Highly Luminescent Cesium Lead Halide Perovskite Nanocrystals with Tunable Composition and Thickness by Ultrasonication

We describe the simple, scalable, single‐step, and polar‐solvent‐free synthesis of high‐quality colloidal CsPbX₃ (X=Cl, Br, and I) perovskite nanocrystals (NCs) with tunable halide ion composition and thickness by direct ultrasonication of the corresponding precursor solutions in the presence of organic capping molecules. High angle annular dark field scanning transmission electron microscopy (HAADF‐STEM) revealed the cubic crystal structure and surface termination of the NCs with atomic resolution. The NCs exhibit high photoluminescence quantum yields, narrow emission line widths, and considerable air stability. Furthermore, we investigated the quantum size effects in CsPbBr₃ and CsPbI₃ nanoplatelets by tuning their thickness down to only three to six monolayers. The high quality of the prepared NCs (CsPbBr₃) was confirmed by amplified spontaneous emission with low thresholds. The versatility of this synthesis approach was demonstrated by synthesizing different perovskite NCs.     

New alkyl derivatives phosphine sulfonate (P-O) ligands. Catalytic activity in Pd-catalysed Suzuki-Miyaura reactions in water

Two novel bis(o-methoxyphenyl) phosphinoalkylsulfonate (P-O) ligands have been prepared through a new and sustainable synthetic route; they are air stable as well as water soluble and have been applied in Pd-catalysed Suzuki-Miyaura cross-coupling reactions in neat water in conjunction with microwave heating.     

Beyond exciton theory: a time-dependent DFT and Franck-Condon study of perylene diimide and its chromophoric dimer

The diimide perylene motif exhibits a dramatic intensity reversal between the 0 --> 0 and 0 --> 1 vibronic bands upon pi-pi stacking; this distinct spectral property has previously been used to measure folding dynamics in covalently bound oligomers and synthetic biological hybrid foldamers. It is also used as a tool to assess organization of the pi-stacking, indicating the presence of H- or J-aggregation. The zeroth-order exciton model, often used to describe the optical properties of chromophoric aggregates, is solely a transition dipole coupling scheme, which ignores the explicit electronic structure of the system as well as vibrational coupling to the electronic transition. We have therefore examined the optical properties of gas-phase perylene tetracarboxylic diimide (PTCDI) and its chromophoric dimer as a function of conformation to relate the excited-state distributions predicted by exciton theory with that of time-dependent density functional theory (TDDFT). Using ground- and excited-state geometries, the Franck-Condon (FC) factors for the lowest energy molecular nature electronic transition have been calculated and the origin of the intensity reversal of 0 --> 0 and 0 --> 1 vibronic bands has been proposed.     

Improved protein identification efficiency by mass spectrometry using N-terminal chemical derivatization of peptides from Angiostrongylus costaricensis, a nematode with unknown genome

Matrix-assisted laser desorption ionization (MALDI), Peptide Mass Fingerprinting (PMF) and MALDI-MS/MS ion search (using MASCOT) have become the preferred methods for high-throughput identification of proteins. Unfortunately, PMF can be ambiguous, mainly when the genome of the organism under investigation is unknown and the quality of spectra generated is poor and does not allow confident identification. The post-source decay (PSD) fragmentation of singly charged tryptic peptide ions generated by MALDI-TOF/TOF typically results in low fragmentation efficiency and/or complex spectra, including backbone fragmentation ions (series b and y), internal fragmentation etc. Interpreting these data either manually and/or using de novo sequencing software can frequently be a challenge. To overcome this limitation when studying the proteome of adult Angiostrongylus costaricensis, a nematode with unknown genome, we have used chemical N-terminal derivatization of the tryptic peptides with 4-sulfophenyl isothiocyanate (SPITC) prior to MALDI-TOF/TOF MS. This methodology has recently been reported to enhance the quality of MALDI-TOF/TOF-PSD data, allowing the obtainment of complete sequence of most of the peptides and thus facilitating de novo peptide sequencing. Our approach, consisting of SPITC derivatization along with manual spectra interpretation and Blast analysis, was able to positively identify 76% of analyzed samples, whereas MASCOT analysis of derivatized samples, MASCOT analysis of nonderivatized samples and PMF of nonderivatized samples yielded only 35, 41 and 12% positive identifications, respectively. Moreover, de novo sequencing of SPITC modified peptides resulted in protein sequences not available in NCBInr database paving the way to the discovery of new protein molecules.     

Effect of surfactant structure on the residual fluorescence of micelle-based fluorescent probes

In the present paper we have investigated some photo-physical characteristics of different micellar-based fluorescent probes containing a fluorophore (pyrene) and a quencher unit (dodecyl-dioxo 2,3,2). The fluorescent response of the probe in the presence of Cu(II) ions was studied using different micellar substrates, and it was found that the pH at which the On-Off jump occurs is not influenced by the chemical structure of surfactant. In addition, the experimental residual fluorescence is not proportionally affected by microviscosity or by the size of the micellar aggregates. The signal of the native fluorescence of pyrene was observed even when the quencher's occupancy number was greater than one. Moreover, we observed discrepancies between experimental values and calculated residual fluorescence using Laplace data. These results were interpreted suggesting that the residual fluorescence has two main components, one that seems to be independent on micellar properties, while the other is directly related to location of molecules inside the surfactant aggregates that serve as substrate.     

Microwave‐assisted synthesis of 2‐(2‐pyridyl)azoles. Study of their corrosion inhibiting properties

An efficient and fast procedure for the synthesis of 2‐(2‐pyridyl)azoles is described using ionic liquids as catalysts under microwave irradiation. The X‐ray crystallographic analyses for three of the four synthesized compounds are presented. Potentiodynamic polarization studies were carried out to analyze the electrochemical behavior of the compounds in corrosive acidic media. Of the four derivatives, one compound was detected to be an effective corrosion inhibitor prototype for oil refinery environments.     

