Aldolisation | EPFL Graph Search

L'aldolisation (appelée aussi cétolisation dans le cadre des cétones) est une réaction de formation de liaisons carbone-carbone importante en chimie organique. Elle implique généralement l'addition nucléophile d'un énolate sur un aldéhyde (ou une cétone), pour former une β-hydroxycétone ou aldol (aldehyde + alcool), une unité structurale présente dans de nombreuses molécules naturelles et médicaments. Parfois, le produit de l'addition aldolique perd une molécule d'eau durant la réaction, pour former une cétone α,β-insaturée. Ceci peut avoir lieu notamment lorsque le produit final est particulièrement stable et le processus (aldolisation + élimination) est appelé crotonisation. La réaction d'aldolisation fut découverte indépendamment par Charles Adolphe Wurtz et Alexandre Porfirievitch Borodine en 1872. Borodine observa la dimérisation du 3-hydroxybutanal avec de l'éthanal (acétaldéhyde) en milieu acide. L'aldolisation est utilisée à grande échelle dans la production de produits chimiq

Synthesis of calcium sensors for labelling fusion proteins-synthesis of modified prolines using aza naked sugar methodology

Agostina Ruggiu

Synthesis of Modified Prolines using aza naked sugar methodology R and S-prolines are secondary, cyclic, pyrrolidine-based amino acids. Proline demonstrated excellent catalytic activity to promote enantio- and diatereoselective, intra- and intermolecular cross aldolizations. This efficient organocalyst have been applied to the synthesis of different carbohydrates. In order to enlarge this asymmetric process to aqueous conditions, 4-hydroxyproline derivatives have been developed for the catalysis of cross aldol reaction in water. In this work, with the aim to develop new catalysts based on proline, the reactivity of azanorbornene systems has been explored and the stereoselective transformation of these synthons has been applied to the synthesis of new proline-based aminoacids. The chemistry, previously developed by Vogel and coll. on "naked sugar" has been applied with success on the aza analogues. In summary we have developed a new route for the synthesis of 5-hydroxymethyl-4- hydroxyproline, in particular the synthesis of a new aminoacid, 5-epimer of (-)-Bulgecinine. We have successfully synthesized using an efficient pathway an advanced precursor of 5-hydroxymethyl-3-hydroxyproline. Synthesis of Calcium Sensors for Labelling Fusion Proteins The free cytosolic concentration of calcium plays a central note in signal transduction. The development of indicators of the calcium concentration in living cells can therefore contribute to the understanding of biological systems. Here we describe synthesis and fluorescence properties of a Fura-2FF-O6-Benzylguanine fluorescence sensor that can be used to sense local calcium concentrations in cells. These sensors can be covalently linked to engineered alkyl-guanine-DNA-alkyl-transferase (AGT) fusion proteins. The indicator ΚD is with 4.3 µM optimal to measure locally increased calcium concentrations. This lowered ΚD is achieved by fluorine substitution of the coordinating BAPTA group, while not compromising the calcium to magnesium selectivity. It reacts quickly with mutant alkyl-guanine-DNA-alkyl-transferase (AGT) and can therefore be used to measure calcium near a specific protein. Ultimately this compound can combine advantages of both genetically encoded calcium indicators by being targetable and synthetic calcium indicators of the most popular Fura-2 series. Figure 1. Chemical structure and fluorescence excitation spectra in vitro of non permeable Fura-2FF benzylguanine derivative.

EPFL2008

The effect of alkali hydroxides and equilibration time on Al uptake by calcium silicate hydrates (C-S-H)

Sonya Barzgar

Cement production accounts for approximately 8% of man-made CO2 emissions. Lowering these CO2 emissions is currently one of the most important and urgent research topics within the cement community. To reduce these emissions, the Portland cement (PC) is partially replaced by supplementary cementitious materials (SCM) such as blast furnace slag, fly ash or silica fumes. Reaction of these SCM with PC during hydration leads to the formation of additional calcium silicate hydrates (C-S-H), which is the single most important phase in cements based on silica-rich SCM. The high Al2O3 and SiO2 content of the SCM results in C-S-H compositions with more Si and Al than in PC, which affects the stability and durability of such cements. Therefore, it is crucial to determine the role of Al on C-S-H properties to predict the formed hydrate phase assemblages and their effect on durability. Al sorption isotherms including very low Al concentrations have been determined for C-S-H with Ca/Si ratios from 0.6 to 1.4. The solubility, structure and composition of calcium silicate hydrates incorporating aluminum âC-A-S-Hâ as a function of different parameters such as Ca/Si ratio, equilibration time, Al and alkali contents were investigated. Elemental measurements were performed with ICP MS and ICP-OES. The presence of secondary phases was investigated by using TGA and XRD and the structure of C A S H was investigated by FTIR. High alkali hydroxide concentrations led to an increased Al(OH)4- formation in solution, which reduced the Al uptake in C-S-H. Increasing the pH values and decreasing the Ca/Si in C-S-H increased not only the Al concentrations but also in parallel the Si concentrations in solution. This comparable behavior of Al and Si towards changes in pH, pointed towards the uptake of Al within the silica chain both at low and high Ca/Si ratios. A higher Al uptake in C-S-H was observed at higher Ca/Si ratios, which indicated a stabilizing effect of Ca in the interlayer on Al uptake. The effect of equilibration time on Al uptake in C-S-H was investigated using equilibration times from 7 days up to 3 years. Lower Al concentrations were measured in the solution after longer equilibration times. In addition, a decrease in the content of secondary phases was observed by TGA indicating a higher uptake of Al in C-S-H. Little further decrease in Al concentrations was observed after 2 years and longer at low Ca/Si ratios. At high Ca/Si ratios no significant change in solution concentrations was observed after more than 3 months, while the destabilization of secondary phases continued up to 1 year, indicating that a (meta)stable equilibrium was reached faster at higher Ca/Si ratios. In addition to the C-A-S-H phase, the formation of secondary phases such as strÃ€tlingite, katoite and Al(OH)3 was observed at Al/Si â¥ 0.03, which limited the Al uptake in C-S-H. More secondary phases were observed at higher Al concentrations and/or lower pH values. At low Al/Si ratios, a more significant decrease of Al concentrations with time was observed indicating a slower equilibration than at higher Al concentrations. The Al sorption isotherms showed a linear trend between the Al in solution and Al in C-A-S-H from Al/Si of 0.001 up to 0.2. The linear trend pointed towards an Al uptake on one or several types of sorption sites, with a high sorption capacity, which would be consistent with an Al uptake in the bridging position of the silica chains suggested based on NMR studies

EPFL2021

The effect of alkali hydroxides and equilibration time on Al uptake by calcium silicate hydrates (C-S-H)

Sonya Barzgar

EPFL2021

Synthesis of calcium sensors for labelling fusion proteins-synthesis of modified prolines using aza naked sugar methodology

Agostina Ruggiu

EPFL2008