Energy Transfer Studies Research Articles

The role of developers in accepting solar energy in Iran: A case study in Golestan province

Iran is one of the largest holders of energy resources in the world and has always enjoyed a special international position in the world in terms of the amount of exports and the extent of available resources. However, the amount of energy consumption in recent years has become one of the most important concerns of the government, and in order to solve it, the government of the Republic of Iran has adopted two policies of reforming the consumption pattern and supplying energy through renewable energies, and specifically, developing the use of solar energy in has taken Meanwhile, various factors such as the market play an essential role in convincing people. Therefore, this research focuses on the social dimension of the issue of energy transfer, considering the human and social factors effective in the adoption of RE, and identifies the social barriers to the adoption of solar energy technologies in Iran (Golestan). This research has been conducted using a qualitative method based on interviews with private sector activists working in the solar energy development market to address the purpose of the research, which is to evaluate the obstacles to the establishment of solar energy technology in Iran from the perspective of market experts. The findings showed that consumers may perceive the need to use solar energy because of the problematic issues arising from the use of non-renewable energy. However, consumers' lack of awareness of solar energy, which is a solution to the problems caused by fossil fuel consumption, the high rate of currency fluctuations, and the government's lack of support for the private sector, are three factors that prevent the adoption of solar energy. Thus, the results of the present study have identified the obstacles to the development of low carbon economy in Iran through the adoption of solar energy. In this regard, all stakeholders including individuals, communities and governments will benefit from the benefits of RE. Since energy transfer studies are classified in one of the three main pillars of small consumer, policy maker or producer and distributor, this research was conducted with the aim of investigating the role of producer or distributor in order to identify the factors affecting it. In this context, it is necessary to examine two other pillars of discussion in future studies.

Investigations on photoluminescence and energy transfer studies of Sm3+ and Eu3+ ions doped Sr9Y2W4O24 red emitting phosphors with high color purity for w-LEDs

Sm3+/Eu3+ co-doped Sr9Y2W4O24 phosphors were prepared using the solid-state reaction process. The structure and micro-morphological analysis of the as-prepared phosphors were explored via x-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) spectroscopy. Optical & spectroscopic characteristics were investigated by the mean of diffuse reflectance spectroscopy (DRS), and photoluminescence (PL) techniques. The Sr9Y2W4O24 phosphor is tetragonal in structure and belongs to the I41/a space group. The excitation spectra recorded demonstrates that near-ultraviolet and blue LED chips can effectively excite the titled Sm3+-Eu3+ co-doped phosphors. The emission intensity pertaining to Eu3+ ions increases at the expense of decrease in intensity of Sm3+ ions with increase in the concentration of Eu3+ ion in titled Sm-Eu co-doped Sr9Y2W4O24 phosphors. The Reisfeld's approximation applied to the emission spectra of the titled Sm3+-Eu3+ co-doped Sr9Y2W4O24 phosphor reveal quadrupole-quadrupole as the mechanism responsible for energy transfer (ET) from Sm3+ to Eu3+ ions. The PL decay lifetimes values recorded for 603 nm emission of Sm3+ ions under 407 nm excitation wavelength were found to be decreasing with increase in Eu3+ ions concentration. This clearly reveal the ET from Sm3+ to Eu3+ ions in the titled phosphors. With increase in Eu3+ ion concentration the calculated CIE parameters are gradually shifting towards the deep red region of the visible spectrum under UV excitation. The temperature dependent PL (TD-PL) spectra demonstrate that the Sr9Y2W4O24: Sm3+/Eu3+ phosphor has relatively better thermally stablity with its thermal activation energy at around 0.256 eV. The results obtained in the present investigation allows us to explore the utility of Sm3+/Eu3+ co-doped Sr9Y2W4O24 phosphors as an effective deep red emitter needed to fabricate white LEDs.

