Preconcentration of copper,lead, cadmium and zinc ions from water with 2-mercaptobenzothiazole loaded on glass beads with the aid of collodion

2-Mercaptobenzothiazole (MBT) loaded on glass beads with the aid of collodion was prepared and used for selective preconcentration of μg l^?1 levels of copper(II) and lead from aqueous solutions. Copper and lead were quantitatively retained on the loaded beads from solutions of pH 5.0–6.0 and >5.0, respectively, while cadmium(II) and zinc(II) were retained at ? pH 6.0 and 7.0, respectively. The retention capacity of the loaded beads was ca. 108 μg Cu g^?1 (1.7 μmol g^?1) at pH 5.5 for beads of 0.3–0.4 mm diameter. The mole ratios of MBT to copper(II) and lead(II) were ca. 10 and 45, respectively, regardless of the amount of MBT loaded on the beads. Copper was completely retained on the column at a high flow rate (21.7 ml min^? cm^?2) and lead(II) at up to 12.7 ml min^? cm^?2. Cadmium(II) and zinc(II) were not retained quantitatively even at low flow rates (< 1.2 ml min^?1 cm^?2). Thus, selective preconcentration of copper and lead was achieved by passing the sample through the column at high flow rate at pH 6.5. The copper and lead retained on the column were complete eluted together with the collodion with 5 ml of MIBK by batch-mode elution, and determined directly by one-drop atomic absorption spectrometry. Copper(II) and lead(II) in several kinds of water were determined.     

Bond-graph description and simulation of membrane processes: Permeation in a compartmental membrane system

Network and numerical analysis of permeation through a membrane under non-stationary, stationary, and pseudo-stationary conditions is described. A compartmentalized membrane system (feed solution|membrane|stripping solution) was represented by a linear network of capacitances, diffusion, and sorption/desorption graphs. Reticulation degree of diffusion layers sufficient for quantitative modeling of the diffusion through a homogeneous membrane was estimated. It was found that for membranes of the thickness from 0.001 cm to 0.1 cm and the diffusion coefficients from 1 × 10^?7 cm² s^?1 to 1 × 10^?5 cm² s^?1, the membrane (or other diffusion layer) partition into ten slices leads to simulated time lags and stationary fluxes differing from the theoretical ones by less than 0.5 % and 1 %, respectively. Extended model with two unstirred interfacial layers and the feed and stripping solution of finite volumes was applied to characterize the effects caused by possible membrane heterogeneity.     

Chiral macrocycles,part II: Transport of amino acid Li+ salts

Complexation of amino acids in both their zwitterionic and Li⁺ salt forms by macrocycles, and carrier-mediated transport of the Li⁺ salts through a CH₂Cl₂ membrane have been investigated: the transport study of four amino acids by a new series of tetrapyrazolic macrocycles with functionalized sidearms shows wide variations of the transport rates depending on both the macrocyclic sidearm and the amino acid structure.     

Separation of Free Amiimo Acids on Reverse Stationary Phases Using an Alkyl Sulfonate Salt as a Mobile Phase Additive

Abstract

Alkylsulfonate (RSO₃ ^?) salts were evaluated as mobile phase additives for the separation of free amino acids on reverse stationary phases using an acidic mobile phase where the amino acids are cations. The enhanced amino acid retention is the result of two major interactions, one being retention of the RSO₃ ^? salt on the stationary phase and the other an ion exchange selectivity between the amino acid analyte cation and the RSO₃ ^? countercation, or other countercations in the mobile phase. Major mobile phase variables are: type and concentration of RSO₃ ^? salt (the studies focused on C₈SO₃ ^? salts), presence of organic modifier, type of countercation present, and mobile phase pH and ionic strength. Alkyl modified silica and polystyrenedivinyl-benzene copolymeric reverse stationary phases were compared. A mobile phase gradient, increasing per cent organic modifier was shown to be best, is necessary for separating complex mixtures of polar and nonpolar or basic amino acids. The procedure is applicable to the identification and/or determination of amino acids in mixtures or in peptides after hydrolysis.     

Separation of bonito extract by composite UF membranes of sulfonated polysulfone coated on ceramics

Separation of ingredients in bonito extract was studied by a composite UF membrane of ceramic/sulfonated polysulfone (SPS). The bonito extract mainly contained inosine-5′-monophosphate (IMP), glutamic acid as a tasty ingredient and hypoxanthine, histidine as a putrefaction ingredient. The composite membrane showed a high rejection against negatively charged IMP, but permeated non-charged hypoxanthine. This is because of the negatively charged repulsion between the membrane and the solute. The permeation of amino acid could be controlled using the difference in isoelectric points of amino acids themselves. When the amino acid solution was filtrated by the composite membrane at pH 7, glutamic acid was rejected and no histidine was rejected. The charges of composite membrane were found to have an effect on the separation of ingredients in bonito extract.The composite membrane was stable within a wide pH range from 3 to 9, and had a thermal durability under 353 K.     

