Exciton quenching by oxidized chlorophyll Z across the two adjacent monomers in a photosystem II core dimer

This study aimed to clarify (1) which pigment in a photosystem II (PSII) core complex is responsible for the 695-nm emission at 77 K and (2) the molecular basis for the oxidation-induced fluorescence quenching in PSII. Picosecond time-resolved fluorescence dynamics was compared between the dimeric and monomeric PSII with and without addition of an oxidant. The results indicated that the excitation-energy flow to the 695-nm-emitting chlorophyll (Chl) at 36 K and 77 K was hindered upon monomerization, clearly demonstrating significant exciton migration from the Chls on one monomer to the 695-nm-emitting pigment on the adjacent monomer. Oxidation of the redox-active Chl, which is named Chl_Z caused almost equal quenching of the 684-nm and 695-nm emission bands in the dimer, and lower quenching of the 695-nm band in the monomer. These results suggested two possible scenarios responsible for the 695-nm emission band: (A) Chl11-13 pair and the oxidized Chl_ZD1 work as the 695-nm emitting Chl and the quenching site, respectively, and (B) Chl29 and the oxidized Chl_ZD2 work as the 695-nm emitting Chl and the quenching site, respectively.

Li@C60 thin films: characterization and nonlinear optical properties

Organic materials have attracted considerable attention in nonlinear optical (NLO) applications as they have several advantages over inorganic materials, including high NLO response, and fast response time as well as low-cost and easy fabrication. Lithium-containing C₆₀ (Li@C₆₀) is promising for NLO over other organic materials because of its strong NLO response proven by theoretical and experimental studies. However, the low purity of Li@C₆₀ has been a bottleneck for applications in the fields of solar cells, electronics and optics. In 2010, highly purified Li@C₆₀ was finally obtained, encouraging further studies. In this study, we demonstrate a facile method to fabricate thin films of Li@C₆₀ and their strong NLO potential for high harmonic generation by showing its comparatively strong emission of degenerate-six-wave mixing, a fifth-order NLO effect.

A facile way is shown to obtain thin films of Li@C₆₀ as well as their characterization and nonlinear optical properties. Our results suggest Li@C₆₀ to be a suitable candidate for high-harmonic generation.

Data on synthesis and characterization of new p-nitro stilbene Schiff bases derivatives as an electrochemical DNA potential spacer

The structural investigation of synthesized compounds can be carried out by various spectroscopic techniques. It is an important prospect in order to elucidate the structure of the desired products before being further utilized. The preparation of new p-nitro stilbene Schiff base derivatives as an electrochemical DNA potential spacer was synthesized using (E)-4-(4-nitrostyryl)aniline from Heck reaction with aldehydes in ethanolic solution. The data presented here in this article contains FTIR, UV-Vis and ¹H and ¹³C NMR of (E)-4-(4-nitrostyryl)aniline and nitrostyryl aniline derivatives.

Time-Resolved Structured Illumination Microscopy for Phase Separation Dynamics of Water and 2-Butoxyethanol Mixtures: Interpretation of "Early Stage" Involving Micelle-Like Structures

Phase separation dynamics of a water/2-butoxyethanol (2BE) mixture was studied with newly developed time-resolved structured illumination microscopy (SIM). Interestingly, an employed hydrophobic fluorescent probe for SIM showed spectral shifts up to 500 ns after a laser-induced temperature jump, which suggests 2BE micellar-like aggregates become more hydrophobic at the initial stage of phase separation. This hydrophobic environment in 2BE aggregates, probably due to the ejection of water molecules, continued up to at least 10 μs. Time-resolved SIM and previously reported light scattering data clearly showed that the size of a periodic structure remained constant (ca. 300 nm) from 3 to 10 μs, and then the growth of periodic structures having the self-similarity started. We think that the former and the latter processes correspond to "early stage" (concentration growth) and "late stage" (size growth), respectively, in phase separation dynamics. Here we suggest that, in the early stage, the entity to bear 2BE phase be water-poor 2BE aggregates, and the number density of these aggregates would simply increase in time.

