PART 2 POST-MODIFICATION

In another part of this study we wished to see the effects of post-modification treatments on the properties of the modified LDPE surface. Polyethylene samples were photosulfonated for different periods of time. Afterwards they were subjected to an after-treatment by conditioning in an electrolyte solution (aqueous KC1, 10-3 M) for 48 hours and then characterized by zeta potential measurements. This conditioning process resulted in a shift of f to even less negative values (see Fig. 8). This finding may be explained by the swelling of the polymer samples (water adsorption) in water that causes a shift of the shear plane of the electrochemical double layer into the liquid phase. This effect demonstrates that storage conditions and pre-conditioning may exert a pronounced influence on the zeta potential recorded for surface-modified polymers. Phenomena of this kind have already been described in previous literature [26,27],... 

After a satisfactory verification film is produced, an assembly may be fabricated specifically for destructive inspection to validate that the verification film was accurate. This correlation allows the use of verification film rather than more expensive destructive inspection for future changes such as duplicate tool fabrication and tool or detail modification. Simple assemblies are usually not destructively inspected because of high confidence that the verification film is entirely representative of the expected bondlines. Complex or large parts may not be destructively inspected because of the cost of the details and assembly time. In these cases other means of validating the verification film are used. Meticulous pre-bond detail and post-bond assembly thickness measurements may be sufficient to prove bondline thickness control. Ultrasonic inspection and X-ray photography (discussed previously) may be sufficient to prove that details are in the correct places and bonds are good. 

Woolfson and Mahmoud have classified the routes to preparation of decorated self-assembling peptide materials [53] as (1) co-assembly, where the functional part is already attached to a self-assembling component prior to assembly, and (2) postassembly, where a non-functionahsed self-assembled structure is modified by covalent or non-covalent means. This discussion adheres to this classification. A third route, beyond the scope of this review, is the use of structured peptides as templates for inorganic materials. Section 4.1 discusses functionalised self-assemblies formed from co-assembly-type approaches, while post-assembly modifications of self-assembled structures are considered in Sect. 4.2. 

In normal cells, the GDP/GTP-binding proteins, after protein synthesis, move to the cell membrane to which they become hooked by a hydrophobic farnesyl group. The y-subunit is anchored in the membrane by a post-translational modification of the C-terminal CAAX sequence (C - cystein, AA - aliphatic amino acids, X - methionine). This protein is first enzymatically farnesylated by a specific farnesyltransferase, then the AAX part is cleaved by specific proteases and finally the cystein residue is converted to a methyl ester. 

The correlation between histone acetylation and eukaryotic transcription were recognized many years ago [128,129]. However, it has not been until very recently, with the discovery that both HATs [130-133] and HDACs [134-138] are an integral part of the basal transcriptional machinery, that the molecular link for this correlation was established. This discovery has rekindled interest in this post-translational histone modification with implications ranging from basic chromatin research to applied medical investigations. Indeed, histone acetylation has been linked to cancer [139-144] and certain types of HDAC inhibitors are already being used to treat certain forms of cancer [145]. 

Post-translational modifications were recognized as additional sources of the structural modification of proteins.(22) Should such a modification occur by an enzyme-mediated process, as had been established for oxidation of sulfhydryl groups or the addition of carbohydrate or phosphate groups, or by the cleavage of the polypeptide with loss of a terminal amino group, or a larger part of the chain, it too could be subject to genetic variation. 

This interconnected network of membrane vesicles is divided into two distinct parts. The rough endoplasmic reticulum (RER), which is studded with ribosomes, is the site of membrane and secretory protein biosynthesis and their post-translational modification. The smooth endoplasmic reticulum (SER) is involved in phospholipid biosynthesis and in the detoxification of toxic compounds. 

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