NH_4Y_3F_10_多孔纳米晶的制备及_省略_在MALDI_TOF_MS中的
收稿日期：2010-05-27。收修改稿日期：2010-07-23。
国家自然科学基金(No.20535020,20671051,20721002,90813020)，国家重大研究计划项目(2007CB925102)和教育部重点研究项目(105081)资助。
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第一作者：陈志明，男，32岁，博士研究生；研究方向：稀土微/纳米材料制备及应用。
NH 4Y 3F 10多孔纳米晶的制备及其在MALDI -TOF -MS 中的应用
陈志明
耿志荣
张志杨
梅毓华
王志林＊
(南京大学化学化工学院配位化学国家重点实验室，南京
210093)
摘要：利用水热法合成出NH 4Y 3F 10多孔纳米晶。由于Y 3+离子的激发态能量可以转移给具有较高振动能的有机分子，因此这些多孔纳米晶可以作为基质辅助激光解析电离飞行时间质谱的基体材料，用于检测小分子和聚乙二醇。通过与商品化的基体材料(CHCA 、DHB)对比，证明NH 4Y 3F 10多孔纳米晶是一种性能优异的基体材料。这种新型基体材料已经成功应用于有机分子、小肽、C 60、缺氧诱导因子(HIFs)和聚乙二醇的分子量的检测，显示出这种基体材料具有广泛的应用前景。关键词：NH 4Y 3F 10；基体；基质辅助激光解析电离飞行时间质谱；小分子；聚乙二醇中图分类号：O614.32+2；O613.41；O657.6
文献标识码：A
文章编号：1001-4861(2010)11-1961-06
Synthesis of Mesoporous NH 4Y 3F 10Nanocrystals and Its Application in MALDI -TOF -MS
CHEN Zhi -Ming
GENG Zhi -Rong
ZHANG Zhi -Yang
MEI Yu -Hua
WANG Zhi -Lin ＊
(State Key Laboratory of Coordination Chemistry,School of Chemistry and Chemical Engineering,
Nanjing University,Nanjing 210093)
Abstract:Mesoporous NH 4Y 3F 10nanocrystals were fabricated to serve as a background -free matrix for analysis of small molecules and polyethylene glycols (PEGs)by matrix assisted laser desorption/ionization time of flight mass spectrometry (MALDI -TOF -MS).The excited state of yttrium ions can transfer energy to high -energy vibrations of organic molecules,which provides the potential technological application in MALDI -TOF -MS analysis of small molecules and PEGs.The advantage of this matrix in comparison with α-cyano -4-hydroxycinnamic acid (CHCA)and 2,5-dihydroxybenzoic acid (DHB)was demonstrated by MALDI -TOF -MS analysis of a peptide mixture.The efficiency of the mesoporous NH 4Y 3F 10nanocrystals as a novel matrix of low molecular weight compounds was verified by analysis of small peptide,organic compounds,C 60and hypoxia -inducible factors (HIFs).This matrix is also successfully used for analysis of PEGs (PEG 8000and PEG 15000),suggesting a potential for monitoring reactions and for synthetic polymers quality control.
