Interaction Of Dyes Research Articles

Functionalization of pine sawdust biochars with Mg/Al layered double hydroxides to enhance adsorption capacity of synthetic azo dyes: Adsorption mechanisms and reusability

This study determined that the adsorption of azo dyes, Methyl Orange (MO) and Sunset Yellow FCF (SYF), using the pristine pine sawdust biochar (PSB) and post-modified PSB with Mg/Al layered double hydroxides (PSB-LDHMgAl) was examined to offer valuable information into the differences in their adsorption mechanisms. Although a lower specific surface area of PSB-LDHMgAl (147.2 m2 g−1) than PSB (495.7 m2 g−1), LDHMgAl were successfully functionalized on the PSB surface through co-precipitation, which was highly related to the improvements of adsorption capacity of PSB-LDHMgAl toward MO and SYF. The MO and SYF adsorption kinetics by PSB and PSB-LDHMgAl were confirmed to the pseudo-second-order and considered chemisorption. The adsorption capacity of MO and SYF adsorbed onto PSB-LDHMgAl (MO = 21.8 mg g−1, SYF = 23.6 mg g−1) were significantly higher than that of PSB (MO = 2.2 mg g−1, SYF = 1.6 mg g−1). The adsorption isotherms of MO and SYF by PSB were well fitted by Freundlich isotherm, whereas the MO and SYF via PSB-LDHMgAl were by Langmuir isotherm. Even after 3 adsorption-desorption cycles using desorbents, the PSB-LDHMgAl remained excellent reusability (reuse efficiency: >81.2%). These findings suggest that post-modification with LDHMgAl might accelerate the adsorption performance (i.e., electrostatic interaction) of azo dyes to PSB in water.

Studying the governing factors on the photo(electro)catalytic activity of surface-modified photocatalysts under visible light illumination

The nature of the interaction at the interface of dye molecules and TiO2 surface has paramount importance in their photosensitization properties for photo(electro)catalytic application. To address this issue, two groups of organic molecules i.e., catechol and salicylic derivatives were used for the surface modification of titania. These hybrid materials were then thoroughly analyzed employing XRD, SEM, UV–Vis, FTIR, Raman, and impedance spectroscopies. The photoactivity was studied using the photoelectrochemical analysis and photocatalytic hydroxylation of terephthalic acid. Moreover, applying principal component analysis on Raman spectra indicated a significant change in the bond strength of Ti–O (B1g band) as a consequence of the chemical bond of adsorbed dye. This study links the nature of the interaction of dye and titania and the photoactivity of materials, which is thoroughly discussed in the presented work.

Utilization of host assisted aggregation-induced emission of ANS dye for ATP sensing

Photoemission efficiency of certain organic dyes gets augmented many fold when they are aggregated in solution. This AIE (Aggregation induced emission) property of dyes opens up new horizon in bio-imaging, fluorescence sensing of bio-analytes, molecular electronics, optoelectronics, chemical sensor etc. Herein, we report AIE enhancement of anionic ANS dye (8-anilinonaphthalene-1-sulfonic acid) aided by multi-cationic polymeric host, PAMA [poly(diallyl dimethyl ammonium) chloride] in aqueous solution. Anionic ANS loses its negative charge partially through charge neutralization at the vicinity of poly cationic PAMA host, leading to the reduction of like charge repulsion between the ANS molecules. This helps the dye molecules to stick together by π-π interaction, forming an aggregated assembly. Hence, there is a substantial reduction in torsional motion of the dye molecules, which is ultimately expressed as significant enhancement in its fluorescence intensity. The interaction of ANS dye with host polymer PAMA is primarily electrostatic in nature as indicated by ionic strength dependent study. This prompted the ANS-PAMA complex to be used as fluorescence probe to detect and quantify an important charged bio-analyte ATP (Adenosine triphosphate) in serum matrix at physiological pH 7.2, exhibiting the applicability of the studied system in the field of bio-sensing.

