Squarate Groups Research Articles

Direct Conjugation of Bacterial Polysaccharides to Proteins by Squaric Acid Chemistry.

Bacterial polysaccharides that contain one amino group can be conjugated using squaric acid chemistry directly to a protein carrier. The conjugation is a two-step process consisting of labeling the polysaccharide with a squarate group and a reaction of the squarate formed with protein. The intermediate squarate derivative and the product glycoconjugate can be easily purified using centrifugal filtration devices. This method is experimentally simple and affords glycoconjugates with predictable carbohydrate-protein ratio (carbohydrate content), high conjugation efficiency, and excellent yield.

Conjugate Vaccines from Bacterial Antigens by Squaric Acid Chemistry: A Closer Look.

By using O-SP-core (O-SPcNH2 ) polysaccharide, isolated from Vibrio cholera O1 lipopolysaccharide (LPS) and related synthetic substances, a detailed study of factors that affect conjugation of bacterial polysaccharides to protein carriers through squaric acid chemistry to form conjugate vaccines has been carried out. Several previously unrecognized processes that take place during the squarate labeling of the O-SPcNH2 and subsequent conjugation of the formed squarate (O-SPcNH-SqOMe) have been identified. The efficiency of conjugation at pH 8.5, 9.0, and 9.5 to bovine serum albumin (BSA) and to the recombinant tetanus toxin fragment C (rTT-Hc) has been determined. The study led to a protocol for more efficient labeling of O-SPcNH2 antigen with the methyl squarate group, to yield a higher-quality, more potent squarate conjugation reagent. Its use resulted in about twofold increases in conjugation efficiency (from 23-26 % on BSA to 51 % on BSA and 55 % on rTT-Hc). The spent conjugation reagent could be recovered and regenerated by treatment with MeI in the absence of additional base. The immunological properties of the experimental vaccine made from the regenerated conjugation reagent were comparable with those of the immunogen made from the parent O-SPcNH-SqOMe.

A second monoclinic polymorph of ethylenediammonium bis(hydrogen squarate) monohydrate

The title compound, C2H10N2 2+·2HC4O4 −·H2O, a new polymorph of ethyl­enediammonium bis­(hydrogen squarate) monohydrate, was synthesized by slow evaporation of an acid solution. The asymetric unit contains two hydrogen squarate anions, two half-mol­ecules of protonated ethyl­enediamine arranged around a twofold axis and one water mol­ecule. In the crystal, N—H⋯O and O—H⋯O hydrogen bonds between the hydrogen squarate anions, protonated N atoms from the amine group and water mol­ecules lead to a three-dimensional framework. In particular, the cohesion between the squarate groups is ensured by very short intermolecular hydrogen bonds bonds. The title compound crystallized together with the previously reported polymorph [Mathew et al. (2002 ▶). J. Mol. Struct. 641, 263–279].

Yttrium ethylenediammonium squarate tetrahydrate

The title compound, {(C2H10N2)1.5[Y(C4O4)3(H2O)4]}n {system­atic name: catena-poly[sesqui(ethyl­enediammonium) [[tetra­aquabis­(squarato-κO)yttrium(III)]-μ-squarato-κ2 O:O′]]}, was synthesized by slow evaporation of an acid solution. The asymetric unit contains one yttrium cation in an anti­prismatic environnement, three squarate groups, one and a half protonated ethyl­enediamine mol­ecules and four water mol­ecules. YO8 polyhedra are connected through bis­(mono­dentate) squarates, leading to infinite zigzag chains, in between which are located ammonium groups. A framework of hydrogen bonds between protonated amine N atoms, water mol­ecules and squarate anions ensures the cohesion of the structure.

Catena-Poly[[{bis[tetraaqua(2-hydroxy-3,4-dioxocyclobut-1-en-1-olato-κO1)bariumstrontium(0.35/0.65)]di-μ-aqua}bis(μ-2-hydroxy-4-oxocyclobut-1-ene-1,3-diolato-κ2O1:O3)] monohydrate

The title structure, {[Ba0.71Sr1.29(C4HO4)4(H2O)10]·H2O}n, is built from dimers of edge-sharing monocapped square anti­prisms [(Ba/Sr)O3(H2O)6], in which barium and strontium are statistically disordered [ratio 0.353 (8):0.647 (8)] on the same crystallographic site. Such dimers are connected via bidentate hydrogen squarate groups [HC4O4]−, leading to chains that propagate along the b axis. Inter- and intra­molecular O—H⋯O hydrogen bonds maintain the crystal packing through a three-dimensional network.

