Generation Polyamidoamine Research Articles

Ferrocene-modified dendrimers as support of copper nanoparticles: evaluation of the catalytic activity for the decomposition of ammonium perchlorate

Ferrocene (Fc)-based systems are frequently used as burning rate catalysts in the decomposition of ammonium perchlorate (AP)-based propellants. However, small Fc derivatives migrate to the surface of the propellant resulting in undesirable changes in the designed burning parameters and unstable combustion. To retard the migration and to increase the combustion rate of AP, fourth-generation polyamidoamine (PAMAM) dendrimers modified with Fc (PAMAM generation 4 [G4]-Fc) were synthetized and used as support for the obtention of copper nanoparticles (CuNPs). PAMAM G4 produced smaller nanoparticles (1–2 nm) with lower aggregation than PAMAM G4-Fc (12–14 nm). X-ray photoelectron spectroscopy (XPS) characterization confirmed the superior stabilizing and protecting effect against oxidation of CuNPs by PAMAM G4 in comparison to PAMAM G4-Fc, whereas molecular dynamics simulations have shown less flexibility and lower presence of stabilizing sites for nanoparticles in PAMAM G4-Fc. Antimigration tests confirmed the negligible migration of PAMAM G4-Fc compared with Fc, whereas PAMAM G4-Fc|CuNP affected the high-temperature decomposition of AP positively, decreasing the decomposition temperature in 87 °C owing to a synergistic effect between CuNPs and Fc. PAMAM G4-Fc can act both as an effective antimigration system of Fc and as a stabilizing framework of metal nanoparticles with application as catalysts of AP.

Nonviral gene delivery using PAMAM dendrimer conjugated with the nuclear localization signal peptide derived from human papillomavirus type 11 E2 protein

Polyamidoamine (PAMAM) dendrimers are biocompatible polymers utilized in multiple biomedical applications including tissue engineering, medical diagnosis, drug and gene delivery systems, and biosensors. Normally, high-generation PAMAM dendrimers are advantageous for use in gene therapy research because they have a relatively high transfection efficiency. A high-generation PAMAM dendrimer has a high charge density, which induces greater damage to the membranous organelles than that induced by a low-generation PAMAM dendrimer. In this study, we added NLS sequences derived from the human papillomavirus (HPV) type 11 E2 protein to the low-generation PAMAM generation 2 (PAMAM G2) dendrimer and simultaneously introduced histidine residues to reduce cytotoxicity. RKRARH-PAMAM G2 showed similar and high transfection efficiencies in Neuro-2A and NIH3T3 cell lines and relatively low cytotoxicities relative to that of polyethylenimine 25 kDa (PEI 25 kDa).

Low generation polyamidoamine dendrimers (PAMAM) and biotin-PAMAM conjugate – the detailed structural studies by 1H and 13C nuclear magnetic resonance spectroscopy

Introduction. The concept of targeted drug delivery is nowadays based on nanoparticle transporters. Such drug delivery systems for cancer cells should follow the requirements like: efficient drug release, selective binding and internalization to cancer cells. The anticancer drug selectivity can be achieved by attachment of cancer cell-recognizing molecules, like biotin. Among nanosized carriers the PAMAM dendrimers are tested intensely, especially they can be modified by covalent attachment of prodrug molecules and biotin as targeting molecule. Aim. We aimed at construction and characterization of a conjugate formed between PAMAM and biotin (Biot). The nuclear magnetic resonances is powerful tool to determine both the structure and stoichiometry of the conjugate. Material and methods. PAMAM G0 has been synthesized and functionalized with biotin by reaction with N-hydroxysuccinimide ester of biotin to obtain G0 double-substituted with biotin. All the compound were thoroughly characterized by the NMR spectroscopy. Results. The conjugate of PAMAM G0 dendrimer with two amide-bonded biotin molecules was obtained and fully characterized by NMR spectroscopy. Conclusion. N-hydroxysuccinimide ester of biotin spontaneously reacts with PAMAM G0 to obtain the conjugate of 2:1 biotin: G0 stoichiometry. The latter was designed as a targeting molecule in formation of megameric multidrug delivery system.

