Spectroscopic and calorimetric studies on the protonation of polymeric amino acids

Synthesis, Acid-Base Properties and Preliminary Cell Compatibility Evaluation of Amphoteric Poly(Amido-Hydrazine)s

“…All this may be attributed to the hydrogen-bonding between the amido C--O groups and the protonated hydrazine nitrogen of the main chain. For BAC-AS-DMHY, this gave rise to a symmetric structure where both the C--O groups were involved in two six-chelate rings, similar to the poly(amidoamine)s previously reported [23]. The more stable orientation of the water molecules around the symmetrical protonated species gave more favorable energy terms leading to the increased log K value.…”

Cyclopolymerization protocol for the synthesis of a poly(zwitterion‐alt‐sulfur dioxide) to investigate the polyzwitterion‐to‐poly(anion‐zwitterion) transition

“…Even though the corresponding transformation of (− ±) PEZ 7 from salt‐free water [Figure 3(c)] to (±) PZA 6 in salt‐free‐water cannot be achieved owing to the insolubility of the later, it can be assumed that the magnitude of the viscosity change would be much larger than in 0.1 N NaCl. Since PEZ 7 in salt‐free water [Figure 3(c)] is the most expanded hence more hydrated, the greater number of water molecules are released as a result of each protonation in salt‐free water than in 0.1 N NaCl thereby leading to an entropy‐driven70 higher basicity constant and n in the former medium (Table III). The basicity constant (log K °) of the carboxyl group was found to be 3.42 and 2.98 in salt‐free water and 0.1 N NaCl, respectively.…”

Aspartic acid in a new role: Synthesis and application of a pH-responsive cyclopolymer containing residues of the amino acid

“…For pK 2 , the n 2 values were determined to be 2.11 and 1.76 in salt-free water and 1 M NaCl, respectively, whereas the corresponding n 1 values for pK 1 (involving (Z = ) 11 + H + ⇋ (ZH ± − ) 10) were found to be 1.24 and 1.16. The greater n 2 values confirm the consequence of the entropy effects [45,46]: as water-soluble (± −) 10 is the most hydrated and water-insoluble (±) 9 is the least hydrated, a greater number of water molecules from the repeating unit of 10 is released as it is transformed to 9. In comparison, both (=) 11 and (± −) 10 are hydrated; the former is slightly more hydrated as a result of its greater charge imbalance.…”

“…The differences in the degree of hydration are reflected in n 2 values being Nn 1 . As the exothermic enthalpy changes (ΔH o ) do not change with the increase in the degree of protonation, α, the ΔG o values are thus dictated by the contribution of the entropy term [46].…”