A retrievable and highly selective fluorescent sensor for detecting copper and sulfide

Sensors and Actuators B 185 (2013) 125–131

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A retrievable and highly selective fluorescent sensor for detecting copper and sulfide Cunji Gao, Xiao Liu, Xiaojie Jin, Jiang Wu, Yujie Xie, Weisheng Liu, Xiaojun Yao, Yu Tang ∗ Key Laboratory of Nonferrous Metal Chemistry and Resources Utilization of Gansu Province, State Key Laboratory of Applied Organic Chemistry, College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, PR China

a r t i c l e

i n f o

Article history: Received 4 February 2013 Received in revised form 19 April 2013 Accepted 24 April 2013 Available online xxx Keywords: Copper Sulfide Selectivity Fluorescent sensor Colorimetry

a b s t r a c t A new selective fluorescent sensor for Cu2+ and S2− , 2-hydroxy-N -((quinolin-2yl)methylene)benzohydrazide (HL), based on 2-methylquinoline derivative has been designed, synthesized and evaluated. The fluorescence of the sensor HL was quenched by Cu2+ with a 1:1 binding ratio, behaving as an “on–off” type sensor even in the presence of a wide range of biological cations. Once binding with Cu2+ , it can display high selectivity for S2− . Among the various anions, only sulfide anion induces the revival of fluorescence of HL, resulting in “off–on” type sensing of sulfide anion. The signal transduction occurs via reversible formation–separation of complex L–Cu and CuS. With the addition of Cu2+ , sensor HL give rise to a colorless to yellow color change. The resulting yellow solution switches to colorless immediately upon the addition of S2− ; however, no changes were observed in the presence of other anions, including CN− , NO3 − , P2 O7 4− , various forms of sulfate, and some other reactive sulfur species (RSS) including SCN− , l-methionine (l-Me) and l-cysteine (l-Cys). Notably, the color change is so distinct that the recycling process can be seen clearly by the naked eye. © 2013 Elsevier B.V. All rights reserved.

1. Introduction Developing fluorescent sensors for chemical species which can be used in biological and environmental detection is currently an attractive field for chemists [1]. Specially, heavy metal ions are earned great concern about their toxicity, because they can lead to serious environmental and health problems [1d,2]. As the third most abundant transition metal ions in the human body, Cu2+ shows a key point in various biological processes, and its homeostasis is critical for the metabolism and development of living organisms [3]. Among a variety of quantification techniques have been developed, fluorescent measurement have been employed the base standard for sensing Cu2+ because of their sensitivity and specificity, and real-time monitoring with fast response time [4]. Cu2+ is a typical ion that has a pronounced quenching effect on fluorophores by mechanisms inherent to the paramagnetic species [5]. More interestingly, the Cu2+ complex can be applied to sense other substances. Sulfide anion can be found not only in industrial settings where it is either used as a reactant or produced as a by-product of manufacturing or industrial processes, but also due to the microbial reduction of sulfate by anaerobic bacteria or formed from the sulfur containing amino acids in meat proteins, for example, conversion

∗ Corresponding author. Tel.: +86 931 8912552; fax: +86 931 8912582. E-mail address: [email protected] (Y. Tang). 0925-4005/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.snb.2013.04.110

into sulfur and sulfuric acid, dyes and cosmetic manufacturing, production of wood pulp, etc. [6]. Continuous and high concentration exposure of sulfide would lead to various physiological and biochemical problems. It can irritate the mucous membranes and even cause unconsciousness and respiratory paralysis [7]. Once sulfide anion is protonated, it becomes even more toxic. Thus, the detection of sulfide anion has become very important from industrial, environmental, and biological requirements [8]. A large quantity of tools for recognizing sulfide anions have been designed [9], for example, titration [10], fluorimetry [11], chemiluminescence [12], spectrophotometry [13], inductively coupled plasma atomic emission spectroscopy [14], hydride generation atomic fluorescence spectrometry [15], an electrochemical method [16], and ion chromatography [17]. Considering practicality and convenience, fluorimetry and colorimetry are acceptable. However, the development of selective fluorescent sensors for the detection of sulfide ions has attracted little interest with respect to other widely investigated anions such as fluoride [18], cyanide [19], and other forms of sulfate [20]. Utilization of metal-anion affinity has been described as another method of sensing anions [21]; however, most of them are irreversible. Among the various approaches to sensing sulfide anions, reversible sensors exploiting copper sulfide affinity [9d,21d,22] attracted our extraordinary attention. Sulfide is known to react with copper ions to make a very stable CuS form with a very low solubility product constant Ksp = 6.3 × 10−36 . Recently, Nagano and Zeng groups reported new approaches for the detection of sulfide in live biological systems through the development of Cu2+