Multicompartment dendrimicelles with binary, ternary and quaternary core composition.

Hierarchically built-up multicompartment nanoaggregate systems are of interest for, e.g., novel materials and medicine. Here we present a versatile strategy to generate and unambiguously characterize complex coacervate-core micelles by exploiting four different dendrimeric subcomponents as core-units. The resulting mesoscale structures have a hydrodynamic diameter of 50 nm and a core size of 33 nm, and host about thirty 6th generation polyamidoamine (PAMAM) dendrimers. We have used FRET (efficiency of ∼0.2) between fluorescein and rhodamine moieties immobilized on separate PAMAM dendrimers (G6-F and G6-R, respectively) to prove synchronous encapsulation in the micelle core. Tuning the proximity of the FRET pair molecules either by varying the G6-F : G6-R ratio, or by co-assembling non-functionalized dendrimer (G6-E) in the core, reveals the optimal FRET efficiency to occur at a minimum of 70% loading with G6-F and G6-R. Additional co-encapsulation of 6th generation gold dendrimer-encapsulated nanoparticles (G6-Au) in the micelle core shows a dramatic reduction of the FRET efficiency, which can be restored by chemical etching of the gold nanoparticles from within the micellar core with thiols, leaving the micelle itself intact. This study reveals the controlled co-assembly of up to four different types of subcomponents in one single micellar core and concomitantly shows the wide variety of structures that can be made with a well-defined basic set of subcomponents. It is straightforward to design related strategies, to incorporate inside one micellar core, e.g., even more than 4 different dendrimers, or other classes of (macro)molecules, with different functional groups, other FRET pairs or different encapsulated metal nanoparticles.

Synthesis of Generation-2 polyamidoamine based ionic liquid: Efficient dendrimer based catalytic green fuel production from yellow grease

A new series of acidic, dendrimeric polyamidoamine based polymeric ionic liquids of [PAMAM3256Cn] were synthesized with a second generation polyamidoamine dendrimer, alkyl bromides and 1, 3-propane sultone via a two-step procedure. The structure of functional ionic liquids was characterized by Fourier-transform infrared spectroscopy, nuclear magnetic resonance spectroscopy. The polyamidoamine -1- dodecyl [PAMAM3256C12] catalyst was used for green fuel production via the transesterification of yellow grease. The influence of reaction variables on the green fuel yield was studied using this catalyst. The catalyst was effective having achieved a 93% green fuel yield from yellow grease after 6 h of reaction at 65 °C, using 306.8 mol (10 mmol) (wt % based on molar concentration of lipids) of [PAMAM3256C12] catalyst, a yellow grease-to-methanol molar ratio of 1:20 with a constant agitation speed 800 rpm. The catalyst was showed excellent stability for yellow grease transesterification over four cycles. Additionally, catalysts showed excellent transesterification activity of Jatropha curcas, Ricinus communis, and Pistacia chinensis oil, with green fuel yields of 90, 91, and 92%, respectively. The properties of green fuel were met the ASTM D6751-02 standards. Results indicate that the [PAMAM3256C12] catalyst system shows promising potential as a viable industrial-scale alternative.

Remineralization of dentine tubules induced by phosphate-terminated PAMAM dendrimers

Various sealants have been developed to treat the exposure of dentinal tubules (DTs) and further dental hypersensitivity. Herein, the phosphate-terminated fourth generation polyamidoamine dendrimers (PAMAM-PO3H2) was successfully synthesized. Six duplicates of demineralized dentin and type I collagen matrix were incubated in artificial saliva solution with or without PAMAM-PO3H2 treatment at 37 °C for 2 weeks, respectively. The artificial saliva solution was replaced every day. These regenerated crystals on the surface of dentin and collagen matrix were confirmed to be hydroxyapatite (HAp). The approach thus demonstrates that PAMAM-PO3H2 can offer an efficient therapy for seal DTs in clinical dentistry.

