Study of soils by thermal analysis

The study of soils is very important in the geological and geological engineering researches. A study of ten samples of soils was carried out by thermal analysis, and X-Ray Fluorescence Spectrometry to understand soil evolution in Angra dos Reis region, Rio de Janeiro State, Brazil. The sample collection sites were chosen based on geological characteristics, the soil layer thickness, the soil composition pattern, and whether or not it was moved either by erosion or by gravitational shifts. Because of the humid tropical climatic condition, natural soils tend to show great thickness of weathered mantles with formation of saprolites and saprolite soils. Kaolinite is an important secondary mineral which can be formed from many different minerals, like k-mica and k-feldspar and can be weathered to gibbsite. The results from TG/DTG and DTA indicated which soils had more weathering, and the same results were obtained by XRF, when silica/aluminum ratios from samples are compared with thermal analysis results.     

Evaluating the potential and limitations of double-spiking species-specific isotope dilution analysis for the accurate quantification of mercury species in different environmental matrices

A new double-spiking approach, based on a multiple-spiking numerical methodology, has been developed and applied for the accurate quantification of inorganic mercury (IHg) and methylmercury (MeHg) by GC–ICPMS in different environmental matrices such as water, sediments and a wide range of biological tissues. For this purpose, two enriched mercury species (²⁰¹MeHg and ¹⁹⁹IHg) were added to the samples before sample preparation in order to quantify the extents of the methylation and demethylation processes, and thereby correct the final species concentrations. A critical evaluation of the applicability of this methodology was performed for each type of matrix, highlighting its main advantages and limitations when correcting for the conversion reactions of the species throughout the whole sample preparation procedure. The double-spike isotope dilution (DSIDA) methodology was evaluated by comparing it with conventional species specific isotope dilution (IDA) when analysing both certified reference materials and environmental samples (water, biotissues and sediment). The results demonstrate that this methodology is able to provide both accurate and precise results for IHg and MeHg when their relative concentrations are not too different (ratio MeHg/IHg > 0.05), a condition that holds for most natural waters and biotissues. Significant limitations on the accurate and precise determination of the demethylation factor are however observed, especially for real sediment samples in which the relative concentrations of the species are substantially different (ratio MeHg/IHg < 0.05). A determination of the sources of uncertainty in the methylation/demethylation factors has demonstrated that the accurate and precise measurement of the isotope ratios in the species involved in the transformations is crucial when quantifying the extents of these reactions. Although the double-spike methodology is established as a reference approach that permits the correction of most analytical biases and the accurate quantification of Hg species, some limitations have been identified for the first time in this work.     

Characterization of Binding Properties of Cr(Phen)33+ and Ru(Phen)32+ Complexes with Human Lactoferrin

This work presents research about [Cr(phen)₃]³⁺ and [Ru(phen)₃]²⁺ interaction with human lactoferrin (HLf), a key carrier protein of ferric cations. The photochemical and photophysical properties of [Cr(phen)₃]³⁺ and [Ru(phen)₃]²⁺ have been widely studied in the last decades due to their potential use as photosensitizers in photodynamic therapy (PDT). The behavior between the complexes and the protein was studied employing UV–visible absorption, fluorescence emission and circular dichroism spectroscopic techniques. It was found that both complexes bind to HLf with a large binding constant (K_b): 9.46 × 10⁴ for the chromium complex and 4.16 × 10⁴ for the ruthenium one at 299 K. Thermodynamic parameters were obtained from the Van't Hoff equation. Analyses of entropy (ΔS), enthalpy (ΔH) and free energy changes (ΔG) indicate that these complexes bind to HLf because of entropy-driven processes and electrostatic interactions. According to circular dichroism experiments, no conformational changes have been observed in the secondary and tertiary structure of the protein in the presence of any of the studied complexes. These experimental results suggest that [Cr(phen)₃]³⁺ and [Ru(phen)₃]²⁺ bind to HLf, indicating that this protein could act as a carrier of these complexes in further applications.     

