Effect of fluoride on the crystallization and spectral properties of cholesterol

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1 Indian Journal of Pure & Applied Physics Vol. 49, August 2011, pp Effect of fluoride on the crystallization and spectral properties of cholesterol P Kanchana 1 & C Sekar 2 * 1 Department of Physics, Periyar University, Salem , TN, India 2 Department of Bioelectronics and Biosensors, Alagappa University, Karaikudi , TN, India * Sekar2025@gmail.com Received 18 October 2010; revised 22 March 2011; accepted 12 May 2011 The effect of sodium fluoride addition on the crystallization of cholesterol has been studied. It has an inhibitory effect, which not only reduce the growth rate and number of crystals but also change the morphology of the cholesterol crystals. The crystal structure, morphology and thermal properties have been analyzed using powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and TG-DSC studies. Functional groups and fluoride doping in the grown cholesterol crystals have been confirmed from the vibrational frequencies of the recorded FTIR spectrum. Results of this study shows that the increase of fluoride content in the growth environment suppresses the formation of cholesterol. Keywords: Crystal growth, Additives, Cholesterol, Fluorides, FTIR Spectroscopy 1 Introduction Cholesterol (C 27 H 46 O) is the most abundant and best-known steroid in animals. It is a fatty substance that is an important part of the outer lining (membrane) of cells in the body of animals 1. Cholesterol and similar compounds are the precursors of the steroid hormones, which are of great importance to the body. Cholesterol is supposed to be the causative agent for coronary heart diseases like arthrosclerosis and gall stones 2. The cholesterol in a person's blood originates from two major sources; dietary intake and liver production. In human body, precipitation of cholesterol gallstones occurs due to a defect of crystallization inhibiting or an abundance of crystallization promoting factors. It is important to understand the physical/chemical events occurring during crystallization in bile which would provide a useful method for the identification of factors delaying or preventing precipitation of cholesterol crystals and, therefore, gallstone formation in humans 3. The solubility of cholesterol in various solvents has been widely studied and reported by Bar et al 4. Cholesterol was crystallized from different solvents under various conditions and the effect of the solvents on the crystal structure was studied by many researchers 5-7. Effect of bioactive compounds like extract of cassia fistula Linn (CF) on in vitro cholesterol crystals has been investigated by Jayakumari et al. 8. They observed that the presence of CF inhibited the crystallization of cholesterol. Fluorides are extremely reactive molecules and the higher intake of these causes considerable harm in biological systems. A sublethal concentration (onetenth of the LD 50 ) of fluoride (F) (5.2 F/kg body weight) administered to mice (male) daily for 35 days was known to decrease in body weight gain, and food and water consumption 9. These animals are also reported to show a decline in albumin, total protein, cholesterol, glucose and alkaline phosphatase activity in the serum. The fact that the fluorides accumulate in the body is the reason that the World Health Organization (WHO) norms suggest the proportion of fluoride accepted in water sources as 1.5 mg/l (Ref. 10). However, ground water in several parts of world is known to contain higher amount of fluorides, which leads to fluoride intake in human body either directly through drinking water or through other diet 11. In the present paper, we have carried out some studies on the effect of sodium fluoride addition on the crystallization and structure of cholesterol crystals. 2 Experimental Details Cholesterol has low solubility in water but it is soluble in organic solvents such as ethanol, methanol, and benzene 4. The single diffusion gel method was employed for growing cholesterol crystals using sodium meta silicate gel (SMS, purity 99.99%). A solution of SMS of specific gravity 1.03 gcc 1 was adjusted to a ph 5.0 by treating it with 20% glacial acetic acid. This SMS solution and acetone were

540 INDIAN J PURE & APPL PHYS, VOL 49, AUGUST 2011 mixed in 2:1 ratio. The final solution was transformed into test tubes and allowed to set into the gel form for 2 days.

99%) in acetone, and the solution was poured carefully over the top of the silica gel without disturbing the latter.

In another series, the supernatant solution was prepared by adding different amount of NaF (0.005, 0.05, 0.1 and 0.

