Adsorption of phenol and aniline on natural and organically modified montmorillonite: experiment and molecular modelling

Natural and intercalated Wyoming montmorillonite (MMT) with the tetramethylammonium (TMA) cations were used for the adsorption of phenol and aniline. Laboratory experiments characterised by adsorption isotherms were compared with the results of molecular modelling simulations. Aniline adsorbed itself strongly on MMT; while using the TMA intercalates (TMA-MMT), its adsorption decreased. On the contrary, the adsorption of phenol on TMA-MMT was moderately higher than on the MMT surface. The MMT surface models were described by empirical force field used in molecular mechanics and dynamics. The Burchart–Universal force field was used in the Cerius² modelling environment. The modelling results revealed the important role of water forming a moderately concentrated layer on the pure MMT surface. Water molecules enable the adsorption of aniline on MMT and, on the contrary, repel phenol molecules from MMT. In the case of TMA-MMT, lower amount of water near a silicate layer caused decrease in the aniline adsorption and, on the contrary, increase in the phenol adsorption.     

Detection of aptamer-protein interactions using QCM and electrochemical indicator methods

We report novel method of detection thrombin-aptamer interaction based on measurement the charge consumption from the electrode covered by DNA aptamers to an electrochemical indicator methylene blue (MB), that is bounded to a thrombin. The binding of thrombin to an aptamers has been detected also by QCM method in flow measuring cell. We showed that using MB it is possible to detect thrombin with high sensitivity and selectivity.     

Montmorillonite and Beidellite Intercalated with Tetramethylammonium Cations

Molecular mechanics simulations, combined with X-ray powder diffraction and infrared spectroscopy, have been used in structure analysis of montmorillonite and beidellite intercalated with tetramethylammonium cations. A complex structure analysis provided us with the detailed structure model, including characterization of the disorder, the total sublimation energy and a charge distribution in the structure of intercalates. The calculated basal spacings (14.36 Å for TMA-montmorillonite and 14.12 Å for TMA-beidellite) are in good agreement with the experimental values (14.31 Å for TMA-montmorillonite and 14.147 Å for TMA-beidellite). Both intercalated structures exhibit positional and orientational disorder in the arrangement of TMA cations, and consequently disorder in layer-stacking. In the present work we analyse the effect of octahedral and tetrahedral substitutions in a 2:1 silicate layer on the arrangement of tetramethylammonium (TMA) cations in the interlayer space of montmorillonite and beidellite. The most significant difference between TMA-montmorillonite and TMA-beidellite is in the charge distribution on the TMA cations and silicate layer. The TMA-beidellite structure is highly polarized, the total charge on one TMA cation is +0.167 e^–, while the total charge on the TMA cation in montmorillonite is +0.050 e^–.     

Electric birefringence and dichroism of acridine orange and methylene blue complexes with polynucleotides

Electro-optic measurements are reported for the polynucleotides poly A, poly U, poly G, and NaDNA, and their complexes with acridine orange (AO). Measurements were also made on the methylene blue (MB) complex with NaDNA. Poly U, poly G, and NaDNA complexes with AO as well as the NaDNA–MB complex were found to exhibit positive birefringence and perpendicular dichroism indicating the dye molecules are oriented with their long axes perpendicular to the applied electric field. The opposite was found for the AO complex with poly A, which showed positive birefringence and parallel dichroism, indicating that in this case the dye molecules are oriented with their long axes parallel to the field.     

Skin and fat necrosis of the breast following methylene blue dye injection for sentinel node biopsy in a patient with breast cancer

Sentinel lymph node biopsy (SLNB) is a simple technique that uses subdermal or peri-tumoral injection of vital blue dye and/or radioactive isotope to identify the first lymph node(s) draining the primary tumor. It has been shown to accurately predict axillary node status in patients with clinically node negative breast cancer. The SLNB is emerging as a new standard of care in patients with early breast cancer. However, the use of methylene blue (MB) dye can be associated with a number of local complications due to its tissue reactive properties. We report a rare case of skin and fat necrosis followed by a dry gangrene of the skin in a female patient with breast cancer who underwent SLNB localization using peri-tumoral injection of MB dye in another institution. This case and literature review suggest that the use of MB dye for SLNB identification should be avoided and replaced with alternative types of blue dye such as Patent Blue V preferably in conjunction with a radioactive isotope tracer.     

