Zwitterionic Functionality Research Articles

Ultrathin Antifouling Coatings with Stable Surface Zwitterionic Functionality by Initiated Chemical Vapor Deposition (iCVD)

Antifouling thin films of poly[N,N-dimethyl-N-methacryloxyethyl-N-(3-sulfopropyl)-co-2-(dimethylamino)ethyl methacrylate-co-ethylene glycol dimethacrylate] (PDDE) were synthesized via a substrate-independent and all-dry-initiated chemical vapor deposition (iCVD) technique followed by a diffusion-limited vapor-phase reaction with 1,3-propane sultone. Coated surfaces exhibited very low absorption of various foulants including bovine serum albumin (BSA), humic acid (HA), and sodium alginate (SA), as measured with the quartz crystal microbalance with dissipation monitoring (QCM-D). The fouling by humic acid was dependent on the presence of divalent cations such as Ca(2+). Both depth profiling and angle-resolved X-ray photoelectron spectroscopy (XPS) measurements indicated that the zwitterionic groups were highly concentrated in the top ~3 nm of the film. The contact angle measurements revealed a limited degree of surface chain reorganization upon contacting water. The dynamic contact angles remained unchanged after 100 days of storage in air, indicating the stability of the interface. The coating was substrate-independent, and the film was conformal on surface nanostructures including trenches, reverse osmosis membranes, and electrospun nanofiber mats.

Amphiphilic Polybetaines: The Effect of Side-Chain Hydrophobicity on Protein Adsorption

Novel amphiphilic polybetaines were synthesized and used as the base material for nonfouling coatings. The amphiphilicity of these polybetaines was systematically tuned by coupling chains of increasing hydrophobicity to the zwitterionic functionality side at the repeat unit level. An oligoethylene glycol (OEG) moiety was selected to yield the most hydrophilic coating, while octyl (C(8)) and fluorinated (F) groups were used to impart lipophilicity and lipophobicity to the coatings, respectively. This unique design allowed us to investigate the effect of the lipophilicity/lipophobicity of the side chain on the nonfouling properties of these zwitterionic systems. Adsorption studies, performed using six different proteins, showed that the fluorinated polybetaine, Poly[NFZI-co-NSi], resisted nonspecific adsorption as effectively as, and in some cases even better than, the most hydrophilic Poly[NOEGZI-co-NSi] coating. The comparison of Poly[NFZI-co-NSi] to its noncharged analog demonstrated the essential nature of the zwitterionic functionality in imparting nonfouling character to the coating.

Temperature Pulsing for Controlling Chromatographic Resolution in Capillary Liquid Chromatography

In this study we introduce the implementation of rapid temperature pulses for selectivity tuning in capillary liquid chromatography. Short temperature pulses improved resolution in discrete sections of chromatograms, demonstrated for ion-exchange chromatography (IC) and hydrophilic interaction chromatography (HILIC) modes. Using a resistively heated column module capable of accurate and rapid temperature changes, this concept is first illustrated with separations of small anions by IC using a packed capillary column as well as a series of nucleobases and nucleosides by HILIC using a silica monolithic column with zwitterionic functionality (ZIC-HILIC). Both positive (increasing temperature) and negative temperature pulses are demonstrated to produce significant changes in selectivity and are useful approaches for improving resolution between coeluted compounds. The approach was shown to be reproducible over a large number of replicates. Finally, the use of temperature gradients as well as other complex temperature profiles was also examined for both IC and HILIC separations.

"Thiol-ene" click chemistry: a facile and versatile route for the functionalization of porous polymer monoliths.

The preparation of porous polymer monoliths with dodecyl and zwitterionic functionalities via the "thiol-ene" click chemistry of thiol-containing monoliths with both hydrophobic and polar methacrylate "ene" monomers has been demonstrated. Selected separations confirmed the excellent potential of these monoliths in chromatography.