Brain gene delivery using histidine and arginine-modified dendrimers for ischemic stroke therapy

Polyamidoamine dendrimer has been studied as an efficient gene carrier. Due to its anti-inflammatory properties, polyamidoamine is a useful gene carrier, especially for inflammatory diseases. However, the commonly used polyamidoamine generation 6 dendrimer (PG6) has higher cytotoxicity than low-molecular weight polyamidoamines, which limits its applications. Therefore, early-generation polyamidoamine dendrimers, such as generation 2 (PG2), have been investigated as an alternative to PG6, although PG2 has a lower transfection efficiency. In this study, to improve gene delivery efficiency, histidine and arginine were conjugated on the primary amines of PG2, synthesizing PG2HR. The gene delivery efficiency of PG2HR was higher than that of PG2 or of PG2 conjugated with only arginine (PG2R), which may be due to higher cellular uptake and endosomal escape of the plasmid DNA (pDNA)/PG2HR complex. In addition, PG2HR had lower cytotoxicity than polyethylenimine (25 kDa, PEI25k), PG2, and PG2R. Mechanism studies showed that PG2HR delivered pDNA into the cells mainly by clathrin-independent endocytosis and partly by macropinocytosis. The therapeutic potential of PG2HR-mediated gene delivery was evaluated in middle cerebral artery occlusion (MCAO)-reperfusion stroke animal models. Heme oxygenase-1 (HO-1) plasmid was delivered into the brain by local injection. The results showed that PG2HR had higher gene delivery efficiency in the brain than did PEI25k, PG2, or PG2R. Furthermore, compared to the pHO-1/PEI25k, pHO-1/PG2, and pHO-1/PG2R complexes, the pHO-1/PG2HR complex had reduced apoptosis levels and infarct sizes in ischemic brains. Therefore, because of its low cytotoxicity and high gene delivery efficiency, PG2HR may be useful for gene therapy of inflammatory diseases including ischemic stroke.

Effect of the lipid composition and cholesterol on the membrane selectivity of low generations PAMAM dendrimers: A molecular dynamics simulation study

Among different nanomaterials, dendrimers stand out because of their inherent broad range of activity against viruses, bacteria, and cancer cells. Herein, a total of 15 molecular systems have been simulated to characterize the structural features and geometry of low generation polyamidoamine (PAMAM) dendrimers (G0-G2) after they attached to various membranes (1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC)/1,2-dipalmitoyl-sn-glycero-3-phosphorylglycerol (DPPG) with a different ratio of cholesterol (CHL) to explain their membrane activity in cancer cells. The results indicated that the local membrane order parameters were increased in membranes containing 20 and 40 mol% cholesterol molecules. Furthermore, the PAMAM dendrimers were able to make a substantial number of holes in the membranes containing cholesterol. The results also showed that hydrogen bonds, and electrostatic interactions, govern the interactions between the PAMAM dendrimers and the membranes. Neutral bilayers could drive back the PAMAM dendrimers from the bilayer surface, whereas phosphatidylcholine (PC) bilayers mixed with phosphatidylglycerol (PG) phospholipids (as mimics of negatively charged cancer cell membranes) bond firmly to the hyperbranched polymers. Moreover, the negatively charged phospholipids crowded in regions where dendrimers interacted with membranes. This investigation provided an explanation and mechanistic insight for the activity of PAMAM dendrimers against the negatively charged cancer cells.

Synthesis and evaluation of a hyperbranched copolymer as viscosity reducer for offshore heavy oil

