Semistar ascending chain conditions over polynomial rings

Ricerche di Matematica - Let D be an integral domain. G. Picozza associated to a stable semistar operation $$\star $$ on D,  a semistar operation $$\star _1$$ on the polynomial ring D[X]....     

Molecule-Responsive Fluorescent Sensors of α-Helix Peptides Bearing α-Cyclodextrin, Pyrene and Nitrobenzene Units in Their Side Chains

-Helix peptides bearing one unit of -cyclodextrin (-CD), one unit of pyrene and one unit of nitrobenzene (NB) in their side chains have been designed and synthesized as novel molecule-responsive devices.In both the CD-peptides, -PR17 and -PL17, the NB unit is separated from the CD unit by two turns of the helix. Two reference peptides (PL17, and -P17,) have also been synthesized. The circular dichroism studies in the peptide absorption region (200–250 nm)of -PR17 and -PL17 suggestthat the CD-peptides form stable-helixstructures (83–77%), which was destabilized by accommodating guest molecules (e.g., n-pentanol) into the CD cavity. It suggests that formation of intramolecular host–guest(CD–NB) complex stabilized thehelical structure and exogenous guest molecule excluded the appending NB moiety from inside to outside of the CD cavity, thereby causing destabilization of the helical structure and increasing the random coil content. The ICD spectra of the peptides in the pyrene and nitrobenzene absorption region (250–40 nm) suggest that NB forms inclusion complex with CD. The fluorescence studies revealed that the fluorescence of the pyrene unit is quenched by the NB unit in -PR17 and -PL17. The fluorescence intensity increases with increasing guest concentration for the CD-peptides.This guest-responsiveenhancement in the fluorescence intensity can be explained in terms of increased distance between the pyrene and NB moieties, which is caused by exclusion of the NB moiety from the CD cavity by guest accommodation. Using the guest-responsive fluorescence quenching properties of the CD-peptides, we have obtained binding constants for various short chain alkanols. -PL17 has higher binding affinity to the guest molecules than its isomer, -PR17, indicating that the location of functional groups on the peptide scaffold is important in molecule detection.     

In situ assembled ZIF superstructures via an emulsion-free soft-templating approach

Assembling well-defined MOF superstructures remains challenging as it requires easily removable hard templates or readily available immiscible solutions for an emulsion-based soft-template approach. In this work, a single-step emulsion-free soft templating approach is reported to spontaneously prepare hollow ZIF-8 and ZIF-67 colloidosomes with no further purification. These superstructures can load different enzymes regardless of the size and charge with a high encapsulation efficiency of 99%. We envisage that this work will expand the repertoires of MOF superstructures by the judicious selection of precursors and the reaction medium.

An emulsion-free approach for the preparation of hollow ZIF-8 superstructures in a single step is established based on metal sulfate hydrates in methanol.     

Note sur le mécanisme réactionnel de la transposition de Dimroth. Une étude ab initio

An ab initio study of the Dimorth rerarrangement of the -amino-1,2,3,4-tetrazole leads to the conclusion teht in vapour phase the rate determining step is not the ring-chain isomerism, but is either the Z-E iomerism around the C?N double bond or the 1,3-sigmatropic shift of the proton.     

Coordination versatility of pyridine-functionalized N-heterocyclic carbenes: a detailed study of the different activation procedures. Characterization of new Rh and Ir compounds and study of their catalytic activity

Three different reaction procedures for the coordination of N-n-butyl-N'-(2-pyridylmethyl)imidazolium salt have produced new N-heterocyclic complexes of Rh and Ir. The direct reaction of the imidazolium salt with [IrCl(cod)](2) provides a NHC-Ir(III)-H complex, while transmetalation from a silver-NHC complex and deprotonation with NEt(3) give new NHC complexes of M(I) and M(III) when reacting with [MCl(cod)](2) or [MCl(coe)(2)](2) (M = Rh, Ir). The crystal structures of the biscarbene Rh(III) and Ir(III) complexes are described. The catalytic properties of the compounds obtained have been tested in the hydrosilylation of acetylenes, the cyclization of acetylenic carboxylic acids, and hydrogen transfer to ketones.     