Molecular Mechanics Studies of Montmorillonite Intercalated with Tetramethylammonium and Trimethylphenylammonium

The intercalation of organoammonium cations into smectite structure is the important step in the technology of non-linear optical materials. In this study we investigated the structure of montmorillonite (MMT), intercalated with two organoammonium cations : tetramethylammonium (TMA) and trimethylphenylammonium (TMPA) using molecular mechanics simulations. The studies were focused to following aspects: arrangement of organoammonium cations in the interlayer, their positions and orientation with respect to silicate layers and their anchoring to the layers. The calculated (basal) d-spacings for MMT with TMA 14.29 Å and 15.36 Å for MMT with TMPA are in good agreement with X-ray diffraction data.     

Surface and interlayer structure of vermiculite intercalated with methyl viologen

Molecular modeling using empirical force field revealed the differences between the surface and interlayer arrangement of the dye guest molecules in vermiculite intercalated with the divalent methyl viologen cation (MV²⁺). Conformation and anchoring of MV²⁺ cations on the silicate layer in the interlayer space of vermiculite host structure is different from that on the crystal surface. A preferential position has been found for the anchoring of guests on the silicate layer. Anyway the arrangement of guests in the interlayer space as well as on the crystal surface exhibits a high degree of disorder due to a certain flexibility in guest molecules arrangement and first of all due to the presence of water molecules in the interlayer space. The presence of water disturbs not only the regularity in guest positions and orientations but also in conformation of guest molecules in the interlayer space of the host structure.     

Binding of methylene blue to a surface cleft inhibits the oligomerization and fibrillization of prion protein

Neurodegenerative protein misfolding diseases, including prionopathies, share the common feature of accumulating specific misfolded proteins, with a molecular mechanism closely related. Misfolded prion protein (PrP) generates soluble oligomers that, in turn, aggregate into amyloid fibers. Preventing the formation of these entities, crucially associated with the neurotoxic and/or infectious properties of the resulting abnormal PrP, represents an attractive therapeutic strategy to ameliorate prionopathies. We focused our attention into methylene blue (MB), a well-characterized drug, which is under study against Alzheimer's disease and other neurodegenerative disorders. Here, we have undertaken an in vitro study on the effects of MB on oligomerization and fibrillization of human, ovine and murine PrP. We demonstrated that MB affects the kinetics of PrP oligomerization and reduces the amount of oligomer of about 30%, in a pH-dependent manner, by using SLS and DSC methodologies. Moreover, TEM images showed that MB completely suppresses fiber formation at a PrP:MB molar ratio of 1:2. Finally, NMR revealed a direct interaction between PrP and MB, which was mapped on a surface cleft including a fibrillogenic region of the protein. Our results allowed to surmise a mechanism of action in which the MB binding to PrP surface markedly interferes with the pathway towards oligomers and fibres. Therefore MB could be considered as a general anti-aggregation compound, acting against proteinopathies.     

Bench-scale and packed bed sorption of methylene blue using treated olive pomace and charcoal

A combination of olive pomace after solvent extraction and charcoal produced from the solid waste of olive oil press industry was used as an adsorbent for the removal of methylene blue (MB) dye from aqueous solutions. Batch tests showed that up to 80% of dye was removed when the dye concentration was 10 mg/ml and the sorbent concentration was 45 mg/ml. An increase in the olive pomace concentration resulted in greater dye removal from aqueous solution, and an increase in MB dye concentration at constant adsorbent concentration increased the dye loading per unit weigh of adsorbent. In the kinetic of the adsorbent process, the adsorption data followed the second-order kinetic model better than first order kinetic model. Charcoal showed higher sorption capacity (uptake) than that of olive pomace. In the fixed bed adsorption experiment, the breakthrough curves showed constant pattern behavior, typical of favorable isotherms. The breakthrough time increased with increasing bed height, decreasing flow rate and decreasing influent concentration and methylene blue dye uptake. The uptake of MB dye was significantly increased when a mixture of olive pomace and charcoal was packed in the column in a multi-layer fashion. Different models were used to describe the behavior of this packed-sorption process.     

