Regioselective Synthesis of Partially Protected Trehalose Analogues and Assignment of Ring Size in Isopropylidene Acetal Derivatives by 13 C Nmr Spectroscopy

ABSTRACT

The ¹³C NMR spectra of a range of di-O-isopropylidene acetals of α,α-trehalose and its analogues 1, 2, 4-7 have been studied Attention has been focussed on the chemical shifts of the acetal carbon and methyl groups of the acetals. These parameters are characteristic of ring-size (1,3-dioxolane and 1,3-dioxane). Di-n-butylstannylene and cyclic orthoester intermediates 9 and 12 of 2,6-di-O-benzoyl-α-D-galactopyranosyl 2,6-di-O-benzoyl-α-D-galactopyranoside (8) were used to synthesize the partially protected trehalose analogue having chain extension at positions 4,4′ and 3,3′ (10 and 13) respectively. Acetonation of the synthetic trehalose type disaccharide yielded mainly 3,4:3′,4′-di-O-isopropylidene derivative 4. The benzoylation of 4 followed by acid hydrolysis gave 8 in 85% yield, which was the key intermediate for the synthesis of 10 and 13     

Improved averaging method for turbulent flow simulation. Part II: Calculations and verification

This is the second of two articles intended to develop, apply and verify a new method for averaging the momentum and mass transport equations for turbulence. Part I presented the theoretical development of a new space-time filter (STF) averaging procedure. The new method, as well as all existing averaging procedures, are applied to the one-dimensional transient equations of momentum and scalar transport in a Burgers' flow field. Dense-grid ‘exact’ results from the unaveraged equations are presented to depict the dynamic behaviour of the flow field and serve as a basis for verifying the coarse-grid STF predictions. In this paper, a finite difference procedure is used to numerically solve the new STF averaged equations, as well as the other forms of the averaged equations derived in Part I. All averaged equations are solved on the same coarse grid. The velocity and scalar fields, predicted from each equation form, are intercompared according to a verification procedure based on the statistical and spectral properties of the results. It is found that the new STF procedure improves coarse-grid dynamic predictions over the existing methods of averaging.     

Study of the Ru/Ce system in the oxidation of carbon black and volatile organic compounds

The relationship between the state of Ru on CeO₂ and catalytic activity in the oxidation of carbon black (CB) and some volatile organic compounds (VOCs) was investigated for Ru/CeO₂ catalysts prepared by wet impregnation. It was demonstrated that the addition of ruthenium to ceria significantly improved the reactivity of the latter. The temperature programmed reduction (TPR) experiments of Ru/CeO₂ showed that the oxygen species of RuO₂ was reduced at low temperatures. In addition, Electronic Paramagnetic Resonance (EPR) studies of outgassed samples at different temperatures showed an anisotropic signal indicating that Ru(IV) was reduced to intermediate valence states like Ru(III) before its total reduction to metallic Ru. It was concluded that Ru-O-Ce bonds in the well-dispersed Ru species are highly fragile and its mobile oxygen is the active species in the catalytic oxidation process. Published in Russian in Kinetika i Kataliz, 2007, Vol. 48, No. 6, pp. 893–898. This article was submitted by the authors in English.     

Classes caracteristiques de Γ(G,H)-structures et finitude de leur evaluation

LetG be a Lie group andH a closed subgroup ofG. We denote by (G,H) the groupoïd of germs of left translations ofG over the homogeneous spaceG/H.LetV be a compact manifold andx the universal characteristic class of dimensionk which belongs to the vector spaceH _cont ^k ((G, H)).The evaluation ofx over all the (G, H)-structures overV determines a subsetA _{(G, H)} (x, V) of the vector spaceH ^k (V;).We show that in some cases this set is finite.     

