Resonance Energy Transfer Rate Research Articles

Effect of Medium Chirality on the Rate of Resonance Energy Transfer

Resonance energy transfer (RET) between two chromophores in an absorptive and dispersive chiral medium is investigated using a quantum electrodynamical formulation. To accurately describe such an environment involves the introduction of electric displacement and auxiliary magnetic field operators that are solutions of the Drude-Born-Fedorov equations and the time-harmonic Maxwell equations. Perturbation theory within the electric and magnetic dipole approximation is used in the derivation of the probability amplitude for energy transfer. Expressions for the contributions to the RET rate arising from the pure electric dipole term, replacing one of the chiral chromophores by its corresponding enantiomer in the mixed electric-magnetic dipole term, and the pure magnetic dipole contribution are obtained. In the near-zone limit in a nonabsorptive medium, the medium chirality amplifies the pure electric dipole contribution to the rate relative to that in a racemic mixture and also increases the discriminatory contribution, but to a lesser extent relative to the pure electric dipole term. On the other hand, under the same conditions, the medium chirality does not affect the pure magnetic dipole contribution to the rate. Measurements of the rate could be used to obtain information on the magnitude of the chirality admittance or concentration of chiral species, by comparing with the rate in an environment comprised of a racemic mixture of the enantiomers. This method could allow for the analysis of macroscopically heterogeneous systems that are comprised of enantiomers and where the chromophores experiencing RET are located in regions of interest.

Photoluminescence of SrGa 2S 4:Sn,Re(=Ce, Gd) phosphors

The photoluminescence (PL) spectra, PL excitation spectra, color coordinates, and X-ray diffraction spectra are reported for SrGa 2S 4:Sn,Re(=Ce and Gd, respectively) phosphors. By mixing SrGa 2S 4:Sn,Ce phosphors with different Ce 3+ concentrations, white emissions can be obtained under the excitation of a 340-nm UV LED. Emissions in the green to yellow color range can be obtained from SrGa 2S 4:Sn,Gd phosphors. The rare earth ions enhance the green emission band, which peaks at 534 nm, instead of the yellow one. The origin of this enhancement is discussed. The resonant energy transfer rates are estimated in the cases from Ce 3+ to the green and yellow centers of Sn 2+ and between the yellow centers and the green centers.

Distance dependence of fluorescence resonance energy transfer

Deviations from the usual R −6 dependence of the rate of fluorescence resonance energy transfer (FRET) on the distance between the donor and the acceptor have been a common scenario in the recent times. In this paper, we present a critical analysis of the distance dependence of FRET, and try to illustrate the non-R −6 type behaviour of the rate for the case of transfer from a localized electronic excitation on the donor, a dye molecule to three different energy acceptors with delocalized electronic excitations namely, graphene, a two-dimensional semiconducting sheet and the case of such a semiconducting sheet rolled to obtain a nanotube. We use simple analytic models to understand the distance dependence in each case.

Molecular dynamics study of chemically engineered green fluorescent protein mutants: Comparison of intramolecular fluorescence resonance energy transfer rate

Because of its unusual spectroscopic properties, green fluorescent protein (GFP) has become a useful tool in molecular genetics, biochemistry and cell biology. Here, we computationally characterize the behavior of two GFP constructs, designed as bioprobes for enzymatic triggering using intramolecular fluorescence resonance energy transfer (FRET). These constructs differ in the location of an intramolecular FRET partner, an attached chemical chromophore (either near an N-terminal or C-terminal site). We apply the temperature replica exchange molecular dynamics method to the two flexible constructs in conjunction with a generalized Born implicit solvent model. The calculated rate of FRET was derived from the interchromophore distance, R, and orientational factor, kappa(2). In agreement with experiment, the construct with the C-terminally attached dye was predicted to have higher energy transfer rate than observed for the N-terminal construct. The molecular basis for this observation is discussed. In addition, we find that the orientational factor, kappa(2), deviates from the commonly assumed value, the implications of which are also considered.

