Pure Exponential Decay Research Articles

Tunable temporal dynamics of dipole response in graphene-wrapped core–shell nanoparticles

The investigation on the temporal dynamics of graphene-wrapped core–shell nanoparticles under the illumination of a Gaussian impulse have been carried out. By altering the graphene layers and the aspect ratio of the core–shell structure, we can adjust the resonant modes into typical cases in regime of terahertz. Accordingly, different scenarios for the temporal evolution are detected, which include two kinds of ultrafast oscillation with exponential decay tendency, pure exponential decay, and Gaussian shape, when the pulse duration of the incident pulse is much shorter than, similar to, and much longer than the localized surface plasmon lifetime. To one's interest, when the coupling between two resonant modes exists, one predicts the long-periodic oscillation, whose period is just the difference between the frequencies of the resonant modes. Hence, the intrinsic properties of the ultrafast oscillation can be hardly influenced by the input signals. Further quantitative calculation demonstrate that the periods of the ultrafast oscillations can be tuned by different physical mechanisms, which are, respectively, based on the self-interacting correction of a single resonance and the strong coupling between the resonant modes in frequency domain. Our results may be applicable in the fields of optical sensors, optical information processing, and other nanophotonic devices.

Correlation between thermoluminescence and optically stimulated luminescence signal in BeO

Beryllium Oxide (BeO) is a promising dosimetric material that is rapidly becoming an essential instrument in Optically Stimulated Luminescence (OSL) dosimetry applications. Despite the potential of BeO as a luminescence dosimeter, gaps remain in understanding how its Thermoluminescence (TL) and Optically Stimulated Luminescence (OSL) signals are connected. Our study aimed at examining Residual Thermoluminescence (R-TL) glow curves after various bleaching times to find an association between TL traps and OSL components across a wide range of doses, at 40 mGy and from 10 to 100 Gy. OSL decay curves and intensities of R-TL glow curves were fitted to either pure exponential decay functions or to stretched exponential decay functions, due to optical attenuation, to determine the OSL components and the bleaching decay rates of each TL peak, respectively. A good correlation between the decay rates of the OSL components and bleaching decay rates of each TL peak for both high and low-dose irradiations was found only for the model functions considering optical attenuation in the material. Taken together, this qualitative method helped to identify various traps, and results revealed a more consistent luminescence mechanism between TL and OSL signals than was previously assumed. Further support for the correlation between TL and OSL was derived from thermal stability studies of the OSL signal and from the dose response of the TL peaks and the OSL signal after different thermal pretreatments. Different bleaching models were discussed to define the appropriate one for BeO. These results may enhance our understanding of BeO as a dosimeter.

Probing multipartite entanglement, coherence and quantum information preservation under classical Ornstein–Uhlenbeck noise

We address entanglement, coherence, and information protection in a system of four non-interacting qubits coupled with different classical environments, namely: common, bipartite, tripartite, and independent environments described by Ornstein–Uhlenbeck (ORU) noise. We show that quantum information preserved by the four qubit state is more dependent on the coherence than the entanglement using time-dependent entanglement witness, purity, and Shannon entropy. We find these two quantum phenomena directly interrelated and highly vulnerable in environments with ORU noise, resulting in the pure exponential decay of a considerable amount. The current Markovian dynamical map, as well as suppression of the fluctuating character of the environments, are observed to be entirely attributable to the Gaussian nature of the noise. The increasing number of environments are witnessed to speed up the amount of decay. Unlike other noises, the current noise parameter’s flexible range is readily exploitable, ensuring long enough preserved memory properties. The four-qubit GHZ state, besides having a large information storage potential, stands partially entangled and coherent in common environments for an indefinite duration. In addition, we derive computational values for each system-environment interaction, which will help quantum practitioners to optimize the related classical environments.