DFT Calculations for Adsorption of Methylene Blue Dye on Neem (Azadirachta indica) Leaves

Organic dyes, present in the aquatic environment, have negative effects on ecosystems. Attempts are being made to remove these dyes by using number of physio-chemical methods. Out of all the methods, adsorption technique is the most economical and efficient technique. For this purpose, efficient and cost-effective adsorbents are needed. Neem leaf powder (NLP) containing Azadirachtin Indica, has been used for methylene blue (MB) dye removal. The interaction of dye on neem leaf containing Azadirachta indica plays an important role. Quantum mechanical calculations using density functional theory have been done in order to have an idea about interaction during adsorption. There is a possibility of both strong and weak interaction depending on the orientation of adsorbent and adsorbate.

Unraveling the effects of ubiquitylation on nucleosome assembly and dynamics with coarse-grain simulations.

Ubiquitylation of histone proteins remodels and destabilizes the structure, assembly, and dynamics of the nucleosome due to the steric hindrance introduced by the bulky ubiquitin moiety. Histone proteins have multiple ubiquitylation sites, and each appears to have distinct effects on the structure and dynamics of the nucleosome. The spatial dependence of ubiquitin in regulating nucleosome dynamics remains poorly understood due to the non-specific interactions of dyes used in FRET experiments and the poor resolution of ubiquitylated nucleosomes in structural experiments. Using coarse-grain simulations along with Markov State Models, we have studied the reassembly of nucleosome intermediates with canonical and ubiquitylated histones. Results show that the reassembly of hexasomes with ubiquitylated H2A histones at lysine 119 have a destabilized tetramer/dimer interface when compared with the reassembly of hexasomes with canonical histones. Ubiquitin moieties undergo stochastic motions and only form transient interactions with the exit and entry DNA strands. These effects are altered by ubiquitylation at other histone sites, which show distinct effects on nucleosomal structures and dynamics. Together, these results provide a molecular-level understanding of the mechanism by which ubiquitylation location creates distinct effects on the structure and dynamics of the nucleosome and higher-order chromatin structures.

Enhancing single-molecule sensing and superresolution with DNA nanotech.

In recent years, DNA nanotechnology has matured to enable robust production of complex nanostructures and hybrid materials. We have combined DNA nanotechnology with sensitive optical detection to create functional single-molecule devices that enable new applications in single-molecule biophysics, biosensing and superresolution. To improve the sensitivity of DNA detection assays, we created DNA origami optical antennas for metal enhanced fluorescence. Two gold nanoparticles or nanorods enhance the light-matter interactions of dyes and biomolecular assays placed between them. We first discuss the influence of the metal nanostructure on the photophysical properties of dyes. We then show how single molecules can even be detected on a battery-driven portable smartphone microscope using DNA origami nanoantennas [1]. We further present our work on other biosensing applications of DNA origami as well as the possibility of isotropic nanometric superresolution by combining graphene energy transfer with pMINFLUX and DNA PAINT [2].

Assembling Near-Infrared Dye on the Surface of Near-Infrared Silica-Coated Copper Sulphide Plasmonic Nanoparticles.

Functionalization of colloidal nanoparticles with organic dyes, which absorb photons in complementary spectral ranges, brings a synergistic effect for harvesting additional light energy. Here, we show functionalization of near-infrared (NIR) plasmonic nanoparticles (NPs) of bare and amino-group functionalized mesoporous silica-coated copper sulphide (Cu2-xS@MSS and Cu2-xS@MSS-NH2) with specific tricarbocyanine NIR dye possessing sulfonate end groups. The role of specific surface chemistry in dye assembling on the surface of NPs is demonstrated, depending on the organic polar liquids or water used as a dispersant solvent. It is shown that dye binding to the NP surfaces occurs with different efficiency, but mostly in the monomer form in polar organic solvents. Conversely, the aqueous medium leads to different scenarios according to the NP surface chemistry. Predominant formation of the disordered dye monomers occurs on the bare surface of mesoporous silica shell (MSS), whereas the amino-group functionalized MSS accepts dye predominantly in the form of dimers. It is found that the dye-NP interaction overcomes the dye-dye interaction, leading to disruption of dye J-aggregates in the presence of the NPs. The different organization of the dye molecules on the surface of silica-coated copper sulphide NPs provides tuning of their specific functional properties, such as hot-band absorption and photoluminescence.

