The Experts below are selected from a list of 135 Experts worldwide ranked by ideXlab platform
Sheryl A. Tucker - One of the best experts on this subject based on the ideXlab platform.
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Intrinsic Fluorescence of Carboxylate-Terminated Polyamido Amine Dendrimers
Applied Spectroscopy, 2001Co-Authors: Charlotte L. Larson, Sheryl A. TuckerAbstract:The "intrinsic" fluorescence of carboxylate-terminated Polyamido Amine (PAMAM-CT) dendrimers is studied by two fluorescence techniques—excitation-emission matrices (EEMs) and lifetimes. The EEMs show similar spectral profiles for all dendrimer generations (a broad peak with an excitation and emission maximum of 380 and 440 nm, respectively) and an overall increase in relative fluorescence emission with increasing generation. Three distinct, fairly discrete lifetimes are also recovered. The shortest lifetime (0.2–0.4 ns) is a background signal from the solvent. The two longer lifetimes (1.3–2.5 and 4.2–7.1 ns) are attributed to the dendrimer. There is a general shift to longer lifetimes in τ2 and τ3, with increasing generation (Gn). Both lifetimes nearly double in magnitude, going from G2.5 to G7.5, which is indicative of a specific fluorescent component being in a more protected or constrained microenvironment. These results imply that the dendrimer becomes densely packed with increasing generation. The weak, but detectable, fluorescence is most likely due to an n → π* transition from the amido groups throughout the dendritic structure. Even though the exact nature of PAMAM-CT fluorescence is not fully understood, it is clear that this property shows the unique aspects of the architecture of these dendrimers and can be utilized in their characterization.
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Spectroscopic Investigations of Polyamido Amine Starburst Dendrimers Using the Solvatochromic Probe Phenol Blue
The Journal of Physical Chemistry A, 2001Co-Authors: Dana L. Richter-egger, Jeff C. Landry, And Aaron Tesfai, Sheryl A. TuckerAbstract:The physical and chemical properties of PAMAM-AT dendrimers' interior were investigated using the fluorescent, solvatochromic probe phenol blue. In aqueous solutions of each generation studied except G0, two discrete dye populations were clearly observed. PAMAM-AT dendrimers were shown to form a tight, nonpolar association with the majority of available dye within the dendrimer interior, probably near its core. In the absorption and steady-state fluorescence emission spectra, a microenvironment of decreasing polarity in increasingly larger-generation PAMAM-AT dendrimers (up to G3) is seen for the associated probe. The remaining larger-generation dendrimers (G4−8) all provide a microenvironment of essentially equal polarity. Fluorescence anisotropy values for phenol blue in the PAMAM-AT dendrimers demonstrate the dye's sensitivity to the changing molecular volumes of the dendrimer generations. Model compounds that mimic PAMAM-AT's surface groups and branching moieties were used to better define the associa...
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Spectroscopic Investigations of Polyamido Amine Starburst Dendrimers with Reichardt's ET-30 Dye
Applied Spectroscopy, 2000Co-Authors: Dana L. Richter-egger, Sheryl A. TuckerAbstract:The association between Reichardt's ET-30 dye and Amine- and carboxylate-terminated Polyamido Amine (PAMAM) dendrimers was investigated and shown to be different from results reported for micelles and traditional polymers. The absorption spectra illustrated that the solvatochromic, microenvironmental polarity probe associated with PAMAM dendrimers in less polar regions with a polarity comparable to 1-decanol. Model compounds that mimic PAMAMs' surface groups and branching moieties were used to better define the associated dye's location and demonstrated that ET-30 penetrated beyond the dendrimer's surface groups, into the interfacial region. Additionally, changing sample preparation methods controlled the nature and extent of the dye/dendrimer association. Under certain experimental conditions, the dye/dendrimer complexes formed large aggregates.
