Controlled Growth of Large-Sized and Phase-Selectivity 2D GaTe Crystals.

GaTe has recently attracted significant interest due to its direct bandgap and unique phase structure, which makes it a good candidate for optoelectronics. However, the controllable growth of large-sized monolayer and few-layer GaTe with tunable phase structures remains a great challenge. Here the controlled growth of large-sized GaTe with high quality, chemical uniformity, and good reproducibility is achieved through liquid-metal-assisted chemical vapor deposition method. By using liquid Ga, the rapid growth of 2D GaTe flakes with high phase-selectivity can be obtained due to its reduced reaction temperature. In addition, the method is used to synthesize many Ga-based 2D materials and their alloys, showing good universality. Raman spectra suggest that the as-grown GaTe own a relatively weak van der Waals interaction, where monoclinic GaTe displays highly-anisotropic optical properties. Furthermore, a p-n junction photodetector is fabricated using GaTe as a p-type semiconductor and 2D MoSe2 as a typical n-type semiconductor. The GaTe/MoSe2 heterostructure photodetector exhibits large photoresponsivity of 671.52 A W-1 and high photo-detectivity of 1.48 × 1010 Jones under illumination, owing to the enhanced light absorption and good quality of as-grown GaTe. These results indicate that 2D GaTe is a promising candidate for electronic and photoelectronic devices.

Effect of pH and mobile phase additives on the chromatographic behaviour of an amide-embedded stationary phase: Cyanocobalamin and its diaminemonochloro-platinum(II) conjugate as a case study.

Several mobile phase additives (i.e., organic acids and their ammonium salts) were used to modulate the chromatographic retention of cyanocobalamin and its cis-diaminemonochloroplatinum(II) conjugate, depending on the specific nature of the stationary phase. Regardless of the mobile phase additive, the positively charged cyanocobalamin-cis-diaminemonochloroplatinum(II) conjugate was systematically less retained than cyanocobalamin on a conventional octadecyl-silica column. In contrast, the amide-embedded C18 column exhibited a progressive increase in the conjugate retention time upon changing the mobile phase additive from organic (acetic, formic and trifluoroacetic) acids to ammonium salts, ultimately leading to an inversion of the elution order. This change of retention was interpreted by invoking the interplay between hydrophobic interactions, hydrogen bonding between the conjugate and the polar amide groups and the ion-pairing ability of the lyophilic counterions, whereby the acetate anion was found to be the most suitable to control the solute retention.

Phase-selective low molecular weight organogelators derived from allylated d-mannose.

In the last decades, synthesis and design of low molecular weight organogelators has gained increasing attention due to their versatile use in, for example, cosmetics, biomedicine and oil spill remediation. In this work, three potential gelators have been prepared from allylated d-mannose. Both the gelators and the corresponding gels formed were thoroughly characterized by crystallography, FTIR spectroscopy, SEM, rheometry and NMR spectroscopy, in solution and in solid state. The results showed that two of the compounds phase-selectively form gels with hydrocarbon solvents. The most promising gelator compound is alkene terminated, with the unsaturated end functionality not critical for gel formation, tentatively providing the possibility for customizing the gelation properties by further chemical modification. Alternatively, the alkene group could possibly be utilized as a linker for future coupling to carrier materials or surfaces to further increase the mechanical strength of the gel.

Investigation into reversed-phase chromatography peptide separation systems part V: Establishment of a screening strategy for development of methods for assessment of pharmaceutical peptides' purity.

The paper describes a simple and rapid reversed-phase UHPLC method development screening strategy for the purity determination of peptide-based pharmaceuticals. The protocol utilises five disparate column and six volatile or non-volatile mobile phases (i.e., 30 combinations). The method development strategy has been demonstrated to be highly effective in identifying conditions which generate complementary selectivity and good peak shape. Columns with varying degrees of charge (positive and negative), in addition to their differing hydrophobic character, were used in combination with mobile phases within the pH range of 2.3 to 5.1. The novel ion-pair / chaotropic reagent ammonium hexafluorophosphate at pH 2.3 was shown to be an extremely useful mobile phase additive in that it produced excellent complementary separation and good peak shape. Methanesulfonic acid was demonstrated to be a good alternative to the ubiquitously employed trifluoroacetic acid which failed to generate optimum separation for the peptides investigated highlighting the importance of screening disparate mobile phase additives. Both ammonium hexafluorophosphate and methanesulfonic acid were shown not to adversely affect the stability of C18 columns or demonstrated any irreversible adsorption / memory effects. No pH hysteresis effects were demonstrated with any of the stationary phases on mobile phase pH cycling. No major problems have been observed with the novel mobile phase additives ammonium hexafluorophosphate and methanesulfonic acid, however, it is recommended that they be used with caution until long-term routine use has been established.

Investigation into reversed-phase chromatography peptide separation systems Part IV: Characterisation of mobile phase selectivity differences.