Attaching NorA efflux pump inhibitors to methylene blue enhances antimicrobial photodynamic inactivation of Escherichia coli and Acinetobacter baumannii in vitro and in vivo

Resistance of bacteria to antibiotics is a public health concern worldwide due to the increasing failure of standard antibiotic therapies. Antimicrobial photodynamic inactivation (aPDI) is a promising non-antibiotic alternative for treating localized bacterial infections that uses non-toxic photosensitizers and harmless visible light to produce reactive oxygen species and kill microbes. Phenothiazinium photosensitizers like methylene blue (MB) and toluidine blue O are hydrophobic cations that are naturally expelled from bacterial cells by multidrug efflux pumps, which reduces their effectiveness. We recently reported the discovery of a NorA efflux pump inhibitor-methylene blue (EPI-MB) hybrid compound INF55-(Ac)en–MB that shows enhanced photodynamic inactivation of the Gram-positive bacterium methicillin-resistant Staphylococcus aureus (MRSA) relative to MB, both in vitro and in vivo. Here, we report the surprising observation that INF55-(Ac)en–MB and two related hybrids bearing the NorA efflux pump inhibitors INF55 and INF271 also show enhanced aPDI activity in vitro (relative to MB) against the Gram-negative bacteria Escherichia coli and Acinetobacter baumannii, despite neither species expressing the NorA pump. Two of the hybrids showed superior effects to MB in murine aPDI infection models. The findings motivate wider exploration of aPDI with EPI-MB hybrids against Gram-negative pathogens and more detailed studies into the molecular mechanisms underpinning their activity.     

Alcohol dehydrogenase activity and electron transport in living yeast

1. The excretion of H(+) ions, with practically equivalent uptake of K(+) ions (from 0.1m-potassium chloride), occurs during the aerobic oxidation of ethanol. 2. Acetaldehyde and acetic acid formed at the same time are quantitatively equal to the amount of ethanol oxidized. 3. A slow uptake of K(+) ions occurs during the oxidation of acetaldehyde and a more rapid uptake during the oxidation of d-glyceraldehyde 3-phosphate. 4. The anaerobic reduction of methylene blue is studied, and the inhibitory effect of K(+) and other inorganic cations on the system demonstrated. 5. The cation requirement for equal inhibitory effect is parallel with the reciprocals of the transport affinities for the ;physiological K-carrier' (as taken from Conway & Duggan, 1958). 6. The cation inhibition of methylene blue reduction is reversed by treatment of the yeast with Teepol or by freezing-and-thawing. 7. Azide is shown to inhibit the reduction of methylene blue with intact cells. The inhibition is partially reversed by Teepol treatment and completely by freezing-and-thawing.     

Interlayer Porosity in Montmorillonite Intercalated with Keggin-like Cation Studied by Molecular Mechanics Simulation

Molecular mechanics simulation using Cerius² modeling environment have been used to investigate the structure of montmorillonite, intercalated with Keggin-like cation⁷⁺. Present work is focused to the strategy of modelling in case of intercalated layered structures and to investigation of structure parameters characterizing the interlayer porosity, that means: the interlayer distance, the position, orientation and distribution of Keggin cations in the interlayer space and the stacking of layers. Molecular simulations revealed the structure of the interlayer and led to the following conclusions: In the most stable configuration the 3-fold axis of Keggin cation is perpendicular to the silicate layer. This orientation of Keggin cations leads to the basal spacing 19.51 (10^-10 m). Energy minimization during the translation of Keggin cation along the silicate layer gives only small fluctuations of basal spacing and no correlation has been found between the shift of cation along the layers and the value of basal spacing. No systematic relationship has been found between the shift of cation and crystal energy and no systematic relationship exists between the mutual shift of two successive layers and the values of basal spacing and crystal energy. Consequently, no two-dimensional ordering of Keggin cations in the interlayer and no regular stacking of layers can be expected. X-ray diffraction diagrams obtained for montmorillonites, intercalated with Keggin cation, confirm present conclusions.     

