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An important issue in ultrasonic nondestructive testing is the detection of flaw echoes in the presence of background noise created by instrumentation and by clutter noise. Signal averaging, autoregressive analysis, spectrum analysis, matched filtering, and the wavelet transform have all been used to filter noise in ultrasonic signals. Widely-used wavelet threshold estimation algorithms are not designed for electromagnetic acoustic transducer (EMAT) pulse-echo signals, and therefore do not exploit their unique impulse nature. The approach to ultrasonic signal filtering proposed in this paper is based on stationary wavelet packet denoising with a threshold influenced by several information sources: a statistical echo detection, the amplitude distribution of the wavelet transform coefficients, and a priori known system frequency characteristics. The proposed method was evaluated on signals measured with EMAT probes and under various SNR conditions; it outperforms the wavelet transform with the Stein unbiased risk estimate (SURE) threshold estimation method and split-spectrum processing (SSP). The results indicate SNR enhancement of 19 dB with real EMAT data. [ABSTRACT FROM AUTHOR]

LaF 3 :1-6 mol%Yb 3+ ,0.1 mol%Tm 3+ nanoparticles with upconversion properties were synthesised by the co-precipitation method. Particles were characterized by transmission electron microscopy coupled with energy-dispersive spectrometry, inductively coupled plasma optical emission spectrometry, X-ray diffraction, and simultaneous thermogravimetry and differential thermal analysis. Upconversion properties were investigated by fluorescence spectroscopy, using 980 nm laser light excitation. The results show that the particles had a hexagonal LaF 3 crystal structure. Crystallite and particle sizes decreased with increasing Yb 3+ content and the average crystallite size changed between 18 and 36 nm, while the average particle diameter was 25-52 nm. The highest upconversion emission intensity at the 480 nm emission peak could be reached with an optimal Yb 3+ content of 3 mol% and an Yb/Tm ratio of ∼75. These upconverting nanoparticles, prepared using a cheap and environmentally friendly co-precipitation method and containing relatively low dopant ion concentrations, will be helpful in a variety of promising fields, such as sensing, solar cells and security applications.

Quantitation of protein-nanoparticle interactions is essential for the investigation of the protein corona around NPs in vivo and when using synthetic polymer nanoparticles as affinity reagents for selective protein recognition in vitro . Here, a method based on steady-state fluorescence anisotropy measurement is presented as a novel, separation-free tool for the assessment of protein-nanoparticle interactions. For this purpose, a long-lifetime luminescent Ru-complex is used for protein labelling, which exhibits low anisotropy when conjugated to the protein but displays high anisotropy when the proteins are bound to the much larger polymer nanoparticles. As a proof of concept, the interaction of lysozyme with poly( N -isopropylacrylamide- co-N-tert -butylacrylamide- co -acrylic acid) nanoparticles is studied, and fluorescence anisotropy measurements are used to establish the binding kinetics, binding isotherm and a competitive binding assay.

The supramolecular complexes of three strongly solvatochromic dyes, Brooker's merocyanine (M1) and its two derivatives (M2, M3) with carboxylato pillar[6]arene (WP6) were studied in aqueous solutions. The dye-WP6 mixtures were described in terms of four equilibrium reactions: the acidic dissociations of the pyridinium phenols into the zwitterionic phenolates, the acidic dissociations of the complexed phenols, the bindings of the phenol form dyes to WP6 and the bindings of the phenolates to WP6. The equilibrium constants were determined by an analysis of the absorption spectra. It was found that the acidity of the phenol form merocyanines were largely reduced on complexation, pK a shifts of 1.1-1.6 units were observed. In neutral solutions, the complexes of the phenol forms of M1 and M2 were dominant, in contrast to the more acidic M3 (a dibromo derivative), of which the phenolate complex was more stable. Comparing the spectral properties, the binding constants and the pK a -s of the dye-WP6 complexes, the complex M3⋅WP6 was chosen to be tested as a displacement assay. It was demonstrated that this complex functioned as a colorimetric indicator displacement assay which discriminated trimethyl lysine from other lysine derivatives., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 The Authors. Published by Elsevier B.V. All rights reserved.)