Zwitterionic silica copolymer based crosslinked organic–inorganic hybrid polymer electrolyte membranes for fuel cell applications

Zwitterionic (ZI) copolymers (consisting of sulfonic acid and amine groups) with plenty of –Si(OCH)3groups similar to stems, branches and fruits of vines from a bionic aspect, were synthesized as a cross-linking agent. Organic–inorganic hybrid zwitterionic membranes (ZIMs), with high flexibility, charge density and conductivity, was prepared using poly(vinyl alcohol) (PVA). Developed ZIMs with dual acidic and basic functional groups, exhibited high stabilities, water retention ability and cation selectivity. The ZIMs (especially Si–70%) were designed to possess all the required properties (water uptake: 40.6%; ion-exchange capacity: 1.52 equiv. g−1; electro-osmotic flux: (2.34 × 10−5 cm s−1A−1); and conductivity: 9.67 × 10−2 S cm−1. ZIMs were designed to possess all of the required properties of a proton-conductive membrane, namely, reasonable swelling, good mechanical, dimensional, and oxidative strength, flexibility, and low methanol permeability along with good proton conductivity due to zwitterionic functionality. Moreover, Si–70% and a Nafion117 membrane exhibited comparable DMFC performance. Also, investigation on a multi-ionic organic–inorganic hybrid ZIM as polymer electrolyte membranes (PEMs) will give rise to a new developing field in materials and membrane science.

A 2H nuclear magnetic resonance study of the state of water in neat silica and zwitterionic stationary phases and its influence on the chromatographic retention characteristics in hydrophilic interaction high-performance liquid chromatography

2H NMR has been used as a tool for probing the state of water in hydrophilic stationary phases for liquid chromatography at temperatures between −80 and +4 °C. The fraction of water that remained unfrozen in four different neat silicas with nominal pore sizes between 60 and 300 Å, and in silicas with polymeric sulfobetaine zwitterionic functionalities prepared in different ways, could be determined by measurements of the line widths and temperature-corrected integrals of the 2H signals. The phase transitions detected during thawing made it possible to estimate the amount of non-freezable water in each phase. A distinct difference was seen between the neat and modified silicas tested. For the neat silicas, the relationship between the freezing point depression and their pore size followed the expected Gibbs–Thomson relationship. The polymeric stationary phases were found to contain considerably higher amounts of non-freezable water compared to the neat silica, which is attributed to the structural effect that the sulfobetaine polymers have on the water layer close to the stationary phase surface. The sulfobetaine stationary phases were used alongside the 100 Å silica to separate a number of polar compounds in hydrophilic interaction (HILIC) mode, and the retention characteristics could be explained in terms of the surface water structure, as well as by the porous properties of the stationary phases. This provides solid evidence supporting a partitioning mechanism, or at least of the existence of an immobilized layer of water into which partitioning could be occurring.

Sulfoalkylbetaine‐based monolithic column with mixed‐mode of hydrophilic interaction and strong anion‐exchange stationary phase for capillary electrochromatography

A novel monolithic stationary phase with mixed mode of hydrophilic and strong anion exchange (SAX) interactions based on in situ copolymerization of pentaerythritol triacrylate (PETA), N,N-dimethyl-N-methacryloxyethyl N-(3-sulfopropyl) ammonium betaine (DMMSA) and a selected quaternary amine acrylic monomer was designed as a multifunctional separation column for CEC. Although the zwitterionic functionalities of DMMSA and hydroxy groups of PETA on the surface of the monolithic stationary phase functioned as the hydrophilic interaction (HI) sites, the quaternary amine acrylic monomer was introduced to control the magnitude of the EOF and provide the SAX sites at the same time. Three different quaternary amine acrylic monomers were tested to achieve maximum EOF velocity and highest plate count. The fabrication of the zwitterionic monolith (designated as HI and SAX stationary phase) was carried out when [2-(acryloyloxy)ethyl]trimethylammonium methylsulfate was used as the quaternary amine acrylic monomer. The separation mechanism of the monolithic column was discussed in detail. For charged analytes, a mixed mode of HI and SAX was observed by studying the influence of mobile phase pH and salt concentration on their retentions on the poly(PETA-co-DMMSA-co-[2-(acryloyloxy)ethyl]trimethylammonium methylsulfate) monolithic column. The optimized monolith showed good separation performance for a range of polar analytes including nucleotides, nucleic acid bases and nucleosides, phenols, estrogens and small peptides. The column efficiencies greater than 192 000 theoretical plates/m for estriol and 135 000 theoretical plates/m for charged cytidine were obtained.

