CRYSTAL GROWTH & DESIGN
Growth of New Nonlinear Optical Crystals of Hydrochlorides of L-Histidine from Solution V.
Kannan,†
R. Bairava
Ganesh,†
and P.
2006 VOL. 6, NO. 8 1876-1880
Ramasamy*,‡
Crystal Growth Centre, Anna UniVersity, Chennai 600 025, India, and Centre for Crystal Growth, SSN College of Engineering, SSN Nagar 603 110, India ReceiVed April 6, 2006; ReVised Manuscript ReceiVed May 29, 2006
ABSTRACT: Single crystals of L-histidine monohydrochloride (LHMHCl) and L-histidine dihydrochloride (LHDHCl) have been grown from aqueous solution by a slow evaporation technique. Single-crystal X-ray diffraction analyses reveal that LHMHCl crystallizes in orthorhombic form with space group P212121 while LHDHCl crystallizes in monoclinic form with space group P21. Laser Raman studies confirmed the structure of the crystal, and the vibration modes have been assigned. UV-vis-NIR spectra show excellent transmission through the visible region up to 1100 nm. Differential thermal analysis (DTA) studies indicate that the LHMHCl crystal is more stable and has higher melting point than the LHDHCl crystal. Laser damage threshold study shows that LHDHCl is more resistant to laser damage than LHMHCl. Crystals of the monoclinic form LHDHCl give strong second-harmonic generation (SHG) signals, while orthorhombic forms do not. Introduction Semiorganic nonlinear optical (NLO) crystals are expected to possess the advantages of both inorganic and organic materials. “Semiorganics” are salts in which the typically high optical nonlinearity of a purely organic ion is combined with the favorable mechanical and thermal properties of an inorganic counterion. In semiorganics, polarizable organic molecules are stoichiometrically bound within an inorganic host.1,2 Other critical material properties exist, including favorable crystal growth properties, high optical damage threshold, large thermal conductivity, adequate birefringence for phase matching, and good mechanical characteristics. A major advantage of most salts is that their ionic bonding network provides a high degree of mechanical integrity and increases the likelihood of favorable growth and mechanical properties for the resulting crystals. Further, many of these crystals are readily grown from solution, thus providing a means for economically obtaining largeaperture, optically homogeneous, high-damage-threshold crystals. Perhaps of greatest significance, however, is the high degree of chemical flexibility of an ionic salt approach. Ionic salt materials offer an important and extremely flexible approach for the development of new materials applicable over a very broad range of frequencies.3 A recent survey shows that the research work has been performed to grow various kinds of semiorganic crystals based on L-arginine phosphate (LAP) type analogues with the aim of growing small size crystals and understanding their growth kinetics, thermograph, and structure, and optical UV-vis absorption spectra. Carvalho et al.4 solved the problem of microorganisms in growing LAP crystals by using a controlled evaporation technique in the presence of sodium azide and also reported no significant change in optical properties. Mukerji et al.5 found a new semiorganic crystal, L-arginine hydrobromide (LAHBr). Ittyachan and Sagayaraj6 reported for the first time successful growth of L-histidine bromide (L-HB) by a slow evaporation technique. In the entire visible region of the spectra, the absorbance was found to be less than 2 units. * Corresponding author. Phone: +91-9283105760. E-mail:
[email protected];
[email protected]. † Anna University. E-mail addresses:
[email protected];
[email protected]. ‡ SSN College of Engineering.
Figure 1. Photograph of as grown crystals of LHMHCl.