Femtosecond laser ablation inductively coupled plasma mass spectrometry: Transport efficiencies of aerosols released under argon atmosphere and the importance of the focus position

Although the utilization of helium as aerosol carrier has been shown to improve both accuracy and sensitivity of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), occasionally, argon is being used due to practical and economic reasons. In order to provide more insight into the mechanisms underlying these performance differences, in this study, transport efficiencies of aerosols released by NIR- and UV-femtosecond laser ablation (LA) of brass applying laminar or turbulent in-cell flow conditions and argon as carrier gas were measured. Aerosol particles were collected by low-pressure impaction or filtered by fine porous membranes. On the basis of aerosol masses collected and mass differences derived from target weighing prior to and after LA, transport efficiencies approximately varied in between 75% and 95%. In addition, LA of a thin Cr layer was performed which allowed to release a well-defined amount of material and, thus, to correct mass balances for debris accumulating around the crater rim. The total aerosol mass released during LA was found to be strongly dependent on the relative focus position, i.e. surface area irradiated, even if the laser pulse energy delivered to the target was kept constant. Furthermore, a physical model only making use of input parameters such as laser spot size and pulse energy was implemented to qualitatively describe the correlation between aerosol mass and laser focus position.     

Design analysis of a laser ablation cell for inductively coupled plasma mass spectrometry by numerical simulation

A laser ablation setup including outer chamber, sample tube, sample holder and transport tubing was modelled and optimized using advanced computational fluid dynamics techniques. The different components of the setup were coupled and the whole device was modelled at once. The mass transport efficiency and transit times of near infrared femtosecond (fs) laser generated brass aerosols in pure argon and helium–argon mixtures were calculated at experimentally optimized conditions and a transient signal was constructed. The use of helium or argon did not influence the mass transport efficiency, but the signal structure changed. The signal fine structure was retrieved and experimentally validated. Bimodal peak structures were observed that seemed to originate from turbulent effects in the tubing connecting a Y-connector and the injector.     

Analysis of iridoids from Harpagophytum and eleutherosides from Eleutherococcus senticosus in horse urine

LC/ESI-MS n methods have been previously set up to detect the administration of (i) Harpagophytum and (ii) preparations containing a plant capable of anti-stress properties: Eleutherococcus senticosus. Harpagoside has been found to be the main indicator of Harpagophytum administration in the horse. These methods have been applied to a large number of horse urine samples of various origins. Regarding the detection of Harpagophytum administration, harpagoside, harpagide and 8-para-coumaroyl harpagide were detected together in only one sample out of 317. Eleutheroside E was found to be the main indicator of Eleutherococcus senticosus administration. It was detected in post-administration samples collected from two horses having received a feed supplement containing Eleutherococcus senticosus for several days. Out of the 382 samples tested, eleutheroside E was found in an unexpected large number of urine samples (39%) of various origins and its presence cannot be only due to the sole use of herbal dietary supplements.     

The origin of the dynamic transition in proteins

Despite extensive efforts in experimental and computational studies, the microscopic understanding of dynamics of biological macromolecules remains a great challenge. It is known that hydrated proteins, DNA and RNA, exhibit a so-called "dynamic transition." It appears as a sharp rise of their mean-squared atomic displacements r2 at temperatures above 200-230 K. Even after a long history of studies, this sudden activation of biomolecular dynamics remains a puzzle and many contradicting models have been proposed. By combining neutron and dielectric spectroscopy data, we were able to follow protein dynamics over an extremely broad frequency range. Our results show that there is no sudden change in the dynamics of the protein at temperatures around approximately 200-230 K. The protein's relaxation time exhibits a smooth temperature variation over the temperature range of 180-300 K. Thus the experimentally observed sharp rise in r2 is just a result of the protein's structural relaxation reaching the limit of the experimental frequency window. The microscopic mechanism of the protein's structural relaxation remains unclear.     

