Aminated dendritic surfaces characterization: a rapid and versatile colorimetric assay for estimating the amine density and coating stability

The functionalization of surfaces with amino groups is used in many application areas such as in industrial biocatalytic processes for the development of medical biomaterials and in the environment for removing pollutants from water. Amino group density and grafting stability are often related to functionalized material performances; thus, their characterizations are of prime importance. The determination of amino density and grafting stability on polymeric material (e.g. polypropylene, polystyrene and cylco olefin copolymer) is often time consuming and sometimes presents technical constraints, more particularly with non-flat materials. In this paper, we report a novel colorimetric assay using the Coomassie Brilliant Blue dye for both amino density determination and grafting stability measurement. The assay named ADECA for “Amino Density Estimation by Colorimetric Assay” is sensitive, rapid, robust and versatile. We demonstrate that ADECA makes the evaluation of aminated materials performances possible for numerous material compositions, formats and chemistries used for grafting. Our study focuses on dendrigraft of poly-l-lysine and poly(amidoamine) dendrimers dendritic materials.     

Immunofunctionalisation of gold transducers for bacterial detection by physisorption

Functionalisation of the sensing surface is a key factor in immunosensor fabrication as it allows target-selective capture and prevents nonspecific adsorption of undesired components. Gold immunofunctionalisation using self-assembled monolayers (SAM) has been widely exploited to this end for the detection of small targets. However, we recently demonstrated that this strategy fails when detecting whole bacteria cells (Baldrich et al., Anal Bioanal Chem 390:1557–1562, 2008). We now investigate different physisorption-based alternatives using E. coli as the target organism. Our results demonstrate that physisorption generates the appropriate substrate for the specific detection of bacteria on gold surfaces, providing detection limits down to 10⁵ cells mL⁻¹ in an ELISA-type colorimetric assay. Additionally, surface coverage is highly reproducible when assayed by impedance spectroscopy and the inter- and intra-assay coefficients of variation are below 10–15% in all cases. These surfaces were stable, retained functionality and did not suffer from significant biomolecule desorption after 10 days storage in PBS at 37 °C, hence confirming physisorption as a cheap, simple and efficient strategy for the detection of bacteria.     

Facile method to prepare monodispersed Ag/polystyrene composite microspheres and their properties

This article presents a facile method to prepare silver/polystyrene composite microspheres. In this approach, monodispersed polystyrene (PS) particles were synthesized with carboxyl acid groups on the surfaces of the PS particles via dispersion polymerization at first. With the addition of [Ag(NH₃)₂]⁺ to the PS dispersion, [Ag(NH₃)₂]⁺ was absorbed to the surfaces of the PS particles, and then by heating the system, [Ag(NH₃)₂]⁺ complex ions were reduced to silver to form the Ag/PS composite microspheres. In the synthesis of PS dispersion, PVP was used as dispersant to stabilize the PS particles, it also acted as reducing agent in the reduction of [Ag(NH₃)₂]⁺ complex ions to silver, so no additional reducing agent was needed. The resulting composite microspheres were characterized by TEM, SEM, XPS, and XRD. The catalytic properties and surface‐enhance Raman scattering (SERS) was studied as well. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4547–4554, 2009     

A novel and consistent method (TriPOD) to characterize an arbitrary porous solid for its accessible volume,accessible geometrical surface area and accessible pore size

We present an improved Monte Carlo integration method to calculate the accessible pore size distribution of a porous solid having known configuration of solid atoms. The pore size distribution obtained with the present method is consistent with the accessible volume and the accessible geometric surface area presented in previous publications (Do and Do, in J. Colloid Interface Sci. 316(2):317–330, 2007; Do et al. in Adsorpt. J., 2010). The accessible volume, accessible geometrical surface area and the pore size distribution method construct an unambiguous and robust single framework to characterize porous solids. This framework is based on the derivation of the space accessible to the center of mass of a probe molecule. The accessible pore size presented is an absolute quantity in the sense that a zero value is possible. We present the entire framework of this characterization method and compare the improved method with the one presented previously for a set of porous solids such as graphitic slit pores, defective slit pores, bundle of carbon nanotubes, zeolite and some metal organic frameworks.     

