Experimental Investigation of Stretch Blow Molding, Part 2: Analysis of Process Variables, Blowing Kinematics, and Bottle Properties

The work presented in this paper takes advantage of newly developed instrumentation suitable for in process monitoring of an industrial stretch blow molding machine. The instrumentation provides blowing pressure and stretch rod force histories along with the kinematics of polymer contact with the mould wall. A Design of Experiments pattern was used to qualitatively relate machine inputs with these process parameters and the thickness distribution of stretch blow molded PET (polyethylene terephtalate) bottles. Material slippage at the mold wall and thickness distribution is also discussed in relation to machine inputs. The key process indicators defined have great potential for use in a closed loop process control system and for validation of process simulations.

Blue bottle light: lecture demonstrations of homogeneous and heterogeneous photo-induced electron transfer reactions

The classic, non-photochemical blue bottle experiment involves the reaction of methylene blue (MB) with deprotonated glucose, to form a bleached form of the dye, leuco-methylene blue (LMB), and subsequent colour recovery by shaking with air. This reaction is a popular demonstrator of key principles in kinetics and reaction mechanisms. Here it is modified so as to highlight features of homogenous and heterogeneous photoinduced electron transfer (PET) (Pure Appl. Chem., 2007, 79, 293-465) reactions, i.e. blue bottle light experiments. The homogeneous blue bottle light experiment uses methylene blue, MB, as the photo-sensitizer and triethanolamine as the sacrificial electron donor. Visible light irradiation of this system leads to its rapid bleaching, followed by the ready restoration of its original colour upon shaking away from the light source. The heterogeneous blue bottle light experiment uses titania as the photo-sensitizer, MB as a redox indicator and glucose as the sacrificial electron donor. UVA light irradiation of this system leads to the rapid bleaching of the MB and the gradual restoration of its original colour with shaking and standing. The latter 'dark' step can be made facile and more demonstrator-friendly by using platinised titania particles. These two photochemical versions of the blue bottle experiment are used to explore the factors which underpin homogeneous and heterogeneous PET reactions and provide useful demonstrations of homogeneous and heterogeneous photochemistry.

THE ULTRASTRUCTURE AND IMMUNOGOLD LABELING OF PANCREATIC POLYPEPTIDE-IMMUNOREACTIVE CELLS ASSOCIATED WITH THE EGG-FORMING APPARATUS OF A MONOGENEAN PARASITE, DICLIDOPHORA-MERLANGI

An electron microscopical examination has been made of the fine structure and disposition of pancreatic polypeptide immunoreactive cells associated with the egg-forming apparatus in Diclidophora merlangi. The cell bodies are positioned in the parenchyma surrounding the ootype and taper to axon-like processes that extend to the ootype wall. The terminal regions of these processes branch and anastomose and, in places, the swollen endings or varicosities form synaptic appositions with the muscle fibres in the ootype wall. The cells are characterized by an extensive GER-Golgi system that is involved in the assembly and packaging of dense-cored vesicles. The vesicles accumulate in the axons and terminal varicosities, and their contents were found to be immunoreactive with antisera raised to the C-terminal hexapeptide amide of pancreatic polypeptide. It is concluded that the cells are neurosecretory in appearance and that, functionally, their secretions may serve to regulate ootype motility and thereby help co-ordinate egg production in the worm.

ELECTRON IMMUNOGOLD LABELING OF REGULATORY PEPTIDE IMMUNOREACTIVITY IN THE NERVOUS-SYSTEM OF MONIEZIA-EXPANSA (CESTODA, CYCLOPHYLLIDEA)

An electron immunogold-labeling technique was used in conjunction with a post-embedding procedure to demonstrate for the first time the ultrastructural distribution of the parasitic platyhelminth neuropeptide, neuropeptide F (NPF), in the nervous system of the cestode Moniezia expansa. Two axon types, distinguished by their populations of different-sized electron-dense vesicles, were identified. Immunogold labeling demonstrated an apparent homogeneity of PP, FMRFamide and NPF (M. expansa) antigenic sites throughout the larger dense-cored vesicles within the central nervous system. Triple labeling clearly demonstrated the co-localisation of immunoreactivities (IR) for NPF, PP and FMRFamide within the same dense-cored vesicles. The presence of NPF-IR within the vesicles occupying the perikaryon of the neuronal cell body indicated that the peptides had undergone post-translational C-terminal amidation prior to entering the axon. Antigen pre-absorption experiments using NPF prevented labeling with either PP or FMRFamide antisera, and the failure of these antisera to block NPF-IR supports the view that some, if not all, of the PP/FMRFamide-IR is due to NPF-like peptides.

Validation of membrane protein topology models by oxidative labeling and mass spectrometry

Computer-assisted topology predictions are widely used to build low-resolution structural models of integral membrane proteins (IMPs). Experimental validation of these models by traditional methods is labor intensive and requires modifications that might alter the IMP native conformation. This work employs oxidative labeling coupled with mass spectrometry (MS) as a validation tool for computer-generated topology models. ·OH exposure introduces oxidative modifications in solvent-accessible regions, whereas buried segments (e.g., transmembrane helices) are non-oxidizable. The Escherichia coli protein WaaL (O-antigen ligase) is predicted to have 12 transmembrane helices and a large extramembrane domain (Pérez et al., Mol. Microbiol. 2008, 70, 1424). Tryptic digestion and LC-MS/MS were used to map the oxidative labeling behavior of WaaL. Met and Cys exhibit high intrinsic reactivities with ·OH, making them sensitive probes for solvent accessibility assays. Overall, the oxidation pattern of these residues is consistent with the originally proposed WaaL topology. One residue (M151), however, undergoes partial oxidation despite being predicted to reside within a transmembrane helix. Using an improved computer algorithm, a slightly modified topology model was generated that places M151 closer to the membrane interface. On the basis of the labeling data, it is concluded that the refined model more accurately reflects the actual topology of WaaL. We propose that the combination of oxidative labeling and MS represents a useful strategy for assessing the accuracy of IMP topology predictions, supplementing data obtained in traditional biochemical assays. In the future, it might be possible to incorporate oxidative labeling data directly as constraints in topology prediction algorithms.