Modified Stern-Volmer Plot Research Articles

Revelation of anti-aggregating and disaggregating characteristic of amodiaquine via inhibition of human lysozyme fibrillation: Therapeutic alternative for treating amyloidopathies

Amyloidopathies are associated with a biochemical change in concerned organ or bio-environment known as inflammation (promoted in case of fibrils accumulation due to their stability) that triggered us to explore anti-aggregating and disaggregating property of an anti-inflammatory drug amodiaquine (AD) against human lysozyme (HL) fibrillation in this study simultaneously evaluating the mechanism of interaction between AD and HL using biophysical and microscopic techniques. The linear modified Stern-Volmer plot obtained from fluorescence quenching of HL by AD at three temperatures and Ksv dependence on temperature with kq > 2.0 × 1010 supports static quenching mechanism with strong binding (Kb = × 106) and negative ΔG value. The change in Trp and Tyr environment due to AD binding were confirmed via synchronous fluorescence. The studies were further extended to analyse aggregation inhibition and disaggregation of HL by AD. RLS, ThT, CD and DLS results suggested aggregation inhibition and disaggregation which was further confirmed via TEM. Overall, our study suggests that AD is an effective drug for fibrillation inhibition and disaggregation. The possible mechanism behind this behaviour is the stabilization of HL in native state by AD via non-covalent interactions and thus AD will not only reduce fibril burden but will also calm severity of the disease (such as regaining cognitive function due to reduced inflammation). This can be an alternative promising approach that can be exploited for treating amyloidopathies such as Alzheimer’s, Parkinson’s disease and systemic amyloidosis.

Propionic Acid Groups and Multiple Aromatic Rings Induce Binding of Ketoprofen and Naproxen to the Hydrophobic Core of Bovine Serum Albumin.

Ketoprofen (KP), which causes photosensitivity by interacting with serum albumin (SA), and three drugs, ibuprofen (IBP), naproxen (NPX), and diazepam (DZP), which share the same binding site, were investigated for their interaction with bovine SA (BSA). For KP, DZP, and IBP, where drug-concentration-dependent quenching of BSA-intrinsic fluorescence was observed, a modified Stern-Volmer plot showed that dynamic quenching was dominant for KP and static quenching was dominant for DZP and IBP. However, this alone cannot be compared with NPX. Therefore, by performing singular value decomposition (SVD) fluorescence spectroscopy, we were able to find the behavior of the drug-concentration-dependent Langmuir-type principal component vectors. KSVD obtained by the Langmuir equation showed a high correlation with the static extinction constant V. Therefore, KSVD indicates the association constant of the drug with BSA and it was found that NPX and IBP had higher values than KP. Finally, in the analysis of the temperature factors of amino acid residues in each drug-binding region and Trp residues, KP and NPX significantly reduced these temperature factors whereas DZP and IBP hardly changed them. This result is consistent with the dynamic and static quenching dominance in the total quenching mechanism. Summarizing the results so far, it was shown that penetration into the hydrophobic core inside BSA can be achieved not only by one of the multiple aromatic rings and propionic acid groups but also by the joint effect of both. In this study, SVD enabled us to extract information on drug adsorption to BSA from fluorescence spectra. Furthermore, the application of SVD is expected to make it possible to perform fluorescence analysis for drug binding to proteins without being limited by the fluorescence properties of the drug.

Binding studies for the interaction between hazardous organophosphorus compound phosmet and lysozyme: Spectroscopic and In-silico analyses