As is well known, resin and asphaltene greatly increase the viscosity of the oil, which causes difficulty for heavy oil to flow and to be displaced. Therefore, reducing the viscosity of heavy oil effectively is the key to enhance oil recovery. A hyperbranched copolymer named as HVR grafted with hydrophilic surfactant monomers, was synthesized and evaluated in this paper as an alternative to reduce the offshore heavy oil viscosity. The synthesis method of HVR through free-radical copolymerizing using the third generation polyamidoamine dendrimer, acrylamide, acrylic acid and surfactant monomers in deionized water was detailed in this paper. Thereupon the characterization of HVR were described by Fourier transform infrared spectroscopy and 1H nuclear magnetic resonance spectroscopy. The physical properties of HVR solution including apparent viscosity, oil viscosity reducing ability, interfacial tension were comprehensively studied. Otherwise the effect of HVR on sheet structure of asphaltene aggregate and asphaltene aggregation inhibition-dispersion activity were measured by X-ray diffraction and ultraviolet–visible spectrophotometer, respectively. The results indicate that apparent viscosities of HVR solution is relatively not high. For example, after shearing with a Waring blender at 3500 rpm for 20 s, the viscosity of 2500 ppm HVR solution is only 22.7 cP. However, the HVR solution has a relatively high viscosity remaining rate, which is approximately 58%. On the other hand, HVR solution has a good viscosity reducing ability on heavy oil. For the oil viscosities from 350 cP to 500 cP, the viscosity reduction rate of HVR at 2000 ppm is approximately 97% under the oil-water ratio of 3:7. In addition, the oil-water interfacial tension can be reduced by HVR solution at the concentration of 2500 ppm to 1.61 × 10−2 mN m−1. Comparing the asphaltene aggregates after interacting with HPAM and HVR, it illustrates that the layer spacing, interchain distance and diameter of the aromatic sheets are lager if interacting with HVR; meanwhile height of the aromatic clusters and effective number of aromatic sheets are smaller due to the reaction with HVR. In addition, if compared with the asphaltene treated by HPAM, with the increase of HVR concentration, the absorbance of asphaltene in toluene treated by HVR solution decreased significantly. Overall, this new hyperbranched copolymer shows potential for applications in heavy oil viscosity reduction.

Enhanced transfection efficiency of low generation PAMAM dendrimer conjugated with the nuclear localization signal peptide derived from herpesviridae

Polyamidoamine (PAMAM) dendrimer is an extensively studied polymer in the biomedical research because of its low polydispersity, distinct molecular structure, and surface functionalities. Generally, a high-generational PAMAM dendrimer is used for gene delivery because transfection efficiency is dependent on charge density; however, an increase in charge density induces disruption of the cellular membrane, and damage to the membrane results in cytotoxicity. In this study, we selected PAMAM generation 2 to reduce the cytotoxic effect and conjugated RRILH and RRLHL sequences, nuclear localization signals (NLS) derived from herpesviridae to PAMAM generation 2. The transfection efficiency of RRILH-PAMAM G2 and RRLHL-PAMAM G2 was similar to that of polyethylenimine (PEI) in Neuro2A, HT22, and HaCaT cells, whereas their transfection efficiency was much higher than that of PEI in NIH3T3 cells. RRILH-PAMAM G2 showed relatively lower cytotoxicity than did RRLHL-PAMAM G2 in all cell lines, but the transfection capacity of the two polymers was similar. Our study shows that low-generational PAMAM dendrimer conjugated with NLS sequences has potential as an alternative to PEI in gene delivery.

Comprehensive investigation of in vitro hemocompatibility of surface modified polyamidoamine nanocarrier.

Polyamidoamine (PAMAM) dendrimers have been investigated for decades and currently applied in various areas throughout nanomedicine, including gene therapy, drug delivery, anti-bacteria and imaging. It is therefore necessary to assess cytotoxicity of PAMAM dendrimers systematically. Because blood component is usually the initial step of contact with any therapeutic agent, comprehensive hemocompatibility study is needed. The triblock dendrimer: polyamidoamine-polyethylene glycol-cyclic RGD (PAMAM-PEG-cRGD), was successfully synthesized. Various in vitro assays to characterize hemocompatibility of both PAMAM (Generation 4.0) and PAMAM-PEG-cRGD were performed, including hemolytic assay, platelet activation examination, platelet counting, assessment of coagulating pathways and evaluation of complement system activation. The hemolytic ratio of PAMAM-PEG-cRGD maintained below 5%. Surface engineering of PEG and cRGD to PAMAM attenuated hemolysis and RBC aggregation as compared with unmodified PAMAM. PAMAM (Generation 4.0) reduced platelet counting in a dose-dependent manner, and the platelet number dropped dramatically at a relatively low incubating dose (1 μM). Such surface modifications also alleviated platelet activation and platelet reduction mediated by PAMAM polycationicity. Finally, high concentration (10 μM) of PAMAM interfered the coagulation system, prolonging prothrombin time significantly. Surface modification of PEG and cRGD to PAMAM (Generation 4.0) improves hemocompatibility. Introduction of PEG and cRGD significantly mitigates hemolytic and RBC aggregation effects as compared with unmodified PAMAM. Similarly, these modifications alleviate platelet activation and platelet reduction mediated by PAMAM polycationicity.

