A pH-Metric, UV, NMR, and X-ray Crystallographic Study on Arsenous Acid Reacting with Dithioerythritol

The aqueous solutions of arsenous acid with the meso and racemic forms of 1,4-dithiol-butane-2,3-diol, namely, dithioerythritol (dte) and dithiothreitol (dtt), respectively, were titrated pH-metrically in different molar ratios. The pKa values determined for As(OH)3, and dtt were in good accordance with the literature data, and we determined for the first time the pKa value of dte. The deprotonation steps of both M (As(OH)3 considered as a central metal ion) and H2L components dte and dtt (considered as ligands) appeared at a higher pH in the titration curves of the ternary systems (M, H2L, H+) than in the individual component. This unusual observation is explained by the condensation reactions between the reagents taking place in the pH cAs(III) > 5·10−3 M, the precipitate formed upon mixing the arsenous acid and H2L solutions in neutral medium, and the formation of the precipitate shifted toward acidic pH on the increase of the total concentrations. This indicated that pH-metry can follow the reactions only in an indirect way. Useful, but not satisfactory, information can be obtained by means of this method alone. Combined with NMR and UV spectroscopic measurements it is revealed that depending on the As(III)/H2L molar ratio, different complexes form in the solutions. In the species with 1:2 composition, one of the ligands is strongly bound to the arsenic(III) probably via its two thiolate, while the second one is attached only weakly. The crystal structure of an As(III)−dte crystal of 1:1 composition, grown from ethanolic solution, shows that As(III) binds the ligand through its three p-orbitals in a manner similar to that expected in aqueous solution. While the uptake of the second ligand cannot be detected by pH-metry, the decomposition of thioether bonds above pH ∼10 is confirmed by the change in UV spectra at ∼265 nm to be a base-consuming process. In such alkaline solutions, most probably, rearrangement of the bonding scheme occurs, resulting in ligands being bound to the arsenic(III) through the oxygen donor atoms

Detecting Substrates Bound to the Secondary Multidrug Efflux Pump EmrE by DNP-Enhanced Solid-State NMR

Escherichia coli EmrE, a homodimeric multidrug antiporter, has been suggested to offer a convenient paradigm for secondary transporters due to its small size. It contains four transmembrane helices and forms a functional dimer. We have probed the specific binding of substrates TPP⁺ and MTP⁺ to EmrE reconstituted into 1,2-dimyrist­oyl-<i>sn</i>-glycero-3-phospho­choline liposomes by ³¹P MAS NMR. Our NMR data show that both substrates occupy the same binding pocket but also indicate some degree of heterogeneity of the bound ligand population, reflecting the promiscuous nature of ligand binding by multidrug efflux pumps. Direct interaction between ¹³C-labeled TPP⁺ and key residues within the EmrE dimer has been probed by through-space ¹³C–¹³C correlation spectroscopy. This was made possible by the use of solid-state NMR enhanced by dynamic nuclear polarization (DNP) through which a 19-fold signal enhancement was achieved. Our data provide clear evidence for the long assumed direct interaction between substrates such as TPP⁺ and the essential residue E14 in transmembrane helix 1. Our work also demonstrates the power of DNP-enhanced solid-state NMR at low temperatures for the study for secondary transporters, which are highly challenging for conventional NMR detection

A Novel Dinuclear Species in the Aqueous Distribution of Aluminum in the Presence of Citrate

The chemistry of aluminum was explored in the presence of the physiological ligand citric acid and in low-pH aqueous media. As a result, the first dinuclear aluminum−citrate complex (NH4)4[Al2(C6H4O7)(C6H5O7)2]·4H2O was isolated at low pH (∼3.5), and was characterized by FT-IR spectroscopy and X-ray crystallography. The structural analysis reveals the presence of a dinuclear assembly of two aluminum ions octahedrally coordinated to three citrate ligands of differing protonation state. The NMR solution behavior of this complex emphasizes its time-dependent transformation into a number of variable nature species, ultimately leading to the thermodynamically stable trinuclear species. It also establishes the participation of the dinuclear complex as a viable component of the aqueous Al(III)−citrate speciation. The chemical and structural features of this novel low molecular mass species provide considerable insight into citrate's ability, as a natural ligand, to influence the chemistry of aluminum in a pH-dependent fashion, and potentially affect aluminum's (bio)distribution, absorption, accumulation, and biotoxicity at sensitive biological sites

A Novel Dinuclear Species in the Aqueous Distribution of Aluminum in the Presence of Citrate

The chemistry of aluminum was explored in the presence of the physiological ligand citric acid and in low-pH aqueous media. As a result, the first dinuclear aluminum−citrate complex (NH4)4[Al2(C6H4O7)(C6H5O7)2]·4H2O was isolated at low pH (∼3.5), and was characterized by FT-IR spectroscopy and X-ray crystallography. The structural analysis reveals the presence of a dinuclear assembly of two aluminum ions octahedrally coordinated to three citrate ligands of differing protonation state. The NMR solution behavior of this complex emphasizes its time-dependent transformation into a number of variable nature species, ultimately leading to the thermodynamically stable trinuclear species. It also establishes the participation of the dinuclear complex as a viable component of the aqueous Al(III)−citrate speciation. The chemical and structural features of this novel low molecular mass species provide considerable insight into citrate's ability, as a natural ligand, to influence the chemistry of aluminum in a pH-dependent fashion, and potentially affect aluminum's (bio)distribution, absorption, accumulation, and biotoxicity at sensitive biological sites

MOESM4 of Neurodevelopmental effect of intracranial hemorrhage observed in hypoxic ischemic brain injury in hypothermia-treated asphyxiated neonates - an MRI study

Additional file 4: MRI findings and neurodevelopmental outcome in cooled infants with ICH and the imaging signs of HIE

MOESM5 of Neurodevelopmental effect of intracranial hemorrhage observed in hypoxic ischemic brain injury in hypothermia-treated asphyxiated neonates - an MRI study

Additional file 5: MRI findings and neurodevelopmental outcome in cooled infants showing the imaging signs of HIE without ICH

MOESM2 of Neurodevelopmental effect of intracranial hemorrhage observed in hypoxic ischemic brain injury in hypothermia-treated asphyxiated neonates - an MRI study

Additional file 2: MRI findings and neurodevelopmental outcome in cooled infants with no signs of HIE and ICH on early MRI

Additional file 1: of Prognostic value of early, conventional proton magnetic resonance spectroscopy in cooled asphyxiated infants

Results of Mann-Whitney test for all metabolite ratios. Data are shown as median [IQR], results were considered significant at p < 0.0014 (after Bonferroni correction). (XLSX 10 kb

MOESM1 of Neurodevelopmental effect of intracranial hemorrhage observed in hypoxic ischemic brain injury in hypothermia-treated asphyxiated neonates - an MRI study

Additional file 1: Inclusion and exclusion criteria of therapeutic hypothermia in the TOBY trial

MOESM3 of Neurodevelopmental effect of intracranial hemorrhage observed in hypoxic ischemic brain injury in hypothermia-treated asphyxiated neonates - an MRI study

Additional file 3: MRI findings and neurodevelopmental outcome in cooled infants with ICH without the imaging signs of HIE