Metal Moiety Research Articles

ABOUT THE COORDINATION CHEMISTRY OF THE PHOSPHORUS-NITROGEN ENTITY

Abstract Triply coordinated trivalent nitrogen atoms are known to lose most or all of their Lewis donor capacity when bonded to a third or higher row element. It is shown here, in the case of P-bonded nitrogen atoms, that structural constraints which maintain the nitrogen atom in a pyramidal configuration can contribute much in preserving their basicity and/or nucleophilic character. In particular, nitrogen atoms apically bonded to 5-coordinated formally penta- or trivalent phosphorus atoms can display definite basicity. Examples of metal- and base-induced opening and closing of P[sbnd]N bonds are also presented. The following unusual coordination modes and/or reaction issues are exemplified: where A can be-depending on the case-H+, CH3 +, BH3, BF3 or a transition metal moiety, as for example CpMo(CO)2Cl or CpMo(CO)2, etc. The factors that affect the rather variable P[sbnd]N bond length are discussed.

The demetallation reaction in radiohalogen labelling: Synthesis of bromine and fluorine labelled compounds

A review on the use of the demetallation reaction in radiohalogen labelling is given, with particular emphasis on bromine and fluorine radiolabelling. The metals which are included are mercury, thallium, boron, tin, silicon and lead. The preparation of organometallics containing these metals, the cleavage of the metal moiety with radiobromine and radiofluorine and the application of this chemistry to radiopharmaceutical synthesis will be discussed.

Novel CO Bond Formation via [3+2] Cycloaddition of Diphenylketene to a Dioxo Metal Moiety

Novel CO Bond Formation via [3+2] Cycloaddition of Diphenylketene to a Dioxo Metal Moiety

The effects of metalloporphyrins, porphyrins and metals on the activity of delta-aminolevulinic acid synthase in monolayers of chick embryo liver cells

The effect of various metals, porphyrins and metalloprphyrins on the activity of delta-aminolevulinate synthase (ALAS) was measured in monolayers of chick embryo liver cells in order to determine whether the metal moiety of heme or heme itself is the regulator of ALAS activity. Iron, magnesium, zinc, copper, manganase and nickel did not decrease ALAS activity in non-induced and in cells induced by allyl-isopropylacetamide (AIA). Cobalt decreased both non-induced and induced activity. Porphyrins inhibited ALAS, apparently only after having been converted into metalloporphyrins. Almost all the metalloporphyrins examined decreased ALAS activity. None of the substances, at the concentrations used, was toxic to the cells. These observations indicate that probably heme and not iron is the regulator of ALAS activity in monolayers of chick embryo liver cells.

ChemInform Abstract: IRON‐STABILIZED CARBOCATIONS AS INTERMEDIATES FOR ORGANIC SYNTHESIS

Attachment of a transition metal moiety to an olefinic ligand presents the organic chemist with unequaled opportunities to control the regio- and stereospecificities of bond formation. Applications of cationic dienyliron-carbonyl complexes to a range of natural product syntheses have been developed. These applications show how the iron-carbonyl unit directs the regio- and stereochemistry of nucleophile addition. They also show that the iron-carbonyl unit can be used to stabilize otherwise inaccessible carbocations, thereby making them readily available as synthetic intermediates.

Iron-Stabilized Carbocations as Intermediates for Organic Synthesis

Attachment of a transition metal moiety to an olefinic ligand presents the organic chemist with unequaled opportunities to control the regio- and stereospecificities of bond formation. Applications of cationic dienyliron-carbonyl complexes to a range of natural product syntheses have been developed. These applications show how the iron-carbonyl unit directs the regio- and stereochemistry of nucleophile addition. They also show that the iron-carbonyl unit can be used to stabilize otherwise inaccessible carbocations, thereby making them readily available as synthetic intermediates.

