Thermodynamic properties of the first to fifth generations of carbosilane dendrimers with allyl terminal groups

Temperature dependences of the specific heats, characteristic temperatures, and enthalpies of physical transformations of the first to fifth generations of carbosilane dendrimers with allyl terminal groups were studied using an adiabatic vacuum calorimeter in the temperature range 6—340 K. The error of measurements was, as a rule, about 0.2%. Thermodynamic characteristics of physical transformations of the dendrimers were determined and their thermodynamic functions C _p°(T), H°(T)—H°(0), S°(T)—S°(0), and G°(T)—H°(0) were calculated for the temperature range 0—340 K. The thermodynamic functions of the dendrimers are linearly related to their molecular weights, the number of allyl groups on their outer spheres, and the number of moles of diallylmethylsilane per mole of the dendrimers formed. Additive dependence of the properties of the dendrimers on their chemical composition and structure indicates that the energy of interaction between structural fragments of the dendrimers is independent of the dendrimer generation number. The fractal dimensions, D, of all dendrimers studied in this work are 1.2—1.3 in the temperature range 30—50 K, thus indicating a chain-layered structure of the dendrimer glasses.     

Synthesis and study of the properties of the homologous series of polyallylcarbosilane dendrimers and their nonfunctional analogs

A synthetic route combining the preparation of functional and nonfunctional carbosilane dendrimers has been developed. Using this route, two representative homologous series of carbosilane dendrimers have been prepared. The use of nonfunctional dendrimer derivatives ensures the possibility of performing long-term experiments both in solution and in the bulk. The intrinsic viscosity and the density of the specimens studied do not depend on the generation number. The obtained dendrimers of later generations were studied by atomic force microscopy and light scattering.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2484–2493, November, 2004.     

Molecular dynamics simulation of poly(butyl)carbosilane dendrimer melts at 600 K

The structural properties of melts of poly(butyl)carbosilane (PBC) dendrimers of the third (G3), fifth (G5), and sixth (G6) generations were studied by molecular dynamics simulation at 600 K. A substantial difference was found between the density of the melt of the G6 generation dendrimer and the densities of the melts of the G3 and G5 generation dendrimers. The obtained computer simulation results do not confirm the hypothesis that these differences are caused by physical entanglements between the branches of the neighboring dendrimers (which take place for G6 to a higher extent) and indicate, most likely, the minimization of the interdendrimer free volume due to a more regular packing.     

Synthesis of Novel Carbosilane Dendrimers with Myo—inositol Cores

The preparation of carbosilane dendrimers with cores of myo-inositol and the outmost periphery grougs of allyl groups has been reported.By using alternate hydrosilylation and alkenyiation reactions,the dendrimer have been carried up to the third generation with 48 allyl groups on the periphery.     

Synthesis of carbosilane dendritic wedges and their use for the construction of dendritic receptors

A divergent route for the synthesis of carbosilane wedges that contain either a bromine or amine as focal point has been developed. These new building blocks enable the construction of various core-functionalized carbosilane dendrimers. As a typical example carbosilane dendrimers up to the third generation containing a N,N',N'-1,3,5-benzenetricarboxamide core (G1-G3) have been synthesized. This new class of molecules has been studied as host molecules and they have been found to bind protected amino acids as guest molecules via hydrogen bonding interactions. A decrease in the association constants was observed for the higher generation dendritic hosts, which is attributed to the increased steric hindrance around the core where the binding site is located. The binding properties of the dendritic host molecules can be tuned by modifying the binding motif at the core of the carbosilane dendrimers. A higher association constant for N-CBZ-protected glutamic acid 1-methyl ester (5) was observed when the third generation N,N',N'-1,3,5-tris(L-alaninyl)benzenetricarboxamide core-functionalized carbosilane dendrimer (G3') was used as the host molecule compared to G3. Different association constants for the formation of the diastereomeric G3'.L-5(K=295 M(-1)) and G3'.(D-5)(2) (K=236 M(-1)) host-guest complexes were observed, pointing to a small enantioselective recognition effect. The difference between the association constants for the formation of the G3'.(L-5)(2) and G3'.(D-5)(2) host-guest complexes was much more pronounced, K=37 M(-1)versus K=10 M(-1), respectively.     

Low-generation carbosilane dendrimers as core for starpolymers using a Ru–ROMP catalyst

Synthesis of new metathesis initiators by coupling Ru-complexes to low generation carbosilane dendrimers (G0–Ru, G1–Ru). These initiators show a very high activity for the ROMP of NBE. Using these dendrimer complexes, multi-arm starpolymers can be developed in a controlled manner.     

