Reactivity of carbon monoxide towards high valent molybdenum complexes

Reaction of carbon monoxide (3 atm) with Mo(O)₂(mes)₂ (mes = MESITYL = C₆H₂Me₃-2,4,6) in pyridine at room temperature affords dimesityl ketone 1 (5%) and 1,1′-bis(mesitoyl)-1,1′,4,4′-tetrahydro-4,4′-bipyridine 2 (25%), the molecular structure of which has been determined by an X-ray diffraction study. The formation of 2 represents the first example of N-acylation of a pyridine by CO mediated by a transition metal complex. It has been shown that the relative ratio of 1 and 2 is dependent on the reaction conditions and that the presence of pyridine is essential for the formation of 1. Reactions of CO with the isoelectronic complex Mo(N^tBu)₂mes₂ contrast sharply with Mo(O)₂mes₂ and, under the same conditions, no dihydropyridine is formed, the sole identified products being 1 (60%) and mesityltertiobutyl amide HN(^tBu)COmes (40%). In light of the experimental results and of extended Hückel calculations on dioxo and diimido d⁰ molybdenum complexes, a tentative mechanism for the formation of 2 is proposed which involves oxycarbene-like intermediates in the case of the more electrophilic dioxo molybdenum species.     

Reactivite comparee des perfluoroiodoalcanes (RFI) et des perfluoroalcoyl-2 iodo-1 ethanes (RFC2H4I) en presence de couple metallique zinc-cuivre dans les solvants phosphates d'alcoyles

Reactivity of perfluoroalkyl iodides R_FI and 1-perfluoroalkyl-2-iodoethanes R_FC₂H₄I, in presence of a zinc-copper couple in alkyl phosphates solvents, is described. R_FI and R_FC₂H₄I react via an organometalllc route to give per- and poly-fluoroorganozinc (R_FZnI and R_FC₂H₄ZnI) compounds. Then, in particular conditions, they react with alkyl to give phosphoro-fluorinated molecules (phosphinates, phosphine oxides, phosphines). The compounds's stabilities are studied.     

Extractability of HgS (cinnabar and metacinnabar) by hydrochloric acid

In this work we investigated the behaviour of pure HgS during extraction with dilute HCl to establish its extractability in 1 and 6 M HCl at the concentration level close to those occurring in natural sediments and soils. We found that neither cinnabar nor metacinnabar were soluble in 1 M HCl, whereas both were partially extracted by 6 M HCl. Metacinnabar precipitated in the laboratory was most prone to dissolution in 6 M HCl (up to 90%), followed by crystalline (commercial) metacinnabar (up to 70%) and cinnabar (up to 15%). Solubility of HgS in 6 M HCl was found to be dependent on its concentration, and an exponential relationship between quantity of HgS added to 20 mL of 6 M HCl (the range of 0.1-10 mg was used) and the solubility in 6 M HCl was established. For higher concentrations of HgS (10 mg in 20 mL of acid), a similarly low solubility of cinnabar was obtained as found in the literature. A study of dissolution kinetics of HgS in 6 M HCl indicated that it was a fairly slow process. Unexpected oxidation of HgS in water or 1 M HCl was found for extractions performed in Teflon vials previously used for the digestion of residual undissolved HgS by aqua regia. We presumed that the Teflon material could preserve some oxidising gases (presumably Cl(2)) developed during digestion with aqua regia which can then oxidise HgS during extraction with water or 1 M HCl. Regarding the extraction of Hg from natural sediments, we concluded that 6 M HCl could not be used to extract reactive Hg and predict bioavailability of mercury in sediments containing HgS and that experiments with model compounds should not be done at a concentration level several orders of magnitude higher than in natural samples.     

The molecular electrostatic potential and steric accessibility of C-DNA

The molecular electrostatic potentials and steric accessibilities associated with reactive sites of C-DNA are calculated for the sequences poly(dG · dC) and poly(dA · dT). The distribution of potential on the surface envelopes of the double helices are also presented. The results are compared with those obtained for B-DNA.     

Second sphere supramolecular chirality: racemic hybrid H-bonded 2-D molecular networks

Neutral hybrid 2-D networks have been generated using a bis-amidinium capable of chelating M(CN)6(3-) anions via hydrogen bonds: the packing of the achiral 2-D networks leads to channels which are occupied by water molecules forming polymeric H-bonded chains; furthermore, owing to the dihapto mode of H-bonding, the presence of supramolecular chirality of the delta' and lambda' types taking place within the second coordination sphere of the metallic centre has been demonstrated.     

