Structural deviations in poly(amidoamine) dendrimers: a MALDI-TOF MS analysis

Mass spectrometry of dendrimers

Mass spectrometry (MS) has become an essential technique to characterize dendrimers as it proved efficient at tackling analytical challenges raised by their peculiar onion-like structure. Owing to their chemical diversity, this review covers benefits of MS methods as a function of dendrimer classes, discussing advantages and limitations of ionization techniques, tandem mass spectrometry (MS/MS) strategies to determine the structure of defective species, as well as most recently demonstrated capabilities of ion mobility spectrometry (IMS) in the field. Complementarily, the well-defined structure of these macromolecules offers major advantages in the development of MS-based method, as reported in a second section reviewing uses of dendrimers as MS and IMS calibration standards and as multifunctional charge inversion reagents in gas phase ion/ion reactions.

Synthesis of β-Cyclodextrin-Decorated Dendritic Compounds Based on EDTA Core: A New Class of PAMAM Dendrimer Analogs

In this work, two dendritic molecules containing an ethylenediaminetetraacetic acid (EDTA) core decorated with two and four β-cyclodextrin (βCD) units were synthesized and fully characterized. Copper(I)-catalyzed alkyne-azide cycloaddition (CuAAC) click chemistry under microwave irradiation was used to obtain the target compounds with yields up to 99%. The classical ethylenediamine (EDA) core present in PAMAM dendrimers was replaced by an EDTA core, obtaining platforms that increase the water solubility at least 80 times compared with native βCD. The synthetic methodology presented here represents a convenient alternative for the rapid and efficient construction of PAMAM analogs. These molecules are envisaged for future applications as drug carriers.

Dendrimers as Antiamyloid Agents

Dendrimer-protein conjugates have significant prospects for biological applications. The complexation changes the biophysical behavior of both proteins and dendrimers. The dendrimers could influence the secondary structure of proteins, zeta-potential, distribution of charged regions on the surface, the protein-protein interactions, etc. These changes offer significant possibilities for the application of these features in nanotheranostics and biomedicine. Based on the dendrimer-protein interactions, several therapeutic applications of dendrimers have emerged. Thus, the formation of stable complexes retains the disordered proteins on the aggregation, which is especially important in neurodegenerative diseases. To clarify the origin of these properties and assess the efficiency of action, the mechanism of protein-dendrimer interaction and the nature and driving force of binding are considered in this review. The review outlines the antiamyloid activity of dendrimers and discusses the effect of dendrimer structures and external factors on their antiamyloid properties.

Investigating the properties of L-lysine dendrimers through physico-chemical characterisation techniques and atomistic molecular dynamics simulations

Poly(L-lysine) (PLL) dendrimers up to generation 6, both as their ammonium trifluoroacetate salts and their boc-protected intermediates were characterised using multi-detector size exclusion chromatography (MD-SEC) and Taylor dispersion analysis (TDA)...

The advanced synthetic modifications and applications of multifunctional PAMAM dendritic composites

The profound advances in dendrimer chemistry have led to new horizons in polymer science.

Synthesis and use of an amphiphilic dendrimer for siRNA delivery into primary immune cells

Using siRNAs to genetically manipulate immune cells is important to both basic immunological studies and therapeutic applications. However, siRNA delivery is challenging because primary immune cells are often sensitive to the delivery materials and generate immune responses. We have recently developed an amphiphilic dendrimer that is able to deliver siRNA to a variety of cells, including primary immune cells. We provide here a protocol for the synthesis of this dendrimer, as well as siRNA delivery to immune cells such as primary T and B cells, natural killer cells, macrophages, and primary microglia. The dendrimer synthesis entails straightforward click coupling followed by an amidation reaction, and the siRNA delivery protocol requires simple mixing of the siRNA and dendrimer in buffer, with subsequent application to the primary immune cells to achieve effective and functional siRNA delivery. This dendrimer-mediated siRNA delivery largely outperforms the standard electroporation technique, opening a new avenue for functional and therapeutic studies of the immune system. The whole protocol encompasses the dendrimer synthesis, which takes 10 days; the primary immune cell preparation, which takes 3-10 d, depending on the tissue source and cell type; the dendrimer-mediated siRNA delivery; and subsequent functional assays, which take an additional 3-6 d.

