Tanaka Yuta, Saito Haruka, Tsutsumi Yusuke, Doi Hisashi, Nomura Naoyuki, Imai Hachiro, Hanawa Takao
Department of Metals, Institute of Biomaterials and Bioengineering, Tokyo Medical and Dental University, Tokyo 101-0062, Japan.
J Colloid Interface Sci. 2009 Feb 1;330(1):138-43. doi: 10.1016/j.jcis.2008.10.042. Epub 2008 Nov 12.
The isoelectric points (IEPs) of two zwitterions, glycine and both-terminals-terminated poly(ethylene glycol) (NH(2)-PEG-COOH), were determined from the titration curves, and the thicknesses of zwitterion layers immobilized on titanium (Ti) with immersion and electrodeposition at various pH based on IEPs were evaluated with ellipsometry to investigate the effect of pH and the immobilization technique on the interactions between the zwitterions and the Ti surface. From the titration curves, pK(1), pK(2), and the IEP of glycine were determined as 2.8, 8.9, and 5.9, respectively, and pK(1), pK(2), and the IEP of NH(2)-PEG-COOH were determined as 2.1, 11.7, and 6.9, respectively. At a certain specific pH, (+)H(3)N-CH(2)-COO(-) or (+)H(3)N-PEG-COO(-) was formed by hydrolysis of glycine or NH(2)-PEG-COOH. In addition, the Ti surface was negatively charged at this pH. As a result, for immersion, the electrostatic reactivity between terminal groups of zwitterions and hydroxyl groups on the Ti surface was the highest and the thickness of the immobilized layer was significantly the largest at pH 12. For electrodeposition, glycine, with its lower molecular weight, was more easily attracted to the Ti surface than NH(2)-PEG-COOH, which has a higher molecular weight, while the thickness of the immobilized layer was the greatest at pH 12 in both zwitterions.
通过滴定曲线测定了两种两性离子（甘氨酸和双端封端的聚乙二醇（NH₂-PEG-COOH））的等电点（IEP），并基于等电点，通过椭偏仪评估了在不同pH值下通过浸泡和电沉积固定在钛（Ti）上的两性离子层的厚度，以研究pH值和固定技术对两性离子与Ti表面之间相互作用的影响。从滴定曲线可知，甘氨酸的pK₁、pK₂和IEP分别测定为2.8、8.9和5.9，NH₂-PEG-COOH的pK₁、pK₂和IEP分别测定为2.1、11.7和6.9。在某个特定的pH值下，甘氨酸或NH₂-PEG-COOH水解形成（⁺）H₃N-CH₂-COO⁻或（⁺）H₃N-PEG-COO⁻。此外，在此pH值下Ti表面带负电。结果表明，对于浸泡法，在pH 12时两性离子端基与Ti表面羟基之间的静电反应性最高，固定层的厚度显著最大。对于电沉积法，分子量较低的甘氨酸比分子量较高的NH₂-PEG-COOH更容易被吸引到Ti表面，而在两种两性离子中，固定层的厚度在pH 12时最大。
