Identification of tubulin isoforms in different tissues of Ascaris suum using anti-tubulin monoclonal antibodies

Three monoclonal antibodies specific to α- and β-tubulin were used to examine the expression of tubulin isofoms in the intestine, reproductive tract and body wall muscle of A. suum. The tubulins were found to be different in their isoelectric points, number of isoforms and peptide maps with Western blot analysis of one-dimensional polyacrylamide gel confirming the presence of α-, β₁- and β₂- tubulin. Commercial cross-reactive anti-α and anti-β MAbs 356 and 357 recognized tubulin from A. suum tissues as well as from pig brain, whereas anti-A. suum β-tubulin specific MAb P3D6 recognized tubulin from the A. suum tissues only. Two-dimensional gel analysis showed different isoform patterns in different A. suum tissues with anti-A. suum β-tubulin MAb P3D6 and cross-reactive β-tubulin MAb 357 recognizing 2–4 β- tubulin isoforms and anti-α-tubulin MAb 356 recognizing 1–6 α-tubulin isoforms. Different peptide maps of tubulin were observed in the three tissues, when subjected to limited proteolysis followed by SDS-PAGE. The data indicate that different tubulins are found in different tissues of adult A. suum.     

Polynuclear copper(II) complexes with μ2-1,1-azide bridges. Structural and magnetic properties

Two novel, weakly antiferromagnetically coupled, tetranuclear copper(II) complexes [Cu₄(PAP)₂(μ₂-1,1-N₃)₂(μ₂-1,3-N₃)₂(μ₂-CH₃OH)₂(N₃)₄ (1) (PAP = 1,4-bis-(2′-pyridylamino)phthalazine) and [Cu₄(PAP3Me)₂ (μ₂-1,1-N₃)₂(μ₂-1,3-N₃)₂(H₂O)₂(NO₂)₂]- (NO₃)₂ (2) (PAP3Me = 1,4-bis-(3′-methyl-2′-pyridyl)aminophthalazine) contain a unique structural with two μ₂-1,1-azide intramolecular bridges, and two μ₂-1,3-azide intermolecular bridges linking pairs of copper(II) centers. Four terminal azide groups complete the five-coordinate structures in 1, while two terminal waters and two nitrates complete the coordination spheres in 2. The dinuclear complexes [Cu₂(PPD)(μ₂-1,1-N₃)(N₃)₂(CF₃SO₃)]CH₃OH) (3) and [Cu₂(PPD)(μ₂-1,1-N₃)(N₃)₂(H₂O)(ClO₄)] (4) (PPD = 3,6-bis-(1′-pyrazolyl)pyridazine) contain pairs of copper centers with intramolecular μ₂-1,1-azid and pyridazine bridges, and exhibit strong antiferromagnetic coupling. A one-dimensional chain structure in 3 occurs through intermolecular μ₂-1,1-azide bridging interactions. Intramolecular Cu-N₃-Cu bridge angles in 1 and 2 are small (107.9 and 109.4°, respectively), but very large in 3 and 4 (122.5 and 123.2°, respectively), in keeping with the magnetic properties. 2 crystallizes in the monoclinic system, space group C2/c with a = 26.71(1), b = 13.51(3), c = 16.84(1) Å, β = 117.35(3)° and R = 0.070, R_w = 0.050. 3 crystallizes in the monoclinic system, space group P2₁/c with a = 8.42(1), b = 20.808(9), c = 12.615(4) Å, β = 102.95(5)° and R = 0.045, R_w = 0.039. 4crystallizes in the triclinic system, space group P1, with a = 10.253(3), b = 12.338(5), c = 8.072(4) Å, = 100.65(4), β = 101.93(3), γ = 87.82(3)° and R = 0.038, R_w = 0.036 . The magnetic properties of 1 and 2 indicate the presence of weak net antiferromagnetic exchange, as indicated by the presence of a low temperature maximum in χ_m (80 K (1), 65 K (2)), but the data do not fit the Bleaney-Bowers equation unless the exchange integral is treated as a temperature dependent term. A similar situation has been observed for other related compounds, and various approaches to the problem will be discussed. Magnetically 3 and 4 are well described by the Bleaney-Bowers equation, exhibiting very strong antiferromagnetic exchange (− 2J = 768(24) cm⁻¹ (3); − 2J = 829(11) cm⁻¹ (4)).     