Light scattering in TIRF microscopy: A theoretical study of the limits to surface selectivity

In TIRF microscopy, the sample resides near a surface in an evanescent optical field that, ideally, decreases in intensity with distance from the surface in a pure exponential fashion. In practice, multiple surfaces and imperfections in the optical system and refractive index (RI) inhomogeneities in the sample (often living cells) produce propagating scattered light that degrades the exponential purity. RI inhomogeneities cannot easily be avoided. How severe is the consequent optical degradation? Starting from Maxwell’s equations, we derive a first-order perturbative approximation of the electric field strength of light scattered by sample RI inhomogeneities of several types under coherent evanescent field illumination. The approximation provides an expression for the scattering field of any arbitrary RI inhomogeneity pattern. The scattering is not all propagating; some is evanescent and remains near the scattering centers. The results presented here are only a first-order approximation, and they ignore multiple scattering and reflections off the total internal reflection (TIR) surface. For simplicity, we assume that the RI variations in the z direction are insignificant within the depth of the evanescent field and consider only scattering of excitation light, not fluorescence emission light. The general conclusion of most significance from this study is that TIR scattering from a sample with RI variations typical of those on a cell culture alters the effective thickness of the illumination to only ∼50% greater than it would be without scattering. The qualitative surface selectivity of TIR fluorescence is largely retained even in the presence of scattering. Quantitatively, however, scattering will cause a deviation from the incident exponential decay at shorter distances, adding a slower decaying background. Calculations that assume a pure exponential decay will be approximations, and scattering should be taken into account. TIR scattering is only slightly dependent on polarization but is strongly reduced for the highest accessible incidence angles.

Mixing time of PageRank surfers on sparse random digraphs

AbstractWe consider the generalized PageRank walk on a digraph G, with refresh probability and resampling distribution . We analyze convergence to stationarity when G is a large sparse random digraph with given degree sequences, in the limit of vanishing . We identify three scenarios: when is much smaller than the inverse of the mixing time of G the relaxation to equilibrium is dominated by the simple random walk and displays a cutoff behavior; when is much larger than the inverse of the mixing time of G on the contrary one has pure exponential decay with rate ; when is comparable to the inverse of the mixing time of G there is a mixed behavior interpolating between cutoff and exponential decay. This trichotomy is shown to hold uniformly in the starting point and uniformly in the resampling distribution .

Comprehensive Analysis of the Kinetics of Radiation-Induced Lymphocyte Loss in Patients Treated with External Beam Radiation Therapy.

Radiation-induced lymphopenia (RIL) is associated with worse survival in patients with solid tumors, as well as lower response rates to checkpoint inhibitors. While single-fraction total-body irradiation is known to result in exponential decreases in the absolute lymphocyte count (ALC), the kinetics of lymphocyte loss after focal fractionated exposures have not previously been characterized. In the current study, lymphocyte loss kinetics was analyzed among patients undergoing focal fractionated radiotherapy for clinical indications. This registry-based study included 419 patients who received either total-body irradiation (TBI; n = 30), stereotactic body radiation therapy (SBRT; n = 73) or conventionally fractionated chemoradiation therapy (CFRT; n = 316). For each patient, serial ALCs were plotted against radiotherapy fraction number. The initial three weeks of treatment for CFRT patients and the entirety of treatment for SBRT and TBI patients were fit to exponential decay in the form ALC(x) = ae-bx, where ALC(x) is the ALC after x fractions. From those fits, fractional lymphocyte loss (FLL) was calculated as FLL = (1 - e-b) * 100, and multivariable regression was performed to identify significant correlates of FLL. Median linearized R2 when fitting the initial fractions was 0.98, 0.93 and 0.97 for patients receiving TBI, SBRT and CFRT, respectively. In CFRT patients, apparent ALC loss rate slowed after week 3. Fitting ALC loss over the entire CFRT course therefore required the addition of a constant term, "c". For TBI and SBRT patients, treatment ended during the pure exponential decay phase. Initial FLL varied significantly with treatment technique. Mean FLL was 35.5%, 24.3% and 10.77% for patients receiving TBI, SBRT and CFRT, respectively (P < 0.001). Significant correlates of FLL varied by site and included field size, dose per fraction, mean spleen dose, chemotherapy backbone and age. Finally, total percentage ALC loss during radiotherapy was highly correlated with FLL (P < 0.001). Lymphocyte depletion kinetics during the initial phase of fractionated radiotherapy are characterized by pure exponential decay. Initial FLL is strongly correlated with radiotherapy planning parameters and total percentage ALC loss. The two groups with the highest FLL received no concurrent chemotherapy, suggesting that ALC loss can be a consequence of radiotherapy alone. This work may assist in selecting patients for adaptive radiotherapy approaches to mitigate RIL risk.

Modeling of full-field optical coherence tomography in scattering media.

