Gas-phase Förster resonance energy transfer in mass-selected ions with methylene or peptide linkers between two dyes: a concerted dance of charges.

Förster Resonance Energy Transfer (FRET) between a photoexcited and a ground-state dye is dictated by how far apart the two dyes are compared to the Förster distance. While there is a significant number of studies on the process for biomacromolecules in solution, there are only a few reports on gas-phase FRET. Here we report on a simple gas-phase model system, synthesized with the rhodamine 575 (R575+) and rhodamine 640 (R640+) FRET pair and a covalent linker with four methylenes, R575+-(CH2)4-R640+. Each dye carries a positive charge which allows for mass-spectroscopy experiments. We have recorded gas-phase dispersed fluorescence spectra of the mass-selected dications excited at different wavelengths using the homebuilt LUNA (LUminescence iNstrument in Aarhus) setup and find in all cases that emission is exclusively from the R640+ acceptor dye. The linker does not interfere electronically with the dyes and simply acts as a spacer. We can therefore establish the direct effect of the interaction between the two dyes when it comes to emission band maximum. Indeed, we find that R640+ experiences a significant shift in its maximum from 560 ± 1 nm for the monomer cation to 577 ± 2 nm in the presence of R575+, independent of initial excitation of R575+ or R640+. This redshift is ascribed to the large polarizability along the long axis of the xanthene core structure, and that this polarizability is larger in the excited state than in the ground state. Experiments were also done on a triply charged 11-mer peptide labelled with the same two dyes, R575+-(Gly-Gln)5-Lys-R640+ + H+ (Gly = glycine, Gln = glutamine, and Lys = lysine) where the extra positive charge is located on the peptide. Again a redshifted emission spectrum of the donor is observed with maximum at 582 ± 2 nm. Our work clearly demonstrates strong sensitivity of the photophysics of one dye to the nearby environment, and that caution is needed when using the energy transfer efficiency to infer dye-dye separations in gas-phase experiments.

Dissolved Gaseous Mercury Production at a Marine Aquaculture Site in the Mercury-Contaminated Marano and Grado Lagoon, Italy.

Dissolved gaseous mercury (DGM) production was examined in relation to ultraviolet radiation within a marine aquaculture site in the contaminated Marano and Grado Lagoon (Italy). The measured rates of DGM production relative to time elapsed (17.06 and 20.68 pg h-1, respectively) were substantially (6-20 times) higher than what has been observed in other marine Hg studies. We measured similar levels of DGM relative to dissolved total mercury (THgD) (0.84%-8.91%) at these sites in comparison to uncontaminated marine sites, however relative to other moderately-contaminated marine sites in Portugal the % DGM/THgD was high. These results suggest a substantial capacity for Hg volatilization from these highly contaminated lagoons to the atmosphere due to photoreduction mechanisms.

Effects of climate warming on photosynthesis in boreal tree species depend on soil moisture.

Climate warming will influence photosynthesis via thermal effects and by altering soil moisture1-11. Both effects may be important for the vast areas of global forests that fluctuate between periods when cool temperatures limit photosynthesis and periods when soil moisture may be limiting to carbon gain4-6,9-11. Here we show that the effects of climate warming flip from positive to negative as southern boreal forests transition from rainy to modestly dry periods during the growing season. In a three-year open-air warming experiment with juveniles of 11 temperate and boreal tree species, an increase of 3.4 °C in temperature increased light-saturated net photosynthesis and leaf diffusive conductance on average on the one-third of days with the wettest soils. In all 11 species, leaf diffusive conductance and, as a result, light-saturated net photosynthesis decreased during dry spells, and did so more sharply in warmed plants than in plants at ambient temperatures. Consequently, across the 11 species, warming reduced light-saturated net photosynthesis on the two-thirds of days with driest soils. Thus, low soil moisture may reduce, or even reverse, the potential benefits of climate warming on photosynthesis in mesic, seasonally cold environments, both during drought and in regularly occurring, modestly dry periods during the growing season.

Highly selective transformation of ammonia nitrogen to N2 based on a novel solar-driven photoelectrocatalytic-chlorine radical reactions system.

