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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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Formation of the N≡N Triple Bond from Reductive Coupling of a Paramagnetic Diruthenium Nitrido Compound

Construction of nitrogen–nitrogen triple bonds via homocoupling of metal nitrides is an important fundamental reaction relevant to a potential Nitrogen Economy. Here, we report that room temperature photolysis of Ru 2 (chp) 4 N 3 (chp– = 2-chloro-6-hydroxypyridinate) in CH 2 Cl 2 produces N 2 via reductive coupling of Ru2(chp)4N nitrido species. Computational analysis reveals that the nitride coupling transition state (TS) features an out-of-plane “zigzag” geometry instead of the anticipated planar zigzag TS. However, with intentional exclusion of dispersion correction, the planar zigzag TS geometry can also be found. Both the out-of-plane and planar zigzag TS geometries feature two important types of orbital interactions: (1) donor–acceptor interactions involving intermolecular donation of a nitride lone pair into an empty Ru–N π* orbital and (2) Ru–N π to Ru–N π* interactions derived from coupling of nitridyl radicals. The relative importance of these two interactions is quantified both at and after the TS. Our analysis shows that both interactions are important for the formation of the N–N σ bond, while radical coupling interactions dominate the formation of N–N π bonds. Comparison is made to isoelectronic Ru 2 -oxo compounds. Formation of an O–O bond via bimolecular oxo coupling is not observed experimentally and is calculated to have a much higher TS energy. As a result, the major difference between the nitrido and oxo systems stems from an extremely large driving force, ~–500 kJ/mol, for N–N coupling vs a more modest driving force for O–O coupling, –40 to –140 kJ/mol.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Catching the role of anisotropic electronic distribution and charge transfer in halogen bonded complexes of noble gases

The systems studied in this work are gas-phase weakly bound adducts of the noble-gas (Ng) atoms with CCl{sub 4} and CF{sub 4}. Their investigation was motivated by the widespread current interest for the intermolecular halogen bonding (XB), a structural motif recognized to play a role in fields ranging from elementary processes to biochemistry. The simulation of the static and dynamic behaviors of complex systems featuring XB requires the formulation of reliable and accurate model potentials, whose development relies on the detailed characterization of strength and nature of the interactions occurring in simple exemplary halogenated systems. We thus selected the prototypical Ng-CCl{sub 4} and Ng-CF{sub 4} and performed high-resolution molecular beam scattering experiments to measure the absolute scale of their intermolecular potentials, with high sensitivity. In general, we expected to probe typical van der Waals interactions, consisting of a combination of size (exchange) repulsion with dispersion/induction attraction. For the He/Ne-CF{sub 4}, the analysis of the glory quantum interference pattern, observable in the velocity dependence of the integral cross section, confirmed indeed this expectation. On the other hand, for the He/Ne/Ar-CCl{sub 4}, the scattering data unravelled much deeper potential wells, particularly for certain configurations of the interacting partners. The experimental data can be properly reproduced only including a shifting of the repulsive wall at shorter distances, accompanied by an increased role of the dispersion attraction, and an additional short-range stabilization component. To put these findings on a firmer ground, we performed, for selected geometries of the interacting complexes, accurate theoretical calculations aimed to evaluate the intermolecular interaction and the effects of the complex formation on the electron charge density of the constituting moieties. It was thus ascertained that the adjustments of the potential suggested by the analysis of the experiments actually reflect two chemically meaningful contributions, namely, a stabilizing interaction arising from the anisotropy of the charge distribution around the Cl atom in CCl{sub 4} and a stereospecific electron transfer that occurs at the intermolecular distances mainly probed by the experiments. Our model calculations suggest that the largest effect is for the vertex geometry of CCl{sub 4} while other geometries appear to play a minor to negligible role.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Bottom-up coarse-grained models with predictive accuracy and transferability for both structural and thermodynamic properties of heptane-toluene mixtures

