Dissolution of Silk Fibroin in Mixtures of Ionic Liquids and Dimethyl Sulfoxide: On the Relative Importance of Temperature and Binary Solvent Composition.

We studied the dependence of dissolution of silk fibroin (SF) in mixtures of DMSO with ionic liquids (ILs) on the temperature (T = 40 to 80 °C) and DMSO mole fraction (χDMSO = 0.5 to 0.9). The ILs included BuMeImAcO, C3OMeImAcO, AlBzMe2NAcO, and Bu4NAcO; see the names and structures below. We used design of experiments (DOE) to determine the dependence of mass fraction of dissolved SF (SF-m%) on T and χDMSO. We successfully employed a second-order polynomial to fit the biopolymer dissolution data. The resulting regression coefficients showed that the dissolution of SF in BuMeImAcO-DMSO and C3OMeImAcO-DMSO is more sensitive to variation of T than of χDMSO; the inverse is observed for the quaternary ammonium ILs. Using BuMeImAcO, AlBzMe2NAcO, and molecular dynamics simulations, we attribute the difference in IL efficiency to stronger SF-IL hydrogen bonding with the former IL, which is coupled with the difference in the molecular volumes and the rigidity of the phenyl ring of the latter IL. The order of SF dissolution is BuMeImAcO-DMSO > C3OMeImAcO-DMSO; this was attributed to the formation of intramolecular H-bonding between the ether oxygen in the side chain of the latter IL and the relatively acidic hydrogens of the imidazolium cation. Using DOE, we were able to predict values of SF-m%; this is satisfactory and important because it results in economy of labor, time, and material.

Isotopic composition of atmospheric precipitation and its tracing significance in the Laohequ Basin, Loess plateau, China.

Based on the δ18O and δD values in precipitation and related meteorological parameters in the Chinese Loess Plateau (CLP) from June 2014 to April 2016, the effects of temperature and precipitation amount effect on stable isotopic compositions were analyzed, as well as the tracing significance of deuterium excess. The results show that the Local Meteoric Water Line (LMWL) was defined as δD = 7.08δ18O + 4.73(R2 = 0.99), with a slope of <8, indicating that a non-equilibrium evaporation process occurred when the drops fell below the cloud base in the arid and semi-arid environment. The temperature effect was defined as δD = 0.4536T-46.937.44 (r = 0.113, n = 150, p = 0.168), which shows a weak positive correlation between temperature and isotopic composition. Meanwhile, the precipitation amount effect was defined as δD = -0.7883P-34.152 (r = -0.223, n = 150, p = 0.011), which shows a weak negative correlation between temperature and isotope composition. The slopes in cross plotting δD - δ18O records were 8.3, 7.7, 7.4, and 6.3, displaying a decreasing trend in the temperature gradient of T ≤ 0 °C, 0 < T ≤ 10 °C, 10 < T ≤ 20 °C and T > 20 °C, respectively. The amount effect is significant (δD = -7.0946P + 48.686, r = -0.548, n = 20, p = 0.012) in the precipitation range from 10 to 20 mm. The average deuterium excess values in winter were 24‰ and 25.3‰ for 2015 and 2016, respectively; however, the low values of 3.1‰ and 5.5‰ occurred in the summers of 2014 and 2015, respectively. These results suggested that intense sub-cloud evaporation decreased the deuterium excess values in the Chinese Loess Plateau under the climate conditions of the rainy season with high temperatures. However, deuterium excess values of snow in wintertime (LT-1, LT-2) could be reflective of the reliable characteristics of atmospheric vapor for weak sub-cloud evaporation and surface evaporation.