Etude de la tétracoordination de l'etain dans deux orthothiostannates: Na4SnS4 et Ba2SnS4 (α)

The crystal structure of Na₄SnS₄ and Ba₂SnS₄ (α) were determined.Na₄SnS₄ crystallizes in tetragonal system, space group $\text{P}\text{4}\text{2}{}_1\text{c}$ with parameters a = 7.837 Å, c = 6.950 Å, Z = 2 and Ba₂SnS₄ (α) in the monoclinic system, space group $\text{P2}{}_1\text{c}$ with a = 8.481 Å, b = 8.526 Å, c = 12.280 Å, β = 112.97° and Z = 4.In these compounds, the crystal structure is built up from discrete orthothiostannate tetrahedra SnS₄. The structure of Ba₂SnS₄ (α) is modified K₂SO₄β type.     

Sol–Gel Derived Organic and Inorganic Hybrid Materials for Photonic Applications: Contribution to the Correlation Between the Material Structure and the Transmission in the Near Infrared Region

A promising way of fabricating integrated optics components is based on the sol–gel synthesis and photocuring of organic-inorganic hybrid materials. However, the main factor limiting the development of passive devices is the propagation losses. Moreover, the possibility to compensate these attenuations by optical amplification is competed with the multiphonon relaxation associated to the presence of OH groups. To our knowledge, OH groups were always shown as the main responsible for attenuation at the telecommunication wavelengths, namely at 1310 and 1550 nm, although the matrix is composed of organic species which can contribute to absorptions in this spectral range. This paper deals with spectroscopic and optical characterizations of a well established organic and inorganic hybrid material in order to determine the contribution of each molecular groups to the attenuation at the aforementioned wavelengths.     

Solvent-controlled additions of organotitanium reagents to olefinic double bonds

Under carefully chosen working conditions (solvent, temperature), methyltitanium reagents smoothly convert homoallyl alcohols having a terminal double-bond into (E)-3-penten-l-ols whereas non-terminal 3-alken-l-ols afford 4-methyl-branched derivatives with configurational inversion of the chain (Z → E; E → Z), stereoselectivities being better than 99%.     

High-speed analysis of dansyl derivatives of polyamines

Summary Analytical conditions for the high-speed, reversed-phase, liquid chromatographic of a diamine (putrescine) and polyamines (spermine and spermidine) were determined. Various elution modes were employed using the same mobile phase constituents: 20mM sodium heptane sulfonate and 20mM acetic acid as solvent A and, pure acetonitrile as solvent B. Samples were derivatized with dansyl chloride before injection.Under isocratic conditions, the separation of the three polyamines was achieved in 7 min. The use of a linear elution gradient led to the same analytical time but with a better resolution of the putrescine peak from non-polyamine frontal peaks. For these measurements, the sample size was 5l. This volume was increased to 20l and the use of a steep gradient combined with the peak-compression technique allowed a fast analysis in 2–3 minutes, which may be compared with a 30 min run time necessary when a conventional column is used.     

Embedding of a Banach algebra

Given a Banach space , we have shown in 1994 that a product can be defined on it in such a way that the resulting Banach algebra is isomorphic to a compact subalgebra of the algebra of all bounded linear operators on the topological dual of . Our purpose here is to prove that, more generally, any Banach algebra admitting a left approximate identity, is isomorphic to a subalgebra of , the isomorphism being isometric, provided the approximate identity is bounded by 1. As a consequence, we get a factorization through , of the elements in .

     

The high-valent iron-oxo species of polyoxometalate, if it can be made, will be a highly potent catalyst for C-H hydroxylation and double-bond epoxidation

This study uses density functional theory (DFT) calculations to explore the reactivity of the putative high-valent iron-oxo reagent of the iron-substituted polyoxometalate (POM-FeO4-), derived from the Keggin species, PW12O40(3-). It is shown that POM-FeO4- is in principle capable of C-H hydroxylation and C=C epoxidation and that it should be a powerful oxidant, even more so than the Compound I species of cytochrome P450. The calculations indicate that in a solvent, the barriers, and especially those for epoxidation, become sufficiently small that one may expect an extremely fast reaction. An experimental investigation (by R.N. and A.M.K.) shows, however, that the formation of POM-FeO4- using the oxygen donor, F5PhI-O, leads to a persistent adduct, POM-FeO-I-PhF5(4-), which does not decompose to POM-FeO4- + F5Ph-I at the working temperature and exhibits sluggish reactivity, in accord with previous experimental results (Hill, C. L.; Brown, R. B., Jr. J. Am. Chem. Soc. 1986, 108, 536 and Mansuy, D.; Bartoli, J.-F.; Battioni, P.; Lyon, D. K.; Finke, R. G. J. Am. Chem. Soc. 1991, 113, 7222). Subsequent calculations indeed reveal that the gas-phase binding energy of F5PhI to POM-FeO4- is high (ca. 20 kcal/mol) compared to the corresponding binding energy of propene (ca. 2-3 kcal/mol). As such, the POM-FeO-I-PhF5(4-) complex is expected to be persistent toward the displacement of F5PhI by a substrate like propene, leading thereby to sluggish oxidative reactivity. According to theory, overcoming this technical difficulty may turn out to be very rewarding. The question is, can POM-FeO4- be made?     

Direct-type catalytic three-component Mannich reaction in aqueous media

Bismuth triflate catalyzed direct-type Mannich reaction of cyclohexanone, aromatic aldehyde, and aromatic amine proceeded smoothly in water to afford the corresponding β-amino ketone with very good yield and moderate to good anti selectivity.     

Facile synthesis of alpha,alpha-diisobutylglycine and anchoring its derivatives onto PAL-PEG-PS resin

alpha,alpha-Diisobutylglycine has been synthesized using a Pd-mediated dialkylation of ethyl nitroacetate as a key first step. The free alphaalphaAA is N(alpha)-protected and has been applied to the assembly of conformationally constrained peptide analogues. Mixed anhydrides from BOP-Cl and Fmoc-alphaalphaAA-OH are used for anchoring alphaalphaAAs onto a trialkoxybenzyl linker on PEG-PS grafted support, upon which a beta-strand mimic with difficult sequence is assembled in a superior quality.