic treatment, fully dissolving, and storing in dark place. 10mL of a 30mM aqueous solution of tetraoctylammonium bromide was prepared as an aqueous emulsifier solution.

And step two, adding the fully dissolved porphyrin solution into an emulsifier aqueous solution under continuous stirring, emulsifying to form uniform microemulsion after 5-minute strong ultrasonic treatment, then putting the microemulsion into a constant-temperature water bath kettle at 65 ℃, heating and stirring for one hour to volatilize and remove chloroform, continuously stirring the mixture at the temperature for 24 hours, and inducing the porphyrin molecules to be assembled under the action of the emulsifier.

And step three, after cooling, centrifuging the final product at 12000rpm, almost colorless supernatant, pouring out the supernatant, and washing the remaining dark green precipitate with deionized water for 3 times.

And step four, drying in a vacuum freeze dryer to obtain sample powder. The product was labeled ZnTPP-TOAB.

2. And (3) characterization:

1. and (3) morphology characterization:

the results of SEM testing of both the ZnTPP and ZnTPP-TOAB materials are shown in FIG. 1. FIGS. 1 (A) and (B) show the morphologies of original ZnTPP and ZnTPP-TOAB, respectively. The ZnTPP precursor presents a random blocky structure, and the random size is 20-60 mu m. However, the synthesized ZnTPP-TOAB has a "rod-like" or "granular" structure with a small size, random size of 100-500nm and an average size of about 350 nm.

2. Structural characterization:

and carrying out ultraviolet-visible spectrum, infrared spectrum and X-ray diffraction spectrum tests on ZnTPP-TOAB, znTPP and TOAB synthesized by a microemulsion method.

In order to explore the assembly process of the ZnTPP-TOAB structure, the spectral properties were characterized. The ZnTPP-TOAB nanostructure showed optical properties that were totally different from those of the original ZnTPP (fig. 2). The UV-visible spectrum of ZnTPP shows a strong Soret band (B band) at 420nm and two Q bands at 555 and 596nm (curve a of FIG. 2A); TOAB has no distinct uv absorption peak (curve b of fig. 2A); as for ZnTPP-TOAB (curve c of FIG. 2A), the maximum Soret band is located at 433nm, the Q band produces a red-shifted band, and finally at 565 and 615nm. This red-shift phenomenon of the Q band reveals a conjugation between the porphyrin substituent and the porphyrin ring, resulting in a decrease in the energy level transition of the porphyrin ring. This is beneficial because it is the exciton coupling between states associated with exciton transport. The change in the ultraviolet spectrum of ZnTPP-TOAB may be due to chelation of TOAB in the assembled structure of the porphyrin.

To further characterize the TCPP nanostructures, an infrared spectroscopy (FT-IR) experiment was performed, as shown in FIG. 2B, at about 1594cm in the FT-IR spectrum of ZnTPP (curve a of FIG. 2B) ^-1 The strong C = C stretching vibration peak can be observed at 1439cm ^-1 And 1337cm ^-1 The peak at (A) is respectively attributed to the bending vibration of C-H and the stretching vibration of C = N, 1065cm ^-1 The absorption peak is consistent with the absorption peak of the phenyl stretching vibration infrared spectrum and is 993cm ^-1 A strong absorption peak was observed, which was attributed to the stretching vibration of N-Zn. FT-IR spectrum of TOAB (curve B of FIG. 2B), 2958, 2922 and 2848cm ^-1 Peaks at (A) are ascribed to the respective antisymmetric and symmetric-CH of the carbon chain ₂ -stretching vibration at 1467cm ^-1 The absorption band at is from-CH at the tail of TOAB ₂ Caused by flexural vibrations, 721cm ^-1 The absorption peak of the region is methylene (-CH) ₂ -) groups, which are in accordance with the reports in the literature. The infrared spectrum of ZnTPP-TOAB (curve c in FIG. 2B) does not differ significantly from that of TOAB, but only at 1594cm ^-1 There appears a peak, which is the characteristic absorption peak of the C = C stretching vibration in the porphyrin. This indicates that the TOAB participates in the porphyrin self-assembly reaction and that the bond in ZnTPP-TOAB is not significantly changed compared to TOAB.

The X-ray diffraction (XRD) analysis in fig. 3 shows that the main peak is between 5 ° and 30 °. The shape of the XRD peak of ZnTPP-TOAB is sharp, indicating that it has a good crystal structure.

3. Electrochemiluminescence performance testing:

the content of ZnTPP-TOAB/GCE in the solution containing 0.3mmol L was investigated ^-1 10mmol L of KCl ^-1 (pH 7.4) HEPES electrolyte in O ₂ ECL behavior in saturated regime. As shown in FIG. 4A, at O ₂ In the saturated electrolyte, no significant ECL signal was observed for ZnTPP/GCE (fig. 4A, curve a); and for ZnTPP-TOAB/GCE, at O ₂ In the saturated state, appearA cathodic ECL signal with an optical intensity of about 12400a.u. and an ECL peak at-1.5V (fig. 4A, curve b). However, ECL intensity decreased after consecutive cycles of scanning (fig. 4B). After 6 weeks of scanning, the ECL signal dropped about 8% and the intensity after 12 cycles was only 72% of the original intensity.

4. Electrochemical testing:

(1) In order to further disclose the ECL signal amplification mechanism of ZnTPP-TOAB/GCE, the electrochemical properties of different modified electrodes are researched.

