| As a plant growth regulator, ethylene can mediate a variety of growth phenomena including ripening and senescence in plants. So ethylene has been regarded as the "ripening hormone".1-methylcyclopropene (1-MCP) have been found to be effective ethylene antagonists of ethylene action. Since it is non-toxic, active at relatively low concentration, and providing protection for a longer period, so 1-methylcyclopropene (1-MCP) has now been approved commercially for application on horticultural products. However, under normal environmental conditions,1-MCP is gaseous and chemically unstable. Furthermore, it presents an explosive hazard when compressed. To solve these problems, several methods have been developed to incorporate 1-MCP into molecular encapsulation agents。Now 1-MCP/a-CD is commercially available under the trade name SmartFreshTM.Cucurbit[n]urils (CB[n], n is the number of glycoluril units) are barrel-like macrocyclic molecules, which has a similar hydrophobic cavity as cyclodextrins, the internal cavity volume vary with the unit number change, and the cavity size of CB[6] is similar to that of a- CD. CB[6] are prepared from cheap starting materials and suitable for industrial production.(1) In this paper, the inclusion complex of 1-methylcyclopropene with CB[6] was prepared, and it was characterized with IR and UV-vis absorption, X-ray powder diffraction(X-RD), thermo-gravimetric analysis and fluorescent spectra. The difference of the inclusion complex was compared in spectral characteristics, which confirms the formation of the inclusion complex.(2) The optimum conditions of the initial concentration of 1-MCP, CB[6] concentration and encapsulation temperature were discussed. The 1-MCP/CB[6] inclusion complex was prepared while the initial concentration of 1-MCP, CB[6] concentration, encapsulation temperature and time was 75 mL/L,30 mM,20℃, and 8 h. The adsorption quantity of 1-MCP in the 1-MCP/CB[6] inclusion complex is around 4.5% by weight.(3) The mass fraction of 1-MCP from inclusion complexes which prepared by different ways were compared, and optimized the best preparation methods by FT-IR, GC and TG.(4) The dynamics of adsorption 1-MCP on CB[6] was discussed. Two equations were tested to interpret the experimental data, compared with the pseudo-first order kinetic model, the pseudo-second order kinetics model was more suitable for describing the process of adsorption 1-MCP on CB[6]. The amount of 1-MCP absorbed by absorbent (Q) by fitting pseudo-second order kinetics model were similar with the value obtained by experiments. The activation energy of the reaction was 48.49 kJ/mol by applying the Arrhenius equation.(5) The release of 1-MCP from the 1-MCP/CB[6] inclusion complex in different solutions, such as benzoic acid, sodium bicarbonate and distilled water was investigated. Gas chromatography was employed for the quantification of the 1-MCP released. It showed that the released 1-MCP immediately reached the concentration peak after only 10 min in sodium bicarbonate solution, while for the benzoic solution it take about 90 min to arrive at the largest concentration. As for distilled water more than 2 h was needed to achieve the largest concentration of released 1-MCP.(6) The stability of the 1-MCP/CB[6] inclusion complex was discussed, and gas chromatography was employed for the quantification of the 1-MCP released from the inclusion complex which saved different time. It can be seen from the gas chromatogram, the concentration of 1-MCP was still not changed after saved 3 months, which proved the good stability of the 1-MCP/CB[6] inclusion complex. |
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