A highly selective method for transforming ammonia nitrogen to N2 was proposed, based on a novel solar-driven photoelectrocatalytic-chlorine radical reactions (PEC-chlorine) system. The PEC-chlorine system was facilitated by a visible light response WO3 nanoplate array (NPA) electrode in an ammonia solution containing chloride ions (Cl-). Under illumination, photoholes from WO3 promote the oxidation of Cl- to chlorine radical (Cl). This radical can selectively transform ammonia nitrogen to N2 (79.9%) and NO3- (19.2%), similar to the breakpoint chlorination reaction. The ammonia nitrogen removal efficiency increased from 10.6% (PEC without Cl-) to 99.9% with the PEC-chlorine system within 90 min operation, which can be attributed to the cyclic reactions between Cl-/Cl and the reaction intermediates (NH2, NHCl, etc.) that expand the degradation reactions from the surface of the electrodes to the whole solution system. Moreover, Cl is the main radical species contributing to the transformation of ammonia nitrogen to N2, which is confirmed by the tBuOH capture experiment. Compared to conventional breakpoint chlorination, the PEC-chlorine system is a more economical and efficient means for ammonia nitrogen degradation because of the fast removal rate, no additional chlorine cost, and its use of clean energy (since it is solar-driven).

Photophysical behavior of a potential drug candidate, trans-[2-(4-methoxystyryl)]quinoline-1-oxide tuned by environment effects.

Styryl and/or quinoline structural fragments, present in a large number of bioactive substances, inspired the design of various new drug candidates. In this paper, we describe the photophysical behavior of trans-[2-(4-methoxystyryl)]quinoline-1-oxide (trans-MSQNO) on the basis of X-ray analysis data, theoretical calculations as well as steady state and time-resolved spectroscopy experiments in various media. The molecule crystallizes in orthorhombic unit cell containing eight molecules of N-oxide, space group Pbca. The NO bond is substantially shorter in comparison with the NO bond in the ZnTPP unit [1.3052(11) Å vs. 1.335(2) Å]. Variation of emission colors from the violet (~450nm) through blue (480nm), green (525nm) and yellow (575nm) is observed in different environments. Comparable values of lifetimes estimated both at ambient temperature and at 77K suggest that excited state dynamics in this case is viscosity independent. DFT and TD DFT B3LYP/6-31G(d, p) calculations performed for four different trans-MSQNO rotamers in the gas phase, as well as nonpolar and polar media (PCM model) suggest that an equilibrium between them can be significantly altered even by a relatively weak interactions with the environment. It is suggested that varying intensity ratios of experimental absorption bands in different media may be due to the dominant share of one or more rotamers of the excited trans-MSQNO molecule. Gas phase calculations show also that the vertical ππ*, S0→S1, transition resulting from the HOMO→LUMO electronic configuration exhibits only a partial CT nature. On the other hand, in polar media, a substantial increment of excited state dipole moment of all rotamers compared to the ground state, its increase with increasing solvent polarity and a significant red shift in the absorption and emission spectra, point to the enhanced CT nature of the S1 excited state. Hence, the trans-MSQNO molecule may be considered a subsequent styrylquinoline drug candidate where the CT drug-receptor interactions are of a high importance.

Loss of gas from echogenic liposomes exposed to pulsed ultrasound.

The destruction of echogenic liposomes (ELIP) in response to pulsed ultrasound excitations has been studied acoustically previously. However, the mechanism underlying the loss of echogenicity due to cavitation nucleated by ELIP has not been fully clarified. In this study, an ultra-high speed imaging approach was employed to observe the destruction phenomena of single ELIP exposed to ultrasound bursts at a center frequency of 6 MHz. We observed a rapid size reduction during the ultrasound excitation in 139 out of 397 (35%) ultra- high-speed recordings. The shell dilation rate, which is defined as the microbubble wall velocity divided by the instantaneous radius, [Formula: see text] /R, was extracted from the radius versus time response of each ELIP, and was found to be correlated with the deflation. Fragmentation and surface mode vibrations were also observed and are shown to depend on the applied acoustic pressure and initial radius. Results from this study can be utilized to optimize the theranostic application of ELIP, e.g. by tuning the size distribution or the excitation frequency.

