One-Step Photochemical Green Synthesis of Water-Dispersible Ag,Au, and Au@Ag Core–Shell Nanoparticles

A simple and green synthetic protocol for the rapid and effective preparation of Ag, Au and Au@Ag core–shell nanoparticles (NPs) is reported based on the light irradiation of a biocompatible, water-soluble dextran functionalized with benzophenone (BP) in the presence of AgNO₃, HAuCl₄, or both. Photoactivation of the BP moiety produces the highly reducing ketyl radicals through fast (<50 ns) intramolecular H-abstraction from the dextran scaffold, which, in turn, ensures excellent dispersibility of the obtained metal NPs in water. The antibacterial activity of the AgNPs and the photothermal action of the Au@Ag core–shell are also shown.     

Enantiopure cis- and trans-2,5-disubstituted-2,5-dihydrofurans from d-allal- and d-galactal-derived vinyl epoxides

Upon treatment with the metal enolates of methylene active compounds (dimethyl malonate and dibenzoylmethane) (C-nucleophiles) and benzyl carbamate (N-nucleophile), d-allal- and d-galactal-derived vinyl epoxides are stereoselectively transformed, in a single step, into diastereoisomeric, highly functionalized, enantiopure cis- and trans-2,5-disubstituted-2,5-dihydrofurans.     

Searching for a response: the intriguing mystery of Feynman’s theoretical reference amplifier

We analyze Feynman’s work on the response of an amplifier performed at Los Alamos and described in a technical report of 1946, as well as lectured on at the Cornell University in 1946–47 during his course on Mathematical Methods. The motivation for such a work was Feynman’s involvement in the Manhattan Project, for which the necessity emerged of feeding the output pulses of counters into amplifiers or several other circuits, with the risk of introducing distortion at each step. In order to deal with such a problem, Feynman designed a theoretical “reference amplifier”, thus enabling a characterization of the distortion by means of a benchmark relationship between phase and amplification for each frequency, and providing a standard tool for comparing the operation of real devices. A general theory was elaborated, from which he was able to deduce the basic features of an amplifier just from its response to a pulse or to a sine wave of definite frequency. Moreover, in order to apply such a theory to practical problems, a couple of remarkable examples were worked out, both for high-frequency cutoff amplifiers and for low-frequency ones. A special consideration deserves a mysteriously exceptional amplifier with best stability behavior introduced by Feynman, for which different physical interpretations are here envisaged. Feynman’s earlier work then later flowed in the Hughes lectures on Mathematical Methods in Physics and Engineering of 1970–71, where he also remarked on causality properties of an amplifier, that is on certain relations between frequency and phase shift that a real amplifier has to satisfy in order not to allow output signals to appear before input ones. Quite interestingly, dispersion relations to be satisfied by the response function were introduced.

     

Fuzzy Entropy-Based Spatial Hotspot Reliability

Cluster techniques are used in hotspot spatial analysis to detect hotspots as areas on the map; an extension of the Fuzzy C-means that the clustering algorithm has been applied to locate hotspots on the map as circular areas; it represents a good trade-off between the accuracy in the detection of the hotspot shape and the computational complexity. However, this method does not measure the reliability of the detected hotspots and therefore does not allow us to evaluate how reliable the identification of a hotspot of a circular area corresponding to the detected cluster is; a measure of the reliability of hotspots is crucial for the decision maker to assess the need for action on the area circumscribed by the hotspots. We propose a method based on the use of De Luca and Termini’s Fuzzy Entropy that uses this extension of the Fuzzy C-means algorithm and measures the reliability of detected hotspots. We test our method in a disease analysis problem in which hotspots corresponding to areas where most oto-laryngo-pharyngeal patients reside, within a geographical area constituted by the province of Naples, Italy, are detected as circular areas. The results show a dependency between the reliability and fluctuation of the values of the degrees of belonging to the hotspots.     

