NMR Insights into Dendrimer-Based Host–Guest Systems

Ligand-Binding Ability of a Porphyrin Core in a Dendrimer with Rigid Branched Terminal Components

A dendrimer with rigid branched terminal components was prepared by a copper-catalyzed Hüisgen 1,3-dipolar cycloaddition reaction. A zinc 5,15-diethynyl-10,20-bis(3,5-di- tert-butylphenyl)porphyrin unit was incorporated at the core of the dendrimer as a receptor site for an added pyridyl ligand. The appearance of an absorption band characteristic of the planar conformer of conjugated chains in the terminal components suggested that the dendrimer adopts a folded higher order structure in dichloromethane at 25 °C. The binding constant between the zinc porphyrin core and a pyridyl ligand was evaluated by means of UV-vis absorption titration and compared with that of a suitable reference compound. The incorporation of the zinc porphyrin core into the folded dendrimer led to considerable suppression of its ligand-binding ability.

Encapsulation property of hyperbranched polyglycerols as prospective drug delivery systems

Hyperbranched polyglycerols (hbPGs) were investigated as nanocarriers to encapsulate and deliver guest molecules.

Investigation of Melts of Polybutylcarbosilane Dendrimers by 1H NMR Spectroscopy

Melts of polybutylcarbosilane (PBC) dendrimers from third (G3) up to sixth (G6) generations are investigated by ¹H NMR spectroscopy in a wide temperature range up to 493 K. At room temperature, NMR spectra of G3-G5 dendrimers exhibit resolved, solution-like spectra (“liquid” phase). In contrast, the spectrum of the G6 dendrimer is characterized by a single unresolved broad line at whole temperature range, which supports the presence of an anomalous phase state of G6 at temperatures higher than glass transition temperature. For the first time, an unexpected transition of G5 dendrimer from a molecular liquid state to an anomalous state/phase upon temperature increase has been detected using NMR data. Specifically, an additional wide background line appears in the G5 spectrum above 473 K, and this line corresponds to a G5 state characterized by restricted molecular mobility, i.e., a state similar to the “anomalous” phase of G6 melt. The fraction of the G5 dendrimers in “anomalous” phase at 493 K is approximately 40%. Analysis of the spectral shapes suggests that changes in the G5 dendrimers are reversible with temperature.

Function Oriented Molecular Design: Dendrimers as Novel Antimicrobials

In recent years innovative nanostructures are attracting increasing interest and, among them, dendrimers have shown several fields of application. Dendrimers can be designed and modified in plentiful ways giving rise to hundreds of different molecules with specific characteristics and functionalities. Biomedicine is probably the field where these molecules find extraordinary applicability, and this is probably due to their multi-valency and to the fact that several other chemicals can be coupled to them to obtain desired compounds. In this review we will describe the different production strategies and the tools and technologies for the study of their characteristics. Finally, we provide a panoramic overview of their applications to meet biomedical needs, especially their use as novel antimicrobials.

Construction of an ultrasensitive non-enzymatic sensor to investigate the dynamic process of superoxide anion release from living cells

In this work, a novel non-enzymatic superoxide anion (O₂•^-) sensor was constructed based on Ag nanoparticles (NPs) / poly (amidoamine) (PAMAM) dendrimers and used to investigate the dynamic process of O₂•^- release from living cells. The AgNPs/PAMAM nanohybrids were characterized by transmission electron microscopy (TEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The fabricated electrode exhibited excellent catalytic activity toward the reaction of O₂•^- with a super low detection limit (LOD) of 2.530 × 10^-13M (S/N = 3) and wide linear range of 8 orders of magnitude. It could fulfill the requirement of real-time measurement O₂•^- released from living cells. Furthermore, zymosan was chosen as the stimulant to induce O₂•^- generation from cancer cells (rat adrenal medulla pheochromocytoma cell (PC12)). The electrochemical experiment results indicated that the levels of intracellular O₂•^- depended on the amount of Zymosan. A large amount of O₂•^- generated in the living cells by added heavy stimulant could damage cells seriously. More importantly, a vitro simulation experiment confirmed the role of superoxide dismutase (SOD) for the first time because it could maintain the O₂•^- concentration at a normal physiological range. These findings are of great significance for evaluating the metabolic processes of O₂•^- in the biological system, and this work has the tremendous potential application in clinical diagnostics to assess oxidative stress.

