TECHNICAL FIELD
The present disclosure provides an apparatus to crystallize organic compounds based on vaporization and condensation by a gradient cooling technique.
BACKGROUND OF DISCLOSURE
The crystal structure determination of organic compounds has become essential to understand structure-property correlation and is of specific importance in the pharmaceutical industry.
In particular, the structure determination is unambiguously carried out using data obtained from a single crystal. One of the essentials for a successful structure determination is the requirement of a good quality single crystal or a single phase polycrystalline sample of the given material. Often crystals are formed with the incorporation of the solvent in the lattice during crystallization. This generally occurs either through randomly absorbed solvent molecules or through the capture of fluid inclusions of solvent. The last mechanism is the most dangerous for the crystal quality and is mainly due to kinetic reasons. As a matter of fact, it is well-known that when the normal growth rate of a given crystal face exceeds a critical value, macro steps form and run on the face surface, and their overhanging generates the privileged locations for the capture of nano or microscopic fluid inclusions. Water of crystallization is invariably preferred in the crystal of many small bio molecules, large proteins, and enzymes.
In order to obtain crystal structures of anhydrous compounds, a novel approach is required where intervention of solvent can be entirely eliminated. There are a large number of methods to synthesize single crystals of a required compound like for example slow evaporation, vapor diffusion, solvent diffusion, sublimation, convection, and zone melting. Out of these techniques, slow evaporation from a solution is frequently adopted to grow single crystals of organics, and frequently this process leads to the incorporation of the solvent in the crystal structure. For example, adenine always crystallizes with the incorporation of three water molecules during crystallization.
Ciprofloxacin is a widely used broad spectrum antibiotic, which is active against both Grampositive and Gram-negative bacteria. An analysis of the Cambridge structure database (CSD 5.3, Updates May 2009) shows 52 hits for ciprofloxacin, which contain both organic and organometallic derivatives. There are only five structures [ref code- UJAGUH, JIRYAL, IDARUA SESZEW and COVPIN which represent salts with ciprofloxacin.
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Midazolam which is a benzodiazepine derivative drug has a wide variety of properties such as amnestic hypnotic, anxiolytic, and sedative and the database contains only one salt structure of midazolam with saccharin ate.
Ofloxacin as a broader spectrum analogue of norfloxacine, the first fluoroquinolone antibiotic. Database analysis of ofloxacin gives seven hits out of which four are organometallic complexes, two are hydrated forms, and one is a perchloric acid salt.
These observations suggest that crystallization of such drugs without the incorporation of solvent and/or hydration due to incorporation of water of crystallization is not an easily reachable target.
STATEMENT OF THE DISCLOSURE
Accordingly, the present disclosure provides for an apparatus to crystallize organic compound, said apparatus comprising, a sample holder (7) to hold sample of the organic compound, a quartz furnace (1) to maintain a constant temperature around the sample holder (7), a plurality coaxial glass tubes constructed with an inner tubes (6a) and an outer tubes (6b), to pass vapors of the organic compound through the inner tube (6a), and an oil pump (4) dipped in a oil bath (5), to pump the oil around the inner tube (6a), to crystallize the organic compound in the inner tube (6a), also provides a method for crystallizing organic compound, said method comprising acts of, placing a sample of organic compound in sample holder (7), maintaining a constant temperature around the sample holder (7) by a quartz furnace (1) to generate vapors of the organic compound, passing vapors of the organic compound through a inner tube (6a) of coaxial glass tube, and controlling temperature gradient along the length of coaxial glass tube by circulating an oil between the inner tubes (6a) and outer tubes (6b) for crystallizing the sample of organic compound, and also provides a method of assembling apparatus to crystallize organic compound, said method comprising acts of, arranging a quartz furnace (1) at one end of sample holder (7) containing a sample of the organic compound to maintain constant temperature, connecting other end of sample holder (7) to coaxial glass tubes to pass vapors of the organic compound through the coaxial glass tube, connecting a inlet and outlet oil passages to the coaxial glass tubes for oil circulation, and providing an external heater and/or cooler (8) to maintain the temperature gradient along the length of the coaxial glass tube.
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The foregoing statement is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The novel features and characteristic of the disclosure are set forth in the appended claims.
The disclosure itself, however, as well as a preferred mode of use, further objectives and
advantages thereof, will best be understood by reference to the following detailed description
of an illustrative embodiment when read in conjunction with the accompanying drawings.
One or more embodiments are now described, by way of example only, with reference to the
accompanying drawings wherein like reference numerals represent like elements and in
which:
FIG.1 shows the schematic diagram of set up used for crystallization.
FIG.2 shows the schematic diagram of quartz furnace.
