What is X-ray diffraction? What is its application in Biomedical field?

 

X-ray Diffraction (XRD):

Definition:

X-ray diffraction (XRD) is a powerful analytical technique used for determining the crystallographic structure of a material. It relies on the principle that when X-rays interact with a crystalline sample, they undergo constructive interference, leading to the formation of diffraction patterns. By analyzing these patterns, scientists can deduce the arrangement of atoms within the crystal lattice.

Components:

• X-ray Source: Generates X-rays.
• Sample Holder: Holds the crystalline sample.
• Detector: Captures the diffraction patterns.
• Analyzer: Processes and interprets the data.

How the Technique Works

X-ray diffraction is a common technique that determine a sample's composition or crystalline structure. For larger crystals such as macromolecules and inorganic compounds, it can be used to determine the structure of atoms within the sample. If the crystal size is too small, it can determine sample composition, crystallinity, and phase purity. This technique sends x-ray beams through it. X-ray beams are chosen because their wavelength is similar to the spacing between atoms in the sample, so the angle of diffraction will be affected by the spacing of the atoms in the molecule, as opposed to using much larger wavelengths, which would be unaltered by the spacing between atoms. The x-rays then pass through the sample, “bouncing” off of the atoms in the structure, and changing the direction of the beam at some different angle, theta, from the original beam. This is the angle of diffraction. Some of these diffracted beams cancel each other out, but if the beams have similar wavelengths, then constructive interference occurs. Constructive interference is when the x-ray beams that are whole number integers of the same wavelength add together to create a new beam with a higher amplitude. The greater amplitude of the wave translates into a greater signal for this specific angle of diffraction. The angle of diffraction can then be used to determine the difference between atomic planes using Bragg’s law,  sinΘ=nλ/2d

where lambda is the wavelength added, theta is the angle of diffraction, and d is the distance between atomic planes. The distance between atomic plates can then be used to determine composition or crystalline structure.

Figure 1. Bragg's Law reflection. The diffracted X-rays exhibit constructive interference when the distance between paths ABC and A'B'C' differs by an integer number of wavelengths (λ). Figure Courtesy of Creative Commons license and found on https://serc. carleton. edu/msu_nanotech/methods/BraggsLaw. html

Applications in the Biomedical Field:

• Protein Crystallography: XRD is extensively used in determining the three-dimensional structures of biological macromolecules, particularly proteins. Understanding the structure of proteins helps in drug design and the development of therapeutic agents.
• Drug Development: XRD assists in the analysis of drug compounds and their interactions with biological molecules. It provides insights into the binding modes of drugs with target proteins, aiding in the optimization of drug design.
• Biomaterial Characterization: In the biomedical field, materials like bones, teeth, and implants can be analyzed using XRD to understand their crystalline structure. This is crucial for designing biocompatible materials.
• Crystallography in Drug Formulation: XRD is used to study the crystalline structure of pharmaceutical compounds. It helps in optimizing drug formulations by understanding the solid-state properties of drug substances.
• Disease Diagnosis: XRD can be employed in the diagnosis of certain diseases. For instance, the crystalline structures of urinary stones can be analyzed to determine their composition, aiding in the diagnosis and treatment of kidney stones.
• Biological Tissue Analysis: XRD is applied to analyze the crystallographic structure of biological tissues. This can provide valuable information about the composition and structure of bones, cartilage, and other tissue types.
• Study of Nanoparticles: In nanomedicine, XRD is used to characterize the crystal structure of nanoparticles. Understanding the structure is essential for predicting the behavior of nanoparticles in biological systems.
• Analysis of Biomolecular Complexes: XRD is instrumental in studying the structures of complexes formed by biomolecules. This includes complexes between proteins, nucleic acids, and other biomolecules, offering insights into their functions.
• Understanding Enzyme Mechanisms: XRD helps in elucidating the structures of enzymes and their active sites. This information is crucial for understanding enzyme mechanisms and developing enzyme-based therapies.
• Vaccine Development: XRD plays a role in the development of vaccines by providing information about the structure of antigens and their interactions with the immune system.

How to interpret the data

The result of X-ray diffraction plots the intensity of the signal for various angles of diffraction at their respective two theta positions. The two theta positions correspond to a certain spacing between the crystals or atoms in the samples, determined by the angle of diffraction from the incident x-ray beam sent into the sample. The intensity of the peaks is related to the amount of molecules in that phase or with that spacing. The greater the intensity of the peak, the greater the amount of crystals or molecules with that distinct spacing.

The width of the peaks is inversely proportional to the crystal size. A thinner peak corresponds to a bigger crystal. A broader peak means that there may be a smaller crystal, defect in the crystalline structure, or that the sample might be amorphous in nature, a solid lacking perfect crystallinity. For smaller samples, the patterns determined using XRD analysis can be used to determine a sample’s composition. There is a large database of elements, compounds, and minerals that contain the diffraction patterns for elements, compounds, and minerals. The pattern for an unknown compound can be compared to the literature and experimentally determined values to verify the identity of an element, matching both the location, width, and relative heights of the diffraction patterns.

Figure "2" Figure courtesy of Creative Commons license and can be found at https://serc. carleton. edu/details/images/20376. html

In summary, X-ray diffraction is a versatile technique with wide-ranging applications in the biomedical field. It contributes to structural biology, drug development, biomaterials research, disease diagnosis, and various other areas critical to advancing medical science and healthcare.