Formation Of Different Species Research Articles

Pyridine Diphosphonate Ligand for Stabilization of Tetravalent Uranium and Neptunium in Aqueous Medium under Aerobic Conditions.

Though uranium is usually present in its +6 oxidation state (as uranyl ion) in aqueous solutions, its conversion to oxidation states such as +4 or +5 is a challenging task. Electrochemical reduction and axial oxo activation are the preferred methods to get stable unusual oxidation states of uranium in an aqueous medium. In previous studies, dicarboxylic acid has been used to stabilize UO2+ in aqueous alkaline solutions. In the present work, a diphosphonate ligand was chosen due to its higher complexing ability compared to that of the carboxylate ligands. Neptunium complexation studies with 2,6-pyridinediphosphonic acid (PyPOH) indicated the formation of different species at different pH values and the complexation facilitates disproportionation of NpO2+ to Np4+ and NpO22+ at pH 2. Hexavalent actinides form insoluble complexes in aqueous media at pH = 2, as confirmed by UO22+ complexation studies. The in situ complexation-driven precipitation resulted in conversion to pure Np4+ in aqueous media as the Np4+-PyPOH complex. A strong complexing ability of the PyPOH ligand toward the Np4+ ion is also seen for the stabilization of the electrochemically generated U4+ in aqueous medium under aerobic conditions. The U4+-PyPOH complex was found to be stable for 3 months. Raman, UV-vis, fluorescence, and cyclic voltametric studies along with density functional theory (DFT) calculations were done to get structural insights into the PyPOH complexes of actinides in different oxidation states.

Speciation of the binary Cr(III)-citrate system in the leachate samples of phosphate ore

This report focuses on the determination of chromium chemical forms in the lixiviates of phosphate ore using speciation modelling with the MATLAB 7.7 Language. Citric acid has been used as aleaching agent for the extraction of chromium (III) from phosphate ore. A computational approach was used to determine the concentration of differentionic species present in the Cr(III)-citric acid system. The results show that the main aqueous species identified in the systemwere both free and complex ions. In addition, it was found that the concentration of total chromium in the leachate was dependent on the concentration of citric acid.On the other hand, the formation of different species and the evolution of their concentration led to an increase in the ionic strength of the solution. The ionic complex CrHCit+ showed the highest activity coefficientamong the different Cr (III) species. It was also observed that free ionic species (H3O+, H2Cit-, Cr3+) have a higher activity than chromium ionic complexes (CrH3Cit3+, CrH2Cit2+, CrHCit+).

Mechanistic Studies of Iron-PyBOX-Catalyzed Olefin Amino-Oxygenation with Functionalized Hydroxylamines.

Iron-catalyzed amino-oxygenation of olefins often uses discrete ligands to increase reactivity and broaden substrate scope. This work is focused on examining ligand effects on reactivity and in situ iron speciation in a system which utilizes a bisoxazoline ligand. Freeze-trapped 57Fe Mössbauer and EPR spectroscopies as well as SC-XRD experiments were utilized to isolate and identify the species formed during the catalytic reaction of amino-oxygenation of olefins with functionalized hydroxylamines, as well as in the precatalytic mixture of iron salt and ligand. Experiments revealed significant influence of ligand and solvent on the speciation in the precatalytic mixture which led to the formation of different species which had significant influence on the reactivity. In situ experiments showed no evidence for the formation of an Fe(IV)-nitrene intermediate, and the isolation of a reactive intermediate was unsuccessful, suggesting that the use of the PyBOX ligand led to the formation of more reactive intermediates than observed in the previously studied system, preventing direct detection of intermediate species. However, isolation of the seven coordinate Fe(III) species with three carboxylate units of the hydroxylamine and spin-trap EPR experiments suggest formation of a species with unpaired electron density on the hydroxylamine nitrogen, which is in accordance with formation of a potential iron iminyl radical species, as recently proposed in literature. An observed increase in yield when substrates devoid of C-H bonds as well as isolation of a ring-closed dead-end species with substrates containing these bonds suggests the identity of the functionalized hydroxylamine can dictate the reactivity observed in these reactions.