Targeting Breast Cancer Cells with G4 PAMAM Dendrimers and Valproic Acid Derivative Complexes.

Our research group has developed some Valproic Acid (VPA) derivatives employed as anti-proliferative compounds targeting the HDAC8 enzyme. However, some of these compounds are poorly soluble in water. Employed the four generations of Polyamidoamine (G4 PAMAM) dendrimers as drug carriers of these compounds to increase their water solubility for further in vitro evaluation. VPA derivatives were subjected to Docking and Molecular Dynamics (MD) simulations to evaluate their affinity on G4 PAMAM. Then, HPLC-UV/VIS, 1H NMR, MALDI-TOF and atomic force microscopy were employed to establish the formation of the drug-G4 PAMAM complexes. The docking results showed that the amide groups of VPA derivatives make polar interactions with G4 PAMAM, whereas MD simulations corroborated the stability of the complexes. HPLC UV/VIS experiments showed an increase in the drug water solubility which was found to be directly proportional to the amount of G4 PAMAM. 1H NMR showed a disappearance of the proton amine group signals, correlating with docking results. MALDI-TOF and atomic force microscopy suggested the drug-G4 PAMAM dendrimer complexes formation. In vitro studies showed that G4 PAMAM has toxicity in the micromolar concentration in MDAMB- 231, MCF7, and 3T3-L1 cell lines. VPA CF-G4 PAMAM dendrimer complex showed anti-proliferative properties in the micromolar concentration in MCF-7 and 3T3-L1, and in the milimolar concentration in MDAMB- 231, whereas VPA MF-G4 PAMAM dendrimer complex didn't show effects on the three cell lines employed. These results demonstrate that G4 PAMAM dendrimers are capableof transporting poorly watersoluble aryl-VPA derivate compounds to increase its cytotoxic activity against neoplastic cell lines.

Cellular internalization of targeted and non-targeted delivery systems for contrast agents based on polyamidoamine dendrimers

New high-molecular-weight contrast agents based on polyamidoamine (PAMAM) dendrimers for targeted imaging of malignant tumors characterized by overexpression of human epidermal growth factor receptor (EGFR) and human alpha-fetoprotein receptor (RECAF) were designed. Conjugates of second (G2) and third (G3) generation polyamidoamine dendrimers with 1,4,7,10-tetraazocyclodecane-1,4,7,10-tetraacetic acid (DOTA) were obtained. The quantitative composition of the conjugates was determined by 1HNMR spectroscopy. It was shown that four out of the 16 terminal NH2 groups in G2-DOTA and nine out of the 32 groups in G3-DOTA were modified with DOTA. The morphology, size, and charge of the synthesized macromolecules were characterized by dynamic light scattering and electrophoresis. Gadolinium(III) was loaded into the conjugates and the Gd content was determined by atomic emission spectroscopy. For increasing the selectivity of accumulation in the tumor cells, two recombinant proteins able to bind selectively to EGFR and RECAF, namely, human recombinant epidermal growth factor (rEGF) and human recombinant 3rd domain of alpha-fetoprotein (3dAFPpG), were conjugated with G2 and G3 dendrimers. The conjugates containing vector molecules were mainly accumulated via clathrin-dependent endocytosis, whereas G2-DOTA and G3-DOTA were absorbed via caveolin-dependent endocytosis and macropinocytosis. The dendrimer conjugates with vector molecules were intensely accumulated in A549 cells characterized by high expression of EGFR (Herl) and RECAF, whereas the accumulation of conjugates in the control K562 cells (with low expression of Her1) and in the CD14− population of human unstimulated mononuclear white blood cells was insignificant. The 3dAFPpG-conjugated dendrimers were partly recycled. All synthesized conjugates had a rather low toxicity in the range of 350–450 µmol L−1 (IC50).

