An efficient procedure for the preparation of (E)-alpha-alkylidenecycloalkanones mediated by a CeCl(3) x 7H(2)O-NaI system. Novel methodology for the synthesis of (S)-(-)-pulegone

2-Alkylidenecycloalkanones are powerful synthons used as the key intermediates in many important syntheses. Because of their potential, a general method of preparation from readily available starting materials, under very mild conditions, was considered to be worthwhile. Cerium(III) chloride heptahydrate in combination with sodium iodide in refluxing acetonitrile promotes a regio- and stereoselective beta-elimination reaction to (E)-2-alkylidenecycloalkanones in 2-(1-hydroxyalkyl)cycloalkanones. The synthetic value of the present procedure is demonstrated by the synthesis of monoterpene (S)-(-)-pulegone (8) in its optically active form.     

Models for copper proteins. Copper(I) and (II) complexes of a novel binucleating tetraamino-tetrathioether ligand

The novel binucleating ligand, 6,6 prime-methylene-bis(5 prime-amino-3 prime,4 prime-benzo-2 prime-thiapentyl)-1,11-diamino-2,3:9,10-dibenzo-4,8-dithiaundecane (H4L) was prepared and reacted with copper(II) salts in dry MeOH to yield mixtures of copper(I) and copper(II) complexes with Cl- and ClO-4 counter ions. The amine functions on the ligand release protons to form copper(I) complexes: (Cu2L)X2, where X=Cl−, ClO4-. The complexes were oxidized to (Cu2L)X4 with H2O2 in DMF; Cu(NO3)2 gave a different complex, [Cu2(H4L)(NO3)2](NO3)2, as regards proton releasing ability, coordination and oxidation number. Evidence for the structures of this new tetraamino-tetrathioether ligand and its copper complexes is provided by 1H-, 13C-n.m.r., mass, u.v.–vis., i.r. spectra, elemental analyses, molar conductivities and magnetic moments. This revised version was published online in June 2006 with corrections to the Cover Date.     

Squarato-metal(II) complexes. 2. unusual bonding mode for a squarato-bridged trinuclear copper(II) complex

Herein, we report the structural characterization and magnetic properties of the unique squarato-bridged-tricopper(II) complex, [Cu3(pmap)3(micro1,2,3-C4O4)](ClO4)(4).2H 2O (1), based on the tripod tripyridylamine ligand bis[2-(2-pyridyl)ethyl]-(2-pyridyl)methylamine (pmap). Each of the three copper centers is penta-coordinated by four N atoms of a pmap ligand and one bridging O atom of the central squarato dianion. This complex is the first example of a non-polymeric X-ray structurally characterized trimeric transition metal complex with the three metal cations being bridged by a single squarato ligand in a micro1,2,3 coordination mode. The magnetic properties of the complex were measured over the temperature range 2-300 K. The complex exhibits moderate bulk antiferromagnetic interaction. The three magnetic exchange pathways have J values of -27.8, -20.8, and -31.9 cm(-1). The DFT calculations corroborate the relatively strong antiferromagnetic couplings obtained from the fitting of the experimental magnetic susceptibility data and allow an assignment of the fitted J values. Several geometrical parameters have been analyzed using theoretical calculations to establish magnetostructural correlations for complex 1.     

Study of the Crystallization Kinetics. Poly(ethylene oxide) and a blend of poly(ethylene oxide) and poly(bisphenol A-co-epichlorohydrin)

A kinetic study of the crystallization of poly(ethylene oxide) (PEO) and of a blend of PEO+poly(bisphenol A-co-epichlorohydrin) (PBE) was performed by using DSC in a non-isothermal program at constant cooling rates. The curves obtained were analyzed by the Kissinger, Ozawa and Friedman methods, with determination of the kinetic parameters in each case. As a consequence of the presence of PBE, the kinetic parameters were altered, leading to the conclusion that PBE has some influence on the crystallization of PEO, modifying its mechanism. This revised version was published online in July 2006 with corrections to the Cover Date.     

