Wavelength-dependent rotation of dye molecules in a polar solution

Investigation of rotation movement of 3-amino-N-methylphthalimide in glycerol was carried out, taking into consideration the fluctuation of solvate structure. It was shown theoretically and experimentally that structural relaxation of the solvate shell, which follows excitation of the dye molecule, causes not only shift of the fluorescence spectrum in time but also additional rotation of the dye molecule. This effect, which may be called wavelength-dependent rotation, depends on the light frequency of both excitation and fluorescence. In particular, at excitation near the maximum of the absorption band, when the relaxation process is followed with the red shift of the fluorescence maximum, the anisotropy of fluorescence decreases faster in the red part of the fluorescence band than in the blue part. On the contrary, in the case of far anti-Stokes excitation, when the temporal shift of fluorescence is going to the blue, the anisotropy in the red part of the spectrum drops more slowly than in the blue part. Finally, there is a special excitation frequency which causes neither change of the fluorescence maximum nor acceleration of the rotational movement of the dye molecule. It is also shown that the temporal evolution of the spectrum and anisotropy of fluorescence in a polar dye solution may be quantitatively described using the socalled inhomogeneous broadening function (IBF). This function gives the distribution of dye molecules in a solution over frequencies of pure electronic transition due to fluctuations of the surrounding shell structure. Measurements of IBF changes in time carried out for 3-amino-N-methylphthalimide showed that during first 3 ns after excitation, the half-width of the IBF grows, and at the same time its maximum quickly shifts to the red. At the later time period there are only small changes of IBF position but considerable exponential decrease in its half-width. The IBF during this period preserves the Gaussian shape.     

Time-resolved fluorescence studies of ribonuclease T1 in reversed micelles

Time-resolved fluorescence intensity and anisotropy decay data were obtained for ribonuclease T₁ entrapped in bis(2-ethylhexyl) sodium sulfosuccinate/heptane reverse micelles, as a function of the size of the inner water pool at neutral pH. Data have been presented previously to show that this protein retains its native structure and undergoes reversible thermal unfolding in these reverse micelles (Shastry and Eftink,Biochemistry 36, in press). The fluorescence decay of entrapped protein is similar to that for the protein in buffer. The rotational correlation time of entrapped ribonuclease T₁ is found to be longer than that in buffer; this rotational correlation time decreases with increasing size of the water pool but is still over twice the value for the protein in buffer for the largest size of water pool investigated, indicating an increased microviscosity within the reverse micelle. Thermal unfolding of the protein results in a significant decrease in the rotational correlation time of the entrapped proteins, consistent with the protein being unfolded but not interacting with the inner surfactant wall of the reverse micelle.Nomenclature _i Amplitude of component i associated with fluorescence decay _i - _i Fractional intensity associated with fluorescence decay time _i - Rotational correlation time g_i Amplitude of component i associated with anisotropy decay _i - _max Fluorescence emission maximum - r_o Fundamental anisotropy of an immobilized fluorophore - _i Fluorescence lifetime of component i - W_o Ratio of water molecules per detergent molecules in a reverse micelle     

1H spin–lattice relaxation in water solution of 209Bi counterparts of Gd3+contrast agents

ABSTRACT

¹H spin–lattice relaxation studies of water solutions of Bismuth-ethylenediamine-tetraacetic acid (Bi-EDTA), Bismuth-ethylenediamine-tetrakis(methylenephosphonic) acid (Bi-EDTP), Bismuth-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (Bi-DOTA), Bismuth-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis(methylenephosphonic acid) (Bi-DOTP) and Bismuth-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (Bi-DO3A) have been performed in order to compare Quadrupole Relaxation Enhancement (QRE) effects with Paramagnetic Relaxation Enhancement (PRE) from the perspective of exploiting the first one as a novel contrast mechanism for Magnetic Resonance Imaging (MRI). The selected compounds can be considered as ²⁰⁹Bi counterparts of Gd³⁺ complexes. The relaxation experiments have been performed in a broad frequency range of 5?kHz–30?MHz. The relaxation contribution associated with QRE has been extracted from the data and compared with PRE. Similarities and differences between the two effects have been discussed.     

