Double Exponential Decay Function Research Articles

Technical note: Excel spreadsheet calculation of the Henssge equation as an aid to estimating postmortem interval

In forensic cases for which the time of death is unknown, several methods are used to estimate the postmortem interval. The quotient (Q) defined as the difference between the rectal and ambient temperature (Tr − Ta) divided by the initial difference (T0 − Ta) represents the progress of postmortem cooling: Q = (Tr − Ta)/(T0 − Ta), (1 ≥ Q ≥ 0). Henssge was able to show that with the body weight and its empirical corrective factor, Q can be reasonably predicted as a double exponential decay function of time (Qp(t)). On the other hand, actual Q is determined as Qd by measuring Tr and Ta under an assumption of T0 = 37.2 °C. Then, the t value at which Qp(t) is equal to Qd (Qd=Qp(t)) would be a good estimate of the postmortem interval (the Henssge equation). Since the equation cannot be solved analytically, it has been solved using a pair of nomograms devised by Henssge. With greater access to computers and spreadsheet software, computational methods based on the input of actual parameters of the case can be more easily utilized. In this technical note, we describe two types of Excel spreadsheets to solve the equation numerically. In one type, a fairly accurate solution was obtained by iteration using an add-in program Solver. In the other type (forward calculation), a series of Qp(t) was generated at a time interval of 0.05 h and the t value at which Qp(t) was nearest to Qd was selected as an approximate solution using a built-in function, XLOOKUP. Alternatively, a series of absolute values of the difference between Qd and Qp(t) (|Dq(t)| = |Qd − Qp(t)|) was generated with time interval 0.1 h and the t value that produces the minimum |Dq(t)| was selected. These Excel spreadsheets are available as Supplementary Files.

Distinct growth regimes of α-synuclein amyloid elongation

Addition of amyloid seeds to aggregation-prone monomers allows for amyloid fiber growth (elongation) omitting slow nucleation. We here combine Thioflavin T fluorescence (probing formation of amyloids) and solution-state NMR spectroscopy (probing disappearance of monomers) to assess elongation kinetics of the amyloidogenic protein, α-synuclein, for which aggregation is linked to Parkinson’s disease. We found that both spectroscopic detection methods give similar kinetic results, which can be fitted by applying double exponential decay functions. When the origin of the two-phase behavior was analyzed by mathematical modeling, parallel paths as well as stop-and-go behavior were excluded as possible explanations. Instead, supported by previous theory, the experimental elongation data reveal distinct kinetic regimes that depend on instantaneous monomer concentration. At low monomer concentrations (toward end of experiments), amyloid growth is limited by conformational changes resulting in β-strand alignments. At the higher monomer concentrations (initial time points of experiments), growth occurs rapidly by incorporating monomers that have not successfully completed the conformational search. The presence of a fast disordered elongation regime at high monomer concentrations agrees with coarse-grained simulations and theory but has not been detected experimentally before. Our results may be related to the wide range of amyloid folds observed.

Electrical double layer interactions between soil colloidal particles: Polarization of water molecule and counterion

The electrical double layer (EDL) interactions strongly affect aggregation and dispersion of soil colloidal particles. In this research a modified model taking the polarization of water molecule and counterion into account was proposed based on nonlinear Poisson-Boltzmann theory to describe electrostatic interaction. The polarizations of both the counterion and the water molecule can increase the interaction between ion/water and soil particle surface, and then decrease the surface potential. Particle surface potential also depends on the surface separation when the EDL overlaps. The midpoint potential between colloidal particles decreases with increase of ion polarization but increases in the presence of water polarization through the change of the double layer thickness. Both the electrostatic repulsive pressure between soil particles and its force range increase markedly in the presence of the polarization of water molecules, but decrease with increase of counterion polarization. The water molecule polarization, rather than the counterion polarization, contributes more to EDL interactions. The counterion polarization is the origin of Hofmeister effects of the EDL interactions, which is affected by water polarization. The theoretical predicted force curve between clay particles by the modified model was verified by the experimental determination of surface force. In addition, the hydration force, fitted to a double exponential decay function, can be estimated by subtraction of the electrostatic interaction force based on DLVO theory from that based on the present model.

