Terminal Groups Of Dendrimers Research Articles

The branching angle effect on the properties of rigid dendrimers studied by Monte Carlo simulation.

We studied the properties of rigid dendrimers with different branching angles by means of Monte Carlo simulations on a coarse-grained level. It was found that the terminal groups of dendrimers with both rigid and flexible spacers could locate near the center of the molecule. In flexible dendrimers, the wide distribution is attributed to the back folding of flexible spacers, while in rigid dendrimers, it is caused by the branching angle effect that a branch will grow laterally due to the restriction of a non-zero branching angle. It has been established that the branching angle is a key parameter for rigid dendrimers, which can be applied to tune the properties of rigid dendrimers: decreasing branching angle is helpful to obtain dendrimers with a larger size, lower density, and more terminal groups locating at periphery.

Functional hydrophilic highly biodegradable PCL nanofibers through direct aminolysis of PAMAM dendrimer

Polycaprolactone (PCL) was modified with second-generation poly(amidoamine) dendrimer (PAMAM-G2) in electrospinning solution through aminolysis of PCL ester bonds. Two factors affected the modification of PCL in the presence of PAMAM dendrimer. One of them was the concentration of PAMAM, and the other one was the mixing time with PCL. Therefore, PCL/PAMAM nanofiber scaffolds with the ratios of 85:15, 75:25, and 65:35 and mixing times of 1 h and 3 h were fabricated. The presence of NH2 terminal groups of dendrimers and OH groups formed after aminolysis reduced the contact angle from 98° for pure PCL to 9° for a PCL/PAMAM with a ratio of 65:35 mixed for three hours. The degradability test showed that 65:35 specimen lost 47.5% of its initial weight after 8 weeks while for pure PCL was less than 3%. To evaluate the host-guest properties of PCL/PAMAM nanofiber, curcumin was incorporated into the solution before electrospinning as a drug model. MTT assay, cell morphology study and anticancer activity of PCL/PAMAM/curcumin nanofibers against breast cancer cells (MCF-7) showed that by increasing the concentration of dendrimer from 15% to 35%, curcumin loading in the sample increased and inhibition of cancer cells increased from 31.5% to 42.4%, respectively.

BF2 complexes of 1,3-diketones on the surface of phosphorus dendrimers: synthesis and study of the photoluminescence properties

Difluoroboron complexes of monomeric and dimeric diketones and of generations 0–4 of phosphorus dendrimers ended by diketone ligands are synthesized and characterized. Their photoluminescence properties are measured. All compounds exhibit an intense absorption band in the near UV region. Both model dimers and dendrimers show a marked hypsochromic shift of this absorption band compared with the monomeric difluoroboron complex. The fluorescence of the dioxaborine complex subunit in the multichromophoric dendritic architectures is quenched compared with the emission of the isolated monomeric fluorophore, presumably due to interactions between the terminal groups of dendrimers.

Molecular Dynamics Simulations of Membrane Translocation of Dendrimers

Dendrimers are a class of hyperbranched polymer whose structure and surface chemistry can be precisely controlled, which makes them suitable for applications in nanomedicine, such as delivery of therapeutics. Terminal groups of dendrimers have been shown to influence the rate of internalization into cells. For instance, previous articles have demonstrated that dendrimers PAMAM-NH2, PAMAM-OH and PAMAM-COOH of generation 4 (G4) can be taken up by A549 lung cells, but at varying rates, depending on the nature of the terminal groups. It was concluded that amine-terminated dendrimers are more rapidly internalized, since they are prone to interact with negative groups of the cell membrane, such as sialic acid. Several studies have addressed the phenomenon of dendrimer translocation across membranes using computer simulations. However, these studies are challenging and largely infeasible, due to the slow diffusion of lipids composing the membranes. In the present study, we take advantage of coarse-grained models based on MARTINI force field, which have been successfully employed to assess membrane binding of proteins. Furthermore, a highly mobile membrane mimetic, HMMM based on a biphasic solvent model was also employed, to compare the behavior of dendrimers in full-atom and a coarse grained system. Both models permit us to study the translocation of new G3-guanidine, G3-NH2 and G3-OH dendrimers on a reasonable time scale. We expect to delineate why some dendrimers have faster rates of translocation and why some produce membrane perturbations that induce cytotoxicity. These results will further the development of dendrimers as carriers of therapeutic molecules.