2 540 INDIAN J PURE & APPL PHYS, VOL 49, AUGUST 2011 mixed in 2:1 ratio. The final solution was transformed into test tubes and allowed to set into the gel form for 2 days. For growing pure cholesterol crystals, the supernatant solution was prepared by dissolving 0.5% (w/v) of cholesterol (purity 99.99%) in acetone, and the solution was poured carefully over the top of the silica gel without disturbing the latter. Within an hour, large number of fibre-like crystals started growing upwards from the interface between the gel and the supernatant solution. In another series, the supernatant solution was prepared by adding different amount of NaF (0.005, 0.05, 0.1 and 0.25 %w/v) to cholesterol solution and the growth was carried out similar to that of pure cholesterol crystals. The growth of the crystals was observed through transparent gel media and test tube continuously. In the NaF added experiments, tiny cholesterol crystals appeared 3 days after adding the supernatant solution and the growth of large platelet crystals completed in about 3 weeks. The grown crystals were harvested by decanting the test tube and the gel was removed using double distilled water. Surface analyses were carried out on cholesterol crystals using scanning electron microscopy (SEM) JSM 5610LV JEOL make. The elemental analyses were done using the OXFORD INCA energy dispersive X-ray fluorescence spectrometer (EDX) attached to SEM. Powder X-ray diffraction pattern was recorded on Bruker advanced diffractometer using Cu as X-ray source (λ = Å). Thermogravimetry of samples was performed using TA instruments SDQ600 simultaneous TGA-DSC device with thermal solution versions 1.2J controller software. Data analysis was carried out using TA Instrument Universal Analyser version 2.3C software. The Fourier transform infrared (FTIR) spectrum was recorded on a Perkin-Elmer (Spectrum RXI) spectrometer in transmission mode in the wave number range 400 to 4000 cm Results and Discussion 3.1 Crystal Growth The growth of cholesterol crystals commenced immediately after the supernatant solution was poured on to the top of the gel. Figure 1 shows the pictures of pure and sodium fluoride added cholesterol crystals grown in acetone. In pure system, filamentous cholesterol crystals with approximate dimension of 45 1 mm 2 grew upwards from the gel-solution interface within 3-4 days. The needles have invaded complete region of the upper solution. Actually, the Fig. 1 Cholesterol crystals in test tube (a) pure (b) NaF added length of the crystals was limited only to the upper end of the supernatant solution above the gel (Fig. 1a) and filamentous crystals can be expected to grow even large if there is enough nutrients in the growth environment. Contrary to the fibrous nature of pure cholesterol, crystals grown in the presence of sodium fluoride were found to be platelet (Fig. 1b) and the growth rate was slower than that of pure crystals. Tiny crystals appeared 3 days after pouring the supernatant solution and the growth completed in about 21 days. The approximate dimension of these platelet crystals were found to be 25 3 mm 2. The long lag time for the initiation of crystal growth represents the time interval in which micronuclei of cholesterol have formed and grown to a detectable size. The harvested pure and fluoride doped cholesterol crystals are shown in Fig. 2. It can be seen from the figure that there is a clear change in crystal habit of the cholesterol from filamentous to platelet morphology. In crystal growth, additives are known to act as a modifier. In particular, the NaF is known to act as a fluoride supplier in many chemical reactions. Thus, the NaF can be expected to dissociate itself and the supernatant solution becomes enriched with F - ions. Presence of F at the growth front may prevent the solute particles from reaching the growth interface. This is probably the reason for the poor crystal yield in the fluoride added growth experiments. 3.2 SEM EDX analyses Figure 3a shows the SEM picture of cholesterol crystals grown in the presence of NaF (0.005% w/v). A small region of platelet crystal under high

KANCHANA & SEKAR: CRYSTALLIZATION AND SPECTRAL PROPERTIES OF CHOLESTEROL 541 magnification shows a step-like growth pattern.

As all the crystal faces remain in contact with the solution, continued growth leads to the establishment of the habit faces. Here, the uneven distribution of solute particles in the Fig.

When the fluoride concentration is increased to higher levels (0.05% w/v), cholesterol crystals still grew like platelets, but usually crystal sizes were small (Fig. 3a).

A part of these deposited crystallites could be removed through repeated washing in double distilled water.

