Copper Reductase Activity and Free Radical Chemistry by Cataract-Associated Human Lens γ-Crystallins.

Cataracts are caused by high-molecular-weight aggregates of human eye lens proteins that scatter light, causing lens opacity. Metal ions have emerged as important potential players in the etiology of cataract disease, as human lens γ-crystallins are susceptible to metal-induced aggregation. Here, the interaction of Cu2+ ions with γD-, γC-, and γS-crystallins, the three most abundant γ-crystallins in the lens, has been evaluated. Cu2+ ions induced non-amyloid aggregation in all three proteins. Solution turbidimetry, sodium dodecyl sulfate poly(acrylamide) gel electrophoresis (SDS-PAGE), circular dichroism, and differential scanning calorimetry showed that the mechanism for Cu-induced aggregation involves: (i) loss of ß-sheet structure in the N-terminal domain; (ii) decreased thermal and kinetic stability; (iii) formation of metal-bridged species; and (iv) formation of disulfide-bridged dimers. Isothermal titration calorimetry (ITC) revealed distinct Cu2+ binding affinities in the γ-crystallins. Electron paramagnetic resonance (EPR) revealed two distinct Cu2+ binding sites in each protein. Spin quantitation demonstrated the reduction of γ-crystallin-bound Cu2+ ions to Cu+ under aerobic conditions, while X-ray absorption spectroscopy (XAS) confirmed the presence of linear or trigonal Cu+ binding sites in γ-crystallins. Our EPR and XAS studies revealed that γ-crystallins' Cu2+ reductase activity yields a protein-based free radical that is likely a Tyr-based species in human γD-crystallin. This unique free radical chemistry carried out by distinct redox-active Cu sites in human lens γ-crystallins likely contributes to the mechanism of copper-induced aggregation. In the context of an aging human lens, γ-crystallins could act not only as structural proteins but also as key players for metal and redox homeostasis.

High Interfacial Viscoelasticity of Aqueous Mixed Dodecyltrimethylammonium Bromide-Sodium Dodecyl Sulfate Surfactants Forming Inclusion Complexes with α-Cyclodextrin.

Mixtures of anionic-cationic surfactants have shown high synergistic effects in the bulk solution and at the liquid/air interface. These studies have been limited to a reduced concentration range, where there is no formation of aggregates or precipitates. The addition of host molecules, such as cyclodextrins, to these systems reduces the effects of precipitation by forming inclusion complexes and also modifies the values of other surfactant properties, like the Krafft temperature and the critical aggregation concentration (CAC). We studied the interfacial synergistic effects promoted by electrostatic interactions, using the Rosen model to calculate an interaction parameter for mixtures of sodium dodecyl sulfate (SDS) and dodecyltrimethylammonium bromide (DTAB) in the presence of α-cyclodextrin (αCD), in aqueous solutions. We measured the CAC of SDS-DTAB-αCD mixtures using a pendant drop tensiometer, with the αCD concentration fixed at 10 mM and at 283.15 K. We performed rheological measurements on the mixtures where the surfactant total concentration is fixed below the measured CAC, varying the αCD concentration and temperature. We found that the dilatational modulus shows a clear correlation with the interaction parameter. It appears that the attractive interactions within the film are those due to the inclusion complexes formed by two αCD and one surfactant molecule, which according to the previous studies, is the dominant species in both the bulk and liquid/air interface. The synergistic effect observed here for SDS-DTAB surfactant mixtures with αCD can be applied to systems and processes (drop emission, drug delivery methods, stabilization of viral capsids and bacterial membranes, and emulsification) where interfacial processes require specific viscoelastic properties.

ATCUN-like Copper Site in ßB2-Crystallin Plays a Protective Role in Cataract-Associated Aggregation.