This work investigates the promise of a “bottom-up” extended ensemble framework for developing coarse-grained (CG) models that provide predictive accuracy and transferability for describing both structural and thermodynamic properties. We employ a force-matching variational principle to determine system-independent, i.e., transferable, interaction potentials that optimally model the interactions in five distinct heptane-toluene mixtures. Similarly, we employ a self-consistent pressure-matching approach to determine a system-specific pressure correction for each mixture. The resulting CG potentials accurately reproduce the site-site rdfs, the volume fluctuations, and the pressure equations of state that are determined by all-atom (AA) models for the five mixtures. Furthermore, we demonstrate that these CG potentials provide similar accuracy for additional heptane-toluene mixtures that were not included their parameterization. Surprisingly, the extended ensemble approach improves not only the transferability but also the accuracy of the calculated potentials. Additionally, we observe that the required pressure corrections strongly correlate with the intermolecular cohesion of the system-specific CG potentials. Moreover, this cohesion correlates with the relative “structure” within the corresponding mapped AA ensemble. Finally, the appendix demonstrates that the self-consistent pressure-matching approach corresponds to minimizing an appropriate relative entropy.

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

Competing Intermolecular and Molecule–Surface Interactions: Dipole–Dipole-Driven Patterns in Mixed Carborane Self-Assembled Monolayers

Carboranedithiol isomers adsorbing with opposite orientations of their dipoles on surfaces are self-assembled together to form mixed monolayers where both lateral dipole–dipole and lateral thiol–thiolate (S–H···S) interactions provide enhanced stability over single-component monolayers. Here, we demonstrate the first instance of the ability to map individual isomers in a mixed monolayer using the model system carboranedithiols on Au{111}. The addition of methyl groups to one isomer provides both an enhanced dipole moment and extra apparent height for differentiation via scanning tunneling microscopy (STM). Associated computational investigations rationalize favorable interactions of mixed pairs and the associated stability changes that arise from these interactions. Both STM images and Monte Carlo simulations yield similarly structured mixed monolayers, where approximately 10% of the molecules have reversed dipole moment orientations but no direct chemical attachment to the surface, leading to homogeneous monolayers with no apparent phase separation. Deprotonating the thiols by depositing the molecules under basic conditions eliminates the lateral S–H···S interactions while accentuating the dipole–dipole forces. The molecular system investigated is composed of isomeric molecules with opposite orientations of dipoles and identical surface packing, which enables the mapping of individual molecules within the mixed monolayers and enables analyses of the contributions of the relatively weak lateral interactions to the overall stability of the assemblies.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

A new metric to control nucleation and grain size distribution in hybrid organic–inorganic perovskites by tuning the dielectric constant of the antisolvent

In perovskite research, there is a widely exploited but poorly explained phenomenon in which the addition of “antisolvents (ATS)” to precursor solutions results in higher-quality films. We explain the mechanism and driving force underlying an antisolvent-driven solvent extraction process. Density functional theory calculations uncover the defining effects of antisolvent choice on the extent of complexation between a lead salt and a methylammonium cation in solution. We experimentally validate the computational results using ultraviolet-visible spectroscopy and 207 Pb nuclear magnetic spectroscopy of methylammonium lead iodide solutions, containing both a processing solvent and an antisolvent. Furthermore, we uncover, and subsequently identify, the appearance of new species in solution as a result of the addition of the antisolvent. Furthermore, we observe that the choice of antisolvent has a substantial effect on the nature of the complexation of the methylammonium lead iodide (MAPbI 3 ) precursor species, whose origin we explain at an atomic level; specifically, the lower the dielectric of the antisolvent, the stronger the intermolecular binding energy between methylammonium cation (MA + ) cation and PbI 3 - plumbate, independent of the solvent or antisolvent interaction with the lead salt. Thin films were characterized using scanning electron microscopy; images of the films show how the addition of an antisolvent influences and, importantly, can be used to alter thin-film grain size. Grain size and distribution in thin films is reflected by the choice of antisolvent, promoting slower nucleation rates, a lower nucleation density, and hence larger final grain size.

