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Terahertz absorption spectra of some saccharides and their metal complexes
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Spectrochimica Acta Part A 69 (2008) 160–166
Terahertz absorption spectra of some saccharides and their metal complexes Limin Yang a,∗ , Hongqi Sun b , Shifu Weng c , Kui Zhao a , Liangliang Zhang b , Guozong Zhao b , Yugang Wang a , Yizhuang Xu c , Xiangyang Lu a , Cunlin Zhang b , Jinguang Wu c , Chen Jia’er a a
Institute of Heavy Ion Physics, Key Laboratory of Heavy Ion Physics, Ministry of Education and School of Physics, Peking University, Beijing 100871, China b Department of Physics, Capital Normal University, Beijing 100037, China c The State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China Received 30 May 2006; accepted 15 March 2007
Abstract In this work, THz absorption spectra of some saccharides and their metal complexes were measured. The main purpose of this work is to investigate the M–O vibrations, intermolecular and intramolecular hydrogen bonds and other vibrations in the FIR region using powerful spectroscopic techniques adopting the metal–sugar complexes prepared in our laboratory. The M–O vibrations in the FIR spectra of metal–sugar complexes indicate the formation of metal complexes. The THz spectrum of glucose below 100 cm−1 was measured at first to confirm the THz experimental method. Characteristic absorption bands in the spectra of various samples are observed. THz spectra of saccharides below 100 cm−1 often have several absorption bands, and different saccharides have various absorption peaks in the THz region, which may be used to distinguish different saccharides. The differences in the number of bands observed are related to different structures of the samples, and these absorption bands are related to the collective motion of molecules. But the THz spectra of their metal complexes are different from the ligands, and no band appears in the region below 50 cm−1 at the present experimental condition, which indicates that THz spectroscopy may also be helpful to identify the formation of metal–sugar complexes, and the changes after complexation in the THz spectra below 100 cm−1 may be related to different metal ions. The metal–sugar complexes with similar crystal structures resemble mid-IR spectra, but their THz spectra may have some differences. © 2007 Elsevier B.V. All rights reserved. Keywords: THz absorption spectra; Saccharides; Metal–sugar complexes
1. Introduction Carbohydrates and their derivatives, as the most abundant class of biomolecules, are known to have a large variety of biological functions [1]. Through the interaction between these poly-functional molecules and metal ions in living organisms, the modification of the biological function of both counterparts may be expected. The interactions between metal ions and carbohydrates are involved in many biochemical processes, such as the transport and storage of metal ions, stabilization of membrane structures, binding of glycoproteins to cell surfaces and
∗
Corresponding author. Tel.: +86 10 62755408; fax: +86 10 62751875. E-mail address: [email protected] (L. Yang).
1386-1425/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2007.03.023
toxic metal metabolism, the binding of protein to sugar and so on [2–9]. The study of the interaction between metal ions and sugars may provide abundant information on the coordination behavior between metal ion and hydroxyl groups, which is very important for understanding the physiological role of metal ions [10–12]. Except for single-crystal X-ray diffraction analysis, IR method, a frequently used technique for investigating hydrogen bonded systems, is also an important technique to characterize the formation of metal–sugar complex and to deduce unknown structures [13–19]. Carbohydrates are often regarded as model systems to investigate hydrogen bonds. Since the bonding forces are weak and the moving masses are considerably large, vibrational modes of hydrogen bonds have resonance frequencies in the still relatively unexplored terahertz (THz) region [20].
L. Yang et al. / Spectrochimica Acta Part A 69 (2008) 160–166
Terahertz time-domain spectroscopy has proved to be a versatile tool for quantitative detection and conformational analysis of biomolecules and molecule recognition [21–25]. The spectral features of crystalline samples in the low-frequency region (below 100 cm−1 ) are associated with collective vibrational modes of molecules mediated by hydrogen bonded networks [21]. Otherwise, M–O vibrations of metal–ligand complexes appearing in the FIR region are definite evidences of the complexes formation [26,27]. Because hydrogen bond network will be changed and M–O bonds will form after metalation, therefore, FIR spectroscopy, an important method to characterize the formation of M–O bonds, and THz time-domain spectroscopy below 100 cm−1 was employed to identify the formation of metal–sugar complexes, to measure the far-infrared properties of sugars and their metal complexes in solid state and to investigate the M–O vibrations, intermolecular hydrogen bonds and other vibrations in the FIR region. It is also an attempt to investigate the M–O vibrations and other vibrations in the THz absorption spectra of metal–ligand complexes using powerful spectroscopic techniques, and for convenience we use the metal–sugar complexes prepared before as examples here. In this paper, d-ribose (C5 H10 O5 , denoted as R), erythritol (C4 H10 O4 , denoted as E), galactitol (C6 H14 O6 , denoted as G) and myo-inositol (C6 H12 O6 , denoted as I) and their metal complexes, PrCl3 ·C5 H10 O5 ·5H2 O (PrR), PrCl3 ·C4 H10 O4 ·6H2 O (PrE), Ca(NO3 )2 ·C4 H10 O4 (CaEN), CuCl2 ·C4 H10 O4 (CuE), SmCl3 ·C4 H10 O4 ·6H2 O (SmE), MnCl2 ·C4 H10 O4 (MnE), 2PrCl3 ·C6 H14 O6 ·14H2 O (PrG) and NdCl3 ·C6 H12 O6 ·9H2 O (NdI), were chosen as models to study M–O vibrations, intermolecular hydrogen bonds and other vibrations of saccharides and their metal complexes in the far-infrared region. 2. Experimental 2.1. Materials Erythritol, galactitol, d-ribose and myo-inositol (A. R. (analytical grade reagent)) were obtained from commercial sources and used as supplied. The syntheses of various metal–sugar complexes were described in our previous papers [13–17].
