A calorimetric investigation into copper–arginine and copper–alanine solid state interactions

Complexes of formula CuCl₂ · 2arg and CuCl₂ · 4ala (arg = arginine; ala = alanine) were prepared at room temperature by a solid state route. The metal–amino acid solid state interactions were studied by i.r. spectroscopy and solution calorimetry. For both complexes, participation of the carboxylate group as well as nitrogen in coordination are inferred, based on the i.r. data. For the copper–arginine compound, the calculated thermochemical parameters are: _rH_m = –114.9 ± 1.42 and _fH_m = –1608.3 ± 11.6 kJ mol^–1. For copper–alanine compound, a complete set of thermochemical parameters were calculated: _rH_m = –18.0 ± 0.9; _fH_m = –2490.4 ± 4.3; _DH_m = 597.2 ± 17.7; _MH_m = 771.9 ± 18.7; _gH_m = 627.1 ± 22.3 and D (Cu–L) = 156.8 ± 5.7 kJ mol^–1. Based on _rH_m and dissolution enthalpy values, a stronger intermolecular solid state interaction can be inferred for the arginine complex, than for the alanine one complex, probably due to the formation of intermolecular hydrogen bonds in the former.     

Adsorptive stripping voltammetric behaviour of copper complexes of some heterocyclic azo compounds

Controlled adsorptive accumulation of copper complexed with TAN, TAC, TAR and TAM (heterocyclic azo-compounds) on a static mercury drop electrode provides the basis for the direct stripping measurement of this element in the nanomolar concentration level. The ligand TAN exhibited great sensitivity and better separation of the peak current of the ligand in relation to the complex. The reduction current of adsorbed complex ions of copper is measured by linear scan cathodic stripping voltammetry, preceded by a period of accumulation of a few minutes. The peak potential is at approximately -0.37 V vs. Ag/AgCl. Optimal experimental parameters were found to be a TAN concentration of 1 x 10(-5)M, an accumulation potential of -0.22 V, and a solution pH of 3.7 (acetate buffer). The detection limit is 0.8nM after a 5-min accumulation with a stirred solution, and the response is linear up to 50 mug/l. Many common cations and anions do not interfere in the determination of copper. The interference of titanium is eliminated by addition of fluoride ion. Results are reported for a fresh water sample.     

A multiscale wavelet data treatment for reliable localization of inflection points for analytical purposes

Instrumental analysis techniques that employ measurements based on inflection points may have their accuracy compromised due to the need for signal differentiation, which is very sensitive to instrumental noise. This paper presents a strategy for localizing inflection points that exploits the multiscale processing capability of the Wavelet Transform and avoids the need for explicit signal differentiation. The strategy is illustrated in simulated examples and also in a real analytical problem involving the determination of Pb and Cd by potentiometric stripping analysis. In this application, the results were in good agreement with the expected values and were slightly better than those obtained from the first derivative of the curves after smoothing by a Windowed Fourier Transform.     

Stripping voltammetry of aluminum based on adsorptive accumulation of its solochrome violet RS complex at the static mercury drop electrode

A very sensitive electrochemical stripping procedure for aluminum is reported. Accumulation is achieved by controlled adsorption of the aluminum/solochrome violet RS complex on the static mercury drop electrode. Optimal experimental parameters include an accumulation potential of ?0.45 V, solochrome violet RS concentration of 1 × 10^?6 M, and a linear-scan stripping mode. The detection limit is 0.15 μg l^?1, the response is linear over the 0–30 μg l^?1 concentration range, and the relative standard deviation (at the 10 μg l^?1 level) is 2%. Most cations do not interfere in the determination of aluminum. The interference of iron(III) is eliminated by addition of ascorbic acid. Results are reported for snow samples.     

Ultratrace determination of adenine in the presence of copper by adsorptive stripping voltammetry

An electrochemical stripping procedure for ultra-trace measurements of adenine is described based on the adsorption of the adenine-copper complex on a static mercury drop electrode. Cyclic voltammetry was used to characterize the interfacial and redox behavior. Optimum experimental conditions were found when using a 0.005 M NaOH solution containing 0.4 ppm of copper, an accumulation potential of -0.30 V, a scan rate of 100 mV s(-1) and a linear scan mode. There is a linear response to adenine concentration in the range of 0.1-1.0 ppb and the detection limit for 6 min accumulation time was of 4.0 ppt (3.0x10(-11) M). Proper conditions for measuring the adenine in presence of guanine, thymine and cytosine were also investigated. The method was applied for the determination of adenine in a sample of single-stranded calf thymus DNA.     

Cathodic adsorptive stripping voltammetry of nickel complexed with hydroxynaphthol blue at a static mercury drop electrode

A new method is described for the determination of Ni based on the cathodic adsorptive stripping of Ni(II) complexed with hydroxynaphthol blue (HNB) at a static mercury drop electrode. Optimal conditions were found to be: accumulation potential -0.50 V (vs. Ag/AgCl); final potential -1.10 V; accumulation time 50 sec; scan rate 200 mV/sec; linear scan mode; filter 0.1 sec; supporting electrolyte acetic acid/acetate (0.25M, pH = 6.0) and concentration of HNB 3.3 x 10(-5)M. The response of the system was found to be linear in a range of Ni concentrations from 25 ppb to the detection limit. The detection limit was found to be 1.7 nM (0.10 ppb) with 2 mins of accumulation time. The effect of various potential interferences (including a variety of cations, anions and organic surfactants) were also studied. With the exception of Co, at less than equimolar concentrations no significant interferences were observed. Al was found to interfere at high concentrations with respect to Ni, but Al concentrations up to 1000 ppb may be masked by sodium citrate or sodium fluoride. The utility of the method is demonstrated by the recovery of Ni in a doped sample of commercial mineral water.     