Micellar Nanocarriers from Dendritic Macromolecules Containing Fluorescent Coumarin Moieties

The design of efficient drug-delivery vehicles remains a big challenge in materials science. Herein, we describe a novel class of amphiphilic hybrid dendrimers that consist of a poly(amidoamine) (PAMAM) dendritic core functionalized with bisMPA dendrons bearing cholesterol and coumarin moieties. Their self-assembly behavior both in bulk and in water was investigated. All dendrimers exhibited smectic A or hexagonal columnar liquid crystal organizations, depending on the generation of the dendrimer. In water, these dendrimers self-assembled to form stable spherical micelles that could encapsulate Nile Red, a hydrophobic model compound. The cell viability in vitro of the micelles was studied in HeLa cell line, and proved to be non-toxic up to 72 h of incubation. Therefore, these spherical micelles allow the encapsulation of hydrophobic molecules, and at the same time provided fluorescent traceability due to the presence of coumarin units in their chemical structure, demonstrating the potential of these dendrimers as nanocarriers for drug-delivery applications.

Efficient modification of PAMAM G1 dendrimer surface with β-cyclodextrin units by CuAAC: impact on the water solubility and cytotoxicity

The toxicity of the poly(amidoamine) dendrimers (PAMAM) caused by the peripheral amino groups has been a limitation for their use as drug carriers in clinical applications. In this work, we completely modified the periphery of PAMAM dendrimer generation 1 (PAMAM G1) with β-cyclodextrin (β-CD) units through the Cu(i)-catalyzed azide–alkyne cycloaddition (CuAAC) to obtain the PAMAM G1-β-CD dendrimer with high yield. The PAMAM G1-β-CD was characterized by ¹H- and ¹³C-NMR and mass spectrometry studies. Moreover, the PAMAM G1-β-CD dendrimer showed remarkably higher water solubility than native β-CD. Finally, we studied the toxicity of PAMAM G1-β-CD dendrimer in four different cell lines, human breast cancer cells (MCF-7 and MDA-MB-231), human cervical adenocarcinoma cancer cells (HeLa) and pig kidney epithelial cells (LLC-PK1). The PAMAM G1-β-CD dendrimer did not present any cytotoxicity in cell lines tested which shows the potentiality of this new class of dendrimers.

The toxicity of the poly(amidoamine) dendrimers (PAMAM) caused by the peripheral amino groups has been a limitation for their use as drug carriers in clinical applications.

Separation, characterization and identification of microplastics and nanoplastics in the environment

Microplastics (MPs) have globally been detected in aquatic and marine environments, which has raised scientific interests and public health concerns during the past decade. MPs are those polymeric particles with at least one dimension <5 mm. MPs possess complex physicochemical properties that vary their mobility, bioavailability and toxicity toward organisms and interactions with their surrounding pollutants. Similar to nanomaterials and nanoparticles, accurate and reliable detection and measurement of MPs or nanoplastics and their characteristics are important to warrant a comprehensive understanding of their environmental and ecological impacts. This review elaborates the principles and applications of diverse analytical instruments or techniques for separation, characterization and quantification of MPs in the environment. The strength and weakness of different instrumental methods in separation, morphological, physical classification, chemical characterization and quantification for MPs are critically compared and analyzed. There is a demand for standardized experimental procedures and characterization analysis due to the complex transformation, cross-contamination and heterogeneous properties of MPs in size and chemical compositions. Moreover, this review highlights emerging and promising characterization techniques that may have been overlooked by research communities to study MPs. The future research efforts may need to develop and implement new analytical tools and combinations of hyphenated technologies to complement respective limitations of detection and yield reliable characterization information for MPs. The goal of this critical review is to facilitate the research of plastic particles and pollutants in the environment and understanding of their environmental and human health effects.

Synthesis of Stimuli-Responsive Heterofunctional Dendrimer by Passerini Multicomponent Reaction

We report the synthesis of a structurally diverse amphiphilic dendrimer with oxidation and ultraviolet light-sensitive groups incorporated in the dendrimer interior. Convergent synthesis is utilized by reacting branched repeating units with a nonbranched functional molecule by two synthetic strategies, Passerini multicomponent reaction and azide-alkyne cycloaddition reaction. The periphery of dendrimer was functionalized by methoxy poly(ethylene glycol) to obtain a dendrimer with a hydrophobic core and hydrophilic peripheral chains. The G2-PEG dendrimer characterized by NMR, GPC, and MALDI-TOF MS for structural integrity and oxidation- and photo-triggered degradations of the G2-PEG dendrimer was investigated. The self-assembled morphology of the dendrimer in the presence of organic dye was also investigated by TEM and DLS analyses, together with dissipative particle dynamics simulation. The encapsulation of dye molecules in self-assembled nanospheres of the dendrimer and their responsive releases, triggered by the efficient disassembly of a dendrimer, have been demonstrated.

