Complexing Agent Ethylenediaminetetraacetic Acid Research Articles

EDTA enables to alleviate impacts of metal ions on conjugative transfer of antibiotic resistance genes

Various heavy metals are reported to be able to accelerate horizontal transfer of antibiotic resistance genes (ARGs). In real water environmental settings, ubiquitous complexing agents would affect the environmental behaviors of heavy metal ions due to the formation of metal-organic complexes. However, little is known whether the presence of complexing agents would change horizontal gene transfer due to heavy metal exposure. This study aimed to fill this gap by investigating the impacts of a typical complexing agent ethylenediaminetetraacetic acid (EDTA) on the conjugative transfer of plasmid-mediated ARGs induced by a range of heavy metal ions. At the environmentally relevant concentration (0.64 mg L−1) of metal ions, all the tested metal ions (Mg2+, Ca2+, Co2+, Pb2+, Ni2+, Cu2+, and Fe3+) promoted conjugative transfer of ARGs, while an inhibitory effect was observed at a relatively higher concentration (3.20 mg L−1). In contrast, EDTA (0.64 mg L−1) alleviated the effects of metal ions on ARGs conjugation transfer, evidenced by 11 %-66 % reduction in the conjugate transfer frequency. Molecular docking and dynamics simulations disclosed that this is attributed to the stronger binding of metal ions with the lipids in cell membranes. Under metal-EDTA exposure, gene expressions related to oxidative stress response, cell membrane permeability, intercellular contact, energy driving force, mobilization, and channels of plasmid transfer were suppressed compared with the metal ions exposure. This study offers insights into the alleviation mechanisms of complexing agents on ARGs transfer induced by free metal ions.

Remediação eletrocinética de elementos potencialmente tóxicos de sedimentos da lagoa de Camorim

ABSTRACT Electrokinetic remediation, effective for low-permeability sediments, can remove both organic and inorganic contaminants simultaneously. This study investigated its application to dredged sediments from Camorim Lagoon (Jacarepaguá lagoon complex, Rio de Janeiro), known to be contaminated with potentially toxic metals (chromium, copper, lead, zinc, and nickel). A buffer solution controlled pH changes, while the complexing agent ethylenediaminetetraacetic acid (EDTA) and humic substances aided metal desorption and removal. Treatments utilizing EDTA (EK2 and EK3) achieved lower final concentrations of zinc and lead. Notably, EK1 (freshwater only) achieved the lowest nickel concentration observed in the anodic section. EK1 also achieved the lowest copper concentration; however, none of the treatments reached regulatory limits for copper. Chromium, which is the least mobile metal, is concentrated in the middle section for all treatments, suggesting the need for further electrolyte optimization to promote efficient chromium transport.

Effects of Laundering on Moisture Management and Air Permeability of Different Chitosan Treated Nylon 6,6 Elastane Fabrics Using EDTA and Triton X-100

Abstract This study investigates the effect of washing fabrics (nylon 6.6 powernet knitted fabrics with 30% spandex) treated with chitosan on their moisture management and air permeability. The knitted fabrics were treated with three different solutions of chitosan and dimethylol dihydroxyethylene urea (DMDHEU); in addition to chitosan and DMDHEU, one solution contained the complexing agent ethylenediaminetetraacetic acid (EDTA) and the other contained the nonionic surfactant and penetration agent octylphenol ethoxylate. The three solutions were compared in terms of their effect on moisture management and air permeability properties. Nylon fabrics treated and washed with these solutions were characterized by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Nylon fabrics treated with chitosan and DMDHEU showed the potential to transfer liquid moisture to the lower layer and keep the layer next to the skin dry after 20 washes.

Infleunce of molar concentration on ethylene diamine tetra acetic acid (EDTA) added to tin sulfide (SnS) thin films grown by silar method

Nano thin films of SnS were prepared for solar cell application as absorber layer to analyse energy band gap. Thin films of Tin Sulphide (SnS) were deposited on glass substrate in room temperature by Successive Ionic Layer Adsorption and Reaction method. The changes in the properties of SnS were studied, when a complexing agent ethylenediaminetetraaceticacid (EDTA) added. The deposition parameters such as Dip duration is 35 s, Ex-dip duration is 5 s, Number of cycles are 25 and Number of dips are four were optimized to obtain good quality of SnS films. The Structural, morphological, topographical and optical properties of EDTA added Tin Sulphide thin films were characterized by X-ray diffraction (XRD), SEM, AFM, UV–Vis spectrometry and FT-IR techniques. The deposited SnS films are in amorphous and polycrystalline structure. The UV–Vis spectra of SnS films in the wavelength range of 200–900 nm have been observed to find the direct band gap. The band gap energy (Eg = 2.31, 2.27, 2.16, 2.09 eV) decreases with increase in molar concentration (0.05, 0.10, 0.15 and 0.20 M). Band gap decreases with increasing particle size.

