Photochemical reactions of transition metal organyl complexes with olefins Part 10. Light-induced formal [5+2] cycloadditions at manganese

Tricarbonyl-η⁵-2,4-dimethyl-2,4-pentadien-1-yl-manganese (1) forms upon UV irradiation in THF at 208 K solvent stabilized dicarbonyl-η⁵-2,4-dimethyl-2,4-pentadien-1-yl-tetrahydrofurane-manganese (2). With butynedioic acid dimethyl ester (3) and diphenylacetylene (5) complex 2 yields tricarbonyl-η⁵-1,2-dimethoxycarbonyl-4,6-dimethyl- cyclohepta-2,4-dien-1-yl-manganese (4) and tricarbonyl-η-4,6-dimethyl-1,2-diphenyl-cyclohepta-2,4-dien-1-yl- manganese (6) in a formal [5+2] cycloaddition. Addition of carbon monoxide and a 1,4-H shift completes the reaction. Propynoic acid methyl ester (7) forms the 2:1 adduct dicarbonyl-η^5:2-1,3-dimethyl-6-methoxycarbonyl-6- (E-2′-methoxycarbonylvinyl)-cyclohepta-2,4-dien-1-yl-manganese (8). The crystal and molecular structure of 8 was determined by X-ray structure analysis. The molecular structures of the complexes 4 and 6 were established by IR and NMR spectroscopy. Formation mechanisms of 4, 6 and 8 are discussed. Crystal data for 8: monoclinic space group P2₁/c, a=802.6(3), b=1136.6(1), c=8872.3(3) pm, β=93.14(2)°, V=1.705 nm³, Z=4.     

Slippage of η-allenyl/propargyl to an η structure and tautomerization of η-propargyl to η-allenyl in ligand addition and substitution reactions of platinum(II) complexes

Reactions of [(PPh₃)₂Pt(η³-CH₂CCPh)]OTf with each of PMe₃, CO and Br⁻ result in the addition of these species to the metal and a change in hapticity of the η³-CH₂CCPh to η¹-CH₂CCPh or η¹-C(Ph)=C=CH₂. Thus, PMe₃ affords [(PMe₃)₃Pt(η¹-C(Ph)=C=CH₂)]⁺, CO gives both [trans-(PPh₃)₂Pt(CO)(η¹-CH₂CCPh)]⁺ and [trans-(PPh₃)₂Pt(CO)(η¹-C(Ph)=C=CH₂)]⁺, and LiBr yields cis-(PPh₃)₂PtBr(η¹-CH₂CCPh), which undergoes isomerization to trans-(PPh₃)₂PtBr(η¹-CH₂CCPh). Substitution reactions of cis- and trans-(PPh₃)₂PtBr(η¹-CH₂CCPh) each lead to tautomerization of η¹-CH₂CCPh to η¹-C(Ph)=C=CH₂, with trans-(PPh₃)₂PtBr(η¹-CH₂CCPh) affording [(PMe₃)₃Pt(η¹-C(Ph)=C=CH₂)]⁺ at ambient temperature and the slower reacting cis isomer giving [trans-(PPh₃)(PMe₃)₂Pt(η¹-C(Ph)=C=CH₂)]⁺ at 54 °C . All new complexes were characterized by a combination of elemental analysis, FAB mas spectrometry and IR and NMR (¹H, ¹³C{¹H} and ³¹P{¹H}) spectroscopy. The structure of [(PMe₃)₃Pt(η¹-C(Ph)=C=CH₂)]BPh₄·0.5MeOH was determined by single-crystal X-ray diffraction analysis.     

