Different Generations Of Dendrimers Research Articles

Exploring the Conformational Landscape of Poly(l-lysine) Dendrimers Using Ion Mobility Mass Spectrometry.

Ion mobility mass spectrometry (IM-MS) measures the mass, size, and shape of ions in the same experiment, and structural information is provided via collision cross-section (CCS) values. The majority of commercially available IM-MS instrumentation relies on the use of CCS calibrants, and here, we present data from a family of poly(l-lysine) dendrimers and explore their suitability for this purpose. In order to test these compounds, we employed three different IM-MS platforms (Agilent 6560 IM-QToF, Waters Synapt G2, and a home-built variable temperature drift tube IM-MS) and used them to investigate six different generations of dendrimers in two buffer gases (helium and nitrogen). Each molecule gives a highly discrete CCS distribution suggestive of single conformers for each m/z value. The DTCCSN2 values of this series of molecules (molecular weight: 330-16,214 Da) range from 182 to 2941 Å2, which spans the CCS range that would be found by many synthetic molecules including supramolecular compounds and many biopolymers. The CCS values for each charge state were highly reproducible in day-to-day analysis on each instrument, although we found small variations in the absolute CCS values between instruments. The rigidity of each dendrimer was probed using collisionally activated and high-temperature IM-MS experiments, where no evidence for a significant CCS change ensued. Taken together, this data indicates that these polymers are candidates for CCS calibration and could also help to reconcile differences found in CCS measurements on different instrument geometries.

Investigation of dendrimer structures by means of reverse atomic bond connectivity index

Topological index is a number attached with the molecular graph of chemical structure. According to the statement of smoothness property, a topological index gives better understanding with structural properties if it has large structure sensitivity (SS) and low abruptness (Abr). Atomic-bound connectivity (ABC) index has low value for structure sensitivity (SS) and large abruptness (Abr). Reverse ABC help us to overcome this deficiency. Here, we will compute reverse ABC index for different generations of dendrimers.

In-situ preparation of amino-terminated dendrimers on TiO2 films by generational growth for potential and efficient surface functionalization

Dendrimers, with their unique structure and polyfunctionality, have shown excellent performance in many biomedicinal applications, such as drug carriers and gene transfection. In this study, titanium dioxide (TiO2) films with four generations (G1, G2, G3, G4) of amino-terminated dendrimers were prepared in situ using a simple iterative Michael addition and aminolysis reaction for generational growth. The TiO2 films with different generations of dendrimers were characterized using X-ray diffraction, water contact angle measurements, and scanning electron microscopy. The chemical compositions of these films were confirmed by Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. Blood compatibility was evaluated using platelet adhesion and activation assays utilizing platelet-rich plasma. The results indicated that the dendrimers immobilized on the surface of the TiO2 films effectively reduced platelet adhesion and aggregation. Endothelial cell culturing on the dendrimer-immobilized surfaces showed that the amino-terminated dendrimers exhibited a certain degree of cytotoxicity due to the positive charges of the amino groups. These results indicated that amino-terminated dendrimers immobilized on TiO2 films provided numerous functional groups for the future immobilization of specific biological molecules and may be used for manufacturing future blood-contacting implants.

Preparation and Characterization of a Cyclophosphamide-Core PAMAM Dendritic Montmorillonite

Polyamidoamine modified organo-montmorillonites (OMMT) bearing flame-retardant elements were prepared through montmorillonite (MMT) and polyamidoamines with different generations. These materials turned out to be a possible use for the flame-retardency of polymers. Different generations of dendrimers, G1.0, G2.0, and G3.0, were synthesized from a cyclotriphosphazene core. Characteristics of these dendrimers were studied by Fourier transform infrared (FTIR) spectroscopy, hydrogen nuclear magnetic resonance (1H-NMR), ultraviolet (UV-Vis) spectroscopy, and intrinsic viscosity (IV). It was demonstrated that different generations of dendrimers had been well synthesized. These dendrimers were used as an organic intercalation agent to modify natural clay, Na +-MMT. Different generations of flame-retardant dendrimer modified OMMT, G1.0-OMMT, G2.0-OMMT, and G3.0-OMMT, were prepared. The interlayer spacing, thermal stability, and surface morphology of these dendritic MMTs were investigated by FTIR, thermogravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy (SEM) as well as energy dispersing spectrometry (EDS). It was seen that the thermal stability of G1.0-OMMT, G2.0-OMMT, and G3.0-OMMT was obviously improved with the increase of generations compared with that of MMT. In addition, an exfoliated structure existed in these dendrimer modified silicate layers.

