Amino acid ionic liquids (AAILs) [AA]X based on amino acid cations are a kind of typical "bio-base" protic ionic liquids (PILs), which are supposed to be acidic ionic liquids. The Brønsted acidity of [AA]X PILs at room temperature were systematically studied for the first time. Acid dissociation constants (pKa) of [AA]X were determined by potentiometric titration method. The first acid dissociation constants (pKa1) are from 1.98 to 2.42. The actual pH values of [AA]X (0.010 mol·L −1 ) obtained from pH meter are from 2.26 to 2.44 which are slightly higher than the calculated pH values according to the above experimental pKa1. The Hammett method performed on UV/Vis spectra with p-nitroaniline as the indicator was used to determine the acid strength of [AA]X. Their H0 values (0.010 mol·L −1 ) are in the range from 2.10 to 2.44. Various frameworks of amino acid cations and five anions (including nitrate (NO3 − ), chloride (Cl − ), perchlorate (ClO4 − ), trifluoromethanesulfonate (OTf − ) and trifluoroacetate (TfA − ) anions) were used to investigate the cationic and anionic effect on the acidity of AAILs. The Brønsted acidity of AAILs depends on the cationic structure, the type of anion and the concentration of [AA]X. In addition, the theoretical pKa1 were studied by the cluster-continuum model using density functional theory (DFT) method. The experimental and theoretical results showed that [AA]X PILs have stronger Brønsted acidity than that of the common PILs prepared by one-pot syntheses.11b Scheme 1 Structures of PILs.

Mixed‐valence compounds with the iso‐cyanidometal‐ligand bridge in different oxidation states are used as models for the investigation of the electron‐transfer process. We synthesized a series of trimetallic isocyanidometal‐bridged compounds with [Fe–CN–Ru–NC–Fe]n+ (n=2–4), in which the one‐electron oxidation product (N3+) and two‐electron oxidation product (N4+) compounds possess an isocyanidometal bridge whose energy is, respectively lower and slightly higher than the terminal metal centers energies. For the N3+ compounds, the bridge state (FeII–RuIII–FeII) and mixed‐valence states (FeIII–RuII–FeII or FeII–RuII–FeIII) could be simultaneously observed on the IR timescale. For the N4+ compounds, as the donor becomes stronger the electron transfer bridge excited state (FeIII–RuII–FeIII) becomes more and more stable, and even becomes ground state due to the strong electronic coupling between Fe and Ru.

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An amino acid-assisted approach is developed to immobilize ultrafine Pd NPs onto mesoporous carbon, which exhibits remarkable catalytic activity for hydrogen generation.

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Mixed‐valence compounds with the iso‐cyanidometal‐ligand bridge in different oxidation states are used as models for the investigation of the electron‐transfer process. We synthesized a series of trimetallic isocyanidometal‐bridged compounds with [Fe–CN–Ru–NC–Fe]n+ (n=2–4), in which the one‐electron oxidation product (N3+) and two‐electron oxidation product (N4+) compounds possess an isocyanidometal bridge whose energy is, respectively lower and slightly higher than the terminal metal centers energies. For the N3+ compounds, the bridge state (FeII–RuIII–FeII) and mixed‐valence states (FeIII–RuII–FeII or FeII–RuII–FeIII) could be simultaneously observed on the IR timescale. For the N4+ compounds, as the donor becomes stronger the electron transfer bridge excited state (FeIII–RuII–FeIII) becomes more and more stable, and even becomes ground state due to the strong electronic coupling between Fe and Ru.

[AAE]X composed of amino acid ester cations is a sort of typically “bio-based” protic ionic liquids (PILs). They possess potential Brønsted acidity due to the active hydrogens on their cations. The Brønsted acidity of [AAE]X PILs in green solvents (water and ethanol) at room temperature was systematically studied. Various frameworks of amino acid ester cations and four anions were investigated in this work from the viewpoint of structure–property relationship. Four different ways were used to study the acidity. Acid dissociation constants (pKa) of [AAE]X determined by the OIM (overlapping indicator method) were from 7.10 to 7.73 in water and from 8.54 to 9.05 in ethanol. The pKa values determined by the PTM (potential titration method) were from 7.12 to 7.82 in water. Their Hammett acidity function (H0) values (0.05 mol·L−1) were about 4.6 in water. In addition, the pKa values obtained by the DFT (proton-transfer reactions) were from 7.11 to 7.83 in water and from 8.54 to 9.34 in ethanol, respectively. The data revealed that the cationic structures of [AAE]X had little effect and the anions had no effect on the acidity of [AAE]X. At the same time, the OIM, PTM, Hammett method and DFT method were reliable for determining the acidic strength of [AAE]X in this study.