A tetranuclear polyfunctional sodium–vanadium(III) complex containing a vanadium(III)–vanadium(III) double bond

Reduction of N,N′-o-phenylenebis(salicylideneiminato)chlorovanadium(III), [(thf)V(salophen)Cl](thf = tetrahydrofuran), with soidum metal caused the dimerization of two metallic moieties through two C–C bonds leading to a tetranucleating ligand binding two sodium cations and two vanadium(III) joined by a double bond [2.406(3)A].

Phosphorus and Arsenic Chalcogenides as Reagents Toward Transition Metal-Ligand Systems

Abstract The compounds obtained by reacting the P4S3, P4Se3 and As4S3 cage molecules with various transition metal-ligand moieties are reported. The transition metal-ligand systems are bound either to the intact molecules or to fragments (hexa- or tri-atomic) originating from the cage molecules. Such compounds provide examples of selective activation of cage molecules by metal moieties.

Übergangsmetall-methylen-komplexe: IXL. Über metallzentrierte umlagerungsreaktionen von diazoalkanen und die einfache synthese von alkylidenamido- sowie isocyanato-komplexen

The dinuclear 2-diazopropane complex 1 undergoes a novel type of fragmentation upon heating in boiling toluene: irreversible nitrogennitrogen bond cleavage of the metal-coordinated heterocumulene with subsequent rearrangement of the intermediate nitrido(carbonyl)metal species yields a terminal isocyanato ligand while the remaining 2-propylidene amido fragment symmetrically bridges the metalmetal double bond ( d(MoMo) 274.5(2) pm) of the reaction product 2. This unexpected rearrangement reaction is to be considered as a further variant of the “Hieber base reaction”. A chemical test of the multiple bond character of the molybdenummolybdenum bond present in compound 2 was provided by the reversible addition of carbon monoxide which reaction yields compound 3. Insertion of a nitrido metal moiety into a methylene bridge was observed, for the first time, in the case of the methodologically related rearrangement process of the diazomethane derivative 4; the resulting dinuclear bis(methylene amido) derivative 5 was again characterized by means of X-ray diffraction techniques.

２‐（アルキルアミノ）エタノールのＮ，Ｏ‐二金属誘導体と硫化カルボニルとの反応

N, O-Dimetal derivatives of 2-(alkylamino)ethanol [1], MOCH2CH2NRM, reacted with carbonyl sulfide at room temperature to afford thiocarbamic S-acid salt type adduct [2a] for M=Li, and a mixture of[2a]and [2b] for M=Me2Si/2 and BrMg. Organostannyl adduct [2a]was decomposed under reflux in toluene for about 10 h to give the oxazolidin-2-one [13a]in a moderate yield, while carbonylated product [2a] was not obtained from the reaction of silyl, boryl, and magnesio derivateves, which were presented as a mixture of [2a] and [2b]type adducts. In marked contrast to this, cyclic thiocarbamic S-acid ester [3c]was formed by thermolysis of lithio adduct [2b] (M=Li) having thiocarbamic O-acid salt structure. The effect of metallic moiety in [1]on the reactivity is briefly discussed.

Conformation moleculaire et empilement cristallin: exemple des derives substitues du benzenechrome tricarbonyle I. Determination theorique de conformations moleculaires. Comparaison avec les conformations cristallines

In order to evaluate the crystal effect on the molecular geometry of substituted derivatives of benzenechromium tricarbonyl, favoured conformations of several complexes (substituted at the arene ring or the metallic moiety) in the gaseous state have been determined by the EHT method and compared to the solid state conformations. In most cases the two conformations are similar.

Cisplatin-induced changes in sodium, chloride, and urea transport by the frog skin

Cisplatin is a platinum-containing antitumor agent whose usefulness is limited by nephrotoxicity. We examined the effects of cisplatin on a representative, transporting epithelium--the frog skin. Cisplatin (10(-3)M) from the mucosal surface increased the active transport of sodium by 35 to 40%, as monitored by short-circuit current. The cisplatin-induced increase in short-circuit current was inhibited by amiloride and was additive to the effects of vasopressin (20 mU/ml of serosal solution). Cisplatin from the mucosal surface also decreased transeptithelial electrical resistance by about 35% and increased the permeability to sodium, chloride, and urea. None of these effects of cisplatin occurred with platinum sulfate, platinum chloride, or the trans-isomer of cisplatin. Accordingly, we conclude that cisplatin increases the permeability of the mucosal surface of the frog skin to sodium, chloride, and urea and that these changes are related to the cis-configuration of the drug rather than simply its heavy metal moiety.

