Tricarboranyl pentaerythritol-based building block

A new tricarborane building block based on pentaerythritol was prepared for applications in boron neutron capture therapy (BNCT). Its X-ray single-crystal structure revealed a high degree of steric congestion. To enable the attachment of the building block to other moieties, a succinimidyl linker has been introduced at the focal point, and a generation-2 hexacarborane-containing dendron carrying 60 boron atoms has been prepared using a 2,2-bis(hydroxymethyl)propionic acid core.     

Lipase-catalyzed asymmetric acylation of boron cluster-containing secondary alcohols

The lipase-catalyzed asymmetric acetylation of secondary alcohols containing a carborane (boron cluster) moiety was investigated. Most lipases examined showed poor catalytic activity toward carborane-containing secondary alcohol 1a, but lipase TL efficiently catalyzed the acetylation of 1a with high enantioselectivity, to afford (R)-3a. This selectivity is similar to that of the general lipase-catalyzed acylation of secondary alcohols. Utilizing lipase TL, we succeeded in the resolution of carborane-containing alcohol 5, synthesized as a progesterone receptor ligand candidate, and evaluated the activities of the two enantiomers.     

Facile iterative synthesis, spectral characterization, electron microscopic study and thermogravimetric analysis of phosphorus dendron with bisphenol A at the focal point

A facile iterative synthesis of a phosphorus dendron with bisphenol A at the focal point by following the divergent procedure is described. The phosphorus dendron peripherally functionalized with phenolic OH group has been accomplished in a very versatile simple fashion, using the Schiff condensation and nucleophilic substitution reactions using P(S)Cl₃, P(O)Cl₃, 3-hydroxybenzaldehyde and 3-aminopheno. The structures of intermediate dendrons were confirmed by IR, NMR (¹H, ¹³C and ³¹P), LC-Mass and C, H, N analysis. The structure of the final dendron (5) was confirmed by IR, NMR (¹H, ¹³C and ³¹P), MALDI-TOF-MS, and C, H, N analysis. The thermal stability of the resulting functionalized dendron has been checked by TGA/DTA analysis. The surface topography observed by scanning electronic microscopic study (SEM) gives the reminiscent of the dendritic structure.     

Chiral carborane-derived thiophosphites: A new generation of ligands for Rh-catalyzed asymmetric hydrogenation

A new class of chiral monodentate ligands - carborane-containing thiophosphites have been synthesized and tested in the Rh-catalyzed asymmetric hydrogenation of prochiral olefins with the result of up to 99% ee. The dependence of the enantioselectivity on the electronic properties of the carboranyl substituent has been studied.     

Properties of dendronized acrylic polymers: Effect of composition and structure of peripheral groups

Two series of new acrylic polymers carrying L-aspartic acid-based dendrons in side chains with terminal hexyloxycarbonyl groups that are both directly and indirectly, via a rigid spacer, attached to polymer chains have been synthesized by the free-radical polymerization of monomers. The polymerization ability of the monomers has been studied. The properties of new polymers are compared with the properties of polymer analogs containing terminal methoxycarbonyl groups of dendrons. Upon incorporation of the rigid spacer, the shielding of reactive centers decreases and the polymerizability of the monomers increases. The replacement of terminal methyl groups in dendrons with hexyl groups in spacer-free polymers leads to a reduction in the degree of polymerization, while in the case of polymers containing spacers, high-molecular-mass products arise. This phenomenon is facilitated by the amphiphilic nature of the polymers and the additional enhancement in the rigidity of chains. A polymer carrying a third-generation dendron has been synthesized only for the latter series.     

Structure-selective dye uptake into an aggregate of a copolymer with linear polyelectrolyte block and hydrophobic block carrying pendant dendritic moiety in water

Selective uptake of various dyes into an aggregate of amphiphilic copolymer consisting of a hydrophilic linear polyelectrolyte block and hydrophobic block carrying pendant dendritic moiety has been investigated in water. The copolymer associated into an aggregate with a hydrophobic interior at concentrations above 0.2 mg cm(-3). The uptake (23 and 36 molecules per aggregate, respectively) of pyrene and Oil Yellow in an aggregate was one order higher than that of benzo[a]pyrene and SudanIII. The hydrophobic dyes are always doped in the interior of the aggregate, but the difference in uptake among dyes may depend on their structure. Even if a large number of guest molecules was doped into the interior of an aggregate, the size of the sphere-like aggregate was conserved. It is suggested that guest molecules are encapsulated into the persisting cavity within and between hydrophobic dendron moieties in an aggregate. Structure-selective uptake reported in this investigation is a unique character of an aggregate of copolymer with dendron moiety because the dendron moiety offers a large void for doping.     

