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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Hydrophobic Metal–Organic Frameworks Enable Superior High-Pressure Ammonia Storage through Geometric Design

Hydrophobic metal–organic frameworks (MOFs) are typically overlooked for ammonia storage due to weak host–guest interactions. Here, we demonstrate that four structurally analogous aluminum-based MOFs exhibit a counterintuitive behavior whereby framework geometry, rather than ligand hydrophilicity, determines high-pressure NH 3 adsorption performance. The hydrophobic CAU-23 achieved an exceptional capacity matching hydrophilic analogs despite its poor low-pressure uptake. This pressure-dependent enhancement stems from the unique 4-cis-4-trans geometry of CAU-23 compared to the purely cis arrangement of MIL-160 and KMF-1 and the alternating cis-trans configuration of MOF-303. Critically, CAU-23 retained 95% capacity over three high-pressure cycles, whereas hydrophilic MOFs suffered 39–46% irreversible losses due to strong NH 3 -framework interactions that compromise structural integrity. Grand canonical Monte Carlo simulations reveal that high pressure enables NH 3 clustering through intermolecular hydrogen bonding, bypassing the need for strong host–guest interactions. High-pressure powder X-ray diffraction measurements confirm the exceptional mechanical resilience of CAU-23, showing complete structural recovery upon decompression despite exhibiting the highest pressure sensitivity among the studied MOFs. An extended analog, HE-CAU-23, validates this design principle with further enhanced capacity. Furthermore, these findings reveal a paradigm shift toward hydrophobic MOFs with optimized geometry for high-performance and regenerable gas storage applications.

MOFs↗
DOE OSTI2019

Directing isomerization reactions of cumulenes with electric fields

Electric fields have been proposed as having a distinct ability to catalyze chemical reactions through the stabilization of polar or ionic intermediate transition states. Although field-assisted catalysis is being researched, the ability to catalyze reactions in solution using electric fields remains elusive and the understanding of mechanisms of such catalysis is sparse. Here we show that an electric field can catalyze the cis-to-trans isomerization of [3]cumulene derivatives in solution, in a scanning tunneling microscope. We further show that the external electric field can alter the thermodynamics inhibiting the trans-to-cis reverse reaction, endowing the selectivity toward trans isomer. Using density functional theory-based calculations, we find that the applied electric field promotes a zwitterionic resonance form, which ensures a lower energy transition state for the isomerization reaction. The field also stabilizes the trans form, relative to the cis, dictating the cis/trans thermodynamics, driving the equilibrium product exclusively toward the trans.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Chiral photochemistry of achiral molecules

Chirality is a molecular property governed by the topography of the potential energy surface (PES). Thermally achiral molecules interconvert rapidly when the interconversion barrier between the two enantiomers is comparable to or lower than the thermal energy, in contrast to thermally stable chiral configurations. In principle, a change in the PES topography on the excited electronic state may diminish interconversion, leading to electronically prochiral molecules that can be converted from achiral to chiral by electronic excitation. Here we report that this is the case for two prototypical examples – cis-stilbene and cis-stiff stilbene. Both systems exhibit unidirectional photoisomerization for each enantiomer as a result of their electronic prochirality. We simulate an experiment to demonstrate this effect in cis-stilbene based on its interaction with circularly polarized light. Our results highlight the drastic change in chiral behavior upon electronic excitation, opening up the possibility for asymmetric photochemistry from an effectively nonchiral starting point.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Carotenoid cleavage enzymes evolved convergently to generate the visual chromophore

The retinal light response in animals originates from the photoisomerization of an opsin-coupled 11-cis-retinaldehyde chromophore. This visual chromophore is enzymatically produced through the action of carotenoid cleavage dioxygenases. Vertebrates require two carotenoid cleavage dioxygenases, β-carotene oxygenase 1 and retinal pigment epithelium 65 (RPE65), to form 11-cis-retinaldehyde from carotenoid substrates, whereas invertebrates such as insects use a single enzyme known as Neither Inactivation Nor Afterpotential B (NinaB). RPE65 and NinaB couple trans–cis isomerization with hydrolysis and oxygenation, respectively, but the mechanistic relationship of their isomerase activities remains unknown. Here we report the structure of NinaB, revealing details of its active site architecture and mode of membrane binding. Structure-guided mutagenesis studies identify a residue cluster deep within the NinaB substrate-binding cleft that controls its isomerization activity. Our data demonstrate that isomerization activity is mediated by distinct active site regions in NinaB and RPE65—an evolutionary convergence that deepens our understanding of visual system diversity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