Photophysical evaluation on the electronic properties of synthesized biologically significant pyrido fused imidazo[4,5-c]quinolines

A single pot microwave assisted method was employed to synthesize a series of novel pyrido fused imidazo[4,5-c]quinolines. The electronic properties of these derivatives were investigated by following their photophysical behaviour under isolated and solvated conditions via computational and experimental approaches. The solvatochromic effect of these derivatives was investigated in the ground and excited singlet states by following the absorption and fluorescence emission and excitation spectra. Further the effect of general and specific solvent effects were also investigated by plotting Stokes shift against Lippert-Mataga, ET(30) and Kamlet-Taft polarity parameters respectively. The deviation from linearity in ET(30) plot indicates that formation of different species in polar protic solvents. The biological applications of these derivatives as potential drug candidates were evaluated by in silico computational methods followed by pharmacokinetic properties predictions. The ability of these derivatives to inhibit human casein kinase 2 (CK2) was evaluated. The structure activity relationships were correlated by evaluating the electronic properties through experimental photophysical investigations including solvatochromic effect and computational electronic structure calculations. Of the various derivatives, p-nitro phenyl substituted pyrido fused imidazo[4,5-c]quinoline exhibited good inhibitory activity against CK2 enzyme and hence could serve as a promising drug candidate.

Detection of radicals produced during electro-oxidation of atrazine using commercial DSA®-Cl2 in methanol media: Keys to understand the process

This work reports the radicals detected and identified during the degradation of atrazine in methanol medium in the presence and absence of different proportions of water (0%, 5%, and 10%). The determination of these radicals is an important step to understand the electrolysis processes in methanol medium and contribute to clarify the degradation mechanism. Furthermore, the parameters for the successful removal of the contaminant were optimized and the results showed that the application of the technique led to the removal of nearly 99.8% of atrazine after 1 h of electrolysis. The oxidation kinetics was found to be very fast and most of the atrazine molecule in the medium was degraded in the first hour of electrolysis. The results obtained from a thorough analysis conducted with a view to evaluating the effects of different current densities and initial pH values on atrazine degradation showed that the application of higher current densities resulted in lower energy consumption, as this led to faster removal of atrazine. Additionally, the initial pH of the solution was found to favor the formation of different species of active chlorine. The radicals formed during the electro-oxidation process were detected by electron paramagnetic resonance spectroscopy and include hydroxyl, methoxy and hydroxymethyl. The use of methanol for the degradation of pollutants is a highly promising technique and this work shows that the identification of the different radicals formed in the process can be the key to understanding the degradation mechanism.

Adsorption behavior of chromium in an aqueous suspension of δ-alumina in absence and in presence of humic substances

Abstract The radioisotope Cr-51 was exploited for studying the chromium adsorption behavior in aqueous media of alumina in aqueous media. Where, it represents 1.8% by weight and exists in earth’s crust in different forms. Factors affecting this adsorption behavior are pH, amount of alumina and humic acid presence. In case of pH adsorption curves, three different areas under peak can be described based on pH changes which lead to the formation of different species too. The first area is the maximum constant adsorption at pH, range 1–3, the second one is adsorption decreasing with increasing pH through pH range 4–7 and the third one is step-down adsorption at higher pH range. The increasing amount of alumina leads to increase in the percent adsorption, where 10 and 2 g/l alumina were found to have 100% while in case of 0.2 g/l it is 80%. The presence of humic acid decreases the adsorption of chromate with increasing pH to be 30% comparing to 80% in case of 0.2 g/l alumna at pH 2. This can be also indicated by adsorption capacity which is found to be 436.8 μg/g in case of 0.2 g alumina; and it decreases in presence of Humic Acid (HA) to 145.8 μg/g at same weight of alumina. Also, the equilibrium capacities are found as 54.6 μg/g for 2 g/l and 1.2 μg/g for 10 g/l. Triple layer model (TLM) was used for simulation of chromium adsorption behavior in presence of alumina with the applied conditions of study. The results showed high coincidence with the practically found data.

A synchrotron radiation photoelectron spectroscopy study on atomic-scale wet etching of InAs (111)-A and (111)-B in acidic peroxide solutions: surface chemistry versus kinetics

Anisotropy in the wet-chemical surface oxidation of indium arsenide (InAs) (111) in HCl/H2O2 and H2SO4/H2O2 was investigated. The atomic-scale etching kinetics was determined by inductively coupled plasma mass spectrometry and the surface chemistry, and electronic property transformation was probed by post operando synchrotron X-ray photoelectron spectroscopy. The oxidation rate is found to be larger for the (111)-B surface (As-terminated) than for the (111)-A surface (In-terminated). HCl/H2O2 solution has shown lower InAs etch rates than H2SO4/H2O2. The nature of etchant plays a role in the band bending, which is attributed to the formation of different species (sulfates/sulfides, chlorides, and hydroxides) on the surface.

