A density functional study of the SERS spectra of pyridine adsorbed on silver clusters

The effect of binding pyridine to silver clusters has been studied by density functional calculations by adopting a hybrid functional. The calculations allow proposing an explanation for the different SERS spectra of the ligand observed on Ag colloids in the presence and in the absence of coadsorbed chloride anions. In the latter case, a better agreement is obtained modeling the system by adsorption of pyridine on a surface cluster.     

Calorimetric Study of the Aggregation of Lithium Perfluorohexanoate on Poly(ethyleneglycol) Oligomers in Water

The interaction of lithium perfluorohexanoate (LiPFHex) with poly(ethylene glycol) (PEG) of different molecular weights (600 Da≤ MW≤20000 Da) was investigated in aqueous solution at 25.00 °C by isothermal titration calorimetry (ITC). The interaction with one of the PEG polymers (MW=8000 Da) was also followed at the same temperature by viscosity and conductivity measurements. The aggregation pattern of this surfactant on the PEG polymeric chain was very similar to that exhibited by the homologous salts of perfluoroheptanoate, perfluorooctanoate and perfluorononanoate ions. The interaction enthalpies with PEG of this class of surfactants are always endothermic and decrease steeply with the decreasing length of the fluorocarbon chain. Experimental data from calorimetry, viscosity and conductivity consistently indicate a very small tendency of PEG polymers to wrap around the small LiPFHex micellar aggregates. The PFHex ion appears to be the shortest member of the series able to interact with a polyoxyethylenic chain. The same CF₂ contribution to the Gibbs energy of micellization or aggregation on the polymers was found within the series, indicating a common hydrophobic driving force for the two processes.     

Stereocontrolled Synthesis of Unnatural Tetrapeptides Containing L‐Valine Units. Part 3

The stereoselective synthesis of the new nonproteinogenic branched tetrapeptides 9a – 9d and 15a , b , containing two L ‐valine units and unnatural α‐amino acids, was accomplished starting from the chiral synthon 1a , a monolactim ether easily obtained from L ‐valine.     

Stereoselective synthesis of new vicinal diaminoalkyl naphthols by three component Mannich type reaction of α,β-unsaturated aldehydes

The application of the aromatic Mannich reaction to α,β-unsaturated aldehydes, affords a series of new diaminoalkyl naphthols, by a convenient solventless reaction, starting from inexpensive and easily available starting materials. The absolute configurations of the products obtained are attributed on the basis of the coupling constant values of ¹H NMR spectra, joined with the conformational analysis of the molecules by molecular modelling. A mechanistic hypothesis is proposed, which involves an imino–amino intermediate.     

The source of differences in population distributions

This note shows that when the distribution of a variable in different populations is affected by two or more factors, differences in population distributions may be due exclusively to differences in the distribution of one factor only.     

Epoxy-nanocomposites containing exfoliated zirconium phosphate: Preparation via cationic photopolymerisation and physicochemical characterisation

Gels of exfoliated α-zirconium phosphate in 3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexane carboxylate (hereafter BCDE) were polymerised by a UV-induced process and the resulting nanocomposites were characterised by TEM, X-ray diffraction, thermogravimetric analysis and dynamic-mechanical thermal analysis. Real-time FT-IR spectroscopy was used to investigate the photopolymerisation kinetics. The polymerisation rate of the gels is faster than that of neat BCDE, especially when the filler is functionalised with aminoalcohols (HO(CH₂)_nNH₂, with n = 3, 4, 5). The composites exhibit lower T_g values in comparison with neat polymerised BCDE. Because of the barrier effect towards oxygen diffusion due to the high aspect ratio of the filler particles, all composites also exhibit enhanced thermal stability.     

DNA biosensors for the detection of aflatoxin producing <Emphasis Type="Italic">Aspergillus flavus</Emphasis> and <Emphasis Type="Italic">A. parasiticus</Emphasis>

Abstract  In this work, we report on the development of a DNA-based piezoelectric biosensor specific for the detection of an amplicon of the aflD gene of Aspergillus flavus and A. parasiticus. Expression of this gene is consistently correlated with a strain’s ability to produce aflatoxins that are considered very potent liver carcinogens in various animal species and humans. The DNA biosensor has been characterized with synthetic oligonucleotides and amplicons. Moreover, it has been applied to the analysis of real samples consisting of amplicons of DNA extracted from flours and feed contaminated with A. flavus and A. parasiticus. Graphical Abstract        

Bifurcated hydrogen bond in lithium nitrate trihydrate probed by ab initio molecular dynamics

The hydrogen-bond dynamics of lithium nitrate trihydrate has been studied by a combined approach based on ab initio molecular dynamics simulations and wavelet analysis. The simultaneous bifurcated interaction between one hydrogen atom of water molecules and two oxygen atoms of nitrate ions is the pivotal feature of the crystal structure: this bifurcated interaction has deep effects on the O-H stretching region of the vibrational spectrum. The structural, dynamic, spectroscopic, and electronic properties of the bifurcated hydrogen bond have been investigated computationally, elucidating at the molecular level the differences with weak and strong hydrogen bonds present in the crystal. These studies corroborate the very recent IR experiments performed on the lithium nitrate trihydrate crystal, offering new perspectives to interpreting the vibrational spectra. In fact, this approach allows obtaining two-dimensional plots, which summarize the essential features of both the hydrogen-bond network and IR spectra, resulting in a peculiar "signature" of the bifurcated interaction.     

Fuzzy logic-based procedures for GMO analysis

Key to sound validation studies is the formalization and harmonization of procedures for design of experiment and interpretation of results. International guidelines (ISO 5725, ENGL) are available for the validation of GMO detection methods, and ad-hoc validation statistics (e.g. per cent bias, repeatability and reproducibility) are used for in-house and inter-laboratory testing and decision-making. Acceptability criteria have been set but not every situation can be covered by a preset rule; the interpretation of results in validation largely depends on expert judgement being a matter of professional judgment and expertise. Fuzzy logic-based techniques may be used to summarize the information obtained by independent validation statistics and are helpful in such respect. A comprehensive indicator of method performance permits direct comparison between methods and facilitates the evaluation of multiple, yet contradictory statistics. The European Union Reference Laboratory for GM Food and Feed has already proposed the fuzzy principle in the context of method validation. Other studies have also proved its applicability in other areas of GMO analysis, but the application has been limited hitherto. In this article, we review the fuzzy logic principle and its potential to support the continuous progress of GMO science and routine laboratory analyses.