In order to explore how cucurbituril hosts accommodate an N -phenyl-pyridinium derivative guest, the complexation of the solvatochromic dye, 4-(4-(dimethylamino)styryl)-1-phenylpyridinium iodide (PhSt) with , ' , δ M , δ ' -tetramethyl-cucurbit[6]uril (Me 4 M K a = 6.0 × 10 6 M - 1 ) than the complex with Me 4 CB6 ( K a = 1.1 × 10 6 M - 1 ). As revealed by NMR experiments and confirmed by theoretical calculations, CB7 encapsulates the whole phenylpyridinium entity of the PhSt cation guest, whereas the cavity of Me 4 CB6 includes only the phenyl ring, the pyridinium ring is bound to the carbonyl rim of the host. The binding of PhSt to cucurbiturils is accompanied by a strong enhancement of the fluorescence quantum yield due to the blocking of the deactivation through a twisted intramolecular charge transfer (TICT) state. The TICT mechanism in PhSt was characterized by fluorescence experiments in polyethylene glycol (PEG) solvents of different viscosities. The PhSt-CB7 system was tested as a fluorescence indicator displacement (FID) assay, and it recognized trimethyl-lysine selectively over other lysine derivatives., Competing Interests: The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

The complexation of three cationic fluorescent dye guests with the anionic host carboxylato-pillar[6]arene (WP6) was investigated by optical and NMR spectroscopy. Among the selected indicators - a stilbazolium dye (i1) and two naphthalimide derivatives with positively charged 'anchor' groups (i2 and i3) - i1 gave a large turn-on, i2 and i3 a large turn-off fluorescence response to the complexation. The size selectivity of the complex formation of pillararenes was demonstrated by comparing the binding constants of the complexes of the three indicators with WP6 and its smaller homologue, WP5. The systems WP6·i1 and WP6·i2 were tested as indicator displacement assays for the sensing of monoamine neurotransmitters. The WP6·i1 system functioned as a turn-off, the WP6·i2 system as a turn-on sensor for neurotransmitters, and both assays showed a good selectivity to histamine over the other neurotransmitter analytes., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The fluorescence properties of 4'-diethylamino-3-hydroxyflavone (FET), a dye probe sensitive to the polarity as well as the hydrogen bonding ability of its environment, have been studied in acetone-water mixtures by measuring spectra and decay curves over the whole composition range and analyzing the results on the basis of theoretical calculations. In acetone, like in most of organic solvents, the dye showed dual fluorescence, due to an excited state intramolecular proton transfer (ESIPT), in which a quasi-equilibrium between the two excited species, N* and T*, was reached. In acetone-water mixtures with lower molar fractions of water, where the water molecules are largely dispersed, only one type of hydrate could be detected, a complex with 1:1 composition, showing only N* emission, but with a high (0.45) fluorescence quantum yield. At higher water concentrations, the interaction of FET with the hydrogen-bonded water clusters resulted in fluorescence quenching. In neat water the fluorescence quantum yield fell to ~0.001. Theoretical calculations on a FET-acetone complex, a FET-water complex and a FET-water-acetone triple complex (the latter as model for the samples with low water concentrations) concluded that ESIPT was energetically favored in all the models, but the E(N*)-E(T*) energy difference for the water complexes was much lower. The kinetic barrier of ESIPT was found greatly higher in the FET-water complex than in the isolated solute. The intermolecular hydrogen bonds in the water complexes became significantly stronger following the excitation, stabilizing the N* form of the hydrated dye., (Copyright © 2018 Elsevier B.V. All rights reserved.)

