The chemical speciation of aluminium in human serum

Chemical speciation of aluminium in the low molecular mass (LMM) and high molecular mass (HMM) fractions of human serum is discussed. A critical review of the literature on different analytical procedures described for the speciation of aluminium in human serum samples is presented here. The methodologies, the experimental and instrumental requirements and the ability of the reported analytical procedures for identification of HMM and LMM aluminium species in human serum are examined in detail. Non-chromatographic separations coupled to electrothermal atomic absorption spectrometry for aluminium detection are compared with chromatographic techniques (size exclusion chromatography, anion exchange chromatography and fast protein liquid chromatography) coupled to ETAAS or inductively coupled plasma mass spectrometry (ICP-MS) detection for Al-HMM species investigations. Studies and techniques reported for Al-LMM compounds are also summarised, both for healthy volunteers and dialysis patients. On the basis of the knowledge obtained from the application of the developed analytical procedures to real serum analysis, it has been demonstrated that most of Al in human serum is bound to Al-transferrin, while the LMM-Al fraction (10-20% of total Al) mainly contains Al-citrate, Al-phosphate and ternary Al-citrate-phosphate complexes.     

One-electron reduction of 8-bromo-2-aminoadenosine in the aqueous phase: radiation chemical and DFT studies of the mechanism

Two tautomeric forms of one-electron oxidized 2-aminoadenosine (2AA) have been produced by reactions of hydrated electrons (e aq-) with 8-bromo-2-aminoadenosine (8-Br-2AA) at natural pH, whereas only one tautomer is formed by oxidation of 2AA. Tailored experiments by pulse radiolysis and time-dependent DFT (TD-B3LYP/6-311G**//B1B95/6-31+G**) calculations allowed the definition of the reaction mechanism in some detail. The electron adducts of 8-Br-2AA protonated at C8 eject Br- and produce the two short-lived tautomers (8 and 9). The first observable species decays by first-order kinetics to produce the second intermediate, which is also obtained by oxidation of 2AA by SO4*-. The rate of tautomerization (k taut = 4.5 x 104 s-1) is strongly accelerated by phosphate and is retarded in D2O (kinetic isotope effect 7). B1B95/6-31+G** calculations showed that the tautomerization is a water-assisted process. In acidic or basic solutions, the "instantaneous" formation of one-electron oxidized 2AA or its deprotonated forms has been produced by reactions of e aq- with 8-Br-2AA. gamma-Radiolysis of 8-Br-2AA in aqueous solutions followed by product studies led to the formation of 2AA as a single product.     

Study on the formation of an amoxicillin adduct with methanol using electrospray ion trap tandem mass spectrometry

The possibility of using the protonated methanol-adduct of antimicrobial amoxicillin for its identification and quantification at residue levels has been investigated, since it is impossible to completely suppress the formation of these adducts when methanol is present in the solvent system. This process has been monitored over time and as a function of concentration. It was determined that adducts were instantly formed and that the abundance of the protonated methanol-adduct at m/z 398 increased at the expense of the protonated molecule m/z 366 with storage time. The effect of several common solvents and mobile-phase additives on the ionization efficiency of amoxicillin and the formation of the methanol adduct has also been investigated. It was shown that the mass spectra of amoxicillin were strongly influenced by the solvent in which the analyte is dissolved and by the analyte concentration, as well as by the composition of mobile phase. Methanol was determined to be the best spray solvent, as it provided spectra with the lowest abundance of dimer ions. It was also determined that acetic acid as the mobile-phase additive provided the highest signal intensities, while ammonium acetate should not be used as an additive for the determination of amoxicillin at residue levels. Using high-performance liquid chromatography/electrospray ionization tandem mass spectrometry (HPLC/ESI-MS/MS), fragmentation of the protonated molecules and the protonated methanol-adduct ions, in both positive and negative ion mode, has been performed. The fragmentation was stable and strong product ion spectra were obtained. The linearity of the MS detector response, and that of the chromatographic method, was tested. Due to the linear behaviour it was concluded that the protonated methanol-adduct ion can be used for analytical purposes, i.e. for identification and quantification of amoxicillin at trace levels.     