Identification of the phosphorylated β-tubulin isotype in differentiated neuroblastoma cells

The tubulin molecule consists of an - and a β-subunit, each of which exists in several isotypic forms. It has been previously shown that one of the isotypes of neuroblastoma β-tubulin is phosphorylated at a serine residue in vivo [(1985) J. Cell Biol. 100, 764–774]. Here we identify the phosphorylated isotype as β₂ (type III). Moreover, the large size of the phosphorylated tryptic peptide and sequence comparisons of vertebrate β-tubulins suggest that one of the two serines in positions 444 and 446 is the phosphorylated residue. Our results raise the possibility that β₂-tubulin differs functionally from the other β-tubulin isotypes.     

Biochemical properties of fat body DNA of the silkworm, Bombyx mori

Some properties of DNA, especially of pupal fat body of the silkworm, Bombyx mori, were studied. Pupal fat body DNA was separated into at least three components called -DNA, β₁-DNA, and β₂-DNA on methylated albumin kieselguhr (MAK) column chromatography. All of these classes of DNA were demonstrated to be pure DNA, neither contaminated nor hybridized with RNA, by their being positive to the diphenylamine reaction, sensitive to DNase, resistant to RNase, and incorporating thymidine-6-³H but not uridine-5-³H. The GC contents calculated from T_m values were around 38 per cent for all of these three components, almost coinciding with that of bulk DNA. But the molecular weight of -DNA, roughly calculated from the sedimentation coefficient on a sucrose density gradient centrifugation was several-fold larger than that of β₁-DNA.

In the pupal stage, fat body DNA was mainly composed of β₁- and β₂-DNA with a minor amount of -DNA, while in larval stage, it consisted only of -DNA. Larval fat body type DNA was observed in the larval silk gland, and in pupal and/or pharate adult tissues like the integument, muscles, and gonads. On the other hand, pupal fat body type DNA was detected in the tissues destined to degenerate or in the process of degeneration, such as pupal silk gland and midgut. These facts indicate that β₁- and β₂-DNA may be the degradation products of -DNA.     

Differential activation of protein kinase C isoforms following chemical ischemia in rat cerebral cortex slices

The aim of the current study was to characterize the effects of chemical ischemia and reperfusion at the transductional level in the brain. Protein kinase C isoforms (, β₁, β₂, γ, δ and ) total levels and their distribution in the particulate and cytosolic compartments were investigated in superfused rat cerebral cortex slices: (i) under control conditions; (ii) immediately after a 5-min treatment with 10 mM NaN₃, combined with 2 mM 2-deoxyglucose (chemical ischemia); (iii) 1 h after chemical ischemia (reperfusion). In control samples, all the PKC isoforms were detected; immediately after chemical ischemia, PKC β₁, δ and isoforms total levels (cytosol + particulate) were increased by 2.9, 2.7 and 9.9 times, respectively, while isoform was slightly reduced and γ isoform was no longer detectable. After reperfusion, the changes displayed by , β₁, γ, δ and were maintained and even potentiated, moreover, an increase in β₂ (by 41 ± 12%) total levels became significant. Chemical ischemia-induced a significant translocation to the particulate compartment of PKC isoform, which following reperfusion was found only in the cytosol. PKC β₁ and δ isoforms particulate levels were significantly higher both in ischemic and in reperfused samples than in the controls. Conversely, following reperfusion, PKC β₂ and isoforms displayed a reduction in their particulate to total level ratios. The intracellular calcium chelator, 1,2-bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid, 1 mM, but not the N-methyl-d-asparate receptor antagonist, MK-801, 1 μM, prevented the translocation of β₁ isoform observed during ischemia. Both drugs were effective in counteracting reperfusion-induced changes in β₂ and isoforms, suggesting the involvement of glutamate-induced calcium overload. These findings demonstrate that: (i) PKC isoforms participate differently in neurotoxicity/neuroprotection events; (ii) the changes observed following chemical ischemia are pharmacologically modulable; (iii) the protocol of in vitro chemical ischemia is suitable for drug screening.     