Optimization of solid-phase extraction for the liquid chromatography-mass spectrometry analysis of harpagoside, 8-para-coumaroyl harpagide, and harpagide in equine plasma and urine

Solid-phase extraction cartridges among those usually used for screening in horse doping analyses are tested to optimize the extraction of harpagoside (HS), harpagide (HG), and 8-para-coumaroyl harpagide (8PCHG) from plasma and urine. Extracts are analyzed by liquid chromatography coupled with multi-step tandem mass spectrometry. The extraction process retained for plasma applies BondElut PPL cartridges and provides extraction recoveries between 91% and 93%, with RSD values between 8 and 13% at 0.5 ng/mL. Two different procedures are needed to extract analytes from urine. HS and 8PCHG are extracted using AbsElut Nexus cartridges, with recoveries of 85% and 77%, respectively (RSD between 7% and 19%). The extraction of HG involves the use of two cartridges: BondElut PPL and BondElut C18 HF, with recovery of 75% and RSD between 14% and 19%. The applicability of the extraction methods is determined on authentic equine plasma and urine samples after harpagophytum or harpagoside administration.     

Microwave‐assisted synthesis of new regioisomeric 6,7‐dihydroindeno[1,2‐e]pyrimido[4,5‐b][1,4]diazepin‐5(5aH)‐ones

Novel 11‐amino‐6‐aryl‐6,7‐dihydroindeno[1,2‐e] pyrimido[4,5‐b][1,4]diazepin‐5(5aH)‐ones 4a‐f were prepared regioselectively by the tricomponent reaction of 4,5,6‐triaminopyrimidine 1, 1,3‐indandione 2 and aromatic aldehydes 3a‐f. The bicomponent approach, using 2,4,5,6‐tetraaminopyrimidine 5 and 2‐aryl‐ideneindandiones 6a‐f as reagents, afforded 9,11‐diamino‐6‐aryl‐6,7‐dihydroindeno[1,2‐e]pyrimido[4,5‐b]‐[1,4]diazepin‐5(5aH)‐ones 7a‐f in good yields and the regioisomeric 8,10‐diamino derivatives 8a‐c in lower yields. Both, bi‐ and tricomponent approaches were performed by microwave irradiation and all products were fully characterized by detailed NMR measurements.     

Synthesis of organometallic Ru(II) and Fe(II) complexes containing fused rings hemi-helical ligands as chromophores. Evaluation of non-linear optical properties by HRS

A new family of three-legged piano stool structured organometallic compounds containing the fragment η⁵-cyclopentadienyl-ruthenium(II)/iron(II) has been synthesized to evaluate the existence of electronic metal to ligand charge transfer upon coordination of the novel benzodithiophene ligands (BDT), benzo[1,2-b;4,3-b′]dithiophen-2-carbonitrile (L1) and benzo[1,2-b;4,3-b′]dithiophen-2′nitro-2-carbonitrile (L2). All the compounds were characterized by ¹H, ¹³C, ³¹P NMR, IR and UV-Vis. spectroscopies and their electrochemistry studied by cyclic voltammetry. The X-ray structures of [Ru(η⁵-C₅H₅)(PPh₃)₂(NCC₁₀H₅S₂)][PF₆] (1Ru), [Ru(η⁵-C₅H₅)(PPh₃)₂(NCC₁₀H₅S₂)][CF₃SO₃] (1′Ru), [Ru(η⁵-C₅H₅)(DPPE)(NCC₁₀H₅S₂)][PF₆] 2Ru and [Fe(η⁵-C₅H₅)(DPPE)(NCC₁₀H₅S₂)][PF₆] (2Fe) were determined by X-ray diffraction showing centric crystallization on groups and P2₁/n, respectively.Quadratic hyperpolarizabilities (β) of some of the complexes (2Fe, 2Ru and 3Fe) have been determined by hyper-Rayleigh scattering (HRS) measurements at a fundamental wavelength of 1500 nm, to minimize the probability of fluorescence due to two-photon absorption and to reduce the effect of resonance enhancement, in order to estimate static β values.