Synthesis of original capping calixarenes with DTPA fragment

Calixarenes 5–8 capped with DTPA bridges were synthesized by condensation of the corresponding 1,3-(distal)-diaminocalixarenes and DTPA dianhydride in DMF. The chelating properties of the DTPA-calixarenes were evaluated towards europium and the resulting complexes were characterized by mass spectroscopy.     

New insights in the formation of deoxynucleoside adducts with the heterocyclic aromatic amines PhIP and IQ by means of ion trap MS<Superscript>n</Superscript> and accurate mass measurement of fragment ions

The formation of adducts by reaction of active metabolites of two heterocyclic aromatic amines (NHOH-PhIP and NHOH-IQ) at nucleophilic sites of deoxynucleosides has been studied by LC-MS(n) analyses of the obtained reaction mixtures. Sequential MS(3) experiments were carried out on an ion trap mass spectrometer to gain extensive structural information on each adduct detected in the first MS step. Attribution of ions was supported by accurate mass measurements performed on an Orbitrap mass analyzer. Particular attention was given to ions diagnostic of the linking between the heterocyclic aromatic amine (HAA) and the deoxynucleoside. By this way, the structures of five adducts have been characterized in this study, among which two are new compounds: dG-N7-IQ and dA-N(6)-IQ. No depurinating adduct was found in the reactions investigated therein. As expected, the C8 and N(2) atoms of dG were found as the most reactive sites of deoxynucleosides, resulting in the formation of two different adducts with IQ and one adduct with PhIP. An unusual non-depurinating dG-N7-IQ adduct has been characterized and a mechanism is proposed for its formation on the basis of the reactivity of arylamines. A dA-N(6)-IQ adduct has been identified for the first time in this work, showing that HAAs can generate DNA adducts with bases other than dG.     

Asymptotics of Block Toeplitz Determinants and the Classical Dimer Model

We compute the asymptotics of a block Toeplitz determinant which arises in the classical dimer model for the triangular lattice when considering the monomer-monomer correlation function. The model depends on a parameter interpolating between the square lattice (t = 0) and the triangular lattice (t = 1), and we obtain the asymptotics for 0 < t ≤ 1. For 0 < t < 1 we apply the Szegö Limit Theorem for block Toeplitz determinants. The main difficulty is to evaluate the constant term in the asymptotics, which is generally given only in a rather abstract form.     

New pH sensitive network: Combination of an amphiphilic degradable polyester with a β-cyclodextrin copolymer

A novel hydrophobic monomer, ethyladamantyl malolactonate, has been synthesized and copolymerized with benzyl malolactonate by anionic ring-opening polymerization. The ratio of adamantyl monomer varied from 0 to 100 mol%. Deprotection of benzyl groups leads to a water soluble copolyester with carboxylic acid lateral functions which give a polyelectrolyte character to the corresponding polymers. The mixture of a copolyester containing 10% of adamantyl groups and a β-cyclodextrin/epichlorohydrin copolymer in aqueous solution leads to a new pH-dependant associating system. The solution behavior of this system was studied by viscosimetry as a function of pH, concentration and ratio of both copolymers. At the initial solution pH (pH=2), the copolyester adopts a coiled structure as a result of hydrophobic interactions between the pendant adamantyl groups. Consequently, no network formation is observed as shown by a very low viscosity. As the pH increase, the viscosity of the medium increases and reaches a maximum at pH=5. At this pH, the copolyester expands because of electrostatic repulsions between the carboxylate pendant functions. Consequently, the adamantyl groups are accessible and can be encapsulated into the β-cyclodextrin cavities resulting in a significant increase of the viscosity.     

