Feroniellins A-C, novel cytotoxic furanocoumarins with highly oxygenated C10 moieties from Feroniella lucida

Three new furanocoumarins, named feroniellins A (1), B (2), and C (3), were isolated from the roots of Feroniella lucida. Compounds 1-3 are novel structures having an oxolane, oxane, and oxepane moiety. Their overall structures and configurations were determined by spectral and chemical methods. The cytotoxicities of 1-3 were evaluated against human KB and HeLa carcinoma cells.     

High-resolution infrared study of vinyl fluoride in the 750-1050 cm(-1) region: rovibrational analysis and resonances involving the nu8, nu10, and nu11 fundamentals

The FTIR spectra of CH2[double bond]CHF have been investigated in the nu(8), nu(10), and nu(11) region between 750 and 1050 cm(-1) at a resolution of about 0.002 cm(-1). The nu(8) vibration of symmetry species A' gives rise to an a/b-type hybrid band, while the nu(10) and nu(11) modes of A' ' symmetry produce c-type absorptions. Due to the proximity of their band origins, the three vibrations perturb each other by Coriolis and high-order anharmonic resonances. In particular, the interactions between the nu(8) and nu(10) modes are very strong and widespread with band origins separated by only 1.37 cm(-1). Besides the expected c-type characteristics, the nu(10) band shows a very intense pseudo a-type component caused by the strong first-order Coriolis resonances with the nu(8) state. Furthermore, the 2nu(9) "dark state" was found to be involved in the interacting band systems. The spectral analysis resulted in the identification of 3144, 3235, and 3577 transitions of the nu(8), nu(10), and nu(11) vibrations, respectively. Almost all the assigned data were simultaneously fitted using the Watson's A-reduction Hamiltonian in the Ir representation and the perturbation operators. The model employed includes nine types of resonances within the tetrad nu(8)/nu(10)/nu(11)/2nu(9) and a set of spectroscopic constants for the nu(8), nu(10), and nu(11) fundamentals as well as parameters for the "dark state" 2nu(9), and fourteen coupling terms have been determined.     

Phototoxic phytoalexins. Processes that compete with the photosensitized production of singlet oxygen by 9-phenylphenalenones

Experiments were performed to elucidate the excited-state behavior of 9-phenylphenalenones, which are phototoxic plant secondary metabolites involved in mechanisms of light-mediated plant defense. Using a combination of time-resolved and steady-state UV/visible spectroscopies, time-resolved IR absorption spectroscopy, time-resolved singlet oxygen phosphorescence measurements and cyclic voltammetry, we provide evidence of an intramolecular charge-transfer process in the excited singlet and the triplet states of 9-phenylphenalenones that modulates the photosensitized production of singlet oxygen.     

Nanofibers of barium strontium titanate (BST) by sol-gel processing and electrospinning

This paper describes the fabrication of barium strontium titanate (Ba0.6Sr0.4TiO3 or BST) nanofibers by electrospinning method using a solution that contained poly(vinylpyrrolidone) and a sol-gel solution of BST. The as-spun and calcined BST/PVP composite nanofibers were characterized by TG-DTA, X-ray diffraction, FT-IR, SEM and TEM, respectively. After calcination of the as-spun BST/PVP composite nanofibers at above 700 degrees C in air for 2 h, BST nanofibers of 188+/-25 nm in diameter having well-developed cubic-perovskite structure were successfully obtained. The crystal structure and morphology of the nanofibers were influenced by the calcination temperature. Calcination at below 700 degrees C resulted in amorphous phase whereas BST with second phase such as barium titanate were formed at above 700 degrees C. Diameters of the nanofibers decreased from 208+/-35 to 161+/-18 nm with increasing calcination temperature between 600 and 800 degrees C.     