Fluorescence photo-bleaching of urine and its applicability in oral cancer diagnosis.

Photo-stability of urine is of crucial importance for the applicability of fluorescence spectroscopy of urine samples for diagnosis of cancer. We report the results of a detailed study on fluorescence photo-bleaching of human urine samples. We also present the results of a preliminary investigation on evaluation of the applicability of photo-bleaching characteristics of urine for discriminating patients with oral cancer from healthy volunteers. The time-lapse fluorescence induced by continuous shining of 405 nm radiation from a diode laser was recorded from the urine samples obtained from 18 patients with oral cancer as well as from 22 healthy volunteers with history of no known major illness in the past two months. The integrated fluorescence intensity (ΣI), calculated for each spectrum, was found to decrease with time till a point after which no further decrease was observed. Further, while significant differences were observed in the spectra of cancerous patients and healthy volunteers, these differences were found to be varying with time till the intensities of the observed fluorescence spectra corresponding to the two categories of urine samples became stable. The curve, generated by plotting ΣI vs. time, was found to be best fitted (R2 > 0.95) with a double-exponential decay function. The photo-bleaching constants, obtained from curve-fitting, were found to have statistically significant differences corresponding to the urine samples of cancerous patients and healthy volunteers. A classification algorithm developed based on nearest-mean classifier (NMC) and applied on the photo-bleaching constants in leave-one-subject-out cross-validation mode was found to provide a sensitivity and specificity of up to ∼ 86% in discriminating the two categories of urine samples.

Time-resolved photoinduced charge dynamics of Cd chalcogenide-based materials

We have performed a comparative analysis of the photocharging dynamics of quantum dots (CdSe–CdS core–shell nanoparticles in toluene) and a bulk CdS single crystal by using time-resolved luminescence and transient grating techniques. The quantum dots were obtained through a colloidal synthesis method in aqueous–organic media with the average sizes of 2 nm and 2.9 nm. It has been shown that the relaxation of the photocharging dynamics in quantum dots is well fitted by the double-exponential decay function with time constants of a few and tens of picoseconds, which indicates that the energy loss of photoinduced charges is mainly the result of electron–phonon interaction.

Solvatochromism of 1-naphthol-4-sulfonate photoacid and its encapsulation in cyclodextrin derivatives

Photophysical properties of the ground and excited states of 1-naphthol-4-sulfonate (1NO4S), photoacid, are investigated in different solvents and cyclodextrin derivatives of different size and structure. Fluorescence decay traces of 1NO4S are well fitted to double exponential decay function in all solvents. The short-lived traces with higher amplitude were assigned to emission of the neutral form (ROH*), while the long-lived traces with low amplitude were assigned to emission of the anionic form (RO−*). The photophysical properties of 1NO4S were correlated with a number of solvent parameters such as the solvent polarity parameters ETN and the reaction field factor Δf. Three linear solvation energy relationships developed by Kamlet-Taft, Catalán, and Laurence et al. were employed to assess the effect of non-specific and specific interactions on the photophysical properties of 1NO4S. All three solvation energy relationships showed that the non-specific interactions mainly control the photophysical properties of 1NO4S while the contribution of the specific interactions are weak. Molecular encapsulation of 1NO4S by α-cyclodextrin (α-CD), β-cyclodextrin (β-CD), γ-cyclodextrin (γ-CD), methyl-β-cyclodextrin (Mβ-CD), 2-hydroxypropyl-β-cyclodextrin (HPβ-CD) in aqueous solution has been studied by steady state and time resolved fluorescence techniques. Steady state fluorescence measurements show 1:1 inclusion of 1NO4S with different cyclodextrin derivatives with an association constant of 7.9 ± 4.0, 59.6 ± 10.0, 0.4 ± 0.5, 169.8 ± 25.0, and 359.0 ± 20.0 M−1 for 1NO4S complexes with α-CD, β-CD, γ-CD, Mβ-CD or HPβ-CD, respectively following the fluorescence intensity changes of the anionic form (RO−*) at 435.0 nm. Association constants obtained following the fluorescence enhancement of the neutral form (ROH*) were the same as determined following fluorescence intensity decrease of RO−* at 372 nm. Data derived from time resolved measurements gave very close value for the association constants as determined from steady state fluorescence measurements.