An in vitro Cr release assay for Ascaris suum infective larvae

This report describes the use of ⁵¹Cr release as a measure of the viability of Ascaris suum inefective larvae after treatment with sodium hypochlorite or kalafungin. Inefective larvae of A. suum were treated with varying dilutions of these compounds and percent ⁵¹Cr release and percent visual larval damage were recorded. An 8% solution of sodium hypochlorite released >90% of the ⁵¹Cr and produced >90% visual larval damage. Kalafungin released >32% ⁵¹Cr and produced >60% visual larval damage at a concentration of 1 μg·ml⁻¹. The results demonstrate that both assays are equal indicators of the viability of A. suum infective larvae when the cytotoxic agent is sodium hypochlorite. Kalafungin, an inhibitor of mitochondrial function, is detected more efficiently using percent visual larval damage when compared to ⁵¹Cr release.     

Beta(3)-adrenoceptor agonists for the treatment of frequent urination and urinary incontinence: 2-[4-(2-[[(1S,2R)-2-hydroxy-2-(4-hydroxyphenyl)-1-methylethyl]amino]ethyl)phenoxy]-2-methylpropionic acid.

In a search for novel analogues of β₃-adrenoceptor (AR) agonists relaxing the bladder for treatment of urinary dysfunction, 2-[4-(2-{[(1S,2R)-2-hydroxy-2-(4-hydroxyphenyl)-1-methylethyl]amino}ethyl)phenoxy]-2-methylpropionic acids (1a–e), into which a fibrate-like structure had been incorporated, were synthesised. Compound 1a was found to be a selective β₃-AR agonist in functional assays using the ferret detrusor (β₃-AR), rat uterus (β₂-AR), and rat atrium (β₁-AR); β₃: EC₅₀=7.8 nM, β₂: IC₅₀=7,300 nM, β₁: EC₂₀=23,000 nM. The introduction of a chlorine atom or methyl substituent at the ortho-position on the phenyl ring of 1a further improved β₃-AR selectivity. In an in vivo study, 1a lowered intrabladder pressure (ED₅₀=31 μg/kg) in rats, without increasing heart rate, in keeping with the in vitro results. Consequently, it is proposed that 1a and its analogues (1b–e), possess β₃-AR agonistic activity in the absence of undesirable β₁- or β₂-AR mediated actions, and may be useful for clinical treatment and pharmacological studies.     

- and β-tubulin mRNAs of Trypanosoma cruzi originate from a single multicistronic transcript

The cluster of alternated - and β-tubulin genes in the genome of Trypanosoma cruzi was shown to be transcribed into a single RNA molecule which upon processing gives rise to the mature - and β-tubulin mRNAs. This conclusion was based on: (i) nuclear RNA species with the same molecular mass hybridize to both - and β-tubulin cDNA probes; (ii) S₁ nuclease assay of the clustered tubulin genes has shown protected DNA fragments of the same size and of greater molecular mass than that corresponding to the mRNAs, hybridizable to both - and β-tubulin cDNA probes; (iii) β-tubulin hybrid selected RNA is still able to hybridize to -tubulin probe.     

The synthesis and structural characterization of carborane oligomers connected by carbon-carbon and carbon-boron bonds between icosahedra

The reaction of dilithiated o-carborane (closo-1,2-Li₂-1,2-C₂B₁₀H₁₀) with CuCl₂ gives 1,1′-bis(o-carborane) (1), 1,3′-bis(o-carborane) (2) and 1,4′-bis(o-carborane) (3). Compound 2 (C₄B₂₀H₂₂) crystallizes in the monoclinic space group P2₁/n with A = 6.9275(6), B = 9.7655(8), C = 12.356(1) Å, β = 90.028(2)° and Z = 2. The structure was solved by direct methods and refined to R = 0.048 and R_w = 0.074. Compound 3 (C₄B₂₀H₂₂) crystallizes in the orthorhombic space group P2₁2₁2₁ with A = 6.8854(5), B = 12.523(1), C = 19.847(1) Å and Z = 4. The structure was solved by direct methods and refined to R = 0.078 and R_w = 0.091. The coupling reaction of dilithiated m-carborane (closo-1,7-Li₂-1,7-C₂B₁₀H₁₀) with CuCl₂ results in the formation of 1,1′-bis(m-carborane) (4) and tetra(m-carborane) (5).     

