Electroactive centers have been incorporated into ordered thin films. So has photochromic functionality with vectorial optical response. There have also been several reports 26 of the construction of molecular thin films with significant abilities for molecular recognition, though again of a fairly rudimentary sort. Siwadasan and P. Somasundaran, Colloids and Surfaces ; S. Biggs, J. Selb, and F. Candau, Langmuir For example, E. Thoden van Velzen, J. Engbersen, P. De Lange, J. Mahy, and D. Reinhoudt, J. Engbersen, and D. Schierbaum, T. Weiss, E. Engbersen, D. Reinhoudt, and W.
Willner, M. Lion-Dagan, S. Marx-Tibbon, and E. Katz, J. Sigal, C. Bamdad, A. Barberia, J. Strominger, and G. Whitesides, Anal. Considerable attention has been given to the influence of thin boundary layer films on the properties of interfaces. Self-assembled monolayers SAMs make it possible to functionalize surfaces in well-defined ways, and it is only natural that they have found considerable application in research on friction, lubrication, and wetting.
It is now understood, as a direct result of the study of SAMs, that wetting phenomena on molecular solids depend sensitively on near-surface structure and composition. An understanding is now emerging from this work of how molecular structure drives the macroscopic properties of surfaces. This understanding is enabling the development of surface modification schemes for technological applications that are based on reason rather than empirical experience alone.
PDMS is poly dimethylsiloxane. Reprinted with permission from P.
Lyotropic liquid crystal - Wikipedia
Hammond and G. Whitesides, Macromolecules SAMs are also beginning to find applications in the biological sciences. There has long been an interest in the interaction of cells with surfaces. SAMs have allowed the tailoring of surface properties in ways that allow considerable control over the ability of cells to bind to a solid. Several recent papers 27 have demonstrated that spatially defined SAMs can be used to pattern cell attachment to a substrate.
Neural synaptic integration in planar neural arrays can also be mediated by SAMs, and the pattern of their interconnections can be controlled by the modification of surface properties. The affinities of surfaces for protein adsorption are also easily modifiable using SAMs. There is considerable interest in the applications of SAMs in the area of sensors. Their potential utility is being demonstrated very powerfully in electrochemical applications. They have been used to control the redox tunneling properties of gold surfaces by allowing the homogeneous placement of electroactive materials at known densities and distances from the surface.
More recently, photoexcited vectorial electron transport has been demonstrated in both monolayer and multilayer assemblies. Several general sensor designs have also been described that involve the use of SAM-modified microelectrode grids. SAMs have also been shown 28 to act as effective masks for the lithographic patterning of metals Figure 8.
These studies have demonstrated that microstructures can easily be fabricated in shapes and architectures that are hard to implement flexibly with conventional multistep lithographic patterning. An exciting application has been demonstrated in the growth of thin films by chemical vapor deposition:. O'Neill, P. Jordan, P.
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Riddle, and G. Ireland, J. Cell Sci. Kleinfeld, K. Kahler, and P. Hockberger, J. Dulcey, J. Georger, V. Krauthamer, D. Stenger, T. Fare, and J. Calvert, Science — ; D. Stenger, J. Georger, C.
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Hickman, A. Rudolph, T. Nielson, S. McCort, and J. Calvert, J. Thompson, L. Gerenser, R. Valentini, P. Aebischer, D. Hook, and J. Gardella, Langmuir — ; K. Prime and G. Whitesides, J. Whitesides, Science — Kumar, N. Abbott, E. Kim, H. Biebuyck, and G. Whitesides, Accounts of Chemical Research — Schematic view of a bacterial membrane with a hexagonal lattice of bacteriorhodopsin trimers.
Reprinted, by permission, from Y. Shen, C. Safinya, K. Liang, A. Ruppert, and K. Rothschild, Nature SAMs were very effective in improving the adhesion of the deposited film, and in several systems it has been demonstrated that they can be used to influence the activated nucleation of thin-film growth. In contrast to phospholipid molecules, which form the passive permeability barrier in biomembranes, membrane-associated proteins serve as active components to facilitate important cellular processes such as nerve conduction, energy conversion, active-ion and molecular transport, and cell-cell adhesion.
Integral membrane proteins are intercalated and firmly tethered to the two-dimensional host lipid membrane plane, in which they are free to diffuse. Research has begun to develop new types of materials that incorporate the functional activity of such proteins into chemical and biological sensors, materials with controlled interfacial properties, and optoelectronic materials.
A notable example of a membrane-associated protein is bacteriorhodopsin bR , 30 which embodies two functions of membrane proteins, energy transduction and active ion transport. The structure of bR has been determined to near-atomic resolution of 3. The detailed mechanism by which bR absorbs light energy and transports protons against an electrochemical gradient is becoming clear.
Several features make bR attractive from the standpoint of biomolecular materials development.
At low temperatures, bR can function as an optically driven bistable switch. For example, when the light-adapted form of bR, which absorbs at nm, is irradiated with green light at 77 K, it is converted to the stable K form, which absorbs near nm. Recent studies 32 using genetic engineering techniques suggest that mutant forms of the protein can be produced that exhibit optical bistability at room temperature.
