王越,呂鑫,郭煒
(山西大學(xué) 化學(xué)化工學(xué)院,山西 太原 030006)
一種選擇性生物硫醇熒光探針
王越,呂鑫,郭煒*
(山西大學(xué) 化學(xué)化工學(xué)院,山西 太原 030006)
利用生物硫醇獨(dú)特的親核性,以5(6)-羧基羅丹明為熒光團(tuán),7-硝基苯呋咱基團(tuán)為硫醇反應(yīng)單元,構(gòu)建了一個(gè)生物硫醇熒光探針。該探針具有良好的水溶性,在PBS緩沖中能選擇性檢測(cè)半胱氨酸,熒光增強(qiáng)240倍,檢出限可達(dá)2.8×10-8mol/L。
熒光探針;生物硫醇;5(6)-羧基羅丹明;7-硝基苯呋咱
半胱氨酸(Cys),同型半胱氨酸(Hcy)以及還原型谷胱甘肽(GSH)等生物硫醇在維持細(xì)胞內(nèi)氧化還原平衡、信號(hào)傳導(dǎo)、基因調(diào)控等諸多生理過(guò)程中扮演了重要角色[1-3],其不正常的表達(dá)與許多疾病相關(guān)。例如,人體內(nèi)半胱氨酸水平的異??梢鹕L(zhǎng)緩慢、水腫、嗜睡、肝功能損傷、肌肉松弛和肥胖等[4-6],同型半胱氨酸水平的異常與某些先天性疾病、老年認(rèn)知障礙、心血管病、阿爾茨海默氏病有關(guān)[7-9],谷胱甘肽的濃度異常與癌癥、阿爾茨海默氏癥和心血管等疾病密切相關(guān)[10-14]。因此,開發(fā)高選擇性檢測(cè)生物硫醇的檢測(cè)方法對(duì)研究生物硫醇的生理病理功能具有重要意義。傳統(tǒng)的生物硫醇檢測(cè)方法主要有電化學(xué)法與高效液相色譜法,但此類方法操作煩瑣,并且對(duì)樣品具有破壞性,因而不適于生物樣品內(nèi)生物硫醇的實(shí)時(shí)檢測(cè)。相比之下,熒光探針?lè)ň哂胁僮骱?jiǎn)單、高靈敏度、檢出限低、可視化、非侵入性等優(yōu)點(diǎn)[15],因此在生物硫醇的檢測(cè)和生物影像方面具有獨(dú)特的優(yōu)勢(shì)。
許多化學(xué)反應(yīng)能被用來(lái)構(gòu)建選擇性生物硫醇熒光探針。這些反應(yīng)主要利用了生物硫醇的親核反應(yīng)性,包括與醛基的環(huán)化反應(yīng)[16]、邁克爾加成反應(yīng)[17]、磺酰胺與磺酸酯的裂解反應(yīng)[18]、親核取代反應(yīng)[19]、二硫鍵交換反應(yīng)[20]、裂解NBD醚[21-23]等[24]。盡管許多生物硫醇熒光探針近年來(lái)被陸續(xù)報(bào)道,但仍然存在合成煩瑣、靈敏度低、水溶性差等缺點(diǎn)。本文設(shè)計(jì)并合成了一種基于裂解7-硝基苯呋咱(NBD)胺機(jī)理的硫醇熒光探針1,該探針以5(6)-羧基-羅丹明為信號(hào)單元,7-硝基苯呋咱作為硫醇識(shí)別單元。由于存在由熒光團(tuán)到識(shí)別單元的d-PET過(guò)程,探針幾乎沒(méi)有熒光,加入硫醇后,NBD胺單元被硫醇裂解,從而釋放出羅丹明信號(hào)單元,產(chǎn)生強(qiáng)的紅色熒光。探針1的結(jié)構(gòu)及對(duì)硫醇的傳感機(jī)理如圖1所示。