Cobalt Porphyrin Functionalized Carbon Nanotubes for Oxygen Reduction

Carbon nanotube (CNT) compositions were prepared by covalently grafting a Co(II) porphyrin to functionalized multiwalled carbon nanotubes (MWCNTs) via zwitterionic functionalization of the CNT sidewalls followed by a SN2 substitution reaction. The MWCNT−Co−porphyrin compositions, mixed with Nafion, displayed excellent catalytic performance for oxygen reduction in acidic media (pH range, 0.0−5.0) at room temperature. With low catalyst loading, the oxygen reduction rates achieved are more than 1 order of magnitude higher than previously reported values for similar Co−porphyrin catalysts. These results demonstrate the advantages of systems of MWCNTs covalently linked to electrocatalytic molecules. The electrodes are easily fabricated by a drop-casting vacuum drying procedure. Rotating disk electrode (RDE) and rotating ring disk electrode (RRDE) measurements revealed the mechanism to be a direct four-proton and four-electron reduction of oxygen to water. These results demonstrate that new MWCNT electrocatalyt...

3-[[3-(Triethoxysilyl)propyl]amino]propane-1-sulfonic Acid−Poly(vinyl alcohol) Cross-Linked Zwitterionic Polymer Electrolyte Membranes for Direct Methanol Fuel Cell Applications

Recently, organic-inorganic nanocomposite zwitterionic polymer electrolyte membranes (PEMs) have attracted remarkable interest for application to the direct methanol fuel cell (DMFC) operated at intermediate temperature (100-200 degrees C). In this paper, we report the synthesis of an organic-inorganic hybrid zwitterionomer silica precursor with ammonium and sulfonic acid functionality by the ring-opening of 3-propanesultone under mild heating conditions and the preparation procedure of a proton-conductive and stable organic-inorganic zwitterion-poly(vinyl alcohol) (PVA) cross-linked PEM by sol-gel in aqueous media. Developed PEMs were extensively characterized by studying their physicochemical and electrochemical properties under DMFC operating conditions. These membranes were designed to possess all of the required properties of a proton-conductive membrane, namely, reasonable swelling, good mechanical, dimensional, and oxidative strength, flexibility, and low methanol permeability along with reasonable proton conductivity (4.85 x 10(-2) S cm(-1)) due to zwitterionic functionality. Moreover, from the selectivity parameter among all developed membranes, ZI-70 [zwitterionomer membrane with 70 wt % of PVA of 3-[[3-(triethoxysilyl)propyl]amino]propane-1-sulfonic acid in the membrane matrix], exhibited the best results in comparison to the Nafion117 membrane for DMFC applications.

Hydrophilic interaction chromatography of small metal species in plants using sulfobetaine‐ and phosphorylcholine‐type zwitterionic stationary phases

Hydrophilic interaction chromatography (HILIC) was applied for the separation of small, noncovalent metal species, and free ligands in plants, using two different zwitterionic stationary phases at pH 7.3. Ligands ranged from amino acids and phytosiderophores to organic acids and synthetic chelators like EDTA. Our results confirmed the suitability of zwitterionic stationary phases for the separation of such ligands and their metal complexes. In particular, the chromatographic behavior of phytosiderophore complexes of copper, nickel, and zinc on a sulfobetaine-type material was compared to that on a phosphorylcholine-type material under otherwise identical conditions. A compression of the usable retention range for phytosiderophore species on the latter phase was found, which can be traced back to the reversed charge orientation of the zwitterionic functionalities. Differences were also found for the integrity of more labile metal chelates during separation on the two columns. In particular, Ni-malate could only be analyzed on the sulfobetaine phase, and Cu-glutathione, Ni-aspartate, and Ni-citrate complexes were only stable on the phosphorylcholine stationary phase at pH 7.3. Ni-histidine species were only found after lowering the pH to 4-5. The identification of separated species is possible by online ESI-MS in the negative ionization mode.