Voltammetric Elucidation of Ion Transfer Through an Extremely Thin Membrane

Digital simulation of the cyclic voltammogram for the ion transfer through a liquid membrane of thickness from 1 mm to 10 nm was performed. The magnitude of current and the shape of the voltammogram simulated for extremely thin membrane (10 nm thick) were similar to those observed experimentally with a bilayer lipid membrane, BLM, of about 10 nm in thick, when the diffusion coefficient of an ion in the BLM was assumed to be extraordinary small (10^?13 to 10^?14 cm² s^?1).     

Permeation of oxygen dissolved in water through substituted polyacetylene membranes

The permeation of oxygen dissolved in water through substituted polyacetylene membranes was studied by using an oxygen electrode at 25°C. Many of the membranes (thickness about 200 μm) showed high apparent permeability coefficients P in the range 10^?9?10^?8 cm³ (STP) cm cm^?2s^?1 cmHg^?1. The resistance r of the boundary layer and the permeability P_∞, at infinite membrane thickness were determined from the dependence of P on membrane thickness. The r values of Si-containing and aliphatic polyacetylenes were usually larger than those of aromatic polyacetylenes. The P_∞, values of Si-containing and aliphatic polyacetylenes agreed closely with the permeability coefficients P_g for gaseous oxygen. In contrast, P_∞ values for aromatic polyacetylenes were larger than P_g values.     

On-line amino acid-based capillary isoelectric focusing-ESI-MS/MS for protein digests analysis

Six amino acids with pIs that ranged from 3.2 to 9.7 were used as ampholytes to establish a pH gradient in capillary isoelectric focusing. This amino acid-based capillary isoelectric focusing (cIEF) was coupled with ESI-MS/MS using an electrokinetically pumped sheath-flow interface for peptide analysis. Amino acid-based isoelectric focusing generates a two-order of magnitude lower background signal than commercial ampholytes in the important m/z range of 300–1800. Good focusing was achieved for insulin receptor, which produced ∼10 s peak width. For 0.1 mg mL⁻¹ bovine serum albumin (BSA) digests, 24 ± 1 peptides (sequence coverage 47 ± 4%) were identified in triplicate analysis. As expected, the BSA peptides were separated according to their pI. The concentration detection limit for the BSA digests is 7 nM and the mass detection limit is 7 fmole. A solution of six bovine protein tryptic digests spanning 5 orders of magnitude in concentration was analyzed by amino acid based cIEF-ESI-MS/MS. Five proteins with a concentration range spanning 4 orders of magnitude were identified in triplicate runs. Using amino acid based cIEF-ESI-MS/MS, 112 protein groups and 303 unique peptides were identified in triplicate runs of a RAW 264.7 cell homogenate protein digest. In comparison with ampholyte based cIEF-ESI-MS/MS, amino acid based cIEF-ESI-MS/MS produces higher resolution of five acidic peptides, much cleaner mass spectra, and higher protein spectral counts.     

The application of 2,4,6-trinitrobenzene-1-sulphonic acid in the differential pulse polarographic determination of amines

The differential pulse polarographic behaviour of 2,4,6-trinitrophenyl (TNP) derivatives of several primary amines and amino acids was investigated in the presence of sulphite ion. All the derivatives produced a polarographic peak for their complexes with sulphite (1 × 10^?2 M) in pH 8.0 phosphate buffer (0.05 M)/0.1 M potassium chloride. The derivatives of proteins and peptides did not give such a peak. A 5-min reaction time at room temperature (or 50°C for lysine) and pH 10.5 using 1 × 10^?4 M 2,4,6-trinitrobenzene-1-sulphonic acid provides the optimal conditions for the determination of 5 × 10^?6?2.5 × 10^?5 M amines. The relative standard deviation for determining 1 × 10^?5 M glycine (n = 5) was 1%.     

N-Terminal Peptide Sequence Repetition Influences the Kinetics of Backbone Fragmentation: A Manifestation of the Jahn-Teller Effect?