Dissolution of [RhCl(PPh3)3] in the ionic liquid, 1-ethyl-3-methyl imidazolium chloroaluminate(III), and its reaction with H2. The stabilization of Rh(I) species in an ionic liquid

The solution of [RhCl(PPh₃)₃] in acidic 1-ethyl-3-methylimidazolium chloroaluminate(III) ionic liquid (AlCl₃ molar fraction, x_AlCl3=0.67) was investigated by ¹H and ³¹P{¹H} NMR. One triphenyl phosphine is lost from the complex and is protonated in the acidic media, and cis-[Rh(PPh₃)₂ClX], (2), where X is probably [AlCl₄]⁻, is formed. On, standing, 2 is converted to trans-[Rh(H)(PPh₃)₂X], (3). The reaction of 2 and H₂ also produces trans-[Rh(H)(PPh₃)₂X], (3). ¹H and ³¹P{¹H} NMR support the suggestion that a weak ligand such as [AlCl₄]⁻, present in solution may interact with the metal centre. When [RhCl(PPh₃)₃] is dissolved in CH₂Cl₂/AlCl₃/HCl for comparison, two exchanging isomers of what is probably [RhH{(μ-Cl)₂AlCl₂}{(μ-Cl)AlCl₃}(PPh₃)₂], (6) and (7), are formed.     

Metabolic activation of unsaturated derivatives of valproic acid. Identification of novel glutathione adducts formed through coenzyme A-dependent and -independent processes

The ability of 2-n-propyl-4-pentenoic acid (Δ⁴-VPA) and 2-n-propyl-2(E)-pentenoic acid ([E]-Δ²-VPA), two unsaturated metabolites of valproic acid (VPA), to form reactive intermediates, deplete hepatic glutathione (GSH) and cause accumulation of liver triglycerides was investigated in the rat. With the aid of ionspray liquid chromatography-tandem mass spectrometry (LC-MS/MS), three GSH adducts were detected in the bile of Δ⁴-VPA-treated animals and were identified as 4-hydroxy-5-glutathion-S-yl-VPA-γ-lactone, 5-glutathion-S-yl-(E)-Δ³-VPA and 3-oxo-5-glutathion-S-yl-VPA. A fourth conjugate was identified tentatively as 4-glutathion-S-yl-5-hydroxy-VPA. Quantitative analysis of the corresponding N-acetylcysteine (NAC) conjugates in urine indicated that metabolism of Δ⁴-VPA via the GSH-dependent pathways accounted for approximately 20% of an acute dose (100 mg kg⁻¹ i.p.). In contrast, when rats were given an equivalent dose of (E)-Δ²-VPA, only one GSH adduct (5-glutathion-S-yl-(E)-Δ³-VPA) was detected at low concentrations in bile. In vitro experiments with rat liver mitochondria demonstrated that Δ⁴-VPA undergoes coenzyme A- and ATP-dependent metabolic activation in this organelle via the β-oxidation pathway to intermediates which bind covalently to proteins. When liver homogenates and hepatic mitochondria from rats injected with Δ⁴-VPA, (E)-Δ²-VPA or VPA were analyzed for GSH content, it was found that only Δ⁴-VPA depleted GSH pools significantly. Treatment of rats with Δ⁴-VPA and (to a lesser extent) VPA led to an accumulation of liver triglycerides, whereas (E)-Δ²-VPA had no measurable effect. It is concluded that Δ⁴-VPA undergoes metabolic activation by both microsomal cytochrome P-450-dependent and mitochondrial coenzyme A-dependent processes, and that the resulting electrophilic intermediates, which are trapped in part by GSH, may mediate the hepatotoxic effects of this compound. In contrast, (E)-Δ²-VPA is not transformed to any appreciable extent to reactive metabolites, which thus accounts for the apparent lack of hepatotoxicity of this positional isomer in the rat.     

Electrospray mass spectrometric investigation of the relative ligand properties of EPh3 ligands (E=P, As, Sb or Bi) towards Ag and Cu

Electrospray mass spectrometry (ESMS) has been used to investigate the relative ligand properties of the triphenylpnictogen ligands EPh₃ (E=P, As, Sb and Bi) towards silver(I) and copper(I) ions. It is found that the preferred species formed increase in coordination number from two for PPh₃ in [Ag(PPh₃)₂]⁺ to four for SbPh₃ in [Ag(SbPh₃)₄]⁺, consistent with the decreasing donor ligand ability and increasing metal –E bond length in the series PPh₃–AsPh₃–SbPh₃. With BiPh_3, the spectra were complex, suggesting considerable decomposition. These studies also suggest that silver(I) and copper(I) ions will have widespread utility in the characterisation of tertiary stibine ligands, as has been described previously for phosphines and arsines. These studies demonstrate the power of the ESMS technique in determining the donor properties of a related series of ligands, and this information is of significance in coordination chemistry.     