Energy transfer between the flavin chromophores of electron-transferring flavoprotein fromMegasphaera elsdenii as inferred from time-resolved red-edge and blue-edge fluorescence spectroscopy

Both a mode-locked argon-ion laser and synchrotron radiation were used as excitation sources to obtain time-resolved polarized fluorescence of the two FAD cofactors in electron transferring flavoprotein fromMegasphaera elsdenii. Red-edge excited and blue-edge detected fluorescence anisotropy decay curves did not contain a fast relaxation process which was observed upon mainband excitation and detection. This relaxation was assigned to homo-energy transfer between the two FAD cofactors. Failure of energy transfer as observed with edge spectroscopy on this protein excludes restricted reorientational motion of the flavins as a possible mechanism of depolarization. From the global analysis of the fluorescence anisotropy decay surface obtained at multiple excitation and detection wavelengths, the distance between and the relative orientation of the flavins could be estimated. The methodology described has general applicability in other multichromophoric biopolymers and has the potential to acquire accurate geometrical parameters in these systems.     

Configurational relaxation of “Van Der Waals complexes” in solution

Novel measurements on the microscopic solvation dynamics of 3-amino-N-methylphthalimide (3ANMP) in nonpolar decalin (decahydronaphthalene) solutions with small concentrations of ethanol and other polar additives have been made, using the time-dependent fluorescence Stokes shift (TDFSS) technique. It is found that the experimentally measured TDFSS slightly differs from that predicted by the theory of the generalized Smoluchowski-Vlasov equation (SVE). The essentially slower character of the TDFSS in binary solutions than given by the SVE approach may be explained by the control of the solvation behavior by the large-wavevector processes involving nearest-neighbor molecules.Abbreviations 3ANMP 3-Amino-N-methylphthalimide - TDFSS time-dependent fluorescence Stokes shift - SVE Smoluchowski-Vlasov equation - VWC van der Waals complexes - DMF dimethylformamide - MSA mean spherical approximation.     

Time-resolved tryptophan fluorescence in flavodoxins

The time-resolved fluorescence characteristics of tryptophan in flavodoxins isolated from the bacteriaDesulfovibrio gigas, Desulfovibrio vulgaris, Clostridium beijerinckii, andMegasphaera elsdenii were examined. The fluorescence decays were recorded using pulsed synchrotron radiation as the excitation source and time-correlated single-photon counting in detection. The results were analyzed as lifetime distributions using the maximum entropy method. Comparison of the fluorescence decays of normal and flavin mononucleotide-depleted flavodoxins demonstrates that radiationless energy transfer from tryptophan to flavin occurs in all flavodoxins investigated. On comparing the lifetime distribution patterns of apo and holoflavodoxins, it was noticed that a certain amount of apoprotein is present in all holoflavodoxin samples. The three-dimensional structure of two flavodoxins allowed us to compare experimental with theoretical transfer rates and the results were in fair agreement.     

Determination of T1-spin-lattice relaxation time in a two-level system by continuous wave multiquantum electron paramagnetic resonance spectroscopy in a presence of tetrachromatic microwave irradiation

Applicability of continuous wave multiquantum EPR methods to study relaxation times at X-band is examined. Multiquantum transitions excited in a two-level system by tetrachromatic irradiation are used for these studies. The Bloch equation model is applied to simulate lineshapes of the three quantum transitions as a function of frequency difference between exciting fields. The dependence of multiquantum transition signals on relaxation times and microwave amplitude is shown. On this basis a method of deducing relaxation times from these signals is formulated. The case of a homogeneously and inhomogeneously broadened resonance line is considered. Two experimental methods are used to verify the proposed hypothesis: the X-band continuous wave multiquantum EPR with four frequencies microwave field and saturation recovery EPR. The values of T₁ obtained from CW MQ EPR and SR EPR are compared.     

Time-resolved fluorescence of crown ether styrul dyes

Photophsical processes are studied in a new class of dyes contining a chromophoric part and a crown ether part. Fluorescence decays were oebserved to be strongly dependent on temperature in the range from 294 to 4 K. Photoinduced isomerization and electron transfer are considered as possible mechanisms to explain the results.     

Time-resolved fluorescence polarization anisotropy and optical imaging of Cybesin in cancerous and normal prostate tissues

Time-resolved polarization-dependent fluorescence of Cybesin in solution and in cancerous and normal prostate tissues were measured. The polarization preservation property of Cybesin in tissue was observed. The fluorescence intensity emitted from a Cybesin-stained cancerous tissue area was found to be much stronger than that from a Cybesin-stained normal tissue area indicating that cancerous prostate tissue takes-up more Cybesin than normal tissue. The polarization anisotropy of Cybesin contained in cancerous prostate tissue was found to be larger than that of Cybesin in normal prostate tissue indicating that a larger degree of polarization was preserved in the Cybesin-stained cancerous tissue due to structures. A static anisotropy component from the emission of cell-bonded Cybesin molecules in tissue and a time-dependent anisotropy component from the emission of un-bonded Cybesin molecules were determined and discussed. The static anisotropy value of Cybesin in stained cancerous tissue was found to be much larger than that in stained normal tissue. The fluorescence polarization difference imaging technique based on the polarization preservation of Cybesin was used to enhance the image contrast between cancerous and normal prostate tissue areas.     

