Improved Quantification of MicroPET/CT Imaging Using CT-derived Scaling Factors.

Purpose: Combined micro-PET/CT scanners are widely employed to investigate models of brain disorders in rodents using PET-based coregistration. We examined if CT-based coregistration could improve estimates of brain dimensions and consequently estimates of nondisplaceable binding potential (BPND) in rodent PET studies. Procedures: PET and CT scans were acquired on 5 female and 5 male CD-1 mice with PET and CT scans were acquired on 5 female and 5 male CD-1 mice with 3-[18F]fluoro-5-(2-pyridinylethynyl)benzonitrile ([18F]FPEB), a radiotracer for the metabotropic glutamate receptor subtype 5 (mGluR5). In the proposed PET/CT (PTCT) approach, the tracer-specific standard volume was dimension-customized to each animal using the scaling factors from CT-to-standard CT coregistration to simplify PET-to-standard PET coregistration (i.e., 3 CT- and 6 PET-derived parameters). For comparison, conventional PET-based coregistration was performed with 9 (PT9) or 12 (PT12) parameters. PET frames were transferred to the standard space by the three approaches (PTCT, PT9, and PT12) to obtain regional time-activity curves (TACs) and BPND in 14 standard volumes of interest (VOIs). Lastly, CT images of the animals were transferred to the standard space by CT-based parameters from PTCT and with the scaling factors replaced with those from PET-based PT9 to evaluate agreement of the skull to the standard CT. Results: The PET-based approaches showed various degrees of underestimations of scaling factors in the posterior-anterior-direction compared to PTCT, which resulted in negatively proportional overestimation of radioactivity in the cerebellum (reference region) up to 20%, and proportional, more prominent underestimation of BPND in target regions down to -50%. The skulls of individual animals agreed with the standard skull for scaling factors from PTCT but not for the scaling factors from PT9, which suggested inaccuracy of the latter. Conclusions: The results indicated that conventional PET-based coregistration approaches could yield biased estimates of BPND due to erroneous estimates of brain dimensions when applied to tracers for which the cerebellum serves as reference region. The proposed PTCT provides evidence of a quantitative improvement over PET-based approaches for brain studies using micro-PET/CT scanners.

Theoretical Study on Thermal Structural Fluctuation Effects of Intermolecular Configurations on Singlet Fission in Pentacene Crystal Models.

Singlet fission (SF) occurs as a result of complex excited state relaxation dynamics in molecular aggregates, where a singlet exciton (FE) state is converted into a double-triplet exciton (TT) state through the interactions with several other degrees of freedom, such as nuclear motions. In this study, we combined quantum dynamics simulation based on the quantum master equation approach with all-atom-based classical molecular mechanics/molecular dynamics to examine the thermal structural fluctuation (i.e., static disorder) effects of intermolecular configuration on SF in pentacene crystal models. In particular, we considered two types of static-disordered models, in which excited states are assumed to interact with nuclear motions of intermolecular modes in the classical mechanical/statistical manner. We found that the introduction of static disorder effects leads to a faster decay of coherence between the FE and charge transfer (CT) states in the early stage of SF, contributing to the accelerations of several FE → TT relaxation pathways. Such acceleration in these models is shown to be attributed to fluctuations in the energies and electronic coupling of the CT states based on relative relaxation factor analysis. The present study is expected to contribute to further development of bottom-up materials design for efficient SF in condensed phases where the exitonic system interacts with nuclear motions in various coupling strengths.

Characterization of resonance structures in aromatic rings of benzene and its heavier-element analogues.

We present the experimental visualization of the valence-electron-density distribution in benzene and its kinetically stabilized heavier-element analogues, i.e., 1,2-disilabenzene and 1,2-digermabenzene. The valence-electron-density-distribution (EDD) analysis on the 1,2-disila- and 1,2-digermabenzenes revealed that these contain incompletely delocalized π electrons on their cyclic conjugation systems, making them less aromatic compared to benzene. Based on the results of this EDD analysis in combination with anisotropy of the current-induced density (ACID) calculations, considerable contributions from the characteristic resonance structures of 1,2-disila- and 1,2-digermabenzenes with cleaved EE bonds can be expected.