Electrospray mass spectrometry of trans-[Ru(NO)Cl(dpaH)2] (dpaH=2,2′-dipyridylamine) and ‘caged NO’, [RuCl3(NO)(H2O)2]: loss of HCl and NO from positive ions versus NO and Cl from negative ions

The positive ion electrospray mass spectrometry (ESI-MS) of trans-[Ru(NO)Cl)(dpaH)₂]Cl₂ (dpaH=2,2′-dipyridylamine), obtained from the carrier solvent of H₂O–CH₃OH (50:50), revealed 1+ ions of the formulas [Ru^II(NO⁺)Cl(dpaH)(dpa)]⁺ (m/z=508), [Ru^IIICl(dpaH)(dpa⁻)]⁺ (m/z=478), [Ru^II(NO⁺)(dpa)₂]⁺ (m/z=472), [Ru^III(dpa)₂]⁺ (m/z=442), originating from proton dissociation from the parent [Ru^II(NO⁺)Cl(dpaH)₂]²⁺ ion with subsequent loss of NO (17.4% of dissociative events) or loss of HCl (82.6% of dissociative events). Further loss of NO from the m/z=472 fragment yields the m/z=442 fragment. Thus, ionization of the NH moiety of dpaH is a significant factor in controlling the net ionic charge in the gas phase, and allowing preferential dissociation of HCl in the fragmentation processes. With NaCl added, an ion pair, {Na[Ru^II(NO)Cl(dpa)₂]}⁺ (m/z=530; 532), is detectable. All these positive mass peaks that contain Ru carry a signature ‘handprint’ of adjacent m/z peaks due to the isotopic distribution of ¹⁰⁴Ru, ¹⁰²Ru, ¹⁰¹Ru, ⁹⁹Ru, ⁹⁸Ru and ⁹⁶Ru mass centered around ¹⁰¹Ru for each fragment, and have been matched to the theoretical isotopic distribution for each set of peaks centered on the main isotope peak. When the starting complex is allowed to undergo aquation for two weeks in H₂O, loss of the axial Cl⁻ is shown by the approximately 77% attenuation of the [Ru^II(NO⁺)Cl(dpaH)(dpa)]⁺ ion, being replaced by the [Ru^II(NO⁺)(H₂O)(dpa)₂]⁺ (m/z=490) as the most abundant high-mass species. Loss of H₂O is observed to form [Ru^II(NO⁺)(dpa)₂]⁺ (m/z=472). No positive ion mass spectral peaks were observed for RuCl₃(NO)(H₂O)₂, ‘caged NO’. Negative ions were observed by proton dissociation forming [Ru^II(NO)Cl₃(H₂O)(OH)]⁻ in the ionization chamber, detecting the parent 1− ion at m/z=274, followed by the loss of NO as the main dissociative pathway that produces [Ru^IIICl₃(H₂O)(OH)]⁻ (m/z=244). This species undergoes reductive elimination of a chlorine atom, forming [Ru^IICl₂(H₂O)(OH)]⁻ (m/z=208). The ease of the NO dissociation is increased for the negative ions, which should be more able to stabilize a Ru^III product upon NO loss.     

Vasoactive intestinal polypeptide binds with high affinity to non-small cell lung cancer cells and elevates cyclic AMP levels

Vasoactive intestinal polypeptide (VIP) receptors were characterized on non-small cell lung cancer (NSCLC) cells. ¹²⁵I-VIP bound specifically to membranes derived from 6 NSCLC cell lines. Specific ¹²⁵I-VIP was time dependent and a linear function of EPLC-65H membrane concentration. ¹²⁵I-VIP bound with high (K_d=0.2 nM) and moderate (K_d=39 nM) affinity to two classes of sites. Pharmacology studies indicated that the order of peptide potency was VIP > rGHRH > PHI = helodermin > secretin > glucagon. Also VIP elevated the cAMP levels 10-fold using cell line ADLC-5M2. These data indicate that functional VIP receptors are present on NSCLC cells.     