Highly luminescent, stable, and water-soluble CdSe/CdS core-shell dendron nanocrystals with carboxylate anchoring groups

A dendron ligand with two carboxylate anchoring groups at its focal point and eight hydroxyl groups as its terminal groups was found to efficiently convert as-synthesized CdSe/CdS core-shell nanocrystals in toluene to water-soluble dendron-ligand stabilized nanocrystals (dendron nanocrystals). The resulting dendron nanocrystals retained 60% of the photoluminescence value of the original CdSe/CdS core-shell nanocrystals in toluene and were significantly brighter than the similar dendron nanocrystals with thiolate (deprotonated thiol group) as the anchoring group which retained just 10% of the photoluminescence value of the original CdSe/CdS core-shell nanocrystals in toluene. The carboxylate-based dendron nanocrystals survived UV irradiation in air for at least 13 days, about 9 times better than the thiolate-based dendron nanocrystals (35 h) and similar to that of the thiolate-based dendron-box stabilized CdSe/CdS core-shell nanocrystals (box nanocrystals). Upon UV irradiation, the dendron nanocrystals became even 2 times brighter than the original CdSe/CdS core-shell nanocrystals in toluene, and the UV-brightened PL can retain the brightness for at least several months. These stable and bright dendron nanocrystals were soluble in various aqueous media, including all common biological buffer solutions tested, for at least 1.5 years. In addition to their superior performance, the synthetic chemistry of carboxylate dendron ligands and the corresponding dendron nanocrystals is relatively simple and with high yield.     

Dendron rodcoils: synthesis of novel organic hybrid structures

Convergent and divergent syntheses of novel organic hybrid structures termed dendron rodcoils (DRC) containing dendritic, rodlike, and coillike segments are described. The aryl ester dendron masked with 32 trifluoromethyl groups is prepared via a convergent approach using 5-(tert-butyldimethylsiloxy)isophthalic acid as the monomer unit. The activation of the focal point of the dendron allows for successful coupling between the dendron and the diblock rodcoil molecules synthesized separately. In another example, the dendritic block is grown via divergent strategy from the terminus of rodcoil using 3,5-bis(tert-butyldimethylsiloxy)benzoic acid as an AB(2) monomer. A combination of catalyzed esterification reactions and silyl deprotection chemistry proved to be a very efficient method for construction of these nanosized structures with unusual molecular architecture. Both synthetic strategies allowed for the preparation of DRCs with nearly monodisperse dendritic blocks as demonstrated by NMR, MALDI-TOF, and GPC measurements.     

Bioconjugation of biotinylated PAMAM dendrons to avidin

The biotin-terminated PAMAM dendron has been synthesized and the asymmetric dendron used to modify the protein avidin via non-covalent bioconjugation.     

Preparation and heck reaction of multidentate carbosilane films derived from focally functionalized and allyl-terminated dendrons on hydrogen-terminated silicon(111) surfaces

Multidentate carbosilane films were prepared by thermally induced hydrosilylation of allyl-terminated carbosilane dendrons of generations 0, 1, and 2 (G0-G2) on hydrogen-terminated silicon(111) surfaces. The dendron molecules contain three (G0), nine (G1), and twenty-seven (G2) allyl groups at the periphery, and a bromophenyl functional group at the focal point. The dendron films were characterized by contact-angle goniometry, ellipsometry, Fourier transform infrared spectroscopy in the attenuated total reflection mode, and X-ray photoelectron spectroscopy (XPS). Upon hydroboration of the remaining allyl groups in the films, the percentage of the introduced boron atoms in the films were measured by XPS. The results indicate the presence of roughly 20%, 27%, and 46% of unreacted allyl groups in the G0, G1, and G2 films, respectively. The mechanistic aspects of the chemisorption of these dendron molecules on H-Si(111) surfaces are discussed. XPS studies indicate that seven G0 molecules cover approximately the same area on the substrate as three G1 molecules and one G2 molecule. After treatment of the G0, G1, and G2 films with 4-fluorostyrene under the Heck reaction conditions, the XPS studies indicate that about 84%, 71%, and 55% of the Br atoms were consumed, yielding the replacement of ca. 58-70% of the reacted Br atoms by the fluorostyryl groups. The remaining bromophenyl groups were inactive toward the Heck reaction, probably due to their disfavorable position/orientation in the films.     

