Sulfate Oxygen Atoms Research Articles

Specific recognition of sulfate esters by bindin, a sperm adhesion protein from sea urchins

Bindin specifically binds to egg surface sulfated fucan polysaccharides and mediates the attachment of sperm to the egg during fertilization. Sulfate esters are critical for this interaction. We have examined the effect of different anionic groups on the relative binding affinities of a series of homologous anionic polymers for bindin to determine the extent to which other charged moieties can substitute for sulfate. We found that bindin displays a remarkable specificity for sulfate- or sulfonic acid-containing polymers. The relative affinities of poly(vinyl sulfate) and poly(styrenesulfonic acid) are four orders of magnitude higher than polymers containing phosphate esters or carboxyl groups. The bindin-mediated aggregation of sea urchin eggs was inhibited by the sulfated polymers but not the other anionic polymers. This high degree of selectivity for sulfated polymers is not observed for the binding of the polyanions to most other proteins and basic polypeptides. These results suggest that the binding is not due to the formation of simple salt bridges, and that all three non-ester oxygen atoms of the sulfate groups are involved in multiple bonding interactions with a complementary ‘docking site’ on the bindin polypeptide. The orientation of the polysaccharide sulfate oxygen atoms relative to the protein binding site may be an important determinant of the specificity of polysaccharide binding.

Charge density in pyroelectric lithium sulfate monohydrate at 80 and 298 K

Lithium sulfate monohydrate has been studied at 80 and 298 K by x-ray diffraction. The monoclinic crystal with space group P21 has lattice dimensions at 298 K of a=5.4553(1), b=4.8690(1), c=8.1761(2) Å, and β=107.337(2)°; lattice dimensions at 80 K were reported in our neutron study [J. Chem. Phys. 80, 423 (1984)]. Least-squares refinement based on 3486 (80 K) and 3390 (298 K) independent reflections, assuming a spherical atom model, results in final R( F 2) values of 0.024 (80 K) and 0.026 (298 K). Static deformation and charge density model refinement, based on Hirshfeld-type multipole functions, greatly reduces the residual electron density and gives R( F 2) values of 0.017 (80 K) and 0.016 (298 K). Refinement of the resulting multipole parameters within the Gaussian radial dependence model allows a qualitative estimation of the differences in electron densities between 80 and 298 K. A change of about 0.2 e Å−3 in the deformation density of the O–H bonds in the water molecule over this temperature range is related to the contraction in hydrogen bonding at 80 K. Changes in the sulfate oxygen atom lone-pair deformation densities, caused by contractions in the SO2−4–Li+ contacts between 298 and 80 K, are also found between the two temperatures. X-ray–neutron diffraction deformation density calculations indicate a substantial electron deficiency in the sulfur valence shell. Kappa refinement leads to a point charge model with positive atomic charge close to 1.8 on sulfur, about −1.0 on each sulfate oxygen atom, and −0.8 on the water oxygen atom. Interatomic distances at 80 and 298 K, particularly those based on a Gaussian radial dependence for the deformation density function, are in excellent agreement with the corresponding neutron diffraction values.

Single-crystal ESR and X-Ray Crystallographical Studies of a Binuclear Copper(II) Complex with a Coaxially Stacked Square-pyramidal Geometry

Abstract A binuclear complex of bis(μ-N,N′-dipicolinoyl-1,3-propanediamine)-bis(sulfato)dicopper(II) has been isolated as a blue single crystal tridecahydrate, [{Cu(SO4)(ppda)}2]·13H2O, from an aqueous solution. The crystals are orthorhombic, C2221, with a=15.42(1), b=24.92(2), c=25.73(2) Å, and Z=8. Each copper(II) ion is in a square-pyramidal coordination with two pyridine nitrogen atoms, two carbonyl oxygen atoms, and a sulfate oxygen atom at the apex. The two equivalent copper(II) ions, about 3.9 Å apart from each other, are aligned coaxially. The eight Cu–Cu vectors are approximately parallel to one another along the c axis. The most important feature of the crystal structure is the presence of the bulky ligands and of many water molecules, which magnetically isolate the Cu–Cu coupled pair from one another. This facilitates the ESR study of the molecular anisotropies by using the single crystal, even at room temperature. The ESR parameters determined are as follows: g⁄⁄=2.280(2), g⊥=2.067(1), |D|=422.4(8), |A⁄⁄|=170(2), and |A⊥|=14(1) in 10−4 cm−1. Bleaney and Bowers treatments of the exchange coupling contribution in the D parameter indicated a ground singlet state about 7 cm−1 below a triplet state for the coupled copper(II) ions. A comparison of the ESR parameters measured for the single crystal with those in the aqueous solution enabled us to conclude that the molecular structure in the solution was very similar to that in the crystalline phase, apart from the coordination of sulfate ions.