We develop a model of full-field optical coherence tomography (FF-OCT) that includes a description of partial temporal and spatial coherence, together with a mean-field scattering theory going beyond the Born approximation. Based on explicit expressions of the FF-OCT signal, we discuss essential features of FF-OCT imaging, such as the influence of partial coherence on the optical transfer function, and on the decay of the signal with depth. We derive the conditions under which the spatially averaged signal exhibits a pure exponential decay, providing a clear frame for the use of the Beer-Lambert law for quantitative measurements of the extinction length in scattering media.

Comprehensive analysis of lymphocyte loss kinetics in patients treated with focal fractionated radiation therapy.

e14191 Background: Radiation (RT)-induced lymphopenia (RIL) is associated with worse survival in patients with solid tumors as well as lower response rates to checkpoint inhibitors. This analysis aimed to model the kinetics of lymphocyte depletion during RT to assist in predicting RIL risk. Methods: This registry-based study included 419 patients who received either total body irradiation (TBI; n = 30), stereotactic body RT (SBRT; n = 73), or conventional chemoradiation (CRT; n = 316). For each patient, serial absolute lymphocyte counts (ALCs) were plotted against RT fraction number. The initial 3 weeks of treatment for conventionally irradiated patients and the entirety of treatment for SBRT and TBI patients were fit to exponential decay in the form ALC(x) = ae-bx. From those fits, percent per fraction loss in ALC (PFLAC) was calculated as PFLAC = (1 – e-b)*100, and multivariable regression was performed to find its significant predictors. Results: Curves were well fitted by exponential decay for all RT techniques (median linearized R2 0.98, 0.93, and 0.97 for patients treated with TBI, SBRT, and CRT, respectively). In CRT patients, apparent ALC loss rate slowed after week 3, potentially due to lymphocyte repopulation or other factors. TBI and SBRT patients completed RT before the end of the exponential decay phase, and their ALC loss rates remained unchanged throughout RT. Initial PFLAC varied significantly with treatment technique. Mean PFLAC was 35.5%, 24.3%, and 10.77% for patients treated with TBI, SBRT, and CRT, respectively (p &lt; 0.001). Significant predictors of PFLAC varied by site and included field size, dose per fraction, mean spleen dose, chemotherapy backbone, and age. In pancreas cancer patients, gemcitabine was associated with a higher PFLAC (mean = 10.7) than 5-FU (mean = 8.3) after adjustment for covariates (p &lt; 0.001). Finally, total % ALC loss during RT was highly correlated with PFLAC (p &lt; 0.001). Conclusions: Lymphocyte depletion kinetics during the initial phase of fractionated RT are characterized by pure exponential decay. Initial PFLAC is strongly correlated with RT planning parameters and predicts total % ALC loss. The highest ALC loss rates were associated with RT-only regimens, implying that concurrent chemotherapy is not solely responsible for lymphopenia in patients receiving CRT. This work may also assist in selecting patients for adaptive RT approaches to mitigate RIL risk.

Model-free description of polymer-coated gold nanoparticle dynamics in aqueous solutions obtained by Bayesian analysis of neutron spin echo data.

We present a neutron spin echo study of the nanosecond dynamics of polyethylene glycol (PEG) functionalized nanosized gold particles dissolved in D_{2}O at two temperatures and two different PEG molecular weights (400D and 2000D). The analysis of the neutron spin echo data was performed by applying a Bayesian approach to the description of time correlation function decays in terms of exponential terms, recently proved to be theoretically rigorous. This approach, which addresses in a direct way the fundamental issue of model choice in any dynamical analysis, provides here a guide to the most statistically supported way to follow the decay of the intermediate scattering functions I(Q,t) by basing on statistical grounds the choice of the number of terms required for the description of the nanosecond dynamics of the studied systems. Then, the presented analysis avoids from the start resorting to a preselected framework and can be considered as model free. By comparing the results of PEG-coated nanoparticles with those obtained in PEG2000 solutions, we were able to disentangle the translational diffusion of the nanoparticles from the internal dynamics of the polymer grafted to them, and to show that the polymer corona relaxation follows a pure exponential decay in agreement with the behavior predicted by coarse grained molecular dynamics simulations and theoretical models. This methodology has one further advantage: in the presence of a complex dynamical scenario, I(Q,t) is often described in terms of the Kohlrausch-Williams-Watts function that can implicitly represent a distribution of relaxation times. By choosing to describe the I(Q,t) as a sum of exponential functions and with the support of the Bayesian approach, we can explicitly determine when a finer-structure analysis of the dynamical complexity of the system exists according to the available data without the risk of overparametrization. The approach presented here is an effective tool that can be used in general to provide an unbiased interpretation of neutron spin echo data or whenever spectroscopy techniques yield time relaxation data curves.

