Electron–electron interaction induced spin thermalization in quasi-low-dimensional spin valves

We study the spin thermalization, i.e., the inter-spin energy relaxation mediated by electron–electron scattering in small spin valves. When one or two of the dimensions of the spin valve spacer are smaller than the thermal coherence length, the direct spin energy exchange rate diverges and needs to be regularized by the sample dimensions. Here we consider two model systems: a long quasi-1D wire and a thin quasi-2D sheet.     

Luminescent energy transfer between cadmium telluride nanoparticle and lanthanide(III) chelate in competitive bioaffinity assays of biotin and estradiol

Fluorescence resonance energy transfer has been studied between lanthanide(III) chelates as donors and protein-coupled CdTe semiconductor nanoparticles as acceptors. Wide excitation spectra and large Stokes shift of semiconductor nanoparticles and timeresolved fluorescence detection were shown to provide a combination for successful energy transfer assay. Different intrinsically fluorescent europium(III) and terbium(III) chelates coupled to single biotin molecules were studied for optimal energy transfer with streptavidin labeled semiconductor nanoparticles. No significant differences between the studied chelates were observed. The strength of the methodology was demonstrated in a clinically relevant competitive and separation-free immunoassay of estradiol, where subnanomolar limit of detection was achieved with the coefficient of variation 2-11%. The data suggested that relatively short distance was needed to obtain adequate energy transfer. Therefore, biomolecules were coupled onto the semiconductor nanoparticles without any spacers.     

Europium(III)-chelates embedded in nanoparticles are protected from interfering compounds present in assay media

Lanthanide chelates are excellent labels in ligand binding assays due to their long lifetime fluorescence, which enables efficient background reduction using time-resolved measurement. In separation-free homogeneous assays, however, some compounds in the sample may cause quenching of the lanthanide fluorescence and extra steps are required before these samples can be measured. In this study we have evaluated whether europium chelates packed inside a polystyrene nanoparticle are better protected from the environment than individual Eu(III)-chelates, and do these particles have higher tolerance against known interfering compounds (bivalent metal ions and variation of pH). We also tested whether metal ions had any effect on a fluorescence resonance energy transfer (FRET) based detection of a bioaffinity binding reaction. The presence of metal ions or variation of pH did not affect the fluorescence of the Eu(III)-chelate dyed nanoparticles, while significant decrease of the fluorescence was detected with a 9-dentate Eu(III)-chelate. Metal ions also decreased the fluorescence lifetime of the 9-dentate Eu(III)-chelate from 0.960 to 0.050 ms. Coloured metal ions caused a minor decrease in sensitised emission generated by FRET when Eu(III)-chelate dyed nanoparticles were used as donor labels. The decreased signal was due to the absorption of the sensitised emission by the coloured metal ions, since the metal ions had no effect on the lifetime of the sensitised emission. Thus the Eu(III)-chelate dyed nanoparticles are preferred labels in homogeneous bioaffinity assays, when interfering compounds are known to be present.     

Measurement of (1)J(NC') and (2)J(H(N))(C') couplings from spin-state-selective two-dimensional correlation spectrum.

A method for the measurement of (1)J(NC') and (2)J(H(N))(C') coupling constants from a simplified two-dimensional [(15)N, (1)H] correlation spectrum is presented. The multiplet components of the (1)J(NC') doublet in the indirect dimension and (2)J(H(N))(C') in the direct dimension are separated into two subspectra by spin-state-selective filters. Thus each subspectrum contains no more peaks than the conventional [(15)N, (1)H]-HSQC spectrum. Furthermore, the method for the measurement of (1)J(NC') and (2)J(H(N))(C') is designed to exploit destructive relaxation interference (TROSY). The results are verified against the measurements of (1)J(NC') from spin-state-selective [(13)C', (1)H] correlation spectra recorded with additional sequence described here.     

Phase-separation of cellulose from ionic liquid upon cooling: preparation of microsized particles

Cellulose - Cellulose is an historical polymer, for which its processing possibilities have been limited by the absence of a melting point and insolubility in all non-derivatizing molecular...     

Chrome tannage using high-intensity ultrasonic field

The process time in chrome tannage in leather making, using an elastic compression cycle followed by irradiation by high-intensity ultrasound, is quite short lasting only a few minutes, compared with a process time of several hours in modern chrome tannage. After ultrasonic irradiation, samples were basified in 17 h in chrome liquor at a pH of 4.0 and the shrinkage temperature was measured. The determination of the efficiency for the chrome liquor penetrating into the hides can be based on the steepness of the shrinkage temperature-processing time curve. An approximate value of 20 degrees C min(-1) can be evaluated for the initial slope of the curve when elastic compression and high-intensity ultrasonic irradiation is used, and a processing time of 2 min is required in chrome liquor (plus 17 h basification and 24 h storage time) to obtain leather stable to boiling. Usually, hides are kept in chrome liquor for 2 h.     

Evaluation of protein 15N relaxation times by inverse Laplace transformation

Relaxation times (T1, T2, T1rho) are usually evaluated from exponential decay data by least-squares fitting methods. For this procedure, the integrals or amplitudes of signals must be determined, which can be laborious with large data sets. Moreover, the fitting requires a priori knowledge of the number of exponential components responsible for the decay. We have adapted inverse Laplace transformation (ILT) for the analysis of relaxation data. Exponential components are resolved with ILT to reciprocal space on their corresponding relaxation rate values. The ILT approach was applied to 3D linewidth-resolved 15N HSQC experiments to evaluate 15N T1 and T2 relaxation times of ubiquitin. The resulting spectrum is a true 3D spectrum, where the signals are separated by their 1H and 15N chemical shifts (HSQC correlations) and by their relaxation rate values (R1 or R2). From this spectrum, the relaxation times can be obtained directly with a simple peak-picking procedure.