Fig.1 Structure and sensing mechanism of probe 1 for biothiols.圖1 探針1的結(jié)構(gòu)及生物硫醇傳感機(jī)理
1.1 實(shí)驗(yàn)儀器與試劑
熒光光譜儀Hitach F-7000,紫外-可見(jiàn)分光光度計(jì)Varian Carry-4000,核磁共振儀Bruker-600 MHz,質(zhì)譜儀Varian QFT-ESI。DMF為色譜純,其余所用試劑均為分析純?cè)噭?水為去離子水。
1.2 探針1的合成
主體化合物的合成步驟如下:
氮?dú)獗Wo(hù)下,將7-羥基-1,2,3,4-四氫喹啉 (1.12 g, 7.5 mmol) 溶解于20 mL甲醇中,然后加入4-氯-7-硝基苯呋咱(1.00 g,5 mmol),加熱回流反應(yīng)4 h。冷卻后旋干溶劑,柱層析分離(石油醚∶乙酸乙酯=3∶1)得到暗紅色固體化合物3(0.31 g, 1.0 mmol), 產(chǎn)率20%。1H-NMR (DMSO-d6, 600MHz) δ (ppm): 9.41 (s, 1H); 8.55 (d, 1H,J=9.0 Hz); 7.11 (d, 1H,J=8.4 Hz); 7.01 (d, 1H,J=9.0 Hz); 6.74 (d, 1H,J=2.4 Hz); 6,65 (d, 1H,J=2.4 Hz); 4.25 (t, 2H,J=6.6 Hz); 2.71 (t, 2H,J=6.6 Hz); 2.00 (m, 2H,J1=6.6 Hz,J2=12.6 Hz).13C-NMR (DMSO-d6, 150 MHz): 156.1, 146.4, 145.2, 144.8, 140.1, 135.9, 130.5, 124.9, 123.5, 114.2, 110.4, 109.8, 50.9, 25.4, 24.2. ESI-MS: calculated for [M-H]-: 311.07858, found: 311.07858.
將間二乙氨基苯酚(6.6 g, 40 mmol)溶解于500 mL干燥的甲苯中,然后加入1,2,4-苯三酸酐(7.7 g,40 mmol),混合物加熱回流過(guò)夜,然后將反應(yīng)液冷卻至室溫,真空抽濾,濾餅用二氯甲烷洗滌得到黃色固體。粗品化合物經(jīng)柱層析分離(石油醚∶乙酸乙酯=1∶4)得到黃色固體化合物4 (8.2 g,23 mmol),該化合物為異構(gòu)體4a和4b的混合物,產(chǎn)率57%。1H-NMR ((CD3)2CO, 400 MHz) δ(ppm): 8.69 (d, 1H,J=1.6 Hz), 8.31 (dd,1H,J1=8.0 Hz,J2=1.6 Hz), 8.22 (dd, 1H,J1=8.0 Hz,J2=1.6 Hz), 8.16 (d, 1H,J=8.0 Hz), 7.98 (d, 1H,J=1.6 Hz), 7.55(d, 1H,J=8.0 Hz), 6.91(d, 1H,J=9.2 Hz), 6.87 (d, 1H,J=8.8 Hz), 6.21-6.17 (m, 2H), 6.09 (s, 2H), 3.44 (q, 8H,J=7.2 Hz), 1.16 (12H, t,J=7.2Hz). ESI-MS: calculated for [M+H]+: 358.1285, found: 358.1286.
