Terminal Primary Amine Groups Research Articles

Ionically cross-linked sodium alginate and polyamidoamine dendrimers for ethanol/water separation through pervaporation

The pervaporation process is an energy-conservative and environmentally friendly method to separate organic solvent from water. It efficiently separates close boiling point and azeotrope mixtures unlike the distillation process. Herein, primary amine-terminated polyamidoamine (PAMAM) dendrimers are proposed to interact with the highly hydrophilic and negatively charged sodium alginate (SA) polymer chains for the preparation of pervaporation composite membranes. Different generations of PAMAM dendrimer (G0, G1, and G2) have different number of terminal primary groups (P4, P8, and P16). That is, a higher generation number means there are more terminal amine groups available for interaction. The addition of PAMAM contributed to the stronger hydrogen bonding of SA and inhibited the swelling of pristine SA/PVDF composite membranes. Interestingly, the free volume characteristics of the SA/PVDF membranes with PAMAM altered the number and size of the free volume spaces as confirmed by positron annihilation spectroscopy (PAS). The more terminal primary amine groups of PAMAM resulted to a higher ionic interaction with the sodium alginate polymer chains producing a denser structure. The denser structure of SA-P8/PVDF and SA-P16/PVDF resulted to a lower flux than with SA-P4/PVDF. The SA-P4/PVSDF at 40 ppm loading achieved the highest separation performance for the dehydration of 90/10 wt% ethanol/water mixture at 25 °C with a permeation flux of 1,039 g m-2h−1 and a water concentration in permeate of 99.41 wt%. Furthermore, the SA-P4/PVDF membrane can withstand high water content in feed up to 50 wt% and high operating temperature of 70 °C showing enhanced stability of the selective layer due to the interactions between SA and PAMAM dendrimer.

Effects of hyperbranched polyamide functionalized graphene oxide on curing behaviour and mechanical properties of epoxy composites

Epoxy composites reinforced by both graphene oxide (GO) and hyperbranched polyamide (HBPA) functionalized GO (HBPA-GO) were fabricated. The effects of GO functionalization on exfoliation, dispersion state and interfacial properties were investigated. The curing kinetics and mechanisms and ultimate mechanical properties of epoxy composites were studied. The results show that the exfoliation and dispersion state of GO is significantly improved after functionalization. The functionalized GO (HBPA-GO) can effectively enhance curing reactions of epoxy matrix by reducing the activation energy due to high density of terminal primary amine groups on HBPA-GO. In addition, HBPA-GO worked as a crosslinker forming a large amount of covalent bonding with epoxy matrix through HBPA-GO/epoxy reaction and, therefore, the interfacial adhesion is enhanced, resulting in excellent mechanical properties of epoxy composites. Moreover, the interfacial properties between HBPA-GO and the epoxy matrix can be tuned by varying the temperature of the HBPA-GO/epoxy reaction before the addition of the curing agent, thereby providing a new route for the design and development of the GO reinforced epoxy composites.

Mixed Matrix PVDF Membranes With in Situ Synthesized PAMAM Dendrimer-Like Particles: A New Class of Sorbents for Cu(II) Recovery from Aqueous Solutions by Ultrafiltration.

Advances in industrial ecology, desalination, and resource recovery have established that industrial wastewater, seawater, and brines are important and largely untapped sources of critical metals and elements. A Grand Challenge in metal recovery from industrial wastewater is to design and synthesize high capacity, recyclable and robust chelating ligands with tunable metal ion selectivity that can be efficiently processed into low-energy separation materials and modules. In our efforts to develop high capacity chelating membranes for metal recovery from impaired water, we report a one-pot method for the preparation of a new family of mixed matrix polyvinylidene fluoride (PVDF) membranes with in situ synthesized poly(amidoamine) [PAMAM] particles. The key feature of our new membrane preparation method is the in situ synthesis of PAMAM dendrimer-like particles in the dope solutions prior to membrane casting using low-generation dendrimers (G0 and G1-NH2) with terminal primary amine groups as precursors and epichlorohydrin (ECH) as cross-linker. By using a combined thermally induced phase separation (TIPS) and nonsolvent induced phase separation (NIPS) casting process, we successfully prepared a new family of asymmetric PVDF ultrafiltration membranes with (i) neutral and hydrophilic surface layers of average pore diameters of 22-45 nm, (ii) high loadings (∼48 wt %) of dendrimer-like PAMAM particles with average diameters of ∼1.3-2.4 μm, and (iii) matrices with sponge-like microstructures characteristics of membranes with strong mechanical integrity. Preliminary experiments show that these new mixed matrix PVDF membranes can serve as high capacity sorbents for Cu(II) recovery from aqueous solutions by ultrafiltration.