Sustainable Synthesis of Iron-Zinc Nanocomposites by Azadirachta indica Leaves Extract for RSM-Optimized Sono-Adsorptive Removal of Crystal Violet Dye.

Environmental pollution has exacerbated the availability of clean water to mankind. In this study, Azadirachta indica leaf extract was used for sustainable synthesis of Fe-Zn nanocomposites (IZNC). The instrumental techniques of Fourier transformed infrared (FTIR) spectroscopy, energy dispersive X-ray spectroscopy (EDS), and scanning electron microscopy (SEM) were used to determine the structural and chemical composition. The overall surface was mildly acidic in nature, as the pHPZC was observed to be 6.00. The ultrasonicated adsorption experiments were designed by central composite design (CCD). The best responses, which proposed a contaminants removal of 80.39%, were assessed using the response surface methodology (RSM). By repeating experimental runs at the expected optimum operating parameters (OOP), the method was experimentally affirmed with the %mean error and %RSD9 being 2.695% and 1.648%, respectively. The interaction of CV dye and the nanocomposite showed tremendous adsorption efficiency towards crystal violet (CV) dye, as revealed by isotherm studies. Fitting kinetics and isotherm models were affirmed by root mean square error (RMSE), χ2, and a Pearson regression coefficient. Thermodynamic studies proved spontaneity of the CV dye adsorption over the nanocomposites. The values for ΔGo, ΔHo, and ΔSo were observed to be -1.089 kJ/mol, 28.59 kJ/mol, and -3.546 kJ/mol, respectively. Recovery of CV dye was carried out in a variety of media, including NaOH, NaCl, and CH3COOH. The maximum CV recovery was achieved in an acidic media. The robustness of adsorption was affirmed by the interference of various matrix ions, including KCl, LiCl, NaCl, and MgCl2, which did not significantly affect the adsorption process. The maximum adsorption capacity was obtained at a low concentration of LiCl. The results show that a green synthesis approach for nanocomposite synthesis might be an effective and economical way to remove organic contaminants from wastewater. Moreover, it is also effective for effluent treatment plants (ETP) for waste management purposes, in which it may be coupled with chlorine as a disinfectant to purify water that can be used for domestic and irrigation purposes.

LSNR:GO template for BSA interaction, photo and sonocatalytic reductions of fluorescent dyes in aqueous solutions

Reaction of 3s1 electron of Na with crystalline 6H2O of LnCl3·6H2O forming Ln(OH)3 and H2 for LSNRs and LGT photocatalyst for photocatalyzing fluorescent dyes in sunlight with different quantum yields with SCR.

Interaction of Victoria Blue Dye in Anionic and Cationic Micellar Media: Spectroscopic Study

This manuscript has reported the micellar interaction of cationic triphenylmethane-based dye andquot;Victoria Blue-B (VBB)andquot;. The study was conducted using ionic surfactants viz. Cetyltrimethylammonium Bromide (CTAB)] Sodium Dodecyl Sulphate (SDS), and Sodium Docusate (SD). The behavior of dye in micellar media at concentration ranges of the surfactants mentioned above was monitored by UV-vis absorption spectroscopic study. The solubilization parameters to reveal the interaction of cationic dye in micellar media were assessed. The mathematical calculations of partition constant (Kc), partition coefficient (Kx), binding coefficient (Kb), Gibb’s free energy for partition (ΔGp) and binding (ΔGb) were derived from UV–Vis absorption data. The presence of anionic surfactants caused more bathochromic shifts in the maximum absorption of the dye, which was indicative of strong interactions as compared to the cationic surfactant.