Acridinium ester conjugated to lectin as chemiluminescent histochemistry marker

Cell differentiation/dedifferentiation includes changes in oligosaccharide composition and distribution in the cell surface glycoconjugates. Lectins have been used as auxiliary tools in histopathological diagnosis of mammary, uterus and brain pathologies. Acridinium ester (AE) conjugated to biomolecules has been employed in chemiluminescent analytical applications. This work aimed to use a lectin, concanavalin A (Con A), conjugated to AE as a chemiluminescent histochemistry tool. Biopsies of normal and infiltrating duct carcinoma (IDC) of mammary tissues were treated by a Con A-AE derivative. Photon emission, observed during the breakage of the chemical bound between Con A and AE, was quantified, expressed in relative light units (RLU) and correlated to the labelling of the normal and transformed tissues. The results demonstrated that RLU presented a linear relationship with the labelled tissue area in the range 0.125-1.0 cm² (r=0.98). Furthermore, RLU was much higher for the IDC (1283.920×10³±220.621×10³) than the normal tissue (2.565×10³±0.247×10³), namely, about 500 times higher. The Con A-AE conjugation efficiency, differential staining of normal and IDC tissues, and quantification of results contribute to a decrease in the subjectivity in routine histopathological diagnoses and indicate that acrydinum ester can join other lectin marker to be used in histochemistry.     

An unexpected ‘4+2’ [N3S]/[NS] rhenium(IV) complex formed upon cleavage of a Re(V) imido bond

The reaction of [Re(NMe)Cl₃(PPh₃)₂] with the pentadentate [N₃S₂] ligand pyN₂H₂S₂---H₂ [2,6-bis(2-mercaptophenylamino)dimethylpyridine] (1) in the presence of triethylamine did not yield the anticipated six-coordinate complex [Re(NMe)(η⁵-pyN₂HS₂)] (2), but rather resulted in cleavage of the Re(V)=NMe bond. A novel six-coordinate Re(IV) [N₃S]/[NS] complex [Re(η⁴-SC₆H₄---2-NCH₂---C₅H₃N---C=NC₆H₄---2-S)(η²-NHC₆H₄---2-S)] (4) was thus obtained with the simultaneous coordination of 2-aminothiophenol, a dianionic bidentate [NS] donor resulting from the decomposition of the parent ligand and ligand 3, a dianionic tetradentate [N₃S] donor formed by partial self-condensation and subsequent oxidation of the parent ligand 1. Crystal data for 4: C₂₅H₁₈N₄S₃Re·CH₂Cl₂, monoclinic, space group P2₁/n, a=9.255(2) Å, b=11.181(2) Å, c=25.316(4) Å, β=97.434(3)°, V=2587.8(7) Å³ and Z=4.     

π-Bonded alkene and arene complexes of silver(I): an electrospray mass spectrometric study

Electrospray mass spectra have been observed for a number of alkene and arene complexes of Ag(I) formed by the interaction of AgNO₃ and the organometallic ligand in water/methanol solution. The ES mass spectra show that almost all the alkene and arene ligands in stoichiometric excess form labile 1:2 cationic complexes with Ag(I) which are easily decomposed by collisional activation to the 1:1 species. However, with a deficiency of organic ligand polymeric species are observed. The cation [Ag(cod)₂]⁺ (cod=1,5-cyclooctadiene) was reacted with a variety of other potential ligands, such as PPh₃, AsPh₃, PhSCH₂SPh etc. In most cases, mixed complexes [Ag(cod)(ligand)]⁺ were observed, and excess ligand usually produced [Ag(ligand)₂]⁺.     

