High stability silver nanoparticles–graphene/poly(ionic liquid)-based chemoresistive sensors for volatile organic compounds’ detection

Hybrids of silver nanoparticle-decorated reduced graphene oxide (Ag-RGO) have been prepared with the use of poly(ionic liquid) (PIL) as a versatile capping agent to develop volatile organic compound (VOC) sensors. The hybrid materials of Ag-RGO/PIL were assembled into three-dimensional-laminated nanostructures, where spherical Ag nanoparticles with diameters between 50 and 300 nm were homogeneously distributed on the graphene sheets and interspaced between them. Ag-RGO/PIL sensors were fabricated by spray layer-by-layer technique and used to detect a set of polar (methanol, ethanol, methyl acetate, acetone and water) and non-polar (chloroform, dichlorobenzene, toluene and styrene) organic vapours. Much higher sensitivity and discriminability were obtained for polar vapours although non-polar ones could also be detected. In comparison with either simple reduced graphene oxide or carbon nanotubes (CNT) functionalised by PIL, the hybrid Ag-RGO/PIL-based sensors showed superior performances in terms of sensitivity, selectivity, stability and high reliability. For example, a signal-to-noise ratio up to 168 was obtained for 1 ppm of methanol and signals drift between two experiments spaced out in the time of 3 months was less than 3 %. It is expected that by extrapolation, a limit of detection at the parts per billion level can be reached. These results are promising to design e-noses based on high stability chemoresistive sensors for emerging applications such as anticipated diagnostic of food degradation or diseases by the analysis of VOC, some of them being in this case considered as biomarkers.     

Influence of saccharide size on the cellular immune response to glycopeptides

Glycopeptides that bind to MHC molecules on antigen presenting cells may elicit carbohydrate selective T cells. In order to investigate how the cellular immune response depends on the size of the carbohydrate moiety, a trigalactosylated derivative of an immunogenic peptide from hen egg-white lysozyme (HEL52-61) was prepared. Synthesis was accomplished by assembly of an alpha-1,4-linked trigalactose peracetate which was coupled to Fmoc serine. After activation as a pentafluorophenyl ester the resulting building block was used in solid-phase synthesis In contrast to the corresponding mono- and digalactosylated derivatives of HEL52-61, the trigalactosylated HEL52-61 was not immunogenic. Somewhat surprisingly, this was found to be because the trigalactosyl derivative bound approximately two orders of magnitude weaker to I-Ak MHC molecules than the mono- and digalactosyl peptides. Our observation suggests an explanation for previous findings, which show that glycopeptides isolated from MHC molecules in nature usually carry small saccharides.     

Characterization of Cobalt(III) Hydroxamic Acid Complexes Based on a Tris(2-pyridylmethyl)amine Scaffold: Reactivity toward Cysteine Methyl Ester

Six Co(III) complexes based on unsubstituted or substituted TPA ligands (where TPA is tris(2-pyridylmethyl)amine) and acetohydroxamic acid (A), N-methyl-acetohydroxamic acid (B), or N-hydroxy-pyridinone (C) were prepared and characterized by mass spectrometry, elemental analysis, and electrochemistry: [Co(III)(TPA)(A-2H)](Cl) (1a), [Co(III)((4-Cl(2))TPA)(A-2H)](Cl) (2a), [Co(III)((6-Piva)TPA)(A-2H)](Cl) (3a), [Co(III)((4-Piva)TPA)(A-2H)](Cl) (4a) and [Co(III)(TPA)(B-H)](Cl)(2) (1b), and [Co(III)(TPA)(C-H)](Cl)(2) (1c). Complexes 1a-c and 3a were analyzed by (1)H NMR, using 2D ((1)H, (1)H) COSY and 2D ((1)H, (13)C) HMBC and HSQC, and shown to exist as a mixture of two geometric isomers based on whether the hydroxamic oxygen was trans to a pyridine nitrogen or to the tertiary amine nitrogen. Complex 3a exists as a single isomer that was crystallized. Its crystal structure revealed the presence of an H-bond between the pivaloylamide and the hydroximate oxygen. Complexes 1a, 2a, and 4a are irreversibly reduced beyond -900 mV versus SCE, while complexes 1b and 1c are reduced at less negative values of -330 and -190 mV, respectively. The H-bond in 3a increased the redox potential up to -720 mV. Reaction of complex 1a with l-cysteine methyl ester CysOMe was monitored by (1)H NMR and UV-vis at 2 mM and 0.2 mM in an aqueous buffered solution at pH 7.5. Complex 1a was successively converted into an intermediate [Co(III)(TPA)(CysOMe-H)](2+), 1d, by exchange of the hydroximate with the cysteinate ligand, and further into Co(III)(CysOMe-H)(3), 5. An authentic sample of 1d was prepared and thoroughly characterized. A detailed (1)H NMR analysis showed there was only one isomer, in which the thiolate was trans to the tertiary amine nitrogen.     

