Organization of a Polar Molecule at the Air−Water Interface

We have studied the behavior of a low molecular mass organosiloxane ferroelectric liquid crystal at the air−water interface. Data obtained with Langmuir isotherms, surface potential measurements, and Brewster angle microscopy are presented and discussed. The compound forms films on the Langmuir trough, with phase transitions to multilayers upon compression. As seen with Brewster angle microscopy, the monolayers are optically isotropic whereas striking birefringent structures develop in the multilayer films. These periodic structures result from a surface elasticity phenomenon

Interfacial Behavior of a Series of Amphiphilic Block Co-dendrimers

Amphiphiles with a dendritic structure are attractive materials as they combine the features of dendrimers with the self-assembling properties and interfacial behavior of amphiphiles. We have designed and synthesized three series of segmented amphiphilic block co-dendrimers (Janus-type) and studied their interfacial properties on the Langmuir trough. Various behaviors are observed with, as a rule, the lowest generation dendrimers behaving more or less like traditional amphiphiles while the larger molecules tend to exhibit more complicated isotherms, with a non-straighforward temperature dependence, one particular molecule seemingly forming supramolecular assemblies spontaneously. The results presented here, obtained on a series of molecules where many parameters have been varied systematically, show the limits that should be kept in mind when designing amphiphilic dendrimers

Supramolecular Organization and Magnetic Properties of Mesogen-Hybridized Mixed-Valent Manganese Single Molecule Magnets [Mn^III₈Mn^IV₄O₁₂(L_{<i>x</i>,<i>y</i>,<i>z</i>‑CB})₁₆­(H₂O)₄]

Single molecule magnets (SMM) may be considered for the construction of future integrated nanodevices, provided however that some degree of ordering is imparted to these molecules (surfaces nanostructuration). Combining such nanoobjects with liquid-crystalline orderings to control their assembly and to potentially address them individually therefore appears as one promising strategy. Four mesomorphic, mixed-valent [Mn^III₈Mn^IV₄O₁₂­(L_{<i>x</i>,<i>y</i>,<i>z</i>‑CB})₁₆​­(H₂O)₄] SMM, differing in the number of liquid-crystalline promoters, (L_{<i>x</i>,<i>y</i>,<i>z</i>‑CB}), were synthesized, and their self-organizing and magnetic properties were investigated. The influence of the peripheral modifications, and precisely how supramolecular ordering and magnetic properties may be affected by the evolution of the proto-mesogenic cyanobiphenyl-based ligands substitution pattern, was explored. Small-angle X-ray scattering studies revealed that all of the hybridized clusters self-organize into room-temperature bilayer smectic phases, mandated by the specific mesogenic functionalization and that the polymetallic cores are further organized according to a short-range pseudo-2D lattice with hexagonal and/or square symmetry. All mesomorphous hybridized dodecamanganese complexes still behave as SMM: they exhibit blocking of the magnetization at about 2.6 K as evidenced by the occurrence of frequency-dependent out-of-phase ac susceptibility signals as well as an opening of the hysteresis cycle with coercive fields varying between 0.13 and 0.6 T, depending on the surface ligands topology. Comparison of the magnetic properties within this series reveals intricate correlations between the structural features of the mesomorphous molecule magnet (i.e., symmetry of the ligands substitution patterns, molecular conformation, average intercluster distances, and respective inclination) with respect to the relative proportion of slow- and fast-relaxing species and the absolute values of the coercive fields

Development of a Dendritic Manganese-Enhanced Magnetic Resonance Imaging (MEMRI) Contrast Agent: Synthesis, Toxicity (in Vitro) and Relaxivity (in Vitro, in Vivo) Studies