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The experimental apparatus for terahertz transmission measurements has been discussed in detail elsewhere [28]. The THz spectrum of glucose was determined at first to prove the reliability of experimental condition. Two spectra were recorded for each sample and the repeatability of the spectra confirms that the spectra are repeatable. The preparation of the samples was by pressing pure sample to pellets for saccharides or mixed pellets with polyethylene powder for metal–sugar complexes and the mass ratio of sample to polyethylene is about 3:2, the weight of whole pellet is around 70 mg for each sample. The resolution of the spectra is 40 GHz. The THz frequency-domain spectra were obtained from the corresponding THz time-domain spectra via Fast Fourier Transform. Through comparison THz frequency-domain spectra of the samples and corresponding references the THz absorption spectra of the samples were obtained. 3. Results and discussion 3.1. FIR spectra of saccharides and their metal complexes The chemical structures of myo-inositol, galactitol, erythritol, d-ribose are shown in Fig. 1. Their FIR spectra and the FIR spectra of their metal complexes, PrE, PrR, PrG, NdI, CaEN, CuE, MnE and SmE are shown in Figs. 2 and 3. The structures of these metal–sugar complexes were described in our previous work [13–17]. A widely used method of studying carbohydrates is vibrational, and in particular, IR spectroscopy. In recent years, a number of works on calculation of frequencies and forms of normal vibrations of mono- and disaccharides have appeared [29–36]. And the bands in the 700–500 cm−1 are related to exocyclic deformations (CCO), below 500 cm−1 are endocyclic (CCO, CCC) deformations and below 200 cm−1 are associated with the molecular interactions (hydrogen bonding, intercrystalline forces), etc. [30]. The FIR method may distinguish different isomers of sugars and obtain information concerning their structure [26,27]. Myo-inositol, d-ribose, erythritol and
2.2. Physical measurements The far-IR spectra of saccharides and their metal complexes were measured using common used Nujol mull method, because mineral oil has no absorption in the far-IR region and the method can protect sample in solid state against wet, avoid distortion of bands or happening of ion exchange. Samples were powdered and suspended in the Nujol mull, and were then inserted between thin polyethylene windows. Far-infrared spectra in the range of 650–50 cm−1 were performed on a Nicolet Magna-IR 750 Spectrometer at room temperature and at 4 cm−1 resolution, 100 scans. The optical bench was purged with dried air. Their THz absorption spectra were recorded on the THz timedomain device of Capital Normal University of China, with N2 atmosphere based on photoconductive switches for generation and electro-optical crystal detection of the far-infrared light.
Fig. 1. Chemical structure of erythritol, myo-inositol, galactitol and d-ribose.
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Fig. 3. The FIR spectra of erythritol and its metal complexes in the 650–50 cm−1 region.
Fig. 2. The FIR spectra of myo-inositol, d-ribose, galactitol and their metal complexes in the 650–50 cm−1 region. (a) The FIR spectra of galactitol and PrCl3 –galactitol. (b) The FIR spectra of d-ribose and PrCl3 –d-ribose complex. (c) The FIR spectra of myo-inositol and NdCl3 –myo-inositol complex.
galactitol have different structures. Myo-inositol and d-ribose have ring structures, but erythritol and galactitol have chain structures. Therefore, their FIR spectra have many differences in peak positions and relative intensities. The results of FIR spectra of four samples originating from inter- and intra-molecular vibrational modes indicate that FIR is a sensitive method to identify different saccharides, and far-infrared absorption features are sensitive to the structure and spatial arrangement of molecules.
Our previous work about investigation on the interaction of saccharides with metals in aqueous solution or in solid state shows that FIR technique can be a useful tool to interpret the formation of metal–saccharide complexes [27]. Strong broad M–O bands appear in the FIR spectra of their metal complexes, which give definite information about metal–saccharide complex formation. Here, the FIR spectra of metal–sugar complexes show that the bands become broad for PrR, PrG and NdI after complexation. And for erythritol, although the bands do not become even broader after metalation, the shift of peak positions and the change of relative intensities are evident. Furthermore, our previous results indicate that similar mid-IR spectra correspond to resemble crystal structures for metal–sugar complexes, but for the samples with similar structures mentioned in this paper, their FIR spectra may not be alike, for example, the spectra of PrE and SmE, and the spectra of CuE and MnE are not similar. For the metal–sugar complexes having similar structures prepared before, their FIR spectra may be similar or different. Especially for transition metal–erythritol complexes, the mid-IR spectra are similar in the 1600–650 cm−1 region (the OH vibrations are different in the 4000–3000 cm−1 region because they have different hydrogen bond lengths); they also have similar structures (it can be confirmed by the fact that CuE and MnE have similar single crystal structures) [13]. But their FIR spectra are
L. Yang et al. / Spectrochimica Acta Part A 69 (2008) 160–166
different and no similarity can be observed (Fig. 2). The results show that FIR may be more sensitive than mid-IR spectra to some extent. It is reasonable. M–O vibrations appear in the FIR region and for the complexes with same ligand and different metal ions, the bands would be various. The hydrogen bonded networks have been changed after complexation, therefore, the appearance of M–O vibrations and the changes of hydrogen bonds, etc., result in different FIR bands. After complexation cyclic structures formed by hydroxyl groups of saccharides and metal ions usually can be observed, therefore, maybe the bands also contain cyclic deformation vibrations [26,37]. The FIR spectra of metal complexes are different from ligand itself. FIR is a useful technique to describe the metal–saccharide complex formation. The evidence for coordination of metal ions by saccharides is the significant differences in the FIR spectra of saccharides and of the metal complexes. The assignment of the bands in the FIR region is complicated. The bands located at about 200 cm−1 are often assigned to M–O vibrations for metal–sugar complexes. For example, for lanthanide complexes with glucose, fructose, sorbose, sucrose, maltose, lactose, etc., the Ln–O vibrations at the bands around 200 cm−1 are considered [27]. Therefore, the bands at 208 cm−1 for PrG, 223 cm−1 for PrR, 198 cm−1 for PrE, 208 cm−1 for SmE, 196 cm−1 for
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MnE, 195 cm−1 for CaEN, 195 cm−1 for CuE, 201 cm−1 for NdI and other peaks near these bands may be related to M–O vibrations. 3.2. THz spectra of saccharides and their metal complexes For verifying of the THz experimental method, the THz spectrum of glucose below 100 cm−1 was determined at first. Its THz spectrum is consistent with the reference [38]. Therefore, the experimental condition of the other samples was adopted as similar to glucose and new THz absorption spectra were obtained for the saccharides and their metal complexes. The THz absorption spectra of myo-inositol, galactitol, erythritol, d-ribose and their metal complexes, including PrE, PrG, NdI, CaEN, CuE, MnE and SmE are shown in Figs. 4 and 5. The peak positions (as THz and cm−1 ) in the THz spectra of these compounds are listed in Table 1. Two formats were used for the FIR and THz spectra because of the custom of different experimental methods. Distinct absorption peaks are seen in the spectral range 0.1–3 THz for the samples. THz absorption spectra of different saccharides at room temperature have various absorption bands. Each molecule has characteristic resonance peaks. Myo-
Fig. 4. The THz spectra of myo-inositol, d-ribose, galactitol and erythritol.
