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Analytical chemistry is key to the functioning of a modern society. From early days, ethics in measurements have been a concern and that remains today, especially as we have come to rely more on the application of analytical science in many aspects of our lives. The main aim of this Feature is to suggest ways of introducing the topic of social responsibility and its relation to analytical chemistry in undergraduate or graduate chemistry courses.

Minor groove hydrogen bonding (HB) interactions between DNA polymerases (pols) and N3 of purines or O2 of pyrimidines have been proposed to be essential for DNA synthesis from results obtained using various nucleoside analogues lacking the N3 or O2 contacts that interfered with primer extension. Because there has been no direct structural evidence to support this proposal, we decided to evaluate the contribution of minor groove HB interactions with family B pols. We have used RB69 DNA pol and 3-deaza-2'-deoxyadenosine (3DA), an analogue of 2-deoxyadenosine, which has the same HB pattern opposite T but with N3 replaced with a carbon atom. We then determined pre-steady-state kinetic parameters for the insertion of dAMP opposite dT using primer/templates (P/T)-containing 3DA. We also determined three structures of ternary complexes with 3DA at various positions in the duplex DNA substrate. We found that the incorporation efficiency of dAMP opposite dT decreased 10(2)-10(3)-fold even when only one minor groove HB interaction was missing. Our structures show that the HB pattern and base pair geometry of 3DA/dT is exactly the same as those of dA/dT, which makes 3DA an optimal analogue for probing minor groove HB interactions between a DNA polymerase and a nucleobase. In addition, our structures provide a rationale for the observed 10(2)-10(3)-fold decrease in the rate of nucleotide incorporation. The minor groove HB interactions between position n - 2 of the primer strand and RB69pol fix the rotomer conformations of the K706 and D621 side chains, as well as the position of metal ion A and its coordinating ligands, so that they are in the optinal orientation for DNA synthesis.

The adenine base analogue 2-aminopurine (2AP) is a potent base substitution mutagen in prokaryotes because of its enhanceed ability to form a mutagenic base pair with an incoming dCTP. Despite more than 50 years of research, the structure of the 2AP-C base pair remains unclear. We report the structure of the 2AP-dCTP base pair formed within the polymerase active site of the RB69 Y567A-DNA polymerase. A modified wobble 2AP-C base pair was detected with one H-bond between N1 of 2AP and a proton from the C4 amino group of cytosine and an apparent bifurcated H-bond between a proton on the 2-amino group of 2-aminopurine and the ring N3 and O2 atoms of cytosine. Interestingly, a primer-terminal region rich in AT base pairs, compared to GC base pairs, facilitated dCTP binding opposite template 2AP. We propose that the increased flexibility of the nucleotide binding pocket formed in the Y567A-DNA polymerase and increased "breathing" at the primer-terminal junction of A+T-rich DNA facilitate dCTP binding opposite template 2AP. Thus, interactions between DNA polymerase residues with a dynamic primer-terminal junction play a role in determining base selectivity within the polymerase active site of RB69 DNA polymerase.

At temperatures above the cloud point, aqueous solutions of nonionic surfactants separate into a coacervate phase and a dilute phase. The distribution of di-, tri-, and tetrachloroethanes between these phases was shown to increasingly favor the coacervate phase as the hydrophobicity (degree of chlorination) of the solute increases. The solute solubilization equilibrium constant was shown to be very similar for solubilization into coacervate surfactant aggregates compared to micellar solubilization per aggregated surfactant molecule for octylphenol polyethoxylate surfactants and to increase with increasing temperature and increasing solute hydrophobicity. As temperature increases above the cloud point, the partition ratio increases primarily because the concentration of surfactant in the coacervate increases, second because the solubilization equilibrium constant in the coacervate surfactant aggregate increases, and third because the concentration of micellized surfactant (and solubilization therein) in th...

Two sublimation techniques have been developed to separate Tc from Mo to support accelerator production of 99Mo/99mTc. After bombardment, the metal target is dissolved in nitric acid, the solution is evaporated, and the precipitated solids are calcined to MoO3. In the first technique, MoO3 is melted to a 0.8 mm layer and oxygen is swept over the 835 °C sample at 30 std cm3/min. Small amounts of MoO3 vapors transported from the 835 °C sample are deposited above 550 °C onto the walls of a quartz tube in a temperature gradient of 4 °C/cm. Greater than 95% of released technetium oxide is collected in a 5 mL condenser at temperatures between 300 and 25 °C. In the second process, technetium oxide deposited on the surface of fine needle crystals of MoO3 is quantitatively released in an oxygen stream at 650 °C. The crystals are regenerated between milkings by dissolving in NH4OH, evaporating, and drying. In this initial work, greater than 90% product recovery is achieved by both processes during multiple milkings...