Effective Elimination of Charge-associated Toxicity of Low Generation Polyamidoamine Dendrimer Eases Drug Delivery of Oxaliplatin

Polyamidoamine (PAMAM) dendrimer is emerging as an effective nanocarrier for delivering anticancer drugs. Still, unmodified PAMAM dendrimer is hardly used in vivo because of unsatisfied drug release, high tendency of interfering with cellular membranes, and rapid clearance by reticuloendothelial system. In this study, low generation polyamidoamine (PAMAM) dendrimer G3.0 is developed and surface modified with methoxypolyethylene glycol (PAMAM G3.0-mPEG) to overcome its limitations. Specifically, PAMAM G3.0 conjugated with mPEG at different ratios are investigated to effectively eliminate its charge-associated toxicity, in which PAMAM G3.0-mPEG- 8 is chosen for oxaliplatin (OX) loading. Results reveal that OX-loaded PAMAM G3.0-mPEG-8 has desirable size, good entrapment efficiency, and sustained release with minimum drug leakage. In addition, Resazurin assay indicates that the toxicity of loaded OX is reduced as compared to free drug but still maintain substantially anticancer activity on HeLa cells, suggesting the potential application of PAMAM G3.0-mPEG-8 for OX delivery in cancer therapy.

A dendritic, redox-responsive, supramolecular (Dr.S) system for lysis-triggered delivery for drug-resistant renal cancer.

Purpose: Aiming to improve the drug loading capacity of dendritic nanoparticles and enhance delivery efficacy in drug-resistant cancer, we developed and optimized a more advanced dendritic, redox-responsive, supramolecular (Dr.S) system for intravenous RAD001 administration. Materials and methods: The Dr.S system was engineered by linking 3rd generation polyamidoamine dendrimers (G3 PAMAM) with 8-arm polyethylene glycol (PEG) to encapsulate a molecular targeted agent RAD001. The drug-loading capacity was measured by ultraviolet-visible spectrophotometry. In vitro release behavior was determined with a two-compartment model, and the in vivo distribution pattern was tracked by Cy5.5 fluorescence. The therapeutic effect of Dr.S/RAD001 was evaluated in RAD001-resistant cancer cells and tumor-bearing nude mice, respectively. Results: The Dr.S system encapsulating RAD001 with a loading efficiency of 10.6% formed a core–shell structure, by shifting hydrophobic PAMAM/RAD001 components towards inner space and exposing the hydrophilic PEG on the surface. The Dr.S/RAD001 system could respond to a lysis-mimicking reduction stimulus, and functionally release cargoes to facilitate tumor accumulation and cellular internalization. These features contributed to the enhanced anti-tumor activity of RAD001 in renal cancers in vitro and in vivo. The Dr.S/RAD001 system also reversed acquired RAD001-resistance by a 60-fold increase in tumor accumulation of the therapeutics. Conclusion: The functional Dr.S/RAD001 system enables lysis-triggered release of RAD001 to achieve better tumor accumulation, which helps overcome acquired drug resistance in renal cancers.

Exploring the Effect of the Irradiation Time on Photosensitized Dendrimer-Based Nanoaggregates for Potential Applications in Light-Driven Water Photoreduction.