氮?dú)獗Wo(hù)下,將化合物4(0.12 g,0.32 mmol)溶解于3 mL甲磺酸中,然后加入中間體3(0.10 g,0.32 mmol),加熱至100℃反應(yīng)5 h。冷卻后將反應(yīng)液倒入100 mL冰水中,緩慢攪拌析出紫黑色固體,過(guò)濾,真空干燥,得粗品化合物1。該化合物經(jīng)柱層析分離(二氯甲烷∶甲醇=20∶1),得到紫紅色固體化合物1(0.13 g,0.2 mmol),產(chǎn)率62.5%。1H-NMR (DMSO-d6, 600 MHz) δ (ppm): 8.62 (d, 1H,J=8.4 Hz); 8.25 (d, 1H,J=8.4 Hz); 8.13 (d, 1H,J=7.8 Hz); 7.69 (s, 1H); 7.31 (s, 1H); 7.26 (d, 1H,J=8.4 Hz); 6.74 (s, 1H); 6.52 (d, 1H,J=9.0 Hz,); 6.46 (d, 1H,J=9.0 Hz); 6.37 (s, 1H); 4.15 (q, 2H,J=6.0 Hz); 3.39 (q, 4H,J=7.2 Hz); 2.70 (m, 2H,J=6.0 Hz); 1.97 (t, 2H,J=6.0 Hz); 1.08 (t, 6H,J=7.2 Hz).13C-NMR (DMSO-d6, 150MHz): 168.5, 166.6, 152.9, 152.5, 149.9, 149.8, 146.7, 145.1, 144.0, 142.1, 135.7, 131.4, 129.2, 128.3, 128.0, 127.1, 125.6, 124.8, 115.4, 113.2, 110.1, 109.2, 104.2, 97.2, 83.9, 50.6, 44.2, 25.6, 23.6, 12.7. ESI-MS: calculated for [M+H]+: 634.1932; found: 634.1924.
1.3 光譜測(cè)定
配制 5 mmol/L探針1的DMF儲(chǔ)備液,將此儲(chǔ)備液用PBS緩沖液(0.01 mol/L,pH=7.4)稀釋到5 μmol/L作為檢測(cè)液。將2 mL的檢測(cè)液轉(zhuǎn)移至1 cm的石英池中,在室溫下分別加入生物硫醇以及其它氨基酸溶液,混合均勻,放置40 min后進(jìn)行光譜測(cè)試。
2.1 探針1與半胱氨酸反應(yīng)的吸收和熒光光譜研究
圖2為探針1與半胱氨酸作用前后的吸收光譜與熒光光譜。 探針1在360 nm、480 nm、597 nm處顯示了三個(gè)主要的吸收峰,加入200 μmol/L的半胱氨酸后,597 nm與480 nm處的吸收峰逐漸減低,并在554 nm處出現(xiàn)新的吸收峰,其強(qiáng)度隨時(shí)間逐漸增加,表明該探針與半胱氨酸發(fā)生了反應(yīng)。498 nm和574 nm 處等吸收點(diǎn)的產(chǎn)生進(jìn)一步表明該反應(yīng)產(chǎn)生了穩(wěn)定的產(chǎn)物(圖2a)。在熒光光譜中,探針1本身幾乎沒(méi)有任何明顯的熒光發(fā)射,加入半胱氨酸后,在585 nm處出現(xiàn)了一個(gè)新的熒光峰,其強(qiáng)度隨時(shí)間逐漸增加,約40 min后達(dá)到飽和(圖2b)。這些實(shí)驗(yàn)表明探針1與半胱氨酸能夠發(fā)生反應(yīng),并且該反應(yīng)可用于熒光檢測(cè)半胱氨酸。
Fig.2 Time-dependent absorption (a) and fluorescence (b) spectra of probe 1(5 μmol/L) in the presence of 40 equiv of Cys. Inset: plot of fluorescence intensity vs reaction time圖2 探針1與半胱氨酸作用前后的紫外-可見(jiàn)吸收光譜 (a)及熒光光譜(b)。插圖:探針在585 nm處的熒光強(qiáng)度隨時(shí)間變化圖
為了驗(yàn)證探針1與半胱氨酸的作用機(jī)制,我們使用高分辨質(zhì)譜儀對(duì)反應(yīng)過(guò)程進(jìn)行了監(jiān)測(cè)。在質(zhì)譜圖中,測(cè)試值m/z=634.192 44對(duì)應(yīng)為探針1的[M+H]+峰(圖3a);加入半胱氨酸后,出現(xiàn)m/z=471.19 183新峰,對(duì)應(yīng)為裂解產(chǎn)物2的M+峰(圖3b)。該結(jié)果與圖1所示機(jī)理是一致的。
