Estimation of electronic coupling for intermolecular electron transfer from cross-reaction data

Sixty-five electron-transfer reactions including 27 new 0, +1 couples have been added to our data set of cross-reactions between 0 and +1 couples, bringing it to 206 reactions involving 72 couples that have been studied by stopped-flow kinetics in acetonitrile containing supporting electrolyte at 25 degrees C, formal potentials determined by cyclic voltammetry, and analyzed using Marcus cross-rate theory. Perhaps surprisingly, a least-squares analysis demonstrates that intrinsic rate constants exist that predict the cross-rate constants to within a factor of 2 of the observed ones for 93% of the reactions studied, and only three of the reactions have a cross-rate constant that lies outside of the factor of 3, that corresponds to a factor of 10 uncertainty in the rate constant for an unknown couple. Many triarylamines, which have very high intrinsic reactivity, are included among the newly studied couples. The enthalpy contribution to the Marcus reorganization energy, lambda'v, has been calculated for 46 of the couples studied, at the (U)B3LYP/6-31+G (or for the larger and lower barrier compounds, at the less time-consuming (U)B3LYP/6-31G) level. In combination with a modified Levich and Dogodnadze treatment that assumes that the rate constant is proportional to (KeHab2/lambda1/2) exp[-DeltaG/RT], this allows estimation of the electronic coupling (Hab) at the transition state for intermolecular electron transfer, (more properly H'ab, the product of the square root of the encounter complex formation constant times Hab) for these couples. Although the principal factor affecting intermolecular electron-transfer rate constants is clearly lambda, H'ab effects are easily detectable, and the dynamic range in our estimates of them is over a factor of 600.     

Single peptide assembly onto a 1.5 nm Au surface via a histidine tag

Nanoparticle surfaces functionalized with proteins or other biomolecules provide a mechanism for interfacing the unique properties of nanomaterials with biological samples. In most of these studies, the biomolecule is conjugated to a gold nanoparticles (AuNP) surface through the thiol group of native or introduced cysteine residues. Here we demonstrate the direct attachment of a hexa-histidine tagged (His(6)) peptide to a 1.5 nm AuNP. Binding occurs via a specific interaction between the Ne of the His imidazole, forming a 1:1 stoichiometric complex. Given the widespread use of histidine tags in producing recombinant proteins, this approach promises to expand the applications of AuNP in biological applications.     

Subpicosecond protein backbone changes detected during the green-absorbing proteorhodopsin primary photoreaction

Recent studies demonstrate that photoactive proteins can react within several picoseconds to photon absorption by their chromophores. Faster subpicosecond protein responses have been suggested to occur in rhodopsin-like proteins where retinal photoisomerization may impulsively drive structural changes in nearby protein groups. Here, we test this possibility by investigating the earliest protein structural changes occurring in proteorhodopsin (PR) using ultrafast transient infrared (TIR) spectroscopy with approximately 200 fs time resolution combined with nonperturbing isotope labeling. PR is a recently discovered microbial rhodopsin similar to bacteriorhodopsin (BR) found in marine proteobacteria and functions as a proton pump. Vibrational bands in the retinal fingerprint (1175-1215 cm(-1)) and ethylenic stretching (1500-1570 cm(-1)) regions characteristic of all-trans to 13-cis chromophore isomerization and formation of a red-shifted photointermediate appear with a 500-700 fs time constant after photoexcitation. Bands characteristic of partial return to the ground state evolve with a 2.0-3.5 ps time constant. In addition, a negative band appears at 1548 cm(-1) with a time constant of 500-700 fs, which on the basis of total-15N and retinal C15D (retinal with a deuterium on carbon 15) isotope labeling is assigned to an amide II peptide backbone mode that shifts to near 1538 cm(-1) concomitantly with chromophore isomerization. Our results demonstrate that one or more peptide backbone groups in PR respond with a time constant of 500-700 fs, almost coincident with the light-driven retinylidene chromophore isomerization. The protein changes we observe on a subpicosecond time scale may be involved in storage of the absorbed photon energy subsequently utilized for proton transport.     

