Solvent effects and photophysical studies of a new class of acridine(1,8)dione dyes

Sub-micron sized cytochrome c particles adsorbing to solid surfaces: A comparison between solution phase and colloidal system

Present work reports on Cytochrome C (Cyt C) adsorption from solution and as sub-micron sized colloidal particles (pH 7.5) at fluid/solid interface. The colloidal particles from 2 methods ((method 1 freeze-thaw); (method 2-Decane/water interface)) have been characterized by UV-Visible spectroscopy, Static and Time resolved Fluorescence spectra and Circular dichroic spectroscopy. Morphology and size studies indicate that the colloids are solid and well-packed. Using Quartz crystal microbalance with dissipation, elastic compliance of the protein on quartz surface has been monitored. Properties of the protein from solution and as colloids assembled from method 2 are similar in elastic compliance (65.53 ± 1.2 and 73.5 ± 1.1 GPa^-1 respectively) due to polar/non-polar interactions at the solid surface. For particles from method 1, irregular desolvation of water on the particle surface results in higher compliance (104.3 ± 1.3 GPa^-1). Change in work of adhesion from contact angle profiles shows optimal adhesion for colloids from method 1 whereas the protein solution and as colloids from method 2, show subnormal adhesion. The work shows the role of extensive H-bonding with the hydrodynamically coupled water leading to a fluid like system in protein colloids from method 1 whereas those from method 2 behaved more like the pure protein adsorbing from solution.

Acridinedione as selective flouride ion chemosensor: a detailed spectroscopic and quantum mechanical investigation

The use of small molecules as chemosensors for ion detection is rapidly gaining popularity by virtue of the advantages it offers over traditional ion sensing methods. Herein we have synthesized a series of acridine(1,8)diones (7a-7l) and explored them for their potential to act as chemosensors for the detection of various anions such as fluoride (F-), acetate (OAc-), bromide (Br-), iodide (I-), bisulfate (HSO4 -), chlorate (ClO3 -), perchlorate (ClO4 -), cyanide (CN-), and thiocyanate (SCN-). Acridinediones were found to be highly selective chemosensors for fluoride ions only. To investigate in detail the mechanism of selective fluoride ion sensing, detailed spectroscopic studies were carried out using UV-visible, fluorescence and 1H NMR spectroscopy. Fluoride mediated (NH) proton abstraction of acridinedione was found to be responsible for the observed selective fluoride ion sensing. Quantum mechanical computational studies, using time dependent density functional theory (TDDFT) were also carried out, whereupon comparison of acridinedione interaction with fluoride and acetate ions explained the acridinedione selectivity for the detection of fluoride anions. Our results provide ample evidence and rationale for further modulation and exploration of acridinediones as non-invasive chemosensors for fluoride ion detection in a variety of sample types.

Studies of the photophysics of highly fluorescent Red Mega 480 laser dye in solutions: Steady state spectroscopy

The absorption and fluorescence spectra of highly fluorescent industrially useful medium sized Red Mega 480 dye have been studied in various solvents at 298 K. The solute photophysical behavior depends strongly on the solute-solvent interactions. In order to understand the effect of inter molecular interactions on spectral behaviors of the dye in different solvents extent of this behavior can be analyzed by linear solvation energy relationships. In addition, ground and excited state dipole moments were evaluated by various methods. It is observed that excited state dipole moment (μe) is larger than the ground state (μg), absorption spectra show a bathochromic shift with increasing polarity indicating that transition involved is π→π(∗) and Onsager cavity radius is determined by atomic increment method.

Role of viscogens on the macromolecular assemblies of fibrinogen at liquid/air and solid/air interfaces

In this study, an attempt has been made to understand the organization and association of fibrinogen (Fg) in solvent environment induced by viscogens such as 1-ethyl 3-methyl imidazolium ethyl sulfate (IL-emes), Ficoll, and Trehalose. The author observed that Fg in IL-emes adsorbed on solid surface shows higher β-sheet conformation. Shear viscosity measured using quartz crystal microbalance, for Fg in IL-emes was highest with a corresponding higher adsorbed mass 3.26 μg/cm(2). Associated assemblies of the protein at the liquid/air interface were monitored with changes in surface tension and were used to calculate work of adhesion. Changes in work of adhesion were used as a tool to measure the adsorption of Fg to solid surfaces in presence of viscogens and highest adsorption was observed for hydrophilic surfaces. Scanning electron microscopy images show Fg in trehalose forms elongated bead like structures implying organization of the protein at the interface. Crowding in the solvent environment induced by viscogens can slow down organization of Fg, leading to macromolecular assemblies near the interface.