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inositol has five bands in the region: 1.00, 1.46, 1.58, 1.85 and 2.05 THz, galactitol has two bands: 0.88 and 2.22 THz, d-ribose has five bands: 1.11, 1.58, 1.93, 2.11 and 2.28 THz, erythritol has three bands: 1.82, 1.93 and 2.11 THz (Fig. 4 and Table 1). Most of the saccharides have bands below 1.5 THz: myo-inositol, galactitol and d-ribose. The samples used in the experiment, being in polycrystalline powder form, are expected to show
intermolecular and intramolecular vibrational modes in this frequency range. Saccharides are a special kind of organic and biomolecular substance in that there are many strong hydrogen bonds in their structures. The intermolecular and intramolecular hydrogen bonding vibrations are shown from the information of the FIR and THz spectra. The spectral features of these crystalline samples in the low-frequency region are associated with
Fig. 5. The THz spectra of metal–sugar complexes.
L. Yang et al. / Spectrochimica Acta Part A 69 (2008) 160–166
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Fig. 5. (Continued ).
collective vibrational modes of molecules mediated by hydrogen bonded networks. Four samples have different structures as shown in Fig. 1, and they have various bands in the region below 100 cm−1 , which should be the collective motions of molecules. Compared to the spectrum of d-glucose (1.46 and 2.11 THz), d-galactose (2.23 and 2.65 THz), etc., the low-frequency translational and rotational lattice vibrational modes in the crystalline structures, the spectra of the four samples shown here have different characteristic bands and the results show that THz spectroscopy is a sensitive method to probe the changes of molecular structures and to do molecule recognition. The results show that each saccharide has different absorption bands and for their metal complexes, no band appears below 50 cm−1 at the present experimental condition, including the apparatus, the mass ratio of sample to polyethylene and measurement at room temperature, etc. Just like the data listed in Table 1, 1.76 THz for PrE, 1.99 THz for PrG, 1.97 THz for NdI, 2.28 THz for CuE, 1.81 THz for SmE, 2.20 THz for MnE were observed (Fig. 5 and Table 1). No band appears below 100 cm−1 at the present experimental condition for PrR. For CaEN, the band is located at 1.82 THz (no band appears in the region for Ca(NO3 )2 at the present experimental condition). The spectra of metal complexes are different with saccharide itself, which confirms the formation of metal–sugar complexes. It may
originate from the changes of hydrogen bonds and the coordination of metal ions. No absorption band appears below 1.5 THz (50 cm−1 ) at the present experimental condition, it may be the characteristic of metal–sugar complexes. Different metal–sugar complexes have various absorption bands, but it seems that there are some relations between the peak positions and the radius of metal ions. From Table 1, for metal ion–erythritol complexes, the absorption peaks are located at 76 and 73 cm−1 for Cu2+ and Mn2+ -complexes, and the two transition metal ions have ˚ The radius of relatively smaller ion radii: 0.72 and 0.80 A. 2+ 2+ ˚ Pr3+ , 1.01 A ˚ Ca is similar to lanthanide ions (Ca , 0.99 A, 3+ ˚ and Sm , 0.96 A), and their THz absorption peak positions are also similar: 61, 59, 60 cm−1 . The THz results of metal ion–erythritol complexes show that metal ion has larger radius, then its erythritol complex has lower absorption peak position, or reverse in some extent. Therefore, it may be deduced that the THz absorption bands below 100 cm−1 are related to different metal ions for metal–sugar complexes. Otherwise, the mid-IR spectra of PrE and SmE, and CuE and MnE are similar in the 1600–650 cm−1 region, respectively, but their THz spectra have differences (Fig. 5 and Table 1). The FIR spectra measured at the Nicolet Far-IR Spectrometer can cover with 650–50 cm−1 region, and THz spectra in the used setup can get spectrum below 100 cm−1 , therefore,
Table 1 The main bands in the THz absorption spectra below 100 cm−1 and radii of metal ions for metal–sugar complexes Materials
Peak positions (THz)
Corresponding peak positions (cm−1 )
Myo-inositol Galactitol d-Ribose Erythritol 2PrCl3 ·C6 H14 O6 ·14H2 O PrCl3 ·C4 H10 O4 ·6H2 O Ca(NO3 )2 ·C4 H10 O4 CuCl2 ·C4 H10 O4 SmCl3 ·C4 H10 O4 ·6H2 O MnCl2 ·C4 H10 O4 NdCl3 ·C6 H12 O6 ·9H2 O
1.00, 1.46, 1.58, 1.82, 2.05 0.88, 2.22 1.11, 1.58, 1.93, 2.11, 2.28 1.82, 1.93, 2.11 1.99 1.76 1.82 2.28 1.81 2.20 1.97
33, 48, 53, 61, 68 29, 74 37, 53, 64, 70, 76 61, 64, 70 66 59 61 76 60 73 66
˚ Radius of metal ion (A)
1.01 0.99 0.72 0.96 0.80
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the combination of the two methods can provide us full information in the FIR region. The bands below 50 cm−1 are often related to intermolecular hydrogen bonds and other vibrations for solid samples and some samples have no bands in the region [39] at the present experimental condition, for example, no band appears in the region below 100 cm−1 for PrR and Ca(NO3 )2 at the present experimental condition. In the 100–cm−1 region, the bands in the FIR and corresponding THz spectra are nearly consistent, for example, for MnE, 74 cm−1 , 2.20 THz; for CaEN, 90, 61 cm−1 , 1.82 THz; for PrE, 93, 77, 59 cm−1 , 1.76 THz. The results indicate that the two methods are consistent in some extent. A detailed assignment of the individual vibrational modes observed in the low-frequency region is a challenging task. The spectroscopic data presented here will be useful for critical benchmark evaluation of future theoretical models of low-energy interactions in molecular crystals. 4. Conclusions In this work, THz absorption spectra of some saccharides and their metal complexes were recorded. The M–O vibrations in the FIR spectra of metal complexes in the 650–50 cm−1 region confirm the formation of metal–sugar complexes. THz absorption spectra of different saccharides have various bands, which may be used to characterize different saccharides, but the bands are changed after complexation and no band appears in the region below 50 cm−1 at the present experimental condition for metal–sugar complexes. The results indicate that the FIR and THz methods are sensitive tools reflecting the minor differences in the structures of saccharides. THz absorption spectra may also be helpful to identify the formation of metal–sugar complexes, and to investigate M–O vibrations, intermolecular hydrogen bonds and other vibrations in the FIR region. Similar structures correspond to resemble mid-IR spectra for metal–sugar complexes, but their FIR spectra may have some differences and THz absorption spectra below 100 cm−1 have more discrimination, which show that FIR and THz methods may be more sensitive tools than mid-IR technique for characterization of metal–sugar complexes. Acknowledgement This work was supported by the National Basic Research Project of China (No. 2002CB713600). References [1] S. Yano, M. Otsuka, in Sigel, H., (Eds.), Metal Ions in Biological Systems 32 (1996) 27. [2] D.M. Templeton, B. Sarkar, Biochem. J. 230 (1985) 35. [3] P.F. Predki, D.M. Whitfield, B. Sarkar, Biochem. J. 281 (1992) 835. [4] W.I. Weis, K. Drickamer, W.A. Hendrickson, Nature 360 (1992) 127. [5] K. Drickamer, Nature 360 (1992) 183.