Preparation of monodisperse polystyrene/silver composite microspheres and their catalytic properties

This article presents a facile method for the preparation of polystyrene/silver (PS/Ag) composite microspheres. In this approach, monodisperse PS spheres were synthesized via dispersion polymerization and modified by sulfonation to obtain sulfonated PS spheres with sulfonic acid groups on the surfaces, and then adsorbed Sn²⁺ ions by electrostatic interaction and used as templates. PS/Ag composite microspheres were prepared successively by addition of [Ag(NH₃)₂]⁺ complex ions to the templates dispersion, adsorbing to the surfaces of templates, and then reduction of [Ag(NH₃)₂]⁺ complex ions to Ag nanoparticles by sodium potassium tartrate. The results showed that monodisperse PS spheres with sulfonic acid groups on the surfaces were coated by an incomplete and nonuniform coverage of Ag nanoparticles in the absence of Sn²⁺ ions. In the presence of Sn²⁺ ions, however, complete and uniform Ag nanoparticles coatings were obtained on the entire PS sphere. And the deposition density and size of Ag nanoparticles can be controlled by [Ag(NH₃)₂]⁺ concentration. The resulting PS/Ag composite microspheres were characterized by SEM, TEM, XRD, TGA, and UV-vis. Preliminary catalytical tests indicated these PS/Ag composite microspheres showed good catalytic properties.     

Characterization and modification of polymer blend films

Films of immiscible blends of (PS) and poly(methyl methacrylate) (PMMA) were characterized by contact-angle measurements with sessile drop and atomic force microscopy (AFM). These blends showed a linear dependence of the contact angles on the composition, as predicted by Cassie's equation for ideal surfaces. The surface structure investigated by AFM showed low roughness and phase-separation features. The ratio between the drop radius and the roughness amounted to the order of 10⁴–10⁵. This magnitude seemed to be sufficient to put the PS/PMMA films close to ideality. Upon sulfonation, the wettability and the microscopic surface roughness of the PS/PMMA blends increased. The treatment with sulfuric acid yielded sulfonated PS domains on the surface, causing an increase in the surface wettability. The SO₃ ⁻ groups were evidenced by X-ray photoelectron spectroscopy. The sulfonation of the PS/PMMA blends enables the formation of multiphase surfaces with hydrophobic, charged and polar domains. Received: 11 December 2000 Accepted: 6 April 2001     

Measurement of the reactive and available solid-supported carboxylic,N-hydroxysuccinylated carboxylic,and aldehydo groups

We describe new colorimetric methods for the determination of the reactive and available solid-supported carboxylic,N-hydroxysuc cinylated carboxylic, and aldehydo groups under conditions usually applied for the coupling of biomolecules. The methods involve the reaction of the solid-supported functional groups with tyramine or cysteine, and the subsequent titration of the ligand coupled onto the solid supports using the commercially available bicinchoninic acid/copper protein assay reagent (BCA). The titration is based on the ability of these ligands to reduce Cu²⁺ to Cu⁺, which forms a chelate complex with bicinchoninic acid absorbing at 562 nm. The quantita tion is finally carried out through standard curves obtained using tyramine or cysteine solutions of known concentrations. The values obtained by the assays developed for several solid supports carrying carboxylic, NHS-ester, and aldehydo groups were well correlated with those obtained by other literature methods or provided by the manu facturers. All of the proposed methods are simple, more sensitive than other relevant literature methods, and require only commericially available reagents.     

Novel 1,8-naphthalimide dye for multichannel sensing of H<Superscript>+</Superscript> and Cu<Superscript>2+</Superscript>

A novel 1,8-naphthalimide dye with simple structure has been produced by a facile synthetic method for colorimetric and fluorescent sensing of H⁺ and Cu²⁺. In CH₃CN/H₂O (1/1, v/v), the dye could monitor H⁺ using dual channels (ratiometric absorbance and fluorescence intensity change) from pH 6.2 to 12.0. Meanwhile, in the pH range of 1.9–5.2, the dye could also be used to detect Cu²⁺ using triple channels [ultraviolet–visible (UV–Vis) absorption, fluorescence intensity reduction, as well as fluorescence blueshift]. The detection limits for Cu²⁺ evaluated by colorimetric and fluorescent titration were 6.10 × 10^?7 and 2.62 × 10^?7 M, respectively. The dye exhibited specific selectivity and sensitivity for H⁺ and Cu²⁺ over various coexisting metal ions. Moreover, the sensing mechanism of the dye for H⁺ and Cu²⁺ was carefully examined.     

