Characterization of Costa Rican potsherds by neutron activation analysis

Neutron activation analysis has been applied to evaluate the concentrations of 24 elements in archaeological potsherds and 5 clay samples with a view of establishing the average composition profiles. Due to their stability in clays, 14 elements were selected as indicators. A statistical treatment of the overall analytical data, including principal component analysis, was applied in an attempt to determine correlations between the concentrations of the elements in the samples, possibly in relation with their ages and/or their places of collection.     

Irregularity detection from noisy data in one and two dimensions

In this work we consider the problem of detecting the irregularities of univariate functions from noisy data and its extension to bivariate functions which present lines of points of irregularity. This revised version was published online in August 2006 with corrections to the Cover Date.     

Glycopeptide and Oligosaccharide Libraries

Despite the burgeoning interest in the various biological functions and consequent therapeutic potential of the vast number of oligosaccharides found in nature on glycoproteins and cell surfaces, the development of combinatorial carbohydrate chemistry has not progressed as rapidly as expected. The reason for this imbalance is rooted in the difficulty of oligosaccharide assembly and analysis that renders synthesis a rather cumbersome endeavor. Parallel approaches that generate series of analogous compounds rather than real libraries have therefore typically been used. Since generally low affinity is obtained for interactions between carbohydrate receptors and modified oligosaccharides designed as mimetics of natural carbohydrate ligands, glycopeptides have been explored as alternative mimics. Glycopeptides have been proven in many cases to be superior ligands with higher affinity for a receptor than the natural carbohydrate ligand. High-affinity glycopeptide ligands have been found for several types of receptors including the E-, P-, and L-selectins, toxins, glycohydrolases, bacterial adhesins, and the mannose-6-phosphate receptor. Furthermore, the assembly of glycopeptides is considerably more facile than that of oligosaccharides and the process can be adapted to combinatorial synthesis with either glycosylated amino acid building blocks or by direct glycosylation of peptide templates. The application of the split and combine approach using ladder synthesis has allowed the generation of very large numbers of compounds which could be analyzed and screened for binding of receptors on solid phase. This powerful technique can be used generally for the identification and analysis of the complex interaction between the carbohydrates and their receptors.     

Assessment of semi-automated catecholamine assay by HPLC: Choice of reverse phase C18 or cation-exchange columns

Summary HPLC with electrochemical detection is useful in the assay of catecholamines in biological samples. Two types of chromatographic column are currently employed by most investigators: reverse phase C-18 (RPC-18) or strong cation-exchange (SCX) columns. Our aim was to evaluate the specificity, sensitivity and reproducibility of plasma and urinary catecholamine assay by these two columns. Our study indicates that both columns give very good performance for clinical purposes but sensitivity, precision at low concentration and specificity seem to be better with ion-exchange columns which are therefore preferred at the present time.     

Add a Pinch of Tetrel: The Transformation of a Centrosymmetric Metal into a Nonsymmorphic and Chiral Semiconductor

Centrosymmetric skutterudite RhP₃ was converted to a nonsymmorphic and chiral compound RhSi_0.3P_2.7 (space group P2₁2₁2₁) by means of partial replacement of Si for P. The structure, determined by a combination of X-ray crystallography and solid state ³¹P NMR, exhibits branched polyanionic P/Si chains that are unique among metal phosphides. A driving force to stabilize the locally noncentrosymmetric cis-RhSi₂P₄ and fac-RhSi₃P₃ fragments is π-electron back-donation between the Rh t_2g-type orbitals and the unoccupied antibonding Si/P orbitals, which is more effective for Si than for P. In situ studies and total energy calculations revealed the metastable nature of RhSi_0.3P_2.7. Electronic structure calculations predicted centrosymmetric cubic RhP₃ to be metallic which was confirmed by transport properties measurements. In contrast, the electronic structure for chiral orthorhombic RhSi_0.3P_2.7 contained a bandgap, and this compound was shown to be a narrow gap semiconductor.     

