環境中包括人體內充斥著各式各樣的金屬離子，因此研發新型的金屬離子化學偵測器是目前許多化學家努力研究的領域之一。目前許多化學偵測器是利用有機小分子修飾，而我們藉由Fmoc保護基的固態胜肽合成法，合成出四種以胜肽小分子為基底的β-hairpin衍生物，希望以純天然的小分子量胜肽也能夠開發出新型的化學偵測器。其中Cu2+和Hg2+，會造成此四條胜肽HP7-H2H11、HP7-H4H9、HP7-H2H4H9H11及HP7-H1H12強烈的螢光淬息效應，而其它測試的 (Al3+、Ba2+、Cd2+、Co2+、Cr3+、Fe2+、Fe3+、Mg2+、Mn2+、Ni2+、Sr2+、Zn2+) 等金屬離子，並沒有此種明顯的螢光淬息效應。在較高的pH值環境條件下，相較於Hg2+而言，Cu2+展現出更為明顯和強烈的螢光淬息效應。此外，當加入Cu2+和Hg2+時，圓二色光譜儀 (CD) 會展現不同的結構變化，藉此亦可以用於分辨出此兩種金屬離子。在pH 7.5時，Cu2+鍵結在HP7-H2H11、HP7-H4H9、HP7-H2H4H9H11、HP7-H1H12的解離常數，分別是6.7 μM、20.3 μM、6.0 μM、8.1 μM。而Hg2+的結合常數分別是50.3 μM、34.4 μM、29.0 μM、35.9 μM。對HP7-H2H11而言，對Cu2+的偵測極限是0.55 μM，而對Hg2+的偵測極限是0.54 μM。至於對HP7-H4H9而言，對Cu2+的偵測極限是0.79 μM，而對Hg2+的偵測極限是0.97 μM。對HP7-H2H4H9H11來看，對Cu2+的偵測極限是0.68 μM，而對Hg2+的偵測極限是1.34 μM。最後，是將His置於N端和C端的HP7-H1H12，對Cu2+的偵測極限是0.62 μM，而對Hg2+的偵測極限是1.04 μM。根據本篇研究，置換了四個組胺酸 (Histidine) 的HP7-H2H4H9H11對Cu2+淬息效果較為明顯，但結構也較不穩定。置換在靠近N端和C端的HP7-H2H11，雖然對Cu2+淬息效果不如HP7-H2H4H9H11，但是結構改變較小。置換在靠近β-turn的HP7-H4H9，因結構也改變較多，解離常數也較大。最後是置換N端和C端上的HP7-H1H12，對Cu2+、Hg2+淬息效果和其它HP7胜肽不同，Hg2+影響大於Cu2+推測應該是其置換的位置較具有彈性 (flexible)。

Four new peptide-based chemosensors derived from a β-hairpin have been synthesized via solid phase peptide synthesis (SPPS) and Fmoc chemistry. The Trp fluorescence of HP7-H2H11 (Lys-His-Trp-Asn-Pro-Ala-Thr-Gly-Lys-Trp- His-Glu), HP7-H4H9 (Lys-Thr-Trp-His-Pro-Ala-Thr-Gly-His-Trp-Thr-Glu), HP7- H2H4H9H11 (Lys-His-Trp-His-Pro-Ala-Thr-Gly-His-Trp-His-Glu) and HP7-H1H12 (His-Thr-Trp-Asn-Pro-Ala-Thr-Gly-Lys-Trp-Thr-His) peptides was significantly quenched in the presence of Cu2+and Hg2+, while adding Al3+, Ba2+, Cd2+, Co2+, Cr3+, Fe2+, Fe3+, Mg2+, Mn2+, Ni2+, Sr2+ and Zn2+dose not cause significant fluorescence changes. Also, pH dependent measurements indicate that Cu2+ has a more profound quenching effect than Hg2+ on the fluorescence at high pH, which could be used to discriminate Cu2+ and Hg2+. Besides, circular dichroism (CD) spectra show that Cu2+ and Hg2+ induce different structural changes on the peptides. At pH 7.5, the dissociation constants (Kd) of Cu2+ binding to HP7-H2H11, HP7-H4H9, HP7-H2H4H9H11 and HP7-H1H12 are 6.7 μM, 20.3 μM, 6.0μM and, 8.1μM respectively. For Hg2+ binding, the Kd is 50.3 μM to HP7-H2H11, 34.4 μM to HP7-H4H9, 29.0 μM to HP7-H2H4H9H11 and 35.9 μM to HP7-H1H12. The detection limit of HP7-H2H11 is 0.55 μM for Cu2+ and 0.54 μM for Hg2+, and that of HP7-H4H9 is 0.79 μM for Cu2+ and 0.97 μM for Hg2+. For HP7-H2H4H9H11, the detection limit of HP7-H2H4H9H11 is 0.68 μM for Cu2+ and 1.34 μM for Hg2+ , and that of HP7-H1H12 is 0.62 μM for Cu2+ and 1.04 μM for Hg2+ . Our results demonstrate that these four new water-soluble peptides can be good chemosensors for the detection of Cu2+ and Hg2+.

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