Thyroid-Stimulating Antibody/Thyroid-Stimulating Hormone Receptor Antibody Ratio as a Sensitive Screening Test for Active Graves' Orbitopathy.

OBJECTIVE: Graves' orbitopathy (GO), an extrathyroidal manifestation of Graves' disease, can seriously threaten a patient's quality of life. Given that immunosuppressive treatment during the early active phase of GO has been found to reduce both disease activity and severity, sensitive screening tests are needed. METHODS: The present study included 86 patients with GO, in whom serum levels of thyroid-stimulating hormone (TSH), free triiodothyronine (T3), free thyroxine, thyroid-stimulating antibody, TSH receptor antibody, thyroid peroxidase antibody, thyroglobulin, and thyroglobulin antibody were measured within 2 months before magnetic resonance imaging (MRI) for orbit assessment. RESULTS: The thyroid-stimulating antibody/TSH receptor antibody ratio was able to distinguish MRI results with a correct classification rate of 81%. When focusing on patients without T3 predominant Graves' diseases, the ratio distinguished MRI results at a rate of 92%. Receiver operating characteristic curve analysis revealed a cutoff antibody ratio of 87, which yielded a sensitivity, specificity, positive likelihood ratio, and negative likelihood ratio of 91%, 95%, 18.2, and 0.0957, respectively, for distinguished MRI results. CONCLUSIONS: The thyroid-stimulating antibody/TSH receptor antibody ratio is a highly sensitive and specific indicator for active GO, especially in patients without T3 predominance, and serves as a good screening test for active GO in primary care settings.

Medium Diradical Character, Small Hole and Electron Reorganization Energies and Ambipolar Transistors in Difluorenoheteroles.

Four difluorenoheteroles having a central quinoidal core with the heteroring varying as furan, thiophene, its dioxide derivative and pyrrole have shown to be medium character diradicals. Solid-state structures, optical, photophysical, magnetic, and electrochemical properties have been discussed in terms of diradical character, variation of aromatic character and captodative effects (electron affinity). Organic field-effect transistors (OFETs) have been prepared, showing balanced hole and electron mobilities of the order of 10-3  cm2 V-1 s-1 or ambipolar charge transport which is first inferred from their redox amphoterism. Quantum chemical calculations show that the electrical behavior is originated from the medium diradical character which produces similar reorganization energies for hole and electron transports. The vision of a diradical as simultaneously bearing pseudo-hole and pseudo-electron defects might justify the reduced values of reorganization energies for both regimes. Structure-function relationships between diradical and ambipolar electrical behavior are revealed.

Adenosine inhibits TNFα-induced MMP-3 production in MH7A rheumatoid arthritis synoviocytes via A2A receptor signaling.

Adenosine causes the anti-inflammatory effect of MTX; however, the contributions of synoviocyte adenosine receptors (AdoRs) are unknown, and matrix metalloproteinase 3 (MMP-3) is released by fibroblast-like synoviocytes in response to inflammatory signaling. To understand the mechanism of the clinical observation that the matrix proteinase-3 concentration of patients with rheumatoid arthritis treated successfully with methotrexate does not usually normalize, we investigated the effects of A2A AdoR activation and inhibition on tumor necrosis factor-alpha (TNFα)-induced MMP-3 release by MH7A human rheumatoid synovial cells. MH7A cells constitutively expressed membrane-associated A2A AdoRs, and HENECA enhanced intracellular cAMP. Stimulation with TNFα markedly enhanced release of MMP-3 from MH7A cells, whereas HENECA partially and dose-dependently inhibited TNFα-evoked MMP-3 release. Similarly, dbcAMP partially inhibited TNFα-induced MMP-3 release. Pretreatment with ZM241385 reversed the inhibitory effects of HENECA. Further, TNFα induced p38 MAPK and ATF-2 phosphorylation, whereas HENECA suppressed p38 MAPK and ATF-2 phosphorylation. We concluded that adenosine signaling via A2A AdoRs, adenylyl cyclase, and cAMP reduces TNFα-induced MMP-3 production by interfering with p38 MAPK/ATF-2 activity. Activation of A2A AdoR signaling alone using HENECA did not reduce TNFα-induced MMP-3 production to the basal levels, which may explain why MTX usually decreases but does not eliminate serum MMP-3.