FIG.3 shows the schematic diagram of oil pump for oil circulation.
FIG.4 shows the Plate type crystals of thymine extracted from the walls of the inner tube.
FIG.5 shows the One to one matching of Powder X-Diffraction pattern of raw thymine with
simulated powder pattern of reported polymorph of thymine.
FIG.6 shows the graph of comparison of powder X-ray diffraction patterns (experimental and
simulated) of both polymorphic forms of thymine.
FIG.7: Shows the ORTEP diagram with 30 % probability thermal ellipsoid.
FIGS.8a and 8b shows the Packing diagram showing hydrogen bonds (8a) C 2/c structure
(8b) P 21/c structure.
FIG.9 shows the ORTEP diagram of anhydrous ciprofloxacin with ellipsoids drawn at 50%
probability.
FIG.10 shows the ORTEP diagram of anhydrous midazolam with ellipsoids drawn at 50%
probability.
FIG.11 shows the ORTEP diagram of anhydrous ofloxacin with ellipsoids drawn at 50%
probability.
The figures depict embodiments of the disclosure for purposes of illustration only. One
skilled in the art will readily recognize from the following description that alternative
embodiments of the structures and methods illustrated herein may be employed without
departing from the principles of the disclosure described herein.
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DETAILED DESCRIPTION
In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, and drawings, are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented herein. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the figures, can be arranged, substituted, combined, and designed in a wide variety of different configurations, all of which are explicitly contemplated and make part of this disclosure.
This disclosure is drawn, inter-alia, to an apparatus to crystallize the low melting organic compounds which includes drugs and pharmaceuticals.
The present disclosure relates to an apparatus to crystallize organic compound, said apparatus comprising: a sample holder (7), to hold sample of the organic compound, a quartz furnace (1) to maintain a constant temperature around the sample holder (7), plurality of coaxial glass tube constructed with an inner tubes (6a) and an outer tubes (6b), to pass vapors of the organic compound through the inner tube (6a), and an oil pump (4) dipped in a oil bath (5), to pump the oil around the inner tube (6a), to crystallize the organic compound in the inner tube (6a).
In yet another embodiment of the present disclosure the organic compound is in anhydrous form.
In still another embodiment of the present disclosure the quartz furnace (1) uses a proportional–integral–derivative (PID) temperature controller, to maintain constant temperature around the sample holder (7).
In still another embodiment of the present disclosure the oil is supplied in the gap between outer circumference of inner tube (6a) and inner circumference of outer tube (6b). In still another embodiment of the present disclosure the oil bath (5) temperature is maintained beyond the melting temperature of the organic compound.
In still another embodiment of the present disclosure the coaxial glass tube is provided with an external heater and/or cooler (8) are to maintain a temperature gradient along its length.
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In still another embodiment of the present disclosure a vacuum pump (2) with pressure gauge (3) is used to control rate of flow of the organic compound.
The present disclosure is in relation to a method for crystallizing organic compound, said method comprising acts of: placing a sample of organic compound in a sample holder (7), maintaining a constant temperature around the sample holder (7) by a quartz furnace (1) to generate vapors of the compound, passing vapors of the organic compound through a inner tube (6a) of coaxial glass tube, and controlling temperature gradient along the length of coaxial glass tube by circulating an oil between the inner tubes (6a) and outer tubes (6b) for crystallization of organic compound.
In yet another embodiment of the present disclosure maintaining constant rate of flow of the vapors along the length of the coaxial glass tube by creating vacuum ranging from about 30 mm/Hg to about 650 mm/Hg using vacuum pump.
The present disclosure is in relation to a method of assembling apparatus to crystallize organic compound, said method comprising acts of: arranging quartz furnace (1) at one end of sample holder (7) containing a sample of the organic compound to maintain a constant temperature, connecting one end of sample holder (7) to coaxial tubes to pass vapors of the organic compound through coaxial glass tubes, connecting a inlet and outlet oil passages to the coaxial glass tubes for oil circulation, and providing an external heater and/or cooler (8) to maintain the temperature gradient along the length of the coaxial glass tube.
In yet another embodiment of the present disclosure placing vacuum pump (2) with pressure gauge (3) at the other end of coaxial glass tube to control the rate of flow vapors along the length of coaxial glass tube.
In the present disclosure, the schematic diagram of the apparatus is shown in FIG.1. One of the advantages here is that, since the process of crystallization involves vaporizing the sample, the purity of the starting material is not of much concern. The apparatus consists of a quartz furnace (1) (FIG.2), with a PID temperature controller (can be changed with a device which dopes the same function), a vacuum pump (2) (30-650 mm/Hg) with pressure gauge (3), a oil pump (4) dipped in oil bath (5) (FIG.3), and a specially designed gradient cooling system as shown in FIG.1.