Comparative Study of Three Models for Moisture Transfer in Hygroscopic Materials

Transport in Porous Media - Prediction of moisture transfer within material using a classic diffusive model may lack accuracy, since numerical simulations underestimate the adsorption process when...     

Voice segregation by difference in fundamental frequency: evidence for harmonic cancellation

Two experiments investigated listeners' ability to use a difference of two semitones in fundamental frequency (F0) to segregate a target voice from harmonic complex tones, with speech-like spectral profiles. Masker partials were in random phase (experiment 1) or in sine phase (experiment 2) and stimuli were presented over headphones. Target's and masker's harmonicity were each distorted by F0 modulation and reverberation. The F0 of each source was manipulated (monotonized or modulated by 2 semitones at 5 Hz) factorially. In addition, all sources were presented from the same location in a virtual room with controlled reverberation, assigned factorially to each source. In both experiments, speech reception thresholds increased by about 2 dB when the F0 of the masker was modulated and increased by about 6 dB when, in addition to F0 modulation, the masker was reverberant. Masker partial phases did not influence the results. The results suggest that F0-segregation relies upon the masker's harmonicity, which is disrupted by rapid modulation. This effect is compounded by reverberation. In addition, F0-segregation was found to be independent of the depth of masker envelope modulations.     

Thermodynamics of water intrusion in nanoporous hydrophobic solids

We report a joint experimental and molecular simulation study of water intrusion in silicalite-1 and ferrerite zeolites. The main conclusion of this study is that water condensation takes place through a genuine first-order phase transition, provided that the interconnected pores structure is 3-dimensional. In the extreme confinement situation (ferrierite zeolite), condensation takes place through a continuous transition, which is explained by a shift of both the first-order transition line and the critical point with increasing confinement. The present findings are at odds with the common belief that conventional phase transitions cannot take place in microporous solids such as zeolites. The most important features of the intrusion/extrusion process can be understood in terms of equilibrium thermodynamics considerations. We believe that these findings are very general for hydrophobic solids, i.e. for both nonwetting as well as wetting water-solid interface systems.     

Synthesis of Benzazepinones via Intramolecular Cyclization Involving Ketene Iminium Intermediates

Herein, we describe a very straightforward and metal free method for the synthesis of benzazepinones through an intramolecular cyclization. This involves an ortho‐vinyl‐anilino‐amide as starting material which is converted to a keteniminium intermediate that spontaneously cyclize to form a 7‐membered ring iminium. Under slightly basic hydrolysis conditions, this latter is ultimately converted to the desired benzazepinone. Control experiments on the electron density of the nitrogen constituting the aniline were performed to support our proposed mechanism and rationalize the selectivity of the reaction.     

Independent Domination in Cubic Graphs

A set S of vertices in a graph G is an independent dominating set of G if S is an independent set and every vertex not in S is adjacent to a vertex in S. The independent domination number of G, denoted by , is the minimum cardinality of an independent dominating set. In this article, we show that if is a connected cubic graph of order n that does not have a subgraph isomorphic to K_{2, 3}, then . As a consequence of our main result, we deduce Reed's important result [Combin Probab Comput 5 (1996), 277–295] that if G is a cubic graph of order n, then , where denotes the domination number of G.