Crystallization and characterization of the compounds Gly·MSO4·mH2O (M=Mg2+, Mn2+, Fe2+, Co2+, Ni2+, Zn2+; m=0, 3, 5, 6)

Preservation of glycine coordination compounds under a gamma radiation dose representative of natural mars radioactivity

The Martian subsurface is more favorable for organic preservation than its surface because of the shielding effect of rocks from cosmic rays and UV radiation with increasing depth. Nevertheless, the natural radioactivity on Mars owing to U, Th, and K must be considered to study the possible extant and/or extinct life. Here, we demonstrate the importance of natural radiation on the amino acid glycine in two different chemical environments, GlyFeSO4 5H2O and GlyMgSO4 5H2O, which are coordination compounds considered relevant to Mars. The results show that after a 600 kGy dose of gamma radiation, glycine was more stable when it bonded to Mg in the GlyMgSO4 5H2O coordination compound, it was less stable when it bonded to Fe in the GlyFeSO4 5H2O compound. Studies on the effects of gamma radiation on preservation of organic molecules bound to minerals and other potential compounds on Mars are significantly important in the search for biosignatures.

Study of the Stability of Gly·MgSO4·5H2O under Simulated Martian Conditions by In Situ Raman Spectroscopy

Identification of spectroscopic fingerprints that correspond to relevant molecules/minerals in a Mars-like environment is a crucial search in astrobiology. Therefore, we studied the stability of Gly·MgSO₄·5H₂O under Mars-like surface conditions and compared it to the behavior of epsomite and glycine. Gly·MgSO₄·5H₂O has been identified as a molecule of astrobiological interest since an amino acid and water molecules, which are essential for life, are part of its structure. Furthermore, this compound may form by the interaction of sulfate minerals with glycine-bearing aqueous solutions, and both could be present on Mars. The main analyses were performed by using in situ Raman spectroscopy, a ground-breaking technique for NASA and ESA Mars planetary missions. We have integrated a Raman spectrometer in a Planetary Atmosphere and Surfaces Chamber (PASC) and have identified the processing of molecules exposed to a simulated martian atmosphere, UV irradiation, and temperature. Our results show that pressure is critical to provoke amorphization of Gly·MgSO₄·5H₂O, and the release of glycine from the compound; the stabilization effect at low temperature and stability of Gly·MgSO₄·5H₂O is greater than to glycine and epsomite. The strategy employed here allows us to evaluate the effect of diverse simulated martian environmental conditions on molecular preservation by using Raman spectroscopy.

Zn/Ni and Zn/Pd Heterobimetallic Coordination Polymers with [SSC-N(CH2COO)2]3− Ligands

In the construction of heterobimetallic coordination polymers based on dithiocarbamato–carboxylate (DTCC ligands), platinum as a thiophilic metal center can be replaced by the cheaper nickel or palladium. The compounds Zn[Pd(HL)2] and Zn2[M(L)2] (M = Ni, Pd; L = {SSC-N(CH2COO)2}3−) were prepared in a sequential approach starting from K3(L). The products were characterized by IR and NMR spectroscopy, thermal analyses, and single-crystal X-ray diffraction. The products decompose under nitrogen between 300 and 400 °C. Zn[Pd(HL)2] · 6H2O forms polymeric chains in the solid state, and the Zn2[M(L)2] · 14H2O (M = Ni, Pd) exhibit two-dimensional polymeric structures, each being isotypic with the respective Zn/Pt analogs. While the carboxylate groups in all these products are coordinated to zinc in a κO-monodentate mode, a structural variant of Zn2[Ni(L)2] having κO:κO′-briding carboxylate groups was also obtained. Exchange of the metal sites in the two Ni/Zn compounds was not observed, and these compounds are therefore diamagnetic.

Glycine zinc sulfate penta-hydrate: redetermination at 10 K from time-of-flight neutron Laue diffraction

Single crystals of glycine zinc sulfate penta-hydrate [systematic name: hexa-aqua-zinc tetra-aquadiglycinezinc bis-(sulfate)], [Zn(H2O)6][Zn(C2H5NO2)2(H2O)4](SO4)2, have been grown by isothermal evaporation from aqueous solution at room temperature and characterized by single-crystal neutron diffraction. The unit cell contains two unique ZnO6 octa-hedra on sites of symmetry -1 and two SO4 tetra-hedra with site symmetry 1; the octa-hedra comprise one [tetra-aqua-diglycine zinc]2+ ion (centred on one Zn atom) and one [hexa-aqua-zinc]2+ ion (centred on the other Zn atom); the glycine zwitterion, NH3+CH2COO-, adopts a monodentate coordination to the first Zn atom. All other atoms sit on general positions of site symmetry 1. Glycine forms centrosymmetric closed cyclic dimers due to N-H⋯O hydrogen bonds between the amine and carboxyl-ate groups of adjacent zwitterions and exhibits torsion angles varying from ideal planarity by no more than 1.2°, the smallest values for any known glycine zwitterion not otherwise constrained by a mirror plane. This work confirms the H-atom locations estimated in three earlier single-crystal X-ray diffraction studies with the addition of independently refined fractional coordinates and Uij parameters, which provide accurate inter-nuclear X-H (X = N, O) bond lengths and consequently a more accurate and precise depiction of the hydrogen-bond framework.

