Identification of 1 distinct pH- and zeaxanthin-dependent quenching in LHCSR3 from chlamydomonas reinhardtii

Under high light, oxygenic photosynthetic organisms avoid photodamage by thermally dissipating absorbed energy, which is called non-photochemical quenching. In green algae, a chlorophyll and carotenoid-binding protein, light-harvesting complex stress17 related (LHCSR3), detects excess energy via a pH drop and serves as a quenching site. Using a combined in vivo and in vitro approach, we investigated quenching within LHCSR3 from Chlamydomonas reinhardtii. In vitro two distinct quenching processes, individually controlled by pH and zeaxanthin, were identified within LHCSR3. The pH21 dependent quenching was removed within a mutant LHCSR3 that lacks the residues that are protonated to sense the pH drop. Observation of quenching in zeaxanthin-enriched LHCSR3 even at neutral pH demonstrated zeaxanthin-dependent quenching, which also occurs in other light-harvesting complexes. Either pH- or zeaxanthin-dependent quenching prevented the formation of damaging reactive oxygen species, and thus the two quenching processes may together provide different induction and recovery kinetics for photoprotection in a changing environment.Human Frontier Science Program (Strasbourg, France) (Grant RGY0076)National Science Foundation (U.S.) (Grant HE-1740645

H/L Chondrite Lapaz Icefield 031047 - A Feather Of Icarus?

Antarctic meteorite LAP 031047 is an ordinary chondrite composed of loosely consolidated chondritic fragments. Its petrography, oxygen isotopic composition and geochemical inventory are ambiguous and indicate an intermediate character between H and L chondrites. Petrographic indicators suggest LAP 031047 suffered a shock metamorphic overprint below ∼10 GPa, which did not destroy its unusually high porosity of ∼27 vol%. Metallographic textures in LAP 031047 indicate heating above ∼700. °C and subsequent cooling, which caused massive transformation of taenite to kamacite. The depletion of thermally labile trace elements, the crystallization of chondritic glass to microcrystalline plagioclase of unusual composition, and the occurrence of coarsely crystallized chondrule fragments is further evidence for post-metamorphic heating to ∼700-750. °C. However, this heating event had a transient character because olivine and low-Ca pyroxene did not equilibrate. Nearly complete degassing up to very high temperatures is indicated by the thorough resetting of LAP 031047\u27s Ar-Ar reservoir ∼100 ± 55 Ma ago. A noble gas cosmic-ray exposure age indicates it was reduced to a meter-size fragment at \u3c0.5. Ma. In light of the fact that shock heating cannot account for the thermal history of LAP 031047 in its entirety, we test the hypothesis that this meteorite belonged to the near-surface of an Aten or Apollo asteroid that underwent heating during orbital passages close to the Sun. © 2011 Elsevier Ltd

Polycation Interactions with Zwitterionic Phospholipid Monolayers on Oil Nanodroplets Suspensions in Water (D2O) Probed by Sum Frequency Scattering

By combining dynamic light scattering (DLS) measurements and infrared (IR) spectroscopy with the interface- and bond-specificity of vibrational sum frequency generation scattering (SFS) spectroscopy, we probe several structural aspects of how zwitterionic DMPC lipids adsorbed to oil droplets suspended in water (D2O) respond to the presence of the common polycation polyallylamine hydrochloride (PAH) in the presence of low and high salt concentration. We show that the polycation interactions with the lipids generally results in two distinct outcomes that depend upon salt and PAH concentration, identified here as Scenario 1 (observed under conditions of high salt concentration) and Scenario 2 (observed under conditions of low salt concentration). The scenarios differ in the extent of changes to droplet size and Olenick et al. Page 2 droplet coalescence coinciding with PAH addition. Our results illustrate that cationic polymers do not always interact in the same fashion with lipid membranes and demonstrate the feasibility of second-order spectroscopic methods to probe those interactions with chemical bond specificity, not only for the alkyl tails (C-H stretches) but also the choline headgroup (P-O stretches)