Organophosphorus compounds are generally toxic compounds found uses in agriculture, pharmaceutics, and other industries. These organophosphorus compounds are life threatening and may cause mortalities on acute exposure. Also, some of these are well known nerve agents. Phosmet is one such organophosphorus compound with moderate nerve toxicity on prolonged exposure. Phosmet is widely used pesticide on various trees including apple, pear, peach, almond and vines like grape vine. Thus, phosmet is the major contaminant of most of the consumed fruits.The present study investigated the binding of phosmet with lysozyme to understand the toxicology and the transport of phosmet using various spectroscopic techniques, molecular modeling and enzymatic assay. The ability of lysozyme to act as a biomarker for phosmet can also be revealed by the current study. The UV–Visible spectrum of lysozyme in presence of phosmet indicated hyperchromicity in the absorbance peak of lysozyme. The fluorescence quenching of lysozyme in presence of phosmet involve predominantly static quenching. The complexation is further quantified in terms of a binding constant (Kb) and the number of sets of equivalent binding sites (n) with the help of double logarithmic regression curve. The Kb value of 103–104 M−1 and n value near 1 indicated that phosmet is binding through non-covalent forces in single set of equivalent binding sites. Static quenching was additionally confirmed by modified Stern-Volmer plot for lysozyme-phosmet interactions. Post binding protein conformation changes and the enhanced protein stability of lysozyme were showed by CD spectrum and melting curves of lysozyme. The FT-IR spectrum also revealed the changes in secondary structure content of protein on interaction with phosmet. The docked structure for binding of phosmet with lysozyme were achieved using molecular docking analysis with a glide score −5.273 k J/mol-1 that indicated towards moderate binding as suggested by other experimental studies. The enzymatic activity of lysozyme depicted an increase of 16% after binding with phosmet indicative of interaction with the active site.

Exploring the binding interactions of janus green blue with serum albumins from spectroscopic and calorimetric studies aided by in silico calculations

Binding interactions of the phenazinium dye Janus green blue (JGB) with human and bovine serum albumins (BSA – and BSA) have been explored for the first time from multi-spectroscopic and calorimetric measurements aided by in silico calculations. The formation of ground state complexes between JGB and the respective serum albumins have been suggested from the UV–Vis and steady-state fluorescence spectroscopic studies. The nonlinear Stern Volmer (SV) plots at higher concentrations of JGB primarily indicate the formation of more than one ground state complexes in BSA –/BSA–JGB systems. Modified SV plots and isothermal titration calorimetry (ITC) studies however signify the possibilities of one type of binding complexes between HSA/BSA – JGB systems. Binding constants and the thermodynamic parameters associated with the HSA/BSA–JGB complexes have also been estimated from the ITC studies. Förster distances (R0 ) for HSA–JGB and BSA–JGB complexes are estimated from Förster resonance energy transfer (FRET) results. Variations in the micro-environment of the Tyr and Trp residues of the serum proteins in presence of JGB have been observed from the synchronous fluorescence measurements. The conformational changes in the protein structures induced by the dye JGB have been revealed from 3 D fluorescence and circular dichroism (CD) studies. The experimental observations are supported by in silico calculations. This in depth investigation on the interactions of serum albumins with JGB may provide the fundamental information toward exploring the therapeutic efficacy of JGB as a potent drug molecule. Communicated by Ramaswamy H. Sarma

Understanding the binding interaction between phenyl boronic acid P1 and sugars: determination of association and dissociation constants using S-V plots, steady-state spectroscopic methods and molecular docking.

Continuous monitoring of glucose and sugar sensing plays a vital role in diabetes control. The drawbacks of the present enzyme-based sugar sensors have encouraged the investigation into alternate approaches to design new sensors. The popularity of fluorescence sensors is due to their ability to bind reversibly to compounds containing diol. In this study we investigated the binding ability of phenyl boronic acid P1 for monosaccharides and disaccharides (sugars) in aqueous medium at physiological pH 7.4 using steady-state fluorescence and absorbance. P1 fluorescence was quenched due to formation of esters with sugars. Absorbance and fluorescence measurements led to results that indicated that the sugars studied could be ordered in terms of their affinity to P1, as stated: sucrose > lactose > galactose > xylose > ribose > arabinose. In each case, the slope of modified Stern-Volmer plots was nearly 1, indicating the presence of only a single binding site in boronic acids for sugars. Docking studies were carried out using Schrodinger Maestro v.11.2 software. The binding affinity of phenyl boronic acid P1 with periplasmic protein (PDB ID 2IPM and 2IPL) was estimated using GlideScore.