One-Pot Synthesis and Characterization of Novel Shape-Memory Poly(ε-Caprolactone) Based Polyurethane-Epoxy Co-networks with Diels⁻Alder Couplings.

The present work aimed at the preparation and investigation of different epoxy-polyurethane (EP-PU) co-networks. The EP-PU co-networks were obtained by applying two different synthetic strategies, in which the coupling element, the Diels–Alder (DA) adduct, was prepared previously or formed “in situ” in the reaction between furan functionalized polyurethane and furfuryl amine-diglycidyl ether bisphenol-A oligomers (FA_DGEBA). For the synthesis of these EP-PU networks, poly(ε-caprolactone)-diol (PCD, Mn = 2 kg/mol) and poly(ε-caprolactone) (PCL) with different molecular weights (Mn = 10, 25 and 50 kg/mol) and 1,6-hexamethylenediisocyanate (HDI) were used. The EP-PU co-networks were characterized by Attenuated Total Reflectance Fourier-Transform Infrared spectroscopy (AT-FT-IR), differential scanning calorimetry (DSC) and dynamical mechanical analysis (DMA). Scanning electron microscopy (SEM) was applied to assess the morphology of the EP-PU samples. It was demonstrated that the stress–strain curves for the EP-PUs could be interpreted based on the Standard Linear Solid (SLS) model. The DMA traces of some EP-PUs (depending on the composition and the synthetic method) revealed a plateau-like region above the melting temperature (Tm) of PCL confirming the presence of cross-linked structure. This feature predicted shape memory (SM) behavior for these EP-PU samples. Indeed, very good shape fixity and moderate shape recovery were obtained. The shape recovery processes of these EP-PU samples were described using double exponential decay functions.

Optical and scintillation properties of Ce:(Gd8AE2)(SiO4)6O2 (AE = Mg, Ca, Sr and Ba) crystals

1% Ce-doped and non-doped (Gd8AE2)(SiO4)6O2 (AE = Mg, Ca, Sr and Ba) (denoted as GMS, GCS, GSrS and GBS, respectively) single crystals were grown by the Floating Zone (FZ) method to evaluate their optical and scintillation properties. The Ce:GCS and Ce:GSrS samples exhibited scintillation and photoluminescence (PL) around 400 nm due to the 5d-4f transitions of Ce3+. On the other hand, Ce:GMS and Ce:GBS showed much weaker emissions in the wavelength range of 500–650 nm, in which the origin was associated with the host matrices. The PL decay curves were approximated by a double exponential decay function for all the Ce-doped samples. The decay times ranged around 10–30 and 40–90 ns, and faster components coincided with those of the non-doped samples. The scintillation decay curves of Ce-doped samples, on the other hand, were approximated by single exponential functions with slower decay constants than those of PL decay. These constants were very similar to those of non-doped samples. In the X-ray induced afterglow measurements, Ce:GCS exhibited the lowest afterglow level. The pulse height spectrum of these samples showed a full-energy peak under 241Am 5.5 MeV α-ray irradiation. Among these samples, Ce:GSrS exhibited the highest light yield which was around 600 ph/5.5 MeV-α.

Investigation of M2 Proton Channel in Membrane by Rapid Laser pH-Jump Technique with TRP Fluorescence as a Probe

Protonsplay a central role in many important biological processes such as ATP synthesis, viral infection, and cellular transportation. The mechanism and kinetics of these fast proton-related processes could be studied by the rapid laser-induced pH-jump technique, utilizing photo-acids which can release protons in 20 ns. Many researchers have used the laser pH-jump technique to investigate kinetics of protein folding, acid denature, or EGFP chromophore protonation in sub-millisecond time regime, but there has been no laser pH-jump study about membrane proteins to date, although many proton-related processes such as cellular transportation and ATP synthesis are associated with membrane and channel proteins. In this study, therefore, the laser pH-jump experiment on a membrane protein, Influenza A M2 proton channel (M2), was first demonstrated. In the pH-jump experiment with a membrane, it was observed that the local proton concentration on the membrane surface was higher than bulk solution because of the interaction between membrane and photo-acid, resulting in faster protonation kinetics than in bulk solution. Moreover, we first utilized Trp fluorescence as a probe for laser pH-jump, expanding on its capability. By observing the Trp fluorescence change of M2, sub-millisecond time scale kinetics of M2 activation process was measured upon rapid acidification. Trp fluorescence change could be described by a double exponential decay function, indicating that the first exponential is attributed to histidine protonation and the second is associated with subsequent conformational change. The V27A mutant of M2 showed faster overall kinetics than WT due to the lack of valine neck. We believe that our results advance our mechanistic knowledge of the M2 activation and could pave the way for the investigation of dynamics, kinetics, and mechanism of other proton-related processes.