DNA-Surfactant Exchange and Quantifying Interactions of Pure (n,m) Single-Enantiomer SWCNTs Towards Biohybrid Self-Assembly

Self-assembled biohybrid nanostructures made from single-wall carbon nanotubes (SWCNTs) and DNA are a promising model system for studying fundamental photo physics phenomena, and have significant potential as building blocks for applications such as biosensing and photovoltaics devices. Precise control of SWCNT bandgap and length in these biohybrid assemblies is highly desirable, but scalable production of such samples often benefits from processing in aqueous polymer and surfactant solutions that are then typically incompatible with DNA-directed assembly. DNA exchange is a promising route for replacing surfactants with self-assembling DNA sequences after these purification steps. Unfortunately, despite advances, DNA exchange remains a challenging technique with limitations due to uncontrolled aggregation and low yields. In this work we focus on improving the process for several well-defined SWCNT samples that are both single chirality and single enantiomer refined through aqueous two-phase separation as well as length sorted to a narrow distribution. With these, we demonstrate improvements in DNA exchange in both yield and control of the aggregation state by modifying DNA exchange processing parameters. We also show that the exchanged DNA-wrapped SWCNTs can be linked together by the addition of a complementary DNA bridge to form self-assembled biohybrid nanostructures for energy transfer studies. We use analytical ultracentrifugation and absorbance and photoluminescence spectroscopies to measure and quantify changes in as these biohybrid structures self-assemble. These developments pave the way for high yield assembly of precise biohybrid nanostructures for energy transfer studies and open potential applications in photovoltaics and biosensing.

Cooperative and Orthogonal Switching in the Solid State Enabled by Metal-Organic Framework Confinement Leading to a Thermo-Photochromic Platform.

Cooperative behavior and orthogonal responses of two classes of coordinatively integrated photochromic molecules towards distinct external stimuli were demonstrated on the first example of a photo-thermo-responsive hierarchical platform. Synergetic and orthogonal responses to temperature and excitation wavelength are achieved by confining the stimuli-responsive moieties within a metal-organic framework (MOF), leading to the preparation of a novel photo-thermo-responsive spiropyran-diarylethene based material. Synergistic behavior of two photoswitches enables the study of stimuli-responsive resonance energy transfer as well as control of the photoinduced charge transfer processes, milestones required to advance optoelectronics development. Spectroscopic studies in combination with theoretical modeling revealed a nonlinear effect on the material electronic structure arising from the coordinative integration of photoresponsive molecules with distinct photoisomerization mechanisms. Thus, the reported work covers multivariable facets of not only fundamental aspects of photoswitch cooperativity, but also provides a pathway to modulate photophysics and electronics of multidimensional functional materials exhibiting thermo-photochromism.

Molecular-Doped Protein-Based Elastomers as a Versatile Platform for Energy-Transfer Studies and Emissive Down-Converting Polymers for Light-Emitting Applications.

Much effort is being employed for designing "green" environmental emissive materials that are capable of color-tuning, i.e., down-converting the emission, and white-light generation (WLG). Here, we introduce a protein-based elastomer that can noncovalently bind a variety of chromophores while preventing their aggregation. Such binding capabilities are unique to the albumin-based materials that we use here in a process we refer to as "molecular doping". In the first part of this study, we explore the energy transfer across five different chromophores within the protein matrix, where the closely packed chromophore organization enables high energy-transfer efficiencies among them. In the second part, we show the easy control of blue, green, and red chromophores within the biopolymer, resulting in tunable emission properties of the film and WLG. The highly affordable chosen protein and the straightforward molecular doping strategy make our protein elastomers an attractive choice for an emissive material, as either a scaffold for investigating energy transfer in proteins or possible integration in light-emitting applications.

From Microstates to Macrostates in the Conformational Dynamics of GroEL: A Single-Molecule Förster Resonance Energy Transfer Study.

The chaperonin GroEL is a multisubunit molecular machine that assists in protein folding in the Escherichia coli cytosol. Past studies have shown that GroEL undergoes large allosteric conformational changes during its reaction cycle. Here, we report single-molecule Förster resonance energy transfer measurements that directly probe the conformational transitions of one subunit within GroEL and its single-ring variant under equilibrium conditions. We find that four microstates span the conformational manifold of the protein and interconvert on the submillisecond time scale. A unique set of relative populations of these microstates, termed a macrostate, is obtained by varying solution conditions, e.g., adding different nucleotides or the cochaperone GroES. Strikingly, ATP titration studies demonstrate that the partition between the apo and ATP-ligated conformational macrostates traces a sigmoidal response with a Hill coefficient similar to that obtained in bulk experiments of ATP hydrolysis. These coinciding results from bulk measurements for an entire ring and single-molecule measurements for a single subunit provide new evidence for the concerted allosteric transition of all seven subunits.

