Structure of a galactosaminoglycan from Cordyceps ophioglossoides

A water- and alkali-insoluble galactosaminoglycan (CON), precipitated with ammonium hydroxide from the culture filtrate of Cordyceps ophioglossoides, is composed mainly of 2-amino-2-deoxy-d-galactose (80.5%) together with small proportions of glucose, galactose, and mannose, protein (3.6%), and acetyl groups (1%). CON was eluted as a single peak in gel filtration, and the average molecular weight was estimated to be ～50,000. Partial, acid hydrolysis of CON gave small CON and homologous 2-amino-2-deoxy-d-galacto-oligosaccharides. Small CON (mol. wt. ～10,000) was soluble in water and composed only of 2-amino-2-deoxy-d-galactose. The results of methylation analysis, ¹³C-n.m.r. studies, and enzymic hydrolysis indicated small CON to be a (1→4)-linked 2-amino-2-deoxy-α-d-galactopyranan, and the ¹³C-n.m.r. data indicated the glycosidic linkage in the polygalactosamine moiety of CON to be the same as that of small CON.     

Étude par r.m.n. de quatre disaccharides peracétylés sélectivement enrichis en 13C

Four peracetylated disaccharides ¹³C-labelled at the C-1′ position and having α-d-(1′→3), β-d-(1′→3), α-d-(1′→4), and β-d-(1′→4) linkages were prepared starting from the commercially available d-[1-¹³C]glucose. They were studied on the basis of their ³J_¹³CH coupling constants in relation with the conformation in solution of oligosaccharides as models for the corresponding polymer. A method of analysis of the n.m.r. spectra is described and the coupling constants J_{¹³C-1′H} given, particularly the ²J coupling (in the same cycle and with sign determination) and the ³J coupling (through the glycosidic bond). In that case, the values obtained give experimental information on the ψ angle values. They are compared with the known X-ray data for similar compounds.     

Synthesis and evaluation of affinity adsorbents for glycoproteins: an artificial lectin

A combination of rational design based on mimicking natural protein–carbohydrate interactions and solid-phase combinatorial chemistry has led to the identification of an affinity ligand which displays selectivity for the mannose moiety of glycoproteins. The ligand, denoted 18/18 and comprising a triazine scaffold bis-substituted with 5-aminoindan, has been synthesised in solution, characterised by TLC, ¹H-NMR and MS. When immobilised to amine-derivatised agarose at concentrations >24 μmol/g moist weight gel, ligand 18/18 selectively binds glucose oxidase. The adsorbed enzyme was quantitatively eluted with 0.5 M α- -methyl-mannoside and to a lesser extent with the equivalent glucoside. An investigation of the comparative retention times of saccharidic solutes showed that significant retardation was observed for α- -mannose, mannobiose and mannan, with little or no evidence for selective retention of other saccharides, with the exception of α- -fucose. Interestingly, α- -fucose and α- -mannose share an identical configuration of the hydroxyl groups on C-2, C-3 and C-4. Analysis of Scatchard plots from partition equilibrium studies on the interaction of glucose oxidase and the p-nitrophenyl-glycosides of -mannose, -glucose, -fucose and -galactose with immobilised 18/18 establish that the affinity constants (K_AX) for the enzyme, the glycosides of mannose, glucose and fucose, and the p-nitrophenyl-galactoside are 4.3×10⁵ M⁻¹, 1.9×10⁴ M⁻¹ and 1.2×10⁴ M⁻¹ respectively. ¹H-NMR studies on the interaction of α- -methyl-mannoside with ligand 18/18 in solution confirm the involvement of the hydroxyl group in the C-2 position. Molecular modelling suggests the formation of four hydrogen bonds between the hydroxyl groups at positions C-2, C-3 and C-4 of α- -methyl-mannoside and the bridging and ring nitrogen atoms of the triazine scaffold, with aromatic stacking of a second ligand against the carbohydrate face. The greater specificity of ligand 18/18 for mannose and glucose than for galactose parallels that exhibited by concanavalin A.     