Reactions of captopril and epicaptopril with transition metal ions and hydroxyl radicals: An EPR spectroscopy study

In the present study, using the technique of EPR spin trapping with DMPO a spin trap, we demonstrated formation of thiyl radicals from thiol-containing angiotensin converting enzyme (ACE) inhibitor captopril (CAP) and from its stereoisomer epicaptopril (EPICAP), a non-ACE inhibitor, in the process of ^.OH radical scavenging. Splitting constants of DMPO/thiyl radical adducts were identical for both thiols and were a_N = 15.3 G, and a_H = 16.2 G. Bimolecular rate constants for the reaction of CAP and EPICAP with ^.OH radicals were close to a diffusion-controlled rate (≈ 2 × 10¹⁰ M⁻¹s⁻¹). Our data also show that both CAP and EPICAP reduce Fe(III) ions and that their respective thiyl radicals are formed in this reaction. In the presence of Fe(III), H₂O₂, and CAP, or EPICAP, ^.OH radicals were produced by a thiol-driven Fenton mechanism. Copper(II) ions were also reduced by these thiols, but no thiyl radicals could be detected in these reactions, and no ^.OH or other Fenton oxidants were observed in the presence of H₂O₂. Our data show direct evidence that thiol groups of CAP and EPICAP are involved in scavenging of ^.OH radicals. The direct ^.OH radical scavenging, together with the reductive “repair” of other sites of ^.OH radical attack, may contribute to the known protective effect of CAP against ischemia/reperfusion-induced arrhythmias. The formation of reactive thiyl radicals in the reactions of the studied compounds with ^.OH radicals and with Fe(III) ions may play a role in some of the known adverse effects of CAP.     

Characterization of amylin binding sites in a human hepatoblastoma cell line

Amylin binding sites in a human hepatoblastoma cell line (HepG2) have been characterized in detail. ¹²⁵I-Amylin (rat) bound to HepG2 cells with high affinity. Binding was reversible and selective, and dependent on time and temperature. Scatchard analysis revealed the presence of high (K_d = 0.11 ± 0.04 nM) and low (K_d = 1.3 ± 0.4 μM) affinity binding sites for ¹²⁵I-amylin in HepG2 cells. The dissociation experiments also showed that ¹²⁵I-amylin dissociated from high- and low-affinity sites. The association data, however, indicated the presence of only one binding site. Rat amylin was more potent than human amylin and rat calcitonin gene-related peptide (CGRP) in displacing ¹²⁵I-amylin bound to HepG2 cells. Nonhomologous peptides did not displace ¹²⁵I-amylin. Rat amylin was, however, less potent than rat CGRP in displacing ¹²⁵I[Tyr⁰]CGRP from HepG2 cells. Pretreatment of HepG2 cells with rat amylin (10 nM) reduced the specific binding of ¹²⁵I-amylin by 75%, whereas rat CGRP (10 nM) pretreatment had no effect on amylin binding. Calcitonin gene-related peptide, as well as rat and human amylin, stimulated the adenylate cyclase activity of HepG2 cell membrane preparation in a dose-dependent manner, with an order of potency of CGRP > rat amylin > human amylin. A CGRP antagonist, CGRP(8–37), significantly attenuated the stimulatory effect of both amylin and CGRP on adenylate cyclase activity. These investigations show that distinct receptors of amylin and CGRP are present in HepG2 cells and that amylin stimulates adenylate cyclase activity through CGRP receptors. This system could now be exploited for studying amylin receptors and amylin-mediated signal transduction.     

On the reduction behaviour of 2-methoxyethyl and 2-methylthioethyl substituted zirconocene dichlorides: crystal structure of (η,σ-C5Me4CH2CH2S)2Zr

A reduction of previously reported 2-methoxyethyl and 2-methylthioethyl functionalized zirconocenedichlorides (η⁵-C₅Me₄CH₂CH₂EMe)(η⁵-C₅Me₅)(ZrCl₂ (E = O, S) and (η⁵-C₅Me₄CH₂CH₂EMe)(η⁵-C₅Me₄CH₂CH₂E′Me)ZrCl₂ (E = O, S; E′ = O, S) with Mg/Hg in THF leads unexpectedly to the products of O---Me and S---Me bond cleavage (η⁵,σ-C₅Me₄CH₂CH₂E)(η⁵-C₅Me₅)ZrMe (E = O, S), (η⁵,σ-C₅Me₄CH₂CH₂E)(η⁵-C₅Me₄CH₂CH₂E′Me)ZrMe (E = O, S; E′ = O), and (η⁵,σ-C₅Me₄CH₂CH₂S)₂Zr respectively. The crystal structure of (η⁵,σ-C₅Me₄CH₂CH₂S)₂Zr was established by X-ray analysis. At that same time the reduction of (ηsu5-C_{5Me4CH2CH2EMe)(η⁵-C5Me5)ZrCl2 (E> = O, S)} under 1 atm of CO gives either only the dicarbonyl derivative (η⁵-C₅Me₄CH₂CH₂EMe) (η⁵-C₆Me₅)Zr(CO)₂ (E = O) or a complex mixture of products (E = S).     