Synthesis of reduced graphene oxide–copper tin sulphide composites and their photoconductivity enhancement for photovoltaic applications

Graphene-based composites are attractive to effectively tune the intrinsic properties of inorganic semiconductors. We report the first study of band gap tuning and photoconductivity enhancement of reduced graphene oxide–Cu2SnS3 (G–CTS) composite. A simple solvothermal route has been used to synthesize G–CTS with and without a complexing agent in the reaction mixture. Raman and FTIR studies confirm the formation of G–CTS and reduced graphene oxide–Cu2SnS3 by the addition of complexing agent ethylenediaminetetraacetic acid (G–CTS(E)) during synthesis. Powder X-ray diffraction reveals the formation of cubic CTS structure in both the composites. Scanning electron microscopy (SEM) study has revealed microbar and nanorod morphologies in the composites. The wide absorption of composites has been measured using absorption spectroscopy study. The band gaps of G–CTS and G–CTS(E) have been calculated using the absorption spectra and found to be 1.33 and 1.61 eV, respectively. This study confirms the suitability of G–CTS and G–CTS(E) for photovoltaic applications. Photoconductivity study reveals that G–CTS(E) generates 60 % more current than G–CTS.

Size-controlled synthesis of copper nanoparticles in supercritical water

In this work the particle size control method of copper nanoparticles synthesized in supercritical water was investigated. The experiments were respectively carried out in a flow-type reaction apparatus and in a batch-type quartz tube apparatus. Results show that particle size of the products was very sensitive to the concentration of copper sulfate and alkalinity of the reactant. When the concentration of copper sulfate increased from 0.05mol/L to 0.5mol/L, the average particle size increased from 14nm to 50nm. When the molar ratio of NaOH to copper ion increased from 0:1 to 2:1, the average particle size decreased from 85nm to 14nm. The homogeneity and dispersity of the products were improved by increasing the concentration of complexing agent ethylenediamine tetraacetic acid (EDTA). The adsorption mechanism of EDTA on the surfaces of nanoparticles was researched by a Fourier transform infrared spectroscopy. It was speculated that EDTA adsorbed on the surfaces of nanoparticles by the dehydration reaction of carboxyl groups in the molecule of EDTA and hydroxyl groups on surfaces of copper nanoparticles (CuOH). These results are expected to be of great interest as basic data for the preparation of size-controlled copper nanoparticles by supercritical hydrothermal synthesis method.

Simultaneous determination of rifampicin, clarithromycin and their metabolites in dried blood spots using LC–MS/MS