Fluorescence quenching of molybdenum disulfide quantum dots for metal ion sensing

In the present work, we have used hydrothermally synthesized in situ functionalized MoS2-QDs for a sensitive (limit of detection ~ 2.06 µM) and selective detection of Fe3+ ions. A detailed study of fluorescence quenching behavior for MoS2-QDs in the presence of Fe3+ ions has been performed using the Stern–Volmer plot, modified Stern–Volmer plot, and time-resolved photoluminescence measurements. Absorption based titration spectra and time-resolved photoluminescence measurements confirmed the fluorescence quenching is static with three decay times originated from the three different fluorescing sites. Interestingly, it is found that emission spectra consist of three bands at positions ~ 450 nm (P1, ~ 2.76 eV), ~ 475 nm (P2, ~ 2.61 eV), and ~ 503 nm (P3, ~ 2.46 eV). These peaks show a systematic quenching with the increasing concentration of Fe3+ ions. Quenching constants corresponding to these emission bands are found of the order of ~ 103 M−1. Large values of bimolecular quenching constants (~ 1011 M−1 s−1) suggest a strong binding interaction between MoS2-QDs and Fe3+ ions. Furthermore, to understand the fluorescence quenching of MoS2-QDs in the presence of Fe3+ ions, a ground-state complex formation-based mechanism has been proposed and elucidated in detail.

RGO integrated MEHPPV and P3HT polymer blends for bulk hetero junction solar cells: A comparative insight

In this paper, a comparative study of reduced graphene oxide (rGO) integrated with poly[2-methoxy,5-(2′-ethylhexyloxy)-p-phenylenevinylene] (MEHPPV) and poly(3-hexylthiophene) (P3HT) conducting polymers have been conducted in order to obtain an efficient active layer material for organic photovoltaic (OPV) device fabrication. The structural and morphological properties have been investigated using techniques such as X-ray diffraction, field emission scanning electron microscopy, thermogravimetric analysis, and Raman spectroscopy. The optical and electrical characterizations have been performed to explore the photoluminescence quenching behaviour, electron transfer properties and efficient energy conversion. Moreover, the quantification of charge transport properties was estimated using Stern-Volmer and modified Stern-Volmer plots. The quenching constants obtained for MEHPPV–rGO nanocomposite was 2.41 × 103 L−1 and 2.72 × 103 L−1 for P3HT–rGO nanocomposite to better charge transfer capabilities found in nanocomposites. Further, the contact angle and surface energy measurement studies conducted on thin films also proposed that P3HT-rGO nanocomposite pairs are more suitable for solar cell applications as compared to MEHPPV- rGO. However, the I-V results obtained from the fabricated devices indicate that the rGO composites blended with P3HT polymer showed an efficiency of 0.045% while those composed with MEHPPV shows only 0.024%.

Silicon Quantum Dot-Based Fluorescent Probe: Synthesis Characterization and Recognition of Thiocyanate in Human Blood.

Allylamine-functionalized silicon quantum dots (ASQDs) of high photostability are synthesized by a robust inverse micelle method to use the material as a fluorescent probe for selective recognition of thiocyanate (a biomarker of a smoker and a nonsmoker). The synthesized ASQDs were characterized by absorption, emission, and Fourier transform infrared spectroscopy. Surface morphology is studied by transmission electron microscopy and dynamic light scattering. The synthesized material exhibits desirable fluorescence behavior with a high quantum yield. A selective and accurate (up to 10–10 M) method of sensing of thiocyanate anion is developed based on fluorescence amplification and quenching of ASQDs. The sensing mechanism is investigated and interpreted with a crystal clear mechanistic approach through the modified Stern–Volmer plot. The developed material and the method is applied to recognize the anion in the human blood sample for identification of the degree of smoking. The material deserves high potentiality in the field of bio-medical science.