Regulation of the CYP27B1 5'-flanking region by transforming growth factor-beta in ROS 17/2.8 osteoblast-like cells

The biologically active form of vitamin D, 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃), regulates osteoblast proliferation and differentiation. Production of 1,25(OH)₂D₃ is catalysed by the enzyme 25-hydroxyvitamin D₃-1-hydroxylase (CYP27B1). Though highly expressed in the kidney, the CYP27B1 gene is also expressed in non-renal tissues including bone. It is hypothesised that local production of 1,25(OH)₂D₃ by osteoblasts plays an autocrine or paracrine role. The aim of this study was to investigate what factors regulate expression of the CYP27B1 gene in osteoblast cells. ROS 17/2.8 osteoblast cells were transiently transfected with plasmid constructs containing the 5′-flanking sequence of the human CYP27B1 gene fused to a luciferase reporter gene. Cells were treated with either parathyroid hormone (PTH), 1,25(OH)₂D₃, transforming growth factor-beta (TGF-β) or insulin-like growth factor-1 (IGF-1) and luciferase activity was measured 24 h later. The results showed that 1,25(OH)₂D₃ did not alter expression of the reporter construct, however treatment with PTH, IGF-1 and TGF-β decreased expression by 18, 53 and 58% respectively. The repressive action of TGF-β was isolated to the region between −531 and −305 bp. These data suggest that expression of the 5′-flanking region for the CYP27B1 gene in osteoblast cells may be regulated differently to that previously described in kidney cells.     

4-Aminopiperidine ureas as potent selective agonists of the human beta(3)-adrenergic receptor.

The preparation and structure–activity relationships (SARs) of potent agonists of the human β₃-adrenergic receptor (AR) derived from a 4-aminopiperidine scaffold are described. Examples combine human β₃-AR potency with selectivity over human β₁-AR and/or human β₂-AR agonism. Compound 29s was identified as a potent (EC₅₀=1 nM) and selective (greater than 400-fold over β₁- with no β₂-AR agonism) full β₃-AR agonist with in vivo activity in a transgenic mouse model of thermogenesis.     

Beta2-adrenoceptor agonists induce the mammalian clock gene, hPer1, mRNA in cultured human bronchial epithelium cells in vitro

The mammalian Per1 gene is one of the most important components of circadian clock function of the suprachiasmatic nucleus and peripheral tissues. We examined whether the β₂-adrenoceptor agonists, procaterol and fenoterol, induce human Per1 mRNA expression in human bronchial epithelium. The in vitro stimulation of β₂-adrenoceptor agonists in BEAS-2B cells led to a remarkable increase in the level of hPer1 mRNA. Moreover, fenoterol or procaterol induced the phosphorylation of CREB in BEAS-2B cells as verified by immunoblot analysis. β₂-adrenoceptor agonists induced human Per1 mRNA expression by the signaling pathways of cAMP-CREB in BEAS-2B cells.     

Importance of the proline residue to the functional activity and metabolic stability of the nematode FMRFamide-related peptide, KPNFIRFamide (PF4)

PF4 has previously been shown to have potent inhibitory effects on myoactivity of somatic muscle strips from the nematode, Ascaris suum. This study examined the bioactivity and metabolic stability of position 2- and position 5-modified analogues of PF4. Although the analogues [Leu⁵]PF4, [Ala²]PF4, [Gly²]PF4, [Ala²,Leu⁵]PF4, and [Gly²,Leu⁵]PF4 all had qualitatively similar inhibitory effects on A. suum somatic muscle strips, their effects were quantitatively distinguishable and had the order of potency: PF4 = [Leu⁵]PF4 [Al²]PF4 = [Ala²,Leu⁵]PF4 [Gly²]PF4 = [Gly²,Leu⁵]PF4. Leu⁵ for Ile⁵ substitutions in PF4 did not alter the activity of this peptide; however, Gly²/Ala² for Pro² substitutions reduced, bud did not abolish, peptide activity. Peptide stability studies revealed that [Gly²]PF4(2–7) and -(3–7) and [Ala²]PF4(2–7), -(3–7), and -(4–7) fragments were generated following exposure to A. suum somatic muscle strips. However, the parent peptide (PF4) was not metabolized and appeared to be resistant to the sequential cleavages of native aminopeptidases. Observed analogue metabolism appeared to be due to the activity of released aminopeptidases as identical fragments were generated by incubation in medium that had been exposed to somatic muscle strips and from which the strips had been removed prior to peptide addition. It was found that the muscle stretching and bath mixing characteristics of the tension assay led to more effective release of soluble enzymes from muscle strips and thus greater peptide degradation. These studies reveal that Pro² in PF4 is not essential for the biological activity of this peptide; however, it does render the peptide resistant to the actions of native nematode aminopeptidases.     