Vibrational spectra and DFT studies of conjugation in poly(phosphorhydrazone) dendrimers

The FTIR and FT Raman spectra of the 11 generations of poly(phosphorhydrazone) dendrimers built from thiophosphoryl core with P−Cl (Gi) and oxybenzaldehyde (G'i) terminal groups have been studied. Spectral pattern of dendrimers depends on the ratio of the number of end groups and repeating units. This ratio tends to r–1 (r– functionality of the repeating unit) and becomes constant when the generation number exceeds 3. The experimental IR and Raman spectra of the different generations of dendrimers are very similar to each other in the agreement with the theory. Optimization of the structure and the analysis of normal vibrations was made for G'0 and G1 using the density functional theory (DFT). Calculations showed that the molecules of the first generation dendrimer have the form of a propeller with three blades and flat repeating units. Bond lengths and angles in the optimized geometry obtained by DFT show good agreement with experiment. Consideration of the molecular orbitals shows that in the repeating units and oxybenzaldehyde end groups of poly(phosphorhydrazone) dendrimers conjugation is realized. The oxybenzaldehyde terminal groups are characterized by a band 1702cm−1 in the experimental IR spectra of G’i. The line in the Raman spectra of Gi and G’i at 1576cm−1 refers to the vibrations of the repeating units.

Evaluation of polyamidoamine dendrimers as potential carriers for quercetin, a versatile flavonoid

The aim of the present research work was to investigate the potential of polyamidoamine (PAMAM) dendrimers as oral drug delivery carriers for quercetin, a Biopharmaceutical Classification System (BCS) class II molecule. The aqueous solubility of quercetin was investigated in different generations of dendrimers, i.e. G0, G1, G2 and G3, with varying concentrations (0.1, 0.5, 1, 2 and 4 µM). Then, it was successfully incorporated in PAMAM dendrimers and they were characterized for incorporation efficacy, nature of nanoformulations, size, size distribution, surface morphology and stability. In vitro release characteristics of quercetin from all quercetin-PAMAM complexes were studied at 37 °C in phosphate buffer saline (PBS; pH 7.4). Furthermore, the efficacy of quercetin-loaded PAMAM dendrimer was assessed by pharmacodynamic experiment, namely, a carrageenan-induced paw edema model to evaluate the acute activity of this nanocarrier in response to inflammation. It was observed that both generation and the respective concentrations of PAMAM dendrimers showed potential positive effects on solubility enhancement of quercetin. All the quercetin-PAMAM complexes were found to be in nanometeric range (<100 nm) with narrow polydispersity index. In vitro study revealed a biphasic release pattern of quercetin which was characterized by an initial faster release followed by sustained release phase and pharmacodynamic study provided the preliminary proof of concept about the potential of quercetin-PAMAM complexes. The study concludes that the dendrimer-based drug delivery system for quercetin has enormous potential to resolve the drug delivery issues associated with it.

Size and branching effects on the fluorescence of benzylic dendrimers possessing one apigenin fluorophore at the core

Different generations of dendrimers incorporating one fluorescent core of apigenin and three Fréchet benzylic dendrons have been prepared. The chief geometric features of these dendrimers have been obtained by Molecular Dynamics simulations. These computational data suggest that the asphericities of dendrimers belonging to the third and fourth generations are considerably larger than those associated with lower radii of gyration. Fluorescence spectra of high generation dendrimers evolve along time and quantum yields show an appreciable lowering for the fourth generation dendrimer. All these data suggest aggregation phenomena and lower quantum yields for nonspheric dendrimers in solution.

Reversible pH Manipulation of the Fluorescence Emission from Sectorial Poly(amido amine) Dendrimers

The first to fourth generation (G1-G4) of sectorial poly(amido amine) (PAMAM) dendrimers with ethanolamine core and amino terminals are synthesized by a divergent route. Blue fluorescence emission from these dendrimers is observed. It is found that there is a remarkable difference in the fluorescence behavior for these different generations of dendrimers. The emission intensity of these dendrimers is almost linearly enhanced along with the increase of their concentrations. A significant pH-dependent profile of the fluorescence intensity is also observed. As the pH value decreases from 8 to 3, the fluorescence intensity increases almost linearly. Furthermore, the fluorescence intensity of the dendrimers shows a reversible behavior depending on pH value within the pH range from 3 to 11. This property enables the reversible manipulation of the fluorescence of these dendrimers by adjusting the pH values, which contributes to a potential application of these materials in fluorescent pH sensors.