Distance and Orientation Dependence of Excitation Energy Transfer: From Molecular Systems to Metal Nanoparticles

The elegant theory developed by Forster to describe the rate of fluorescence resonance energy transfer between a donor and an acceptor has played a key role in understanding the structure and dynamics of polymers, biopolymers (proteins, nucleic acids), and self-assemblies (photosystems, micellar systems). Forster theory assumes the transition charge densities of donor and acceptor molecules are point dipoles and hence predicts a 1/R(6) dependence of energy transfer rate on center-to-center separation distance, R. In addition, a preaveraging over the orientations of the two dipoles is usually performed. The present review examines the validity of these assumptions in following different donor-acceptor (D-A) systems: (i) dye molecules attached to a flexible polymer chain in solution, (ii) extended conjugated dye molecules in quenched conformation, (iii) dye and a spherical metal nanoparticle of different sizes, (iv) two spherical metal nanoparticles, and (v) two prolate shaped metal nanoparticles at different relative orientations. In the case of dye molecules attached to a flexible polymer chain, we discuss the recent theoretical and computer simulation studies of energy transfer dynamics. It includes an analysis of Wilemski-Fixman (WF) theory of a bimolecular reaction in solution, applied to the excitation energy transfer between two ends of the polymer. We briefly describe the limitation of the WF theory and its generalizations that lead to a better agreement between the theory and the simulation results. The orientational dynamics of dye molecules is found to significantly influence the rate of excitation energy transfer, and may play a "hidden role" in influencing the observed distance dependence. For extended conjugated D-A systems and those involving nonspherical metal nanoparticles, even at intermediate separations, a significant deviation from 1/R(6)-type distance dependence of the energy transfer rate is found. Surprisingly, however, this distance dependence is robust for D-A systems involving spherical metal nanoparticles. For both spherical and nonspherical metal nanoparticles (MNps), the functional dependence of rate on the surface-to-surface separation distance (d) is quite different, at small to intermediate distances (compared to the size of the MNps). The rate calculations of excitation energy transfer between extended conjugated dye molecules reveal that optically dark states can significantly contribute toward enhancing the energy transfer rate. It is further found that the rate of energy transfer between nonspherical metal nanoparticles exhibits an interesting orientation dependence not anticipated in Forster's approach.

The fluorescence resonance energy transfer between dye compounds in micellar media

The fluorescence resonance energy transfer from fluorescein to merocyanine 540 in aqueous sodium dodecyl sulfate, cetyltrimethylammonium bromide and Triton X-100 micellar solutions as well as deionized water was investigated at room temperature using steady-state and time-resolved fluorescence spectroscopy techniques. Fluorescence resonance energy transfer rate constants ( k T), obtained using both Stern–Volmer and Förster theories, were in good agreement. Moreover, energy transfer efficiency values of 0.14, 0.38, 0.77 and 0.85 for deionized water, sodium dodecyl sulfate, TX-100 and cetyltrimethylammonium bromide micellar solution were obtained at the highest acceptor concentration at which fluorescence resonance energy transfer was achieved. The data obtained from steady-state absorption, fluorescence spectral studies and time-resolved lifetime measurements indicated that the fluorescence resonance energy transfer from fluorescein to merocyanine 540 occurred most effectively in aqueous cetyltrimethylammonium bromide micellar solutions.

Mesoscopic order and the dimensionality of long-range resonance energy transfer in supramolecular semiconductors

We present time-resolved photoluminescence measurements on two series of oligo-p-phenylenevinylene materials that self-assemble into supramolecular nanostructures with thermotropic reversibility in dodecane. One set of derivatives form chiral helical stacks, while the second set form less organized "frustrated" stacks. Here we study the effects of supramolecular organization on the resonance energy transfer rates. We measure these rates in nanoassemblies formed with mixed blends of oligomers and compare them with the rates predicted by Forster theory. Our results and analysis show that control of supramolecular order in the nanometer length scale has a dominant effect on the efficiency and dimensionality of resonance energy transfer.

Resonance energy transfer from a dye molecule to graphene

We study the distance dependence of the rate of resonance energy transfer from the excited state of a dye to the pi system of graphene. Using the tight-binding model for the pi system and the Dirac cone approximation, we obtain the analytic expression for the rate of energy transfer from an electronically excited dye to graphene. While in traditional fluorescence resonance energy transfer, the rate has a (distance)(-6) dependence, we find that the distance dependence in this case is quite different. Our calculation of rate in the case of the two dyes, pyrene and nile blue, shows that the distance dependence is Yukawa type. We have also studied the effect of doping on energy transfer to graphene. Doping does not modify the rate for electronic excitation energy transfer significantly. However, in the case of vibrational transfer, the rate is found to be increased by an order of magnitude due to doping. This can be attributed to the nonzero density of states at the Fermi level that results from doping.

