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High pressure Raman spectra of DL-lysine hydrochloride
Vibrational Spectroscopy 86 (2016) 337–342
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Vibrational Spectroscopy journal homepage: www.elsevier.com/locate/vibspec
High pressure Raman spectra of DL-lysine hydrochloride$ J.C. Batistaa,b , J.A. Lima Jr.a,* , P.T.C. Freirea , F.E.A. Meloa , J. Mendes-Filhoa a b
Departamento de Física, Universidade Federal do Ceará, C.P. 6030, Campus do Pici, 60455-760, Fortaleza, CE, Brazil Instituto Federal de Educação, Ciência e Tecnologia do Piauí, CEP 64.605-500, Picos, PI, Brazil
A R T I C L E I N F O
Article history: Received 21 March 2016 Received in revised form 19 August 2016 Accepted 20 August 2016 Available online 22 August 2016 Keywords: L-lysine hydrochloride Amino acid High-pressure Phase transition Raman spectroscopy
A B S T R A C T
DL-lysine hydrochloride crystals were studied by Raman spectroscopy under hydrostatic pressure using a diamond anvil cell from ambient pressure up to 9.8 GPa in the spectral range from 1150 to 40 cm 1. Changes in the Raman spectrum were observed in all spectral regions analyzed. In particular, modifications in the lattice modes indicate that the crystal undergoes a phase transition. The classification of the vibrational modes, the behavior of their band wavenumber as a function of the pressure and the reversibility of the phase transitions are also discussed. ã 2016 Elsevier B.V. All rights reserved.
1. Introduction In crystalline state, amino acid molecules (small molecules that form proteins) are mainly linked by hydrogen bonds, giving rise to a series of structures. Raman spectroscopy is a useful tool to verify any modification when these structures are submitted to variations of temperature or pressure. High pressure usually induces modifications in the interatomic distances, changing the electronic distribution and, in organic materials, hydrogen bonds can easily be deformed implicating in phase transitions or even amorphization. The number of articles dealing with DL amino acid crystals has increased in the last 10 years [1–11], but a complete understanding of similarities and differences of the L counterpart is yet to come. The following examples can illustrate how different the behavior of the pure enantiomer and the racemic forms can be. Raman spectroscopic measurements show that L-methionine undergoes a phase transition at 2.2 GPa [12]. The sulfur atom present in the structure of L-methionine is related to this modification since the CS stretching is the main vibration affected by compression. The D conformer [13] also exhibits a phase transition at around 2.6 GPa related to sulfur, but an additional one at 1.5 GPa is also observed. Under pressure DL-serine maintains its atmospheric pressure structure, which is stable up to 8.0 GPa [7]. Dittrich et al. [14] verified that the structure of DL-serine remains
$ Selected paper from for IV Encontro Brasileiro de Espectroscopia Raman (EnBraER), in Juiz de Fora, December 06–09, 2015. * Corresponding author. E-mail address: alves@fisica.ufc.br (J.A. Lima).
http://dx.doi.org/10.1016/j.vibspec.2016.08.011 0924-2031/ã 2016 Elsevier B.V. All rights reserved.
stable at low temperatures, as well as that of the L enantiomer [15]. DL-cysteine (DL-cysteine I) undergoes a phase transition to a new phase (DL-cysteine II) at low temperature that is the same phase of the polymorph when obtained with increasing pressure at 0.1 GPa [16]. Phase II of DL-cysteine gives different responses on changing of pressure or temperature. Until 3 K it is stable, but phase transitions were observed at 1.5 and 6.2 GPa [16]. Both forms of alanine (L and DL) do not modify their structures at high pressures as analyzed by X-ray diffraction [17,18] or at low temperatures [19,20], although L-alanine undergoes a crystal–amorphous phase transition at 15.46 GPa [21]. Contrasting with L-alanine, L-threonine [22], L-asparagine monohydrated [23] and a-Glycine [24] do not exhibit a transition from crystal to amorphous state even when submitted to pressures larger than 20 GPa. Moreno et al. [25] have reported the occurrence of three phase transitions on L-asparagine monohydrate observed up to 2.0 GPa. Silva et al. [23] revisited the L-asparagine monohydrate, reporting on new phase transitions, in addition to the phase transitions previously observed. However, its structure remains crystalline up to 29.6 GPa. In relation to the three polymorphous of glycine (a, b, and g), it is interesting to compare the results recorded during increasing pressure. b-glycine undergoes a phase transition at 0.76 GPa [26]; this modification is accompanied by many changes in the Raman spectrum of the crystal, including jumps and kinks at the curves of wavenumber band positions vs. pressure. Surprisingly, the structure of the a-form is stable for pressures up to 23 GPa [24]. g-glycine presents a very long phase transition beginning at 2.7 GPa, when changes in the volume of the unit cell extending at least up to 7.8 GPa are verified. On decompression, part of the new phase – the d-phase – remains stable down to
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atmospheric pressure; additionally, another phase, assigned as z-phase, was observed for pressures below 0.62 GPa [27–30]. Single-crystal X-ray diffraction experiments revealed that DL-norvaline undergoes two phase transitions upon cooling. The first occurs at 80 C and the second at 100 C [8]. For DL-norleucine a reversible phase transition was reported upon heating at 118 C with a very narrow hysteresis [31]. DL-valine was recently studied under pressure up to 20 GPa and phase transitions around 1.4 and 8.8 GPa were observed [32]. Additionally, two phase transitions were also reported for L-valine [33] at different pressures. In order to fill the gap of information concerning the stability of amino acid crystals under pressure, especially for the racemate forms, we present a detailed analysis of the Raman spectra of a DLlysine hydrochloride (C6H15O2N2Cl) crystal up to 9.8 GPa. The pressure dependence of all the modes in the spectral range (1150–40 cm 1) is presented and the observed modifications in the Raman spectra are discussed. 2. Experimental details DL-lysine hydrochloride single crystals were obtained by slow evaporation of an aqueous solution at 298 K. The obtained crystals were colorless and the crystallographic structure was confirmed by single crystal X-ray diffraction experiments. The Raman spectra were obtained in a triple-grating spectrometer, Jobin Yvon T64000, which is equipped with an N2-cooled charge coupled device detection system. The 514.5 nm line of an argon laser was used as the excitation source. An Olympus microscope lens with a focal distance of 20.5 mm and a numerical aperture of 0.35 was used to focus the laser beam on the sample surface. The spectrometer slits were set for a resolution of 2 cm 1. In the high pressure experiment, we studied the sample increasing pressure between 0.0 GPa (ambient pressure) and 9.8 GPa using a membrane diamond anvil cell (MDAC) [34] with a stainless steel gasket with 200 mm of initial thickness and a 200 mm diameter hole. Nujol was used as the pressure transmitting medium, and pressure was monitored using the ruby emission lines [35]. 3. Results and discussion DL-lysine hydrochloride crystallizes in the monoclinic system (P21/c) with four molecules (i.e. 88 atoms) [36] per unit cell. Cell parameters obtained through Rietveld refinement are a = 9.209 (2) Å, b = 11.247(2) Å, c = 8.558(2) Å, and b = 105.7529 (4) which agree with Ref. [27]. DL-lysine hydrochloride molecules and the crystalline structure projection of its unit cell in bc plane are presented in Fig. 1. Fig. 2a shows the Raman spectra of DL-lysine hydrochloride recorded from 0.1 to 9.8 GPa in the 225–40 cm 1 spectral region. Eleven low-wavenumber modes (v < 175 cm 1) were observed and all of them can be classified as lattice modes. Upon increasing pressure significant changes in the Raman spectra can be noticed. The first mode (centered at 53 cm 1) decreases its intensity under compression and is no longer seen for a pressure higher than 2.8 GPa. A broad band around 80 cm 1 was adjusted suggesting the existence of three modes (numbered as 2, 3 and 4). Modes 2 and 3 change their relative intensities at 0.8 GPa and by increasing pressure they merge in one single mode for pressures higher than 4.0 GPa. The low-intensity mode numbered as 4 is seen as a shoulder and is for some spectra hidden and only fitted up to 3.5 GPa. Modes numbered as 5 and 6 also merge into one mode at 3.5 GPa. The next three modes (7, 8 and 9) change their relative intensities upon increasing pressure but at the largest pressure value obtained (9.8 GPa) the relative intensity is the same of that at the starting pressure (0.1 GPa). A broad and low-intensity band was
Fig. 1. Lysine HCl molecule (a); crystalline structure projection of DL-lysine HCl unit cell in the bc plane (b).