Bis-periazulene (Cyclohepta[def]fluorene) as a Nonalternant Isomer of Pyrene: Synthesis and Characterization of Its Triaryl Derivatives.

Bis-periazulene (cyclohepta[def]fluorene), which is an unknown pyrene isomer, was synthesized as kinetically protected forms. Its triaryl derivatives 1c-e exhibited the superimposed electronic structures of peripheral, polarized, and open-shell π-conjugated systems. In contrast to previous theoretical predictions, bis-periazulene derivatives were in the singlet ground state. Changing an aryl group controlled the energy gap between the lowest singlet-triplet states.

Dianion and Dication of Tetracyclopentatetraphenylene as Decoupled Annulene-within-an-Annulene Models.

The dianion and dication of tetramesityl-substituted tetracyclopentatetraphenylene, a circulene consisting of alternating five- and six-membered rings, have been generated by reduction with alkali metals and oxidation with antimony(V) halides, respectively. They are theoretically predicted to adopt double annulenoid structures called annulene-within-an-annulene models in which the outer and inner conjugation circuits are significantly decoupled. The theoretical structures were experimentally proven by X-ray crystallographic analyses and the electronic configurations were supported by MCD spectra. Based on the 13 C NMR chemical shifts, negative and positive charges are shown to be located mainly at the outer periphery, indicating that the dianion and dication have delocalized 22-π and 18-π electron outer perimeters, respectively, and 8-π electron structure at the inner ring. Notably, the dianion has an open-shell character, whereas the dication has a closed-shell ground state.

Theoretical Study on Redox Potential Control of Iron-Sulfur Cluster by Hydrogen Bonds: A Possibility of Redox Potential Programming.

The effect of hydrogen bonds around the active site of Anabaena [2Fe-2S] ferredoxin (Fd) on a vertical ionization potential of the reduced state (IP(red)) is examined based on the density functional theory (DFT) calculations. The results indicate that a single hydrogen bond increases the relative stability of the reduced state, and shifts IP(red) to a reductive side by 0.31-0.33 eV, regardless of the attached sulfur atoms. In addition, the IP(red) value can be changed by the number of hydrogen bonds around the active site. The results also suggest that the redox potential of [2Fe-2S] Fd is controlled by the number of hydrogen bonds because IP(red) is considered to be a major factor in the redox potential. Furthermore, there is a possibility that the redox potentials of artificial iron-sulfur clusters can be finely controlled by the number of the hydrogen bonds attached to the sulfur atoms of the cluster.

Long Carbon-Carbon Bonding beyond 2 Å in Tris(9-fluorenylidene)methane.

We report on our investigation of C-C bonding longer than 2.0 Å, which can be realized by perpendicularly facing two fluorenyl rings in the title compound. A small orbital overlap between the distantly positioned carbon atoms is observed as a small concentration of electrons on the X-ray electron density map. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the compound originate from the in-phase and out-of-phase interactions of the overlapping orbitals, respectively, with a gap of 2.39 eV. Solid-state 13C NMR spectroscopy shows a sharp peak at 82.9 ppm for the long-bonded carbons, and a CASSCF(6,6) calculation indicates small diradical character. The experimental and theoretical analyses reveal sufficient covalent-bonding interaction in the long-bonded carbon pair.

A Tale of Two Isomers: Enhanced Antiaromaticity/Diradical Character versus Deleterious Ring-Opening of Benzofuran-fused s-Indacenes and Dicyclopenta[b,g]naphthalenes.

We examine the effects of fusing two benzofurans to s-indacene (indacenodibenzofurans, IDBFs) and dicyclopenta[b,g]naphthalene (indenoindenodibenzofurans, IIDBFs) to control the strong antiaromaticity and diradical character of these core units. Synthesis via 3-functionalized benzofuran yields syn-IDBF and syn-IIDBF. syn-IDBF possesses a high degree of paratropicity, exceeding that of the parent hydrocarbon, which in turn results in strong diradical character for syn-IIDBF. In the case of the anti-isomers, synthesized via 2-substituted benzofurans, these effects are decreased; however, both derivatives undergo an unexpected ring-opening reaction during the final dearomatization step. All the results are compared to the benzothiophene-fused analogues and show that the increased electronegativity of oxygen in the syn-fused derivatives leads to enhancement of the antiaromatic core causing greater paratropicity. For syn-IIDBF increased diradical character results from rearomati-zation of the core naphthalene unit in order to relieve this paratropicity.

