Configurational assignment of alpha-chiral carboxylic acids by complexation to dimeric Zn-porphyrin: host-guest structure,chiral recognition and circular dichroism

A circular dichroic (CD) excition chirality method based on host-guest chiral recognition has been developed to determine the absolute configuration of carboxylic acids with an alpha-stereogenic center; an amide C = O-->Zn coordination, identified by infrared spectroscopy and computations, is involved in this complexation.     

Absolute configurational assignments of secondary amines by CD-sensitive dimeric zinc porphyrin host

A general chiroptical protocol for determination of absolute configuration of secondary amines including acyclic and cyclic aliphatic amines, aromatic amines, amino acids, and amino alcohols is described. The chiral substrate is linked to the achiral carrier moiety (3-N-Boc-amino-propyl-N-Boc-amino)acetic acid 1 (BocHNCH(2)CH(2)CH(2)BocNCH(2)COOH), which after deprotection, yields a bidentate conjugate, capable of forming a 1:1 host/guest complex with dimeric zinc porphyrin host 2. As in the cases of primary amines and secondary alcohols reported earlier, the complexation of secondary amine conjugates to porphyrin tweezer host 2 represents a stereodifferentiating process, where the large (L) group at the stereogenic center (assigned on the basis of conformational energies A value) protrudes from the porphyrin binding pocket. This leads to formation of host/guest complexes with a preferred porphyrin helicity that exhibit intense exciton split CD spectra. It was found that the chiral sense of porphyrin twist is clearly controlled by the stereogenic center despite the Z/E conformational complexity around the tertiary amide bond of secondary amine conjugates that has greatly hampered previous configurational assignments. Thus, in cases where there is no ambiguity regarding the relative steric size of substituents, the observed CD couplet can be applied for straightforward assignment of absolute configurations. In addition, to extend the application to more difficult cases a molecular mechanics calculation approach using the Merck Molecular Force Field (MMFFs) was developed; this provides conformational information of host/guest complexes and leads to prediction of preferred porphyrin helicity independent of conformational A values. This chiroptical protocol in combination with molecular modeling represents a general method for configurational assignments of secondary amines.     

PMMA Based Nanocomposites Filled with Modified CaCO3 Nanoparticles

PMMA based nanocomposites filled with calcium carbonate nanoparticles (CaCO₃) have been prepared by in situ polymerization approach. In order to improve inorganic nanofillers/polymer compatibility, PBA chains have been grafted onto CaCO₃ nanoparticle surface. Morphological analysis performed on nanocomposite fractured surfaces has revealed that the CaCO₃ modification induces homogeneous and fine dispersion of nanoparticles into PMMA as well as strong interfacial adhesion between the two phases. Mechanical tests have shown that both unmodified and modified CaCO₃ are responsible for an increase of the Young's Modulus, whereas only PBA-grafted nanoparticles allow to keep unchanged impact strength, strongly deteriorated by adding unmodified CaCO₃. Finally, the presence of CaCO₃ nanoparticles significantly improves the abrasion resistance of PMMA also modifying its wear mechanism.     

Erratum to “Heavy neutral gauge bosons at the LHC in an extended MSSM” [Nucl. Phys. B 866 (3) (2013) 293–336]

We correct a Feynman diagram presented in the paper ‘Heavy neutral gauge bosons at the LHC in an extended MSSM’, published in Nuclear Physics B 866 (2013) 293.     

Insights About CHAPS Aggregation Obtained by Spin Label EPR Spectroscopy

CHAPS is a zwitterionic surfactant derivative of bile salts, widely used in membrane protein isolation. While some studies regarding CHAPS self-aggregation suggest continuous increase in micelle size at increasing CHAPS concentration, other works point to the existence of two definite micelle types. In this work, stearic acid spin labels (5, 12, or 16-SASL) were added to CHAPS solutions to obtain information about the micellar structure using electron paramagnetic resonance spectroscopy. The spectra of 12-SASL were processed using Principal Factor Analysis, and at all concentrations they could be reproduced as linear combinations of only three fundamental spectra, the first one corresponding to free 12-SASL in aqueous solution. This fact suggests only two hydrophobic environments that host 12-SASL, assigned to primary and secondary CHAPS micelles. The relative populations of the label in each environment were obtained as a function of CHAPS concentration. Our results suggest barrel-shaped primary micelles with a minimum mean radius of 1.46 nm, and a critical micelle concentration cmc_I = 4 mM. Secondary micelles are formed by aggregation of primary ones, with cmc_II = 10 mM. They have several elongated hydrophobic pockets, with similar dimensions for all aggregate sizes. Our results contribute to the understanding of the mechanism of interaction of chain amphiphiles with CHAPS micelles.     

