In order to elucidating the exact effect mechanism of polyphenols on the assembly of collagen, the assembled architectures of collagen treated with different amounts of procyanidin (PA) were investigated in details. The assembled morphologies of collagen were greatly influenced by the content of PA according to atomic force microcopy (AFM) images.When the content of PA was more than 20% (w/w), the fibrillar morphologies were substituted by globular aggregates, which were driven by the intense hydrogen bonding action originating from PA. While the formation of the non-fibrous aggregates was due to the coiling and entangling of flexible collagen molecules rather than their gelatinization based on the appearance of typical adsorption peaks at 222nm and 197nm on circular dichroism (CD) spectra. After being crosslinked by glutaraldehyde (GA), not only the diameters but also the lengths of fibrils increased. Unfortunately, the fibrillogenesis was still inhibited when the collagen suffered from 20% PA firstly and then 4% GA. Conversely, the fibrous morphologies of the fibrils stabilized by 4% GA and then underwent 20% PA maintained well, in spite of accompanying with grievous intertwining. This difference was derived from the change of flexibilities of collagen before and after being crosslinked by GA. Additionally, the differential scanning calorimeter (DSC) analysis confirmed the PA had no positive effect on the improvement of thermal stability of hydrous collagen, whereas the denaturation temperature of hydrated collagen stabilized by 4% GA increased from 40 °C to 80 °C.

In this paper, we established a sequential injection method to monitoring the concentration of total dissolved nitrogen (TDN) in seawater, which combined with an UV-thermal digestion. The sequential injection method consumes less reagents and less time, mixes more evenly than the flow injection method. TDN detection process mainly includes three parts: the digestion process of conversion organic nitrogen to nitrate, the reduction process of nitrate to nitrite, and the process of reaction between nitrite and chromogenic agent. The UV-thermal digestion that transforms dissolved organic nitrogen (DON) into nitrate has the highest digestion efficiency. The nitrate reduction process with a UV lamp is considered a greener choice which avoids the toxic substance and complicated operation of cadmium column reduction. We analyzed the optimal concentrations of all the reagents used in the experiment with the univariate experimental design. The reaction conditions were optimized by using three kinds of DON, which were C2H5NO2, CH4N2S and C10H14N2Na2O8. Under the optimal reaction conditions, we tested the seawater in the Qingdao Sculpture Garden and the recovery rate of adding standard. In May, the TDN concentration of seawater in Qingdao Sculpture Garden was 122.94μg/L, the relative standard deviation was 0.34%. The recovery rate was as high as 99.94% to 100.39%. The outcomes indicate that the proposed method can apply to the potential in-situ monitor.