Assessment of Phytomass and Carbon Stock in the Ecosystems of the Central Forest Steppe of the East European Plain: Integrated Approach of Terrestrial Environmental Monitoring and Remote Sensing with Unmanned Aerial Vehicles.

The rapid and accurate estimation of aboveground forest phytomass remains a challenging research task. In general, methods for estimating phytomass fall mainly into the category of field measurements performed by ground-based methods, but approaches based on remote sensing and ecological modelling have been increasingly applied. The aim is to develop the scientific and methodological framework for the remote sensing estimation of qualitative and quantitative characteristics of forest stands, using the combination of surveys and machine learning models to determine phytomass of forest stands and calculate the carbon balance. Even-aged stands of different tree species growing in the forest steppe zone of the East European Plain were chosen as test objects. We have applied the modernized methodological approaches to compare and integrate forest and tree stand characteristics obtained by ground-based and UAV-based comprehensive surveys; additionally, we developed computer vision models and methods for determining the same characteristics by remote sensing methods. The key advantage of the proposed methodology for remote monitoring and carbon balance control over existing analogues is the minimization of the amount of groundwork and, consequently, the reduction inlabor costs without loss of information quality. Reliable data on phytomass volumes will allow for operational control of the forest carbon storage, which is essential for decision-making processes. This is important for the environmental monitoring of forests and green spaces of various economic categories. The proposed methodology is necessary for the monitoring and control of ecological-climatic and anthropogenic-technogenic transformations in various landscapes. The development is useful for organizing the management of ecosystems, environmental protection, and managing the recreational and economic resources of landscapes with natural forests and forest plantations.

Specificity of Individual Response Radial Increment of Scots Pine in the Voronezh Biosphere Reserve on the Differentiated Forest Conditions.

The purpose of our study was to assess the individual variability of the response to climatic conditions of the radial increment of Pinus sylvestris L. trees aged 100-140 years. The studied pine stand grows in the conditions of a site with a heterogeneous microrelief in the Voronezh Reserve. The calculated coefficients of synchronicity and correlation of radial increment of a sample of individual Scots pine trees (wood cores). It has been established that in the radial increment of pine trees in the Voronezh Reserve, there is a significant diversity in the reflection of the climatic signal, which, as a rule, manifests itself in certain years that are not extreme in terms of climatic conditions. The reasons for the differentiated reaction of trees to climate are the differentiated conditions of the microrelief, and also, probably, the genetic diversity of forest stands. In natural stands there are individual trees showing very low values of synchronicity coefficients (GLK, %) or correlation coefficients (CC, %) with stand average values. Intrapopulation differences in the response of pine forest stands to fluctuations in climatic factors are one of the forms of protective mechanisms for the survival of a species that have developed as a result of evolutionary development. As our study showed, intrapopulation differences are large in stands of natural origin and not subject to anthropogenic impacts.

Multiscale Mechanical Performance of Wood: From Nano- to Macro-Scale across Structure Hierarchy and Size Effects.

This review describes methods and results of studying the mechanical properties of wood at all scales: from nano- to macro-scale. The connection between the mechanical properties of material and its structure at all these levels is explored. It is shown that the existing size effects in the mechanical properties of wood, in a range of the characteristic sizes of the structure of about six orders of magnitude, correspond to the empirical Hall-Petch relation. This "law" was revealed more than 60 years ago in metals and alloys and later in other materials. The nature, as well as the particular type of the size dependences in different classes of materials can vary, but the general trend, "the smaller the stronger", remains true both for wood and for other cellulose-containing materials. The possible mechanisms of the size effects in wood are being discussed. The correlations between the mechanical and thermophysical properties of wood are described. Several examples are used to demonstrate the possibility to forecast the macromechanical properties of wood by means of contactless thermographic express methods based on measuring temperature diffusivity. The research technique for dendrochronological and dendroclimatological studies by means of the analysis of microhardness and Young's modulus radial dependences in annual growth rings is described.