Synthesis of Highly Fluorinated Di-O-alk(en)yl-glycerophospholipids and Evaluation of Their Biological Tolerance

The syntheses of various fluorocarbon/fluorocarbon and fluorocarbon/hydrocarbon rac-1,2- and 1,3-di-O-alk(en)ylglycerophosphocholines and rac-1,2-di-O-alkylglycerophosphoethanolamines (see Fig.2), which may be used as components for drug-carrier and delivery systems, are described together with some results concerning their biological tolerance. They were obtained by phosphorylation of perfluoroalkylated rac-di-O-alk(en)ylgly-cerols using POCl₃, then condensation with choline tosylate or N-Boc-ethanolamine (2-[(tert-butoxy)carbonyl-amino]ethanol) followed by Boc-deportection (Schemes 6–8). The fluorcarbon/fluorocarbon 1,2-di-O-alkylgly-cerols were prepared by O-alkylation of rac-1-O-benzylglycerol using perfluoroalkylated mesylates, then hydrogenolysis for benzyl deprotection (Scheme 1). The two different hydrophobic chains in the mixed fluorocarbon/fluorocarbon and fluorocarbon/hydrocarbon 1,2-di-O-alk(en)ylglycerols were introduced starting from 1,2-O-iso-propylidene- then O-trityl-protected glycerols or from 1,3-O-benzylidene-glycerol (Schemes 3 and 4). The perfluoroalkylated O-alkenylglycerols were obtained by O-alkylation of a glycerol derivative using an ω-unsaturated alkenyl reagent, the perfluoroalkyl segment being connected onto the double bond in a subsequent step (Schemes 1) and 3. The perfluoroalkylated symmetrical and mixed 1,3-di-O-alkylglycerols were synthesized by displacement of the Cl-atom in epichlorohydrin by perfluoroalkylated alcohols, then catalytic (SnCl₄) opening of the oxirane ring of the resulting alkyl glycidyl ethers in neat alcohols (Scheme 5). When injected intravenously into mice, acute maximum tolerated doses higher than 1500 and 2000 mg/kg body weight were observed for the fluorinated glycerophosphocholines, indicating a very promising in vivo tolerance.     

Synthesis and cytotoxic and antitumor activity of 1,2-dihydroxy-1,2-dihydrobenzo[b]acronycine diacid hemiesters and carbamates

A series of cis-1,2-dihydroxy-1,2-dihydrobenzo[b]acronycine diacid hemiesters and dicarbamates were prepared by acylation of cis-1,2-dihydroxy-6-methoxy-3,3,14-trimethyl-1,2,3,14-tetrahydro-7H-benzo[b]pyrano[3,2-h]acridin-7-one. The cytotoxicity of the dicarbamates depended on the steric hindrance of the esterifying groups at positions 1 and 2. Diacid hemiesters displayed significant in vitro cytotoxic activities and induced cell cycle perturbations similar to those obtained with cis-1,2-diacetoxy-1,2-dihydrobenzo[b]acronycine (S23906-1) currently under preclinical development. cis-1-Acetoxy-2-hemiglutaryloxy-1,2-dihydrobenzo[b]acronycine was the most promizing compound of the series, inducing complete inhibition of tumor growth when tested against C38 colon adenocarcinoma implanted in mice.     

On the multiplicity of parts in a random partition

Let λ be a partition of an integer n chosen uniformly at random among all such partitions. Let s(λ) be a part size chosen uniformly at random from the set of all part sizes that occur in λ. We prove that, for every fixed m≥1, the probability that s(λ) has multiplicity m in λ approaches 1/(m(m+1)) as n→∞. Thus, for example, the limiting probability that a random part size in a random partition is unrepeated is 1/2. In addition, (a) for the average number of different part sizes, we refine an asymptotic estimate given by Wilf, (b) we derive an asymptotic estimate of the average number of parts of given multiplicity m, and (c) we show that the expected multiplicity of a randomly chosen part size of a random partition of n is asymptotic to (log n)/2. The proofs of the main result and of (c) use a conditioning device of Fristedt. ©1999 John Wiley & Sons, Inc. Random Struct. Alg., 14, 185–197, 1999     

Analysis by fast-atom bombardment tandem mass spectrometry of phosphatidylcholine isolated from heart mitochondrial fractions: Evidence of incorporation of monohydroxylated fatty acyl moieties

Phosphatidylcholine (PC) is one of the main phospholipids present in mitochondrial membranes. According to current knowledge, the predominant fatty acyl moieties in this phospholipid are 16, 18, 20, or 22 carbon atoms long with chains that contain only carbon and hydrogen atoms. We have conducted a detailed analysis of the fatty acid substituents of the phospholipids present in mitochondrial fractions by using fast-atom bombardment tandem PC extracted from mitochondrial fractions of rat heart. The structure of one of these monohydroxylated fatty acids has been elucidated and corresponded to 12-hydroxy 9-octadecenoic acid. Indications that concern the structure of the five other monohydroxylated fatty acids are presented. These monohydroxylated fatty acyl groups are preferentially associated in the PC molecule with C-18 and C-20 fatty acyl moieties. We present arguments to suggest that the formation of these compounds is probably not due to a free-radical initiated mechanism. The potential implication of these monohydroxylated fatty acids in several physiological functions is suggested by the fact that free hydroxylated fatty acids that are identical or closely related to those found in the mitochondrial fractions possess various biological activities.