Evaluation of cellular and transcriptional targeting of breast cancer stem cells via anti-HER2 nanobody conjugated PAMAM dendrimers

According to the cancer stem cell (CSC) theory, a small subset of cells with stem cell-like characteristics is responsible for tumor initiation, progression, and recurrence. CD44⁺/CD24^- phenotype is assumed to be one of the main characteristics of the breast CSCs. We developed an MDA-MB-231 cell line overexpressing cell surface HER2 antigen for the evaluation of targeting efficiency of anti-HER2 nanobody (Nb)-conjugated polyamidoamine (PAMAM) polyplexes. Apoptosis-inducing tBid gene under control of CXCR1 promoter was delivered by this nanoparticle. Cellular uptake study showed higher uptake of Nb-targeted PAMAM carriers compared to non-targeted nanoparticles after 6 h of incubation. Gene expression analysis showed a significant rise in the expression of tBid in both MDA-MB-231/HER2⁺ and MDA-MB-231 compared to the two other cell lines. The same effect was observed after transfection with Nb-conjugated polyplexes within MDA-MB-231/HER2⁺ cell line compared to non-conjugated PAMAM polyplexes. We confirmed the killing efficiency of the gene construct in both MDA-MB-231/HER2⁺ and MDA-MB-231 cell lines by caspase 3 activity assay. These findings suggest that imposing pre-entry and post-entry restrictions on tBid killer gene might be a promising approach to specifically target the breast CSCs.

Perspectives on dendritic architectures and their biological applications: From core to cell

The challenges of medicine today include the increasing stipulation for sensitive and effective systems that can improve the pathological responses with a simultaneous reduction in accumulation and drug side effects. The demand can be fulfilled through the advancements in nanomedicine that includes nanostructures and nanodevices for diagnosing, treating, and prevention of various diseases. In this respect, the nanoscience provides various novel techniques with carriers such as micelles, dendrimers, particles and vesicles for the transportation of active moieties. Further, an efficient way to improve these systems is through stimuli a responsive system that utilizes supramolecular hyperbranched structures to meet the above criteria. The stimuli-responsive dendritic architectures exhibit spatial, temporal, convenient, effective, safety and controlled drug release in response to specific trigger through electrostatic interactions plus π stacking. The stimuli-responsive systems are capable of sequestering the drug molecules underneath a predefined set of conditions and discharge them in a different environment through either exogenous or endogenous stimulus. The incorporation of photoresponsive moieties at various components of dendrimer such as core, branches or at the peripheral end exaggerates its significance in various allied fields of nanotechnology which includes sensors, photoswitch, electronic widgets and in drug delivery systems. This is due to the light instigated geometrical modifications at the core or at the surface molecules which generates huge conformational changes throughout the hyperbranched structure. Further, numerous synthetic methodologies have been investigated for utilization of dendrimers in therapeutic drug delivery and its applicability towards stimuli responsive systems such as photo-instigated, thermal-instigated, and pH-instigated hyperbranched structures and their advancement in the field of nanomedicine. This paper highlights the fascinating theoretical advances and principal mechanisms of dendrimer synthesis and their ability to capture light that strengthens its applicability from radiant energy to medical photonics.

Detecting the Formation and Transformation of Oligomers during Insulin Fibrillation by a Dendrimer Conjugated with Aggregation-Induced Emission Molecule

The fibrillation of protein is harmful and impedes the use of protein drugs. It also relates to various debilitating diseases such as Alzheimer's diseases. Thus, investigating the protein fibrillation process is necessary. In this study, poly(amido amine) dendrimers (PAMAM) of generation 3 (G3) and generation 4 (G4) were synthesized and conjugated with 4-aminobiphenyl, an aggregation-induced emission (AIE) moiety, at varied grafting ratios. Among them, one fluorescence probe named G3-biph-3 that was grafted average 3.25 4-aminobiphenyl to the G3, can detect the transformations both from native insulin to oligomers and from oligomers to fibrils. The size difference of native insulin, oligomers, and fibrils was proposed to be the main factor leading to the detection of the above transformations. Different molecular weights of sodium polyacrylate (PAAS) were also applied as a model to interact with G3-biph-3 to further reveal the mechanism. The results indicated that PAMAM with a certain generation and grafted with appropriate AIE groups can detect the oligomer formation and transformation during the insulin fibrillation process.