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Subramaniam, J. Ahl, L. Stern, T. Mogi, H. Khorana, and K. Rothschild, Biochemistry Biomineralization 33 is precisely controlled by complex templating relationships and coordinated secretory processes that are ultimately encoded in genes. During formation of abalone shell, for example, secreted proteins self-assemble into two-dimensional polyanionic b-pleated sheets that serve as templates for the nucleation and epitaxial growth of calcium carbonate crystalline domains Figure A microlaminate composite is formed that has exceptional regularity, strength, and crystalline ordering.
The unique properties of biosynthetic microlaminates are due to the organic matrix layers' capacity for flexible deformation and to the retardation of crack propagation at each mineral-organic interface. The biological templating process that controls the structure of molluscan shell has been mimicked in the formation of sub-micron structures built up on tubules.
The cylindrical structure of a tubule is intrinsically interesting as a template.
motlerennorth.ga It leads directly to a large degree of shape anisotropy, which can be tuned by adjusting the dimensions of the tubules either by manipulating the molecular structure of the protein or other molecule attached to the substrate or by changing the processing conditions under which the tubules form. A beautiful example of the use of spontaneously self-assembled mesoscopic ordering to produce new materials is the use of the lyotropic hexagonal phase as a template to make mesoporous solids. These materials have periodic arrays of nanometer-sized pores of unprecedented regularity and density.
Mesoporous metallic surface films have also been generated via molecular templating, by employing the self-assembled two-dimensional crystalline protein arrays of bacterial cell walls as patterning elements. Much of the molecular transport in biological systems occurs not by diffusion but by active transport by biomotors. Scanning electron micrograph of the growth front of abalone shell. The aragonite CaCO 3 crystals in the shell form very regular stacking and interdigitating plates. A combination of polyanionic proteins and matrix proteins produces this hierarchical structure, which gives the shell its unique optical properties and its increased strength.
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Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available. Do you enjoy reading reports from the Academies online for free? Sign up for email notifications and we'll let you know about new publications in your areas of interest when they're released. Get This Book. Visit NAP. Looking for other ways to read this? No thanks. Suggested Citation: "2 Status. Complex Fluids and Liquid Crystals. Page 9 Share Cite. Figure 2 Schematic representation of some self-assembled lipid-based microstructures.
Surfactant-based Self-Assembly. Page 10 Share Cite. Figure 3 Vesicles: top sketch of multilamellar and unilamellar vesicles and the phospholipid bilayer of which they are made; bottom sketch of a mechanism whereby drug-containing vesicles adhere to a cell surface and present drugs for uptake by endocytosis. Page 11 Share Cite.
Figure 4 Electron micrograph of nickel-coated tubules approximately 0. Page 12 Share Cite. Figure 5 Key steps in the in vivo synthesis of protein-like polymers under direct genetic control in bacteria. Page 13 Share Cite. Page 14 Share Cite. Figure 7 Schematic illustration of the molecular structure of a self-assembled monolayer SAM on a substrate surface.
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Chiellini, Polymer Bulletin , 9, pp. Starting with chiral glycols an enantiomer of a specific sign as the spacer, a polymer with the same optical sign was obtained in all cases. Chiellini, R. Carro2zino, G. Galli and 8. Lisciani, G. Solaro, L. EP A2 Po, S.
Carrozzino, G. Galli and B. Galls, R. Chiellini, G. A parallelism can be established between the behavior of the liquid crystals in material science ana lipids in life sciences H. Lipids are also self-organizable combinin5 order and mobility. Alison, eds. WO-A discloses lipid-polymer conjugates and the combination thereof with liposomes, said conjugates comprising a vesicle-forming lipid and a polymer covalently attached to the lipid. To be able to attach to the lipid the lipid must have a polar head group.
The previously synthesized polymers M. Perez-Mende2, C. Marco Rocha, Spanish patent no. The techniques chosen to study the interaction were, transmission electronic microscopy TEM by the Lechniques of preparation of a cryomieroscopy sample and negative staining sample and stationary state fluorescen. The fluorescent probe used for its study by fluorescence was diphenylhexatriene DPH. These data confirmed the interaction of both polymers with the liposome DPMC. These systems have biomedical and pharmacologic applications such as "stealth liposomes" or "ghost liposomes", for the encapsulation of drugs with, as a result, an extension of their average life in the blood flow.
A process according to claim 1, wherein the lipid is dimyristoyl phopsphatidyl choline. A polymer coated liposome according to claim 6, wherein the lipid is dimyristoyl phopsphatidyl choline. A polymer coated liposome according to claim 6, wherein the hydrophobic groups of the liquid crystals are inserted within said membrane of the liposome. Use of polymer coated liposomes prepared in accordance with the process of any of claims , for encapsulating drugs.
Use of the polymer coated liposome according to any of claims , for encapsulating drugs. Production of new polymer liquid crystals capable of having an interaction with liposomes. USB1 en. EPA1 en. JPA en. AUB2 en. CAA1 en. ESB1 en. WOA1 en. Hydrophilic light absorbing indole compounds for determination of physiological function in critically ill patients.
USB2 en. Liquid crystal containing cosmetic and pharmaceutical compositions and methods for utilizing such compositions. DET2 en. ITB en. Hydrogels based on synthetic polycarboxylates and proteins for the controlled release of drugs and process for their preparation. FRB1 en. ESA1 en. AUA en. Iwaura et al.