Eleven bis-ureas have been synthesized, and some of their properties are reported. Several of these compounds form supramolecular polymers in organic solvents. The self-association is shown by FTIR spectroscopy to display cooperativity at two levels. The first level of cooperativity is due to the synergistic association of the two urea functions of a single molecule. The second level of cooperativity is revealed by the fact that the formation of dimers is less favored than that of long oligomers.

Introduction.Polylactides are important biodegradable materials having biomedical, pharmaceutical, and environmental applications. [1][2][3][4][5] These polymers can be synthesized by ring-opening polymerization of lactides using anionic, cationic, or coordinated type initiators. [6][7][8][9][10] In order to obtain polymers with controlled characteristics (structure, molecular weight), initiators leading to a living type process are desirable. Ideally, they should also promote rapid polymerization.Anionic initiators such as alkali-metal alkoxides lead to some side reactions. 6,11 Aluminum alkoxides can be used for controlled polymerization, but they exhibit a relatively low activity. 8,9 The livingness of the polymerization systems was discussed in terms of the selectivity of the involved elementary reactions. 12 It was reported recently that rare-earth alkoxides show a very high reactivity for the polymerization of lactones and lactides. [13][14][15][16][17][18] A living type behavior was observed for some of them. Yttrium oxo isopropoxide is presently a commercially available compound. Stevels et al. 19,20 have recently studied the kinetics and mechanism of L-lactide polymerization with commercial yttrium oxo alkoxide and with other yttrium alkoxides prepared in situ from exchange reaction between the bulky tris(2,6-di-tert-butylphenoxy)yttrium and various alcohols. The rate of polymerization with the latter initiators was found to be several orders of magnitude higher than that observed with the commercial yttrium oxo isopropoxide.Originally, the synthesis and the characteristics of yttrium oxo isopropoxide Y 5 (µ-O)(OiPr) 13 was described by Poncelet et al. 21 It is a cluster compound in which five yttrium atoms are linked to a single central oxygen atom.In this paper we describe the results of the polymerization of D,L-lactide using different rare-earth oxo alkoxide clusters of Ln 5 (µ-O)(OiPr) 13 type where Ln is La, Sm, Y, and Yb. Previously, only the polymerization of L-lactide with commercial yttrium oxo isopropoxide was reported. 17,20 Experimental Section. All µ-oxo isopropoxide initiators were prepared according to the procedure described by Poncelet et al. 21 for yttrium. Commercial yttrium oxo isopropoxide (Aldrich, France) was also used after washing with toluene, removal of insolubles by filtration, and drying in vacuo. D,L-Lactide (Purac Biochem b.v., Gorinchem, the Netherlands) was purified by sublimation under vacuum. Dichloromethane was distilled from calcium hydride and toluene from sodium

Polylactide samples obtained by the ring‐opening polymerization of (D,L)‐lactide by using different lanthanide alkoxide initiators were examined by SEC, 13C NMR and MALDI‐TOF MS techniques. The evidence of substantial transesterification was observed in the case of a polymerization initiated by lanthanum alkoxide and bimetallic aluminium‐yttrium alkoxide initiators. In the case of Y and Sm alkoxide initiators, the MWD remains narrow up to high conversions for reasonable polymerization times, but the prolongation of the post‐polymerization time increases the amount of ester‐exchange reactions. The extent of the transesterification reactions was evaluated on the basis of the intensity of the stereosequence resonances for the methine carbon signal in the 13C NMR spectra. MALDI‐TOF MS analysis revealed the presence of odd‐membered oligomers in all spectra. Thus, transesterification reactions occur from the beginning of the polymerization. Linear and cyclic oligomers were detected in some cases indicating the simultaneous occurrence of inter‐ and intramolecular exchange reactions. The microstructure analysis of the polymers by 13C NMR spectroscopy indicates a preference for a syndiotactic addition during the polymerization process.

et al.. Peptide nucleic acid-nanodiamonds: covalent and stable conjugates for DNA targeting.This article highlights our recent application of functional nanodiamonds (NDs) with peptide nucleic acids (PNA) to develop tools for DNA detection. NDs appear as an ideal nanocarrier due to their versatile surface chemistry, their non-cytotoxicity and since they could benefit from intrinsic luminescent properties. In this work, we report for the first time the possibility to prepare a covalent, stable and functional conjugate of PNA with 20 nm HPHT (High Pressure High Temperature) nanodiamonds. Peptide nucleic acid is a DNA mimic related to both peptides via its backbone and to nucleic acid via its bases. It binds more specifically and more strongly than DNA itself to either DNA or RNA. We have initiated a novel functionalization route based on an optimized amidation of ND carboxylic acid groups, to produce ND-PNA conjugates via an efficient, simple and reproducible method. We describe the synthesis and characterization of those conjugates. The covalent binding of the ND-PNA and the loading of nucleic acid grafted onto the NDs were performed using various characterization methods including FTIR, Kaiser tests and thermogravimetry. Then, ND-PNA conjugates were validated through a successful recognition of complementary DNA in a mixture, showing their efficiency toward nucleic acid detection. Moreover, the impact of ND-PNA on A 549 cells' viability was analysed with flow cytometry and showed an absence of ND-PNA conjugates cytotoxicity. Such nucleic acid-functionalized nanodiamonds offer a wide range of applications and namely the possibility to target and to recognize DNA.