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SeO2 80oC

N

H

N O 1

O H +

N

N H OH

O NH2

EtOH reflux

O

N H OH

N

N

HL

sodium salts of F− , Cl− , Br− , I− , CO3 2− , NO2 − , NO3 − , PO4 3− , HPO4 2− , H2 PO4 − , P2 O7 4− , HS− , HSO3 2− , S2 O3 2− , S2 O8 2− , SO3 2− , S2− , SO4 2− , CN− and HSO4 − were prepared in the second distilled water. Stock solutions (10 mM) of the potassium salts of SCN− were prepared in the second distilled water. l-Methionine (l-Me) and l-cysteine (l-Cys) were prepared in the second distilled water. The volume of cationic stock solution added was less than 100 ␮L to remain the concentration of HL unchanged. All fluorescence spectra were recorded at 25 ◦ C with the excitation wavelength set at 410 nm. 2.2. Calculation methods

Scheme 1. Synthesis of the fluorescent sensor HL.

complex for chemoselective sulfide-responsive fluorescent sensors [9b,23]. The mechanism we expected is that Cu2+ would be dragged out from the complex when sulfide binds to copper ion, resulting in fluorescence enhancement. Consequently, the inorganic-reaction based method could be developed and created a platform for discovering new sulfide sensors that may be potentially useful for sulfide detection from industrial, environmental, and biological requirements. On the basis of this hypothesis, we designed and synthesized a new small molecular fluorescent sensor 2-hydroxy-N ((quinolin-2-yl)methylene)benzohydrazide (HL, Scheme 1) based on 2-methylquinoline derivative. Sensor HL demonstrates obvious fluorescence quenching after the addition of Cu2+ . Once interacted with Cu2+ to form complex L–Cu, the new complex showed high sensitivity and selectivity for sulfide over other possible competitive anions, meaning that the sulfide anion may react with the complex and release the sensor HL. The synthesis, photophysical characterization of sensor HL which is selective for copper ions were described, and the subsequent complex L–Cu displays characteristic fluorescence “off–on” behavior for sulfide. Notably, the color change of the system from colorless to yellow and then to colorless was accompanied during the whole course, which would be detected easily by the naked eye. 2. Experimental 2.1. General information and materials All of the materials for synthesis were purchased from commercial suppliers and used without further purification. 1 H and 13 C NMR spectra were taken on a Varian mercury-400 spectrometer in CDCl3 and d6 -DMSO solutions, with tetramethylsilane (TMS) as an internal standard. Fourier transform infrared (FTIR) spectra of the materials were conducted within the 4000–400 cm−1 wavenumber range using a Nicolet 360 FTIR spectrometer with the KBr pellet technique. Absorption spectra were determined on a Varian UV-Cary100 spectrophotometer. Mass spectra were obtained on a Bruker esquire 6000 and a Bruker maxis 4G respectively. Xray diffraction patterns (XRD) were determined with Rigaku-Dmax 2400 diffractometer using Cu K␣ radiation. Fluorescence spectra measurements were performed on a Hitachi F-4500 spectrofluorimeter. All pH measurements were made with METTLER TOLEDO EL20 pH meter. Quantum yields were determined by an absolute method using an integrating sphere on Edinburgh Instrument FLS920. All of the detections of metal ions were operated in HEPES/DMSO (20 mM, pH 7.22, 1:9, v/v). The stock solution of HL was prepared in DMSO (10 mM). Stock solutions (10 mM) of the perchlorate salts of Na+ , K+ , Mg2+ , Ca2+ , Cu2+ , Al3+ , Hg2+ , Zn2+ , Cr3+ , Cd2+ , Ag+ , Fe3+ , Mn2+ , Co2+ , and Ni2+ were prepared in ethanol, respectively. Stock solutions (10 mM) of the chloride salt of Cu+ were prepared in acetonitrile. Stock solutions (10 mM) of the

