Covalent carbon-carbon bonds are hard to break. Their strength is evident in the hardness of diamonds 1,2 and tensile strength of polymeric fibres [3][4][5][6] ; on the single-molecule level, it manifests itself in the need for forces of several nanonewtons to extend and mechanically rupture one bond. Such forces have been generated using extensional flow [7][8][9] , ultrasonic irradiation 10 , receding meniscus 11 and by directly stretching a single molecule with nanoprobes [12][13][14][15][16] . Here we show that simple adsorption of brush-like macromolecules with long side chains on a substrate can induce not only conformational deformations 17 , but also spontaneous rupture of covalent bonds in the macromolecular backbone. We attribute this behaviour to the fact that the attractive interaction between the side chains and the substrate is maximized by the spreading of the side chains, which in turn induces tension along the polymer backbone. Provided the side-chain densities and substrate interaction are sufficiently high, the tension generated will be strong enough to rupture covalent carbon-carbon bonds. We expect similar adsorption-induced backbone scission to occur for all macromolecules with highly branched architectures, such as brushes and dendrimers. This behaviour needs to be considered when designing surface-targeted macromolecules of this typeeither to avoid undesired degradation, or to ensure rupture at predetermined macromolecular sites.A series of brush-like macromolecules with the same number average degree of polymerization of a poly(2-hydroxyethyl methacrylate) backbone, N n ¼ 2,150^100, and different degrees of polymerization of poly(n-butyl acrylate) (pBA) side chains ranging from n ¼ 12^1 to n ¼ 140^12 were synthesized by atom transfer radical polymerization (see 'Polymer Characterization' in the Methods) 18 . Owing to the high grafting density, the side chains repel each other and thereby stretch the backbone into an extended conformation. Placing these macromolecules on a surface enhances the steric repulsion between the side chains, which results in both an extension of the polymer backbone and an increase of the persistence length.The effect is illustrated in Fig. 1, which shows atomic force microscopy (AFM) micrographs of monolayers of pBA brushes with short ( Fig. 1a) and long side chains (Fig. 1b). Measurements on both types of molecules yielded a number average contour length per monomeric unit of the backbone of l ¼ L n =N n ¼ 0:23^0:02 nm (see 'Atomic Force Microscopy' in Methods), which is close to l 0 ¼ 0.25 nm, the length of the tetrahedral C-C-C section. This means that even for short side chains (n ¼ 12), the backbone is already fully extended and adopts an all-trans conformation. As the side chains become longer, we observe global straightening of the backbone reflected in the increase of the persistence length (Fig. 1c).Chain extension requires a substantial amount of force, which we estimate using simple spreading arguments (Fig. 2). Just as in normal liquids, the polymer...

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We report the design of a platform for the delivery of hydrophobic drugs conjugated to block copolymer micelles via pH-responsive linkage that are assembled within hydrogen bonded polymer multilayer thin films.

Soluble proteins retained in the lumen of the endoplasmic reticulum (ER) contain a carboxyl-terminal tetrapeptide sequence that functions presumably to recycle these proteins from a subsequent compartment. Biochemical and genetic evidence indicate that the ERD2 gene product is the receptor for these ER retention signals. Here we report the identification of a cDNA clone from Arabidopsis thaliana (aERD2) similar in sequence and size to members of the ERD2 gene family. Southern and Northern blot analyses indicate that Arabidopsis contains a single aERD2 gene which is expressed at different levels in various plant tissues. A functional assay demonstrates that the Arabidopsis homologue, unlike the mammalian protein, can complement the lethal phenotype of the erd2 deletion mutant of Saccharomyces cerevisiae, indicating that this protein may have a similar function in plants. As the plant protein may have a binding specificity similar to the human Erd2 protein but can function in yeast, we suggest that the plant homologue is the functional link between yeast and animals.