Compounds with the formula CmH2m+1(CH3)2N+(CsH2s)N+(CH3)2CmH2m+1·2Br-, abbreviated as m-s-m according to a previous convention, are considered to be dimeric cationic surfactants. The Krafft tempera...

Equilibrium dialysis is used to investigate the binding of chromate anions to the cationic polyelectrolyte, poly(diallyldimethylammonium chloride), in the presence and in the absence of added sodium chloride. The binding of chromate to the polyelectrolyte is predicted by using a model which combines thermodynamic relations with the Oosawa two-state polyelectrolyte theory. Allowances are made for the nonideality of the bulk aqueous phase by introducing ion activities and ion activity coefficients. The model quite successfully accounts for the experimental data when the theoretical value of a potential parameter is utilized and when the fraction of the apparent volume containing the bound counterions is determined by considering the dimensions of the bound chromate ions.

An automated system for performing rapid immunoassay, kinetic measurements, and affinity ranking of biomolecular interactions using fluorescence-labeled ligands is described. Its distinctive feature is the automated renewal of solid phase for each measurement, which avoids the need for regeneration of the sensing surface. This system--flow injection renewable surface immunoassay (FIRSI)--is used for the first time here for determination of rate constants for an antibody/antigen interaction and for affinity ranking of several related antigens against one antibody. The performance of the system is compared with a commercial BIAcore system that uses surface plasmon resonance for monitoring biomolecular interactions. While the values of association and dissociation rate constants for human serum albumin (HSA) with monoclonal anti-HSA antibody obtained by these techniques were comparable, it is shown that the FIRSI techniques requires simpler instrumentation, handles a broader size range of analytes, and does not suffer from disturbances caused by changes in the refractive index.

The solubilization of synthetic perfumes (eugenol, linalool, benzyl acetate, α-ionone, α-hexylcinnamaldehyde, and d-limonene) by sodium dodecyl sulfate (SDS)/hexadecyl poly(oxyethylene) ethers (C 16 POE 20 ) mixed surfactants has been studied by measurement of the maximum additive concentration (MAC) and the distribution coefficient between the micellar and bulk phase (K). The MAC of the perfume at any mole fraction of C 16 POE 20 increases with the hydrophilicity of the perfume. The MAC of the more hydrophilic perfume in the mixed systems is smaller than the calculated MAC (assuming additivity) because of hydrophilic-hydrophilic interactions between the head groups of anionic and nonionic surfactants in the mixed micelle. On the other hand, the radius of the mixed micelle in these systems is large compared to the radii of pure component micelles, causing the MAC values of the less hydrophilic perfumes in the mixed systems to be larger than the calculated MAC. Moreover, the values ofKfor each perfume in the mixture ofthe surfactants are smaller than the ideal K values ; this effect increases with a decrease in the hydrophilicity of the perfume, except in the case of d-limonene. The magnitude of these changes in K values in the surfactant mixtures depends on the relative importance of surfactant-surfactant and surfactant-perfume interactions.

A mixture of a cationic polyelectrolyte, poly(diallyldimethylammonium chloride) or PDADMAC, and the anionic ligand diethylenetriaminepentaacetic acid (DTPA) can be added to aqueous streams as a water-soluble colloid to bind simultaneously divalent cations, such as Cu[sup 2+] and Pb[sup 2+], and anions, such as CrO[sub 4][sup 2[minus]]. At pH values greater than about 4, most of DTPA is attached electrostatically to the PDADMAC, so that the ligand remains in the retentate in ultrafiltration (UF) separations. Equilibrium dialysis studies show the effectiveness of the PDADMAC-DTPA mixture in binding ions of various types; the data also show that cations such as Ca[sup 2+], which do not bind to the ligand, are expelled and become concentrated in the permeate solution passing through the membrane. In equilibrium dialysis and UF experiments, with the PDADMAC-DTPA mixture added to a feed stream containing a mixture of Cu[sup 2+] and CrO[sub 4][sup 2[minus]], the bound cations and anions become highly concentrated in the retentate solution. 10 refs., 5 figs., 5 tabs.

