14-11-2012, 05:05 PM
Diffusion
[attachment=39475]
Definition
Diffusion is a spontaneous process. In this process there occurs transfer of anisotropic materials (matters with the same structural and diffusional properties in all directions) from a region of higher conc. to a region of lower conc. through a semi permeable membrane until equillibrium state is reached. The process is characteristically selective. For example
- protein molecules, gums, starch can’t undergo diffusion. These are non diffusible; while particles of colloidal size range exhibiting Brownian movement undergoes diffusion
- movement of solute is unidirectional i.e. in one direction
- movement involves no expenditure of energy and the process is automatic and slow. Moreover migration occurs in absence of influence of any external force
- this can give a measure of escaping tendency of solute
Importance of Diffusion or Purpose of study
Diffusion is a common process that occurs in in - vivo, in vitro even in drug delivery system.
Diffusion in in –vivo :
In biological system diffusion aids absorption of weak acidic or basic drugs. In GI tract salicylic acid remains undissociated and is absorbed through bio membrane. (i.e gastric wall). Actually these bio membranes are not compact structures. These have pores which are channel like structures. These structures are un-uniform, tortuous and at random. Through these networked channels solute molecules pass (on their own) from a higher conc region to lower conc region and ultimately absorbed and is circulated. Through circulation ultimately reaches the site of action and drug response occurs. Orally administered drugs like salicylates (weakly acidic drugs) and amino pyrine (weakly basic drugs) are absorbed in this manner.Thus diffusion phenomenon prevails in drug action.
Importance of Diffusion or Purpose of study
Passing of small solutes across ‘gelatuin’ gel and ‘agar gel’ diffusion occurs. Gelatin or agar is a partial water soluble agents. So in water these molecules swells up (here some part of the molcule is soluble, some are not). Such swelling is due to the formation of 3-D structure within which water molecules are entrapped in a large amount. This water fraction is immobile and forms a continuous phase through which solute molecules diffuses out. Such passing of solute molecules is because of formation of conc grad in and outside the structure.
Factors affecting the rate
D is not a fixed quantuty. It varies withn temperature, conc., pressure, solvent properties and chemical nature of diffusant. So D is called as coefficient than a constant and its value is dependent on –
- sieve like structure of membrane
pH of gel
Viscosity of the medium
Presence of ions
[attachment=39475]
Definition
Diffusion is a spontaneous process. In this process there occurs transfer of anisotropic materials (matters with the same structural and diffusional properties in all directions) from a region of higher conc. to a region of lower conc. through a semi permeable membrane until equillibrium state is reached. The process is characteristically selective. For example
- protein molecules, gums, starch can’t undergo diffusion. These are non diffusible; while particles of colloidal size range exhibiting Brownian movement undergoes diffusion
- movement of solute is unidirectional i.e. in one direction
- movement involves no expenditure of energy and the process is automatic and slow. Moreover migration occurs in absence of influence of any external force
- this can give a measure of escaping tendency of solute
Importance of Diffusion or Purpose of study
Diffusion is a common process that occurs in in - vivo, in vitro even in drug delivery system.
Diffusion in in –vivo :
In biological system diffusion aids absorption of weak acidic or basic drugs. In GI tract salicylic acid remains undissociated and is absorbed through bio membrane. (i.e gastric wall). Actually these bio membranes are not compact structures. These have pores which are channel like structures. These structures are un-uniform, tortuous and at random. Through these networked channels solute molecules pass (on their own) from a higher conc region to lower conc region and ultimately absorbed and is circulated. Through circulation ultimately reaches the site of action and drug response occurs. Orally administered drugs like salicylates (weakly acidic drugs) and amino pyrine (weakly basic drugs) are absorbed in this manner.Thus diffusion phenomenon prevails in drug action.
Importance of Diffusion or Purpose of study
Passing of small solutes across ‘gelatuin’ gel and ‘agar gel’ diffusion occurs. Gelatin or agar is a partial water soluble agents. So in water these molecules swells up (here some part of the molcule is soluble, some are not). Such swelling is due to the formation of 3-D structure within which water molecules are entrapped in a large amount. This water fraction is immobile and forms a continuous phase through which solute molecules diffuses out. Such passing of solute molecules is because of formation of conc grad in and outside the structure.
Factors affecting the rate
D is not a fixed quantuty. It varies withn temperature, conc., pressure, solvent properties and chemical nature of diffusant. So D is called as coefficient than a constant and its value is dependent on –
- sieve like structure of membrane
pH of gel
Viscosity of the medium
Presence of ions