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45(1) (2000), 40-50
Multilayer films of complexes of polycytidylic acid with dioctadecyldimetylammonium were obtained by the Langmuir- Blodgett method (LB films), and complexes of poly(C) with polycations (poly-L-lysisne, polyethyleneimine, polyallylamine) were obtained by the method of alternate adsorption (polyionic assembly) from solutions of oppositely charged polyelectrolytes on the solid carrier (SA films). It was shown that poly(C) exists in SA films in a single-stranded state irrespective of whether in the starting solution it occurred in the single- stranded nonprotonated or double-stranded protonated conformation. Conversely, in the LB film poly(C) preferred to be in a double protonated conformation. UV-spectra of water- insoluble LB and SA films at different pH values of surrounding water medium were investigated. Proton titration curves of poly(C) immobilized in LB films were obtained. The analysis of the shape of titration curves showed that the molecular-ionic transformation of poly(C) in LB films is accompanied by both the conformational transition of the polynucleotide and the molecular rearrangement in the whole film. Poly(C) was found to transform from the double- to single-stranded state and vice versa in the <> cycle of LB film due to cooperative release/binding of hydrogen ions by cytosine bases. In contrast, poly(C) <
> in SA films occurred without conformational transitions of the polynucleotide. As opposed to poly(C) in solution a rather big hysteresis of forward and back titration curves was found for both types of multilayer films, indicating molecular rearrangements in films. The reason for the structural transformations of poly(C) upon fabrication of LB or SA films and the mechanism of molecular ionic transformations of poly(C) in films art: discussed ill terms of a simple model of ion exchange. An assumption about the nature of structural transformations of LB and SA films during their protonation- deprotonation is put forward.

[26] Effect of Media Composition on Long-Term in-Vitro Stability of Barium Alginate and Polyacrylic-Acid Multilayer Microcapsules

A. Gaumann, M. Laudes, B. Jacob, R. Pommersheim, C. Laue, W. Vogt and J. Schrezenmeir

Biomaterials 21(18) (2000), 1911-1917

For a number of applications stability of microcapsules is a critical factor. Since the maintenance of polyelectrolyte complexes depends considerably on the ion composition we tested the physical properties of barium alginate capsules and searched for conditions to improve stability by a multilayer coating with polyethylenimine (PEI) and polyacrylic acid (PAA). Mechanical stability and diameters were determined in barium alginate capsules and compared with multilayer capsules. Multilayer coating resulted in smaller capsules than barium complexing alone. The difference was more pronounced when CaCl2 was used instead of NaCl during coating. Barium alginate capsules and application of CaCl2 during coating led to continuous pressure profiles, whereas NaCl resulted in bursting at a defined pressure, indicating the additional contribution to mechanical stability by the outer layers. After 7 d culture: mechanical stability of coated capsules decreased in RPMI and NaCl but was most pronounced in sodium citrate. The capsule diameter increased in sodium citrate, less pronounced in NaCl and was significantly different to RPMI and double distilled water. During long-term culture in RPMI, the diameter increased and mechanical stability decreased significantly, Multilayer coating improved mechanical stability which was impeded most in sodium citrate, to a lesser extent by NaCl and RPMI even after long-term exposure. (C) 2000 Elsevier Science Ltd, All rights reserved.

[27] Reagentless Biosensors Based on Self-Deposited Redox Polyelectrolyte-Oxidoreductases Architectures