Chemical process to separate iron oxides particles in pottery sample for EPR dating

Ancient potteries usually are made of the local clay material, which contains relatively high concentration of iron. The powdered samples are usually quite black, due to magnetite, and, although they can be used for thermoluminescene (TL) dating, it is easiest to obtain better TL reading when clearest natural or pre-treated sample is used. For electron paramagnetic resonance (EPR) measurements, the huge signal due to iron spin-spin interaction, promotes an intense interference overlapping any other signal in this range. Sample dating is obtained by dividing the radiation dose, determined by the concentration of paramagnetic species generated by irradiation, by the natural dose so as a consequence, EPR dating cannot be used, since iron signal do not depend on radiation dose. In some cases, the density separation method using hydrated solution of sodium polytungstate [Na6(H2W12O40).H2O] becomes useful. However, the sodium polytungstate is very expensive in Brazil; hence an alternative method for eliminating this interference is proposed. A chemical process to eliminate about 90% of magnetite was developed. A sample of powdered ancient pottery was treated in a mixture (3:1:1) of HCl, HNO(3) and H(2)O(2) for 4h. After that, it was washed several times in distilled water to remove all acid matrixes. The original black sample becomes somewhat clearer. The resulting material was analyzed by plasma mass spectrometry (ICP-MS), with the result that the iron content is reduced by a factor of about 9. In EPR measurements a non-treated natural ceramic sample shows a broad spin-spin interaction signal, the chemically treated sample presents a narrow signal in g=2.00 region, possibly due to a radical of (SiO(3))(3-), mixed with signal of remaining iron [M. Ikeya, New Applications of Electron Spin Resonance, World Scientific, Singapore, 1993, p. 285]. This signal increases in intensity under gamma-irradiation. However, still due to iron influence, the additive method yielded too old age-value. Since annealing at 300 degrees C, Toyoda and Ikeya [S. Toyoda, M. Ikeya, Geochem. J. 25 (1991) 427-445] states that E1'-signal with maximum intensity is obtained, while annealing at 400 degrees C E1'-signal is completely eliminated, the subtraction of the second one from 300 degrees C heat-treated sample isolate E1'-like signal. Since this is radiation dose-dependent, we show that now EPR dating becomes possible.     

Forged Under the Sun: Life and Art of Extremophiles from Andean Lakes

High‐altitude Andean lakes (HAAL) are a treasure chest for microbiological research in South America. Their indigenous microbial communities are exposed to extremely high UV irradiation and to multiple chemical extremes (Arsenic, high salt content, alkalinity). Microbes are found both, free‐living or associated into microbial mats with different degrees of mineralization and lithification, including unique modern stromatolites located at 3570 m above sea level. Characterization of these polyextremophilic microbes began only recently, employing morphological and phylogenetic methods as well as high‐throughput sequencing and proteomics approach. Aside from providing a general overview on microbial communities, special attention is given to various survival strategies; HAAL's microbes present a complex system of shared genetic and physiological mechanisms (UV‐resistome) based on UV photoreceptors and stress sensors with their corresponding response regulators, UV avoidance and protection strategies, damage tolerance and UV damage repair. Molecular information will be provided for what is, so far the most studied HAAL molecule, a CPD‐Class I photolyase from Acinetobacter Ver3 (Laguna Verde, 4400 m). This work further proposes some strategies that make an appeal for the preservation of HAAL, a highly fragile environment that offers promising and ample research possibilities.     

Amphiphilic polylactide-poly(ethylene oxide)-poly(propylene oxide) block copolymers: Self-assembly behavior and cell affinity

Polylactide (PLA) is a biodegradable polyester recognized for its potential use as a biomedical material. Poly(ethylene oxide) (PEO) and copolymers based on PEO and poly(propylene oxide) (PPO) are biocompatible polyethers widely applied in the biomedical field, particularly as macromolecular nonionic surfactants. In this work, PLA blocks were attached to the PEO and to the PEO and PPO-based triblock copolymer PEO–PPO–PEO, through ring-opening polymerization of racemic lactide (rac-LA) to obtain the amphiphilic triblock PLA–PEO–PLA and pentablock PLA–PEO–PPO–PEO–PLA copolymers containing hydrophilic/hydrophobic blocks with variable block mass ratios. The copolymers were evaluated for chemical composition, molar mass, and thermal properties, and they were used to prepare self-assemble aggregates in water from tetrahydrofuran polymer solutions. The combination of scattering light experiments and microscopy techniques revealed the spherical morphology of the aggregates with diameters around 180–200 nm, which comprises a hydrophobic PLA core and a hydrophilic polyether shell. The aggregates are nontoxic to human cervical cancer cell line — HeLa cells, as determined by MTS assay, and the aggregates are potential candidates to be applied in the encapsulation of hydrophobic compounds. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2203–2213