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

Heterodimerization of Retinoid X Receptor with Xenobiotic Receptor partners occurs in the cytoplasmic compartment: Mechanistic insights of events in living cells

Retinoid X Receptor (RXR) serves as the heterodimeric partner of two major xenobiotic nuclear receptors, Pregnane and Xenobiotic Receptor (PXR) and Constitutive Androstane Receptor (CAR). These receptors are primarily involved in the metabolism and clearance of endobiotics and xenobiotics (including clinical drugs) from the body. Here, we report for the first time that intermolecular interactions between RXR-PXR and RXR-CAR occurs in the cytoplasmic compartment of the cell in a ligand-independent manner. These interactions lead to nuclear import of the heterodimeric complex thereby making them competent for chromatin binding and transactivation of target genes. To explore the cellular site involved in the process of heterodimerization we created various RFP- and GFP-tagged receptor chimeras and also the mutants of their nuclear localization signal (NLS). From the study it is apparent that NLS of PXR/CAR/RXR play a major role in the import of the heterodimeric complex from the cytoplasm to the nucleus in a ligand-independent manner. We observed that along with the heterodimeric partner and/or respective ligand a functional NLS is necessary for activation of target gene. The data suggests that RXR is the major driving force to import the heterodimeric complex into the nucleus since the mutation in the NLS region of RXR weakens this import process dramatically, whereas mutations in the NLS regions of PXR and CAR have little or no significant effect. This RXR-dependent nuclear translocation of the heterodimeric complex also modulates the individual transcriptional activity of PXR and CAR by increasing the basal transcriptional activity. Finally, it is documented that the heterodimerization of RXR with both the partners (PXR, CAR) occurs in the cytoplasm and implies that these dynamic interactions have functional and regulatory attributes in gene expression. In addition, this RXR-dependent enhancement of the transcriptional activity of PXR and CAR may be utilized for evaluating the receptor-drug interactions. - Highlights: • RFP-tagged RXR, PXR and CAR are used to study receptor heterodimerization. • Tagged receptors shifted to cytoplasm and imported to nucleus after heterodimerization. • Wild-type nuclear receptor can translocate cytoplasmic NLS-mutant to the nucleus. • Receptor heterodimerization is a ligand-independent event and occurs in cytoplasm. • Transcriptional activity of nuclear receptor is enhanced by heterodimerization.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

Chirality of weakly bound complexes: The potential energy surfaces for the hydrogen-peroxide−noble-gas interactions

We consider the analytical representation of the potential energy surfaces of relevance for the intermolecular dynamics of weakly bound complexes of chiral molecules. In this paper we study the H{sub 2}O{sub 2}−Ng (Ng=He, Ne, Ar, Kr, and Xe) systems providing the radial and the angular dependence of the potential energy surface on the relative position of the Ng atom. We accomplish this by introducing an analytical representation which is able to fit the ab initio energies of these complexes in a wide range of geometries. Our analysis sheds light on the role that the enantiomeric forms and the symmetry of the H{sub 2}O{sub 2} molecule play on the resulting barriers and equilibrium geometries. The proposed theoretical framework is useful to study the dynamics of the H{sub 2}O{sub 2} molecule, or other systems involving O–O and S–S bonds, interacting by non-covalent forces with atoms or molecules and to understand how the relative orientation of the O–H bonds changes along collisional events that may lead to a hydrogen bond formation or even to selectivity in chemical reactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Rotational study of the NH{sub 3}–CO complex: Millimeter-wave measurements and ab initio calculations

The rotational spectrum of the van der Waals complex NH{sub 3}–CO has been measured with the intracavity OROTRON jet spectrometer in the frequency range of 112–139 GHz. Newly observed and assigned transitions belong to the K = 0–0, K = 1–1, K = 1–0, and K = 2–1 subbands correlating with the rotationless (j{sub k}){sub NH3} = 0{sub 0} ground state of free ortho-NH{sub 3} and the K = 0–1 and K = 2–1 subbands correlating with the (j{sub k}){sub NH3} = 1{sub 1} ground state of free para-NH{sub 3}. The (approximate) quantum number K is the projection of the total angular momentum J on the intermolecular axis. Some of these transitions are continuations to higher J values of transition series observed previously [C. Xia et al., Mol. Phys. 99, 643 (2001)], the other transitions constitute newly detected subbands. The new data were analyzed together with the known millimeter-wave and microwave transitions in order to determine the molecular parameters of the ortho-NH{sub 3}–CO and para-NH{sub 3}–CO complexes. Accompanying ab initio calculations of the intermolecular potential energy surface (PES) of NH{sub 3}–CO has been carried out at the explicitly correlated coupled cluster level of theory with single, double, and perturbative triple excitations and an augmented correlation-consistent triple zeta basis set. The global minimum of the five-dimensional PES corresponds to an approximately T-shaped structure with the N atom closest to the CO subunit and binding energy D{sub e} = 359.21 cm{sup −1}. The bound rovibrational levels of the NH{sub 3}–CO complex were calculated for total angular momentum J = 0–6 on this intermolecular potential surface and compared with the experimental results. The calculated dissociation energies D{sub 0} are 210.43 and 218.66 cm{sup −1} for ortho-NH{sub 3}–CO and para-NH{sub 3}–CO, respectively.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Rotational study of the CH{sub 4}–CO complex: Millimeter-wave measurements and ab initio calculations