Influence of Green Synthesized Zinc Oxide Nanoparticles on Molecular Interaction and Comparative Binding of Azure Dye with Chymotrypsin: Novel Nano-Conjugate for Cancer Phototherapy.

Till date, different types of conventional drugs have been used to fight tumors. However, they have significant flaws, including their usage being constrained because of their low bioavailability, poor supply, and serious side effects. The modern combination therapy has been viewed as a potent strategy for treating serious illnesses, including cancer-type feared diseases. The nanoparticles are a promising choice for cancer therapeutic and diagnostic applications because of their fascinating optoelectronic and physicochemical features. Among the metallic nanoparticles, Zinc oxide nanoparticles possess interesting physicochemical and anti-cancer characteristics, such as ROS generation, high retention, enhanced permeability etc., making them attractive candidates for the treatment and diagnosis of cancer. Zinc oxide nanoparticles showed anti-cancer property via excessive reactive oxygen species (ROS) production, and by the destruction of mitochondrial membrane. Here, we have synthesized organic/inorganic hybrid nanosystem composed of chymotrypsin protein (Chymo) with AzureC (AzC) conjugated with Zinc oxide nanoparticles (ZnONPs). The conjugation of AzureC with ZnONPs was confirmed by transmission electron microscopy (TEM), zeta potential, and dynamic light scattering (DLS) experiment. The interaction of Chymo with AzC alone and AzC-ZnONPs was investigated, and it was observed that the interaction was enhanced in the presence of ZnONPs, which was concluded by the results obtained from different spectroscopic techniques such as UV-Visible spectroscopy, fluorescence spectroscopy and circular dichroism in combination with molecular docking. UV-Visible spectroscopic studies and the corresponding binding parameters showed that the binding of AzC-ZnONPs complex with Chymo is much higher than that of AzC alone. Moreover, the fluorescence measurement showed enhancement in static quenching during titration of Chymo with AzC-ZnONPs as compared to dye alone. In addition to this, circular dichroism results show that the dye and dye-NPs conjugate do not cause much structural change in α-Chymo. The molecular docking and thermodynamic studies showed the predominance of hydrogen bonding, Van der Waal force, and hydrophobic forces during the interactions. After correlation of all the data, interaction of Chymo with AzC-ZnONPs complex showed strong interaction as compared to dye alone. The moderate binding with chymo without any alteration in the structure makes it desirable for the distribution and pharmacokinetics. In addition, the in vitro cytotoxicity of the AzC-ZnONPs was demonstrated on A-549 adenocarcinoma cell line. Our findings from physiochemical investigations suggested that the chymotrypsin coated AzC conjugated ZnONPs could be used as the novel nanoconjugates for various cancer phototherapies.

Broadening Color Shade Range of Rubia tinctorum L. Natural Colorants on Wool Fibers via Combination of Metal Mordants: Color Characteristics and Fastness Studies

ABSTRACT This study aims to extend color shade range of Rubia tinctorum L. (Dyer’s madder) natural dye on wool textiles via binary combination of Al, Sn, Cr, Fe, Cu, Ni, Co, Zn mordants. Wool yarns were premordanted, dyed with 75.0%owf madder dye, and characterized for their color strength, colorimetric parameters, and color fastness. Nature of single and binary metal cations substantially affected color shades, color strength, and fastness properties due to different interactions of dye, metal mordants, and wool polymer chains. This resulted in the development of novel color shades having different lightness, enhanced color strength, and color fastness properties. Combination of mordants had a synergistic effect on dye uptake which enhanced color strength values. Moreover, with the aid of binary metal mordants, colors of some legally restricted mordants like chromium can be reproduced which is important from ecological viewpoint. Binary mordanted samples exhibited superior color fastness. Results represent that this viable method can extend the color gamut of madder natural dye on wool with satisfactory color fastness and lessen the hazards associated with the use of some toxic metal mordants.