Multispectroscopic and bioimaging approach for the interaction of rhodamine 6G capped gold nanoparticles with bovine serum albumin

Binding interaction of Bovine Serum Albumin (BSA) with newly prepared rhodamine 6G-capped gold nanoparticles (Rh6G-Au NPs) under physiological conditions (pH 7.2) was investigated by a wide range of photophysical techniques. Rh6G-Au NPs caused the static quenching of the intrinsic fluorescence of BSA that resulted from the formation of ground-state complex between BSA and Rh6G-Au NPs. The binding constant from fluorescence quenching method (Ka = 1.04 × 104 L mol−1; LoD = 14.0 μM) is in accordance with apparent association constant (Kapp = 1.14 × 101 M−1), which is obtained from absorption spectral studies. Förster resonance energy transfer (FRET) efficiency between the tryptophan (Trp) residue of BSA and fluorophore of Rh6G-Au NPs during the interaction was calculated to be 90%. The free energy change (ΔG = −23.07 kJ/mol) of BSA–Rh6G-Au NPs complex was calculated based on modified Stern-Volmer Plot. The time-resolved fluorescence analysis confirmed that quenching of BSA follows static mechanism through the formation of ground state complex. Furthermore, synchronous and three-dimensional fluorescence measurement, Raman spectral analysis and Circular Dichroism spectrum results corroborate the strong binding between Rh6G-Au NPs and BSA, which causes the conformational changes on BSA molecule. In addition, fluorescence imaging experiments of BSA in living human breast cancer (HeLa) cells was successfully demonstrated, which articulated the value of Rh6G-Au NPs practical applications in biological systems.

Exploring the Binding Mechanism of Flavonoid Quercetin to Phospholipase A2: Fluorescence Spectroscopy and Computational Approach

The interaction of flavonoid Quercetin with Phospholipase A2 isolated from snake venom Bothrops brazili (MTX-II) was investigated by fluorescence spectroscopy and molecular modeling. The fluorimetric titrations were conducted at 288, 298 and 308 K and at pH 8.0. Stern-Volmer quenching constant (KSV) and binding constant (Kb) were calculated along with the corresponding thermodynamic parameters ΔG, ΔH and ΔS at 288 and 298 K. From these analysis evidences of complex formation in between MTX-II and QCT are found. Besides that modified Stern-Volmer plot show evidences for two types of intrinsic fluorophores with different accessibilities at 308 K. The mean distance between the donor (MTX-II) and acceptor (QCT) was determined by fluorescence resonance energy transfer (FRET). The optimized structure of QCT was obtained by ab initio calculation, which geometry was performed in its ground states by using DFT/B3LYP functional with 6-311+G (d,p) basis set. The molecular docking analysis show that QCT may be localized at two main clusters, the first is at the dimer interface and the second at the active site like region. The clusters positions and binding energies reinforce the experimental data.

Importance of fluorine in 2,3-dihydroquinazolinone and its interaction study with lysozyme

The main aim of this study is to investigate the interaction of 7-fluoro-2,2-dimethyl-2,3-dihydroquinazolin-4(1H)-one with lysozyme through various spectrophotometric studies. The graph such as Stern-Volmer plot, modified Stern Volmer plot, double logarithmic plot and Van't Hoff plot were plotted to determine the various parameters essential for predicting the interaction. The interaction of the ligand with the protein was further confirmed by circular dichroism and NMR study. The molecular docking was performed and the results obtained were correlated with the other studies. The importance of fluorine was justified through the prediction of pKa values and the possible metabolic pathway using the in silico tools. In addition, the cytotoxicity of the compound was carried out using HeLa cancer cell.

