Multifunctional Supramolecular Dendrimers with an s‐Triazine Ring as the Central Core: Liquid Crystalline,Fluorescence and Photoconductive Properties

Novel liquid crystal (LC) dendrimers have been synthesised by hydrogen bonding between an s‐triazine as the central core and three peripheral dendrons derived from bis(hydroxymethyl)propionic acid. Symmetric acid dendrons bearing achiral promesogenic units have been synthesised to obtain 3:1 complexes with triazine that exhibit LC properties. Asymmetric dendrons that combine the achiral promesogenic unit and an active moiety derived from coumarin or pyrene structures have been synthesised in order to obtain dendrimers with photophysical and electrochemical properties. The formation of the complexes was confirmed by IR and NMR spectroscopy data. The liquid crystalline properties were investigated by differential scanning calorimetry, polarising optical microscopy and X‐ray diffractometry. All complexes displayed mesogenic properties, which were smectic in the case of symmetric dendrons and their complexes and nematic in the case of asymmetric dendrons and their dendrimers. A supramolecular model for the lamellar mesophase, based mainly on X‐ray diffraction studies, is proposed. The electrochemical behaviour of dendritic complexes was investigated by cyclic voltammetry. The UV/Vis absorption and emission properties of the compounds and the photoconductive properties of the dendrons and dendrimers were also investigated     

Hexameric MnII Dendrimer as MRI Contrast Agent

A Mn^II chelating dendrimer was prepared as a contrast agent for MRI applications. The dendrimer comprises six tyrosine‐derived [Mn(EDTA)(H₂O)]^2? moieties coupled to a cyclotriphosphazene core. Variable temperature ¹⁷O NMR spectroscopy revealed a single water co‐ligand per Mn^II that undergoes fast water exchange (k_ex=(3.0±0.1)×10⁸ s^?1 at 37 °C). The 37 °C per Mn^II relaxivity ranged from 8.2 to 3.8 mM ^?1 s^?1 from 0.47 to 11.7 T, and is sixfold higher on a per molecule basis. From this field dependence a rotational correlation time was estimated as 0.45(±0.02) ns. The imaging and pharmacokinetic properties of the dendrimer were compared to clinically used [Gd(DTPA)(H₂O)]^2? in mice at 4.7 T. On first pass, the higher per ion relaxivity of the dendrimer resulted in twofold greater blood signal than for [Gd(DTPA)(H₂O)]^2?. Blood clearance was fast and elimination occurred through both the renal and hepatobiliary routes. This Mn^II containing dendrimer represents a potential alternative to Gd‐based contrast agents, especially in patients with chronic kidney disease where the use of current Gd‐based agents may be contraindicated.     

2,2′‐Bipyridine‐Based Dendritic Structured Compounds for Second Harmonic Generation

Parallel alignment of dipolar electron‐donor–π‐bridge‐electron‐acceptor entities can strongly enhance their nonlinear optical properties. This favorable arrangement can be in principle achieved by linking these units covalently or through metal coordination. Four dipolar single‐strand chromophores decorated with a 5‐electron‐donor–5′‐electron‐acceptor‐modified 2,2′‐bipyridine functionality were synthesized. For two of these chromophores triple‐stranded dendritic structures were successfully formed. All of the compounds were characterized with respect to their linear and nonlinear optical properties. For the aldehyde derivatives an enhancement of the first hyperpolarizability of 4.5 rather than 3 was obtained when going from single to triple strands. Theoretical calculations with density functional theory suggest that interstrand transitions contribute to the optical properties of the dendritic structures.     

A New Class of Tunable Dendritic Diphosphine Ligands: Synthesis and Applications in the Ru‐Catalyzed Asymmetric Hydrogenation of Functionalized Ketones

A series of tunable G₀–G₃ dendritic 2,2′‐bis(diphenylphosphino)‐1,1′‐binaphthyl (BINAP) ligands was prepared by attaching polyaryl ether dendrons onto the four phenyl rings on the P atoms. Their ruthenium complexes were employed in the asymmetric hydrogenation of β‐ketoesters, α‐ketoesters, and α‐ketoamides to reveal the effects of dendron size on the catalytic properties. The second‐ and third‐generation catalysts exhibited excellent enantioselectivities, which are remarkably higher than those obtained from the small molecular catalysts and the first‐generation catalyst. Molecular modeling indicates that the incorporation of bulky dendritic wedges can influence the steric environments around the metal center. In addition, the ruthenium catalyst bearing a second‐generation dendritic ligand could be recycled and reused seven times without any obvious decrease in enantioselectivity.     

Supermolecular Columnar Liquid‐Crystalline Phosphorus Dendrimers Decorated with Sulfonamide Derivatives

A series of supermolecular liquid crystals has been synthesized by combining phosphorus dendrimers of the zero, first, and fourth generations with sulfonamide derivatives, thus generating dendromesogens bearing 6, 12, and 96 mesogenic units on their surfaces. The relevant reactions could be monitored by ¹H, ¹⁹F, and ³¹P{¹H} NMR spectroscopies. The thermal and mesomorphic properties of the products have been studied by optical microscopy, differential scanning calorimetry, and X‐ray diffraction. All of the new macromolecules prepared in this work have been found to show mesomorphic properties over a wide temperature range; moreover, for all of the compounds, the columnar mesophases observed were maintained or vitrified at room temperature. On increasing the generation of these dendromesogens, mesophases appear at lower temperatures and remain stable over a wider temperature interval. In all cases, on the basis of X‐ray analysis, a cylindrical symmetry of the molecules can be proposed to promote the supramolecular columnar arrangement observed in the mesophases. In this type of model, the height of the dendrimer clearly increases with increasing dendrimer generation, whereas its cross‐ sectional area increases only slightly, probably due to compression of the highly hyperbranched structures as a consequence of their progressive steric constraints. The mesomorphic arrangement is governed by the peripheral sulfonamide units.     