Efficient decolorization and detoxification of triarylmethane and azo dyes by porous-cross-linked enzyme aggregates of Pleurotus ostreatus laccase

In this preset study, porous-cross-linked enzyme aggregates (CLEAs) of Pleurotus ostreatus laccase were utilized for the spontaneous decolorization and detoxification of triarylmethane and azo dyes, reactive blue 2 (RB) and malachite green (MG). The specific surface area and pore radius of the porous-CLEAs are 136.3 m2/g and 19.47 Ao, and the higher specific surface indicated greater biocatalytic efficiency, as increased mass transfer and dye interaction with the CLEAs laccase. CLEAs laccase decolorized 500 ppm of MG and RB with 98.12–58.33% efficiency after 120 min, at pH 5.0 and 50°C, without a mediator. Furthermore, the biotransformation of the MG and RB with immobilized laccase was confirmed with the help of UV–visible spectroscopy, high-performance liquid chromatography, and Fourier transform infrared spectroscopy. The reusability potential of CLEAs was assessed in batch mode for 10 cycles of dye decolorization. The decolorization activities for the immobilized laccase were 89% and 12% at the 6th cycle for MG and RB, respectively. This immobilized enzyme could effectively remove dyes from aqueous solution, and demonstrated significant detoxification in experimental plants (Triticum aestivum and Phaseolus mungo) and plant growth-promoting rhizobacteria (Azospirillum brasilense, Bacillus megaterium, Rhizobium leguminosarum, Bacillus subtilis, and Pseudomonas fluorescens). In conclusion, porous CLEAs laccase could be useful as a potential bioremediation tool for the detoxification and decolorization of dyeing wastewater in future.

Molecular spectroscopic and docking analysis of the interaction of fluorescent thiadicarbocyanine dye with biomolecule bovine serum albumin

Binding studies of the water-soluble thiadicarbocyanine dye 3,3’-diethylthiadicarbocyanine acetate (DTC) with bovine serum albumin (BSA) were examined under physiological conditions using spectroscopic techniques like fluorescence, UV-Visible, circular dichroism (CD), FT-IR and molecular docking methods. Compiled experimental results envisage that DTC quench the fluorescence intensity of BSA. The increasing binding constants (K) were found to be in the order of 103 Mol−1 as a function of temperature, as calculated from the fluorescence quenching data. The quenching mechanism, thermodynamic parameters (ΔH0, ΔS0 and ΔG0) and the number of binding sites have been explored. CD values showed that the secondary structure of the BSA has been altered upon binding to DTC. Displacement experiments were carried out with different site probes to find out the binding site of DTC on BSA and it was found that binding interaction at site II of sub-domain IIIA. The interference of common metal ions on the interaction of DTC with BSA has also been studied. The experimental data exhibit that DTC interacts with BSA by hydrophobic forces. The experimental findings from BSA binding studies were validated by using in silico molecular docking technique. The results of the investigations were accurately supported by studies on molecular docking. The optimal shape of the molecular probe demonstrated the affinity as a free binding energy release of −7.37 Kcal/mol. The present research report endeavors to the approachable nature of water-soluble DTC dye and paves way for targeted biological interactions. Communicated by Ramaswamy H. Sarma

Efficient Adsorption of Methyl Orange on Nanoporous Carbon from Agricultural Wastes: Characterization, Kinetics, Thermodynamics, Regeneration and Adsorption Mechanism

