Two-Dimensional correlation method applied to Yb3+ vibronic sideband spectroscopy: Discrimination of fluorescence spectral features arising from different yb3+ binding sites

Continuing progress in the field of two-dimensional correlation spectroscopy (2D-COS), part I. Yesterday and today

This comprehensive survey review, as the first of three parts, compiles past developments and early concepts of two-dimensional correlation spectroscopy (2D-COS) and subsequent evolution, as well as its early applications in various fields for the last 35 years. It covers past review articles, books, proceedings, and numerous research papers published on 2D-COS. 2D-COS continues to evolve and grow with new significant developments and versatile applications in diverse scientific fields. The healthy, vigorous, and diverse progress of 2D-COS studies in many fields confirms that it is well accepted as a powerful analytical technique to provide the in-depth understanding of systems of interest.

Feasibility of the simultaneous determination of polycyclic aromatic hydrocarbons based on two-dimensional fluorescence correlation spectroscopy

A new approach for quantitative determination of polycyclic aromatic hydrocarbons (PAHs) in environment was proposed based on two-dimensional (2D) fluorescence correlation spectroscopy in conjunction with multivariate method. 40 mixture solutions of anthracene and pyrene were prepared in the laboratory. Excitation-emission matrix (EEM) fluorescence spectra of all samples were collected. And 2D fluorescence correlation spectra were calculated under the excitation perturbation. The N-way partial least squares (N-PLS) models were developed based on 2D fluorescence correlation spectra, showing a root mean square error of calibration (RMSEC) of 3.50μgL^-1 and root mean square error of prediction (RMSEP) of 4.42μgL^-1 for anthracene and of 3.61μgL^-1 and 4.29μgL^-1 for pyrene, respectively. Also, the N-PLS models were developed for quantitative analysis of anthracene and pyrene using EEM fluorescence spectra. The RMSEC and RMSEP were 3.97μgL^-1 and 4.63μgL^-1 for anthracene, 4.46μgL^-1 and 4.52μgL^-1 for pyrene, respectively. It was found that the N-PLS model using 2D fluorescence correlation spectra could provide better results comparing with EEM fluorescence spectra because of its low RMSEC and RMSEP. The methodology proposed has the potential to be an alternative method for detection of PAHs in environment.

Fast two-dimensional fluorescence correlation spectroscopy technique for tea quality detection

A fast two-dimensional fluorescence correlation spectroscopy technique based on light emitting diodes is developed, which uses light intensity and excitation wavelength as quickly changeable and easily controllable external perturbations. A compact and automatic system is set up to detect tea quality. A partial least square regression method is used to create predictive models for tea grades. Compared to the traditional fluorescence spectroscopy method, this convenient two-dimensional correlation spectroscopy technique is more accurate according to our experimental results and is promising for practical applications.

Synchronous two-dimensional MIR correlation spectroscopy (2D-COS) as a novel method for screening smoke tainted wine

In this study, two-dimensional correlation spectroscopy (2D-COS) combined with mid-infrared (MIR) spectroscopy was evaluated as a novel technique for the identification of spectral regions associated with smoke-affected wine, for the purpose of screening taint arising from grapevine exposure to smoke. Smoke-affected wines obtained from experimental and industry sources were analysed using MIR spectroscopy and chemometrics, and calibration models developed. 2D-COS analysis was used to generate synchronous data maps for red and white cask wines spiked with guaiacol, a marker of smoke taint. Correlations were observed at wavelengths that could be attributable to aromatic C-C stretching, i.e., between 1400 and 1500 cm(-1), indicative of volatile phenols. These results demonstrate the potential of 2D-COS as a rapid, high-throughput technique for the preliminary screening of smoke tainted wine.

Two-dimensional fluorescence correlation spectroscopy IV: resolution of fluorescence of tryptophan residues in alcohol dehydrogenase and lysozyme

Generalized two-dimensional (2D) fluorescence correlation spectroscopy has been used to resolve the fluorescence spectra of two tryptophan (Trp) residues in alcohol dehydrogenase and lysozyme. In each protein, one Trp residue is buried in a hydrophobic domain of the protein matrix and the other Trp residue is located at a hydrophilic domain close to the protein-water interface. Fluorescence quenching by iodide ion, a hydrophilic quencher, was employed as a perturbation to induce the intensity change in the spectra. The Trp residue which is located at the hydrophilic domain is effectively quenched by the quencher, while the Trp residue located at the hydrophobic domain is protected from the quenching. Therefore, the fluorescence of these two Trp residues have a different sensitivity to the quenching, showing a different response to the concentration of the quencher. Fluorescence spectra of the two Trp residues in alcohol dehydrogenase, which are heavily overlapped in conventional one-dimensional spectra, have been successfully resolved by the 2D correlation technique. From the asynchronous correlation map, it was revealed that the quenching of Trp located at the hydrophobic part was brought about after that of Trp located at the hydrophilic part. In contrast, the fluorescence spectra of the two Trp residues could not be resolved after the alcohol dehydrogenase was denatured with guanidine hydrochloride. These results are consistent with the well-known structure of alcohol dehydrogenase. Furthermore, it was elucidated that the present 2D analysis is not interfered by Raman bands of the solvent, which sometimes bring difficulty into the conventional fluorescence analysis. Fluorescence spectra of the Trp residues in lysozyme could not be resolved by the 2D correlation technique. The differences between the two proteins are attributed to the fact that the Trp residue in the hydrophobic site of lysozyme is not sufficiently protected from the quenching.