Franck-Condon transitions and thermodynamics of photoinduced processes of orientational relaxation in polar solutions

Polar luminescence probe+polar medium subsystems are considered. True minimization parameters of the free energy F are obtained. It is shown that Franck-Condon transitions between F-terms of different electronic states are generally not “vertical”. A complete thermodynamic classification of photoinduced processes of orientational relaxation in the excited S₁ and ground S₀ states is presented. Depending on the excitation conditions they can be either exo- or endothermic, spontaneous or induced (not spontaneous), and accompanied by an increase or decrease in entropy. Indifferent processes also take place. Regularities of shifts of fluorescence spectral bands and burned holes in time-resolved experiments are discussed. Institute of Molecular and Atomic Physics, Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 6, pp. 753–765, November–December, 1997.     

Influence of lipid composition and membrane curvature on fluorescence and solvent relaxation kinetics in unilamellar vesicles

Time-resolved fluorescence on unilamellar vesicles shows that increasing amounts of anionic, natural lipid lead to a larger increase in polarity close to the headgroups than in the hydrophobic core of the bilayer. The region close to the headgroups is less polar in vesicles containing phosphatic acid rather than phosphatidylserine. A greater membrane curvature increases the mobility of the hydrated headgroups.     

调控声子提高Tm3+掺杂体系的频率上转换荧光

应用激光光谱学技术,探讨了Tm³⁺离子掺杂透明氟氧化物玻璃陶瓷体系中声子调控对红色激光抽运荧光辐射性质的影响. 研究了基质结构和样品环境温度与电声子相互作用的联系以及声子变化对于荧光辐射产生的影响. 发现改变基质材料的SiO₂含量能影响蓝色上转换荧光效率. 另外,依据温度与声子能量之间的联系,通过改变样品环境温度可明显调节低声子基质材料中掺杂离子激发态能级的布居速率,改变上转换效率. 关键词： 荧光辐射 声子 无辐射弛豫 荧光寿命     

Long-lived states in solution NMR: theoretical examples in three- and four-spin systems

Long-lived spin states have been observed in a variety of systems. Although the dynamics underlying the long lifetimes of these states are well understood in the case of two-spin systems, the corresponding dynamics in systems containing more spins appear to be more complex. Recently it has been shown that a selection rule for transitions mediated by intramolecular dipolar relaxation may play a role in determining the lifetimes of long-lived states in systems containing arbitrary numbers of spins. Here we present a theory of long-lived states in systems containing three and four spins and demonstrate how it can be used to identify states that have little or no intramolecular dipolar relaxation.     

Selective nonspecific solvation under dielectric saturation and fluorescence spectra of dye solutions in binary solvents

The influence of selective nonspecific solvation on the fluorescence spectra of three substitutedN-methylphthalimides in a binary solvent system consisting of a nonpolar (n-heptane) and a polar (pyridine) component has been studied under conditions close to dielectric saturation. The substantially nonlinearity of the effect is confirmation that the spectral shifts of fluorescence bands depend on the number of polar solvent molecules involved in solvating the dye molecule. The measured fluorescence spectral shifts determined by substituting one nonpolar solvent molecula with a polar one in the proximity of the dye molecule agree quantitatively with the forecasts of the previously proposed semiempirical theory which describes this nonlinear solvation phenomenon.     

Improved Estimation of CSA–Dipolar Coupling Cross-Correlation Rates from Laboratory-Frame Relaxation Experiments

We have investigated the underlying assumptions in estimating cross-correlation rates between chemical shift anisotropy (CSA) and dipolar coupling mechanisms in a scalar-coupled two-spin IS system, from laboratory frame relaxation experiments. It has been shown that for an arbitrary relaxation delay, the difference in relaxation rates of the individual components of an in-phase (or antiphase) doublet is not related to the CSA–dipolar coupling cross-correlation rate in a simple way. This is especially true in the case where the difference in the decay rates of the in-phase and antiphase terms of the density matrix becomes comparable to the magnitude of the scalar coupling between the two spins. Improved means of extracting cross-correlation rates in these cases are presented.     