ARA290 Improves Insulin Release and Glucose Tolerance in Type 2 Diabetic Goto-Kakizaki Rats

Effects of ARA290 on glucose homeostasis were studied in type 2 diabetic Goto-Kakizaki (GK) rats. In GK rats receiving ARA290 daily for up to 4 wks, plasma glucose concentrations were lower after 3 and 4 wks, and hemoglobin A_1c (Hb A_1c) was reduced by ~20% without changes in whole body and hepatic insulin sensitivity. Glucose-stimulated insulin secretion was increased in islets from ARA290-treated rats. Additionally, in response to glucose, carbachol and KCl, islet cytoplasmic free Ca²⁺ concentrations, [Ca²⁺]_i, were higher and the frequency of [Ca²⁺]_i oscillations enhanced compared with placebo. ARA290 also improved stimulus–secretion coupling for glucose in GK rat islets, as shown by an improved glucose oxidation rate, ATP production and acutely enhanced glucose-stimulated insulin secretion. ARA290 also exerted an effect distal to the ATP-sensitive potassium (K_ATP) channel on the insulin exocytotic pathway, since the insulin response was improved following islet depolarization by KCl when K_ATP channels were kept open by diazoxide. Finally, inhibition of protein kinase A completely abolished effects of ARA290 on insulin secretion. In conclusion, ARA290 improved glucose tolerance without affecting hematocrit in diabetic GK rats. This effect appears to be due to improved β-cell glucose metabolism and [Ca²⁺]_i handling, and thereby enhanced glucose-induced insulin release.     

Structural characterization of extracellular polysaccharides produced by the marine fungus Epicoccum nigrum JJY-40 and their antioxidant activities

Two extracellular polysaccharides, ENP1 and ENP2, were isolated from the fermentation liquid of the marine fungus Epicoccum nigrum JJY-40 by anion-exchange chromatography and gel-filtration chromatography, and their structures were investigated using chemical and spectroscopic methods including methylation analysis and NMR spectroscopy. The results demonstrated that ENP1 was composed of mannose, glucose, and galactose in the molar ratio of 5.0:2.1:1.0, and the main chain of the polysaccharide consisted of (1?→?2)-linked mannose, (1?→?3)-linked mannose, terminal mannose, (1?→?6)-linked glucose, (1?→?4)-linked glucose, and (1?→?4)-linked galactose. ENP2 was composed of mannose, galactose, glucose, and glucuronic acid in a molar ratio of 12.4:11.2:8.3:1.0, and its glycosidic linkage patterns included terminal mannose, (1?→?6)-linked glucose, (1?→?4)-linked galactose, and (1?→?3)-linked mannose. The two polysaccharides had a partially branched structure with branch point located at C-3 position of (1?→?6)-linked glucose residue. The molecular weights of ENP1 and ENP2 were 19.2 kDa and 32.7 kDa, respectively. Antioxidant properties of the two polysaccharides were evaluated with hydroxyl, superoxide, and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activities and lipid peroxidation inhibition in vitro, and results showed that ENP2 and ENP1 had good antioxidant activities, especially ENP2. ENP2 could be effective as a potential antioxidant.     

The primary structure of the COOH-terminal half of cholera toxin subunit A1 containing the ADP-ribosylation site

The sequence of 96 amino acid residues from the COOH-terminus of the active subunit of cholera toxin, A₁, has been determined as PheAsnValAsnAspVal LeuGlyAlaTyrAlaProHisProAsxGluGlu GluValSerAlaLeuGlyGly IleProTyrSerGluIleTyrGlyTrpTyrArg ValHisPheGlyValLeuAsp GluGluLeuHisArgGlyTyrArgAspArgTyr TyrSerAsnLeuAspIleAla ProAlaAlaAspGlyTyrGlyLeuAlaGlyPhe ProProGluHisArgAlaTrp ArgGluGluProTrpIleHisHisAlaPro ProGlyCysGlyAsnAlaProArg(OH). This is the largest fragment obtained by BrCN cleavage of the subunit A₁ (M_r 23,000), and has previously been indicated to contain the active site for the adenylate cyclase-stimulating activity. Unequivocal identification of the COOH-terminal structure was achieved by separation and analysis of the terminal peptide after the specific chemical cleavage at the only cysteine residue in A₁ polypeptide. The site of self ADP-ribosylation in the A₁ subunit [C. Y. Lai, Q.-C. Xia, and P. T. Salotra (1983) Biochem. Biophys. Res. Commun.116, 341–348] has now been identified as Arg-50 of this peptide, 46 residues removed from the COOH-terminus. The cysteine that forms disulfide bridge to A₂ subunit in the holotoxin is at position 91.     