To investigate the interaction mode, we carried out density functional theory (DFT) calculations with B3LYP/6-31G (d) method. The geometry of the molecules was optimized with Gaussian 09 [24] package at the B3LYP/6-31G (d) levels for C, H, O, N atoms and LANL2DZ [25] levels for Cu. 2.3. Synthesis 2.3.1. Synthesis of quinoline-2-carbaldehyde (1) 2-Methylquinoline (500 mg, 3.50 mmol) was dissolved in 1,4dioxane (30 ml), and SeO2 (805 mg, 7.00 mmol) was added to the solution. The mixture was stirred at 80 ◦ C for 2 h, and then cooled to ambient temperature. The precipitate was filtered off. The solvents were evaporated to give the crude product, which was purified by flash chromatography on silica gel (1:1 petroleum ether/ethyl acetate as eluent) to give 1 (401 mg, 2.56 mmol, 73%) as a yellow solid. IR (KBr disk, cm−1 ): 1708 (C O), 1641, 1588, 1566, 1500, 1300, 1263, 1201, 838, 751. 1 H NMR (400 MHz, CDCl3 ): ı 10.21 (1H, S), 8.22–8.28 (4H, m), 8.99 (2H, d, J = 8.4 Hz), 7.87 (1H, d, J = 8.0 Hz), 7.80 (1H, t), 7.67 (1H, t). 13 C NMR (100 MHz, CDCl3 ): ı 193.6, 152.5, 147.9, 137.3, 130.4, 130.4, 130.0, 129.1, 127.8, 117.3. MS (ESI+): m/z 158 (M+H)+ . 2.3.2. Synthesis of 2-hydroxy-N -((quinolin-2-yl)methylene)benzohydrazide (HL) Quinoline-2-carbaldehyde (400 mg, 2.56 mmol) and 2hydroxybenzohydrazide (389 mg, 2.56 mmol) were mixed in boiling ethanol with stirring for 4 h, then brown precipitates obtained were filtered off, washed with ethanol and dried over P4 O10 under vacuum to give HL (581 mg, 2.00 mmol, 78%) as an ivory white solid. IR (KBr disk, cm−1 ): 3437, 1632 (C O), 1545, 1500, 1457, 1427, 1315, 1231, 1150, 830, 755. 1 H NMR (400 MHz, DMSO): ı 12.12 (1H, S), 11.60 (1H, S), 8.62 (1H, S), 8.45 (1H, d, J = 8.8 Hz), 8.13 (1H, d, J = 8.8 Hz), 8.07–7.01 (2H, m), 7.88 (1H, d, J = 7.6 Hz), 7.81 (1H, t, J = 7.2 Hz), 7.65 (1H, t, J = 7.6 Hz), 7.47 (1H, t, J = 7.2 Hz), 7.02–6.97 (2H, m) (Fig. S1). 13 C NMR (100 MHz, DMSO): ı 164.9, 158.6, 153.6, 148.5, 147.4, 136.8, 133.9, 130.1, 128.9, 128.9, 128.0, 127.9, 127.4, 119.0, 117.5, 117.2, 116.5 (Fig. S2). MS (ESI+): m/z 292 (M+H)+ (Fig. S3). 3. Results and discussion 3.1. Fluorescence detection toward Cu2+ After systematically looking for selective signaling toward different metal ions for potential applications, the selectivity of HL to various metal ions was examined in DMSO–H2 O (9:1, v/v) solution at pH 7.22 in HEPES buffer. The sensor HL exhibits the emission maximum at 468 nm excited at 410 nm with quantum yield (Ф) ca. 0.097. Upon the addition of 1.0 equiv. of Cu2+ , a clear fluorescence quench is observed (Ф = 0.059) (Fig. 1). The quench in emission intensity may be attributed to the formation of the L–Cu complex. As shown in Fig. 1, all other cations have little effect on the

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Fig. 1. Selectivity of HL for Cu2+ in the presence of other metal ions in DMSO/HEPES (20 mM, pH 7.22, 9:1, v/v), ex = 410 nm. Gray bars represent the addition of the appropriate metal ion (50 ␮M) to a solution of HL (50 ␮M). Black bars represent the subsequent addition of Cu2+ (50 ␮M) to the solution.