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.

Single-component films of different generations of dendrimers bearing a diphenylanthracene core

Different generations of carboxyl-terminated poly(aryl ether) dendrimers bearing a diphenylanthracene core were designed and synthesized. It is interesting to see that not only two-generation dendrimers but also one-generation dendrimers can be fabricated into thin films by self-deposition. Fluorescence spectra indicate that increasing the generation number of a dendrimer can effectively control the quenching of the fluorescence. Moreover, the fluorescence property of the diphenylanthracene core of the dendrimers in a solid film is quite similar to that of one in a solution, which is important for designing light-emitting materials.

Dendritic polymers containing a dimethylsilyl linked dihydroxybenzyl alcohol backbone: divergent synthesis, aggregation, functionalization, and an evaluation of their applications in catalysis

A divergent synthetic approach to the construction of dimethylsilyl linked dihydroxybenzyl alcohol based dendrimers via acid–base hydrolytic chemistry of bis(dimethylamino)dimethylsilane with 3,5-dihydroxybenzyl alcohol, is reported. The peripheral OH groups lead to significant aggregation that was studied using FT-IR and UV-Vis spectroscopies, light scattering and transmission electron microscopy. Different generations of dendrimers could be easily functionalized at the periphery with phosphorus donor groups that were subsequently bound to RhCl(1,5-C8H12). Such organometallic dendrimers were found to be active and recoverable catalysts for hydrogenation of decene. The catalytic efficiency was found to be dependent on the number of generations and reaction time. An uncontrolled reaction of Me2Si(NMe2)2 with 3,5-dihydroxybenzyl alcohol in a multi-step addition process or one-pot reaction, led to the formation of hyperbranched polymers in which the build-up of the polymeric backbone was found to be dependent on the preferential reactivity and sterics at the benzylic center, as observed during dendrimer construction.

The lectin-binding properties of six generations of mannose-functionalized dendrimers.

[structure: see text] First- through sixth-generation PAMAM dendrimers have been functionalized with mannose residues. Characterization with MALDI-TOF MS and (1)H NMR is reported. Different binding enhancements consistent with monovalent interaction, glycoside clustering, and multivalent binding are observed for different generations of dendrimers.

Functionalized Poly(propylene imine) Dendrimers as Novel Phase Transfer Catalysts in Supercritical Carbon Dioxide

Perfluoro-functionalized poly(propylene imine) dendrimers have been used as reactive extractants for anionic species and as phase transfer catalysts for two types of reactions. Different generations of dendrimers have been used for applications in carbon dioxide. First, the reactive extraction of the inorganic ions permanganate and dichromate, from an aqueous phase to a supercritical carbon dioxide phase, has been studied using the functionalized dendrimers. The yield for these extractions is rather low, indicating that the perfluoro-functionalized poly(propylene imine) dendrimers are not suited for oxidation reactions with these ions in carbon dioxide. Second, the poly(propylene imine) dendrimers have been used as a phase transfer catalyst for the halogen exchange reaction of benzyl chloride into benzyl bromide and for the esterification of oxalic acid with pentafluorobenzylbromide. In contrast with the low extraction yield for the inorganic permanganate and dichromate ions, a high reaction rate was obtained for the halogen exchange reaction with the functionalized dendrimers as phase transfer catalysts. It is found that the rate of reaction for both cases depends on the generation number of the dendrimer. For the higher-generation dendrimers, it is more difficult for the substrate to migrate from the bulk carbon dioxide phase to the interior of the dendrimer. This indicates that the mass transfer of the reagents from the organic phase into the interior of the dendrimer determines the reaction rate for the fourth and higher generation dendrimers. A model is proposed to describe the extraction and the phase transfer catalysis based on the fact that the modified dendrimers combine micellar properties with those of standard phase transfer catalysts. From the different experiments it can be concluded that the perfluoro-functionalized poly(propylene imine) dendrimers have great potential as multisite phase transfer catalysts.