Direct nitration of aryl groups σ-bound to ruthenium(II)

A new method has been developed for the preparation of nitroaryl transition metal complexes using copper(II) nitrate in the presence of acetic anhydride (Menke conditions) to directly nitrate an aryl group which is already σ-bound to a transition metal centre. Under these conditions ruthenium(II) aryl complexes of the type: (where R₁=R₂=H; R₁=H, R₂=CH₃; R₁=CH₃, R₂=H) react to yield three distinct types of nitroaryl-containing products (I–III).

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The preparation and characterisation of these compounds are described. X-ray crystallographic data for one example of each of the three types of compound, are also reported. The compounds that have been studied crystallographically are Ru(C₆H₄NO₂-4)(η²-O₂CCH₃)(CO)(PPh₃)₂ (1a), C₄₅H₃₇NO₅P₂Ru·(CH₂Cl₂)_0.5, a = 20.254(5), b=19.437(8), c=22.629(3) Å, β=115.390(10)°, monoclinic, space group C2/c, Z=8; Ru(C6H4N[O]O-2)- Cl(CO)(PPh₃)₂ (4a), C₄₃H₃₄ClNO₃P₂Ru, a=9.331(3), b=12.443(2), c=16.346(3) Å, =82.81(2), β=85.03(2), γ=74.76(2)°, triclinic, space group P , Z=2; Ru(C₆H₂CH₃-2,NO₂-4,N[O]O-6)Cl(CO)(PPh₃)₂ (5b), C₄₄H₃₅Cl- N₂O₅P₂Ru·(CH₂Cl₂)₂, a=19.497(3), b=14.502(3), c=19.340(5) Å, β=122.79(1)°, monoclinic, space group Cc, Z=4.     

Laminar distribution of noradrenergic markers in rat visual cortex

The laminar distribution of ₁-, ₂- and β-adrenoreceptors was studied in the visual cortex of adult rat together with an investigation of noradrenaline uptake sites. The different layers of the visual cortex were separated by cutting serial cryostat sections and binding studies were performed in slide-mounted tissue sections of 10μm thickness collected from one individual cortical layer. [³H]desipramine binding, assumed to label noradrenaline uptake sites, was found to be highest in layer I by about 37%, whereas binding in the remaining layers was uniformly distributed. The laminar distribution of the ₁- and ₂-adrenoreceptors studied using [³H]prazosin and [³H]clonidine as radioligands, was similar to that of the noradrenaline uptake sites: markedly higher binding was detectable in layer I compared to the remaining layers. In contrast, the density of β-adrenoreceptors, as revealed by [³H]dihydroalprenolol binding, was highest in layers I and IV, followed by layer II/III, (58% of that in layer I and IV). Lowest binding was observed in layers V and VI (36%). The similarity in laminar distributions of -adrenoreceptors and noradrenaline uptake sites suggests a close correlation of receptor localization and fibre termination, whereas the localization of β-adrenoreceptors cannot be easily related to the pattern of noradrenergic fibres and terminals.     

The synthesis and reactions of A-ring aromatic steroid complexes of manganese tricarbonyl

Treatment of the A-ring aromatic steroids estrone 3-methyl ether and β-estradiol 3, 17-dimethyl ether with Mn(CO)₅⁺BF₄⁻ in CH₂Cl₂ yields the corresponding [(steroid)Mn(CO)₃]BF₄ salts 1 and 2 as mixtures of and β isomers. The X-ray structure of [(estrone 3-methyl ether)Mn(CO)₃]BF₄ · CH₂Cl₂ (1) having the Mn(CO)₃ moiety on the side of the steroid is reported: space group P2₁ with a=10.3958(9), b=10.9020(6), c=12.6848(9) Å, β=111.857(6)°, Z=2, V=1334.3(2) ų, _calc=.481 cm⁻³, R=0.0508, and wR=0.0635. The molecule has the traditional ‘piano stool’ structure with a planar arene ring and linear Mn---C---O linkages. The nucleophiles NaBH₄ and LiCH₂C(O)CMe₃ add to [(β-estradiol 3,17-dimethyl ether)Mn(CO)₃]BF₄ (2) in high yield to give the corresponding - and β-cyclohexadienyl manganese tricarbonyl complexes (3). The nucleophiles add meta to the arene -OMe substituent and exo to the metal. The and β isomers of 3 were separated by fractional crystallization and the X-ray structure of the β isomer with an exo-CH₂C(O)CMe₃ substituent is reported (complex 4): space group P2₁2₁2₁ with a=7.5154(8), b=15.160(2), c=25.230(3) Å, Z=4, V=2874.4(5) ų, _calc=1.244 g cm⁻³, R=0.0529 and wR2=0.1176. The molecule 4 has a planar set of dienyl carbon atoms with the saturated C(1) carbon being 0.592 Å out of the plane away from the metal. The results suggest that the manganese-mediated functionalization of aromatic steroids is a viable synthetic procedure with a range of nucleophiles of varying strengths.     