Effect of polymer matrix on the performance of pressure‐sensitive paint comprising 5,10,15,20‐tetrakis(pentafluorophenyl)porphinato platinum(II) and poly(1,1,1,3,3,3‐hexafluoroisopropyl‐co‐tert‐butyl methacrylates)

ABSTRACTCopolymers of 1,1,1,3,3,3‐hexafluoroisopropyl methacrylate (HFIPM) and tert‐butyl methacrylate (TBM) were prepared by conventional radical copolymerization as a novel binders for pressure‐sensitive paints (PSP). The monomer reactivity ratios rHFIPM and rTBM were determined as 0.45 and 0.67, respectively. The glass transition temperature of the copolymers increased from 77 to 126°C with increasing mole fraction of TBM units in the copolymer. The PSP were formed by combining the resulting copolymers and 5,10,15,20‐tetrakis(pentafluorophenyl)porphinato platinum(II). The pressure and temperature sensitivities of the PSPs were measured at air pressures ranging from 5 to 120 kPa and at temperatures ranging from 0 to 60°C. Modified Stern–Volmer plots indicated slight increases in the pressure sensitivity, but significant decrease in the temperature sensitivity as the mole fraction of HFIPM units increased in the copolymer. Applying a theoretical model to our calibration data, we inferred that luminescence quenching is primarily responsible for increasing the temperature sensitivity in the resulting copolymers. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43316.

Spectroscopic and DFT investigation of interactions between cyclophosphamide and aspirin with lysozyme as binary and ternary systems

Multi-spectroscopic and density functional theory (DFT) calculations was used to study the interaction between cyclophosphamide (CYP) and aspirin (ASA) with lysozyme (LYS). The experimental results showed that fluorescence quenching of LYS by drug was a result of the formation of drug–LYS complex; static quenching was confirmed to result in fluorescence quenching. Modified Stern–Volmer plots of interaction between CYP and ASA with protein in the binary and ternary systems were used to determine the binding parameters. Molecular distances between the donor (LYS) and acceptor (CYP and ASA) for all systems were estimated according to Forster’s theory. The quantitative analysis obtained by CD spectra suggested that the presence of ASA and CYP decreased the α-helical content of LYS and induced the destabilizing of it. Theoretical studies on the interaction between LYS with ASA and CYP have been carried out using DFT at the B3LYP/6-31G level in the solvent phase. Binding energy of the mentioned complexes was calculated. It showed that tryptophan (Trp) 62 had the most affinity toward ASA and CYP. Analyzing the calculated results revealed that the five member ring of Trp has a key role in interaction of LYS with ASA and CYP.

Norfloxacin Zn(II)-based complexes: acid base ionization constant determination, DNA and albumin binding properties and the biological effect against Trypanosoma cruzi

Zn(II) complexes with norfloxacin (NOR) in the absence or in the presence of 1,10-phenanthroline (phen) were obtained and characterized. In both complexes, the ligand NOR was coordinated through a keto and a carboxyl oxygen. Tetrahedral and octahedral geometries were proposed for [ZnCl2(NOR)]·H2O (1) and [ZnCl2(NOR)(phen)]·2H2O (2), respectively. Since the biological activity of the chemicals depends on the pH value, pH titrations of the Zn(II) complexes were performed. UV spectroscopic studies of the interaction of the complexes with calf-thymus DNA (CT DNA) have suggested that they can bind to CT DNA with moderate affinity in an intercalative mode. The interactions between the Zn(II) complexes and bovine serum albumin (BSA) were investigated by steady-state and time-resolved fluorescence spectroscopy at pH 7.4. The experimental data showed static quenching of BSA fluorescence, indicating that both complexes bind to BSA. A modified Stern-Volmer plot for the quenching by complex 2 demonstrated preferential binding near one of the two tryptophan residues of BSA. The binding constants obtained (K b ) showed that BSA had a two orders of magnitude higher affinity for complex 2 than for 1. The results also showed that the affinity of both complexes for BSA was much higher than for DNA. This preferential interaction with protein sites could be important to their biological mechanisms of action. The analysis in vitro of the Zn(II) complexes and corresponding ligand were assayed against Trypanosoma cruzi, the causative agent of Chagas disease and the data showed that complex 2 was the most active against bloodstream trypomastigotes.

