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The organizational forms of infrastructure in China are divided into two categories, the traditional Public Procurement Model (PUB) model and Public–Private Partnership(PPP) model. The main difference is the separation or binding of the construction and operation phases. A systematic understanding is needed of how Chinese local governments choose between these two models. In this paper, we take public capital congestion and local government objectives as the entry point to study the effects of both on PPP choice. Firstly, by constructing an endogenous economic growth model under the PPP model, and comparing it with the model under the PUB model, this paper initially explains how the rise in public capital congestion affects the choice of the PPP by growth-oriented local governments. Then the data from prefecture-level cities from 2009–2018 are utilized to conduct empirical tests. We find that urban economic growth pressures have a positive effect on the choice of PPP when the congestion of public capital increases. Furthermore, the implementation of PPP is indeed conducive to economic performance, and its core mechanism is to provide more infrastructure (like roads) rather than tax competition. The PPP model is more sustainable. We are the first to employ both modeling approach and the empirical research to address the implementation of Public–Private Partnership in China. And we have systematically analyzed the conditions and results of PPP selection by local governments. It formulates the Chinese PPP theory. [ABSTRACT FROM AUTHOR]

As a global environmental pollution problem, heavy metal pollution has brought great harm to human beings. In this work, we studied the toxicity of Hg2+ on allophycocyanin (APC) at the molecular level. Firstly, APC was extracted and purified from Spirulina platensis mud and its purity (A650/A280) reached 3.75. In addition, the fluorescence intensity of APC decreased with increasing Hg2+ concentration from 0 to 5 × 10-6 mol L−1. The theoretical calculation and experimental results showed that the fluorescence quenching of APC by Hg2+ was static and had a good linear relationship. Moreover, the UV-Vis spectra of APC showed a significant decrease at 200 nm and 650 nm with the increase of Hg2+ concentration from 0 to 5×10−6 mol L−1, and a red-shift at 200 nm, which indicated that Hg2+ not only affected the structure of APC but also affected the light absorption and photosynthetic function of APC. Furthermore, the results of molecular simulation demonstrate that Hg2+ combinations with the Met77, Cys81 in the α chain and the Arg77, Cys81 in the β chain, which interact between the peptide chain and the chromophore, and Hg2+ forms a Hg-S bond with -SH. This study provides new insights into the structure and how Hg2+ effect the optical properties of APC. [ABSTRACT FROM AUTHOR]