Theoretical study of the gas-phase Fe<Superscript>+</Superscript>-mediated oxidation of ethane by N<Subscript>2</Subscript>O

We report herein a comprehensive study of the gas-phase Fe⁺-mediated oxidation of ethane by N₂O on both the sextet and quartet potential energy surfaces (PESs) using density functional theory. The geometries and energies of all the relevant stationary points are located. Initial oxygen-atom transfer from N₂O to iron yields FeO⁺. Then, ethane oxidation by the nascent oxide involves C–H activation forming the key intermediate of (C₂H₅)Fe⁺(OH), which can either undergo C–O coupling to Fe⁺ + ethanol or experience β-H shift giving the energetically favorable product of FeC₂H₄ ⁺ + H₂O. Reaction of FeC₂H₄ ⁺ with another N₂O constitutes the third step of the oxidation. N₂O coordinates to FeC₂H₄ ⁺ and gets activated by the metal ion to yield (C₂H₄)Fe⁺O(N₂). After releasing N₂ through the direct H abstraction and/or cyclization pathways, the system would be oxidized to ethenol, acetaldehyde, and oxirane, regenerating Fe⁺. Oxidation to acetaldehyde along the cyclization –C–to–C hydrogen shift pathway is the most energetically favored channel.     

Colorimetric detection of potassium ions using aptamer-functionalized gold nanoparticles

Herein, a simple and novel colorimetric method for detection of potassium ions (K⁺) was developed. The colorimetric experiments revealed that upon the addition of K⁺, the conformation of anti-K⁺ aptamer in solution changed from random coil structure to compact rigid G-quadruplex one. This compact rigid G-quadruplex structure could not protect AuNPs against K⁺-induced aggregation, and thus the visible color change from wine-red to blue-purple could be observed by the naked eye. The linear range of the colorimetric aptasensor covered a large variation of K⁺ concentration from 5 nM to 1 μM and the detection limit of 5 nM was obtained. Moreover, this assay was able to detect K⁺ with high selectivity and had great potential applications.     

Introduction of Primary Amino Groups on Poly(ethylene terephthalate) Surfaces by Ammonia and a Mix of Nitrogen and Hydrogen Plasma

With the aim of introducing primary amino groups on the surface of poly(ethylene terephthalate) (PET), two methods were compared—the use of ammonia or a combination of nitrogen and hydrogen low-pressure microwave plasma. Several plasma parameters were optimized on the reactor to increase the –NH₂ surface density, which was estimated by colorimetric titration and X-ray photoelectron spectroscopy (XPS). These techniques show that whatever the plasma treatment, almost 2 –NH₂/nm2 are incorporated on PET films. Emission spectroscopy highlighted a correlation between the density of primary amino groups and the ratio between an NH peak intensity and an Ar peak intensity (I_NH/I_Ar). Variation in surface hydrophilicity with aging in air after plasma treatment was monitored with contact angle measurements and showed a hydrophobic recovery. This was confirmed by XPS, which suggests also that surfaces treated by NH₃ plasma are more stable than surfaces treated by N₂/H₂.     

Tailoring and investigation of surface chemical nature of virgin and ion beam modified muscovite mica

We report that the surface chemical properties of muscovite mica [KAl₂(Si₃Al)O₁₀(OH)₂] like important multi-elemental layered substrate can be precisely tailored by ion bombardment. The detailed X-ray photoelectron spectroscopic studies of a freshly cleaved as well as 12-keV Ar⁺ and N⁺ ion bombarded muscovite mica surfaces show immense changes of the surface composition due to preferential sputtering of different elements and the chemical reaction of implanted ions with the surface. We observe that the K atoms on the upper layer of mica surface are sputtered most during the N⁺ or Ar⁺ ions sputtering, and the negative aluminosilicate layer is exposed. Inactive Ar atoms are trapped, whereas chemically reactive N atoms form silicon nitride (Si₃N₄) and aluminum nitride (AlN) during implantation. On exposure to air after ion bombardment, the mica surface becomes more active to adsorb C than the virgin surface. The adsorbed C reacts with Si in the aluminosilicate layer and forms silicon carbide (SiC) for both Ar and N bombarded mica surfaces. Besides the surface chemical change, prolonged ion bombardment develops a periodic ripple like regular pattern on the surface.     