Feasibility of dual-contrast fluorescence imaging of pathological breast tissues

The combination of intravital dye, methylene blue (MB), with molecular cancer marker, pH low insertion peptide (pHLIP) conjugated with fluorescent Alexa532 (Alexa532-pHLIP), was evaluated for enhancing contrast of pathological breast tissue ex vivo. Fresh, thick breast specimens were stained sequentially with Alexa532-pHLIP and aqueous MB and imaged using dual-channel fluorescence microscopy. MB and Alexa532-pHLIP accumulated in the nuclei and cytoplasm of cancer cells, respectively. MB also stained nuclei of normal cells. Some Alexa532-pHLIP fluorescence emission was detected from connective tissue and benign cell membranes. Overall, Alexa532-pHLIP showed high affinity to cancer, while MB highlighted tissue morphology. The results indicate that MB and Alexa532-pHLIP provide complementary information and show promise for the detection of breast cancer.     

Cell surface alterations induced by methylene blue and direct electric current in Escherichia coli.

Cell surface properties, including hydrophobicity, zeta potential, carbohydrate and fatty acid components, were altered on treatment of E. coli K12 with methylene blue (MB) and direct electric current (DC). The treatment of fimbriated E. coli cells with MB greatly increased the agglutination of yeast cells when compared to untreated bacteria. However, this increased agglutination was markedly reduced when the bacteria were treated with MB plus DC. These results suggest that MB modifies cell surface components in the absence of light and these alterations are more pronounced when cells are treated simultaneously with MB and DC.     

Molecular distribution and charge of polylysine layers at the surface of lipid membranes and mica

Electrophoretic mobility of cardiolipin liposomes was measured in the presence of polylysines of different molecular weight at various concentrations of the background electrolyte (KCl). The electrophoretic mobility in a liposome suspension changes its sign and reaches a plateau at high polylysine content. The surface charge in the plateau region was determined according to the Gouy-Chapman model of the electrical double layer. The average charge density was found to equal 0.005 and 0.016 Coulomb/m² for the polymer length of 5 and 12 units (bases), respectively, and 0.032 Coulomb/m² for polylysines with the length of 130 and 1435 units. The molecular distribution of these polylysines was studied at the mica surface using atomic force microscopy in the 10-mM KCl solution. It was shown that pentalysine molecules covered uniformly about 90% of the surface with the layer thickness of about 0.8 nm. The high-molecular polylysines cover about 60% of the surface with the layer thickness of more than 1.5 nm. The data suggest that the polymer forms a compact layer on the membrane surface; the charge density at the outer surface is determined both by the polymer properties and by the total amount of anionic lipids, irrespective of their ionization state.     

Analysis of methylene blue in human urine by capillary electrophoresis

A capillary electrophoresis method for the determination of the dye methylene blue (tetramethylthionine, MB) in human urine depending on liquid/liquid-extraction and diode array detection has been developed, validated, and applied to samples of healthy individuals, who had been dosed with methylene blue within clinical studies. After extraction with dichloromethane and sodium hexanesulfonate, sample extracts were measured on an extended light path capillary. The dye was detected simultaneously at 292 and 592 nm using methylene violet 3 RAX as internal standard. The limit of quantification was 1.0 microg/ml. The accuracy of the method varied between -15.2 and +0.8% and the precision ranged from 2.0 to 12.0%. The method was linear at least within 1.0 and 60 microg/ml. In contrast to earlier indirect determinations no leuco methylene blue (LMB) was directly detected in urine, whereas in aqueous test solutions containing surplus amounts of ascorbic acid leuco methylene blue was well separated from MB in a single run.     