This paper discusses the growth of single crystals of Lhistidine monohydrochloride (LHMHCl) and L-histidine dihydrochloride (LHDHCl) from aqueous solution slow evaporation technique and their characterization. Crystal Growth Commercially available LHMHCl of purity 98% has been used as the source material. Recrystallized salt of LHMHCl has been taken as raw material. Saturated LHMHCl solutions were prepared at room temperature with water (Milli-Q) as solvent. LHMHCl is found to have positive gradient of solubility. The prepared solution was filtered with a microfilter. The solution was taken in vessels closed with perforated covers and kept in a dust-free atmosphere. The crystals were harvested when they attained an optimal size and shape in a week. The grown crystals are square shaped, optically transparent, and nonhygroscopic. The grown crystal is shown in the Figure 1. For LHDHCl, the starting material was synthesized by stoichiometric incorporation of L-histidine (98% pure) and hydrochloric acid in the ratio 1:2. The crystals were grown by a slow evaporation method. The optically transparent, slightly
10.1021/cg0601960 CCC: $33.50 © 2006 American Chemical Society Published on Web 07/08/2006
Optical Crystals of L-Histidine with Hydrochloride
Crystal Growth & Design, Vol. 6, No. 8, 2006 1877 Table 1. Unit Cell Parameters of L-Histidine Monohydrochloride chemical formula cell parameters molecules per unit cell molecular weight system space group
C6H9N3O2‚HCl‚H2O a ) 15.36 Å b ) 8.92 Å c ) 6.88 Å 4 209.63 orthorhombic P212121
Table 2. Unit Cell Parameters of L-Histidine Dihydrochloride chemical formula cell parameters molecules per unit cell molecular weight system space group
Figure 2. Solubility curves for LHMHCl and LHDHCl.
Figure 3. Photograph of as grown crystals of LHDHCl.
hygroscopic crystals were harvested after two months. The crystals were elongated along the c-axis. The solubility curve is shown in Figure 2. The considerable difference between the growth periods of these two hydrochlorides of L-histidine can be attributed to the fact that the pH and solubility of the dihydrochloride solution (0.8) is far less than those of the monohydrochloride (3.6). The low pH can be attributed to the presence of twice the amount of hydrochloric acid in the dihydrochloride solution. Low pH implies high solubility and hence low supersaturation for a given amount of solute ratio in a fixed volume of solvent. LHDHCl has higher solubility (lower pH) as observed from the solubility curves. For a given volume of solvent, the solutions of LHMHCl and LHDHCl are expected to have different saturation levels leading to different growth periods. The grown crystals are shown in Figure 3. X-ray Analysis. X-ray powder pattern of the crystal Lhistidine monohydrochloride was recorded on a SIEFERT X-ray diffractometer using Cu KR (1.540 Å) radiation. The sample was scanned for a 2θ range 10-50° and at a scan rate 1°/min. The pattern matches well with the previously reported values.7,8 The recorded X-ray spectra and the corresponding data obtained for the grown crystal reveal that it belongs to the orthorhombic
C6H9N3O2‚2HCl a ) 5.243 Å b ) 7.257 Å c ) 13.35 Å 2 227.90 monoclinic: β ) 92.65° P21
system with space group P212121. From the X-ray data, the values of the cell parameters, such as a, b, c, are listed in Table 1. The structure consists of L-His+ cation protonated at the R amino and imidazole group and deprotonated at carboxyl group [N2C3H4]+ CH2CH(NH3+)COO-. The cations are connected to each other by hydrogen bonds. A water molecule forms hydrogen bonds with the carboxylate group and chloride ion as a donor and with the R-amino group as an acceptor. In addition, a chloride ion forms two more hydrogen bonds with neighboring amino groups and two weak C-H‚‚‚Cl-type hydrogen bonds with the imidazole group.8,9 Single-crystal X-ray analysis reveals that L-histidine dihydrochloride exhibits a monoclinic system with space group P21. The cell parameters are presented in Table 2. The structure consists of divalent L-His2+ cations, in which there is an additionally protonated neutral carboxyl group ([N2C3H4]+CH2CH(NH3+)COOH), and two Cl ions. One of the chloride ions, Cl(1)-, forms four hydrogen bonds (three N-H‚‚‚Cl(1) type with protonated amino groups of neighboring L-His2+ cations and a fourth with a hydroxyl group O-H‚‚‚Cl(1)). The second Cl(2)- ion is connected with three imidazole groups of neighboring L-His2+ cations through two N-H‚‚‚Cl(2) and one C-H‚‚‚Cl(2) type hydrogen bonds.10 Laser Raman Spectra of LHMHCL and LHDHCL The recorded laser Raman spectra for LHMHCl and LHDHCl are shown in Figures 4 and 5, respectively. The bands appearing in the region for wavenumbers 200 cm-1 are generally associated with internal modes. These internal vibrations are of various parts of the amino acid molecule, among them the CH, NH3, CO2, and imidazole groups, and also of the water molecule in hydrated crystals. Histidine is the only proteic amino acid where an imidazole group is present, and this furnishes a particular vibrational fingerprint for the crystal under investigation. Assignment of Bands to Internal Modes. In this section, we give a tentative assignment for some of the bands to internal modes of the LHMHCl crystal, summarized in Table 3. The bands appearing at 382 cm-1 are tentatively assigned to torsion of NH3C, τ(NH3), following Diem et al. and Moreno et al.11,12 The band at 491 cm-1 is also assigned to a deformation vibration of the structure, υ(struct). The band at 532 cm-1 is assigned to a rocking vibration of CO2-, r(CO2); in the L-alanine crystal, r(CO2) is observed at exactly 532 cm-1. The τ(NH3) and r(CO2)
1878 Crystal Growth & Design, Vol. 6, No. 8, 2006
Kannan et al.