Red shift in the spectrum of a chlorophyll species is essential for the drought-induced dissipation of excess light energy in a poikilohydric moss, Bryum argenteum

Some mosses are extremely tolerant of drought stress. Their high drought tolerance relies on their ability to effectively dissipate absorbed light energy to heat under dry conditions. The energy dissipation mechanism in a drought-tolerant moss, Bryum argenteum, has been investigated using low-temperature picosecond time-resolved fluorescence spectroscopy. The results are compared between moss thalli samples harvested in Antarctica and in Japan. Both samples show almost the same quenching properties, suggesting an identical drought tolerance mechanism for the same species with two completely different habitats. A global target analysis was applied to a large set of data on the fluorescence-quenching dynamics for the 430-nm (chlorophyll-a selective) and 460-nm (chlorophyll-b and carotenoid selective) excitations in the temperature region from 5 to 77 K. This analysis strongly suggested that the quencher is formed in the major peripheral antenna of photosystem II, whose emission spectrum is significantly broadened and red-shifted in its quenched form. Two emission components at around 717 and 725 nm were assigned to photosystem I (PS I). The former component at around 717 nm is mildly quenched and probably bound to the PS I core complex, while the latter at around 725 nm is probably bound to the light-harvesting complex. The dehydration treatment caused a blue shift of the PS I emission peak via reduction of the exciton energy flow to the pigment responsible for the 725 nm band.

Extensive first-principles molecular dynamics study on Li encapsulation into C60 and its experimental confirmation

The aim of increasing the production ratio of endohedral C₆₀ by impinging foreign atoms against C₆₀ is a crucial matter of the science and technology employed towards industrialization of these functional building block materials. Among these endohedral fullerenes, Li⁺@C₆₀ exhibits a wide variety of physical and chemical phenomena and has the potential to be applicable in areas spanning the medical field to photovoltaics. However, currently, Li⁺@C₆₀ can be experimentally produced with only ∼1% ratio using the plasma shower method with a 30 eV kinetic energy provided to the impinging Li⁺ ion. From extensive first-principles molecular dynamics simulations, it is found that the maximum production ratio of Li⁺@C₆₀ per hit is increased to about 5.1% (5.3%) when a Li⁺ ion impinges vertically on a six-membered ring of C₆₀ with 30 eV (40 eV) kinetic energy, although many C₆₀ molecules are damaged during this collision. On the contrary, when it impinges vertically on a six-membered ring with 10 eV kinetic energy, the production ratio remains at 1.3%, but the C₆₀ molecules are not damaged at all. On the other hand, when the C₆₀ is randomly oriented, the production ratio reduces to about 3.7 ± 0.5%, 3.3 ± 0.5%, and 0.2 ± 0.03% for 30 eV, 40 eV, and 10 eV kinetic energy, respectively. Based on these observations we demonstrate the possibility of increasing the production ratio by fixing six-membered rings atop C₆₀ using the Cu(111) substrate or UV light irradiation. In order to assess the ideal experimental production ratio, the ⁷Li solid NMR spectroscopy measurement is also performed for the multilayer randomly oriented C₆₀ sample irradiated by Li⁺ using the plasma shower method combined with inductively coupled plasma atomic emission spectroscopy (ICP-AES). Time-of-flight mass spectroscopy measurements are also performed to cross check whether Li⁺@C₆₀ molecules are produced in the sample. The resulting experimental estimate, 4% for 30 eV incident kinetic energy, fully agrees with our simulation results mentioned above, suggesting the consistency and accuracy of our simulations and experiments.

Fluorescence property of photosystem II protein complexes bound to a gold nanoparticle

Development of an efficient photo-anode system for water oxidation is key to the success of artificial photosynthesis. We previously assembled photosystem II (PSII) proteins, which are an efficient natural photocatalyst for water oxidation, on a gold nanoparticle (GNP) to prepare a PSII-GNP conjugate as an anode system in a light-driven water-splitting nano-device (Noji et al., J. Phys. Chem. Lett., 2011, 2, 2448-2452). In the current study, we characterized the fluorescence property of the PSII-GNP conjugate by static and time-resolved fluorescence measurements, and compared with that of free PSII proteins. It was shown that in a static fluorescence spectrum measured at 77 K, the amplitude of a major peak at 683 nm was significantly reduced and a red shoulder at 693 nm disappeared in PSII-GNP. Time-resolved fluorescence measurements showed that picosecond components at 683 nm decayed faster by factors of 1.4-2.1 in PSII-GNP than in free PSII, explaining the observed quenching of the major fluorescence peak. In addition, a nanosecond-decay component arising from a 'red chlorophyll' at 693 nm was lost in time-resolved fluorescence of PSII-GNP, probably due to a structural perturbation of this chlorophyll by interaction with GNP. Consistently with these fluorescence properties, degradation of PSII during strong-light illumination was two times slower in PSII-GNP than in free PSII. The enhanced durability of PSII is an advantageous property of the PSII-GNP conjugate in the development of an artificial photosynthesis device.