Self detachment of free-standing porous silicon membranes in moderately doped n-type silicon

In this article we describe a reliable etching method to fabricate porous silicon free-standing membranes (FSMs) based on a self detachment of the porous layer in moderately doped n-type silicon substrates. We found that stable growth of smooth and straight pores is restricted to a narrow range of etching conditions and, unlike p-type substrates, the lift-off of the membrane is a self-limited process that does not require a large burst of current. The detachment of the porous membrane is independent of the structure of the already porosified layer, meaning that the average pore diameter can be tuned from nano to macro size within the same membrane. We also demonstrate that, despite their limited thickness, FSMs are quite robust and can sustained further processing. Thus, the etching receipt we are proposing here extends the range of sensors and filters that can be fabricated using porous silicon technology.     

Noether–Lefschetz theory with base locus

Let \(Z\) be a closed subscheme of a smooth complex projective variety \(Y\subseteq \mathbb {P}^N\) , with \(\dim \,Y=2r+1\ge 3\) . We describe the intermediate Néron–Severi group (i.e. the image of the cycle map \(A_r(X)\rightarrow H_{2r}(X;\mathbb {Z})\) ) of a general smooth hypersurface \(X\subset Y\) of sufficiently large degree containing \(Z\) .     

Simultaneous determination of sixteen underivatized biogenic amines in human urine by HPLC-MS/MS

The broad group of biogenic amines includes polyamines and catecholamines, whose presence in human tissues and biological fluids can give important diagnostic information and act as marker of many pathologies. In particular, polyamines are involved in cancer cell growth while catecholamines act as neurotransmitters and hormones. Their simultaneous determination in biological tissues and fluids is therefore an important task. A high-performance liquid chromatography tandem mass spectrometry method is presented here for the simultaneous determination in urine of 16 biogenic amines: adrenaline (epinephrine), agmatine, cadaverine, dopamine, histamine, 3-methoxytyramine, noradrenaline (norepinephrine), norephedrine, octopamine, 2-phenylethylamine, putrescine, serotonin, spermidine, spermine, tryptamine, and tyramine. The method does not require any derivatization step. To guarantee the maximum of sensitivity, the mass spectrometer works in selected reaction monitoring mode, monitoring for each analyte the two most intensive transitions. Method validation includes the evaluation of limits of detection (that range from 0.3 to 6.6 μg L^?1), limits of quantitation (that range from 1.0 to 21.9 μg L^?1), linearity range (three orders of magnitude), recovery, intra- and inter-day precision on both concentration, and retention time. Recovery (R) is shown not to depend on the analyte concentration: the average R percent ranges from 72.9 to 100.0 %. Particular attention is devoted to the matrix effect and the correlated phenomena of ion enhancement or suppression in mass spectrometry detection.

Breath Analysis: Comparison among Methodological Approaches for Breath Sampling

Despite promising results obtained in the early diagnosis of several pathologies, breath analysis still remains an unused technique in clinical practice due to the lack of breath sampling standardized procedures able to guarantee a good repeatability and comparability of results. The most diffuse on an international scale breath sampling method uses polymeric bags, but, recently, devices named Mistral and ReCIVA, able to directly concentrate volatile organic compounds (VOCs) onto sorbent tubes, have been developed and launched on the market. In order to explore performances of these new automatic devices with respect to sampling in the polymeric bag and to study the differences in VOCs profile when whole or alveolar breath is collected and when pulmonary wash out with clean air is done, a tailored experimental design was developed. Three different breath sampling approaches were compared: (a) whole breath sampling by means of Tedlar bags, (b) the end-tidal breath collection using the Mistral sampler, and (c) the simultaneous collection of the whole and alveolar breath by using the ReCIVA. The obtained results showed that alveolar fraction of breath was relatively less affected by ambient air (AA) contaminants (p-values equal to 0.04 for Mistral and 0.002 for ReCIVA Low) with respect to whole breath (p-values equal to 0.97 for ReCIVA Whole). Compared to Tedlar bags, coherent results were obtained by using Mistral while lower VOCs levels were detected for samples (both breath and AA) collected by ReCIVA, likely due to uncorrected and fluctuating flow rates applied by this device. Finally, the analysis of all data also including data obtained by explorative analysis of the unique lung cancer (LC) breath sample showed that a clean air supply might determine a further confounding factor in breath analysis considering that lung wash-out is species-dependent.