Cataract is the leading cause of blindness worldwide, and it is caused by crystallin damage and aggregation. Senile cataractous lenses have relatively high levels of metals, while some metal ions can directly induce the aggregation of human γ-crystallins. Here, we evaluated the impact of divalent metal ions in the aggregation of human ßB2-crystallin, one of the most abundant crystallins in the lens. Turbidity assays showed that Pb2+, Hg2+, Cu2+, and Zn2+ ions induce the aggregation of ßB2-crystallin. Metal-induced aggregation is partially reverted by a chelating agent, indicating the formation of metal-bridged species. Our study focused on the mechanism of copper-induced aggregation of ßB2-crystallin, finding that it involves metal-bridging, disulfide-bridging, and loss of protein stability. Circular dichroism and electron paramagnetic resonance (EPR) revealed the presence of at least three Cu2+ binding sites in ßB2-crystallin, one of them with spectroscopic features typical for Cu2+ bound to an amino-terminal copper and nickel (ATCUN) binding motif, which is found in Cu transport proteins. The ATCUN-like Cu binding site is located at the unstructured N-terminus of ßB2-crystallin, and it could be modeled by a peptide with the first six residues in the protein sequence (NH2-ASDHQF-). Isothermal titration calorimetry indicates a nanomolar Cu2+ binding affinity for the ATCUN-like site. An N-truncated form of ßB2-crystallin is more susceptible to Cu-induced aggregation and is less thermally stable, indicating a protective role for the ATCUN-like site. EPR and X-ray absorption spectroscopy studies reveal the presence of a copper redox active site in ßB2-crystallin that is associated with metal-induced aggregation and formation of disulfide-bridged oligomers. Our study demonstrates metal-induced aggregation of ßB2-crystallin and the presence of putative copper binding sites in the protein. Whether the copper-transport ATCUN-like site in ßB2-crystallin plays a functional/protective role or constitutes a vestige from its evolution as a lens structural protein remains to be elucidated.

Dipole-dipole interactions control the interfacial rheological response of cyclodextrin/surfactant solutions.

A recent surface rheological study has shown that aqueous solutions of α-cyclodextrin (αCD) with anionic surfactants (S) display a remarkable viscoelasticity at the liquid/air interface, which has not been observed in similar systems. The dilatational modulus is various orders of magnitude larger than those for the binary mixtures αCD + water and S + water. The rheological response has been qualitatively related to the bulk distribution of species, the 2 : 1 inclusion complexes (αCD2 : S) playing a fundamental role. In this work, we have developed a model that considers dipole-dipole interactions between 2 : 1 inclusion complexes ordered on the liquid/air interface. When the model is applied to the specific experimental conditions, the dependencies on concentration and temperature of the dilatational modulus and the surface tension were found to be in excellent agreement with the data, indicating clearly that dipole-dipole interactions determine and control the rheological behavior of the interface.

AFFINImeter: A software to analyze molecular recognition processes from experimental data.

The comprehension of molecular recognition phenomena demands the understanding of the energetic and kinetic processes involved. General equations valid for the thermodynamic analysis of any observable that is assessed as a function of the concentration of the involved compounds are described, together with their implementation in the AFFINImeter software. Here, a maximum of three different molecular species that can interact with each other to form an enormous variety of supramolecular complexes are considered. The corrections currently employed to take into account the effects of dilution, volume displacement, concentration errors and those due to external factors, especially in the case of ITC measurements, are included. The methods used to fit the model parameters to the experimental data, and to generate the uncertainties are described in detail. A simulation tool and the so called kinITC analysis to get kinetic information from calorimetric experiments are also presented. An example of how to take advantage of the AFFINImeter software for the global multi-temperature analysis of a system exhibiting cooperative 1:2 interactions is presented and the results are compared with data previously published. Some useful recommendations for the analysis of experiments aimed at studying molecular interactions are provided.

A strategy based on thermal flexibility to design triosephosphate isomerase proteins with increased or decreased kinetic stability.

Kinetic stability of proteins determines their susceptibility to irreversibly unfold in a time-dependent process, and therefore its half-life. A residue displacement analysis of temperature-induced unfolding molecular dynamics simulations was recently employed to define the thermal flexibility of proteins. This property was found to be correlated with the activation energy barrier (Eact) separating the native from the transition state in the denaturation process. The Eact was determined from the application of a two-state irreversible model to temperature unfolding experiments using differential scanning calorimetry (DSC). The contribution of each residue to the thermal flexibility of proteins is used here to propose multiple mutations in triosephosphate isomerase (TIM) from Trypanosoma brucei (TbTIM) and Trypanosoma cruzi (TcTIM), two parasites closely related by evolution. These two enzymes, taken as model systems, have practically identical structure but large differences in their kinetic stability. We constructed two functional TIM variants with more than twice and less than half the activation energy of their respective wild-type reference structures. The results show that the proposed strategy is able to identify the crucial residues for the kinetic stability in these enzymes. As it occurs with other protein properties reflecting their complex behavior, kinetic stability appears to be the consequence of an extensive network of inter-residue interactions, acting in a concerted manner. The proposed strategy to design variants can be used with other proteins, to increase or decrease their functional half-life.