Jones-Ray effect on the organization of lysozyme in the presence of NaNO3 at an air/water interface: is it a cause or consequence?

Interfacial rheology confirms the Jones-Ray effect resulting from a synergy between lysozyme and NaNO₃ at an air/fluid interface.

Conformational transitions of cytochrome c in sub-micron-sized capsules at air/buffer interface

This work presents the design of sub-micron-sized capsules of Cytochrome c (cyt c) in the range 300-350 nm and the conformational transitions of the protein that occur when the films of these capsules spread at the air/buffer interface are subjected to repeated compression-expansion cycles. Steady state fluorescence, time-resolved fluorescence, and circular dichroic (CD) spectra have been used to study the highly compact native conformation (70% helicity) of the protein in the capsules and its stability has been analyzed using cyclic voltammetry. The capsules have been characterized using zeta sizer and high resolution transmission electron microscopy (HRTEM). Surface concentration-surface pressure (Γ-π) isotherms of the films of the capsules spread at air/buffer interface following compression-expansion show destabilizing effect on cyt c. FTIR and CD spectra of these films skimmed from the surface show that the protein transitions gradually from its native helical to an anomalous beta sheet aggregated state. This results from a competition between stabilizing hydrated polar segments of the protein in the capsule and destabilizing nonspecific hydrophobic interactions arising at the air/buffer interface. This 2D model could further our understanding of the spatial and temporal roles of proteins in confined spaces and also in the design of new drug delivery vehicles using proteins.

A new VGLUT-specific potent inhibitor: pharmacophore of Brilliant Yellow

The increased concentration of glutamate in synaptic vesicles, mediated by the vesicular glutamate transporter (VGLUT), is an initial vital step in glutamate synaptic transmission. Evidence indicates that aberrant overexpression of VGLUT is involved in certain pathophysiologies of the central nervous system. VGLUT is subject to inhibition by various types of agents. The most potent VGLUT-specific inhibitor currently known is Trypan Blue, which is highly charged, hence membrane-impermeable. We have sought a potent, VGLUT-specific agent amenable to easy modification to a membrane-permeable analog. We provide evidence that Brilliant Yellow exhibits potent, VGLUT-specific inhibition, with a Ki value of 12 nM. Based upon structure-activity relationship studies and molecular modeling, we have defined the potent inhibitory pharmacophore of Brilliant Yellow. This study provides new insight into development of a membrane-permeable agent to lead to specific blockade, with high potency, of accumulation of glutamate into synaptic vesicles in neurons.

Photophysical behavior of new acridine(1,8)dione dyes

The photophysical behavior of five acridine(1,8)dione dyes of biological interest was studied by absorption and fluorescence spectroscopy, photoacoustics and time resolved phosphorescence techniques. The results obtained in ethanol and acetonitrile solutions show that the main spectroscopic and photophysical parameters of these compounds depend strongly on both the solvent and oxygen concentrations. Oxygen completely quenched the triplet state of all dyes. In nitrogen-saturated solutions, quantum efficiencies of triplet formation in ethanol were lower than those in acetonitrile.

Interfacial viscoelasticity of myoglobin at air/water and air/solution interfaces: role of folding and clustering

This study describes the folding and organization of myoglobin (Mb) at the solution/air interface at different pH values of 2.5, 3.5, 5.5, 7.5, and 8.5. Dynamic surface tension and the associated dilational and shear viscoelasticity for Mb at these pH's have been studied using a sinusoidal surface compression and expansion for frequencies ranging from 0.01 to 0.4 Hz. The changes in dilational viscosity, elasticity, and fluorescence lifetime measurements have been related to the conformational changes of the protein films at the interface. It is observed that while acid-induced denaturation of the protein does not lead to large changes in dilational properties, the shear properties on the other hand are strongly influenced by it, and the protein behaves like a shear-thickening fluid. At higher pH, particularly at the isoelectric point, Mb is pseudoplastic indicating an increase in the shear viscosity. These results are strongly suggestive of formation of hydrophobic clusters at the protein-buffer interface because of the change in the overall charge distributions.