[6] K. Burger, L. Nagy, Biocoord. Chem. Coord. Equilib. Biologically Active Syst. (1990) 236. [7] B. Gyurcsik, L. Nagy, Coord. Chem. Rev. 203 (2000) 81. [8] J.F. Verchere, S. Chapelle, F. Xin, D.C. Crans, Progr. Inorg. Chem. 47 (1998) 837. [9] S.J. Angyal, Adv. Carbohydr. Chem. Biochem. 47 (1989) 1. [10] Y. Sun, R.D. Soloway, Y.Z. Han, G.D. Yang, Z.J. Liu, Z.L. Yang, Y.Z. Xu, J.G. Wu, Steroids 67 (2002) 385. [11] W. Tian, S. Cheng, L.M. Yang, X.L. Jin, S.F. Weng, J.G. Wu, J. Inorg. Biochem. 78 (3) (2000) 197. [12] W. Tian, L.M. Yang, Y.Z. Xu, S.F. Weng, J.G. Wu, Carbohyd. Res. 324 (1) (2000) 45. [13] L.M. Yang, Y.L. Su, Y.Z. Xu, Z.H. Guo, Z.M. Wang, S.F. Weng, C.H. Yan, S.W. Zhang, J.G. Wu, Inorg. Chem. 42 (19) (2003) 5844. [14] L.M. Yang, Y. Zhao, Y.Z. Xu, X.L. Jin, W. Tian, S.F. Weng, J.G. Wu, G.X. Xu, Carbohydr. Res. 334 (2001) 91. [15] L.M. Yang, Y. Zhao, W. Tian, X.L. Jin, S.F. Weng, J.G. Wu, Carbohydr. Res. 330 (2001) 125. [16] L.M. Yang, D.L. Tao, Y. Sun, X.L. Jin, Y. Zhao, Z.L. Yang, S.F. Weng, J.G. Wu, G.X. Xu, J. Mol. Struct. 560 (2001) 105. [17] L.M. Yang, W. Tian, Y.Z. Xu, Y.L. Su, S. Gao, Z.M. Wang, S.F. Weng, C.H. Yan, J.G. Wu, J. Inorg. Biochem. 98 (2004) 1284. [18] L.M. Yang, D.T. Xie, Y.Z. Xu, Y.L. Wang, S.W. Zhang, S.F. Weng, K. Zhao, J.G. Wu, J. Inorg. Biochem. 99 (2005) 1090. [19] L.M. Yang, Y.L. Su, Y.Z. Xu, S.W. Zhang, J.G. Wu, K. Zhao, J. Inorg. Biochem. 98 (2004) 1251. [20] P.C. Upadhya, Y.C. Shen, A.G. Davies, E.H. Linfield, Vib. Spectrosc. 35 (2004) 139. [21] M. Walther, B.M. Fischer, P.U. Jepsen, Chem. Phys. 288 (2003) 261. [22] J. Nishizawa, K. Suto, T. Sasaki, T. Tanabe, T. Kimura, J. Phys. D 36 (2003) 2958. [23] A. Markelz, S. Whitmire, J. Hillbrecht, R. Birge, Phys. Med. Biol. 47 (2002) 3797. [24] M. Walther, P. Plochocka, B. Fischer, H. Helm, P. Uhd Jepsen, Biopolymers 67 (2002) 310. [25] M. Walther, B. Fischer, M. Schall, H. Helm, P. Uhd Jepsen, Chem. Phys. Lett. 320 (2000) 389. [26] J.G. Wu, Modern Fourier Transform Spectroscopic Techniques and Its Applications, vol. II, Science and Technology References Press, Beijing, 1994, p. 159. [27] L.Q. Yang, J.G. Wu, Q. Zhou, J. Bian, Y.M. Yang, D.F. Xu, G.X. Xu, Microchim. Acta 14 (1997) 251. [28] Y. Hu, X.H. Wang, L.T. Guo, C.L. Zhang, H.B. Liu, X.C. Zhang, Acta Phys. Sinica 54 (2005) 4124 (in Chinese). [29] P.D. Vasko, J. Blackwell, J.L. Koenig, Carbohydr. Res. 32 (1974) 297. [30] M. Hineno, Carbohydr. Res. 56 (1977) 219. [31] R.G. Zhbankov, V.M. Andrianov, M.K. Marchewka, J. Mol. Struct. 436–437 (1997) 637. [32] M.V. Korolevich, R.G. Zhbankov, V.V. Sivchik, J. Mol. Struct. 220 (1990) 301. [33] R.G. Zhbankov, V.M. Andrianov, H. Ratajczak, M. Marchewka, J. Struct. Chem. 36 (1995) 416. [34] M. Mathlouthi, J.L. Koenig, Adv. Carbohydr. Chem. Biochem. 44 (1986) 7. [35] R.G. Zhbankov, V.M. Andrianov, H. Ratajczak, M. Marchewka, J. Struct. Chem. 36 (1995) 287. [36] R.G. Zhbankov, J. Mol. Struct. 275 (1992) 65. [37] L.M. Yang, S.F. Weng, J.R. Ferraro, J.G. Wu, Vib. Spectrosc. 25 (2001) 57. [38] P.C. Upadhya, Y.C. Shen, A.G. Davies, E.H. Linfield, J. Biol. Phys. 29 (2003) 117. [39] S.F. Weng, Fourier Transform Infrared Spectrometer, Chemical Industry Press, Beijing, 2005, p. 218.