Theoretical Study on Singlet Fission Dynamics in Slip-Stack-like Pentacene Ring-Shaped Aggregate Models.

We investigate the singlet fission (SF) dynamics of a slip-stack-like pentacene ring-shaped aggregate model, which is constructed by rotating each pentacene unit around its longitudinal axis in an H-aggregate ring. The aggregate size (N) and rotation angle (α) dependences of SF rates and double triplet (TT) yields are clarified using the quantum master equation method. It is found that there exist optimal ranges of the rotation angle α for each N, yielding efficient SF with high SF rates and TT yields. For example, in an 8-mer model, SF rates at α = 23 and 43° are 18.9 and 38.6 times as high as that at α = 30°, respectively, and the TT yields are as high as 0.871, 0.988, and 0.882 at α = 23, 30, and 43°, respectively. Analysis of the relative relaxation factors shows that the many-to-many relaxation paths from adiabatic Frenkel exciton (FE)-like states to TT-like states are opened by tuning α at relevant aggregate sizes, causing fast and high-TT-yield SF, and efficient SF occurs at α = 40° for medium N (7 ≤ N ≤ 10) or at α = 30° for large N (>10). This mechanism is interpreted by the second-order perturbation theory for electronic couplings. Namely, the inequality in the energies of charge-transfer states [CA and AC states, where the cation (C) and anion (A) are located at two neighboring sites in anticlockwise and clockwise directions, respectively] and the change in the amplitude and sign of the couplings between the FE, CT, and TT states are found to cause quantum superposition of the FE and TT states, which contribute to the high TT yield and SF rate. The present results contribute to a deeper understanding of SF dynamics in ring-shaped aggregates as well as to the development of their new design guidelines.

Theoretical study on the effect of applying an external static electric field on the singlet fission dynamics of pentacene dimer models.

We investigate the effect of applying an external static electric field on the singlet fission (SF) dynamics of pentacene dimer models using quantum chemical calculations and exciton dynamics simulations. It is found that the excitation energies of anion-cation (AC) and cation-anion (CA) pair exciton states in the SF process are significantly stabilized and destabilized, respectively, by applying an external static electric field (F) in the intermolecular direction. As a result, this change of excitation energies is found to accelerate the SF dynamics in pentacene dimer models. In particular, in the tilted- and parallel-type pentacene dimer models, SF rates at F = 0.001 a.u. are predicted to be about 2.3 and 3.0 times as large as those at F = 0.0 a.u. while keeping the TT yields large. The present result contributes to paving the way for novel physical and chemical controls, that is, an external static electric field application and donor/acceptor substitution on SF molecules, of SF dynamics.

Theoretical Study on Singlet Fission in Aromatic Diaza s-Indacene Dimers.

We theoretically show that diaza (N2)-substitution to s-indacene with 4n π-electrons, by which the number of π-electrons in N2-s-indacene amounts to 4n+2, is a new strategy to design efficient singlet fission (SF) molecules. By N2-substitution, the diradical character and the exchange integral are found to be tuned moderately, leading to satisfying the excitation energy level matching condition for SF with a large triplet excitation energy. On the basis of the effective electronic coupling related to the SF rate, we explore the optimal slip-stack dimer packings for fast SF. Their underlying mechanisms are well understood from the odd-electron density, resonance structure, and frontier orbital distribution, as the functions of the N2-substituted positions. Furthermore, aromaticities of N2-s-indacenes are evaluated explicitly on the basis of the magnetically induced current. Although N2-s-indacenes display strengths of aromaticities similar to that of anthracene, a local decrease in aromaticity is found to correlate to the spatial feature of diradical character, i.e., odd-electron density. The present findings not only newly propose N2-s-indacenes as feasible SF molecules but also contribute to comprehending the interplay between aromaticity and diradical electronic structures contributing to SF.

Characterization of Benzo[a]naphtho[2,3-f]pentalene: Interrelation between Open-shell and Antiaromatic Characters Governed by Mode of the Quinoidal Subunit and Molecular Symmetry.