Studies on the Non-starchy Polysaccharides of the Endosperm of Buckwheat

Water soluble polysaccharides from the buckwheat endosperm was fractionated by salting out and a DEAE-cellulose column (phosphate form) chromatography and the main component (polysaccharide A₁) was isolated as an ultracentrifugally and electrophoretically pure preparation.

The content of polysaccharide A₁ in the buckwheat endosperm was 0.1~0.2%.

Its water solution showed high viscosity and [α]_d was +39.4°. The molecular weight was 240,000~260,000.

Polysaccharide A₁ consisted of xylose, mannose, galactose and glucuronic acid. The hydrolysis of methylated polysaccharide A₁ gave 2,3,4-tri-O-methyl-xylose, 2,3,4,6-tetra-O-methyl-galactose, 2,4,6-tri-O-methyl-galactose, di-O-methyl-mannose and 4-O-methyl- and 5-O-methyl-glucuronic acid. These results suggested that the main chain of this polysaccharide consisted of glucuronic acid, mannose and galactose and the former two occupied branching position with xylose and galactose residues as nonreducing end.     

Water-soluble glycoproteins from Cannabis sativa (Thailand)

Glycoproteins were extracted with water from leaves of Cannabis sativa grown from seeds of Thailand origin. By ion exchange chromatography the material was separated into a neutral and an acidic fraction. Both glycoprotein fractions contained arabinose, galactose, glucose, mannose and xylose, and in addition rhamnose and galacturonic acid were present in the acidic fraction. The carbohydrate moieties were investigated by methylation analysis and Smith-degradation, whereas the glycopeptide linkage was studied by alkaline hydrolysis in the presence of NaBH₄ and Na₂SO₃, respectively. This linkage was shown to be of the serine-O-galactoside type. The carbohydrate structure is highly branched, the majority of branches terminating in arabinofuranose end groups. Arabinose is also present in the chain, predominantly (1 → 4)- and/or (1 → 5)-linked. Galactose makes up most of the main chain as (1 → 3)-linked residues but also constitutes end groups and branch points, as do mannose and/or glucose. Xylose and rhamnose are present as (1 → 4)- and (1 → 2)-linked units, respectively. Galacturonic acid is assumed to be (1 → 4)- linked with some branching at 3 position. The amino acid hydroxyproline, present in the glycoprotein of South African Cannabis leaves, was absent in the corresponding Thailand material.     

Effect of 7-fluoro prostacyclin,a stable prostacyclin analogue,on cAMP accumulation and prostaglandin binding in mastocytoma P-815 cells

The effect of 7-fluoro proscyclilin (PGI₂-F), a chemically stable analogue of prostacyclin, on cAMP accumulation in and [³H]PGE binding to mastocytoma P-815 cells was compared with those of the Na salt and methyl ester of prostacyclin (PGI₂Na or PGI₂Me), which are rapidly inactivated in aqueous solution or metabolized in the tissue.PGIF was as effective as PGI₂Me, and slightly less effective than PGI₂Na in stimulating cAMP accumulation in mastocytoma cells and rabbit platelets. PGI₂F was also more stable than PGI₂Me or PGI₂Na, and retained its original cAMP elevating activity even after incubation with or without cells for 4 h at 37°C. Cells which had been exposed to PGI₂F and then washed free of unbound reagent continued to produced cAMP for more than 3 h. PGI₂F was also as effective as PGE₁ or PGE₂ in displacing [³H]PGE₂ bound to the cells. Non-competitive inhibition by PGI₂F or PGI₂Me of [³H]PGE₂ binding to the cells, with apparent K_is of 1.29 μM and 1.13 μM, respectively, indicates the presence of different receptors for PGE₂ and for PGI₂F or PGI₂Me in mastocytoma P-815 cells.     

Partial purification and characterization of the glucosidases involved in the processing of asparagine-linked oligosaccharides

A glucosidase preparation with activity toward certain glucose-containing oligosaccharides was partially purified from calf liver membranes by Triton X-100 solubilization and DEAE-cellulose and hydroxylapatite chromatography. The enzyme preparation hydrolyzed the glucose residues from (glucose)₁,(mannose)₉(N-acetylglucosamine)₁, and (glucose)₂(mannose) ₉(N-acetylglucosamine)₁ but was totally inactive toward (glucose)₃(mannose)₉(N-acetylglucosamine) ₁. In contrast, crude membrane preparations of the calf liver were active toward all three substrates. The partially purified enzyme had a pH optimum of 6.7 and was very unstable in the absence of added 20% glycerol. The rate of glucose release from the one-and two-glucose-containing oligosaccharides was significantly decreased when four or five of the mannose residues were first removed from the substrate. The release of glucose from (glucose)₁(mannose)₉(N-acetylglucosamine)₁ was inhibited by p-nitrophenyl-α-d-glucoside much more effectively than by p-nitrophenyl-β-d-glucoside, suggesting that this glucose residue may be linked α to the mannose residue. We conclude that during oligosaccharide processing at least two different glucosidases are involved in glucose removal.     

