Abiotic phosphorus recycling from adsorbed ribonucleotides on a ferrihydrite-type mineral: Probing solution and surface species

Iron (Fe) (oxyhydr)oxide minerals, which are amongst most reactive minerals in soils and sediments, are known to exhibit strong adsorption of inorganic phosphate (P_i) and organophosphate (P_o) compounds. Beyond synthetic P_o compounds, much still remains unknown about the reactivity of these minerals to transform naturally-occurring P_o compounds to P_i, particularly with respect to solution versus surface speciation of P_o hydrolysis. To investigate this reactivity with a ferrihydrite-type mineral and ribonucleotides, we employed high-resolution liquid chromatography-mass spectrometry (LC-MS), X-ray absorption near-edge structure (XANES), Fourier-transform infrared (FTIR) spectroscopy, and molecular modeling. Kinetic experiments were conducted with the mineral (1 g L^-1) reacted with adenosine monophosphate, diphosphate, or triphosphate (respectively AMP, ADP, ATP; 50 µM). Analysis of solution organic species by LC-MS implied that only adsorption occurred with AMP and ADP but both adsorption and dephosphorylation of ATP were evident. Maximum adsorption capacities per gram of mineral were 40.6 ± 0.8 µmol AMP, 35.7 ± 1.6 µmol ADP, and 10.9 ± 1.0 µmol ATP; solution dephosphorylated by-products accounted for 15% of initial ATP. Subsequent XANES analysis of the surface species revealed that 16% of adsorbed AMP and 30% of adsorbed ATP were subjected to dephosphorylation, which was not fully quantifiable from the solution measurements. Molecular simulations predicted that ADP and ATP were complexed mainly via the phosphate groups whereas AMP binding also involved multiple hydrogen bonds with the adenosine moiety; our FTIR data confirmed these binding confirmations. Our findings thus imply that specific adsorption mechanisms dictate the recycling and subsequent trapping of P_i from ribonucleotide-like biomolecules reacted with Fe (oxyhydr)oxide minerals.

On the structure of thorium and americium adenosine triphosphate complexes

PURPOSE

The actinides are chemical poisons and radiological hazards. One challenge to better appraise their toxicity and develop countermeasures in case of exposure of living organisms is to better assess pathways of contamination. Because of the high chemical affinity of those actinide elements for phosphate groups and the ubiquity of such chemical functions in biochemistry, nucleotides and in particular adenosine triphosphate nucleotide (ATP) may be considered critical target building blocks for actinides.

MATERIALS AND METHODS

Combinations of spectroscopic techniques (Fourier transformed Infra Red [FTIR], Electrospray Ionization Mass Spectrometry [ESI-MS], and Extended X-ray Absorption Fine Structure [EXAFS]) with quantum chemical calculations have been implemented in order to assess the actinides coordination arrangement with ATP.

RESULTS

We describe and compare herein the interaction of ATP with thorium and americium; thorium(IV) as a representative of actinide(IV) like plutonium(IV) and americium(III) as a representative of all heavier actinides. In the case of thorium, an insoluble complex is readily formed. In the case of americium, a behavior identical to that described previously for lutetium has been observed with insoluble and soluble complexes.

CONCLUSIONS

The comparative study of ATP complexation with Th(IV) and Am(III) shows their ability to form insoluble complexes for which a structural model has been proposed by analogy with previously described Lu(III) complexes.

Hydration of AMP and ATP molecules in aqueous solution and solid films

Water enables life and plays a critical role in biology. Considered as a versatile and adaptive component of the cell, water engages a wide range of biomolecular interactions. An organism can exist and function only if its self-assembled molecular structures are hydrated. It was shown recently that switching of AMP/ATP binding to the insulin-independent glucose transporter Human Erythrocyte Glucose Transport Protein (GLUT1) may greatly influence the ratio of bulk and bound water during regulation of glucose uptake by red blood cells. In this paper, we present the results on the hydration properties of AMP/ATP obtained by means of dielectric spectroscopy in aqueous solution and for fully ionized forms in solid amorphous films with the help of gravimetric studies.

