Biosynthesis, Characterization, and Bioactivity of L-Alanyl-L-tyrosine in Promoting Melanin Synthesis.

L-Alanyl-L-tyrosine (L-Ala-Tyr) is a dipeptide formed by the condensation of L-alanine methyl ester and L-tyrosine. After entering the body, it can be rapidly broken down to release tyrosine. In this study, L-Ala-Tyr was successfully prepared by using α-ester acyltransferase as biocatalyst and alanine methyl ester (L-Ala-OMe) and tyrosine (L-Tyr) as acyl donor and nucleophile, respectively. The dipeptide yield was increased from 15 to 50% by optimizing the conditions: boric acid-borax (0.2 mol/L), 30°C, pH 9.5, 2:1 acyl donor to nucleophile ratio, DES (ChCl/urea), and 15%(v/v) water content. The catalytic product is then isolated and purified. The structure of the product was identified by high-performance liquid chromatography, mass spectrometry, proton nuclear magnetic resonance, and carbon spectroscopy. Its biological activity was preliminarily determined by the B16-F10 mouse melanoma cell model. The results showed that the purity of L-Ala-Tyr prepared by the separation and purification method of this study was 96.8%, and the mass spectrometry and nuclear magnetic resonance spectroscopy showed that the structure of the peptide was consistent with the expected structure. In addition, the preliminary physiological activity identification results show that L-Ala-Tyr has no toxic effect on cells in the concentration range of 100-800 µmol·L-1, and at the optimal concentration, compared with the positive control 8-methoxypsoralen, it can promote the production of melanin.

Effects of tall fescue biochar on the adsorption and desorption of atrazine in different types of soil.

The excessive application of atrazine in agriculture has resulted in serious environmental contamination. The addition of biochar could reduce the bioavailability and mobility of atrazine in soil through adsorption-desorption processes. In this study, tall fescue biochar was prepared at 500 °C, and its effect on the adsorption-desorption behavior of atrazine in red soil, brown soil, and black soil was investigated. The tall fescue biochar with the pH value of 9.64 had a developed porous structure and large specific area that contained abundant surface functional groups. The element composition of the tall fescue biochar was C (50.46%), O (15.01%), N (4.54%), H (2.56%), and S (1.47%). The adsorption process of atrazine in the three soil types with and without biochar addition was divided into a fast stage, slow stage, and equilibrium stage. A pseudo second-order kinetic model was suitable for fitting the adsorption process of atrazine, and the determination coefficient (R2) ranged from 0.985 to 0.999. The adsorption-desorption processes of atrazine were described accurately by the Freundlich model (R2 of 0.967-0.999). The adsorption capacity of the three soil types for atrazine increased significantly with the addition of biochar, whereby the equilibrium adsorption amount increased from an initial range of 3.968 to 5.902 µg g-1 to a final range of 21.397 to 21.968 µg g-1. The desorption of atrazine was also inhibited as the hysteresis coefficient (HI) increased from an initial range of 0.451 to 0.586 to a final range of 0.916 to 0.941. The adsorption capacity of the red soil improved more than did the brown soil or black soil. Moreover, spontaneous adsorption of atrazine by the biochar-soil system occurred more easily at 35 °C than at 15 °C and 25 °C. Overall, tall fescue biochar was a prospective soil amendment material.

Spatiotemporal distributions of Cu, Zn, metribuzin, atrazine, and their transformation products in the surface water of a small plain stream in eastern China.

The intensive use of fertilizers and pesticides in agriculture has led to widespread nonpoint source pollution in surface waterbodies. In this work, the occurrence and distribution of nonpoint source metals (Cu and Zn) and herbicides (metribuzin; atrazine; and its degradates, including desethyl atrazine (DEA), desisoproylatrazine (DIA), and deethyldeisopropylatrazine (DEDIA)) in the surface water of the Baima River, which is located in a region noted for its intense agricultural activities, were investigated during a high water period in August and a low water period in October. The results showed that the heavy metals and herbicides investigated were detected frequently in the surface water of the river during the two periods. The average concentrations of Cu during the high water period and low water period were 9.3 (0-20.7) and 8.7 (0-15.55) µg/L, and the average concentrations of Zn during the two periods were 11.4 (6.65-22.15) and 10.6 (7.55-15.15) µg/L, respectively. The concentrations of atrazine were higher than those of metribuzin, which ranged from 0.07 to 1.12 µg/L during the high water period and 0.01-0.74 µg/L during the low water period. The total concentrations of atrazine and its transformation products in 60.00% of the samples during the high water period exceeded the maximum contaminant level (MCL) of 3 µg/L for the drinking water criteria in the USA, and 33.33% of the samples exceeded the MCL during the low water period. The spatial and temporal distributions of nonpoint source pollutants along the Baima River were influenced by land use and hydrogeomorphic settings. The ecotoxicological risk assessment indicated that atrazine and DIA have moderate risks to aquatic environment in Baima River.