Biomimetics: From Bioinformatics to Rational Design of Dendrimers as Gene Carriers.

Biomimetics, or the use of principles of Nature for developing new materials, is a paradigm that could help Nanomedicine tremendously. One of the current challenges in Nanomedicine is the rational design of new efficient and safer gene carriers. Poly(amidoamine) (PAMAM) dendrimers are a well-known class of nanoparticles, extensively used as non-viral nucleic acid carriers, due to their positively charged end-groups. Yet, there are still several aspects that can be improved for their successful application in in vitro and in vivo systems, including their affinity for nucleic acids as well as lowering their cytotoxicity. In the search of new functional groups that could be used as new dendrimer-reactive groups, we followed a biomimetic approach to determine the amino acids with highest prevalence in protein-DNA interactions. Then we introduced them individually as terminal groups of dendrimers, generating a new class of nanoparticles. Molecular dynamics studies of two systems: PAMAM-Arg and PAMAM-Lys were also performed in order to describe the formation of complexes with DNA. Results confirmed that the introduction of amino acids as terminal groups in a dendrimer increases their affinity for DNA and the interactions in the complexes were characterized at atomic level. We end up by briefly discussing additional modifications that can be made to PAMAM dendrimers to turned them into promising new gene carriers.

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 1600cm−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.

DFT study of Raman spectra of phosphorus-containing dendrimers built from thiophosphoryl core

The FT-Raman spectra of the first and second generations of phosphorus-containing dendrimers with terminal benzaldehyde and P–Cl 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 core, 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 1600cm−1 show marked changes of intensity in dependence of aldehyde (CHO) or azomethyne (CHN) substituents in the aromatic ring. The polarizabilities and lipophilicity of the eleven generations of dendrimers were estimated based on the calculated values of the first generations.

Raman spectroscopy study of phosphorus-containing dendrimers built from thiophosphoryl core

The FT-Raman spectra of 10 generations of phosphorus-containing dendrimers containing P=S and P=O bonds with terminal benzaldehyde and P-Cl groups have been recorded and analyzed. The Raman spectra of dendrimers are determined by the ratio T(n)/R(n) (T(n)--number of terminal groups, R(n)--number of repeating units). This ratio trends to r-1 (r--branching functionality of repeating unit), and becomes constant, when the generation number is higher than 3. The lines full width at half height in Raman spectra of 10 generations was measured. The possibility appears to separate the lines assigned to the core, repeating units and terminal groups of dendrimers by difference spectroscopy method. 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. Some lines in the Raman difference spectra have characteristic EPR-like form. The strong line at 1600 cm(-1) show marked changes of intensity in dependence of aldehyde (-CH=O) or azomethyne (-CH=N) substituents in the aromatic ring.

Vibrational spectroscopy studies of dendrimers built from cyclophosphazene core with terminal oxybenzaldehyde groups

The FTIR and FT Raman spectra of four generations of phosphorus dendrimers built from cyclotriphosphazene core with terminal oxybenzaldehyde groups have been recorded and analyzed. Their spectral pattern is determined by the ratio T n/R n ( T n – the number of terminal groups, R n – the number of repeating units). This ratio tends to r − 1 (r – branching functionality of repeating unit), and becomes constant, when the generation number is higher than 3–5. Experimental IR and Raman spectra of different generations of dendrimers built of thiophosphoryl and cyclophosphazene cores are very close similar, according theoretical approach. The dependence of band full width at half height in the IR and Raman spectra on generation number and on the number of dendrons is established. Bands assigned to the core, repeating units and terminal groups of dendrimers were separated by the difference spectroscopy method. The rather rigid repeating units with little conformational flexibility define the perfect microstructure of phosphorus-containing dendrimers. FTIR and FT Raman spectroscopies provide the unique detailed information about the structure of technologically relevant materials, which could not be obtained before with any other technique.