Sample-sample and wavenumber-wavenumber two-dimensional correlation analyses of attenuated total reflection infrared spectra of polycondensation reaction of bis(hydroxyethyl terephthalate)

Polycondensation reaction of bis(hydroxyethylterephthalate) was monitored in situ by attenuated total reflection (ATR)/infrared (IR) spectroscopy. The obtained spectra are analyzed by means of generalized two-dimensional (2D) sample-sample and wavenumber-wavenumber correlation spectroscopies. The sample-sample correlation analysis reveals the correlations among the concentration features of the components, and the wavenumber-wavenumber correlation analysis elucidates the relations among the spectral features. Before the experimental data are analyzed by the 2D correlation spectroscopies, a synthetic two-component spectral model composed of the first and the last experimental spectra, is examined. The results of an analysis of the real data are related to those obtained from the synthetic data. It is found that the sample-sample correlation analysis of the IR data of polycondensation explains the concentration variance in the system and classifies two groups of the samples. The wavenumber-wavenumber correlations are derived upon the results of the sample-sample correlations and explained in terms of the spectral variations of three components. The convolute patterns in both types of correlations are attributed to the weak presence of ethylene glycol.

Two-dimensional fluorescence correlation spectroscopy with modulated excitation

Overlap of multiple states or multiple species in a chemical system often creates a congested fluorescence spectrum that is difficult to interpret. The resolution of component spectra is essential for the understanding of the structure and dynamics of such multicomponent systems. In this paper, two-dimensional fluorescence correlation spectroscopy (2D FCS) is presented for the dissection of component spectra using the time correlation function. In 2D FCS, the time response of fluorescence intensity is collected at various wavelengths upon an external perturbation. The time correlation function is evaluated between wavelengths. A two-dimensional fluorescence correlation spectrum, or a plot of the correlation intensity as a function of two wavelength axes, resolves the overall spectrum into component spectra. The characteristics of the two-dimensional time correlation function are demonstrated in the frequency domain fluorescence spectroscopy in which the sinusoidally modulated excitation provides the external perturbation. Using 2D FCS, fine vibronic structures of the component fluorescence emission spectra were completely resolved from a strongly overlapped one-dimensional mixture spectrum. The existence of multiple microenvironments of a probe molecule in a biological system is evidenced by nonzero asynchronous correlation intensities. The corresponding spectra are retrieved from correlation analysis. Unlike traditional resolution methods in fluorescence spectroscopy based on statistical fitting of fluorescence decays, 2D FCS can resolve species whose fluorescence decays are linked by the rate constants in chemical reactions and species displaying multiexponential decay kinetics.

Calcium binding to the photosystem II subunit CP29

We have identified a Ca(2+)-binding site of the 29-kDa chlorophyll a/b-binding protein CP29, a light harvesting protein of photosystem II most likely involved in photoregulation. (45)Ca(2+) binding studies and dot blot analyses of CP29 demonstrate that CP29 is a Ca(2+)-binding protein. The primary sequence of CP29 does not exhibit an obvious Ca(2+)-binding site therefore we have used Yb(3+) replacement to analyze this site. Near-infrared Yb(3+) vibronic side band fluorescence spectroscopy (Roselli, C., Boussac, A., and Mattioli, T. A. (1994) Proc. Natl. Acad. Sci. U. S. A. 91, 12897-12901) of Yb(3+)-reconstituted CP29 indicated a single population of Yb(3+)-binding sites rich in carboxylic acids, characteristic of Ca(2+)-binding sites. A structural model of CP29 presents two purported extra-membranar loops which are relatively rich in carboxylic acids, one on the stromae side and one on the lumenal side. The loop on the lumenal side is adjacent to glutamic acid 166 in helix C of CP29, which is known to be the binding site for dicyclohexylcarbodiimide (Pesaresi, P., Sandonà, D., Giuffra, E. , and Bassi, R. (1997) FEBS Lett. 402, 151-156). Dicyclohexylcarbodiimide binding prevented Ca(2+) binding, therefore we propose that the Ca(2+) in CP29 is bound in the domain including the lumenal loop between helices B and C.

Detection of a Yb3+ binding site in regenerated bacteriorhodopsin that is coordinated with the protein and phospholipid head groups

Near infrared Yb3+ vibronic sideband spectroscopy was used to characterize specific lanthanide binding sites in bacteriorhodopsin (bR) and retinal free bacteriorhodopsin (bO). The VSB spectra for deionized bO regenerated with a ratio of 1:1 and 2:1 ion to bO are identical. Application of a two-dimensional anti-correlation technique suggests that only a single Yb3+ site is observed. The Yb3+ binding site in bO is observed to consist of PO2- groups and carboxylic acid groups, both of which are bound in a bidentate manner. An additional contribution most likely arising from a phenolic group is also observed. This implies that the ligands for the observed single binding site are the lipid head groups and amino acid residues. The vibronic sidebands of Yb3+ in deionized bR regenerated at a ratio of 2:1 ion to bR are essentially identical to those in bO. The other high-affinity binding site is thus either not evident or its fluorescence is quenched. A discussion is given on the difference in binding of Ca2+ (or Mg2+) and lanthanides in phospholipid membrane proteins.