Redox active, hybrid dendrimers containing Fréchet- and Newkome-type blocks

A new series of dendrimers was prepared by covalently attaching a Newkome dendron, a Fréchet dendron, and a redox active, aminoferrocene group to a central triazine core. Growth of the Newkome dendron has a more pronounced effect on the half-wave potential for the one-electron oxidation of the ferrocene residue than growth of the Fréchet dendron. All dendrimers show reversible or quasireversible voltammetric behavior at scan rates in the range 0.10-2.0 V s-1.     

Approaches to the preparation of carborane-containing carbosilane compounds

[Structure: see text] A novel type of carborane cluster assembly has been successfully prepared using carbosilane derivatives as a scaffold. Two synthetic routes have been used: One involves the reaction of a carbosilane containing terminal Si-Cl functions with the lithium salt of the phenyl-o-carborane, and the second one consists of a highly efficient hydrosilylation of tetravinylsilane with the corresponding carboranylsilane. The crystal structure of this carborane-containing carbosilane compound has been determined by X-ray diffraction.     

Synthesis and characterization of carborane bisphenol resol phenolic resins with ultrahigh char yield

Two carborane-containing resol phenolic resins(P1 and P2) with high boron content were synthesized via the reaction of carborane bisphenols(1 and 2) with formaldehyde in the presence of alkaline. HRMS results indicate that P1 is mainly composed of hydroxymethylated o-carborane bisphenols, the Mw of which was restrained around 500 due to the strong steric hindrance of o-carborane bisphenol. In contrast, the molecular weight of P2 was well regulated under various reaction conditions. The obtained resins were characterized with spectroscopic techniques including FTIR, 1H-NMR, 13C-NMR, and 11B-NMR, which gave satisfactory results. TGA studies show that P2 shows char yield of 88.9% and 92.9% at 900 ?C under nitrogen and air respectively. The imported carborane cage endows phenolic resin with ultrahigh char yield. Particularly, the char yield of the obtained carborane-containing phenolic resin under air is higher than that under nitrogen. FTIR and XRD confirm that the carborane cage could react with oxygen to form B2O3 at elevated temperatures, which postpones the thermal decomposition of phenolic resin and accounts for the high char yield.     

Interfacial assembly and host-guest interaction of anthracene-conjugated L-glutamate dendron with cyclodextrin at the air/water interface

The interfacial assembly of photo-induced dimerization of atypical anthracene-containing amphiphilic dendron and host-guest interaction with γ-cyclodextrin has been investigated.It has been proved that even without long alkyl chain the amphiphilic dendron could still form stable Langmuir monolayer at the air/water interface.Through the host-guest interaction,γ-cyclodextrin can be used to encapsulate two headgroups of amphiphilic dendron in the antiparallel direction.However,the formed host-guest complex was sensitive to the surface pressure.Slight compression of surface pressure led amphiphilic dendron to reassemble into nanofibers through the strong π-π stacking between headgroups.On the other hand,under in sitv irradiation,the amphiphilic dendron was stabilized in the cavity of γ-cyclodextrin through headgroup dimerization and the host-guest complex further irregularly aggregated to nanoparticles.Meanwhile,γ-cyclodextrin,as a silencer,blocked the supramolecular chirality transfer.Our conclusion was demonstrated through UV/vis,FT-IR,CD spectrum and AFM images,respectively.     

Novel chiral dendritic diphosphine ligands for Rh(I)-catalyzed asymmetric hydrogenation: remarkable structural effects on catalytic properties

[reaction: see text] A series of dendritic ligands with a chiral diphosphine located at the focal point have been synthesized through coupling of pyrphos 2 with Fréchet-type polyether dendron 3. The relationship between the primary structure of the dendrimer and its catalytic properties was established in the Rh-catalyzed asymmetric hydrogenation of alpha-acetamido cinnamic acid 4. A remarkable structural effect on catalytic activity was observed.     

A novel nanocomposite material prepared by intercalating photoresponsive dendrimers into a layered double hydroxide

A novel combination for an inorganic-organic nanocomposite material was demonstrated. Anthryl dendron, i.e., poly(amidoamine) dendron with an anthracene chromophore group at the focal point, was incorporated in the interlayer space of ZnAl-NO₃ type layered double hydroxide (LDH) through an anion-exchange reaction. The photoabsorption and fluorescence properties of the resulting material were different from those of the bare anthryl dendron molecule. It was suggested that the change in photochemical properties was due to the organization and π-π interaction of anthracene chromophores within the interlayer of the LDH.     

