Establishment of mass spectrometric fingerprints of novel synthetic cholesteryl neoglycolipids: The presence of a unique <Emphasis Type="Italic">C</Emphasis>-glycoside species during electrospray ionization and during collision-induced dissociation tandem mass spectrometry

In this study we evaluated the fragmentation pattern of 16 novel amphiphilic neoglycolipid cholesteryl derivatives that can be efficiently used to increase cationic liposomal stability and to enhance gene transfer ability. These neoglycolipids bear different sugar moieties, such as D-glucosamine, N-acetyl-D-glucosamine, N-trideuterioacetyl-D-glucosamine, N-acetyllactosamine, L-fucose, N-allyloxycarbonyl-D-glucosamine, and some of their per-O-acetylated derivatives. Regardless of the structure of the tested neoglycolipid, QqToF-MS analysis using electrospray ionization (ESI) source showed abundant protonated [M+H]+ species. We also identified by both QqToF-MS and low-energy collision tandem mass spectrometry (CID-MS/MS) of the [M+H]+ ion, the presence of specific common fingerprint fragment ions: [Cholestene]+, sugar [oxonium]+, [(Sugar-spacer-OH)+H]+, [oxonium-H2O]+, and [(Cholesterol-spacer-OH)+H]+. In addition, we observed a unique ion that could not be rationally explained by the expected fragmentation of these amphiphilic molecules. The structure of this ion was tentatively proposed with that of a C-glycoside species formed by a chemical reaction between the sugar portion and the cholesterol. MS/MS analysis of this unique [C-glycoside]+ confirmed the validity of the proposed structure of this ion. The presence of an amino group at position C-2 and free hydroxyl groups of the sugar motif is crucial for the formation of a "reactive" sugar oxonium ion that can form the [C-glycoside]+ species. In summary, we precisely established the fragmentation patterns of the tested series of neoglycolipid cholesteryl derivatives and authenticated their structure as well; moreover, we speculated on the formation of a C-glycoside with the ESI source under atmospheric pressure and in the collision cell during MS/MS analysis.     

Experimental and theoretical study of the quantum-confined Stark effect in a single InGaN/GaN quantum dot under applied vertical electric field

We present a study of the effect of externally applied vertical electric field on the optical properties of single InGaN/GaN quantum dots via microphotoluminescence spectroscopy. This is achieved by incorporating the quantum dot layer in the intrinsic region of a p–i–n diode structure. We observe a large blue energy shift of 60 meV, which is explained by the partial compensation of the internal piezoelectric field. The energy shift dependence on the applied field allows the determination of the vertical component of the permanent dipole and the polarizability. We also present theoretical modelling of our results based on atomistic semi-empirical tight-binding simulations. A good quantitative agreement between the experiment and the theory is found.     

Simultaneous determination of two major snow crab aeroallergens in processing plants by use of isotopic dilution tandem mass spectrometry

Snow crab is a major fishery in the North Atlantic region. During crab processing the proteins are aerosolized and some are responsible for development of occupational asthma. Tropomyosin and arginine kinase have recently been reported as major snow crab allergens. A liquid chromatographic tandem mass spectrometric method has been developed for simultaneous analysis of these two proteins in air samples collected from processing plants. These proteins were initially isolated then characterized by use of mass spectrometry to determine their primary structure and signature peptides. The signature peptides were chemically synthesized in light and heavy forms and used as standards for developing the multiple-reaction monitoring transitions to monitor allergen levels. A validation study was performed; precision and accuracy were 1.8–8% and 91–104%, respectively. Replicate air samples were collected on air filters from two crab-processing plants in Newfoundland and Labrador (NL) and four located in Quebec. In NL, measured levels of both tropomyosin and arginine kinase were between 1 and 20 ng m⁻³. In Quebec plants, however, levels were found to be much higher at 2–2400 ng m⁻³. Significant differences were also observed among the plants and individual processing workstations. For the first time arginine kinase has been detected in its aerosolized form in processing plants. In general, levels of the allergens were highest in the butchering and cooking areas; plant design can, however, have a significant effect on levels of the allergens.     

Purification and Characterisation of a 31-kDa Chitinase from the <Emphasis Type="Italic">Myzus Persicae</Emphasis> Aphid: A Target for Hemiptera Biocontrol

Hydrolytic enzymes involved in chitin degradation are important to allow moulting during insect development. Chitinases are interesting targets to disturb growth and develop alternative strategies to control insect pests. In this work, a chitinase from the aphid Myzus persicae was purified with a 36-fold purification rate in a three step procedure by ammonium sulphate fractionation, anion-exchange chromatography on a DEAE column and on an affinity Concanavalin A column. The purified chitinase purity assessed by 1D and 2D SDS–PAGE revealed a single band and three spots at 31 kDa, respectively. Chitinases were found to have high homologies with Concanavalins A and B, two chitinase-related proteins, a fungal endochitinase and an aphid acetylhydrolase by peptide identification by Maldi-Tof-Tof. The efficiency of two potent chitinase inhibitors, namely allosamidin and psammaplin A, was tested and showed significant rate of enzymatic inhibition.     

Quantum Properties of the Superposition of Two Nearly Identical Coherent States

In this paper, we examine the properties of the state obtained when two nearly identical coherent states are superimposed. We found that this state exhibits many nonclassical properties such as sub-Poissonian statistics, squeezing and a partially negative Wigner function. These and other properties indicate that such states, here termed near coherent states, are significantly closer to coherent states more than the generalized Schrördinger cat states. We finally provide an experimental procedure for generating the near coherent states.     

Correction to: The Mth Coherent State

International Journal of Theoretical Physics - The original article has been corrected. The left image of Figure 3 was previously not correct.     

Enabling Control over Mechanical Conformity and Luminescence in Molecular Crystals: Interaction Engineering in Action

Molecular crystals of π-conjugated molecules are of great interest as the highly ordered dense packing offers superior charge and exciton transport compared with its amorphous counterparts. However, integration into optoelectronic devices remains a major challenge owing to its inherently brittle nature. Herein, control over the mechanical conformity in single crystals of pyridine-appended thiazolothiazole derivatives is reported by modulating the molecular packing through interaction engineering. Two polymorphs were prepared by achieving control over the thermodynamic/kinetic factors of crystallization; one of the polymorphs exhibits elastic bending whereas the other is brittle. The control over the bending ability was achieved by forming co-crystals with hydrogen/halogen bond donors. A seamless extended crisscross pattern with respect to the bend plane through a ditopic hydrogen-bonding motif showed the highest compliance towards mechanical bending, whereas the co-crystals with a layered crisscross arrangement with segregated layers of co-formers exhibit slightly lower bending conformity. These results update the rationale behind the plastic/elastic bending in molecular crystals. The co-crystals of ditopic halogen bond co-assemblies are particularly appealing for waveguiding applications as the co-crystals blend high mechanical flexibility and luminescence properties. The hydrogen bonded co-crystals are non-emissive in nature owing to excited state proton transfer dynamics. The rationale behind the fluorescence properties of these materials was also established from DFT calculations in a quantum mechanics/molecular mechanics (QM/MM) framework.