Supersolid phase induced by correlated hopping in spin-1/2 frustrated quantum magnets

We show that correlated hopping of triplets, which is often the dominant source of kinetic energy in dimer-based frustrated quantum magnets, produces a remarkably strong tendency to form supersolid phases in a magnetic field. These phases are characterized by simultaneous modulation and ordering of the longitudinal and transverse magnetization, respectively. Using quantum Monte Carlo and a semiclassical approach for an effective hard-core boson model with nearest-neighbor repulsion on a square lattice, we prove, in particular, that a supersolid phase can exist even if the repulsion is not strong enough to stabilize an insulating phase at half-filling. Experimental implications for frustrated quantum antiferromagnets in a magnetic field at zero and finite temperature are discussed.     

Antimicrobial and Antioxidant Potential of Scenedesmus obliquus Microalgae in the Context of Integral Biorefinery Concept

Small-scale photobioreactors (PBRs) in the inoculum stage were designed with internal (red or green) and external white LED light as an initial step of a larger-scale installation aimed at fulfilling the integral biorefinery concept for maximum utilization of microalgal biomass in a multifunctional laboratory. The specific growth rate of Scenedesmus obliquus (Turpin) Kützing biomass for given cultural conditions was analyzed by using MAPLE software. For the determination of total polyphenols, flavonoids, chlorophyll “a” and “b”, carotenoids and lipids, UHPLC-HRMS, ISO-20776/1, ISO-10993-5 and CUPRAC tests were carried out. Under red light growing, a higher content of polyphenols was found, while the green light favoured the flavonoid accumulation in the biomass. Chlorophylls, carotenoids and lipids were in the same order of magnitude in both samples. The dichloromethane extracts obtained from the biomass of each PBR synergistically potentiated at low concentrations (0.01–0.05 mg/mL) the antibacterial activity of penicillin, fluoroquinolones or oregano essential oil against the selected food-borne pathogens (Staphylococcus aureus, Escherichia coli and Salmonella typhimurium) without showing any in vitro cytotoxicity. Both extracts exhibited good cupric ion-reducing antioxidant capacity at concentrations above 0.042–0.08 mg/mL. The UHPLC-HRMS analysis revealed that both extracts contained long chain fatty acids and carotenoids thus explaining their antibacterial and antioxidant potential. The applied engineering approach showed a great potential to modify microalgae metabolism for the synthesis of target compounds by S. obliquus with capacity for the development of health-promoting nutraceuticals for poultry farming.     

The discrimination between triplet state and radical cation in the pulse radiolysis of bithiophene in CCl4

The triplet state (³2T) and the radical cation (2T⁺√) of 2,2′-bithiophene (2T) are characterized by pulse radiolysis in CCl₄. Two main absorption bands at 360 and 420 nm are respectively attributed to ³2T* and to 2T⁺√. The triplet, induced in an excited state through a Förster mechanism, undergoes a conformational rearrangement (k₆=(6.8±0.9)×10⁶ s⁻¹). The radical cation is produced both through a resonance charge transfer and a second diffusional process; the two oxidizing species are respectively CCl₄⁺√ and (CCl⁺₃Cl⁻)_solv through the mediation of a singlet excited state, ¹2T*.     

A kinetic, spectral and theoretical investigation on the role of oxygen in the radiolytic oxidation of a sorbityl cyclic acetal

The oxidation process of the cyclic acetal sorbitylfurfural (SF) has been thoroughly examined from the kinetic, spectroscopic and theoretical point of view. Oxidation has been initiated by the radiolitically produced OH radical in the presence of variable oxygen amounts. Two competing reaction pathways are evidenced which lead to quite different products, although they do not affect the acetal ring integrity. The peroxidation of the hydroxylated furanic ring (k ₄=(6.1±0.9)×10⁸ M⁻¹ s⁻¹) maintains the ring structurevia HO₂^• elimination (k ₆=(1.9±0.4)×10⁵ s⁻¹). Unlike that, the peroxidation of the pseudo-allylic radical (k ₅=(1.9±0.9)×10⁹ M⁻¹ s⁻¹), formedvia β-cleavage, fixes the destructured intermediate, leading to a tetroxide, which slowly decomposes through a Russell mechanism (k ₈=(2.3±0.6)×10² s⁻¹). It is confirmed that the steady state concentration of the tetroxide is very low, which suggests a molar absorption coefficient for it around 1.2×10⁴ M⁻¹ cm⁻¹ at 265 nm. The end products of the latter pathway have been characterized as carboxylic and butenald-sorbitol derivatives. The kinetic and spectral data of every step of the process have been fitted by the above outlined mechanism. The energetics of the mechanism has been detailed byab initio computations as well, carrying further substantiation to it. Semi-empirical calculations were also employed to describe the spectral properties of each intermediate.