A series of organically modified iron(III) terephthalate MIL-88B and iron(III) 4,4'-biphenyl dicarboxylate MIL-88D flexible solids have been synthesized and characterized through a combination of X-ray diffraction, IR spectroscopy, and thermal analysis (MIL stands for Material from Institut Lavoisier). The swelling amplitude of the highly flexible MOFs tuned by introducing functional groups onto the phenyl rings shows a clear dependence on the steric hindrance and on the number of groups per aromatic ring. For instance, while the introduction of four methyl groups per spacer in dried MIL-88B results in a large permanent porosity, introducing two or four methyl groups in MIL-88D allows an easier pore opening in the presence of liquids without drastically decreasing the swelling magnitude. The influence of the degree of saturation of the metal center and the nature of the solvent on the swelling is also discussed. Finally, a computationally assisted structure determination has led to a proposal of plausible structures for the closed (dried) and open forms of modified MIL-88B and MIL-88D and to evaluation of their framework energies subject to the nature of the functional groups.

SummaryThe 16S ribosomal DNA based distinction between the bacterial and archaeal domains of life is strongly supported by the membrane lipid composition of the two domains; Bacteria generally contain dialkyl glycerol diester lipids, whereas Archaea produce isoprenoid dialkyl glycerol diether and membranespanning glycerol dialkyl glycerol tetraether (GDGT) lipids. Here we show that a new group of ecologically abundant membrane-spanning GDGT lipids, containing branched instead of isoprenoid carbon skeletons, are of a bacterial origin. This was revealed by examining the stereochemistry of the glycerol moieties of those branched tetraether membrane lipids, which was found to be the bacterial 1,2-di-O -alkyl-snglycerol stereoconfiguration and not the 2,3-di-Oalkyl-sn -glycerol stereoconfiguration as in archaeal membrane lipids. In addition, unequivocal evidence for the presence of cyclopentyl moieties in these bacterial membrane lipids was obtained by NMR. The biochemical traits of biosynthesis of tetraether membrane lipids and the formation of cyclopentyl moieties through internal cyclization, which were thought to be specific for the archaeal lineage of descent, thus also occur in the bacterial domain of life.

The Cu(I)-catalysed 1,3-dipolar "click" cycloaddition is utilised as an efficient reaction for the preparation of novel fluorene-based conjugated polymers.

This review article presents how nitrogen-centred Lewis bases were modified in order to increase their reactivity in catalytic processes. As examples, we focus on alcohol acylation and Morita-Baylis-Hilman reactions in order to showcase the fundamental parameters at play in transformations initiated by catalysts bearing respectively an active sp(2) or sp(3) nitrogen atoms. These two aspects are epitomised by two leading compounds, the Steglich base 4-dimethylaminopyridine (DMAP), and 1,4-diazabicyclo[2.2.2]octane (DABCO). Throughout this review, we stress the role played and the information brought by physical organic chemistry. Comprehension of these complex transformations relies on the fundamental knowledge of parameters, such as, nucleophilicity, nucleofugality, Lewis basicity, and crucially also the knowledge of their divergent impacts on each elementary step of the catalytic cycle.

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Adsorption of n-alkane vapors was performed to probe the unusual highly flexible character of a series of iron­(III) dicarboxylate materials of the MIL-88 structure type. In agreement with the presence of strong intraframework interactions within the dried closed pores form of MIL-88, it appears first that an increase of the size and aromaticity of the spacer makes it more difficult to adsorb alkanes at room temperature. Thus, this led to a high level of adsorption in the iron fumarate MIL-88A and poor levels in the terephthalate and naphthalenedicarboxylate based MIL-88­(B and C, respectively). Second, upon increase in the length of the alkane, diffusion limitations of the guest occur within the very narrow pores, also illustrated through kinetics of adsorption measurements, which result in an overall decrease in the adsorption capacity. Noteworthy, the swelling of the flexible non modified MIL-88 solids occurs only for the MIL-88A sample, because of the number and orientation of aromatic rings that are arranged in trimers within the MIL-88 structures and, therefore, making those more difficult to open than those where the rings are arranged in dimers such as the metal terephthalate MIL-53 structures. Interestingly, modification of the organic linkers by grafting several bulky functional groups (2CF3, 4CH3) makes the adsorption of n-alkanes easier because of a strong decrease in interactions within these trimers associated with a lower pore contraction upon drying, while the substitution of a hydrogen atom by a bromine one on the spacer proved to be not sufficient for an improvement of the adsorbed amounts.

The excited state hydrogen atom transfer reaction (ESHT) has been studied in pyrrole-ammonia clusters [PyH-(NH(3))(n)+hnu-->Py.+.NH(4)(NH(3))(n-1)]. The reaction is clearly evidenced through two-color R2P1 experiments using delayed ionization and presents a threshold around 235 nm (5.3 eV). The cluster dynamics has also been explored by picosecond time scale experiments. The clusters decay in the 10-30 ps range with lifetimes increasing with the cluster size. The appearance times for the reaction products are similar to the decay times of the parent clusters. Evaporation processes are also observed in competition with the reaction, and the cluster lifetime after evaporation is estimated to be around 10 ns. The kinetic energy of the reaction products is fairly large and the energy distribution seems quasi mono kinetic. These experimental results rule out the hypothesis that the reaction proceeds through a direct N-H bond rupture but rather imply the existence of a fairly long-lived intermediate state. Calculations performed at the CASSCF/CASMP2 level confirm the experimental observations, and provide some hints regarding the reaction mechanism.