The excited state processes in N-propyl-4-piperidinyl-1,8-naphthalimide have been studied by measuring its fluorescence spectra and decay curves in solvents of different polarity and viscosity and also in a frozen solvent glass. The results unanimously proved the formation of a dark twisted intramolecular charge transfer (TICT) state from the emissive charge transfer (CT) species, the direct product of excitation. The rate coefficients of the TICT process and the deactivations of the CT and TICT species were determined, using a reversible two-state kinetic model. The temperature dependence of the kinetic data was consistent with a kinetic barrier consisting of three terms, the inherent barrier of the reaction, and the contributions of the solute-solvent interactions related to the solvent viscosity and polarity. The potential energy surfaces were calculated in the S0 and the S1 states along the coordinate of turning motion which was conclusive concerning the direction of the twisting and indicated a possible conformational change of the piperidinyl unit. The theoretical calculations confirmed that the TICT species is dark and has a stronger charge transfer character compared to the CT state.

Background: Nucleotides are essential molecules in living systems due to their paramount importance in various physiological processes. In the past years, numerous attempts were made to selectively recognize and detect these analytes, especially ATP using small-molecule fluorescent chemosensors. Despite the various solutions, the selective detection of ATP is still challenging due to the structural similarity of various nucleotides. In this paper, we report the conjugation of a uracil nucleobase to the known 4'-dimethylamino-hydroxyflavone fluorophore. Results: The complexation of this scaffold with ATP is already known. The complex is held together by stacking and electrostatic interactions. To achieve multi-point recognition, we designed the uracil-appended version of this probe to include complementary base-pairing interactions. The theoretical calculations revealed the availability of multiple complex structures. The synthesis was performed using click chemistry and the nucleotide recognition properties of the probe were evaluated using fluorescence spectroscopy. Conclusions: The first, uracil-containing fluorescent ATP probe based on a hydroxyflavone fluorophore was synthesized and evaluated. A selective complexation with ATP was observed and a ratiometric response in the excitation spectrum.

The photolysis reactions of 4'-diethylamino-3-hydroxyflavone (D), a versatile fluorescent probe showing excited-state intramolecular proton transfer (ESIPT), and the magnesium chelate of D (MgD(2+)) have been studied in acetonitrile solution. Upon UV irradiation both species were oxidized into O-4-diethylaminobenzoyl salicylic acid, differently from the photoreaction of the parent compound 3-hydroxyflavone (3HF) which was described to undergo rearrangement to 3-hydroxy-3-phenyl-indan-1,2-dione. The photooxygenation of the Mg(2+) complex was found to be significantly faster than the reaction of the pure dye. As the kinetic analysis of the absorption spectra of samples under irradiation showed, the rate coefficients for the oxygenations of the excited state dye and complex have close values, kox(D*) = 2.4 × 10(7) min(-1), kox(MgD(2+)*) = 3.9 × 10(7) min(-1); the difference arises from the higher photooxygenation quantum yield of the complex, Φ(MgD(2+)) = 2.3 × 10(-3), than the respective value for the pure dye, Φ(D) = 1.5 × 10(-4). The potential energy surface of the photooxygenation of D was calculated assuming a reaction path in which the phototautomer formed from Dvia ESIPT, reacts in its triplet state with triplet molecular oxygen O2, a mechanism similar to that suggested for the photoreaction of the parent 3HF. The moderate values for the transition state energies confirmed the plausibility of the hypothetical mechanism.

The ground- and excited-state protonation of Coumarin 102 (C102), a fluorescent probe applied frequently in heterogeneous systems with an aqueous phase, has been studied in aqueous solutions by spectroscopic experiments and theoretical calculations. For the dissociation constant of the protonated form in the ground state, pKa = 1.61 was obtained from the absorption spectra; for the excited-state dissociation constant, pKa* = 2.19 was obtained from the fluorescence spectra. These values were closely reproduced by theoretical calculations via a thermodynamic cycle (the value of pKa* also by calculations via the Förster cycle) using an implicit–explicit solvation model (polarized continuum model + addition of a solvent molecule). The theoretical calculations indicated that (i) in the ground state, C102 occurs primarily as a hydrogen-bonded water complex, with the oxo group as the binding site, (ii) this hydrogen bond becomes stronger upon excitation, and (iii) in the ground state, the amino nitrogen atom is the protonation site, and in the excited state, the carboxy oxygen atom is the protonation site. A comprehensive analysis of fluorescence decay data yielded the values kpr = 3.27 × 10(10) M(–1) s(–1) for the rate constant of the excited-state protonation and kdpr = 2.78 × 10(8) s(–1) for the rate constant of the reverse process (kpr and kdpr were treated as independent parameters). This, considering the relatively long fluorescence lifetimes of neutral C102 (6.02 ns) and its protonated form (3.06 ns) in aqueous media, means that a quasi-equilibrium state of excited-state proton transfer is reached in strongly acidic solutions.