Development of Sustainable Chemistry in Madagascar: Example of the Valuation of CNSL and the Use of Chromones as an Attractant for Mosquitoes

This article describes a part of the results obtained from the cooperation between the University of Lyon1 (France) and the University of Antananarivo (Madagascar). It shows (among others) that useful research can be carried out in developing countries of the tropics if their social, technical, and economic conditions are taken into account. The concepts and methods associated with so-called “green chemistry” are particularly appropriated for this purpose. To illustrate this approach, two examples are shown. The first deals with industrial ecology and concerns waste transformation from the production of cashew nut into an amphiphilic product, oxyacetic derivatives. This product was obtained with a high yield and in a single step reaction. It exhibited an important surfactant property similar to those of the main fossil-based ones but with a much lower ecological impact. The second talks about chemical ecology as an alternative to insecticides and used to control dangerous mosquito populations. New substituted chromones were synthesized and showed biological activities toward Aedes albopictus mosquito species. Strong repellent properties were recorded for some alkoxylated products if others had a significant attractant effect (Kairomone) depending on their stereochemistry and the length of the alkyl chain.     

Synthesis and Characterization of Multinanometer‐Sized Expanded Dendralenes with an iso‐Poly(triacetylene) Backbone

A series of [n]dendralenes (n =3, 4, 8, 3b – d (Fig. 1)) expanded with buta‐1,3‐diynediyl moieties between the CC bonds were prepared by repetitive acetylenic scaffolding of 3‐(cyclohexylidene)penta‐1,4‐diyne building blocks (Scheme). These remarkably unstable iso‐poly(triacetylene) (iso‐PTA) oligomers were characterized by ¹H‐ and ¹³C NMR (Fig. 3 and Table 1), IR, and UV/VIS (Figs. 4 and 6 and Table 2) spectroscopy, as well as mass spectrometry (Fig. 2). The expanded [8]dendralene contains 40 C(sp)‐ and C(sp²)‐atoms in the backbone and represents the longest iso‐PTA oligomer prepared to date. HOMO‐LUMO Gap energies were determined as a function of oligomeric length (Fig. 5 and Table 3), providing insight into the degree of π‐electron delocalization in these cross‐conjugated chromophores. A continous drop in the HOMO‐LUMO gap with increasing number of monomeric repeating units provides evidence that cross‐conjugation along the oligomeric backbone is effective to some extent. The limiting HOMO‐LUMO gap energy for an infinitely long, buta‐1,3‐diynediyl‐expanded dendralene was extrapolated to about 3.3–3.5 eV. The conformational preferences of the expanded dendralenes were analyzed in semi‐empirical calculations, revealing energetic preferences for planar or slightly twisted s‐cis and ‘U‐shaped' geometries.     

Secondary isotope effects in liquid chromatography behaviour of 2H and 3H labelled solutes and solvents

The separation of solutes that differ only in the extent of isotopic substitution of their hydrogen atoms, using either mixtures of isotopically non-modified or perdeuterated solvents as mobile phases, is described. The occurrence of a secondary isotope effect is demonstrated in reversed-phase liquid chromatography, which is independent of the nature of the stationary phase (different octadecyl-bonded silicas, an embedded alkylamide-bonded silica, as well as one polymeric stationary phase were tested), and the water content and the nature of organic modifier of the mobile phase. The separation of 24 structurally different isotopologue pairs (apolar compounds and polar compounds with exchangeable or non-exchangeable hydrogen atoms) is examined using reversed-phase liquid chromatography. It is found that the greater the number of isotopically substituted hydrogen atoms in a given organic solute, the better is the separation of a particular isotopologue pair. The single secondary isotope effect is shown to be dependent on the number of isotopic substitutions. The greater the number of these substitutions, the smaller is the single isotope effect. The single secondary isotope effect is higher for aromatic hydrocarbons than for aliphatic hydrocarbons. A secondary isotope effect is also observed in chiral chromatography and normal-phase liquid chromatography, as well as on changing the nature of the substituting isotope, i.e.: tritium instead of deuterium. Thus, we have demonstrated that the total secondary isotopic effect for hydrogen/tritium is higher than for hydrogen/deuterium. This isotope effect involves only the consequences of changes in interactions due to nuclear motions. Overall this study confirms the predominance of hydrophobic effects in retention processes in reversed-phase liquid chromatography. In reversed-phase liquid chromatography, a secondary isotope effect related to mobile phase composition is also observed. The behaviour of deuterium oxide and water in mobile phases of the same composition (%, w/w) is compared. Independent of the nature of the organic modifier (methanol, acetonitrile or ethanol), the effect of replacing H2O with 2H2O in the mobile phase, is an increase in the retention factors and an improvement in the chromatographic resolution of isotopologue pairs. This increase in the resolution is not accompanied by a change in the chromatographic selectivity. The measurement of liquid-liquid extraction coefficients proves that the effect is mainly due to the modification of the phase ratio. In general the effect of 2H-labelled solvents (2H2O and C2H3CN) as mobile phase components, compared to their isotopically non-modified isomers, can be rationalized on the basis of their lower polarisabilities. Overall the use of perdeuterated rather than isotopically non-modified solvents as mobile phase components leads to the most efficient separation systems.     