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In yet another embodiment, the gradient cooling apparatus is an assembly of six ( could be even more) crystallization zones, each made up of coaxial glass tubes length is 15 cm, having an inner tube (6a) diameter of 10 mm and wall thickness of 1.5 mm. The outer tube (6b) of these coaxial glass tubes has a diameter of 30 mm and a wall thickness of 1.5 mm. Each of these coaxial tubes has 19/23 ground joint at the two ends for extension.
In yet another embodiment, each crystallization zone is divided into two compartments having an inlet and an outlet for the circulation of the hot oil around the inner tube.
In yet another embodiment, silicone oil is used in the oil bath (5) whose temperature can be programmed such that the initial temperature at the oil bath (5) is well beyond the melting point of the compound to be crystallized. On vaporization, the compound goes through the inner tube (6a) with each compartment providing a temperature gradient. It is to be noted that the temperature gradient can be controlled by hot oil circulation through the outer tube (6b). The hot oil enters the outer tube through inlet and gets out through outlet and passes through a coil whose temperature can be varied by using an external heating or a cooling (8) device (a hot zone or an ice bath) before entering other zone. Thus, it is possible to predetermine a temperature gradient which ensures the formation of the crystals in the inner tube of any one of the compartment. Further, the rate of flow can be controlled by the vacuum pump attachment through the pressure gauge (FIG.1).
In yet another embodiment, the sample holder (7) is made up of a 19/23 ground joint which can be easily connected and disconnected to the gradient cooling part. The inner tube (6a) allows the vaporized sample to pass through the compartments only after entering through a fine nozzle at the main entry point which ensures cooling by the Joule-Thompson effect and also provides an aspirator effect on the sample. It may be noted that several vaporizers can be attached to converge at the fine nozzle which ensures a facile mixing of more than one component vapor required for co-crystallization experiments.
The technology of the instant Application is further elaborated with the help of following examples. However, the examples should not be construed to limit the scope of the invention.
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Examples:
1. Crystallization of anhydrous thymine: a new polymorph
100 mg of thymine (Sigma Aldrich, 99%) was taken in the sample holder and heated in the quartz furnace of the apparatus described above, where the melting of the sample is clearly visible from outside. A pressure of 320 mm was maintained at the melting point (317 ˚C) of the sample. Plates like crystals (FIG.4) were formed on the wall of the inner tube and were recovered after cooling and dismantling the set up. Powder X-ray diffraction data of raw thymine taken from the supply container (Aldrich, 99%) was recorded on a Philips X’pertPro diffractometer with 2θ starting from 3 to 80º (absolute scan) with step size of 0.018 and 800 sec per step. The recorded powder pattern of raw thymine matches with the simulated powder pattern reported for the single crystal structure of anhydrous thymine (FIG 5).
Single crystal diffraction data of the crystal grown using the above apparatus were collected on a Bruker AXS SMART APEX CCD diffractometer, at 292(2) K and the structure was solved using direct methods. The crystals belong to the space group C 2/c with the cell dimension “a” nearly double (a = 25.107) as compared to the earlier study (Habit: needles; a = 12.87, b = 6.83, c = 6.70 Å and β = 105 ° ,P 21/c ) with b and c values remaining almost the same and the value of β (β= 90.529) significantly different (Table 1).
The reciprocal lattice images were carefully examined to check the possibility of converting the cell dimensions of the plate like crystal to those of the needle type. However, the possibility of reduced cell is not indicated. In order to provide further evidence to this observation, the simulated powder X-ray diffraction pattern based on the coordinates obtained after the structure determination and refinement is compared with the experimentally recorded powder X-ray diffraction data obtained from crushed crystals (FIG.6). The ORTEP diagram is shown in FIG.7 and packing diagrams of the two polymorphic forms are given in FIG.8. This hence demonstrates that the apparatus can be used for polymorph generation, a much sought after process in drug industry.
2. Crystallization of Ciprofloxacin, Midazolam, and Ofloxacin
A. Crystallization:
Crystallization of anhydrous ciprofloxacin, midazolam, and ofloxacin resulted from the use
of the device. Depending on the melting point of each drug, the oil temperature was
maintained at 270, 165, and 275º C, respectively. During the experiment, a vacuum is
maintained at 650 mm. Because of gradient cooling, crystals were grown at the inner wall of
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the crystallization zone and subsequently taken out for single crystal X-ray diffraction. The crystal morphology for ciprofloxacin was “block type”, while for both midazolam and ofloxacin the crystals were “plate like”.