The resolution methods applying (-)-(4R,5R)-4,5-bis(diphenylhydroxymethyl)-2,2-dimethyldioxolane ("TADDOL"), (-)-(2R,3R)-α,α,α',α'-tetraphenyl-1,4-dioxaspiro[4.5]decan-2,3-dimethanol ("spiro-TADDOL"), as well as the acidic and neutral Ca(2+) salts of (-)-O,O'-dibenzoyl- and (-)-O,O'-di-p-toluoyl-(2R,3R)-tartaric acid were extended for the preparation of 1-n-butyl-3-methyl-3-phospholene 1-oxide in optically active form. In one case, the intermediate diastereomeric complex could be identified by single-crystal X-ray analysis. The absolute P-configuration of the enantiomers of the phospholene oxide was also determined by comparing the experimentally obtained and calculated CD spectra., (© 2014 Wiley Periodicals, Inc.)

An efficient synthetic method has been developed for the preparation of a new family of atropisomeric amino alcohols with 1-phenylpyrrole backbone. The synthesis is based on the different reactivities of the two carboxylic groups in optically active 1-[2-carboxy-6-(trifluoromethyl)phenyl]-1H-pyrrole-2-carboxylic acid (1). The chemical structures of the key intermediates were confirmed by spectroscopic methods and single crystal X-ray diffraction measurements. The very first application of a new optically active amino alcohol as catalyst for the enantioselective addition of diethylzinc to benzaldehyde demonstrated the practical usefulness of atropisomeric compounds in which there are six-atom chains between the two functional groups., (© 2012 Wiley Periodicals, Inc.)

The photophysical properties of indoline (I) and three of its derivatives, namely, N-methylindoline (MI), 5-cyanoindoline (CI), and 5-cyano-N-methylindoline (CMI), are studied in H-donating solvents of varying polarity. Based on measurements of fluorescence yield and lifetime, and of triplet yield and hydrated-electron formation, two distinct mechanisms of solvent-induced fluorescence quenching are evidenced. The first mechanism involves the cyano substituent and leads to an increase in the rate constant of internal conversion of one order of magnitude in ethanolic solution and of more than two orders of magnitude in water, as compared to solutions in n-hexane or acetonitrile. A similar trend had previously been observed in the case of 4-N,N-dimethylaminobenzonitrile (DMABN). The second mechanism reduces the fluorescence lifetimes of the non-cyanated derivatives in aqueous solution by one order of magnitude and is related to the formation of hydrated electrons. Neither of these mechanisms is influenced by methylation at the ring nitrogen. Quantum chemical calculations are performed on the ground and excited states of the hydrogen-bonded complexes between protic solvents and MI as well as CMI. Stable hydrogen-bonded configurations involving the CN substituent and a solvent OH group are found; these configurations are stable both in the ground and the first excited singlet states, whereas the corresponding complex at the ring amino nitrogen is stable in the ground state only. The CN--HO configuration is therefore a prime candidate for a mechanistic explanation of the observed quenching by the first mechanism. These findings may have useful applications for the design of fluorescence probes for water in biological systems.

We have unraveled the effects of an amino substituent in the ortho position on the excited-state dynamics of 4-nitropyridine N-oxide by studying the picosecond fluorescence kinetics and femtosecond transient absorption of a newly synthesized compound, 2-butylamino-6-methyl-4-nitropyridine N-oxide, and by quantum chemical calculations. Similar to the parent compound, the S(1) state of the target molecule has significant charge-transfer character and shows a large (approximately 8000 cm(-1)) static Stokes shift in acetonitrile. Analysis of the experimental and the theoretical results leads, however, to a new scenario in which this intramolecular charge transfer triggers in polar, aprotic solvents an ultrafast (around 100 fs) intramolecular proton transfer between the amino and the N-O group. The electronically excited N-OH tautomer is subsequently subject to solvent relaxation and decays with a lifetime of approximately 150 ps to the ground state.