Determining the impact of biofilm in the bioaugmentation process of benzene-contaminated resources

Recently, petroleum contamination in groundwater has become one of the most common environmental problems. Bioaugmentation is proposed as a fully functional and economical technology by the addition of microorganisms to remove pollutants. The aim was to study the effect of biofilm formation of different species during the bioaugmentation of benzene removal in a Permeable Reactive Barrier (PRB) system based on calcium peroxide (CaO2) nanoparticles. Therefore, at first 3 strains identified with the ability to form biofilms and benzene degradation were isolated from groundwater. Subsequently, dissolved oxygen (DO), pH, the concentration of benzene, and microbial count of experimental columns were measured. Further, the examination of the biofilm formation on glass bead surfaces in bioaugmented and control reactors was also studied by confocal laser scanning microscopy (CLSM). The results of bioaugmentation show that adding Pseudomonas lini and Pseudarthrobacter polychromogenes can remove almost 80% of benzene from effluent after 70 days. Therefore, the study reveals the effect of bioaugmentation over intrinsic bioremediation. Also, the thicker and concentrated biofilm of Pseudomonas lini can be seen. This system provides a novel environmentally friendly technology for the in situ bioremediation of benzene.

Synthesis and characterization of aryltellurium compounds including mixed-valence derivatives − evaluation of Te⋅⋅⋅S, Te⋅⋅⋅X and X⋅⋅⋅X (X = Br, I) interactions

In this article we describe the synthesis and characterization of [PhTe(tu)2][PhTeI4] and [MesTe(tu)][PhTeX4] (tu = thiourea, X = Br, I), containing multivalent tellurium species. During the syntheses of the compounds, the formation of different species, such as [PhTe(tu)I] or [I(tu)2][PhTeI4] was found, which were isolated and characterized. Thiourea was used in order to explore the relevance of Te···S bonds in the solid state structures of the products compared to related compounds with Te···X and X···X bonds in their molecular structures. Different types of chalcogen-chalcogen, chalcogen-halogen and halogen-halogen interactions are described by the combination of crystallographic data and computational methods. The nature of these interactions was evaluated by the noncovalent interaction index (NCI), and quantum theory of atoms in molecules (QTAIM) analyses.

Solvent extraction and molecular modeling studies of Dy(III) using acidic extractants

Abstract In the present work, solvent extraction of Dy(III) from chloride solutions using 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (PC88A) and Cyanex 572 (a mixture of phosphonic and phosphinic acid extractants) diluted in kerosene has been reported. Pourbaix and speciation diagrams were plotted to understand the chemistry and formation of different species of Dy(III) in chloride solutions. The effects of different extraction parameters such as pH (1–5), extractant concentration (1–60 mM) and chloride concentration (0.05–1 M) were investigated. PC88A was found to extract Dy(III) ions better than Cyanex 572 under similar conditions. Experimental results showed that Dy(III) extraction reaction occurred via a cation exchange mechanism, which was further supported by Fourier-transform infrared spectroscopy (FTIR) studies of organic solutions loaded with Dy(III). Separation studies of Dy(III) from a mixed solution of 16 rare earth elements (REEs) indicate that PC88A works better for light REEs/Dy separation while selectivity of middle and heavy REEs over Dy(III) are superior with Cyanex 572. Molecular modeling was employed to calculate the Gibbs energies of Dy ions in aqueous and organic phases (consisting of phosphonic acid in heptane), which supported the experimental results.

Theobromine Improves Working Memory by Activating the CaMKII/CREB/BDNF Pathway in Rats.