Key words:NH 4Y 3F 10;matrix;MALDI -TOF -MS;small molecules;PEG
Rare -earth compounds attract a great deal of attention due to the potential technological applications in MALDI matrix [1],opticals [2-4],biolabels [5-8]and catalysts [9]based on their unique properties arising from the transitions of 4f electrons.As a rare -earth ions host
matrix,rare -earth fluorides have many advantageous features which the conventional oxygen -based systems (e.g.oxides and inorganic salts)do not have,such as low vibrational energies,good optical transparency over a wide wavelength range,and the subsequent
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minimization of the quenching of the excited state of the rare-earth ions[10-13].Among various rare-earth fluorides, MF-LnF3(M=alkaline metal,NH4+and Ln=rare earth) has been widely studied due to its potential applications in biological labels[8],solid-state lasers and display panels[14].NH4Ln3F10is a typical ionic family that consists of a large number of compounds.To obtain NH4Ln3F10crystals with different shapes and sizes,many wet chemistry approaches have been developed.For instance,NH4Ln3F10(Ln=Dy,Ho,Y,Er,Tm)has been synthesized using a hydrothermal method[15].Cubic NH4Gd3F10,NH4Tb3F10,NH4Dy3F10,NH4Ho3F10, NH4Er3F10and NH4Tm3F10could be obtained by precip-itation from a solution containing ammonium ions[16-17]. NH4Y3F10sub-microcrystals were prepared using a solution method[18-19].Herein,we present a hydrothermal route to the synthesis of mesoporous NH4Y3F10 nanocrystals by reaction of aqueous Y3+with ammonium fluoride in the presence of EDTA.Since NH4Y3F10have a high UV absorbance and can be used as UV absorbents.These mesoporous NH4Y3F10nanocrystals can be employed as a background-free matrix for analysis of small molecules and polyethylene glycols (PEGs)by matrix assisted laser desorption/ionization time of flight mass spectrometry(MALDI-TOF-MS).The performance of mesoporous NH4Y3F10nanocrystals matrix was demonstrated by determining a series of analytes,including peptide,organic compounds,C60, hypoxia-inducible factors(HIFs)and PEGs.Mass spectra of analytes were observed without the interference of background ions,revealing the matrix of mesoporous NH4Y3F10nanocrystals to be background free.
1Experimental
1.1Materials
Acetonitrile(ACN),2-phenylbenzimidazole,2-nitrobenzaldehyde,trifluoroacetic acid(TFA),matrix of CHCA and DHB were purchased from Sigma(St.Louis, MO).Peptides of Val-Gly-Gly,Pro-Glu,Met-Phe,Trp-Leu,and Val-Tyr-Val were obtained from Serva (Feinbiochemica,Heidelberg,Germany).Citric acid, propranolol,Y2O3,ethylenediaminetetraacetic acid (EDTA)and NH4F were purchased from Sinopharm Chemical Reagent Co.,Ltd.(Shanghai,China).C60was obtained from Yongxin Technology Co.,Ltd.Hypoxia-inducible factors(HIFs)was obtained from GenScript USA Inc.PEG8000and PEG15000were obtained from American Polymer Standards Corp.(Mentor,OH). Other reagents were analytical grade and purchased from Nanjing Chemical Reagent Co.,Ltd.(Nanjing, China).The water used throughout the experiment was prepared from a Milli-Q water purification system (Millipore,Milford,MA).
1.2Synthesis of mesoporous NH4Y3F10nanocrystals
In a typical synthesis,EDTA solution was obtained by dissolving500mg EDTA in6.5mL of1mol·L-1 ammonium hydroxide solution.NH4F solution was obtained by dissolving200mg NH4F in7mL water/ ethanol(2/5,V/V).Y2O3(0.5mmol)was completely dissolved in6.8mL of0.74mol·L-1HNO3to form Y(NO3)3solution.Then,the EDTA solution and10mL ethanol were added to the obtained Y(NO3)3solution in sequence.After5min ultrasonic bath,the NH4F solution was introduced.Subsequently,the mixed system was sonolyzed for5min to ensure homogeneous dispersion of all reagents in the solutions and transferred into a Teflon-lined autoclave.After the autoclave was tightly sealed and heated at110℃for 12h,the system was allowed to cool to room temperature naturally.The as-obtained white precipitate was collected,washed with distilled water and absolute ethanol several times,and finally dried at 110℃in air for0.5h.
1.3Preparation of analyte solution
Peptides of Val-Gly-Gly,Met-Phe,Trp-Leu,and Val-Tyr-Val were all dissolved in water(0.1%TFA)at the concentration of5mmol·L-1as storage solutions, separately,the mixture solution of the4peptides were obtained by mixing storage solutions and diluting with water(0.1%TFA)to the concentration of1.0mmol·L-1 each.The storage solutions for citric acid,propranolol, 2-phenylbenzimidazole,2-nitrobenzaldehyde and HIFs were prepared by dissolving them in water(0.1%TFA) at the concentration of0.1mg·mL-1,separately.The storage solutions for C60were obtained by dissolving
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第11期陈志明等：NH4Y3F10多孔纳米晶的制备及其在MALDI-TOF-MS中的应用
them in toluene(0.1%TFA)at the concentration of 1.0mg·mL-1,separately.The storage solutions for PEG8000and PEG15000were obtained by dissolving them in water(0.5%TFA)at the concentration of2.0mg·mL-1,separately.All storage solutions were refrigerated at around4℃for future use.