assigned to two modes (10 and 11), and with increasing pressure only the mode 11 is observed; for pressures higher than 4.6 GPa it was not observed. The disappearance of these external modes is indicative that the crystal has undergone a phase transition, starting at 2.8 GPa and being completed at 4.0 GPa. Phase transitions with modifications in lattice modes of certain amino acids were reported in other works [12,37,38]. In fact, it is interesting to remember at this point that the main signature of the phase transition undergone by DL-lysine hydrochloride involves lattice modes of the crystal. As previously presented in the literature, the phase transition can involve lattice modes or internal modes related to vibrations of specific parts of the molecule such as CH, CH2, CH3 groups etc. A well established example was furnished by a study on two polymorphs of L-cysteine investigated simultaneously in the same experiment. While the orthorhombic form showed the most significant modifications in the lattice mode region of the Raman spectrum, the monoclinic form of L-cysteine showed changes, mainly, in modes in the high-wavenumber range, involving stretching of SH, CH and CH2 units [29]. As another example, a series of modifications were observed in the lattice mode spectral region of the Raman spectrum of L-asparagine monohydrate, when the crystal was compressed to pressures up to 30 GPa, indicating the occurrence of many phase transitions [28]. In this sense, we can put DL-lysine hydrochloride into the same class of amino acid crystals, in which one finds L-asparagine monohydrate and orthorhombic L-cysteine. It is also important to note that the steady change of intensities of the bands in the spectra of Fig. 2 points to a continuous modification of conformation of the molecules in the unit cell. Eventually, the conformational change tunes a phase transition, as occurs with the L-lysine hydrochloride crystal between 2 and 4 GPa. Fig. 2b shows the fitted spectra obtained at 0.4 GPa (before the phase transition) and at 4.0 GPa (after the phase transition). The behavior of the band position wavenumber as a function of the pressure v(P) for the modes observed in Fig. 2a is illustrated in Fig. 3. A linear function was used to adjust the experimental data, and the discontinuities observed corroborate with our hypothesis that a phase transition has taken place.
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Fig. 3. Wavenumber vs. pressure plots of the bands appearing in the spectral range of 225–40 cm 1.
Fig. 2. Raman spectra of DL- lysine hydrochloride in the spectral range of 225– 40 cm 1 for selected values of pressure. Values represent the pressure in GPa. Observe that the continuous variation of the band intensity can be ascribed to the continuous conformational change of the molecules in the unit cell (a); fitting of the spectra of DL- lysine hydrochloride at 0.4 and 4.0 GPa (b).
Raman spectra of DL-lysine hydrochloride in the interval of 600–200 cm 1 recorded within the 0.1–9.8 GPa pressure range are shown in Fig. 4. Between 280 and 200 cm 1 three low-intensity modes were observed, appearing in the Raman spectrum up to 4.6 GPa. As these modes have low-intensity even at 0.1 GPa, these disappearances cannot be indisputably attributed to the phase transition. The next two modes centered at 347 and 299 cm 1, can – according to Refs. [39,40] – be both assigned as skeletal
Fig. 4. Raman spectra of DL-lysine hydrochloride in the spectral range of 600– 200 cm 1 for selected values of pressure (values represent the pressure in GPa).
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deformation, d(skl). With increasing pressure, these modes change their relative intensities at 1.8 GPa; at 2.8 GPa, a new mode centered at 328 cm 1 appears. We believe that the intensity change of modes 15 and 16 and the appearance of the mode 15a are related to conformational modifications of the DL-lysine molecule that occurs as a consequence of the structural phase transition mentioned before. Again, it is interesting to compare the present results with data of other amino acid crystals. For example, in the phase transition undergone by L-cysteine in the orthorhombic form, beyond the changes of relative intensities of low-wavenumber bands, changes in the relative intensities of bands associated with CS stretching were also observed. This modification was interpreted as a consequence of molecular conformation [29]. Additionally, (i) a slight change in the intensity of a band in the low wavenumber region of the Raman spectrum of DL-serine was interpreted as being a consequence of molecular reorientation in the unit cell of the crystal [4]; as well (ii) a series of modifications, observed in the Raman spectra of L-asparagine monohydrate during compression up to 30 GPa, suggested a continuous reorientation of the molecules [28]. Such a picture indicates the conformational modification of lysine molecules during the compression experiment. The last two modes (numbered as 18 and 19) centered at 515 and 535 cm 1 were both assigned as rocking of CO2, r(CO2), in accordance with references [39,40]. The two modes are observed in all spectra recorded and upon increasing pressure the intensity decreases up to 1.2 GPa. Interestingly enough, at 1.8 GPa the intensity seems to increase and then start decreasing again. In most of amino acid crystals studied, the mode associated with r (CO2) appears as bands of medium intensity and, for this reason, it can be used as a kind of sensor to monitor the behavior of hydrogen bonds. One impressive example occurs with the DL-alanine crystal at low temperatures: the wavenumber of the r(CO2) mode presents both discontinuity and change of slope. In fact, in this study where polarized Raman measurements were used, the change of the wavenumber of r(CO2) was understood as modification of the hydrogen bonds in one direction (x-axis) predominantly on the other (z-axis) [20]. Another kind of behavior for r(CO2) modes was verified for L-methionine [12] and for D-methionine [13]; at atmospheric pressure one observes only one band associated with r(CO2 ) but above a pressure-induced phase transition the splitting of modes is verified. Such a splitting should be interpreted as indication of two distinct configurations allowed for CO2 groups at high pressure, in contrast to only one for the atmospheric pressure phases of both L– and D– methionine [12,13]. In DL-lysine hydrochloride investigated