In vitro and in vivo uptake studies of PAMAM G4.5 dendrimers in breast cancer

Background

Breast cancer is the second leading cause of cancer death worldwide. Nanotechnology approaches can overcome the side effects of chemotherapy as well as improve the efficacy of drugs. Dendrimers are nanometric size polymers which are suitable as drug delivery systems. To the best of our knowledge, studies on the application of PAMAM G4.5 (polyamidoamine half generation 4) dendrimers as potential drug delivery systems in breast cancer have not been reported. In this work we developed a PAMAM G4.5 dendrimer containing FITC (fluorescein isothiocyanate) dye to study their uptake by murine breast cancer cells and BALB/c mice breast tumors.

Results

We performed a reaction between FITC and PAMAM G4.5 dendrimers which were previously derivatized with piperazine (linker molecule), characterized them by ¹H NMR (proton nuclear magnetic resonance) spectroscopy and MALDI-TOF (matrix-assisted laser desorption/ionization- time-of-flight) mass spectrometry. The experimental data indicated that 2 FITC molecules could be bound covalently at the PAMAM G4.5 dendrimer surface, with 17 FITC molecules probably occluded in PAMAM dendrimers cavity. PAMAM-FITC dendrimer (PAMAM G4.5-piperazinyl-FITC dendrimer) size distribution was evaluated by DLS (dynamic light scattering) and TEM (transmission electron microscopy). The nanoparticle hydrodynamic size was 96.3 ± 1.4 nm with a PdI (polydispersion index) of 0.0296 ± 0.0171, and the size distribution measured by TEM was 44.2 ± 9.2 nm. PAMAM-FITC dendrimers were neither cytotoxic in 4T1 cells nor hemolytic up to 24 h of incubation. In addition, they were uptaken in vitro by 4T1 cells and in vivo by BALB/c mice breast tumors. PAMAM G4.5-piperazinyl-FITC dendrimer intracellular distribution was observed through histologic analysis of the tumor by laser confocal microscopy.

Conclusion

These results indicate that PAMAM G4.5 dendrimers enter tumor tissue cells, being good candidates to be used as antitumor drug delivery systems for breast cancer treatment and diagnosis.

Solventless synthesis of Ru(0) composites stabilized with polyphosphorhydrazone (PPH) dendrons and their use in catalysis

Ruthenium is in the air: small Ru NPs are obtained by milling RuCl₃, NaBH₄ and polyphosphorhydrazone dendrons under air. The whole dendron structure is involved in the stabilization process. These NPs catalyze the selective hydrogenation of styrene.

Generation 3 PAMAM dendrimer TAMRA conjugates containing precise dye/dendrimer ratios

The synthesis, isolation, and characterization of generation 3 poly(amidoamine) (G3 PAMAM) dendrimer containing precise ratios of 5-carboxytetramethylrhodamine succinimidyl ester (TAMRA) dye (n = 1-3) per polymer particle are reported. Stochastic conjugation of TAMRA dye to the dendrimer was followed by separation into precise dye-polymer ratios using rp-HPLC. The isolated materials were characterized by rp-UPLC, MALDI-TOF-MS, and 1H NMR spectroscopy, UV-vis, and fluorescence spectroscopies.

Multivalent polymers for drug delivery and imaging: the challenges of conjugation

Multivalent polymers offer a powerful opportunity to develop theranostic materials on the size scale of proteins that can provide targeting, imaging, and therapeutic functionality. Achieving this goal requires the presence of multiple targeting molecules, dyes, and/or drugs on the polymer scaffold. This critical review examines the synthetic, analytical, and functional challenges associated with the heterogeneity introduced by conjugation reactions as well as polymer scaffold design. First, approaches to making multivalent polymer conjugations are discussed followed by an analysis of materials that have shown particular promise biologically. Challenges in characterizing the mixed ligand distributions and the impact of these distributions on biological applications are then discussed. Where possible, molecular-level interpretations are provided for the structures that give rise to the functional ligand and molecular weight distributions present in the polymer scaffolds. Lastly, recent strategies employed for overcoming or minimizing the presence of ligand distributions are discussed. This review focuses on multivalent polymer scaffolds where average stoichiometry and/or the distribution of products have been characterized by at least one experimental technique. Key illustrative examples are provided for scaffolds that have been carried forward to in vitro and in vivo testing with significant biological results.