Effect of solvent and encapsulation in β-cyclodextrin on the photophysical properties of 4-[5-(thiophen-2-yl)furan-2-yl]benzamidine

Abstract Photophysical characteristics of the ground and excited states of the bichalcophene derivative 4-[5-(thiophen-2-yl)furan-2-yl]benzamidine (TFB) were investigated in different solvents and in β-cyclodextrin (β-CD). The photophysical properties of TFB were correlated with the two commonly used solvent polarity parameters viz., ETN and reaction field factor Δf. In addition, the photophysical properties of TFB were also found to be well correlated with Kamlet–Taft relationship. Multiple linear regression analysis of solvent dependent photophysical parameters indicated that both non-specific dipolar interaction and specific hydrogen bonding interactions play important roles in determining the photophysical properties of TFB. It has been found that the non-specific dipolar interaction is the dominating parameter. Fluorescence decay curves are well fitted to double exponential decay function, with shorter component having the higher relative integrated intensity. Molecular encapsulation of TFB by β-CD in aqueous solution has been studied by steady state and time resolved fluorescence techniques. Steady state measurements show that the fluorescence quantum yield is enhanced strongly upon the addition of β-CD and increases from 0.03 ± 0.01 in aqueous solution to 0.11 ± 0.02 at 7.5 mM concentration of β-CD. Steady state fluorescence measurements show 1:1 inclusion of TFB in the β-cyclodextrin cavity with an association constant of 2.3 ± 0.2 × 103 M−1, while data derived from time resolved measurements gave very close value for the association constant of 2.6 ± 0.3 × 103 M−1. Time resolved measurements and global analysis of the results indicated that the excited state lifetime is strongly affected by the presence of β-CD. The changes observed for the chemical shifts of TFB and β-CD 1H NMR spectra and corresponding 1H NMR spectra of their mixture confirmed the formation of the inclusion complex and showed that TFB is partially encapsulated in β-CD cavity.

Intramolecular Excimer Formation Dynamics of 1,3-Bis-(1-pyrenyl)propane within 1-Butyl-3-methylimidazolium Hexafluorophosphate and Its Polyethylene Glycol Mixtures.

Mixtures of ionic liquid with polyethylene glycol (PEG) have shown interesting features as solubilizing media. Intramolecular excimer formation dynamics of 1,3-bis-(1-pyrenyl)propane [1Py(3)1Py] is investigated within mixtures of a common and popular ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) with PEGs of average molecular weight (MW) 200 (PEG200), average MW 400 (PEG400), number-average MW Mn 570-630 (PEG600), and number-average MW Mn 950-1050 (PEG1000) over the complete composition range at a 10° interval in the temperature range 10-90 °C. Irrespective of the composition of the medium and the temperature, excited-state intensity decay of the excimer fluorescence best fits to a three-exponential decay function, suggesting the presence of one excited-state monomer and two kinetically distinguishable excimers where both excimers are populated simultaneously by the excited monomer with no interconversion between the two excimers. In neat PEGs for temperatures ≤ 50 °C, intensity decay data of monomer fluorescence best fits to a single-exponential decay function, which implies the dissociation of both excimers back to the monomer to be insignificant. As the temperature is increased, the fits become closer to a double-exponential decay function, implying dissociation of one of the excimers to become significant. In neat [bmim][PF6], while a double-exponential decay function is required to fit the monomer excited-state intensity decay data at lower temperatures, three exponentials are required to satisfactorily fit the data at higher temperatures, suggesting both excimers significantly dissociate back to the monomer at higher temperatures within the ionic liquid. Within long-chain PEG-containing ([bmim][PF6] + PEG) mixtures, PEG as opposed to [bmim][PF6] controls the excimer formation dynamics by supposedly wrapping around the excimer, thus hindering dissociation back to the monomer. The overall rate constant of the excimer formation within ([bmim][PF6] + PEG) mixtures is found to scale better with the microviscosity rather than the bulk viscosity of the mixtures.