On the use of X-ray absorption spectroscopy to elucidate the structure of lutetium adenosine mono- and triphosphate complexes

Although the physiological impact of the actinide elements as nuclear toxicants has been widely investigated for half a century, a description of their interactions with biological molecules remains limited. It is however of primary importance to better assess the determinants of actinide speciation in cells and more generally in living organisms to unravel the molecular processes underlying actinide transport and deposition in tissues. The biological pathways of this family of elements in case of accidental contamination or chronic natural exposure (in the case of uranium rich soils for instance) are therefore a crucial issue of public health and of societal impact. Because of the high chemical affinity of those actinide elements for phosphate groups and the ubiquity of such chemical functions in biochemistry, phosphate derivatives are considered as probable targets of these cations. Among them, nucleotides and in particular adenosine mono- (AMP) and triphosphate (ATP) nucleotides occur in more chemical reactions than any other compounds on the earth's surface, except water, and are therefore critical target molecules. In the present study, we are interested in trans-plutonium actinide elements, in particular americium and curium that are more rarely considered in environmental and bioaccumulation studies than early actinides like uranium, neptunium and plutonium. A first step in this strategy is to work with chemical analogues like lanthanides that are not radioactive and therefore allow extended physical chemical characterization to be conducted that are difficult to perform with radioactive materials. We describe herein the interaction of lutetium(III) with adenosine AMP and ATP. With AMP and ATP, insoluble amorphous compounds have been obtained with molar ratios of 1:2 and 1:1, respectively. With an excess of ATP, with 1:2 molar ratio, a soluble complex has been obtained. A combination of spectroscopic techniques (IR, NMR, ESI-MS, EXAFS) together with quantum chemical calculations has been implemented in order to assess the lutetium coordination arrangement for the two nucleotides. In all the complexes described in the article, the lutetium cation is coordinated by the phosphate groups of the nucleotide plus additional putative water molecules with various tridimensional arrangements. With AMP 1:2 and ATP 1:1 solid-state compounds, polynuclear complexes are assumed to be obtained. In contrast, with ATP 1:2 soluble compound, the Lu coordination sphere is saturated by two ATP ligands, and this favors the formation of a mononuclear complex. In order to further interpret the EXAFS data obtained at the Lu LIII edge, model structures have been calculated for the 1:1 and 1:2 ATP complexes. They are discussed and compared to the EXAFS best fit metrical parameters.

A comparative study of ATP and GTP complexation with trivalent Al, Ga and Fe cations. Determination of cation binding site and nucleotide conformation by FTIR difference spectroscopy

The interactions of adenosine-5'-triphosphate (Na2H2ATP) and guanosine-5'-triphosphate (Na2H2GTP) with trivalent Al, Ga and Fe cations are investigated in aqueous solution at pH = 6-7 with metal/nucleotide ratios (r) 1/10, 1/2, 1 and 4. Fourier Transform infrared (FTIR) difference spectroscopy is used to characterize the nature of metal cation binding and nucleotide conformational variations, in aqueous solution. Spectroscopic evidences show that at low cation concentration (r = 1/10), metal binding is mainly through the -PO2- and -PO3(2-) groups of the nucleotide moiety (outer-sphere), while at r > 1/10, in addition to direct metal-phosphate binding (chelation), minor metal-base complexes are also formed via indirect metal-NH2 or metal-carbonyl interaction (through H2O). At r = 1, metal macrochelate formation occurs, involving direct cation coordination to phosphate groups and imidazol N-7 atom with an indirect metal-NH2 or metal-carbonyl interaction. At r = 4, polymerization of these metal complexes is observed through nucleotide phosphate chain. The amount of cation/phosphate binding is considerably larger than that of metal/base binding. Evidence for metal-phosphate coordination comes from major spectral changes (shifting and intensity variations) of the alpha-, beta- and gamma-PO2- vibrations in the region 1250-900 cm-1, while metal-base binding is characterized by spectral alterations of the bands at 1700 (guanine carbonyl stretch), 1695 (adenine N-1-H+ mode), 1650-1660 (NH2 bending), 1610-1613 (pyrimidine), 1575 (pyrimidine), 1535-1540 (imidazol), 1470-1480 (imidazol) and 1377 cm-1 (imidazol). The ribose moiety shows C2'-endo/anti conformation for the free ATP and its metal-ATP complexes with an infrared marked band at 821 cm-1. A mixture of both C2'-endo/anti and C3'-endo/anti conformations are occurring for the free GTP and its trivalent metal-complexes with marker bands at 820 and 800 cm-1.