in the present paper, one observes two bands associated with r(CO2) in the whole pressure interval (from 101.3 kPa to 9.8 GPa). Fig. S2 of the Supplementary material shows the wavenumber vs. pressure plot of all modes appearing in the Raman spectra of DL-lysine.HCl for 101.3 kPa–9.8 GPa between 550 and 200 cm 1. From this figure one notes that the band position wavenumber of r(CO2 ) presents any discontinuity. X-ray diffraction measurements showed that the oxygen atoms of the carboxylic groups form hydrogen bonds with hydrogens from NH3+ groups of different molecules with average distances of 2.89 Å [27]. The continuous evolution of the wavenumber of r (CO2 ) can be interpreted as a continuous evolution of the hydrogen bonds involving oxygen atoms of the carboxyl group, without any abrupt modification, even in the pressure range where the phase transition occurs. Fig. 5 shows the Raman spectra of DL-lysine hydrochloride in the spectral range of 1150–750 cm 1 recorded in the 0.1–9.8 GPa interval. Modes numbered as 20, 21 and 22 were observed up to 9.8 GPa and a splitting of mode 21 was observed. In this region the bands observed between1000 and 900 cm 1 (marked with numbers 23 and 24) were tentatively assigned as stretching of
CC, n(CC); the bands marked as 25 and 26 were assigned as stretching of CN, n(CN); and the bands marked as 27 and 28 were assigned as rocking of NH3+, r(NH3+) [30]. There are few modifications in this region of the Raman spectrum. Among the changes observed we can cite the splitting of a band of low intensity (marked by number 21) and the inversion of intensities of the doublets 23–24 and 25–26. The evolution of the bands intensities along the compression run indicates that a slight molecular conformation occurs during the process. The same behavior was observed previously in an investigation performed on DL-leucine crystals submitted to high pressure [11]. This means that although the phase transition should be established between 2.8 and 4.0 GPa, as discussed in the paragraph relative to the low wavenumber modes, the molecular conformation of lysine molecule is verified for the whole pressure range. Discontinuities in the pressure-dependent wavenumber plot are observed for some modes between 2.8 and 3.5 GPa as can be seen in the Supplementary material (Fig. S3). An aspect of high-pressure research on amino acids that has burst into the scene in recent times is related to recrystallization of part of the crystal – contained in the diamond anvil cell – into a polycrystalline sample. In fact, such an intriguing aspect was verified for the first time in a study performed on an L-alanine crystal [17]. During a slow compression run, the authors of Ref. [17] verified that part of the crystal recrystallized taking up all hole of the gasket. On reverse decompression, the authors observed a recrystallization, allowing the crystal recover its original size. In the present work we looked carefully at the occurrence of a similar phenomenon with DL-lysine hydrochloride, but no evidence was found. It is possible that the time during which the sample was kept under pressure explains the phenomenon, as suggested by the authors of Ref. [17]. While in the experiments performed on Lalanine each pressure point was kept constant during about 6 h [17], in the experiment on L-lysine hydrochloride the time between two different pressures was not more than 2 h. Further
Fig. 5. Raman spectra of DL-lysine hydrochloride in the spectral range of 1150– 750 cm 1 for selected values of pressure (values represent the pressure in GPa).
J.C. Batista et al. / Vibrational Spectroscopy 86 (2016) 337–342 Table 1 Experimental wanumber at 0.1 GPa (vexp) and pressure coefficients of DL-lysine hydrochloride at ambient pressure (vexp) and parameters obtained from the linear fitting (v = v0 + aP) to the experimental points. Pressure (P) values are in GPa. vexp and v0 values are in cm 1.
vexp Mode
Assignment
28 27 26 25 24 23 22 21 20 19 18 17 16 15 15a 14 13 12 11 10 9 8 7 6 5 4 3 2 1
r(NH3) n(CN) n(CN) n(CC) n(CC) n(CC) n(CC) d(CO2) d(CO2) r(CH2) r(CO2) r(CO2) d(skl) d(skl)
d(skl) d(skl) t(CO2) Lattice Lattice Lattice Lattice Lattice Lattice Lattice Lattice Lattice Lattice Lattice
1113 1069 1028 1005 929 913 872 812 805 786 535 515 404 347 – 299 266 215 162 147 140 126 112 105 94 84 78 73 53
v0
a
v0
a
0.1 P 2.8 GPa
4.0 P 9.8 GPa
1113.2 1072.1 1031.5 1007.3 930.4 914.7 871.1 812.8 807.4 788.5 535.9 517.6 405.6 345.8 – 297.2 268.5 215.9 164.1 153.3 138.9 127.1 115.5 106.8 95.5 85.1 80.5 77.5 55.7
1105.8 1078.3 1031.5 1007.3 930.4 917.3 871.1 812.8 807.4 788.5 535.9 517.6 – – 324.4 290.8 264.9 – – – 150.7 132.3 125.2 112.8 – – 82.5 – –
0.2 5.4 2.7 3.1 2.8 2.3 3.3 2.1 1.5 1.2 2.5 3.1 0.8 5.7 – 2.9 1.1 13.2 9.70 8.30 8.60 7.70 9.2 10.30 9.60 4.40 4.00 2.20 7.20
1.9 3.5 2.7 3.1 2.8 1.4 3.3 2.1 1.5 1.2 2.5 3.1 – – 3.7 6.0 4.4 – – – 5.00 5.70 5.30 3.00 – – 1.70 – –
n- stretching; d-deformation; t- torsion; r-rocking.
work on this impressive subject will be needed. Coefficients of the fitting to the experimental data and the wavenumber of the modes at ambient pressure as well as the assignment of the modes are presented in Table 1. Finally, we discuss the reversibility of the phase transition. Previous work has shown that the phase transitions undergone by amino acid crystals can be reversible, as occurs with L-methionine [12], or irreversible, as is well represented by the orthorhombic form of L-cysteine [2]. For DL-lysine hydrochloride, after reaching 9.8 GPa the pressure was completely released and a spectrum acquired at ambient pressure. As can be seen in Fig. 6 the profile of the spectrum was recovered including the number and the relative
Fig. 6. Raman spectra of DL-lysine hydrochloride in the spectral range of 600– 40 cm 1 for selected values of pressure.
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intensity of the modes. This means that the Raman spectra (i) before compression in the beginning of the experiment and (ii) after decompression, at the end of the experiment, are the same, indicating that the initial and final phases are exactly the same. As a consequence, the phase transition can be considered as reversible. Unfortunately, no spectrum was recorded upon decompression and it is not possible to mention if any hysteresis took place. Future investigations by X-ray diffraction under pressure will be needed to confirm our hypotheses and determine the structure of the high pressure phase.