Nanoporous carbon derived from Moringa oleifera seed waste was synthesized by an original process of flash pyrolysis followed by zinc chloride impregnation. The N2-adsorption–desorption results of the optimized sample revealed a BET surface area of 699.6 m2/g and a pore size of 2 nm. It was evaluated for the adsorption of a mono azo dye, methyl orange (MeO), from aqueous solution. Four isothermal models (Langmuir, Freundlich, Dubinin–Radushkevic and Temkin) were applied to fit the experimental data. The results revealed that Langmuir is the most appropriate isothermal adsorption model to describe the adsorption process (X2 = 1.16); with an adsorption capacity 367.83 mg/g at 298 K, the interaction of MeO dye with the nanoporous carbon surface is a localized monolayer adsorption. The adsorption kinetics was consistent with the pseudo-second-order model and found to correlate well with the experimental data (X2 = 9.06). The thermodynamic study revealed a spontaneous and endothermic adsorption process, and the substances are adsorbed in a random manner. The desorption of MeO dye from MOC-ZnCl2 by sodium hydroxide solution was achieved to a level of about 84%, and the nanoporous carbon was recycled and reused at the fifth cycle. This work demonstrates that MOC-ZnCl2 could be employed as an alternative to commercially available activated carbon in the removal of dyes from wastewater.

Unveiling Halogen-Bonding Interactions between a Pyridine-Functionalized Fluoroborate Dye and Perfluorohaloarenes with Fluorescence Spectroscopy.

We have studied the halogen-bonding interactions of a pyridine-functionalized fluoroborate dye with perfluorohaloarenes (C6F6, C6F5Cl, C6F5Br, and C6F5I) in the two-component-only liquid phase using fluorescence spectroscopy. Based on the results of spectroscopic measurements and electronic-structure calculations, we have confirmed the stability only for the complex between C6F5I and the emissive dye, and it has been demonstrated that halogen-bonding interactions are accompanied by significant Stokes shifts for the ππ* band. We also provide experimental evidence that for this complex, the emission is quenched due to a simultaneous decrease of radiative and increase of nonradiative decay rate constants upon halogen-bonding interactions.

USING N-OVEL COATED SAND AS REACTIVE BED IN PERMEABLE BARRIER FOR ELIMINATION OF METHYL ORANGE DYE FROM GROUNDWATER*

This study investigates the efficacy of sand coated with calcium / aluminum (Ca/Al)-layered double hydroxide (LDH) in the elimination of methyl orange dye from simulated groundwater using method of permeable reactive barrier. For green (sustainable) manufacturing of this sand, aluminum prepared from dissolution of alum (cheap coagulant) can be interacted chemically with calcium extracted from cement kiln dust byproduct to create nanoparticles of Ca and Al that precipitate on the filter sand. Sorption measurements for interaction of methyl orange dye and coated sand was well formulated by Langmuir model with highest value of correlation (determination coefficient= 0.999) and lowest errors (sum of squared errors= 0.0122). Also, the maximum capacity of adsorption was valued of 0.9453 mg/g and the sorption curve can classify as “favorable” type. According to desorption measurements, little percentage of dye (0.91%) can desorb from exhausted coated sand through washing with water due to strength of bonding between sorbent and dye molecules. Also, the exhausted sorbent can regenerate with efficiency not less than 85% after eight of regeneration cycles. Finally, measurements of breakthrough curves in the continuous mode operation using column setup proved that the propagation of dye front (and consequently the longevity of barrier) would increase significantly with thicker barrier and lowest values of influent concentration and flow rate. COMSOL (computer solution) package can use effectively in the simulation of these curves.

Interaction of metanil yellow dye with cationic surfactants: Conductometric and spectroscopic studies

Conductometric and spectroscopic methods were used to examine the interactions among the cationic surfactants, tetradecyltrimethylammonium bromide (TTAB) and cetylpyridinium chloride (CPC), and the anionic azo dye metanil yellow (MY) in an aqueous solution. The standard Gibb’s energy (ΔGm0), enthalpy (ΔHm0), and entropy (ΔSm0) of micellization were determined with the help of the equilibrium model. With temperature rise, the critical micelle concentration (cmc) increases because of the interruption of the organized water (WR) molecules enclosing the surfactant’s hydrophobic groups. As the total carbon atoms of the hydrophobic group are more in CPC than TTAB, a considerable fall in cmc value was observed. The presence of MY caused a higher degree of ionization (α) of micelles of TTAB and CPC. The negative values of ΔGm0 and ΔHm0 for both the surfactants in WR and aqueous MY solution (WR-MY) show that the micellization process is spontaneous and exothermic. As indicated by the -TΔSm0 values, which were found to be greater than ΔHm0 values, the entropy gain is typically what regulates the micellization process and the micellization was found to have a negative heat capacity (ΔCp,m0). UV–Visible spectra show that CPC has a higher binding constant (Kb) value as compared to TTAB implying that CPC has a comparatively greater binding affinity with MY dye in aqueous media (WR). The decreasing value of ΔGb for CPC indicates that the chance for the MY–CPC complex formation is more than that of the MY–TTAB complex. As shown by the rise in absorbance values as surfactant concentrations increase, a large number of the MY molecules are attracted to TTAB and CPC micelles.

