Proline-catalyzed diastereoselective direct aldol reaction between 4-oxoazetidine-2-carbaldehydes and ketones

The reaction of enantiopure 4-oxoazetidine-2-carbaldehydes with unmodified ketones was catalyzed by L-proline as well as by D-proline, to give the corresponding gamma-amino-beta-hydroxy ketones with good yields and diastereoselectivities. The obtained results implied that (2R,3R)-4-oxoazetidine-2-carbaldehydes and L-proline are a matched pair for diastereoselective induction.     

Mössbauer,far-infrared and Raman spectra of tetrachloro[1,4-di(p-methoxyphenyl)-2,3-dimethyl-1,4-diazabutadiene] tin(IV)

Summary The dependence of the logarithm of the area under the tin-119 Mössbauer resonance (A at different temperatures are normalized toA ₇₇) vs. temperature is measured for tetrachloro[1,4-di(p-methoxyphenyl)-2,3-dimethyl-1,4-diazabutadiene] tin(IV). The slope of the plot of lnA vs.T is –2.46·10^–2K^–1, suggesting a monomeric structure. In the vibrational spectra the significant stretching vibrations agree with acis octahedral configuration of C_2v symmetry.

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Mössbauer-, Fernes-Infrarot- und Raman-Spektren von Tetrachlor[1,4-di(p-methoxyphenyl)-2,3-dimethyl-1,4-diazabutadien]zinn(IV)

Zusammenfassung Die Abhängigkeit des Logarithmus der Fläche unter der Zinn-119-Mössbauer-Resonanz (A in verschiedenen Temperaturen werden zuA ₇₇ normalisiert) von der Temperatur wurde für Tetrachlor[1,4-di(p-methoxyphenyl)-2,3-dimethyl-1,4-diazabutadien]zinn(IV) gemessen. Der Anstieg lnA gegenT von –2.46·10^–2K^–1 spricht für eine monomere Struktur. In den Vibrations-Spektren stimmen die wichtigsten Dehnungsschwingungen mit einercis-oktaedrischen Konfiguration von C_2v-Symmetrie überein.

     

Synthesis and phase behaviour of a homologous series of polymethacrylate-based side-chain liquid crystal polymers

The homologous series of side chain liquid crystal polymers, the poly[ω-(4-methoxyazobenzene-4′-oxy)alkyl methacrylate]s, has been prepared in which the length of the flexible alkyl spacer has been varied from 3 to 11 methylene units. All the polymers exhibit liquid crystalline behaviour. The propyl and butyl members show exclusively nematic behaviour. The pentyl, hexyl, octyl and decyl members show a nematic and a smectic A phase while the heptyl, nonyl and undecyl homologues exhibit only a smectic A phase. The smectic A phase has been studied using X-ray diffraction and assigned as a smectic A₁ phase in which the side chains are fully overlapped and the backbones are confined to lie between the smectic layers. For the nonyl member an incommensurate smectic phase is observed. The dependence of the transition temperatures on the length of the flexible spacer is understood in terms of the average shapes of the side chains.     

Spectroelectrogravimetry of the electrical conductivity activation in poly(o-toluidine) films

Journal of Solid State Electrochemistry - The study of the first stages of the transformation of conducting films from the insulating to the conducting form by oxidation is essential to understand...     

Character of the electronic ground state and of charge-transfer excited states in ionic solids: An ab initio cluster model approach

The electronic structure of the ground electronic state and of some special charge-transfer excited states in ionic solids is examined from the ab initio cluster model approach. Different ab initio wave functions, including a frozen orbital approach, the Hartree–Fock self-consistent field, and multireference configuration interaction wave functions, are considered and analyzed using different theoretical techniques. We explicitly consider some alkaline–earth oxides such as CaO, a more difficult case such as A1₂O₃, a transition-metal oxide such as NiO, and a system with a more complicated structure such as KNiF₃. Analysis of ab initio wave functions in terms of valence bond components shows that all these compounds are largely ionic, thus supporting the simple picture arising from the ionic model. However, the nature of the excited states is more complex. Alkaline–earth oxides lowest excited states are essentially described as charge-transfer excitations dominated by a single resonant valence bond structure and the calculated energy difference is comparable to the experimental optical gap. In the case of A1₂O₃, the electronic spectra presents excitonic features and the local charge-transfer excitation excited states provide a reasonable representation of these phenomena. Finally, several different valence bond structures are present in the lowest electronic states of KNiF₃. © 1994 John Wiley & Sons, Inc.     

Well‐Defined and Robust Rhodium Catalysts for the Hydroacylation of Terminal and Internal Alkenes

A Rh‐catalyst system based on the asymmetric ligand ^tBu₂PCH₂P(o‐C₆H₄OMe)₂ is reported that allows for the hydroacylation of challenging internal alkenes with β‐substituted aldehydes. Mechanistic studies point to the stabilizing role of both excess alkene and the OMe‐group.     