Thermodynamic Properties of a First-Generation Carbosilane Dendrimer with Terminal Phenylethyl Groups

The heat capacity of a first-generation carbosilane dendrimer with terminal phenylethyl groups as a function of temperature in the range from 6 to 520 K is studied for the first time via precision adiabatic vacuum calorimetry and differential scanning calorimetry. Physical transformations, such as low-temperature structural anomaly and glass transition are detected in the above-mentioned range of temperatures, and their standard thermodynamic characteristics are determined and analyzed. The standard thermodynamic functions of the studied dendrimer in the range of T → 0 to 520 K are calculated from the experimental data, as is the standard entropy in the devitrified state at T = 298.15 K. The standard thermodynamic characteristics of the carbosilane dendrimers studied in this work and earlier are compared.     

"A posteriori" modification of carbosilane dendrimers and dendrons: their activation in core and branch positions

The introduction of phenyl groups at different points on carbosilane dendrimers allows their acidolytic conversion to highly reactive triflato groups which in turn are readily substituted by anionic nucleophiles. Core phenylated first-fourth generation dendrimers were synthesized from tri(allyl)phenylsilane by an alternating sequence of hydrosilylation and allylation steps. Similarly, carbosilane dendrimers containing phenyl-Si groups at the branching points and in the periphery were prepared from tetraallylsilane which was hydrosilylated with PhHSiCl2. Reaction of the phenylated dendrimers with triflic acid in toluene cleanly gave the silyl triflate derivatives, provided that the correct stoichiometry of the reagents was used. In the presence of a large excess of triflic acid the SiMe3-end groups are slowly converted to SiMe2(OTf)-units. The proof of concept was provided by the fixation of a {Ph2PCH2} group using the lithiated diphenylphosphinomethanide Ph2PCH2Li, obtained by cleavage of Ph3SnCH2PPh2 with PhLi, as well as a lithiated ether-alcohol functionalized triphos derivative to the core of a third generation carbosilane dendrimer.     

碳硅烷树枝状化合物的功能化研究

本文根据碳硅烷树枝状化合物功能基的种类及反应特性,介绍了有关含硅树枝状化合物的功能化的方法,并对功能化含硅树枝状化合物的用途做了相应评述.     

Synthesis of chiral carbosilane dendrimers with l-cysteine and N-acetyl-l-cysteine on their surface and their application as chiral selectors for enantiomer separation by capillary electrophoresis

The synthesis of chiral carbosilane dendrimers functionalized with cysteine and N-acetylcysteine groups is presented. These dendrimers were obtained through thiol–ene addition reactions and their application as chiral selectors in capillary electrophoresis was investigated. Four drugs used as model compounds were analyzed under different experimental conditions observing that the use of a first generation dendrimer containing 4 terminal N-acetyl-l-cysteine groups enabled the enantiomeric discrimination of razoxane with a discrimination power similar to that obtained with other powerful chiral selectors such as cyclodextrins.     

Synthesis and physical behavior of amphiphilic dendrimers with layered organization of hydrophilic and hydrophobic blocks

Amphiphilic carbosilane dendrimers with novel architectural layout have been synthesized. These dendrimers contain peripheral groups consisting of covalently bound promesogenic fragments and hydrophilic (oligoethyleneglycolic) linkages which are connected to a carbosilane core in two distinct ways: as spacer or as tail arrangement. Such molecules have a block structure where the hydrophilic and hydrophobic blocks are distributed within the dendrimer forming layers of different polarity. The hydrophilic layer is either enclosed between two hydrophobic parts of the molecule or is situated on the periphery. The synthetic strategy for achieving these structures is described. The interfacial properties of the dendrimers were studied and the influence of the dendritic structure’s organization on the Langmuir film formation process is assessed.     

Globular carbosilane dendrimers with mannose groups at the periphery: synthesis, characterization and toxicity in dendritic cells

A synthetic strategy has been developed for the preparation of new globular carbosilane dendrimers with mannose groups at the periphery. It consists of hydrosilylation reaction of allyl tetraacetylmannose with carbosilane dendrimers containing monohydrosilane end groups and the subsequent deacetylation reaction. Evaluation of dendrimer toxicities in dendritic cells by MTT assay were carried out, and evidence a good biocompatibility.     

Synthesis,structure, and phase behavior of carbosilane LC dendrimers with terminal butoxyphenylbenzoate mesogenic groups

Two series of carbosilane LC dendrimers with terminal protonated and deuterated butoxyphenylbenzoate mesogenic groups linked to carbosilane dendritic matrices of the first to fifth generations via an undecylene spacer have been synthesized. The chemical structure of new dendrimers has been studied by ¹H NMR spectroscopy and gel-permeation chromatography. The dendrimers of first-fourth generations are characterized by formation of the smectic C mesophase in a wide temperature range, whereas much more complex columnar supramolecular structures are formed in dendrimers of the fifth generation. Structural studied of mesophases by X-ray diffraction and small-angle neutron scattering show that segregation takes place in mixtures of deuterated and protonated LC dendrimers; as a result, huge aggregates composed of hundreds of chemically unbound molecules develop and the sizes of these aggregates reversibly change with temperature.     