Magnetization and EPR of a series of Cr 3+ squarate dimers

A series of Cr(III) dimers were synthesized from a parent compound [Cr 2(μ-oxo) 2(μ 1,2-C 4O 4) 2(H 2O) 4]·2H 2O ( I) by ligand substitution. The compounds have been analyzed using variable frequency EPR (9–110 GHz) and magnetic susceptibility as a function of field (0–9 T) and temperature (1.9–300 K) to obtain their electronic g-values, exchange energies, and zero-field parameters. The parent compound exhibits a broad maximum around 34 K characteristic of a dimer with antiferromagnetic coupling that fit the Van Vleck susceptibility model well. It was found that the maxima could be tuned from 34 to 80 K by ligand substitution of the waters. Each compound possesses a characteristic color spanning the range of teal to pink. The g-value of each compound was found to be ∼1.98 using spectral simulation. The DMSO derivative is water soluble and has a high LC 50 for PC3 cancer cells, suggesting its use as a magnetic resonance imaging agent. X-ray crystal structure of the DMSO derivative [Cr 2(μ-oxo) 2(μ 1,2-C 4O 4) 2(C 2H 6SO) 4]·2H 2O ( II) revealed that the DMSO ligands are equatorial, and the squarate groups bridge the two chromiums. This is in contrast to the previously proposed structure of the parent compound where the water ligands were axial and the equatorial squarate groups did not bridge the chromiums. These compounds are interesting because of their ease of synthesis, and their wide range of magnetic behavior. The compounds are good probes into antiferromagnetic dimer exchange by controlling the ligand field surrounding the superexchange pathway present in the molecule.

A monoclinic pseudopolymorph of manganese squarate dihydrate, Mn(μ-C4O4)(H2O)2, built from cubic units

The structure of poly[[[hexaaquatrimanganese(II)]-tri-mu-squarato] monohydrate], {[Mn(3)(C(4)O(4))(3)(H(2)O)(6)].H(2)O}(n), synthesized hydrothermally, consists of a new three-dimensional framework described by secondary building units (SBUs) containing two MnO(6) octahedra and three squarate groups in a cube-shaped arrangement. In the asymmetric unit, one squarate group is located around an inversion centre (4a; 0, 0, 0), two Mn atoms [4d (3/4, 1/4, 0) and 4c (1/4, 1/4, 0)] are located on inversion centres and the third Mn atom is on a twofold axis (4e; 0, y, 1/4). This report illustrates the concept of the SBU and the flexibility of the squarate spacer in the design of new porous topologies.

VF(C4O4)(H2O)2: a new layer type of diaquavanadium(III) fluoride squarate

Single crystals of the title compound, poly[diaqua-mu-fluoro-mu-squarato-vanadium(III)], [V(C4O4)F(H2O)2]n, have been prepared hydrothermally at 423 K. This compound is shown to have a layer-type structure. The V and F atoms are localized on the symmetry centers 2a and 2d, respectively, of the monoclinic system (space group P2(1)/n) and they form infinite chains which are bridged by the squarate group acting as a bidentate ligand in a trans position. Two water molecules complete the octahedral coordination of vanadium(III). The three-dimensionality is ensured by a strong O-H...O hydrogen bond.

Synthesis, Crystal Structure from Single-Crystal and Powder X-ray Diffraction Data, and Thermal Behavior of Mixed Potassium Lanthanide Squarates: Thermal Transformations of Layered [Ln(H2O)6]K(H2C4O4)(C4O4)2into Pillared LnK(C4O4)2(Ln = Y, La, Gd, Er)

A new series of mixed potassium and rare-earth squarates, [Ln(H(2)O)(6)]K(H(2)C(4)O(4))(C(4)O(4))(2) (Ln = Y, La, Gd, Er), has been synthesized and structurally characterized from single-crystal X-ray diffraction and spectroscopic analyses. The yttrium-based compound crystallizes with a monoclinic symmetry, space group C2/c [a = 8.3341(2) A, b = 37.7094(9) A, c = 11.7195(3) A, beta = 90.3959(9) degrees , V = 3683.1(2) A(3), Z = 8]. The structure is built from layers maintained together via hydrogen bonds. Within a layer, squarate ligands act as linkers between lanthanide and potassium cations. The thermal decomposition of the precursors has been studied by powder thermodiffractometry and thermal analyses. It is shown that crystalline intermediate phases are formed during the degradation. Among them, unprecedented mixed anhydrous squarates, LnK(C(4)O(4))(2), could be isolated. The crystal structure of the Y compound has been solved ab initio from X-ray powder diffraction data, using direct-space methods [a = 6.2010(5) A, c = 11.639(1) A, V = 447.55 A(3), Z = 2]. The structure consists of layers of edge-sharing YO(8) and KO(8) antiprisms, pillared by mu(8)-squarate groups. The end of the precursor decomposition is marked by the formation of cubic sesquioxides Ln(2)O(3), including lanthanum oxide.