31P NMR of Mg-ATP in dilute solutions: complexation and exchange

1. Monovalent-cation [(CH3)4N+, K(I), Na(I)] ATP, 1 mM in nucleotide, in aqueous solutions at pH 7.2, 24 degrees C, generates 2 different 31P NMR spectra, depending upon the salt content of the solution. At salt concentrations below 10 mM, the 31P NMR signals are chemically-shifted upfield (Na salt: alpha, -11.44 delta; beta, -22.91 delta; gamma, -8.36 delta) and the beta- and gamma-groups are broadened (at half-height: alpha, 3.5 Hz; beta, 9.6 Hz; gamma, 69 Hz). Above 10 mM salt, the signals are shifted downfield and are narrow (Na salt: alpha, -11.09 delta, 1.9 Hz; beta, -21.75 delta, 3.3 Hz; gamma, -6.30 delta, 3.9 Hz). 2. The Na-Mg-ATP complex, corresponding to the composition Na6Mg1ATP2, yields a single set of 31P resonances at concentrations of nucleotide of 100 mM, that upon dilution to 0.2 mM, resolve into 2 sets of ATP resonances characterized by low-field and high-field beta- and gamma-group resonance pairs. This set of ATP resonances, in contrast to the resonance set at 100 mM ATP, are broad (100 mM in ATP: alpha, -10.7 delta, 3.7 Hz; beta, -20.1 delta, 15 Hz; gamma, -5.7 delta, 7.3 Hz. 0.2 mM in ATP: alpha, -10.7 delta, 47 Hz; beta, -18.8 and -21.6 delta, 316 and 274 Hz; gamma, -5.5 and -8.7 delta, 460 and 374 Hz). 3. This new data, in combination with data derived from a survey of metal-ion-ATP studies, are interpreted in terms of ATP dimers, incorporating 2 molecules of ATP and 2 metal cations, that exist in water under the physiological conditions of neutral pH, high salt content [135 mM K(I)] and ATP concentrations in the range of 3 mM. 4. A compilation of 31P in vivo and ex vivo data compared to a reference Mg-ATP chemical shift vs Mg/ATP ratio plot indicates that ATP is not fully Mg-saturated in living systems and that 41% exists as the Mg(ATP)2 complex.

Interaction of adenylic acid with alkaline earth metal ions in the crystalline solid and aqueous solution. Evidence for the sugar C'2-endo/anti, C'3-endo/anti and C'4-exon/anti conformational changes

The reaction of adenosine 5'-monophosphoric acid (H2-AMP) with the alkaline earth metal ions has been investigated in aqueous solution at neutral pH. The solid salts of Mg-AMP.5H2O, Ca-AMP.6H2O, Sr-AMP.7H2O and Ba-AMP.7H2O were isolated and characterized by Fourier transform infrared, 1H-NMR spectroscopy and X-ray powder diffraction measurements. Spectroscopic and other evidence showed that the Sr-AMP.7H2O and Ba-AMP.7H2O are isomorphous, whereas the Mg-AMP.5H2O and Ca-AMP.6H2O are not similar. The Mg2+ binding is through the N-7 (inner-sphere) and the phosphate group (outer-sphere via H2O), while the Ca2+ binds to the phosphate group (inner-sphere) and to the base N-7 site (outer-sphere through H2O). The Sr2+ and Ba2+ bind to H2O molecules, H-bonding to the N-7, N-1 and the phosphate group (outer-sphere). In aqueous solution, an equilibrium between the inner- and outer-sphere metal ion bindings can be established. The sugar moiety exhibited C'2-endo/anti conformation, in the free H2-AMP acid and the magnesium salt, C'3-endo/anti in the calcium salt and unusual C'4-exo/anti, in the strontium and barium salts.

Interaction of cis-Pt(ino)2Cl2 with amino acids

The reactions of cis-Pt(ino)2Cl2 with the amino acids Gly, L-Ala, L-Val, L-Ileu, L-Phe and L-Pro were studied in methanolic solutions. The (1:1) adducts of the formulas cis-[Pt(ino)2(am-ac)]Cl were isolated from these reactions in the solid state, which in turn produce the cis-[Pt(ino)2(am-acH)Cl]Cl complexes, by treating the former with equivalent amounts of HCl, in aqueous solutions. The complexes were characterized with elemental analysis, conductivity measurements, IR, 1H NMR, and 13C NMR spectra. The results show that the purine ring of inosine interacts with the aliphatic side chain of the amino acids. The platination increases the percentage of the C3'-endo-anti conformation of the sugar part of inosine.