Amine-decorated nanocrystalline cellulose surfaces: synthesis, characterization, and surface properties

In this present work, terminal amino-functionalized nanocrystalline cellulose derivatives were prepared using a simple two-step protecting group-free protocol under aqueous reaction conditions at room temperature. Carboxylate groups were first introduced onto the surface of nanocrystalline cellulose (NCC) via a TEMPO-mediated oxidation. Then, reaction of surface-carboxylated NCC with bifunctional amines of small alkyl chain length by EDC/NHS-mediated coupling furnished the desired aminated NCC via an amide linkage. Surface covalent functionalization was confirmed by Fourier transform infrared spectroscopy, elemental analysis, and X-ray photoelectron spectroscopy. Size, surface charge, morphology, and thermal properties were obtained by various techniques. STEM images revealed no change in structure and morphology of the materials after TEMPO-mediated oxidation but a slight agglomeration was observed after surface covalent functionalization with diamines. While amide linkage confers stability, terminal primary amine groups on the surface of NCC represent a versatile reactive functional group for bioconjugation with other biomolecules for potential biomedical applications.

Synthesis and cellular studies of polyamine conjugates of a mercaptomethyl–carboranylporphyrin

Seven polyamine conjugates of a tri(p-carboranylmethylthio)tetrafluorophenylporphyrin were prepared in high yields by sequential substitution of the p-phenyl fluoride of tetrakis(pentafluorophenyl)porphyrin (TPPF), and investigated as boron delivery agents for boron neutron capture therapy (BNCT). The polyamines used were derivatives of the natural-occurring spermine with different lengths of the carbon chains, terminal primary amine groups and, in two of the conjugates, additional aminoethyl moieties. A tri(polyethylene glycol) conjugate was also synthesized for comparison purposes. The polyamine conjugates showed low dark cytotoxicity (IC50 >400μM) and low phototoxicity (IC50 >40μM at 1.5J/cm2). All polyamine conjugates, with one exception, showed higher uptake into human glioma T98G cells (up to 12-fold) than the PEG conjugate, and localized preferentially in the cell ER, Golgi and the lysosomes. Our results show that spermine derivatives can serve as effective carriers of boronated porphyrins for the BNCT of tumors.

Surface Properties of Water-Soluble Glycine-Cysteamine-Protected Gold Clusters

We report the synthesis of water-soluble, nearly monodisperse glycine-cysteamine (Gly-CSA) gold monolayer protected clusters (MPCs) via base deprotection of Fmoc-Gly-CSA MPCs. The resulting Gly-CSA MPCs, which have terminal primary amine groups, are fully characterized by (1)H and (13)C NMR, UV-vis spectroscopy, and TEM, and their surface properties were probed by dynamic light scattering and acid-base titrations. The characterization methods indicate that the as-synthesized particles are nearly monodisperse with an average particle size of 1.8 +/- 0.3 nm, but are only stable to aggregation in water at pHs of 4 and below. Acid-base titrations of the Gly-CSA MPCs show that the primary ammonium groups have a pK(a) of approximately 5.5, which is several orders of magnitude lower than the pK(a2) for the ammonium group of glycine (9.6). Thus, the particles are only partially protonated at intermediate pH's, which then drives the aggregation of the nanoparticles via hydrogen-bond formation. Dynamic light scattering results confirm the pH-driven aggregation of the nanoparticles, and studies with ninhydrin confirm that the primary amine groups are reactive and have potential for further functionalization. These results show that amine-terminated MPCs can be synthesized; however, their aggregation at intermediate pH's can limit their utility as building blocks for multifunctional nanoparticle syntheses.