Hydrothermal synthesis and structure of the first tin(II) squarate Sn 2O(C 4O 4)(H 2O)—comparison with Sn 2[Sn 2O 2F 4

A tin(II) squarate Sn 2O(C 4O 4)(H 2O) was synthesized by hydrothermal technique. It crystallizes in the monoclinic system, space group C2/ m (no. 12) with lattice parameters a=12.7380(9) Å, b=7.9000(3) Å, c=8.3490(5) Å, β=121.975(3)°, V=712.69(7) Å 3, Z=4. The crystal structure determined with an R=0.042 factor, consists of [(Sn 4O 10)(H 2O) 2] units connected from one another in the [101] and [010] directions via squarate groups to form layers separated by Sn(II) lone pairs. This compound presents the same remarkable structural arrangement as observed in the tin-oxo-fluoride Sn 2[Sn 2O 2F 4] inorganic compound with Sn(II) lone pairs E(1) and E(2) concentrated in large rectangular-shape tunnels running along [001] direction.

Hydrothermal synthesis and structural characterization of Fe(II)-squarate Fe 2(OH) 2(C 4O 4)

Fe 2(OH) 2(C 4O 4) was obtained by hydrothermal synthesis starting from a mixture of FeC 2O 4:H 2C 4O 4:(CN 3H 5) 2,H 2CO 3 (guanidinium carbonate):H 2O in the molar ratio 1:0.5:1.5:200 after a heat treatment at 200 °C for 96 hours. It crystallizes in the monoclinic system, space group P2 1/c with lattice parameters a=3.3500(2) Å, b=10.033(1) Å, c=8.5010(7) Å, β=99.686(5)°, V=281.65(4) Å 3, Z=2. The framework is built up from isolated double chains of [Fe(OH) 3O 3] octahedra sharing edges along the direction [100] and which are connected in the [010] and [001] directions via squarate groups [C 4O 4] 2−: each squarate group being connected to four iron (II)-oxygen double chains.

Synthesis, crystal structure and magneto-structural correlation of two bi-bridging 1D copper(ii) chainsElectronic supplementary information (ESI) available: magnetization curve for 1 between 0 and 5 K and an EPR spectrum for 1. See http://www.rsc.org/suppdata/dt/b2/b204728b/

Two 1D bi-bridging Cu(II) chains, catena-oxalate-bis[1-(2-aminoethyl)pyrrolidine-copper(II)]-0.5(squarate) perchlorate hydrate (1) and catena-pyrazine-oxalate-tetraaquo-dicopper(II) diperchlorate (2) have been synthesised and their molecular structures determined by X-ray crystallography. Compound 1 exhibits a polymeric arrangement with a ladder-like structure running parallel to crystallographic axis a, in which two [(Cu(ampy))2(ox)] chains (ampy = 1-(2-aminoethyl)pyrrolidine; ox = oxalate) are linked by squarate groups. The oxalate behaves simultaneously as bis-bridging and bis-monodentate towards four coplanar copper ions, a coordination mode which has never been reported for Cu(II). Compound 2 is characterized by a polymeric array with alternate repetition of bridging oxalate and ‘pyz’ (pyz = pyrazine). Low temperature magnetic behaviour reveals the existence of a dominant weak antiferromagnetic interaction within 1 whereas in 2 a strong antiferromagnetic interaction is observed. The results obtained experimentally corroborate the structural parameters in both 1 and 2.

Luminescence and non-radiative processes in lanthanide squarate hydrates

The luminescence properties of solid hydrated lanthanide squarates (Ln2(C4O4)3(H2O)x; x = 8or13;Ln 3+ = Gd, La, Eu, Tb, Pr) are reported for temperatures down to 4.2 K. The luminescence of the squarate group is observed for the Gd 3+ and La 3+ compounds at low temperatures (below 150 K). The Pr 3+ compound does not show any emission at all, not even at 4.2 K. This is ascribed to the quenching of the Pr 3+ emission by multiphonon relaxation and/or concentration quenching. The quantum efficiencies of the 5D0 emission of Eu 3+ and of the 5D4 emission of Tb 3+ in these squarate complexes are strikingly different. Whereas the Tb 3+ emission shows a temperature independent quantum efficiency of 50% upon ligand excitation, the Eu 3+ emission is strongly quenched, showing a temperature dependent quantum efficiency of 0.8% at 4.2 K upon ligand excitation. This quenching is ascribed to the low energy position of the chargetransfer state of Eu 3+ in these compounds.