Spectrochimica Acta Part A 69 (2008) 160–166
Terahertz absorption spectra of some saccharides and their metal complexes Limin Yang a,∗ , Hongqi Sun b , Shifu Weng c , Kui Zhao a , Liangliang Zhang b , Guozong Zhao b , Yugang Wang a , Yizhuang Xu c , Xiangyang Lu a , Cunlin Zhang b , Jinguang Wu c , Chen Jia’er a a
Institute of Heavy Ion Physics, Key Laboratory of Heavy Ion Physics, Ministry of Education and School of Physics, Peking University, Beijing 100871, China b Department of Physics, Capital Normal University, Beijing 100037, China c The State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China Received 30 May 2006; accepted 15 March 2007
Abstract In this work, THz absorption spectra of some saccharides and their metal complexes were measured. The main purpose of this work is to investigate the M–O vibrations, intermolecular and intramolecular hydrogen bonds and other vibrations in the FIR region using powerful spectroscopic techniques adopting the metal–sugar complexes prepared in our laboratory. The M–O vibrations in the FIR spectra of metal–sugar complexes indicate the formation of metal complexes. The THz spectrum of glucose below 100 cm−1 was measured at first to confirm the THz experimental method. Characteristic absorption bands in the spectra of various samples are observed. THz spectra of saccharides below 100 cm−1 often have several absorption bands, and different saccharides have various absorption peaks in the THz region, which may be used to distinguish different saccharides. The differences in the number of bands observed are related to different structures of the samples, and these absorption bands are related to the collective motion of molecules. But the THz spectra of their metal complexes are different from the ligands, and no band appears in the region below 50 cm−1 at the present experimental condition, which indicates that THz spectroscopy may also be helpful to identify the formation of metal–sugar complexes, and the changes after complexation in the THz spectra below 100 cm−1 may be related to different metal ions. The metal–sugar complexes with similar crystal structures resemble mid-IR spectra, but their THz spectra may have some differences. © 2007 Elsevier B.V. All rights reserved. Keywords: THz absorption spectra; Saccharides; Metal–sugar complexes
1. Introduction Carbohydrates and their derivatives, as the most abundant class of biomolecules, are known to have a large variety of biological functions [1]. Through the interaction between these poly-functional molecules and metal ions in living organisms, the modification of the biological function of both counterparts may be expected. The interactions between metal ions and carbohydrates are involved in many biochemical processes, such as the transport and storage of metal ions, stabilization of membrane structures, binding of glycoproteins to cell surfaces and
∗
Corresponding author. Tel.: +86 10 62755408; fax: +86 10 62751875. E-mail address: [email protected] (L. Yang).
1386-1425/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2007.03.023
toxic metal metabolism, the binding of protein to sugar and so on [2–9]. The study of the interaction between metal ions and sugars may provide abundant information on the coordination behavior between metal ion and hydroxyl groups, which is very important for understanding the physiological role of metal ions [10–12]. Except for single-crystal X-ray diffraction analysis, IR method, a frequently used technique for investigating hydrogen bonded systems, is also an important technique to characterize the formation of metal–sugar complex and to deduce unknown structures [13–19]. Carbohydrates are often regarded as model systems to investigate hydrogen bonds. Since the bonding forces are weak and the moving masses are considerably large, vibrational modes of hydrogen bonds have resonance frequencies in the still relatively unexplored terahertz (THz) region [20].
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Terahertz time-domain spectroscopy has proved to be a versatile tool for quantitative detection and conformational analysis of biomolecules and molecule recognition [21–25]. The spectral features of crystalline samples in the low-frequency region (below 100 cm−1 ) are associated with collective vibrational modes of molecules mediated by hydrogen bonded networks [21]. Otherwise, M–O vibrations of metal–ligand complexes appearing in the FIR region are definite evidences of the complexes formation [26,27]. Because hydrogen bond network will be changed and M–O bonds will form after metalation, therefore, FIR spectroscopy, an important method to characterize the formation of M–O bonds, and THz time-domain spectroscopy below 100 cm−1 was employed to identify the formation of metal–sugar complexes, to measure the far-infrared properties of sugars and their metal complexes in solid state and to investigate the M–O vibrations, intermolecular hydrogen bonds and other vibrations in the FIR region. It is also an attempt to investigate the M–O vibrations and other vibrations in the THz absorption spectra of metal–ligand complexes using powerful spectroscopic techniques, and for convenience we use the metal–sugar complexes prepared before as examples here. In this paper, d-ribose (C5 H10 O5 , denoted as R), erythritol (C4 H10 O4 , denoted as E), galactitol (C6 H14 O6 , denoted as G) and myo-inositol (C6 H12 O6 , denoted as I) and their metal complexes, PrCl3 ·C5 H10 O5 ·5H2 O (PrR), PrCl3 ·C4 H10 O4 ·6H2 O (PrE), Ca(NO3 )2 ·C4 H10 O4 (CaEN), CuCl2 ·C4 H10 O4 (CuE), SmCl3 ·C4 H10 O4 ·6H2 O (SmE), MnCl2 ·C4 H10 O4 (MnE), 2PrCl3 ·C6 H14 O6 ·14H2 O (PrG) and NdCl3 ·C6 H12 O6 ·9H2 O (NdI), were chosen as models to study M–O vibrations, intermolecular hydrogen bonds and other vibrations of saccharides and their metal complexes in the far-infrared region. 2. Experimental 2.1. Materials Erythritol, galactitol, d-ribose and myo-inositol (A. R. (analytical grade reagent)) were obtained from commercial sources and used as supplied. The syntheses of various metal–sugar complexes were described in our previous papers [13–17].