Application of the hydro(solvo)thermal technique to the synthesis of metal carbonyl chalcogenide clusters Part 3. Synthesis, structural characterization, and spectroscopic studies of the clusters [{M(CO)4}n(MS4)] (M = Mo, W; N=1, 2)

The methanothermal reactions of M(CO)₆ (M = Mo, W) with Na₂S₂ gave a series of homonuclear clusters [{M(CO)₄}_n(MS₄)]²⁻ (M=Mo, W; N=1, 2), i.e. (Ph₄P)₂[(CO)₄Mo(MoS₄)] (I), (Ph₄P)₂[(CO)₄W(WS₄)] (II), (Ph₄P)₂[(CO)₄Mo(MoS₄)Mo(CO)₄] (III) and (Ph₄P)₂[(CO)₄W(WS₄)W(CO)₄] (IV). The two dimers, I and II, as well as the two trimers, III and IV, are isostructural to each other, respectively. All compounds crystallize in the triclinic space group with Z=2. The cell dimensions are: a=12.393(8), b=19.303(9), c=11.909(6) Å, =102.39(5), β=111.54(5), γ=73.61(5)°, V=2522(3) ų at T=23 °C for I; a=12.390(3), b=19.314(4), c=11.866(2) Å, =102.66(2), β=111.49(1), γ=73.40(2)°, V=2511(1) ų at T=23 °C for II; a=11.416(3), b=22.524(4), c=10.815(4) Å, =91.03(2), β=100.57(3), γ=88.96(2)°, V=2733(1) ų at T=−100 °C for III, a=11.498(1), b=22.600(4), c=10.864(3) Å, =90.92(2), β=100.85(1), γ=88.58(1)°, V=2771(2) ų at T=23 °C for IV. The dimers are each formed by the coordination of the tetrathiometalate as a bidentate chelating ligand to an M(CO)₄ fragment while addition of another M(CO)₄ fragment to the dimers results in the trimers. All compounds contain both tetrahedral and octahedral metal centers with the formal 6+ and 0 oxidation states, respectively.     

Hetero-polynuclear complexes containing bridging diphenylphosphino-alkenes and -alkynes. The crystal structure of an Rh2{μ−ν:ν−P(Ph2) (CH2)3C≡CR}Co2 complex

The phosphinoalkenes Ph₂P(CH₂)_nCH=CH₂ (n= 1, 2, 3) and phosphinoalkynes Ph₂P(CH₂)_n C≡CR (R = H, N = 2, 3; R = CH₃, N = 1) have been prepared and reacted with the dirhodium complex (η−C₅H₅)₂Rh₂(μ−CO) (μ−η²−CF₃C₂CF₃). Six new complexes of the type (ν−C₅H₅)₂(Rh₂(CO) (μ−η¹:η¹−CF₃C₂CF₃)L, where L is a P-coordinated phosphinoalkene, or phosphinoalkyne have been isolated and fully characterized; the carbonyl and phosphine ligands are predominantly trans on the Rh---Rh bond, but there is spectroscopic evidence that a small amount of the cis-isomer is formed also. Treatment of the dirhodium-phosphinoalkene complexes with (η−CH₃C₅H₄)Mn(CO)₂thf resulted in coordination of the manganese to the alkene function. The Rh₂---Mn complex [(η−C₅H₅)₂Rh₂(CO) (μ−η¹:η¹−CF₃C₂CF₃) {Ph₂P(CH₂)₃CH=CH₂} (η−CH₃C₅H₄)Mn(CO)₂] was fully characterized. Simi treatment of the dirhodium-phosphinoalkyne complexes with Co₂(CO)₈ resulted in the coordination of Co₂(CO)₆ to the alkyne function. The Rh₂---Co₂ complex [(η−C₅H₅)₂Rh₂(CO) (μ−η¹:η¹−CF₃C₂CF₃) {Ph₂PCH₂C≡CCH₃}Co₂(CO)₂], C₃₇H₂₅Co₂F₆O₇PRh₂, was fully characteriz spectroscopically, and the molecular structure of this complex was determined by a single crystal X-ray diffraction study. It is triclinic, space group (C_i¹, No. 2) with a = 18.454(6), B = 11.418(3), C = 10.124(3) Å, = 112.16(2), β = 102.34(3), γ = 91.62(3)°, Z = 2. Conventional R on |F| was 0.052 fo observed (I > 3σ(I)) reflections. The Rh₂ and Co₂ parts of the molecule are distinct, the carbonyl and phosphine are mutually trans on the Rh---Rh bond, and the orientations of the alkynes are parallel for Rh₂ and perpendicular for Co₂. Attempts to induce Rh₂Co₂ cluster formation were unsuccessful.     

