Synthesis, crystal-structure determination and magnetic properties of two new transition-metal carbodiimides: CoNCN and NiNCN

Synthesis, structure determination, and magnetic properties are reported for the metastable and crystal-chemically isotypic phases cobalt carbodiimide, CoNCN, and nickel carbodiimide, NiNCN, adopting the hexagonal system and space group P63/mmc (NiAs type) with interatomic distances of Co-N = 2.17 Angstrom and Ni-N = 2.12 Angstrom and an octahedral coordination of the transition-metal ions; the NCN(2-) units reveal the carbodiimide shape with two C=N double bonds. The low-susceptibility data go back to strong antiferromagnetic spin-spin coupling, similar to the behavior of the electronically related oxides CoO and NiO.     

A Bayesian approach to assess data from radionuclide activity analyses in environmental samples

A Bayesian statistical approach is introduced to assess experimental data from the analyses of radionuclide activity concentration in environmental samples (low activities). A theoretical model has been developed that allows the use of known prior information about the value of the measurand (activity), together with the experimental value determined through the measurement. The model has been applied to data of the Inter-laboratory Proficiency Test organised periodically among Spanish environmental radioactivity laboratories that are producing the radiochemical results for the Spanish radioactive monitoring network. A global improvement of laboratories performance is produced when this prior information is taken into account. The prior information used in this methodology is an interval within which the activity is known to be contained, but it could be extended to any other experimental quantity with a different type of prior information available.     

Time-resolved spectroscopy of silver nanocubes: observation and assignment of coherently excited vibrational modes

The response of single crystal, cubic silver particles to ultrafast laser-induced heating has been examined experimentally and theoretically. The transient absorption traces display clear modulations due to coherently excited vibrational modes. Nanocube samples with edge lengths smaller than 50 nm show a single modulation, whereas samples larger than 50 nm show two vibrational modes. The results are compared to finite element calculations, where the cubes are modeled as having cubic crystal symmetry with the principal axes parallel to the sides of the particle. The action of the laser pulse is treated in two ways, first, as creating a uniform initial strain. In this case the predominant mode excited is the breathing mode. The period of this mode is in reasonable agreement with the vibrational periods measured for the smaller cubes and with the higher frequency modulation observed for the larger cubes. A nonuniform initial strain is also considered, which could arise from nonuniform heating for particles larger than the optical skin depth of the metal. In this case the predominant mode excited is a nontotally symmetric mode. The calculated periods from this analysis are in reasonable agreement with the lower frequency modulations observed for the larger samples. The results from this study show that, to within the accuracy of these measurements, the elastic constants of cubic silver nanoparticles are the same as bulk silver.     

Dearomatizing anionic cyclization of N-alkyl-N-benzyl(dinaphthyl)phosphinamides. A facile route to gamma-(amino)dihydronaphthalenylphosphinic acids

The dearomatizing anionic cyclization of N-alkyl-N-benzyldi(n-naphthyl)phosphinamides (n = 1, 2) and subsequent trapping with a series of electrophiles (MeOH, MeI, CF3SO3Me, Me3O+BF4-, AllylBr, and PhCH2Br) have been accomplished. Optimized reaction conditions (base, temperature, reaction time) allow for synthesizing tetrahydro-1H-naphtho[1,2-c][1,2]-azaphosphole 1-oxides 13 and 18 and tetrahydro-1H-naphtho[2,1-c][1,2]azaphosphole 3-oxides 16 and 27-29 in high yield and diastereoselectivity. Appropriate selection of the base proved to be critical for promoting anionic cyclization of 2-naphthyl derivatives. The dearomatized heterocycles are transformed quantitatively into gamma-(N-alkylamino)phosphinic acids by acid hydrolysis of the P-N linkage. Bioactivity assays on five human tumor cell lines for one of these amino acids revealed growth inhibition factors (GI50) at a micromolar scale. Additionally, evidence for the feasibility of intermolecular nucleophilic dearomatization and sequential nucleophilic attack to both aromatic rings of dinaphthylphosphinamides have been obtained.     