Evaluating dispersion forces for optimization of van der Waals complexes using a non-empirical functional.

Modelling dispersion interactions with traditional density functional theory (DFT) is a challenge that has been extensively addressed in the past decade. The exchange-dipole moment (XDM), among others, is a non-empirical add-on dispersion correction model in DFT. The functional PW86+PBE+XDM for exchange, correlation and dispersion, respectively, compromises an accurate functional for thermochemistry and for van der Waals (vdW) complexes at equilibrium and non-equilibrium geometries. To use this functional in optimizing vdW complexes, rather than computing single point energies, it is necessary to evaluate accurate forces. The purpose of this paper is to validate that, along the potential energy surface, the distance at which the energy is minimum is commensurate with the distance at which the forces vanish to zero. This test was validated for 10 rare gas diatomic molecules using various integration grids and different convergence criteria. It was found that the use of either convergence criterion, 10-6 or 10-8, in Gaussian09, does not affect the accuracy of computed optimal distances and binding energies. An ultra-fine grid needs to be used when computing accurate energies using generalized gradient approximation functionals.This article is part of the themed issue 'Multiscale modelling at the physics-chemistry-biology interface'.

Microwave-activated nanodroplet vaporization for highly efficient tumor ablation with real-time monitoring performance.

The fast development of nanotechnology has provided a new efficient strategy for enhancing the therapeutic efficiency of various treatment modalities against cancer. However, the improvement of minimally invasive microwave therapy based on nanomaterials has not been realized. In this work, we successfully designed and synthesized a novel folate-targeted nanodroplet (TPN) with a composite mixture of perfluorocarbons as the core and lipid as the shell, which exerts the distinctive dual functions as the adjuvant for highly efficient percutaneous ultrasound imaging-guided microwave ablation (MWA) of tumors. Based on the unique phase-changeable performance of TPN nanosystem, a novel microwave-droplet vaporization (MWDV) strategy was proposed, for the first time, to overcome the critical issues of traditional acoustic-droplet vaporization (ADV) and optical-droplet vaporization (ODV) for cancer theranostics. Especially, the elaborately designed TPN can overcome the challenges of indistinct imaging of ablation margin and the limited ablation zone of MWA modality against cancer. The high efficiency of this new MWDV strategy has been systematically elucidated in vitro, ex vivo and in vivo. Therefore, such a successful demonstration of the role of nanomaterials (TPN in this case) in ultrasound imaging-guided MWA therapy against cancer provides a highly feasible strategy to effectively enhance the MWA outcome with the specific features of high efficiency and biosafety.

Growth and Properties of Cl- Incorporated ZnO Nanofilms Grown by Ultrasonic Spray-Assisted Chemical Vapor Deposition.

Pure and Cl- incorporated ZnO nanofilms were grown by the ultrasonic spray-assisted chemical vapor deposition (CVD) method. The properties of the nanofilms were investigated. The effects of growth temperature and Cl- concentration on the crystal structure, morphology, and optical properties of the nanofilms were studied. Temperature plays an important role in the growth mode and morphology of the pure nanofilms. Preferential growth along the c-axis occurs only at modulating temperature. Lower temperature suppresses the preferential growth, and higher temperature suppresses the growth of the nanofilms. The morphologies of the nanofilms change from lamellar and spherical structures into hexagonal platelets, then into separated nanoparticles with an increase in the temperature. Incorporating Cl- results in the lattice contracting gradually along with c-axis. Grains composing the nanofilms refine, and the optical gap broadens with increasing of Cl- concentration in growth precursor. Incorporating Cl- could reduce oxygen vacancies and passivate the non-irradiated centers, thus enhancing the UV emission and suppressing the visible emission of ZnO nanofilms.

Acoustic Cavitation Enhances Focused Ultrasound Ablation with Phase-Shift Inorganic Perfluorohexane Nanoemulsions: An In Vitro Study Using a Clinical Device.

