Electron propagator theory and application

Summary The electron propagator theory is presented with somewhat of a historical perspective and the working equations are developed with the aim of taking advantage of molecular point group symmetry. A new electron propagator code, the vectorized electron propagator program (VEP), is introduced without full details about its structure and capabilities (such details are being published elsewhere). Applications to the (UV) photoelectron spectra of some donor-acceptor complexes of borane with carbon monoxide and water are presented at the level of second-order theory as an illustration of the theory and the VEP code.     

Metallcarbonyl-synthesen: XIII. Eine mangan—mangan-dreifachbindung

Photolysis of the manganese half-sandwich complex (η⁵-C₅Me₅)Mn(CO)₃ (1) in tetrahydrofuran (THF) yields cleanly the solvent complex (η⁵-C₅Me₅)(Mn(CO)₂THF (2). Compound 2 undergoes spontaneous elimination of carbon monoxide to give at ambient temperature in approx. 20 h, or upon removal of solvent in vacuo, the novel dinuclear derivative (η⁵-C₅Me₅)₂Mn₂(μ-CO)₃ (3). Elemental analyses and infrared and mass as wel as the ¹H and ¹³C NMR spectra unequivocally demonstrate this compound to adopt a triply carbonyl-bridged structure containing the first example of a manganesemanganese multiple bond.     

The determination of trace metals in lubricating oils by atomic spectrometry

The determination of trace metals in lubricating oils using atomic spectrometric methods is reviewed. The importance of such analyses for technical diagnostics as well as the specific sample characteristics related to the analyte form (metallo-organic and metal particles) is discussed. Problems related to sample pre-treatment for appropriate sample introduction and calibration are addressed as well as the strategies to overcome them. Recent trends aimed at simplifying sample manipulation are presented. The applications and scope of AAS, ICP OES and ICP MS techniques for the determination of trace metals in lubricating oil is individually discussed, as well as some present instrumental trends.     

Unfolding Tin–Cobalt Interactions in Oxide‐Based Composite Electrodes for Li‐Ion Batteries by Mössbauer Spectroscopy

With a view to the development of new composite electrodes for lithium-ion batteries with electroactive tin and cobalt, Co-doped tin dioxide samples are studied. The role played by oxygen and cobalt atoms in the electrochemical behavior of tin-based electrodes for Li-ion batteries is examined by the powerful and selective (119)Sn M?ssbauer spectroscopy. For the discharged electrodes, the oxygen atoms in the lithia matrix tend to destabilize the Sn(0) atoms. In contrast, the presence of cobalt atoms helps to form a matrix that stabilizes the reduced tin atoms. Cobalt-tin interactions in electrochemical reduced Co(x)Sn(1-x)O(2) electrodes are deduced from the electrochemical and M?ssbauer results.     

Continuous organelle separation in an insulator-based dielectrophoretic device

Heterogeneity in organelle size has been associated with devastating human maladies such as neurodegenerative diseases or cancer. Therefore, assessing the size-based subpopulation of organelles is imperative to understand the biomolecular foundations of these diseases. Here, we demonstrated a ratchet migration mechanism using insulator-based dielectrophoresis in conjunction with a continuous flow component that allows the size-based separation of submicrometer particles. The ratchet mechanism was realized in a microfluidic device exhibiting an array of insulating posts, tailoring electrokinetic and dielectrophoretic transport. A numerical model was developed to elucidate the particle migration and the size-based separation in various conditions. Experimentally, the size-based separation of a mixture of polystyrene beads (0.28 and 0.87 $\mu$m) was accomplished demonstrating good agreement with the numerical model. Furthermore, the size-based separation of mitochondria was investigated using a mitochondria mixture isolated from HepG2 cells and HepG2 cells carrying the gene Mfn-1 knocked out, indicating distinct size-related migration behavior. With the presented continuous flow separation device, larger amounts of fractionated organelles can be collected in the future allowing access to the biomolecular signature of mitochondria subpopulations differing in size.     

Metal-ion induced amplification of three receptors from dynamic combinatorial libraries of peptide-hydrazones

Three building blocks of general structure (MeO)2 CH-aromatic linker-Pro-amino acid-NHNH2 have been prepared and tested in acid-catalysed dynamic combinatorial libraries. Exposure of these libraries to LiI and NaI led to the amplification of three macrocyclic pseudopeptide receptors. The receptors were isolated and their interactions with LiI and NaI were analysed using NMR, IR and ITC. Binding of the metal ions to the receptors is invariably entropy-driven. Nevertheless, all receptors were found to be flexible with substantial conformational rearrangements accompanying guest binding. This type of receptor is extremely difficult to access through rational design and the fact that dynamic combinatorial chemistry allows facile access to these challenging molecules underlines the power of the dynamic approach.     