Comparative structural studies of the first row early transition metal(III) chloride tetrahydrofuran solvates

Two compounds of empirical formula MCl₃- (THF)₃, M = V and Cr, have been characterized by single crystal X-ray studies. The VCl₃(THF)₃ molecule, which has a mer octahedral stereochemistry, crystallizes in the monoclinic space group P2₁/c with a= 8.847(2),b= 12.861(5),c= 15.134(3) Å, β = 91.94(2)°, V = 1721(1) ų and Z = 4. The V-Ci(1) and V-CI(2) distances have a mean value of 2.330 [3] Å while V-CI(3) = 2.297(2) Å, The VO(1) and VO(2) distances have a mean value of 2.061[8] Å while V-O(3) = 2.102(3) Å cis ClVCl angles average 92.0[5]° and cis OVO angles average 86.2[2]° . The isostmctural complex, CrCl₃(THF)₃, has a crystal structure made up of discrete octahedral mer-CrCl₃(THF)₃ molecules with the following unit cell dimensions (space group P2₁/c): a = 8.715(1), b= 12.786(3), c = 15.122(3) Å, β = 92.15(1)°, V = 1684(1) ų and Z = 4. The CrCl(1) and CrCl(2) distances have a mean value of 2.310131 Å while CrCl(3) = 2.283(2) Å. The CrO(1) and CrO(2) distances have a mean value of 2.0101171 Å while CrO(3) = 2.077(4) Å. cis ClCrCl angles average 90.9[4]° and cis OCrO angles average 86.1 [2]°. The structures of these two octahedral complexes and those previously reported for ScCl₃(THF)₃ and TiCl₃(THF)₃ are compared and certain general trends are discussed.     

Crystal structure of methyl 2,6-dichloro-2,6-dideoxy-3,4-O-isopropylidene-α-D-altropyranoside. A pyranoside system close to a skew-boat conformation

The crystal structure of methyl 2,6-dichloro-2,6-dideoxy-3,4-O-isopropylidene-α-D-altropyranoside (1) has been determined by X-ray diffraction. The compound crystallizes in the orthorhombic system, space group P2₁2₁2₁, with unit-cell dimensions a  7.932, b  8.133, and c  20.447 Å. The structure was solved by the heavy-atom method and refined by the least-squares technique to an R value of 0.047 by using 736 intensities measured on a diffractometer. The pyranoside ring is close to a skew-boat conformation, with C-2 and C-5 being maximally displaced from the least-squares plane through the remaining four atoms. The H-1H-2 dihedral angle of  158° is in agreement with the J_1,2 value of 4.5 Hz. Thus the solid-state conformation appears to correspond with the conformation in solution. The dioxolane ring is in a twist form, with O-4 and, C-8 puckered on opposite sides of the plane of the other ring atoms. The pyranose-ring substituents are in equatorial and pseudoequatorial orientations. The hydrogen atoms at C-3 and C-4 are in a cis arrangement. The orientations of both the methoxyl group and the chloromethyl group with respect to the ring are gauche—trans. The exocyclic anomeric C-1O-1 bond-distance (1.39 Å) is the shortest CO bond in the structure. The intracyclic CO bonds are significantly different, C-1O-5 being less than C-5O-5.     

