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Labeling of smart PEG-dendron hybrids with fluorinated groups transformed their assemblies into enzyme-responsive micellar probes for

Labeling of smart PEG–dendron hybrids with fluorinated groups transformed their assemblies into enzyme-responsive micellar probes for 19F-magnetic resonance (MR). Two distinct labeling approaches were used to study the ability of these smart hybrids to be turned OFF at the assembled micellar state and to turn ON their 19F-MR signal upon enzymatic activation.

[reaction: see text] Bimetallic alkylzinc calixarene inclusion complexes were prepared and used in the ring-opening polymerization of L-lactide. Polymers with high molecular weight and a low degree of polydispersity were obtained. 1H NMR and diffusion NMR experiments suggest that a single-site mechanism is operative.

Intermolekulare Wechselwirkungen in Losung spielen eine wichtige Rolle bei der molekularen Erkennung und sind somit von besonderer Bedeutung in der Supramolekularen und Kombinatorischen Chemie. Die Untersuchung der molekularen Diffusion liefert Aufschlusse uber solche Wechselwirkungen, wobei sich die hochaufgeloste Diffusions-NMR-Spektroskopie als Methode der Wahl fur die gleichzeitige Bestimmung von Diffusionskoeffizienten in einem Mehrkomponentensystem erwiesen hat. Der Diffusionskoeffizient ist dabei ein Mas fur die effektive Grose und Form eines Molekuls. Zu den Anwendungen dieser Technik gehoren die Abschatzung von Assoziationskonstanten, die Kartierung intermolekularer Wechselwirkungen in Mehrkomponentensystemen sowie Untersuchungen zum Aggregationsverhalten, zur Ionenpaarbildung, zur Bildung von Einschlussverbindungen und zur Bestimmung der Grose und Struktur von labilen Systemen. Mithilfe der Diffusions-NMR-Spektroskopie kann man aber auch Gemische virtuell auftrennen und gezielt nach Liganden fur Rezeptoren suchen. Diese Methode kann so bei der Identifizierung von Leitverbindungen von Nutzen sein.

Intermolecular interactions in solution play an important role in molecular recognition, which lies at the heart of supramolecular and combinatorial chemistry. Diffusion NMR spectroscopy gives information over such interactions and has become the method of choice for simultaneously measuring diffusion coefficients of multicomponent systems. The diffusion coefficient reflects the effective size and shape of a molecular species. Applications of this technique include the estimation of association constants and mapping the intermolecular interactions in multicomponent systems as well as investigating aggregation, ion pairing, encapsulation, and the size and structure of labile systems. Diffusion NMR spectroscopy can also be used to virtually separate mixtures and screen for specific ligands of different receptors, and may assist in finding lead compounds.

Bacteriorhodopsin is a membrane protein of the purple membrane (PM) of Halobacterium salinarum, which is isolated as sheets of highly organized two-dimensional hexagonal microcrystals and for which water molecules play a crucial role that affects its function as a proton pump. In this paper we used single- and double-quantum (2)H NMR as well as (1)H and (2)H diffusion NMR to characterize the interaction of water molecules with the PM in D(2)O suspensions. We found that, under the influence of a strong magnetic field on a concentrated PM sample (0.61 mM), the PM sheets affect the entire water population and a residual quadrupolar splitting (upsilon(q) approximately 5.5 Hz, 298 K, at 11.7 T) is observed for the D(2)O molecules. We found that the residual quadrupolar coupling, the creation time in which a maximal DQF signal was obtained (tau(max)), and the relative intensity of the (2)H DQF spectrum of the water molecules in the PM samples (referred to herein as NMR order parameters) are very sensitive to temperature, dilution, and chemical modifications of the PM. In concentrated PM samples in D(2)O, these NMR parameters seem to reflect the relative organization of the PM. Interestingly, we have observed that some of these parameters are sensitive to the efficiency of the trimer packing, as concluded from the apo-membrane behavior. The data for dionized blue membrane, partially delipidated sample, and detergent-treated PM show that these D(2)O NMR order parameters, which are magnetic field dependent, are sensitive to the structural integrity of the PM. In addition, we revealed that heating the PM sample inside or outside the NMR magnet has, after cooling, a different effect on the NMR characteristics of the water molecules in the concentrated PM suspensions. The difference in the D(2)O NMR order parameters for the PM samples, which were heated and cooled in the presence and in the absence of a strong magnetic field, corroborates the conclusions that the above D(2)O order parameters are indirect reflections of both microscopic and macroscopic order of the PM samples. In addition, (1)H NMR diffusion measurements showed that at least three distinct water populations could be identified, based on their diffusion coefficients. These water populations seem to correlate with different water populations previously reported for the PM system.

Diffusion coefficients, as obtained by the PGSE NMR technique, were used to probe encapsulation of guests in self-assembled tetraurea calix[4]arene dimers in organic solvents and to demonstrate their destruction by DMSO.