4. Conclusions DL-lysine hydrochloride single crystals were grown by the slow evaporation method and their structures were confirmed by X-ray diffraction experiments and Rietveld refinement. High-pressure Raman spectroscopic measurements using a diamond anvil cell were done up to 9.8 GPa. Band changes associated with external modes were interpreted as an indicator that the crystal has undergone a phase transition between 2.8 and 4.0 GPa. A linear function was used to adjust the wavenumber versus pressure plot for all modes and the coefficients were furnished. No evidence of recrystallization during decompression was obtained. Finally, upon decompression the phase transition was observed to be reversible. Acknowledgments Authors acknowledge CNPq (Universal 454941/2014-5), and FUNCAP for financial support. We also acknowledge C.W.A. Paschoal and S.D.S. Reis for reading and correcting the manuscript. 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. vibspec.2016.08.011. References [1] K. Machida, A. Kagayama, Y. Saito, J. Raman Spectrosc. 7 (1978) 188–193. [2] A. Pawlukojc, L. Bobrowicz, I. Natkaniec, J. Leciejewicz, Spectrochim. Acta A 51 (1995) 303–308. [3] H.N. Bordallo, B.A. Kolesov, E.V. Boldyreva, F. Juranyi, J. Am. Chem. Soc. 129 (2007) 10984–10985. [4] B.A. Kolesov, E.V. Boldyreva, J. Phys. Chem. B 111 (2007) 14387–14397. [5] P. Chatzigeorgiou, N. Papakonstantopoulos, N. Tagaroulia, E. Pollatos, P. Xynogalas, K. Viras, J. Phys. Chem. B 114 (2010) 1294–1300. [6] V.S. Minkov, A.S. Krylov, E.V. Boldyreva, S.V. Goryainov, S.N. Bizyaev, A.N. Vtyurin, J. Phys. Chem. B 112 (2008) 8851–8854. [7] B.A. Zakharov, B.A. Kolesov, E.V. Boldyreva, Acta Crystallogr. B 68 (2012) 275–286. [8] C.H. Gorbitz, J. Phys. Chem. B 115 (2011) 2447–2453. [9] S. Jarmelo, I. Reva, M. Rozenberg, P.R. Carey, R. Fausto, Vib. Spectrosc. 41 (2006) 73–82. [10] V.S. Minkov, Y.A. Chesalov, E.V. Boldyreva, J. Struct. Chem. 51 (2010) 1052–1063. [11] B.T.O. Abagaro, P.T.C. Freire, J.G. Silva, F.E.A. Melo, J.A. Lima Jr., J. Mendes Filho, P. S. Pizani, Vib. Spectrosc. 66 (2013) 119. [12] J.A. Lima Jr, P.T.C. Freire, F.E.A. Melo, V. Lemos, J. Mendes Filho, P.S. Pizani, J. Raman Spectrosc. 39 (2008) 1356–1363. [13] W.D.C. Melo, P.T.C. Freire, J.M. Filho, F.E.A. Melo, J.A. Lima, W. Paraguassu, Vib. Spectrosc. 72 (2014) 57–61. [14] B. Dittrich, C.B. Hubschle, M. Messerschmidt, R. Kalinowski, D. Girnt, P. Luger, Acta Crystallogr. A 61 (2005) 314–320. [15] E.V. Boldyreva, E.N. Kolesnik, T.N. Drebushchak, H. Ahsbahs, J.A. Beukes, H.P. Weber, Z. Kristallogr. 220 (2005) 58-65. [16] V.S. Minkov, N.A. Tumanov, R.Q. Cabrera, E.V. Boldyreva, CrystEngComm 12 (2010) 2551–2560. [17] N.A. Tumanov, E.V. Boldyreva, B.A. Kolesov, A.V. Kurnosov, R.Q. Cabrera, Acta Crystallogr. B 66 (2010) 458–471. [18] N.A. Tumanov, E.V. Boldyreva, Acta Crystallogr. B 68 (2012) 412–423. [19] B.A. Kolesov, E.V. Boldyreva, J. Raman Spectrosc. 42 (2011) 696–705.
342
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[20] J.A. Lima Jr., P.T.C. Freire, F.E.A. Melo, J. Mendes Filho, G.P. de Sousa, R.J.C. Lima, P.F. Façanha Filho, H.N. Bordallo, J. Raman Spectrosc. 41 (2010) 808–813. [21] N.P. Funnell, W.G. Marshall, S. Parsons, CrystEngComm 13 (2011) 5841–5848. [22] R.O. Holanda, J.A. Lima, P.T.C. Freire, F.E.A. Melo, J. Mendes, A. Polian, J. Molec. Struct. 1092 (2015) 160–165. [23] J.A.F. Silva, P.T.C. Freire, J.A. Lima, J.M. Filho, F.E.A. Melo, A.J.D. Moreno, A. Polian, Vib. Spectrosc. 77 (2015) 35–39. [24] C. Murli, S.M. Sharma, S. Karmakar, S.K. Sikka, Physica B 339 (2003) 23–30. [25] A.J.D. Moreno, P.T.C. Freire, F.E.A. Melo, M.A.A. Silva, I. Guedes, J.M. Mendes, Solid State Commun. 103 (1997) 655–658. [26] S.V. Goryainov, E.N. Kolesnik, E. Boldyreva, Physica B 357 (2005) 340–347. [27] S.V. Goryainov, E.V. Boldyreva, E.N. Kolesnik, Chem. Phys. Lett. 419 (2006) 496–500. [28] A. Dawson, D.R. Allan, S.A. Belmonte, S.J. Clark, W.I.F. David, P.A. McGregor, S. Parsons, C.R. Pulham, L. Sawyer, Cryst. Growth Des. 5 (2005) 1415–1427. [29] E.V. Boldyreva, S.N. Ivashevskaya, H. Sowa, H. Ahsbahs, H.P. Weber, Effect of high pressure on crystalline glycine: a new high-pressure polymorph, Dokl. Phys. Chem. 396 (2004) 111–114 (Parte 111).
[30] E.V. Boldyreva, S.N. Ivashevskaya, H. Sowa, H. Ahsbahs, H.P. Weber, Z. Kristallogr., 220 (2005) 50–57. [31] S.J. Coles, T. Gelbrich, U.J. Griesser, M.B. Hursthouse, M. Pitak, T. Threlfall, Cryst. Growth Des. 9 (2009) 4610–4612. [32] F.S.C. Rêgo, J.A. Lima Jr, P.T.C. Freire, F.E.A. Melo, J.M. Filho, A. Polian, J. Mol. Struct. 1109 (2016) 220–225. [33] J.H. da Silva, V. Lemos, P.T.C. Freire, F.E.A. Melo, J. Mendes Filho, J.A. Lima Jr., P.S. Pizani, Phys. Status Solidi B 246 (2009) 553–557. [34] J.C. Chervin, B. Canny, J.M. Besson, P. Pruzan, Rev. Sci. Instrum. 66 (1995) 2595– 2598. [35] J.D. Barnett, S. Block, G. Piermari, Rev. Sci. Instrum. 44 (1973) 1–9. [36] D. Bhaduri, N.N. Saha, J. Cryst. Mol. Struct. 9 (1979) 311–316. [37] J.A.F. Silva, P.T.C. Freire, J.A. Lima, J. Mendes, F.E.A. Melo, A.J.D. Moreno, A. Polian, Vib. Spectrosc. 77 (2015) 35–39. [38] V.S. Minkov, S.V. Goryainov, E.V. Boldyreva, C.H. Gorbitz, J. Raman Spectrosc. 41 (2010) 1748–1758. [39] A.M. Petrosyan, V.V. Ghazaryan, J. Mol. Struct. 917 (2009) 56–62. [40] V. Krishnakumar, R. Nagalakshmi, S. Manohar, L. Kocsis, Spectrochim. Acta A 71 (2008) 471–479.