Uranyl Adsorption at the Muscovite (Mica)/Water Interface Studied by Second Harmonic Generation

Uranyl adsorption at the muscovite (mica)/water interface was studied by second harmonic generation (SHG). Using the nonresonant χ³ technique and the Gouy–Chapman model, the initial surface charge density of the mica surface was determined to be −0.022(1) C/m² at pH 6 and in the presence of dissolved carbonate. Under these same conditions, uranyl adsorption isotherms collected using nonresonant χ³ experiments and resonantly enhanced SHG experiments that probe the ligand-to-metal charge transfer bands of the uranyl cation yielded a uranyl binding constant of 3(1) × 10⁷ M^–1, corresponding to a Gibbs free energy of adsorption of −52.6(8) kJ/mol, and a maximum surface charge density at monolayer uranyl coverage of 0.028(3) C/m². These results suggest favorable adsorption of uranyl ions to the mica interface through strong ion-dipole or hydrogen interactions, with a 1:1 uranyl ion to surface site ratio that is indicative of monovalent cations ((UO₂)₃(OH)₅⁺, (UO₂)₄(OH)₇⁺, UO₂OH⁺, UO₂Cl⁺, UO₂(CH₃COO^–)⁺) binding at the interface, in addition to neutral uranyl species (UO₂(OH)₂ and UO₂CO₃). This work provides benchmark measurements to be used in the improvement of contaminant transport modeling

Identification of distinct pH-and zeaxanthin-dependent quenching in LHCSR3 from Chlamydomonas reinhardtii

Under high light, oxygenic photosynthetic organisms avoid photodamage by thermally dissipating absorbed energy, which is called non-photochemical quenching. In green algae, a chlorophyll and carotenoid-binding protein, light-harvesting complex stress-related (LHCSR3), detects excess energy via a pH drop and serves as a quenching site. Using a combined in vivo and in vitro approach, we investigated quenching within LHCSR3 from Chlamydomonas reinhardtii. In vitro two distinct quenching processes, individually controlled by pH and zeaxanthin, were identified within LHCSR3. The pH-dependent quenching was removed within a mutant LHCSR3 that lacks the residues that are protonated to sense the pH drop. Observation of quenching in zeaxanthin-enriched LHCSR3 even at neutral pH demonstrated zeaxanthin-dependent quenching, which also occurs in other light-harvesting complexes. Either pH- or zeaxanthin-dependent quenching prevented the formation of damaging reactive oxygen species, and thus the two quenching processes may together provide different induction and recovery kinetics for photoprotection in a changing environment

Polycation Interactions with Zwitterionic Phospholipid Monolayers on Oil Nanodroplet Suspensions in Water (D₂O) Probed by Sum Frequency Scattering

By combining dynamic light scattering (DLS) measurements with the interface and bond specificity of vibrational sum frequency generation scattering (SFS) spectroscopy, we probe several structural aspects of how zwitterionic DMPC lipids adsorbed to oil droplets suspended in water (D₂O) respond to the presence of the common polycation poly­(allylamine hydrochloride) (PAH) in the presence of low and high salt concentration. We show that the polycation interactions with the lipids generally result in two distinct outcomes that depend upon salt and PAH concentration, identified here as Scheme 1 (observed under conditions of high salt concentration) and Scheme 2 (observed under conditions of low salt concentration). The schemes differ in the extent of changes to droplet size and droplet coalescence coinciding with PAH addition. Our combined DLS and SFS results illustrate that cationic polymers do not always interact in the same fashion with lipid membranes and demonstrate the feasibility of second-order spectroscopic methods to probe those interactions with chemical bond specificity, not only for the alkyl tails (C–H stretches) but also for the choline headgroup (P–O stretches)

Second Harmonic Generation Studies of Fe(II) Interactions with Hematite (α-Fe₂O₃)