Theoretical Study of the Dimerization of Chlorophyll (a) and Its Hydrates: Implication for Chlorophyll (a) Aggregation

Dimeric structures chlorophyll (a) (Chla) and their mono‐ and dihydrated have been suggested to play an important role in the mechanism of photoreaction center chlorophyll special pairs PSI and PSII. Despite their functional importance, the molecular basis structures for interacting two Chla molecules and the structural stabilization role of H₂O in the formation of hydrated Chla dimer complexes is poorly understood. In this article, the different coordination modes between two interacting Chla molecules and the configurational (orientation and distance) features between the dimer and bound H₂O molecules are characterized by means of super molecule approach the density functional theory DFT. An estimation of the thermodynamic quantities is made for Chla dimerization and hydration processes. The results indicate that structure including ester linkages via H₂O hydrogen bonding is the most favorable conformation for the dihydrated chlorophyll (a) dimer at B3LYP/6‐31G*‐DCP level of calculation. The dispersion interaction is shown to be of great significance for the Chla dimer stabilization. In aqueous nonpolar solvent, the thermodynamics show that Chla has a slightly stronger driving force for full hydration than for dimerization and that hydration of the dimers is rather weakly exergonic. The tetrahydrated dimers having a similar arrangement to that in crystals of ethyl chlorophyllide (a) dihydrate are found to be more stable than the Chla dihydrated dimer. The data underscore the key role of H‐bonding in the stability of Chla‐H₂O adducts and, in particular, the great importance of the Chla monomeric dihydrated species in the hydration and dimerization of Chla in aqueous media. Clearly, the Chla dihydrates (Chla‐2 H₂O) are found more stable than the monohydrates (Chla‐H₂O) and the Chla dimers (Chla₂), owing to a particular structure in which cooperative interactions occur between the H₂O molecules and Chla. Calculations also indicate that the most thermodynamically preferred pathway for the formation of Chla dimer hydrates can be represented by two steps: the first corresponds to the formation of Chla monomeric dihydrates and the second is the dimerization of the dihydrates on to tetrahydrated Chla dimers. These results allow to obtain a new possible pathway for Chla dimer formation processes and could provide new insights to the aggregation of chlorophyll (a) in solution.     

Degradation of a poly(ester urethane) elastomer. II. Kinetic modeling of the hydrolysis of a poly(butylene adipate)

In preparation for studying the kinetics of the hydrolysis of Estane® 5703, published hydrolysis data for a similar poly(butylene adipate) (herein called 63 PBA) have been modeled. Poly(ester urethanes) are known to degrade by acid‐catalyzed hydrolysis of the ester links, and the data on 63 PBA show that this degradation is reversible at low relative humidities (RHs). Previous work with these data was unable to fit them with concentration‐independent rate coefficients. It is shown herein that, with the water‐concentration model of the preceding article and the A_AC2 mechanism of reversible hydrolysis/esterification, the experimental kinetic data that vary across temperature, RH, and starting molecular weight can be fit with a single set of concentration‐independent rate coefficients. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 192–200, 2002     

Sc(III) porphyrins. The molecular structure of two Sc(III) porphyrins and a re-evaluation of the parameters for the molecular mechanics modelling of Sc(III) porphyrins

The crystal structures of two new Sc(III) porphyrins, [Sc(TPP)Cl]·2.5(1-chloronaphthalene), (5,10,15,20-tetraphenylporphyrin)-chloro-scandium(III)·2.5(1-chloronaphthalene) solvate, (Mo Kα, 0.71073 Å, triclinic system  = 9.9530(2) Å, b = 15.4040(3) Å, c = 17.7770(3) Å, α = 86.5190(10)°, β = 89.7680(10)°, γ = 86.9720(10)°, 13101 independent reflections, R₁ = 0.0712) and the dimeric [μ₂-(OH)₂(Sc(TPP))₂], bis-(μ-hydroxo)-(5,10,15,20-tetraphenylporphyrin) scandium(III) (Mo Kα, 0.71073 Å, monoclinic system C2, a = 24.2555(16) Å, b = 11.1598(7) Å, c = 25.6468(17) Å, β = 91.980(2)°, 13084 independent reflections, R₁ = 0.0485) are reported. In [Sc(TPP)Cl] the metal is five-coordinate and the porphyrin is domed with the metal displaced by 0.63 Å from the mean porphyrin towards the axial Cl⁻ ligand. The average Sc-N bond length is 2.143(3) Å, which is shorter than the average bond length of previously reported structures. Two of the phenyl rings are nearly orthogonal to the porphyrin core and the other two are significantly tilted because of contacts with 1-chloronaphthalene solvent molecules, and the phenyl rings of neighbouring porphyrins. In [μ₂-(OH)₂(Sc(TPP))₂] both porphyrins are domed, with the metal displaced from the mean porphyrin plane towards the bridging hydroxo ligands. The average Sc-N bond length is 2.197(12) Å, which is in the upper range of Sc-N bond lengths in known Sc(III) porphyrins but not dissimilar to the average Sc-N bond lengths in another other bis-μ₂-hydroxo Sc(III) porphyrin, [μ₂-(OH)₂(Sc(OEP))₂]. One porphyrin is rotated relative to the upper porphyrin by 25° due to steric contacts between the phenyl substituents. We have used these new structures to re-evaluated our previously reported molecular mechanics force field parameters for modelling Sc(III) porphyrins using the MM2 force field; the training set was augmented from two to seven structures by using all available Sc(III) porphyrin structures and the two new structures. The modelling reproduces the porphyrin core very accurately; bond lengths are reproduced to within 0.01 Å, bond angles to within 0.5° and torsional angles to within 2°. The optimum parameters for modelling the Sc(III)-N bond lengths, determined by finding the minimum difference between the crystallographic and modelling mean bond lengths with the aid of artificial neural network architectures, were found to be 0.90 ± 0.03 mdyn Å⁻¹ for the bond force constant and2.005 ± 0.005 Å for the strain-free bond length. Modelling the seven Sc(III) porphyrins with the new parameters gives an average Sc-N bond length of 2.182 ± 0.018 Å, indistinguishable from the crystallographic mean of 2.181 ± 0.024 Å.     