Spectrophotometric and physicochemical investigations of Congo, alizarin red dyes and BSA interactions with Au, Ag and Au/Ag mix nanoparticles, and their antimicrobial activities

Individual and mix metal nanoparticles of Ag and Au have been prepared by the reducing method where citrate was used as reducing/stabilizing agent. The prepared NPs were characterized with UV/Visible and transmission electron microscopic (TEM) tools. The characteristic peak in UV/Visible at 525, 444 and 531 nm for Au, Ag and Ag/Au mix NPs respectively, gave primary confirmation of prepared NPs. TEM analysis showed the size of nanoparticles as 44.04, 19.78 and 30.93 nm for Ag, Au and Ag/Au mix NPs respectively. Congo and alizarin red dye interactions studies have been performed with prepared NPs to see the removal of the pollutants from water. Congo dye has shown weaker interaction as compared to alizarin due to structural symmetry. Amongst all, the AgNPs have shown maximum 67% and 75% interactions with Congo red and alizarin respectively due to high negative charges on the surface. The Au, Ag and Au/Ag mix NPs have shown stronger interaction with bovine serum albumin (BSA) protein up to 51, 59, 55% respectively, estimated through UV/Vis and physicochemical analysis. The biological evaluations of the prepared NPs have shown their antibacterial activity against Gram + ve and –ve species showing up to 9 cm zone of inhibition. The BSA interaction and antibacterial activity of NPs reveal the importance of NPs in medicinal field.

Adsorption-Induced Fluorescence of Pseudoisocyanine Monomers in Systems with Layered Silicates

Interaction of organic dyes with layered silicates can cause various changes in dye properties, such as metachromasia (color change), fluorescence quenching, resonance energy transfer, or even fluorescence enhancement. These phenomena are caused by the molecular aggregation or adsorption of dye molecules on silicate particles. The present work studied the photophysical properties of pseudoisocyanine (PIC) in colloidal dispersions of five samples of layered silicates (smectites) at variable PIC/smectite loadings. The silicates of variable composition and layer charge included one synthetic saponite, one synthetic hectorite, two synthetic Laponites, and one montmorillonite. Chemometric analysis of the absorption spectra revealed the formation of four spectral species: monomers and three types of molecular aggregates exhibiting light absorption in both H- and J-band regions. In addition, the samples of hybrid systems with silicates of lower layer charge under the condition of the lowest PIC/silicate ratio (0.01 mmol g–1) exhibited strong fluorescence surpassing that of J-aggregates. The luminescent species achieving quantum yields of about 50% were assigned to the adsorbed PIC monomers, a phenomenon that has never been observed for this dye. Theoretical calculations found that in water solution bending of the molecule supports nonradiative deactivation of the excited state of the free molecule. Adsorption of PIC molecules on the surface of silicate particles caused the change of the dihedral angle between pyridine subunits, which hinders the nonradiative deactivation channel and favors emission. Fluorescence from adsorbed monomers exhibited a maximum at ≈535 nm, which is at significantly lower wavelengths with respect to the J-aggregates emitting at ≈570 nm and thus cannot be related to dye aggregation as supported by the fact that this phenomenon occurs only at the lowest surface concentrations of the dye.