The rotational spectrum of the van der Waals complex CH{sub 4}–CO has been measured with the intracavity OROTRON jet spectrometer in the frequency range of 110–145 GHz. Newly observed and assigned transitions belong to the K = 2–1 subband correlating with the rotationless j{sub CH4} = 0 ground state and the K = 2–1 and K = 0–1 subbands correlating with the j{sub CH4} = 2 excited state of free methane. The (approximate) quantum number K is the projection of the total angular momentum J on the intermolecular axis. The new data were analyzed together with the known millimeter-wave and microwave transitions in order to determine the molecular parameters of the CH{sub 4}–CO complex. Accompanying ab initio calculations of the intermolecular potential energy surface (PES) of CH{sub 4}–CO have been carried out at the explicitly correlated coupled cluster level of theory with single, double, and perturbative triple excitations [CCSD(T)-F12a] and an augmented correlation-consistent triple zeta (aVTZ) basis set. The global minimum of the five-dimensional PES corresponds to an approximately T-shaped structure with the CH{sub 4} face closest to the CO subunit and binding energy D{sub e} = 177.82 cm{sup −1}. The bound rovibrational levels of the CH{sub 4}–CO complex were calculated for total angular momentum J = 0–6 on this intermolecular potential surface and compared with the experimental results. The calculated dissociation energies D{sub 0} are 91.32, 94.46, and 104.21 cm{sup −1} for A (j{sub CH4} = 0), F (j{sub CH4} = 1), and E (j{sub CH4} = 2) nuclear spin modifications of CH{sub 4}–CO, respectively.

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

Effect of Dispersion on Surface Interactions of Cobalt(II) Octaethylporphyrin Monolayer on Au(111) and HOPG(0001) Substrates: a Comparative First Principles Study

A density functional theory study of a cobalt(II) octaethylporphyrin (CoOEP) monolayer on Au(111) and HOPG(0001) surfaces was performed under periodic boundary conditions. Calculations with and without dispersion corrections are performed and the effect of van der Waals forces on the interface properties is analyzed. Calculations have determined that the CoOEP molecule tends to bind at the 3-fold and the 6-fold center sites on Au(111) and HOPG(0001), respectively. Geometric optimizations at the center binding sites have indicated that the porphyrin molecules (in the monolayer) lie flat on both substrates. Calculations also reveal that the CoOEP monolayer binds slightly more strongly to Au(111) than to HOPG(0001). Charge density difference plots disclose that charge is redistributed mostly around the porphyrin plane and the first layer of the substrates. Dispersion interactions cause a larger substrate to molecule charge pushback on Au(111) than on HOPG. CoOEP adsorption tends to lower the work functions of either substrate, qualitatively agreeing with the experimental photoelectron spectroscopic data. Comparison of the density of states (DOS) of the isolated CoOEP molecule with that on gold and HOPG substrates showed significant band shifts around the Fermi energy due to intermolecular orbital hybridization. Simulated STM images were plotted with the Tersoff–Hamann approach using the local density of states, which also agree with the experimental results. This study elucidates the role of dispersion for better describing porphyrin–substrate interactions. A DFT based overview of geometric, adsorption and electronic properties of a porphyrin monolayer on conductive surfaces is presented.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2024