1.4Sample preparation for MALDI-TOF-MS
Matrix of CHCA was prepared as a saturated solution in TA(0.1%TFA in water/acetonitrile,2/1, V/V).Matrix of DHB was obtained by dissolving DHB in TA at20mg·mL-1.The matrix solution of mesoporous NH4Y3F10nanocrystals was prepared by dispersing them in acetonitrile with sonication for 2min at the concentration of0.5mg·mL-1.Solution of analyte(1μL)was pipetted onto the sample target and left in air at room temperature for5to10min to form a thin layer of analyte by evaporating water. Then1μL solution of matrix was pipetted onto the layer of analyte and left in air for5to10min for the evaporation of the solvent and for further analysis by MALDI-TOF-MS.
1.5Characterization
XRD patterns of the products were recorded on a Shimadzu XRD-6000X-ray diffractometer with Cu Kαradiation(λ=0.15406nm)at a scanning rate of0.1°·s-1 in the2θrange from20°to80°.The morphologies of the products were characterized by a JEM-200CX transmission electron microscope and a JEM2010high-resolution transmission electron microscope.Mass spectra were performed on Bruker Autoflex with a nitrogen laser(λ=337nm)at-20~20kV.2Results and discussion
2.1Structure and morphology
The synthesis of mesoporous NH4Y3F10 nanocrystals has been achieved in water/ethanol solution containing Y(NO3)3and NH4F by thermal treatment in the presence of EDTA for6h.Fig.1a shows the XRD pattern of the as-prepared sample.All the positions of the peaks can be readily indexed to cubic NH4Y3F10(ICSD93690).No other impurity peaks are detected in the XRD pattern,indicating high purity of our products.Well-resolved diffraction peaks reveal good crystallinity of the NH4Y3F10specimens.
The morphology of the as-obtained product was investigated by transmission electron microscopy (TEM).Fig.2a shows a typical TEM image of the product obtained at110℃for6h,indicating that the sample is composed of ellipsoidal particles.The enlargement shows that these ellipsoidal nanocrystals have obvious porous structures(Fig.2b).The Fig.1XRD pattern of mesoporous mesoporous NH4Y3F10 nanocrystals
(a)and(b)TEM images;(c)a selected area electron diffraction pattern(SAED);(d)high-resolution TEM(HRTEM)image of mesoporous NH4Y3F10nanocrystals
Fig.2morphology characterization of mesoporous NH4Y3F10nanocrystals
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corresponding selected area electron diffraction(SAED) pattern in Fig.2c indicates that the NH4Y3F10ellipsoidal nanocrystals are polycrystalline and the most distinct four concentric diffraction rings can be indexed to (022),(222),(333)and(006)planes from the center, sequentially.The high-resolution transmission electron microscopy(HRTEM)image of a single NH4Y3F10 nanocrystals(Fig.2d),indicates that the distance between the adjacent lattice planes is0.329nm,is ascribed to(222)crystal planes of the cubic phase NH4Y3F10.
2.2MALDI matrix
NH4Y3F10mesoporous nanocrystals can be employed as matrix for MALDI-TOF-MS analysis of small molecules.In order to evaluate the performance of NH4Y3F10mesoporous nanocrystals as a background-free ionization element,a peptide mixture containing Val-Gly-Gly,Met-Phe,Trp-Leu and Val-Tyr-Val,were chosen as models.We compared the MALDI-TOF mass spectra obtained from the conventional matrixes of CHCA,DHB and NH4Y3F10mesoporous nanocrystals. As shown in Fig.3,all the analytes were detected as [M+H]+(Val-Gly-Gly,232;Met-Phe,297;Trp-Lea,318 and Val-Tyr-Val,380),but strong interference of backgrounds caused by matrix of CHCA(Fig.3a)and DHB(Fig.3b)makes it difficult to identify analytes. Moreover,the suppression effects among analyte molecules result in the poor reproducibility and resolution of peaks for analytes.It is clear that the mass spectrum of NH4Y3F10mesoporous nanocrystals with the peptide mixture were obtained in the negative-ion reflection mode.Four prominent peaks without the interference of background ions for Val-Gly-Gly (230,[M-H]-),Met-Phe(295,[M-H]-),Trp-Lea(316, [M-H]-),and Val-Tyr-Val(378,[M-H]-)were observed as displayed in Fig.3c,suggesting that NH4Y3F10 mesoporous nanocrystals should be an excellent matrix for MALDI-TOF-MS analysis of small molecules.