Adsorption of lecithin liposomes to acid clay

The interaction between lecithin liposomes and acid clay was investigated to clarify the mechanism for liposome adsorption to the clay. It was found that the multilamellar vesicular structure of the liposomes was broken as a result of primary adsorption. The acid clay particles aggregated and were eventually covered by the lecithin layer structure. In the case of kaolin, on the other hand, the liposomes were weakly adsorbed to the clay and maintained the vesicular structure. The amount of primary adsorption to the clay surface, which was estimated from the adsorption isotherm, was more for acid clay than for kaolin, and the total amount adsorbed to the acid clay was also more than to kaolin. This result can be explained by the much higher density of the negative charge on the acid clay surface than that for kaolin. The liposomes are therefore considered to be adsorbed to the acid clay mainly by the choline positive charge residing at the end of the lecithin molecule, although this is of no net charge as a whole.     

Adsorption of Five Model Organic Compounds on a Peat at Different Stages of Drying

Acridine orange (AO), dinitrobenzoic acid (DNB), bromocresol green (BCG), bromophenol blue (BPB), and methylene blue (MB) were chosen as model aromatic compounds of different polarity, charge, and solubility in water to examine the effects of solute properties on hydrophobic adsorption. These compounds show strict structural similarities to some herbicides and other potential xenobiotic pollutants and exhibit distinct absorption maxima in the visible region, which allows for their easy determination. A well-decomposed peat (medisaprist) at four different stages of drying was used to determine compound adsorption/desorption influences based on the degree of hydrophobicity and charge density of an organic surface. Adsorption and desorption isotherms were investigated using the batch equilibration method and determining the concentration of free chemicals by UV-Vis spectrophotometry. AO had a high tendency of adsorption and was strongly sorbed on peat samples that had been air-dried for 12 months. The lower Freundlich coefficient values found for MB when compared with AO at all the drying stages of the peat indicated that electrostatic attraction has a secondary contribution to sorption. On the contrary, the higher energy that must be spent to break solute-solvent interactions in the case of charged or polar molecules is one of the main factors in determining the position of the equilibrium. For a given solute, K_f values varied with the degree of hydrophobicity and the charge density of the surface, but again solute-solvent interactions appear to be much more important in the overall energy balance of hydrophobic pollutants than the electrostatic sorbate-sorbent interactions. A change in the solution pH does not improve the adsorption of the relatively polar DNB molecule, but sorption increases strongly for BCG and BPB when these molecules are in non-dissociated forms. The larger increase in BPB sorption observed on H⁺ saturated peat suggests that the degree of interaction increases with the suppression of the negative charge, but charge repulsion has a small effect in preventing adsorption of molecules bearing hydrophobic groups such as BCG. Desorption results differed depending on the chemical structure of the compound examined. For example, with AO there was no desorption from the more hydrophobic peat surfaces. A negative hysteresis was observed for DNB; the magnitude of hysteresis, evaluated using the ratio of Freundlich coefficients for adsorption and desorption, increased with the drying stage of the sorbent and was larger on oven-dried samples.     

Impact of metal oxide nanoparticles on oral release properties of pH-sensitive hydrogel nanocomposites

In this article, modified κ-carrageenan hydrogel nanocomposites were synthesized to increase the release ability of carrageenan hydrogels under gastrointestinal conditions. The effect of MgO nanoparticle loading in a model drug (methylene blue) release is investigated. Characterization of hydrogels were carried out using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Field Emission Scanning Electron Microscope (FESEM) and Differential Scanning Calorimetry (DSC). Genipin was used to increase the delivery performance in gastrointestinal tract delivery by decreasing release in simulated stomach conditions and increasing release in simulated intestine conditions. It is shown that the amount of methylene blue released from genipin-cross-linked nanocomposites can be 67.5% higher in intestine medium and 56% lower in the stomach compared to κ-carrageenan hydrogel. It was found that by changing the nanoparticle loading and genipin concentration in the composite, the amount of drug released can be monitored. Therefore, applying nanoparticles appears to be a potential strategy to develop controlled drug delivery especially in gastrointestinal tract studies.