Starburstr̀ dendrimers — Nanoscopic supermolecules according to dendritic rules and principles

Construction of dendritic macromolecules based on the mimicry of macroscopic branching patterns found in trees is reviewed. From this mimicry, synthetic strategies have been developed for the preparation of precise macromolecular building blocks referred to as Starburstr̀/Cascade dendrimers. These dendrimer constructions involve the amplifications of matter (mass) by organizing monomer units around initiator cores according to geometrically driven mathematical rules and principles. The predictable precision of mass and valency (i.e., number of reactive surface groups) displayed by these dendrimers, as a function of generation, validates their proposed role as fundamental nanoscopic building blocks (i.e., particle sizes of 10 −1000Å). This emerging area of “structure-controlled polymers” is defining a fourth new major class of macromolecular architecture. Ideal, defect free structures of Starburst^r̀ polyamidoamine (PAMAM) dendrimers (e.g., NH₃ core; generation = 2.0, MWt. 2,414) have been synthesized in kilogram quantities with overall yields of 60-70%. The precise masses and surface valencies associated with these dendrimer structures allow one to view these entities as “nanoscopic analogues” to atoms. As such, basic rules of chemical combination between dendrimers to give definite, stoichiometric compositions can be defined much as first noted by Dalton for atoms. The use of these nanoscopic building blocks (i.e., 10–1000Å species) to construct supramolecular/supermolecular structures such as nanoscopic compounds, clusters and macro-lattices will be reviewed. Registered trademark of Dendritech Inc.     

Synthesis of a carbosilane dendrimer with the functional inner shell

The carbosilane dendrimer of the fifth generation with the functional inner and nonfunctional outer shells in the molecular structure was synthesized for the first time. The efficiency of the hybrid scheme of carbosilane dendrimer synthesis based on the use of organomagnesium and organolithium reagents at different steps of molecular structure formation and hydrosilylation was shown.     

Self-organization of amphiphilic liquid-crystalline dendrimers in bulk and at the interface

A comparative analysis of the structure and phase behavior of synthesized carbosilane amphiphilic LC dendrimers of the third generation containing mesogenic phenyl and oligo(ethylene glycol) fragments is performed. When phenol groups are replaced with oligo(ethylene glycol) moieties, the temperature interval of the existence of the LC phase in the mesogen-containing dendrimers decreases. The chemical nature of hydrophilic terminal groups is found to control the organization of dendrimers in the smectic mesophase. Structural models for their packing are proposed. Amphiphilic dendrimers are shown to form stable Langmuir films at the water/air interface. Surface-pressure-surface area-isotherms are constructed. The effect of the chemical nature of hydrophilic groups on the formation of a monolayer at the interface and on the packing density of dendrimer molecules in the monolayer is discussed.     

Synthesis of anionic carbosilane dendrimers via “click chemistry” and their antiviral properties against HIV

The synthesis and characterization of four families of anionic carbosilane dendrimers bearing carboxylate, phosphonate, naphthylsulfonate, and sulfate terminal groups prepared by cycloaddition of azide–alkyne catalyzed by copper (CuAAC) are presented here. For the preparation of these anionic carbosilane dendrimers, two strategies starting from azide‐terminated carbosilane dendrimers were followed: (i) click coupling of neutral alkynes followed by derivatization into anionic moieties or (ii) click coupling of anionic alkynes. Both strategies require different reaction conditions in order to accommodate the different substrate polarities. These anionic dendrimers, in general, do not present cell toxicity in vitro until concentration up to 20 µM. Therefore, they can be used in inhibition experiments in concentrations below this limit. We have observed that dendrimers bearing phosphonate groups possess poor anti‐HIV capabilities in vitro in PBMCs, while carboxylate dendrimers can reduce HIV infection levels moderately. On the other hand, sulfate and naphthylsulfonate dendrimers are powerful anti‐HIV agents and their antiviral activity is generation and concentration dependent. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1099–1112     

Carbosilane dendrimers NN8 and NN16 form a stable complex with siGAG1

A new mechanism of gene expression inhibition has been discovered as RNA interference, in which the ability of double-stranded RNA to stimulate specific degradation of an mRNA target with a complementary sequence to one of the double-stranded RNA strands. Water-soluble carbosilane dendrimers containing ammonium or amine groups at their periphery are biocompatible molecules that may be good candidates as non-viral carriers of small interfering RNA. In studying the formation of complex between anti-HIV siRNA siGAG1 and carbosilane dendrimers NN8 and NN16 by circular dichroism, fluorescence, and zeta-potential, the size of nanoparticles formed has been estimated by dynamic light scattering. At a charge ratio of 1:3-4 (siGAG1:dendrimer), the dendriplexes formed were in the size range of 250-350 nm.     

The Preparation of the Carbosilane Dendrimers with Pentafluorophenyl Groups

Dendrimers as intriguing macromolecules possess potential in phase transfer catalysis, hosts-guest chemistry, controlled release drugs or might serve as recyclable extracting agents1,2,3. The fluorine-containing dendrimers can be used as low surface-energ…