Spectral characterization and energy transfer study of Nd3+/Yb3+ in borosilicate glasses

Very sharp emission in near infrared region is observed for Nd3+/Yb3+ codoped 60B2O3-10SiO2-5PbO-10Al2O3-10Li2O-5ZnO (BSPbLAZ) glasses which were prepared by melt-quenching method along with Nd3+ doped BSPbLAZ glass. Photoluminescence excitation (PLE) spectra of 1 mol% of Nd2O3 doped BSPbLAZ glass shows intense band at 584 nm at an emission wavelength of 1062 nm. Photoluminescence emission (PL) spectra for 1 mol% of Nd2O3 doped BSPbLAZ glass at an excitation wavelength of 584 nm shows three characteristics emission bands in NIR range, 4F3/2→4I9/2, 4I11/2 and 4I13/2, most intense among these being the one at 1062 nm corresponding to 4F3/2→4I11/2. In the codoped system (Nd2O3/Yb2O3), prominent emission bands for Nd3+ are observed at 887, 1062 and 1336 nm corresponding to 4F3/2→4I9/2, 4I11/2 and 4I13/2 respectively, while for Yb3+ ions transition is observed at 980 nm corresponding to 2F5/2→2F7/2. Detailed investigation of characteristics like NIR emission, lifetime and energy transfer efficiency on increment of Yb2O3 doping concentration helps in understanding the utility of these glasses in the fields like photonic and optical devices. In BSPbLAZ glass Yb3+ can be easily sensitized by Nd3+ ions on account of its 4f-4f transitions. These factors provide healthy possibility for usage of Nd3+/Yb3+codoped BSPbLAZ glasses as multiple pump channel sources for laser fiber system based on Yb3+ ions.

Synthesis, Characterization, DNA/HSA Interaction, and Cytotoxic Activity of a Copper(II) Thiolate Schiff Base Complex and Its Corresponding Water-Soluble Stable Sulfinato-O Complex Containing Imidazole as a Co-ligand.

A Cu(II) thiolato complex [CuL(imz)] (1) (H2L = o-HOC6H4C(H)=NC6H4SH-o) and the corresponding water-soluble stable sulfinato-O complex [CuL'(imz)] (2) (H2L' = o-HOC6H4C(H)=NC6H4S(=O)OH) were synthesized and characterized using physicochemical techniques. Compound 2 is found to be a dimer in the solid state as characterized using single-crystal X-ray crystallography. XPS studies clearly showed the differences in the sulfur oxidation states in 1 and 2. Both compounds are found to be monomers in solution as revealed from their four-line X-band electron paramagnetic resonance spectra in CH3CN at room temperature (RT). 1-2 were tested to assess their ability to exhibit DNA binding and cleavage activity. Spectroscopic studies and viscosity experiments suggest that 1-2 bind to CT-DNA through the intercalation mode having moderate binding affinity (Kb ∼ 104 M-1). This is further supported by molecular docking studies of complex 2 with CT-DNA. Both complexes display significant oxidative cleavage of pUC19 DNA. Complex 2 also showed hydrolytic DNA cleavage. The interaction of 1-2 with HSA revealed that they have strong ability to quench the intrinsic fluorescence of HSA by a static quenching mechanism (kq ∼ 1013 M-1 s-1). This is further complemented by Förster resonance energy transfer studies that revealed binding distances of r = 2.85 and 2.75 nm for 1 and 2, respectively, indicating high potential for energy transfer from HSA to complex. 1-2 were capable of inducing conformational changes of HSA at secondary and tertiary levels as observed from synchronous and three-dimensional fluorescence spectroscopy. Molecular docking studies with 2 indicate that it forms strong hydrogen bonds with Gln221 and Arg222 located near the entrance of site-I of HSA. 1-2 showed potential toxicity in human cervical cancer HeLa cells, lung cancer A549 cells, and cisplatin-resistant breast cancer MDA-MB-231 cells and appeared to be most potent against HeLa cells (IC50 = 2.04 μM for 1 and 1.86 μM for 2). In HeLa cells, 1-2 mediated cell cycle arrest in S and G2/M phases, which progressed into apoptosis. Apoptotic features seen from Hoechst and AO/PI staining, damaged cytoskeleton actin viewed from phalloidin staining, and increased caspase-3 activity upon treatment with 1-2 collectively suggested that they induced apoptosis in HeLa cells via caspase activation. This is further supported by western blot analysis of the protein sample extracted from HeLa cells treated with 2.