Structure and conformational stability of the triosephosphate isomerase from Zea mays. Comparison with the chemical unfolding pathways of other eukaryotic TIMs.

We studied the structure, function and thermodynamic properties for the unfolding of the Triosephosphate isomerase (TIM) from Zea mays (ZmTIM). ZmTIM shows a catalytic efficiency close to the diffusion limit. Native ZmTIM is a dimer that dissociates upon dilution into inactive and unfolded monomers. Its thermal unfolding is irreversible with a Tm of 61.6 ±â€¯1.4 °C and an activation energy of 383.4 ±â€¯11.5 kJ mol-1. The urea-induced unfolding of ZmTIM is reversible. Transitions followed by catalytic activity and spectroscopic properties are monophasic and superimposable, indicating that ZmTIM unfolds/refolds in a two-state behavior with an unfolding ΔG°(H20) = 99.8 ±â€¯5.3 kJ mol-1. This contrasts with most other studied TIMs, where folding intermediates are common. The three-dimensional structure of ZmTIM was solved at 1.8 Å. A structural comparison with other eukaryotic TIMs shows a similar number of intramolecular and intermolecular interactions. Interestingly the number of interfacial water molecules found in ZmTIM is lower than those observed in most TIMs that show folding intermediates. Although with the available data, there is no clear correlation between structural properties and the number of equilibrium intermediates in the unfolding of TIM, the identification of such structural properties should increase our understanding of folding mechanisms.

Localized conformational changes trigger the pH-induced fibrillogenesis of an amyloidogenic λ light chain protein.

Solvent conditions modulate the expression of the amyloidogenic potential of proteins. In this work the effect of pH on the fibrillogenic behavior and the conformational properties of 6aJL2, a model protein of the highly amyloidogenic variable light chain λ6a gene segment, was examined. Ordered aggregates showing the ultrastructural and spectroscopic properties observed in amyloid fibrils were formed in the 2.0-8.0 pH range. At pH <3.0 a drastic decrease in lag time and an increase in fibril formation rate were found. In the 4.0-8.0 pH range there was no spectroscopic evidence for significant conformational changes in the native state. Likewise, heat capacity measurements showed no evidence for residual structure in the unfolded state. However, at pH <3.0 stability is severely decreased and the protein suffers conformational changes as detected by circular dichroism, tryptophan and ANS fluorescence, as well as by NMR spectroscopy. Molecular dynamics simulations indicate that acid-induced conformational changes involve the exposure of the loop connecting strands E and F. These results are compatible with pH-induced changes in the NMR spectra. Overall, the results indicate that the mechanism involved in the acid-induced increase in the fibrillogenic potential of 6aJL2 is profoundly different to that observed in κ light chains, and is promoted by localized conformational changes in a region of the protein that was previously not known to be involved in acid-induced light chain fibril formation. The identification of this region opens the potential for the design of specific inhibitors.

The effect of specific proline residues on the kinetic stability of the triosephosphate isomerases of two trypanosomes.

The effect of specific residues on the kinetic stability of two closely related triosephosphate isomerases (from Trypanosoma cruzi, TcTIM and Trypanosoma brucei, TbTIM) has been studied. Based on a comparison of their ß-turn occurrence, we engineered two chimerical enzymes where their super secondary ß-loop-α motifs 2 ((ßα)2 ) were swapped. Differential scanning calorimetry (DSC) experiments showed that the (ßα)2 motif of TcTIM inserted into TbTIM (2Tc) increases the kinetic stability. On the other hand, the presence of the (ßα)2 motif of TbTIM inserted into TcTIM (2Tb) gave a chimerical protein difficult to purify in soluble form and with a significantly reduced kinetic stability. The comparison of the contact maps of the (ßα)2 of TbTIM and TcTIM showed differences in the contact pattern of residues 43 and 49. In TcTIM these residues are prolines, located at the N-terminal of loop-2 and the C-terminal of α-helix-2. Twelve mutants were engineered involving residues 43 and 49 to study the effect over the unfolding activation energy barrier (EA ). A systematic analysis of DSC data showed a large decrease on the EA of TcTIM (ΔEA ranging from 468 to 678 kJ/mol) when the single and double proline mutations are present. The relevance of Pro43 to the kinetic stability is also revealed by mutation S43P, which increased the free energy of the transition state of TbTIM by 17.7 kJ/mol. Overall, the results indicate that protein kinetic stability can be severely affected by punctual mutations, disturbing the complex network of interactions that, in concerted action, determine protein stability. Proteins 2017; 85:571-579. © 2016 Wiley Periodicals, Inc.

