title: Vitrification from solution in restricted space: formation and stabilization of amorphous nifedipine in a nanoporous silica xerogel carrier.
abstract: OBJECTIVE
  The goal was to find thermodynamic criteria that must be satisfied in order to prevent formation of crystalline state of drugs within a confined space (e.g., nanopores of inorganic solid). Similarly, criteria that lead to stabilization of amorphous drug within such pores were investigated.
  
  
  METHODS
  In the theoretical part, the classical thermodynamics of nucleation is applied to the conditions of a restricted space. The theoretical findings are verified using porous silica as a carrier and nifedipine as a model drug. The amorphicity of the latter is checked using XRD and thermal analysis (DTA, DSC) in combination with BET measurements.
  
  
  RESULTS
  It is shown that there exists a critical pore radius of a host below which the entrapped substance will solidify in an amorphous form. There also exists a critical pore radius below which the entrapped amorphous solid will not be able to crystallize. Specifically, incorporation of NIF into a silica xerogel with an average pore diameter of about 2.5 nm produces and stabilizes its amorphous form.
  
  
  CONCLUSIONS
  Entrapment of drugs into solid nanoporous carriers could be regarded as a potentially useful and simple method for production and/or stabilization of non-crystalline forms of a wide range of drugs.
authors.affiliation: National Institute of Chemistry, Hajdrihova 19, 1000 Ljubljana, Slovenia.
authors.forename: Aljaz
authors.initials: A
authors.lastname: Godec
authors.forename: Uros
authors.initials: U
authors.lastname: Maver
authors.forename: Marjan
authors.initials: M
authors.lastname: Bele
authors.forename: Odon
authors.initials: O
authors.lastname: Planinsek
authors.forename: Stane
authors.initials: S
authors.lastname: Srcic
authors.forename: Miran
authors.initials: M
authors.lastname: Gaberscek
authors.forename: Janko
authors.initials: J
authors.lastname: Jamnik
mesh_terms: D003460:Crystallization; D004055:Differential Thermal Analysis; D004337:Drug Carriers; D005782:Gels; D009543:Nifedipine / Q000737:chemistry*; D016062:Porosity; D033362:Powder Diffraction; D012822:Silicon Dioxide / Q000737:chemistry*; D013818:Thermogravimetry; D014961:X-Ray Diffraction
chemical_list: D004337:Drug Carriers; D005782:Gels; D012822:Silicon Dioxide; D009543:Nifedipine