Figure 6. TG-DTA plot of the LHMHCl crystal.
Figure 4. Laser Raman spectra of the LHMHCl crystal.
Figure 5. Laser Raman spectra of the LHDHCl crystal. Table 3. Vibrational Wavenumbers (cm-1) and Tentative Assignments for L-Histidine Monohydrochloride wavenumber (cm-1)
assignments
382 491 532 697 809 824 1068 1161 1145 1360 1600, 1650
τ(NH3) υ(struct) r(CO2) δ(CO2) w(H2O) γ(CO2) ip(CH)ia ip(NH)ib r(NH3) δ(CH) ν(CdO), νa(CO2)
a In-plane CH deformation of imidazole group. b In-plane NH deformation of imidazole.
modes may play an important role in anharmonicity of the vibrations since oxygen and hydrogen atoms of these two structures participate in hydrogen bonds [this anharmonicity was discussed earlier for the τ(NH3) mode in taurine crystal].13 The band at 697 cm-1 is tentatively assigned to a deformation vibration of CO2-, δ(CO2), following Diem et al.11
The band at 809 cm-1 is possibly associated with a wagging vibration of the water molecule, w(H2O), because it is not observed in L-alanine, L-threonine, or L-asparagine11,12 but is present in monohydrated L-asparagine. The band at 824 cm-1 is assigned to an out-of-plane vibration of CO2-, γ(CO2), following Moreno et al.12 In the range 750-1000 cm-1, it is possible to observe the symmetric stretching vibration of C-C and C-C-N structures.11,12,14 The band at 1068 cm-1 is assigned to an in-plane CH deformation of the imidazole ring. The band at 1161 cm-1 is also assigned to a vibration of the imidazole ring, specifically an in-plane NH deformation following Wang et al.14 The band at 1145 cm-1 is assigned to a rocking vibration of NH3C, r(NH3); in monohydrated Lasparagine the same vibration is observed between 1141 and 1147 cm-1. The 1264 cm-1 band is assigned to an in-plane HC deformation of the imidazole ring. The band observed at 1317 cm-1 is possibly associated with stretching of the imidazole ring. The band at 1360 cm-1 is assigned to a bending of CH, δ(CH), following Moreno et al.12 The two bands at 1450 and 1485 cm-1 can also be assigned to a stretching vibration of the imidazole rings, and the bands between 1600 and 1650 cm-1 are assigned to a stretching vibration of CdO, ν(CdO), or an asymmetric stretching of CO2, νa(CO2), following Wang et al.14 In the same manner assignments could be given for LHDHCl. The band at 800 cm-1 associated with a wagging vibration of the water molecule, w(H2O), in LHMHCl is absent in LHDHCl, which can be attributed to the absence of a water molecule. Thermogravimetric-Differential Thermal Analysis The sample was analyzed using a NETZSCH-Gerateban GmbH thermal analysis instrument. Alumina was taken as reference material in an Al2O3 crucible. Thermogravimetric (TG)-differential thermal analysis (DTA) of LHMHCl and LHDHCl at a heating rate of 5 °C/min under nitrogen atmosphere is shown in Figures 6 and 7, respectively. The final residue weight left was 56% after heating to 400 °C for LHMHCl and 50% for LHDHCl. The peak at 170 °C for LHMHCl is due to the release of the water molecule from the crystal structure; a similar observation has been reported by Petrosyan et al.10 This peak is not present in the case of LHDHCl, which can be attributed to the absence of a water molecule in the structure. Similar observation has been made in laser Raman spectral studies also. LHMHCl melts completely at 257 °C, while LHDHCl decomposes at 243 °C.
