Polarographic behavior of Cd2+ and Zn2+—PGA complexes. Polarographic and circular dichroism spectroscopic studies on the Cd2+ and/or Zn2+—poly(α-L-glutamic acid) complex in aqueous solution
“…Coil-to-Helix Transition Induced by Divalent Metal Ion (Ca 2+ ). The conformational transition of free PLGA can also be induced by divalent metal ions, such as Ca 2+ , Mg 2+ , Cd 2+ , or Zn 2+ . , In this study, we examine the effects of a biologically important ion, Ca 2+ , on the surface-grafted films. Figure shows the CD spectra of a surface-grafted PLGA before and after complexation with Ca 2+ at pH 8.…”
Section: Resultsmentioning
confidence: 99%
“…Hence, external stimulants that are able to neutralize or ionize the side chains would be able to induce the helix−coil transition of the polypeptide backbones, and such a transition is conceivably reversible. In this study, we use three known stimulants, (1) H + /OH - (pH), , (2) surfactant (decylammonium chloride (DAC)), − and (3) divalent metal ion (Ca 2+ ), , to induce the reversible helix−coil transition at surfaces, as schematically shown in Scheme . 1 Schematic Illustration of the Reversible Helix−Coil Transition of a High-Density, Surface-Grafted PLGA Monolayer Induced by Typical External Stimulants…”
Supporting Information1. Chemicals. The polypeptide monomer N-carboxyanhydride (NCA) of γ-benzyl Lglutamate (BLG) was synthesized by phosgenating BLG with triphosgene. It was then purified by rephosgenation according to the procedure published by Dorman et al. 1 3-Aminopropyltriethoxysilane (APS) was used as the initiator. Hydrogen bromide (30% anhydrous hydrogen bromide in glacial acetic acid) was used as the debenzylation reagent. Buffer solutions (2 mM concentration in all cases) were prepared by sodium phosphate and tris(hydroxymethyl)aminomethane (Tris). Decylammonium chloride (DAC) was prepared from n-decylamine: concentrated HCl (2 M) was added to neutralize n-decylamine in acetone, then the solution was dried in vacuum overnight, and finally the obtained DAC was dissolved in water. Solution of Ca 2+ was prepared from reagent grade anhydrous calcium chloride. All chemicals were purchased from Sigma-Aldrich (Milwaukee, WI) and used as received.
Cleaning of Substrates.Two substrates were used in this study depending on the intended characterization techniques. Silicon wafers (Siltec Silicon, single side polished, 500 µm, orientation <100>) with a native oxide layer of 11.4 ± 0.2 Å thickness were cut to 2 cm × 4 cm and used for ellipsometry and transmission FTIR measurements. Quartz plates (Starna Cells Inc., with a dimension of 45 × 12.5 × 1 mm) were used for CD measurements.All substrates were cleaned with a freshly prepared mixture of concentrated sulfuric acid and 30% hydrogen peroxide (70/30, v/v) at 120 °C for 30 minutes. They were then washed with a large amount of distilled water, and rinsed with acetone. The substrates were blown dried under a stream of nitrogen and immediately used in the silanization reaction.
“…Coil-to-Helix Transition Induced by Divalent Metal Ion (Ca 2+ ). The conformational transition of free PLGA can also be induced by divalent metal ions, such as Ca 2+ , Mg 2+ , Cd 2+ , or Zn 2+ . , In this study, we examine the effects of a biologically important ion, Ca 2+ , on the surface-grafted films. Figure shows the CD spectra of a surface-grafted PLGA before and after complexation with Ca 2+ at pH 8.…”
Section: Resultsmentioning
confidence: 99%
“…Hence, external stimulants that are able to neutralize or ionize the side chains would be able to induce the helix−coil transition of the polypeptide backbones, and such a transition is conceivably reversible. In this study, we use three known stimulants, (1) H + /OH - (pH), , (2) surfactant (decylammonium chloride (DAC)), − and (3) divalent metal ion (Ca 2+ ), , to induce the reversible helix−coil transition at surfaces, as schematically shown in Scheme . 1 Schematic Illustration of the Reversible Helix−Coil Transition of a High-Density, Surface-Grafted PLGA Monolayer Induced by Typical External Stimulants…”
Supporting Information1. Chemicals. The polypeptide monomer N-carboxyanhydride (NCA) of γ-benzyl Lglutamate (BLG) was synthesized by phosgenating BLG with triphosgene. It was then purified by rephosgenation according to the procedure published by Dorman et al. 1 3-Aminopropyltriethoxysilane (APS) was used as the initiator. Hydrogen bromide (30% anhydrous hydrogen bromide in glacial acetic acid) was used as the debenzylation reagent. Buffer solutions (2 mM concentration in all cases) were prepared by sodium phosphate and tris(hydroxymethyl)aminomethane (Tris). Decylammonium chloride (DAC) was prepared from n-decylamine: concentrated HCl (2 M) was added to neutralize n-decylamine in acetone, then the solution was dried in vacuum overnight, and finally the obtained DAC was dissolved in water. Solution of Ca 2+ was prepared from reagent grade anhydrous calcium chloride. All chemicals were purchased from Sigma-Aldrich (Milwaukee, WI) and used as received.