Rifampicin (RIF) and clarithromycin (CLR) are common drugs for the treatment of infections like Mycobacterium tuberculosis and Mycobacterium ulcerans. Treatment for these diseases are long-term and the individual pharmacokinetic variation, drug-drug interactions or non-adherence may introduce sub-therapeutic exposure or toxicity. The application of therapeutic drug monitoring (TDM) can be used to ensure efficacy and avoid toxicity. With the use of dried blood spot (DBS), TDM may be feasible in rural areas. During DBS method development, unexpected interactions or matrix effects may be encountered due to endogenous components in the blood. Another complication compared to plasma analysis is that RIF can form chelate complexes with ferric ions or can bind with hemes, which are potentially present in the extracts of dried blood spots. The investigation focused on the interaction between RIF and the endogenous components of the DBS. The use of ethylenediaminetetraacetic acid (EDTA) and deferoxamine (DFX) as chelator agents to improve recoveries and matrix effects were investigated. A rapid analytical method was developed and validated to quantify RIF and CLR and their active metabolites desacetyl rifampicin (DAc-RIF) and 14-hydroxyclarythromcin (14OH-CLR) in DBS samples. A clinical application study was performed in tuberculosis patients by comparing DBS concentrations with plasma concentrations. The interaction between RIF and the DBS matrix was avoided using the complexing agents EDTA and DFX, which improved recoveries and matrix effects. The developed sample procedure resulted in a simple and fast method for the simultaneous quantification of RIF, CLR and their metabolites in DBS samples. High stability was observed as all four substances were stable at ambient temperature for 2 months. Deming regression analysis of the clinical application study showed no significant differences for RIF, DAc-RIF, CLR and 14OH-CLR between patient plasma and DBS analysis. The slopes of the correlation lines between DBS and plasma concentrations of RIF, DAc-RIF, CLR and 14OH-CLR were 0.90, 0.99, 0.80 and 1.09 respectively. High correlations between plasma and DBS concentrations were observed for RIF (R(2)=0.9076), CLR (R(2)=0.9752) and 14OH-CLR (R(2)=0.9421). Lower correlation was found for DAc-RIF (R(2) of 0.6856). The validated method is applicable for TDM of RIF, CLR and their active metabolites. The stability of the DBS at high temperatures can facilitate the TDM and pharmacokinetic studies of RIF and CLR even in resource limited areas. The role of EDTA and DFX as complexing agents in the extraction was well investigated and may provide a solution for potential applications to other DBS analytical methods.

Identification of relevant micropollutants in Austrian municipal wastewater and their behaviour during wastewater treatment

The European Union has defined environmental quality standards (EQSs) for surface waters for priority substances and several other pollutants. Furthermore national EQSs for several chemicals are valid in Austria. The study investigated the occurrence of these compounds in municipal wastewater treatment plant (WWTP) effluents. In a first screening of 15WWTPs relevant substances were identified, which subsequently were monitored in 9WWTPs over 1year (every 2months). Out of 77 substances or groups of substances (including more than 90 substances) 13 were identified as potentially relevant in respect to water pollution and subjected to the monitoring, whereas most other compounds were detected in concentrations far below the respective EQS for surface waters and therefore not further considered. The preselected 13 compounds for monitoring were cadmium (Cd), nickel (Ni), copper (Cu), selenium (Se), zinc (Zn), diuron, polybrominated diphenyl ethers (PBDEs), di(ethyl-hydroxyl)phthalate (DEHP), tributyltin compounds (TBT), nonylphenoles (NP), adsorbable organic halogens (AOX) and the complexing agents ethylenediaminetetraacetic acid (EDTA) as well as nitrilotriacetic acid (NTA). In the effluents of WWTPs the concentrations of the priority substances Cd, NP, TBT and diuron frequently exceeded the respective EQS, whereas the concentrations for DEHP and Ni were below the respective EQS. The effluent concentrations for AOX, EDTA, NTA, Cu, Se and Zn frequently are in the range or above the Austrian EQS for surface waters. Besides diuron and EDTA all compounds are removed at least partially during wastewater treatment and for most substances the removal via the excess sludge is the major removal pathway. For the 13 compounds which were monitored in WWTP effluents population equivalent specific discharges were calculated. Since for many compounds no or only few information is available, these population equivalent specific discharges can be used to assess emissions from municipal WWTPs to surface waters as well as to make a first assessment of the impact of a discharge on surface waters chemical status. Comparing discharges and river pollution on a load basis, the influence of diffuse sources becomes obvious and therefore should also be taken into consideration in river management.

INFLUENCE OF SELECTED METAL IONS ON STABILITY OF HYDROGEN PEROXIDE IN PRESENCE OF EDTA

UDK 546.215:546.4/.8
 Stability of hydrogen peroxide in time was investigated in the presence of various metal ions and a complexing agent ethylenediaminetetraacetic acid (EDTA). Metal ions: Fe(III), Mn(II), Co(II), Cu(II), Ni(II), Zn(II) and Pb(II) were applied at different concentrations with a chelator in a concentration of 1 ·10-5 mol/dm3, and the solutions were kept at 4oC between the measurements. Obtained data indicate the existence of pronounced catalytic effect for Fe(III), Mn(II), Co(II) ions on stability of hydrogen peroxide. Cu(II) ions showed significant catalytic influence only when applied at high concentration. Ni(II), Pb(II) and Zn(II) did not show significant catalytic effect on the decay of hydrogen peroxide at applied concentrations.