Conformational changes in inhibitory PAS domain protein associated with binding of HIF-1α and Bcl-xL in living cells

Inhibitory PAS domain protein (IPAS) is a dual function protein acting as a transcriptional repressor and as a pro-apoptotic protein. Simultaneous dual-color single-molecule imaging of EGFP-IPAS coexpressed with Mit-TagRFP-T in living HeLa cells revealed that fraction of EGFP-IPAS was arrested in the nucleus and on mitochondria. Transiently expressed Cerulean-IPAS in HEK293T cells was present in nuclear speckles when coexpressed with Citrine-HIF-1α or Citrine-HLF. Fluorescence lifetime imaging microscopy (FLIM) analysis of Citrine-IPAS-Cerulean in living CHO-K1 cells clarified the presence of intramolecular FRET. Reduced lifetimes of the donor were partially restored by coexpression of HIF-1α or Bcl-xL, binding proteins of IPAS in the nucleus and mitochondria, respectively. This alteration in lifetimes demonstrates that conformational changes occurred in IPAS by their binding.

Phase behavior of a binary fluid mixture of quadrupolar molecules

We propose a model molecule to investigate microscopic properties of a binary mixture with a closed-loop coexistence region. The molecule is comprised of a Lennard-Jones particle and a uniaxial quadrupole. Gibbs ensemble Monte Carlo simulations demonstrate that the high-density binary fluid of the molecules with the quadrupoles of the same magnitude but of the opposite signs can show closed-loop immiscibility. We find that an increase in the magnitude of the quadrupoles causes a shrinkage of the coexistence region. Molecular dynamics simulations also reveal that aggregates with two types of molecules arranged alternatively are formed in the stable one-phase region both above and below the coexistence region. String structures are dominant below the lower critical solution temperature, while branched aggregates are observed above the upper critical solution temperature. We conclude that the anisotropic interaction between the quadrupoles of the opposite signs plays a crucial role in controlling these properties of the phase behavior.

Structure-Based Modeling of Fluorescence Kinetics of Photosystem II: Relation between Its Dimeric Form and Photoregulation

A photosystem II-enriched membrane (PSII-em) consists of the PSII core complex (PSII-cc) which is surrounded by peripheral antenna complexes. PSII-cc consists of two core antenna (CP43 and CP47) and the reaction center (RC) complex. Time-resolved fluorescence spectra of a PSII-em were measured at 77 K. The data were globally analyzed with a new compartment model, which has a minimum number of compartments and is consistent with the structure of PSII-cc. The reliability of the model was investigated by fitting the data of different experimental conditions. From the analysis, the energy-transfer time constants from the peripheral antenna to CP47 and CP43 were estimated to be 20 and 35 ps, respectively. With an exponential time constant of 320 ps, the excitation energy was estimated to accumulate in the reddest chlorophyll (Red Chl), giving a 692 nm fluorescence peak. The excited state on the Red Chl was confirmed to be quenched upon the addition of an oxidant, as reported previously. The calculations based on the Förster theory predicted that the excitation energy on Chl29 is quenched by ChlZD1(+), which is a redox active but not involved in the electron-transfer chain, located in the D1 subunit of RC, in the other monomer with an exponential time constant of 75 ps. This quenching pathway is consistent with our structure-based simulation of PSII-cc, which assigned Chl29 as the Red Chl. On the other hand, the alternative interpretation assigning Chl26 as the Red Chl was not excluded. The excited Chl26 was predicted to be quenched by another redox active ChlZD2(+) in the D2 subunit of RC in the same monomer unit with an exponential time constant of 88 ps.