Fourth generation polyamidoamine dendrimer (PAMAM, G4) modified with fluorescein units (F) at the periphery and Pt nanoparticles stabilized by L-ascorbate were prepared. These dendrimers modified with hydrophobic fluorescein were used to achieve self-assembling structures, giving rise to the formation of nanoaggregates in water. The photoactive fluorescein units were mainly used as photosensitizer units in the process of the catalytic photoreduction of water propitiated by light. Complementarily, Pt-ascorbate nanoparticles acted as the active sites to generate H2. Importantly, the study of the functional, optical, surface potential and morphological properties of the photosensitized dendrimer aggregates at different irradiation times allowed for insights to be gained into the behavior of these systems. Thus, the resultant photosensitized PAMAM-fluorescein (G4-F) nanoaggregates (NG) were conveniently applied to light-driven water photoreduction along with sodium L-ascorbate and methyl viologen as the sacrificial reagent and electron relay agent, respectively. Notably, these aggregates exhibited appropriate stability and catalytic activity over time for hydrogen production. Additionally, in order to propose a potential use of these types of systems, the in situ generated H2 was able to reduce a certain amount of methylene blue (MB). Finally, theoretical electronic analyses provided insights into the possible excited states of the fluorescein molecules that could intervene in the global mechanism of H2 generation.

Covalent immobilization and enhanced electrical wiring of hemoglobin using gold nanoparticles encapsulated PAMAM dendrimer for electrochemical sensing of hydrogen peroxide

Design and development of electrochemical biosensors with improved selectivity, sensitivity and stability is one of the thrust areas of research in analytical and materials chemistry. In the present work, hemoglobin (Hb) was covalently immobilized on polyamidoamine (PAMAM) dendrimer encapsulated with gold nanoparticles (AuNPs), which was further utilized for the electrochemical detection of hydrogen peroxide (H2O2). Third generation PAMAM dendrimers were synthesized and AuNPs were encapsulated within the dendrimer network. Hb was covalently immobilized through glutaraldehyde cross-linking between the free amino groups of Hb and that of the PAMAM dendrimer. Hb/PAMAM-AuNPs was immobilized on a glassy carbon electrode (GCE) and the Hb/PAMAM-AuNPs/GCE modified electrode thus fabricated was characterized with electrochemical impedance spectroscopy and cyclic voltammetry. The Hb/PAMAM-AuNPs/GCE biosensor displayed well resolved redox peaks with anodic peak potential at −0.252 V and cathodic potential at −0.321 V, corresponding to Fe(III)/Fe(II) redox couple of heme active centre. Further, the developed Hb/PAMAM-AuNPs/GCE showed very good electrocatalytic activity for the reduction of H2O2 at a potential of −0.35 V. The Hb/PAMAM-AuNPs/GCE biosensor has shown impressive performance towards H2O2 determination in the concentration range from 20 μM to 950.22 μM. The sensitivity of the biosensor was calculated to be 35.07 μA μM−1 cm−2 with a detection limit of 6.1 μM. Also, the Hb/PAMAM-AuNPs/GCE modified electrode exhibited higher stability and good reproducibility.

Assembling structurally customizable synthetic carriers of siRNA through thermodynamically self-regulated process

This study demonstrates that our previously reported polywraplex, a synthetic siRNA carrier consisting of a uni-molecular polyplex core of customizable size and a self-assembled tri-block copolymer envelop, may be constructed using dendrimers as the crosslinking junctions. Replacing the branched low molecular weight PEI with polyamidoamine (PAMAM) dendrimer in the zeta potential regulated polymerization resulted in the similar network structured cationic polymer with electron microscopically visible crosslinking junctions. This visibility may offer a convenient way to characterize the molecular structure of the rationally designed networked siRNA-packing cationic polymer without altering its chemical properties and biologic functions. A series of physical-chemical characterizations and biological assays, comprising size, zeta potential, pre-phagocytic siRNA leaking and degradation, and silencing of functional genes, confirmed that the advanced properties of polywraplexes remained with the dendrimer junctions. Although sixth generation PAMAM dendrimer was used as the crosslinking junctions in the size-customizable polymerization for electron microscopic observation, lower generation dendrimer should also work in case more practical and structurally defined cationic polymer is needed.