Analysis of large (>10,000 entries) databases consisting of high-resolution tandem mass spectra of peptide dications revealed with high statistical significance (P?<?1?10^–3) that peptides with non-identical first two N-terminal amino acids undergo cleavages of the second peptide bond at higher rates than repetitive sequences composed of the same amino acids (i.e., in general AB- and BA- bonds cleave more often than AA- and BB- bonds). This effect seems to depend upon the collisional energy, being stronger at lower energies. The phenomenon is likely to indicate the presence of the diketopiperazine structure for at least some b₂ ⁺ ions. When consisting of two identical amino acids, these species should form through intermediates that have a symmetric geometry and, thus, must be subject to the Jahn-Teller effect that reduces the stability of such systems.

Bisquaternary-drug membrane electrodes with high sensitivity

The construction and performance characteristics of ion-selective plastic membrane electrodes for succinylcholine, hexamethonium and decamethonium are described. The electrodes, based on ion-pair complexes with triphenylstillbenyl borate (TPSB), show near-Nernatian responses over the range 10^?2–10^?6 M or less, with very low limits of detection at around 10^?7 M. The responses are not affected by pH in the range 2–10. The selectivity relative to some inorganic ions, amino acids, neurotransmitters, drugs and various drug excipients is reported.     

DETERMINATION OF PERMEATION PROPERTIES OF GAS THROUGH POLYMER MEMBRANE BY GAS CHROMATOGRAPHY

An apparatus constructed for measuring permeation properties of polymer membranes using a mixture of gases is described. A gas chromatographic system was applied to determine the individual transport characteristics of component gases without a vacuum line. This paper also discusses some experimental factors effecting the precision of measurement. The results show that there is a linear relationship between the permeation time and the volume of the gas permeated through the membrane within certain permeation period, which depends on the permeation rate (from 10~(-4) to 10~(-7) cm~3 (STP)/cm~2. sec. cmHg) of the membrane. The reproducibility has been found to be good with a relative standard deviation of 3.5%. This method is more sensitive, considerably faster and more convenient for determining both the permeability coefficient and the separation factor of a polymer membrane from a chromat ogram using mixed penetrant gases.     

Application of Electrochemiluminescence Sensor to a Rapid Method of Estimating Activity of Enzyme in Hydrolysis of Peptides

An advanced flow‐through electrochemiluminescence (ECL) detector was applied to determination of resulting amino acids and oligopeptides in hydrolysis of four peptides by leucine aminopeptidase. For 20mer polypeptide PRGPDRPEGIEEEGGERDRD, the ECL intensity due to the polypeptide and produced proline was analyzed to give the dissociation contant K_m (1.2×10^?4 M) and the catalytic reaction constant k_cat (3.7 s^?1), which were good agreement with those obtained by HPLC. The enzymatic parameters were similarly obtained for the other peptides.     

A Graphene Oxide Membrane with Highly Selective Molecular Separation of Aqueous Organic Solution

A graphene oxide (GO) membrane is supported on a ceramic hollow fiber prepared by a vacuum suction method. This GO membrane exhibited excellent water permeation for dimethyl carbonate/water mixtures through a pervaporation process. At 25 °C and 2.6 wt % feed water content, the permeate water content reached 95.2 wt % with a high permeation flux (1702 g m^?2 h^?1).     

Separation of peptide diastereomers using CEC and a hydrophobic monolithic column

A neutral hydrophobic monolith prepared by radical in situ copolymerization of lauryl methacrylate and ethylene dimethacylate has been evaluated for the CEC separation of diastereomers of small peptides using acidic mobile phases containing ACN as organic modifier. Using an acidic mobile phase, the peptides migrated due to their own electrophoretic mobility. Hydrophobic interactions with the stationary phase contributed to the separation. Peptide mobility and resolution increased with increasing the ACN content. Retention times increased with the pH of the mobile phase. Peak resolution increased with buffer pH and concentration. Di‐ and tripeptides composed only of L ‐configured amino acids migrated faster than peptides containing D ‐amino acids. A mixture of isomeric Asp tripeptides that could not be completely resolved by either CZE or HPLC as well as the 24mer peptides tetracosactide and ¹⁶[D ‐Lys]‐tetracosactide could also be separated by CEC on the hydrophobic monolith.     