Stimuli-responsive dendrimers in drug delivery

Dendrimers have shown great promise as carriers in drug delivery due to their unique structures and superior properties. However, the precise control of payload release from a dendrimer matrix still presents a great challenge. Stimuli-responsive dendrimers that release payloads in response to a specific trigger could offer distinct clinical advantages over those dendrimers that release payloads passively. These smart polymers are designed to specifically release their payloads at targeted regions or at constant release profiles for specific therapies. They represent an attractive alternative to targeted dendrimers and enable dendrimer-based therapeutics to be more effective, more convenient, and much safer. The wide range of stimuli, either endogenous (acid, enzyme, and redox potentials) or exogenous (light, ultrasound, and temperature change), allows great flexibility in the design of stimuli-responsive dendrimers. In this review article, we will highlight recent advances and opportunities in the development of stimuli-responsive dendrimers for the treatment of various diseases, with emphasis on cancer. Specifically, the applications of stimuli-responsive dendrimers in drug delivery as well as their mechanisms are intensively reviewed.

Spectroscopic and calorimetric studies on the interaction between PAMAM G4-OH and 5-fluorouracil in aqueous solutions

The results of spectroscopic measurements (an increase in solubility, equilibrium dialysis, ¹H NMR titration) and calorimetric measurements (isothermal titration ITC) indicate spontaneous (ΔG<0) binding of 5-fluorouracil molecules by PAMAM G4-OH dendrimer with terminal hydroxyl groups in an aqueous solution. PAMAM G4-OH dendrimer bonds about n=8±1 molecules of the drug with an equilibrium constant of K=70±10. The process of saturating the dendrimer active sites by the drug molecules is exothermal (ΔH<0) and is accompanied by an advantageous change in entropy (ΔS>0). The parameters of binding 5-fluorouracil by PAMAM G4-OH dendrimer were compared with those of binding this drug by the macromolecules of PAMAM G3-OH and G5-OH.

Pulsed-field gradient nuclear magnetic resonance measurements (PFG NMR) for diffusion ordered spectroscopy (DOSY) mapping

The advent of Diffusion Ordered SpectroscopY (DOSY) NMR has enabled diffusion coefficients to be routinely measured and used to characterize chemical systems in solution. Indeed, DOSY NMR allows the separation of the chemical entities present in multicomponent systems and provides information on their intermolecular interactions as well as on their size and shape.

Structure-activity relationships of fluorinated dendrimers in DNA and siRNA delivery

Fluorinated dendrimers have shown great promise in gene delivery due to their high transfection efficacy and low cytotoxicity, however, the structure-activity relationships of these polymers still remain unknown. Herein, we synthesized a library of fluorinated dendrimers with different dendrimer generations and fluorination degrees and investigated their behaviors in both DNA and siRNA delivery. The results show that fluorination significantly improves the transfection efficacy of G4-G7 polyamidoamine dendrimers in DNA and siRNA delivery. Fluorination on generation 5 dendrimer yields the most efficient polymers in gene delivery, and the transfection efficacy of fluorinated dendrimers depends on fluorination degree. All the fluorinated dendrimers cause minimal toxicity on the transfected cells at their optimal transfection conditions. This study provides a general and facile strategy to prepare high efficient and low cytotoxic gene carriers based on fluorinated polymers.