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High pressure Raman spectra of DL-lysine hydrochloride$ J.C. Batistaa,b , J.A. Lima Jr.a,* , P.T.C. Freirea , F.E.A. Meloa , J. Mendes-Filhoa a b
Departamento de Física, Universidade Federal do Ceará, C.P. 6030, Campus do Pici, 60455-760, Fortaleza, CE, Brazil Instituto Federal de Educação, Ciência e Tecnologia do Piauí, CEP 64.605-500, Picos, PI, Brazil
A R T I C L E I N F O
Article history: Received 21 March 2016 Received in revised form 19 August 2016 Accepted 20 August 2016 Available online 22 August 2016 Keywords: L-lysine hydrochloride Amino acid High-pressure Phase transition Raman spectroscopy
A B S T R A C T
DL-lysine hydrochloride crystals were studied by Raman spectroscopy under hydrostatic pressure using a diamond anvil cell from ambient pressure up to 9.8 GPa in the spectral range from 1150 to 40 cm 1. Changes in the Raman spectrum were observed in all spectral regions analyzed. In particular, modifications in the lattice modes indicate that the crystal undergoes a phase transition. The classification of the vibrational modes, the behavior of their band wavenumber as a function of the pressure and the reversibility of the phase transitions are also discussed. ã 2016 Elsevier B.V. All rights reserved.
1. Introduction In crystalline state, amino acid molecules (small molecules that form proteins) are mainly linked by hydrogen bonds, giving rise to a series of structures. Raman spectroscopy is a useful tool to verify any modification when these structures are submitted to variations of temperature or pressure. High pressure usually induces modifications in the interatomic distances, changing the electronic distribution and, in organic materials, hydrogen bonds can easily be deformed implicating in phase transitions or even amorphization. The number of articles dealing with DL amino acid crystals has increased in the last 10 years [1–11], but a complete understanding of similarities and differences of the L counterpart is yet to come. The following examples can illustrate how different the behavior of the pure enantiomer and the racemic forms can be. Raman spectroscopic measurements show that L-methionine undergoes a phase transition at 2.2 GPa [12]. The sulfur atom present in the structure of L-methionine is related to this modification since the CS stretching is the main vibration affected by compression. The D conformer [13] also exhibits a phase transition at around 2.6 GPa related to sulfur, but an additional one at 1.5 GPa is also observed. Under pressure DL-serine maintains its atmospheric pressure structure, which is stable up to 8.0 GPa [7]. Dittrich et al. [14] verified that the structure of DL-serine remains
$ Selected paper from for IV Encontro Brasileiro de Espectroscopia Raman (EnBraER), in Juiz de Fora, December 06–09, 2015. * Corresponding author. E-mail address: alves@fisica.ufc.br (J.A. Lima).
http://dx.doi.org/10.1016/j.vibspec.2016.08.011 0924-2031/ã 2016 Elsevier B.V. All rights reserved.
stable at low temperatures, as well as that of the L enantiomer [15]. DL-cysteine (DL-cysteine I) undergoes a phase transition to a new phase (DL-cysteine II) at low temperature that is the same phase of the polymorph when obtained with increasing pressure at 0.1 GPa [16]. Phase II of DL-cysteine gives different responses on changing of pressure or temperature. Until 3 K it is stable, but phase transitions were observed at 1.5 and 6.2 GPa [16]. Both forms of alanine (L and DL) do not modify their structures at high pressures as analyzed by X-ray diffraction [17,18] or at low temperatures [19,20], although L-alanine undergoes a crystal–amorphous phase transition at 15.46 GPa [21]. Contrasting with L-alanine, L-threonine [22], L-asparagine monohydrated [23] and a-Glycine [24] do not exhibit a transition from crystal to amorphous state even when submitted to pressures larger than 20 GPa. Moreno et al. [25] have reported the occurrence of three phase transitions on L-asparagine monohydrate observed up to 2.0 GPa. Silva et al. [23] revisited the L-asparagine monohydrate, reporting on new phase transitions, in addition to the phase transitions previously observed. However, its structure remains crystalline up to 29.6 GPa. In relation to the three polymorphous of glycine (a, b, and g), it is interesting to compare the results recorded during increasing pressure. b-glycine undergoes a phase transition at 0.76 GPa [26]; this modification is accompanied by many changes in the Raman spectrum of the crystal, including jumps and kinks at the curves of wavenumber band positions vs. pressure. Surprisingly, the structure of the a-form is stable for pressures up to 23 GPa [24]. g-glycine presents a very long phase transition beginning at 2.7 GPa, when changes in the volume of the unit cell extending at least up to 7.8 GPa are verified. On decompression, part of the new phase – the d-phase – remains stable down to
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atmospheric pressure; additionally, another phase, assigned as z-phase, was observed for pressures below 0.62 GPa [27–30]. Single-crystal X-ray diffraction experiments revealed that DL-norvaline undergoes two phase transitions upon cooling. The first occurs at 80 C and the second at 100 C [8]. For DL-norleucine a reversible phase transition was reported upon heating at 118 C with a very narrow hysteresis [31]. DL-valine was recently studied under pressure up to 20 GPa and phase transitions around 1.4 and 8.8 GPa were observed [32]. Additionally, two phase transitions were also reported for L-valine [33] at different pressures. In order to fill the gap of information concerning the stability of amino acid crystals under pressure, especially for the racemate forms, we present a detailed analysis of the Raman spectra of a DLlysine hydrochloride (C6H15O2N2Cl) crystal up to 9.8 GPa. The pressure dependence of all the modes in the spectral range (1150–40 cm 1) is presented and the observed modifications in the Raman spectra are discussed. 2. Experimental details DL-lysine hydrochloride single crystals were obtained by slow evaporation of an aqueous solution at 298 K. The obtained crystals were colorless and the crystallographic structure was confirmed by single crystal X-ray diffraction experiments. The Raman spectra were obtained in a triple-grating spectrometer, Jobin Yvon T64000, which is equipped with an N2-cooled charge coupled device detection system. The 514.5 nm line of an argon laser was used as the excitation source. An Olympus microscope lens with a focal distance of 20.5 mm and a numerical aperture of 0.35 was used to focus the laser beam on the sample surface. The spectrometer slits were set for a resolution of 2 cm 1. In the high pressure experiment, we studied the sample increasing pressure between 0.0 GPa (ambient pressure) and 9.8 GPa using a membrane diamond anvil cell (MDAC) [34] with a stainless steel gasket with 200 mm of initial thickness and a 200 mm diameter hole. Nujol was used as the pressure transmitting medium, and pressure was monitored using the ruby emission lines [35]. 3. Results and discussion DL-lysine hydrochloride crystallizes in the monoclinic system (P21/c) with four molecules (i.e. 88 atoms) [36] per unit cell. Cell parameters obtained through Rietveld refinement are a = 9.209 (2) Å, b = 11.247(2) Å, c = 8.558(2) Å, and b = 105.7529 (4) which agree with Ref. [27]. DL-lysine hydrochloride molecules and the crystalline structure projection of its unit cell in bc plane are presented in Fig. 1. Fig. 2a shows the Raman spectra of DL-lysine hydrochloride recorded from 0.1 to 9.8 GPa in the 225–40 cm 1 spectral region. Eleven low-wavenumber modes (v < 175 cm 1) were observed and all of them can be classified as lattice modes. Upon increasing pressure significant changes in the Raman spectra can be noticed. The first mode (centered at 53 cm 1) decreases its intensity under compression and is no longer seen for a pressure higher than 2.8 GPa. A broad band around 80 cm 1 was adjusted suggesting the existence of three modes (numbered as 2, 3 and 4). Modes 2 and 3 change their relative intensities at 0.8 GPa and by increasing pressure they merge in one single mode for pressures higher than 4.0 GPa. The low-intensity mode numbered as 4 is seen as a shoulder and is for some spectra hidden and only fitted up to 3.5 GPa. Modes numbered as 5 and 6 also merge into one mode at 3.5 GPa. The next three modes (7, 8 and 9) change their relative intensities upon increasing pressure but at the largest pressure value obtained (9.8 GPa) the relative intensity is the same of that at the starting pressure (0.1 GPa). A broad and low-intensity band was
Fig. 1. Lysine HCl molecule (a); crystalline structure projection of DL-lysine HCl unit cell in the bc plane (b).