Dermatan sulfate: Molecular conformations and interactions in the condensed state

The molecular conformations and manner of aggregation has been determined for three allomorphs of the connective tissue polysaccharide dermatan sulfate by analysis of X-ray diffraction from oriented, polycrystalline fibers of sodium salts. One allomorph is unique among glycosaminoglycans in having right-handed (8(3)) helical chains. Two such chains pack antiparallel in a tetragonal unit cell (a = b = 1.267 nm, c = 7.353 nm) with P4(3)2(1)2 space group symmetry. The 3(2) chains of the second allomorph are organized in a trigonal unit cell (a = b = 1.460 nm, c = 2.823 nm, space group symmetry P3(2)21) containing two left-handed antiparallel polysaccharide molecules. (The chirality of this allomorph has been assumed to be the same as in other 3-fold glycosaminoglycan helices, since discrimination between 3(1) and 3(2) symmetries was found not to be possible.) The archiral 2(1) helices of the third allomorph, pack probably in an orthorhombic unit cell (a = 1.151 nm, b = 1.065 nm, c = 1.878 nm, space group symmetry P2(1)2(1)2(1)) that contains again two antiparallel polymer molecules. Each dermatan sulfate chain is stabilized intramolecularly by O3-O5 hydrogen bonds across the beta (1 leads to 4) linkage. There are two intermolecular hydrogen bonds per tetrasaccharide repeat in the tetragonal structure and two per disaccharide in the trigonal structure. Fourier difference syntheses indicated equivalents of four sodium ions per tetrasaccharide and two sodium ions per disaccharide in the tetragonal and trigonal structures, respectively. The cations are either partially or fully hydrated and link dermatan sulfate chains either intra- or intermolecularly by involving besides other polyanion oxygen atoms, carboxylate and sulfate oxygen atoms. The probable mode of packing in the orthorhombic structure indicates a pair of hydrogen bonds between adjacent antiparallel polysaccharide chains and suggests plausible cationic sites in the unit cell.

The crystal structure of hydrogen cerium(III) sulfate hydrate, [H 3O][Ce(SO 4) 2] · H 2O

[H 3O][Ce(SO 4) 2] · H 2O crystallizes in the monoclinic system with unit-cell dimensions (from single-crystal data) a = 9.359(4), b = 9.926(4), c = 8.444(3) Å, β = 96.53(9)° and space group P2 1/ n, z = 4. The structure was solved by conventional heavy-atom methods using 1787 counter-measured reflections (Mo Kα radiation), and refined using full-matrix least-squares techniques to an R of 0.0465 ( ωR = 0.0413). The structure consists of cerium(III) ions in irregular nine-coordination to oxygen atoms from two bidentate sulfate ions, four monodentate sulfate oxygen atoms, and one water molecule. The oxonium ions are present as isolated ions in the structure and take par in the hydrogen bonding network. The Ce-O bond lengths range from 2.454(7) to 2.626(6) Å.

On the crystal chemistry of salt hydrates. V. The determination of the crystal structure of CuSO4.3H2O (bonattite)

CuSO4.3HzO crystallizes in space group Cc with a= 5.592, b= 13.029, c=7.341 A, B= 97°3 ', Z=4. The structure has been determined from Patterson and Fourier syntheses using three-dimensional data collected on a precession camera with Mo Ke radiation. The structure was refined by the method of least squares. The final R value for 936 observed structure factors is 0.069. The coordination polyhedra around the Cu2+ ions do not share any edges or corners with each other; they are connected by hydrogen bonds and via linking sulfate groups. The square planar coordination around the copper ion consists of three water oxygen atoms and one sulfate oxygen atom at an average distance of 1.96/~. Two more sulfate oxygen atoms at 2.40 and 2.45 A, complete the distorted octahedral coordination. The average S-O bond length in the sulfate tetrahedron is 1.472 A. The positions of the hydrogen atoms were not determined experimentally; they were calculated theoretically assuming that the hydrogen atoms are in positions of least electrostatic energy. Only four of the six crystallographically nonequivalent hydrogen atoms are involved in normal hydrogen bonds.