Alkynyliodonium salts in organic synthesis. Development of a unified strategy for the syntheses of (-)-agelastatin A and (-)-agelastatin B

The total syntheses of natural agelastatin A and agelastatin B were accomplished via a strategy that utilized an alkynyliodonium salt --> alkylidenecarbene --> cyclopentene transformation to convert a relatively simple amino alcohol derivative to the functionalized core of the agelastatin system. Subsequent manipulations delivered debromoagelastatin, which served as a precursor to both agelastatin A and agelastatin B. Alkylidenecarbene insertion chemoselectivity issues were explored en route to the final targets.     

Hydroxyoxo(5,10,15,20-tetraphenylporphinato)tungsten(V) as a receptor for foodstuff and drug components. Thermodynamics of supramolecular complexation

The thermodynamics of stepwise reactions of hydroxyoxo(5,10,15,20-tetraphenylporphinato)tungsten(V) (O=W(OH)TPP) with biologically active base molecules was studied. For the reaction of O=W(OH)TPP with benzimidazole, four steps were found and studied; the equilibrium constants K _n were determined to be 2.55 × 10⁴, 1.87 × 10³ L/mol, 1.06 × 10⁶, 4.09 × 10⁴ L²/mol². The reaction of O=W(OH)TPP with pyrazine was a one-step reversible process of Pyz coordination to the eighth coordination site (K = 399 L/mol). The correlation equations relating the stability of supramolecular complexes to pK of the bases were obtained. The thermodynamic data were used to demonstrate the prospects of applying the metal porphyrin as a receptor for N-bases in membranes, sensors, and analytical devices for quality control of foodstuffs, drugs, and gas mixtures for the content of VOCs.     

(1)H and (13)C NMR assignments for five anthraquinones from the mangrove endophytic fungus Halorosellinia sp. (No. 1403)

We report the unambiguous assignments of the (1)H and (13)C NMR spectra of two new natural products, namely, 1,4,5,6,7,9-hexahydroxy-2-methoxy-7-methyl-5beta,9beta,8abeta, 6alpha,10aalpha-hexahydroanthracen-10 (10aH)-one (1) and 1,4,6-trihydroxy-2-methoxy-7-methylanthracene-9, 10-dione (2), together with three known anthraquinones. These compounds were all isolated from the marine endophytic fungus No. 1403 collected from the South China Sea. Compounds 3 and 4 were isolated from the marine fungus for the first time. The structures were elucidated by the spectroscopic methods 1D and 2D NMR including COSY, HMQC, HMBC and NOE, and HREIMS. In our cytotoxicity assays, compound 5 showed cytotoxicity toward KB and KBv-200 cells with IC(50) of 1.40 and 2.58 microg/ml, respectively. In addition, the plausible biogenic relationship of compounds 1, 2, 3 and 4 is discussed.     

Methods for the synthesis of mono- and polynuclear NH-tetrazoles. (Review)

Data on methods for the synthesis of monocyclic and polynuclear NH-unsubstituted tetrazoles are reviewed.Dedicated to Prof. H. Elguero on the occasion of his 65th birthday.St. Petersburg State Technological Institute (Technical University), St. Petersburg 198013, Russia; Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 867–884, July, 2000.     

Synthesis and characterization of sulfur-voided cubanes. Structural analogues for the MoFe(3)S(3) subunit in the nitrogenase cofactor.