Solubilization of styrene in the catanionic system dodecyltrimethylammonium hydroxide–n′-dodecanephosphonic acid

 The solubilization of styrene in micelles of the catanionic surfactant dodecyltrimethylammonium hydroxide (DTAOH)–n-dodecane-phosphonic acid (DPA) was studied by UV–Vis. spectrometry, as a function of the DTAOH:DPA proportion in the surfactant mixture. The styrene molecules are adsorbed at the surface of the micelles, with the vinyl group closer to the hydrocarbon core than the aromatic ring, which is oriented to the water. In micelles with an excess of DTAOH, the dielectric constant of the water surrounding the micelles was strongly affected by the non-neutralized –N(CH₃)⁺ ₃ groups at the Stem layer. In micelles with an excess of DPA, the –PO₃H₂ groups which are not neutralized by –N(CH₃)⁺ ₃, remain almost unionized and hydrogen-bonded. The effect of the micellar surface on the surrounding water dielectric constant dropped sharply. The dielectric constant in the hydrogen-bonded polar layer is ∼65, rising to the value of pure water very close to the micellar surface. Received: 2 September 1997 Accepted: 20 October 1997     

Structure and Reactivity of the <Emphasis Type="BoldItalic">N</Emphasis>-Acetyl-Cysteine Radical Cation and Anion: Does Radical Migration Occur?

The structure and reactivity of the N-acetyl-cysteine radical cation and anion were studied using ion-molecule reactions, infrared multi-photon dissociation (IRMPD) spectroscopy, and density functional theory (DFT) calculations. The radical cation was generated by first nitrosylating the thiol of N-acetyl-cysteine followed by the homolytic cleavage of the S–NO bond in the gas phase. IRMPD spectroscopy coupled with DFT calculations revealed that for the radical cation the radical migrates from its initial position on the sulfur atom to the α-carbon position, which is 2.5 kJ mol^–1 lower in energy. The radical migration was confirmed by time-resolved ion-molecule reactions. These results are in contrast with our previous study on cysteine methyl ester radical cation (Osburn et al., Chem. Eur. J. 2011 , 17, 873–879) and the study by Sinha et al. for cysteine radical cation (Phys. Chem. Chem. Phys. 2010 , 12, 9794–9800) where the radical was found to stay on the sulfur atom as formed. A similar approach allowed us to form a hydrogen-deficient radical anion of N-acetyl-cysteine, (M – 2H) ^•– . IRMPD studies and ion-molecule reactions performed on the radical anion showed that the radical remains on the sulfur, which is the initial and more stable (by 63.6 kJ mol^–1) position, and does not rearrange.     

Structural characterization of heparins from different commercial sources

Seven commercial heparin active pharmaceutical ingredients and one commercial low molecular weight from different manufacturers were characterized with a view profiling their physicochemical properties. All heparins had similar molecular weight properties as determined by polyacrylamide gel electrophoresis (M _N, 10–11 kDa; M _W, 13–14 kDa; polydispersity (PD), 1.3–1.4) and by size exclusion chromatography (M _N, 14–16 kDa; M _W, 21–25 kDa; PD, 1.4–1.6). one-dimensional ¹H- and ¹³C-nuclear magnetic resonance (NMR) evaluation of the heparin samples was performed, and peaks were fully assigned using two-dimensional NMR. The percentage of glucosamine residues with 3-O-sulfo groups and the percentage of N-sulfo groups and N-acetyl groups ranged from 5.8–7.9%, 78–82%, to 13–14%, respectively. There was substantial variability observed in the disaccharide composition, as determined by high performance liquid chromatography (HPLC)-mass spectral analysis of heparin lyase I–III digested heparins. Heparin oligosaccharide mapping was performed using HPLC following separate treatments with heparin lyase I, II, and III. These maps were useful in qualitatively and quantitatively identifying structural differences between these heparins. The binding affinities of these heparins to antithrombin III and thrombin were evaluated by using a surface plasmon resonance competitive binding assay. This study provides the physicochemical and activity characterization necessary for the appropriate design and synthesis of a generic bioengineered heparin.     

Tetraethanolammonium counterions in surfactant and classical colloidal systems

Interaction forces between mica surfaces as a function of added tetraethanolammonium bromide, (EtOH)₄NBr, were determined using surface forces measurements. Critical micelle concentrations and aggregation numbers were determined for tetraethanolammonium dodecylsulfate, (EtOH)₄NDS, using surface tension and fluorescence probe-quencher measurements. The properties of the large hydrophilic counterion (EtOH)₄N⁺ are compared to those of its hydrophobic analogue Pr₄N⁺.     