Charge-conjugation-parity violation of neutral K-mesons in a temporal wave function model

The founding fathers of the quantum theory already struggled with the different roles of space and time in quantum theory. Position is by default represented by an operator, whereas time is usually treated as a parameter. Time operator models exist, in particular a certain Time Operator model denoted the Temporal Wave Function (T.W.F.). This one extends the Born's rule to the time domain. The statistics of pure exponential decay does not allow to exclude this Born rule for time. However the tiny violation of the combined discrete symmetries $P$ (parity) and $C$ (charge conjugation) observed in the K-meson system allows us, as we prove in this paper, to discriminate between the standard predictions, made in the framework of the so-called mass-decay matrix formalism, and the T.W.F. predictions. We also present experimental data of a particular $CP$ violating decay channel, that is in contrast with the prediction of T.W.F. approach model, resulting in its falsification.

Beer-Lambert law in the time domain

According to the Beer-Lambert law, the spectral density of weak electromagnetic radiation is attenuated exponentially, with the characteristic length depending on atomic density and the frequency-dependent photoabsorption cross section of the target. We discuss an analog of the Beer-Lambert law in the time domain, showing that the temporal profile of the initial light pulse enters explicitly into each term of expansion of the exponential function as a multiconvolution with the corresponding temporal response of an atom. The form invokes a description of pulse propagation in terms of the temporal base functions, which may be precalculated for a chosen initial pulse shape, allowing us to obtain the attenuated profile at a given target depth simply by summing up a sufficient number of weighted base functions. The variant with a 100-fs initial Gaussian pulse is worked out in detail, with the atomic response exhibiting either pure exponential or mixed prompt-exponential decay, characteristic of a photoexcited bound state or a Fano resonance. The method is shown to be valid for an arbitrary temporal profile of the initial electric field and is illustrated for pulses resonantly tuned to the low-lying doubly excited states of the He atom.

On the Limitations of Taylor’s Hypothesis in Parker Solar Probe’s Measurements near the Alfvén Critical Point

Abstract In this Letter, we present an analysis of two-point, two-time correlation functions from high-resolution numerical simulations of Reflection-driven Alfvén Turbulence near the Alfvén critical point r c. The simulations model the turbulence in a prescribed background solar wind model chosen to match observational constraints. This analysis allows us to investigate the temporal decorrelation of solar wind turbulence and the validity of Taylor’s approximation near the heliocentric distance r c, which Parker Solar Probe (PSP) is expected to explore in the coming years. The simulations show that the temporal decay of the Fourier-transformed turbulence decorrelation function is better described by a Gaussian model rather than a pure exponential time decay, and that the decorrelation frequency is almost linear with perpendicular wave number k ⊥ (perpendicular with respect to the background magnetic field ). Based on the simulations, we conclude that Taylor’s approximation cannot be used in this instance to provide a connection between the frequency ω of the time signal (measured in the probe frame) and the wavevector k ⊥ of the fluctuations because the frequency k ⊥ V sc (V sc is the spacecraft speed) near r c is comparable to the estimated decorrelation frequency. However, the use of Taylor’s approximation still leads to the correct spectral indices of the power spectra measured at the spacecraft frame. In this Letter, based on a Gaussian model, we suggest a modified relationship between ω and k ⊥, which might be useful in the interpretation of future PSP measurements.

Transient signal isotope analysis: validation of the method for isotope signal synchronization with the determination of amplifier first-order time constants.

During transient signal acquisition by Multi-Collection Inductively Coupled Plasma Mass Spectrometry (MC-ICPMS), an isotope ratio increase or decrease (isotopic drift hereafter) is often observed which is related to the different time responses of the amplifiers involved in multi-collection. This isotopic drift affects the quality of the isotopic data and, in a recent study, a method of internal amplifier signal synchronization for isotope drift correction was proposed. In this work the determination of the amplifier time constants was investigated in order to validate the method of internal amplifier signal synchronization for isotope ratio drift correction. Two different MC-ICPMS instruments, the Neptune and the Neptune Plus, were used, and both the lead transient signals and the signal decay curves of the amplifiers were investigated. Our results show that the first part of the amplifier signal decay curve is characterized by a pure exponential decay. This part of the signal decay was used for the effective calculation of the amplifier first-order time constants. The small differences between these time constants were compared with time lag values obtained from the method of isotope signal synchronization and were found to be in good agreement. This work proposes a way of determining amplifier first-order time constants. We show that isotopic drift is directly related to the amplifier first-order time constants and the method of internal amplifier signal synchronization for isotope ratio drift correction is validated.