FIG. 5 shows a comparison of different modified electrodes containing 0.3mol L in the absence and presence of oxygen ^-1 CV curve in KCl in 10mM HEPES solution. It can be seen that in the absence of O ₂ When is at N ₂ In the saturated electrolyte, neither TOAB/GCE nor ZnTPP/GCE had any significant electrochemical redox peaks (FIGS. 5A and B, curve a). Curve a in FIG. 5C shows that there are four reduction processes for ZnTPP-TOAB/GCE, at-0.58V, -1.16V, -1.43V and-1.57V, respectively, and the corresponding oxidation peaks at-0.06V, -0.37V, -1.13V and-1.49V, respectively. According to literature reports, it is speculated that a possible mechanism for the electrochemical behaviour of ZnTPP-TOAB/GCE is the cationic tetraoctylammonium cation (TOA) ⁺ ) So that the electron cloud of the porphyrin is unevenly distributed and easy to polarize. Thus TOA ⁺ Can be used as an accelerant for exciting the redox activity in the porphyrin ZnTPP, and is beneficial to the generation of the redox product of the porphyrin in the ZnTPP-TOAB structure. Thus, according to the electrochemical analogy of porphyrins, porphyrins in ZnTPP-TOAB/GCE undergo four electron reductions: zn ²⁺ TPP-TOAB→Zn ^·+ TPP-TOAB→Zn ⁰ TPP-TOAB→Zn ⁰ TPP ^·- -TOAB→Zn ⁰ TPP ^2— TOAB, corresponding to four electrochemical reduction peaks, respectively. At O ₂ In the saturated electrolyte, TOAB/GCE and ZnTPP/GCE have obvious reduction peaks at-0.59V and-0.84V respectively (FIGS. 5A and B, curve B), which indicates that both ZnTPP and TOAB are on O ₂ Has a certain catalytic action. For ZnTPP-TOAB/GCE, in O ₂ When present, all cathodic peak currents increased and the potentials shifted little (FIG. 5C, curve b), demonstrating ZnTPP-TOAB vs. O ₂ Has good catalytic action, and ZnTPP-TOAB nano-scale is added with the assistance of TOABThe structure can catalyze O at lower potential (-0.58V) ₂ Thereby generating a large amount of oxygen radicals O ₂ ^·- This is a key material for ECL luminescence. Combining the ECL and electrochemical behavior described above, it can be concluded that: the presence of TOAB can stimulate the redox in ZnTPP, the redox transition products of ZnTPP and O ₂ ^·- The presence of groups plays a crucial role in ECL systems.

5. Signal amplification mechanism for electrochemiluminescence

FIG. 6 shows the ECL behavior of ZnTPP-TOAB/GCE in electrolytes containing different concentrations of dissolved oxygen. As shown, the modified electrode is at O ₂ ECL intensity under saturated conditions was as high as 12400a.u. (fig. 6, curve c), which is 3.9 times the ECL intensity measured under air saturated conditions (fig. 6, curve b), which is at N ₂ 60 times the ECL intensity measured under saturated conditions (fig. 6, curve a). This indicates that oxygen as a co-reactant has a non-negligible effect on the enhancement of ECL performance.

The intensity of the ECL spectrum depends on the quality of the luminophore and its photochemical properties. As mentioned above, znTPP has no significant ECL performance because the internal redox properties of the monomeric porphyrins are not excited. For the synthesized ZnTPP-TOAB nanocrystal, TOAB is used as an accelerant to excite the internal redox activity of porphyrin ZnTPP, so that transition state products of a series of porphyrins are obtained, and the products are key substances for generating ECL signals.

Thus, based on experimental results and based on the general discussion above, a possible ECL mechanism is described by the following reaction equation:

O ₂ +e ^- →O ₂ ^·-

Zn ²⁺ TPP-TOAB+e ^- →Zn ^·+ TPP-TOAB

Zn ^·+ TPP-TOAB+O ₂ →Zn ²⁺ TPP-TOAB+O ₂ ^·-

Zn ^·+ TPP-TOAB+e ^- →Zn ⁰ TPP-TOAB

Zn ⁰ TPP-TOAB+O ₂ →Zn ^·+ TPP-TOAB+O ₂ ^·-

Zn ⁰ TPP-TOAB+e ^- →Zn ⁰ TPP ^·- -TOAB

Zn ⁰ TPP ^·- -TOAB+O ₂ →Zn ⁰ TPP-TOAB+O ₂ ^·-

Zn ⁰ TPP ^·- -TOAB+e ^- →Zn ⁰ TPP ^2- -TOAB

Zn ⁰ TPP ^2- -TOAB+O ₂ →Zn ⁰ TPP ^·- -TOAB+O ₂ ^·-

Zn ⁰ TPP ^2- -TOAB+O ₂ ^·- →Zn ^* TPP ^·- -TOAB+O ₂ ^-

Zn ^* TPP ^·- -TOAB→Zn ⁰ TPP ^·- -TOAB+hν。

Claims (3)

1. the method for preparing the porphyrin self-assembly nano structure by the microemulsion method is characterized by comprising the following specific steps:

adding a chloroform solution of zinc tetraphenylporphyrin into a tetraoctylammonium bromide aqueous solution, carrying out ultrasonic treatment to emulsify the solution to form a uniform microemulsion, heating the microemulsion in a water bath to remove chloroform, continuously stirring the solution for more than 24 hours, inducing porphyrin molecules to assemble under the action of an emulsifier, cooling, centrifuging, washing with water and drying after assembly is completed to obtain a self-assembled porphyrin nanostructure, wherein the concentration of the chloroform solution of zinc tetraphenylporphyrin is 10mg/mL, the concentration of the tetraoctylammonium bromide aqueous solution is 30mM, and the ratio of the mass of zinc tetraphenylporphyrin to the molar weight of tetraoctylammonium bromide is 50: mmol, temperature of water bath heating 65 + -5 deg.C.

2. The method of claim 1, wherein the sonication time is 5min or more.

3. The method of claim 1, wherein the centrifugation speed is 12000rpm.

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