A new dendritic manganese(II) chelate 1 has been evaluated by in vivo (relaxivity) and in vitro (toxicity and relaxivity) experiments as a manganese enhanced magnetic resonance imaging (MEMRI) contrast agent. Also, a comparison with its corresponding gadolinium(III) homologue 2 and the commercially available MEMRI agent MnDPDP (Teslascan, Amersham Health) was achieved in order to determine respectively the real influence of the paramagnetic ion in terms of toxicity and relaxivity for this precise treelike structure and the potential of 1 to be a favorable candidate for brain-targeting MRI. Complexes 1 and 2 displayed high hydrosolubility (0.1 M) and revealed no in vitro neuronal toxicity at concentrations as high as 1 mM. Considering manganese(II) complex 1, the in vivo nontoxicity at 20 mM (100% rats survival) is very likely due to a slow diffusion of the compound, meaning a controlled release of the paramagnetic ions. Finally, T1 relaxivity of 4.2 mM−1.s−1 for 2 and T2 relaxivity of 17.4 mM−1.s−1 for 1 at 4.7 T were measured and are higher than that of the commercial MRI contrast agents GdDTPA and MnDPDP, respectively

Micelle Formation in Langmuir Films of C₆₀ Derivatives

Langmuir and Langmuir−Blodgett films of three new amphiphilic [60]fullerene derivatives have been investigated. The molecular design of these compounds was chosen to control the position of the C60 core relative to the water and to strongly influence the resulting physical properties. The first compound (MonoC8) is a methanofullerene, whereas the two other compounds (BisC8 and BisC12) are C60 cis-2-bis adducts. All of these compounds form stable Langmuir films. Even though the isotherms show some hysteresis, it was possible to transfer the films onto solid substrates, with the Langmuir−Blodgett method for two compounds and the Langmuir−Schaeffer technique for the last one. Grazing-incidence X-ray analysis indicates that LB films have a low roughness, i.e., are of good quality. MonoC8 forms monolayers, whereas the structure of the films of the two other compounds is more complex, with a micellar substructure within the film. These results show how sensitive the molecular design is to the molecular arrangement and to the conformation of the molecules in the films

Amphiphilic Diblock Dendrimers: Synthesis and Incorporation in Langmuir and Langmuir−Blodgett Films^†

A new dendron with peripheral long alkyl chains and containing five C60 units in the branching shell has been prepared and attached to a Fréchet-type dendron functionalized with ethylene glycol chains. The peripheral substitution of the resulting globular dendrimer with hydrophobic chains on one hemisphere and hydrophilic groups on the other provides the perfect hydrophobic/hydrophilic balance allowing the formation of stable Langmuir films. Furthermore, a perfect reversibility has been observed in successive compression/decompression cycles. The diblock structure of the dendrimer has been also crucial for the efficient transfer of the Langmuir films in order to obtain well-ordered multilayered Langmuir−Blodgett films. This approach appears particularly interesting since functional groups not well adapted for the preparation of Langmuir and Langmuir−Blodgett films such as fullerenes can be attached into the branching shell of the dendritic structure and, thus, efficiently incorporated in thin ordered films

Preparation of Highly Stable Organic Steps with a Fullerene-Based Molecule

We report the formation of highly stable Langmuir−Blodgett (LB) organic steps made with a hexa-adduct fullerene-based amphiphile. This amphiphile forms films of excellent quality, with a very low roughness, that are structurally stable: X-ray reflectivity spectra recorded on fresh and 12-month-old samples are undiscernible. Such a behavior contrasts with that of more traditional amphiphiles, which are unfortunately well-known for their instability in time. The stability of the films stems, among others, from the spheroidal shape of the constitutive molecules. These experiments show that it is possible to circumvent the major drawback of LB films and to prepare materials more suited for applications. We show that the LB film prepared with this fullerene derivative can successfully be used as thickness gauges for atomic force microscopy or light microscopy studies

Self-assembly, DNA Complexation, and pH Response of Amphiphilic Dendrimers for Gene Transfection

Cationic lipids and polymers are routinely used for cell transfection, and a variety of structure−activity relation data have been collected. Few studies, however, focus on the structural aspects of self-assembly as a crucial control parameter for gene delivery. We present here the observations collected for a set of cationic dendritic amphiphiles based on a stiff tolane core (1−4) that are built from identical subunits but differ in the number and balance of their hydrophobic and cationic hydrophilic moieties. We established elsewhere that vectors 3 and 4 have promising transfection properties. Scanning probe microscopy (AFM, STM), cryo-transmission electron microscopy (cryo-TEM), and Langmuir techniques provide insight into the self-assembly properties of the molecules under physiological conditions. Furthermore, we present DNA and pH “jump” experiments where we study the response of Langmuir films to a sudden increase in DNA concentration or a drop in pH. We find that the primary self-assembly of the amphiphile is of paramount importance and influences DNA binding, serum sensitivity, and pH response of the vector system

Magnetic Interactions in Cu^II−Ln^III Cyclic Tetranuclear Complexes: Is It Possible to Explain the Occurrence of SMM Behavior in Cu^II−Tb^III and Cu^II−Dy^III Complexes?

