A new colorimetric and fluorimetric sensor for metal cations based on poly(propilene amine) dendrimer modified with 1,8-naphthalimide

A new fluorescent first generation poly(propylene amine) dendrimer (PPI), peripherally modified with 4(butylamino-substituted-1,8-naphthalimide), has been synthesized and characterized. Its photophysical characteristics in organic solvents of different polarities were studied, and the influence of sodium hydroxide on its spectral characteristics in N,N-dimethylformamide is discussed. The complexes formed between the dendrimer and metal cations in solution have been studied with regard to the potential applications of the new dendrimer as a colorimetric and fluorescent sensor for metal ions. The fluorescence intensity of the dendrimer in the presence of metal cations (Zn²⁺, Co²⁺, Pb²⁺, Mn²⁺, Cu²⁺ and Fe³⁺) increases substantially revealing its sensor potential.     

Sensor activity, photodegradation and photostabilisation of a PAMAM dendrimer comprising 1,8-naphthalimide functional groups in its periphery

The colouristic and fluorescent characteristics of a new composite material based on a PAMAM dendrimer of second generation whose periphery is modified with 4-N,N-dimethylaminoethylamino-1,8-naphthalimide and polyamide-6 have been investigated. This dendrimer has been investigated with regard to its application as a heterogenic sensor capable of detecting metal cations and protons in aqueous solutions. In the presence of metal cations (Ni²⁺, Fe²⁺, Fe³⁺ and Co²⁺) and protons the fluorescence intensity of the composite increases due to their coordination with dendrimer molecule. The results obtained reveal the capacity of this system to act as a sensitive sensor of environmental pollution by metal cations and protons. It has been shown that in N,N-dimethylformamide solution the metal cations inhibit the processes of photodegradation of the dendrimer.     

Phase equilibria in liquid crystalline systems based on polypropylenimine dendrimer

The thermodynamic characteristics of infinitely dilute solutions of saturated hydrocarbons in the columnar and isotropic polypropylenimine dendrimer phases were studied by gas chromatography. The contribution of the entropy Gibbs energy component to the solution of sorbates in a liquid crystalline solvent at a positive deviation from ideality was found to be predominant. A phase diagram of the binary system consisting of the dendrimer and nematic p-amyloxy-p′-cyanobiphenyl was constructed. The effect of the chemical nature and shape of component molecules on the mesomorphism of the mixtures is discussed.     

Thermodynamic parameters for the dissolution of n-alkanes and n-alkanols in a liquid-crystalline polypropylenimine dendrimer: A gas-chromatographic study

Thermodynamic parameters for the dissolution of n-alkanes (C₇-C₁₁) and n-alcohols (C₅-C₉) under infinite dilution in the columnar and isotropic phases of a polypropylenimine dendrimer have been determined by inverse gas chromatography. Thermodynamic functions have been investigated as a function of the phase state of a mesogen, the length of alkyl chains of sorbates, and temperature. For the dissolution of low-molecular-mass organic compounds, a higher endothermic effect corresponds to a larger entropy factor with its positive deviation from ideality. The dominant effect of the entropy constituent of the Gibbs energy on the dissolution of sorbates in a high-molecular-mass LC solvent has been revealed. The Rohrschneider constants have been estimated for the stationary phase based on the dendrimer. The experimental data indicate the low polarity of the sorbent that is close to those of phenyl-containing siloxane phases.     

Decomposition of poly(amidoamine) (PAMAM) dendrimers under O2 plasma conditions

Results of FTIR and XPS measurements of bulk and γ-Al₂O₃-supported fourth generation hydroxyl-terminated (G4OH) poly(amidoamine) (PAMAM) dendrimers during O₂ plasma treatment at room temperature indicate that such treatment can effectively decompose the structure of the dendrimer. No new functionalities appear in the dendrimer structure during such treatment, but instead fragmentation of this structure is taking place. The dendrimer backbone likely disintegrates into small molecules (i.e., NO_x, CO, CO₂) which in the case of the supported dendrimers interact with the γ-Al₂O₃ support and form surface nitrate and carboxy species. Subsequent treatment in H₂ at 300 °C leads to the complete removal of the nitrogen-containing species from the surface of γ-Al₂O₃. However, carbon-containing species still remain on the surface in relatively small amounts. Finally, XRD measurements further show that the crystallinity of the support is not affected substantially by the O₂ plasma treatment.     