Fast generation of T2⁎ maps in the entire range of clinical interest: Application to thalassemia major patients

T2⁎ maps obtained by the processing of multiecho MR sequences can be useful in several clinical applications. T2⁎ map generation procedures should join a processing time compatible with on-line image analysis with a good precision in the entire T2⁎ range of clinical interest. Fast generation of T2⁎ maps can be achieved by the estimation of the T2⁎ values by the weighted linear fitting of the logarithm of the signal (WLSL) method. This approach fails if the signal decay diverges from a pure exponential decay, as happens at low T2⁎ values where the rapid decay in the signal intensity leads to a plateau in the later echo times (TE). The proposed method implements the automatic truncation of the signal decay curves to be fitted in order to compensate for the signal collapse at low T2⁎ values, allowing the extension of the WLSL method through the entire clinical range of T2⁎ values.Validation was performed on synthetic images and on 60 thalassemia major patients with different levels of myocardial iron overload. Phantom experiments showed that a 5% fitting error threshold represented the best compromise between T2⁎ value measurement precision and processing time. A good agreement was found between T2⁎ map pixel-wise measurements and ROI-based measurements performed by expert readers (CoV=1.84% in global heart T2⁎, CoV=5.8% in segmental analysis). In conclusion, the developed procedure was effective in generating correct T2⁎ maps for the entire T2⁎ clinical range.

Excited state dynamics in the matrix-assisted laser desorption/ionization matrix 2,4,6-trihydroxyacetophenone: evidence for triplet pooling charge separation reactions.

Excited state pooling reactions are a central part of some models of ultraviolet matrix-assisted laser desorption/ionization (MALDI) mechanisms. Evidence has been found for pooling in several matrix materials, but a recent report of pure exponential fluorescence decay at MALDI-relevant laser fluences suggested that 2,4,6-trihydroxy-acetophenone (THAP) may be an example of a matrix in which pooling does not occur (Lin et al., Rapid Commun. Mass Spectrom. 2014, 28, 77). However, those data were instrumentally limited in dynamic range and signal/noise ratio, and the conclusion does not take into account several aspects of THAP excited state dynamics. Using time-correlated single photon counting, and absorption and emission spectroscopies, the excited state dynamics of THAP are reexamined. Like many other aromatic ketones and acetophenone, isolated THAP molecules undergo very efficient intersystem crossing. No fluorescence is observed in dilute solution. In the solid state, efficient fluorescence reappears, but is non-exponential even at very low excitation intensity. The solvent used for sample preparation was found to have a large effect on the spectra and decay curves. Needle-like crystals seem to be correlated with reduced intersystem crossing. THAP solid state fluorescence is entirely due to intermolecular interactions. Activation of fluorescence, instead of quenching, is a clear indicator of delocalized excited state phenomena in THAP. Contrary to the conclusions of Lin et al., the greatly increased singlet lifetime in the solid state substantially increases the probability that pooling-type reactions are indeed involved in ionization processes. The sensitivity of fluorescence and phosphorescence on sample morphology appears to reflect changes in intermolecular interactions due to crystal packing. Pooling charge separation pathways based on known triplet-triplet ionization reactions of aromatic ketones are proposed.

Distinctive characteristics of the decay function for phosphorescence in the presence of reabsorption

The phosphorescence decay under the effect of significant excited-state absorption has a distinctive signature: it is initially concave, switching to convex (pure exponential decay) after a certain time. A simple one-parameter decay function satisfactorily reproducing the experimental decays is discussed, and some of its peculiar mathematical properties analyzed.

Photodecarbonylation mechanism of cyclopropenone in the gas phase: electronic structure calculation and AIMS dynamics simulation.