An extensive series of tetranuclear CuII2LnIII2 complexes [CuIILLnIII(hfac)2]2 (with LnIII being all lanthanide(III) ions except for the radioactive PmIII) has been prepared in order to investigate the nature of the CuII−LnIII magnetic interactions and to try to answer the following question:  What makes the CuII2TbIII2 and CuII2DyIII2 complexes single molecule magnets while the other complexes are not? All the complexes within this series possess a similar cyclic tetranuclear structure, in which the CuII and LnIII ions are arrayed alternately via bridges of ligand complex (CuIIL). Regular SQUID magnetometry measurements have been performed on the series. The temperature-dependent magnetic susceptibilities from 2 to 300 K and the field-dependent magnetizations from 0 to 5 T at 2 K have been measured for the CuII2LnIII2 and NiII2LnIII2 complexes, with the NiII2LnIII2 complex containing diamagnetic NiII ions being used as a reference for the evaluation of the CuII−LnIII magnetic interactions. These measurements have revealed that the interactions between CuII and LnIII ions are very weakly antiferromagnetic if Ln = Ce, Nd, Sm, Yb, ferromagnetic if Ln = Gd, Tb, Dy, Ho, Er, Tm, and negligible if Ln = La, Eu, Pr, Lu. With the same goal of better understanding the evolution of the intramolecular magnetic interactions, X-ray magnetic circular dichroism (XMCD) has also been measured on CuII2TbIII2, CuII2DyIII2, and NiII2TbIII2 complexes, either at the L- and M-edges of the metal ions or at the K-edge of the N and O atoms. Last, the CuII2TbIII2 complex exhibiting SMM behavior has received a closer examination of its low temperature magnetic properties down to 0.1 K. These particular measurements have revealed the unusual very slow setting-up of a 3D order below 0.6 K

Magnetic Interactions in Cu^II−Ln^III Cyclic Tetranuclear Complexes: Is It Possible to Explain the Occurrence of SMM Behavior in Cu^II−Tb^III and Cu^II−Dy^III Complexes?

An extensive series of tetranuclear CuII2LnIII2 complexes [CuIILLnIII(hfac)2]2 (with LnIII being all lanthanide(III) ions except for the radioactive PmIII) has been prepared in order to investigate the nature of the CuII−LnIII magnetic interactions and to try to answer the following question:  What makes the CuII2TbIII2 and CuII2DyIII2 complexes single molecule magnets while the other complexes are not? All the complexes within this series possess a similar cyclic tetranuclear structure, in which the CuII and LnIII ions are arrayed alternately via bridges of ligand complex (CuIIL). Regular SQUID magnetometry measurements have been performed on the series. The temperature-dependent magnetic susceptibilities from 2 to 300 K and the field-dependent magnetizations from 0 to 5 T at 2 K have been measured for the CuII2LnIII2 and NiII2LnIII2 complexes, with the NiII2LnIII2 complex containing diamagnetic NiII ions being used as a reference for the evaluation of the CuII−LnIII magnetic interactions. These measurements have revealed that the interactions between CuII and LnIII ions are very weakly antiferromagnetic if Ln = Ce, Nd, Sm, Yb, ferromagnetic if Ln = Gd, Tb, Dy, Ho, Er, Tm, and negligible if Ln = La, Eu, Pr, Lu. With the same goal of better understanding the evolution of the intramolecular magnetic interactions, X-ray magnetic circular dichroism (XMCD) has also been measured on CuII2TbIII2, CuII2DyIII2, and NiII2TbIII2 complexes, either at the L- and M-edges of the metal ions or at the K-edge of the N and O atoms. Last, the CuII2TbIII2 complex exhibiting SMM behavior has received a closer examination of its low temperature magnetic properties down to 0.1 K. These particular measurements have revealed the unusual very slow setting-up of a 3D order below 0.6 K