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The experimental apparatus for terahertz transmission measurements has been discussed in detail elsewhere [28]. The THz spectrum of glucose was determined at first to prove the reliability of experimental condition. Two spectra were recorded for each sample and the repeatability of the spectra confirms that the spectra are repeatable. The preparation of the samples was by pressing pure sample to pellets for saccharides or mixed pellets with polyethylene powder for metal–sugar complexes and the mass ratio of sample to polyethylene is about 3:2, the weight of whole pellet is around 70 mg for each sample. The resolution of the spectra is 40 GHz. The THz frequency-domain spectra were obtained from the corresponding THz time-domain spectra via Fast Fourier Transform. Through comparison THz frequency-domain spectra of the samples and corresponding references the THz absorption spectra of the samples were obtained. 3. Results and discussion 3.1. FIR spectra of saccharides and their metal complexes The chemical structures of myo-inositol, galactitol, erythritol, d-ribose are shown in Fig. 1. Their FIR spectra and the FIR spectra of their metal complexes, PrE, PrR, PrG, NdI, CaEN, CuE, MnE and SmE are shown in Figs. 2 and 3. The structures of these metal–sugar complexes were described in our previous work [13–17]. A widely used method of studying carbohydrates is vibrational, and in particular, IR spectroscopy. In recent years, a number of works on calculation of frequencies and forms of normal vibrations of mono- and disaccharides have appeared [29–36]. And the bands in the 700–500 cm−1 are related to exocyclic deformations (CCO), below 500 cm−1 are endocyclic (CCO, CCC) deformations and below 200 cm−1 are associated with the molecular interactions (hydrogen bonding, intercrystalline forces), etc. [30]. The FIR method may distinguish different isomers of sugars and obtain information concerning their structure [26,27]. Myo-inositol, d-ribose, erythritol and
2.2. Physical measurements The far-IR spectra of saccharides and their metal complexes were measured using common used Nujol mull method, because mineral oil has no absorption in the far-IR region and the method can protect sample in solid state against wet, avoid distortion of bands or happening of ion exchange. Samples were powdered and suspended in the Nujol mull, and were then inserted between thin polyethylene windows. Far-infrared spectra in the range of 650–50 cm−1 were performed on a Nicolet Magna-IR 750 Spectrometer at room temperature and at 4 cm−1 resolution, 100 scans. The optical bench was purged with dried air. Their THz absorption spectra were recorded on the THz timedomain device of Capital Normal University of China, with N2 atmosphere based on photoconductive switches for generation and electro-optical crystal detection of the far-infrared light.
Fig. 1. Chemical structure of erythritol, myo-inositol, galactitol and d-ribose.
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Fig. 3. The FIR spectra of erythritol and its metal complexes in the 650–50 cm−1 region.
Fig. 2. The FIR spectra of myo-inositol, d-ribose, galactitol and their metal complexes in the 650–50 cm−1 region. (a) The FIR spectra of galactitol and PrCl3 –galactitol. (b) The FIR spectra of d-ribose and PrCl3 –d-ribose complex. (c) The FIR spectra of myo-inositol and NdCl3 –myo-inositol complex.
galactitol have different structures. Myo-inositol and d-ribose have ring structures, but erythritol and galactitol have chain structures. Therefore, their FIR spectra have many differences in peak positions and relative intensities. The results of FIR spectra of four samples originating from inter- and intra-molecular vibrational modes indicate that FIR is a sensitive method to identify different saccharides, and far-infrared absorption features are sensitive to the structure and spatial arrangement of molecules.
Our previous work about investigation on the interaction of saccharides with metals in aqueous solution or in solid state shows that FIR technique can be a useful tool to interpret the formation of metal–saccharide complexes [27]. Strong broad M–O bands appear in the FIR spectra of their metal complexes, which give definite information about metal–saccharide complex formation. Here, the FIR spectra of metal–sugar complexes show that the bands become broad for PrR, PrG and NdI after complexation. And for erythritol, although the bands do not become even broader after metalation, the shift of peak positions and the change of relative intensities are evident. Furthermore, our previous results indicate that similar mid-IR spectra correspond to resemble crystal structures for metal–sugar complexes, but for the samples with similar structures mentioned in this paper, their FIR spectra may not be alike, for example, the spectra of PrE and SmE, and the spectra of CuE and MnE are not similar. For the metal–sugar complexes having similar structures prepared before, their FIR spectra may be similar or different. Especially for transition metal–erythritol complexes, the mid-IR spectra are similar in the 1600–650 cm−1 region (the OH vibrations are different in the 4000–3000 cm−1 region because they have different hydrogen bond lengths); they also have similar structures (it can be confirmed by the fact that CuE and MnE have similar single crystal structures) [13]. But their FIR spectra are
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different and no similarity can be observed (Fig. 2). The results show that FIR may be more sensitive than mid-IR spectra to some extent. It is reasonable. M–O vibrations appear in the FIR region and for the complexes with same ligand and different metal ions, the bands would be various. The hydrogen bonded networks have been changed after complexation, therefore, the appearance of M–O vibrations and the changes of hydrogen bonds, etc., result in different FIR bands. After complexation cyclic structures formed by hydroxyl groups of saccharides and metal ions usually can be observed, therefore, maybe the bands also contain cyclic deformation vibrations [26,37]. The FIR spectra of metal complexes are different from ligand itself. FIR is a useful technique to describe the metal–saccharide complex formation. The evidence for coordination of metal ions by saccharides is the significant differences in the FIR spectra of saccharides and of the metal complexes. The assignment of the bands in the FIR region is complicated. The bands located at about 200 cm−1 are often assigned to M–O vibrations for metal–sugar complexes. For example, for lanthanide complexes with glucose, fructose, sorbose, sucrose, maltose, lactose, etc., the Ln–O vibrations at the bands around 200 cm−1 are considered [27]. Therefore, the bands at 208 cm−1 for PrG, 223 cm−1 for PrR, 198 cm−1 for PrE, 208 cm−1 for SmE, 196 cm−1 for
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MnE, 195 cm−1 for CaEN, 195 cm−1 for CuE, 201 cm−1 for NdI and other peaks near these bands may be related to M–O vibrations. 3.2. THz spectra of saccharides and their metal complexes For verifying of the THz experimental method, the THz spectrum of glucose below 100 cm−1 was determined at first. Its THz spectrum is consistent with the reference [38]. Therefore, the experimental condition of the other samples was adopted as similar to glucose and new THz absorption spectra were obtained for the saccharides and their metal complexes. The THz absorption spectra of myo-inositol, galactitol, erythritol, d-ribose and their metal complexes, including PrE, PrG, NdI, CaEN, CuE, MnE and SmE are shown in Figs. 4 and 5. The peak positions (as THz and cm−1 ) in the THz spectra of these compounds are listed in Table 1. Two formats were used for the FIR and THz spectra because of the custom of different experimental methods. Distinct absorption peaks are seen in the spectral range 0.1–3 THz for the samples. THz absorption spectra of different saccharides at room temperature have various absorption bands. Each molecule has characteristic resonance peaks. Myo-
Fig. 4. The THz spectra of myo-inositol, d-ribose, galactitol and erythritol.