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Spectrochemical investigations in dendritic media : evaluation of nitromethane as a selective fluorescence quenching agent in aqueous carboxylate-terminated Polyamido Amine (PAMAM) dendrimers
Analytica Chimica Acta, 1999Co-Authors: Deborah A. Wade, Paulette A. Torres, Sheryl A. TuckerAbstract:Abstract Alternant and nonalternant polycyclic aromatic hydrocarbons (PAHs) are employed to compare carboxylate-terminated Polyamido Amine (PAMAM) dendrimers to typical anionic micelles. Nitromethane is a known, selective, quenching agent of alternant PAHs. However, recent studies by Acree and co-workers have found that nitromethane will also quench the fluorescence emission intensity of nonalternant PAHs in the presence of anionic surfactants above the critical micelle concentration. The quenching of alternant and nonalternant PAHs by nitromethane is used to compare dendritic ‘unimolecular micelles’ to traditional micelles. Experimental results indicate that the PAHs’ association with these dendrimers does not appear to occur in the ‘palisade’ region, as seen in traditional micelles, but rather deeper within the dendrimer structure. Solvent polarity probe studies and quenching in the absence of nitromethane also support this conclusion. Due to the fact that the PAHs do not reside near the negatively charged surface groups, the nitromethane selective quenching rule is obeyed in carboxylate-terminated PAMAM dendrimers (10 mM in surface groups).
Joel B. Alderete - One of the best experts on this subject based on the ideXlab platform.
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Cytotoxicity and in vivo plasma kinetic behavior of surface-functionalized PAMAM dendrimers.
Nanomedicine : nanotechnology biology and medicine, 2018Co-Authors: Carola Díaz, Carolina Benitez, Felipe Vidal, Luis F. Barraza, Verónica A. Jiménez, Leonardo Guzmán, Jorge Fuentealba, Gonzalo E. Yévenes, Joel B. AldereteAbstract:Abstract Understanding the molecular features responsible for the plasma kinetics of surface-modified Polyamido Amine (PAMAM) dendrimers is critical to explore novel biomedical applications for these nanomaterials. In this report, polyethylene glycol (PEG) and folic acid (FA) were employed to obtain partially-substituted PAMAM dendrimers as model biocompatible nanomaterials with different size, charge and surface functionality. Cytotoxicity assays on HEK cells at 1-500 μM concentration confirmed that PEG and FA incorporation increased the cell viability of PAMAM-based nanomaterials. Measurements of plasma kinetics in vivo revealed that PEG-PAMAM has an extended circulation time in mice blood (71.7 min) over native PAMAM (53.3 min) and FA-PAMAM (41.8 min). Molecular dynamics simulations revealed a direct relationship between circulation time and dendrimer size, thus providing valuable evidence to increase understanding about the modulation of functional properties of PAMAM-based systems through surface modification, and to guide future efforts on the rational design of novel biomedical nanomaterials.
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Polyamido Amine (PAMAM)-grafted magnetic nanotubes as emerging platforms for the delivery and sustained release of silibinin
Journal of Materials Science, 2017Co-Authors: Gloria Chávez, Carola Díaz, Verónica A. Jiménez, Leonardo Guzmán, Cristian H. Campos, Cecilia C. Torres, Gorka Salas, Joel B. AldereteAbstract:This work reports the synthesis of surface-modified iron oxide magnetic nanotubes (Fe_3O_4NT) with poly(amido Amine) dendrimers of the third generation (PAMAM-G3) as novel nanomaterials for potential drug-delivery applications. Fe_3O_4NT were obtained by reduction of α-Fe_2O_3 nanotubes, which were synthesized following a hydrothermal strategy using SO_4 ^2−/H_2PO_4 ^− to control the size and morphology of the prepared materials. Fe_3O_4NT were further functionalized with PAMAM-G3 moieties using a silane coupling agent. Pristine and PAMAM-modified Fe_3O_4NT were characterized through TEM, FTIR, XRD, N_2 adsorption–desorption isotherms and VSM measurements, which confirmed the nanotubular morphology and magnetic behavior for both systems, and TGA analyses, which revealed a PAMAM grafting percentage of 16.8%. The effect of PAMAM conjugation on the adsorption and release properties of Fe_3O_4NT was exAmined using silibinin as model poorly soluble drug compound. Our results revealed that PAMAM grafting increased the maximum amount of adsorbed drug from 675 mg g^−1 in pristine Fe_3O_4NT to 825 mg g^−1 in PAMAM-Fe_3O_4NT. These quantities exceed by far the drug-loading capacity of other pristine and PAMAM-modified nanotubular systems, which constitutes a relevant outcome for the present study.