Optical Crystals of L-Histidine with Hydrochloride
Crystal Growth & Design, Vol. 6, No. 8, 2006 1879
Figure 7. TG-DTA plot of the LHDHCl crystal. Figure 9. UV-vis-NIR transmission spectra of the LHDHCl crystal. Table 4. Laser Damage in LHMHCl and LHDHClsTest Parameters and Results Test Parameters wavelength pulse width repetition rate beam diameter
1064 nm 25 ns 10 Hz 1.5 mm Results (J/cm2)
LHMHCl LHDHCl KDP
Figure 8. UV-vis-NIR transmission spectra of the LHMHCl crystal.
UV-Vis-NIR Spectral Analysis The UV-vis-NIR spectral transmittance was studied using a Shimadzu UV-1061 spectrophotometer with a single crystal of 3 mm thickness in the range of 200-1200 nm for both LHMHCl and LHDHCl. The recorded spectra for LHMHCl and LHDHCl are shown in Figures 8 and 9, respectively. The crystal has sufficient transmission in the entire visible and IR region. The lower cut off wavelength for LHMHCl is around 260 nm and that for LHDHCl is 265 nm. The transmittance window in the visible region and IR region enables good optical transmission of the second harmonic frequencies of Nd:YAG lasers. Laser-Induced Damage Threshold Studies One of the decisive criteria for a NLO crystal to progress as a device is its resistance to laser damage, since high optical intensities are involved in nonlinear processes. This is the main criterion that restricts the highly nonlinear organic materials in several applications. Inorganic crystals are usually known to have high resistance to laser damage. It is worth noting that the semiorganic crystals combine the positives of organic and inorganic crystals to result in high nonlinear optical properties, as well as high laser damage threshold. In this section, the results
10.1 14 6.8
of laser-induced damage threshold studies performed on LHMHCl and LHDHCl are presented. The experimental arrangement consists of a Nd:YAG laser source, an attenuator, and a beam splitter, which transmits 15% of the power to the probe. The power meter was triggered by synchronous pulses from Q-switch of the Nd:YAG laser. A lowpower He-Ne beam was also simultaneously focused onto the crystal. When the damage occurs, this He-Ne beam gets scattered, which could easily be detected even by naked eye. The transmitted He-Ne beam from the crystal was collected on a screen to further facilitate the detection of damage occurrence. The laser parameters and the results obtained are given in Table 4. It can be clearly noted that LHDHCl is more resistant to laser damage than LHMHCl. Also these values are comparable with the well-known semiorganic crystal LAP.15 Conclusion Single crystals of mono- and dihydrochlorides of L-histidine were synthesized and grown from aqueous solution. The grown crystals were characterized by single-crystal XRD analysis. The study reveals that the grown crystals belong to orthorhombic and monoclinic systems. Laser Raman spectra were used to assign the internal vibrational modes of the crystals. The thermal behavior of the grown crystals was studied by using TG-DTA. Laser damage threshold investigations indicate that their resistance to laser damage is comparable to LAP and higher than potassium dihydrogen phosphate (KDP). Acknowledgment. One of the authors (V. Kannan) is grateful to the Council of Scientific and Industrial Research (CSIR), Government of India, for the award of Senior Research Fellowship.
1880 Crystal Growth & Design, Vol. 6, No. 8, 2006
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