Crystal structure and pseudosymmetry analysis of the triclinic prodrug cloxazolam (Z′ = 4)

The prodrug cloxazolam [systematic name: 13‐chloro‐2‐(2‐chlorophenyl)‐3‐oxa‐6,9‐diazatricyclo[8.4.0.0^2,6]tetradeca‐1(10),11,13‐trien‐8‐one], C₁₇H₁₄Cl₂N₂O₂, crystallizes in the triclinic space group P, with four chemically identical independent molecules in the asymmetric unit. However, in order to facilitate the analysis of the striking pseudosymmetry relating the four independent molecules, the structure has been analysed and reported in the nonconventional centred B space‐group setting. Pseudosymmetry is an eminently local property, valid only in the realm of the unit‐cell boundary and not propagating to the whole crystal structure. It has been analyzed using the MP procedure described in the preceding article [Baggio (2019). Acta Cryst. C 75 , 837–850]. The molecules consist of a rigid core made up of three rings (five‐, six‐ and seven‐membered) and an extra six‐membered ring joined to the latter group by a single C—C bond, together with a clamping intramolecular C—H…O interaction preventing free rotation and providing additional rigidity. The four molecules in the asymmetric unit pair into dimers with almost exact twofold pseudosymmetry, further linked into (001) slabs as the building bricks of the structure. Interpenetration of slabs finally leads to a three‐dimensional structure of unusual compactness for an organic structure, with a Kitaigorodskii packing index of ca 0.71.     

Pungency evaluation of onion cultivars from the Venezuelan West-Center region by flow injection analysis-UV-visible spectroscopy pyruvate determination

A flow injection analysis (FIA) method was developed for the determination of pyruvate in onion cultivars (Allium cepa L.) from the West-Center region of Venezuela. The reference Schwimmer and Weston (1961) (J. Agric. Food Chem. 9 (1961) 301) Batch method was modified and adapted to FIA conditions. The formation kinetic of the 2,4-dinitrophenylhydrazine (DNPH)–pyruvate complex was evaluated at room temperature and at 37 °C. It was demonstrated the suitability of the chromopher formation at room temperature. The optimal values for the FIA parameters were: sample injection volume 3 mL, flow rate 6 mL min⁻¹, reactor length 1.5 m, sodium hydroxide concentration 1.0 mol L⁻¹ and hydrochloric acid concentration 0.5 mol L⁻¹. The working calibration range was extended from 80 mg L⁻¹ (Batch method) to 700 mg L⁻¹ with the FIA set up. The sample dilution step is thus avoided, simplifying the whole analysis process. The pungency in representative samples of the cultivars Yellow granex 438, Ultra Hybrid and Red onion “Sangre de Toro” was evaluated by the flow injection analysis (FIA)–pyruvate method and the results were compared to the reference Batch pyruvate method and to the taste panel test. Non-significant differences were found at the 95% of confidence level between the FIA method and the Batch reference method. Correlation coefficient when comparing the FIA results to the taste panel test was r² = 0.8353. Significant differences (P < 0.05) were found in the pungency of the cultivars, the Ultra Hybrid having the highest pungency. The pungency order from minor to major was: Red onion, Texas Grano 438 and Ultra Hybrid.     

Potentiometric,NMR, and Fluorescence‐Emission Studies on the Binding of Adenosine 5′‐Triphosphate (ATP) by Open‐Chain Polyamine Receptors Containing Naphthylmethyl and/or Anthrylmethyl Groups

The interaction in aqueous solution of adenosine 5′‐triphosphate (ATP) with a series of open‐chain polyamines linked at one or both ends to anthrylmethyl or naphthylmethyl fragments was followed by potentiometric titration, ¹H‐, ¹³C‐, and ³¹P‐NMR spectroscopy, and by steady‐state fluorescence measurements. The results revealed greater stabilities for the compounds containing one anthracene moiety than for those with one naphthalene moiety, the stabilities of the compounds with both ends N‐substituted with naphthylmethyl groups being close to those containing just one anthrylmethyl unit. The ¹H‐NMR spectra showed that in all systems, there is involvement of π‐π stacking interactions in the stabilization of the adduct species. The competitive effect of the anions afforded by the supporting electrolyte was checked in some of the studied systems working at two different ionic strenghts (0.15M and 1.0M NaCl). The joint analysis of the spectrofluorimetric titrations and pH‐metric species‐distribution curves showed that for all the ATP? receptor systems, a quenching of the fluorescence occurred upon protonation of the adenine N(1)atom. Steady‐state fluorescence and time‐correlated single‐photon‐counting analysis of a system made up of ATP and a bis‐chromophoric polyamine receptor containing anthracene and naphthalene fluorophores established that the energy‐transfer process between the naphthalene and anthracene moieties is still operative despite the presence of ATP.     

Analytical curve or standard addition method: how to elect and design--a strategy applied to copper determination in sugarcane spirits using AAS

In most instrumental analysis, the analyte concentration is usually obtained the by Analytical Curve Method (ACM) or Standard Addition Method (SAM). Thus, it is important for the analyst to select the most appropriate method, to seek the best conditions of analysis, and to provide parameters of analytical performance. A strategy to do so is proposed in this paper in conjunction with MATLAB software to implement it. The proposed strategy was applied to copper determination by atomic absorption spectrometry in Brazilian sugarcane spirits termed 'Cacha?a' and SAM was chosen as the most appropriate method. To select the best experimental design for SAM, the influence of some factors, such as the number of standard additions and concentration levels, the location of the levels and the average concentration of the standard additions were demonstrated. The design with six standard additions, four concentration levels located near the inferior and superior levels and the average concentration of the standard additions closer to zero yielded SAM with an adequate compromise between precision, cost and time of analysis. The uniform distribution of concentration levels, usually used in routine analysis, is not a good design regarding precision. On the other hand, it is adequate when the linear range is unknown. Generally, the proposed strategy can be applied to different instrumental techniques and samples, which aim to improve their analytical performance.