Advantages of monodisperse and chemically robust "SpheriCal" polyester dendrimers as a "universal" MS calibrant

The utilization of dendrimer calibrants as an alternative to peptides and proteins for high mass calibration is explored. These synthetic macromolecules exhibited a number of attractive advantages, including exceptional shelf-lives, broad compatibility with a wide range of matrices and solvents, and evenly spaced calibration masses across the mass range examined, 700-30,000 u. The exceptional purity of these dendrimers and the technical simplicity of this calibration platform validate their broad relevance for high molecular weight mass spectrometry.

Carboxymethyl chitosan-poly(amidoamine) dendrimer core-shell nanoparticles for intracellular lysozyme delivery

Intracellular delivery of native, active proteins is challenging due to the fragility of most proteins. Herein, a novel polymer/protein polyion complex (PIC) nanoparticle with core-shell structure was prepared. Carboxymethyl chitosan-grafted-terminal carboxyl group-poly(amidoamine) (CM-chitosan-PAMAM) dendrimers were synthesized by amidation and saponification reactions. (1)H NMR was used to characterize CM-chitosan-PAMAM dendrimers. The TEM images and results of lysozyme loading efficiency indicated that CM-chitosan-PAMAM dendrimers could self-assemble into core-shell nanoparticles, and lysozyme was efficiently encapsulated inside the core of CM-chitosan-PAMAM dendrimer nanoparticles. Activity of lysozyme was completely inhibited by CM-chitosan-PAMAM Dendrimers at physiological pH, whereas it was released into the medium and exhibited a significant enzymatic activity in an acidic intracellular environment. Moreover, the CM-chitosan-PAMAM dendrimer nanoparticles did not exhibit significant cytotoxicity in the range of concentrations below 3.16 mg/ml. The results indicated that these CM-chitosan-PAMAM dendrimers have excellent properties as highly potent and non-toxic intracellular protein carriers, which would create opportunities for novel applications in protein delivery.

Quantitative analysis of generation and branch defects in G5 poly(amidoamine) dendrimer

Although methods have been developed to synthesize and isolate generation 5 (G5) PAMAM dendrimers containing precise numbers of ligands per polymer particle, the presence of skeletal and generational defects in this material can substantially hamper the process. Here we provide a quantitative analysis of G5 PAMAM dendrimer defects via high performance liquid chromatography, potentiometric titration, mass spectrometry, size exclusion chromatography, and nuclear magnetic resonance. We identified, isolated, and characterized the major structural defects of G5 dendrimer, trailing generations, and dimer, trimer, and tetramer species. We determine that the G5 material present in the as-received mixture contains 93 arms on average. We have developed two model systems capable of generating the experimentally observed mass range and polydispersity at defect rates of 8-15%.

Traveling wave ion mobility mass spectrometry study of low generation polyamidoamine dendrimers

We reported the use of ion mobility (IM) combined with mass spectrometry (MS) as an analytical tool to investigate low generation polyamidoanine (PAMAM) dendrimers. This analytical approach has been employed to separate ions of defective structures with different charge state but exactly the same m/z value. Tandem mass spectrometry (MS/MS) after IM separation allowed a comprehensive structural characterization of defective dendrimers. In addition, IM was used to evaluate the collision cross-sections of ions of perfect dendrimers. They showed a good correlation with calculated collision cross-sections obtained by the trajectory method (TM) and were also consistent with dimensions reported by other established analytical methods.

Serum tolerance and endosomal escape capacity of histidine-modified pDNA-loaded complexes based on polyamidoamine dendrimer derivatives

Aiming to aid polyamidoamine (PAMAM, generation 4, PG4) to overcome gene delivery barriers like extrinsic serum inhibition, intrinsic cytotoxicity and lysosome digestion, histidine motifs modified PAMAM was prepared. The histidine activated PAMAM generation 4 (HPG4) was synthesized via aminolysis reaction and characterized by 1H NMR spectrum and MALDI-TOF-MS. Cytotoxicity profiles of HPG4 on MD-MB-231 cells were significantly improved in the form of polymer and polymer/DNA complexes comparing to PG4. The luciferase protein expression level of HPG4 was 20-, 2.7- and 1.2- fold higher than that of PG4, SuperFect and PEI 25k. Most importantly, flow cytometry and gene transfection studies showed that histidine motifs of HPG4 not only acted as enhancer for faster cellular uptake, but also played an important role on enhancing serum tolerance of the system on cellular uptake and transfection. Among the serum concentrations of 10%-50%, HPG4 showed 10-100 folds higher transfection efficiency than PG4. Intracellular fate observation conducted by confocal microscope provided visual and quantitative evidence that endsomal escape efficiency of HPG4 system was higher than that of PG4. Lastly, the endosomal escape mechanism of HPG4 system was analyzed by endosome destabilization and proton pump inhibition treatment. Collectively, compared to PG4/pDNA, HPG4/pDNA showed improvement on cellular uptake, serum tolerance, cytotoxicity profile, and endosomal escape.

