Solid-state complexes of poly(L-histidine) with metal chlorides from the first row of thed-block

Abstract

Solid‐state characterization of poly(L‐histidine) was obtained via differential scanning calorimetry, thermogravimetric analysis, optical microscopy, and infrared spectroscopy. The glass transition temperature of poly(L‐histidine) is 169°C. This thermal transition has not been reported previously. Poly(L‐histidine)'s Tg increases when complexes are produced with the following divalent transition metal chlorides: cobalt chloride hexahydrate, nickel chloride hexahydrate, copper chloride dihydrate, and anhydrous zinc chloride. At 10 mol % salt, nickel chloride increases Tg by 69°C. The enhancement in poly(L‐histidine)'s Tg correlates well with ligand field stabilization energies for pseudo‐octahedral dn complexes (n = 7, 8, and 10) from the first row of the d‐block. However, d9 copper(II) complexes do not conform to this empirical correlation. Infrared spectroscopic evidence indicates that these metal chlorides form complexes with the imidazole ring in the histidine side group and the amide group in the main chain of the polymer. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 301–309, 1999

Organic-Inorganic Hybrid Polymers as Adsorbents for Removal of Heavy Metal Ions from Solutions: A Review

“…For example, metal-centered polymers [138] and products of coordination of metallic ions to the polymer backbone [139] and polymerization of metal-coordinated monomers [140] are called metal-containing polymers [99]. …”

“…At the end of this section, it is noteworthy that the inclusion of metals in organic-inorganic hybrid polymers occurs at the molecular scale and the incorporation of metal complexes and metallic ions in polymers by coordination interactions does not produce organic-inorganic hybrid polymers [ 99 ]. For example, metal-centered polymers [ 138 ] and products of coordination of metallic ions to the polymer backbone [ 139 ] and polymerization of metal-coordinated monomers [ 140 ] are called metal-containing polymers [ 99 ].…”

pH‐induced Micelle Formation of Poly(histidine‐co‐phenylalanine)‐block‐Poly(ethylene glycol) in Aqueous Media

“…Since the pK a value of the imidazole group in histidine residue is around 6.5, both charged and uncharged forms of histidine are present in PLH at neutral pH, and the concentration ratio of the charged form to the uncharged one is very sensitive to small change in pH under physiological conditions. [21][22][23] When L-histidine is copolymerized with hydrophobic amino acid such as L-phenylalanine, it is expected that the pK a value of the copolymer can be controlled by adjusting the ratio of histidine to phenylalanine in copolypeptide and its molecular weight. This interesting property motivates us to use the histidinebased copolymer as a core material of pH-sensitive micelle for gene delivery.…”

“…PLH can be used as a core material of micelle, since it has an amphoteric nature due to the imidazole group of histidine. Since the pK a value of the imidazole group in histidine residue is around 6.5, both charged and uncharged forms of histidine are present in PLH at neutral pH, and the concentration ratio of the charged form to the uncharged one is very sensitive to small change in pH under physiological conditions 21–23. When L ‐histidine is copolymerized with hydrophobic amino acid such as L ‐phenylalanine, it is expected that the pK a value of the copolymer can be controlled by adjusting the ratio of histidine to phenylalanine in copolypeptide and its molecular weight.…”

A Novel Class of 1H‐MRI Contrast Agents Based on the Relaxation Enhancement Induced on Water Protons by 14N‐Containing Imidazole Moieties

“…As pH controls the physical state of the poly‐His solid/liquid status and given that the 14 N‐QPs are only observed for immobilized systems, [16] changes in the intensity of the imidazole QPs can act as a reporter of the pH of the microenvironment. In fact, the protonation of the imidazole group of the histidine (p K a =6.8) [23, 24] increases the polymer solubility with a consequent increase in mobility and progressive disappearance of the QPs (Figure 2 E).…”