3 KANCHANA & SEKAR: CRYSTALLIZATION AND SPECTRAL PROPERTIES OF CHOLESTEROL 541 magnification shows a step-like growth pattern. This suggests that the growth mechanism is twodimensional in nature and that the growth was incomplete possibly due to the non-availability of sufficient solute particles. As all the crystal faces remain in contact with the solution, continued growth leads to the establishment of the habit faces. Here, the uneven distribution of solute particles in the Fig. 2 Cholesterol crystals (a) pure (b) NaF added supernatant solution and poor diffusivity of solute particles causes the defects such as step-growth pattern. When the fluoride concentration is increased to higher levels (0.05% w/v), cholesterol crystals still grew like platelets, but usually crystal sizes were small (Fig. 3a). Further, the higher F - content led to the agglomerations of secondary phase on the crystal surface. A part of these deposited crystallites could be removed through repeated washing in double distilled water. EDX studies were carried out on pure and fluoride doped cholesterol crystals to assess their elemental composition. The results confirmed that the cholesterol crystals are doped with F in different concentrations; 7.09 and 9.19 atm. % of F - in 0.005% (w/v) and 0.05% (w/v) NaF added crystals, respectively. These results suggest that the amount of F entering into cholesterol increases with the increase in fluoride concentration in supernatant solutions. These F ions may be present in the interstitial sites of the cholesterol crystals. 3.3 Thermo gravimetric analyses Figure 4 illustrates the TG-DSC curves of pure cholesterol crystals grown from acetone solution. A small weight loss (0.1-2 wt %) occurs at 150 C. An endothermic peak seen at a negative peak on the DSC trace at 150 C corresponds to the melting point of cholesterol. Upon further heating, the sample begins to decompose at 316 C and 96.58% of the mass is lost already at 366 C. There was no further change in the mass until 800 C. The mass loss corresponds well with the DSC data, which reveals sharp exothermic peak at 357 C. Fig. 3 Scanning electron micrograph of NaF added cholesterol crystals (a) 0.005% w/v and (b) 0.05% w/v Fig. 4 TG DSC curve of pure cholesterol crystal

542 INDIAN J PURE & APPL PHYS, VOL 49, AUGUST 2011 In case of fluoride doped samples, the mass loss begins relatively at low temperature of 118 C, which is followed by a sharp mass loss of 93 wt.

4 542 INDIAN J PURE & APPL PHYS, VOL 49, AUGUST 2011 In case of fluoride doped samples, the mass loss begins relatively at low temperature of 118 C, which is followed by a sharp mass loss of 93 wt. % in the temperature range 325 to 366 C as shown in Fig. 5. The initial mass loss (3.35 wt.%) could be attributed to the loss of water from the cholesterol crystals. These results suggest that the cholesterol form as cholesterol monohydrate when they are grown in the presence of sodium fluoride (0.005% w/v). Laird et al. 12 reported that water intake in the cholesterol crystals depends on the solvent used for crystallization process. Here, the presence of NaF in the supernatant solution seems to promote the formation of cholesterol monohydrate. 3.4 Powder XRD analyses Figure 6 shows powder XRD pattern of pure and fluoride doped cholesterol crystals grown in acetone. Anhydrous cholesterols are known to crystallize in triclinic structure with the following lattice parameters; a = 14.10Å, b =33.74Å, c = 10.46Å, α = 94.60, β = 90.0 and γ = (Ref. 13). Similarly, the cholesterol monohydrate is known to crystallize in triclinic structure with the following lattice parameters; a = 12.39Å, b = 34.46Å, c = 12.41Å, α = 91.90, β = 98.1, and γ = (Ref. 14). In the present work, Fig. 6a corresponds to pure cholesterol and all the observed peaks have been indexed by using JCPDS data (No ). Contrary to the pure cholesterol, the XRD pattern of fluoride doped crystals shows broader peaks which indicates its poor crystalline nature [Figs 6(b and c)]. The decrease in crystallinity is attributed to the formation of cholesterol monohydrate due to the presence of sodium fluoride 6,15. This result further suggests that the fluoride doping induces the transformation of cholesterol to cholesterol monohydrate in agreement with morphology change and TG results. 3.5 FT-IR Studies The FTIR spectra of pure and fluoride doped cholesterol crystals grown from solutions of same ph values are shown in Fig. 7. The observed wavenumbers from the recorded spectra and the assignments proposed for the cholesterol crystals under investigation are found to be in good agreement with the reported literature 16,17. The observed vibrational frequencies and their assignments are given in Table 1. The bands at 2902 cm 1 for both pure and fluorine doped cholesterols stem from the C-H stretching mode. Both CH 2 and CH 3 groups give rise to bands at 1377 and 1374 cm 1, respectively owing to hydrogen bending vibrations. The bands involving the in-plane bending vibration of C-H are observed at 1276, 1274, 1195 and 1190 cm 1 in pure and fluorine doped cholesterol crystals. The strong peak appeared at cm 1 can be assigned to ring deformation of cholesterol. The occurrence of a medium peak at 883 cm 1 can be assigned to C-C-C stretching mode. The peaks observed at 1028, 1023, 990, 987, 838, 835 cm 1 are attributed to C-H out-of -plane bending in both pure and doped samples 8. The weak broad peaks corresponding to C-OH in-plane bending are Fig. 5 TG-DSC curve of 0.005% w/v NaF added cholesterol crystals Fig. 6 Powder XRD patterns of (a) pure and fluoride doped cholesterol, (b) 0.005% w/v and (c) 0.05% w/v

KANCHANA & SEKAR: CRYSTALLIZATION AND SPECTRAL PROPERTIES OF CHOLESTEROL 543 Pure cholesterol Table 1 Vibrational band assignments of pure and fluoride doped cholesterol 0.