Fluorescence sensing system by Soret-band LED light excitation for estimating relative talaporfin sodium concentration in skin

The purpose of this study is to establish a sensing system to estimate relative talaporfin sodium concentration in skin to evaluate the risk of skin photosensitivity after photodynamic therapy (PDT) using percutaneous fluorescence spectroscopy. A prototype fluorescence sensing probe was made using a pair of 5-cm-long diffuse tips of plastic optical fibers for excitation light irradiation and fluorescence collection. Talaporfin sodium (2.5mg/kg) was intravenously administrated to three pigs, and the talaporfin sodium concentration in plasma was measured. The fluorescence sensing probe was attached to the skin and excited by a LED light with a peak wavelength of 409 ± 16 nm to obtain the mean area of the talaporfin sodium fluorescence spectral peak (Sfluo). The time history of the talaporfin sodium concentration in tissue was estimated using a two-compartment pharmacokinetic model. The time history of Sfluo was described as a composite function of the time history of the measured talaporfin sodium concentration in plasma and that of the estimated concentration in tissue as a double exponential decay function. The relative talaporfin sodium concentration in tissue and the relative contributions of fluorescence from tissue and plasma to Sfluo were estimated by the fluorescence system with the numerical pharmacokinetic model. Results also show that tissue compression equivalent to venous pressure might be effective to suppress the contribution of talaporfin sodium fluorescence in plasma.

The temporal course of recovery from brief (sub-second) adaptations to spatial contrast

Visual adaptation is a critical and ubiquitous mechanism that occurs for any stimulus feature and involves a continuous adjustment of the neuronal contrast gain. These adjustments prevent our visual system from dropping in sensitivity for the prevailing ranges of stimulus features that are processed at a given time. In addition to the classical adaptation, which arises over several seconds to minutes, a number of psychophysical, electrophysiological and interference studies have documented a much faster form of adaptation occurring with motion stimuli. This faster adaptation operates on a sub-second scale. In the present study, we investigated whether a fast form of adaptation also exists for spatial contrast and whether its characteristics (e.g., dependence on the duration of adaptation, time course of recovery) are similar to the classical, slower contrast adaptation. We found that a fast form of adaptation does exist and is maximal at intervals of 16–50ms after the offset of the adapting stimulus. Similar to what previous studies have found regarding the classical contrast adaptation, the initial threshold elevation of this study did not depend on the duration of the adapting stimulus, but only on its contrast. Our results showed that the function which best describes the decay of brief adaptations to high-contrast stimuli was a double exponential decay function, whereas the best function for describing adaptation to low-contrast stimuli was a single exponential decay function with a very fast recovery rate. Thus, adapting contrast influences both the threshold elevation, which rises with increasing adapting contrast, and the time course of recovery from adaptation. Overall, our data suggest the presence of a mechanism that is similar to the classical contrast adaptation involved in longer adaptations, but it operates over much shorter timescales.

The response of CO2 flux to rain pulses at a saline desert

AbstractAs the substantial component of the ecosystem respiration, soil CO2 flux is strongly influenced by infrequent and unpredictable precipitation in arid region. In the current study, we investigated the response of soil CO2 flux to rain pulses at a saline desert in western China. Soil CO2 flux was measured continuously during the whole growing season of 2009 at six sites. We found that there were remarkable changes in amplitude or diurnal patterns of soil CO2 flux induced by rainfall events: from bimodal before rain to a single peak after that. Further analysis indicated that there is a significant linear relationship (P < 0.001) between soil CO2 flux and soil temperature (Tsoil). However, a hysteresis between the waveform of diurnal course of CO2 flux and Tsoil was observed: with soil CO2 flux always peaked earlier than Tsoil. Furthermore, a double exponential decay function was fitted to the soil CO2 flux after rainfall, and total carbon (C) releases were estimated by numerical integration for rainfall events. The relative enhancement and total C release, in association with the rain pulses, was linearly related to the amount of precipitation. According to the size and frequency of rainfall events, the total amount of C release induced by rain pulses was computed as much as 7.88 g C·m–2 in 2009, equivalent to 10.25% of gross primary production. These results indicated that rain pulses played a significant role in the carbon budget of this saline desert ecosystem, and the size of them was a good indicator of rain‐induced flux enhancement. Copyright © 2012 John Wiley & Sons, Ltd.