Fig.3 HRMS chart of probe 1 (a) and probe 1 treated with Cys (b)圖3 探針1(a)以及探針1與半胱氨酸作用后的質(zhì)譜圖(b)
2.2 探針1與半胱氨酸反應(yīng)的動(dòng)力學(xué)研究
圖4為向含有探針的溶液中加入200 μmol/L的半胱氨酸后,585 nm處的熒光強(qiáng)度隨時(shí)間的變化關(guān)系圖。利用單指數(shù)函數(shù)關(guān)系對(duì)其進(jìn)行擬合可以到反應(yīng)的準(zhǔn)一級(jí)反應(yīng)速率常數(shù)kobs=0.048 min-1,進(jìn)一步計(jì)算得到反應(yīng)的二級(jí)速率常數(shù)k2=4.0 mol/L-1s-1。
Fig.4 Time course experiment of probe 1 (5 μmol/L) reacting with Cys (200 μmol/L) in PBS buffer圖4 探針1(5 μmol/L)與半胱氨酸(200 μmol/L)作用后熒光強(qiáng)度隨時(shí)間變化
2.3 探針1對(duì)半胱氨酸的檢出限研究
如圖5a所示,在PBS溶液中,探針自身幾乎沒(méi)有熒光,加入半胱氨酸后,585 nm處出現(xiàn)新的發(fā)射峰,其熒光強(qiáng)度隨著半胱氨酸的加入(0~220 μmol/L)而逐漸增加,當(dāng)半胱氨酸的加入量達(dá)到200 μmol/L時(shí),熒光強(qiáng)度達(dá)到最大。從圖5b中可以發(fā)現(xiàn),在半胱氨酸濃度為0~80 μmol/L范圍內(nèi),熒光強(qiáng)度與半胱氨酸濃度呈良好的線性關(guān)系,線性擬合方程為Y=16.160 7X+14.705 1 (Y表示585 nm處的熒光強(qiáng)度,X表示加入半胱氨酸的濃度),R=0.999 4?;谌兜男旁氡?計(jì)算得到探針1對(duì)半胱氨酸的檢出限為2.8×10-8mol/L。
Fig.5 (a) Fluorescence spectra changes of probe 1(5 μmol/L) treated with Cys (0~220 μmol/L) Inset: plot of fluorescence intensities of probe 1 at 585 nm vs Cys concentrations (b) Liner relationship between the fluorescence intensity and Cys concentrations (0~80 μmol/L)圖5 (a)探針1(5 μmol/L)與不同濃度的半胱氨酸(0~220 μmol/L)作用的熒光光譜變化。 插圖:585 nm處的熒光強(qiáng)度隨半胱氨酸濃度變化點(diǎn)狀圖;(b)585 nm處熒光強(qiáng)度隨半胱氨酸濃度變化線性關(guān)系
2.4 探針1的選擇性研究
Fig.6 (a)Fluorescence spectra changes of probe 1(5 μmol/L) treated with various amino acids (200 μmol/L) (b) Fluorescence intensity ratios of probe 1(5 μmol/L) treated with various amino acids (200 μmol/L)圖6 (a)探針1(5 μmol/L)與各種氨基酸(200 μmol/L)作用后的熒光光譜變化;(b)探針1與各種氨基酸作用后的熒光增強(qiáng)響應(yīng)圖