Reaction mechanism of calcium-ATPase of sarcoplasmic reticulum. Substrates for phosphorylation reaction and back reaction, and further resolution of phosphorylated intermediates.

Reaction of the purified Ca2+-ATPase of sarcoplasmic reticulum at 0 degrees C at low [gamma-32P]ATP (0.1 to 0.67 microM) and enzyme (0.025 to 0.24 microM) concentration in the presence of 0.11 to 30 mM Ca2+ without added Mg2+ has resulted in the formation of phosphorylated intermediate (EP:maximal level of EP = 0.45 mol/mol of enzyme) at a very slow rate. Under these conditions, the reaction steps in which EP decomposition takes place are completely prevented. This has permitted us to study the EP formation reaction and its reversal specifically, with a considerably improved time resolution. An apparent rate constant of EP formation (Vf) increases in parallel with the concentration of Ca . ATP, but not with those of Mg . ATP, or of protonated or fully ionized free ATP. This suggests that Ca . ATP is the substrate under these conditions. If Co2+ or Mn2+ are in excess over the other ions during the reaction, Vf varies in parallel with [Co . ATP] or [Mn . ATP]. Thus, it appears that either Ca2+, Co2+, or Mn2+ can be complexed with ATP to form the effective substrate. An apparent rate constant of the back reaction of EP initiated by addition of ADP to EP (Vr) increases in proportion to [ADP] or [H . ADP], but is inhibited by increasing concentrations of the ADP complex with Ca2+ or Mg2+, indicating that free ADP or protonated ADP, or both, are actual substrates for the back reaction of EP. These results suggest a new type of site to which the metal moiety of metal . ATP complex remains bound after the release of ADP from the enzyme. An acid-stable phosphorylated intermediate (EP) produced in the presence of high Ca2+ concentrations (e.g. 0.11 mM) without added Mg2+ does not decompose spontaneously, and the major portion (approximately 90%) of this EP (EPD+) reacts with ADP to form ATP (ADP-sensitive). Upon chelating Ca2+ with ethylene glycol bis(beta-amino-ethyl ether)N,N,N',N'-tetraacetic acid (EGTA), EPD+ is converted to another form of EP (EPD-), which is unreactive with ADP (or ADP-insensitive). Addition of Mg2+, after initiation of the reaction leading to EPD- by EGTA, results in rapid production of Pi from a portion of EPD- with KMg approximately equal to 3.3 x 10(3) M-1. The fraction of EPD- that is Mg2+-sensitive (EPD-,M+) increases with reaction time at a much slower rate than the Mg2+-insensitive portion of EPD- (EPD-,M-). These results suggest that the enzyme reaction involves the sequential formation of at least three forms of acid-stable EP, viz. in the order of formation, EPD+, EPD-,M-, and EPD-,M+. The equilibrium between EPD+ and EPD-,M- is shifted by higher [K+] and [Ca2+] towards EPD+.

PHOSPHAZENES AND PHOSPHAZANES

Abstract Three types of phosphazene and four types of phosphazane structural units are classified on the basis of the coordination number of the phosphorus atoms involved. Phosphorus-nitrogen bond lengths are discussed in acyclic compounds and this information is used in analysing ring systems consisting wholly or partially of phosphorus-nitrogen skeletons. Four-, five-, six-, seven-, eight-, ten-, and twelve-membered rings are surveyed, as are polycyclic systems. Methods of synthesis for cyclophosphazanes, and mixed cyclo-phosphazene-phosphazanes are briefly considered, as are some of their reactions. The minimum ring size where stable phosphazenes have been observed is referred to. The effect of protonation, methylation, or coordination to a metal moiety on adjacent phosphorus-nitrogen bonds is discussed. The conformations of dimethylamino and phenyl substituents on phosphorus are considered, as is the conformations of the ring skeletons. The flexibility of a cyclic and cyclic phosphorus-nitrogen skeletons is noted, and factors governing phosphorus-nitrogen bond lengths are analysed. On the basis of this and by analogy with sulphur-nitrogen chemistry predictions are made about conditions favouring very long and very short phosphorus-nitrogen bonds.