Molecularly Precise Dendrimer–Drug Conjugates with Tunable Drug Release for Cancer Therapy

The structural preciseness of dendrimers makes them perfect drug delivery carriers, particularly in the form of dendrimer–drug conjugates. Current dendrimer–drug conjugates are synthesized by anchoring drug and functional moieties onto the dendrimer peripheral surface. However, functional groups exhibiting the same reactivity make it impossible to precisely control the number and the position of the functional groups and drug molecules anchored to the dendrimer surface. This structural heterogeneity causes variable pharmacokinetics, preventing such conjugates to be translational. Furthermore, the highly hydrophobic drug molecules anchored on the dendrimer periphery can interact with blood components and alter the pharmacokinetic behavior. To address these problems, we herein report molecularly precise dendrimer–drug conjugates with drug moieties buried inside the dendrimers. Surprisingly, the drug release rates of these conjugates were tailorable by the dendrimer generation, surface chemistry, and acidity.     

Supramolecular Architectures from Bent‐Core Dendritic Molecules

Control of the self‐assembly of small molecules to generate architectures with diverse shapes and dimensions is a challenging research field. We report unprecedented results on the ability of ionic, bent dendritic molecules to aggregate in water. A range of analytical techniques (TEM, SEM, SAED, and XRD) provide evidence of the formation of rods, spheres, fibers, helical ribbons, or tubules from achiral molecules. The compact packing of the bent‐core structures, which promotes the bent‐core mesophases, also occurs in the presence of a poor solvent to provide products ranging from single objects to supramolecular gels. The subtle balance of molecule/solvent interactions and appropriate molecular designs also allows the transfer of molecular conformational chirality to morphological chirality in the overall superstructure. Functional motifs and controlled morphologies can be combined, thereby opening up new prospects for the generation of nanostructured materials through a bottom‐up strategy.     

Ionizable Amphiphilic Dendrimer‐Based Nanomaterials with Alkyl‐Chain‐Substituted Amines for Tunable siRNA Delivery to the Liver Endothelium In Vivo

A library of dendrimers was synthesized and optimized for targeted small interfering RNA (siRNA) delivery to different cell subpopulations within the liver. Using a combinatorial approach, a library of these nanoparticle‐forming materials was produced wherein the free amines on multigenerational poly(amido amine) and poly(propylenimine) dendrimers were substituted with alkyl chains of increasing length, and evaluated for their ability to deliver siRNA to liver cell subpopulations. Interestingly, two lead delivery materials could be formulated in a manner to alter their tissue tropism within the liver—with formulations from the same material capable of preferentially delivering siRNA to 1) endothelial cells, 2) endothelial cells and hepatocytes, or 3) endothelial cells, hepatocytes, and tumor cells in vivo. The ability to broaden or narrow the cellular destination of siRNA within the liver may provide a useful tool to address a range of liver diseases.     

Blue Luminescence of Dendrimer‐Encapsulated Gold Nanoclusters

Direct evidence for the blue luminescence of gold nanoclusters encapsulated inside hydroxyl‐terminated polyamidoamine (PAMAM) dendrimers was provided by spectroscopic studies as well as by theoretical calculations. Steady‐state and time‐resolved spectroscopic studies showed that the luminescence of the gold nanoclusters consisted largely of two electronic transitions. Theoretical calculations indicate that the two transitions are attributed to the different sizes of the gold nanoclusters (Au₈ and Au₁₃). The luminescence of the gold nanoclusters was clearly distinguished from that of the dendrimers.     

Comparative DFT study of Raman spectra of phosphorus-containing dendrimers built from thiophosphoryl,cyclotriphosphazene and phthalocyanine cores

The FT Raman spectra of the zero and first generations of phosphorus-containing dendrimers built from thiophosphoryl, cyclotriphosphazene and phthalocyanine core with terminal oxybenzaldehyde groups have been recorded and analyzed. The structural optimization and normal mode analysis were performed for dendrimers on the basis of the density functional theory (DFT). The calculated geometrical parameters, harmonic vibrational frequencies and Raman scattering activities are predicted in a good agreement with the experimental data. The experimental Raman spectra of dendrimers were interpreted by means of potential energy distribution. Relying on DFT calculations the lines of the cores, repeating units and terminal groups of dendrimers were assigned.The influence of the encirclement on the line frequencies and intensities was studied and due to the predictable, controlled and reproducible structure of dendrimers the information, usually inaccessible is obtained. The strong line at 1600 cm⁻¹ show marked changes of intensity in dependence of aldehyde (CHO) or azomethyne (CHN) substituents in the aromatic ring. The polarizabilities and lipophilicity of dendrimers were estimated.