A guide to the effects of a large portion of the residues of triosephosphate isomerase on catalysis, stability, druggability, and human disease.

Triosephosphate isomerase (TIM) is a ubiquitous enzyme, which appeared early in evolution. TIM is responsible for obtaining net ATP from glycolysis and producing an extra pyruvate molecule for each glucose molecule, under aerobic and anaerobic conditions. It is placed in a metabolic crossroad that allows a quick balance of the triose phosphate aldolase produced by glycolysis, and is also linked to lipid metabolism through the alternation of glycerol-3-phosphate and the pentose cycle. TIM is one of the most studied enzymes with more than 199 structures deposited in the PDB. The interest for this enzyme stems from the fact that it is involved in glycolysis, but also in aging, human diseases and metabolism. TIM has been a target in the search for chemical compounds against infectious diseases and is a model to study catalytic features. Until February 2017, 62% of all residues of the protein have been studied by mutagenesis and/or using other approaches. Here, we present a detailed and comprehensive recompilation of the reported effects on TIM catalysis, stability, druggability and human disease produced by each of the amino acids studied, contributing to a better understanding of the properties of this fundamental protein. The information reviewed here shows that the role of the noncatalytic residues depend on their molecular context, the delicate balance between the short and long-range interactions in concerted action determining the properties of the protein. Each protein should be regarded as a unique entity that has evolved to be functional in the organism to which it belongs. Proteins 2017; 85:1190-1211. © 2017 Wiley Periodicals, Inc.

Stability and aggregation propensity do not fully account for the association of various germline variable domain gene segments with light chain amyloidosis.

Variable domain (VL) gene segments exhibit variable tendencies to be associated with light chain amyloidosis (AL). While few of them are very frequent in AL and give rise to most of the amyloidogenic light chains compiled at the sequence databases, other are rarely found among the AL cases. To analyze to which extent these tendencies depend on folding stability and aggregation propensity of the germline VL protein, we characterized VL proteins encoded by four AL-associated germline gene segments and one not associated to AL. We found that the AL-associated germline rVL proteins differ widely in conformational stability and propensity to in vitro amyloid aggregation. While in vitro the amyloid formation kinetics of these proteins correlate well with their folding stabilities, the folding stability does not clearly correlate with their germline's frequencies in AL. We conclude that the association of the VL genes segments to amyloidosis is not determined solely by the folding stability and aggregation propensity of the germline VL protein. Other factors, such as the frequencies of destabilizing mutations and susceptibility to proteolysis, must play a role in determining the light chain amyloidogenicity.

Size product modulation by enzyme concentration reveals two distinct levan elongation mechanisms in Bacillus subtilis levansucrase.

Two levan distributions are produced typically by Bacillus subtilis levansucrase (SacB): a high-molecular weight (HMW) levan with an average molecular weight of 2300 kDa, and a low-molecular weight (LMW) levan with 7.2 kDa. Previous results have demonstrated how reaction conditions modulate levan molecular weight distribution. Here we demonstrate that the SacB enzyme is able to perform two mechanisms: a processive mechanism for the synthesis of HMW levan and a non-processive mechanism for the synthesis of LMW levan. Furthermore, the effect of enzyme and substrate concentration on the elongation mechanism was studied. While a negligible effect of substrate concentration was observed, we found that SacB elongation mechanism is determined by enzyme concentration. A high concentration of enzyme is required to synthesize LMW levan, involving the sequential formation of a wide variety of intermediate size levan oligosaccharides with a degree of polymerization (DP) up to ∼70. In contrast, an HMW levan distribution is synthesized through a processive mechanism producing oligosaccharides with DP <20, in reactions occurring at low enzyme concentration. Additionally, reactions where levansucrase concentration was varied while the total enzyme activity was kept constant (using a combination of active SacB and an inactive SacB E342A/D86A) allowed us to demonstrate that enzyme concentration and not enzyme activity affects the final levan molecular weight distribution. The effect of enzyme concentration on the elongation mechanism is discussed in detail, finding that protein-product interactions are responsible for the mechanism shift.