A water-soluble mixture of a cationic polyelectrolyte, poly(diallyldimethylammonium chloride) or PDADMAC, and an anionic ligand, 4,5-dihydroxy-1,3-benzenedisulfonic acid, or Tiron, is used as an agent for binding divalent cations, such as Cu[sup 2+] and Pb[sup 2+]. In equilibrium dialysis experiments, the PDADMAC-Tiron mixture is shown to be effective in binding Cu[sup 2+] and Pb[sup 2+] in the retentate, while enhancing the concentration of the noncomplexed cation, Ca[sup 2+], in the permeate. In the pH range employed, the uncomplexed and complexed forms of Tiron exist primarily as divalent anions. As a consequence they are bound electrostatically to the cationic polyelectrolyte, and little of the ligand is lost through the membrane. The effects of pH, cation concentration, and presence of a competing cation (Ca[sup 2+]), and added NaCl on the retention of Cu[sup 2+] and Pb[sup 2+] are discussed. 25 refs., 4 figs., 2 tabs.

The solubilization of pentanol in aqueous solutions of individual cationic surfactants and binary mixtures of cationic surfactants at 20[degree]C has been investigated using head-space chromatography. Complete solubilization isotherms have been determined for pentanol in micelles of the surfactants hexadecyl-pyridinium chloride (CPC), trimethyltetradecylammonium chloride (C[sub 14]Cl), benzyldimethyltetradecyl-ammonium chloride (C[sub 14]BzCl), benzyldimethylhexadecylammonium chloride (C[sub 16]BzCl), and hexadecyltrimethylammonium bromide (C[sub 16]Cl). In every case, a large decrease in the solubilization equilibrium (or partition) constant occurs on increasing the mole fraction of pentanol in the micelles (X); a factor of 3-5 reduction in the equilibrium constant occurs as X increases from nearly zero to nearly 0.9. Solubilization results have also been determined for mixed micelles of C[sub 14]Cl and C[sub 14]BzCl (system I) and CPC and C[sub 16]BzCl (system II). Large positive synergistic effects reported previously for system I and large antisynergistic effects for system II are not confirmed by the results of the present studies. For both of these mixed micellar systems, small decreases in the value of the solubilization equilibrium constant, relative to values predicted with an assumed additivity relationship, are observed. 38 refs., 10 figs., 1 tab.

An automated vapor pressure method has been used to obtain solubilization isotherms for trichloroethylene (TCE) in N-hexadecylpyridinium chloride (CPC) micelles, throughout a wide range of solute activities and at temperatures varying from 15 to 45[degree]C. The simple empirical expression K = K[sub 0](1 - [alpha]X + [beta]X[sup 2]) is used to correlate the solubilization equilibrium constant (K) with the mole fraction of TCE in the micelles (X) at each temperature. The solubilization equilibrium constant has a maximum value at approximately 30[degree]C, the temperature at which the solubility of TCE in water is a minimum. Activity coefficients are also reported for TCE in the micelle; these values increase slightly with increasing mole fraction of TCE. The general solubilization behavior of TCE in CPC micelles resembles that of benzene or toluene in CPC, suggesting that TCE solubilizes in ionic micelles both within the hydrocarbon micellar interior and near the micellar surface. The values of [alpha] for TCE are much smaller than those for phenol and phenol derivatives, indicating that TCE is not as tightly anchored in the head group region of the CPC micelles as are more polar solutes such as phenol and chlorinated phenols. With increasing temperature, the tendency of TCEmore » to solubilize within the hydrocarbon core region of the micelles increases, relative to its tendency to solubilize in the micellar surface region. 31 refs., 7 figs., 1 tab.« less

The detailed analysis of data obtained with the semiequilibrium dialysis (SED) method for studying solubilization in surfactant micelles requires accounting for the formation of micelles in the permeate compartment and for the presence of solubilized organic solute in these micelles. An extension of the SED method is proposed in which the concentration of surfactant is maintained well above the critical micelle concentration (cmc) in both compartments of the dialysis cell. Under these conditions, it is shown that the validity of the «semiequilibrium» assumption, viz., that the organic solute reaches equilibrium simultaneously with both surfactant solutions be demonstrated for solutions of small organic molecules and typical ionic surfactants