STATEMENT OF SIGNIFICANCE

The structure-activity relationships of fluorinated dendrimers in gene delivery is still unknown and the behavior of fluorinated dendrimers in siRNA delivery has not yet been investigated. Herein, we synthesized a library of fluorinated PAMAM dendrimers with different dendrimer generations and fluorination degrees and investigated their behaviors in both DNA and siRNA delivery. The results clearly indicate that fluorination significantly improves the transfection efficacy of dendrimers in both DNA and siRNA delivery without causing additional toxicity. G5 PAMAM dendrimer is best scaffold to synthesize fluorinated dendrimers and the transfection efficacy of fluorinated dendrimers depends on fluorination degree. This systematic study provides a general and facile strategy to prepare high efficient and low cytotoxic gene carriers based on fluorinated polymers.

Amplifying undetectable NMR signals to study host-guest interactions and exchange

The characteristics of host-guest systems, such as molecular recognition, complexation, encapsulation, guest composition, and dynamic exchange, are manifested by changes in the chemical shifts (Δω) in the NMR spectrum. However, in cases where NMR signals cannot be detected, due to low concentrations, poor solubility, or relatively fast exchange, an alternative is needed. Here, we show that by using the magnetization transfer (MT) method, the undetectable NMR signals of host-guest assemblies can be amplified by two orders of magnitude. It is shown that the binding kinetics characteristics of a fluorinated guest and cucurbit[n]uril (CB[n]) hosts in aqueous solutions determine the NMR signal amplification of host-guest assemblies. In addition, by using the MT technique within the 19F-NMR framework, one can detect μM concentrations of the complex and study the effect of different solutes on the resulting host-guest system. The results expand the "NMR toolbox" available to explore a wider range of dynamic host-guest systems in which NMR signals cannot be detected.

Spatial Distributions of Guest Molecule and Hydration Level in Dendrimer-Based Guest-Host Complex

Using the electrostatic complex of G4 poly(amidoamine) (PAMAM) dendrimer with an amphiphilic surfactant as a model system, contrast variation small angle neutron scattering (SANS) is implemented to resolve the key structural characteristics of dendrimer-based guest-host system. Quantifications of the radial distributions of the scattering length density and the hydration level within the complex molecule reveal that the surfactant is embedded in the peripheral region of dendrimer and the steric crowding in this region increases the backfolding of the dendritic segments, thereby reducing the hydration level throughout the complex molecule. The insights into the spatial location of the guest molecules as well as the perturbations of dendrimer conformation and hydration level deduced here are crucial for the delicate design of dendrimer-based guest-host system for biomedical applications.

Converting Nonliquid Crystals into Liquid Crystals by N-Methylation in the Central Linker of Triazine-Based Dendrimers

Two triazine-based dendrimers were successfully prepared in 60-75% yields. These newly prepared dendrimers 2a and 2b containing the -NMe(CH2)2NMe- and the -NMe(CH2)4NMe- linkers between two G3 dendrons, respectively, exhibit columnar phases during the thermal process. However, the corresponding dendrimers 1a and 1b containing the -NH(CH2)2NH- and the -NH(CH2)4NH- linkers between two G3 dendrons, respectively, do not show any LC phases on thermal treatment. Computational investigations on molecular conformations reveal that N-methylation of the dendritic central linker leads dendrimers to possess more isomeric conformations and thus successfully converts non-LC dendrimers (1a and 1b) into LC dendrimers (2a and 2b).

Nanocarriers for delivery of siRNA and co-delivery of siRNA and other therapeutic agents

A major problem in cancer treatment is the multidrug resistance. siRNA inhibitors have great advantages to solve the problem, if the bottleneck of their delivery could be well addressed by the various nanocarriers. Moreover, co-delivery of siRNA together with the various anticancer agents in one nanocarrier may maximize their additive or synergistic effect. This review provides a comprehensive summary on the state-of-the-art of the nanocarriers, which may include prodrugs, micelles, liposomes, dendrimers, nanohydrogels, solid lipid nanoparticles, nanoparticles of biodegradable polymers and nucleic acid nanocarriers for delivery of siRNA and co-delivery of siRNA together with anticancer agents with focus on synthesis of the nanocarrier materials, design and characterization, in vitro and in vivo evaluation, and prospect and challenges of nanocarriers.