Targeting peptide-mediated 131I-polyamidoamine in medullary thyroid carcinoma bearing mice

Objective To construct 131I-the fifth generation polyamidoamine (PAMAM(G5.0)) with targeting peptide Ser-Arg-Glu-Ser-Pro-His-Pro (SRESPHP; SR) or Gly-Pro-Leu-Pro-Leu-Arg (GPLPLR; GP) and double targeting peptide SR/GP, and evaluate the targeting ability in medullary thyroid carcinoma (MTC) model. Methods PAMAM(G5.0), PAMAM(G5.0)-SR, PAMAM(G5.0)-GP and PAMAM(G5.0)-SR/GP were radiolabeled with 131I by chloramine T method. The radiolabeled yield and radiochemical purity were determined by thin layer chromatography. MTC xenografts were developed and the percentage radio-activity of injection dose per gram of tissue (%ID/g) in tumor and organs was measured at 24 h post-injection. Region of interest (ROI) was drawn and the tumor/non-tumor (T/NT) ratios at 4, 8 and 24 h post-injection were calculated and compared among different groups. One-way analysis of variance, repetitive measurement analysis of variance and Dunnett-t test were used to compare the data of different groups. The relationship between %ID/g and T/NT was analyzed with Pearson correlation. Results The radiolabeled yield was more than 75% and radiochemistry purity was more than 90%. The difference of %ID/g at 24 h post-injection was significant (F=14.400, P<0.001) in tumors of all groups. The radioactive uptake in tumor of 131I-PAMAM(G5.0)-SR group was the highest at 24 h post-injection((1.80±0.18) %ID/g). There were significant differences of T/NT ratios among different groups(F=4.776, P<0.05)and between different time points(F=8.630, P<0.05). Compared with negative control group (Na131I), the T/NT ratios significantly increased in 131I-PAMAM(G5.0)-SR group at 4, 8 and 24 h post-injection (t=4.169, 7.123 and 4.032, all P<0.05) and in 131I-PAMAM(G5.0)-GP group at 4 h post-injection (t=5.893, P<0.05). The T/NT ratio in 131I-PAMAM(G5.0)-SR group was higher than that in 131I-PAMAM(G5.0)-GP group at 24 h post-injection (t=2.871, P<0.05). Conclusions PAMAM(G5.0)-SR, PAMAM(G5.0)-GP and PAMAM(G5.0)-SR/GP can target the MTC models. 131I-PAMAM(G5.0)-SR has the best biological properties and may provide a new precision method for MTC diagnosis, treatment and prognosis evaluation. Key words: Carcinoma, medullary; Thyroid neoplasms; Molecular probes; Polyamines; Peptides; Iodine radioisotopes; Tomography, emission-computed, single-photon; Mice, nude

Simple approach for cleaning up 2,4,6‐trichloroanisole from alcoholic‐beverage‐reconstituted solutions using polymeric materials

Background and Aims 2,4,6-Trichloroanisole (TCA) is a well-recognised contaminant in the wine and whisky industries. In this work, several polymeric materials were tested through a hybrid strategy (computational and experimental studies) as potential fining agents for elimination of TCA. Methods and Results Sodium alginate, polyaniline emeraldine base (PANI-EB), polyaniline emeraldine salt (PANI-ES) and three cross-linked derivatives of different generations (G3, G4 and G5) of polyamidoamine (PAMAM) were tested. Materials were characterised by Fourier transform infrared spectroscopy and thermogravimetric analysis. The amount of material and the interaction time needed to achieve TCA sorption were optimised in a screening study. The binding capacity of the materials was then determined in methanol-reconstituted wine and whisky solutions to demonstrate their effectiveness. The proportion of TCA in wine retained by PANI-ES, PANI-EB and PAMAM-G5-CD was greater than 75%, and for whisky all polymers except PANI-ES retained greater than 75% of TCA. The concentration of phenolic substances of both methanol-reconstituted solutions was measured after treatment; most of the polymers had no impact on the concentration of phenolic substances. The intermolecular interactions between the polymeric materials and TCA were characterised by computational studies involving molecular dynamics simulations. Conclusions The polymers PAMAM G5-CD and PANI-EB retained the most TCA in reconstituted red wine and whisky solutions. Significance of the Study The provision of efficient materials for the removal of TCA will improve the purification processes employed in beverage production.