Development of a novel cryogenic microscope with numerical aperture of 0.9 and its application to photosynthesis research

A novel cryogenic optical-microscope system was developed in which the objective lens is set inside of the cryostat adiabatic vacuum space. Being isolated from the sample when it was cooled, the objective lens was maintained at room temperature during the cryogenic measurement. Therefore, the authors were able to use a color-aberration corrected objective lens with a numerical aperture of 0.9. The lens is equipped with an air vent for compatibility to the vacuum. The theoretically expected spatial resolutions of 0.39μm along the lateral direction and 1.3μm along the axial direction were achieved by the developed system. The system was applied to the observations of non-uniform distributions of the photosystems in the cells of a green alga, Chlamydomonas reinhardtii, at 94K. Gaussian decomposition analysis of the fluorescence spectra at all the pixels clearly demonstrated a non-uniform distribution of the two photosystems, as reflected in the variable ratios of the fluorescence intensities assigned to photosystem II and to those assigned to photosystem I. The system was also applied to the fluorescence spectroscopy of single isolated photosystem I complexes at 90K. The fluorescence, assigned to be emitted from a single photosystem I trimer, showed an intermittent fluctuation called blinking, which is typical for a fluorescence signal from a single molecule. The vibronic fluorescence bands at around 790nm were observed for single photosystem I trimers, suggesting that the color aberration is not serious up to the 800nm spectral region.

Picosecond dynamics of hydrogen bond rearrangements during phase separation of a triethylamine and water mixture

A picosecond temperature jump experiment reveals that phase separation in a liquid triethylamine (TEA)–water mixture started from hydrogen bond scission of TEA–water aggregates in TEA-rich regions and then in water-rich regions.

A silver nanowire-based tip suitable for STM tip-enhanced Raman scattering

A chemically synthesized silver nanowire was used for atomic-resolution STM imaging and tip-enhanced Raman scattering (TERS) spectroscopy, yielding excellent reproducibility.

Nano-scale characterization of binary self-assembled monolayers under an ambient condition with STM and TERS

Gold surfaces were modified by benzyl-mercaptan (BM) and then partly replaced with benzenethiol (BT), which formed binary self-assembled monolayers (SAM).

Additive-free size-controlled synthesis of gold square nanoplates using photochemical reaction in dynamic phase-separating media

Ultrafast phase separation of water and 2-butoxyethanol mixture was induced by nanosecond IR laser pulse irradiation. After a certain delay time, a UV laser pulse was introduced to induce photoreduction of aurate ions, which led to the formation of gold nanoparticles in dynamic phase-separating media. The structure and size of the nanoparticles varied depending on the delay time between the IR and UV pulses. For a delay time of 5 and 6 μs, gold square plates having edge lengths of 150 and 100 nm were selectively obtained, respectively. With a delay time of 3 μs, on the other hand, the size of the square plates varied widely from 100 nm to a few micrometers. The size of the gold square plates was also varied by varying the total irradiation time of the IR and UV pulses. The size distribution of the square plates obtained under different conditions suggests that the growth process of the square plates was affected by the size of the nanophases during phase separation. Electron diffraction patterns of the synthesized square plates showed that the square plates were highly crystalline with a Au(100) surface. These results showed that the nanophases formed during laser-induced phase separation can provide detergent-free reaction fields for size-controlled nanomaterial synthesis.

Dynamics of Volume Expansion of De-Mixing Liquids after Pulsed IR Heating

Triethylamine (TEA)–water mixtures have a critical-temperature (Tc). Below Tc the mixture exists as one phase and above Tc it exists in two phases. The de-mixed volume is different to the mixed volume. A nanosecond pulsed-laser heated a TEA–water mixture so that it de-mixed. The resulting dynamics of volume expansion were monitored using interferometry. For T-jumps within the one phase region the dynamics of volume change were limited by the speed of sound. However, T-jumps between the one and two phase regions also manifested a slower volume change associated with the de-mixing process. After 150 ns, the volume of the de-mixed TEA–water was consistent with the equilibrium volume change. This suggests that, within 150 ns, the system had split into phase-domains having equilibrium compositions of TEA and water. Subsequently the phase domains would simply merge and grow resulting in no further volume change to reduce surface tension between the phases.

Loose interaction between glyceraldehyde-3-phosphate dehydrogenase and phosphoglycerate kinase revealed by fluorescence resonance energy transfer-fluorescence lifetime imaging microscopy in living cells

Loose interaction between the glycolytic enzymes glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and phosphoglycerate kinase (PGK) was visualized in living CHO-K1 cells by fluorescence resonance energy transfer (FRET), using time-domain fluorescence lifetime imaging microscopy. FRET between active tetrameric subunits of GAPDH linked to cerulean or citrine was observed, and this FRET signal was significantly attenuated by coexpression of PGK. Also, direct interaction between GAPDH-citrine and PGK-cerulean was observed by FRET. The strength of FRET signals between them was dependent on linkers that connect GAPDH to citrine and PGK to cerulean. A coimmunoprecipitation assay using hemagglutinin-tagged GAPDH and FLAG-tagged PGK coexpressed in CHO-K1 cells supported the FRET observation. Taken together, these results demonstrate that a complex of GAPDH and PGK is formed in the cytoplasm of living cells.