Organic pollution in a Ramsar site (Piallassa Baiona, northern Adriatic Sea)

A core collected in the Piallassa Baiona lagoon, a salt-marsh area already studied for Hg contamination related to nearby industrial sites, was analysed for organic micropollutants. Surface sediments show high concentrations of total PCBs (1148 ng g-1), PCDD/Fs (64 ng g-1) and PAHs (4801 ng g-1). According to a sedimentation rate of 0.4 cm y-1, the high increases in total PAH, PCB and PCDD/F concentrations began in the 1960s and peaked in the 1970s, in parallel with the highest Hg concentrations. Instead, the recent contamination, which primarily involves PCBs and PCDD/Fs, has been observed to be unrelated to Hg concentrations. Organic micropollutant concentrations in the sample core were compared with the sediment quality criteria provided by international guidelines, and revealed high toxic potential. This heavy contamination was also confirmed by comparison with similar environments, particularly the Lagoon of Venice. Further investigations are needed to understand better the sources of the recent contamination and to explain the different transfer pathways involved during sedimentation of the "old" material, dumped 20-30 years ago.     

Stability studies with a high-performance liquid chromatographic method for the determination of a new anthracycline analogue, 3'-deamino-3'-[2-(S)-methoxy-4-morpholino)doxorubicin (FCE 23762), in the final drug formulation.

A high-performance liquid chromatographic method was studied to optimize the separation of FCE 23762, a new antitumour agent, from both synthetic impurities and degradation products having very similar molecular structures. The main problems faced in the analytical method development using the most common reversed-phase columns available arose from the presence of analytical peaks with poor symmetry, a long analysis time and the separation between FCE 23762 and its R-isomer, which was often unsuitable for the correct determination of the drug substance. The use of a new stationary phase, Zorbax Rx-C8, together with a suitable mobile phase resulted in a good separation between the diastereomers, with satisfactory peak symmetry and run time. The method permitted the study of the stability of the drug substance in formulations for clinical trials.     

Estimation of the effective and functional human cortical connectivity with structural equation modeling and directed transfer function applied to high-resolution EEG

Different brain imaging devices are presently available to provide images of the human functional cortical activity, based on hemodynamic, metabolic or electromagnetic measurements. However, static images of brain regions activated during particular tasks do not convey the information of how these regions are interconnected. The concept of brain connectivity plays a central role in the neuroscience, and different definitions of connectivity, functional and effective, have been adopted in literature. While the functional connectivity is defined as the temporal coherence among the activities of different brain areas, the effective connectivity is defined as the simplest brain circuit that would produce the same temporal relationship as observed experimentally among cortical sites. The structural equation modeling (SEM) is the most used method to estimate effective connectivity in neuroscience, and its typical application is on data related to brain hemodynamic behavior tested by functional magnetic resonance imaging (fMRI), whereas the directed transfer function (DTF) method is a frequency-domain approach based on both a multivariate autoregressive (MVAR) modeling of time series and on the concept of Granger causality.

This study presents advanced methods for the estimation of cortical connectivity by applying SEM and DTF on the cortical signals estimated from high-resolution electroencephalography (EEG) recordings, since these signals exhibit a higher spatial resolution than conventional cerebral electromagnetic measures. To estimate correctly the cortical signals, we used a subject's multicompartment head model (scalp, skull, dura mater, cortex) constructed from individual MRI, a distributed source model and a regularized linear inverse source estimates of cortical current density. Before the application of SEM and DTF methodology to the cortical waveforms estimated from high-resolution EEG data, we performed a simulation study, in which different main factors (signal-to-noise ratio, SNR, and simulated cortical activity duration, LENGTH) were systematically manipulated in the generation of test signals, and the errors in the estimated connectivity were evaluated by the analysis of variance (ANOVA). The statistical analysis returned that during simulations, both SEM and DTF estimators were able to correctly estimate the imposed connectivity patterns under reasonable operative conditions, that is, when data exhibit an SNR of at least 3 and a LENGTH of at least 75 s of nonconsecutive EEG recordings at 64 Hz of sampling rate.

Hence, effective and functional connectivity patterns of cortical activity can be effectively estimated under general conditions met in any practical EEG recordings, by combining high-resolution EEG techniques and linear inverse estimation with SEM or DTF methods. We conclude that the estimation of cortical connectivity can be performed not only with hemodynamic measurements, but also with EEG signals treated with advanced computational techniques.     

CGC-MS determination of mixtures of long chain aliphatic esters

A method is described for the determination of the acid and alcohol moieties in long chain wax esters. The co-eluting esters are differentiated by means of CGC-MS operating in the ion monitoring mode. The technique allows to detect ester components present in very low amounts in plant surface waxes.