Structure-delivery relationships of lysine-based gemini surfactants and their lipoplexes.

The synthesis and properties of gemini surfactants of the type (R(1)(CO)-Lys(H)-NH)2(CH2)n are reported. For a spacer length of n = 6, the hydrophobic acyl tail was varied in length (R(1) = C8, C10, C12, C14, C16, and C18) and, for R(1) = C18, the degree of unsaturation. For R(1)(CO) = oleoyl (C18:1 Z) the spacer length (n = 2-8) and the stereochemistry of the lysine building block were varied; a 'half-gemini' derivative with a single oleoyl tail and head group was also prepared. The potential of the gemini surfactants to transfer polynucleotides across a cell membrane was investigated by transfection of HeLa cells with beta-galactosidase, both in the presence and absence of the helper lipid DOPE. Oleoyl was found to be by far the best hydrophobic tail for this biological activity, whereas the effect of the lysine stereochemistry was less pronounced. The effect of an optimum spacer length (n = 6) was observed only in the absence of helper lipid. The most active surfactant, i.e. the one with oleoyl chains and n = 6, formed liposomes with sizes in the range of 60-350 nm, and its lipoplex underwent a transition from a lamellar to a hexagonal morphology upon lowering the pH from 7 to 3.

Processive catalysis.

Nature's enzymes are an ongoing source of inspiration for scientists. The complex processes behind their selectivity and efficiency is slowly being unraveled, and these findings have spawned many biomimetic catalysts. However, nearly all focus on the conversion of small molecular substrates. Nature itself is replete with inventive catalytic systems which modify, replicate, or decompose entire polymers, often in a processive fashion. Such processivity can, for example, enhance the rate of catalysis by clamping to the polymer substrate, which imparts a large effective molarity. Reviewed herein are the various strategies for processivity in nature's arsenal and their properties. An overview of what has been achieved by chemists aiming to mimic one of nature's greatest tricks is also included.

A three-enzyme cascade reaction through positional assembly of enzymes in a polymersome nanoreactor.

Porous polymersomes based on block copolymers of isocyanopeptides and styrene have been used to anchor enzymes at three different locations, namely, in their lumen (glucose oxidase, GOx), in their bilayer membrane (Candida antarctica lipase B, CalB) and on their surface (horseradish peroxidase, HRP). The surface coupling was achieved by click chemistry between acetylene-functionalised anchors on the surface of the polymersomes and azido functions of HRP, which were introduced by using a direct diazo transfer reaction to lysine residues of the enzyme. To determine the encapsulation and conjugation efficiency of the enzymes, they were decorated with metal-ion labels and analysed by mass spectrometry. This revealed an almost quantitative immobilisation efficiency of HRP on the surface of the polymersomes and a more than statistical incorporation efficiency for CalB in the membrane and for GOx in the aqueous compartment. The enzyme-decorated polymersomes were studied as nanoreactors in which glucose acetate was converted by CalB to glucose, which was oxidised by GOx to gluconolactone in a second step. The hydrogen peroxide produced was used by HRP to oxidise 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) to ABTS(.+). Kinetic analysis revealed that the reaction step catalysed by HRP is the fastest in the cascade reaction.

A reagent-based dynamic trigger for cell adhesion, shape change, or cocultures.

The described protocol is a simple and easily implemented method for making dynamic micropatterns for cell culture. It is based on the use of a surface coating material (azido-PLL-g-PEG (APP)) that initially repels cells, but which can be made strongly adherent by addition of a small functional peptide (BCN-RGD) to the cell culture medium. The method can be applied to trigger the adhesion, migration, or shape change of single cells or of populations of cells, and it can be used to create patterned cocultures. The entire process can be subdivided into three main parts. The first part describes the creation of patterned APP substrates. The second part describes cell seeding and "click" triggering of cell adhesion; the final part describes variations that allow the overlay of multiple patterns or the creation of patterned cocultures. The APP coating of substrates and the triggering of adhesion only involves treating the surface with aqueous stock solutions, allowing any biology lab to adopt this technique.

Triggering cell adhesion, migration or shape change with a dynamic surface coating.

There's an APP for that: cell-repellent APP (azido-[polylysine-g-PEG]) is used to create substrates for spatially controlled dynamic cell adhesion. The simple addition of a functional peptide to the culture medium rapidly triggers cell adhesion. This highly accessible yet powerful technique allows diverse applications, demonstrated through tissue motility assays, patterned coculturing and triggered cell shape change.

Delivery of DNA and siRNA by novel gemini-like amphiphilic peptides.

We report the design, synthesis, and characterization of a novel type of cationic lipopeptide, gemini-like amphiphilic peptides or 'geminoids'. As an example, the SPKR peptide, inspired by biological nucleic acid binding motifs, was appended with unsaturated (oleoyl/oleyl) alkyl tails. The compound shows remarkable DNA and siRNA delivery, without lysogenic helper lipid, in a variety of cells, with a moderate cytotoxic effect. It aggregates to nanoparticles that combine with DNA to lipoplexes, which undergo a change from lamellar to the more lysogenic hexagonal packing upon lowering the pH. The versatility of the chemical approach allowed us to study peptides related to SPKR, and to establish that the Pro and at least one of the cationic (Lys, Arg) residues are essential for the biological activity.