1 (% w/v) Assignment 2935 2902 2905 2934 2902 2936 2905 C-H stretching C-H stretching 2868 2870 2867 2870 2647 2647 2645 2648 2368 2368 2365 2367 2340 2339 2344 2340 1638 1639 1638 1639 C=O

5 KANCHANA & SEKAR: CRYSTALLIZATION AND SPECTRAL PROPERTIES OF CHOLESTEROL 543 Pure cholesterol Table 1 Vibrational band assignments of pure and fluoride doped cholesterol (% w/v) 2936 Cholesterol grown in presence of NaF 0.05 (% w/v) 0.1 (% w/v) Assignment C-H stretching C-H stretching C=O stretching C=O stretching C-H deformation band Combination band C-H in- plane bend C-H in-plane bend C-C-C in-plane bend C-C-C in-plane bend Ring deformation C-H out-of-plane bend Ring breathing C-C-C stretching C-H out-of-plane bend Skeletel distortion Ring deformation C-OH in-plane bend observed at around 600 cm 1 in all the investigated crystals. When compared to the pure cholesterol, the intensity of the combination band at around 1374 cm 1 was found to be higher in the fluoride doped crystal. The intensity of the peak at 1464 cm 1 corresponding to C-H deformation band got increased as the concentration of fluoride increased. Further, peak intensities of the C=O stretching (1564 and 1638 cm 1 ) got interchanged due to fluoride doping. There has been no significant change at lower concentration of fluoride (0.005% w/v) and the peak intensity interchange became prominent at higher concentration of fluorides. Fig. 7 IR spectra of (a) pure and fluoride doped cholesterol, (b) 0.005% w/v, (c) 0.05% w/v and (d) 0.1% w/v 4 Conclusions Long fiber-like cholesterol crystals have been grown by gel method using acetone as solvent. The presence of sodium fluoride as additive resulted in platelet shaped crystals and the number of crystals were much less than that of pure crystals. The fluoride ions seem to act as an antinucleating agent. FTIR results confirmed the presence of functional groups of cholesterol. EDX analyses confirmed the F - doping into cholesterol and the fluoride content increases with increasing NaF concentration. Powder XRD and

6 544 INDIAN J PURE & APPL PHYS, VOL 49, AUGUST 2011 TG-DSC results confirmed the formation of cholesterol monohydrate due to the presence of NaF in the growth environment. Acknowledgement One of the authors (P K) acknowledges the Council of Scientific and Industrial Research (CSIR), India for providing the Senior Research Fellowship. References 1 Bruice P Y & Rajendra Prasad K J, Essential Organic Chemistry, 2 nd Edn (Dorling Kindersley, India), 2008, p Ira Thabrew, Ayling R M & Claire Wicks, Biochemistry for Clinical Medicine, 1 st Edn (Greenwich Medical Media, London), 2001, p Meenakshi Sundaram N, Arivuoli D, Dhanasekaran R & Kalkura S N, J Cryst Growth, 267 (2004) Bar L K, Garti N, Sarig S & Bar R, J Chem Eng Data, 29 (1984) Garti N, Karpuj L & Sarig S, Thermochi Acta, 35 (1980) Garti N, Karpuj L & Sarig S, J Lipid Res, 22 (1981) Kalkura S N & Devanarayanan S, J Mat Sci Lett, 5 (1986) Jayakumari I, Seethalakshmi Ammal M & George K V, Cryst Res Technol, 42 (2007) Pillai K S, Mathai A T & Deshmukh P B, Toxicology Lett, 44 (1988) Fawell J, Bailey K, Chilton J, et al., Fluoride in Drinkingwater, World Health Organization (WHO). ISBN: (IWA Publishing, London, UK), Viswanathan G, Jaswanth A, Gopalakrishnan S, Siva ilango S & Aditya G, Sci Total Environ, 407 (2009) Dougal F. Laird, Michael R. Mucalo & Yoshiyuki Yokogawa, J Colloid Interface Sci, 295 (2006) Sheih H S, Hoard L G & Nordman C E, Acta Cryst, B 37 (1978) Craven B M, Acta Cryst, B 35 (1979) Konikoff F M, Chung D S, Donovan J M, Small D M & Carey M C, J Clin Invest, 90 (1992) Kalkura S N, Ramakrishnan V & Devanarayanan S, Infrared Physics, 27 (1987) Saraswathi N T & F D Gnanam, J Cryst Growth, 179 (1997) 611.

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