assigned to two modes (10 and 11), and with increasing pressure only the mode 11 is observed; for pressures higher than 4.6 GPa it was not observed. The disappearance of these external modes is indicative that the crystal has undergone a phase transition, starting at 2.8 GPa and being completed at 4.0 GPa. Phase transitions with modifications in lattice modes of certain amino acids were reported in other works [12,37,38]. In fact, it is interesting to remember at this point that the main signature of the phase transition undergone by DL-lysine hydrochloride involves lattice modes of the crystal. As previously presented in the literature, the phase transition can involve lattice modes or internal modes related to vibrations of specific parts of the molecule such as CH, CH2, CH3 groups etc. A well established example was furnished by a study on two polymorphs of L-cysteine investigated simultaneously in the same experiment. While the orthorhombic form showed the most significant modifications in the lattice mode region of the Raman spectrum, the monoclinic form of L-cysteine showed changes, mainly, in modes in the high-wavenumber range, involving stretching of SH, CH and CH2 units [29]. As another example, a series of modifications were observed in the lattice mode spectral region of the Raman spectrum of L-asparagine monohydrate, when the crystal was compressed to pressures up to 30 GPa, indicating the occurrence of many phase transitions [28]. In this sense, we can put DL-lysine hydrochloride into the same class of amino acid crystals, in which one finds L-asparagine monohydrate and orthorhombic L-cysteine. It is also important to note that the steady change of intensities of the bands in the spectra of Fig. 2 points to a continuous modification of conformation of the molecules in the unit cell. Eventually, the conformational change tunes a phase transition, as occurs with the L-lysine hydrochloride crystal between 2 and 4 GPa. Fig. 2b shows the fitted spectra obtained at 0.4 GPa (before the phase transition) and at 4.0 GPa (after the phase transition). The behavior of the band position wavenumber as a function of the pressure v(P) for the modes observed in Fig. 2a is illustrated in Fig. 3. A linear function was used to adjust the experimental data, and the discontinuities observed corroborate with our hypothesis that a phase transition has taken place.
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Fig. 3. Wavenumber vs. pressure plots of the bands appearing in the spectral range of 225–40 cm 1.
Fig. 2. Raman spectra of DL- lysine hydrochloride in the spectral range of 225– 40 cm 1 for selected values of pressure. Values represent the pressure in GPa. Observe that the continuous variation of the band intensity can be ascribed to the continuous conformational change of the molecules in the unit cell (a); fitting of the spectra of DL- lysine hydrochloride at 0.4 and 4.0 GPa (b).
Raman spectra of DL-lysine hydrochloride in the interval of 600–200 cm 1 recorded within the 0.1–9.8 GPa pressure range are shown in Fig. 4. Between 280 and 200 cm 1 three low-intensity modes were observed, appearing in the Raman spectrum up to 4.6 GPa. As these modes have low-intensity even at 0.1 GPa, these disappearances cannot be indisputably attributed to the phase transition. The next two modes centered at 347 and 299 cm 1, can – according to Refs. [39,40] – be both assigned as skeletal
Fig. 4. Raman spectra of DL-lysine hydrochloride in the spectral range of 600– 200 cm 1 for selected values of pressure (values represent the pressure in GPa).
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deformation, d(skl). With increasing pressure, these modes change their relative intensities at 1.8 GPa; at 2.8 GPa, a new mode centered at 328 cm 1 appears. We believe that the intensity change of modes 15 and 16 and the appearance of the mode 15a are related to conformational modifications of the DL-lysine molecule that occurs as a consequence of the structural phase transition mentioned before. Again, it is interesting to compare the present results with data of other amino acid crystals. For example, in the phase transition undergone by L-cysteine in the orthorhombic form, beyond the changes of relative intensities of low-wavenumber bands, changes in the relative intensities of bands associated with CS stretching were also observed. This modification was interpreted as a consequence of molecular conformation [29]. Additionally, (i) a slight change in the intensity of a band in the low wavenumber region of the Raman spectrum of DL-serine was interpreted as being a consequence of molecular reorientation in the unit cell of the crystal [4]; as well (ii) a series of modifications, observed in the Raman spectra of L-asparagine monohydrate during compression up to 30 GPa, suggested a continuous reorientation of the molecules [28]. Such a picture indicates the conformational modification of lysine molecules during the compression experiment. The last two modes (numbered as 18 and 19) centered at 515 and 535 cm 1 were both assigned as rocking of CO2, r(CO2), in accordance with references [39,40]. The two modes are observed in all spectra recorded and upon increasing pressure the intensity decreases up to 1.2 GPa. Interestingly enough, at 1.8 GPa the intensity seems to increase and then start decreasing again. In most of amino acid crystals studied, the mode associated with r (CO2) appears as bands of medium intensity and, for this reason, it can be used as a kind of sensor to monitor the behavior of hydrogen bonds. One impressive example occurs with the DL-alanine crystal at low temperatures: the wavenumber of the r(CO2) mode presents both discontinuity and change of slope. In fact, in this study where polarized Raman measurements were used, the change of the wavenumber of r(CO2) was understood as modification of the hydrogen bonds in one direction (x-axis) predominantly on the other (z-axis) [20]. Another kind of behavior for r(CO2) modes was verified for L-methionine [12] and for D-methionine [13]; at atmospheric pressure one observes only one band associated with r(CO2 ) but above a pressure-induced phase transition the splitting of modes is verified. Such a splitting should be interpreted as indication of two distinct configurations allowed for CO2 groups at high pressure, in contrast to only one for the atmospheric pressure phases of both L– and D– methionine [12,13]. In DL-lysine hydrochloride investigated