The differentiation of mobile phase compositions between sub-classes which exhibit distinct chromatographic selectivity (i.e. termed characterisation) towards a range of peptide probes with diverse functionality and hence the possibility for multi-modal retention mechanisms has been undertaken. Due to the complexity of peptide retention mechanisms in given mobile phase conditions, no attempt has been made to explain these, instead mobile phases have simply been classified into distinct groups with an aim of identifying those yielding differing selectivities for use in strategic method development roadmaps for the analysis of peptide mixtures. The selectivity differences between nine synthetic peptides (fragments of [Ile27]-Bovine GLP-2) were used to assess how fifty-one RPC mobile phase compositions of differing pH (range 1.8 - 7.8), salt types, ionic strengths, ion-pair reagents and chaotropic / kosmotropic additives affected chromatographic selectivity on a new generation C18 stationary phase (Ascentis Express C18). The mobile phase compositions consisted of commonly used and novel UV or MS compatible additives. The chemometric tool of Principal Component Analysis (PCA) was used to visualise the differences in selectivity generated between the various mobile phases evaluated. The results highlight the importance of screening numerous mobile phases of differing pH, ion-pair reagents and ionic strength in order to maximise the probability of achieving separation of all the peptides of interest within a complex mixture. PCA permitted a ranking of the relative importance of the various mobile phase parameters evaluated. The concept of using this approach was proven in the analysis of a sample of Bovine GLP-2 (1-15) containing synthesis related impurities. Mobile phases with high ionic strength were demonstrated to be crucial for the generation of symmetrical peaks. The observations made on the C18 phase were compared on three additional stationary phases (i.e. alkyl amide, fluorophenyl and biphenyl), which had previously been shown to possess large selectivity differences towards these peptides, on a limited sub-set of mobile phases. With the exception of the ion-pair reagent, similar trends were obtained for the C18, fluorophenyl and biphenyl phases intimating the applicability of these findings to the vast majority of RPC columns (i.e. neutral or weakly polar in character) which are suitable for the analysis of peptides. The conclusions were not relevant for columns with a more disparate nature (i.e. containing a high degree of positive charge).

Active Mechanisms of Vibration Encoding and Frequency Filtering in Central Mechanosensory Neurons.

To better understand biophysical mechanisms of mechanosensory processing, we investigated two cell types in the Drosophila brain (A2 and B1 cells) that are postsynaptic to antennal vibration receptors. A2 cells receive excitatory synaptic currents in response to both directions of movement: thus, twice per vibration cycle. The membrane acts as a low-pass filter, so that voltage and spiking mainly track the vibration envelope rather than individual cycles. By contrast, B1 cells are excited by only forward or backward movement, meaning they are sensitive to vibration phase. They receive oscillatory synaptic currents at the stimulus frequency, and they bandpass filter these inputs to favor specific frequencies. Different cells prefer different frequencies, due to differences in their voltage-gated conductances. Both Na+ and K+ conductances suppress low-frequency synaptic inputs, so cells with larger voltage-gated conductances prefer higher frequencies. These results illustrate how membrane properties and voltage-gated conductances can extract distinct stimulus features into parallel channels.

Toluene diisocyanate based phase-selective supramolecular oil gelator for effective removal of oil spills from polluted water.

Due to tremendous resource wastes and great harm to ecological environment caused by the accidental oil spills, an alkyl bicarbamate supramolecular oil gelator was synthesized and applied to selectively gelate oils from oil/water mixtures. Interestingly, the oil gelator could be self-assembled in a series of organic solvents, i.e., edible oils and fuel oils to form 3D networks and then turned into thermally reversible organogels, allowing easy separation and removal of oil spills from oil/water mixtures. The possible self-assembly mode for the formation of organogels was proposed. What's more, the optimal conditions for using the oil gelator to recover oils were experimentally determined. Inspiringly, taking gasoline as the co-congealed solvent, a complete gelation of oil phase was achieved within 15 min with high oil removal rate and oil retention rate after convenient salvage and cleanup of oil gels from oil/water mixtures. The oil gelator had some advantages in solidifying oil spills on water surface, exhibiting fast oil gelation, convenient and thorough oil removal and easy recovery. This work illustrates the significant role of oil gelators in the potential cleanup of spilled oils for water purification.

Ultra high performance liquid chromatography versus high performance liquid chromatography: stationary phase selectivity for generic carotenoid screening.

Aim of study was to find the most suitable LC column for generic carotenoid screening. To represent the diversity of carotenoids in nature and to optimize chromatographic separation, a set of carotenoid standards was carefully chosen to account for the various classes of carotenoids. The HPLC C30 column has since long been the 'golden standard' in the chromatographic separation of carotenoids. Since approximately one decade, new UHPLC technology has led to much shorter analysis times, smaller peak widths and higher chromatographic resolution. However, there are currently no UHPLC columns on the market containing the specific stationary phase chemistry of the HPLC C30 column. Therefore during this study, we investigated the separation of carotenoids on a set of UHPLC columns and compared it to their separation on the HPLC C30 column. Comparison of carotenoids separations on the different stationary phases with objective column comparison parameters clearly indicated that the HPLC C30 column is an overall better performer in the separation of carotenoids. This is due to the lack of UHPLC column chemistries that are adapted for carotenoid analysis. However, analysis time on the HPLC C30 column takes about four times longer compared to UHPLC analysis. Therefore, with the range of columns that are commercially available nowadays, a choice has to be made between very high selectivity (HPLC C30 column) and analysis times that are adapted to modern laboratory requirements (UHPLC technology). Therefore, carotenoid separations would be even more performing if an appropriate UHPLC C30 column would be available.