A. Narvaez, G. Suarez, I. C. Popescu, I. Katakis and E. Dominguez

Biosensors and Bioelectronics 15(1-2) (2000), 43-52

Reagentless fructose and alcohol biosensors have been produced with a versatile enzyme immobilisation technique which mimics natural interactions and flexibility of living systems. The electrode architecture is built up on electrostatic interactions by the sequential adsorption of redox polyelectrolytes and redox enzymes giving rise to the efficient transformation of substrate fluxes into electrocatalytic currents. All investigated multilayer structures were self- deposited on 3-mercapto-1-propanesulfonic acid monolayers self- assembled on gold electrodes. Fructose dehydrogenase, horseradish peroxidase (HRP) and the couple HRP-alcohol oxidase were electrochemically connected with a cationic poly[(vinylpyridine)Os(bpy)(2)Cl] redox polymer (RP) interface in a layer-by-layer self-deposited architecture. The dependence of the distance on the electrochemical response of this interface was also studied showing a clear decrease in the Faradaic current when the distance to the electrode surface was increased. The sensitivities obtained for each biosensor were 19.3, 58.1 and 10.6 mA M-1 cm(-1) for fructose, H2O2 and methanol, respectively. The sensitivity values can be easily controlled by a rational deposition and manipulation of the charge in the catalytic layers. The electrostatic assembly of the electrochemical interface and the catalytic layers resulted in integrated biochemical systems in which mass transfer diffusion and heterogeneous catalytic and electron transfer steps are efficiently coupled and can be easily manipulated. (C) 2000 Elsevier Science S.A. All rights reserved.

[28] Construction of Multicomponent Catalytic Films Based on Avidin- Biotin Technology for the Electroenzymatic Oxidation of Molecular-Hydrogen

A. L. Delacey, M. Detcheverry, J. Moiroux and C. Bourdillon

Biotechn. Bioeng. 68(1) (2000), 1-10

Two methods based on the avidin-biotin technology were developed for the multimonolayer immobilization of Desulfovibrio gigas hydrogenase on glassy carbon or gold electrodes. In both methods the molecular structure of the modified interface was the result of a step-by-step process. The first method alternates monolayers of avidin and biotinylated hydrogenase, the mediator (methyl viologen) being free to diffuse in the structure. In the second method, the avidin monolayers were used to immobilize both the biotinylated enzyme and a long-chain biotinylated viologen derivative. The viologen head of this hydrophilic arm shuttles the electrons between the electrode and the enzyme. The modified electrodes were evaluated for the electroenzymatic oxidation of molecular hydrogen, which has interest for the development of enzymatic fuel cells. The parameters that affect the current density of mediated oxidation of H-2 at the modified electrodes was studied. The second structure, which has given typical catalytic currents of 25 mu A per cm(2) for 10 monolayers, was found clearly less efficient than the first structure (500 mu A per cm(2) for 10 monolayers). In both methods the catalytic currents increased linearly with the number of monolayers of hydrogenase immobilized, which indicates that the multilayer structures are spatially ordered. (C) 2000 John Wiley & Sons, Inc.

[29] Polyelectrolyte Adsorption

D. Andelman and J. F. Joanny

C. R. Acad. Sci. Ser. IV, Phys. Astr. 1(9) (2000), 1153-1162

The problem of charged polymer chains (polyelectrolytes) as they adsorb on a planar surface is addressed theoretically. We review the basic mechanisms and theory underlying polyelectrolyte adsorption on a single surface in two situations: adsorption of a single charged chain, and adsorption from a bulk solution in theta solvent conditions. The behavior of flexible and semi-rigid chains is discussed separately and is expressed as function of the polymer and surface charges, ionic strength of the solution and polymer bulk concentration. We mainly review mean-field results and briefly comment about fluctuation effects. The phenomenon of polyelectrolyte adsorption on a planar surface as presented here is of relevance to the stabilization of colloidal suspensions. In this respect we also mention calculations of the inter-plate force between two planar surfaces in presence of polyelectrolyte. Finally, we comment on the problem of charge overcompensation and its implication to multi-layers formation of alternating positive and negative polyelectrolytes on planar surfaces and colloidal particles. (C) 2000 Academie des sciences/Editions scientifiques et medicales Elsevier SAS.

[30] Oxidation-Induced Variation in Polyelectrolyte Multilayers Prepared from Sulfonated Self-Dopable Poly(Alkoxythiophene)

J. Lukkari, A. Viinikanoja, J. Paukkunen, M. Salomaki, M. Janhonen, T. Aaritalo and J. Kankare

J. Chem. Soc., Chem. Commun. Iss 7 (2000), 571-572

Polyelectrolyte multilayers have been prepared using both the neutral and oxidised forms of a poly(alkoxythiophene) derivative with pendant sulfonate groups and it is shown that the oxidation state of the polymer affects multilayer formation.