The role of proton coupled electron transfer in water oxidation

Water oxidation is a key half reaction in energy conversion schemes based on solar fuels and targets such as light driven water splitting or carbon dioxide reduction into CO, other oxygenates, or hydrocarbons. Carrying out these reactions at rates that exceed the rate of solar insolation for the extended periods of time required for useful applications presents a major challenge. Water oxidation is the key “other” half reaction in these schemes and it is dominated by PCET given its multi-electron, multi-proton character, 2H2O → O2 + 4e- + 4H+. Identification of PCET was an offshoot of experiments designed to investigate energy conversion by electron transfer quenching of molecular excited states. The concepts “redox potential leveling” and concerted electron–proton transfer came from measurements on stepwise oxidation of cis-RuII(bpy)2(py)(OH2)2+ to RuIV(bpy)2(py)(O)2+. The Ru “blue dimer”, cis,cis-(bpy)2(H2O)RuORu(OH2)(bpy)24+, was the first designed catalyst for water oxidation. It undergoes oxidative activation by PCET to give the transient (bpy)2(O)RuVORuV(O)(bpy)24+, O-atom attack on water to give a peroxidic intermediate, and further oxidation and O2 release. More recently, a class of single site water oxidation catalysts has been identified, e.g., Ru(tpy)(bpm)(OH2)2+ (tpy is 2,2':6',2''-terpyridine; bpm is 2,2'-bipyrimidine). They undergo stepwise PCET oxidation to RuIV=O2+ or RuV(O)3+ followed by O-atom transfer with formation of peroxidic intermediates which undergo further oxidation and O2 release. PCET plays a key role in the three zones of water oxidation reactivity: oxidative activation, O•••O bond formation, oxidation and O2 release from peroxidic intermediates. Similar schemes have been identified for electrocatalytic water oxidation on oxide electrode surfaces based on phosphonated derivatives such as [Ru(Mebimpy)(4,4'-(PO3H2CH2)2bpy)(OH2)]2+. A PCET barrier to RuIII–OH2+ → RuIV=O2+ oxidation arises from the large difference in pKa values between RuIII–OH2+ and RuIV(OH)3+. On oxide surfaces this oxidation occurs by multiple pathways. Kinetic, mechanistic, and DFT results on single site catalysts reveal a new pathway for the O•••O bond forming step (Atom-Proton Transfer, APT), significant rate enhancements by added proton acceptor bases, and accelerated water oxidation in propylene carbonate as solvent with water added as a stoichiometric reagent. Lessons learned about water oxidation and the role of PCET and concerted pathways appear to have direct relevance for water oxidation in Photosystem II (PSII) with PSII a spectacular example of PCET in action. This includes a key role for Multiple Site-Electron Proton Transfer in oxidative activation of the Oxygen Evolving Complex (OEC) in the S0 → S1 transition in the Kok cycle.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Reduced dimension rovibrational variational calculations of the S{sub 1} state of C{sub 2}H{sub 2}. I. Methodology and implementation

The bending and torsional degrees of freedom in S{sub 1} acetylene, C{sub 2}H{sub 2}, are subject to strong vibrational resonances and rovibrational interactions, which create complex vibrational polyad structures even at low energy. As the internal energy approaches that of the barrier to cis-trans isomerization, these energy level patterns undergo further large-scale reorganization that cannot be satisfactorily treated by traditional models tied to local minima of the potential energy surface for nuclear motion. Experimental spectra in the region near the cis-trans transition state have revealed these complicated new patterns. In order to understand near-barrier spectroscopic observations and to predict the detailed effects of cis-trans isomerization on the rovibrational energy level structure, we have performed reduced dimension rovibrational variational calculations of the S{sub 1} state. In this paper, we present the methodological details, several of which require special care. Our calculation uses a high accuracy ab initio potential surface and a fully symmetrized extended complete nuclear permutation inversion group theoretical treatment of a multivalued internal coordinate system that is appropriate for large amplitude bending and torsional motions. We also discuss the details of the rovibrational basis functions and their symmetrization, as well as the use of a constrained reduced dimension rovibrational kinetic energy operator.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Electronic and vibrational spectra of protonated benzaldehyde-water clusters, [BZ-(H{sub 2}O){sub n≤5}]H{sup +}: Evidence for ground-state proton transfer to solvent for n ≥ 3

