Stimuli-responsive polymers based on L-phenylalanine residues: the protonation thermodynamics of free polymers and cross-linked hydrogels

ABSTRACT: Vinyl polymers carrying L-phenylalanine residues were synthesized in the free and in the cross-linked hydrogel form, as homo- and copolymers with N-isopropylacrylamide (NIPAAm). The protonation reaction thermodynamics of the COO- group were studied in aqueous media, at different temperatures and at increased concentrations of sodium chloride, mainly by potentiometry and solution calorimetry. The soluble polymer, namely poly(N-acryloyl-L-phenylalanine), and its copolymers with low NIPAAm content displayed characteristic features. Their basicity constants (log K), as well as the enthalpy (-¢H°) changes in relation to R (degree of protonation) showed an abrupt drop at R ) 0.5. This was ascribed to the formation of hydrogen bonds between the protonated and the ionized neighboring COOgroups. The process was driven by the side-chain aromatic rings that improved hydrophobic interactions. The entropy (¢S°) changes sharply increased as a result of the increased macromolecular conformational freedom and the release of water molecules surrounding the hydrophilic groups of the polymer. The corresponding cross-linked polymers formed hydrogels that were responsive to pH, temperature, and ionic strength. The two hydrogels, P9 (homopolymer with 9 mol% cross-links) and CP2 (copolymer with 90 mol% of NIPAAm and 2 mol% cross-links), were characterized for their pH- and temperature-responsive behavior by equilibrium and oscillatory swelling studies. They demonstrated a strong pH-dependent volume phase-transition and an unusual sodium chloride phase-transition phenomenon. Moreover, the hydrogel CP2 exhibited a temperature-dependent volume phase-transition (LCST, lower critical solution temperature) behavior in aqueous solution, where the LCST decreased by lowering the pH. It was nontoxic against the RAW264 cell line

Photoimmobilization of sulphated hyaluronic acid for antithrombogenicity

Anticoagulant polymer sulfated hyaluronic acid was patterned immobilized on a poly(ethylene terephthalate) (PET) film in a specific pattern by photolithography. Hyaluronic acid was sulfated by a sulfur trioxide-pyridine complex. The polymer was coupled with azidoaniline. The derivatized polymer was cast on a PET film from aqueous solution. After drying, the film was photoirradiated in the presence or absence of a photomask. The micropatterning was confirmed by staining with a dye, brilliant green. Since the anticoagulant polymer has negative charges, the cationic dye was adsorbed on the regions where the anticoagulant polymer was immobilized. Platelet adhesion was reduced on the sulfated hyaluronic acid-immobilized areas. The immobilized sulfated hyaluronic acid significantly reduced thrombus formation

Study of 254Es by Coulomb Excitation Gamma-Ray Spectroscopy

The 254Es gamma-ray spectrum was investigated by making coincidence between the gamma rays and scattered 58Ni nuclei. The gamma spectrum is made from coincidence data after gain matching and Doppler shift correction. From the gamma spectrum, energy and relative intensity of transitions of 254Es are deduced. The extracted data could help to extend the 254Es level scheme and in the future may permit to determine its quadrupole deformation.日本物理学会2021年次大

Nuclear structure study of 254Es via Coulomb Excitation Gamma-ray Spectroscopy

Exploring the new elements toward the high end of the nuclear chart is one of the most interesting topics in nuclear physics. A region of long-lived superheavy elements with proton and neutron numbers near Z=114, Z=120, N=184 – the so-called “Island of Stability” (IoS) is predicted to be the next “promised land”. Currently, access to the IoS is limited by the very low cross sections that affect present experimental techniques. Single-particle orbitals neighboring the deformed shell gaps in the region near Z=100 and N=152 are predicted to be linked to the spherical shells in the IoS. This link provides indirect information on the shell structure of nuclei in the IoS. 254Es (Einsteinium-254, Z=99, N=155) is an isotope in the region of deformed shell gaps and currently the heaviest target available for Coulomb excitation experiments.A 254Es Coulomb excitation experiment was performed at the JAEA-Tokai Tandem accelerator using 58Ni beam with an energy of 250 MeV. The very rare 254Es was produced at the High-Flux Isotope Reactor at ORNL, USA, and the target was produced using less than a microgram of material. The scattered beam particles were detected by two segmented CD-silicon detectors placed backward and forward from the target in coincidence with γ rays detected by 4 LaBr3(Ce) scintillators, 4 single-crystal Ge detectors and 4 Clover-type Ge detectors. Safe Coulomb excitation of 254Es was achieved for the first time to study its excited states. The particle-gamma coincidence spectrum created after Doppler-shift correction was analyzed. From the gamma spectrum, several new transitions of 254Es were observed indicating a rotational band structure. The extracted data will permit extending the 254Es level scheme and to determine its quadrupole deformation.日本物理学会第77回年次大