(a)CHCA matrix,detected in the positive-ion reflection mode;(b)DHB matrix,detected in the positive-ion reflection mode;
(c)NH4Y3F10mesoporous Nanocrystals,detected in the negative-ion reflection mode
Fig.3Mass spectra of a peptide mixture containing Val-Gly-Gly,Met-Phe,Trp-Leu,and Val-Tyr-Val
To demonstrate the general applicability of the matrix of NH4Y3F10mesoporous nanocrystals,we analyzed 4small-molecule compounds with distinct chemical structures,including citric acid,propranolol,2-phenylbenzimidazole,2-nitrobenzaldehyde(0.1mg·mL-1).The matrix of NH4Y3F10mesoporous nanocrystals generated very clean spectra that show the presence of only the small-molecule compound-related peaks for each analyte,including the cationic parent,sodium adduct, potassium adduct,and anion parent,as shown in Fig.4.
NH4Y3F10mesoporous nanocrystals can also be employed as matrix for MALDI-TOF-MS analysis of larger molecules.Fig.5shows the mass spectrum of C60and Hypoxia-inducible factors(HIFs)with matrix of NH4Y3F10mesoporous nanocrystals.The peak of m/z at 720Da could be easily indexed to[M-e]+cationic parent of C60(Fig.5a),and peaks of m/z at2278and 2294Da could be attributed to[M+H]+and[M+O+H]+ adduct ions(Fig.5b).
MALDI-TOF-MS has an advantage in the high-speed determination of structural information, molecular weight averages,and purity of macromolecules.We characterized PEG8000and PEG 15000with NH4Y3F10mesoporous nanocrystals to explore the application of this matrix in the detection of synthetic polymers.Fig.6shows the mass spectra of
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Fig.6Mass spectra of PEG 8000and PEG 15000with matrix of NH 4Y 3F 10mesoporous nanocrystals
(a)citric acid (191,[M-H]-);(b)propranolol (260,[M+H]+;282,[M+Na]+;298,[M+K]+);(c)2-phenylbenzimidazole (195,[M+H]+);(d)2-nitrobenzaldehyde (150,[MH]-)
Fig.4Mass spectra of citric acid,propranolol,2-phenylbenzimidazole and 2-nitrobenzaldehyde with matrix
of NH 4Y 3F 10mesoporous nanocrystals
PEG 8000and PEG 15000with matrix of NH 4Y 3F 10mesoporous nanocrystals,indicating that the upper limit of detectable mass range was ~15000Da.It is noted that the mass ranges of PEG 8000and PEG 15000are at 7129~9561Da and 12000~15000Da,respectively.
3Conclusion
In summary,mesoporous NH 4Y 3F 10nanocrystals were fabricated via a straightforward method.These
mesoporous NH 4Y 3F 10nanocrystals were employed as an ionization platform,in which the NH 4Y 3F 10nanocrystals matrix functions as the energy receptacle for UV laser radiation and the energy transporter for the desorption/ionization of analytes with the minimization of interference signals caused by matrix ion.The suitability of the mesoporous NH 4Y 3F 10nanocrystals matrix was demonstrated by MALDI -TOF -MS analysis of a series of analytes,including organic compounds,
(a)C 60(720,[M-e]+);(b)HIFs (2278,[M+H]+;2294,[M+O+H]+)
Fig.5Mass spectra of C 60and HIFs with matrix of NH 4Y 3F 10mesoporous nanocrystals
陈志明等：NH 4Y 3F 10多孔纳米晶的制备及其在MALDI -TOF -MS 中的应用
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