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inositol has five bands in the region: 1.00, 1.46, 1.58, 1.85 and 2.05 THz, galactitol has two bands: 0.88 and 2.22 THz, d-ribose has five bands: 1.11, 1.58, 1.93, 2.11 and 2.28 THz, erythritol has three bands: 1.82, 1.93 and 2.11 THz (Fig. 4 and Table 1). Most of the saccharides have bands below 1.5 THz: myo-inositol, galactitol and d-ribose. The samples used in the experiment, being in polycrystalline powder form, are expected to show
intermolecular and intramolecular vibrational modes in this frequency range. Saccharides are a special kind of organic and biomolecular substance in that there are many strong hydrogen bonds in their structures. The intermolecular and intramolecular hydrogen bonding vibrations are shown from the information of the FIR and THz spectra. The spectral features of these crystalline samples in the low-frequency region are associated with
Fig. 5. The THz spectra of metal–sugar complexes.
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Fig. 5. (Continued ).
collective vibrational modes of molecules mediated by hydrogen bonded networks. Four samples have different structures as shown in Fig. 1, and they have various bands in the region below 100 cm−1 , which should be the collective motions of molecules. Compared to the spectrum of d-glucose (1.46 and 2.11 THz), d-galactose (2.23 and 2.65 THz), etc., the low-frequency translational and rotational lattice vibrational modes in the crystalline structures, the spectra of the four samples shown here have different characteristic bands and the results show that THz spectroscopy is a sensitive method to probe the changes of molecular structures and to do molecule recognition. The results show that each saccharide has different absorption bands and for their metal complexes, no band appears below 50 cm−1 at the present experimental condition, including the apparatus, the mass ratio of sample to polyethylene and measurement at room temperature, etc. Just like the data listed in Table 1, 1.76 THz for PrE, 1.99 THz for PrG, 1.97 THz for NdI, 2.28 THz for CuE, 1.81 THz for SmE, 2.20 THz for MnE were observed (Fig. 5 and Table 1). No band appears below 100 cm−1 at the present experimental condition for PrR. For CaEN, the band is located at 1.82 THz (no band appears in the region for Ca(NO3 )2 at the present experimental condition). The spectra of metal complexes are different with saccharide itself, which confirms the formation of metal–sugar complexes. It may
originate from the changes of hydrogen bonds and the coordination of metal ions. No absorption band appears below 1.5 THz (50 cm−1 ) at the present experimental condition, it may be the characteristic of metal–sugar complexes. Different metal–sugar complexes have various absorption bands, but it seems that there are some relations between the peak positions and the radius of metal ions. From Table 1, for metal ion–erythritol complexes, the absorption peaks are located at 76 and 73 cm−1 for Cu2+ and Mn2+ -complexes, and the two transition metal ions have ˚ The radius of relatively smaller ion radii: 0.72 and 0.80 A. 2+ 2+ ˚ Pr3+ , 1.01 A ˚ Ca is similar to lanthanide ions (Ca , 0.99 A, 3+ ˚ and Sm , 0.96 A), and their THz absorption peak positions are also similar: 61, 59, 60 cm−1 . The THz results of metal ion–erythritol complexes show that metal ion has larger radius, then its erythritol complex has lower absorption peak position, or reverse in some extent. Therefore, it may be deduced that the THz absorption bands below 100 cm−1 are related to different metal ions for metal–sugar complexes. Otherwise, the mid-IR spectra of PrE and SmE, and CuE and MnE are similar in the 1600–650 cm−1 region, respectively, but their THz spectra have differences (Fig. 5 and Table 1). The FIR spectra measured at the Nicolet Far-IR Spectrometer can cover with 650–50 cm−1 region, and THz spectra in the used setup can get spectrum below 100 cm−1 , therefore,
Table 1 The main bands in the THz absorption spectra below 100 cm−1 and radii of metal ions for metal–sugar complexes Materials
Peak positions (THz)
Corresponding peak positions (cm−1 )
Myo-inositol Galactitol d-Ribose Erythritol 2PrCl3 ·C6 H14 O6 ·14H2 O PrCl3 ·C4 H10 O4 ·6H2 O Ca(NO3 )2 ·C4 H10 O4 CuCl2 ·C4 H10 O4 SmCl3 ·C4 H10 O4 ·6H2 O MnCl2 ·C4 H10 O4 NdCl3 ·C6 H12 O6 ·9H2 O
1.00, 1.46, 1.58, 1.82, 2.05 0.88, 2.22 1.11, 1.58, 1.93, 2.11, 2.28 1.82, 1.93, 2.11 1.99 1.76 1.82 2.28 1.81 2.20 1.97
33, 48, 53, 61, 68 29, 74 37, 53, 64, 70, 76 61, 64, 70 66 59 61 76 60 73 66
˚ Radius of metal ion (A)
1.01 0.99 0.72 0.96 0.80
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the combination of the two methods can provide us full information in the FIR region. The bands below 50 cm−1 are often related to intermolecular hydrogen bonds and other vibrations for solid samples and some samples have no bands in the region [39] at the present experimental condition, for example, no band appears in the region below 100 cm−1 for PrR and Ca(NO3 )2 at the present experimental condition. In the 100–cm−1 region, the bands in the FIR and corresponding THz spectra are nearly consistent, for example, for MnE, 74 cm−1 , 2.20 THz; for CaEN, 90, 61 cm−1 , 1.82 THz; for PrE, 93, 77, 59 cm−1 , 1.76 THz. The results indicate that the two methods are consistent in some extent. A detailed assignment of the individual vibrational modes observed in the low-frequency region is a challenging task. The spectroscopic data presented here will be useful for critical benchmark evaluation of future theoretical models of low-energy interactions in molecular crystals. 4. Conclusions In this work, THz absorption spectra of some saccharides and their metal complexes were recorded. The M–O vibrations in the FIR spectra of metal complexes in the 650–50 cm−1 region confirm the formation of metal–sugar complexes. THz absorption spectra of different saccharides have various bands, which may be used to characterize different saccharides, but the bands are changed after complexation and no band appears in the region below 50 cm−1 at the present experimental condition for metal–sugar complexes. The results indicate that the FIR and THz methods are sensitive tools reflecting the minor differences in the structures of saccharides. THz absorption spectra may also be helpful to identify the formation of metal–sugar complexes, and to investigate M–O vibrations, intermolecular hydrogen bonds and other vibrations in the FIR region. Similar structures correspond to resemble mid-IR spectra for metal–sugar complexes, but their FIR spectra may have some differences and THz absorption spectra below 100 cm−1 have more discrimination, which show that FIR and THz methods may be more sensitive tools than mid-IR technique for characterization of metal–sugar complexes. Acknowledgement This work was supported by the National Basic Research Project of China (No. 2002CB713600). References [1] S. Yano, M. Otsuka, in Sigel, H., (Eds.), Metal Ions in Biological Systems 32 (1996) 27. [2] D.M. Templeton, B. Sarkar, Biochem. J. 230 (1985) 35. [3] P.F. Predki, D.M. Whitfield, B. Sarkar, Biochem. J. 281 (1992) 835. [4] W.I. Weis, K. Drickamer, W.A. Hendrickson, Nature 360 (1992) 127. [5] K. Drickamer, Nature 360 (1992) 183.