Vibrational and electronic photodissociation spectra of mass-selected protonated benzaldehyde-(water){sub n} clusters, [BZ-(H{sub 2}O){sub n}]H{sup +} with n ≤ 5, are analyzed by quantum chemical calculations to determine the protonation site in the ground electronic state (S{sub 0}) and ππ{sup *} excited state (S{sub 1}) as a function of microhydration. IR spectra of [BZ-(H{sub 2}O){sub n}]H{sup +} with n ≤ 2 are consistent with BZH{sup +}-(H{sub 2}O){sub n} type structures, in which the excess proton is localized on benzaldehyde. IR spectra of clusters with n ≥ 3 are assigned to structures, in which the excess proton is located on the (H{sub 2}O){sub n} solvent moiety, BZ-(H{sub 2}O){sub n}H{sup +}. Quantum chemical calculations at the B3LYP, MP2, and ri-CC2 levels support the conclusion of proton transfer from BZH{sup +} to the solvent moiety in the S{sub 0} state for hydration sizes larger than the critical value n{sub c} = 3. The vibronic spectrum of the S{sub 1} ← S{sub 0} transition (ππ{sup *}) of the n = 1 cluster is consistent with a cis-BZH{sup +}-H{sub 2}O structure in both electronic states. The large blueshift of the S{sub 1} origin by 2106 cm{sup −1} upon hydration with a single H{sub 2}O ligand indicates that the proton affinity of BZ is substantially increased upon S{sub 1} excitation, thus strongly destabilizing the hydrogen bond to the solvent. The adiabatic S{sub 1} excitation energy and vibronic structure calculated at the ri-CC2/aug-cc-pVDZ level agrees well with the measured spectrum, supporting the notion of a cis-BZH{sup +}-H{sub 2}O geometry. The doubly hydrated species, cis-BZH{sup +}-(H{sub 2}O){sub 2}, does not absorb in the spectral range of 23 000–27 400 cm{sup −1}, because of the additional large blueshift of the ππ{sup *} transition upon attachment of the second H{sub 2}O molecule. Calculations predict roughly linear and large incremental blueshifts for the ππ{sup *} transition in [BZ-(H{sub 2}O){sub n}]H{sup +} as a function of n. In the size range n ≥ 3, the calculations predict a proton transfer from the (H{sub 2}O){sub n}H{sup +} solvent back to the BZ solute upon electronic ππ{sup *} excitation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Analytic derivative couplings for spin-flip configuration interaction singles and spin-flip time-dependent density functional theory

We revisit the calculation of analytic derivative couplings for configuration interaction singles (CIS), and derive and implement these couplings for its spin-flip variant for the first time. Our algorithm is closely related to the CIS analytic energy gradient algorithm and should be straightforward to implement in any quantum chemistry code that has CIS analytic energy gradients. The additional cost of evaluating the derivative couplings is small in comparison to the cost of evaluating the gradients for the two electronic states in question. Incorporation of an exchange-correlation term provides an ad hoc extension of this formalism to time-dependent density functional theory within the Tamm-Dancoff approximation, without the need to invoke quadratic response theory or evaluate third derivatives of the exchange-correlation functional. Application to several different conical intersections in ethylene demonstrates that minimum-energy crossing points along conical seams can be located at substantially reduced cost when analytic derivative couplings are employed, as compared to use of a branching-plane updating algorithm that does not require these couplings. Application to H{sub 3} near its D{sub 3h} geometry demonstrates that correct topology is obtained in the vicinity of a conical intersection involving a degenerate ground state.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Bicolor Mn-doped CuInS{sub 2}/ZnS core/shell nanocrystals for white light-emitting diode with high color rendering index

We synthesized bicolor Mn-doped CuInS{sub 2} (CIS)/ZnS core/shell nanocrystals (NCs), in which Mn{sup 2+} ions and the CIS core were separated with a ZnS layer, and both Mn{sup 2+} ions and CIS cores could emit simultaneously. Transmission electron microscopy and powder X-ray diffraction measurements indicated the epitaxial growth of ZnS shell on the CuInS{sub 2} core, and electron paramagnetic resonance spectrum indicated that Mn{sup 2+} ions were on the lattice points of ZnS shell. By integrating these bicolor NCs with commercial InGaN-based blue-emitting diodes, tricolor white light-emitting diodes with color rendering index of 83 were obtained.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Tunneling splitting in double-proton transfer: Direct diagonalization results for porphycene