Monitoring of Enzymatic Proteolysis Using Self‐Assembled Quantum Dot‐Protein Substrate Sensors

We have previously utilized hybrid semiconductor quantum dot‐ (QD‐) peptide substrates for monitoring of enzymatic proteolysis. In this report, we expand on this sensing strategy to further monitor protein‐protease interactions. We utilize QDs self‐assembled with multiple copies of dye‐labeled proteins as substrates for the sensing of protease activity. Detection of proteolysis is based on changes in the rate of fluorescence resonance energy transfer (FRET) between the QDs and the proximal dye‐labeled proteins following protein digestion by added enzyme. Our study focused on two representative proteolytic enzymes: the cysteine protease papain and the serine protease endoproteinase K. Analysis of the enzymatic digestion allowed us to estimate minimal values for the enzymatic activities of each enzyme used. Mechanisms of enzymatic inhibition were also inferred from the FRET data collected in the presence of inhibitors. Potential applications of this technology include drug discovery assays and in vivo cellular monitoring of enzymatic activity.

Intramolecular and intermolecular resonant energy transfer of a free-base tetraphenylporphyrin–fullerene dyad: A DFT and TDDFT study

Abstract Intramolecular and intermolecular resonant energy transfer (RET) of a free-base tetraphenylporphyrin– N -methyl-pyrrolidinofullerene (TPP–MPC 60 ) molecular dyad are studied by using the density functional theory (DFT) and the time-dependent DFT. The Fermi golden rule is used along with the extended dipole model to describe the electronic coupling in calculating the energy transfer rates. Among the PBE, PBE0, and B3LYP functionals the PBE is observed to predict the experimentally observed intramolecular RET rate the best, as well as the spectroscopic properties of TPP. The PBE calculated intramolecular RET rate is of the same order of magnitude as the experimentally observed rate and is observed to be also almost the same as the intermolecular energy transfer between two adjacent molecules.

A Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TDDFT) Study on Optical Transitions in Oligo(p-phenylenevinylene)−Fullerene Dyads and the Applicability to Resonant Energy Transfer

The optical transitions of three different size oligo(p-phenylenevinylene)-fullerene dyads (OPV(n)-MPC(60); n = 2-4) and of the corresponding separate molecules are studied using density functional theory (DFT) and time-dependent density functional theory. The DFT is used to determine the geometries and the electronic structures of the ground states. Transition energies and excited-state structures are obtained from the TDDFT calculations. Resonant energy transfer from OPV(n) to MPC(60) is also studied and the Fermi golden rule is used, along with two simple models to describe the electronic coupling to calculate the energy transfer rates. The hybrid-type PBE0 functional is used with a split-valence basis set augmented with a polarization function (SV(P)) in calculations and the calculated results are compared to the corresponding experimental results. The calculated PBE0 spectra of the OPV(n)-MPC(60) dyads correspond to the experimental spectra very well and are approximately sums of the absorption spectra of the separate OPV(n) and MPC(60) molecules. Also, the absorption energies of OPV(n) and MPC(60) and the emission energies of OPV(n) are predicted well with the PBE0 functional. The PBE0 calculated resonant energy transfer rates are in a good agreement with the experimental rates and show the existence of many possible pathways for energy transfer from the first excited singlet states of the OPV(n) molecules to the MPC(60) molecule.