A single cation or anion dendrimer-based liquid electrolyte

We propose here a novel liquid dendrimer-based single ion conductor as a potential alternative to conventional molecular liquid solvent-salt solutions in rechargeable batteries, sensors and actuators. A specific change from ester (-COOR) to cyano (-CN) terminated peripheral groups in generation-one poly(propyl ether imine) (G1-PETIM)-lithium salt complexes results in a remarkable switchover from a high cation (tLi+ = 0.9 for -COOR) to a high anion (tPF6- = 0.8 for -CN) transference number. This observed switchover draws an interesting analogy with the concept of heterogeneous doping, applied successfully to account for similar changes in ionic conductivity arising out of dispersion of insulator particle inclusions in weak inorganic solid electrolytes. The change in peripheral group simultaneously affects the effective ionic conductivity, with the room temperature ionic conductivity of PETIM-CN (1.9 × 10-5 Ω-1 cm-1) being an order of magnitude higher than PETIM-COOR (1.9 × 10-6 Ω-1 cm-1). Notably, no significant changes are observed in the lithium mobility even following changes in viscosity due to the change in the peripheral group. Changes in the peripheral chemical functionality directly influence the anion mobility, being lower in PETIM-COOR than in PETIM-CN, which ultimately becomes the sole parameter controlling the effective transport and electrochemical properties of the dendrimer electrolytes.

Tailoring the dendrimer core for efficient gene delivery

Dendrimers have been widely used as non-viral gene vectors due to well-defined chemical structures, high density of cationic charges and ease of surface modification. Although a large number of studies have reported the important roles of dendrimer architecture, component, generation and surface functionality in gene delivery, the effect of dendrimer core on this issue still remains unclear. Recent literatures suggest that a slight alternation in dendrimer core has a profound effect in the transfection efficacy and biocompatibility. In this review, we will discuss the transfection mechanism of dendrimers with different types of cores in respect of flexibility, hydrophobicity and functionality. We hope to open a possibility of designing efficient dendrimers for gene delivery by choosing a proper dendrimer core.

STATEMENT OF SIGNIFICANCE

As a branch of researches on dendrimers and dendritic polymers, the design of biocompatible and high efficient polymeric gene carriers has attracted increasing attentions during these years. Although the effect of dendrimer generation, species, architecture and surface functionality on gene delivery have been widely reported, the effect of dendrimer core on this issue still remains unclear. Recent literatures suggest that a minor variation on the dendrimer core has a profound effect in the transfection efficacy and biocompatibility. This critical review summarized the dendrimers with different types of cores and discussed the transfection mechanism with particular focus on the flexibility, hydrophobicity, and functionality. It is hoped to provide a new insight to design efficient and safe dendrimer-based gene vectors by choosing a proper core. To the best of our knowledge, this is the first review on the effect of dendrimer core on gene delivery. The findings obtained in this filed are of central importance in the design of efficient polymeric gene vectors. This article will appeal a wide readership such as physical chemist, dendrimer chemist, biological chemist, pharmaceutical scientist, and biomaterial researchers. We hope that this review article can be published by Acta Biomaterialia, a top journal that publishes important reviews in the field of biomaterials science.

Unexpected Temperature Behavior of Polyethylene Glycol Spacers in Copolymer Dendrimers in Chloroform

We have studied copolymer dendrimer structure: carbosilane dendrimers with terminal phenylbenzoate mesogenic groups attached by poly(ethylene) glycol (PEG) spacers. In this system PEG spacers are additional tuning to usual copolymer structure: dendrimer with terminal mesogenic groups. The dendrimer macromolecules were investigated in a dilute chloroform solution by ¹H NMR methods (spectra and relaxations). It was found that the PEG layer in G = 5 generations dendrimer is “frozen” at high temperatures (above 260 K), but it unexpectedly becomes “unfrozen” at temperatures below 250 K (i.e., melting when cooling). The transition between these two states occurs within a small temperature range (~10 K). Such a behavior is not observed for smaller dendrimer generations (G = 1 and 3). This effect is likely related to the low critical solution temperature (LCST) of PEG and is caused by dendrimer conformations, in which the PEG group concentration in the layer increases with growing G. We suppose that the unusual behavior of PEG fragments in dendrimers will be interesting for practical applications such as nanocontainers or nanoreactors.