Fig. 3. Fluorescence emission spectra of HL (5 ␮M) upon addition of Cu2+ (0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8 and 2.0 equiv. with respect to HL) in DMSO/HEPES (20 mM, pH 7.22, 9:1, v/v), ex = 410 nm. The inset is the corresponding Cu2+ titration profile according the emission at 468 nm.

fluorescence spectra of HL. What’s more, the stability constant value of HL for Cu2+ was determined to be 1.11 × 105 M−1 (Fig. S4). These results clearly demonstrate that the sensor HL has excellent affinity for Cu2+ over these ions. To further explore the selectivity of HL for Cu2+ , we measured the fluorescence intensity of HL in the presence of Cu2+ mixed with various metal ions in DMSO–H2 O (9:1, v/v) solution at pH 7.22 in HEPES buffer. While a range of metal ions mixed with the sensor, add 1 equiv. of Cu2+ to the above system. As a result, all tested cations exerted no or little influence on the fluorescence detection of Cu2+ (Fig. 1), so the binding of the sensor and Cu2+ was not affected by concomitant ions. The detection limit (LOD) for Cu2+ is measured to be 8.68 × 10−6 M (Fig. S5).

gradual increase of the absorption band centered at 406 nm were observed with a distinct isosbestic point at 356 nm, which indicates the formation of only one UV-active copper complex. The absorption spectrum remained at a plateau upon further addition of Cu2+ (>1.0 equiv.) implicating a 1:1 complexation of the sensor with the Cu2+ ion, accompanied by a perceived color change from colorless to yellow. The color change of HL upon addition of Cu2+ may be caused by the charge transfer (CT) between the ligand L−1 and Cu2+ in the complex. These observations imply the undoubted conversion of free sensor HL to the corresponding copper complex. The coordination mode of HL to Cu2+ was also studied by fluorescence titration (Fig. 3). Free HL showed strong fluorescence emission at 468 nm upon excitation at 410 nm. Upon addition of Cu2+ (0–2.0 equiv.), the emission intensity decreases significantly, indicating a Cu2+ selective ON–OFF fluorescent signaling behavior. In the titration spectra, the titration of Cu2+ into HL gave a maximum emission band centered at 468 nm which showed a linear quench with the increase of [Cu2+ ]total when the ratio of [Cu2+ ]total /HL is below or equal to 1:1. When the ratio reached 1:1, however, higher [Cu2+ ]total did not lead to any further emission quench. The fluorescence quench of HL was due to the coordination to a paramagnetic Cu2+ [26]. The linear relationship of the fluorescence titration showed that sensor HL responded to Cu2+ in 1:1 stoichiometry (Fig. 3, inset). This result has also been confirmed by ESI-MS, where a peak at m/z 477 ([Cu2+ + L− + ClO4 − + Na+ ]+ ) corresponding to the 1:1 complex is observed (Fig. S6).

3.2. Absorption, fluorescence titration spectra To investigate the binding property of sensor HL toward Cu2+ , we measured the UV–vis spectra of HL (25 ␮M) in the presence of various concentrations of Cu2+ (0–50 ␮M), as shown in Fig. 2. During photometric titrations of HL with Cu2+ (0–2.0 equiv.), a gradual decrease of the absorbance at 334 nm and a concomitant

3.3. Theoretical calculations

Fig. 2. UV–vis spectra of HL (25 ␮M) upon the titration of Cu2+ (0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0 equiv.) in DMSO/HEPES (20 mM, pH 7.22, 9:1, v/v) at room temperature. The inset shows the plot of absorbance of HL at 406 nm versus Cu2+ concentration.