Effect of monovalent and divalent cations on the photoinactivation of bacteria with meso-substituted cationic porphyrins

It is well established that for successful photoinactivation (PI) of gram-negative bacteria a cationic photosensitizer is required. This requirement suggests a charge-dependent interaction between the photosensitizer and the gram-negative bacterium, which may be influenced by the presence of ions in the suspending medium. The aim of the present study was to investigate the effect of cations Na+ and Ca2+ on the efficacy of the PI of the gram-negative Pseudomonas aeruginosa and the gram-positive Staphylococcus aureus. The bacteria were suspended in buffer containing either meso-tetra(N-methyl-4-pyridyl)-porphyrin or meso-mono-phenyl-tri(N-methyl-4-pyridyl)-porphyrin as photosensitizer and various concentrations of Na+ or Ca2+. The cell suspensions were exposed to a broadband light dose of 9 J/cm2. In buffer without added cations, P. aeruginosa and S. aureus were equally sensitive to PI. Addition of cations strongly decreased the sensitivity of both bacteria to PI, with the PI of P. aeruginosa being much more decreased than that of S. aureus, and Ca2+ being more effective than Na+. The decreased sensitivity was accompanied by a reduced binding of the photosensitizers to the bacteria.     

Formation of Cyclodextrin Inclusion Complexes with Doxycyclin-Hyclate: NMR Investigation of Their Characterisation and Stability

The solubility of cyclodextrin (CD) can be notably improved when it is included in a polymeric structure. CD was reacted with citric acid, yielding a water-soluble polymer whose inclusion properties towards doxycyclin-hyclate (DOX) as guest molecule were investigated by NMR. The new DOSY (Diffusion Ordered SpectroscopY) method, based on diffusion coefficient measurements is convenient study complexes made of large molecules and it was applied to determine the association constants between DOX and parent β and γ-CD and their polymerised forms. The association constant obtained by DOSY was compared with that determined more classically by the chemical shift variation measurement using Scott's plot.     

Surface properties and catalytic activity of pure and silica-coated aluminas

The surface properties of predominantly microporous, mesoporous, and nonporous alumina samples were studied and compared with samples modified by coating with a fixed amount of silica on their surfaces. The samples were characterized in terms of their specific surface areas, pore structure, and the chemistry of the surface, namely, surface acidity and surface OHs. An attempt was made to relate the activity toward cumene cracking with the chemistry as well as the predominant pore size. This study will hopefully reveal the role of the pore structure of alumina in determining its adsorption and catalytic activity and also the effect of doping with silica in modifying the surface properties of alumina.     

Spectrophotometric and derivative spectrophotometric study of the reaction of palladium (II) and rhodium (III) with 5-(3,4-methoxyhydroxybenzylidene)rhodanine and cationic surfactants

Spectrophotometric and derivative spectrophotometric methods for the determination of Pd(II) and Rh(III) are proposed. Pd(II) forms with 5-(3,4-methoxyhydroxybenzylidene)rhodanine [3,4-MHBR], in the absence and presence of cetylpyridinium bromide [CPB], 14 binary and 134 ternary complexes having molar absorptivities of 5.77 × 10⁴ and 7.46 × 10⁴ M ^–1cm^–1 at 525 and 530 nm, respectively. Rh(III) forms a 14 complex with 3,4-MHBR in the presence of cetyltrimethylammonium bromide [CTAB], which gives a maximum absorbance at 445 nm with a molar absorptivity of 5.13 × 10⁴ M ^–1cm^–1. Derivative spectrophotometric methods are employed for the determination of Pd(II) and Rh(III) at ng ml^–1 levels utilizing these complexes. Under the optimum conditions the calibration lines for Pd(II) and Rh(III) determination fit the equations d⁴ A/d⁴ = 1.10 × 10⁶ [Pd] – 0.018 (r = 0.9967) and d⁴ A/d⁴ = 2.25 × 10⁶ [Rh] + 0.03 (r = 1.0426) and have detection limits of 5.6 and 1.2 ng ml^–1, respectively. The influences of experimental variables and foreign ions are studied. The methods are free of interference from most common metal ions and anions. The results of the analysis of some synthetic mixtures of Pd(II) and Rh(III) are reported.