A new method has been developed for determining binding constants of complexes of cyclodextrins with surface-active compounds, including water-soluble ionic surfactants. The technique requires measuring the change in surface tension caused by addition of a cyclodextrin (CD) to aqueous solutions of the surfactant; the experimental results lead directly to inferred values of the thermodynamic activity of the surfactant. Surface tension results are reported for three different surfactants sodium dodecyl sulfate (SDS), cetylpyridinium chloride (CPC), and cetyltrimethylammonium bromide (CTAB) in the presence and in the absence of added [beta]-CD. Data for CPC have been obtained at surfactant concentrations below and above the critical micelle concentration. Correlations between surface tension and surfactant activity are expressed by the Szyszkowski equation, which subsumes the Langmuir adsorption model and the Gibbs equation. It is observed that the surface tension increases monotonically as [beta]-cyclodextrin is added to ionic surfactant solutions. At concentrations of CD well in excess of the surfactant concentration, the surface tension approaches that of pure water, indicating that neither the surfactant-CD complexes nor CD itself are surface active. Binding constants are inferred from a model that incorporates the parameters of the Szyszkowski equation and mass action constants relating to the formation of micellesmore » from monomers of the surfactant and the counterion. Evidence is given that two molecules of CD can complex the C-16 hydrocarbon chain of the cetyl surfactants. 30 refs., 5 figs., 1 tab.« less

A novel sequential injection immunoassay (SIIA) method is described which utilizes immunomagnetic beads to investigate short-time antibody binding. The method is versatile and flexible and may therefore be adapted to many different applications. Initial results for a competitive assay are also presented. The immunomagnetic bead reactor is created within the flowing stream by retaining immunomagnetic beads with an electromagnet to form an open tube reactor. Thus, the spent beads may be discharged after each analysis. This eliminates the problems of instability of reaction surfaces and eliminates the need for additional time traditionally required for regeneration of the solid-reacting phase in order to not only save time and increase sampling frequency but also to provide each individual sampling cycle with a fresh, uniform portion of beads. The spent beads are collected off line and may be regenerated later. Short-time binding kinetic studies demonstrate linear initial binding under 1 min, which then begins to reach saturation in approximately 10 min. Competitive binding assays of monoclonal mouse IgG (MRC OX-19) to polyclonal sheep anti-mouse IgG immobilized to the immunomagnetic beads show reproducible linear displacement in 30-120-s reactions. Fluorescence detection is utilized with a detection limit of 155 ng/mL, and since the reaction time is typically 2 min or shorter, the sampling frequency is 30 samples/h.

Spectrophotometric detection, chemiluminescence, gas diffusion, membrane separation, and their combinations have been successfully performed in a flow cell, which combines fiber optics, flow channels, spacers, reflecting surfaces, and separation membranes into a robust sandwich type sensing unit. Applications which include a separation step were carried out using a suitable membrane, which acted as an opaque surface, reflectiing the transmitted light into a bifurcated optical cable

A flow injection analysis (FIA) system is presented in which the reagent and sample are simultaneously injected for multicomponent analysis. A simple eight-port valve is described to perform the double injection. The method is illustrated by the determination of nickel and iron in a model plating bath solution

Solubilization isotherms of polar aromatic solutes (phenols, anilines, and benzaldehydes) in N-hexadecylpyridinium chloride micelles have been determined at 25{degree}C by using the semiequilibrium dialysis method. Effects of various substituent groups (H, F, Cl, Br, CH{sub 3}O, NO{sub 2}, CH{sub 3}, Et, i-Pr, and CF{sub 3}) have been studied for the solubilization of phenol, aniline, and benzaldehyde derivatives in aqueous solutions of the surfactant. Both hydrophobic and electrostatic effects are shown to be important in influencing the solubilization behavior. The simple expression, K = K{sub 0}(1 {minus} BX){sup 2}, is used to correlate the solubilization equilibrium constant (K) with the mole fraction of solute in the micelles (X). Linear free energy relationships can be used to correlate the solubilization results for the different classes of compounds.

