Properties and examples of FCR-algebras

An algebra A over a field k is FCR if every finite dimensional representation of A is completely reducible and the intersection of the kernels of these representations is zero. We give a useful characterization of FCR-algebras and apply this to C ^*-algebras and to localizations. Moreover, we show that “small” products and sums of FCR-algebras are again FCR. Received: 25 October 2000     

Neural expression and post-transcriptional dosage compensation of the steroid metabolic enzyme 17β-HSD type 4

Background  

Steroids affect many tissues, including the brain. In the zebra finch, the estrogenic steroid estradiol (E₂) is especially effective at promoting growth of the neural circuit specialized for song. In this species, only the males sing and they have a much larger and more interconnected song circuit than females. Thus, it was surprising that the gene for 17β-hydroxysteroid dehydrogenase type 4 (HSD17B4), an enzyme that converts E₂ to a less potent estrogen, had been mapped to the Z sex chromosome. As a consequence, it was likely that HSD17B4 was differentially expressed in males (ZZ) and females (ZW) because dosage compensation of Z chromosome genes is incomplete in birds. If a higher abundance of HSD17B4 mRNA in males than females was translated into functional enzyme in the brain, then contrary to expectation, males could produce less E₂ in their brains than females.     

Nanostructure of silver metal produced photocatalytically in TiO2 films and the mechanism of the resulting photochromic behavior

The optical activity of composite films created by the photocatalytic reduction of silver or gold ions in TiO(2) upon irradiation by UV light has up to now been discussed in terms of the formation and light-induced destruction of distinct nanoparticles molded inside the porous nanocrystalline film. We present results from classical light scattering calculations and a logical analysis of experimental observations to add detail to the mechanism. As opposed to large, solid metal nanoparticles, coatings and small particles in heterogeneous external dielectric environments account for observations such as the broad optical spectrum and multiwavelength photochromic responses. For some steps of the photochromic process, we propose that visible light permits an equilibrium promoting the growth of small metal features or suspended particles. We use a new expression for the restricted path length in our size-dependent broadening corrections of metal shells and discuss this briefly. We conclude by discussing the consequence of plasmon absorption in the proximity of the electronically active TiO(2) surrounding matrix, leading to mass transfer and shape change of the metal and photochromic properties of the film.     

Dendritic Macromolecules as Inhibitors to Protein-Protein Binding

Summary: Our initial studies into protein binding using a series of dendrimers as size selective inhibitors have been described. Two different proteins, cytochromo-c and chymotrypsin have been selected for these binding experiments.     

On the Spectra of Left-Definite Operators

If A is a self-adjoint operator that is bounded below in a Hilbert space H, Littlejohn and Wellman (J Diff Equ 181(2):280–339, 2002) showed that, for each r > 0, there exists a unique Hilbert space H _r and a unique self-adjoint operator A _r in H _r satisfying certain conditions dependent on H and A. The space H _r and the operator A _r are called, respectively, the rth left-definite space and rth left-definite operator associated with (H, A). In this paper, we show that the operators A, A _r , and A _s (r, s > 0) are isometrically isomorphically equivalent and that the spaces H, H _r , and H _s (r, s > 0) are isometrically isomorphic. These results are then used to reproduce the left-definite spaces and left-definite operators. Furthermore, we will see that our new results imply that the spectra of A and A _r are equal, giving us another proof of this phenomenon that was first established in Littlejohn and Wellman (J Diff Equ 181(2):280–339, 2002).     

Directed-Backbone Dissociation Following Bond-Specific Carbon-Sulfur UVPD at 213 nm

Ultraviolet photodissociation or UVPD is an increasingly popular option for tandem-mass spectrometry experiments. UVPD can be carried out at many wavelengths, and it is important to understand how the results will be impacted by this choice. Here, we explore the utility of 213 nm photons for initiating bond-selective fragmentation. It is found that bonds previously determined to be labile at 266 nm, including carbon-iodine and sulfur-sulfur bonds, can also be cleaved with high selectivity at 213 nm. In addition, many carbon-sulfur bonds that are not subject to direct dissociation at 266 nm can be selectively fragmented at 213 nm. This capability can be used to site-specifically create alaninyl radicals that direct backbone dissociation at the radical site, creating diagnostic d-ions. Furthermore, the additional carbon-sulfur bond fragmentation capability leads to signature triplets for fragmentation of disulfide bonds. Absorption of amide bonds can enhance dissociation of nearby labile carbon-sulfur bonds and can be used for stochastic backbone fragmentation typical of UVPD experiments at shorter wavelengths. Several potential applications of the bond-selective fragmentation chemistry observed at 213 nm are discussed.

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