Heavy‐Atom Labeled Transmembrane β‐Peptides: Synthesis,CD‐Spectroscopy,and X‐ray Diffraction Studies in Model Lipid Multilayer

Transmembrane β‐peptides are promising candidates for the design of well‐controlled membrane anchors in lipid membranes. Here, we present the synthesis of transmembrane β‐peptides with and without tryptophan anchors, as well as a novel iodine‐labeled d ‐β³‐amino acid. By using one or more of the heavy‐atom labeled amino acids as markers, the orientation of the helical peptide was inferred based on the electron‐density profile determined by X‐ray reflectivity. The β‐peptides were synthesized through manual Fmoc‐based solid‐phase peptide synthesis (SPPS) and reconstituted in unilamellar vesicles forming a right‐handed 3₁₄‐helix secondary structure, as shown by circular dichroism spectroscopy. We then integrated the β‐peptide into solid‐supported membrane stacks and carried out X‐ray reflectivity and grazing incidence small‐angle X‐ray scattering to determine the β‐peptide orientation and its effect on the membrane bilayers. These β‐peptides adopt a well‐ordered transmembrane motif in the solid‐supported model membrane, maintaining the basic structure of the original bilayer with some distinct alterations. Notably, the helical tilt angle, which accommodates the positive hydrophobic mismatch, induces a tilt of the acyl chains. The tilted chains, in turn, lead to a membrane thinning effect.     

A weak cation-exchange phase for the separation of biogenic amines by open tubular liquid chromatography

Summary The preparation and performance of a weak cation-exchange stationary phase for Open Tubular Liquid Chromatography (OT-LC) was investigated. The stationary phase was prepared in 5.4 μm I.D. fused silica capillaries byin situ photopolymerization of a mixture of silicon acrylate and acrylic acid. The influence of pH, counter ion concentration and organic modifier concentration of the mobile phase on the retention was studied with catecholamines as test solutes using LIF detection. Other biological amines like amino acids, small peptides and nucleic acid derivatives could be separated on this stationary phase as well. The kinetic performance of the stationary phase was studied with several cations and neutral solutes.     

Kinetics and mechanism of the decomposition of N-brominated alanine in aqueous solution

Aqueous bromine reacts with alkyl-sidechain amino acids through a series of steps resulting in the formation of the corresponding alkyl aldelydes and nitriles. The kinetics and the mechanism of the interaction of bromine with alanine are examined. The products and the rates of this reaction are dependent in a complex way on the initial reactant concentration and pH. Acetaldeyde production is favored at low bromine-to-alanine ratios, low bromine concentrations, and pH values above 6. The first-order rate constant for the formation of acetaldelyde from alanine under these conditions is k₄ = 1.98 × 10¹⁵ e^?22,500/RT min^?1. At higher concentration the nitrile is formed through a bromoimine intermediate. Under most conditions the nitrile appears to form from a catalyzed decomposition of the bromoimine which is too fast to be followed by the methods used in this study. However, residual amounts of the bromoimine decay by a slower first-order mechanism. The rate constant for this slower reaction in the case of alanine at pH 6.8–6.9 and alanine concentrations of 1 × 10^?4M is k₆ = 1.75 × 10⁵ e^?10,400/RT min^?1.     

A fluorescence sensor for quantifying pH in the range from 6.5 to 8.5

A sensor for quantifying pH values in the physiological range has been prepared by immobilizing the trisodium salt of 8-hydroxyl-1,3,6-pyridine trisulfonic acid (HOPSA) on an anion-exchange membrane. Because electronically excited HOPSA undergoes rapid deprotonation, both acid and base forms of HOPSA lead to fluorescence from the excited state of OPSA^?. However, the acid and base forms of HOPSA can be selectively detected by appropriate choice of excitation wavelengths. The ratio of fluorescence intensities resulting from excitation at 470 and 405 nm can be used to quantify pH values between 6 and 9. The ratio is unaffected by variables such as temperature and ionic strength which affect abslute intensities. At coverages below 15 μg cm^?2, the ratio varies only slightly with the amount of HOPSA immobilized on the membrane. Membranes treated with HOPSA can be stored for extended periods of time without changing characteristics. However, they undergo slow photodegradation which will limit their useful lifetimes.     

Facile Synthesis of Biologically Active Peptides Using Phase Transfer Reagents as C-Terminal Protecting Group

Phase-transfer reagents (basic, neutral, and acidic) can temporarily protect carboxyl groups by salt formation of C-terminal free amino acids or peptides during peptide synthesis. The salts of amino acids or peptides behave as RNH₂ rather than RNH₃⁺. At least there is a sufficient concentration of the free amine to act as a nucleophile under the reaction conditions. Many biologically active small peptides have been synthesized by this procedure. No racemization was detected. Unusual amino acids such as β-alanine, and ε-aminohexanoic acid can be incorporated into peptides in high yields.