Exchangeable random measures in the plane

A random measure on [0,1]², [0, 1]}₊ or ₊ ² is said to be separately exchangeable, if its distribution is invariant under arbitrary Lebesgue measure-preserving transformations in the two coordinates, and jointly exchangeable if is defined on [0,1]² or ₊ ² , and its distribution is invariant under mappings by a common measure-preserving transformation in both directions. In each case, we derive a general representation of in terms of independent Poisson processes and i.i.d. random variables.     

Action and Ion Mobility Spectroscopy of a Shortened Retinal Derivative

The development of tandem ion mobility spectroscopy (IMS) known as IMS-IMS has led to extensive research into isomerizations of isolated molecules. Many recent works have focused on the retinal chromophore which is the optical switch used in animal vision. Here, we study a shortened derivative of the chromophore, which exhibits a rich IM spectrum allowing for a detailed analysis of its isomerization pathways, and show that the longer the chromophore is, the lower the barrier energies for isomerization are.

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Influence of surface modification of Ti-SBA15 catalysts on the epoxidation mechanism for cyclohexene with aqueous hydrogen peroxide

The thermolytic molecular precursor method was used to introduce site-isolated Ti(IV) centers onto the surface of a mesoporous SBA15 support. The resulting surface Si-OH/Ti-OH sites of the Ti-SBA15 catalysts were modified with a series of (N,N-dimethylamino)trialkylsilanes, Me(2)N-SiMe(2)(R) (where R = Me, (n)Bu, or (n)Oc). Compared with the unmodified catalysts, the surface-modified catalysts are more active in the oxidation of cyclohexene with H(2)O(2) and exhibit a significantly higher selectivity (up to 58%) for cyclohexene oxide formation (vs allylic oxidation products). In situ Fourier transform infrared (FTIR) and diffuse reflectance UV visible (DRUV-vis) spectroscopies were used to probe this phenomenon, and it was determined that active sites with capped titanol centers, (SiO(surface))(3)Ti(OSiR(3)), likely undergo Ti-OOH formation upon addition of H(2)O(2) in a manner analogous to that for active sites of the type (SiO(surface))(3)TiOH. On the basis of the observation of similar Ti-OOH intermediates for both species, the electron-withdrawing effects on the Ti(IV) active site, resulting from the surface modification, are likely responsible for the observed increase in selectivity.     

Uncialamycin, a new enediyne antibiotic

[structure: see text] Laboratory cultures of an undescribed streptomycete obtained from the surface of a British Columbia lichen produce uncialamycin (1), a new enediyne antibiotic. The structure of uncialamycin (1) has been elucidated by analysis of spectroscopic data. Uncialamycin (1) exhibits potent in vitro antibacterial activity against gram-positive and gram-negative human pathogens, including Burkholderia cepacia, a major cause of morbidity and mortality in patients with cystic fibrosis.     

Preparation and structural studies on organotin(IV) complexes with flavonoids

Fourteen complexes of di-n-butyltin(IV)²⁺ cations with flavonoid glycosides (rutin, hesperidin, 2′,4′,3-trihydroxy-5′,4-dimetoxychalkone 4-rutinoside) and flavonoid aglycones (quercetin, morin, hesperitin and sorte flavones) were prepared. The composition of the complexes was determined by standard analytical methods. The results showed that complexes containing diorganotin(IV)²⁺ moiety and the ligand in 1∶1, 2∶1 or 3∶1 ratio are formed. The FTIR spectra were consistent with the presence of Sn-O (phenol or carbohydrate) vibration in the compounds. The structure of the complexes was measured by Mössbauer spectroscopy. Comparison of the experimental quadrupole splitting with those calculated on the basis of partial quadrupole splitting concept revealed that the complexes are of four types: with the central tin atoms surrounded by donor atoms in a purely trigonal-bipyramidal, octahedral+trigonal-bipyramidal, trigonal-bipyramidal+tetrahedral and octahedral+tetrahedral arrangement. This procedure also distinguished between the different structural isomers of both trigonal-bipyramidal and octahedral complexes. Conclusions could therefore be drawn on the factors determining which of the isomers are formed in the systems. The Mössbauer parameters obtained for organotin(IV)-flavonoid complexes were compared with those measured for organotin(IV)-carbohydrate complexes.