Structure-activity relationship of dendrimers engineered with twenty common amino acids in gene delivery

Systematic explorations on the structure-activity relationship of surface-engineered dendrimers are essential to design high efficient and safe gene vectors. The chemical diversity of residues in naturally occurring amino acids allows us to generate a library of dendrimers with various surface properties. Here, we synthesized a total number of 40 dendrimers engineered with the twenty common amino acids and investigated their performances in gene delivery. The results show that gene transfection efficacy of the synthesized materials depends on both the type of amino acid and the conjugation ratio. Dendrimers engineered with cationic and hydrophobic amino acids possess relatively higher transfection efficacies. Engineering dendrimers with cationic amino acids such as arginine and lysine facilitates polyplex formation and cellular uptake, with histidine improves endosomal escape of the polyplexes, and with hydrophobic amino acids such as tyrosine and phenylalanine modulates the balance between hydrophobicity and hydrophilicity on dendrimer surface, which is beneficial for efficient cellular internalization. Dendrimers engineered with anionic or hydrophilic amino acids show limited transfection efficacy due to poor DNA binding capacity and/or limited cellular uptake. In the aspect of cytotoxicity, dendrimers engineered with arginine, lysine, tyrosine, phenylalanine and tryptophan show much higher cytotoxicity than other engineered dendrimers. These results are helpful for us to tailor the surface chemistry of dendrimers for efficient gene delivery.

STATEMENT OF SIGNIFICANCE

Cationic polymers such as dendrimers were widely used as gene vectors but are limited by relatively low delivery efficacy and high toxicity. To achieve efficient and low toxic gene delivery, the polymers were modified with various ligands. However, these ligand-modified polymers in gene delivery are reported by independent researchers using different polymer scaffolds and cell lines. It is hard to provide structure-function information of these materials based on current knowledge and experience, which are essential for the design of ideal polymeric vectors for gene delivery. Here, we prepared a small library of amino acid-modified dendrimers, which is used as a screening pool to discover efficient gene vectors. The results obtained from this study, especially the structure-activity relationship of the screened materials are helpful for us to further design efficient and biocompatible polymers for gene delivery. This manuscript will appeal to a wide readership such as nanomaterial chemist, dendrimer chemist, biological chemist, pharmaceutical scientist, and biomedical researchers.

Host–guest binding motifs based on hyperbranched polymers

Host–guest systems based on hyperbranched polymers together with their unique properties and various applications have been summarized.

Guest-Host Chemistry with Dendrimers—Binding of Carboxylates in Aqueous Solution

Recognition and binding of anions in water is difficult due to the ability of water molecules to form strong hydrogen bonds and to solvate the anions. The complexation of two different carboxylates with 1-(4-carbomethoxypyrrolidone)-terminated PAMAM dendrimers was studied in aqueous solution using NMR and ITC binding models. Sodium 2-naphthoate and sodium 3-hydroxy-2-naphthoate were chosen as carboxylate model compounds, since they carry structural similarities to many non-steroidal anti-inflammatory drugs and they possess only a limited number of functional groups, making them ideal to study the carboxylate-dendrimer interaction selectively. The binding stoichiometry for 3-hydroxy-2-naphthoate was found to be two strongly bound guest molecules per dendrimer and an additional 40 molecules with weak binding affinity. The NOESY NMR showed a clear binding correlation of sodium 3-hydroxy-2-naphthoate with the lyophilic dendrimer core, possibly with the two high affinity guest molecules. In comparison, sodium 2-naphthoate showed a weaker binding strength and had a stoichiometry of two guests per dendrimer with no additional weakly bound guests. This stronger dendrimer interaction with sodium 3-hydroxy-2-naphthoate is possibly a result of the additional interactions of the dendrimer with the extra hydroxyl group and an internal stabilization of the negative charge due to the hydroxyl group. These findings illustrate the potential of the G4 1-(4-carbomethoxy) pyrrolidone dendrimer to complex carboxylate guests in water and act as a possible carrier of such molecules.