Purpose. To investigate whether acoustic cavitation could increase the evaporation of a phase-shift inorganic perfluorohexane (PFH) nanoemulsion and enhance high intensity focused ultrasound (HIFU) ablation. Materials and Methods. PFH was encapsulated by mesoporous silica nanocapsule (MSNC) to form a nanometer-sized droplet (MSNC-PFH). It was added to a tissue-mimicking phantom, whereas phosphate buffered saline (PBS) was added as a control (PBS-control). HIFU (P ac = 150 W, t = 5/10 s) exposures were performed in both phantoms with various duty cycles (DC). US images, temperature, and cavitation emissions were recorded during HIFU exposure. HIFU-induced lesions were measured and calculated. Results. Compared to PBS-control, MSNC-PFH nanoemulsion could significantly increase the volume of HIFU-induced lesion (P < 0.01). Peak temperatures were 78.16 ± 5.64°C at a DC of 100%, 70.17 ± 6.43°C at 10%, 53.17 ± 4.54°C at 5%, and 42.00 ± 5.55°C at 2%, respectively. Inertial cavitation was much stronger in the pulsed-HIFU than that in the continuous-wave HIFU exposure. Compared to 100%-DC exposure, the mean volume of lesion induced by 5 s exposure at 10%-DC was significantly larger, but smaller at 2%-DC. Conclusions. MSNC-PFH nanoemulsion can significantly enhance HIFU ablation. Appropriate pulsed-HIFU exposure could significantly increase the volume of lesion and reduce total US energy required for HIFU ablation.

Infrared Laser Activation of Soluble and Membrane Protein Assemblies in the Gas Phase.

Collision-induced dissociation (CID) is the dominant method for probing intact macromolecular complexes in the gas phase by means of mass spectrometry (MS). The energy obtained from collisional activation is dependent on the charge state of the ion and the pressures and potentials within the instrument: these factors limit CID capability. Activation by infrared (IR) laser radiation offers an attractive alternative as the radiation energy absorbed by the ions is charge-state-independent and the intensity and time scale of activation is controlled by a laser source external to the mass spectrometer. Here we implement and apply IR activation, in different irradiation regimes, to study both soluble and membrane protein assemblies. We show that IR activation using high-intensity pulsed lasers is faster than collisional and radiative cooling and requires much lower energy than continuous IR irradiation. We demonstrate that IR activation is an effective means for studying membrane protein assemblies, and liberate an intact V-type ATPase complex from detergent micelles, a result that cannot be achieved by means of CID using standard collision energies. Notably, we find that IR activation can be sufficiently soft to retain specific lipids bound to the complex. We further demonstrate that, by applying a combination of collisional activation, mass selection, and IR activation of the liberated complex, we can elucidate subunit stoichiometry and the masses of specifically bound lipids in a single MS experiment.

Acoustic Cluster Therapy: In Vitro and Ex Vivo Measurement of Activated Bubble Size Distribution and Temporal Dynamics.

Acoustic cluster technology (ACT) is a two-component, microparticle formulation platform being developed for ultrasound-mediated drug delivery. Sonazoid microbubbles, which have a negative surface charge, are mixed with micron-sized perfluoromethylcyclopentane droplets stabilized with a positively charged surface membrane to form microbubble/microdroplet clusters. On exposure to ultrasound, the oil undergoes a phase change to the gaseous state, generating 20- to 40-µm ACT bubbles. An acoustic transmission technique is used to measure absorption and velocity dispersion of the ACT bubbles. An inversion technique computes bubble size population with temporal resolution of seconds. Bubble populations are measured both in vitro and in vivo after activation within the cardiac chambers of a dog model, with catheter-based flow through an extracorporeal measurement flow chamber. Volume-weighted mean diameter in arterial blood after activation in the left ventricle was 22 µm, with no bubbles >44 µm in diameter. After intravenous administration, 24.4% of the oil is activated in the cardiac chambers.

Image-Guided Ultrasound Characterization of Volatile Sub-Micron Phase-Shift Droplets in the 20-40 MHz Frequency Range.