Photo-controlled phase separation and mixing of a mixture of water and 2-butoxyethanol caused by photochromic isomerisation of spiropyran

Photo induced phase separation of a mixture of water and 2-butoxyethanol, in which spiropyran was dissolved as a photoresponsive molecule, was investigated. It was found that the phase separation temperature of the merocyanine (MC) form solution was higher than that of the spiropyrane (SP) form; therefore phase separation was induced by visible light irradiation to the solution which caused the photoisomerization from the MC form to the SP form. The system also exhibits reversible photoinduced phase mixing by irradiation of UV light. The photo-chemical phase separation was also induced by the nanosecond laser pulse irradiation and the dynamics of the phase domain growth were studied.

Transactivation activity of LBP-1 proteins and their dimerization in living cells

LBP-1 proteins form dimers and act as transcription factors that activate a number of genes related to cell growth and differentiation. LBP-1a and LBP-1c are localized in the cytoplasm when transiently expressed in cultured cells, but translocated into the nucleus after forming heterodimers with LBP-1b, which is a splicing variant of LBP-1a with an intrinsic nuclear localization signal (NLS). Here, we report that LBP-1b showed potent transactivation activity, and that forcibly expressed LBP-1a and LBP-1c in the nucleus essentially exhibited very little or no transactivation activity. Mutations in the NLS that abolished the NLS activity of LBP-1b also abrogated the transactivation activity. We have found that LBP-1 proteins contain a putative sterile alpha motif domain indispensable for their dimerization capability in the C-terminal region. To demonstrate whether homo- and heterodimers composed of LBP-1a and/or LBP-1c are generated in the nucleus, we applied the FLIM-based fluorescence resonance energy transfer imaging technique to living cells. It revealed that dimers composed of LBP-1a and LBP-1c were re-formed probably by a partner-exchange of LBP-1b-containing heterodimers.

Subdiffraction limited, remote excitation of surface enhanced Raman scattering

We demonstrate that focused laser excitation at the end of silver nanowires of 50-150 nm diameter excites SERS hot-spots at points of nanoparticle adsorption many micrometers along the wire due to the plasmon waveguide effect. The total SERS intensity detected at the hot-spots following wire-end excitation correlates with the known wavelength, polarization, and distance dependences of surface plasmon polariton (SPP) propagation in nanowires. The SERS spectra obtained at the hot-spots following wire-end excitation show very little background compared to when excitation occurs directly at the hot-spot, suggesting that a much smaller SERS excitation volume is achieved by remote, waveguide excitation. The ability to transfer SERS excitation over several micrometers, through a structure with a subdiffraction limit diameter, is discussed with respect to potential high-resolution SERS imaging applications.

Spin-phonon coupling in multiferroic YbMnO(3) studied by Raman scattering

Hexagonal YbMnO(3) bulk polycrystals were prepared and studied by Raman scattering in the temperature range of 15-300 K. A total of 15 phonon modes of A(1), E(1) and E(2) type were identified. Some E(2) phonon modes showed anomalous temperature variations in frequency at T(N)∼80 K, suggesting a coupling between the spin and phonon systems below T(N). As another evidence of spin-phonon coupling, softening of an A(1)-phonon mode for the O-Mn vibration was observed at ∼T(N). Substitution of Mn by Al suggests this view.