Isolating Pure Donor and Acceptor Signals by Polarization-Controlled Transient Absorption Spectroscopy.

The optical spectra of molecules are often highly congested, inhibiting definite assignment of features and dynamics. In this work, we demonstrate and apply a polarization-based strategy for the decomposition of time-resolved optical spectra to analyze the electronic structure and energy transfer in a molecular donor-acceptor (D-A) dyad. We choose a dyad with orthogonal transition dipole moments for D and A and high fluorescence quantum yield to show that polarization-controlled ultrafast transient absorption spectra can isolate the pure D and A parts of the total signal. This provides a strategy to greatly reduce spectral congestion in complex systems and thus allows for detailed studies of electronic structure and electronic energy transfer.

Parameter study of decaying magnetohydrodynamic turbulence.

It is well known that helical magnetohydrodynamic (MHD) turbulence exhibits an inverse transfer of magnetic energy from small to large scales, which is related to the approximate conservation of magnetic helicity. Recently, several numerical investigations noticed the existence of an inverse energy transfer also in nonhelical MHD flows. We run a set of fully resolved direct numerical simulations and perform a wide parameter study of the inverse energy transfer and the decaying laws of helical and nonhelical MHD. Our numerical results show only a small inverse transfer of energy that grows as with increasing Prandtl number (Pm). This latter feature may have interesting consequences for cosmic magnetic field evolution. Additionally, we find that the decaying laws E∼t^{-p} are independent of the scale separation and depend solely on Pm and Re. In the helical case we measure a dependence of the form p_{b}≈0.6+14/Re. We also make a comparison between our results and previous literature and discuss the possible reason for the observed disagreements.

Design and Synthesis of Cofacially-Arrayed Polyfluorene Wires for Electron and Energy Transfer Studies.

A study of cofacially arrayed π-systems is of particular importance for the design of functional materials for efficient long-range intra-chain charge transfer through the bulk semiconducting materials in the layers of photovoltaic devices. The effect of π-stacking between a pair of aromatic rings has been mainly studied in the form of cyclophanes, where aromatic rings are forced into a sandwich-like geometry, which extensively deforms the aromatic rings from planarity. The synthetic difficulties associated with the preparation of cyclophane-like structures has prevented the synthesis of many examples of their multi-layered analogues. Moreover, the few available multi-layered cyclophanes are not readily amenable to the structural modification required for the construction of D-spacer-A triads needed to explore mechanisms of electron and energy transfer. In this review, we recount how a detailed experimental and computational analysis of 1,3-diarylalkanes led to the design of a new class of cofacially arrayed polyfluorenes that retain their π-stacked structure. Thus, efficient synthetic strategies have been established for the ready preparation of monodisperse polyfluorenes with up to six π-stacked fluorenes, which afford ready access to D-spacer-A triads by linking donor and acceptor groups to the polyfluorene spacers via single methylenes. Detailed 1H NMR spectroscopy, X-ray crystallography, electrochemistry, and He(I) photoelectron spectroscopy of F2-F6 have confirmed the rigid cofacial stacking of multiple fluorenes in F2-F6, despite the presence of rotatable C-C bonds. These polyfluorenes (F2-F6) form stable cation radicals in which a single hole is delocalized amongst the stacked fluorenes, as judged by the presence of intense charge-resonance transition in their optical spectra. Interestingly, these studies also discern that delocalization of a single cationic charge could occur over multiple fluorene rings in F2-F6, while the exciton is likely localized only onto two fluorenes in F2-F6. Facile synthesis of the D-spacer-A triads allowed us to demonstrate that efficient triplet energy transfer can occur through π-stacked polyfluorenes; the mechanism of energy transfer crosses over from tunneling to hopping with increasing number of fluorenes in the polyfluorene spacer. We suggest that the development of rigidly held π-stacked polyfluorenes, described herein, with well-defined redox and optoelectronic properties provides an ideal scaffold for the study of electron and energy transfer in D-spacer-A triads, where the Fn spacers serve as models for cofacially stacked π-systems.