Application of the generalised SAFT-VR approach for long-ranged square-well potentials to model the phase behaviour of real fluids

In a recent generalisation of the SAFT-VR equation of state the method was extended so as to deal with short as well as long square-well ranges, namely, 1.2≤λ≤3.0$1.2\le \lambda \le 3.0$ [B.H. Patel, H. Docherty, S. Varga, A. Galindo, G.C. Maitland., Mol. Phys. 103 (1) (2005) 129–139]. Here, we confirm the accuracy of the approach by comparison with numerical calculations of the first perturbation term and with vapour pressure and coexistence density computer simulation data. The approach is then used to model a number of real substances, from non-polar to strongly polar. We discuss in particular the values of the square-well potential model found. For this purpose we construct a relative least squares objective function and the percentage absolute average deviation (%AAD) to determine the intermolecular model parameters (m  , λ$\lambda$, σ$\sigma$, ?/_kB$?/k_B$, _?hb/_kB${?}_{hb}/k_B$ and _rc$r_c$) by comparison to experimental vapour-pressure and saturated liquid density data. In order to ensure in each case that the global minimum is identified, the dimensionality of the problem is reduced by discretising the parameter-space [G.N.I. Clark, A.J. Haslam, A. Galindo, G. Jackson., Mol. Phys. 104 (22–24) (2006) 3561–3581]. Applying this method to the study of argon, n  -alkanes, nitrogen, benzene, carbon dioxide, carbon monoxide, the refrigerant R1270, hydrogen chloride hydrogen bromide and water we find that the optimal models always present square-well ranges λ<1.8$\lambda <1.8$, meaning that an upper bound value of λ=1.8$\lambda =1.8$ set in the original approach is sufficient to model real fluids; even polar ones. This finding is explained in terms of the averaged dipole–dipole interaction and of the long-range mean-field limit of the square-well potential.     

Near-critical carbon dioxide extraction and liquid chromatography determination of UV filters in solid cosmetic samples: a green analytical procedure

Near-critical carbon dioxide extraction of four UV filters used as sunscreens in lipsticks and makeup formulations is reported. Extraction parameters were optimized. Efficient recoveries were obtained after 15 min of dynamic extraction with a 80:20 CO2/ethanol mixture at 300 atm and 54 degrees C, using a 1.8 mL/min flow rate. Extracts were collected in ethanol, and appropriately diluted with ethanol and 1% acetic acid to obtain a 70:30 v/v ethanol/1% acetic acid solution. The four UV filters were determined by LC with gradient elution using ethanol/1% acetic acid as mobile phase. The accuracy of the analytical procedure was estimated by comparing the results with those obtained by methods based on classical extraction. The proposed method only requires the use of CO2, ethanol and acetic acid avoiding the use of more toxic organic solvents, thus it could be considered as both operator and environment friendly.     

Supercritical fluid extraction and HPLC determination of relevant polyphenolic compounds in grape skin

The polyphenols determined are: (+)-catechin, (-)-epicatechin, rutin, quercetin and trans-resveratrol. Suitable conditions of supercritical fluid extraction were established using ethanol as a modifier of the polarity solvent (supercritical carbon dioxide). Final extraction conditions were: 20% v/v ethanol, 60degreesC, 250 bars and flow rate 2 mL/min. Static step time and dynamic step time were established using a selected grape skin sample. The extract was collected in water; the more polar polyphenols ((+)-catechin and (-)-epicatechin) remain in solution but rutin, quercetin and trans-resveratrol precipitate in this medium, thereby the solution of the extracted polyphenols was filtered. (+)-Catechin and (-)-epicatechin were determined in the liquid fraction, while the solid fraction, containing rutin, quercetin and trans-resveratrol, was solved with ethanol/H20 (40:60). HPLC determination was carried out at C18 stationary phase, with ethanol/water/acetic acid as mobile phases and UV-visible diode array detection. Due to the significant differences between the polarity of the polyphenols, two different mobile phases were used. An ethanol/water/acetic acid (5:93:2) mobile phase was used to determine (+)-catechin (280 nm) and (-)-epicatechin (280 nm). On the other hand, rutin (254 nm), quercetin (254 nm) and trans-resveratrol (306 nm) were resolved using ethanol/water/acetic acid (40:58:2) as mobile phase. Instrumental parameters were optimised and analytical parameters obtained. The analytical method was validated and applied to five different varieties of Vitis vinifera from the geographical area of Valencia.     

The Photosensitizing Efficacy of Micelles Containing a Porphyrinic Photosensitizer and KI against Resistant Melanoma Cells

Photodynamic therapy (PDT) is a promising alternative to overcome the resistance of melanoma to conventional therapies. Currently applied photosensitizers (PS) are often based on tetrapyrrolic macrocycles like porphyrins. Unfortunately, in some cases the use of this type of derivative is limited due to their poor solubility in the biological environment. Feasible approaches to surpass this drawback are based on lipid formulations. Besides that, and inspired in the efficacy of potassium iodide (KI) for antimicrobial photodynamic therapy (aPDT), the combined effect of singlet oxygen (¹O₂) with KI was assessed in this work, as an alternative strategy to potentiate the effect of PDT against resistant melanoma cells.