Comparative analysis of the PET and ICT sensor properties of 1,8-naphthalimides containing aza-15-crown-5 ether moiety

International audienceNovel 4-amino- and 4-(acetyl)amino-N-aryl-1,8-naphthalimides containing aza-15-crown-5 ether receptor unit in the N-aryl fragment and at C-4 of the naphthalimide residue were designed and prepared. Significant internal charge transfer from electron donating amino or amido group at C-4 of the naphthalene ring to the acceptor carboxyimide moiety as well as photoinduced electron transfer between N-aryl receptor and the naphthalimide fragment was revealed by the UV/Vis absorption spectroscopy and considerable fluorescence quenching. The addition of calcium perchlorate to an acetonitrile solution of naphthalimides with the receptor at imide nitrogen hindered the photoinduced electron transfer process and accordingly restored the quenched fluorescence of the free ligands. In the case of the compound in which the aza-15-crown-5 receptor is located at C-4, the coordination with Ca2+ reduced the internal charge transfer interaction in the chromophore and caused a significant blue-shift of the absorption and emission peak. The observed spectral effects were analyzed using PM6 semiempirical calculations. Formation of complexes was also confirmed by 1H NMR spectroscopy

Band structure and broadband compensation of absorption by amplification in layered optical metamaterials

The frequency dependence of the gain required to compensate for absorption is determined for a layered structure consisting of alternating absorbing and amplifying layers. It is shown that the fulfillment of the same conditions is required for the existence of a band structure consisting of alternating bands allowed and forbidden for optical radiation propagation in the frequency-wave vector parametric region. Conditions are found under which the gain required for compensation is smaller than thresholds for absolute (parasitic lasing) and convective (waveguide amplification of radiation) instabilities

Metal-ion induced FRET in macrocyclic dynamic tweezers

International audienceAbstract We report here about effective FRET process (73-99%) in mono-Mg2+ complexes of symmetrical crown ether bis(styryl) dyes. The FRET process has not been observed in the free state and in binuclear complexes. The formation of mononuclear complex provides two styrylic fragments with appropriate positions of absorption and emission bands for FRET. The other important parameter for FRET is the proper geometric orientation of both chromophores, which attain sandwich conformation with close positioning of complexed and free styryl fragments induced by ion-modulated geometry reorganization of the bis-dye

Three natural mechanical systems on Stiefel varieties

We consider integrable generalizations of the spherical pendulum system to the Stiefel variety $V(n,r)=SO(n)/SO(n-r)$ for a certain metric. For the case of V(n,2) an alternative integrable model of the pendulum is presented. We also describe a system on the Stiefel variety with a four-degree potential. The latter has invariant relations on $T^*V(n,r)$ which provide the complete integrability of the flow reduced on the oriented Grassmannian variety $G^+(n,r)=SO(n)/SO(r)\times SO(n-r)$.Comment: 14 page

Discrete Nonholonomic LL Systems on Lie Groups

This paper applies the recently developed theory of discrete nonholonomic mechanics to the study of discrete nonholonomic left-invariant dynamics on Lie groups. The theory is illustrated with the discrete versions of two classical nonholonomic systems, the Suslov top and the Chaplygin sleigh. The preservation of the reduced energy by the discrete flow is observed and the discrete momentum conservation is discussed.Comment: 32 pages, 13 figure

Cloning and Characterization of Polyhydroxybutyrate Synthase from Methylobacterium extorquens AM1

В результате поиска генов, кодирующих вероятные ПГБ-синтазы в геномах бактерий рода Methylobacterium, выявлены множественные (до пяти у одного штамма) гены ПГБ-синтаз. Филогенетическим анализом показано, что белки PhaC1, PhaC2, PhaC3 относятся к I классу ПГБ-синтаз, белки PhaC4 – к ПГБ-синтазам III класса, тогда как PhaC5, по-видимому, представляет неохарактеризованный класс ПГБ-синтаз. Впервые выделена и охарактеризована рекомбинантная ПГБ-синтаза I класса (КФ 2.3.1.B2) из Methylobacterium extorquens AM1, кодируемая геном phaC1. Молекулярная масса мономера фермента составила 78 кДа. Константа Михаэлиса (Km) для PhaC1 из штамма AM1 составила 1,3 мМ, а максимальная скорость реакции (Vmax) – 0,1 мкмоль∙мин-1∙мг-1. Получен делеционный мутант Methylobacterium extorquens по гену phaC, перспективный для дальнейшего исследования особенностей биосинтеза ПГБ метилобактериямиMultiple genes encoding putative PHB synthases (up to 5 in single strain) were found in Methylobacterium genomes. As a result of phylogenetic analysis proteins PhaC1, PhaC2, PhaC3 were identified as class I PHB synthases, PhaC4 proteins were identified as class III PHB synthases, while PhaC5 apparently belongs to uncharacterized class of PHB synthases. Firstly, the recombinant class I PBH synthase (EC 2.3.1.B2) encoded by phaC1 gene from Methylobacterium extorquens AM1 was purified and characterized. Molecular mass of enzyme monomer was 78 kDa. Michaelis constant (Km) for PhaC1 was 1,3 mM and maximal reaction rate (Vmax) was 0,1 μmol∙min–1∙mg–1. The deletion mutant of Methylobacterium extorquens in the phaC gene was obtained which is promising for further study of peculiarities of methylobacteria’s PHB biosynthesi