Luminescence properties and energy transfer studies in thermally stable Bi2O3: Sm3+, Eu3+ phosphor

The advent of innovative rare-earth based metal oxide phosphors has prompted increasing interest in the search for highly efficient red emitting phosphors for various optoelectronic devices, lighting and display applications and motivated the research community to develop some promising, state-of-the-art, and potential red phosphors to meet the necessary requirements. In this study, a series of Sm3+ (1–7 mol%) doped, Sm3+ (5%) doped and Eu3+ (2–5 mol%) co-doped Bi2O3 red phosphors were synthesized by a facile urea assisted auto-combustion process. The X-ray diffraction (XRD) analysis of the phosphors ascertains the tetragonal crystal structure without any trace of impurity. The UV-Vis-NIR absorption study of the phosphors was carried out in 200–1000 nm range and the estimated optical band gap of the phosphors was lying in the range of 2.778–2.831 eV. The photoluminescence (PL) emission studies were performed at an excitation wavelength of 481 nm in the 550–720 nm range. The effective energy transfer mechanism from Sm3+ to Eu3+ in the Bi2O3 phosphor has been ascribed to the dipole-dipole (d-d) interaction. The energy transfer process was further validated by PL decay time measurements. The CIE color coordinates were obtained using PL emission data. The CIE chromaticity diagram ascertains that the emission color of Bi2O3: Sm3+ phosphors were tuned from reddish-orange to the red region by varying the concentration of Eu3+ ions. The temperature dependent PL study of the phosphors was taken out in the range of 293–453 K and was found thermally stable at elevated temperatures.

Temporal and spatial association between microwaves and type III bursts in the upper corona

One of the most important tasks in solar physics is the study of particles and energy transfer from the lower corona to the outer layers of the solar atmosphere. The most sensitive methods for detecting fluxes of non-thermal electrons in the solar atmosphere is observing their radio emission using modern large radioheliographs. We analyzed joint observations from the 13 April 2019 event observed by LOw-Frequency ARray (LOFAR) at meter wavelengths, and the Siberian Radio Heliograph (SRH) and the Badary Broadband Microwave Spectropolarimeter (BBMS) spectropolarimeter in microwaves performed at the time of the second PSP perihelion. During a period without signatures of non-thermal energy release in X-ray emission, numerous type III and/or type J bursts were observed. During the same two hours we observed soft X-ray brightenings and the appearance of weak microwave emission in an abnormally narrow band around 6 GHz. At these frequencies the increasing flux is well above the noise level, reaching 9 sfu. In the LOFAR dynamic spectrum of 53−80 MHz a region is found that lasts about an hour whose emission is highly correlated with 6 GHz temporal profile. The flux peaks in the meter waves are well correlated with extreme UV (EUV) emission variations caused by repeated surges from the bright X-point. We argue that there is a common source of non-thermal electrons located in the tail of the active region, where two loop systems of very different sizes interacted. The frequencies of type III and/or type J bursts are in accordance with large loop heights around 400 Mm, obtained by the magnetic field reconstruction. The microwave coherent emission was generated in the low loops identified as bright X-ray points seen in soft X-ray and EUV images, produced by electrons with energies several tens of keV at about twice the plasma frequency.

Photoluminescence and energy transfer studies on Tm3+/Dy3+/Eu3+doped borosilicate glasses for color tunability and warm white light generation

Potassium Zinc Alumino Borosilicate (KZABS) glasses doped with Dy3+, Tm3+ and Eu3+ have been prepared by a quench melting technique. The glasses show characteristic blue (1D2 → 3F4) and yellow (4F9/2 → 6H13/2) emission bands under 362 nm excitation. To produce warm white light, a red component was required in luminescence for which Eu3+ ions were added to the KZABS glass. A red emission (5D0 → 7F2) was seen under 362 nm excitation along with the blue and yellow bands. Photoluminescence (PL) studies show energy transfer from Tm3+ and Dy3+ ions to Eu3+ ions. The average lifetimes of the tri-doped glasses for all emission wavelengths decrease with increasing concentration of Eu3+ions. CIE chromaticity study also proves that tri-doped KZABS glasses can generate warm white light. Thus, we propose to use KZABS: Tm3+/Dy3+/Eu3+ glasses for warm white light generation in solid-state lighting (SSL) and white light emitting diode (w-LED) applications.