Crystallization trigger of Mn-doped zinc silicate in supercritical water via Zn, Mn, Si sources and complexing agent ethylenediamine tetraacetic acid

Crystallization of Mn-doped zinc silicate, α-Zn 2SiO 4:Mn 2+ was studied using several Zn, Mn, and Si sources in supercritical water with and without ethylenediamine tetraacetic acid (EDTA). Oxalate, hydroxide, oxide, and sulfate were used as the Zn and Mn sources and amorphous, crystalline, and colloidal SiO 2 and tetraethoxyorthosilicate (TEOS) were used as the Si sources. Zn and Mn sources acted as a trigger for Zn 2SiO 4 crystallization through dissolution, while the solubility of the Si source affected reaction velocity. The oxalate source gave single phase α-Zn 2SiO 4:Mn 2+, while the hydroxide source provided mainly β-Zn 2SiO 4:Mn 2+ with a small amount of α-Zn 2SiO 4:Mn 2+. The oxide sources did not readily react and only gave small amounts of α- and β-Zn 2SiO 4:Mn 2+. Although the sulfate source did not give any Zn 2SiO 4 phases, addition of EDTA as a complexing agent for Zn 2+ ions caused α-Zn 2SiO 4 crystallization. Remarkably, addition of EDTA into the sulfate source and TEOS gave botryoidal druses of rod-like shaped α-Zn 2SiO 4 crystals, which are similar to natural α-Zn 2SiO 4 deposits (willemite) that only occur in La Calamine, Belgium (Moresnet). In conclusion, Zn and Mn oxalates and amorphous SiO 2 were the best combinations for crystallizing single phase α-Zn 2SiO 4:Mn 2+ from supercritical water.

Effect of adsorption of Pb(II) and Cd(II) ions in the presence of EDTA on the characteristics of electrical double layers at the ion exchanger/NaCl electrolyte solution interface

The main propose of this work was to describe the basic parameters of electrical double layer structures of the ion exchanger/NaCl before and after the sorption process of Pb(II) and Cd(II) ions from aqueous solutions in the presence of the complexing agent EDTA (ethylenediaminetetraacetic acid). In the studies the following ion exchangers were used: cation exchangers Micro-ionex (in the H + and NH + 4 forms), Dowex 50W×4 (in the H + form), and Dowex 50W×12 (in the H + form); anion exchangers Dowex 1×4 (in the Cl − form) and Dowex 1×8 (in the Cl − form). Study of the physicochemical properties of the sample surface was carried out. The influence of ionic strength, pH, and solution interface was investigated. Electrophoretic mobility, surface charge density, and parameters for different concentrations of the electrolytes under question were presented. pH was changed from 3 to 10. The studies were carried out for the M(II)–EDTA = 1:1 system. The effects of the concentration of the solution containing the above-noted complexes and of the ion exchange/solution phase contact time on sorption capacities of the ion exchangers under consideration were studied. Kinetic parameters of the sorption process were also determined.

Sonochemical synthesis of nanocrystalline mercury sulfide, selenide and telluride in aqueous solutions

Nanocrystalline mercury chalcogenides HgE (E=S, Se, Te) were synthesized in a single step by a convenient, simple sonochemical method. Mercury nitrate, Hg(NO3)2, dissolved in 0.1M ethylenediamine tetraacetic acid (EDTA), was used as the source of mercury and elemental chalcogenes, dissolved in a NaOH solution, as the sources of chalcogenide. The products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDAX). The synthesis procedure is simple and uses less toxic reagents than the previously reported methods. The results showed that the complexing agent EDTA plays a crucial role in the process.

Surfactant-Enhanced Removal of Cu (II) and Zn (II) from a Contaminated Sandy Soil

Batch tests were conducted to know the effectiveness of using surfactants only and surfactants with a complexing agent to remove Cu (II) and Zn (II) from an artificially contaminated sandy soil. SDS (sodium dodecyl sulfate), AOT (alpha-olefin sulfonate) and Tx-100 (Triton X-100) were the surfactants selected as the washing liquids. Complexing agent EDTA (ethylenediaminetetraacetic acid) was also selected for washing the soil. To avoid external factors from interfering with the cleaning process, artificial soil formed by a mixture of clean sand and bentonite was used to form contaminated soil samples. The amount of organic matter present was insignificant. Compared to extraction by distilled water, tests indicated that a six-fold increase in copper extraction occurred due to the presence of surfactants and/or the complexing agent EDTA. Compared to extraction by distilled water, zinc extraction by surfactants and or the complexing agent EDTA was nearly 1.2 to 1.3 times more. Effects of competition as well as interference associated with the adsorption and desorption of these metals are also very briefly reported.