B. Single Crystal X-ray Diffraction:
The single crystal X-ray diffraction data for all compounds were collected on a Oxford diffractometer (Microsource (MOVA), detector: Eos) and solved using direct methods of the three samples (ciprofloxacin, midazolam, and ofloxacin) only the crystals of ciprofloxacin were sealed in a Lindemann capillary to ensure that the sample is not affected by its highly hygroscopic character when exposed to air.
C. X-ray Powder Diffraction:
Powder patterns of all compounds were recorded on a Philips X’pert Pro diffractometer in a range of 2θ=3-60º with a 0.02º step size and 500 s per step.
D. Analysis:
i. Crystal Structure of Anhydrous Ciprofloxacin: The ORTEP diagram of anhydrous ciprofloxacin is shown in FIG. 9, and crystallographic details are listed in Table 2. The characteristic (O-H…O) intramolecular hydrogen bond found in all the structures reported in the literature remains unaltered even in the anhydrous form. However, a unique N-H…N intermolecular interaction across the center of inversion brings an altogether different packing motif in the anhydrous form. Additional C-H…O intermolecular interactions provide further stability to the packing motif. In all the salts of ciprofloxacin studied earlier, there is no N-H…N hydrogen bond holding the ciprofloxacin molecule together; instead, the hydrogen bonding involves the solvate.
A reasonable single crystal data set was collected on a capillary mounted tiny crystal because in open mounting, the single crystal becomes polycrystalline after a few minutes of data collection.
ii. Crystal Structure of Anhydrous Midazolam: The ORTEP diagram of anhydrous midazolam with ellipsoids drawn at 50% probability is shown in FIG.10, and the crystallographic details are given in Table 2. The structure of anhydrous midazolam presents unique packing characteristics with a type I Cl…Cl interaction holding the molecule together. Additional C-H…π and π…π interactions provide further
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stability to the packing. The only other derivative of midazolam is a saccharinate, and the intermolecular interactions are significantly different with the saccharin ate forming a dimer through well-defined C-H…O intermolecular interactions.
iii. Crystal Structure of Anhydrous Ofloxacin:
The ORTEP diagram with 50% probability for anhydrous ofloxacin is shown in FIG. 11, and the crystallographic details are given in Table 2. The structure has been refined to a reasonable residual factor (Table 2). Ofloxacin does not possess strong complementary hydrogen bond functionality; only C-H…O interactions across the 2-fold axis results in the packing of the molecules in the crystal.
In the disclosure, structure determination of anhydrous compounds and the variation observed in the crystal packing clearly bring out the importance of growing the anhydrous form of any given drug. The understanding of structural features certainly enhances the potential for engineering newer drug complexes since they offer variability in hydrogen bonding character. It appears that analysis of the structural features of anhydrous compounds would also provide inputs for the design of cocrystal involving drug molecules.
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Table 1- Crystallographic and Refinement Data of anhydrous thymine
Details New polymorph Reported form (Plate) (Needle)
Crystal size (mm) 0.3x0.2x0.1 (Plate) Needle
Formula C5H6N2O2 C5H6N2O2
Formula weight (g mol-1) 126.12 126.12
Temperature (K) 292 292
Wavelength (Å) 0.7107 0.7107
Crystal system Monoclinic Monoclinic
Space group C 2/c P21/c
a (Å) 25.107 (7) 12.87
b (Å) 6.846 (2) 6.830
c (Å) 6.715 (2) 6.70
fiO 90.529 (2) 105
Volume (Å3) 1154.1 (5) 568.876
Z 8 4
Density (g/cm3) 1.452 1.455
μ (mm-1) 0.115 -
F (000) 528 -
θ (min, max) 0.97, 27.98 -
hmin, max, kmin, max, lmin, max (0, 29), (0, 8), (-7, 7) -
No. of reflections measured 2064 -
No. of unique reflections 973 724
No. of parameters 83 -
R_all, R_obs 0.2182, 0.088 0.149
wR2_all, wR2_obs 0.2694, 0.1998 -
APmin, max (eÅ-3) -0.148, 0.217 -
G. O. F 0.965 -
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Table 2-Crystal Data and Structural Refinement Parameters of Anhydrous Ciprofloxacin, Midazolam, and Ofloxacin

Details Ciprofloxacin Midazolam Ofloxacin
Molecular formula C17H18FN3O3 C18H13ClFN3 C18H20FN3O4
Crystal size (mm) 0.30, 0.20, 0.20 0.3, 0.1, 0.02 0.2, 0.18, 0.1
Formula weight 331.34 325.76 361.37
Crystal system triclinic monoclinic monoclinic
Space group P1 P21/n C2/c
a (Å) 8.062(1) 7.5588(3) 30.322(4)
b ( Å ) 9.730(2) 13.6840(5) 6.8607(8)
c ( Å ) 10.321(1) 15.1242(8) 16.9199(16)
a(º) 99.927(17) 90 90
P( º) 104.541(17) 92.497(5) 105.271(11)
Y( º) 98.073(17) 90 90
Volume ( Å3) 757.5(3) 1562.88(12) 3395.6(7)
Z 2 4 8
Density calc (g/cm3) 1.453 1.385 1.414
Temperature (K) 298 298 298
0.109 0.257 0.108
F(000) 348 672 1520
hmin,max -9, 9 -9, 9 -41, 41
kmin,max -11, 11 -16, 16 -9, 9
lmin,max -12, 12 -18, 18 -23, 22
3.09-25.50 2.98-26.00 3.05-29.46
No. of measured Reflections 19153 16196 19418
Rint 0.2845 0.0880 0.3075
No. of unique Reflections 2818 3073 4135
No. of parameters 218 208 237
0.072 0.0453 0.0552
wR [I >2a(I)] 13.25 0.0902 0.0752
GOF 0.780 0.811 0.681
max/min AF (e/
Å3) 0.266/-0.234 0.281/-0.243 0.188/-0.179
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Referral numerals

Referral Number Description
1 Quartz furnace
2 Vacuum pump
3 Pressure gauge
4 Oil pump
5 Oil bath
6a Inner tubes
6b Outer tubes
7 Sample holder
8 External heater and/or cooler
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We claim:

1. An apparatus to crystallize organic compound, said apparatus comprising:
a) a sample holder (7) to hold sample of the organic compound,
b) a quartz furnace (1) to maintain a constant temperature around the sample holder (7),
c) plurality of coaxial glass tubes constructed with an inner tubes (6a) and an outer tubes (6b), to pass vapors of the organic compound through the inner tubes (6a), and
d) an oil pump (4) dipped in a oil bath (5), to pump the oil around the inner tube (6a), to crystallize the organic compound in the inner tube (6a).

2. The apparatus as claimed in claim 1, wherein the organic compound is in anhydrous form.
3. The apparatus as claimed in claim 1, wherein the quartz furnace (1) uses a proportional–integral–derivative (PID) temperature controller to maintain constant temperature around the sample holder (7).
4. The apparatus as claimed in claim 1, wherein the oil is supplied in the gap between outer circumference of inner tube (6a) and inner circumference of outer tube (6b).
5. The apparatus as claimed in claim 1, wherein the oil bath (5) temperature is maintained beyond the melting temperature of the organic compound.
6. The apparatus as claimed in claim 1, wherein the coaxial glass tube is provided with an external heater and/or cooler (8) to maintain temperature gradient along its length.
7. The apparatus as claimed in claim 1, wherein a vacuum pump (2) with pressure gauge (3) is used to control rate of flow of the organic compound.
8. A method for crystallizing organic compound, said method comprising acts of:

a) placing sample of organic compound in sample holder (7) ,
b) maintaining constant temperature around the sample holder (7) by a quartz furnace (1) to generate vapors of the compound,
c) passing the vapors through inner tubes (6a) of coaxial glass tubes, and
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d) controlling temperature gradient along length of the coaxial glass tubes by circulating oil in between the inner tubes (6a) and outer tubes (6b) for crystallizing the sample of the organic compound.
9. The method as claimed in claim 8, wherein said method optionally comprise an act of maintaining constant rate of flow of the vapors along the length of the coaxial glass tube by creating vacuum ranging from about 30 mm/Hg to about 650 mm/Hg using vacuum pump.
10. A method of assembling apparatus to crystallize organic compound, said method comprising acts of:

a) arranging quartz furnace (1) at one end of sample holder (7) containing a sample of the organic compound to maintain constant temperature,
b) connecting other end of the sample holder (7) to coaxial glass tubes to pass vapors of the organic compound through the coaxial glass tubes,
c) connecting inlet and outlet oil passages to the coaxial glass tubes for oil circulation, and
d) providing an external heater and/or cooler (8) to maintain the temperature gradient along the length of the coaxial glass tube.
11. The method as claimed in claim 10, wherein placing vacuum pump (2) with pressure
gauge (3) at the other end of coaxial glass tube to control the rate of flow of vapors
along the length of coaxial glass tube.

Dated this 24th day of August, 2010

P.H.D.RANGAPPA
IN/PA 1538
OF K & S PARTNERS
AGENT FOR THE APPLICANT