Protein binding studies and antioxidant activities of two mononuclear dioxomolybdenum(VI) complexes with 2-(3-methyl-5-phenyl pyrazol-1-yl) benzthiazole

Two yellow air-stable mononuclear dioxomolybdenum(VI) complexes, MoO2Cl2L (1) and MoO2Br2L (2) [where L = N,N donor ligand 2-(3-methyl-5-phenyl pyrazol-1-yl) benzthiazole], have been synthesized from their parent oxomolybdenum(V) complexes in dichloromethane. The binding affinity and binding mode of the molybdenum complexes with bovine serum albumin (BSA) have been explored by absorption and fluorescence titrations and time resolved fluorescence measurements. The number of binding sites for the complexes is nearly equal to unity, indicating there is only one binding site per BSA molecule. Molecular docking studies are also carried out to elucidate the binding mechanism, indicating that the complexes could quench the intrinsic fluorescence of BSA in a static quenching manner. Fluorescence resonance energy transfer study reveals that energy transfer takes place from Tryptophan residue of BSA to the synthesized complexes. The anti-oxidative properties of the complexes are examined by ABTS radical scavenging activities and DPPH radical quenching. The complexes exhibit different activities due to the influence of halogen substitution to the metal ion. MoO2Br2L (2) exhibits better activities than MoO2Cl2L (1) according to their EC50 values.

Energy transfer between optically trapped single ligand-free upconversion nanoparticle and dye

The quenching in luminescence emission of an optically trapped ligand-free hydrophilic NaYF4:Yb, Er upconversion nanoparticle (UCNP) as a function of rose Bengal dye molecule is investigated here. The removal of oleate capping of the as-prepared UCNPs was achieved via acid treatment and characterized via FTIR and Raman spectroscopic techniques. Further, the capping removed hydrophilic single UCNP is optically trapped and the emission studies were carried out as a function of excitation laser power. Compared to the studies using the bulk solution, the single UCNP luminescence spectrum exhibited additional spectral lines. The excitation laser power-dependent studies using the bulk solution yield a slope value between 1 and 2 for Blue, Green 1, Green 2, and Red emission and thus indicate that upconversion is a two-photon upconversion process. On the other hand, in the case of laser power-dependent studies on an optically trapped single-particle study, Blue and Green 1 yield a slope value of less than 1 whereas Green 2 and Red emission gave a slope value between 1 and 2. The energy transfer studies between an optically trapped ligand-free single UCNP and the rose Bengal dye show a concentration-dependent quenching in the emission of Green emissions and illustrate the potential of developing sensor platforms.

Förster resonance energy transfer studies of an intrinsically disordered peptide using a cyanophenylalanine derivative.

We report Förster Resonance Energy Transfer (FRET) studies of an intrinsically disordered peptide (IDP) using a phenylalanine derivative as the donor fluorophore. Due to its increased spectroscopic selectivity compared to phenylalanine, 2-cyanophenylalanine (2-PheCN) can be used as a site-specific probe of solvent environment and in FRET with tryptophan (Trp) as the acceptor for analysis of protein structure with an R0 of roughly 16 Å. Replacing phenylalanine with 2-PheCN in a 12 residue, intrinsically disordered olfactory peptide (OFP) where tryptophan occupies the N-terminus position provides two model IDPs: OFP Long, where 2-PheCN occupies the C-terminus, and OFP Short, in which 2-PheCN is two residues away from Trp. Measurement of the FRET efficiency within various solvent environments that either promote or inhibit secondary structures allows for examination of structural changes in the IDPs induced by the solvent environment. As expected, the energy transfer is highly efficient, approximately 0.99, between the nearly proximal fluorophores in OFP Short for all solvents examined. However, surprisingly the largest FRET efficiency for OFP Long is observed in solvent inhibiting secondary structures. Future FRET studies of both OFP Long and OFP Short will further investigate the solvent environment and temperature dependencies of the dynamics and structure of the disordered olfactory peptides.

Single molecule FRET reveals distinct MutS conformational dynamics on different DNA mismatches.