Kinetics and mechanism of ethylenediaminetetraacetic acid-, 2,2′-bipyridyl-, and 1,10-phenanthroline-assisted chromium(VI) oxidation of 2-propanol

Complexing agents ethylenediaminetetraacetic acid (EDTA), 2,2′-bipyridyl (bpy), and 1,10-phenanthroline (phen) influence the rate of chromic acid oxidation of 2-propanol in aqueous HClO4 solutions. EDTA and bpy catalyse the oxidation rate, whereas phen has no effect, but at higher concentration it acts as an inhibitor. Dependent on conditions, the reactions follow differing order kinetics. In the presence of EDTA and bpy, at the end of the reaction, chromium(III) is present as the EDTA–CrIII and bpy–CrIII complexes. Probable mechanisms are proposed involving a negatively charged termolecular intermediate complex formed from chromic acid, complexing agent, and 2-propanol.

Electrolytic recovery of binary metals and EDTA from strong complexed solutions

Electrolytic recovery of binary Cu(II) and Pb(II) from solutions containing strong complexing agent EDTA (ethylenediaminetetraacetic acid) was studied in a two-chamber cell separating with a cation exchange membrane Neosepta CM-1. An equimolar solution of EDTA and total metals was focused. The iridium oxide coated on titanium (Ti/IrO 2) and stainless steel were used as the anode and cathode, respectively. Experiments were carried out at different current densities (18.5–185 A/m 2), initial catholyte pH (1.47–6), the total metal concentrations (5–20 mM) and their concentration ratios. It was shown that the deposition recovery of Cu(II) was faster and more efficient than that of Pb(II). Compared to single metal–EDTA solutions, lower metal recovery and current efficiency were obtained in binary solutions regardless of what metal concentration ratios. This was probably related to the deposit structure of binary metals onto the cathode.

The effects of chemical species on bioaccumulation of rare earth elements in rice grown in nutrient solution

In this study, the effects of the complexing agent ethylenediamine tetraacetic acid (EDTA) on the species of Rare Earth Elements (REE) Lanthanum, Gadolinium and Yttrium in nutrient solution and bioaccumulation of REEs in rice seedling were investigated. The results showed that addition of EDTA can reduce the bioaccumulation values in the rice root, on the other hand, the bioaccumulation values in the aboveground parts (stem and leaves) increased. Considering the different parts of rice, root had higher bioaccumulation ability than that in aboveground parts of rice. During the experimental concentration range, for different species REEs, the bioaccumulation processes on rice's root were almost controlled by adsorption and because of the effects of adding EDTA, ionic and complexed species REEs showed two different patterns during the bioaccumulation process. All these indicated that EDTA had strong effects on the bioavail‐abilities of REEs through controlling their species in nutrient solution.

Analysis of Metal‐EDTA Complexes by Electrospray Mass Spectrometry

AbstractSolutions of the strong complexing agent ethylenediaminetetraacetic acid (EDTA) and Cu, Pb, Cd, Al, and Fe(III) were examined by electrospray mass spectrometry (ES/MS). Uncomplexed EDTA and metal‐EDTA complexes survive the electrospray process intact and can be detected simultaneously by mass spectrometry. Best sensitivity was achieved in the positive ion mode in which EDTA and EDTA‐metal complexes (present in solution as anions) were detected as protonated species with a single positive charge. Except for the protonation, the aqueous metal‐EDTA complexes are preserved and neither fragmentation of complexes nor formation of clusters with more than one metal or ligand were observed in the mass spectra. Detection limits are between approximately 1 to 2 µM for uncomplexed EDTA and for the Cu‐EDTA and Pb‐EDTA complexes, with a linear range up to 10−4 M. Calibrations based on solutions with equimolar concentrations of EDTA and Cu or Pb can be used to quantify EDTA‐metal complexes in solutions with excess EDTA or metal, and in solutions with more than one metal present. Isotopic signatures of metals in the metal‐ligand complexes are preserved, allowing the identification of the metal in a metal‐ligand complex. Isotopic signatures of metals can therefore aid in the identification of metal‐ligand complexes in unknown samples.

