HNO(H2O) n (n = 1–4) clusters: a theoretical study

Adsorption and Separation of Aromatic Amino Acids from Aqueous Solutions Using Metal-Organic Frameworks

Metal-organic frameworks (MOFs) are investigated for the adsorption of aromatic amino acids l-phenylalanine (l-Phe), l-tryptophan (l-Trp), and l-tyrosine (l-Tyr) from aqueous solutions. After screening a range of water-stable MOFs, the hydrophobic Zr-MOF MIL-140C emerged as the best performing material, exhibiting uptakes of 15 wt % for l-Trp and 20 wt % for l-Phe. These uptakes are 5-10 wt % higher than those of large-pore zeolites Beta and Y. Both single-compound and competitive adsorption isotherms for l-Phe and l-Trp were experimentally obtained at the natural pH of these amino acid mixtures (pH 6.5-7) without additional pH modification. We find that the hydrophobic nature of MIL-140C and the capacity of l-Trp to form hydrogen bonds favor the uptake of l-Trp with its larger indole moiety compared to the smaller phenyl side group of l-Phe. On the basis of literature and vibrational analysis, observations of hydrogen-bonded l-Trp within the MIL-140C framework are evidenced by red- and blue-shifted -NH vibrations (3400 cm^-1) in Fourier transform infrared spectroscopy, which were attributed to types N-H_l-Trp···π_MIL-140C and N-H_l-Trp···O_MIL-140C, respectively. MIL-140C is shown to be recycled at least three times for both aromatic amino acids without any loss of adsorption capacity, separation performance, or crystallinity. Desorption of aromatic amino acids proceeds easily in aqueous ethanol. Substantial coadsorption of negatively charged amino acids l-glutamate and l-aspartate (l-Glu and l-Asp) was observed from a model solution for wheat straw protein hydrolysate at pH 4.3. On the basis of these results, we conclude that MIL-140C is an interesting material for the recovery of essential aromatic amino acids l-Tyr, l-Phe, and l-Trp and of l-Glu and l-Asp from waste protein hydrolysates.

New equation for calculating total interaction energy in one noncyclic ABC triad and new insights into cooperativity of noncovalent bonds

In this work, a new equation consist of A⋅⋅⋅B, B⋅⋅⋅C, A⋅⋅⋅BC, and AB⋅⋅⋅C interactions is proposed for calculating the total interaction energy of noncyclic ABC triads. New equations are also proposed for calculating the changes in values of A⋅⋅⋅B and B⋅⋅⋅C interactions on the formation of triad from the corresponding dyads. The advantages of equations proposed here in comparison with many-body interaction energy approach are discussed. All proposed equations were tested in F₃ MLi⋅⋅⋅NCH⋅⋅⋅HLH and F₃ MLi⋅⋅⋅HLH⋅⋅⋅HCN (M = C, Si; L = Be, Mg) as well as H₃ N⋅⋅⋅XY⋅⋅⋅HF (X, Y = F, Cl, Br) noncyclic A⋅⋅⋅B⋅⋅⋅C triads. The data show that the total cooperativity of triad correlates well with the sum of the changes in values of A⋅⋅⋅B and B⋅⋅⋅C interactions calculated through new equations proposed here. © 2016 Wiley Periodicals, Inc.