In this paper, a sensitive and simple method for the determination of methionine (Met) was developed based on the fluorescence quenching and recovery of l-tryptophan (l-Trp). In pH 9.7 Na2CO3-NaHCO3 ...buffer medium, Cu2+ could react with l-Trp to form 1:1 complex because of the strong electrostatic interaction, which resulted in the fluorescence quenching of l-Trp. However, the quenched fluorescence of l-Trp could be recovered upon the addition of Met due to the strong affinity between Cu2+ and thiols. Under the optimized experimental conditions, the recovered fluorescence intensities were linearly proportional to the concentration of Met within the range of 4.8×10−6–3.0×10−5molL−1. The detection limit was 1.4×10−6molL−1.
•Cu2+ reacted with l-Trp to form 1:1 complex, which resulted in the fluorescence quenching.•The quenched fluorescence of l-Trp was recovered upon the addition of some amounts of Met.•The recovery fluorescence intensity was linearly proportional to the concentration of Met.
A dual-wavelength overlapping resonance Rayleigh scattering (DWO-RRS) methodology based on the specific multi-site coordination between lanthanum(III) and doxycycline (DOTC) has been successfully ...designed (rather than accidently encountered) for highly sensitive and selective assay of doxycycline in several meat samples.
•A rapid assay of doxycycline was performed.•Dual-wavelength overlapping resonance Rayleigh scattering was employed.•The detection limit (1.1nmolL−1) was lower than or comparable to most of the reported methods.•The generating mechanisms of multi-response RRS signals were proposed.•A semi-empirical principle was established for better design of multi-response RRS probes.
A dual-wavelength overlapping resonance Rayleigh scattering (DWO–RRS) method was developed and validated for highly sensitive and selective assay of doxycycline residues in several meat samples. The response signals were dependent on the specific multi-site coordination between lanthanum(III) and doxycycline (DOTC). And La(III)–DOTC complex would further aggregate to form La(III)–DOTCn nanoparticles, resulting in the occurrence of two new scattering peaks. Notably, with the addition of DOTC, the increments of both of these two wavelengths were proportional to the concentration of DOTC over the ranges of 3.9–4.0×103nmolL−1 (1.7–1.8×103μg/kg). The detection limit of DWO–RRS was 1.1nmolL−1 (0.5μg/kg), which was lower than or comparable to most of the published methods. Additionally, the generating mechanisms of multi-response RRS signals were discussed and a semi-empirical principle was established for better design of multi-response RRS probes.
Palladium chloride could react with adenine to form a 1:1 chelate, which led to the remarkable enhancement of resonance Rayleigh scattering (RRS) with the peak at 311
nm. The enhanced intensities ...present a good linear relationship with the concentration of adenine, which suggests that the system can be used for the quantitative determination of adenine.
Display omitted
► This method is sensitive, the detection limit for adenine is 5.4
×
10
−9
mol
L
−1. ► Other nucleobases have no similar reaction, the method has high selectivity. ► The interaction are characterized by many methods.
In pH 1.7–3.5 acid medium, palladium chloride could react with adenine (A) to form a ternary complex of PdCl
2·A, which would self-aggregate to form uniformly dispersed nanoparticles-PdCl
2·A
n with an average size of 42
nm through the squeezing effect of aqueous phase and van der Waals force. This resulted in an enhancement of resonance Rayleigh scattering (RRS), second-order scattering (SOS) and frequency doubling scattering (FDS). The maximum wavelengths were located at 311
nm, 611
nm and 395
nm, respectively. The scattering intensities of the three methods were proportional to the concentration of adenine in certain ranges, and the detection limit of the most sensitive RRS method was 5.4
×
10
−9
mol
L
−1 (0.73
ng
mL
−1). The experimental conditions were optimized and effects of coexisting substances were evaluated. The method showed excellent selectivity because a certain amount of other nucleobase, nucleoside or nucleotide would not influence the measurement. Accordingly, a novel rapid, convenient, sensitive and selective RRS method for determination of adenine was proposed and applied to detect adenine in tablet and hydrolyzates of ctDNA samples with satisfactory results. The shape of nanoparticles was characterized by atomic force microscopy. The reaction mechanism and the reasons for enhancement of scattering were discussed by infrared spectra, quantum chemical calculations and absorption spectroscopy.