Dendron-like Polypeptide/Linear Poly(ethylene oxide) Biohybrids with Both Asymmetrical and Symmetrical Topologies Synthesized via the Combination of Click Chemistry and Ring-Opening Polymerization

Dendron-like poly(γ-benzyl-l-glutamate)/linear poly(ethylene oxide) block copolymers with both asymmetrical and symmetrical topologies (i.e., ABn type Dm-PBLG-b-PEO and BnABn type Dm-PBLG-b-PEO-b-Dm-PBLG; n = 2m, m = 0, 1, 2, and 3; Dm are the propargyl focal point poly(amido amine) type dendrons having 2m terminal primary amine groups) were synthesized via the combination of ring-opening polymerization (ROP) of γ-benzyl-l-glutamate N-carboxyanhydride (BLG-NCA) and click chemistry according to the “arm-first” and “core-first” strategies. In the arm-first method, the propargyl focal point dendrons Dm having 2m terminal primary amine groups were first used for initiating the ROP of BLG-NCA, generating “clickable” dendron-like Dm-PBLG homopolymers having 2m branches, which were then click conjugated with azide-terminated PEO (PEO-N3) to produce asymmetrical Dm-PBLG-b-PEO. In the core-first strategy, the propargyl focal point Dm was first click conjugated with PEO-N3 to generate primary amine-terminated PEO d...

Synthesis and Characterization of a Tertiary Amine Polymer Series from Surface-Grafted Poly(tert-butyl acrylate) via Diamine Reactions

A sequence of reaction steps was used to graft poly(tert-butyl acrylate) (PtBA) to silicon (Si) wafers and to modify the pendant groups of the tethered PtBA to create chemically tailored surface modifying layers. The Si wafers were first prepared for grafting by the deposition of a self-assembled monolayer (SAM) of N-aminopropyldimethylethoxysilane. The terminal primary amine groups on the SAM provided sites for reaction with carboxy-terminated PtBA. The choice of PtBA as the tethered polymer was due to the ability to substitute the tert-butyl ester groups with other functionalities. In this study, the tert-butyl esters were replaced with various diamines to create a series of polymers with tertiary amine pendant groups. The reactions and surface properties were monitored with external reflectance (ER) and transmission FTIR spectroscopies, ellipsometry, X-ray photoelectron spectroscopy (XPS), and static water contact angle goniometry. Hydrolysis and novel diamine conversion reactions were successfully per...

Synthesis of Novel Folic Acid-Functionalized Biocompatible Block Copolymers by Atom Transfer Radical Polymerization for Gene Delivery and Encapsulation of Hydrophobic Drugs

Two synthetic routes to folic acid (FA)-functionalized diblock copolymers based on 2-(methacryloyloxy)ethyl phosphorylcholine [MPC] and either 2-(dimethylamino)ethyl methacrylate [DMA] or 2-(diisopropylamino)ethyl methacrylate [DPA] were explored. The most successful route involved atom transfer radical polymerization (ATRP) of MPC followed by the tertiary amine methacrylate using a 9-fluorenylmethyl chloroformate (Fmoc)-protected ATRP initiator. Deprotection of the Fmoc groups produced terminal primary amine groups, which were conjugated with FA to produce two series of novel FA-functionalized biocompatible block copolymers. Nonfunctionalized MPC-DMA diblock copolymers have been previously shown to be effective synthetic vectors for DNA condensation; thus, these FA-functionalized MPC-DMA diblock copolymers appear to be well suited to gene therapy applications based on cell targeting strategies. In contrast, the FA-MPC-DPA copolymers are currently being evaluated as pH-responsive micellar vehicles for the delivery of highly hydrophobic anticancer drugs.

Molecular basis for the polyamine-OmpF porin interactions: inhibitor and mutant studies

By testing the sensitivity of Escherichia coliOmpF porin to various natural and synthetic polyamines of different lengths, charge and other molecular characteristics, we were able to identify the molecular properties required for compounds to act as inhibitors of OmpF in the nanomolar range. Inhibitors require at least two amine groups to be effective. For diamines, the optimum length of the hydrocarbon spacer was found to be of eight to ten methylene groups. Triamine molecules based on a 12-carbon motif were found to be more effective that spermidine, an eight-carbon trivalent derivative. But differences in inhibition efficiencies were also found for trivalent compounds depending on the relative position of the internal secondary amine group with respect to the terminal groups. Finally, quaternary ammonium derivatives had no effect, suggesting that the nature of the terminal amine is important for the interaction. From these observations, we deduce that inhibition efficiency in the nanomolar range requires a 12-carbon chain triamine with terminal primary amine groups and replacement of the eighth methylene by a secondary amine. The need for this type of molecular architecture suggests that inhibition is governed by interactions between specific amine groups and protein residues, and that this is not simply due to the accumulation of charges into the pore. Together with previous observations from site-directed mutagenesis studies and inspection of the crystal structure of OmpF, these results allowed us to propose three residues (D113, D121 and Y294) as putative sites of interaction between the channel and spermine. Alanine substitution at each of these three residues resulted in a loss of inhibition by spermine, while mutations of only D113 and D121 affected inhibition by spermidine. Based on these observations, we suggest a model for the molecular determinants involved in the porin-polyamine interaction.