掺Cu~+氟磷玻璃的分时荧光及能量转移

本文分别在室温和低温下测定了氟磷酸盐玻璃中用不同波长激发Cu~+的分时荧光光谱以及不同发光波长的荧光寿命.随延迟时间增加,发光峰值移向长波.当采用长波长激发时,在发光主峰两边出现多个子峰结构,展现了激活离子之间的能量转移.     

Review of fluorescence anisotropy decay analysis by frequency-domain fluorescence spectroscopy

This didactic paper summarizes the mathematical expressions needed for analysis of fluorescence anisotropy decays from polarized frequency-domain fluorescence data. The observed values are the phase angle difference between the polarized components of the emission and the modulated anisotropy, which is the ratio of the polarized and amplitude-modulated components of the emission. This procedure requires a separate measurement of the intensity decay of the total emission. The expressions are suitable for any number of exponential components in both the intensity decay and the anisotropy decay. The formalism is generalized for global analysis of anisotropy decays measured at different excitation wavelengths and for different intensity decay times as the result of quenching. Additionally, we describe the expressions required for associated anisotropy decays, that is, anisotropy decays where each correlation time is associated with a decay time present in the anisotropy decay. And finally, we present expressions appropriate for distributions of correlation times. This article should serve as a reference for researchers using frequency-domain fluorometry.     

Characterization of molecular motion in the solid state by carbon-13 spin-lattice relaxation times

Relaxation calculations for rapidly spinning samples show that spin-lattice relaxation time (T(1Z)) anisotropy varies with the angle between the rotor spinning axis and the external field. When the rate of molecular motion is in the extreme narrowing limit, the measurement of T(1Z) anisotropies for two different values of the spinning angle allows the determination of two linear combinations of the three static spectral densities, J(0)(0), J(1)(0), and J(2)(0). These functions are sensitive to molecular geometry and the rate and trajectory of motion. The utility of these linear combinations in the investigation of molecular dynamics in solids has been demonstrated with natural abundance (13)C NMR experiments on ferrocene. In an isolated (13)C-(1,2)H group, the dipole-dipole interaction has the same orientational dependence as the quadrupole interaction. Thus, the spectral densities that are responsible for dipolar relaxation of (13)C are the same as those responsible for deuteron quadrupolar relaxation. For ferrocene-d(10), deuteron T(1Z) and T(1Q) anisotropies and the relaxation time of the (13)C magic angle spinning peak provide sufficient information to determine the orientation dependence of all three individual spectral densities.     

1H relaxation and dynamics of triphenylbismuth in deuterated solvents

ABSTRACT

¹H spin–lattice relaxation experiments have been performed for triphenylbismuth dissolved in fully deuterated glycerol and tetrahydrofuran. The experiments have been carried out in a broad frequency range, from 10?kHz to 40?MHz, versus temperature. The data have been analysed in terms of a relaxation model including two relaxation pathways: ¹H-¹H dipole–dipole interactions between intrinsic protons of triphenylbismuth molecule and ¹H-²H dipole–dipole interactions between the solvent and solute molecules. As a result of the analysis, rotational correlation times of triphenylbismuth molecules in the solutions and relative translational diffusion coefficient between the solvent and solute molecules have been determined. Moreover, the role of the intramolecular ¹H-¹H relaxation contribution has been revealed, depending on the motional parameters, as a result of decomposing the overall relaxation dispersion profile into contributions associated with the ¹H-¹H and ¹H-²H relaxation pathways. The possibility of accessing the contribution of the relaxation of the intrinsic protons is important from the perspective of exploiting Quadrupole Relaxation Enhancement effects as possible contrast mechanisms for Magnetic Resonance Imaging.     

Femtosecond Dynamics of Optically Induced Anisotropy of Complex Molecules in the Gas Phase

The evolution of optically induced anisotropy in an equilibrium ensemble of free asymmetric tops under collisionless conditions has been investigated theoretically and experimentally. The dynamics of the orientation correlation functions has been studied, the results of femtosecond experiments on measurement of relaxation of the optically induced anisotropy for perylene in the gas phase are presented, and their interpretation within the framework of the theory developed is given. It is shown that in contrast to stationary anisotropy, its time kinetics has more complete characteristic information about the dynamics of vector correlations in a molecular ensemble.