It has been established by combined absorption and fluorescence measurements that the cationic dye Oxazine 1 (OX) and the polyvalent anionic host calix[8]arenesulfonate (SCA8) form two complexes in simultaneous reactions: OX + SCA8 <--> OX.SCA8 (1), and OX.SCA8 + OX <--> OX(2).SCA8 (2). The equilibrium constants for the two reactions, as functions of the ionic strength (I), and the absorption and fluorescence spectra of the two complex species have been determined by a least-squares fitting method from the experimental data. The variations of the binding constants with the ionic strength could be described on the basis of Debye-Huckel theory. The equilibrium constants are large; their values extrapolated to I = 0 are K(1) = 5.5 x 10(6) M(-1) and K(2) = 4.4 x 10(5) M(-1). The fluorescence of OX undergoes a strong static quenching upon complexation. These results indicate that the complexes are held together by strong electrostatic forces. The addition of non-fluorescent tetramethylammonium chloride to OX-SCA8 mixtures results in a dramatic fluorescent enhancement, which demonstrates the potential applicability of this supramolecular system in fluorescence assays.

The (R)- and (S)-enantiomers of a binaphthyl-appended calix[4]crown-6 ether with two 2,4-dinitrophenylazo chromophore units ((R)-1 and (S)-1) as chiral hosts were tested in their reactions with the enantiomers of alpha-methylbenzylamine ((R)-MBA, (S)-MBA)) and phenylglycinol ((R)-PGL, (S)-PGL) as chiral guests. The visible absorption spectra indicate a two-step process: the first is a nonenantioselective proton transfer from the host to the guest, which is followed by the enantioselective real complexation. In the visible range of the CD spectra a positive/negative band belongs to the absorption of pure (R)-1/(S)-1, and a negative/positive exciton couplet to the absorption of (R)-1-(S)-MBA/(S)-1-(R)-MBA complexes. The latter phenomenon suggests that the complexation of amines is accompanied by a chiral arrangement of the two chromophore units in the hosts. The UV fluorescence of (R)-1/(S)-1 arising from the binaphthyl moiety is quenched by K+ ions, but not by the amine guests, showing that the interaction between the binaphthyl group and the complexed amines is weak., (Copyright 2004 Wiley-Liss, Inc.)

The effects of interference on the photoinduced-absorption signals of thin absorbing films have been studied by recording the picosecond photoinduced-absorption decay curves of an amorphous and a polycrystalline silicon film and applying various probe-beam wavelengths and angles of incidence. The normalized decay curves measured at close to normal incidence have been found to depend strongly on the probe-beam wavelength. By contrast the decay curves obtained at the Brewster angle of incidence have shown a satisfactory coincidence. Theoretical calculations for the photoinduced changes of the transmittance of the film have been performed. These calculations prove that at normal incidence the contributions of the photoinduced changes of the absorption coefficient Δα and of the refractive index Δn to the change in the transmittance Δ T are comparable, whereas when the Brewster angle arrangement is employed, Δ T is proportional to Δα and the effect of the change in the refractive index is negligible.

Infective animal sources and persons in contact with animals were investigated for Yersinia enteroclotica. The 68 isolates from 3115 animals belonged to four serogroups. The most frequent was serogroup O3 (62 strains) found mainly in pigs (41 strains). The same serogroup was isolated from dogs (9 strains), cats (6 strains) and from other animals (6 strains). A total of 556 animals living in the Budapest Zoo were examined. Y. enterocolitica was isolated from the faecal specimens of one chimpanzee and one gibbon. Using the Widal-type agglutination, out of sera of 877 persons in contact with animals, 4.56% were positive with antigens O3 and O9, compared to 0.33% in healthy controls. The study indicates that beside the occasional role of other animal species, pigs should be regarded as the main source of human enteric yersinosis.