[31] Self-Assembly of Freebase-Tetrapyridylporphyrins and Metalated- Tetrapyridylporphyrins to Modified Gold Surfaces

C. V. K. Sharma, G. A. Broker, G. J. Szulczewski and R. D. Rogers

J. Chem. Soc., Chem. Commun. Iss 12 (2000), 1023-1024

Freebase- and metallated-tetrapyridylporphyrins self-organize through multiple hydrogen bonding to carboxylic acid terminated self-assembled monolayers on gold surfaces, thereby producing surfaces with two additional functional sites, the porphyrin cavity and the terminal pyridyl groups.

[32] Nano-Size Stripes of Self-Assembled Bolaform Amphiphiles

S. Gao, B. Zou, L. F. Chi, H. Fuchs, J. Q. Sun, X. Zhang and J. C. Shen

J. Chem. Soc., Chem. Commun. Iss 14 (2000), 1273-1274

Self-assembled nano-sized stripes are obtained spontaneously by electrostatic adsorption of bolaform amphiphiles onto mica sheets. The ordered stripes are separated from each other by about 10 nm, and the ordered region can extend over macroscopic areas.

[33] Fabrication of Hollow Zeolite Spheres

X. D. Wang, W. L. Yang, Y. Tang, Y. J. Wang, S. K. Fu and Z. Gao

J. Chem. Soc., Chem. Commun. Iss 21 (2000), 2161-2162

Hollow spheres of zeolite have been fabricated through a layer- by-layer technique using polystyrene spheres as templates and nanozeolites as 'building blocks', followed by calcination.

[34] Multilayer Ultrathin Films of Molecular Titania Nanosheets Showing Highly Efficient UV-Light Absorption

T. Sasaki, Y. Ebina, M. Watanabe and G. Decher

J. Chem. Soc., Chem. Commun. Iss 21 (2000), 2163-2164

Titania nanosheet crystallites have been self-assembled layer- by-layer with poly(dimethyldiallyl ammonium chloride) onto substrates to produce ultrathin nanostructured films which exhibit highly efficient optical absorption with a sharp peak at 266 nm.

[35] Template Synthesis of Polymer-Insulated Colloidal Gold Nanowires with Reactive Ends

J. S. Yu, J. Y. Kim, S. Lee, J. K. N. Mbindyo, B. R. Martin and T. E. Mallouk

J. Chem. Soc., Chem. Commun. Iss 24 (2000), 2445-2446

Alternate adsorption of anionic and cationic polyelectrolytes creates smooth organic films on the walls of template-grown Au nanowires, which can be made chemically reactive on their ends by removal of a sacrificial Ag layer.

[36] Hollow Capsule Processing Through Colloidal Templating and Self- Assembly

F. Caruso

Chem. Eur. J. 6(3) (2000), 413-419

Hollow capsules of nanometer to micrometer dimensions constitute an important class of materials that are employed in diverse technological applications, ranging from the delivery of encapsulated products for cosmetic and medicinal purposes to their use as lightweight composite materials and as fillers with low dielectric constant in electronic components. Hollow capsules comprising polymer, glass, metal, and ceramic are nowadays routinely produced by using various chemical and physicochemical methods. The current article focuses on a recent novel and versatile technique, based on a combination of colloidal templating and self-assembly processes, developed for synthesizing uniform hollow capsules of a broad range of materials. The strategy outlined readily affords control over the size, shape, composition, and wall thickness of the hollow capsules.

[37] Fabrication of Hollow Zeolite Fibers Through Layer-by-Layer Adsorption Method

Y. J. Wang, Y. Tang, X. D. Wang, W. L. Yang and Z. Gao

Chem. Lett. Iss 11 (2000), 1344-1345

Hollow fibers with nanozeolite walls are firstly fabricated through layer-by-layer (LbL) technique, using carbon fibers as templates, coupled with removal of the templates by calcination. The thickness and the composition of the walls can be readily controlled by varying the number of the deposition cycles and the zeolite types used, respectively.