Synthesis and in vitro evaluation of chitosan-EDTA-protease-inhibitor conjugates which might be useful in oral delivery of peptides and proteins.

To develop a novel mucoadhesive polymer that protects peptide drugs from degradation by secreted as well as membrane-bound proteases in the intestine, and to evaluate this polymer in vitro. The serine protease inhibitors antipain, chymostatin and elastatinal were covalently linked to chitosan (poly-[1-->4]-beta-D-glucosamine). Thereafter, the complexing agent ethylenediaminetetraacetic acid (EDTA) was bound to the remaining primary amino groups of the polymer. The inhibitory effect of the resulting polymer-conjugate towards trypsin (EC 3.4.21.4), chymotrypsin (EC 3.4.21.1), elastase (3.4.21.36), carboxypeptidase A (EC 3.4.17.1), carboxypeptidase B (EC 3.4.17.2) and aminopeptidase N (EC 3.4.11.2) as well as its mucoadhesive properties were evaluated in vitro. Whereas the novel polymer-conjugate exhibited excellent swelling properties, its adhesive force was under our assay conditions 42% lower than that of unmodified chitosan. However, the polymer-conjugate showed a strong inhibitory activity towards all tested serine proteases. Due to its additional high binding affinity towards bivalent metal ions, it also inhibited the Zn(2+)-dependent exopeptidases carboxypeptidase A, B and aminopeptidase N. The novel mucoadhesive polymer-conjugate described in this study seems to be a useful tool in overcoming the enzymatic barrier to perorally administered therapeutic peptides and proteins.

The effects of chemical species on bioaccumulation of rare earth elements in wheat grown in nutrient solution

In this study, the effects the of complexing agent ethylenediamine tetraacetic acid (EDTA) on the species of Rare Earth Elements Lanthanum Gadolinium and Yttrium in nutrient solution and bioaccumulation of REEs in wheat seedling were investigated. The results showed that addition of EDTA can reduce the bioaccumulation values in the root, on the other hand, the bioaccumulation values in the aboveground part (stem and leaves) increased. Considering the different parts of wheat, root had higher bioaccumulation ability than that in the aboveground part of wheat. During the range of experiment concentrations (0–4 mg L −1), both ionic and complexed species REEs in nutrient solution had positive linear correlation with their concentrations in root. All these indicated that EDTA had strong effects on the bioavailabilities of REEs through controlling their species in nutrient solution and transportation processes from root to aboveground part of wheat.

Inhibition of the biological self‐purification by chlorophenols, sodium dodecyl sulfate, and the complexing agents ethylenediaminetetraacetic acid and nitrilotriacetic acid

AbstractThe determination of enzymatic activities in surface water allows the control of the biological selfpurification as well as being an indicator for microbial degradation of xenobiotics. As for this matter it is a good instrument for controlling alterations in the ecosystem. Inhibition of enzymatic activities (esterases, β‐glucosidases, and alanin‐aminopeptidases) were analyzed using linear dilution of the water under test, then correlating the resulting enzyme activities of each dilution step and the concentration of the sample. Because of the complex matrix of surface water, chemical analysis of inhibiting substances has been and still is very difficult. A characterization of these substances is therefore only possible by pretreatment of the samples. In order to simulate definite inhibition effects, surface water was spiked with 2‐chlorophenol and 4‐chlorophenol, as well as with the surfactant sodium dodecyl sulfate and the complex agents ethylenediaminetetraacetic acid and nitrilotriacetic acid. The simulated inhibition effects on the enzyme activities were characterized closely by an additional pretreatment of the water under test. The elimination of the inhibiting substances by adsorption on water‐insoluble polyvinylpyrrolidone or activated carbon and the reduction of the inhibitory effect on the enzyme activities were investigated. The oxidation of inhibiting chemicals using stripping or treatment with H2O2 was also found to be a reliable method to diminish the inhibitory effects on the enzymatic activities. © 1994 by John Wiley & Sons, Inc..