Synchronous fluorescence spectroscopic study of solvatochromic curcumin dye

Curcumin, the main yellow bioactive component of turmeric, has recently acquired attention by chemists due its wide range of potential biological applications as an antioxidant, an anti-inflammatory, and an anti-carcinogenic agent. This molecule fluoresces weakly and poorly soluble in water. In this detailed study of curcumin in thirteen different solvents, both the absorption and fluorescence spectra of curcumin was found to be broad, however, a narrower and simple synchronous fluorescence spectrum of curcumin was obtained at Δ λ = 10–20 nm. Lippert–Mataga plot of curcumin in different solvents illustrated two sets of linearity which is consistent with the plot of Stokes’ shift vs. the E T30. When Stokes's shift in wavenumber scale was replaced by synchronous fluorescence maximum in nanometer scale, the solvent polarity dependency measured by λ SFS max vs. Lippert–Mataga plot or E T30 values offered similar trends as measured via Stokes’ shift for protic and aprotic solvents for curcumin. Better linear correlation of λ SFS max vs. π* scale of solvent polarity was found compared to λ abs max or λ em max or Stokes’ shift measurements. In Stokes’ shift measurement both absorption/excitation as well as emission (fluorescence) spectra are required to compute the Stokes’ shift in wavenumber scale, but measurement could be done in a very fast and simple way by taking a single scan of SFS avoiding calculation and obtain information about polarity of the solvent. Curcumin decay properties in all the solvents could be fitted well to a double-exponential decay function.

SU‐GG‐I‐146: Characterization of Mouse Mammary Glands by Measuring T2*: A Comparison of SV40Tag and FVB/N Mice

Purpose: An improved understanding of T2* in normal breast and intraductal cancer could lead to improvements in diagnostic accuracy. This study characterizes T2* in both a preclinical model of breast/mammary cancer (SV40Tag) and in healthy (FVB/N) mice. At ∼12 weeks, C3(1)SV40Tag mice develop mammary in situ neoplasms (MIN) that resemble ductal carcinoma in situ (DCIS) in women. Method and Materials: Eight SV40Tag and six FVB/N mice were imaged using a 9.4T Bruker magnet. Respiratory gated multi‐gradient echo pulse sequences were used to measure T2* with equivalent TR ∼1000ms, minimum TE of 1.5ms, 9 echoes at 3ms spacing. Generally, T2* was calculated by fitting the MRI signal intensity to a single exponential decay function. However, when fat was present, a modulus of complex double exponential decay function was needed. Results: For SV40Tag mice, T2* of muscle, lymph node, and tumor can be calculated from a single exponential function. T2* of normal mammary gland (NMG) and MIN need to be extracted from the modulus of complex function due to the fatty signal. Conversely, for FVB/N mice, all T2* can be calculated from single exponential function. On average muscle, tumor and NMG water components have slightlysmaller T2* values (∼15ms), but lymph node and NMG water components have slightly smaller T2* values (∼9.5ms). The fat in NMG and MIN have the smallest T2* values (∼3.8ms). In addition, NMG in SV40Tag is fattier than in FVB/N mice (57% vs. 12%, p<0.0001) for the selected ROIs. Conclusion: To accurately determine T2*, it is necessary to separate water/fat in fat‐rich mammary glands. In this pilot study, MIN lesions exhibit a larger separation between the long and short T2* values in comparison to NMG. Additionally, SV40Tag mice exhibit a higher percentage fat in NMG ROIs due to genetic differences.