Zero-point and excited level splittings due to double-proton tunneling are calculated for porphycene and the results are compared with experiment. The calculation makes use of a multidimensional imaginary-mode Hamiltonian, diagonalized directly by an effective reduction of its dimensionality. Porphycene has a complex potential energy surface with nine stationary configurations that allow a variety of tunneling paths, many of which include classically accessible regions. A symmetry-based approach is used to show that the zero-point level, although located above the cis minimum, corresponds to concerted tunneling along a direct trans − trans path; a corresponding cis − cis path is predicted at higher energy. This supports the conclusion of a previous paper [Z. Smedarchina, W. Siebrand, and A. Fernández-Ramos, J. Chem. Phys. 127, 174513 (2007)] based on the instanton approach to a model Hamiltonian of correlated double-proton transfer. A multidimensional tunneling Hamiltonian is then generated, based on a double-minimum potential along the coordinate of concerted proton motion, which is newly evaluated at the RI-CC2/cc-pVTZ level of theory. To make it suitable for diagonalization, its dimensionality is reduced by treating fast weakly coupled modes in the adiabatic approximation. This results in a coordinate-dependent mass of tunneling, which is included in a unique Hermitian form into the kinetic energy operator. The reduced Hamiltonian contains three symmetric and one antisymmetric mode coupled to the tunneling mode and is diagonalized by a modified Jacobi-Davidson algorithm implemented in the Jadamilu software for sparse matrices. The results are in satisfactory agreement with the observed splitting of the zero-point level and several vibrational fundamentals after a partial reassignment, imposed by recently derived selection rules. They also agree well with instanton calculations based on the same Hamiltonian.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Near-infrared and ultraviolet induced isomerization of crotonic acid in N{sub 2} and Xe cryomatrices: First observation of two high-energy trans C–O conformers and mechanistic insights

E-crotonic acid was isolated in cryogenic solid N{sub 2} and xenon matrices, and subjected to Laser ultraviolet (UV) and near-infrared (NIR) irradiations. In the deposited matrices, the two low-energy cis C–O E-cc and E-ct conformers, which are the only forms significantly populated in the gas phase, were observed. UV irradiation (λ= 250 nm) of the compound in N{sub 2} matrix allows for experimental detection, not just of the two low-energy cis C–O isomers of Z-crotonic acid previously observed in the experiments carried out in argon matrix [Z-cc and Z-ct; R. Fausto, A. Kulbida, and O. Schrems, J. Chem. Soc., Faraday Trans. 91, 3755–3770 (1995)] but also of the never observed before high-energy forms of both E- and Z-crotonic acids bearing the carboxylic acid group in the trans arrangement (E-tc and Z-tc conformers). In turn, NIR irradiation experiments in the N{sub 2} matrix allow to produce the high-energy E-tc trans C–O conformer in a selective way, from the initially deposited E-cc form. The vibrational signatures of all the 6 rotameric structures of the crotonic acids experimentally observed, including those of the new trans C–O forms, were determined and the individual spectra fully assigned, also with support of theoretically obtained data. On the other hand, as found before for the compound isolated in argon matrix, the experiments performed in xenon matrix failed to experimental detection of the trans C–O forms. This demonstrates that in noble gas matrices these forms are not stable long enough to allow for their observation by steady state spectroscopy techniques. In these matrices, the trans C–O forms convert spontaneously into their cis C–O counterparts, by tunnelling. Some mechanistic details of the studied processes were extracted and discussed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

An extended E$\otimes$e Jahn-Teller Hamiltonian for large-amplitude motion: Application to vibrational conical intersections in CH 3 SH and CH 3 OH