DNA mismatch repair (MMR) is an essential biological process that is common to all living organisms. The proteins involved in the MMR pathway identify and correct base mismatch errors and small insertion/deletions that are made during replication as well as some types of DNA damage. MutS is the MMR protein that scans DNA and locates mismatches. Previous single molecule fluorescent resonant energy transfer (smFRET) studies have found that binding to a GT mismatch or T-insert loop in DNA induces Thermus aquaticus MutS to undergo ATP-dependent conformational changes that convert it to a long-lived sliding clamp. This post-mismatch-recognition state of MutS is associated with downstream repair signaling in many models. Because different mismatches are repaired with the varying efficiencies, here we extend the smFRET studies to characterize the interactions between MutS and several additional mismatches. We further examine some mismatches in different local sequence contexts. Our results reproduce the binding affinities expected for these mismatches and characterize a range of tendencies for sliding clamps to result from MutS interacting with them. We compare our results to reported repair efficiencies to correlate the conversion to sliding clamp with eventual mismatch repair.

Regulation of Kir2.1 channels by ubiquitin-like modifier proteins.

The strong inward-rectifying subclass of potassium channel Kir2.1 produces IK1 current in the human myocardium which stabilizes the resting membrane potential of the heart and shapes the cardiac action potential. Perturbation or disruption of IK1 is associated with various arrhythmic phenotypes. Multiple studies have provided extensive evidence for the modulation of potassium channels by endogenous regulatory proteins. This group has studied extensively the relationship between the small ubiquitin-like modifier SUMO and Kir2.1 biophysical properties. Using patch clamp and Förster resonance energy transfer (FRET) studies in heterologous cells and rat ventricular cardiomyocytes (RVCM), we have demonstrated that SUMO interacts with Kir2.1 at a key lysine residue K49; the proximate physical association of which SUMO associates with the channel interferes with the binding pocket for phosphatidylinositol bisphosphate 2 (PIP2) required for channel gating, resulting in decreased IK1 current. Recent studies have posited an important role for another ubiquitin-like modifier, FAT10 in the regulation of ion channels that are expressed in the myocardium. While our group has characterized that acute hypoxia inhibits IK1 current in RVCM by an increased SUMOylation mechanism, another group has shown that FAT10 expression is markedly increased in hypoxia RVCMs. Together with studies showing evidence of competition for common target proteins between SUMO and FAT10, we seek to elucidate a mechanism of FAT10ylation of Kir2.1. Using FRET, we show disrupted SUMOylation in the presence of FAT10 in the heterologous cell system. Using electrophysiological techniques, we also demonstrate a change in Kir2.1 channel dynamics when FAT10 is co-expressed in both Xenopus laevis oocytes and HEK293T cells. Lastly, this work establishes a foundation for the study of Kir2.1 channel FAT10ylation in the native cardiomyocyte system in which FAT10 is posited to have a cardioprotective effect.

Single-component full-color emitting Ca6Y2Na2(PO4)6F2:Eu2+,Tb3+,Mn2+ phosphors with superior performance: color-tunable and energy transfer study.

Highly efficient single-component full-color emitting Ca6Y2Na2(PO4)6F2 (CYNPF):Eu2+,Tb3+,Mn2+ phosphors have been synthesized by a high-temperature solid-state reaction. Coupled with the Eu2+, Tb3+, and Mn2+ emission bands centered at 455 nm, 547 nm, and 580 nm, color-tunable white light can be generated. The energy transfer (ET) process from Eu2+ to Tb3+ and Mn2+ is attributed to the resonant dipole-dipole/dipole-dipole interaction mechanism with ultra-high ET efficiency (>90%). The emission color of the phosphors can be tuned from blue to yellowish green and orange with the corresponding CIE chromaticity coordinates of (0.1719, 0.1215), (0.2852, 0.4289), and (0.4752, 0.3903), respectively. Through controlling the concentration ratio of Tb3+ and Mn2+ ions, optimal white light emission can be obtained with CIE coordinates of (0.3381, 0.3353) excited at 365 nm, which is very close to the National Television Standards Committee white (0.330, 0.330). The thermal stability of the Eu2+, Tb3+, and Mn2+ codoped CYNPF phosphors has been investigated systematically. A single-component white LED (wLED) device has been fabricated by combining the CYNPF:Eu2+,Tb3+,Mn2+ phosphor with a 365 nm near-ultraviolet (n-UV) LED chip, which exhibits a high color rendering index (Ra = 80.2) along with a low color temperature of 5207 K and CIE coordinates of (0.3212, 0.3221). The results suggest that the phosphors can be used as a candidate material for single-component white phosphors for n-UV excited full-visible-spectrum wLEDs.