Phase-shift perfluorocarbon droplets are designed to convert from the liquid to the gas state by the external application of acoustic or optical energy. Although droplet vaporization has been investigated extensively at ultrasonic frequencies between 1 and 10 MHz, few studies have characterized performance at the higher frequencies commonly used in small animal imaging. In this study, we use standard B-mode imaging sequences on a pre-clinical ultrasound platform to both image and activate sub-micron decafluorobutane droplet populations in vitro and in vivo at center frequencies in the range of 20-40 MHz. Results show that droplets remain stable against vaporization at low imaging pressures but are vaporized at peak negative pressures near 3.5 MPa at the three frequencies tested. This study also found that a small number of size outliers present in the distribution can greatly influence droplet performance. Removal of these outliers results in a more accurate assessment of the vaporization threshold and produces free-flowing microbubbles upon vaporization in the mouse kidney.

Dynamic Behavior of Microbubbles during Long Ultrasound Tone-Burst Excitation: Mechanistic Insights into Ultrasound-Microbubble Mediated Therapeutics Using High-Speed Imaging and Cavitation Detection.

Ultrasound (US)-microbubble (MB)-mediated therapies have been found to restore perfusion and enhance drug/gene delivery. On the presumption that MBs do not persist during long US exposure under high acoustic pressures, most schemes use short US pulses when a high US pressure is employed. However, we recently observed an enhanced thrombolytic effect using long US pulses at high acoustic pressures. Therefore, we explored the fate of MBs during long tone-burst exposures (5 ms) at various acoustic pressures and MB concentrations via direct high-speed optical observation and passive cavitation detection. MBs first underwent stable or inertial cavitation depending on the acoustic pressure and then formed gas-filled clusters that continued to oscillate, break up and form new clusters. Cavitation detection confirmed continued, albeit diminishing, acoustic activity throughout the 5-ms US excitation. These data suggest that persisting cavitation activity during long tone bursts may confer additional therapeutic effects.

MR-based detection of individual histotripsy bubble clouds formed in tissues and phantoms.

PURPOSE: To demonstrate that MR sequences can detect individual histotripsy bubble clouds formed inside intact tissues. METHODS: A line-scan and an EPI sequence were sensitized to histotripsy by inserting a bipolar gradient whose lobes bracketed the lifespan of a histotripsy bubble cloud. Using a 7 Tesla, small-bore scanner, these sequences monitored histotripsy clouds formed in an agar phantom and in vitro porcine liver and brain. The bipolar gradients were adjusted to apply phase with k-space frequencies of 10, 300 or 400 cm-1 . Acoustic pressure amplitude was also varied. Cavitation was simultaneously monitored using a passive cavitation detection system. RESULTS: Each image captured local signal loss specific to an individual bubble cloud. In the agar phantom, this signal loss appeared only when the transducer output exceeded the cavitation threshold pressure. In tissues, bubble clouds were immediately detected when the gradients created phase with k-space frequencies of 300 and 400 cm-1 . When the gradients created phase with a k-space frequency of 10 cm-1 , individual bubble clouds were not detectable until many acoustic pulses had been applied to the tissue. CONCLUSION: Cavitation-sensitive MR-sequences can detect single histotripsy bubble clouds formed in biologic tissue. Detection is influenced by the sensitizing gradients and treatment history. Magn Reson Med 76:1486-1493, 2016. © 2015 International Society for Magnetic Resonance in Medicine.

Acoustic signal characteristics of laser induced cavitation in DDFP droplet: Spectrum and time-frequency analysis.

Cavitation has great application potential in microvessel damage and targeted drug delivery. Concerning cavitation, droplet vaporization has been widely investigated in vitro and in vivo with plasmonic nanoparticles. Droplets with a liquid dodecafluoropentane (DDFP) core enclosed in an albumin shell have a stable and simple structure with good characteristics of laser absorbing; thus, DDFP droplets could be an effective aim for laser-induced cavitation. The DDPF droplet was prepared and perfused in a mimic microvessel in the optical microscopic system with a passive acoustic detection module. Three patterns of laser-induced cavitation in the droplets were observed. The emitted acoustic signals showed specific spectrum components at specific time points. It was suggested that a nanosecond laser pulse could induce cavitation in DDPF droplets, and specific acoustic signals would be emitted. Analyzing its characteristics could aid in monitoring the laser-induced cavitation process in droplets, which is meaningful to theranostic application.