Metabolism of CO2 by leaves of different photosynthetic types of Neurachne species

Following a series of continuous exposures to ¹⁴CO₂ for different lengths of time, leaves from Neurachne munroi (C₄), N. minor (C₃-C₄) and N. tenuifolia (C₃| were estimated to assimilate 100%, 9% and 2–4%, respectively, of atmospheric CO₂ by the C₄ pathway. The percentage of ¹⁴C-label appearing in malate and aspartate in leaves of N. minor progressively increased with longer exposure times indicating that a significant proportion of its C₄ acids are formed as secondary products. In ¹⁴CO₂/¹²CO₂ pulse/chase experiments, the ¹⁴C-label in leaves of N. munroi was rapidly transferred from C₄ acids to sugar monophosphates plus sugar diphosphates, and finally to sucrose. In leaves of N. minor, the ¹⁴C-label was slowly metabolized from the C-4 carboxyl of malate and asparate (apparent half-time = 250 s), and the formation of C₄ acids as secondary products was again evident. ¹⁴C-label in serine/glycine accumulated to comparable magnitudes in both N. minor and in N. tenuifolia, but there was an initial lag phase in the accumulation of label in N. minor. C₄ photosynthesis is apparently of minimal importance in reducing photorespiration in N. minor, but leaf anatomical specializations and a possible compartmentation of photorespiratory metabolism may be of considerable importance.     

Identification of a novel 5-HT1 binding site in rat spinal cord

High affinity, specific [³H]5-hydroxytryptamine (5-HT) binding to spinal cord synaptosomes was examined to identify the 5-HT receptor subtypes present. Computer nonlinear regression analysis of competition studies employing 8-OH-DPAT indicated that this 5-HT_1A selective agonist demonstrated high affinity competition (K_{i = 1.3 nM}) for 24.6 ± 0.7% of the total [³H]5-HT binding sites. Competition studies employing the 5-HT_1B selective agonist RU24969, in the presence of 100 nM 8-OH-DPAT, indicated that RU24969 demonstrated high affinity (K_{i = 1.1 nM}) competitive inhibition for 26.2 ± 1.4% of all [³H]5-HT binding sites. Neither 5-HT_1C, 5-HT_1D, 5-HT₂ nor 5-HT₃ selective compounds demonstrated any high affinity competition for the residual 49% of specific [³H]5-HT binding. Therefore, three major classes of [³H]5-HT binding sites could be demonstrated in spinal cord synaptosomes: 5-HT_1A, 5-HT_1B and a novel [³H]5-HT binding site which respectively represented 25, 26 and 49% of spinal cord synaptosomal [³H]5-HT binding. Further studies focusing on the function of the latter binding site are needed to determine if the presently identified novel binding site is the major 5-HT₁ receptor subtype present in spinal cord.     

施钾对甘薯氮素转移分配及氮代谢酶活性的影响

利用¹⁵N示踪技术,研究了施钾对甘薯发根结薯期、薯块膨大期地上和地下部氮素转移分配、光合特性及氮代谢酶活性的影响.结果表明: 在发根结薯期,施钾显著提高¹⁵N向地上部的转移分配,其中K₃(K₂O, 300 mg·kg^-1)处理与对照相比¹⁵N向叶片转移速率提高了76.2%,¹⁵N积累量提高了92.1%.在薯块膨大期,随施钾量增加地上部叶片¹⁵N总分配率由33.7%降低至24.4%,块根¹⁵N分配率由5.8%升高至17%,其中K₃处理块根¹⁵N积累量是对照的3倍.两个关键生长期硝酸还原酶、谷氨酸脱氢酶、谷氨酰胺合酶、谷氨酸合酶和净光合速率(P_n)均随施钾量的增加而提高.逐步回归分析表明,氮代谢酶活性和P_n是影响甘薯¹⁵N转移和分配的主要因素(R分别为0.965和0.942),通径分析表明,在发根结薯期主要通过促进硝酸还原酶和谷氨酸脱氢酶介导的氮素催化能力促进氮素向地上部分配;在薯块膨大期主要通过提高谷氨酰胺合酶/谷氨酸合酶循环介导的氮素同化能力促进氮素向地下部分配.     