Understanding dynamics of myoglobin in heterogeneous aqueous environments using coupled water fractions

This work presents an analysis of near environment of myoglobin (Mb) in different aqueous solutions (in the presence of NaCl, sucrose, trehalose, urea, and glycerol) using the coupled water fractions measured using a quartz crystal microbalance (QCM). The secondary structural features of the protein from circular dichroic (CD) spectroscopy and the coupled water fractions give important clues to the overall dynamics of the protein. Using time resolved fluorescence, these leads have been applied to understand the observed lifetime relaxations of Mb. Though the time scales of observation of coupled water and the lifetimes are very different, our study suggests that the trends in coupled water fraction seem to be good indicators for regulation of the relaxation dynamics of the protein. The relaxations generally show a triphasic distribution of time scales. The initial relaxation in the picoseconds time scale represents the local motions of coupled water followed by a slightly slower decay in hundreds of picoseconds attributable to coupled water-'quasi free' water interactions. The third nanosecond lifetime is due to changes in transitions in isomers of hydrated protein. The dynamics of coupled water in Mb with NaCl is the fastest (around 21 ps) and is slowest in glycerol (250 ps). The results strongly indicate that it is the resident times of water molecules that play a dominant role in the overall stability of protein in a particular hydrated isomer and not just always the number of such water molecules in the hydrated protein.

Preferential solvation of acridine in binary mixtures

Preferential solvation studies of acridine have been investigated using optical absorption technique. The preferential solvation parameter shows that in dimethyl formamide (DMF)+ethanol mixture, the acridine is preferentially solvated by ethanol in DMF rich region and by DMF in ethanol rich region. In the case of DMF+Carbon tetrachloride mixture acridine is preferentially solvated by DMF.

Thermal and microwave assisted synthesis of N-aroylamino acridinediones

A series of N-aroylamino acridinediones (3a–3d and6a–6e) have been synthesized from tetraketones (1 and 4) and benzoic hydrazides (2a–2d and 5a–5e) under thermal and microwave irradiation conditions with solid supports.Key words: acridine, hydrazide, microwave irradiation.

Rotational diffusion and solvatochromic correlation of coumarin 6 laser dye

Rotational diffusion of coumarin 6 (C6) laser dye has been examined in n-decane and methanol as a function of temperature. The rotational reorientation of this probe has been measured in these solvents. It is observed that the decrease in viscosity of the solution is responsible for the decrease in the rotational relaxation time of the probe molecule. The molecule C6 has long reorientation times in n-decane solvent as compared to methanol over all temperatures. It is found that the coumarin 6 rotates slower in n-decane than in methanol especially at higher values of viscosity over temperature. Two methods are chosen to determine the ground state and excited state dipole moments. The change in dipole moments is estimated from Bakhshiev-Chamma-Viallet equations and, the ground and excited state dipole moments from Kawski et al. equations, by using the variations of the Stokes shifts with the dielectric constant and refractive index of the solvent. Our results are quite reliable which are solvatochromic correlation obtained using solvent polarity functions. The reported results show that excited state dipole moment is greater than ground state dipole moment, which indicates that the excited state is more polar than the ground state.

The styrylpyridine dye for the silane sol-gel transition studies by time-dependent fluorescence

A trans-4-(p-N,N-dimethylaminostyryl)-N-vinylbenzylpyridinium chloride (vbDMASP) fluorescence probe was optimized in ground and excited state as a function of change in the microenvironment polarity, using the Amsol HyperChem program package. In the calculations, protic and aprotic solvents were used. On this basis a change in the molecule geometry after excitation, depending on the surrounding solvent, was determined. Absorption and steady-state fluorescence spectra of vbDMASP in the solvent of different polarity and in the model water-glycerol solutions were also recorded. On the basis of Stokes' shift change with the Onsager polarity scale a change in the dipole moment of the probe during transition from ground to excited state, in protic and aprotic solvents was determined. Since during the sol-gel transition of tetraethylorthosilane in the acidic environment both polarity and viscosity of the microenvironment change the vbDMASP probe was applied and fluorescence time-resolved measurements were done. On this basis the correlations between the results of time-resolved measurements for the multichromophoric probe applied in the gelation process and molecular optimization data are discussed.

Determination of dipole moment in the ground and excited state by experimental and theoretical methods of N-nonyl acridine orange

The absorption and fluorescence spectra of N-nonyl acridine orange are determined at room temperature (298 K) in cyclohexane, benzene, carbon tetrachloride, chloroform, chlorobenzene and dichloromethane. The ground state of dipole moment was obtained by impedance measurements using Guggenheim-Debeye's method. The experimental excited state dipole moment of N-nonyl acridine orange was determined using Bakhshiev's and Kawski-Chamma-Viallet's formulae and solvent polarity parameter proposed by Reichardt. These experimental results were completed with theoretical results using quantum chemical methods. The experimental (muexp=10.76 D) and theoretical (mucal=9.9 D) dipole moments in the ground and excited state (muexp*=14.56 D) were compared.