Bio‐Functional Mesolamellar Nanocomposites Based on Inorganic/Polymer Intercalation in Purple Membrane (Bacteriorhodopsin) Films

Abstract

Fabrication of self-assembled structures using multiple building blocks with diverse functionalities such as biomolecules, polymers and inorganic nanoparticles has attracted considerable interest due to the potential applications of hybrid constructs in biotechnology and bio-electronic devices. [1,2] A principal candidate biomolecule for incorporation into multi-functional devices is the photoactive protein-retinal complex, bacteriorhodopsin (BR), [3] which acts as a light-activated proton pump in the purple membrane (PM) of halophilic bacteria. Extracted PM fragments exhibit photoelectric, photochromic and photo-induced proton transport properties, and have been investigated as potential materials for holography, non-linear optics, and optical information processing. [3,4] PM films are only stable over a limited range of pH, humidity and temperature conditions, and are fragile and difficult to manipulate, which severely limit their application in photoelectric devices. PM fragments can be readily extracted from halophilic bacteria such as Halobacterium salinarum in the form of micronsized, 5 nm-thick lipid bilayer sheets that consist of a 2D protein/lipid crystalline array of unidirectionally oriented BR molecules. Proton transport from the cytoplasmic to extracellular side of the PM is initiated by light-activated isomerisation of the BR-bound retinal chromophore, and coupled with a thermally activated photocycle involving a series of spectroscopic intermediates (J, K, L, M, N, and O states) associated with deprotonation/protonation of the Schiff-base retinal linkage. A significant blue shift occurs between the protonated ground state (B 568 ) and stable unprotonated intermediate (M 412 ) that gives rise to photochromism and the possibility of using PM patches in imaging and recording devices such as photochromic inks, holographic interferometry and volumetric memories.[4] The response to steady state illumination is extremely sensitive and the photocycle can be cycled many times more than for synthetic materials, as well as enhanced in efficiency by increasing the M lifetime by site-directed mutagenesis (notably replacing Asp96 by Asn96). [4,5] Previous research has been undertaken on the incorporation of PM flakes into polymer gels [6,7] and sol-gel derived glasses [8][9][10][11][12] in order to produce bulk composite materials for potential photochromic applications. In contrast, the photoelectric response of BR, which depends on a net charge separation (voltage) across the lipid membrane, necessitates the fabrication of films in which PM fragments are uniformly oriented in order to facilitate unidirectional proton transport. Several approaches, involving layer by layer deposition, [13][14][15] Langmuir-Blodgett deposition, [16][17][18][19] electrophoretic sedimentation, [20,21] antibody recognition [22] and chemiadsorption selfassembly [23] have been developed to achieve this objective.The films are generally soft and brittle, and the photoelectric response sensitive to changes in environmental conditions...

3-aminopropyl functionalized magnesium phyllosilicate as an organoclay based drug carrier for improving the bioavailability of flurbiprofen

“…Clay minerals of layered organic-inorganic hybrid materials resembling the talc parent structure Si 8 Mg 6 O 20 (OH) 4 have been synthesized by a sol-gel reaction in ambient conditions, with various combinations of metal ions such as magnesium, nickel, and zinc. [2][3][4][5] Their organofunctionalities have also been extensively investigated to improve biocompatibility.…”

“…The cationic and water-soluble properties of AMP clay have been used to construct hybrid materials with biomolecules and drug delivery systems. [8][9][10][11][12][13] Considering AMP clay is a nontoxic host material, 14 it should have high potential as a promising drug delivery carrier. There have been a few reports indicating the application of AMP clay as an efficient drug delivery system; 9,11-13 however, most of the previous studies were limited to in vitro evaluation.…”

Insitu X-ray reflectivity studies of molecular and molecular-cluster intercalation within purple membrane films

“…It has been shown that hybrid lms consisting of PM sheets intercalated with a condensed organosilane can be formed by adding an aqueous precursor to a PM lamellar lm and then allowing the samples to dry. 12,16,17 These composite lms demonstrate enhanced mechanical tolerance and solvent resistance in addition to functional photocycle and photochromic responses. Importantly, the composite lms retain their lamellar structure as opposed to dispersal of the PM sheets randomly within an organic or inorganic supporting matrix.…”

“…Intercalation in PM lms of non-sol-gel precursors such as polysaccharides, inorganic polymers and polycationic organoclay oligomers has also been demonstrated, but the mechanism by which the guest materials permeated into the PM host structure was not fully elucidated. 16,18 In this paper we have used X-ray surface scattering to study the mechanism of formation of PM lms intercalated with aminopropyl silicic acid (APS) or cationic oligomers of aminopropyl-functionalised magnesium phyllosilicate (AMP), as two model guest species presented in molecular or molecularcluster forms, respectively. Both of these guests have been previously used to produce PM-based composite lms with an AB-type lamellar structure.…”

“…Both of these guests have been previously used to produce PM-based composite lms with an AB-type lamellar structure. 16 The composite lms are prepared under aqueous conditions by guest inltration into preformed PM lms, or by co-assembly from an aqueous dispersion of PM sheets and guest molecules/clusters. Our results show that addition of an aqueous solution of guest molecules to a dried preformed PM lm results in loss of the lamellar phase, and that subsequent air-drying induces re-stacking of the lipid/ protein membranes along with retention of a 2-3 nm hydration layer within the inter-lamellar spaces.…”