Raman scattering study of multiferroic Ho(3)Fe(5)O(12) thin films

Ho(3)Fe(5)O(12) crystallizes in a body-centered cubic lattice and shows no ferroelectricity because of its highly symmetric (centrosymmetric) crystal structure. However, in heteroepitaxially grown thin films, Ho(3)Fe(5)O(12) may exhibit ferroelectricity because of lattice strains induced by the substrate. In this work, heteroepitaxial films of Ho(3)Fe(5)O(12) were grown with different thicknesses of 50-160 nm and studied by x-ray diffraction and Raman scattering. The results were compared with those of bulk polycrystals to characterize residual strains. At room temperature, Raman spectra of films revealed a phonon frequency shift from those of bulk samples, showing lattice distortion. There was a difference in the lattice distortion scheme between the thinner and thicker films. Results of x-ray diffraction were well correlated with the Raman data. Raman measurements at 300-800 K showed the existence of lattice strain up to ∼650 K. This suggests a remanent-polarization character of Ho(3)Fe(5)O(12) films up to this temperature. Closeness between the magnetic ordering temperature T(N) = 567 K and T(C)∼650 K may bring us the ideal multiferroic material with an enhanced magnetoelectric effect at room temperature.

Time-resolved brewster angle microscopy for photochemical and photothermal studies on thin-films and monolayers

Transient events in thin films and interfaces have been studied using the technique of time resolved pump-probe nanosecond Brewster angle microscopy. For p-polarized light there is a minimum reflectivity at the Brewster angle. When the interface is viewed with light that is both incident and reflected at the Brewster angle the resulting image is dark. Subsequent small changes is refractive index will then cause an increase in the reflectivity in affected regions providing high contrast images of an altered interface with a dark background level. This is the basis of Brewster angle microscopy. In the present work two synchronized nanosecond pulsed lasers were used in the pump-probe configuration in order to induce changes at an air-liquid interface and to monitor the resulting morphology changes over a range of time delays from nanosecond to milliseconds after laser-excitation. This method can be used to observe morphological changes in phase altering thin-films and molecular monolayers. Further it can be used to obtain information about transient photochemistry even in optically thin materials and nano-films. In the current work the method is used to monitor laser induced processes in phase separating binary liquid mixtures as well as in monolayers of photo-responsive amphiphilic molecules derived from spiropyran on water. The two systems are quite different but provide valuable comparisons.

Chirp effect in hard X-ray generation from liquid target when irradiated by femtosecond pulses

The chirp effect on a X-ray emission intensity from a CsCl aqueous solution jet irradiated by femtosecond pulses was systematically studied. The p-polarized chirped pulses were more efficient as compared with the shortest pulses determined by the spectral bandwidth. The negatively-chirped pulses of approximately 240 fs duration produced up to 10 times larger X-ray intensity as compared with the transform-limited 160 fs pulses. The angular dependence of X-ray generation can be explained by the resonant absorption. Numerical simulations of electron density evolution due to the avalanche and multi-photon absorption supports qualitatively well the experimental observations.

What silicon nanocluster is most likely formed in etching experiments? Theoretical DFT study

Density functional calculations at the B3LYP/6-31G* level were performed for Si nanoclusters of ca. 1 nm in size. The structural, energetic, electronic as well as the estimated absorption spectra by the time-dependent DFT (TDDFT) calculations using varied functionals and basis sets for the representative cluster models are all in favor of the formation of most probable Si35H36 nanocluster in recent electrochemical etching experiments. The nanostructure has a complete H-termination at the borderline regions and lacks from the presence of any defects like surface Si-Si dimer units formed via self-healing of dangling Si-Si bonds or from any relatively short H...H contacts.

Observation of phonons in multiferroic BiFeO(3) single crystals by Raman scattering

We have grown BiFeO(3) bulk single crystals by a flux method and characterized the phonon spectra in detail by Raman scattering in the temperature range 4-1100 K. All the 13 Raman-active phonon modes predicted by group theory, 4A(1)+9E, were observed at low temperature and successfully assigned by a polarized Raman measurement. Moreover, drastic spectral changes in the Raman spectra were observed at temperatures 600-700 K and 1000-1100 K. These features are discussed from the viewpoint of phonon coupling with the magnetic ordering and the structural phase transition, respectively.

Raman scattering studies on multiferroic YMnO(3)

YMnO(3) is a multiferroic material in which ferroelectric and antiferromagnetic ordering can coexist. We have studied a YMnO(3) bulk crystal in detail by Raman scattering in a wide temperature range of 15-1200 K, with comparison to a previous experiment at room temperature and a theoretical prediction for Raman-active phonon modes. In the low-temperature ferroelectric phase, the observed phonon spectra showed anomalous temperature variation at the Néel temperature, T(N)∼80 K, suggesting a coupling between the spin and phonon systems below T(N). Furthermore, spectra for the high-temperature paraelectric phase, reported here for the first time, showed a sudden change at the Curie temperature T(C)>900 K, suggesting an abrupt structural phase change from the ferroelectric to the paraelectric phase.

