Effect of MnO on the Phase Development, Microstructures, and Dielectric Properties of 0.95Na0.5K0.5NbO3–0.05LiTaO3 Ceramics

Lead-free piezoelectric ceramics in the system 0.95Na_0.5K_0.5NbO₃–0.05LiTaO₃ were modified with ≤1 mol% MnO. Maximum densities occurred at a sintering temperature of 1050°C. Characteristic changes in the relative intensity of X-ray diffraction peaks were consistent with Mn ions substituting on the perovskite lattice to produce a change from orthorhombic to a mixture of tetragonal and orthorhombic phases. Grain growth during secondary recrystallization was also affected, leading to increased grain sizes. The dielectric constant increased from ∼600 in unmodified ceramics to ∼1040 in ceramics prepared with 0.5 mol% MnO.     

Effect of synthetic polymers on polymer–protein interaction

Synthetic polymers are often used for delivery of therapeutic drugs and proteins. We report the binding of milk β-lactoglobulin (β-LG) with poly(ethylene glycol) (PEG), methoxypoly(ethylene glycol) polyamidoamine (mPEG-PAMAM-G-3) and polyamidoamine (PAMAM-G4) nanoparticles in aqueous solution at pH 7.4, using Fourier Transform infrared (FTIR), circular dichroism (CD), fluorescence spectroscopic methods, transmission electron microscopy (TEM) and molecular modeling. Structural analysis showed that polymers bind β-LG via both hydrophilic and hydrophobic contacts with overall binding constants K_{PEG-8000-β-LG} = 4.8 (±0.4) × 10⁴ M⁻¹ and K_{mPEG-PAMAM-G3-β-LG} = 5.8 (±0.6) × 10⁵ M⁻¹ and K_{PAMAM-G4-β-LG} = 6.7 (±0.9) × 10⁴ M⁻¹. The number of binding sites were occupied by polymers on protein (n) was 0.3 for PEG-8000, 0.4 for mPEG–PAMAM-G3 and 0.4 for PAMAM-G4. The order of binding is mPEG-PAMAM-G3 > PAMAM-G4 > PEG-8000. Transmission electron microscopy showed significant changes in protein morphology as polymer–protein complexation progressed with major increase in the diameter of the protein aggregate (180%). Furthermore, modeling showed several H-bonding systems between PEG and different amino acids stabilize polymer–β-LG complexes. mPEG-PAMAM-G3 is a stronger protein binder than PAMAM-G4 and PEG-8000.