To further verify the configuration of L–Cu, we carried out DFT calculations. In theoretical calculations, the geometry of the molecules was optimized with Gaussian 09 package at the B3LYP/6-31G (d) levels for C, H, O, N atoms and LANL2DZ levels for Cu. The minimum nature of the structure was confirmed by frequency calculations at the same computational level. The optimized configuration is shown in Fig. 4, which shows that the Cu2+ ion is four coordinated with one tridentate ligand L− and one monodentate perchlorate. And the whole coordination sphere forms a nearly planar structure. The bond lengths were obtained from the natural bond orbital (NBO) analysis. The four bond lengths are R1 = 1.9117 A˚ (Cu Nquinoline–nitrogen ), R2 = 2.0584 A˚ (Cu Nschiff base–nitrogen ), R3 = 2.0508 A˚ (Cu Ohydroxy ), R4 = 1.9737 (Cu Operchlorate ), which are comparable to the corresponding Cu O

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Fig. 4. Calculated energy-minimized structure of HL with Cu2+ .

and Cu N bond lengths found in related complexes [27]. These data indicate that L− could provide suitable space to better accommodate the corresponding ions. 3.4. Fluorescence detection L–Cu toward S2− The selectivity of L–Cu for a variety of anions was evaluated to assess the value of this small molecule as a multi-ion sensor. It is very exciting and noteworthy that sensor HL could be regenerated only by adding S2− to the solution containing L–Cu. Common anions, such as F− , Cl− , Br− , I− , CO3 2− , NO2 − , NO3 − , CN− , HS− , PO4 3− , HPO4 2− , H2 PO4 − , P2 O7 4− and various forms of sulfate did not generate the positive results (Fig. 5). The L–Cu system revealed remarkably selective fluorescence “on” behavior exclusively with S2− . Besides, the selectivity of L–Cu for S2− was not affected by the presence of some other reactive sulfur species (RSS) including SCN− , l-methionine (l-Me), l-cysteine (l-Cys), and some types of sulfates (Fig. 6). Thus, the results strongly proved that L–Cu can selectively detect S2− . 3.5. Fluorescence titration, absorption spectra The “off–on” property of the sensor was researched further. Fig. 7 explains the fluorescence enhancement upon the addition

Fig. 5. Selectivity of L–Cu for S2− in the presence of other anions in DMSO/HEPES (20 mM, pH 7.22, 9:1, v/v), ex = 410 nm. Gray bars represent the emission intensities of HL (10 ␮M). Black bars represent the addition of the Cu2+ (10 ␮M) to a solution of HL (10 ␮M) and after addition of different anions (10 ␮M).

Fig. 6. Selectivity of L–Cu for S2− in the presence other forms of sulfates in DMSO/HEPES (20 mM, pH 7.22, 9:1, v/v), ex = 410 nm. Gray bars represent the addition of the Cu2+ (10 ␮M) to a solution of HL (10 ␮M) and after addition of different anions (10 ␮M). Black bars represent the subsequent addition of S2− (10 ␮M) in the same media.

of sulfide ions in the presence of 1 equiv. of Cu2+ added to the solution of HL. Both the intensity and shape of the system’s emission spectrum closely match those of sensor HL (Fig. 3), that is to say, not only the fluorescence intensity but also the maximum emission peak was totally revived. This showed that Cu2+ was released from complex L–Cu, and CuS formed. The formation of CuS was ascertained by the XRD measurement of the media. The result was also confirmed through ESI-MS analysis. ESI-MS of the above media displayed a HL molecular-ion peak [HL + Na+ ]+ at m/z 314.1. The calibration curve of the fluorescence intensity at 468 nm of HL (Fig. 7, inset) elucidated that sulfide anion interacted with copper ion. The detection limit (LOD) for S2− is measured to be 9.49 × 10−7 M (Fig. S7). Besides, it is almost matched between the UV–vis absorption spectrum of sulfide titration in the presence of L–Cu with 2 equiv. of S2− (Fig. 8) and that of copper ion titration (Fig. 2). In the system of L–Cu, the absorption peak and intensity changes were similar to the former (Fig. 2); under these conditions, S2− restored the UV–vis spectra. This suggests that signal transduction is reversible; therefore, this highly efficient sensor would be recyclable. As illustrated

Fig. 7. Fluorescence titration of HL (10 ␮M) and Cu2+ (10 ␮M) upon the addition of different concentrations of S2− (0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8 and 2.0 equiv. with respect to HL) in DMSO/HEPES (20 mM, pH 7.22, 9:1, v/v), ex = 410 nm. The inset is the corresponding S2− titration profile according the emission at 468 nm.

