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PubMed2005

Optimization of a hybrid chromatography-crystallization process for the separation of Tröger's base enantiomers.

This paper presents an analysis of a hybrid process consisting of simulated moving bed (SMB) chromatography and crystallization and studies its performance for the separation of the Tröger's base enantiomers. The SMB is simulated using a detailed model including column efficiency, thus, implying a proper evaluation of the effect of column size on column efficiency and separation performance. The crystallization operations are accounted for through material balances, assuming equilibrium between enantiopure crystals and mother liquor. A genetic algorithm is used to optimize the combined process, using proper definitions of objective functions. Multi-objective optimization of this hybrid process for productivity and evaporation cost in terms of operating parameters, column length, and SMB feed concentration shows an optimum SMB purity value as a trade off between increased SMB performance and recycle of the mother liquor.

Adsorption↗

PubMed1982

Only the chemotactic subpopulation of human blood monocytes expresses receptors for the chemotactic peptide N-formylmethionyl-leucyl-phenylalanine.

Human peripheral blood monocytes comprise a subpopulation of 20 to 40% that is capable of responding to chemoattractants and a remaining subpopulation that cannot respond. We were able to obtain 99%-pure attractant-responsive monocytes by using a newly constructed separation chamber. The binding of the radioactive chemotactic peptide N-formylmethionyl-leucyl-[3H]phenylalanine to migrating and nonmigrating populations was then studied. The binding was saturable at room temperature in the presence of azide. Saturation occurred at 5 x 10(-8) M, and 50% of the maximal binding was obtained at 10(-8) M, the concentration that induced optimal chemotaxis. The nonmigrating monocytes did not bind the peptide under the same conditions, which shows that at least one reason for a nonresponsiveness to chemotaxin is apparently a lack of receptors. By Scatchard analysis we calculated an equilibrium dissociation constant ranging from 23 to 37 nM; the number of binding sites per cell ranged from 64,000 to 77,000. The binding was very rapid. Fifty percent of the optimal binding occurred at 3.5 min, and equilibrium was reached after 20 to 30 min. Chemotactic deactivation of the monocytes reduced the number of available binding sites by 60%.

Azides↗

PubMed2002

Muscle force evaluation and the role of posture in human lumbar spine under compression.

Using two nonlinear finite element models of the lumbar spine, the concept of optimal posture is explored by minimizing the segmental sagittal moments required for the equilibrium of the passive lumbar spine under a total of 2800 N axial compression while varying the pelvic tilt and lumbar lordosis. The redundant active-passive system is subsequently solved for this posture using a novel kinematics-based muscle calculation algorithm along with minimization approach. Some flattening in the lumbar spine substantially reduces the required moments and internal passive shear forces under 2800 N axial compression force. Small muscle forces are calculated for this optimal posture. The role of flattening in the lumbar lordosis and posterior pelvic tilt in diminishing the lumbar muscle activities in neutral postures is demonstrated. Without such changes in posture, the required moments probably exceed the moment-generating capability of local lumbar muscles. Consideration of such active-passive synergy and lack of its restriction may prove crucial in many activities. Moreover, a kinematics-based algorithm is proposed for the solution of spinal redundancy that fully accounts for the existing passive-active synergy while simultaneously satisfying all kinematics and equilibrium conditions along the length of the spine.

Biomechanical Phenomena↗

PubMed2001

Biomechanical analysis of movement strategies in human forward trunk bending. I. Modeling.

Two behavioral goals are achieved simultaneously during forward trunk bending in humans: the bending movement per se and equilibrium maintenance. The objective of the present study was to understand how the two goals are achieved by using a biomechanical model of this task. Since keeping the center of pressure inside the support area is a crucial condition for equilibrium maintenance during the movement, we decided to model an extreme case, called "optimal bending", in which the movement is performed without any center of pressure displacement at all, as if standing on an extremely narrow support. The "optimal bending" is used as a reference in the analysis of experimental data in a companion paper. The study is based on a three-joint (ankle, knee, and hip) model of the human body and is performed in terms of "eigenmovements", i.e., the movements along eigenvectors of the motion equation. They are termed "ankle", "hip", and "knee" eigenmovements according to the dominant joint that provides the largest contribution to the corresponding eigenmovement. The advantage of the eigenmovement approach is the presentation of the coupled system of dynamic equations in the form of three independent motion equations. Each of these equations is equivalent to the motion equation for an inverted pendulum. Optimal bending is constructed as a superposition of two (hip and ankle) eigenmovements. The hip eigenmovement contributes the most to the movement kinematics, whereas the contributions of both eigenmovements into the movement dynamics are comparable. The ankle eigenmovement moves the center of gravity forward and compensates for the backward center of gravity shift that is provoked by trunk bending as a result of dynamic interactions between body segments. An important characteristic of the optimal bending is the timing of the onset of each eigenmovement: the ankle eigenmovement onset precedes that of the hip eigenmovement. Without an earlier onset of the ankle eigenmovement, forward bending on the extremely narrow support results in falling backward. This modeling approach suggests that during trunk bending, two motion units--the hip and ankle eigenmovements--are responsible for the movement and for equilibrium maintenance, respectively.

Biomechanical Phenomena↗

PubMed2006

Adsorptive removal of chlorophenols from aqueous solution by low cost adsorbent--Kinetics and isotherm analysis.

Adsorptive removal of parachlorophenol (PCP) and 2,4,6-trichlorophenol (TCP) from aqueous solutions by activated carbon prepared from coconut shell was studied and compared with activated carbon of commercial grade (CAC). Various chemical agents in different concentrations were used (KOH, NaOH, CaCO(3), H(3)PO(4) and ZnCl(2)) for the preparation of coconut shell activated carbon. The coconut shell activated carbon (CSAC) prepared using KOH as chemical agent showed high surface area and best adsorption capacity and was chosen for further studies. Batch adsorption studies were conducted to evaluate the effect of various parameters such as pH, adsorbent dose, contact time and initial PCP and TCP concentration. Adsorption equilibrium reached earlier for CSAC than CAC for both PCP and TCP concentrations. Under optimized conditions the prepared activated carbon showed 99.9% and 99.8% removal efficiency for PCP and TCP, respectively, where as the commercially activated carbon had 97.7% and 95.5% removal for PCP and TCP, respectively, for a solution concentration of 50mg/L. Adsorption followed pseudo-second-order kinetics. The equilibrium adsorption data were analysed by Langmuir, Freundlich, Redlich-Peterson and Sips model using non-linear regression technique. Freundlich isotherms best fitted the data for adsorption equilibrium for both the compounds (PCP and TCP). Similarly, acidic pH was favorable for the adsorption of both PCP and TCP. Studies on pH effect and desorption revealed that chemisorption was involved in the adsorption process. The efficiency of the activated carbon prepared was also tested with real pulp and paper mill effluent. The removal efficiency using both the carbons were found highly satisfactory and was about 98.7% and 96.9% as phenol removal and 97.9% and 93.5% as AOX using CSAC and CAC, respectively.

Adsorption↗

PubMed2003

Colloidal epitaxy: playing with the boundary conditions of colloidal crystallization.

We have studied, with quantitative confocal microscopy, epitaxial colloidal crystal growth of particles interacting with an almost hard-sphere (HS) potential in a gravitational field and density matched colloids interacting with a long-range (LR) repulsive potential with a body-centred cubic (BCC) equilibrium crystal phase. We show that in both cases it is possible to grow thick, stacking fault-free metastable crystals: close-packed crystals with any stacking sequence, including hexagonal close packed (HCP), for the HS particles and face-centred cubic (FCC) in the case of the LR colloids. In accordance with recent computer simulations done for HS particles it was found that the optimal lattice constant to grow HS HCP crystals was larger than that of equilibrium FCC crystals. In addition, because of the absence of gravity, pre-freezing could be observed for the particles with the LR potential on a template of charged lines. We also argue that the ability to manipulate colloids with highly focused light, optical traps or tweezers, will become an important tool in both the study of colloidal crystallization and in making new structures. We show how cheap 2D and 3D templates can be made with optical tweezers and demonstrate, in proof of principle experiments with core-shell colloids, how light fields can generate crystal nuclei and other structures in the bulk of concentrated dispersions and how the effect of these structures on the rest of a dispersion can be studied quantitatively in 3D.

Journal Article↗

PubMed1996

Calcium-mediated DNA adsorption to yeast cells and kinetics of cell transformation by electroporation.

Detailed kinetic data suggest that the direct transfer of plasmid DNA (YEp 351, 5.6 kbp, supercoiled, Mr approximately 3.5 x 10(6)) by membrane electroporation of yeast cells (Saccharomyces cerevisiae, strain AH 215) is mainly due to electrodiffusive processes. The rate-limiting step for the cell transformation, however, is a bimolecular DNA-binding interaction in the cell interior. Both the adsorption of DNA, directly measured with [32P]dCTP DNA, and the number of transformants are collinearly enhanced with increasing total concentrations [Dt] and [Cat] of DNA and of calcium, respectively. At [Cat] = 1 mM, the half-saturation or equilibrium constant is KD = 15 +/- 1 nM at 293 K (20 degrees C). The optimal transformation frequency is TFopt = 4.1 +/- 0.4 X 10(-5) if a single exponential pulse of initial field strength E0 = 4 kV cm-1 and decay time constant tauE = 45 ms is applied at [Dt] = 2.7 nM and 10(8) cells in 0.1 ml. The dependence of TF on [Cat] yields the equilibrium constants KCazero = 1.8 +/- 0.2 mM (in the absence of DNA) and K'Ca (at 2.7 nM DNA), comparable with and derived from electrophoresis data. In yeast cells, too, the appearance of a DNA molecule in its whole length in the cell interior is clearly an after-field event. At Eo = 4.0 kV cm-1 and T = 293 K, the flow coefficient of DNA through the porous membrane patches is Kto = 7.0 +/- 0.7 x 10(3)S-1 and the electrodiffusion of DNA is approximately 10 times more effective than simple diffusion: D/D0 approximately 10.3. The mean radius of these pores is rp = 0.39 +/- 0.05 nm, and the mean number of pores per cell (of size ø approximately 5.5 microns) is Np = 2.2 +/- 0.2 x 10(4). The maximal membrane area that is involved in the electrodiffusive penetration of adsorbed DNA into the outer surface of the electroporated cell membrane patches is only 0.023% of the total cell surface. The surface penetration is followed either by additional electrodiffusive or by passive (after-field) diffusive translocation of the inserted DNA into the cell interior. For practical purposes of optimal transformation efficiency, 1 mM calcium is necessary for sufficient DNA binding and the relatively long pulse duration of 20-40 ms is required to achieve efficient electrodiffusive transport across the cell wall and into the outer surface of electroporated cell membrane patches.

Adsorption↗

PubMedDate not supplied

Codon equilibrium I: Testing for homogeneous equilibrium.

We present theoretical considerations that suggest that synonymous-codon usage might be expected to be close to an equilibrium distribution given a very homogeneous process of silent substitution. By homogeneous we mean that substitution depends only on the two bases involved, so that 12 base-substitution rates completely describe the silent substitution process. We have developed a method of statistically testing for such homogeneous equilibrium and applied it to reported data on the codon usages of different classes of organisms. Weakly expressed bacterial sequences and both mammalian and nonmammalian eukaryotic sequences deviate significantly from a random pattern of codon usage, in the direction of homogeneous equilibrium. On the other hand, highly expressed bacterial sequences do not exhibit homogeneous equilibrium, which may be correlated with recent experimental results showing that they are optimized to accept the most abundant tRNAs. To examine the effect of amino acid replacements on the homogeneous model of silent substitution, we divided the amino acids with degenerate codes into two classes, those with high mutabilities and those with low, and performed the same analysis on bacterial and eukaryotic data sets. The codon sets of the highly mutable class of amino acids are not further from homogeneous equilibrium than are the codon sets of the class with low mutabilities. We also found for the eukaryotic data that these independent classes of codon sets show very similar equilibrium patterns. The various results suggest a high level of uniformity in the process of silent fixation in the different synonymous-codon sets, especially in eukaryotes.

Amino Acid Sequence↗

PubMed1996

Pharmacological characterization of inositol-1,4,5,-trisphosphate binding to membranes from retina and retinal cultures.

Light and excitatory amino acids (EAA) stimulate the phosphoinositide cycle in the vertebrate retina. The regulation of Ca2+ release from intracellular stores by inositol-1,4, 5-trisphosphate (IP3) involves an interaction of this compound with specific receptors. By means of [3H]IP3-specific binding, we studied the kinetic and pharmacological properties of IP3 receptors in the chick retina as well as in primary cultures of neurons and glia from this tissue. The equilibrium time for the binding reaction was 15 min and was optimal at alkaline pH (8.3). IP3 receptor displayed high affinity (K(B) approximately 40 nM) and selectivity for D-IP3, compared to D-IP4 > L-IP3 > D-IP2 > D-IP1. These characteristics were the same in subcellular fractions from outer (P1) and thinner (P2) plexiform layers, binding sites being more abundant in P2 (2.65 pmol/mg protein). IP3 receptors were present in both neuronal and glial cultures, but were concentrated in neuronal cultures. Binding was not affected by ryanodine, or caffeine, related to calcium-induced calcium release (CICR) channels, nor by the endoplasmic reticulum Ca2+ ATPase inhibitor thapsigargin, while heparin affectively inhibited IP3 binding. GSSG and thimerosal increased the affinity of [3H]IP3 binding from IC50 approximately 80 nM to IC50 approximately 40 nM; this effect was reversed by DTT. Binding in zero Ca2+ was decreased by low concentrations of Ca2+ (350 nM). These results suggest that actions of IP3 in the retina are regulated by physiological changes in intracellular pH and Ca2+ concentrations, as well as by the oxidation state of the receptor. Additionally, the presence of IP3 receptors in Müller glia opens the possibility of IP3 participation in nonsynaptic signalling through Ca2+ waves in glial cells.

Analysis of Variance↗

PubMed1998

Temperature titration: a new approach to the thermodynamics of oxygen binding to hemoglobin.

A cell was constructed in order to study hemoglobin's reaction with gaseous ligands. The temperature of the hemoglobin sample is systematically altered within a given temperature range (275-310 degrees K), while the percentage of oxygen in the equilibrating gas is kept constant. The equilibration time of the sample at each temperature step depends on sample concentration, ligand affinity, and absolute temperature; in most cases, the equilibration time is on the order of minutes. The construction of the optical compartment allows the experimenter to vary the optical pathlength using specially designed spacers, thus making it possible to study hemoglobin-ligand interactions over a wide range of protein concentrations (0.1-200 mg/ml). Optical glass is used in the construction of the cuvette in order to optimize its optical stability over a long period of time. At equilibrium the absorption spectrum of the sample is collected and decomposed into the relative contributions of oxy-Hb, deoxy-Hb, and ferric-Hb, thus revealing the fraction of oxyhemoglobin as well as any baseline drifts and protein degradation. Temperature steps of 1 degree K are already sufficient to change the absorption spectra in a significant way. This type of setup is also advantageous in that the experimenter can change the sample at any point (temperature) without having to restart the entire experiment. This makes it possible to study the oxygen binding characteristics of unstable hemoglobins. Analyses of the binding curves obtained with this technique immediately yield the overall oxygen binding constants beta i together with the respective standard enthalpies delta H(i).

Hemoglobins↗

PubMed2002

Measurement of the surface dilational viscoelasticity of adsorbed layers with a capillary pressure tensiometer.

A capillary pressure tensiometer has been set up to measure the dilational surface viscoelasticity in liquid-air and liquid-liquid surfactant systems, according to the oscillating drop/bubble technique. A specific model which allows the dilational surface viscoelasticity to be inferred from the acquired pressure data is proposed and the critical points concerning the experimental procedure and the data interpretation are discussed. In order to optimize the method, side measurements utilizing the same tensiometer to evaluate equilibrium interfacial tensions and the system compressibility are coupled to this technique. Some nonionic surfactants, polyoxyethylene glycol ethers (C(i)EO(j)) and alkyl dimethyl phosphine oxide (C(12)DMPO), at water-air and water-hexane interfaces have been investigated by this technique. The measured dynamic dilational viscoelasticities are compared with the predictions of theoretical models which consider different adsorption mechanisms.

Journal Article↗

PubMed1990

Sodium-dependent D-aspartate 'binding' is not a measure of presynaptic neuronal uptake sites in an autoradiographic assay.

The binding of D-[3H]aspartate to sections of rat brain was examined in an autoradiographic assay. Binding was entirely dependent on the presence of sodium ions, but not chloride ions, and was optimal at 2 degrees C. D-Aspartate bound rapidly, reached equilibrium within 20 min and remained stable for 45 min. The rate of dissociation was relatively rapid with a t1/2 of 56 s, but was not as fast as anticipated, perhaps because of some sequestration of ligand. Binding had a Kd of 6.8 +/- 1.2 microM and a Bmax of 49.4 +/- 8.6 pmol/mg protein. The high Bmax value may further indicate some sequestration of D-aspartate. L-Glutamate, unlabeled D-aspartate, and D,L-threo-hydroxyaspartate, a potent inhibitor of synaptosomal uptake, each competed for D-[3H]aspartate binding with IC50s of 7.0 +/- 4.3 microM, 5.4 +/- 1.5 microM, and 2.5 +/- 1.0 microM, respectively. N-methyl-D-aspartate (NMDA), quisqualate, and kainate had no affinity for this site. The regional distribution of D-aspartate binding sites was unique and did not conform to the distribution of neuronal uptake sites described by others. Striatal D-aspartate binding was unaffected by unilateral decortication or striatal quinolinic acid lesions. In contrast, binding to NMDA, quisqualate, and kainate receptors was reduced by 80-90% by quinolinate lesions of the striatum. The results of D-aspartate binding after lesions strongly suggest that this site is not associated with either lesioned glutamatergic afferents or intrinsic neurons of the striatum; it may be associated with glia.

Animals↗

PubMed1983

Specific binding of [3H]+/- 2-amino-7-phosphono heptanoic acid to rat brain membranes in vitro.

The specific binding of [3H]+/- 2-amino-7-phosphono heptanoic acid (3H-APH), a potent N-methyl-D-aspartate (NMDA) antagonist, to extensively washed, previously frozen crude mitochondrial fractions of rat brain is described. Binding was optimal at physiological pH and temperature and, in Triscitrate buffer, attained equilibrium within 60 minutes. Scatchard analysis of the equilibrium data for forebrain revealed a single, non-interacting population of binding sites (BMapp = 15 picomoles/mg protein; KDapp = 3.6 uM; Hill coefficient = 0.92, r = 0.99; N = 5). Specific binding of the ligand was readily reversible by unlabeled APH and was absent in peripheral tissues including heart, lung, kidney, liver, spleen and striate muscle and in heat treated brain sonicates. An 8-fold variation in the amount of ligand bound to brain membranes prepared from different regions was observed with binding being greatest in the hippocampal formation and least in the midbrain. Kainic acid, NMDA and aspartic acid exhibited negligible affinity for the [3H]-APH site; in contrast, quisqualic acid, ibotenic acid, glutamatic acid, homocysteic acid and 2-amino-4-phosphono butyric acid were moderately potent displacers. The results indicate that [3H]-APH labels a quisqualate preferring site in vitro. Unlike the receptor labeled by [3H]-glutamate however, [3H]-APH binding was attenuated in the presence of chloride ions suggesting that this ligand may label a subpopulation of excitatory amino acid receptors.

2-Amino-5-phosphonovalerate↗

PubMed1989

Semisynthetic hemoglobin A: reconstitution of functional tetramer from semisynthetic alpha-globin.

The optimal conditions for the semisynthesis of alpha-globin through Staphylococcus aureus V8 protease condensation of a synthetic fragment (alpha 1-30) with the complementary apo fragment (alpha 31-141) in the presence of structure-inducing organic cosolvents and the reconstitution of the functional tetramer from semisynthetic alpha-globin have been investigated. The protease-catalyzed ligation of the complementary apo fragments alpha 1-30 and alpha 31-141 proceeds with very high selectivity at pH 6.0 and 4 degrees C in the presence of 1-propanol as the organic cosolvent. A 30% 1-propanol solution was optimal for the semisynthetic reaction, and the synthetic reaction attained an equilibrium (approximately 50%) in 72 h. The synthetic reaction proceeds smoothly over a wide pH range (pH 5-8). Besides, the semisynthetic system is flexible, and it also proceeded well if trifluoroethanol or 2-propanol was used instead of 1-propanol. However, glycerol, a versatile organic cosolvent used in all other proteosynthetic reactions reported in the literature, was not very efficient as an organic cosolvent in the present synthetic reaction. The semisynthetic alpha-globin prepared with 1-propanol as the organic cosolvent has been reconstituted into HbA. The semisynthetic HbA was then purified by CM-cellulose chromatography. The semisynthetic HbA is indistinguishable from native HbA, in terms of its structural and functional properties. The semisynthetic approach provides the flexibility in protein engineering studies for the incorporation of spectroscopic labels (13C- and/or 15N-labeled amino acids), noncoded amino acids, or unnatural bond functionalities, which at present is not possible with genetic approaches.

Circular Dichroism↗

PubMed2001

Determination of solid-phase loading for the removal of metal ion from effluents using fixed-bed adsorbers.

The sorption of cadmium and copper ions from aqueous solutions onto bone char using fixed-bed adsorbers has been studied. A film-pore diffusion model has been utilized to predict theoretical breakthrough curves, which are compared with experimental breakthrough curves by means of error analysis. The key parameters for correlating the theoretical model are the external film mass-transfer coefficient (kf), the effective diffusion coefficient (Deff), and the solid-phase loading (q). The kf is determined from fixed-bed empirical correlations, and Deff is determined by a best-fit optimization routine. The q value has traditionally been determined using the equilibrium isotherm, which is applicable when the column adsorbent reaches equilibrium, or using the breakthrough curve mass balance when the column does not reach equilibrium. The breakthrough curve mass balance method needs experimental curves for each system and is not a practical solution for general design models. This paper presents two novel predictive equations for q in terms of process variables. The accuracy of the equations is sufficient for application in design models for nonequilibrium and equilibrium systems.

Adsorption↗

PubMed2001

Characterization of Hoxd1 protein-DNA-binding specificity using affinity chromatography and random DNA oligomer selection.

1. Hoxd1 is member of the labial subfamily of Hox genes that has a conserved 60 amino acid homeodomain region. The homeodomain is an important determining factor in the binding of the protein to specific DNA sequence(s). DNA-binding specificity for the Hoxd1 protein has not been determined previously. 2. We have employed a rapid affinity chromatography method to determine optimal DNA binding sequences for the 109 amino acid Hoxd1 peptide, comprising the homeodomain and the entire carboxy terminal region of the Hoxd1 protein. 3. Labial Hox proteins have intrinsically weak DNA-binding activity that has been attributed to the nonbasic residues at positions 2 and 3 in the N-terminal arm of the homeodomain. The presence of the Hoxd1 carboxy terminal region negated the influence of the nonbasic residues and facilitated Hoxd1 DNA-binding specificity. 4. DNA sequences bound to the Hoxd1 peptide-affinity column were separated from a random pool of oligonucleotide sequences by gradient elution and enriched by polymerase chain reaction. Preferred sequences were identified on 5' and 3' of a TAAT core, extending the binding site to T/AT/gTAATTGTA. 5. Stability and specificity of optimal DNA-binding sequence for Hoxd1 homeodomain were determined by equilibrium and kinetic studies. Dissociation coefficient constant (KD) was estimated to be 8.6 x 10(-9) M and the DNA-Hoxd1 homeodomain complex has a half life (t(1/2)) of 12.7 min. 6. A molecular model of Hoxd1 homeodomain-DNA interaction based on the X-ray coordinates of Antennapedia homeodomain-DNA complex has revealed novel interactions of key Hoxd1 residues at the protein-DNA interface.

Amino Acid Sequence↗

PubMed2004

TreT, a novel trehalose glycosyltransferring synthase of the hyperthermophilic archaeon Thermococcus litoralis.

The gene cluster in Thermococcus litoralis encoding a multicomponent and binding protein-dependent ABC transporter for trehalose and maltose contains an open reading frame of unknown function. We cloned this gene (now called treT), expressed it in Escherichia coli, purified the encoded protein, and identified it as an enzyme forming trehalose and ADP from ADP-glucose and glucose. The enzyme can also use UDP- and GDP-glucose but with less efficiency. The reaction is reversible, and ADP-glucose plus glucose can also be formed from trehalose and ADP. The rate of reaction and the equilibrium favor the formation of trehalose. At 90 degrees C, the optimal temperature for the enzymatic reaction, the half-maximal concentration of ADP-glucose at saturating glucose concentrations is 1.14 mm and the V(max) is 160 units/mg protein. In the reverse reaction, the half-maximal concentration of trehalose at saturating ADP concentrations is 11.5 mm and the V(max) was estimated to be 17 units/mg protein. Under non-denaturating in vitro conditions the enzyme behaves as a dimer of identical subunits of 48 kDa. As the transporter encoded in the same gene cluster, TreT is induced by trehalose and maltose in the growth medium.

ATP-Binding Cassette Transporters↗

PubMed2004

Activated carbons application to remove nonionic surfactants from wastewater produced by an Italian metallurgic plant.

The performance of different activated carbons for the removal of nonionic surfactants from metallurgic wastewater was assessed through lab scale experiments. Two different matrices were used: a simple one, obtained by dissolving different amounts of a single nonionic surfactant (Triton X100) in distilled water, and a complex matrix, prepared as above but using surfactants-free wastewater from an Italian metallurgic plant as solvent. In this way the main operative parameters that affect the adsorption process in the simple matrix have been studied avoiding the interference due to the complex matrix: then the results were utilized to define and optimize the tests carried out on the complex matrix. The adsorption equilibrium experimental data were best fitted with a Langmuir isotherm, allowing defining the contact time and the proper design parameters for the adsorption column. The different tests were performed on four different activated carbon types, and the removal efficiency and the treatment cycle duration for each of the tested carbons were discussed and compared. The experimental results showed that the saturation adsorption capacity is not notably correlated either with the pH value or with the water matrix, whereas the slope of the isotherm, defined by the Henry constant, is sensibly higher at strong acidic or alcaline conditions, with a minimum value at nearly neutral pH. Therefore, it was concluded that the removal efficiency is maximized when the operative pH was in the 2-4-unit value range. The best activated carbon, in terms of removal efficiency, resulted to be a mineral activated carbon, characterized by the highest iodine number, and thus with the largest porosity. Removal efficiencies were in the 60 to 80% range.

Carbon↗