Structure and physicochemical properties of barley non-starch polysaccharides—II. Alkaliextractable β-glucans and arabinoxylans

Three fractions containing hemicellulosic material were obtained by sequential extraction of barley residue (left after removal of water-extractable polysaccharides) with saturated barium hydroxide [Ba(OH)₂ fraction], distilled water [Ba(OH)₂/H₂O fraction], and 1 m sodium hydroxide [NaOH fraction]. The yields of the fractions were 1.6, 1.7, and 2.6% (w/w), respectively, of the dry barley grist. The Ba(OH)₂ fraction contained mainly arabinose and xylose, 35.8% and 60.9%, respectively. The Ba(OH)₂/H₂O fraction in addition to 26.7% Ara and 36.6% Xyl contained also 34.8% Glc. The NaOH fraction was composed of 14.2% Ara, 44.0% Xyl, and 40.9% Glc. The Ba(OH)₂/H₂O and NaOH extracts were further fractionated by stepwise (NH₄)₂SO₄ precipitation into several subfractions with varying amounts of β-glucans and arabinoxylans. β-Glucans in Ba(OH)₂/H₂O and NaOH fractions were characterized by high ratios of β-(1→4)/β-(1→3) linkages, large amounts of contiguously linked β-(1→4) segments, and high ratios of cellotriosyl/cellotetraosyl units. The alkali-extractable arabinoxylans, especially those NaOH-extractable, were characterized by a very low degree of substitution, high xylose/arabinose ratio, and a small content of doubly substituted xylose residues. Some populations of arabinoxylans displayed structural features that would enable them to self-associate or to interact with β-glucans.     

Kinetics and mechanisms of ligand substitution reactions of molybdenum SO2 complexes. Synthesis and X-ray structure of trans-Mo(CO)2 (dmpe) (PPh3) (SO2)

Kinetic results are reported for intramolecular PPh₃ substitution reactions of Mo(CO)₂(η¹-L)(PPh₃)₂(SO₂) to form Mo(CO)₂(η²-L)(PPh₃)(SO₂) (L = DMPE = (Me)₂PC₂H₄P(Me)₂ and dppe=Ph₂PC₂H₄PPh₂) in THF solvent, and for intermolecular SO₂ substitutions in Mo(CO)₃(η²-L)(η²-SO₂) (L = 2,2′-bipyridine, dppe) with phosphorus ligands in CH₂Cl₂ solvent. Activation parameters for intramolecular PPh₃ substitution reactions: ΔH^≠ values are 12.3 kcal/mol for dmpe and 16.7 kcal/mol for dppe; ΔS^≠ values are −30.3 cal/mol K for dmpe and −16.4 cal/mol K for dppe. These results are consistent with an intramolecular associative mechanism. Substitutions of SO₂ in MO(CO)₃(η²-L)(η²-SO₂) complexes proceed by both dissociative and associative mechanisms. The facile associative pathways for the reactions are discussed in terms of the ability of SO₂ to accept a pair of electrons from the metal, with its bonding transformations of η²-SO₂ to η¹-pyramidal SO₂, maintaining a stable 18-e count for the complex in its reaction transition state. The structure of Mo(CO)₂(dmpe)(PPh₃)(SO₂) was determined crystallographically: P2₁/c, A=9.311(1), B = 16.344(2), C = 18.830(2) Å, ß=91.04(1)°, V=2865.1(7) ų, Z=4, R(F)=3.49%.