Complex Behavior of Aqueous α-Cyclodextrin Solutions. Interfacial Morphologies Resulting from Bulk Aggregation.

The spontaneous aggregation of α-cyclodextrin (α-CD) molecules in the bulk aqueous solution and the interactions of the resulting aggregates at the liquid/air interface have been studied at 283 K using a battery of techniques: transmission electron microscopy, dynamic light scattering, dynamic surface tensiometry, Brewster angle microscopy, neutron reflectometry, and ellipsometry. We show that α-CD molecules spontaneously form aggregates in the bulk that grow in size with time. These aggregates adsorb to the liquid/air interface with their size in the bulk determining the adsorption rate. The material that reaches the interface coalesces laterally to form two-dimensional domains on the micrometer scale with a layer thickness on the nanometer scale. These processes are affected by the ages of both the bulk and the interface. The interfacial layer formed is not in fast dynamic equilibrium with the subphase as the resulting morphology is locked in a kinetically trapped state. These results reveal a surprising complexity of the parallel physical processes taking place in the bulk and at the interface of what might have seemed initially like a simple system.

Isothermal titration calorimetry determination of individual rate constants of trypsin catalytic activity.

Determination of individual rate constants for enzyme-catalyzed reactions is central to the understanding of their mechanism of action and is commonly obtained by stopped-flow kinetic experiments. However, most natural substrates either do not fluoresce/absorb or lack a significant change in their spectra while reacting and, therefore, are frequently chemically modified to render adequate molecules for their spectroscopic detection. Here, isothermal titration calorimetry (ITC) was used to obtain Michaelis-Menten plots for the trypsin-catalyzed hydrolysis of several substrates at different temperatures (278-318K): four spectrophotometrically blind lysine and arginine N-free esters, one N-substituted arginine ester, and one amide. A global fitting of these data provided the individual rate constants and activation energies for the acylation and deacylation reactions, and the ratio of the formation and dissociation rates of the enzyme-substrate complex, leading also to the corresponding free energies of activation. The results indicate that for lysine and arginine N-free esters deacylation is the rate-limiting step, but for the N-substituted ester and the amide acylation is the slowest step. It is shown that ITC is able to produce quality kinetic data and is particularly well suited for those enzymatic reactions that cannot be measured by absorption or fluorescence spectroscopy.

Reversibility and two state behaviour in the thermal unfolding of oligomeric TIM barrel proteins.

Temperature is one of the main variables that modulate protein function and stability. Thermodynamic studies of oligomeric proteins, the dominant protein natural form, have been often hampered because irreversible aggregation and/or slow reactions are common. There are no reports on the reversible equilibrium thermal unfolding of proteins composed of (ß/α)8 barrel subunits, albeit this "TIM barrel" topology is one of the most abundant and versatile in nature. We studied the eponymous TIM barrel, triosephosphate isomerase (TIM), belonging to five species of different bacterial taxa. All of them were found to be catalytically efficient dimers. The three-dimensional structure of four enzymes was solved at high/medium resolution. Irreversibility and kinetic control were observed in the thermal unfolding of two TIMs, while for the other three the thermal unfolding was found to follow a two-state equilibrium reversible process. Shifts in the global stability curves of these three proteins are related to the organismal temperature range of optimal growth and modulated by variations in maximum stability temperature and in the enthalpy change at that temperature. Reversibility appears to correlate with the low isoelectric point, the absence of a residual structure in the unfolded state, small cavity volume in the native state, low conformational stability and a low melting temperature. Furthermore, the strong coupling between dimer dissociation and monomer unfolding may reduce aggregation and favour reversibility. It is therefore very thought-provoking to find that a common topological ensemble, such as the TIM barrel, can unfold/refold in the Anfinsen way, i.e. without the help of the cellular machinery.

Different contribution of conserved amino acids to the global properties of triosephosphate isomerases.