Theobromine (TB) is a primary methylxanthine found in cacao beans. cAMP-response element-binding protein (CREB) is a transcription factor, which is involved in different brain processes that bring about cellular changes in response to discrete sets of instructions, including the induction of brain-derived neurotropic factor (BDNF). Ca2+/calmodulin-dependent protein kinase II (CaMKII) has been strongly implicated in the memory formation of different species as a key regulator of gene expression. Here we investigated whether TB acts on the CaMKII/CREB/BDNF pathway in a way that might improve the cognitive and learning function in rats. Male Wistar rats (5 weeks old) were divided into two groups. For 73 days, the control rats (CN rats) were fed a normal diet, while the TB-fed rats (TB rats) received the same food, but with a 0.05% TB supplement. To assess the effects of TB on cognitive and learning ability in rats: The radial arm maze task, novel object recognition test, and Y-maze test were used. Then, the brain was removed and the medial prefrontal cortex (mPFC) was isolated for Western Blot, real-time PCR and enzyme-linked immunosorbent assay. Phosphorylated CaMKII (p-CaMKII), phosphorylated CREB (p-CREB), and BDNF level in the mPFC were measured. In all the behavior tests, working memory seemed to be improved by TB ingestion. In addition, p-CaMKII and p-CREB levels were significantly elevated in the mPFC of TB rats in comparison to those of CN rats. We also found that cortical BDNF protein and mRNA levels in TB rats were significantly greater than those in CN rats. These results suggest that orally supplemented TB upregulates the CaMKII/CREB/BDNF pathway in the mPFC, which may then improve working memory in rats.

Chitosan complements entrapment of silicon inside nitrogen doped carbon to improve and stabilize the capacity of Li-ion batteries

A facile strategy to entrap milled silicon (m-Si) particles using nitrogen-doped-carbon (N-C@m-Si) to overcome the dramatic volume changes in Si during intercalation of lithium ions and to improve its electronic conductivity is reported here. The only natural nitrogen containing biomaterial alkaline polysaccharide, i.e., chitosan, is used as the carbon source. Simple hydrothermal technique followed by a subsequent carbonization process is used to synthesize N-C and N-C@m-Si particles. N-C@m-Si exhibited significantly improved electrochemical performance as compared to bare m-Si, which is confirmed by the obtained discharge capacity of 942.4 mAh g−1 and columbic efficiency of 97% after 50 cycles at 0.1C rate. With regard to the N-C electrodes, the obtained discharge capacity of 485.34 mAh g−1 and columbic efficiency of 99.78%, after 50 cycles at 0.1C rate is superior to the commercial graphite electrodes. The solid electrolyte interphase (SEI) layer that formed over m-Si and N-C@m-Si electrodes is characterized using X-ray photoelectron spectroscopy. Compared to the SEI layer that formed over m-Si electrode after 10 charge-discharge cycles, the N-C@m-Si electrode had a stable lithium fluoride and carbonate species. Brief reaction mechanisms, representing the formation of different species in the SEI layer, is derived to explain its behavior during the electrochemical processes.

Colloidal Model for the Prediction of the Extraction of Rare Earths Assisted by the Acidic Extractant.

We propose the statistical thermodynamic model for the prediction of the liquid–liquid extraction efficiency in the case of rare-earth metal cations using the common bis(2-ethyl-hexyl)phosphoric acid (HDEHP) extractant. In this soft matter-based approach, the solutes are modeled as colloids. The leading terms in free-energy representation account for: the complexation, the formation of a highly curved extractant film, lateral interactions between the different extractant head groups in the film, configurational entropy of ions and water molecules, the dimerization, and the acidity of the HDEHP extractant. We provided a full framework for the multicomponent study of extraction systems. By taking into account these different contributions, we are able to establish the relation between the extraction and general complexation at any pH in the system. This further allowed us to rationalize the well-defined optimum in the extraction engineering design. Calculations show that there are multiple extraction regimes even in the case of lanthanide/acid system only. Each of these regimes is controlled by the formation of different species in the solvent phase, ranging from multiple metal cation-filled aggregates (at the low acid concentrations in the aqueous phase), to the pure acid-filled aggregates (at the high acid concentrations in the aqueous phase). These results are contrary to a long-standing opinion that liquid–liquid extraction can be modeled with only a few species. Therefore, a traditional multiple equilibria approach is abandoned in favor of polydisperse spherical aggregate formations, which are in dynamic equilibrium.

Coupled Cooperative Supramolecular Polymerization: A New Model Applied to the Competing Aggregation Pathways of an Amphiphilic aza-BODIPY Dye into Spherical and Rod-Like Aggregates.