[6] K. Burger, L. Nagy, Biocoord. Chem. Coord. Equilib. Biologically Active Syst. (1990) 236. [7] B. Gyurcsik, L. Nagy, Coord. Chem. Rev. 203 (2000) 81. [8] J.F. Verchere, S. Chapelle, F. Xin, D.C. Crans, Progr. Inorg. Chem. 47 (1998) 837. [9] S.J. Angyal, Adv. Carbohydr. Chem. Biochem. 47 (1989) 1. [10] Y. Sun, R.D. Soloway, Y.Z. Han, G.D. Yang, Z.J. Liu, Z.L. Yang, Y.Z. Xu, J.G. Wu, Steroids 67 (2002) 385. [11] W. Tian, S. Cheng, L.M. Yang, X.L. Jin, S.F. Weng, J.G. Wu, J. Inorg. Biochem. 78 (3) (2000) 197. [12] W. Tian, L.M. Yang, Y.Z. Xu, S.F. Weng, J.G. Wu, Carbohyd. Res. 324 (1) (2000) 45. [13] L.M. Yang, Y.L. Su, Y.Z. Xu, Z.H. Guo, Z.M. Wang, S.F. Weng, C.H. Yan, S.W. Zhang, J.G. Wu, Inorg. Chem. 42 (19) (2003) 5844. [14] L.M. Yang, Y. Zhao, Y.Z. Xu, X.L. Jin, W. Tian, S.F. Weng, J.G. Wu, G.X. Xu, Carbohydr. Res. 334 (2001) 91. [15] L.M. Yang, Y. Zhao, W. Tian, X.L. Jin, S.F. Weng, J.G. Wu, Carbohydr. Res. 330 (2001) 125. [16] L.M. Yang, D.L. Tao, Y. Sun, X.L. Jin, Y. Zhao, Z.L. Yang, S.F. Weng, J.G. Wu, G.X. Xu, J. Mol. Struct. 560 (2001) 105. [17] L.M. Yang, W. Tian, Y.Z. Xu, Y.L. Su, S. Gao, Z.M. Wang, S.F. Weng, C.H. Yan, J.G. Wu, J. Inorg. Biochem. 98 (2004) 1284. [18] L.M. Yang, D.T. Xie, Y.Z. Xu, Y.L. Wang, S.W. Zhang, S.F. Weng, K. Zhao, J.G. Wu, J. Inorg. Biochem. 99 (2005) 1090. [19] L.M. Yang, Y.L. Su, Y.Z. Xu, S.W. Zhang, J.G. Wu, K. Zhao, J. Inorg. Biochem. 98 (2004) 1251. [20] P.C. Upadhya, Y.C. Shen, A.G. Davies, E.H. Linfield, Vib. Spectrosc. 35 (2004) 139. [21] M. Walther, B.M. Fischer, P.U. Jepsen, Chem. Phys. 288 (2003) 261. [22] J. Nishizawa, K. Suto, T. Sasaki, T. Tanabe, T. Kimura, J. Phys. D 36 (2003) 2958. [23] A. Markelz, S. Whitmire, J. Hillbrecht, R. Birge, Phys. Med. Biol. 47 (2002) 3797. [24] M. Walther, P. Plochocka, B. Fischer, H. Helm, P. Uhd Jepsen, Biopolymers 67 (2002) 310. [25] M. Walther, B. Fischer, M. Schall, H. Helm, P. Uhd Jepsen, Chem. Phys. Lett. 320 (2000) 389. [26] J.G. Wu, Modern Fourier Transform Spectroscopic Techniques and Its Applications, vol. II, Science and Technology References Press, Beijing, 1994, p. 159. [27] L.Q. Yang, J.G. Wu, Q. Zhou, J. Bian, Y.M. Yang, D.F. Xu, G.X. Xu, Microchim. Acta 14 (1997) 251. [28] Y. Hu, X.H. Wang, L.T. Guo, C.L. Zhang, H.B. Liu, X.C. Zhang, Acta Phys. Sinica 54 (2005) 4124 (in Chinese). [29] P.D. Vasko, J. Blackwell, J.L. Koenig, Carbohydr. Res. 32 (1974) 297. [30] M. Hineno, Carbohydr. Res. 56 (1977) 219. [31] R.G. Zhbankov, V.M. Andrianov, M.K. Marchewka, J. Mol. Struct. 436–437 (1997) 637. [32] M.V. Korolevich, R.G. Zhbankov, V.V. Sivchik, J. Mol. Struct. 220 (1990) 301. [33] R.G. Zhbankov, V.M. Andrianov, H. Ratajczak, M. Marchewka, J. Struct. Chem. 36 (1995) 416. [34] M. Mathlouthi, J.L. Koenig, Adv. Carbohydr. Chem. Biochem. 44 (1986) 7. [35] R.G. Zhbankov, V.M. Andrianov, H. Ratajczak, M. Marchewka, J. Struct. Chem. 36 (1995) 287. [36] R.G. Zhbankov, J. Mol. Struct. 275 (1992) 65. [37] L.M. Yang, S.F. Weng, J.R. Ferraro, J.G. Wu, Vib. Spectrosc. 25 (2001) 57. [38] P.C. Upadhya, Y.C. Shen, A.G. Davies, E.H. Linfield, J. Biol. Phys. 29 (2003) 117. [39] S.F. Weng, Fourier Transform Infrared Spectrometer, Chemical Industry Press, Beijing, 2005, p. 218.