New dinuclear catalysts Rh(2)(N-O)(2)[(C6H4)P(C6H5)2]2 with imidate ligands: synthesis and isomerization from head-to-tail to head-to-head configuration of the imidate ligands

Two new dirhodium(II) catalysts of general formula Rh(2)(N-O)(2)[(C(6)H(4))P(C(6)H(5))(2)](2) (N-O = C(4)H(4)NO(2)) are prepared, starting from Rh(2)(O(2)CCH(3))(2)(PC)(2)L(2) [PC = (C(6)H(4))P(C(6)H(5))(2) (head-to-tail arrangement); L = HO(2)CCH(3)]. The thermal reaction of Rh(2)(O(2)CCH(3))(2)(PC)(2).L(2) with the neutral succinimide stereoselectively gives one compound that according to the X-ray structure determination has the formula Rh(2)(C(4)H(4)NO(2))(2)[(C(6)H(4))P(C(6)H(5))(2)](2) (1). It corresponds to the polar isomer with two bridging imidate ligands in a head-to-head configuration. However, stepwise reaction of Rh(2)(O(2)CCH(3))(2)(PC)(2).L(2) with (CH(3))(3)SiCl and potassium succinimidate yields a mixture of 1 and one of the two possible isomers (structure B) with a head-to-tail configuration of the imidate ligands, Rh(2)(C(4)H(4)NO(2))(2)[(C(6)H(4))P(C(6)H(5))(2)](2) (2), also characterized by X-ray methods. In solution, compound 2 undergoes slow isomerization to 1; the rate of this process is enhanced by the presence of acetonitrile. Compounds 1 and 2 are obtained as pure enantiomers starting from (M)- and (P)-Rh(2)(O(2)CCH(3))(2)(PC)(2).L(2) rather than from the racemic mixture. Their enantioselectivities in cyclopropanation of 1-diazo-5-penten-2-one are similar to those reported for the dirhodium amidate catalysts.     

The synthesis and physical evaluation of 5-alkoxy-1,3-thiazoles prepared via Lawesson's reagent-mediated cyclisation of α-benzamido esters

The synthesis of the first series of 5-alkoxy-1,3-thiazole-based liquid crystals is reported. The aforementioned liquid crystals were synthesised through a Lawesson's reagent-mediated cyclisation of appropriate α-benzamido esters. This methodology was found to be highly efficient, even on a large scale, and the resulting 5-alkoxy-1,3-thiazoles could be purified without the use of column chromatography. The synthesis and mesomorphic properties of a family of 5-alkoxy-2-(4-cyanophenyl)-1,3-thiazole liquid crystals prepared via this approach are discussed and compared with their thiophene and phenyl analogues.     

Multifunctional mesoporous silica nanoparticles in poly(ethylene‐co‐vinyl acetate) for transparent heat retention films

Transparent inorganic‐polymer nanocomposite films are of tremendous current interest inemerging solar coverings including photovoltaic encapsulants and commercial greenhouse plastics, but suffer from significant radiative heat loss. This work provides a new and simple approach for controlling this heat loss by using mesoporous silica/quantum dot nanoparticles in poly(ethylene‐co‐vinyl acetate) (EVA) films. Mesoporous silica shells were grown on CdS‐ZnS quantum dot (QDs) cores using a reverse microemulsion technique, controlling the shell thickness. These mesoporous silica nanoparticles (MSNs) were then melt‐mixed with EVA pellets using a mini twin‐screw extruder and pressed into thin films of concentration variable controlled thickness. The results demonstrate that the experimental MSNs showed improved infrared and thermal wavebands retention in the EVA transparent films compared to commercial silica additives, even at lower concentrations. It was also found MSNs enhanced the quantum yield and photostability of the QDs, providing high visible light transmission and blocking of UV transmission of interest for next generation solar coatings. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 851–859