An extended E$\otimes$e Jahn-Teller Hamiltonian is presented for the case where the (slow) nuclear motion extends far from the symmetry point and may be described approximately as motion on a sphere. Rather than the traditional power series expansion in the displacement from the C 3v symmetry point, an expansion in the spherical harmonics is employed. Application is made to the vibrational Jahn-Teller effect in CH 3 XH, with X = S, O, where the equilibrium CXH angles are 83° and 72°, respectively. In addition to the symmetry-required conical intersection (CI) at the C 3v symmetry point, ab initio calculations reveal sets of six symmetry-allowed vibrational CIs in each molecule. The CIs for each molecule are arranged differently in the large-amplitude space, and that difference is reflected in the infrared spectra. The CIs in CH 3 SH are found in both eclipsed and staggered geometries, whereas those for CH 3 OH are found only in the eclipsed geometry near the torsional saddle point. Finally, this difference between the two molecules is reflected in the respective high-resolution spectra in the CH stretch fundamental region.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Verification of Doppler coherence imaging for 2D ion velocity measurements on DIII-D

Coherence Imaging Spectroscopy (CIS) has emerged as a powerful tool for investigating complex ion phenomena in the boundary of magnetically confined plasma devices. The combination of Fourier-transform interferometry and high-resolution fast-framing cameras has made it possible to make sensitive velocity measurements that are also spatially resolved. However, this sensitivity makes the diagnostic vulnerable to environmental effects including thermal drifts, vibration, and magnetic fields that can influence the velocity measurement. Additionally, the ability to provide an absolute calibration for these geometries can be impacted by differences in the light-collection geometry between the plasma and reference light source, spectral impurities, and the presence of thin-films on in-vessel optics. This work discusses the mitigation of these effects and demonstration that environmental effects result in less than 0.5 km/s error on the DIII-D CIS systems. A diagnostic comparison is used to demonstrate agreement between CIS and traditional spectroscopy once tomographic artifacts are accounted for.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2018

Erratum: “Non-orthogonal configuration interaction with single substitutions for the calculation of core-excited states” [J. Chem. Phys. 149, 044116 (2018)]

In our recent publication, we incorrectly stated some of the CIS and TDDFT k-edge excitations. Specifically the errors were in the CIS k-edge for all molecules except C2N2 and C2H6 and the TDDFT k-edge for only C2H2, N2, CO2 O, F2, and C2H2, all of which are shown in Table II of the original paper. A corrected version of that table can be found below. This changes our results slightly in that the RMSEs of the CIS and the TDDFT results are slightly reduced, but it does not change the primary conclusion that NOCIS is a promising method for calculating core excitations though it lacks dynamical correlation. (Table Presented).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

High-resolution infrared spectroscopy of jet cooled trans -deuteroxycarbonyl ( trans -DOCO) radical

The rovibrational spectrum of jet cooled trans-deuteroxycarbonyl (trans-DOCO) radical has been explored at suppressed-Doppler resolution via direct infrared absorption spectroscopy. The trans-DOCO is produced in a supersonic slit discharge of rare-gas/CO mixture doped with D 2 O, whereby the OD forms an energized adduct with CO, cooling in the supersonic expansion and stabilizing DOCO in the trans well. Active laser-frequency stabilization and collisional quenching of Doppler broadening along the slit axis yield <10 MHz frequency precision, with the absorbance noise approaching the quantum shot-noise limit. The current high-resolution spectral results are in excellent agreement with recent studies of the trans-DOCO radical by infrared frequency comb spectroscopy under room temperature conditions [Bui et al., Mol. Phys. 116, 3710 (2018)]. Combined with previous microwave/millimeter wave rotational studies, the suppressed-Doppler infrared data permit characterization of the vibrational ground state, improved structural parameters for the OD stretch vibrational level, and trans-DOCO spin-rotation information in both ground and excited vibrational states. Additionally, the infrared data reveal a-type and much weaker b-type contributions to the spectrum, analysis of which yields orientation of the OD stretch transition dipole moment in the body fixed frame. Of dynamical interest is whether the nascent trans-DOCO complex formed in the entrance channel has sufficient time to convert into the cis-DOCO isomer, or whether this is quenched by rapid stabilization into the trans-DOCO well. Finally, ab initio and Rice–Ramsperger–Kassel–Marcus analysis of the intrinsic reaction coordinate for trans-DOCO to cis-DOCO interconversion rates supports the latter scenario, which helps explain the failure of previous high resolution infrared efforts to detect cis-hydroxycarbonyl.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

Isomers and band assignments in the cryogenic vibrational spectrum of the binary complex between water and protonated formic acid using two color, IR–IR photobleaching and H/D isotopic substitution