A fiber-optic caustic sensor is described in which a weakly buffered acid-base indicator reagent (bromothymol blue) is continuously delivered to the sensor tip which consists of a length of Nafion hollow fiber membrane, an analyte exchange region, and an optical cell. In this study, caustic concentrations of 1.5-23.0% (w/w) (0.38-7.2 M) were measured, with a relative standard deviation of 1.6%. Sensor performance was studied at several reagent compositions, at various reagent delivery rates, in the presence of brine, and with respect to probe-to-probe reproducibility and long-term use

Discussion des principes a la base de l'utilisation d'un ecoulement sinusoidal dans des strategies variees de programmation du flux pour l'analyse par FIA en utilisant un modele aleatoire de marche. La faisabilite de ces principes est demontree par l'utilisation d'un prototype de pompe a flux sinusoidal

A single-line flow injection analysis (FIA) system for simultaneous determination of hydrolyzable metals and free acid has been developed. As a model for hydrolyzable metals iron was chosen. The setup allows determination of 0.5-6 M acid and 0.1-1.6 M iron. The resulting prediction error is 7% for acid and 3.8% for iron. Data were obtained by using a diode array detector. The calibration models were developed by using partial least-squares (PLS) regression. These results were compared with results obtained by traditional univariate calibration. The project aimed at developing a simple and robust FIA system to be applicable in an industrial process setting. Necessary modifications of present FIA instrumentation to fit such an environment are discussed.

Le modele de separation des pseudophases est utilise pour decrire l'influence du pH et de la concentration sur l'activite des solutions micellaires de dimethyldodecylamine oxyde

Semiequilibrium dialysis measurements have been made to determine solubilization equilibrium constants and activity coefficients of mono- and dichlorophenols in aqueous solutions of hexadecylpyridinium chloride (CPC) at 25{degree}C. Solubilization equilibrium constants (which relate the concentration of solubilizate in the micelle to the concentration of free organic in the bulk solution) are well correlated by the expression K = K{sub 0}(1 {minus} BX){sup 2}, where B is an empirical constant, K{sub 0} is the limiting value of the solubilization constant, and X is the mole fraction of the phenol present in the surfactant micelles.

A method for determining surface tension is proposed in which vertical pull measurements are made by weighing the liquid phase, while a ring, plate, or rod is allowed to contact the surface of the solution and then pulled slowly upward. This contrasts with conventional vertical pull methods in which the ring, plate, or rod is suspended from a microbalance mounted above the solution. The utility and simplicity of the alternative approach are discussed, and procedures are given for using a top-loading analytical balance to determine the maximum vertical force exerted on either a rod or a plate.

A novel, miniaturized titration was developed using beads 35 μm in diameter as semisolid aqueous titrant retained in a nonaqueous sample stream. Agarose beads with internally bound pH indicator served as a pH sensing membrane material swollen with aqueous NaOH titrant. The indicator monitored the remaining titrant within the agarose beads during perfusion with H(2)SO(4) in 1-butanol samples. Irreversible reaction of 2 mg bead layers was made possible by automated packing and disposal in a flow cell. This strategy substituted membrane advantages for the burdens of mixing and unnecessary dilution under laminar flow conditions. The agarose environment was conditioned with NaCl to tolerate dissolved salt in the sample. Transmittance measurements were made via fiber optics through FEP PTFE optical windows. A simple inverse relationship held between endpoint volume and acid concentration so that calibration curves were linear, R(2) = 0.9980.

Educators from across Europe discuss new courses and approaches for teaching analytical chemistry.

Reglage des conditions de dilution et evaluation du systeme. Utilisation d'une solution de vert bromocresol comme etalon. Ce systeme automatique peut diluer jusqu'a 15000 fois un echantillon extremement concentre, independamment de sa viscosite

In micellar-enhanced ultrafiltration (MEUF), solubilization of organic solutes in micelles, combined with ultrafiltration of these micellar solutions, leads to the removal of dissolved, low molecular weight organic compounds from water. The permeate from MEUF contains the organic solute at concentrations equal to the unsolubilized solute concentration in the rejected (retentate) solution. Therefore, the equilibrium solubilization of the solute dictates the permeate purity or rejection of the solute by the membrane. The semiequilibrium dialysis method has been used to investigate the equilibrium solubilization of o-, m-, and p-cresol by aqueous solutions of 1-hexadecylpyridinium chloride, throughout a range of concentrations of the cresols and the surfactant. The apparent solubilization constant, K = X/sub c//(concentration of unsolubilized cresol), has been correlated with X/sub c/, the mole fraction of cresol in the micelle.

Preparation de nouveaux composes diamide lipophile et essai comme ionophores pour Li avec des electrodes a membrane de PVC