Surface-enhanced spectroscopy of Langmuir—Blodgett films of N-octyl,N′-isobutyl-3,4:9,10-perylene-bis(dicarboximide)

The infrared, resonant Raman and surface-enhanced resonant Raman spectra of N-octyl, N′-isobutyl-3,4:9,10-perylene-bis(dicarboximide) (PBDC) were obtained and the aggregation of PBDC molecules was studied using surface-enhanced fluorescence. Langmuir—Blodgett (LB) films of the neat dye as well as mixed layers with arachidic acid, were prepared and transferred to glass slides and surface-enhanced active surfaces for spectroscopic characterization. A strong red shifted excimer emission was characteristic of LB layers of the neat material and of the thin solid films formed by dipping a glass slide into a solution containing the dye and a volatile solvent. However, using mixed LB monolayers of PBDC and arachidic acid, the surface-enhanced fluorescence of the monomer was observed. The surface-enhanced scattering was measured for both neat and mixed LB layers.     

Mesoporous Hybrid Materials Containing Nanoscopic “Binding Pockets” for Colorimetric Anion Signaling in Water by using Displacement Assays

Mesoporous solids functionalized with anion‐binding groups have proved to be suitable anion hosts and have been used in selective colorimetric displacement assays. The material UVM‐7, a mesoporous MCM41‐type support characterized by the presence of nanometric mesoporous particle conglomerates, was selected as inorganic scaffolding. Reaction of the template‐free UVM‐7 solid with 3‐aminopropyltriethoxysilane ( 1 ) yielded solid S1 , from which the derivatives S2 and S3 were obtained by reaction with 2‐methylthio‐2‐imidazoline hydroiodide ( 2 ) and butyl isocyanate ( 3 ), respectively. Solids S4 and S5 were prepared by reaction of the starting mesoporous UVM‐7 scaffolding with N‐methyl‐N′‐propyltrimethoxysilyl imidazolium chloride ( 4 ) and with 3‐(trimethoxysilyl)propyl‐N,N,N‐trimethylammonium chloride ( 5 ), respectively. The solids synthesized contain mesoporous binding pockets that can interact with anions through electrostatic attractive forces ( S1 , S2 , S4 , S5 ) and hydrogen‐bonding interactions ( S1 , S2 , S3 , S4 ). These functionalized solids were loaded with a dye ( d ) capable of interacting coordinatively with the anchored binding sites, in our case 5‐carboxyfluorescein, to yield the hybrid materials S1d, S2d , S3d , S4d and S5d . These dye‐containing solids are the signaling reporters. Their sensing ability towards a family of carboxylates, namely acetate, citrate, lactate, succinate, oxalate, tartrate, malate, mandelate, glutamate and certain nucleotides, has been studied in pure water at pH 7.5 (Hepes, 0.01 mol dm^?3). In the sensing protocol, a particular analyte may be bonded preferentially by the nanoscopic functionalized pocket, leading to delivery of the dye to the solution and resulting in colorimetric detection of the guest. The response to a given anion depends on the characteristics of the binding pockets and the specific interaction of the anion with the binding groups in the mesopores. We believe that the possibility of using a wide variety of mesoporous supports that can easily be functionalized with anion‐binding sites, combined with suitable dyes as indicators, make this approach significant for opening new perspectives in the design of chromogenic assays for anion detection in pure water.     

Surface modification of thin polystyrene films

 The sulfonation of polystyrene (PS) films with 50 and 96% sulfuric acid as a function of time is presented. In contrast to previous literature reports, we showed that the treatment of PS films even with dilute sulfuric acid yields sulfonated surfaces after reaction times of 30 s–1 h. The hydrophilicity of the modified PS increased considerably in comparison to the unreacted PS films. X-ray photoelectron spectroscopy yielded evidence for the sulfonation of PS at the surface. Unreacted spin-coated PS films were very smooth, while modified PS showed some clumps dispersed on a flat surface, as analyzed by atomic force microscopy. The surface morphology was identified as a phase-separated system composed of domains of unreacted PS and a matrix of sulfonated PS by fluorescence microscopy using the positively charged dye rhodamine B. The adsorption of the polycation diallyldimethylammonium chloride on the sulfonated PS surface could be detected. The thickness of the adsorbed polycation was 2.2 nm. Received: 3 November 1998 Accepted in revised form: 23 February 1999