Cleaning of Substrates.Two substrates were used in this study depending on the intended characterization techniques. Silicon wafers (Siltec Silicon, single side polished, 500 µm, orientation <100>) with a native oxide layer of 11.4 ± 0.2 Å thickness were cut to 2 cm × 4 cm and used for ellipsometry and transmission FTIR measurements. Quartz plates (Starna Cells Inc., with a dimension of 45 × 12.5 × 1 mm) were used for CD measurements.All substrates were cleaned with a freshly prepared mixture of concentrated sulfuric acid and 30% hydrogen peroxide (70/30, v/v) at 120 °C for 30 minutes. They were then washed with a large amount of distilled water, and rinsed with acetone. The substrates were blown dried under a stream of nitrogen and immediately used in the silanization reaction.
“…Finally, as alluded to earlier, PLAA, and PDAA to some extent, may form helical species. − The extent of helix formation has been described by the Zimm−Bragg model 27 in eq 2, where f is the fraction of helix (in helical conformation), s is the propagation parameter, and σ ZB is the initiation parameter. The propagation parameter is the key to helix formation, and is a function of the electrostatic (Δμ el ), binding (Δμ binding ), and nonelectrostatic (Δμ nonel ) chemical potential contributions .…”
Section: Background and Theorymentioning
confidence: 99%
“…Increases in Δμ el and Δμ binding , by ionization of the chain, will counterbalance Δμ nonel , and s will approach 0, the coil limit (i.e., fully stretched conformation). Ionic strength and metal cations will also affect helix formation …”
Functionalized membranes represent a field with multiple applications. Examination of specific metal−macromolecule interactions on these surfaces presents an excellent method for characterization of these
materials. These interactions may also be exploited for heavy metal sorption from drinking and industrial
water sources. Various low-capacity, silica-based ion-exchange and chelating sorbents (about 0.5 mmol of
metal/g of resin) are available for treatment of such waters. Cellulosic membrane-based sorbents,
functionalized with polyamino acids, present an excellent approach for high-capacity (3−14 mmol of metal/g
of sorbent) metal sorption. Silica-based membrane sorbents possess metal sorption capacities approaching
those of cellulosic-based membranes, with the added benefits of excellent acid and solvent resistance.
Metal sorption capacities of silica-based membrane sorbents with various polyamino acids range from 0.6
mmol to 1.4 mmol of metal/g of sorbent. Ion exchange, chelation, and electrostatic interactions form the
basis of metal sorption. Electrostatic interactions are greatly magnified in membrane-based sorbents, and
are partly responsible for their high capacities. Regeneration of these sorbents has also been shown,
including the possibility for selective desorption of metals.
“…The diffusion currents (id) for the ions were the same as those obtained in the absence of this reagent. The diffusion coefficient in the Ilkovic equation becomes significantly small in the presence of a polymer if the polymer can form a complex with the ion before it reaches the dropping mercury electrode [4,5]. The above results suggest that poly 3-CD does not form any kind of complex with In(III) before it reaches the DME.…”
The difference in the peak potentials of In(III) and Cd(II), whose reduction potentials are very close to each other, becomes large in the presence of poly beta-cyclodextrin in sodium perchlorate medium. The relationships between the peak currents for these two ions and their concentrations are linear, suggesting that the simultaneous determination of the ions is possible in the presence of this reagent.
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