Fully reversible procedure for silver staining improves densitometry of complex mixtures of biopolymers resolved by sodium dodecyl sulfate-polyacrylamide gel electrophoresis

Due to its high sensitivity, silver staining is a widely popular method for the revelation of biopolymers separated by both native and denaturing electrophoresis. A step-by-step method for the destaining and restaining of overdeveloped/overloaded silver-stained bands is described that is applicable to both proteins and nucleic acids. The procedure significantly improves densitometric analysis of gels that have been silver stained with either commercial kits or solutions made in-house. The method permits reproducible densitometry of silver-stained gels and allows quantification of both main and minor components in complex mixture of molecules resolved on the same gel slab. All steps may be interrupted and are readily reversible, allowing for facile densitometric analyses and photographic recording under optimized conditions. Furthermore, common artifacts such as differential staining of the two gel surfaces, localized uneven yellow-ochre background, and the presence of fold marks and fingerprints can be easily removed.     

Advanced pulse calibration techniques for the quantitative analysis of TG–FTIR data

Two different pulse calibration techniques to estimate the total quantities of evolved gaseous substances formed in thermogravimetric (TG)–FTIR runs were compared and assessed. A gas-pulse calibration method was based on the use of a specific device able of sending a known quantity of a gaseous compound of interest to the FTIR analyzer. A second calibration method was based on the vaporization in the TG analyzer of liquid solutions of the compound of interest. Data obtained by these techniques were compared to those from conventional concentration-based calibration. The results confirmed the reliability of pulse calibration techniques to obtain quantitative data on evolved gaseous products in TG–FTIR applications. Moreover, both the gas-pulse and the vaporization-based calibration techniques proved to have several advantages with respect to conventional techniques. Among these are the need of a more limited number of standards and no need for online gas dilution systems.     

New flavonol tetraglycosides from Astragalus caprinus

A new flavonol tetraglycoside, together with four acylated derivatives, were isolated from the leaves of Astragalus caprinus. Their structures were elucidated by spectroscopic methods, mainly 2D NMR, as kaempferol-3-O-[[beta-D-xylopyranosyl(1-->3)-alpha-L-rhamnopyranosyl(1-->6)][alpha-L-rhamnopyranosyl(1-->2)]]-beta-D-galactopyranoside (1), its 3(Gal)-p-coumaric (2) and 3(Gal)-ferulic (3) esters, and its 4(Gal)-p-coumaric (4) and 4(Gal)-ferulic (5) esters.     

FT-IR spectral imaging of blood vessels reveals protein secondary structure deviations induced by tumor growth

Vascular basement membrane remodeling is involved in tumor angiogenesis to enable tumor invasion and growth. FT-IR spectral imaging was used to determine changes in tumor blood vessels to reveal protein secondary structure in Rag-gamma immuno-deficient mice sacrificed 14 and 21 days after subcutaneous glioma implantation. For the oldest blood capillaries (diameter >20 microns), tumor growth induced a decrease in triple-helix content (1638 cm(-1); -7.3%; P < 0.05) and an increase in beta turns (1666 and 1615 cm(-1); +4%; P < 0.01). These protein-structure alterations, mainly from type IV collagen, reflected the high angiogenic stress of growing tumors. We propose to use these molecular markers of vascular basement membrane protein alterations for gradation of solid tumors by FT-IR spectral imaging.     

Harmonic generation in a two-dimensional nonlinear quasi-crystal

Second-harmonic generation in a two-dimensional nonlinear quasi-crystal is demonstrated for the first time to our knowledge. Temperature and wavelength tuning of the crystal reveal the uniformity of the pattern while angle tuning reveals the dense nature of the crystal's Fourier spectrum. These results compare well with theoretical predictions showing the excellent uniformity of the crystal and suggest that more-complicated nonlinear holograms should be possible.     

Forced and unforced unsteadiness in an axial turbomachine

Different sources of unsteadiness in low-speed axial turbomachinery are identified and classified in this paper. From the classical picture segregating non-periodic mechanisms (turbulence) from periodic phenomena (unsteadiness), a further decomposition is outlined to distinguish between forced (deterministic periodicities) and unforced (non-deterministic) unsteadiness. Raw velocity traces, measured for several test conditions in a typical industrial fan with hot-wire anemometry, are ensemble-averaged to obtain time-resolved fluctuations. Then, a frequency-based filtering procedure is employed to isolate non-deterministic, but also non-chaotic, disturbances from the remaining turbulent fluctuations, resulting in the so-called unforced unsteadiness. This term reveals coherent flow structures that involve “large-scale” unsteadiness with other periodic features different to the blade rotation scales (BPF). As a starting point, the kinetic energy associated to the total unsteadiness (in terms of a percentage of the kinetic energy of the time-averaged flow) is analyzed as a function of the operating conditions. Next, the different components contributing to the total unsteadiness of the flow are also observed, in order to determine their particular significance on the global unsteady scenario. It is shown that the turbulent kinetic energy reaches up to approximately a 50–60% of the total unsteady energy, while both forced and unforced components contribute equally to the rest of the energy. In addition, it is observed that higher levels of unforced unsteadiness are concentrated towards the endwall boundary layers where forced unsteadiness is notably reduced due to the loss of the wake–core structure. Conversely, forced unsteadiness is more evident at inner regions of the rotor passage. Furthermore, unforced unsteadiness is especially intense in the tip regions where large-scales associated to the tip leakage vortex are established. It is demonstrated that the estimation of the unforced unsteadiness constitutes an accurate indicator of the presence of tip leakage flows for low-speed axial turbomachinery. Moreover, this is confirmed through the representation of the degree of anisotropy, where typical anisotropic structures are revealed. Finally, with the introduction of power spectrum densities for the unforced components, it is possible to identify typical eddy sizes of these large fluctuations.     

Modification of ultra‐high‐molecular weight polyethylene by various fluorinating routes

Chemical–physical properties of ultra‐high‐molecular weight polyethylene (UHMWPE) treated by direct fluorination, direct fluorination accompanied with UV irradiation, by XeF₂ and by TbF₄, were tested by FTIR spectroscopy, visible spectroscopy, 19F and 13C NMR, scanning electron microscopy, XRD, and EPR. Surface energy measurements were carried out. The direct fluorination of UHMWPE is a diffusion‐controlled process, but treatment with XeF₂ is a kinetically controlled one. Direct fluorination and direct fluorination accompanied with UV irradiation results mainly in a formation of ? CF₂? groups. On the contrary, ? CHF? groups are prevailing in UHMWPE treated with XeF₂ and TbF₄. Surface texture of UHMWPE treated with XeF₂ and with F₂ is quite different. Direct fluorination results in a higher polarity of the polymer surface when compared with treatment with XeF₂. For the case of direct fluorination, both long‐lived peroxy and fluoroalkylradicals are formed. For the case of treatment with XeF₂, only fluoroalkylradicals were detected. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49:3559–3573, 2011