Water–Hydrocarbon Interactions in Anionic Pyrene Monohydrate

Interactions between water and polycyclic aromatic hydrocarbons are essential in many aspects of chemistry, from interstellar and atmospheric processes to interfacial hydrophobicity and wetting phenomena. Despite their growing importance, the intermolecular potentials of the water-hydrocarbon interactions are underdeveloped compared to water-water potentials, and there are similarly few experimental probes that are sensitive to the details of the water-hydrocarbon potential. We present a combined experimental and computational study of anionic pyrene monohydrate, one of the simplest water/hydrocarbon clusters. The action spectrum in the OH region of the mass-selected cluster ion provides a rigorous benchmark for intermolecular potentials and computational methodologies. We identify missing intermolecular interactions and shortcomings in conventional dynamics calculations by comparing experimental data to density functional theory and classical molecular dynamics calculations. Kinetic trapping is prevalent, even for one water molecule and one pyrene molecule, leading to slow equilibration in conventional molecular dynamics calculations, even on nanosecond timescales and at low temperatures (50 K). At constant energy, temperature fluctuations for the pair of molecules are substantial. Immersing the system in a bath of soft spheres and employing parallel tempering alleviates kinetic trapping and dampens temperature fluctuations, bringing the system closer to the thermodynamic limit. With such augmented sampling, a simple, flexible water model reproduces the linewidth and the asymmetric broadening of the symmetric OH stretching mode, which we assign to spectral diffusion. In the OH stretching region, dynamics calculations predict a more intense antisymmetric peak than experiments observe but do not predict the bimodal split symmetric peak that the experiments show. Furthermore, our work suggests that electronic polarization, missing in the empirical force field, is responsible for the first discrepancy and that quantum nuclear effects, captured neither in density functional theory nor in classical dynamics, may be responsible for the second.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Amphiphile conformation impacts aggregate morphology and solution structure across multiple lengthscales

Although the self-assembly of amphiphiles is well-studied in aqueous solutions, much less is understood about the fundamental driving forces and structure property relationships in non-polar media. In recent work [Journal of Physical Chemistry B, 2020, 124, 10822.] the authors have studied a series of malonomide-based amphiphiles that are relevant to liquid-liquid extraction. That work demonstrated that aggregation is largely driven by local dipole-dipole interactions between molecules. Here, we build upon this observation to develop a more detailed understanding of how the balance of dipole-dipole interactions (controlled by conformation) and molecular architecture influences the morphology of the aggregates across lengthscales. Using constrained molecular dynamics about key degrees of freedom, we demonstrate that the conformation of N,N-dimethyl,N,N-dioctylhexylethoxy malonamide (DMDOHEMA) and N,N-dimethyl,N,N-dibutyltetradecyl malonamide (DMDBTDMA) has a significant impact upon self-association - where appropriate conformational sampling is essential. To quantify the aggregate morphology, several graph theoretic and persistent homology based properties are determined. The former examines the patterns of intermolecular interactions within clusters, while the latter examines the 3-dimensional spatial distribution. Based upon these analyses, we find that the morphology of aggregates, particularly at higher malonamide concentration, depends on a balance of dipole alignment and alkyl tail sterics. Dipole alignment encourages linear patterns of the intermolecular interactions within aggregates, while the alkyl tail steric interactions between the malonamide result in noticeably less linear aggregates for DMDOHEMA than DMDBTDMA. This is reflected in the spatial distribution, where more holes or voids exist between extractants within the DMDOHEMA that distribute within the solution in more of a "swiss cheese" arrangement as opposed to the more filamentous distribution of DMBDTDMA. This study links conformation and molecular structure to the morphology of amphiphile assemblies, and serves as a basis for ongoing study of multicomponent amphiphile solutions with polar and other solutes, and how these impact aggregation phenomena.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Combining density functional and incremental post-Hartree-Fock approaches for van der Waals dominated adsorbate-surface interactions: Ag{sub 2}/graphene