Rapid Bacterial Recognition over a Wide pH Range by Boronic Acid-Based Ditopic Dendrimer Probes for Gram-Positive Bacteria

We have developed a convenient and selective method for the detection of Gram-positive bacteria using a ditopic poly(amidoamine) (PAMAM) dendrimer probe. The dendrimer that was modified with dipicolylamine (dpa) and phenylboronic acid groups showed selectivity toward Staphylococcus aureus. The ditopic dendrimer system had higher sensitivity and better pH tolerance than the monotopic PAMAM dendrimer probe. We also investigated the mechanisms of various ditopic PAMAM dendrimer probes and found that the selectivity toward Gram-positive bacteria was dependent on a variety of interactions. Supramolecular interactions, such as electrostatic interaction and hydrophobic interaction, per se, did not contribute to the bacterial recognition ability, nor did they improve the selectivity of the ditopic dendrimer system. In contrast, the ditopic PAMAM dendrimer probe that had a phosphate-sensing dpa group and formed a chelate with metal ions showed improved selectivity toward S. aureus. The results suggested that the targeted ditopic PAMAM dendrimer probe showed selectivity toward Gram-positive bacteria. This study is expected to contribute to the elucidation of the interaction between synthetic molecules and bacterial surface. Moreover, our novel method showed potential for the rapid and species-specific recognition of various bacteria.     

Switching the selectivity of a polyglycerol dendrimer monomolecularly imprinted with d-(−)-fructose

A polyglycerol dendrimer monomolecularly imprinted with d-(−)-fructose (Fru) was synthesized. The dendrimer formed adducts with several monosaccharides, Fru, d-(+)-galactose, d-(+)-glucose, d-(+)-mannose, and methyl-α-d-mannopyranoside (MMan), by removal of four water molecules. The dendrimer preferred Fru in the absence of N,N,N′,N′-tetramethyldiaminomethane (TMDAM), whereas it preferred MMan in the presence of TMDAM.     

Norbornene polymerization using multinuclear nickel catalysts based on a polypropyleneimine dendrimer scaffold

Four multinuclear nickel complexes derived from generation 1 (G1) and generation 2 (G2) dendrimeric salicylaldimine ligands based poly(propyleneimine) dendrimer scaffolds of the type, DAB-(NH₂)_n (n = 4 or 8, DAB = diaminobutane) were evaluated as catalysts precursors in the polymerization of norbornene, using methylaluminoxane as co-catalyst. All four catalyst evaluated were found to be active for norbornene polymerization giving polymers with moderate to high molecular weights and low polydispersity indices. The polymerization results indicate that there is some sort of dendritic effect, in that the catalyst activity appears to be influenced by the dendrimer generation.     

Ferrocenylthiosemicarbazones conjugated to a poly(propyleneimine) dendrimer scaffold: Synthesis and in vitro antimalarial activity

First-generation ferrocenylthiosemicarbazone metallodendrimers based on a poly(propyleneimine) dendrimer scaffold were synthesised with ferrocenylthiosemicarbazone moieties conjugated to the periphery of the branched polyamine scaffolds. The compounds were characterised by NMR and IR spectroscopy, elemental analysis and ESI-mass spectrometry. These new complexes were evaluated as bioorganometallic antimalarial agents against the Plasmodium falciparum chloroquine-resistant W2 strain. In vitro antiplasmodial assays of the dendritic ferrocenylthiosemicarbazones against the malaria parasite P. falciparum show increased efficacy compared to the precursor non-conjugated thioesters.     

The influence of the generation number of liquid-crystalline polypropyleneimine dendrimers on the sorption of low-molecular-weight compounds

The thermodynamic characteristics of ultimately dilute solutions of n-alkanes and n-alkanols in columnar and isotropic poly(propyleneimine) dendrimer phases of three generations (G1-G3) were studied by reversed-phase gas chromatography. The influence of the structure of dendrimers and the chemical nature and the size of nonmesogen molecules on their ability to be dissolved in liquid crystalline phases is discussed. It was found that the compatibility of low-molecular-weight compounds with anisotropic phases increased as the number of dendrimer generation grew.     

Poly(amidoamine) dendrimers peripherally modified with 4-ethylamino-1,8-naphthalimide. Synthesis and photophysical properties

New fluorescent poly(amidoamine) (PAMAM) dendrimers, comprising 4-ethylamino-1,8-naphthalmide units on the periphery have been synthesized. Their photophysical properties in organic solvents of different polarity have been determined. The photodegradation of the dendrimers in organic solvents has been investigated. The effect of the coordination of the dendrimer with transition metal cations in N,N-dimethylformamide solution has been discussed.     

