Isotope abundance ratio measurements using femtosecond laser ablation ionization mass spectrometry

Accurate isotope ratio measurements are of high importance in various scientific fields, ranging from radio isotope geochronology of solids to studies of element isotopes fractionated by living organisms. Instrument limitations, such as unresolved isobaric inferences in the mass spectra, or cosampling of the material of interest together with the matrix material may reduce the quality of isotope measurements. Here, we describe a method for accurate isotope ratio measurements using our laser ablation ionization time‐of‐flight mass spectrometer (LIMS) that is designed for in situ planetary research. The method is based on chemical depth profiling that allows for identifying micrometer scale inclusions embedded in surrounding rocks with different composition inside the bulk of the sample. The data used for precise isotope measurements are improved using a spectrum cleaning procedure that ensures removal of low quality spectra. Furthermore, correlation of isotopes of an element is used to identify and reject the data points that, for example, do not belong to the species of interest. The measurements were conducted using IR femtosecond laser irradiation focused on the sample surface to a spot size of ~12 μm. Material removal was conducted for a predefined number of laser shots, and time‐of‐flight mass spectra were recorded for each of the ablated layers. Measurements were conducted on NIST SRM 986 Ni isotope standard, trevorite mineral, and micrometer‐sized inclusions embedded in aragonite. Our measurements demonstrate that element isotope ratios can be measured with accuracies and precision at the permille level, exemplified by the analysis of B, Mg, and Ni element isotopes. The method applied will be used for in situ investigation of samples on planetary surfaces, for accurate quantification of element fractionation induced by, for example, past or present life or by geochemical processes.     

On the fracture mechanism of partially healed interfaces of glassy polymers: an ATR-FTIR investigation

Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) has been employed to analyse the surfaces of poly(2,6-dimethyl-1,4-phenylene-oxide) (PPO) samples prior to contact and after fracture of the PPO–PPO auto-adhesive joints which formed during the contact of two identical PPO samples at temperatures of 146 or 156 °С that are lower than the PPO bulk glass transition temperature by 70 or 60 °С, respectively. The differences in the intensity of ATR-FTIR spectra for the original and fractured PPO surfaces found have been discussed in the frameworks of the molecular mechanisms of fracture.     

Novel water-soluble quaternary piperazine derivatives of chitosan: synthesis and characterization

Novel synthesis methods for the preparation of quaternary piperazine derivatives of chitosan were developed. Quaternary ammonium moiety can be selectively inserted into either one or both of the piperazine nitrogens, yielding structurally uniform chitosan derivative structures. Water-soluble end products were thoroughly characterized with FT-IR, 1H NMR, 13C NMR and 2D 1H-13C HSQC NMR. The molecular weights of the end products were determined by GPC with triple detection.     

Bordism groups of special generic mappings

The Pontrjagin-Thom construction expresses a relation between the oriented bordism groups of framed immersions , and the stable homotopy groups of spheres. We apply the Pontrjagin-Thom construction to the oriented bordism groups of mappings n$">, with mildest singularities. Recently, O. Saeki showed that for , the group is isomorphic to the group of smooth structures on the sphere of dimension . Generalizing, we prove that is isomorphic to the -th stable homotopy group , , where is the group of oriented auto-diffeomorphisms of the sphere and is the group of rotations of .

     

Membrane extraction of alkaline earth metal by phosphorylated azapodands

ABSTRACT

Membrane transport properties of the new lipophilic phosphorylated azapodands toward Сa(II), Ва (II), Mg(II), and Sr(II) were studied. The investigation of the processes of passive membrane ion transport showed the high values of the transfer flow of the alkaline earth metals’ ions with all carriers. It was found that N,N’-bis(di-p-tolylphosphorylmethyl)-1,8-diamino-3,6-dioxaoctane (I) is the most effective carrier among all compounds studied.     

Routes to covalent catalysis by reactive selection for nascent protein nucleophiles

Reactivity-based selection strategies have been used to enrich combinatorial libraries for encoded biocatalysts having revised substrate specificity or altered catalytic activity. This approach can also assist in artificial evolution of enzyme catalysis from protein templates without bias for predefined catalytic sites. The prevalence of covalent intermediates in enzymatic mechanisms suggests the universal utility of the covalent complex as the basis for selection. Covalent selection by phosphonate ester exchange was applied to a phage display library of antibody variable fragments (scFv) to sample the scope and mechanism of chemical reactivity in a naive molecular library. Selected scFv segregated into structurally related covalent and noncovalent binders. Clones that reacted covalently utilized tyrosine residues exclusively as the nucleophile. Two motifs were identified by structural analysis, recruiting distinct Tyr residues of the light chain. Most clones employed Tyr32 in CDR-L1, whereas a unique clone (A.17) reacted at Tyr36 in FR-L2. Enhanced phosphonylation kinetics and modest amidase activity of A.17 suggested a primitive catalytic site. Covalent selection may thus provide access to protein molecules that approximate an early apparatus for covalent catalysis.     

Voltammetric Determination of Hesperidin on the Electrode Modified with SnO2 Nanoparticles and Surfactants

Highly sensitive voltammetric method for hesperidin determination is developed using glassy carbon electrode modified with SnO₂ nanoparticles (SnO₂ NPs) and surfactants. The highest oxidation currents of hesperidin are observed in the case of cationic 0.50 mM cetylpyridinium bromide (CPB). Parameters of hesperidin electrooxidation have been calculated. Adsorptive anodic differential pulse voltammetry (AdADPV) in phosphate buffer pH 7.0 after 120 s accumulation provides linear dynamic ranges of 0.10–10 and 10–75 μM with the detection limit of 0.077 μM. The selectivity of hesperidin response is proved in the presence of inorganic ions, saccharides, ascorbic acid and other natural phenolics.