A combined density functional (DFT) and incremental post-Hartree-Fock (post-HF) approach, proven earlier to calculate He-surface potential energy surfaces [de Lara-Castells et al., J. Chem. Phys. 141, 151102 (2014)], is applied to describe the van der Waals dominated Ag{sub 2}/graphene interaction. It extends the dispersionless density functional theory developed by Pernal et al. [Phys. Rev. Lett. 103, 263201 (2009)] by including periodic boundary conditions while the dispersion is parametrized via the method of increments [H. Stoll, J. Chem. Phys. 97, 8449 (1992)]. Starting with the elementary cluster unit of the target surface (benzene), continuing through the realistic cluster model (coronene), and ending with the periodic model of the extended system, modern ab initio methodologies for intermolecular interactions as well as state-of-the-art van der Waals-corrected density functional-based approaches are put together both to assess the accuracy of the composite scheme and to better characterize the Ag{sub 2}/graphene interaction. The present work illustrates how the combination of DFT and post-HF perspectives may be efficient to design simple and reliable ab initio-based schemes in extended systems for surface science applications.

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

Rotational Spectroscopy of the NH{sub 3}–H{sub 2} Molecular Complex

We report the first high resolution spectroscopic study of the NH{sub 3}–H{sub 2} van der Waals molecular complex. Three different experimental techniques, a molecular beam Fourier transform microwave spectrometer, a millimeter-wave intracavity jet OROTRON spectrometer, and a submillimeter-wave jet spectrometer with multipass cell, were used to detect pure rotational transitions of NH{sub 3}–H{sub 2} in the wide frequency range from 39 to 230 GHz. Two nuclear spin species, ( o )-NH{sub 3}–( o )-H{sub 2} and ( p )-NH{sub 3}–( o )-H{sub 2}, have been assigned as carriers of the observed lines on the basis of accompanying rovibrational calculations performed using the ab initio intermolecular potential energy surface (PES) of Maret et al. The experimental spectra were compared with the theoretical bound state results, thus providing a critical test of the quality of the NH{sub 3}–H{sub 2} PES, which is a key issue for reliable computations of the collisional excitation and de-excitation of ammonia in the dense interstellar medium.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

Sub-diffusion and trapped dynamics of neutral and charged probes in DNA-protein coacervates

The physical mechanism leading to the formation of large intermolecular DNA-protein complexes has been studied. Our study aims to explain the occurrence of fast coacervation dynamics at the charge neutralization point, followed by the appearance of smaller complexes and slower coacervation dynamics as the complex experiences overcharging. Furthermore, the electrostatic potential and probe mobility was investigated to mimic the transport of DNA / DNA-protein complex in a DNA-protein complex coacervate medium [N. Arfin and H. B. Bohidar, J. Phys. Chem. B 116, 13192 (2012)] by assigning neutral, negative, or positive charge to the probe particle. The mobility of the neutral probe was maximal at low matrix concentrations and showed random walk behavior, while its mobility ceased at the jamming concentration of c = 0.6, showing sub-diffusion and trapped dynamics. The positively charged probe showed sub-diffusive random walk followed by trapped dynamics, while the negatively charged probe showed trapping with occasional hopping dynamics at much lower concentrations. Sub-diffusion of the probe was observed in all cases under consideration, where the electrostatic interaction was used exclusively as the dominant force involved in the dynamics. For neutral and positive probes, the mean square displacement 〈R{sup 2}〉 exhibits a scaling with time as 〈R{sup 2}〉 ∼ t{sup α}, distinguishing random walk and trapped dynamics at α = 0.64 ± 0.04 at c = 0.12 and c = 0.6, respectively. In addition, the same scaling factors with the exponent β = 0.64 ± 0.04 can be used to distinguish random walk and trapped dynamics for the neutral and positive probes using the relation between the number of distinct sites visited by the probe, S(t), which follows the scaling, S(t) ∼ t{sup β}/ln (t). Our results established the occurrence of a hierarchy of diffusion dynamics experienced by a probe in a dense medium that is either charged or neutral.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Tailoring the Weight of Surface and Intralayer Edge States to Control LUMO Energies