Molecular batteries: ferrocenylsilylation of dendrons, dendritic cores, and dendrimers: new convergent and divergent routes to ferrocenyl dendrimers with stable redox activity

The ferrocenylsilylation of the phenol triallyl dendron 2, of the phenol nonaallyl dendron 4, and of the 9-, 27-, 81-, and 243-allyl dendrimers 7-10 (monitored by the disappearance of the signals of the olefinic protons in 1H NMR spectra) has been achieved using ferrocenyldimethylsilane 1 and Karstedt's catalyst in diethyl ether at 40 degrees C, yielding the corresponding ferrocenyl dendrons and dendrimers. An alternative convergent synthesis of the nonaferrocenyl dendron 5 was carried out by reaction of the triferrocenyl dendron 2 with a protected triododendron followed by deprotection. Reaction of the nonaferrocenyl dendron 5 with hexakis(bromomethyl)benzene gave the 54-ferrocenyl dendron 6. All the ferrocenyl dendron and dendrimers produce a chemically and electrochemically reversible ferrocenyl oxidation wave at seemingly the same potential. Stable platinum electrodes modified with the high ferrocenyl dendrimers were fabricated. The soluble orange-red ferrocenyl dendrimers can also be oxidized in CH2Cl2 by [NO][PF6] to the insoluble deep blue polyferrocenium dendrimers. For instance, the 243-ferrocenium dendrimer has been characterized by its Mossbauer spectrum, which is of the same type as that of ferrocenium itself. The ferrocenium dendrimers can be reduced without any decomposition back to the ferrocenyl dendrimer, indicating that these multielectronic redoxstable dendrimers behave as molecular batteries.     

Synthesis and functionalization of dendron‐polymer conjugate based hydrogels via sequential thiol‐ene “click” reactions

Fabrication and functionalization of hydrogels from well‐defined dendron‐polymer‐dendron conjugates is accomplished using sequential radical thiol‐ene “click” reactions. The dendron‐polymer conjugates were synthesized using an azide‐alkyne “click” reaction of alkene‐containing polyester dendrons bearing an alkyne group at their focal point with linear poly(ethylene glycol)‐bisazides. Thiol‐ene “click” reaction was used for crosslinking these alkene functionalized dendron‐polymer conjugates using a tetrathiol‐based crosslinker to provide clear and transparent hydrogels. Hydrogels with residual alkene groups at crosslinking sites were obtained by tuning the alkene‐thiol stoichiometry. The residual alkene groups allow efficient postfunctionalization of these hydrogel matrices with thiol‐containing molecules via a subsequent radical thiol‐ene reaction. The photochemical nature of radical thiol‐ene reaction was exploited to fabricate micropatterned hydrogels. Tunability of functionalization of these hydrogels, by varying dendron generation and polymer chain length was demonstrated by conjugation of a thiol‐containing fluorescent dye. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 926–934     

Construction of regulated nanospace around a porphyrin core

A series of 1,3,5-phenylene-based rigid dendritic porphyrins were synthesized by Suzuki coupling between a porphyrin core and dendron units. The intramolecular energy transfer was studied by absorption and fluorescence spectroscopies. The encapsulation of the porphyrin core within the 1,3,5-phenylene dendron units was found to provide highly efficient energy transfer from the dendron units to the porphyrin core. The dendritic wedge structure affected the energy transfer efficiency. The 1,3,5-phenylene-based rigid dendron units act as highly efficient light-harvesting antennae. These dendritic porphyrins have also been examined as C(60) hosts and substrate-selective oxidation catalysts. The attachment of the second generation of 1,3,5-phenylene-based dendron units with the porphyrin core enabled a stable inclusion of C(60) in toluene. Furthermore, the size and shape of the nanospace in the rigid dendritic porphyrins were found to affect the selectivity of substrates in the catalytic olefin oxidations.     

Liquid‐Crystalline Thiol‐ and Disulfide‐Based Dendrimers for the Functionalization of Gold Nanoparticles. Preliminary Communication

Liquid‐crystalline dendrons carrying either a thiol or disulfide function which display nematic, smectic A, columnar, or chiral nematic phases have been synthesized. Their mesomorphic properties are in agreement with the nature of the mesogenic units and structure of the dendrons. The first‐generation poly(aryl ester) dendron containing two cyanobiphenyl mesogenic units was used to functionalize gold nanoparticles. For full coverage, a smectic‐like supramolecular organization on the nanometer scale is observed, when the gold nanoparticles are spread onto carbon‐coated copper grids. This result indicates that the dendritic ligands reported here act as self‐organization promoters.