Recent advances in targeted drug delivery approaches using dendritic polymers

Since they were first synthesized over 30 years ago, dendrimers have seen rapid translation into various biomedical applications. A number of reports have not only demonstrated their clinical utility, but also revealed novel design approaches and strategies based on the elucidation of underlying mechanisms governing their biological interactions. This review focuses on presenting the latest advances in dendrimer design, discussing the current mechanistic understandings, and highlighting recent developments and targeted approaches using dendrimers in drug/gene delivery.

Spectroscopic and calorimetric studies of formation of the supramolecular complexes of PAMAM G5-NH₂ and G5-OH dendrimers with 5-fluorouracil in aqueous solution

The results of spectroscopic measurements (increase in solubility, equilibrium dialysis, (1)H NMR titration) and calorimetric measurements (isothermal titration ITC) indicate exothermic (ΔH<0) and spontaneous (ΔG < 0) combination of an antitumor drug, 5-fluorouracil, by both cationic PAMAM G5-NH2 dendrimer and its hydroxyl analog PAMAM G5-OH in aqueous solutions at room temperature. PAMAM G5-NH2 dendrimer combines about 70 molecules of the drug with equilibrium constant K ≅ 300, which is accompanied by an increase in the system order (ΔS < 0). Hydroxyl dendrimer, PAMAM G5-OH, combines about 14 molecules of 5-fluorouracil with equilibrium constant K ≅ 100. This process is accompanied by an increase in the system disorder (ΔS > 0).

Synthesis of all-aliphatic polyamide dendrimers based on a 3,3′-diaminopivalic acid scaffold

Iterative 3,3′-diaminopivalic acid connections act as building blocks in the production of new all-aliphatic polyamide dendrimers. 3,3′-Diazidopivalic acid units underpin a two-step pathway involving carboxylic acid–amine condensation, followed azide reduction.

Tumor extracellular acidity activated “off–on” release of bortezomib from a biocompatible dendrimer

A nanoparticle with a specific response to tumor extracellular acidity provides a new option in the design of tumor-targeted delivery systems.

A lipopolysaccharide binding heteromultivalent dendrimer nanoplatform for Gram negative cell targeting

Heteromultivalent design of PAMAM dendrimer by conjugation with polymyxin B (PMB) ligand and excess auxiliary ethanolamine (EA) branches led to lipopolysaccharide (LPS) avidity two orders of magnitude greater than free PMB.

Association of small aromatic molecules with PAMAM dendrimers

Dendrimer pockets enable association by reducing naphthalene hydration even near the dendrimer periphery.

Evidence of guest encapsulation within G8 and G10 dendrimers using NMR techniques

Encapsulation of guest molecules within the interior cavities of dendrimers is promising, but high generation dendrimers show limited encapsulation capacity due to their dense surface shell. Here, for the first time, we prove that high generation polyamidoamine dendrimers, such as generation 8 and generation 10, are able to encapsulate hydrophobic guests using NMR spectroscopy. Guest molecules such as phenylbutazone, dexamethasone sodium phosphate and 9-anthracenecarboxylic acid with molecular weights up to 516 Da are in close proximity to the interior scaffold protons of high generation dendrimers. This encapsulation behavior depends on guest hydrophobicity. Chemical defects and back-folding of terminal groups make it possible for these guest molecules to penetrate through the dense surface shell of high generation dendrimers. These results provide new insights into the host-guest chemistry of dendrimers.