[38] In-Situ Nucleation and Growth of Gamma-FeOOH Nanocrystallites in Polymeric Supramolecular Assemblies

A. K. Dutta, G. Jarero, L. Q. Zhang and P. Stroeve

Chem. Mater. 12(1) (2000), 176-181

This paper reports the nucleation and growth of lepidocrocite (gamma-FeOOH) crystallites in supramolecular polymer multilayers. Organized, polymeric thin films were formed by the layer by layer deposition technique that consisted of adsorbing alternate layers of a polycation and a polyanion on a quartz substrate. Nucleation of nanoparticles was initiated by absorbing ferric nitrate in the thin film polymer matrix, followed by hydrolysis with ammonium hydroxide-1 Repeating the above process resulted in an increase in the density of the nanoparticles initially formed and further growth in the dimensions of the crystallites with the number of absorption and hydrolysis-cycles;Analysis of the UV-visible absorption spectra of the films revealed the formation of lepidocrocites, which was confirmed by FTIR and selected area electron diffraction (SAED) studies. An important feature of this work is that lepidocrocite (gamma-FeOOH) is formed instead of akaganeite (beta-FeOOH),which is generated when ferrous chloride is used as the starting material and is converted to iron oxyhydroxide through oxidative hydrolysis as reported in our previous work (Langmuir 1999, 15, 2176). It therefore seems likely that the initial starting material plays a key role in determining the structural and morphological characteristics of the iron oxyhydroxides although their chemical compositions are the same.

[39] Surface Sol-Gel Synthesis of Ultrathin Semiconductor-Films

N. I. Kovtyukhova, E. V. Buzaneva, C. C. Waraksa, B. R. Martin and T. E. Mallouk

Chem. Mater. 12(2) (2000), 383-389

Ultrathin films of ZnS, Mn-doped ZnS, ZnO, and SiO2 were grown on silicon substrates using surface sol-gel reactions, and the film growth process was characterized by ellipsometry, atomic force microscopy, X-ray photoelectron spectroscopy, UV-visible absorbance, and photoluminescence (PL) spectroscopy. The, Si substrates were pretreated by chemical oxidation, or by derivatization with 4- (dimethylmethoxy)silyl)butylamine. On the oxidized Si/SiOx surface, nanoparticulate films of ZnS and Mn-doped ZnS were grown by sequential immersion in aqueous metal acetate and sodium sulfide solutions. During the first four adsorption cycles, there was little film growth, but thereafter the amount of material deposited was linear with the number of adsorption cycles. This behavior is consistent with the formation of ZnS nuclei at low coverage, followed by particle growth in subsequent cycles. PL spectra are consistent with incorporation of Mn2+ into the ZnS nanoparticles. In contrast, the growth of SiO2 films from nonaqueous SiCl4 an the same Si/SiOx substrates was regular from the first adsorption cycle, indicating a high density of nucleation sites. On amine- derivatized substrates, ZnO thin films grew as relatively smooth islands, suggesting that the interaction of Zn2+ ions or primary ZnO clusters with the amine surface priming layer was sufficiently strong to prevent the formation of isotropic nanoparticles upon exposure to aqueous base.

[40] Nucleation and Growth of Lead Sulfide Nanocrystallites and Microcrystallites in Supramolecular Polymer Assemblies

A. K. Dutta, T. T. Ho, L. Q. Zhang and P. Stroeve

Chem. Mater. 12(4) (2000), 1042-1048

Multilayer thin film assemblies fabricated by the sequential adsorption of polyelectrolytes on a quartz substrate were used as a supramolecular reaction template to study the in situ nucleation and growth of PbS nano- and microparticles. Chemical reaction within the polymer film was initiated by absorbing pb(2+) from an aqueous solution of Pb(NO3)(2) followed by exposing the film to H2S gas. Electron microscopic examination of the films revealed that while nanoparticles are formed in films that were subject to one or two reaction cycles, large crystallites were formed when these films were exposed to a large number (10) of reaction cycles. In the latter case, a broad distribution of particle sizes is observed and may be attributed to Ostwald ripening. Detailed studies show the nucleation and growth of the PbS particles into crystallites of different shapes. UV-vis absorption studies reveal that the absorption spectral profiles of the films are dependent on the size of the PbS crystallites. The broadened absorption spectral profile observed for films subject to a large number of reaction cycles may be attributed to the superposition of the spectral profiles of the small clusters that tend to be blueshifted due to quantum confinement effects and the large clusters that are redshifted.