In this article, structures and energies of cyclopropenone in the low-lying electronic states have been determined by the CASSCF and MS-CASPT2 calculations with different basis sets. Two minimum-energy conical intersections (CI-1 and CI-2) between S0 and S1 were obtained and their topographic characters were characterized by the SA4-CAS(10,9) calculated energy gradients and nonadiabatic coupling vectors. The AIMS method was used to carry out nonadiabatic dynamics simulation with ab initio calculation performed at the SA4-CAS(10,9) level. On the basis of time evolution of wave functions simulated here, the S1 lifetime is fitted to be 125 fs with a pure exponential decay for the S1 electronic population. The CI-1 intersection is mainly responsible for ultrafast S1→S0 nonadiabatic transition and the photoinduced decarbonylation is a sequential process, where the first C-C bond is broken in the S1 state and fission of the second C-C bond occurs in the S0 state as a result of the S1→S0 internal conversion via the CI-1 region. As a minor channel through the CI-2 region, the decarbonylation proceeds in an asynchronous concerted way. Effects of the S1 excess energies and the S1-S0 energy gap on the nonadiabatic dynamics were examined, which reveals that the S1→S0 nonadiabatic transition occurs within a small energy gap and high-energy conical intersection regions can play an important role. The present study provides new insights into mechanistic photochemistry of cyclopropenones and reveals that the AIMS dynamics simulation at a high-accuracy ab initio level is a powerful tool for exploring a mechanism of an ultrafast photochemical reaction.

3:46 PM Abstract No. 105 - Modeling the rate of bilirubin decay after percutaneous drainage prior to chemotherapy

Purpose To evaluate the potential of two models of bilirubin decay to predict response to drainage in patients who underwent biliary drainage to lower serum bilirubin prior to chemotherapy. Materials and Methods IRB-approved retrospective review identified 77 patients with malignant biliary obstruction who underwent a single biliary drainage to decrease bilirubin prior to chemotherapy administration and who had at least four subsequent serum bilirubin determinations (regardless of value) at 7-10 day intervals for the first 4 weeks following the procedure. Data were analyzed in both mono-exponential (ME) (bilirubin level is described in terms of pure exponential decay) and mono-exponential-static (MS) (bilirubin level is described in terms of exponential decay followed by an inflection point where the bilirubin level levels off to a constant value) models. Responders were defined as patients who achieved total serum bilirubin levels Results Across all patients, the MS model had better fit with total serum bilirubin values after drainage than the ME model (R2 0.82 vs 0.62, respectively). When patients were stratified into responders and non-responders, the MS model similarly had better fit to patient data (responders: R2 0.91 v 0.71; non-responders R2 0.66 v 0.45). Parameters extracted from both models (ME and MS) suggest that both estimated pre-drainage bilirubin (10.4 and 10.7 mg/dL, respectively) and the exponential decay rate (0.14 and 0.22 mg/dL/day) of responders was significantly different from the estimated pre-drainage bilirubin (15.0 and 15.1 mg/dL) (P=0.0003 and P Conclusion Models of bilirubin response to percutaneous drainage may be useful to provide early clinical separation of responders from non-responders, prompting additional drainage or internalization of drainage when clinically appropriate.

The Single T65S Mutation Generates Brighter Cyan Fluorescent Proteins with Increased Photostability and pH Insensitivity

Cyan fluorescent proteins (CFP) derived from Aequorea victoria GFP, carrying a tryptophan-based chromophore, are widely used as FRET donors in live cell fluorescence imaging experiments. Recently, several CFP variants with near-ultimate photophysical performances were obtained through a mix of site-directed and large scale random mutagenesis. To understand the structural bases of these improvements, we have studied more specifically the consequences of the single-site T65S mutation. We find that all CFP variants carrying the T65S mutation not only display an increased fluorescence quantum yield and a simpler fluorescence emission decay, but also show an improved pH stability and strongly reduced reversible photoswitching reactions. Most prominently, the Cerulean-T65S variant reaches performances nearly equivalent to those of mTurquoise, with QY = 0.84, an almost pure single exponential fluorescence decay and an outstanding stability in the acid pH range (pK1/2 = 3.6). From the detailed examination of crystallographic structures of different CFPs and GFPs, we conclude that these improvements stem from a shift in the thermodynamic balance between two well defined configurations of the residue 65 hydroxyl. These two configurations differ in their relative stabilization of a rigid chromophore, as well as in relaying the effects of Glu222 protonation at acid pHs. Our results suggest a simple method to greatly improve numerous FRET reporters used in cell imaging, and bring novel insights into the general structure-photophysics relationships of fluorescent proteins.

Reservations on the reservoir

Reservations on the reservoir