Self-assembly Protocol Research Articles

Optimal seamless self-assembly of files in linear networks

A file F is sited at one end (the root) of a path in some network. Each non-root node in the path is able to cache part or all of F, and each node may also have a client wanting to download F. Links between neighbors on the path have given transmission delays associated with them, but the delay from a node to its own client, if it has one, is zero. In the seamless, self-assembly paradigm all clients issue requests simultaneously at time 0, each starts to receive segments of F immediately, and continues to receive them until F is fully downloaded. The process must be implemented by means of a distributed self-assembly protocol which is unaware of network structure beyond links to immediate neighbors. We exhibit such a protocol, and show how to assign segments of F to the node caches in such a way that, no matter which nodes are chosen as clients, seamless self-assembly is realized and, simultaneously, the total cache size achieves a lower bound determined solely by the link delays. The paper concludes with a brief discussion of the many open problems arising in systems requiring seamless, or nearly seamless, self assembly of files.

Design and Self‐Assembly of Ditopic and Tetratopic Cavitand Complexes

The self-assembly of open ditopic and tetratopic cavitand complexes has been investigated by using monofunctionalized cavitand ligands and suitable metal precursors. In the case of ditopic complexes, self-assembly protocols, leading exclusively to the formation of both thermodynamically stable cis-Pt square-planar complexes 8 and 9 and the kinetically inert fac-Re octahedral complex 14, have been elaborated. The use of cis-[Pt(CH3)CN)2Cl2] as metal precursor led to the formation of monotopic trans-10 and ditopic trans-11 cavitand complexes, while cis-[Pt(dmso)2Cl2] afforded both cis-13 and trans-11 isomers. The self-assembly of tetratopic cavitand complexes has been achieved by using mononuclear [Pd(CH3CN)4(BF4)2] and dinuclear [M2(tppb)(OTf)4] (19: M = Pt; 20: M = Pd) metal precursors. Only the tetratopic dinuclear complexes 21 and 22 were stable. The ligand configuration with two phosphorus and two cavitand ligands at the metal centers is the most appropriate to build tetratopic cavitand complexes with sufficient kinetic stability.

Exploring Dynamics and Stereochemistry in Mechanically-Interlocked Compounds

The advent of self-assembly and template-directed synthetic protocols has led to a tremendous surge in the number of mechanically-interlocked compounds being prepared and studied. As these investigations are being carried out, it is becoming increasingly apparent that many of these compounds, known as catenanes and rotaxanes, possess unique dynamic and stereochemical properties. In addition, the drive to create molecular switches and machines for nanotechnological applications has generated a need to understand how to control those properties in condensed phases. Here, we present an overview of the field with regard to the solution dynamics and stereochemistry of mechanically-interlocked compounds - as well as to some related structural types - and review the recent results from our own research in some detail. 1H NMR spectroscopy has proven to be a powerful tool for probing both degenerate and nondegenerate dynamic processes in these compounds, as well as for identifying stereoisomers if they are present in solution. The results of several variable temperature NMR investigations on the effects of structural changes upon the dynamic processes and stimulated relative motions of components in catenanes and rotaxanes, as well as in some self-complexes and pretzelanes, are discussed. A review with 90 references.

Self-Assembly of Polyacrylate-Capped Platinum Nanoparticles on a Polyelectrolyte Surface: Kinetics of Adsorption and Effect of Ionic Strength and Deposition Protocol

Polyacrylate-capped Pt nanocrystallites of 2.5 ± 0.6 nm diameter were synthesized by reduction of Pt(IV) with citrate in the presence of polyacrylate and were self-assembled layer-by-layer in poly(diallyldimethylammonium chloride) by virtue of the Coulombic attraction between the negatively charged capping agent and the cationic polyelectrolyte. The self-assembly protocol resulted in a reproducible consecutive surface-charge buildup, leading to a linear incorporation of nano-Pt per layer. TEM imaging revealed a chainlike distribution of the nanoparticles on the polymer surface at submonolayer coverage. The density of assembled nanoparticles per layer can be controlled by varying the dipping time, the Pt solution ionic strength, and its composition or by resorting to an interrupted-deposition protocol involving multiple rinsing/drying cycles per layer. The dynamics of nano-Pt assembly on PDDA was followed ex-situ by UV−visible spectroscopy. The adsorption was found to take place via two kinetics regimes at different time scales. Initially, the adsorption rate is believed to be limited by the nanoparticles availability at the solution/surface interface. At high surface coverage, the slower polyelectrolyte−nanoparticle surface rearrangement necessary for further attachment becomes the rate-determining step, leading to a pseudosaturation within ∼1 h.

Dynamic materials through metal-directed and solvent-driven self-assembly of cavitands.

A dual-coded dynamic material was created by the bimodal self-assembly protocol sketched in the scheme. The combination of two orthogonal and reversible interactions, namely solvophobic aggregation (SA) and metal coordination (MC), allows precise control at each step of the self-assembly cycle, leading to the formation of rodlike supramolecular architectures.

Design and self-assembly of wide and robust coordination cages.

The self-assembly of a new class of coordination cages formed from two tetrapyridyl-substituted cavitands connected through four square-planar palladium or platinum complexes is reported. The shape of the internal cavity resembles an ellipsoid with a calculated volume of 840 A(3). The four lateral portals have a diameter of about 6 A, large enough to allow the fast entrance/egress of counterions in solution. The platinum cages 3a,e cannot be disassembled using triethylamine as competitive ligand and they are kinetically stable at room temperature, whereas the palladium cages 3b-d, 3f-h are disassembled and kinetically labile under the same conditions. The different solubility properties of the cage components have allowed the extension of this self-assembly protocol to the liquid-liquid interface.

Chiral recognition by molecularly imprinted polymers in aqueous media

Molecularly imprinted polymers were prepared using 2-vinylpyridine and/or methacrylic acid as functional monomers in a self-assembly imprinting protocol. The resulting polymers were analyzed in aqueous media, and the effects from the pH of the mobile phase and the degree of added organic solvent were investigated. The results are indicative of the importance of ionic bonds in conjunction with hydrophobic interactions in the formation of the complexes between the analyte and the polymers.