[41] Electrostatically Controlled Organization of Carboxylic-Acid Derivatized Colloidal Silver Particles on Amine-Terminated Self- Assembled Monolayers

A. Gole, S. R. Sainkar and M. Sastry

Chem. Mater. 12(5) (2000), 1234-1239

The formation of self-assembled monolayers (SAMs) of an aromatic bifunctional molecule, 4-aminothiophenol (4-ATP) on gold and the subsequent organization of carboxylic acid derivatized silver colloidal particles is described. Quartz crystal microgravimetry (QCM) measurements have been used to follow the formation of 4-ATP SAMs as well as electrostatic assembly of the colloidal silver particles on the SAM surface. It is shown that the electrostatic interaction between the negatively charged colloidal particle surface-bound carboxylic acid groups and the terminal amine groups in the SAM can be modulated by variation of the colloidal solution pH. This enables control over the surface coverage of the colloidal particles on the SAM surface with a maximum surface coverage of 18% being attained. The SAMs as well as the colloidal particle covered SAM films were further characterized with X-ray photoemission spectroscopy (XPS) and energy-dispersive analysis of X-rays (EDAX) measurements.

[42] Layer-by-Layer Assembled Films of HgTe Nanocrystals with Strong Infrared-Emission

A. L. Rogach, D. S. Koktysh, M. Harrison and N. A. Kotov

Chem. Mater. 12(6) (2000), 1526

Layer-by-layer sequential adsorption (LBL) has been applied to the preparation of composite multilayer thin films of thiol- capped HgTe nanocrystals with strong IR luminescence. The films can be used as active coatings for novel optical sources for telecommunications.

[43] Layered Polyelectrolyte Films as Selective, Ultrathin Barriers for Anion Transport

J. J. Harris, J. L. Stair and M. L. Bruening

Chem. Mater. 12(7) (2000), 1941-1946

Synthesis of high-flux composite membranes requires methods for deposition of ultrathin, defect-free films on highly permeable supports. Layer-by-layer deposition of polyelectrolytes on porous alumina (0.02 mu m pore diameter) produces such membranes. Electron microscopy shows that five bilayers (<25 nm) of poly(allylamine hydrochloride) (PAH)/ poly(styrenesulfonate) (PSS) are sufficient to cover porous alumina and that underlying pores are not clogged during the deposition process. The selectivity of anion transport through these membranes increases with the number of bilayers until the substrate is fully covered. Five-bilayer PAH/PSS membranes have Cl-/SO42- and Cl-/Fe(CN)(6)(3-) selectivity values of 7 and 310, respectively. PAH/poly(acrylic acid) membranes show selectivity values similar to those of PAH/PSS membranes but with a 3-fold decrease in anion flux. Selectivity in both of these systems likely results from Donnan exclusion.

[44] Sol-Gel Processing of Ordered Multilayers to Produce Composite Films of Controlled Thickness

J. H. Rouse, B. A. Macneill and G. S. Ferguson

Chem. Mater. 12(8) (2000), 2502-2507

Sol-gel processing of a multilayered film formed by the alternate adsorption of poly(diallyldimethylammonium chloride) and a synthetic silicate sheet mineral, Laponite RD, resulted in an interpenetrating composite network. Kinetic data indicate that the amount of material added due to sorption and gelation of tetraethyl orthosilicate (TEOS) reached a steady-state value within a day. Sol-gel growth occurred within the multilayer, with very little silicate being deposited at the surface. The resulting composite film showed the same order as an untreated multilayer, indicating that sorption and gelation did not disrupt the structural order of the multilayer. Curing the TEOS- treated films at 175 degrees C for 24 h to drive off excess water and complete the gelation process again resulted in an ordered composite structure. Cured films exposed to various levels of relative humidity demonstrated a dramatic decrease in swellability compared to an untreated multilayer.