The singlet open-shell character and antiaromaticity are intriguing features in π-conjugated carbocycles. These two exhibit similar chemical and physical properties. However, they rarely coexist in the same molecule. Understanding the interrelation between the open-shell and antiaromatic characteristics in the same molecule is crucial to control the electronic properties. Herein we describe the synthesis and characterization of a new member of diareno[a,f]pentalene, benzo[a]naphtho[2,3-f]pentalene 6. Unlike its isomer 5 with a closed-shell ground state, 6 exhibits an appreciable open-shell character and a moderate antiaromatic feature. The behaviors of the open-shell index (y0 ) against the difference of the proton chemical signal (Δδ(H1 )) between pentalenide dianions/neutral pentalenes for our reported pentalenes 1, 4, 5, and 6 give a thought-provoking conclusion about the interrelation between open-shell and antiaromatic characteristics in this series. The mode of the incorporated quinoidal moiety and the formal molecular symmetry are critical to balance these two characteristics.

Theoretical Study on Third-Order Nonlinear Optical Properties for One-Hole-Doped Diradicaloids.

We investigate the relationships between open-shell character and longitudinal static second hyperpolarizabilities γ for one-hole-doped diradicaloids using the strong-correlated ab initio molecular orbital methods and simple one-dimensional (1D) three-site two-electron (3s-2e) models. As examples of one-hole-doped diradicaloids, we examine H3 +, methyl radical trimer cation ((CH3)3 +), silyl radical trimer cation ((SiH3)3 +), and 1,2,3,5-dithiadizolyl trimer cation (DTDA3 +). For H3 +, the static γ exhibits negative values and shows a monotonic increase in amplitude with an increase in the open-shell character defined by a neighbor-site interaction (y S). On the other hand, it is found for (CH3)3 +, (SiH3)3 +, and DTDA3 + that the static γ value exhibits similar behavior to that for H3 + up to an intermediate y S value, while it takes the negative maximum at a large y S value, followed by a decrease in γ amplitude, and subsequently, γ changes to positive values with a drastic increase for larger y S values. For example, in DTDA3 +, the negative/positive γ values, -69 × 105/700 × 105 au at y S = 0.75/0.87, exhibit significant enhancements in amplitude, 2.4/24 times as large as that (-29 × 105 au) at intermediate y S = 0.59 as is often the case in DTDA2. Using the 1D 3s-2e valence-bond configuration interaction model, these sign inversions and drastic increase in the amplitude of γ are found to originate in the differences in Coulomb interactions between valence electrons, between valence and core electrons, and between valence electrons and nuclei. These results contribute to pave the way for the construction of novel control guidelines for the amplitude and sign of γ for one-hole-doped diradicaloids.

Monoradicals and Diradicals of Dibenzofluoreno[3,2-b]fluorene Isomers: Mechanisms of Electronic Delocalization.

The preparation of a series of dibenzo- and tetrabenzo-fused fluoreno[3,2-b]fluorenes is disclosed, and the diradicaloid properties of these molecules are compared with those of a similar, previously reported series of anthracene-based diradicaloids. Insights on the diradical mode of delocalization tuning by constitutional isomerism of the external naphthalenes has been explored by means of the physical approach (dissection of the electronic properties in terms of electronic repulsion and transfer integral) of diradicals. This study has also been extended to the redox species of the two series of compounds and found that the radical cations have the same stabilization mode by delocalization that the neutral diradicals while the radical anions, contrarily, are stabilized by aromatization of the central core. The synthesis of the fluorenofluorene series and their characterization by electronic absorption and vibrational Raman spectroscopies, X-ray diffraction, SQUID measurements, electrochemistry, in situ UV-vis-NIR absorption spectroelectrochemistry, and theoretical calculations are presented. This work attempts to unify the properties of different series of diradicaloids in a common argument as well as the properties of the carbocations and carbanions derived from them.

Vibronic coupling density analysis and quantum dynamics simulation for singlet fission in pentacene and its halogenated derivatives.