Magnetic impurities in gapless Fermi systems: perturbation theory

We consider a symmetric Anderson impurity model with a soft-gap hybridization vanishing at the Fermi level, with r>0. Three facets of the problem are examined. First the non-interacting limit, which despite its simplicity contains much physics relevant to the U>0case: it exhibits both strong coupling (SC) states (for r<1) and local moment states (for r>1), with characteristic signatures in both spectral properties and thermodynamic functions. Second, we establish general conditions upon the interaction self-energy for the occurence of a SC state for U>0. This leads to a pinning theorem, whereby the modified spectral function is pinned at the Fermi level for any U where a SC state obtains; it generalizes to arbitrary r the pinning condition upon familiar in the normal r=0 Anderson model. Finally, we consider explicitly spectral functions at the simplest level: second order perturbation theory in U, which we conclude is applicable for and r>1 but not for . Characteristic spectral features observed in numerical renormalization group calculations are thereby recovered, for both SC and LM phases; and for the SC state the modified spectral functions are found to contain a generalized Abrikosov-Suhl resonance exhibiting a characteristic low-energy Kondo scale with increasing interaction strength. Received 26 August 1999     

A note on the decomposition of the exterior algebra of the adjoint representation

This note points out a factor of the Poincaré polynomial of the λ-isotypic component of the exterior algebra λL, where L is a complex semisimple Lie algebra and λ is a dominant weight. Although these polynomials have been studied with regard to their factorizations, this particular factor seems to have gone unstated.     

Density Functional Theory Guided Investigation of Ligand-Induced Neptunyl-Neptunyl Interactions

Actinyl-actinyl interactions are particularly prevalent for the pentavalent neptunyl cation (Np(V)O₂)⁺ where these interactions appear either as a T - or D -shape (diamond-shape). T -shaped interactions have been previously identified in high concentration Np(V) solutions containing simple anions (NO₃⁻, ClO₄⁻, Cl⁻) whereas D -shaped have only been isolated in the solid-state in the presence of carboxylate ligands. In this study, Density Functional Theory (DFT) calculations were paired with Raman spectroscopy to evaluate the formation of D -shaped interactions in the presence of aliphatic (R=H (formate), CH₃ (acetate), CH₂CH₃ (propionate)) and aromatic (R=C₆H₅ (benzoate), C₆H₄OH (4-hydroxybenzoate), C₅H₄N (isonicotinate)) carboxylate ligands. DFT studies indicate that the ΔG to form hydrated T - and D -shaped forms are not spontaneous but become so with the addition of the carboxylate ligands. Raman spectra of the Np(V) carboxylate solutions contained vibrational modes associated with the D -shaped interactions, but spectral changes observed over time indicate a dynamic system. Crystallization experiments from the Np(V) carboxylate systems confirmed the presence of D- shaped dimers for the aromatic carboxylates, suggesting that the choice of the anion in solution favors actinyl-actinyl interactions even at low concentrations (≤20 mM) of Np(V).     

Assessment of synthetic cannabinoid FUB-AMB and its ester hydrolysis metabolite in human liver microsomes and human blood samples using UHPLC–MS/MS

FUB-AMB, an indazole carboxamide synthetic cannabinoid recreational drug, was one of the compounds most frequently reported to governmental agencies worldwide between 2016 and 2019. It has been implicated in intoxications and fatalities, posing a risk to public health. In the current study, FUB-AMB was incubated with human liver microsomes (HLM) to assess its metabolic fate and stability and to determine if its major ester hydrolysis metabolite (M1) was present in 12 authentic forensic human blood samples from driving under the influence of drug cases and postmortem investigations using UHPLC–MS/MS. FUB-AMB was rapidly metabolized in HLM, generating M1 that was stable through a 120-min incubation period, a finding that indicates a potential long detection window in human biological samples. M1 was identified in all blood samples, and no parent drug was detected. The authors propose that M1 is a reliable marker for inclusion in laboratory blood screens for FUB-AMB; this metabolite may be pharmacologically active like its precursor FUB-AMB. M1 frequently appears in samples in which the parent drug is undetectable and can point to the causative agent. The results suggest that it is imperative that synthetic cannabinoid laboratory assay panels include metabolites, especially known or potential pharmacologically active metabolites, particularly for compounds with short half-lives.     

Internal bremsstrahlung and double internal bremsstrahlung in initial p-state electron capture

Internal bremsstrahlung (IB) and double internal bremsstrahlung (DIB) have been studied for initial p-state electron capture. In the case of IB the relative contributions of discrete and continuum intermediate states have been calculated and, in contrast to IB in initial Is state capture, it has been found that the contributions from the discrete intermediate states are dominant. Calculations for DIB have been extended and some approximations used in earlier calculations are shown to be reasonable. Predictions are made for DIB in the EC decay of SU55 Fe and ¹³¹Cs, nuclei which may be suitable for experimental investigations.