119Sn Mössbauer Spectra of Sn–Ni Compounds

Sn Mössbauer spectra have been recorded for eleven tin-nickel compounds of the type Clx,Sn[NiLCp]4−x (L = CO, PPh3;x = 2,3) and Cl3SnNiL2Cp.S (S = solvent molecule). The center shifts are used to distinguish coordinated SnCl3 and uncoordinated ionic SnCl3−, respectively. In the SnCl3− compounds, the Mössbauer parameters indicate that the solvent molecules are not bonded to the Sn atom. In compounds containing Sn—Ni bonds, the center shifts and quadropole splittings show that Ni(PPh3)Cp is the best donor of the first row transition metal moieties, and that the Sn—Ni bond has the highest Sn s character. Ni(CO)Cp is a slightly poorer donor than Ni(PPh3)Cp, and the Sn—Ni bond has a smaller s character.

Further Purification and Properties of Neurospora Nitrate Reductase

Abstract Neurospora crassa (5297a) NADPH-nitrate reductase (NADPH:nitrate oxidoreductase, EC 1.6.6.2), a soluble, sulfhydryl-containing protein with FAD, a cytochrome b designated cytochrome b557 (N. crassa), and molybdenum as prosthetic groups, has been purified 500-fold by procedures including pH adjustment, ammonium sulfate fractionation of the resultant supernatant solution, phase separation to remove nucleic acids, diethylaminoethyl cellulose chromatography, hydroxylapatite chromatography, and, finally, Sephadex G-200 gel filtration. Other enzymatic activities associated with NADPH-nitrate reductase throughout the purification and maintaining a proportional relationship with it are NADPH-cytochrome c reductase, FADH2-nitrate reductase, and reduced methyl viologen-nitrate reductase. Polyacrylamide gel electrophoresis of the most highly purified enzyme preparations yielded a major buffalo black-staining zone containing the above enzymatic activities, a somewhat smaller zone, and several faint zones. In unstained gels, a red zone, which was apparently due to the presence of cytochrome b557, was visible at the position corresponding to the major buffalo black-staining zone. By the use of sucrose density gradient centrifugation, a relative s20, w0.725 value of 8.0 for the nitrate reductase was found, and with Sephadex G-200 gel filtration techniques, a Stokes radius of 70 A was determined. From the relationship, mol wt = 6πeNas/(1 - vp), a molecular weight of 228,000 was calculated, assuming v = 0.725 cc per g. All enzymatic activities associated with nitrate reductase are heat-labile but to varying degrees, with the NADPH-nitrate and -cytochrome c reductases being most sensitive, and FADH2- and reduced methyl viologen-nitrate reductase activities being progressively less so, in that order. The reduced methyl viologen-nitrate reductase activity showed a marked increase in activity as the NADPH activities declined. The cytochrome b557 associated with nitrate reductase activity shows a typical cytochrome b type visible absorption spectrum at liquid nitrogen temperature and is a protoporphyrin IX heme as judged from the spectrum of its pyridine hemochromogen derivative. Studies with the inhibitor, p-hydroxymercuribenzoate, reveal the presence of one or more readily accessible sulfhydryl groups functioning between NADPH and FAD. FADH2-nitrate reductase and reduced methyl viologen-nitrate reductase are considerably less sensitive to this —SH reagent. Inhibition by metal-binding agents has suggested the possible involvement of a second metal moiety (in addition to the molybdenum), functioning earlier in the electron transfer scheme. No negative feedback phenomena at the enzymatic level could be found with the variety of nitrogen compounds tested.

