3,5-Pyridyne--a heterocyclic meta-benzyne derivative

3,5-Pyridyne (3) has been generated by flash vacuum pyrolysis of 3,5-diiodopyridine (20) and 3,5-dinitropyridine (21) and characterized by IR spectroscopy in cryogenic argon matrices. The aryne can clearly be distinguished from other side products by its photolability at 254 nm, inducing a rapid ring-opening presumably to (Z)-1-aza-hex-3-ene-1,5-diyne. As byproducts of the pyrolysis, HCN and butadiyne were identified, together with traces of acetylene, cyanoacetylene, (E)-1-aza-hex-3-ene-1,5-diyne, and the 3-iodo-5-pyridyl radical (from 20). Several pathways for rearrangements and fragmentations of 3 and of the parent meta-benzyne (1) have been explored computationally by density functional theory and ab initio quantum chemical methods. The lowest energy decomposition pathway of biradicals 1 and 3 is a ring-opening process accompanied by hydrogen migration, leading to (Z)-hex-3-ene-1,5-diyne [(Z)-10] and (Z)-3-aza-hex-3-ene-1,5-diyne [(Z)-24], respectively. Both reactions require activation energies of 45-50 kcal mol(-1). Mechanisms leading from (Z)-24 or directly from 3 to the experimentally observed byproducts are discussed. Upon replacement of the C(5)H moiety by N in meta-benzyne, high-level calculations predict a modest shortening of the interradical distance by 5-7 pm and a reduction of the singlet-triplet energy splitting by 3 kcal mol(-1), in good agreement with isodesmic equations, according to which the singlet ground state of 3 is destabilized relative to 1 by 3-4 kcal mol(-1). In contrast to 3,5-borabenzyne (2), which is found to be doubly aromatic, nucleus-independent chemical shifts of 3 are almost identical to that of pyridine, indicating the absence of paramagnetic ring current effects that may be associated with "in-plane antiaromaticity". As compared with 1, the overall perturbation caused by the nitrogen atom in 3 is weak, and four electron, three center interaction is of minor importance in this molecule.     

Synthesis, characterization and chromotropic properties of MnII, CoII, NiII and CuII with bis (acesulfamato) bis ( 3 -methylpyridine) complexes

The novel 3- [M: Mn^II, Co^II, and Ni^II] and 3- complexes (acs: acesulfamate; 3-pic: 3-methylpyridine) have been synthesized and characterized using elemental analyses, magnetic moments, UV–Vis and FT-IR spectra. The thermal behaviour of the complexes was also studied by simultaneous TG, DTG and DTA methods in static air atmosphere. The chromotropic properties of all complexes have been studied using thermal and spectral analysis. While the complexes of Co^II and Ni^II show reversible continuous thermochromism, an irreversible discontinuous thermochromism is observed in the Mn^II and Cu^II) complexes in the solid state. The observed thermochromism in the Mn^II, Co^II and Ni^II complexes is due to the different ligand field strength associated with the deaquation reaction. The solvatochromic behaviour of the complexes is also studied and all anhydrous complexes (except Mn^II) exhibit solvatochromic properties depending on the donor number of the solvent.     

Synthesis,characterization, antioxidant properties and DFT calculation of some new pyrimidine derivatives

Abstract

In this study, 5-benzoyl-4-(4-(methylthio)phenyl)-6-phenyl-1,2,3,4-tetrahydro-2-thioxo (1), oxo (2) and imino (3) pyrimidine derivatives were prepared via Multicomponent Cyclocondensation Reactions (MCRs). The compounds thiazolo[3,2-a]pyrimidin-3(5H)-one (4) and thiazin-4(6H)-one (5) were obtained via the reaction of compound 1 with bromoacetic acid and 3-bromopropionic acid, respectively. Structures were determined by using FT-IR, ¹H/¹³C NMR and elemental analyses. Also the compounds 4 and 5 were analyzed by X-ray single crystal analysis. All compounds were investigated as corrosion inhibitors using density functional theory (DFT) at the level of B3LYP/6-31G (d, p). According to the calculations, the compound 3 appears to be a good inhibitor for corrosion. On the other hand, total antioxidant properties were measured in vitro by DPPH^?, ABTS^?+ test, hemolysis of phenylhydrazine erythrocytes and metal chelating effect. The results were compared with standard antioxidants such as trolox and α-tocopherol. These data revealed that compounds 1, 2 and 5 are more active with respect to 3 and 4 in scavenging the radicals.     

The synthesis, Na+ binding properties of new coumarin-crown ethers

o-Dihydroxy-3-(methylphenyl)-chromenones (coumarins; 3a–3c) were synthesized from trimethoxybenzaldehydes through a reaction with the corresponding methylphenyl-acrylonitrile in pyridine·HCl and then H₃O⁺. Dihydroxycoumarins reacted with the ditosylate or dichloride derivatives of tri- or tetraethyleneglycols in the presence of CH₃CN/Na₂CO₃ and macrocyclic ethers with a coumarin moiety were obtained. The chromatographically purified new coumarin-crown ethers (5a–5f) were identified by IR, ¹H NMR, and Mass spectrometry. The binding constants of Na⁺ with the coumarin-crown ethers were determined in an 80 % dioxane/water binary solvent system at 25 °C from conductance measurements.     

