One-pot synthesis of β-amino acid derivatives from α-amino acids

The one-pot transformation of α-amino acid into β-amino acid derivatives is described. The application of this method to the synthesis of modified dipeptides was also illustrated.     

Understanding Reactivity Patterns of Radical Cations

Over the last 15 years electron transfer activation has emerged as a valuable concept for accomplishing novel reactions and has found widespread application in the selective transformation of increasingly complex molecules. This review presents in a conceptualized manner the vast number of radical cation reactions obtained after chemical, electrochemical, and photoinduced one-electron oxidation. To familiarize the reader with the concepts of electron transfer a simple and straightforward classification of radical cation reactions has been devised to allow the presentation of a manifold of reactions in a readily understandable manner. Whenever possible, thermochemical and kinetic data are provided.     

Cycloruthenated complexes as homogeneous catalysts for atom-transfer radical additions

Various cycloruthenated complexes were used as homogeneous catalysts for the atom-transfer radical addition of polyhalogenated compounds to several olefinic substrates. Yields obtained through conventional or microwave heating could reach high values (up to 98% with CBrCl₃ and 88% with CCl₄).     

The calculated enthalpies of the nine pyrazole anions, cations, and radicals: a comparison with experiment

Enthalpies of 12 pyrazole species including neutral, anions, cations, and radicals have been calculated at the G3B3 level. The main conclusions are: (i) there are ten equilibria between species of which six have been measured experimentally and the agreement is excellent; (ii) two structures, cyclic and chain, have been found for the pyrazolium-radical 8 that are able to explain the electrochemistry of pyrazolium salts; (iii) the aromaticity, calculated as the NICS indexes, is related to the unexpected stability of the pyrazole anion 3.     

Retinal phosphenes and discrete dark noises in rods: A new biophysical framework

Spontaneous rhodopsin activation produces discrete noises indistinguishable from single-photon responses. However, there is a serious discrepancy between the apparent energy barrier of thermal events compared with that of the photon-driven process. Current estimates of the activation energies of discrete dark noises in vertebrate rod and cone pigments are 40–50 kcal/mol for activation by photon and 20–25 kcal/mol for activation by heat. To reconcile this discrepancy, it was assumed that thermal activation and photon activation of rhodopsin follow different molecular mechanisms. The most convincing hypothesis for a separate low-energy thermal pathway is that the discrete dark noises of rods arise in a small subpopulation of rhodopsins, where the Schiff base linking the chromophore to the protein part has been deprotonated.According to Narici et al.’ experiments (2009, Radiation Measurements), phosphene perception in space travel is due to the ionizing radiation-induced free radicals that generate chemiluminescent photons from lipid peroxidation. These photons are absorbed by the photoreceptors chromophores, which modify the rhodopsin molecules (bleaching) and start the photo-transduction cascade resulting in the perception of phosphenes.Here, we point out that not only retinal phosphenes but also the discrete dark noise of rods can be due to the natural redox related (free radical) bioluminescent photons in the retina. In other words, under regulated conditions, lipid peroxidation is a natural process in cells and also in retinal membranes. Since the natural lipid peroxidation is one of the main sources of bioluminescent photons and the photoreceptors have the highest oxygen demand and polyunsaturated fatty acid (PUFA) concentration, there is a continuous, low level bioluminescent photon emission in the retina without any external photonic stimulation. During photopic or scotopic vision, evanescent bioluminescent photon emission is negligible. In contrast, in dark-adapted retinal cells this evanescent bioluminescent photon emission is not negligible. Therefore, our hypothesis is that the discrete dark noise of rods can be due to these bioluminescent photons.     

Synthesis, biological evaluation, and modeling of a C,D-seco-taxoid

A C,D-seco-paclitaxel derivative 12 was prepared and tested for biological activity. The key step in the synthesis was a free radical fragmentation of the bicyclic tertiary alcohol 7 under the conditions of the hypobromite reaction. The compound 12 showed no activity in the tubulin test.     

Injectivity and Graded Injectivity

In this paper, we study the injectivity and graded injectivity of modules. Injective testing sets of semiprime Noetherian rings and FBN rings are Particularly investigated. For commutative Artinian Z-graded rings, we prove that gr-injectivity implies injectivity and hence show that the gr-global dimesion and global dimesion are the same.AMS Subject Classification (1991): Primary 18G05, Secondary 18G20, 16P40.     

New strategy to identify radicals in a time evolving EPR data set by multivariate curve resolution-alternating least squares

Electron paramagnetic resonance (EPR) spectroscopy is a powerful technique that is able to characterize radicals formed in kinetic reactions. However, spectral characterization of individual chemical species is often limited or even unmanageable due to the severe kinetic and spectral overlap among species in kinetic processes. Therefore, we applied, for the first time, multivariate curve resolution-alternating least squares (MCR-ALS) method to EPR time evolving data sets to model and characterize the different constituents in a kinetic reaction. Here we demonstrate the advantage of multivariate analysis in the investigation of radicals formed along the kinetic process of hydroxycoumarin in alkaline medium. Multiset analysis of several EPR-monitored kinetic experiments performed in different conditions revealed the individual paramagnetic centres as well as their kinetic profiles. The results obtained by MCR-ALS method demonstrate its prominent potential in analysis of EPR time evolved spectra.     

Development of Single‐Molecule Magnets†

Single‐molecule magnets (SMMs) are paramagnetic molecules that can be magnetized below a certain temperature and have potential applications in high‐density information storage, magnetic qubits, spintronic devices, etc. The discovery of the first SMM, Mn₁₂, opened a new era of molecular magnetism and promoted collaborative researches between chemists and physicists for their exotic quantum as well as classical magnetic properties. In the recent past, great efforts have been made to develop strategies for constructing new SMMs with high energy barriers (U_eff) and blocking temperatures (T_B), resulting in great and fast development of SMMs. In this concise review, we highlight the main synthetic approaches and representative results in the design and synthesis of high performance SMMs. We hope to give the readers a basic understanding of SMMs and a snapshot of the representative researches on SMMs from a perspective of synthetic chemists.