It is generally assumed that the amino acids that exist in all homologous enzymes correspond to residues that participate in catalysis, or that are essential for folding and stability. Although this holds for catalytic residues, the function of conserved noncatalytic residues is not clear. It is not known if such residues are of equal importance and have the same role in different homologous enzymes. In humans, the E104D mutation in triosephosphate isomerase (TIM) is the most frequent mutation in the autosomal diseases named "TPI deficiencies." We explored if the E104D mutation has the same impact in TIMs from four different organisms (Homo sapiens, Giardia lamblia, Trypanosoma cruzi, and T. brucei). The catalytic properties were not significantly affected by the mutation, but it affected the rate and extent of formation of active dimers from unfolded monomers differently. Scanning calorimetry experiments indicated that the mutation was in all cases destabilizing, but the mutation effect on rates of irreversible denaturation and transition-state energetics were drastically dependent on the TIM background. For instance, the E104D mutation produce changes in activation energy ranging from 430 kJ mol(-1) in HsTIM to -78 kJ mol(-1) in TcTIM. Thus, in TIM the role of a conserved noncatalytic residue is drastically dependent on its molecular background. Accordingly, it would seem that because each protein has a particular sequence, and a distinctive set of amino acid interactions, it should be regarded as a unique entity that has evolved for function and stability in the organisms to which it belongs.

Mercury ions impact the kinetic and thermal stabilities of human lens γ-crystallins via direct metal-protein interactions.

Loss of metal homeostasis may be involved in several age-related diseases, such as cataracts. Cataracts are caused by the aggregation of lens proteins into light-scattering high molecular weight complexes that impair vision. Environmental exposure to heavy metals, such as mercury, is a risk factor for cataract development. Indeed, mercury ions induce the non-amyloid aggregation of human γC- and γS crystallins, while human γD-crystallin is not sensitive to this metal. Using Differential Scanning Calorimetry (DSC), we evaluate the impact of mercury ions on the kinetic stability of the three most abundant human γ-crystallins. The metal/crystallin interactions were characterized using Isothermal Titration Calorimetry (ITC). Human γD-crystallins exhibited kinetic stabilization due to the presence of mercury ions, despite its thermal stability being decreased. In contrast, human γC- and γS-crystallins are both, thermally and kinetically destabilized by this metal, consistent with their sensitivity to mercury-induced aggregation. The interaction of human γ-crystallins with mercury ions is highly exothermic and complex, since the protein interacts with the metal at more than three sites. The isolated domains of human γ-D and its variant with the H22Q mutation were also studied, revealing the importance of these regions in the mercury-induced stabilization by a direct metal-protein interaction.

Thermodynamic and kinetic analysis of the LAO binding protein and its isolated domains reveal non-additivity in stability, folding and function.

Substrate-binding proteins (SBPs) are used by organisms from the three domains of life for transport and signalling. SBPs are composed of two domains that collectively trap ligands with high affinity and selectivity. To explore the role of the domains and the integrity of the hinge region between them in the function and conformation of SBPs, here, we describe the ligand binding, conformational stability and folding kinetics of the Lysine Arginine Ornithine (LAO) binding protein from Salmonella thiphimurium and constructs corresponding to its two independent domains. LAO is a class II SBP formed by a continuous and a discontinuous domain. Contrary to the expected behaviour based on their connectivity, the discontinuous domain shows a stable native-like structure that binds l-arginine with moderate affinity, whereas the continuous domain is barely stable and shows no detectable ligand binding. Regarding folding kinetics, studies of the entire protein revealed the presence of at least two intermediates. While the unfolding and refolding of the continuous domain exhibited only a single intermediate and simpler and faster kinetics than LAO, the folding mechanism of the discontinuous domain was complex and involved multiple intermediates. These findings suggest that in the complete protein the continuous domain nucleates folding and that its presence funnels the folding of the discontinuous domain avoiding nonproductive interactions. The strong dependence of the function, stability and folding pathway of the lobes on their covalent association is most likely the result of the coevolution of both domains as a single unit.

Dynamical shapes of droplets of cyclodextrin-surfactant solutions.

We present a series of experiments with droplets of aqueous cyclodextrin-surfactant solutions, in which the volume is reduced after the equilibrium spherical shape is reached. The final shape of the drop after this perturbation is found to be dependent on the concentration of inclusion complexes in the bulk of the solution. These inclusion complexes are formed by two cyclodextrin molecules and one surfactat molecule. We propose a model to describe these dynamical processes. Dipole-dipole interactions on the surface of the drop trigger a competition between water surface tension and dipole-dipole interaction energies. The results of the model reproduce the spherical and rod-like shapes found in the experiments.