Fluorescence resonance energy transfer in dye-labeled DNA

We present the results of molecular modeling of dye-labeled, double-stranded DNA. The structural information obtained from the simulations are used as input to an analysis of energy transfer in this system. The simulations reveal the nature of the interaction between a pair of fluorophores and DNA. The donor, tetramethylrhodamine, TMR, attached to the 5′-end of DNA with a six-carbon tether, interacts primarily with DNA's minor groove, but occasionally stacks against the DNA base pairs. The acceptor, Cy5, attached to the opposite strand at positions n ( n = 7, 12, 14, 16, 19, 24, 27), binds in the major groove in two distinct locations on the upper and lower part of the groove. We analyzed in detail the dye-to-dye distances, dipole orientation factors and fluorescence resonance energy transfer (FRET) rates. Tests of the validity of the Förster model were conducted using the transition density cube (TDC) method, which provides the exact Coulombic interaction within a certain model chemistry. Our studies show that the use of long tethers does not guarantee rotational freedom of the dyes, as intended in the experiments. Instead, the tethers allow Cy5 to bind in two different geometries, which causes a large uncertainty in the dye-to-dye distances. Our results also show significant fluctuation in the orientation factor, κ 2, which, together with uncertainty in dye-to-dye distances, cause considerable uncertainty in interpreting FRET measurements. We suggest that molecular modeling, combined with the TDC method, provides a useful tool in designing and interpreting FRET experiments.

Corrected Article: “The electronic influence of a third body on resonance energy transfer” [J. Chem. Phys. 116, 6701 (2002)

This investigation concerns an analysis of the effect, on the rate of resonance energy transfer between a pair of chromophores (the donor and acceptor), of a third chromophore species in their vicinity. Particularly when it is polar, the third body can exert an electrostatic influence on the energy-exchanging species that may result in a significant increase or decrease of their transfer rate. Furthermore it is shown how the presence of the third species can effectively “switch on” the energy transfer process, under circumstances where conventional energy transfer is forbidden due to orientational effects or on symmetry grounds. For example it is indicated that it is possible to instigate energy transfer when the salient acceptor or donor transitions are one-photon forbidden. In addition to results for structurally rigid systems, a rotationally averaged result applicable to fluids or disordered systems is presented.

The electronic influence of a third body on resonance energy transfer

This investigation concerns an analysis of the effect, on the rate of resonance energy transfer between a pair of chromophores (the donor and acceptor), of a third chromophore species in their vicinity. Particularly when it is polar, the third body can exert an electrostatic influence on the energy-exchanging species that may result in a significant increase or decrease of their transfer rate. Furthermore it is shown how the presence of the third species can effectively “switch on” the energy transfer process, under circumstances where conventional energy transfer is forbidden due to orientational effects or on symmetry grounds. For example it is indicated that it is possible to instigate energy transfer when the salient acceptor or donor transitions are one-photon forbidden. In addition to results for structurally rigid systems, a rotationally averaged result applicable to fluids or disordered systems is presented.

Luminescence Energy Transfer with Lanthanide Chelates: Interpretation of Sensitized Acceptor Decay Amplitudes

Lanthanide chelates used as donors offer several advantages over classical fluorescence probes in resonance energy transfer distance measurements. One of these advantages is that energy transfer can be conveniently measured using sensitized acceptor decay measurements. In these measurements a long microsecond lifetime of the lanthanide donor and a short nanosecond lifetime of the acceptor allow elimination of a signal from the unquenched donor. Therefore, the decay of sensitized acceptor emission reflects decay properties of the donor engaged in energy transfer. The purpose of this work is to point out the importance of the fact that the amplitude of the sensitized acceptor signal is dependent on the resonance energy transfer rate constant. Thus, in the case where there are two or more populations of donors with different energy transfer rate constants, the relative amplitudes of corresponding decay components observed in sensitized acceptor emission do not represent the relative populations of the donors. We use simulations to show that these effects can be very significant. A minor population of donors with a high rate of energy transfer can produce sensitized acceptor decay which is dominated by a decay component corresponding to this minor donor population. Using a simple experimental system of rapid diffusion limit energy transfer between a europium chelate and Cy5 acceptor we show that the predicted dependency of sensitized acceptor decay amplitude on the energy transfer rate is indeed observed. We suggest that the relative importance of decay components observed in sensitized acceptor emission should be evaluated after an appropriate correction of their values such that they properly reflect possible different populations of donors. We describe a method to perform such correction.

Localization and function of ferredoxin:NADP(+) reductase bound to the phycobilisomes of Synechocystis.