X-ray and neutron powder diffraction analyses of Gly·MgSO4·5H2O and Gly·MgSO4·3H2O, and their deuterated counterparts

We have identified a new compound in the glycine-MgSO4-water ternary system, namely glycine magnesium sulfate trihydrate (or Gly·MgSO4·3H2O) {systematic name: catena-poly[[tetraaquamagnesium(II)]-μ-glycine-κ(2)O:O'-[diaquabis(sulfato-κO)magnesium(II)]-μ-glycine-κ(2)O:O']; [Mg(SO4)(C2D5NO2)(D2O)3]n}, which can be grown from a supersaturated solution at ∼350 K and which may also be formed by heating the previously known glycine magnesium sulfate pentahydrate (or Gly·MgSO4·5H2O) {systematic name: hexaaquamagnesium(II) tetraaquadiglycinemagnesium(II) disulfate; [Mg(D2O)6][Mg(C2D5NO2)2(D2O)4](SO4)2} above ∼330 K in air. X-ray powder diffraction analysis reveals that the trihydrate phase is monoclinic (space group P21/n), with a unit-cell metric very similar to that of recently identified Gly·CoSO4·3H2O [Tepavitcharova et al. (2012). J. Mol. Struct. 1018, 113-121]. In order to obtain an accurate determination of all structural parameters, including the locations of H atoms, and to better understand the relationship between the pentahydrate and the trihydrate, neutron powder diffraction measurements of both (fully deuterated) phases were carried out at 10 K at the ISIS neutron spallation source, these being complemented with X-ray powder diffraction measurements and Raman spectroscopy. At 10 K, glycine magnesium sulfate pentahydrate, structurally described by the `double' formula [Gly(d5)·MgSO4·5D2O]2, is triclinic (space group P-1, Z = 1), and glycine magnesium sulfate trihydrate, which may be described by the formula Gly(d5)·MgSO4·3D2O, is monoclinic (space group P21/n, Z = 4). In the pentahydrate, there are two symmetry-inequivalent MgO6 octahedra on sites of -1 symmetry and two SO4 tetrahedra with site symmetry 1. The octahedra comprise one [tetraaquadiglcyinemagnesium](2+) ion (centred on Mg1) and one [hexaaquamagnesium](2+) ion (centred on Mg2), and the glycine zwitterion, NH3(+)CH2COO(-), adopts a monodentate coordination to Mg2. In the trihydrate, there are two pairs of symmetry-inequivalent MgO6 octahedra on sites of -1 symmetry and two pairs of SO4 tetrahedra with site symmetry 1; the glycine zwitterion adopts a binuclear-bidentate bridging function between Mg1 and Mg2, whilst the Mg2 octahedra form a corner-sharing arrangement with the sulfate tetrahedra. These bridged polyhedra thus constitute infinite polymeric chains extending along the b axis of the crystal. A range of O-H...O, N-H...O and C-H...O hydrogen bonds, including some three-centred interactions, complete the three-dimensional framework of each crystal.

In situ single-crystal to single-crystal (SCSC) transformation of the one-dimensional polymer catena-poly[[diaqua(sulfato)copper(II)]-μ₂-glycine] into the two-dimensional polymer poly[μ₂-glycine-μ₄-sulfato-copper(II)]

The one-dimensional coordination polymer catena-poly[diaqua(sulfato-κO)copper(II)]-μ2-glycine-κ(2)O:O'], [Cu(SO4)(C2H5NO2)(H2O)2]n, (I), was synthesized by slow evaporation under vacuum of a saturated aqueous equimolar mixture of copper(II) sulfate and glycine. On heating the same blue crystal of this complex to 435 K in an oven, its aspect changed to a very pale blue and crystal structure analysis indicated that it had transformed into the two-dimensional coordination polymer poly[(μ2-glycine-κ(2)O:O')(μ4-sulfato-κ(4)O:O':O'':O'')copper(II)], [Cu(SO4)(C2H5NO2)]n, (II). In (I), the Cu(II) cation has a pentacoordinate square-pyramidal coordination environment. It is coordinated by two water molecules and two O atoms of bridging glycine carboxylate groups in the basal plane, and by a sulfate O atom in the apical position. In complex (II), the Cu(II) cation has an octahedral coordination environment. It is coordinated by four sulfate O atoms, one of which bridges two Cu(II) cations, and two O atoms of bridging glycine carboxylate groups. In the crystal structure of (I), the one-dimensional polymers, extending along [001], are linked via N-H···O, O-H···O and bifurcated N-H···O,O hydrogen bonds, forming a three-dimensional framework. In the crystal structure of (II), the two-dimensional networks are linked via bifurcated N-H···O,O hydrogen bonds involving the sulfate O atoms, forming a three-dimensional framework. In the crystal structures of both compounds, there are C-H···O hydrogen bonds present, which reinforce the three-dimensional frameworks.