向探針1的溶液中分別加入200 μmol/L的各種氨基酸后,測(cè)定其熒光光譜變化。如圖6a所示,加入各種氨基酸后,只有半胱氨酸、同型半胱氨酸以及谷胱甘肽引起明顯的熒光變化,而其他氨基酸均未引起任何明顯的熒光響應(yīng)。探針1與半胱氨酸、同型半胱氨酸以及谷胱甘肽作用后,熒光強(qiáng)度分別增加240,36和44倍 (圖6b),表明該探針與這三種生物硫醇的反應(yīng)活性次序?yàn)榘腚装彼?谷胱甘肽>同型半胱氨酸。該差異的產(chǎn)生主要?dú)w咎于三者的巰基具有不同的pKa值,半胱氨酸(~8.2)、同型半胱氨酸(~10.0)、谷胱甘肽(~9.2),即巰基的pKa值越小,則越容易電離出親核性的巰基陰離子,該硫醇的親核性也越強(qiáng)[25]。另外,硫化氫(H2S)作為一種最簡(jiǎn)單的生物硫醇在生物體內(nèi)也扮演著重要角色[26],因此我們進(jìn)一步研究了探針對(duì)硫化氫的選擇性。當(dāng)硫化氫濃度為200 μmol/L時(shí),體系熒光增強(qiáng)約65倍,遠(yuǎn)低于對(duì)半胱氨酸的240倍,表明探針1能夠選擇性識(shí)別生物硫醇,并對(duì)半胱氨酸具有最高的選擇性。
2.5 探針1的pH響應(yīng)研究
Fig.7 Fluorescence intensity at 585 nm of probe 1 (5 μmol/L) in the absence and presence of Cys (200 μmol/L) at varied pH values圖7 pH值對(duì)探針1(5 μmol/L)及探針與半胱氨酸(200 μmol/L)作用的影響
如圖7所示,探針1在pH 2-9 范圍內(nèi)熒光均很弱,說(shuō)明探針在此pH范圍內(nèi)可以穩(wěn)定存在。向體系中加入半胱氨酸后,在pH 6-9 范圍內(nèi)發(fā)生明顯的熒光增強(qiáng)。當(dāng)pH=7.0時(shí),熒光增強(qiáng)最顯著,說(shuō)明探針1可以用于生理?xiàng)l件下對(duì)半胱氨酸的檢測(cè)。
基于硫醇裂解7-硝基苯呋咱(NBD)胺機(jī)理,以5(6)-羧基-羅丹明為信號(hào)單元,7-硝基苯呋咱為硫醇識(shí)別單元,設(shè)計(jì)合成了一種新的熒光增強(qiáng)型硫醇熒光探針,并通過(guò)核磁、質(zhì)譜、熒光光譜、紫外-可見(jiàn)吸收光譜對(duì)其進(jìn)行了表征。該探針對(duì)生物硫醇表現(xiàn)出良好的選擇性識(shí)別,不受其他氨基酸的干擾,對(duì)半胱氨酸的檢出限達(dá)到2.8×10-8mol/L。與文獻(xiàn)報(bào)道的同類型硫醇熒光探針相比[21-23],該探針具有更好的水溶性及靈敏度,有望用于生物樣品中硫醇的檢測(cè)。
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A Highly Selective Fluorescence Probe for Biothiols
WANG Yue,Lü Xin,GUO Wei*
(SchoolofChemistryandChemicalEngineering,ShanxiUniversity,Taiyuan030006,China)
A new biothiol fluorescent probe bearing 5(6)-carboxy-rhodamine as fluorophore and 7-nitro-1,2,3-benzoxadiazole as biothiols reaction group was designed and synthesized based on the thiolysis of 7-nitro-1,2,3-benzoxadiazole (NBD) amine reaction group. The probe is water soluble, and could selectively detect cysteine with a big fluorescence enhancement of 240-fold and a low detection limit of 2.8×10-8mol/L.
fluorescent probe;biothiols;5(6)-carboxy-rhodamine;7-nitro-1,2,3-benzoxadiazole
10.13451/j.cnki.shanxi.univ(nat.sci.).2017.01.021
2016-09-14;
2016-12-08
國(guó)家自然科學(xué)基金 (21172137; 21302114)
王越(1988- ),男,山西太原人,博士研究生,研究領(lǐng)域?yàn)橛袡C(jī)化學(xué)。E-mail:2006294063@163.com
*通信作者:郭煒(GUO Wei), E-mail:guow@sxu.edu.cn
O657
A
0253-2395(2017)01-0123-07