Based on our studies on biphasic self-assembly behavior of an amphiphilic BF2 -azadipyrromethene (aza-BODIPY) dye 1, a new analytical model to quantitatively describe the thermodynamic properties of the aggregation involving two competing supramolecular polymerization processes is proposed. In this model, the formation of the metastable as well as the thermodynamically stable aggregates was considered to follow a nucleated polymerization mechanism. The numerical calculation based on the new model gives insight into the formation of different species in such complicate aggregate systems. Moreover, the aggregation of the biphasic self-assembly processes for dye 1 was investigated by concentration-dependent UV/Vis spectroscopy. The experimental data were analyzed by using the new model to evaluate the thermodynamic parameters including aggregation constants, the size of nuclei, and the cooperativity the two types of aggregates.

Kinetics of Melanin Polymerization during Enzymatic and Nonenzymatic Oxidation.

Melanin is an abundant biopigment in the animal kingdom, but its structure remains poorly understood. This is a substantial impediment to understanding the mechanistic origin of its observed functions. Proposed models of melanin structure include aggregates of both linear and macrocyclic units and noncovalently held monomers. Both models are broadly in agreement with current experimental data. To constrain the structural and kinetic models of melanin, experimental data of high resolution with chemical specificity accompanied by atomistic modeling are required. We have addressed this by obtaining electronic absorption, infrared, and ultraviolet resonance Raman (RR) spectra of melanin at several wavelengths of excitation that are sensitive to small changes in structure. From these experiments, we observed kinetics of the formation of different species en route to melanin polymerization. Exclusive chemical signatures of monomer 3,4-dihydroxyphenylalanine (dopa), intermediate dopachrome (DC), and early-time polymer are established through their vibrational bands at 1292, 1670, and 1616 cm-1 respectively. Direct evidence of reduced heterogeneity of melanin oligomers in tyrosinase-induced formation is provided from experimental measurements of vibrational bandwidths. Models made with density functional theory show that the linear homopolymeric structures of 5,6-dihydroxyindole can account for experimentally observed wavenumbers and broad bandwidth in Raman spectra of dopa-melanin. We capture resonance Raman (RR) signature of DC, the intermediate stabilized by the enzyme tyrosinase, for the first time in an enzyme-assisted melanization reaction using 488 nm excitation wavelength and propose that this wavelength can be used to probe reaction intermediates of melanin formation in solution.

Formation of copper nanoparticles in LTL nanosized zeolite: spectroscopic characterization.

The state of copper species stabilized in nanosized LTL zeolite subjected to various post-synthesis treatments was unveiled by a range of spectroscopic techniques. FTIR and UV-Vis studies demonstrated that the reduction process of copper in the LTL nanosized zeolite leads to the formation of different species including Cu2+, Cu+ and Cu nanoparticles (Cu NPs). The adsorption of probe molecules (NO and CO) was used to selectively monitor the copper species in the LTL nanosized zeolite upon oxidation and reduction post-synthesis treatments. Both the Cu2+ and Cu+ species were probed by NO and CO, respectively. The amount of Cu+ in the LTL zeolite nanocrystals was about 43% as determined by FTIR, while the amount of Cu NPs was about 55% determined by the UV-Vis spectroscopic characterization. These results were complemented by EPR, 29Si and 63Cu MAS NMR spectroscopic data. The EPR spectroscopy was further applied to monitor the effective reduction of the Cu2+ species and their re-oxidation, while the 63Cu MAS NMR verified the presence of Cu NPs in the LTL nanosized zeolite crystals.

Speciation of uranium-mandelic acid complexes using electrospray ionization mass spectrometry and density functional theory.