Preparation of Clickable Poly(3‐hydroxyalkanoate) (PHA): Application to Poly(ethylene glycol) (PEG) Graft Copolymers Synthesis

A new synthesis of amphiphilic biodegradable copolymers consisting of hydrophobic poly(3‐hydroxyalkanoate) (PHA) backbone and hydrophilic poly(ethylene glycol) (PEG) units as side chains is described. Poly[(3‐hydroxyoctanoate)‐co‐(3‐hydroxyundecenoate)] (PHOU) was first methanolyzed and its unsaturated side chains were quantitatively oxidized to carboxylic acid. Esterification with propargyl alcohol led to an alkyne‐containing “clickable” PHA in 71% conversion. Its reactivity was successfully demonstrated by grafting azide‐terminated PEG chains of 550 and 5 000 g · mol⁻¹, respectively. All products were fully characterized using GPC, ¹H, and COSY NMR.

     

Microfluidic platform for combinatorial synthesis in picolitre droplets

This paper presents a droplet-based microfluidic platform for miniaturized combinatorial synthesis. As a proof of concept, a library of small molecules for early stage drug screening was produced. We present an efficient strategy for producing a 7 × 3 library of potential thrombin inhibitors that can be utilized for other combinatorial synthesis applications. Picolitre droplets containing the first type of reagent (reagents A(1), A(2), …, A(m)) were formed individually in identical microfluidic chips and then stored off chip with the aid of stabilizing surfactants. These droplets were then mixed to form a library of droplets containing reagents A(1-m), each individually compartmentalized, which was reinjected into a second microfluidic chip and combinatorially fused with picolitre droplets containing the second reagent (reagents B(1), B(2), …, B(n)) that were formed on chip. The concept was demonstrated with a three-component Ugi-type reaction involving an amine (reagents A(1-3)), an aldehyde (reagents B(1-7)), and an isocyanide (held constant), to synthesize a library of small molecules with potential thrombin inhibitory activity. Our technique produced 10(6) droplets of each reaction at a rate of 2.3 kHz. Each droplet had a reaction volume of 3.1 pL, at least six orders of magnitude lower than conventional techniques. The droplets can then be divided into aliquots for different downstream screening applications. In addition to medicinal chemistry applications, this combinatorial droplet-based approach holds great potential for other applications that involve sampling large areas of chemical parameter space with minimal reagent consumption; such an approach could be beneficial when optimizing reaction conditions or performing combinatorial reactions aimed at producing novel materials.     

Poly(3-hydroxyalkanoate)-derived amphiphilic graft copolymers for the design of polymersomes

Amphiphilic graft copolymers composed of biocompatible bacterial poly(3-hydroxyalkanoate) and poly(ethylene glycol) have been synthesized by thiol-ene addition. They were demonstrated to form well-defined nanoscale vesicles in water by cryo-transmission electron microscopy.