Interactions between gemini surfactants and polymers: thermodynamic studies

Aqueous mixtures containing a homopolymer, poly(vinylpyrrolidone) (PVP), or a hydrophobically modified graft copolymer, HM-pullulan, (PULAU9, where 9 stands for the nominal substitution degree), and different Gemini surfactants have been investigated at 25.0 degrees C. A wide variety of experimental conditions were addressed by changing the amount of polymer and of surfactant. The Gemini surfactants were synthesized, purified, and characterized by routine methods. They differ from each other in polar head groups (two sulfonate-, two quaternary ammonium-, or two arginine-based groups), in alkyl chain length (11 or 12 carbon atoms), and in the distance between the polar head groups. The spacers consist of 2, 3, and 6 methylene units or 3 oxyethylene units. Surface activity and solution calorimetry measurements yield some physicochemical features inherent to micelle formation and polymer-surfactant interactions. The data are supported by ionic conductivity, detecting the critical thresholds and quantifying the modifications in binding associated with critical association (CAC) and micelle formation (CMC*). The Gibbs energy of transfer from the micelles to a polymer-binding site, DeltaGtrans, was evaluated from the CAC/CMC* ratios versus the amount of added polymer. A similar procedure determined the enthalpy of transfer, DeltaHtrans. DeltaGtrans decreases with added polymer, whereas DeltaHtrans becomes more negative on increasing the amount of polymer in the medium. According to the selected data presented here, cationic Geminis do not interact with PVP, while significant interactions have been observed in other surfactants. In mixtures with PULAU9, the interaction is significant for all Geminis. This effect is due to interactions between the surfactants and the hydrophobic alkyl groups on the main polymer chain. The pendent groups facing away from the polysaccharide chain act as binding sites for aggregates onto such polymers.     

Ligand effects in the non-alternating CO-ethylene copolymerization by palladium(II) catalysis

In this paper we report on a comparative study of the non-alternating CO-C(2)H(4) copolymerization catalyzed by neutral Pd(II) complexes with the phosphine-sulfonate ligands bis(o-methoxyphenyl)phosphinophenylenesulfonate and bis(o-methoxyphenyl)phosphino-ethylenesulfonate. The former ligand, featuring a lower skeletal flexibility, has been found to form more active catalysts as well as produce polyketones with higher molecular weight and higher extra-ethylene incorporation. Operando high-pressure NMR studies have allowed us to intercept, for the first time, Pd(II)(phosphine-sulfonate) beta-chelates in the non-alternating copolymerization cycle, while model organometallic reactions have contributed to demonstrate that Pd(II) (phosphine-sulfonate) fragments do not form stable carbonyl complexes. The opening of the beta-chelates has been found to be a viable process by either comonomer, which contrasts with the behaviour of Pd(II) (chelating diphosphine) catalysts for the perfectly alternating copolymerization.     

Correlation between rheological properties of zinc carboxylate liquids and molecular structure

Using Fourier transform infrared spectroscopy (FTIR), the viscosity of zinc 2-ethylhexanoate liquid has been found to correlate with the intensity of an asymmetric COO stretching resonance at 1632 cm-1. This is consistent with the presence of the zinc carboxylate polymer, catena-2-ethylhexanato-(O,O')-tri-micro-2-ethylhexanato-(O,O')-dizinc(II) as the origin of the viscosity, a conclusion that is further supported by theoretical predictions. Density functional theory has been used to assign the IR spectra of the zinc carboxylate dimer, catena-2-ethylhexanato-(O,O')-di-(tri-micro-2-ethylhexanato-(O,O')-dizinc(II)-formic) acid, and the model of the molecular liquid, micro-4-oxo-hexakis-(micro-2-ethylhexanato)-tetrazinc(II). The predicted spectra indicate that the decreased symmetry of the polymer relative to the zinc 2-ethylhexanoate liquid increases the intensity of the asymmetric carboxylate stretch at 1632 cm-1 and leads to the observed correlation.     

Unexpected inverse correlations and cooperativity in ion-pair phase transfer

Liquid/liquid extraction is one of the most widely used separation and purification methods, where a forefront of research is the study of transport mechanisms for solute partitioning and the relationships that these have to solution structure at the phase boundary. To date, organized surface features that include protrusions, water-fingers, and molecular hinges have been reported. Many of these equilibrium studies have focused upon small-molecule transport – yet the extent to which the complexity of the solute, and the competition between different solutes, influence transport mechanisms have not been explored. Here we report molecular dynamics simulations that demonstrate that a metal salt (LiNO₃) can be transported via a protrusion mechanism that is remarkably similar to that reported for H₂O by tri-butyl phosphate (TBP), a process that involves dimeric assemblies. Yet the LiNO₃ out-competes H₂O for a bridging position between the extracting TBP dimer, which in-turn changes the preferred transport pathway of H₂O. Examining the electrolyte concentration dependence on ion-pair transport unexpectedly reveals an inverse correlation with the extracting surfactant concentration. As [LiNO₃] increases, surface adsorbed TBP becomes a limiting reactant in correlation with an increased negative surface charge induced by excess interfacial NO₃⁻, however the rate of transport is enhanced. Within the highly dynamic interfacial environment, we hypothesize that this unique cooperative effect may be due to perturbed surface organization that either decreases the energy of formation of transporting protrusion motifs or makes it easier for these self-assembled species to disengage from the surface.

A forefront of research in separations science (specifically liquid–liquid extraction) is the study of transport mechanisms for solute partitioning, and the relationships that these have to solution structure at the phase boundary.