Each phycobilisome complex of the cyanobacterium Synechocystis PCC 6803 binds approximately 2.4 copies of ferredoxin:NADP(+) reductase (FNR). A mutant of this strain that carries an N-terminally truncated version of the petH gene, lacking the 9 kDa domain of FNR that is homologous to the phycocyanin-associated linker polypeptide CpcD, assembles phycobilisome complexes that do not contain FNR. Phycobilisome complexes, consisting of the allophycocyanin core and only the core-proximal phycocyanin hexamers from mutant R20, do contain a full complement of FNR. Therefore, the binding site of FNR in the phycobilisomes is not the core-distal binding site that is occupied by CpcD, but in the core-proximal phycocyanin hexamer. Phycobilisome complexes of a mutant expressing a fusion protein of the N-terminal domain of FNR and green fluorescent protein (GFP) contain this fusion protein in tightly bound form. Calculations of the fluorescence resonance energy transfer (FRET) characteristics between GFP and acceptors in the phycobilisome complex indicate that their donor-acceptor distance is between 3 and 7 nm. Fluorescence spectroscopy at 77K and measurements in intact cells of accumulated levels of P700(+) indicate that the presence of FNR in the phycobilisome complexes does not influence the distribution of excitation energy of phycobilisome-absorbed light between photosystem II and photosystem I, and also does not affect the occurrence of 'light-state transitions'.

Direct observation of optically controlled energy transfer in Tb 3+-doped glasses

We developed a novel method to control the resonant energy transfer rate between Tb 3+ ions by exciting a resonant level other than the main excitation. The result opened the possibility of wavelength-tunable active display panels as well as analyzing the resonant energy transfer in detail especially in a high concentration range. In this paper we studied the time-resolved photoluminescence with the two wavelength excitations, and obtained the non-exponential decay of 5D 4 level. This shows the restriction of the energy transfer and from this result we considered the inter-ionic interaction in more detail.

Resonance energy transfer imaging of phospholipid vesicle interaction with a planar phospholipid membrane: undulations and attachment sites in the region of calcium-mediated membrane--membrane adhesion.

Membrane fusion of a phospholipid vesicle with a planar lipid bilayer is preceded by an initial prefusion stage in which a region of the vesicle membrane adheres to the planar membrane. A resonance energy transfer (RET) imaging microscope, with measured spectral transfer functions and a pair of radiometrically calibrated video cameras, was used to determine both the area of the contact region and the distances between the membranes within this zone. Large vesicles (5-20 microns diam) were labeled with the donor fluorophore coumarin-phosphatidylethanolamine (PE), while the planar membrane was labeled with the acceptor rhodamine-PE. The donor was excited with 390 nm light, and separate images of donor and acceptor emission were formed by the microscope. Distances between the membranes at each location in the image were determined from the RET rate constant (kt) computed from the acceptor:donor emission intensity ratio. In the absence of an osmotic gradient, the vesicles stably adhered to the planar membrane, and the dyes did not migrate between membranes. The region of contact was detected as an area of planar membrane, coincident with the vesicle image, over which rhodamine fluorescence was sensitized by RET. The total area of the contact region depended biphasically on the Ca2+ concentration, but the distance between the bilayers in this zone decreased with increasing [Ca2+]. The changes in area and separation were probably related to divalent cation effects on electrostatic screening and binding to charged membranes. At each [Ca2+], the intermembrane separation varied between 1 and 6 nm within each contact region, indicating membrane undulation prior to adhesion. Intermembrane separation distances < or = 2 nm were localized to discrete sites that formed in an ordered arrangement throughout the contact region. The area of the contact region occupied by these punctate attachment sites was increased at high [Ca2+]. Membrane fusion may be initiated at these sites of closest membrane apposition.

Resonance energy transfer and laser actions in strongly scattering optical media

The resonance energy transfer rate in dyes embedded in aqueous suspensions of polystyrene particles is enhanced when the particle density is increased. This enhancement results in increment of the laser threshold in strongly scattering media.

Energy transfer between lanthanide ions in elpasolite lattices

Illustrations are given of the importance of resonant magnetic dipole-magnetic dipole, and resonant electric quadrupole-electric quadrupole interactions in the three-dimensional energy migration and quenching of luminescence of lanthanide ions, Ln 3+, in Cs 2NaLnCl 6. Calculations of resonant electronic energy transfer rates are in agreement with experimental results, but the calculated nonresonant transfer rates are very slow.