Mechanics of DNA bridging by bacterial condensin MukBEF in vitro and in singulo

Structural maintenance of chromosome (SMC) proteins comprise the core of several specialized complexes that stabilize the global architecture of the chromosomes by dynamically linking distant DNA fragments. This reaction however remains poorly understood giving rise to numerous proposed mechanisms of the proteins. Using two novel assays, we investigated real-time formation of DNA bridges by bacterial condensin MukBEF. We report that MukBEF can efficiently bridge two DNAs and that this reaction involves multiple steps. The reaction begins with the formation of a stable MukB-DNA complex, which can further capture another protein-free DNA fragment. The initial tether is unstable but is quickly strengthened by additional MukBs. DNA bridging is modulated but is not strictly dependent on ATP and MukEF. The reaction revealed high preference for right-handed DNA crossings indicating that bridging involves physical association of MukB with both DNAs. Our data establish a comprehensive view of DNA bridging by MukBEF, which could explain how SMCs establish both intra- and interchromosomal links inside the cell and indicate that DNA binding and bridging could be separately regulated.

Extended Model Free Approach To Analyze Correlation Functions of Multidomain Proteins in the Presence of Motional Coupling

Interdomain motion in proteins plays an important role in biomolecular interaction. Its presence also complicates interpretation of many spectroscopy measurements. Nuclear magnetic resonance (NMR) study of domain dynamics relies on knowledge of its rotational correlation function. The extended model free (EMF) approach has been implemented to analyze coupled domain and overall motions for calmodulin, a dual-domain protein; however, the validity of EMF treatment in coupled motion has not been tested. We performed stochastic simulations on a dual-vector system employing two simple restraints to drive hydrodynamics and domain coupling: (1) both unitary vectors diffuse randomly on the surface of a sphere and (2) vectors are correlated through user-defined intervector potential. The resulting correlation curve can be adequately fit with either a single- or double-exponential decay function. The latter is consistent with the EMF treatment. The derived order parameters S (2) range from about 0.4 to 1, while the motion separation, the ratio of overall and domain motion time scales (tau m/tau s), ranges from 1 to 4. A complete overlap between time scales occurs when S (2) is less than 0.4, and the correlation function effectively behaves as a single-exponential. The S (2) values are consistent with theoretical predictions from the given potential function, differing by no more than 0.03, suggesting EMF to be a generally valid approach. In addition, from the dependence of S (2) on tau m/tau s obtained from simulation, we found a cosine potential, favoring extended conformers, as opposed to the normally assumed cone potential, reached a better agreement to experimental data.

Multispectral fluorescence lifetime imaging by TCSPC

We present a fluorescence lifetime imaging technique with simultaneous spectral and temporal resolution. The technique is fully compatible with the commonly used multiphoton microscopes and nondescanned (direct) detection. An image of the back-aperture of the microscope lens is projected on the input of a fiber bundle. The input of the fiber bundle is circular, and the output is flattened to match the input slit of a spectrograph. The spectrum at the output of the spectrograph is projected on a 16-anode PMT module. For each detected photon, the encoding logics of the PMT module deliver a timing pulse and the number of the PMT channel in which the photon was detected. The photons are accumulated by a multidimensional time-correlated single photon counting (TCSPC) process. The recording process builds up a four-dimensional photon distribution over the times of the photons in the excitation pulse period, the wavelengths of the photons, and the coordinates of the scan area. The method delivers a near-ideal counting efficiency and is capable of resolving double-exponential decay functions. We demonstrate the performance of the technique for autofluorescence imaging of tissue.

Room temperature relaxation of irradiated InP, GaAs and InAs characterized with the perturbed angular correlation technique

The structural relaxation of irradiated III–V compound semiconductors InP, GaAs and InAs arising from room temperature annealing has been studied using perturbed angular correlation spectroscopy. Amorphous zones were produced by MeV Ge ion implantation in single crystal substrates at liquid nitrogen temperature. These amorphous zones were found to relax continuously to a disordered state of lower energy with characteristic relaxation times of a few hours to a few days which are described by a double exponential decay function. We attribute this transformation or relaxation of amorphous to disordered material to a process akin to solid-phase-epitaxial-growth.