Mandelic acid is a complexing agent employed for the liquid chromatographic separation of actinides. However, the types of species and the structural details of the uranyl-mandelate complexes are still unknown. Understanding the nature of these complex species would provide better insight into the mechanism of their separation in liquid chromatography. Formation of different species of the uranyl ion (UO2 ) with mandelic acid was studied using electrospray ionization mass spectrometry (ESI-MS) with a quadrupole time-of-flight analyzer. The different species of uranyl nitrate with mandelic acid (MA) at ligand (L) to metal ratios in the range 1-10 were examined in both positive and negative ion modes. The stability of different species with the possible pathways of formation was scrutinized using density functional theory (DFT) calculations. In negative ion mode, nitrate-containing UO2 (MA)1 , UO2 (MA)2 and UO2 (MA)3 species were found in good abundance. In positive ion mode, under-coordinated uranyl-mandelate species, and solvated (S) species of types UO2 (MA)1 (S), UO2 (MA)1 (S)2 and UO2 (MA)2 (S), were observed whereas nitrate-containing species were absent. Interestingly, doubly and singly charged dimeric species were also identified in positive ion mode. The theoretically computed energetics of the various species are in close agreement with their experimentally observed intensities in ESI-MS. The most intense peak observed in ESI-MS, UO2 (MA)3 , was found to be the energetically most favorable amongst different UO2 (MA)n type species. Metal-ligand equilibria studied in the two modes yielded similar results. The combined experimental and quantum chemical investigations predict that T-shape complexes may be formed even in the gas phase. Copyright © 2016 John Wiley & Sons, Ltd.

Organo-Metallic Compounds: Novel Molecules in Cancer Therapy

The discovery of cis-platin in the treatment of cancer there has been a considerable exploration on the antitumoral activity of other transition metal complexes. One of the main problems about the application of transition metal complexes for chemotherapy is their potential toxicity. Recently the attention has been focused on titanium based complexes, which could have significant potential effect against solid tumor. The advantage of Ti (IV) complexes is their relative biological compatibility, which mostly leads to mild and revisable side effects. However, the hydrolytic instability of known Ti(IV) complexes and formation of different species upon water addition makes their therapeutic application problematic, and raises a strong interest in the development of relatively stable Ti(IV) complexes with well defined hydrolytic behavior that demonstrate appreciable cytotoxic activity. Strong ligand binding is also of interest to avoid complete ligand stripping by transferrin, so that the ligand may be used as a target for structure–activity relationship investigations. Titanocene dichloride (Cp2TiCl2) shows an average antiproliferative activity in vitro and promising result in vivo. Recent work has been performed in developing therapeutic analogues of Cp2TiCl2 by varying the central metal, the labile ligands (Cl) and the biscyclopentadienyl moiety. In particular, small changes to the Cp ligand can strongly affect the hydrolytic stability and water solubility properties of the metallocenes and have an impact on the cytotoxic activity. In this review we want summarize the importance of different organo-mettalic compounds in cancer therapy with focus on possible structure modification.

Synthesis and characterization of silver and gold NHC complexes: Crystal structures and mass spectral studies

Mononuclear silver and gold complexes [Ag(BzlCy)(Cl)] (1) and [Au(BzlCy)(Cl)] (2) were synthesized starting from the N-heterocyclic carbene (NHC) BzlCy∙HCl (1,3-Dicyclohexylbenzimidazolium chloride) and characterized by NMR and ESI-MS spectral studies. Molecular structures of complexes [Ag(BzlCy)(Cl)] (1) and [Au(BzlCy)(Cl)] (2·THF) were determined by X-ray crystallography. Formation of different species of these complexes 1 and 2 in gas phase was investigated by electrospray ionization mass spectrometry in positive mode and compared with solution formulation. To better understand the nature of NHC complexes and their reactivity with phenyl acetylene in gas phase, we synthesized a negatively charge tag gold complex [Au(SBzlCy)(Cl)] starting from SBzlCy∙HCl which prepared by the sulphonation of BzlCy. We investigated the formation of intermediate species [Au(SBzlCy)(PhC≡C)] by the coordination of phenyl acetylene to the charge-tag gold complex in gas phase. We compared the stability of these NHC complexes and also investigated the decomposed mixture by electrospray ionization.

Pyrene photochemical species in commercial clays

The photochemistry of pyrene, a polycyclic aromatic hydrocarbon, adsorbed on kaolinite, sodium montmorillonite and acid bentonite K10® was investigated to determine how the concentration and structure of the clay minerals affect the formation of different species of pyrene. Fluorescence emission spectra were obtained using reflection geometry for pyrene at the concentrations ranging from 0.5 to 100.0μmolg−1 (pyrene:clay). Two pyrene photochemical species were observed, the monomer, which fluoresces at 396nm, and its excimer which fluoresces at 470nm. The formation of excimers occurred first on the kaolinite, due to the smaller surface area. In the acid montmorillonite, the fixed interlamellar space provided greater specific area, leading to lower formation of excimers. Emission from pyrene crystals was also detected for samples with high loadings.