Best practices for purification and characterization of PAMAM dendrimer

Poly(amidoamine) (PAMAM) dendrimer are branched polymers with low degrees of heterogeneity. Current synthesis methods, however, result in substantial batch variability. We present our optimized procedure for post-synthesis (and post-market) purification of a generation 5 PAMAM dendrimer by membrane dialysis and demonstrate its effectiveness and limitations using a representative lot of biomedical grade dendrimer. This method successfully removes trailing generation defect structures, thereby reducing the heterogeneity of the material (PDI reduced from 1.04 to 1.02). Optimized analytical techniques to characterize the unpurified and purified dendrimer are also detailed. The efficiency of the purification method is successfully monitored by these analytics and dendrimer parameters that are critical for subsequent modification reactions and biological evaluation (M(n), M(w), PDI, average number of end groups) obtained. To provide better definition of the variability that should be expected between lots of synthesized material, HPLC traces for three additional commercial lots of dendrimer are also presented.

Stability, antimicrobial activity, and cytotoxicity of poly(amidoamine) dendrimers on titanium substrates

In this article, we present the first report on the antibacterial activity and cytotoxicity of poly(amidoamine) (PAMAM) dendrimers immobilized on three types of titanium-based substrates with and without calcium phosphate coating. We show that the amino-terminated PAMAM dendrimers modified with various percentages (0-60%) of poly(ethylene glycol) (PEG) strongly adsorbed on the titanium-based substrates. The resultant dendrimer films effectively inhibited the colonization of the Gram-negative bacteria Pseudomonas aeruginosa (strain PAO1) and, to a lesser extent, the Gram-positive bacteria Staphylococcus aureus (SA). The antibacterial activity of the films was maintained even after storage of the samples in PBS for up to 30 days. In addition, the dendrimer films had a low cytotoxicity to human bone mesenchymal stem cells (hMSCs) and did not alter the osteoblast gene expression promoted by the calcium phosphate coating.

Studies of gas-phase reactions of cationic iron complexes of 2-pyrimidinyloxy-N-arylbenzylamines by electrospray ionization tandem mass spectrometry

Electrospray ionization triple quadrupole mass spectrometry (ESI-TSQ-MS) and electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS) were used to investigate the interesting gas-phase reactions of the cationic iron (Fe) complexes of 2-pyrimidinyloxy-N-arylbenzylamines (1-6), which are generated by ESI when mixing their methanolic solutions. Further studies of these Fe complexes by collision-induced dissociation (CID) show that Fe(III) complexes undergo an interesting gas-phase single electron transfer (SET) reaction to give 1(•+) -6(•+) ,with loss of neutral FeCl(2) , whereas Fe(II) can catalyze gas-phase Smiles rearrangement reactions of compounds 1-6. By using different Fe(II)X(2) salts (X = Cl or Br) with a set of reactants, the role of the counterion (X(-) ) and the structure effect of the reactants on Fe(II)-catalyzed gas-phase Smiles rearrangement reactions are studied. Evidence obtained from by TSQ-MS and FTICR-MS experiments, hydrogen/deuterium (H/D) exchange experiments and theoretical computations supported some unique gas-phase chemistries initiated by introduction of Fe(II) into 1. Importantly, by comparing the distinct gas-phase reaction results of the cationic Fe(III) complexes with those of Fe(II) complexes, the charge state effects of iron on the gas-phase chemistries of Fe complexes are revealed.

Characterization of nanoparticles by matrix assisted laser desorption ionization time-of-flight mass spectrometry

Determining the molecular weight of nanoparticles can be challenging. The molecular weight characterization of dendrimers, for example, with varying covalent and noncovalent modifications is critical to their use as therapeutics. As such, we describe in this chapter a protocol for the analysis of these molecules by matrix assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS).