Ditopic molecular architectures for the recognition of anionic species

Dissertation presented to obtain the Ph.D degree in Chemistry

Modelling and optimization of the ion exchange membrane bioreactor for removal of anionic pollutants from drinking water streams

Dissertação para obtenção do Grau de Doutor em Engenharia Química, especialidade de Engenharia Bioquímica

Biochemical Effects of Anionic, Cationic and Non Ionic Surfactants on a Tropical Teleost Oreochromis Mossambicus(Peters) and a Marine Cyanobacterium Synechocystis Salina Wislouch

The present work is a base line attempt to investigate and assess the toxicities of three surfactants viz. anionic sodium dodecyl sulfate (SDS), non ionic Triton X-1OO (TX-IOO) and cationic cetyl trimethyl ammonium bromide (CTAB). These compounds represent simple members of the often neglected group of aquatic pollutants i.e. the anionic alkyl sulfates, non ionics and the cationics. These compounds are widely used In plastic industry, pesticide/herbicide formulations, detergents, oil spill dispersants, molluscicides etc. The test organisms selected for the present study are the cyanobacterium Synechocystis salina Wislouch representing a primary producer in the marine environment and a fresh water adapted euryhaline teleost Oreochromis mossambicus (peters) at the consumer level of the ecological pyramid. The fish species, though not indigenous to our country, is now found ubiquitously in fresh water systems and estuaries. Also it is highly resistant to pollutants and has been suggested as an indicator of pollution in tropical region .

The electronic structure of anionic halide complexes of element 105 in aqueous solutions and their extraction by aliphatic amines

To study the complex formation of group 5 elements (Nb, Ta, Ha, and pseudoanalog Pa) in aqueous HCI solutions of medium and high concentrations the electronic structures of anionic complexes of these elements [MCl_6]^-, [MOCl_4]^-, [M(OH)-2 Cl_4]^-, and [MOCl_5]^2- have been calculated using the relativistic Dirac-Slater Discrete-Variational Method. The charge density distribution analysis has shown that tantalum occupies a specific position in the group and has the highest tendency to form the pure halide complex, [TaCl_6-. This fact along with a high covalency of this complex explains its good extractability into aliphatic amines. Niobium has equal trends to form pure halide [NbCl_6]^- and oxyhalide [NbOCl_5]^2- species at medium and high acid concentrations. Protactinium has a slight preference for the [PaOCl_5]^2- form or for the pure halide complexes with coordination number higher than 6 under these conditions. Element 105 at high HCl concentrations will have a preference to form oxyhalide anionic complex [HaOCl_5]^2- rather than [HaCl_6]^-. For the same sort of anionic oxychloride complexes an estimate has been done of their partition between the organic and aqueous phases in the extraction by aliphatic amines, which shows the following succession of the partition coefficients: P_Nb < P_Ha < P_Pa.

Copper(II) complexes of mono-anionic glutamate: anionic influence in the variations of molecular and supramolecular structures

Three new polynuclear copper(II) complexes of singly deprotonated L-glutamic acid (L-glu), {[Cu(bipy)(2)][Cu(bipy)(L-glu)H2O](2)(BF4)(4)center dot(H2O)(3)}(n) (1), {[Cu(bipy)(L-glu)H2O][Cu(bipy)(L-glu)(ClO4)]( ClO4)center dot(H2O)(2)}(n) ((2)) and [Cu(phen)(L-glu)H2O](2)(NO3)(2)center dot(H2O)(4) (3) (bipy = 2,2-bipyridine, phen = 1,10-phenanthroline), were synthesized in acidic pH (ca. 2.5) and characterized structurally. In all the complexes, L-glutamic acid acts as a bidentate chelating ligand, leaving the protonated carboxylic acid free. Both in 1 and 2, two different types of species [Cu(bipy)(2)](BF4)(2) and [Cu(bipy)(L-glu)H2O] BF4 for 1 and [Cu(bipy)(L-glu)H2O]ClO4 and [Cu(bipy)(L-glu)(ClO4)] for 2 coexist in the solid state. In complex 1, the [C( bipy)(L-glu)H2O]+ units are joined together by syn-anti carboxylate bridges to form an enantiopure (M) helical chain and the [Cu(bipy)(2)](2+) presents a very rare example of the four-coordinate distorted tetrahedral geometry of Cu(II). In complex 2, the [Cu(bipy)(L gluClO(4))] units are joined together by weakly coordinating perchlorate ions to form a 1D polymeric chain while the [Cu(bipy)(L-glu)H2O]+ units remain as mononuclear species. The different coordinating ability of the two counter anions along with their involvement in the H-bonding network seems likely to be responsible for the difference in the final polymeric structures in the two compounds. Variable-temperature (2-300 K) magnetic susceptibility measurements show negligible coupling for both the complexes. The structure of 3 consists of two independent monomeric [Cu(phen)(L-glu)H2O]+ cations, two nitrate anions and four water molecules. The copper atom occupies a five-coordinate square pyramidal environment with a water molecule in the axial position.

Interactions of an anionic surfactant with poly(oxyalkylene) copolymers in aqueous solution

The interactions of sodium dodecyl sulfate (SDS) with poly(ethylene oxide)/poly(alkylene oxide) (E/A) block copolymers are explored in this study: With respect to the specific compositional characteristics of the copolymer, introduction of SDS can induce fundamentally different effects to the self-assembly behavior of E/A copolymer solutions. In the case of the E18B10-SDS system (E = poly(ethylene oxide) and B = poly(butylene oxide)) development of large surfactant-polymer aggregates was observed. In the case of B20E610-SDS, B12E227B12-SDS, E40B10E40-SDS, E19P43E19-SDS (P = poly(propylene oxide)), the formation of smaller particles compared to pure polymeric micelles points to micellar suppression induced by the ionic surfactant. This effect can be ascribed to a physical binding between the hydrophobic block of unassociated macromolecules and the non-polar tail of the surfactant. Analysis of critical micelle concentrations (cmc*) of polymer-surfactant aqueous solutions within the framework of regular solution theory for binary surfactants revealed negative deviations from ideal behavior for E40B10E40-SDS and E19P43E19-SDS, but positive deviations for E18B10-SDS. Ultrasonic studies performed for the E19P43E19-SDS system enabled the identification of three distinct regions, corresponding to three main steps of the complexation; SDS absorption to the hydrophobic backbone of polymer, development of polymer-surfactant complexes and gradual breakdown of the mixed aggregates. (C) 2008 Elsevier Inc. All rights reserved.

Copper(II) azide complexes with mono-anionic tridentate Schiff-base ligands: monomer versus dimer

Three new copper(II) complexes [(CuLN3)-N-1](2) (1), [(CuLN3)-N-2] (2) and [(CuLN3)-N-3] (3) with three very similar tridentate Schiff base ligands [HL1=6-diethylamino-3-methyl-1-phenyl-4-azahex-3-en1- one, HL2= 6-amino-3-methyl-1-phenyl-4-azahex-3-en-1-one and HL3= 6-amino-3-methyl1- phenyl-4-azasept-3-en-1-one] have been synthesized and structurally characterized by X-ray crystallography. In complex 1 half of the molecules are basal-apical, end-on azido bridged dimers and the remaining half are square-planar monomers whereas all the molecules in complexes 2 and 3 are monomers with square-planar geometry around Cu(II). A competition between the coordinate bond and H-bond seems to be responsible for the difference in structure of the complexes.

Recovery of lactoferrin and lactoperoxidase from sweet whey using colloidal gas aphrons (CGAs) generated from an anionic surfactant, AOT

The recovery of lactoferrin and lactoperoxidase from sweet whey was studied using colloidal gas aphrons (CGAs), which are surfactant-stabilized microbubbles (10-100 mum). CGAs are generated by intense stirring (8000 rpm for 10 min) of the anionic surfactant AOT (sodium bis-2-ethylhexyl sulfosuccinate). A volume of CGAs (10-30 mL) is mixed with a given volume of whey (1 - 10 mL), and the mixture is allowed to separate into two phases: the aphron (top) phase and the liquid (bottom) phase. Each of the phases is analyzed by SDS-PAGE and surfactant colorimetric assay. A statistical experimental design has been developed to assess the effect of different process parameters including pH, ionic strength, the concentration of surfactant in the CGAs generating solution, the volume of CGAs and the volume of whey on separation efficiency. As expected pH, ionic strength and the volume of whey (i.e. the amount of total protein in the starting material) are the main factors influencing the partitioning of the Lf(.)Lp fraction into the aphron phase. Moreover, it has been demonstrated that best separation performance was achieved at pH = 4 and ionic strength = 0.1 mol/L i.e., with conditions favoring electrostatic interactions between target proteins and CGAs (recovery was 90% and the concentration of lactoferrin and lactoperoxidase in the aphron phase was 25 times higher than that in the liquid phase), whereas conditions favoring hydrophobic interactions (pH close to pI and high ionic strength) led to lower performance. However, under these conditions, as confirmed by zeta potential measurements, the adsorption of both target proteins and contaminant proteins is favored. Thus, low selectivity is achieved at all of the studied conditions. These results confirm the initial hypothesis that CGAs act as ion exchangers and that the selectivity of the process can be manipulated by changing main operating parameters such as type of surfactant, pH and ionic strength.

Dimetallic complexes of macrocycles with two rigid dibenzofuran units as receptors for detection of anionic substrates

The hexaazamacrocycles [28](DBF)2N6 {cyclo[bis(4,6-dimethyldibenzo[b,d]furaniminoethyleneiminoethylene]} and [32](DBF)2N6 {cyclo[bis(4,6-dimethyldibenzo[b,d]furaniminopropyleneiminopropylene]} form stable dinuclear copper(II) complexes suitable to behave as receptors for several anionic substrates. These two receptors were used to study the binding interactions with several substrates, such as imidazole (Him) and some carboxylates [benzoate (bz−), oxalate (ox2−), malonate (mal2−), phthalate (ph2−), isophthalate (iph2−), and terephthalate (tph2−)] by spectrophotometric titrations and EPR spectroscopy in MeOH (or H2O):DMSO (1:1 v/v) solution. The largest association constant was found for ox2− with Cu2[32](DBF)2N64+, whereas for the aromatic dicarboxylate anions the binding constants follow the trend ph2− > iph2− > tph2−, i.e. decrease with the increase of the distance of the two binding sites of the substrate. On the other hand, the large blue shift of 68 nm observed by addition of Him to Cu2[32](DBF)2N64+ points out for the formation of the bridged CuimCu cascade complex, indicating this receptor as a potential sensor for the detection and determination of imidazole in solution. The X-band EPR spectra of the Cu2[28](DBF)2N64+ and Cu2[32](DBF)2N6]4+ complexes and the cascade complexes with the substrates, performed in H2O:DMSO (1:1 v/v) at 5 to 15 K, showed that the CuCu distance is slightly larger than the one found in crystal state and that this distance increases when the substrate is accommodated between the two copper centres. The crystal structure of [Cu2[28](DBF)2N6(ph)2]·CH3OH was determined by X-ray diffraction and revealed the two copper centres bridged by two ph2− anions at a Cu···Cu distance of 5.419(1) Å. Each copper centre is surrounded by three carboxylate oxygen atoms from two phthalate anions and three contiguous nitrogen atoms of the macrocycle in a pseudo octahedral coordination environment.

The role of protein hydrophobicity in thionin–phospholipid interactions: a comparison of α1 and α2-purothionin adsorbed anionic phospholipid monolayers

The plant defence proteins α1- and α2-purothionin (Pth) are type 1 thionins from common wheat (Triticum aestivum). These highly homologous proteins possess characteristics common amongst antimicrobial peptides and proteins, that is, cationic charge, amphiphilicity and hydrophobicity. Both α1- and α2-Pth possess the same net charge, but differ in relative hydrophobicity as determined by C18 reversed phase HPLC. Brewster angle microscopy, X-ray and neutron reflectometry, external reflection FTIR and associated surface pressure measurements demonstrated that α1 and α2-Pth interact strongly with condensed phase 1,2-dipalmitoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (DPPG) monolayers at the air/liquid interface. Both thionins disrupted the in-plane structure of the anionic phospholipid monolayer, removing lipid during this process and both penetrated the lipid monolayer in addition to adsorbing as a single protein layer to the lipid head-group. However, analysis of the interfacial structures revealed that the α2-Pth showed faster disruption of the lipid film and removed more phospholipid (12%) from the interface than α1-Pth. Correlating the protein properties and lipid binding activity suggests that hydrophobicity plays a key role in the membrane lipid removal activity of thionins.

Effect of anionic co-ligands on structure and magnetic coupling of bis(μ-phenoxo-bridged dinuclear copper(II) complexes

Two phenoxo bridged dinuclear Cu(II) complexes, [Cu2L2(NO2)(2)] (1) and [Cu2L2(NO3)(2)] (2) have been synthesized using the tridentate reduced Schiff-base ligand 2-[(2-dimethylamino-ethylamino)-methyl]-phenol (HL). The complexes have been characterized by X-ray structural analyses and variable-temperature magnetic susceptibility measurements. The structures of the two compounds are very similar having the same tridentate chelating ligand (L) and mono-dentate anionic ligand nitrite for 1 and nitrate for 2. In both complexes Cu(II) is penta-coordinated but the square pyramidal geometry of the copper ions is severely distorted (Addison parameter (tau) = 0.33) in 1 while the distortion is quite small (average tau = 0.11) in 2. These differences have marked effect on the magnetic properties of two compounds. Although both are antiferromagnetically coupled, the coupling constants (J = -140.8 and -614.7 cm (1) for 1 and 2, respectively) show that the coupling is much stronger in 2.

Oppositely charged polyelectrolytes: complex formation and effects of chain asymmetry

The formation of complexes in solutions of oppositely charged polyions has been studied by Monte Carlo simulations. The amount as well as the length, and thus, the absolute charge of one of the polyions have been varied. There is an increasing tendency to form large clusters as the excess of one kind of polyion decreases. When all polyions have the same length, this tendency reaches a maximum near, but off, equivalent amounts of the two types of polyions. When one kind of polyion is made shorter, the propensity to form large clusters decreases and the fluctuations in cluster charge increases. Simple free-energy expressions have been formulated on the basis of a set of simple rules that help rationalize the observations. By calculating cluster distributions in both grand canonical and canonical ensembles, it has been possible to show the extent of finite-size effects in the simulations.

Complex formation in solutions of oppositely charged polyelectrolytes at different polyion compositions and salt content

The formation of complexes in solutions containing positively charged polyions (polycations) and a variable amount of negatively charged polyions (polyanions) has been investigated by Monte Carlo simulations. The polyions were described as flexible chains of charged hard spheres interacting through a screened Coulomb potential. The systems were analyzed in terms of cluster compositions, structure factors, and radial distribution functions. At 50% charge equivalence or less, complexes involving two polycations and one polyanion were frequent, while closer to charge equivalence, larger clusters were formed. Small and neutral complexes dominated the solution at charge equivalence in a monodisperse system, while larger clusters again dominated the solution when the polyions were made polydisperse. The cluster composition and solution structure were also examined as functions of added salt by varying the electrostatic screening length. The observed formation of clusters could be rationalized by a few simple rules.

A Monte Carlo study of solutions of oppositely charged polyelectrolytes

The formation of complexes appearing in solutions containing oppositely charged polyelectrolytes has been investigated by Monte Carlo simulations using two different models. The polyions are described as flexible chains of 20 connected charged hard spheres immersed in a homogenous dielectric background representing water. The small ions are either explicitly included or their effect described by using a screened Coulomb potential. The simulated solutions contained 10 positively charged polyions with 0, 2, or 5 negatively charged polyions and the respective counterions. Two different linear charge densities were considered, and structure factors, radial distribution functions, and polyion extensions were determined. A redistribution of positively charged polyions involving strong complexes formed between the oppositely charged polyions appeared as the number of negatively charged polyions was increased. The nature of the complexes was found to depend on the linear charge density of the chains. The simplified model involving the screened Coulomb potential gave qualitatively similar results as the model with explicit small ions. Finally, owing to the complex formation, the sampling in configurational space is nontrivial, and the efficiency of different trial moves was examined.