Theoretical DFT Study on the Interaction of NO and Br2 with the Pt(111) Surface

Density functional calculations were performed at the B3LYP level using combined basis sets for the NO and bromine interactions with the Pt(111) surface mimicked by the two-layer Pt10 cluster model. It explains well an attractive bonding interaction not only for bromine and Pt(111) but also for all three adsorption modes of NO on the Pt(111) surface. In accordance with the experimental observations, the calculations predict that the first peak in the IR spectra appears at around 1515 cm(-)(1) at the initial stage of low NO coverage, while it would shift to 1707 cm(-)(1) at high NO coverage. The bonding of NO on the 3-fold hollow fcc and hcp sites of Pt(111) proceeds via predominant back-donation interactions, while for the on-top adsorption, both the donation and back-donation interactions become equally important. Energetic criteria show also that the STM tip (made from Pt and Ir alloys) immersed into a bromine solution may contain only dissociated bromine atoms that bind strongly with the surface Pt atoms. As a result, the νBrBr stretching vibration mode for the bromine molecule may not be seen in the IR spectra because of its dissociation into adsorbed atoms. This leads to an appearance of a blue shifted band centered at ca. 202 cm(-)(1).

Experimentally determined growth exponents during the late stage of spinodal demixing in binary liquid mixtures

Spinodal demixing was initiated in two systems, with critical and off-critical compositions, using nanosecond pulsed laser-induced temperature jumps (T-jumps) of various magnitude. In this way, deep quenches could be imposed on the systems. One system was the simple triethylamine (TEA)/water mixture and the other was the ionic mixture of 2-butoxyethanol (2BE)/water/KCl. The demixing process was followed using the technique of nanosecond time-resolved microscopic shadowgraphy. The growth of the evolving phase-separated domains followed a simple power law with respect to time in every case. For a given composition, the magnitude of the T-jump had little effect on the growth exponent, however the composition was found to influence the rate of domain growth. At off-critical mole fractions of 0.2 with respect to TEA, the domains grew according to the following expression: L(t)=t(0.70) (where L(t)= the domain size) whereas at the critical TEA mole fraction of 0.08 the domains grew as L(t)=t(0.52). 2BE/water/KCl mixtures quenched at the just off-critical composition of fraction with respect to 2BE evolved as L(t)=t(0.63). These results will be compared to theoretical models and simulations and discussed in terms of estimated Reynolds numbers as well as the consumption and conversion of the available surface energy that fuels the demixing process.

Application of time- and space-resolved fluorescence spectroscopy to the distribution of guest species into micrometer-sized zeolite crystals

We measured the fluorescence decays and spectra of perylene adsorbed from solution into zeolite X crystals of 2-3 microm in diameter at the level of individual crystals by the application of a microscopy method coupled with a single photon counting apparatus and a multichannel spectrophotometer. We found that both decays and spectra are particle-dependent, i.e. a particle-to-particle difference was observed for the fluorescence decay curves at a fixed loading level along with a particle-dependent spectral change due to the various contribution of excimer emission band relative to those of three monomers. These findings are due to a non-homogeneous distribution which is confirmed by the various emission intensities of perylene-loaded zeolite crystals observed by fluorescence microscopy. Previously, a homogeneous distribution of the guest between zeolite crystals has been just taken for granted and not justified by experiment. The present result suggests that commonly employed collective measurements such as UV-VIS absorption and emission spectroscopies, IR and Raman spectroscopies, and NMR of bulk zeolite powders provide only averaged results and may sometimes suffer from acquiring precise molecular level pictures.