Investigation on the Interaction between Cyclophosphamide and Lysozyme in the Presence of Three Different Kind of Cyclodextrins: Determination of the Binding Mechanism by Spectroscopic and Molecular Modeling Techniques

The interactions between cyclophosphamide (CYC) and lysozyme (LYZ) in the presence of different cyclodextrins (CDs) were investigated by UV absorption, fluorescence spectroscopy, circular dichroism (CD), and molecular modeling techniques under imitated physiological conditions. The UV absorption results showed the formation of complexes between CYC and LYZ in the presence of different CDs. Fluorescence data show that CYC has a stronger quenching effect on LYZ, and the red shifts suggested that the microenvironment of Trp residues was changed and became more hydrophilic. The interaction of CYC with LYZ and quenching properties of the complexes caused strong static fluorescence quenching in binary and ternary systems. The binding affinities as well as the number of binding sites were obtained from interaction between CYC and LYZ in the presence of different CDs as binary and ternary systems by modified Stern-Volmer plots. The Resonance Light Scattering (RLS) technique was utilized to investigate the effect of drug and CDs on conformational changes of LYZ as separate and simultaneous. The results suggested that the enhancement of RLS intensity was attributed to the formation of a complex between drug and protein in absence and presence of CDs. The effect of CYC and cyclodextrins on the conformation of LYZ was analyzed using synchronous fluorescence spectroscopy. Our results revealed that the fluorescence quenching of LYZ originated from the Trp and Tyr residues, and demonstrated conformational changes of LYZ with the addition of CYC and CDs. The molecular distances between the donor (LYZ) and acceptor (CYC and CDs) in binary and ternary systems were estimated according to Forster’s theory and showed static quenching for protein with CYC in the presence of CDs. The CD spectra indicated that the binding of the CYC induced secondary structural changes in LYZ in binary and ternary systems. Molecular modeling suggested the binding sites of CYC in the ternary systems differ from those in the binary systems. estimated the distance between CYC and Trp residues in binary and ternary systems in the presence of CDs and confirmed the experimental results.

Investigation of the Molecular Origins of Protein-arginine Methyltransferase I (PRMT1) Product Specificity Reveals a Role for Two Conserved Methionine Residues

Protein-arginine methyltransferases aid in the regulation of many biological processes by methylating specific arginyl groups within targeted proteins. The varied nature of the response to methylation is due in part to the diverse product specificity displayed by the protein-arginine methyltransferases. In addition to site location within a protein, biological response is also determined by the degree (mono-/dimethylation) and type of arginine dimethylation (asymmetric/symmetric). Here, we have identified two strictly conserved methionine residues in the PRMT1 active site that are not only important for activity but also control substrate specificity. Mutation of Met-155 or Met-48 results in a loss in activity and a change in distribution of mono- and dimethylated products. The altered substrate specificity of M155A and M48L mutants is also evidenced by automethylation. Investigation into the mechanistic basis of altered substrate recognition led us to consider each methyl transfer step separately. Single turnover experiments reveal that the rate of transfer of the second methyl group is much slower than transfer of the first methyl group in M48L, especially for arginine residues located in the center of the peptide substrate where turnover of the monomethylated species is negligible. Thus, altered product specificity in M48L originates from the differential effect of the mutation on the two rates. Characterization of the two active-site methionines provides the first insight into how the PRMT1 active site is engineered to control product specificity.

A spectroscopic investigation into the interactions of 3′‐O‐carboxy esters of thymidine with bovine serum albumin

Binding studies of 3'-O-carboxy esters of thymidine, reported inhibitors of ribonucleases, with bovine serum albumin (BSA) have been explored in this report. Fluorescence spectroscopy in combination with Fourier transform infrared (FTIR) and circular dichroism (CD) spectroscopy have been used to determine the nature and mode of binding. The binding and quenching parameters were determined from tryptophan fluorescence quenching by Scatchard plots and modified Stern-Volmer plots. The association constants are of the order of 10(4) M(-1) for both the ligands. Thermodynamic parameters suggest that apart from an initial hydrophobic association, hydrogen bonding and van der Waals interactions play a decisive role during protein-ligand complex formation. Minor changes were observed in the secondary structures of human serum albumin (HSA) as revealed by FTIR and CD. Docking studies suggest that the ligands are close to Trp 213, which causes fluorescence quenching.

