Copper,gold, and silver decorated magnetic core–polymeric shell nanostructures for destruction of pathogenic bacteria

Fe₃O₄ magnetic nanoparticles (MNPs) were prepared by co-precipitation method. The nanoparticles were silica coated using TEOS, and then modified by the polymeric layers of polypropylene glycol (PPG) and polyethylene glycol (PEG). Finally, the core-shell samples were decorated with Ag, Au, and Cu nanoparticles. The products were characterized by vibrating sample magnetometry (VSM), TGA, SEM, XRD, and FTIR methods. The antibacterial activity of the prepared samples was evaluated in inactivation of E. coli and S. aureus microorganisms, representing the Gram-negative and Gram-positive species, respectively. The effect of solid dosage, bacteria concentration and type of polymeric modifier on the antibacterial activity was investigated. TEM images of the bacteria were recorded after the treatment time and according to the observed changes in the cell wall, the mechanism of antibacterial action was discussed. The prepared nanostructures showed high antibacterial activity against both Gram-negative and Gram-positive bacteria. This was due to the leaching of metal ions which subsequently led to the lysis of bacteria. A theoretical investigation was also done by studying the interaction of loaded metals with the nucleotide components of the microorganism DNA, and the obtained results were used to explain the experimental data. Finally, based on the observed inactivation curves, we explain the antibacterial behavior of the prepared nanostructures mathematically.

     

A Low-Temperature Broadband NMR Probe for Multinuclear Cross-Polarization

Dissolution dynamic nuclear polarization (D-DNP) probes are usually designed for one or at most two specific nuclei. Investigation of multiple nuclei usually requires manufacturing a number of costly probes. In addition, changing the probe is a time-consuming process since a system that works at low temperature (usually between 1.2 and 4.2 K) must be warmed up, thus increasing the risks of contamination. Here, an efficient apparatus is described for D-DNP designed not only for microwave-enhanced direct observation of a wide range of nuclei S such as ¹H, ¹³C, ²H, ²³Na, and ¹⁷O, but also for cross-polarization (CP) from I=¹H to such S nuclei. Unlike most conventional designs, the tuning and matching circuits are partly immersed in superfluid helium at temperatures down to 1.2 K. Intense radio-frequency (RF) fields with amplitudes on the order of 50 kHz or better can be applied simultaneously to both nuclei I and S using RF amplifiers with powers on the order of 90 and 80 W, respectively, without significant losses of liquid helium. The system can operate at temperatures over a wide range between 1.2 and 300 K.     

A promising green method in cyclization reaction.Oxidation of 3-methylcatechol in the presence of 1,10-phenanthroline

Electrochemical oxidation of 3-methylcatechol as a model compound has been studied in the presence of 1,10-phenanthroline as a bi-dentate nucleophile in water/acetonitrile(70/30,v/v) solution using cyclic voltammetry and controlled-potential coulometry. The results revealed that anodically generated 3-methylcyclohexa-3,5-diene-1,2-dione participates in inter and intramolecular Michael addition reactions with 1,10-phenanthroline and via an ECEC pathway converts to the corresponding heterocyclic compound.The present work has led to the development of a facile and one-pot method with high atom economy under ambient conditions and in an undivided cell using a carbon electrode.     

On the sensitivity of ASL MRI in detecting regional differences in cerebral blood flow

Arterial-spin-labeling (ASL) magnetic resonance imaging (MRI) provides a noninvasive tool to measure cerebral blood flow (CBF) and is increasingly used as a surrogate for baseline neural activity. However, the power of ASL MRI in detecting CBF differences between patient and control subjects is hampered by inter-subject variations in global CBF, which are associated with non-neural factors and may contribute to the noise in the across-group comparison. Here, we investigated the sensitivity of this technique and proposed a normalization strategy to better detect such a difference. A “model” situation was employed in which two visual stimuli (i.e. cross fixation and flashing checkerboard) were presented to two groups of subjects to mimic “control” and “patient” groups (N=7 for each group), respectively. It was found that absolute CBF (aCBF) in the occipital lobe in the checkerboard group was 26.0% greater compared to the fixation group, but the level of significance was modest (P=.03). In contrast, when normalizing the CBF with whole-brain CBF or CBF in a reference region [termed relative CBF (rCBF)], the statistical significance was improved considerably (P<.003). For voxel-based analysis, the rCBF indices correctly detected CBF differences in the occipital lobe in the across-group comparison, while aCBF failed to detect any significant cluster using the same statistical threshold. We also performed Monte Carlo simulation to confirm the experimental findings and found that the power improvement was most pronounced when signal-to-noise-ratio is moderate and the underlying CBF difference was small. The simulation also showed that, with the proposed normalization, a detection power of 80% can be achieved using a sample size of about 20. In summary, rCBF is a more sensitive index to detect small differences in CBF, rather than the much-sought-after aCBF, since it reduces data noise caused by inter-subject variations in global CBF.