Purification and methylation analysis of cell wall material from Solanum tuberosum

Cell wall material (CWM) of potatoes was prepared by sequentially extracting the wet ball-milled tissue with 1 % aq. Na deoxycholate, PhOHHOAcH₂O and 90 % (v/v) aq. DMSO. The purity of the CWM (e.g. absence of residual starch) was established by carbohydrate analysis using different acid hydrolysis conditions and by methylation studies. The partially methylated alditol acetates from the CHCl₃MeOH soluble fraction (S) of the methylated CWM were separated into 15 main peaks by GLC. Fourteen of these peaks were carbohydrate derivatives and the identity of most of these was established by MS. Reduction of the hydrolysate of S with NaBD₄ was used to identify the carbohydrate derivatives present in peaks 7 and 11 above. The occurrence of 4-linked galacturonosyl residues in the methylated polymers was established after reduction of S with LiAlH₄ and LiAlD₄. The main glycosidic linkages present in the non-cellulosic polysaccharides of the wall in descending order of concentration are: 4-linked galactose, 4-linked galacturonic acid, 5-linked arabinose and 4,6-linked glucose. The major branch points are those through 0–6 of glucose and 0–4 of rhamnose. Arabinose, galactose and xylose residues constituted the non-reducing ends. Graded acid hydrolysis of the CWM made it possible to assess the relative strengths of some of the glycosidic linkages. The general structural features of the CWM are discussed in the light of these results.     

Ethnic disparity in hemoglobin A1c levels among normoglycemic offspring of parents with type 2 diabetes mellitus

ObjectiveTo investigate the racial/ethnic disparities in hemoglobin A_1c levels among nondiabetic persons with similar parental history of type 2 diabetes mellitus.MethodsWe studied a community-based sample of adult offspring of parents with type 2 diabetes mellitus. Measurements included anthropometry, hematology assessments, serial fasting plasma glucose, oral glucose tolerance testing, plasma insulin, hemoglobin A_1c, insulin sensitivity, and b-cell function, using a homeostasis model assessment.ResultsThe study included 302 participants (135 white, 167 black). Compared with white participants, black participants had lower fasting plasma glucose levels (91.9 ± 0.51 mg/dL vs 93.6 ± 0.50 mg/dL, P = .015), lower area under the curve of plasma glucose during oral glucose tolerance testing (P = <.001), higher body mass index (31.1 ± 0.61 kg/m² vs 28.5 ± 0.57 kg/m², P = <.001), and similar insulin sensitivity and b-cell function. Hemoglobin A_1c was higher in black participants than in white participants (5.68 ± 0.033% vs 5.45 ± 0.028%, P <.001). The absolute black-white difference in hemoglobin A_1c level of approximately 0.22% persisted after adjusting for age, hemoglobin, hematocrit, body mass index, waist circumference, fasting plasma glucose, glucose area under the curve, and other covariates.ConclusionsAmong healthy offspring of parents with type 2 diabetes mellitus in this study, African American participants had higher hemoglobin A_1c levels than white participants after adjusting for age, adiposity, blood glucose, and known variables. Thus, plasma glucose level is more valid than hemoglobin A_1c for diagnosing prediabetes or diabetes in black persons. (Endocr Pract. 2012; 18:356-362)     

Quaternary structures and low frequency molecular vibrations of haems of deoxy and oxyhaemoglobin studied by resonance Raman scattering

The influence of quaternary structure on the low frequency molecular vibrations of the haem within deoxyhaemoglobin (deoxy Hb) and Oxyhaemoglobin (oxy Hb) was studied by resonance Raman scattering. The FeO₂ stretching frequency was essentially identical between the high affinity (R) state (Hb A) and low affinity (T) state (Hb Kansas and Hb M Milwaukee with inositol hexaphosphate). However in deoxy Hb, only one of the polarized lines showed an appreciable frequency shift upon switch of quaternary structure, i.e. 215 to 218 cm^?1 for the T state (Hb A, des-His(146β) Hb, and des-Arg(141α) Hb (pH 6.5)) and 220 to 221 cm^?1 for the R state (des-Arg(141α) Hb (pH 9.0), des-His(146β)-Arg(141α) Hb and NES des-Arg(141α) Hb). Based on the observed ⁵⁴Fe isotopic frequency shift of the corresponding Raman lines of deoxy Hb A (214 → 217 cm^?1), of deoxy NES des-Arg Hb (220 → 223 cm^?1), of the protoporphyrinato-Fe(II)-(2-methylimidazole) complex in the ferrous high spin state (207 → 211 cm^?1) and of deoxymyoglobin (220 → 222 cm^?1) (Kitagawa et al., 1979), and on substitution of perdeuterated for protonated 2-methylimidazole in the deoxygenated picket fence complex (T_pivPP)Fe²⁺ (2-MeIm) (209 → 206 cm^?1), and on the results of normal co-ordinates calculation carried out previously, we proposed that the 216 cm^?1 line of deoxy Hb is associated primarily with the FeN_ε(HisF8) stretching mode and accordingly that the FeN_ε(HisF8) bond is stretched in the T state due to a strain exerted by globin.     