Adsorption of the fusogenic peptide B18 onto solid surfaces: insights into the mechanism of peptide assembly

The adsorption and assembly of B18 peptide on various solid surfaces were studied by reflectometry techniques and atomic force microscopy. B18 is the minimal membrane binding and fusogenic motif of the sea urchin protein bindin, which mediates the fertilization process. Silicon substrates were modified to obtain hydrophilic charged surfaces (oxide layer and polyelectrolyte multilayers) and hydrophobic surfaces (octadecyltrichlorosilane). B18 does not adsorb on hydrophilic positively charged surfaces, which was attributed to electrostatic repulsion since the peptide is positively charged. In contrast, the peptide irreversibly adsorbs on negatively charged hydrophilic as well as on hydrophobic surfaces. B18 showed higher affinity for hydrophobic surfaces than for hydrophilic negatively charged surfaces, which must be due to the presence of hydrophobic side chains at both ends of the molecule. Atomic force microscopy provided the indication that lateral diffusion on the surface affects the adsorption process of B18 on hydrophobic surfaces. The adsorption of the peptide on negatively charged surfaces was characterized by the formation of globular clusters.     

19-epi-okadaic acid, a novel protein phosphatase inhibitor with enhanced selectivity

A new protein phosphatase inhibitor, 19-epi-okadaic acid, was isolated from the marine dinoflagellate Prorocentrum belizeanum. Its structure and conformation in solution has been determined, and important differences were found when compared with the lead compound okadaic acid. The new metabolite showed nanomolar activities, and its selectivity for PP2A versus PP1 surpasses that shown by okadaic acid 10-fold, making it one of the most selective inhibitors of this class.     

Metrizable extensions of dynamical systems from function algebras

Peters and Pennings introduced and studied in [9] and [11] a kind of extensions of dynamical systems induced by certain C^*-algebras, which they calltame extensions. In this paper we study the behaviour of metrizable tame extensions when some of the most important dynamical concepts related to the metric (such as sources, sinks, saddles, the shadowing property and distallity) are considered. We will confirm that these extensions can be troublesome in this context. We show, however, that sources and sinks are preserved under certain conditions. Entrata in Redazione il 24 febbraio 1997. Research partially supported by Generalitat Valenciana, (2223/94).     

Synthesis of novel 5-aryl-6-cyano-3H,8H-pyrido[2,3-d]pyrimidine-4,7-diones in the reaction of 6-amino-4-pyrimidinones with benzaldehyde and ethyl cyanoacetate

The title compounds 4 and 5 have been prepared in one-step reaction from 6-amino-4-pyrimidinones 1 , the corresponding 4-substituted benzaldehyde 2 and ethyl cyanoacetate 3 in very good yields. The structure of the final compounds was determined on the basis of nmr measurements, especially by ¹H, ¹H-, ¹H,¹³C COSY, and DEPT.     

Basic Sequences in the Dual of a Fréchet Space

In this paper we study some properties of basic sequences in the dual of a Fréechet space. As a consequence we obtain that if E is a Fréechet space with the property that for each closed subspace F of E and each bounded subset B of E/F there is a bounded subset A of E with φ(A) = B, where φ denotes the canonical surjection of E onto E/F, then one of the following conditions is at least satisfied: 1. E is a Banach space, 2. E is a Schwartz space, 3. E is the product of a Banach space by ω. Finally, we also obtain some results concerning totally reflexive spaces.     

Lipid-mimicking phosphorus-based glycosidase inactivators as pharmacological chaperones for the treatment of Gaucher's disease

Gaucher''s disease, the most prevalent lysosomal storage disorder, is caused by missense mutation of the GBA gene, ultimately resulting in deficient GCase activity, hence the excessive build-up of cellular glucosylceramide. Among different therapeutic strategies, pharmacological chaperoning of mutant GCase represents an attractive approach that relies on small organic molecules acting as protein stabilizers. Herein, we expand upon a new class of transient GCase inactivators based on a reactive 2-deoxy-2-fluoro-β-d-glucoside tethered to an array of lipid-mimicking phosphorus-based aglycones, which not only improve the selectivity and inactivation efficiency, but also the stability of these compounds in aqueous media. This hypothesis was further validated with kinetic and cellular studies confirming restoration of catalytic activity in Gaucher cells after treatment with these pharmacological chaperones.

Engineered 2-fluoroglucosides containing a phosphorus-based leaving group rapidly form a stable covalent intermediate with GCase, thus stabilising the enzyme during transit to the lysosome, where it is released on a clinically appropriate timescale.