Polymerization of N‐vinylearbazole with vanadium compounds. Part I. Polymerization with vanadium pentoxide and metal vanadates

AbstractBulk polymerization of N‐Vinylcarbazole (NVC) has been carried out using vanadium pentoxide as the contact catalyst. The rate of polymerizatlon has been found to depend upon catalyst to monomer ratio. A cationic mechanism has been suggested and the role of V2O5 surface in the polymerization has been tentatively analyzed. The π‐acid characteristies of V5⊕ ion is believed to be involved in initiating the polymerization. The effect of a number of additives on the polymerization rate has been studied, which endorses the cationic mechanism. The catalytic efficiency of a number of metal vanadates for the polymerization of NVC has also been studied. A fairly good correlation between the activity and electronegativity of the metallic moiety has been established.

A mechanism of protection against intoxication with various metals

Calcergens are compounds that cause topical calcification upon subcutaneous injection in unpretreated rats, whereas calciphylactic challengers do so only after systemic pretreatment with a conditioning factor (e.g., vitamin D compounds, parathyroid hormone). Both the mortality and the splenic calcification, commonly elicited by the intravenous injection of various calcergens (rare earth metal chlorides), are prevented, or at least greatly diminished, by pretreatment with calciphylactic challengers (ferric dextran, chromium dextran and, to a lesser extent, aluminum dextran). This prophylactic effect is due to the challenging metal moiety of the chelates, since dextran alone does not protect. These findings are reminiscent of earlier observations that had shown that the topical calcifying effect of calcergens is likewise inhibited by the admixture of calciphylactic challengers. It is possible that the antagonism depends upon changes in calcium or phosphorus metabolism since the eliciting agents are limited to metals having specific calcinotic effects.

Syngenesis of sulfide ores; an evaluation of biochemical aspects

Syngenetic theories of sulfide ore formation often include microbial sulfate-reduction as the source of sulfide. The conditions required for large scale reduction of sulfate, quantitative aspects, the potential and the limitations of microbial sulfate-reduction are sometimes not fully appreciated or may even be misunderstood by those participating in the debate on syngenesis of sulfides. The biochemical factors involved are considered separately and this is followed by a general discussion. Both qualitative and quantitative aspects of microbial sulfate-reduction are adequate for syngenetic theory. The conditions required for sulfate-reduction cannot be specified simply but are satisfied by various combinations of circumstances that result in oxygen depletion in a wide variety of physical environments. Metals entering such environments, whether adsorbed or not, are converted to metal sulfides. Sulfate-reduction does not explain the origin of the metal moiety. Separation and concentration of adsorbed metals and the identification of biochemicals in ore-bearing strata need further research. Objections to syngenesis based upon toxicity of metals are not valid. Biochemical factors cannot conclusively establish the origin of sulfide deposits but are consistent with a sedimentary origin. Microfossils in Precambrian pyrite are not identifiable with modern sulfate-reducers but do contain organic matter. On biochemical grounds, it is probable that microbial sulfate-reduction had evolved by the early Precambrian.

Erythropoietic effect of red blood cell components and heme-related compounds.

1. Regardless of age, sex, or species of the donor animals, lysed mammalian red blood cells show erythropoietic stimulating activity. 2. Comparison of the stimulating effects of red blood cell components on erythropoiesis shows that hemoglobin and hemin are active; stroma and globin are not. 3. The following compounds related to heme appear to increase erythropoiesis: compounds containing 4 pyrrole rings connected by methene bridges; an open 4-pyrrole ring configuration, as in biliverdin and bilirubin. The nature of the side-chain groups is not critical for activity; a metal moiety is not essential to activity. 4. Several precursors involved in synthesis of the porphyrin ring, a single pyrrole ring, and cyanocobalamin which has a corrinoid ring structure, did not increase erythropoietic activity.