Metal—phenoxyalkanoic acid interactions. Part 14. The crystal and molecular structures of diaquabis(4-fluorophenoxyacetato)copper(II) bis(4-fluorophenoxyacetic acid)dihydrate and tetra-μ-(4-fluorophenoxyacetato-0,0′)-bis[(2-aminopyrimidine)copper(II)]

The crystal structures of two copper(II) complexes of 4-fluorophenoxyacetic acid (4-FPAH) have been determined by X-ray diffraction. [Cu(4-FPA)₂(H₂O)₂]·2(4-FPAH)·2H₂O (1) is triclinic, space group P1 with Z = 1 in a cell of dimensions a = 14.808(2), b = 9.832(2), c = 6.847(2) Å, α = 87.77(2), β = 98.41(2), γ = 112.33(2)° and was refined to a residual of 0.038 for 1697 ‘observed’ reflections. The coordination sphere in this complex is tetragonally distorted octahedral comprising two waters [CuO, 1.940(3) Å], two unidentate carboxylate oxygens [CuO, 1.942(2) Å] and two ether oxygens [CuO, 2.471(2) Å]. Two adducted [4-FPAH] acid molecules are linked to the un-coordinated oxygens of the acid ligands by hydrogen bonds [2.547(4) Å]. [Cu₂(4-FPA)₄(2-aminopyrimidine)₂] (2) is triclinic, space group P1 with Z = 1 in a cell of dimensions a = 12.688(2), b = 11.422(2), c = 7.951(1) Å, α = 78.74(1), β = 107.51(1), γ = 75.78(1)°, and was refined to a residual of 0.042 for 2683 ‘observed’ reflections. (2) is a centrosymmetric tetracarboxylate bridged dimer with four similar CuO (equatorial) distances [1.967–1.987 Å; 1.977(3) Å mean] and the axial position occupied by the hetero nitrogen of the 2-aminopyrimidine ligand [CuN, 2.176(3) Å]. The Cu---Cu separation is 2.710(1) Å. Crystal data are also presented which confirm the isostructurality of complex (2) with [Cu₂(phenoxyacetate)₄(2-aminopyrimidine)₂], the Co^II, Mg^II and Mn^II4-fluorophenoxyacetate complexes with their phenoxyacetic and 4-chlorophenoxyacetic acid analogues, and of Cd^II4-fluorophenoxyacetate with Cd^II and Zn^II phenoxyacetates.     

Hemoglobins Austin and Waco: two hemoglobins with substitutions in the alpha 1 beta 2 contact region.

Hemoglobins (Hbs) Austin and Waco were detected by their electrophoretic migration on cellulose acetate (pH 8.4) and citrate agar (pH 6.2). By these methods, both variants migrated between Hbs A and F. Globin chain analysis at pH 8.6 indicated that the mutant β chain of Hb Austin was faster moving than the β^A chain; however, the mutant chain of Hb Waco was indistinguishable from the β^A chain by this technique. The two variants were isolated by ion-exchange column chromatography. Sequence studies demonstrated a substitution of serine (Hb Austin) and lysine (Hb Waco) for arginine at position 40 in the β chain. These mutations involve an amino acid residue in the α₁β₂ contact region, which, before this report, had been considered invariant in all hemoglobin sequences. Hb Austin was found to exist as dimers when oxygenated and as tetramers when deoxygenated. The equilibrium constant (K_d) for the tetramer to dimer transition was approximately 300 × 10^?6m, as calculated from sedimentation velocity studies. This variant also had high oxygen affinity, a much reduced heme-heme interaction, and a normal Bohr effect. The functional properties of Hb Waco were similar to those of Hb A.     