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Scheme 2. Graphic of the proposed mechanism of the sensing of sulfide.

construction of various other kinds of fluorescent sensors to monitor metal ions, anions, and other species. Acknowledgements This work was financially supported by the National Natural Science Foundation of China (Project 20931003, 21071068) and the Fundamental Research Funds for the Central Universities (Project lzujbky-2011-17). Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.snb.2013.04.110. References Fig. 8. UV–vis response of HL (25 ␮M) and Cu2+ (25 ␮M) upon the addition of different concentrations of S2− (0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8 and 2.0 equiv.) in DMSO/HEPES (20 mM, pH 7.22, 9:1, v/v). The inset are photographs of HL, HL + Cu2+ , and HL + Cu2+ + S2− in color changes.

in the inset of Fig. 8, the colorless HL turns yellow after the addition of 1 equiv. of Cu2+ , and then returns to colorless with the addition of 1 equiv. of S2− , which can be detected by the naked eye. 3.6. Mechanism of the sensing of sulfide In short, the addition of copper ion can cause fluorescence quenching of the sensor HL simultaneously inducing a color change from colorless to yellow. The added sulfide can capture copper ion, resulting in fluorescence revival of HL (˚3 = 0.098) and inducing a yellow to colorless colorimetric change. This fluorescence quenching of HL by Cu2+ can be attributed to complex L–Cu formation upon the addition of Cu2+ , as shown in Scheme 2, and then the copper ions were captured by sulfide anion to produce CuS, resulting in the revival of the HL, which is accompanied by fluorescence and color regeneration. Therefore, the addition of sulfide can be monitored by the naked eye. 4. Conclusion In conclusion, a small molecular fluorescent sensor with the potential capability to detect Cu2+ by quenching and S2− by enhancement of fluorescence intensity has been established successfully, besides the color changed from colorless to yellow and then recovered. An inorganic reaction resulting in dosimetric anion determination, which based on a complex L–Cu formation–separation process and CuS formation, is described in the paper. We expect that this approach is applicable for the

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Biographies Cunji Gao received his B.S. degree from Xuzhou Normal University, PR China, in 2009. He is currently a Ph.D. candidate at College of Chemistry and Chemical Engineering, Lanzhou University, PR China. His research interests focus on developing fluorescent sensors. Xiao Liu received his B.S. degree from Lanzhou University, PR China, in 2008. He is currently a M.S. candidate at College of Chemistry and Chemical Engineering, Lanzhou University. His research interests focus on developing fluorescent sensors.

C. Gao et al. / Sensors and Actuators B 185 (2013) 125–131 Xiaojie Jin received his B.S. degree from Lanzhou University, PR China, in 2010. He is currently a Ph.D. candidate at College of Chemistry and Chemical Engineering, Lanzhou University. His research interests focus on developing computer-aided molecular design. Jiang Wu received his B.S. degree from Lanzhou University, PR China, in 2005. He received his Ph.D. degree from Georgia State University, USA, in 2011. He is a lecturer of Inorganic Chemistry in College of Chemistry and Chemical Engineering, Lanzhou University. His current research interests include biosensors and protein. Yujie Xie is currently a B.S. candidate at College of Chemistry and Chemical Engineering, Lanzhou University, PR China. Weisheng Liu received his Ph.D. degree from Lanzhou University, PR China, in 1996. He is a professor of Inorganic Chemistry in College of Chemistry and Chemical

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Engineering, Lanzhou University. His current research interests include rare earth coordination chemistry and Function Materials Chemistry. Xiaojun Yao received his Ph.D. degree from Lanzhou University, PR China, in 2003. He is a professor of Computational Chemistry in College of Chemistry and Chemical Engineering, Lanzhou University. His current research interests include computer-aided molecular design, studies of biological macromolecules and drug small molecular interactions, bioinformatics. Yu Tang received his Ph.D. degree from Lanzhou University, PR China, in 1999. She is a professor of Inorganic Chemistry in College of Chemistry and Chemical Engineering, Lanzhou University. Her current research interests include new rare earth complexes composite luminescence materials, supramolecular function complexes and chemosensors.