Protonated formic acid (PFA) is purported to be the active species in the catalytic activation of condensation reactions at the acidic interface of microdroplets. Here, we investigate the fundamental interaction between PFA and water with cryogenic ion vibrational spectroscopy of the binary PFA–H 2 O complexes generated via electrospray ionization followed by buffer gas cooling to about 20 K. The patterns displayed by the isomer-specific IR spectra of D 2 -tagged PFA–H 2 O indicate that two distinct, non-interconverting rotamers are present at low temperatures based on the cis and trans structures of the HCO 2 $H$$^{+}_{2}$ core ion. Both of these occur with the water molecule attached to the OH that is in a cis-configuration relative to the CH group (denoted E), but differ in the E vs Z (cis vs trans relative to the CH group) orientation of the spectator OH. This assignment scheme corrects a previous theoretical analysis that invoked a scenario in which structures with E- and Z-bound water molecules interconvert at low (20 K) temperatures. Isomer-specific bands arising from the OH stretches and water bending modes are deconvoluted using isotopomer-specific spectroscopy of the complexes with partial H/D exchange. The dependence of the nominal shared proton OH stretch frequency on the deuteration of the tethered water confirms strong coupling between this mode and the water bending fundamental.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Direct kinetic measurements and theoretical predictions of an isoprene-derived Criegee intermediate

Isoprene has the highest emission into Earth’s atmosphere of any nonmethane hydrocarbon. Atmospheric processing of alkenes, including isoprene, via ozonolysis leads to the formation of zwitterionic reactive intermediates, known as Criegee intermediates (CIs). Direct studies have revealed that reactions involving simple CIs can significantly impact the tropospheric oxidizing capacity, enhance particulate formation, and degrade local air quality. Methyl vinyl ketone oxide (MVK-oxide) is a four-carbon, asymmetric, resonance-stabilized CI, produced with 21 to 23% yield from isoprene ozonolysis, yet its reactivity has not been directly studied. We present direct kinetic measurements of MVK-oxide reactions with key atmospheric species using absorption spectroscopy. Direct UV-Vis absorption spectra from two independent flow cell experiments overlap with the molecular beam UV-Vis-depletion spectra reported recently [M. F. Vansco, B. Marchetti, M. I. Lester, J. Chem. Phys. 149, 44309 (2018)] but suggest different conformer distributions under jet-cooled and thermal conditions. Comparison of the experimental lifetime herein with theory indicates only the syn -conformers are observed; anti -conformers are calculated to be removed much more rapidly via unimolecular decay. We observe experimentally and predict theoretically fast reaction of syn -MVK-oxide with SO 2 and formic acid, similar to smaller alkyl-substituted CIs, and by contrast, slow removal in the presence of water. We determine products through complementary multiplexed photoionization mass spectrometry, observing SO 3 and identifying organic hydroperoxide formation from reaction with SO 2 and formic acid, respectively. The tropospheric implications of these reactions are evaluated using a global chemistry and transport model.

09 BIOMASS FUELS↗
DOE OSTI2016

Structural Basis for Interactions Between Contactin Family Members and Protein-tyrosine Phosphatase Receptor Type G in Neural Tissues

Protein-tyrosine phosphatase receptor type G (RPTPγ/PTPRG) interacts in vitro with contactin-3-6 (CNTN3-6), a group of glycophosphatidylinositol-anchored cell adhesion molecules involved in the wiring of the nervous system. In addition to PTPRG, CNTNs associate with multiple transmembrane proteins and signal inside the cell via cis-binding partners to alleviate the absence of an intracellular region. Here, we use comprehensive biochemical and structural analyses to demonstrate that PTPRG·CNTN3-6 complexes share similar binding affinities and a conserved arrangement. Furthermore, as a first step to identifying PTPRG·CNTN complexes in vivo, we found that PTPRG and CNTN3 associate in the outer segments of mouse rod photoreceptor cells. In particular, PTPRG and CNTN3 form cis-complexes at the surface of photoreceptors yet interact in trans when expressed on the surfaces of apposing cells. Further structural analyses suggest that all CNTN ectodomains adopt a bent conformation and might lie parallel to the cell surface to accommodate these cis and trans binding modes. Taken together, these studies identify a PTPRG·CNTN complex in vivo and provide novel insights into PTPRG- and CNTN-mediated signaling.

59 BASIC BIOLOGICAL SCIENCES↗