in the present paper, one observes two bands associated with r(CO2) in the whole pressure interval (from 101.3 kPa to 9.8 GPa). Fig. S2 of the Supplementary material shows the wavenumber vs. pressure plot of all modes appearing in the Raman spectra of DL-lysine.HCl for 101.3 kPa–9.8 GPa between 550 and 200 cm 1. From this figure one notes that the band position wavenumber of r(CO2 ) presents any discontinuity. X-ray diffraction measurements showed that the oxygen atoms of the carboxylic groups form hydrogen bonds with hydrogens from NH3+ groups of different molecules with average distances of 2.89 Å [27]. The continuous evolution of the wavenumber of r (CO2 ) can be interpreted as a continuous evolution of the hydrogen bonds involving oxygen atoms of the carboxyl group, without any abrupt modification, even in the pressure range where the phase transition occurs. Fig. 5 shows the Raman spectra of DL-lysine hydrochloride in the spectral range of 1150–750 cm 1 recorded in the 0.1–9.8 GPa interval. Modes numbered as 20, 21 and 22 were observed up to 9.8 GPa and a splitting of mode 21 was observed. In this region the bands observed between1000 and 900 cm 1 (marked with numbers 23 and 24) were tentatively assigned as stretching of
CC, n(CC); the bands marked as 25 and 26 were assigned as stretching of CN, n(CN); and the bands marked as 27 and 28 were assigned as rocking of NH3+, r(NH3+) [30]. There are few modifications in this region of the Raman spectrum. Among the changes observed we can cite the splitting of a band of low intensity (marked by number 21) and the inversion of intensities of the doublets 23–24 and 25–26. The evolution of the bands intensities along the compression run indicates that a slight molecular conformation occurs during the process. The same behavior was observed previously in an investigation performed on DL-leucine crystals submitted to high pressure [11]. This means that although the phase transition should be established between 2.8 and 4.0 GPa, as discussed in the paragraph relative to the low wavenumber modes, the molecular conformation of lysine molecule is verified for the whole pressure range. Discontinuities in the pressure-dependent wavenumber plot are observed for some modes between 2.8 and 3.5 GPa as can be seen in the Supplementary material (Fig. S3). An aspect of high-pressure research on amino acids that has burst into the scene in recent times is related to recrystallization of part of the crystal – contained in the diamond anvil cell – into a polycrystalline sample. In fact, such an intriguing aspect was verified for the first time in a study performed on an L-alanine crystal [17]. During a slow compression run, the authors of Ref. [17] verified that part of the crystal recrystallized taking up all hole of the gasket. On reverse decompression, the authors observed a recrystallization, allowing the crystal recover its original size. In the present work we looked carefully at the occurrence of a similar phenomenon with DL-lysine hydrochloride, but no evidence was found. It is possible that the time during which the sample was kept under pressure explains the phenomenon, as suggested by the authors of Ref. [17]. While in the experiments performed on Lalanine each pressure point was kept constant during about 6 h [17], in the experiment on L-lysine hydrochloride the time between two different pressures was not more than 2 h. Further
Fig. 5. Raman spectra of DL-lysine hydrochloride in the spectral range of 1150– 750 cm 1 for selected values of pressure (values represent the pressure in GPa).
J.C. Batista et al. / Vibrational Spectroscopy 86 (2016) 337–342 Table 1 Experimental wanumber at 0.1 GPa (vexp) and pressure coefficients of DL-lysine hydrochloride at ambient pressure (vexp) and parameters obtained from the linear fitting (v = v0 + aP) to the experimental points. Pressure (P) values are in GPa. vexp and v0 values are in cm 1.
vexp Mode
Assignment
28 27 26 25 24 23 22 21 20 19 18 17 16 15 15a 14 13 12 11 10 9 8 7 6 5 4 3 2 1
r(NH3) n(CN) n(CN) n(CC) n(CC) n(CC) n(CC) d(CO2) d(CO2) r(CH2) r(CO2) r(CO2) d(skl) d(skl)
d(skl) d(skl) t(CO2) Lattice Lattice Lattice Lattice Lattice Lattice Lattice Lattice Lattice Lattice Lattice
1113 1069 1028 1005 929 913 872 812 805 786 535 515 404 347 – 299 266 215 162 147 140 126 112 105 94 84 78 73 53
v0
a
v0
a
0.1 P 2.8 GPa
4.0 P 9.8 GPa
1113.2 1072.1 1031.5 1007.3 930.4 914.7 871.1 812.8 807.4 788.5 535.9 517.6 405.6 345.8 – 297.2 268.5 215.9 164.1 153.3 138.9 127.1 115.5 106.8 95.5 85.1 80.5 77.5 55.7
1105.8 1078.3 1031.5 1007.3 930.4 917.3 871.1 812.8 807.4 788.5 535.9 517.6 – – 324.4 290.8 264.9 – – – 150.7 132.3 125.2 112.8 – – 82.5 – –
0.2 5.4 2.7 3.1 2.8 2.3 3.3 2.1 1.5 1.2 2.5 3.1 0.8 5.7 – 2.9 1.1 13.2 9.70 8.30 8.60 7.70 9.2 10.30 9.60 4.40 4.00 2.20 7.20
1.9 3.5 2.7 3.1 2.8 1.4 3.3 2.1 1.5 1.2 2.5 3.1 – – 3.7 6.0 4.4 – – – 5.00 5.70 5.30 3.00 – – 1.70 – –
n- stretching; d-deformation; t- torsion; r-rocking.
work on this impressive subject will be needed. Coefficients of the fitting to the experimental data and the wavenumber of the modes at ambient pressure as well as the assignment of the modes are presented in Table 1. Finally, we discuss the reversibility of the phase transition. Previous work has shown that the phase transitions undergone by amino acid crystals can be reversible, as occurs with L-methionine [12], or irreversible, as is well represented by the orthorhombic form of L-cysteine [2]. For DL-lysine hydrochloride, after reaching 9.8 GPa the pressure was completely released and a spectrum acquired at ambient pressure. As can be seen in Fig. 6 the profile of the spectrum was recovered including the number and the relative
Fig. 6. Raman spectra of DL-lysine hydrochloride in the spectral range of 600– 40 cm 1 for selected values of pressure.
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intensity of the modes. This means that the Raman spectra (i) before compression in the beginning of the experiment and (ii) after decompression, at the end of the experiment, are the same, indicating that the initial and final phases are exactly the same. As a consequence, the phase transition can be considered as reversible. Unfortunately, no spectrum was recorded upon decompression and it is not possible to mention if any hysteresis took place. Future investigations by X-ray diffraction under pressure will be needed to confirm our hypotheses and determine the structure of the high pressure phase.