PATHWAYS OF INCORPORATION OF FATTY ACID INTO GLYCEROLIPIDS OF THE MURINE PERIPHERAL NERVOUS SYSTEM IN VIVO: ALTERATIONS IN THE DYSMYELINATING MUTANT TREMBLER MOUSE

In vivo glycerolipid metabolism was studied in sciatic nerves of normal and Trembler mice. The results showed that two kinetically independent pathways were implicated in the labeling of diacylglycerophospholipids from [³H]palmitate: the Kennedy pathway and a ‘direct acylation’ pathway. In normal nerves, 45% of the glycerophospholipids were labeled, with a rate constant k₃ = 3.9 × 10⁻³ min⁻¹, from phosphatidic acid and diacylglycerol intermediates, themselves formed with a rate constant of k₁ = 0.24 min⁻¹ from a free ³H-fatty acid pool, FFA₁, that represents 45% of the total injected label. The remaining 55% of the glycerophospholipids were labeled from a kinetically distinct free ³H-fatty acid pool, FFA₂, with a rate constant of k₄ = 9.8 × 10⁻², via a process that does not implicate a detectably labeled metabolic intermediate (‘direct acylation’). Glycerophospholipid labeling via the Kennedy pathway in the Trembler mouse sciatic nerves was reduced to 75% of the normal level, while labeling via the ‘direct acylation’ pathway was increased 1.4-fold. The values of the rate constants for free ³H-fatty acid utilisation (k₁ and k₄) were both increased about 2.5-fold, while that of glycerophospholipid formation from diacylglycerol (k₃) was close to normal. Copyright © 1996 Elsevier Science Ltd     

Synthesis and characterization of organomolybdenum and organotungsten halides containing the η-pentabenzylcyyclopentadienyl ligand η-Bz5C5M(CO)3X (M = Mo, W; X = Cl, Br, I). The X-ray molecular structure of η-Bz5C5Mo(CO)3I

An improved synthetic procedure for pentabenzylcyclopentadiene Bz₅C₅H was developed. Six new organomolybdenum and organotungsten halides η⁵-Bz₅C₅M(CO)₃X(M = Mo, W; X = Cl, Br, I) were syntesized through the reaction of η⁵-Bz₅C₅M(CO)₃Li (derived from Bz₅C₅H, n-BuLi and M(CO)₆) with PCl₃, PBr₃ or I₂ and characterized by elemental analysis, IR and ¹H NMR spectroscopy. The structure of η⁵-Bz₅C₅Mo(CO)₃I was determined by single-crystal X-ray diffraction techniques. It crystallized in the monoclinic space groupp P2/c with cell parameters a = 13.294(4), B = 15.147(4), C = 19.027(3) Å, β = 108.32(2)°, V = 3637(2) ų, Z = 4 and D_x = 1.50 g cm⁻³. The final R value was 0.035 for 4564 observed reflections.     

Monitoring Anaerobic Natural Attenuation of Petroleum Using a Novel In Situ Respiration Method in Low-Permeability Sediment

