Cationic Porphyrin–Anionic Surfactant Mixtures for the Promotion of Self‐Organized 1:4 Ion Pairs in Water with Strong Aggregation Properties

We performed a systematic study on the spectroscopic and aggregation properties of stoichiometric mixtures (1:4) of the tetracationic meso‐tetrakis(4‐N‐methylpyridinium)porphyrin (H₂TMPyP) and three sodium alkylsulfate surfactants (tetradecyl, hexadecyl, and octadecylsulfate) in an aqueous solution. The objective was to build a supramolecular aggregate, which would favor the internalization of tetracationic porphyrins in cells without chemical modification of the structure of the porphyrin. We show that stoichiometric H₂TMPyP/alkylsulfate (1:4) mixtures lead to the formation of large hollow spherical aggregates (60–160 nm). The TEM images show that the membrane of these aggregates are composed of smaller aggregates, which are probably rod‐like micelles. These rod‐like micelles have a hydrophobic core composed of the alkyl chains of the alkylsulfate surfactant, whereas the charged surface corresponds to the tetracationic porphyrins.     

Spatial and vertical distributions of natural and anthropogenic radionuclides and cesium fractionation in sediments of the Var river and its tributaries (southeast France)

This paper reports results on the natural and anthropogenic radionuclides activity concentrations in sediments of the Var river and its tributaries. Natural (²³⁸U, ²³²Th and ⁴⁰K) and artificial (¹³⁷Cs) radionuclides activities were measured using high purity germanium detector. Measured activity concentrations differ widely; they depend on the pertinent environmental situation such as the presence of dams, and sediments type. Other factors controlling the distribution of the studied radioisotopes have been discussed. A sequential extraction method consisting of six operationally-defined fractions has been used for determining the geochemical partitioning of anthropogenic radionuclide ¹³⁷Cs in a 405–410 cm deep sediments collected in the lower valley of the Var river. This method corresponds to a modification of the three-stage sequential extraction procedure proposed by the Commission of the European Communities Bureau of Reference (BCR, now Standards, Measurements and Testing Program). Two steps with weak reagents, (fraction A: water; fraction B: nitric acid 0.001 M), were added before the first step of BCR (carbonate fraction) in order to better detect anthropogenic components. A total acid digestion of solid residues by microwave assisted was also added. The 6-steps extraction method was tested and validated by certified reference materials. ¹³⁷Cs was found mostly in the hydrosoluble fraction (20–24 %), oxide and hydroxide fraction (22–25 %) and in the residue (51–58 %), while ¹³³Cs was mostly found in the residual fraction (>97 %).     

Semisynthesis of (+)- and (−)-goniomitine from (−)- and (+)-vincadifformine

The first biomimetic semisynthesis of goniomitine has been accomplished in nine steps with 11% overall yield starting from vincadifformine. Natural (?)- and unnatural (+)-goniomitine were prepared from (+)- and (?)-vincadifformine, respectively. The evaluation of the antiproliferative effect of both enantiomers proved unnatural (+)-goniomitine to be more potent, but this enantiomer as well as some close derivatives displayed a moderate activity only.     

Imputation of Mixed Data With Multilevel Singular Value Decomposition

Statistical analysis of large datasets offers new opportunities to better understand underlying processes. Yet, data accumulation often implies relaxing acquisition procedures or compounding diverse sources. As a consequence, datasets often contain mixed data, that is, both quantitative and qualitative, and many missing values. Furthermore, aggregated data present a natural multilevel structure, where individuals or samples are nested within different sites, such as countries or hospitals. Imputation of multilevel data has therefore drawn some attention recently, but current solutions are not designed to handle mixed data, and suffer from important drawbacks, such as their computational cost. In this article, we propose a single imputation method for multilevel data, which can be used to complete either quantitative, categorical, or mixed data. The method is based on multilevel singular value decomposition (SVD), which consists in decomposing the variability of the data into two components, the between and within groups variability, and performing an SVD on both parts. We show on a simulation study that in comparison to competitors, the method has the advantages of handling datasets of various size, and being computationally faster. Furthermore, it is the first so far to handle mixed data. We apply the method to impute a medical dataset resulting from the aggregation of several hospitals datasets. This application falls in the framework of a larger project on Trauma patients. To overcome obstacles associated to the aggregation of medical data, we turn to distributed computation. The method is implemented in the R package missMDA. Supplementary materials for this article are available online.     

Quantitative comparison between a multiecho sequence and a single-echo sequence for susceptibility-weighted phase imaging

The aim of this study was to investigate the benefits arising from the use of a multiecho sequence for susceptibility-weighted phase imaging using a quantitative comparison with a standard single-echo acquisition. Four healthy adult volunteers were imaged on a clinical 3-T system using a protocol comprising two different three-dimensional susceptibility-weighted gradient-echo sequences: a standard single-echo sequence and a multiecho sequence. Both sequences were repeated twice in order to evaluate the local noise contribution by a subtraction of the two acquisitions. For the multiecho sequence, the phase information from each echo was independently unwrapped, and the background field contribution was removed using either homodyne filtering or the projection onto dipole fields method. The phase information from all echoes was then combined using a weighted linear regression. R2 maps were also calculated from the multiecho acquisitions. The noise standard deviation in the reconstructed phase images was evaluated for six manually segmented regions of interest (frontal white matter, posterior white matter, globus pallidus, putamen, caudate nucleus and lateral ventricle). The use of the multiecho sequence for susceptibility-weighted phase imaging led to a reduction of the noise standard deviation for all subjects and all regions of interest investigated in comparison to the reference single-echo acquisition. On average, the noise reduction ranged from 18.4% for the globus pallidus to 47.9% for the lateral ventricle. In addition, the amount of noise reduction was found to be strongly inversely correlated to the estimated R2 value (R=-0.92). In conclusion, the use of a multiecho sequence is an effective way to decrease the noise contribution in susceptibility-weighted phase images, while preserving both contrast and acquisition time. The proposed approach additionally permits the calculation of R2 maps.     

Radical deamination reactions of relevance to aminoglycoside chemistry

Reduction of tert.-, sec.- and prim.- isonitriles with tributylstanne affords in good yields, but at progressively higher temperatures, the corresponding hydrocarbons. Sec.-thio-cyanates and selenocyanates are also smoothly reduced but $\text{via}$ the isonitriles. All reactions are radical in character.