Synthesis of Functionalized Novel α‐Amino‐β‐alkoxyphosphonates through Regioselective Ring Opening of Aziridine‐2‐phosphonates

Aziridines are highly useful compounds as building blocks for the synthesis of important organic compounds. Amino acid synthesis by aziridine ring opening reaction is a good example to the use of aziridines. Although this reaction is studied by many groups, the synthesis of amino phosphonic acids is less explored. In this study, we have carried out the ring opening reaction of aziridinyl phosphonates with a variety of alcohols including the more functional propargylic and allylic alcohols. These reactions provided functionalized α‐amino‐β‐alkoxyphosphonates in 40–91 % yield.     

Modelling of calcium dynamics in brain energy metabolism and Alzheimer's disease

Functional imaging techniques play a major role in the study of brain activation by monitoring the changes in blood flow and energy metabolism. In order to interpret functional neuroimaging data better, the existing mathematical models describing the links that may exist between electrical activity, energy metabolism and hemodynamics in literature are thoroughly analyzed for their advantages and disadvantages in terms of their prediction of available experimental data. Then, these models are combined within a single model that includes membrane ionic currents, glycolysis, mitochondrial activity, exchanges through the blood-brain barrier, as well as brain hemodynamics. Particular attention is paid to the transport and storage of calcium ions in neurons since calcium is not only an important molecule for signalling in neurons, but it is also essential for memory storage. Multiple efforts have underlined the importance of calcium dependent cellular processes in the biochemical characterization of Alzheimer's disease (AD), suggesting that abnormalities in calcium homeostasis might be involved in the pathophysiology of the disease. The ultimate goal of this study is to investigate the hypotheses about the physiological or biochemical changes in health and disease and to correlate them to measurable physiological parameters obtained from functional neuroimaging data as in the time course of blood oxygenation level dependent (BOLD) signal. When calcium dynamics are included in the model, both BOLD signal and metabolite concentration profiles are shown to exhibit temporal behaviour consistent with the experimental data found in literature. In the case of Alzheimer's disease, the effect of halved cerebral blood flow increase results in a negative BOLD signal implying suppressed neural activity.     

Radar cross section (RCS) modeling and simulation, part 1: a tutorial review of definitions, strategies, and canonical examples

Modeling and simulation strategies for radar cross section (RCS) prediction are reviewed, and a novel FDTD-based virtual RCS prediction tool is introduced in this two-part paper. Part 1 is reserved for a tutorial review. Concepts and definitions related to RCS modeling are outlined. Analytical approaches, i.e., high-frequency asymptotics (HFA), as well as powerful time- and frequency-domain numerical methods, are given. Canonical examples using the finite-difference time-domain (FDTD) Method, the method of moments (MoM), and physical optics (PO) are presented.     

The interaction of cysteine with chromium(VI) ions under UV irradiation

In 0.1 M phosphate buffer (pH 7.2), the interaction of chromium(VI) with cysteine in the presence and absence of UV irradiation was studied by cyclic voltammetry and electronic spectroscopy techniques. The reduction of Cr(VI) by cysteine takes place through the formation of Cr(VI)-thioester intermediate. On the cyclic voltammograms of cysteine and Cr(VI) mixture, the peaks at -0.315 and -0.800 V were observed, and these peaks are corresponding to the reduction of Cr(VI)-thioester and thiyl radical, respectively. In the cysteine solution exposed to UV irradiation, the formation of free cystine was observed at -0.792 V. In the cysteine and Cr(VI) mixture exposed to UV irradiation, the peak current of thiyl radical increases while the peak current of Cr(VI)-thioester reaches a maximum at 15 min and then decreases by increasing UV irradiation time. The formation of the thioester in the reaction between Cr(VI) and cysteine in aqueous media has been studied by monitoring the decrease of Cr(VI) at 370 nm. It was observed that the reaction is catalyzed by the UV irradiation of the Cr(VI) and cysteine mixture.     

Heterograft brush copolymers via romp and triple click reaction strategies involving CuAAC,diels–alder,and nitroxide radical coupling reactions

In this study, an equimolar mixture of oxanorbornenyl‐anthracene (ONB‐anthracene), oxanorbornenyl‐bromide (ONB‐Br), and oxanorbornenyl tosylate (ONB‐OTs) was polymerized via ring opening metathesis polymerization using the first generation Grubbs' catalyst in CH₂Cl₂ at room temperature to form poly(ONB‐anthracene‐co‐ONB‐Br‐co‐ONB‐OTs)₁₀ copolymer as a main backbone. Next, this main backbone was sequentially clicked with a furan protected maleimide‐terminated poly(methyl methacrylate), 2,2,6,6‐tetramethyl‐1‐piperidinyloxy‐terminated poly(ethylene glycol), and alkyne‐terminated poly(ε‐caprolactone) (PCL₂₀‐alkyne) via Diels–Alder, nitroxide radical coupling, and copper‐catalyzed azide‐alkyne cycloaddition, respectively, to yield a poly(ONB‐g‐PMMA‐co‐ONB‐g‐PEG‐co‐ONB‐g‐PCL)₁₀ heterograft brush copolymer © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013