[45] Ultrathin Composite Films Incorporating the Nanoporous Isopolyoxomolybdate Keplerate (NH4)(42)(Mo132O372(Ch3Coo)(30)(H2O)(72))

D. G. Kurth, D. Volkmer, M. Ruttorf, B. Richter and A. Muller

Chem. Mater. 12(10) (2000), 2829

Ultrathin Composite Films Incorporating the Nanoporous Isopolyoxomolybdate ''Keplerate'' (NH4)(42)[Mo132O372- (CH3COO)(30)(H2O)(72)] The giant, nanoporous Keplerate (NH4)(42)- [Mo132O372(CH3COO)(30)(H2O)(72)] was incorporated into a permeable ultrathin film using a stepwise self-assembly strategy. Alternating adsorption of the Keplerate anions and PAH results in single layers with an apparent surface coverage of approximate to 50%. Such permeable composite coatings may lead into a practical approach to utilize nanoporous polyoxometalate clusters in sensors or heterogeneous catalysts.

[46] Hierarchical Assembly of Zeolite Nanoparticles into Ordered Macroporous Monoliths Using Core-Shell Building-Blocks

K. H. Rhodes, S. A. Davis, F. Caruso, B. J. Zhang and S. Mann

Chem. Mater. 12(10) (2000), 2832

Hierarchical Assembly of Zeolite Nanoparticles into Ordered Macroporous Monoliths Using Core-Shell Building Blocks Latex beads are used as a combined template and porogen in the fabrication of monolithic silica containing a hierarchy of pores. Prefabricated core/shell particles, prepared by the layer-by-layer assembly of zeolite (silicalite) nanoparticles onto spherical latex templates, are assembled into macroscopic close-packed structures. Calcination removes all organic components and causes densification of the inorganic structure producing a macroporous zeolite in which both the pore size and wall thickness can be varied.

[47] Metal-Films Prepared by Stepwise Assembly - 2 - Construction and Characterization of Colloidal Au and Ag Multilayers

M. D. Musick, C. D. Keating, L. A. Lyon, S. L. Botsko, D. J. Pena, W. D. Holliway, T. M. Mcevoy, J. N. Richardson and M. J. Natan

Chem. Mater. 12(10) (2000), 2869-2881

This manuscript describes the stepwise, ligand-directed assembly, characterization, and prospective applications of three-dimensional Au and Ag nanoparticle, multlilayered films. Films were prepared by successive treatments of a Au nanoparticle monolayer with a bifunctional cross-linker and colloidal Au or Ag solutions. Changes in film electrical and optical properties are reported for a series of bifunctional cross-linkers of varying molecular lengths. Interestingly, these films exhibit Beer's law behavior despite the presence of strong interparticle optical coupling. Multilayer films with greater than six exposures to 2-mercaptoethylamine and Au colloid were highly conductive and resembled bulk Au in appearance. In contrast, films of similar particle coverage generated using a longer cross-linker (1,6-hexanedithiol) exhibited higher transmission in the near-infrared region and exhibited a reduced conductivity. Measurement of the multilayer morphology with atomic force microscopy, electrostatic force microscopy, and field emission scanning electron microscopy revealed a porous, discontinuous morphology composed of large, continuous regions of aggregated nanoparticles. This, in turn, results in a surface roughness contribution to surface plasmon scattering and surface-enhanced Raman scattering observed for Au, Au/Ag, and Ag colloid multilayers. Particulate multilayer films made using horseradish peroxidase as a cross-linker remained enzymatically active, even beneath three layers of colloidal Au. Multilayers could also be prepared on surfaces patterned by microcontact printing. These data show how Au colloid multilayers grown in solution are a viable alternative to evaporated metal films for a number of applications.

[48] Buildup of Polymer/Au Nanoparticle Multilayer Thin-Films Based on Hydrogen-Bonding

E. C. Hao and T. Q. Lian

Chem. Mater.