Molecular modeling as a promising tool to study dendrimer prodrugs delivery

Molecular modeling methodologies were applied to perform preliminary studies concerning the release of active agents from potentially antichagasic and antileishmanial dendrimer prodrugs. The dendrimer was designed having myo-inositol as a core, l-malic acid as a spacer group, and hydroxymethylnitrofurazone (NFOH), 3-hydroxyflavone or quercetin, as active compounds. Each dendrimer presented a particular behavior concerning to the following investigated properties: spatial hindrance, map of electrostatic potential (MEP), and the lowest unoccupied molecular orbital energy (E_LUMO). Additionally, the findings suggested that the carbonyl group next to the active agent seems to be the most promising ester breaking point.     

Design,synthesis and structure of new dendritic melamines. First use of a tandem C-2-substituted serinol—O,O-masked 4-piperidone as a peripheral unit in iterative synthesis

The iterative chemoselective amination of cyanuric chloride to dimers of new G-2 dendritic N-substituted-2,4,6-triamino-s-triazines (melamines) having C-2-substituted 2-aminopropane-1,3-diols (‘serinols’) in tandem with the ethylene ketal of 4-piperidone as peripheral units is reported. The structure as a function of increasing molecular size was studied by NMR spectroscopy, DFT calculation and AFM imaging. A concise nomenclature defining the restricted rotational phenomena about the newly created C(s-triazine)–N(exocyclic) partial double bonds, seen as axes of (pro)diastereomerism, is used. We propose a new form of frontier rotamerism for the dendrimer surface, which operates over a long range.     

Theory of orientational relaxation of individual specified units in a dendrimer

The theory of orientational relaxation properties of certain individual segments in a dendrimer macromolecule depending on the generation number and the position of a given segment in the dendrimer was developed. The time dependence for the dipole moment after switching an electric field off and the frequency dependence of the permittivity for this segment were calculated, which are determined by the autocorrelation function P ₁ of the average projection of the single element. The dielectric properties of the dendrimer at the random distribution of dipole moments (e.g., as a result of sorption of solvent polar groups on the macromolecule) are considered. The time and frequency dependences of the autocorrelation function P ₂ for the mean squared projection of the single element that are detectable by means of some experimental techniques (NMR, luminescence, birefringence, etc.) were studied. The theory qualitatively agrees with both the computer simulation results on the autocorrelation function P ₁ for the dendrimer macromolecules and the available experimental data on the dependence of orientational mobility for the terminal segments of the number of generations.     

Curcumin Loaded Dendrimers Specifically Reduce Viability of Glioblastoma Cell Lines

Glioblastoma (GB) is a deadly and aggressive cancer of the CNS. Even with extensive resection and chemoradiotherapy, patient survival is still only 15 months. To maintain growth and proliferation, cancer cells require a high oxidative state. Curcumin, a well-known anti-inflammatory antioxidant, is a potential candidate for treatment of GB. To facilitate efficient delivery of therapeutic doses of curcumin into cells, we encapsulated the drug in surface-modified polyamidoamine (PAMAM) dendrimers. We studied the in vitro effectiveness of a traditional PAMAM dendrimer (100% amine surface, G4 NH₂), surface-modified dendrimer (10% amine and 90% hydroxyl-G4 90/10-Cys), and curcumin (Cur)-encapsulated dendrimer (G4 90/10-Cys-Cur) on three species of glioblastoma cell lines: mouse-GL261, rat-F98, and human-U87. Using an MTT assay for cell viability, we found that G4 90/10-Cys-Cur reduced viability of all three glioblastoma cell lines compared to non-cancerous control cells. Under similar conditions, unencapsulated curcumin was not effective, while the non-modified dendrimer (G4 NH₂) caused significant death of both cancerous and normal cells. By harnessing and optimizing the components of PAMAM dendrimers, we are providing a promising new route for delivering cancer therapeutics. Our results with curcumin suggest that antioxidants are good candidates for treating glioblastoma.     

Diffusion and trapping in dendrimer structures

We investigate diffusion on models of large molecules with dendrimer structure. The models we use are topological Cayley trees. We focus on diffusion properties, such as the excursion distance, the mean square displacement of the diffusing particles, and the area probed, as given by the random walk parameter S_N, the number of the distinct sites visited. Finally we look at the trapping kinetics for randomly distributed stationary traps of low concentrations. We use different coordination numbers, z, and different generation orders g of a dendrimer structure. We show that for calculations on dendrimers where we simulate the entire structure the finite size effects dominate making the results worthless. We, therefore, implemented two algorithms that do not retain the underlying structure, and thus effectively the random walk is performed on an equivalent infinite structure. We find a universal linear behavior for all the properties examined, thus differing from the regular lattices. The average displacement R grows linearly with time, implying that R² grows as t² instead of t. The S_N property also grows linearly with time, which resembles the random walk case in three-dimensional lattices, but with a different prefactor which strongly depends on z. Trapping is dependent on S_N, as expected, and follows exactly its behavior. Due to the nature of these structures the random walk is indeed a type of a “biased” walk. We devise a model in which we take out this “bias” factor, and in this model we show that the system becomes diffusive in nature, i.e. the mean square displacement is linear with time. These results could be utilized if one is to design a dendrimer system with specifically desired properties.     