The interaction between bovine serum albumin and the self-aggregated nanoparticles of cholesterol-modified O-carboxymethyl chitosan

The interaction between bovine serum albumin (BSA) and self-aggregated nanoparticles of cholesterol-modified O-carboxymethyl chitosan (CCMC) with different degrees of substitution (DS) of cholesterol moiety was studied by transmission electron microscopy (TEM), fluorescence quenching method and circular dichroism (CD) measurement. This interaction was started at the disaggregation of CCMC self-aggregated nanoparticles and reached equilibrium after 3–4 h. The apparent quenching constant ( K q) between BSA and CCMC self-aggregated nanoparticles calculated by the modified Stern–Volmer plot increased from 4.14 × 10 4 to 1.95 × 10 5 M −1 with DS of cholesterol moiety increasing from 3.2% to 9.8%, whereas the fraction of tryptophan residues in BSA molecule involved in the interaction decreased at the same time. Compared with free BSA, the relative α-helix content of BSA decreased and the unfolding of BSA by a denaturant such as urea was largely suppressed upon interaction with CCMC self-aggregated nanoparticles. DS of cholesterol moiety significantly affected the interaction between BSA and CCMC self-aggregated nanoparticles.

Facile fabrication of poly( p-phenylene ethynylene)/colloidal silica composite for nucleic acid detection

Fabrication, characterization, and application of poly(phenylene ethynylene) (PPE)/silica composite particles are described. PPE is a class of conjugated polymers, which has been used for various sensory materials. However, its hydrophobic nature makes its application difficult in the aqueous phase, especially for biological substance detection. In this report, we utilized non-aqueous soluble PPE, 15 nm of colloidal silica particles, and aminosilane to fabricate a biosensory platform. The resulting composite showed high aqueous compatibility, large surface area, high quantum efficiency, and versatile chemical modification including oligonucleotide coupling. By monitoring the fluorescence quenching of PPE, we could detect a quencher-labeled target oligonucleotide specifically. Stern–Volmer (SV) analysis showed different accessibility of fluorophores (PPE) to a quencher labeled target oligonucleotide. The accessibility of fluorophores and SV constant are determined to be 0.54 and 4.2 × 10 7 M −1 , respectively, from a modified SV plot. This method will broaden the capability of conjugated polymers for the sensitive detection of biological substances.

Binding Properties of 2-Acetylnaphthalene with Hydroxypropyl Cyclodextrins from Fluorescence Quenching Experiments

The quenching of 2-acetylnaphthalene (2-AN) fluorescence by hydroxypropyl cyclodextrins (HP-CD) has been analyzed using modified Stern-Volmer plots to obtain binding constants as a function of temperature for 2-AN:HP-CD complexes. The HP-CDs were commercially available and contained 4-7 HP groups per CD molecule for alpha-CD, beta-CD, and gamma-CD. HP substitution causes a 12 to over 40% increase in binding constant (K(ave)) for 2-AN compared to that for unsubstituted CDs, although the K(ave) value is not strongly dependent on the extent of HP substitution for beta-CD. No evidence of formation of a 2:2 complex, such as that observed with 2-AN and gamma-CD, is observed with 2-AN and HP-gamma-CD. Thermodynamic parameters (DeltaH degrees and DeltaS degrees ) suggest that the increase in K(ave) with HP substitution is due to an enlarged binding site for the HP-CDs that allows greater motional freedom for 2-AN. Comparison is made to the binding of 2-methylnaphthoate (2-MN) to CDs and HP-CDs, and the larger K(ave) values for 2-MN over 2-AN are attributed to greater dispersion forces for 2-MN complex formation.