Homophymine A, an anti-HIV cyclodepsipeptide from the sponge Homophymia sp

A new anti-HIV cyclodepsipeptide, homophymine A, was isolated from a New Caledonian collection of the marine sponge Homophymia sp. The structure of homophymine A was determined by interpretation of spectroscopic data, acid hydrolysis, and LC-MS analysis. Homophymine A contains 11 amino acid residues and an amide-linked 3-hydroxy-2,4,6-trimethyloctanoic acid moiety. Along with four D-, two L-, and one N-methyl amino acids, it also contains four unusual amino acid residues: (2S,3S,4R)-3,4-diMe-Gln, (2R,3R,4S)-4-amino-2,3-dihydroxy-1,7-heptandioic acid, L-ThrOMe, and (2R,3R,4R)-2-amino-3-hydroxy-4,5-dimethylhexanoic acid. In a cell-based XTT assay, homophymine A exhibited cytoprotective activity against HIV-1 infection with a IC50 of 75 nM.     

1H and 17O NMR relaxometric study in aqueous solution of Gd(III) complexes of EGTA-like derivatives bearing methylenephosphonic groups

The Gd(III) complexes of three new octadentate chelators, prepared by substitution of four, two, and one carboxylate groups of EGTA with phosphonate groups, have been investigated by 1H and 17O NMR relaxometric techniques in aqueous solutions. The analysis of the solvent proton relaxivity data as a function of pH, temperature, and magnetic field strength (nuclear magnetic relaxation dispersion (NMRD) profiles) in combination with the 17O transverse relaxation rate data at variable temperature allowed assessing the hydration state of the complexes, the occurrence of pH-dependent oligomerization processes for the tetraphosphonate derivative, the presence of a well-defined second sphere of hydration that markedly contributes to the relaxivity, and the values of the structural and dynamic relaxation parameters. In addition, in the case of the monophosphonate derivative the presence of a coordinated water molecule has allowed evaluation of the kinetic parameters of the exchange process, highly relevant for the possible use of this Gd(III) complex as an MRI probe. The rate of exchange of the water molecule, (298)k(ex) = 4.2 x 10(8)s(-1), is one of the highest measured so far for a nonacoordinate Gd(III) chelate and optimal for developing contrast-enhancing probes of high efficacy at high magnetic fields.     

Synthesis of Glycosylrifamycins,a new type of semisynthetic rifamycins

Glycosylrifamycins, a new type of semisynthetic rifamycin derivatives, can be easily obtained by reaction of 3-(2-aminoethylthio)rifamycin SV ( 2 ) with a glycosyl compound carrying a coupling group, such as isothicyanate or carboxy. We prepared O-acetylated and free glucopyranosyl and arabinopyranosyl derivatives of rifamycin S and SV (see 3–10 ). Additionally, derivatives with D -saccharo-1,4-lactone and with shikimic acid were obtained (see 11–15 ). Glycosylrifamycins show an interesting inhibitory power on Gram-positive bacteria (Table).     

MAPLE deposition of biomaterial multilayers

Double layers of polyethylene glycol (PEG) and 3-(3,4-dihydroxyphenyl)-2-methyl-l-alanine (m-DOPA) thin films were obtained by matrix assisted pulsed laser evaporation (MAPLE) technique, by depositing a first layer of m-DOPA on Si substrate and a second layer of PEG on top of it. The films were characterized by low angle X-ray diffraction (LAXRD), X-ray reflectivity (XRR), atomic force microscopy (AFM), and micro-Raman spectroscopy. From these analyses it resulted that PEG was deposited without any relevant damage both in terms of chemical structure and molecular weight. Furthermore, PEG chains were mostly in the extended conformation, although PEG micelles appeared.     

An entropy-based approach to automatic image segmentation of satellite images

An entropy-based image segmentation approach is introduced and applied to color images obtained from Google Earth. Segmentation refers to the process of partitioning a digital image in order to locate different objects and regions of interest. The application to satellite images paves the way to automated monitoring of ecological catastrophes, urban growth, agricultural activity, maritime pollution, climate changing and general surveillance. Regions representing aquatic, rural and urban areas are identified and the accuracy of the proposed segmentation methodology is evaluated. The comparison with gray level images revealed that the color information is fundamental to obtain an accurate segmentation.     

First order linear partial differential equations with discontinuous coefficients

Summary Si dà un teorema di esistenza e di unicità di soluzione generalizzata per il problema di Cauchy relativo all'equazione . Le ipotesi fatte sui coefficienti a_i(t, x) permettono discontinuità di tipo molto generale, purchè sia soddisfatta una certa «condizione di trasversalità» tra le caratteristiche dell'equazione e le discontinuità del campo di vettori che le definisce.