Comparative IR spectroscopic study of phosphorus-containing dendrimers built of thiophosphoryl, cyclophosphazene and phthalocyanine cores

The FTIR spectra of four generations of phosphorus-containing dendrimers built of thiophosphoryl, cyclophosphazene and phthalocyanine cores with terminal benzaldehyde and P–Cl groups have been recorded and analyzed. FT-Raman spectra of four generations of phosphorus dendrimers built of cyclotriphosphazene core with terminal benzaldehyde groups have been detected. Their spectral pattern is determined by the ratio T n / R n ( T n —number of terminal groups, R n —number of repeating units). This ratio trends to r − 1 ( r—branching functionality of repeating unit), and becomes constant, when the generation number is higher than 3. Experimental IR spectra of dendrimers built of thiophosphoryl, cyclophosphazene and phthalocyanine cores are very closely similar. The dependence of band full width at half height in IR spectra on the number of dendrons is established. The possibility appears to separate the bands assigned to the core, repeating units and terminal groups of dendrimers by difference spectroscopy method.

FTIR spectroscopy studies of dendrimers built from cyclophosphazene core

The FTIR spectra of seven generations of phosphorus dendrimers built from cyclotriphosphazene core with terminal phenoxy groups and theirs all-D isotope species have been recorded and analyzed. Their spectral pattern is determined by the ratio T/ R ( T, the number of terminal groups, R, the number of repeating units). This ratio trends to r − 1 ( r, branching functionality of repeating unit), and becomes constant, when the generation number is higher than 3–5. Experimental IR spectra of generations higher than four are very close similar, according theoretical approach. The dependence of band full width at half height in the IR spectra on generation number is established. The influence of the encirclement on the band frequencies and intensity was studied and due to the predictable, controlled and reproducible structure of dendrimers the information usually inaccessible was obtained. Bands assigned to the core, repeated units and terminal groups of dendrimers were separated by the differential spectroscopy method. From the differential IR spectra of dendrimers it follows that for the generations higher than four, the steric congestion disturbs the conformations of the terminal groups. The rather rigid repeated units with little conformational flexibility define the perfect microstructure of phosphorus-containing dendrimers up to six generation. FTIR spectroscopy provides the unique detailed information about the structure of technologically relevant materials, which could not be obtained before with any other technique.

Spectral additive properties of phosphorus-containing dendrimers

The FT-Raman and FTIR spectra of 12 generations of phosphorus-containing dendrimers: [Display omitted] with terminal aldehyde and P Cl groups have been recorded and analyzed. Their spectral pattern is determined by the ratio T/ R ( T, the number of terminal groups; R, the number of repeating units). The influence of the encirclement on the band frequencies and intensity was studied and due to the predictable, controlled and reproducible structure of dendrimers the information usually inaccessible was obtained. Bands assigned to the core, repeated units and terminal groups of dendrimers were separated by the differential spectroscopy method. The strong band at 1600 cm −1 show marked changes of optical density in dependence of the aldehyde ( CH O) or azomethyne ( CH N ) substitution in aromatic ring. From the differential IR and Raman spectra of dendrimers it follows that for the generations higher than 6, the steric congestion disturbs the conformations of the terminal groups. The rather rigid repeated units with little conformational flexibility define the perfect microstructure of phosphorus-containing dendrimers up to 11 generation. FT-Raman and FTIR spectroscopy provides the unique detailed information about the structure of technologically relevant materials, which could not be obtained before with any other technique.

Elementoorganic dendrimer characterization by Raman spectroscopy

The FT-Raman (10–3500 cm −1) spectra of ten generations of the elementoorganic dendrimers have been recorded and analyzed for the first time. Their spectral pattern is determined by the ratio N t/ N r ( N t—number of terminal groups, N r—number of repeating units). This ratio trends to m r−1 ( m r—branching functionality of repeating unit), and becomes constant, when the generation number is higher than 3–5. Experimental Raman spectra of generations higher than 4 are very close similar, according theoretical approach. The dependence of line full width at half height in Raman spectra on generation number is established. The low frequency Raman spectra in R( ν) representation are used to investigate the librations of terminal groups. The possibility appears to separate the lines assigned to the core, repeated units and terminal groups of dendrimers by difference spectroscopy method. From the difference Raman spectra of dendrimers it follows that for the generations higher than six steric congestion disturb the conformations of terminal groups. FT-Raman spectroscopy provides unique detailed information about the structure of the technologically relevant materials, which could not be obtained before with any other technique.