Hyaluronic acid: The role of divalent cations in conformation and packing

X-ray diffraction data typical of helical structures have been obtained from strontium and calcium salts of hyaluronic acid. The data indicate three disaccharides in each helix repeat with an average pitch of 2.84 nm and therefore suggest a conformational similarity with other highly extended hyaluronate polymorphs, the packing of which in crystalline arrays is influenced both by the particular cation involved and by the extent of hydration.Intensity data from a high humidity calcium salt were used in a detailed structure refinement. Six chains were found to pack in a trigonal unit cell with symmetry P3₂12 and dimensions a = b = 2.093 nm, c = 2.830 nm. The polyanion conformation is stabilized by O(3)_AO(5)_B and O(4)_BO(5)_A hydrogen bonds across the (1 → 4) and (1 → 3) linkages, respectively. Both crystallographic and steric considerations imply a non-equivalence of the three disaccharide residues in each helix turn.Adjacent antiparallel chains are tied together through COO^?Ca²⁺^?OOC bridges while the co-ordination of each Ca²⁺ ion is completed by three pairs of dyadically related water molecules. These water molecules are also extensively hydrogen-bonded to the polyanions. Sensitivity of the a and b unit cell dimensions to the ambient relative humidity further supports the conclusion that water of hydration surrounds the polyanions.Consideration of isolation and purification procedures together with elemental analysis for a large number of hyaluronate samples demonstrates the importance of divalent cations, even in small quantities, in inducing extended 3-fold helical conformations. If interactions between chain segments have a role in determining the properties of hyaluronate-containing tissues and fluids then it is likely, because of the abundant calcium which is also present, that any polymer secondary structures usually will be similar to the conformer described in this study.     

Coordination modes of polydentate ligands. 4. The crystal and molecular structure of an oxo-bridged iron(III) complex containing a pentadentate imino-alkoxy ligand

In the presence of Fe³⁺, template condensation of the fluorinated keto-alcohol CH₃C(O)CH₂C- (CF₃)₂OH with the triamine CH₃C(CH₂NH₂)₃ leads to two products: a fully condensed, imino-alkoxy, iron(III) complex, Fe{CH₃C[CH₂NC(CH₃)CH₂C(CF₃)₂O]₃}, and a partially condensed iron(III) complex, O{FeCH₃C[CH₂NC(CH₃)CH₂C(CF₃)₂O]₂(CH₂NH₂)}₂, in which two six-coordinate iron(III) centers are linked by an oxide ion. A complete crystal and molecular structure determination of the latter has been made.Crystals are monoclinic, space group C2/c, a= 13.886(4); b=23.206(5); c=15.241(4) Å; β= 106.55(2)°; V=4708 ų; Z=4. Least-squares refinement on F of 322 variables using 2627 observations converged at a conventional agreement factor of 3.8%. The Fe to bridging oxide distance is 1.811(1) Å, the FeFe distance 3.468 Å, and the FeOFe angle 146.6(2)°. A comparison is made between this structure and those of natural hemerythrin systems.     

Preparation,properties and crystal structures of nickel(II) complexes with acyclic schiff bases derived from 2,6-diformyl-4-chlorophenol and 1,5-diamino-3-thiapentane or 3,3′-diamino-N-methyl-dipropylamine

Nickel(II) complexes with the compartmental Schiff bases derived from 2,6-diformyl-4-chlorophenol and 1,5-diamino-3-thiapentane (H₂L¹) or 3,3′-diamino-N-methyl-dipropylamine (H₂L²) were synthesized, and the crystal structures of [Ni(L¹)- (py)₂] and [Ni(L²)(dmf)]·H₂0 were determined by X-ray crystallography.Ni(L¹)(py)₂ is monoclinic, space group C2/c, with a= 18.457(6), b = 11.116(7), c= 16.098(6) Å, and β = 115.79(5)°; D_c = 1.49 g cm⁻³ for Z = 4. The structure was refined to the final R of 6.9%. The molecule has C₂ symmetry. The nickel atom is six-coordinated octahedral. Selected bond lengths are: NiO 2.04(1) Å, NiN (L¹) 2.08(1) Å, NiN(py) 2.17(1) Å.[Ni(L²)(dmf)]·H₂O is monoclinic, space group P2₁/n, with a = 17.329(6), b = 13.322(7), c = 12.476(7) Å and β = 95.43(5)°; D_c = 1.45 g cm⁻³ for Z = 4. The structure was refined to the final R of 5.1%. The nickel atom is bonded in the octahedral geometry to the bianionic pentadentate ligand L² and to one molecule of dimethylformamide. Selected bond lengths are: NiO (charged) 2.063(3) Å (mean value), NiO (neutral) 2.120(3) Å, NiN (planar) 2.050(3) Å (mean value), NiN (tetrahedral) 2.177(3) Å.