Photoinduced intermolecular cross-linking of gas phase triacylglycerol lipid ions.

Complex mixtures of plant derived triglycerol (TG) lipids are commonly used as feedstock components for the production of industrial polymers. However, there remains a need for the development of analytical strategies to investigate the intrinsic intermolecular cross-linking reactivity of individual TG molecules within these mixtures as a function of their structures and physicochemical properties, and for the characterization of the resultant products. Here, to address this need, we describe a novel multistage tandem mass spectrometry based method for intermolecular cross-linking and subsequent structural characterization of TG lipid ions in the gas phase. Cross-linking reactions were initiated using 266 nm ultraviolet photodissociation tandem mass spectrometry (UVPD-MS/MS) of saturated or unsaturated TG dimers introduced via electrospray ionization into a linear ion trap mass spectrometer as noncovalent complexes with protonated 3,4-, 2,4- or 3,5- diiodoaniline (diIA). UVPD resulted in the initial formation of an anilinyl biradical via the sequential loss of two iodine radicals, which underwent further reaction to yield multiple cross-linked TG products along with competing noncross-linking processes. These chemistries are proposed to occur via sequential combinations of hydrogen abstraction (H-abstraction), radical addition and radical recombination. Multistage collision induced dissociation tandem mass spectrometry (CID-MS(n)) was used to obtain evidence for the structures and mechanisms of formation for these products, as a function of both the TG lipid and diIA ion structures. The efficiency of the UVPD reaction was shown to be dependent on the number of unsaturation sites present within the TG lipids. However, when unsaturation sites were present, formation of the cross-linked and noncross-linked product ions via H-abstraction and radical addition mechanisms was found to be competitive. Finally, the identity of the anilinyl biradical (e.g., 3,4- versus 2,4-substituted) was found to significantly affect the distribution of these two types of product ions. Importantly, owing to the observed propensity for cross-linking to occur via H-abstraction-initiated processes, this novel gas-phase cross-linking reaction provides a convenient method to link two molecules covalently without the requirement of any specific functional group, and therefore could be applied to examine the gas-phase intermolecular interactions and cross-linking of a wide range of biomolecular classes.

Spectroscopic Properties of Naphthalene on the Surface of Ice Grains Revisited: A Combined Experimental-Computational Approach.

An experimental-computational method is used to investigate the spectroscopic behavior of naphthalene on the surface of ice grains. UV-vis diffuse reflectance and fluorescence spectroscopies of naphthalene combined with DFT and ADC(2) calculations provide evidence for the occurrence of excited-state associates. The measured and calculated bathochromic shifts of the S0 → S1 electronic transitions related to naphthalene dimers or naphthalene-ice interactions do not exceed 3 nm. The bands observed in the emission spectrum of frozen naphthalene solutions are assigned to excited dimers of different mutual orientations, naphthalene phosphorescence, and fluorescence of anthracene present as a trace impurity and populated by the energy transfer from excited naphthalene. Photochemical reactivity in/on ice and snow is dependent on the absorption properties and speciation of the compounds present in these media. Hence, within this study, we exploit frozen solutions of naphthalene to demonstrate both the absence of considerable bathochromic shift and a strong tendency to aggregate.

Gas-phase study on uridine: Conformation and X-ray photofragmentation.

Fragmentation of RNA nucleoside uridine, induced by carbon 1s core ionization, has been studied. The measurements by combined electron and ion spectroscopy have been performed in gas phase utilizing synchrotron radiation. As uridine is a combination of d-ribose and uracil, which have been studied earlier with the same method, this study also considers the effect of chemical environment and the relevant functional groups. Furthermore, since in core ionization the initial core hole is always highly localized, charge migration prior to fragmentation has been studied here. This study also demonstrates the destructive nature of core ionization as in most cases the C 1s ionization of uridine leads to concerted explosions producing only small fragments with masses ≤43 amu. In addition to fragmentation patterns, we found out that upon evaporation the sugar part of the uridine molecule attains hexagonal form.