The C(1)-symmetrical complex [Ru(bpy)(2)(ieil)][PF(6)](2) exhibits unique electrochemical and photophysical properties, and forms discrete dimers in solution and in the solid state held by weak pi-pi stacking interactions via its isoeilatin ligand, preferentially from one of its faces and in a specific orientation.

The interactions of the tetra- cationic meso-tetrakis(N-methyl-4-pyri- dyl)porphyrin (H2TMPyP) and its met- allo derivatives (MTMPyP) (where M = copper(ii), zinc(ii), and gold(iii) with the octa-anionic form (at neutral pH) of 5,11,17,23-tetrasulfonato- 25,26,27,28-tetrakis(hydroxycarbonyl- methoxy)calix(4)arene (C4TsTc) lead to a series of complex species whose stoichiometry and porphyrin sequence can be easily tuned. Crystallographic, spectroscopic, and diffusion NMR stud- ies converge towards a common picture in which a central 1:4 porphyrin/calix- arene unit serves as a template for the formation of more complex species. These species arise by successive, step- wise addition of single porphyrin mole- cules above and below the plane of the 1:4 central core to ultimately give a 7:4 complex. Noticeably, the stoichiometry of the various complex species corre- sponds to the actual concentration ratio of porphyrins and calixarenes in solution allowing the stoichiometry of these species to be easily tuned. This behavior and the remarkable stability of these species allow homo-porphyrin and hetero-(metallo)porphyrin species to be formed with control of not only the stoichiometry but also the sequence of the porphyrin array. The flexibility and ease of this approach permit, in principle, the design and synthesis of porphyrin arrays for predetermined purposes. For example, we have shown that it is very easy to design and obtain mixed porphyrin species in which a foreseen photoinduced electron-trans- fer is indeed observed.

Tetraanions of alkyl-substituted derivatives of cycloocta[1,2,3,4-def;5,6,7,8-d'e'f']bisbiphenylene (BPD) and their counter lithium cations self-assemble to form helically stacked assemblies, including a dimer, a trimer, and a tetramer. NMR self-diffusion measurements and unprecedented magnetic shielding effects for the sandwiched lithium cations support their aggregated nature. The D(2)-tetramer assembly is fully characterized by NMR spectroscopy, providing unequivocal evidence for a helix of four tetraanionic BPD layers with an estimated relative twist angle of about 45 degrees and interlayer spacing of ca. 4 A. The barrier for racemization through the in-plane inter-deck rotation is DeltaG(200)= 9.5 +/- 0.2 kcal mol(-1) in the dimer compared to >15 kcal mol(-1) in the tetramer.

Nature self-assembles molecules into large supramolecular aggregates which are capable of performing specific biological functions [1]. Therefore it is not surprising that supramolecular chemistry has become an important theme of chemistry in recent years [2]. One of the main problem of supramolecular sciences is the elucidation of the structure of the supramolecular aggregate that prevails in solution. Consequently, new analytical methods that may assist these structural determinations are required, especially those techniques that may provide some information regarding the mutual interactions between the different molecular components of the supramolecular system. In this context it seems to us that the diffusion coefficient, as measured by the pulsed gradient spin echo (PGSE) NMR technique [3], may provide such information.

The interaction between tropylium salts and tetraurea calix[4]arene derivatives (such as 1 and 2) was studied in solution using 1D, 2D, diffusion, VT NMR and UV–visible spectroscopy. It was found that tropylium salts form charge transfer complexes with both the monomers and dimers of the tetraurea calix[4]arene derivatives depending on the experimental conditions. Compound 1 increases dramatically the solubility of tropylium salts in apolar solvents such as C2D4Cl2, CDCl3 and CD2Cl2 by forming the molecular capsule 1·C7H7+·1. In contrast to the benzene capsule of 1, in 1·C7H7+·1 the hydrogen bonds in the equatorial region that hold together the two parts of the dimer change their directionality faster than the NMR time scale (at 400 MHz) at temperatures higher than 298 K. Interestingly, the free energy barrier for this dynamic process at 298 K (ΔG‡298), depends on the nature of the counter-anion. Free energies of activation of 14.3 ± 0.2 kcal mol−1 and 12.6 ± 0.2 kcal mol−1 were found by total lineshape analysis for the dimeric capsules of C7H7+PF6− and C7H7+BF4−, respectively. The affinity of the tropylium cation toward the dimer's cavity is much higher than that of neutral organic guests. Although exact quantitative values are not available due to the low solubility of tropylium salts in apolar solvents, a rough estimation in CD2Cl2 shows that the tropylium cation affinity is several orders of magnitude higher than that of benzene, which is known to be a good guest. These results show that once the steric requirements are met, electronic effects may serve as an additional driving force for the formation of such molecular capsules demonstrating the importance of cation–π interactions in such systems.