A new class of Mo/Fe/S clusters with the MoFe(3)S(3) core has been synthesized in attempts to model the FeMo-cofactor in nitrogenase. These clusters are obtained in reactions of the (Cl(4)-cat)(2)Mo(2)Fe(6)S(8)(PR(3))(6) [R = Et (I), (n)Pr (II)] clusters with CO. The new clusters include those preliminarily reported: (Cl(4)-cat)MoFe(3)S(3)(PEt(3))(2)(CO)(6) (III), (Cl(4)-cat)(O)MoFe(3)S(3)(PEt(3))(3)(CO)(5) (IV), (Cl(4)-cat)(Pyr)MoFe(3)S(3)(PEt(3))(2)(CO)(6) (VI), and (Cl(4)-cat)(Pyr)MoFe(3)S(3)(P(n)Pr(3))(3)(CO)(4) (VIII). In addition the new (Cl(4)-cat)(O)MoFe(3)S(3)(P(n)Pr(3))(3)(CO)(5) cluster (IVa), the (Cl(4)-cat)(O)MoFe(3)S(3)(PEt(3))(2)(CO)(6)cluster (V), the (Cl(4)-cat)(O)MoFe(3)S(3)(P(n)Pr(3))(2)(CO)(6) cluster (Va), the (Cl(4)-cat)(Pyr)MoFe(3)S(3)(P(n)Pr(3))(2)(CO)(6) cluster (VIa), and the (Cl(4)-cat)(P(n)Pr(3))MoFe(3)S(3)(P(n)Pr(3))(2)(CO)(6) cluster (VII) also are reported. Clusters III-VIII have been structurally and spectroscopically characterized. EPR, zero-field (57)Fe-M?ssbauer spectroscopic characterizations, and magnetic susceptibility measurements have been used for a tentative assignment of the electronic and oxidation states of the MoFe(3)S(3) sulfur-voided cuboidal clusters. A structural comparison of the clusters with the MoFe(3)S(3) subunit of the FeMo-cofactor has led to the suggestion that the storage of reducing equivalents into M-M bonds, and their use in the reduction of substrates, may occur with the FeMo-cofactor, which also appears to have M-M bonding. On the basis of this argument, a possible N(2)-binding and reduction mechanism on the FeMoco-cofactor is proposed.     

Resolving Agents. I. (R)-(-)-2-Amino-1-benzyloxybutane,a New Base for the Resolution of Racemic Acids

Treatment of the readily available (R)-(-)enantiomer of 2-aminobutan-1-ol 1 with sodium hydride followed by benzyl chloride afforded the O-benzyl base (R)-(-)-2. The latter was successfully used for the resolution of racemic α-methylsuccinic and α-bromosuccinic acids, as well as of the racemic α-benzylhemisuccinic esters 8 and 9 resectively.     

Poly(ethylene glycol) (PEG) as a reusable solvent medium for organic synthesis. Application in the Heck reaction

[reaction: see text] PEG has been used as a solvent medium for regioselective Heck reactions with easy recyclability of solvent and Pd catalyst for the first time.     

Environmental certification: a scientific tool for sustainability. Evaluation of possible indicators for the environmental performance evaluation (EPE) of Ravenna province (Italy)

Environmental certification is becoming the main tool for application of sustainable development principles. The European Regulation Emas and the international standard ISO 14001 both require for certification, to perform an environmental management system to prevent environmental impacts and to continuously improve environmental performance. For a good environmental performance evaluation (EPE), certification needs to use scientific methodologies and to interface with scientific research; here we proposed emergy analysis as a valid method for EPE and emergetic environmental performance and condition indicators (EPIs, ECIs) to monitor a territorial system: Ravenna province (Italy). Together with emergy indicators were selected other indicators for a deeper EPE: emitted/adsorbed CO2, energy consumptions, air and water pollution measures. The paper showed that Ravenna system has a good environmental performance and demonstrated how different indicators from the most advanced chemical research (chemical-physical, analytical, etc.) contribute to a complete EPE of a complex territorial system and are useful for environmental certification and sustainable development.     

Thiotropolone as a chromogenic reagent for the simultaneous determination of cobalt(II) and nickel(II)

Thiotropolone forms chloroform-soluble reddish-brown and violet complexes with cobalt(II) and nickel(II), in the pH range 7.0-8.5 and 6.0-9.0 respectively. Based on this, a sensitive and rapid method for the spectrophotometric determination of traces of cobalt and nickel in metals and alloys has been developed. The two metals can be determined accurately in the range 0.6-2.6 ppm of cobalt and 0.75-4.57 ppm of nickel, simultaneously.