Abstract The energies of the frontier molecular orbitals determine the optoelectronic properties in organic films, which are crucial for their application, and strongly depend on the morphology and supramolecular structure. The impact of the latter two properties on the electronic energy levels relies primarily on nearest‐neighbor interactions, which are difficult to study due to their nanoscale nature and heterogeneity. Here, an automated method is presented for fabricating thin films with a tailored ratio of surface to bulk sites and a controlled extension of domain edges, both of which are used to control nearest‐neighbor interactions. This method uses a Langmuir–Schaefer‐type rolling transfer of Langmuir layers (rtLL) to minimize flow during the deposition of rigid Langmuir layers composed of π‐conjugated molecules. Using UV–vis absorption spectroscopy, atomic force microscopy, and transmission electron microscopy, it is shown that the rtLL method advances the deposition of multi‐Langmuir layers and enables the production of films with defined morphology. The variation in nearest‐neighbor interactions is thus achieved and the resulting systematically tuned lowest unoccupied molecular orbital (LUMO) energies (determined via square‐wave voltammetry) enable the establishment of a model that functionally relates the LUMO energies to a morphological descriptor, allowing for the prediction of the range of accessible LUMO energies.

36 MATERIALS SCIENCE↗
DOE OSTI2018

In vivo cross-linking supports a head-to-tail mechanism for regulation of the plant plasma membrane P-type H + -ATPase

In higher plants, a P-type proton pumping ATPase generates the proton-motive force essential for the function of all other transporters and for proper growth and development. X-ray crystallographic studies of the plant plasma membrane proton pump have provided information on amino acids involved in ATP catalysis but provided no information on the structure of the C-terminal regulatory domain. Despite progress in elucidating enzymes involved in the signaling pathways that activate or inhibit this pump, the site of interaction of the C-terminal regulatory domain with the catalytic domains remains a mystery. Genetic studies have pointed to amino acids in various parts of the protein that may be involved but direct chemical evidence for which ones are specifically interacting with the C-terminus is lacking. In this study we used in vivo cross-linking experiments with a photo-reactive unnatural amino acid, p-benzoyl-phenylalanine (BPA) and tandem mass spectrometry, to obtain direct evidence that the carboxyl terminal regulatory domain directly interacts with amino acids located within the N-terminal actuator domain. Our observations are consistent with a mechanism in which intermolecular, rather than intramolecular, interactions are involved. Our model invokes a ‘head-to-tail’ organization of ATPase monomers in which the carboxyl terminal domain of one ATPase molecule interacts with the actuator domain of another ATPase molecule. This model serves to explain why cross-linked peptides are found only in dimers and trimers, and is consistent with prior studies suggesting that within the membrane, the protein can be organized as homopolymers, including dimers, trimers and hexamers.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2016

Character of intermolecular interaction in pyridine-argon complex: Ab initio potential energy surface, internal dynamics, and interrelations between SAPT energy components

The pyridine-Ar (PAr) van der Waals (vdW) complex is studied using a high level ab initio method. Its structure, binding energy, and intermolecular vibrational states are determined from the analytical potential energy surface constructed from interaction energy (IE) values computed at the coupled cluster level of theory with single, double, and perturbatively included triple excitations with the augmented correlation consistent polarized valence double-ζ (aug-cc-pVDZ) basis set complemented by midbond functions. The structure of the complex at its global minimum with Ar at a distance of 3.509 Å from the pyridine plane and shifted by 0.218 Å from the center of mass towards nitrogen agrees well with the corresponding equilibrium structure derived previously from the rotational spectrum of PAr. The PAr binding energy D{sub e} of 392 cm{sup −1} is close to that of 387 cm{sup −1} calculated earlier at the same ab initio level for the prototypical benzene-Ar (BAr) complex. However, under an extension of the basis set, D{sub e} for PAr becomes slightly lower than D{sub e} for BAr. The ab initio vdW vibrational energy levels allow us to estimate the reliability of the methods for the determination of the vdW fundamentals from the rotational spectra. To disclose the character of the intermolecular interaction in PAr, the symmetry-adapted perturbation theory (SAPT) is employed for the analysis of different physical contributions to IE. It is found that SAPT components of IE can be approximately expressed in the binding region by only two of them: the exchange repulsion and dispersion energy. The total induction effect is negligible. The interrelations between various SAPT components found for PAr are fulfilled for a few other complexes involving aromatic molecules and Ar or Ne, which indicates that they are valid for all rare gas (Rg) atoms and aromatics.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