Metallocene catalysis was employed to prepare model polypropylenes (PP) with very high molecular weights and narrow molecular weight distributions (MWDs) of M w/M n ≈ 2, typical for “single site” metallocene catalysts. The viscoelastic properties of PP melts were investigated by means of oscillatory rheometry. Arrhenius and WLF equations were applied to model the influence of temperature on PP rheology. With very high molecular weight polypropylene samples it became possible to determine the onset of the plateau zone, reflecting the rubber-like properties of PP. For the first time plateau moduli and entanglement molecular weights M es were determined and found to be depend upon stereoregularity. The entanglement molecular weights were found to be 6900 g/mol for isotactic PP, 7050 g/mol for atactic PP, and 2170 g/mol for syndiotactic PP. This influence of stereoregularity was attributed to the different conformations of syndiotactic PP with respect to isotactic and atactic PP in PP melts.

Tumor necrosis factor α is an inflammatory cytokine which has been linked with many infectious and inflammatory diseases. Detection and quantification of this key biomarker is commonly achieved by use of an enzyme-linked immunosorbent assay (ELISA). This fundamental technique uses the spectroscopic detection of a chromogen such as 3,3',5,5'-tetramethylbenzidine (TMB). Horseradish peroxidase (HRP), bound to the detection antibody, catalyzes the oxidation of TMB by hydrogen peroxide to generate colored products which may be measured spectrophotometrically. In this study we have used a conventional ELISA kit and shown that, by replacing the traditional colorimetric detection with resonance Raman spectroscopy, we can achieve 50 times lower detection limits and the potential for multiplexed analysis is increased. In this approach, the laser wavelength was tuned to be in resonance with an electronic transition of the oxidized TMB. The relative intensity of the enhanced Raman bands is proportional to the amount of TMB, thus providing a means of improved quantification. Furthermore, TMB is one of the most widely used chromogenic substrates for HRP-based detection and commercial ELISA test kits, indicating that this detection technique is applicable to a large number of target analytes.

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The role of agostic bonds in chemistry is highlighted. In particular, attention is given to the origin of the term, methods of investigations and their function in chemistry.