Keith J. Stevenson - One of the best experts on this subject based on the ideXlab platform.
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Spectrophotometric Titration of Bimetallic Metal Cation Binding in Polyamido(Amine) Dendrimer Templates
Analytical chemistry, 2012Co-Authors: Katherine A. Marvin, Justin A. Johnson, Stacia E. Rodenbusch, Lucy Gong, David A. Vanden Bout, Keith J. StevensonAbstract:Spectrophotometric titration and a binding isotherm were used to accurately assess the loading capacity of generation four Polyamido(Amine) (PAMAM) dendrimer templates with terminal alcohol groups (G4-OH). Preparation of bimetallic G4-OH dendrimer-encapsulated metal nanoclusters (DENs) necessitates knowledge of the precise metal-ion binding capacity. The binding of metal ions such as Pt2+ and Pd2+ has proven difficult to assess via UV–vis spectroscopy because the absorbance shifts associated with metal-ion binding within the dendrimer template are masked by the absorbance of the PAMAM dendrimer itself. In contrast, the binding of Cu2+ to G4-OH PAMAM dendrimer results in a strong, distinct absorption band at 300 nm, making UV–vis spectrophotometric titration with copper straightforward. Here we use copper binding as a means to assess the number of binding sites remaining within the PAMAM G4-OH dendrimer after the complexation of a specified molar excess of Pd2+ or Pt2+. In addition, we use a binding isothe...
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Spectrophotometric Titration of Bimetallic Metal Cation Binding in Polyamido(Amine) Dendrimer Templates
2012Co-Authors: Katherine A. Marvin, Justin A. Johnson, Stacia E. Rodenbusch, Lucy Gong, David A. Vanden Bout, Keith J. StevensonAbstract:Spectrophotometric titration and a binding isotherm were used to accurately assess the loading capacity of generation four Polyamido(Amine) (PAMAM) dendrimer templates with terminal alcohol groups (G4-OH). Preparation of bimetallic G4-OH dendrimer-encapsulated metal nanoclusters (DENs) necessitates knowledge of the precise metal-ion binding capacity. The binding of metal ions such as Pt2+ and Pd2+ has proven difficult to assess via UV–vis spectroscopy because the absorbance shifts associated with metal-ion binding within the dendrimer template are masked by the absorbance of the PAMAM dendrimer itself. In contrast, the binding of Cu2+ to G4-OH PAMAM dendrimer results in a strong, distinct absorption band at 300 nm, making UV–vis spectrophotometric titration with copper straightforward. Here we use copper binding as a means to assess the number of binding sites remaining within the PAMAM G4-OH dendrimer after the complexation of a specified molar excess of Pd2+ or Pt2+. In addition, we use a binding isotherm to mathematically estimate the loading capacity of the dendrimer in each case. The loading capacities for M2+ in the G4-OH dendrimer were found to be ∼16 for copper alone, ∼21 for copper combined with palladium, and ∼25 for copper combined with platinum