4. Conclusions DL-lysine hydrochloride single crystals were grown by the slow evaporation method and their structures were confirmed by X-ray diffraction experiments and Rietveld refinement. High-pressure Raman spectroscopic measurements using a diamond anvil cell were done up to 9.8 GPa. Band changes associated with external modes were interpreted as an indicator that the crystal has undergone a phase transition between 2.8 and 4.0 GPa. A linear function was used to adjust the wavenumber versus pressure plot for all modes and the coefficients were furnished. No evidence of recrystallization during decompression was obtained. Finally, upon decompression the phase transition was observed to be reversible. Acknowledgments Authors acknowledge CNPq (Universal 454941/2014-5), and FUNCAP for financial support. We also acknowledge C.W.A. Paschoal and S.D.S. Reis for reading and correcting the manuscript. 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. vibspec.2016.08.011. References [1] K. Machida, A. Kagayama, Y. Saito, J. Raman Spectrosc. 7 (1978) 188–193. [2] A. Pawlukojc, L. Bobrowicz, I. Natkaniec, J. Leciejewicz, Spectrochim. Acta A 51 (1995) 303–308. [3] H.N. Bordallo, B.A. Kolesov, E.V. Boldyreva, F. Juranyi, J. Am. Chem. Soc. 129 (2007) 10984–10985. [4] B.A. Kolesov, E.V. Boldyreva, J. Phys. Chem. B 111 (2007) 14387–14397. [5] P. Chatzigeorgiou, N. Papakonstantopoulos, N. Tagaroulia, E. Pollatos, P. Xynogalas, K. Viras, J. Phys. Chem. B 114 (2010) 1294–1300. [6] V.S. Minkov, A.S. Krylov, E.V. Boldyreva, S.V. Goryainov, S.N. Bizyaev, A.N. Vtyurin, J. Phys. Chem. B 112 (2008) 8851–8854. [7] B.A. Zakharov, B.A. Kolesov, E.V. Boldyreva, Acta Crystallogr. B 68 (2012) 275–286. [8] C.H. Gorbitz, J. Phys. Chem. B 115 (2011) 2447–2453. [9] S. Jarmelo, I. Reva, M. Rozenberg, P.R. Carey, R. Fausto, Vib. Spectrosc. 41 (2006) 73–82. [10] V.S. Minkov, Y.A. Chesalov, E.V. Boldyreva, J. Struct. Chem. 51 (2010) 1052–1063. [11] B.T.O. Abagaro, P.T.C. Freire, J.G. Silva, F.E.A. Melo, J.A. Lima Jr., J. Mendes Filho, P. S. Pizani, Vib. Spectrosc. 66 (2013) 119. [12] J.A. Lima Jr, P.T.C. Freire, F.E.A. Melo, V. Lemos, J. Mendes Filho, P.S. Pizani, J. Raman Spectrosc. 39 (2008) 1356–1363. [13] W.D.C. Melo, P.T.C. Freire, J.M. Filho, F.E.A. Melo, J.A. Lima, W. Paraguassu, Vib. Spectrosc. 72 (2014) 57–61. [14] B. Dittrich, C.B. Hubschle, M. Messerschmidt, R. Kalinowski, D. Girnt, P. Luger, Acta Crystallogr. A 61 (2005) 314–320. [15] E.V. Boldyreva, E.N. Kolesnik, T.N. Drebushchak, H. Ahsbahs, J.A. Beukes, H.P. Weber, Z. Kristallogr. 220 (2005) 58-65. [16] V.S. Minkov, N.A. Tumanov, R.Q. Cabrera, E.V. Boldyreva, CrystEngComm 12 (2010) 2551–2560. [17] N.A. Tumanov, E.V. Boldyreva, B.A. Kolesov, A.V. Kurnosov, R.Q. Cabrera, Acta Crystallogr. B 66 (2010) 458–471. [18] N.A. Tumanov, E.V. Boldyreva, Acta Crystallogr. B 68 (2012) 412–423. [19] B.A. Kolesov, E.V. Boldyreva, J. Raman Spectrosc. 42 (2011) 696–705.
342
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[20] J.A. Lima Jr., P.T.C. Freire, F.E.A. Melo, J. Mendes Filho, G.P. de Sousa, R.J.C. Lima, P.F. Façanha Filho, H.N. Bordallo, J. Raman Spectrosc. 41 (2010) 808–813. [21] N.P. Funnell, W.G. Marshall, S. Parsons, CrystEngComm 13 (2011) 5841–5848. [22] R.O. Holanda, J.A. Lima, P.T.C. Freire, F.E.A. Melo, J. Mendes, A. Polian, J. Molec. Struct. 1092 (2015) 160–165. [23] J.A.F. Silva, P.T.C. Freire, J.A. Lima, J.M. Filho, F.E.A. Melo, A.J.D. Moreno, A. Polian, Vib. Spectrosc. 77 (2015) 35–39. [24] C. Murli, S.M. Sharma, S. Karmakar, S.K. Sikka, Physica B 339 (2003) 23–30. [25] A.J.D. Moreno, P.T.C. Freire, F.E.A. Melo, M.A.A. Silva, I. Guedes, J.M. Mendes, Solid State Commun. 103 (1997) 655–658. [26] S.V. Goryainov, E.N. Kolesnik, E. Boldyreva, Physica B 357 (2005) 340–347. [27] S.V. Goryainov, E.V. Boldyreva, E.N. Kolesnik, Chem. Phys. Lett. 419 (2006) 496–500. [28] A. Dawson, D.R. Allan, S.A. Belmonte, S.J. Clark, W.I.F. David, P.A. McGregor, S. Parsons, C.R. Pulham, L. Sawyer, Cryst. Growth Des. 5 (2005) 1415–1427. [29] E.V. Boldyreva, S.N. Ivashevskaya, H. Sowa, H. Ahsbahs, H.P. Weber, Effect of high pressure on crystalline glycine: a new high-pressure polymorph, Dokl. Phys. Chem. 396 (2004) 111–114 (Parte 111).
[30] E.V. Boldyreva, S.N. Ivashevskaya, H. Sowa, H. Ahsbahs, H.P. Weber, Z. Kristallogr., 220 (2005) 50–57. [31] S.J. Coles, T. Gelbrich, U.J. Griesser, M.B. Hursthouse, M. Pitak, T. Threlfall, Cryst. Growth Des. 9 (2009) 4610–4612. [32] F.S.C. Rêgo, J.A. Lima Jr, P.T.C. Freire, F.E.A. Melo, J.M. Filho, A. Polian, J. Mol. Struct. 1109 (2016) 220–225. [33] J.H. da Silva, V. Lemos, P.T.C. Freire, F.E.A. Melo, J. Mendes Filho, J.A. Lima Jr., P.S. Pizani, Phys. Status Solidi B 246 (2009) 553–557. [34] J.C. Chervin, B. Canny, J.M. Besson, P. Pruzan, Rev. Sci. Instrum. 66 (1995) 2595– 2598. [35] J.D. Barnett, S. Block, G. Piermari, Rev. Sci. Instrum. 44 (1973) 1–9. [36] D. Bhaduri, N.N. Saha, J. Cryst. Mol. Struct. 9 (1979) 311–316. [37] J.A.F. Silva, P.T.C. Freire, J.A. Lima, J. Mendes, F.E.A. Melo, A.J.D. Moreno, A. Polian, Vib. Spectrosc. 77 (2015) 35–39. [38] V.S. Minkov, S.V. Goryainov, E.V. Boldyreva, C.H. Gorbitz, J. Raman Spectrosc. 41 (2010) 1748–1758. [39] A.M. Petrosyan, V.V. Ghazaryan, J. Mol. Struct. 917 (2009) 56–62. [40] V. Krishnakumar, R. Nagalakshmi, S. Manohar, L. Kocsis, Spectrochim. Acta A 71 (2008) 471–479.