Origin of negative temperatures in systems interacting with external fields

The controversial existence of negative temperatures has stirred interesting debates that have reached the foundations of thermodynamics, including questions on the second law, the Carnot efficiency and the statistical definition of entropy. Here we show that for systems interacting with an external field, negative temperatures may arise when the interaction energy with the field is treated as a form of internal energy. We discuss how negative temperatures are avoided when using a thermodynamic formalism that accounts for the intensive and extensive variables associated to the external field. We use the paramagnetic system and a perfect gas in a gravitational field to illustrate these ideas. Considerations about the isothermal and adiabatic work done by the field or the system also shed light on the inconsistency of super-Carnot efficiencies.     

Some thoughts about enantioseparations in capillary electrophoresis

In this overview the goal of the authors was to analyze from the historical perspective the reasons of success and failure of chiral capillary electrophoresis. In addition, the current trends are analyzed, unique advantages of capillary electrophoresis are highlighted and some future directions are discussed.     

Disulfide Bond Replacement with 1,4- and 1,5-Disubstituted [1,2,3]-Triazole on C-X-C Chemokine Receptor Type 4 (CXCR4) Peptide Ligands: Small Changes that Make Big Differences

Here we investigated the structural and biological effects ensuing from the disulfide bond replacement of a potent and selective C-X-C chemokine receptor type 4 (CXCR4) peptide antagonist, with 1,4- and 1,5- disubstituted 1,2,3-triazole moieties. Both strategies produced candidates that showed high affinity and selectivity against CXCR4. Notably, when assessed for their ability to modulate the CXCL12-mediated cell migration, the 1,4-triazole variant conserved the antagonistic effect in the low-mid nanomolar range, while the 1,5-triazole one displayed the ability to activate the migration, becoming the first in class low-molecular-weight CXCR4 peptide agonist. By combining NMR and computational studies, we provided a valuable model that highlighted differences in the interactions of the two peptidomimetics with the receptor that could account for their different functional profile. Finally, we envisage that our findings could be translated to different GPCR-interacting peptides for the pursuit of novel chemical probes that could assist in dissecting the complex puzzle of this fundamental class of transmembrane receptors.     

A New Validity Index Based on Fuzzy Energy and Fuzzy Entropy Measures in Fuzzy Clustering Problems

Two well-known drawbacks in fuzzy clustering are the requirement of assigning in advance the number of clusters and random initialization of cluster centers. The quality of the final fuzzy clusters depends heavily on the initial choice of the number of clusters and the initialization of the clusters, then, it is necessary to apply a validity index to measure the compactness and the separability of the final clusters and run the clustering algorithm several times. We propose a new fuzzy C-means algorithm in which a validity index based on the concepts of maximum fuzzy energy and minimum fuzzy entropy is applied to initialize the cluster centers and to find the optimal number of clusters and initial cluster centers in order to obtain a good clustering quality, without increasing time consumption. We test our algorithm on UCI (University of California at Irvine) machine learning classification datasets comparing the results with the ones obtained by using well-known validity indices and variations of fuzzy C-means by using optimization algorithms in the initialization phase. The comparison results show that our algorithm represents an optimal trade-off between the quality of clustering and the time consumption.     

DNA-Targeted NO Release Photoregulated by Green Light

A novel molecular hybrid has been designed and synthesized in which acridine orange (AO) is covalently linked to an N-nitrosoaniline derivative through an alkyl spacer. Photoexcitation of the AO antenna with the highly biocompatible green light results in intense fluorescence emission and triggers NO detachment from the N-nitroso appendage via an intramolecular electron transfer. The presence of the AO moiety encourages the binding with DNA through both external and partially intercalative fashions, depending on the DNA:molecular hybrid molar ratio. Importantly, this dual-mode binding interaction with the biopolymer does not preclude the NO photoreleasing performances of the molecular hybrid, permitting NO to be photogenerated nearby DNA with an efficiency similar to that of the free molecule. These properties make the presented compound an intriguing candidate for fundamental and potential applicative research studies where NO delivery in the DNA proximity precisely regulated by harmless green light is required.