This study investigates water vapor isotopic patterns and controls over China using high-quality water vapor δD data retrieved from the Scanning Imaging Absorption Spectrometer for Atmospheric ...Chartography （SCIAMACHY） observations. The results show that water vapor δD values on both annual and seasonal time-scales broadly exhibit a continental effect, with values largely decreasing northwestward from coastal lowlands to high-elevation mountainous regions. However, region-specific analysis reveals spatially distinct patterns of water vapor dD between seasons. In the monsoon domain （e.g., China south of 35~N）, depletion in D in the summer and fall seasons is closely tied to monsoon moisture sources （the Indian and Pacific oceans） and subsequent amount effect, but higher 8D values in winter and spring are a result of isotopically-enriched conti- nental-sourced moisture proceeded by less rainout. In contrast, farther inland in China （non-monsoon domain）, moisture is de- rived overwhelmingly from the dry continental air masses and local evaporation, and 8D values are largely controlled by the temperature effect, exhibiting a seasonality with isotopically enriched summer and depleted winter/spring. The observation that the spatial pattern of water vapor δD is the opposite to that of precipitation δD in the summer season also suggests that partial evaporation of falling raindrops is a key driver of water vapor isotope in the non-monsoon domain. This study highlights the importance of non-Rayleigh factors in governing water vapor isotope, and provides constraints on precipitation isotope inter- pretation and modern isotope hydrological processes over China.
In a near-neutral medium, a combination of heparin with some basic diphenyl naphthylmethane dyes such as victoria blue 4R (VB4R), victoria blue B (VBB), or night blue (NB) can result in a significant ...enhancement of resonance. Rayleigh scattering (RRS) and their maximum scattering wavelengths λmax appear at 523, 534, and 540 nm for VB4R, VBB, and NB, respectively. The characteristics of RRS spectra of the heparin−dye complexes, the influencing factors, and the optimum conditions of these reactions have been investigated. The RRS intensity is directly proportional to the concentration of heparin in the range of ∼0 to 0.4 μg/mL for all systems. The methods exhibit high sensitivities, and the detection limits for heparin are 3.35 ng/mL for the VB4R system, 6.62 ng/mL for the VBB system, and 6.29 ng/mL for the NB system. Because the VB4R system is the most sensitive, it was taken as an example to study the selectivity of the method. A new method for the determination of trace amounts of heparin based on RRS technique has been developed. Moreover, the enhancement reasons of RRS and the relationship between RRS spectral characteristics of the heparin−dye complex and its absorption spectra have been primarily discussed.
Large-scale climate teleconnections such as the Pacific/North American (PNA) pattern strongly influence atmospheric processes and continental climate. Here we show that precipitation δ
18O values in ...the contiguous United States are correlated with an index of the PNA pattern. The δ
18O/PNA relationship varies across the study region and exhibits two prominent modes, with positive correlation in the western USA and negative correlation in the east. This spatial pattern appears not to reflect variation in local climate variables, but rather primarily reflects differences in atmospheric circulation and moisture sources associated with PNA. Our results suggest that strong antiphase variation in paired paleo-water δ
18O proxy records from regions characterized by the two modes of δ
18O/PNA correlation, especially in the Midwest and southwestern USA, may provide a robust basis for reconstruction of past variation in the PNA pattern.
► Precipitation δ
18O values correlate with the PNA pattern across the contiguous USA. ► δ
18O/PNA correlation is of opposite sign in the eastern and western USA. ► A δ
18O difference index isolates PNA from variation in other climate modes. ► Paleo-isotope data could reveal past changes in atmospheric circulation modes.
When Eosin Y with carbazochrome to combine new complex, their fluorescence spectrum characteristics are almost the same, and fluorescent intensities are significant quenching. Fluorescence quenching ...values (ΔF) are proportional to the concentration of carbazochrome. Display omitted
► A new method of fluorescence quenching is used to determination carbazochrome. ► Eosin Y and Phloxine B can react with carbazochrome to form 1:2 complexes. ► The quenching of fluorescence of EY and PB by CBZC is a static quenching process.