Synthesis of enantiomerically enriched β-hydroxy selenides by catalytic asymmetric ring opening of meso-epoxides with (phenylseleno)silanes

The first example of the enantioselective ring opening of meso-epoxides by (phenylseleno)silanes using salen(Cr)complexes as catalyst is described. This desymmetrization reaction constitutes a simple and convenient approach to synthetically versatile optically active β-hydroxy selenides.     

Bis(arylimino)pyridine derivatives of Group 4 metals: preparation, characterization and activity in ethylene polymerization

Titanium tetrachloride reacts with 2,6-bis[(1-phenylimino)ethyl]pyridine, 1, and 2,6-bis[1-(2,6-diisopropylphenylimino)ethyl]pyridine, 2, giving the adducts of general formulae [Ti1Cl3]Cl, 3, and [Ti2Cl3]Cl, 6, the latter through the intermediacy of the covalently bonded [Ti2Cl4], 4. Heating 6 leads to reduction to the titanium(III) derivative [Ti2Cl3], 12, the latter characterized by X-ray diffraction methods. The reaction of [Ti1Cl3]Cl with a toluene solution of MAO proceeds with methylation at the ortho-position of the pyridine ring to give the titanium(iv) derivative [Ti(C22H21N3)Cl3], 8. The reaction of [Ti2Cl3]Cl with MAO gives a mixture of products containing [Ti2Cl2(OAlCl3)], 9. Compound 9, which has been prepared independently by reacting 6 with AlOCl, is a rare case of a compound containing the -OAlCl3 moiety, as shown by a single-crystal X-ray diffraction study. From the tetrachlorides of zirconium and hafnium with 1 or 2, the corresponding adducts [M(L)Cl4] have been obtained in high yields. These derivatives of Group 4 metals act as ethylene polymerization catalytic precursors: the substitution of the phenyl ring of the imino fragment strongly influences the catalytic activity which is 5,544 kg(PE) mol(Ti)(-1) h(-1) in the case of 3 and 267 kg(PE) mol(Ti)(-1) h(-1) with 6. Catalytic activity has been observed for zirconium and hafnium too, the activity decreasing from zirconium to hafnium, under comparable conditions.     

An algorithm for tracing the boundary curves of mushy regions in some degenerate diffusion problems

We present an algorithm for approximating the solution of the degenerate diffusion problem u_t = (?(u))_xx in (0,1) × R⁺ (with zero Dirichlet boundary conditions, and nonnegative initial datum u₀), where ?(u) = min {ku1} for some ? > 0. The algorithm also provides an approximation for the interface curves which represent the boundary of the Mushy Region ?? = {(x, t): ? (u(x, t)) = 1}. The convergence of the algorithm is proved.     

Polymerization,copolymerization, and terpolymerization of 1-isopropylidene-dicyclopentadiene by anionic coordination catalysts

A detailed investigation of the terpolymerization reaction of ethylene and propylene with 1-isopropylidene-dicyclopentadiene (II) was carried out by empolying vanadiumbased anionic coordinate catalysts [preferentially V(Acac)₃? AlEt₂Cl]. The influence of some polymerization parameters, i.e., concentration of II, of the catalyst; polymerization time, etc., were particularly examined. The catalysts were found to be active in C₂H₄? II copolymerization also, but neither C₃H₆? II copolymer nor II homopolymer were obtained. By using the 5,6-dihydro derivative of II as comonomer, it was found through ultraviolet, infrared, and NMR analyses that the incorporation of II in polyethylene or ethylene–propylene chains took place randomly and by selective opening of the norbornene double bond. The quantitative determination of the unsaturation present in C₂H₄? C₃H₆? II terpolymer was studied by means of absorption of iodine halides and through a spectroscopic ultraviolet method. Reference was made to terpolymer samples containing ¹⁴C-labeled II. The content of II was generally less than 35 wt-% both in copolymer and in terpolymer prepared. The relatively high reactivity of II is discussed in terms of norbornene ring strain and compared with the reactivity of 1-isopropylidene-3a,4,7,7a-tetrahydroindene (I) previously reported.