Iron oxides are a ubiquitous class of compounds that are involved in many biological, geological, and technological processes, and the Fe­(III)/Fe­(II) redox couple is a fundamental transformation pathway; however, the study of iron oxide surfaces in aqueous solution by powerful spectroscopic techniques has been limited due to “strong absorber problem”. In this work, atomic layer deposition (ALD) thin films of polycrystalline α-Fe₂O₃ were analyzed using the Eisenthal χ⁽³⁾ technique, a variant of second harmonic generation that reports on interfacial potentials. By determining the surface charge densities at multiple pH values, the point of zero charge was found to be 5.5 ± 0.3. The interaction of aqueous Fe­(II) at pH 4 and in 1 mM NaCl with ALD-prepared hematite was found to be fully reversible and to lead to about 4 times more ferrous iron ions adsorbed per square centimeter than on fused-silica surfaces under the same conditions. The data are consistent with a recently proposed conceptual model for net Fe­(II) uptake or release that is underlain by a dynamic equilibrium between Fe­(II) adsorbed onto hematite, electron transfer into favorable surface sites with attendant Fe­(III) deposition, and electron conduction to favorable remote sites that release and replenish aqueous Fe­(II)

Alteration of Membrane Compositional Asymmetry by LiCoO₂ Nanosheets

Given the projected massive presence of redox-active nanomaterials in the next generation of consumer electronics and electric vehicle batteries, they are likely to eventually come in contact with cell membranes, with biological consequences that are currently not known. Here, we present nonlinear optical studies showing that lithium nickel manganese cobalt oxide nanosheets carrying a negative ζ-potential have no discernible consequences for lipid alignment and interleaflet composition in supported lipid bilayers formed from zwitterionic and negatively charged lipids. In contrast, lithiated and delithiated LiCoO₂ nanosheets having positive and neutral ζ-potentials, respectively, alter the compositional asymmetry of the two membrane leaflets, and bilayer asymmetry remains disturbed even after rinsing. The insight that some cobalt oxide nanoformulations induce alterations to the compositional asymmetry in idealized model membranes may represent an important step toward assessing the biological consequences of their predicted widespread use

On Electronic and Charge Interference in Second Harmonic Generation Responses from Gold Metal Nanoparticles at Supported Lipid Bilayers

Second harmonic generation (SHG) is useful for studying the properties of interfaces, including the surfaces of nanoparticles and the interaction of nanoparticles with biologically relevant surfaces. Gold nanoparticles at the biological membrane represent a particularly interesting system to be probed by SHG spectroscopy given the rich electronic structure of gold nanoparticles and the charged nature of the nano-bio interface. Here we describe the interplay between the resonant and nonresonant components of the second harmonic response as 4 and 14 nm spherical gold nanoparticles (AuNPs) wrapped in the cationic polyelectrolyte poly­(allylamine hydrochloride) (PAH) adsorb to negatively charged supported lipid bilayers. In contrast to the SHG response of 4 nm PAH-AuNPs, that we have shown previously to be dominated by resonance enhancement, the SHG response from the adsorption of the 14 nm PAH-AuNPs, with similar hydrodynamic diameters, to a 9:1 DOPC:DOTAP bilayer is dominated by the nonresonant, interfacial, potential-dependent component of the signal. We hypothesize that the difference in the SHG response is attributable to the differences in the number of PAH molecules associated with the particles and, therefore, differences in the number of positively charged ammonium groups associated with the 4 vs the 14 nm particles. For 14 nm PAH-AuNPs with larger hydrodynamic diameters, we determined two regimes in the adsorption behavior, one where the resonance enhancement from the gold core of the nanoparticle dominates the signal and a second where the nonresonant, interfacial, potential-dependent term dominates the signal. The results presented in this study provide insight into the interplay between resonant and nonresonant components of the second harmonic signal from the adsorption of charged AuNPs and are valuable for future studies with other functionalized particles and lipid systems by SHG