Study of a rigid-chain dendrimer by inverse gas chromatography

A fourth-generation rigid-chain pyridine-containing polyphenylene dendrimer is studied by inverse gas chromatography. Two types of sorbates are investigated: C₇-C₁₁ n-alkanes and C₆H₆-C₆H₅C₅H₁₁ alkylbenzenes. In the range 35−150°C, specific retention volumes of the indicated sorbates are measured and their solubility coefficients are calculated. It is shown that aliphatic sorbates exhibit reduced solubility coefficients in the aromatic dendrimer compared to those observed for aliphatic polymers and the earlier studied carbosilane dendrimer. At the same time, alkylbenzenes are characterized by enhanced solubility coefficients and this effect is more pronounced for the first members of the homologous series. An analysis of excess partial molar thermodynamic functions shows that π-electron interactions in the dendrimer and among dendrimer and aromatic sorbates are responsible for the thermodynamic properties of the dendrimer under study.     

Valence isomerization in dendrimers by photo-induced electron transfer and energy transfer from the dendrimer backbone to the core

A series of poly(aryl ether) dendrimers with a norbornadiene (NBD) group attaching to the core (Gn-NBD), generations 1–4, were synthesized and characterized, and their photophysical and photochemical properties were examined. The fluorescence of the dendrimer backbone is quenched by the norbornadiene group as a result of the electron transfer and energy transfer from the dendrimer backbone to the norbornadiene group in Gn-NBD. Selective excitation of the dendrimer backbone results in an isomerization of the norbornadiene group to the quadricyclane (QC) group. The intramolecular electron transfer and energy transfer efficiencies are ca. 0.93, 0.73, 0.54, 0.30 in dichloromethane, and ca. 0.90, 0.70, 0.55, 0.34 in tetrahydrofuran for generations 1–4, respectively, with the rate constant ca. 10¹⁰ s⁻¹. The light-harvesting ability of these dendritic molecules is demonstrated by the enhanced valence isomerization rate of NBD to QC with increasing generation.     

Thermodynamics of the sorption of organic vapors in a carbosilane dendrimer and a hyperbranched polymer

Fluorinated derivatives of the carbosilane G6 dendrimer and the hyperbranched polymer of the same chemical structure are synthesized and characterized via the method of inverse gas chromatography. For various organic compounds (n-alkanes, aromatic hydrocarbons, partially fluorinated and perfluorinated organic compounds), the following thermodynamic parameters of their interaction with the above polymers are defined: solubility coefficient S, the sorption enthalpy, the partial molar enthalpy of mixing, the Flory-Huggins parameter, and the solubility parameter. The thermodynamic behavior of vapors in the dendrimer is similar to that in the hyperbranched polymer. For a dendrimer and a hyperbranched polymer, a linear correlation between the logarithm of S and T _cr ² is established, where T _cr is the critical temperature of a probe. For both polymers, the partial enthalpy of mixing of n-alkanes is shown to be independent of the dimensions of the probe molecules. This behavior is typical of the vapor sorption in linear polymers at temperatures above the glass transition temperature.     

A third generation chiral phosphorus-containing dendrimer as ligand in Pd-catalyzed asymmetric allylic alkylation

The synthesis of a third generation phosphorus-containing dendrimer possessing 24 chiral iminophosphine end groups derived from (2S)-2-amino-1-(diphenylphosphinyl)-3-methylbutane is described. In situ complexation of this dendrimer by [Pd(η³-C₃H₅)Cl]₂ affords a catalyst, which is used in asymmetric allylic alkylations of rac-(E)-diphenyl-2-propenyl acetate and pivalate. The percentage of conversion, the yield of isolated 2-(1,3-diphenylallyl)-malonic acid dimethyl ester, and its enantiomeric excess have been measured in each case, and were found to be good to very good (ee from 90% to 95%). Furthermore, the dendritic catalyst can be recovered and reused at least two times, with almost the same efficiency.