Can any one explain the use of XRD and its appropriate interpretation for drug development and formulation?
The most widespread use of x-ray powder diffraction is for the identification of crystalline compounds by their diffraction pattern. Some of the specific uses are:
• Identification of single-phase materials – minerals, chemical compounds, ceramics or other engineered materials.
• Identification of multiple phases in microcrystalline mixtures (i.e., rocks)
• Determination of the crystal structure of identified materials
• Identification and structural analysis of clay minerals
• Recognition of amorphous materials in partially crystalline mixtures
• Crystallographic structural analysis and unit-cell calculations for crystalline materials.
• Quantitative determination of amounts of different phases in multi-phase mixtures by peak-ratio calculations.
• Quantitative determination of phases by whole-pattern refinement.
• Determination of crystallite size from analysis of peak broadening.
• Determine of crystallite shape from study of peak symmetry.
• Study of thermal expansion in crystal structures using in-situ heating stage equipment.
Although it possible to solve crystal structures from powder X-ray data alone, its single crystal analogue is a far more powerful technique for structure determination. This is directly related to the fact that much information is lost by the collapse of the 3D space onto a 1D axis. Nevertheless powder X-ray diffraction is a powerful and useful technique. It is mostly used to characterize and identify phases rather than solving structures.
The great advantages of the technique are:
*simplicity of sample preparation
*rapidity of measurement
*the ability to analyze mixed phases, e.g. soil samples
*"in situ" structure determination
There are many materials for which despite many attempts it has not proven possible to obtain single crystals. Many materials are readily available with sufficient microcrystallinity for powder diffraction, or samples may be easily ground from larger crystals. In the field of solid-state chemistry that often aims at synthesizing new materials, single crystals thereof are typically not immediately available. Powder diffraction is therefore one of the most powerful methods to identify and characterize new materials in this field.
Since all possible crystal orientations are measured simultaneously, collection times can be quite short even for small and weakly scattering samples. This is not merely convenient, but can be essential for samples which are unstable either inherently or under X-ray or neutron bombardment, or for time-resolved studies. The advent of synchrotron radiation and modern neutron sources has done much to revitalize the powder diffraction field because it is now possible to study temperature dependent changes, reaction kinetics and so forth by means of time dependent powder diffraction.
Regards
one of the important approaches in drug development is the use of polymers to modify the physical properties of API of class II (low solubility, high permeability) to improve the solubility, dissolution rate and finally the bioavailability. since many of these API are crystalline in nature, so, reduction of crystallinity and increasing amorphization by incorporation into different polymers using variable techniques is a good approach to achieve the goal. XRD is one of the good, easy and reliable tests to detect the nature of interaction between the drug & the polymer and consequently explain the behavior of drug release from the formula.
Best regards
As Nashwan suggested, use of XRD in drug development is to assess the state i.e. amorphous or crystalline nature of the drug and degree of crystallinity in the particular substances as some drugs may be active in only one of their forms i.e. either in crystalline or in amorphous form. so it really matters
Normally, PXRD study used for finding the crystalline or amorphous or polymorphous nature of the drug.
For example: If pure paracetamol and recrystallized paracetamol gives same high intensity value and same 2 theta value, indicate crystalline nature of both.
suppose the recrystallized paracetamol gives same 2 theta value but low intensity value, indicates that the crystallized paracetamol is an amorphous form.
however, The recrystallized paracetamol gives same or low intensity but different in 2 theta value, indicates that the recrystallized paracetamol is showing polymorphous nature of paracetamol.
Dr C Bothiraja, Pune, India.
The following information could be useful for a better understanding of XRD applications.
https://en.wikipedia.org/wiki/Powder_diffraction
epswww.unm.edu/xrd/xrdclass/01-xrd-intro.pdf
http://serc.carleton.edu/research_education/geochemsheets/techniques/XRD.html
thanks prakash.is The 2nd link is not working but I could open the 3rd. it is very well explained.
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