Assessing petroleum biodegradation rates is an important part of predicting natural attenuation in subsurface sediments. Monitoring carbon dioxide (CO₂) and methane (CH₄) produced in situ, and their radiocarbon ¹⁴C), stable carbon (¹³C) and deuterium (D). signature provide a novel method to assess anaerobic microbial processes. Our objectives were to: (1) estimate the rate of anaerobic petroleum hydrocarbon (PH) mineralization by monitoring the production of soil gas CH₄ and CO₂ in the vadose zone of low-permeability sediment, (2) evaluate the dominant microbial processes using δ¹³C and δD, and (3) determine the proportion of CH₄ and CO₂ attributable to anaerobic mineralization of PH using ¹⁴C analysis. Argon was sparged into the subsurface to dilute existing CO₂ and CH₄ concentrations. Vadose zone CO₂, CH₄, oxygen, total combustible hydrocarbons, and argon concentrations were measured for 75 days. CO₂ and CH₄ samples were collected on day 86 and analyzed for ¹⁴C, δ¹³C, and δD. Based on CH₄ soil gas production, the anaerobic biodegradation rate was estimated between 0.017 to 0.055 mg/kg soil-d. CH₄ ¹⁴C (2.6 pMC), δ¹³C (-45.64‰), and δD (-316‰) values indicated that fermentation of PH was the sale source of CH₄ in the vadose zone. CO₂ ¹⁴C (62 pMC) indicated that approximately 47% of the total CO₂ was from PH mineralization and 53% from plant root respiration. Although low-permeability sediment increases the difficulty of completely replacing in situ soil gas and assuring anaerobic conditions, this novel respiration method distinguished between anaerobic processes responsible for PH degradation.     

Synthesis, platinum(II) complexes and structural aspects of the new tetradentate phosphine cis,trans,cis-1,2,3,4-tetrakis(diphenylphosphino)cyclobutane

Several novel dimers of the composition [M₂Cl₄(trans-dppen)₂] (M=Ni (1), Pd (2), Pt (3)) containing trans-1,2-bis(diphenylphosphino)ethene (trans-dppen) have been prepared and characterized by X-ray diffraction methods, NMR spectroscopy (¹⁹⁵Pt{¹H}, ³¹P{¹H}), elemental analyses, and melting points. The intramolecular [2+2] photocycloaddition of the two diphosphine-bridges in 3 produces [Pt₂Cl₄(dppcb)] (4), where dppcb is the new tetradentate phosphine cis,trans,cis-1,2,3,4-tetrakis(diphenylphosphino)cyclobutane. Neither 1 nor the free diphosphine trans-dppen shows this reaction. In the case of 2 the photocycloaddition is slower than in 3. This difference can be explained by the shorter distance between the two aliphatic double bonds in 3 than in 2, but also different transition probabilities within ground and excited states of the used metals could be involved. Furthermore, variable-temperature ³¹P{¹H} NMR spectroscopy of 2 or 3 reveals a negative activation entropy of 2 for the [2+2] photocycloaddition, but a positive of 3. The removal of chloride from 4 by precipitating AgCl with AgBF₄, and subsequent treatment with 2,2′-bipyridine (bipy) or 1,10-phenanthroline (phen) leads to [Pt₂(dppcb)(bipy)₂](BF₄)₄ (5) and [Pt₂(dppcb)(phen)₂](BF₄)₄ (6), respectively. In an analogous reaction of 4 with PMe₂Ph or PMePh₂, [Pt₂(dppcb)(PMe₂Ph)₄](BF₄)₄ (7) and [Pt₂(dppcb)(PMePh₂)₄](BF₄)₄ (8) are formed. Complexes 1–8 show square–planar coordinations, where the compounds 4–8 have also been characterized by the above mentioned methods together with fast atom bombardment mass spectrometry (7, 8). The crystal structure of 4 reveals two conformations, which arise from an energetic competition between the sterical demands of dppcb and an ideal square–planar environment of Pt(II). The free tetraphosphine dppcb can be obtained easily from 4 by treatment with NaCN. It has been characterized fully by the above methods including ¹³C{¹H} and ¹H NMR spectroscopy. The X-ray structure analysis shows the pure MMMP-enantiomer in the solid crystal, which is therefore optically active. This chirality is induced by a conformation of dppcb, where all four PPh₂ groups are non-equivalent. Variable-temperature ³¹P{¹H} NMR spectroscopy of dppcb confirms this explanation, since the single signal at room temperature is split into two doublets at 183 K. The goal of this article is to demonstrate the facile production of a new tetradentate phosphine from a diphosphine precursor via Pt(II) used as a template.