Structure−Property Correlation of CdSe Clusters Using Experimental Results and First-Principles DFT Calculations

Structures and properties of CdSe quantum dots (clusters) up to a diameter of approximately 2 nm were investigated by combining experimental absorption, photoluminescence (PL), and X-ray diffraction (XRD) spectroscopies as well as ab initio DFT calculations. These CdSe clusters were nucleated and grown from solutions containing respective cadmium and selenium precursors following the hot-injection technique that allows one to obtain size-controlled CdSe clusters having PL efficiency up to 0.5. The DFT calculations were performed at the B3LYP/Lanl2dz level and followed by time-dependent TDDFT calculations to estimate n energy singlet transitions. On the basis of the results of these experimental and theoretical studies, an approach to determine whether the proposed cluster with a mean diameter of approximately 2 nm is more physically reasonable is discussed. It was shown that the minimum nucleus of a CdSe cluster consists of (CdSe)(3) with a six-membered ring and planar structure. No PL is observed for this structure. The formation of the next stable cluster depends on whether hexadecylamine (HDA) was used for the growth of the CdSe clusters. In the absence of HDA, the second cluster was found to be (CdSe)(6) characterized by a broad PL spectrum, while in the presence of HDA, it was found to be (CdSe)(n) (where n > or = 14) with a sharp PL spectrum.

Image Contrast Analysis of STM Images of Self-Assembled Dioctadecyl Chalcogenides on Graphite at the Liquid-Solid Interface

The structures of self-assembled monolayers of dioctadecyl selenide (CH3(CH2)17)2Se and dioctadecyl telluride (CH3(CH2)17)2Te, as well as dioctadecyl ether (CH3(CH2)17)2O and dioctadecyl sulfide (CH3(CH2)17)2S, on graphite at the liquid-solid interface were systematically investigated by scanning tunneling microscopy (STM). Both dioctadecyl selenide and telluride formed monolayer structures in which the tilt angle between the molecular axis of the alkyl chain and the lamellae axis was 90 degrees , while dioctadecyl ether assembled with a tilt angle of 60 degrees . Dioctadecyl sulfide was found to make two different self-assembled structures having tilt angles of 60 and 90 degrees . When selenide was embedded in ether compounds in mixed self-assembled monolayers, the alkyl chains of the selenide became blurred, implying that the alkyl chains in the monolayers were unstable. This is in contrast with the structure of co-adsorbed monolayers of the ether and sulfide compounds, where the images of all alkyl chains had high spatial resolution. For the co-adsorbed monolayers, the image contrast of chalcogen atoms was normalized compared with that of alkyl chains of the ether compound in the same image frame. The normalized image contrast was found to be independent of the measurement conditions involving tip shapes, having the following trend, Te>Se>S>C>O. The difference in the normalized image contrast among chalcogen atoms are discussed based on fundamental parameters like polarizability and atomic radii.

Density Changes Accompanying Wave Propagation in the Cerium-Catalyzed Belousov−Zhabotinsky Reaction

Refractive index measurement using an interferometric imaging system and observation of chemical wave shapes were carried out during chemical wave propagation of a cerium-catalyzed Belousov-Zhabotinsky (BZ) reaction. Densities increased as chemical waves propagated in samples without NaBr, and decreased in samples with NaBr. Concentration changes of malonic acid, bromomalonic acid, and BrO3- were estimated from Raman spectral measurements in a stirred batch BZ reaction, and these also exhibited differences between samples with and without NaBr. It is proposed that a reaction subset yielding low molecular weight carboxylic acids is predominant in samples with NaBr, whereas a pathway leading to dibromoacetic acid or tribromoacetic acid production is the major process in samples without NaBr.

Dynamics of Re(2,2'-bipyridine)(CO)3Cl MLCT formation and decay after picosecond pulsed X-ray excitation and femtosecond UV excitation

The dynamics of Re(2,2'-bipyridine)(CO)3Cl MLCT state formation and decay were determined after femtosecond UV laser excitation and picosecond pulsed X-ray excitation, in an N,N-dimethylformamide (DMF) solution as well as in its solid form. At room temperature, after UV excitation, this MLCT excited state emits both in DMF solution and in the solid form. Transient absorption spectra were measured in solution at various delay times following excitation by a 160 fs, 390 nm laser pulse. There was a prompt absorption increase at around 460 nm occurring within the pump probe convolution (<1 ps), which was assigned to the formation of the 3MLCT state. This transient absorbance was constant over 100 ps. In contrast to the solution state, in the solid state, the emission maximum slightly red-shifts with increasing time after laser excitation. In both solid and solution the emission rises within the system response time. The solid sample exhibited a 1.4 ns emission decay that was not observed for the solution sample. The emission rise from a solid sample after 20 ps pulsed X-ray excitation was significantly slower than the system's time resolution. It is proposed that kinetically energetic electrons are ejected following X-ray induced ionisation, creating ionised tracks in which energetic cations and electrons take time to recombine yielding delayed 3MLCT states that emit.