A sensitive, simple and selective spectrofluorimetric method for the reaction of carbazochrome (CBZC) and Eosin Y (EY) or Phloxine B (PB) in acidic medium is developed for the determination of carbazochrome in biological fluids, which gives a highly fluorescent derivative measured at 545 and 565nm at excitation wavelengths of 301 and 305nm. The fluorescence quenching extent (ΔF) is proportional to the concentration of CBZC for CBZC–EY and CBZC–PB system at the range of 0.03–1.50μg/mL and 0.08–1.25μg/mL, respectively. The detection limit is 9.1ng/mL for EY system and 22.7ng/mL for PB system. The intra-day and inter-day reproducibility (RSD values) are less than 8.3% under three concentrations. Moreover, the affecting factors of fluorescence intensity of the product are carefully investigated and optimized, as well as the effect of coexisting substances. Judging from temperature, the Stern–Volmer plots and fluorescence emission decay curves, the quenching of fluorescence of EY and PB by CBZC is a static quenching process, caused by electrostatic attraction and aromatic stacking interaction.
The lacewing Chrysoperla sinica (Tjeder) (Neuroptera: Chrysopidae) is an important predator of several insect pests in China and has considerable potential as a biological control agent. An ...inoculative approach would be the releasing adults early in the season to ensure that populations are present before pest densities increase. However, an understanding of adult flight activity under different conditions is necessary to develop appropriate release strategies. Therefore, we used a 32-channel, computer-monitored flight mill system to determine the effect of age on the flight activity of unmated female and male adults. Both sexes had high total flight activity levels as well as the longest individual flight bouts 2 and 3 d after emergence. The effects of temperature (between 13 and 33°C at 75% RH) and relative humidity (between 30 and 90% RH at 23°C) on the flight activity of 3-d-old unmated adults also were determined. Flight activity declined at the lowest (13°C) and highest (33°C) temperatures tested, as well as at the lowest relative humidity (30% RH). These findings are discussed within the context of selecting the appropriate environmental conditions for releasing C. sinica.
A method is presented for the sensitive and selective determination of trace allura red (AR) with ethyl violet (EV) in drink samples, based on triple-wavelength overlapping resonance Rayleigh ...scattering (TWO-RRS). At pH 10.0 in a Britton–Robinson (BR) buffer medium, AR combined with EV to form an ion-association complex, which resulted in the RRS intensity getting enhanced significantly with new RRS peaks appearing at 341, 508 and 666 nm. The scattering intensities of the three peaks were proportional to the concentration of AR in the range of 0.057–5.0 μmol L
−1
(0.028–2.48 μg mL
−1
). The detection limits for the three single peaks were 0.048 μmol L
−1
(0.024 μg mL
−1
), 0.050 μmol L
−1
(0.025 μg mL
−1
), and 0.057 μmol L
−1
(0.028 μg mL
−1
), while that of the TWO-RRS method was 0.017 μmol L
−1
(0.008 μg mL
−1
), indicating that the TWO-RRS method could detect trace AR with high sensitivity. In addition, the optimum reaction conditions and the effects of foreign substances were studied. The composition of the ion-association complex, and the reasons for the enhancement of RRS were also investigated. The proposed method was successfully applied in a real sample analysis with satisfactory results.
In weak acidic medium, bovine hemoglobin would bind with salmon DNA (sDNA) to form a complex. This resulted in changes of absorption and circular dichroism spectra, fluorescence quenching of ...hemoglobin and remarkable enhancement of resonance Rayleigh scattering (RRS), as well as the appearance of a new RRS spectrum. The spectral characteristics of these spectra were investigated. The type of fluorescence quenching was discussed via the fluorescence lifetime of hemoglobin before and after the reaction as well as effects of temperature on fluorescence intensity. The conformational change of bovine hemoglobin was explored through circular dichroism spectra. The reasons of RRS enhancement were also discussed. In addition, it was found that the fluorescence quenching and RRS methods using bovine hemoglobin as a probe could be used to the determination of DNA. The detection limits (3σ) for sDNA were 5.5ngmL−1 (RRS method) and 202.3ngmL−1 (fluorescence quenching method). The optimum reaction conditions of the two methods were tested. The selectivity of RRS method was examined owing to its higher sensitivity. The RRS method was used for the determination of DNA in synthetic samples with satisfactory results.
► Interaction between bovine hemoglobin and sDNA was discussed. ► The conformational change of bovine hemoglobin was explored. ► A fluorescence quenching and a RRS method were established for determination of DNA.