Dendrimer-surfactant interactions

In this article, we reviewed the interactions between dendrimers and surfactants with particular focus on the interaction mechanisms and physicochemical properties of the yielding dendrimer-surfactant aggregates. In order to provide insight into the behavior of dendrimers in biological systems, the interactions of dendrimers with bio-surfactants such as phospholipids in bulk solutions, in solid-supported bilayers and at the interface of phases or solid-states were discussed. Applications of the dendrimer-surfactant aggregates as templates to guide the synthesis of nanoparticles and in drug or gene delivery were also mentioned.

Pharmacoinformatic approaches to understand complexation of dendrimeric nanoparticles with drugs

Nanoparticle based drug delivery systems are gaining popularity due to their wide spectrum advantages over traditional drug delivery systems; among them, dendrimeric nano-vectors are the most widely explored carriers for pharmaceutical and biomedical applications. The precise mechanism of encapsulation of drug molecules inside the dendritic matrix, delivery of drugs into specific cells, interactions of nano-formulation with biological targets and proteins, etc. present a substantial challenge to the scientific understanding of the subject. Computational methods complement experimental techniques in the design and optimization of drug delivery systems, thus minimizing the investment in drug design and development. Significant progress in computer simulations could facilitate an understanding of the precise mechanism of encapsulation of bioactive molecules and their delivery. This review summarizes the pharmacoinformatic studies spanning from quantum chemical calculations to coarse-grained simulations, aimed at providing better insight into dendrimer-drug interactions and the physicochemical parameters influencing the binding and release mechanism of drugs.

Spectroelectrochemical characterization of dendrimer-porphyrin associates at polarized liquid|liquid interfaces

Molecular encapsulation of anionic porphyrins in NH2-terminated polyamidoamine (PAMAM) dendrimers and the interfacial behavior of the dendrimer-porphyrin associates were studied at the polarized water|1,2-dichloroethane (DCE) interface. Formation of the ion associates was significantly dependent on the pH condition and on generation of dendrimers. 5,10,15,20-Tetrakis(4-sulfonatophenyl)porphyrin (ZnTPPS(4-)) associated with the positively charged fourth-generation (G4) PAMAM dendrimer was highly stabilized in acidic aqueous solution without protolytic demetalation in a wide range of pH values (pH > 2). In contrast to the zinc(II) complex, the free base porphyrin (H2TPPS(4-)) was readily protonated under acidic conditions even in the presence of the dendrimers. In addition, the J-aggregates of diprotonated species, (H4TPPS(2-))n, were preferably formed on the dendrimer. The interfacial mechanism of the dendrimer-porphyrin associates was analyzed in detail by potential-modulated fluorescence (PMF) spectroscopy. PMF results indicated that the dendrimers incorporating porphyrin molecules were transferred across the positively polarized water|DCE interface via adsorption step, whereas the transfer responses of the porphyrin ions released from the dendrimers were observed at negatively polarized conditions. A negative shift of the transfer potential of porphyrin ions compared to the intrinsic transfer potential was apparently observed for each ion association system. The ion association stability between the dendrimer and the porphyrin molecules could be estimated from a negative shift of the transfer potential. ZnTPPS(4-) exhibited relatively strong interaction with the higher generation dendrimer, whereas H2TPPS(4-) was less effectively associated with the dendrimers.

Benzylic viologen dendrimers: a review of their synthesis, properties and applications

Dendrimers containing benzylic viologen branching units, their guest complexation, photophysical and biological applications has been reviewed.

Dually functionalized dendrimers by temperature-sensitive surface modification and gold nanoparticle loading for biomedical application

Stimuli-sensitive dendrimers of a new type were developed through dual functionalization of polyamidoamine (PAMAM) dendrimers with temperature-sensitive surface modification using propoxy diethylene glycol (PDEG) and Au nanoparticle (AuNP) loading.