powder_1 Flashcards
properties of mesophase molecules
- organic molecules
- elongated or rectilinear molecules
- rigid molecules
- possess strong dipoles and easily polarisable groups
what are mesophase molecules classified as
thermotropic (solvent-free), and lyotropic (with solvent)
uses of mesophase molecules
- temperature sensor
- display- liquid crystals provide colors
- stabilisation of emulsions, by increasing viscosity
- improve solubilization drugs
characteristics of solids
- least amount of kinetic energy (more stable)
- structural rigidity, resist informative forces (short IM distance, densed and fixed)
- organised as crystalline or amorphous solid
calculated path of liquid molecules
- volume with no set shape, takes shape of container
- flow w relative ease
- molecules move freely, unrestricted
calculated path of solid particles
- definite mass, volume, and shape
- molecules remain relatively immobile, oscillate about their mean positions
- mechanically strong and incompressible
multi-particulate solid dosage form includes:
- powders: crystals, nanoparticles, microcapsules, microspheres
- granules, agglomerate
- pellets, spheroids, beads
final solid dosage form
- capsules; hard, soft
- tablets, caplets
- others: films, gums
why solid dosage form?
- when dry does not promote microbial growth
- markedly better chemical stability
- lower bulk volume
- ease of handling, added convenience
- flexible, single or multiple chemical components
what are crystals
crystals are ordered structures with arranged atoms, ions or molecules, forming symmetrical and repeating patterns in 3D; the basic repeating pattern is the unit cell of the structure
polymorphism
the ability of a solid to exist in more than one form or crystal structure, difference in crystal packing
what differs between different polymorphic forms
physical properties: solubility, dissolution, bioavailability, morphology thermal
why does solid exist in different polymorphs
minimise their crystal lattice energy under specific thermodynamic conditions (like temp and solute concentration)
properties of crystalline structures
- orderly arrangement of constituents, defined structures
- anisotropic, sharp x-ray diffraction patterns
- sharp melting points
- definite heat of fusion
- more stable
properties of amorphous structure
- no arrangement, irregular or undefined shapes
- isotropic, no well-resolved x-ray patterns
- melt over a range
- no definite heat of fusion
- more liable for degradation
preparation methods of amorphous state
- milling
- compaction
- dehydration
- vapor condensation
- spray drying
- precipitation
- supercooling
- freeze drying
types of amphorous states
- amorphous
- improve drug solubility (note 90% of new drugs under development are poorly water soluble) - nanocrystalline (crystallite size of only few nanometers)
- improve stability (but also good solubility)
how to determine crystallinity/ polymorphism
- x-ray diffractometry (standard)
- melt behaviour (visual- hot stage microscopy; differential scanning calorimetry)
- raman spectroscopy
- infrared spectroscopy
- nuclear magnetic resonance spectroscopy
x-ray diffraction by crystals
concept: planes of atoms in molecules give reflecting layers for xrays
what is the relationship between grinding and diffraction of solids
milling can produce amorphous drugs, causing less diffractions, hence the x-ray diffraction pattern will have reducing peaks
hot stage microscopy
visual characterisation of thermal transitions, may also have in-built sensor for calorimetric measurement
differential scanning calorimetry
measure enthalpy change as a function of temperature or time, difference in the amount of heat required to increase the temperature of a sample and reference
raman spectroscopy
when electromagnetic radiation is scattered, one photon of incident radiation is annihilated. at the same time, one photon of the scattered radiation is created.
what is rayleigh scattering
when the energy of incident photo is equal to scattered on, the process is call rayleigh scattering
what is raman scattering
when energy of incident photon is different to that of the scattered one
advantage of raman spectroscopy
- provide distinct spectroscopic properties of a material
- fast measurement time
- able to measure from small spot size, to few microns
- can take measure in presence of water
uses of raman spectroscopy
non-destructive, microscopic, chemical analysis applications
how to use raman spectroscopy to tell between crystalline and amorphorous
crystalline: sharper narrower peaks
amorphous: rounder broader shorter peaks