V. Yegnaraman - One of the best experts on this subject based on the ideXlab platform.
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Platinum–Dendrimer Nanocomposite Films on Gold Surfaces for Electrocatalysis
Catalysis Letters, 2007Co-Authors: S. Raghu, R. G. Nirmal, J. Mathiyarasu, Sheela Berchmans, K. L. N. Phani, V. YegnaramanAbstract:In this communication, we report a strategy for the preparation of Pt nanoparticles encapsulated in Generation 4.5 (Polyamido Amine) PAMAM dendrimer and subsequent chemical linking of the nanocomposite to the gold electrode through a self assembled cystAmine monolayer. The modification resulted in the formation of a robust electrochemically active thin film with very high surface area, reflected by the enhanced hydrogen adsorption coverage. Interestingly, TEM images revealed self-assembly of Pt nanoparticles and the SAED (Selected Area Electron Diffraction) patterns showed the presence of Pt single crystals (111). The Pt-dendrimer nanocomposite film obtained using the novel modification procedure exhibited high electrocatalytic activity for the oxidation of organic fuels like methanol, ethanol and ethylene glycol. The film did not suffer from degradation even after repeated use in solution-phase voltammetry. It is however observed that the intermediate SAM layer and the bulky PAMAM dendrimer (generation 4.5) have slowed down the electron transfer kinetics which is reflected by a relatively high overpotential for methanol oxidation. Nevertheless this shortcoming is more than compensated by the existence of Pt(111) planes, which alleviate CO poisoning.
Carola Díaz - One of the best experts on this subject based on the ideXlab platform.
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Cytotoxicity and in vivo plasma kinetic behavior of surface-functionalized PAMAM dendrimers.
Nanomedicine : nanotechnology biology and medicine, 2018Co-Authors: Carola Díaz, Carolina Benitez, Felipe Vidal, Luis F. Barraza, Verónica A. Jiménez, Leonardo Guzmán, Jorge Fuentealba, Gonzalo E. Yévenes, Joel B. AldereteAbstract:Abstract Understanding the molecular features responsible for the plasma kinetics of surface-modified Polyamido Amine (PAMAM) dendrimers is critical to explore novel biomedical applications for these nanomaterials. In this report, polyethylene glycol (PEG) and folic acid (FA) were employed to obtain partially-substituted PAMAM dendrimers as model biocompatible nanomaterials with different size, charge and surface functionality. Cytotoxicity assays on HEK cells at 1-500 μM concentration confirmed that PEG and FA incorporation increased the cell viability of PAMAM-based nanomaterials. Measurements of plasma kinetics in vivo revealed that PEG-PAMAM has an extended circulation time in mice blood (71.7 min) over native PAMAM (53.3 min) and FA-PAMAM (41.8 min). Molecular dynamics simulations revealed a direct relationship between circulation time and dendrimer size, thus providing valuable evidence to increase understanding about the modulation of functional properties of PAMAM-based systems through surface modification, and to guide future efforts on the rational design of novel biomedical nanomaterials.
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Polyamido Amine (PAMAM)-grafted magnetic nanotubes as emerging platforms for the delivery and sustained release of silibinin
Journal of Materials Science, 2017Co-Authors: Gloria Chávez, Carola Díaz, Verónica A. Jiménez, Leonardo Guzmán, Cristian H. Campos, Cecilia C. Torres, Gorka Salas, Joel B. AldereteAbstract:This work reports the synthesis of surface-modified iron oxide magnetic nanotubes (Fe_3O_4NT) with poly(amido Amine) dendrimers of the third generation (PAMAM-G3) as novel nanomaterials for potential drug-delivery applications. Fe_3O_4NT were obtained by reduction of α-Fe_2O_3 nanotubes, which were synthesized following a hydrothermal strategy using SO_4 ^2−/H_2PO_4 ^− to control the size and morphology of the prepared materials. Fe_3O_4NT were further functionalized with PAMAM-G3 moieties using a silane coupling agent. Pristine and PAMAM-modified Fe_3O_4NT were characterized through TEM, FTIR, XRD, N_2 adsorption–desorption isotherms and VSM measurements, which confirmed the nanotubular morphology and magnetic behavior for both systems, and TGA analyses, which revealed a PAMAM grafting percentage of 16.8%. The effect of PAMAM conjugation on the adsorption and release properties of Fe_3O_4NT was exAmined using silibinin as model poorly soluble drug compound. Our results revealed that PAMAM grafting increased the maximum amount of adsorbed drug from 675 mg g^−1 in pristine Fe_3O_4NT to 825 mg g^−1 in PAMAM-Fe_3O_4NT. These quantities exceed by far the drug-loading capacity of other pristine and PAMAM-modified nanotubular systems, which constitutes a relevant outcome for the present study.