We theoretically investigate microscopic origins of vibronic coupling (VC) contributing to singlet fission (SF) dynamics in pentacene and its halogenated derivatives. The features of VCs related to diabatic exciton states and interstate electronic couplings (Holstein and Peierls couplings, respectively) are interpreted by the VC density (VCD) analysis, which allows one to clarify the relationship between the chemical structure and VC as spatial contribution. It is found for the pentacene dimer face-to-edge configuration in a herringbone crystal that characteristic intermolecular vibrations with low frequencies exhibit strong Holstein couplings for the intermediate charge-transfer (CT) exciton states as well as Peierls couplings. From VCD analysis, the comprising density of the intermolecular CT and that of the intermolecular vibration are found to be constructively mixed in the intermolecular space, leading to the enhancement of VC. Moreover, in order to assess the chemical modification manner for controlling VC, we design several halogenated pentacene derivatives with slip-stack configurations. Our strategy to enhance VCD by halogenation is found to be rational, whereas the peaks of VC spectra for the CT states in the slip-stack packings are observed in high frequency regions. We compare their SF dynamics based on the quantum master equation explicitly including the exciton state-dependent VCs. From the analysis on relative relaxation factors between the adiabatic exciton states, their difference in the SF rate is highlighted by exciton configurations in addition to VCs. The present study is expected to be a first step toward efficient SF based on the design of VC in terms of both the chemical structure and intermolecular packing.

Quantum design for singlet-fission-induced nonlinear optical systems: Effects of π-conjugation length and molecular packing of butterfly-shaped acenes.

Theoretical molecular design of efficient nonlinear optical (NLO) systems using singlet fission (SF) is performed for butterfly-shaped acenes with/without nitrogen and sulfur substitutions using quantum chemical calculations, exciton dynamics simulations, and Marcus theory. It is found that these large systems meet the energy level matching conditions of efficient SF and exhibit superior third-order NLO properties (second hyperpolarizability γ at the molecular scale) to a typical SF molecule, pentacene. In addition, we investigate SF rates and γ in the correlated triplet pair [1(TT)] state generated by SF for various slip-stacked dimer models of these systems. For molecular packing with relatively large 1(TT) yields, a significant increase in γ/monomer in the 1(TT) state is observed, which is in good agreement with the electronic-coupling-based design guidelines obtained from our previous study. In particular, the butterfly-shaped acenes involving heteroatoms are found to exhibit a significant increase in γ/monomer as compared to the other systems. By analyzing the excitation properties in the 1(TT) state and intermolecular orbital interactions, we clarify the origin of such γ enhancement. The obtained results contribute to the construction of design guidelines for efficient SF-induced-NLO materials and demonstrate that butterfly-shaped acenes have the potential to surpass conventional NLO systems.

Unclassified four-repeat tauopathy associated with familial parkinsonism and progressive respiratory failure.

We describe an autopsied patient with familial parkinsonism and unclassified four repeat-tau (4R-tau) aggregation. She presented with bradykinesia, truncal dystonia, and mild amnesia at the age of 61 and then exhibited body weight loss (15 kg over 8 months), sleep disturbances, and progressive respiratory failure with CO2 narcosis. She died of respiratory failure at the age of 62, 14 months after disease onset. Her brother also showed parkinsonism at the age of 58 and suddenly died 6 months later. Postmortem examination revealed 4R-tau aggregation, which was characterized by neuronal globose-type tangles or pretangles, bush-like or miscellaneous astrocytic inclusions, and coiled bodies. The temporal tip, the striatum, the substantia nigra, the tegmentum of the midbrain, the medullary reticular formation, and the spinal cord were severely involved with tau aggregation. Argyrophilic grains and ballooned neurons were also found in the medial temporal structures, however, extensions of the 4R-aggregations in the case were clearly broader than those of the argyrophilic grains. Western blot analysis of sarkosyl-insoluble fractions from brain lysates revealed prominent bands of tau at both 33 kDa and 37 kDa. Genetic examinations did not reveal any known pathogenic mutations in MAPT, DCTN-1, PSEN-1, or familial or young-onset parkinsonism-related genes. The clinical manifestations, pathologic findings, and biochemical properties of aggregated tau in our patient cannot be explained by argyrophilic grain disease or other known 4R-tauopathies alone. Our results further extend the clinical and neuropathologic spectra of 4R-tauopathy.