Monolayers of Thiol-Terminated Dendrimers on the Surface of Planar and Colloidal Gold

The synthesis of fourth-generation poly(amido−amine) (PAMAM) dendrimers having terminal groups partially or fully functionalized with thiol groups is described. These thiolated dendrimers form stable monolayers on planar Au substrates. X-ray photoelectron spectroscopy studies reveal that most of the thiol groups on dendrimers having 20% of their terminal primary amine groups functionalized can directly interact with the Au surface. This suggests that the dendrimer molecules are flexible and arrange themselves so as to maximize the number of Au/thiol interactions. Reduction of tetrachloroauric acid in the presence of thiol-modified dendrimers results in formation of water-soluble, dendrimer-stabilized nanoparticles. The particles are 1.5−2.1 nm in diameter depending on the Au/dendrimer ratio used. Stable nanoparticles can be obtained at Au/dendrimer ratios as large as 120:1.

New conducting polymer networks

These new polymer networks are based on cross-linked polyethers. The cross-link reaction is carried out by reaction of a diglycidyl compound with a polyether having two terminal primary amine groups. Ionic conductivity depends on the level of cross-linking, the salt concentration and the nature of the polyether. At room temperature, the best obtained conductivity exceeds 4 × 10 −5 S/cm. Mechanical properties are good. These polymer electrolytes are completely amorphous and stable up to 250 °C. The measured glass-transition temperature is close to −56 °C. These networks are also used to synthesize hybrid electrolytes which include a liquid polymer or a high dielectric constant solvent. The conductivity of these electrolytes is close to organic liquid electrolytes.

Association of polyacrylamide beads to polyethylene terephthalate prostheses.

A method for the coupling of polyacrylamide beads to polyethylene terephthalate (PET) vascular prostheses is described. The reactional procedure used is performed along several steps; acrylic acid grafting on PET textile fibres, in order to introduce reactive carboxylic groups, introduction of terminal primary amine groups onto the beads, and then, attachment method which consists in coupling carboxylic groups of prostheses with amine groups of modified beads. The relative weight increase of the samples before and after the coupling reaction and, microscopic observations of beads distribution onto the prostheses surface demonstrate the binding feasibility of polyacrylamide matrices to PET prostheses. In the near future, authors expect to replace these beads by microcapsules with polyacrylamide wall and containing active compounds to improve the vascular prostheses biocompatibility.

Complexes of Diamines with Cellulose: Study of Symmetrical and Unsymmetrical Terminal Group Effects

Cellulose formed complexes of limited stability with a di-secondary diamine, symmetrical dimethylethylenediamine, and with a diamine containing primary and tertiary amine groups, unsymmetrical dimethylethylenediamine. Pretreat ment of the cellulose with liquid ammonia was required for complex formation. X-ray diffractometer tracings were obtained of the complexes. More stable complexes were formed between cellulose and each of two diamines, N-methyl- ethylenediamine and N-methyl-1,3-propanediamine, both of which contain primary and secondary amine groups. Pre treatment with liquid ammonia was not required for formation of these complexes. Unit cell determinations were made of the latter complexes. A di-tertiary diamine, N,N,N',N'-tetramethylethylenediamine, did not form a complex with cellulose even when the cellulose was preswollen with liquid ammonia. A complex formed with cellulose and diethyl enetriamine confirmed the results of previous workers who found that crosslinkage of the cellulose chains occurs through primary and secondary amine groups when the complex is washed with carbon tetrachloride after vacuum distillation. However, if the complex is not washed, the terminal primary amine groups bond with the cellulosic hydroxyl groups with greater distention of the 101 interplanar spacing of the complex. Nitrogen content of the complexes corresponded to a 1:1 ratio of diamine molecules to anhydroglucose units. Thermal studies were made of the more stable complexes.