Relationship between Thermal Diffusivity and Mechanical Properties of Wood.

This paper describes an experimental study of the relationships between thermal diffusivity and mechanical characteristics including Brinell hardness, microhardness, and Young's modulus of common pine (Pinus sylvestris L.), pedunculate oak (Quercus robur L.), and small-leaf lime (Tilia cordata Mill.) wood. A dependence of Brinell hardness and thermal diffusivity tensor components upon humidity for common pine wood is found. The results of the measurement of Brinell hardness, microhardness, Young's modulus, and main components of thermal diffusivity tensor for three perpendicular cuts are found to be correlated. It is shown that the mechanical properties correlate better with the ratio of longitude to transversal thermal diffusivity coefficients than with the respective individual absolute values. The mechanical characteristics with the highest correlation with the abovementioned ratio are found to be the ratio of Young's moduli in longitude and transversal directions. Our technique allows a comparative express assessment of wood mechanical properties by means of a contactless non-destructive measurement of its thermal properties using dynamic thermal imaging instead of laborious and material-consuming destructive mechanical tests.

Regulation-based probabilistic substance quality index and automated geo-spatial modeling for water quality assessment.

Natural environments are recognized as complex heterogeneous structures thus requiring numerous multi-scale observations to yield a comprehensive description. To monitor the current state and identify negative impacts of human activity, fast and precise instruments are in urgent need. This work provides an automated approach to the assessment of spatial variability of water quality using guideline values on the example of 1526 water samples comprising 21 parameters at 448 unique locations across the New Moscow region (Russia). We apply multi-task Gaussian process regression (GPR) to model the measured water properties across the territory, considering not only the spatial but inter-parameter correlations. GPR is enhanced with a Spectral Mixture Kernel to facilitate a hyper-parameter selection and optimization. We use a 5-fold cross-validation scheme along with [Formula: see text]-score to validate the results and select the best model for simultaneous prediction of water properties across the area. Finally, we develop a novel Probabilistic Substance Quality Index (PSQI) that combines probabilistic model predictions with the regulatory standards on the example of the epidemiological rules and hygienic regulations established in Russia. Moreover, we provide an interactive map of experimental results at 100 m2 resolution. The proposed approach contributes significantly to the development of flexible tools in environment quality monitoring, being scalable to different standard systems, number of observation points, and region of interest. It has a strong potential for adaption to environmental and policy changes and non-unified assessment conditions, and may be integrated into support-decision systems for the rapid estimation of water quality spatial distribution.

Transformation of an Embedded Five-Membered Ring in Polycyclic Aromatic Hydrocarbons via the Hydrogen-Abstraction-Acetylene-Addition Mechanism: A Theoretical Study.

Five-membered rings are constituents of many polycyclic aromatic hydrocarbons (PAHs), and their presence on the edges of large PAHs has been repeatedly observed experimentally. However, modern kinetic combustion models often do not consider the growth of PAHs through the transformation of the five-membered rings. In connection with the above, we carried out a theoretical study of the mechanism of hydrogen-abstraction-acetylene-addition (HACA) transformation of an embedded five-membered ring on the armchair PAH edge to a six-membered ring, considering cyclopenta[d,e,f]phenanthrene (4,5-methylenephenanthrene) as a prototype system for this process. The potential energy surface for the reactions of cyclopenta[d,e,f]phenanthrenyl radicals produced by direct H abstractions from cyclopenta[d,e,f]phenanthrene with acetylene has been compiled at the G3(MP2,CC)//B3LYP/6-311G(d,p) level of theory including zero-point vibrational energy corrections. The computed energies and molecular parameters were then used to solve the Rice-Ramsperger-Kassel-Marcus master equation in order to calculate the reaction rate at various pressures and temperatures, which were fitted to the modified Arrhenius equation for further kinetic modeling. The results show that the HACA transformation of the embedded five-membered ring to a six-membered ring is possible, albeit slow. The most viable reaction mechanism involves the R2 + C2H2 reaction, where the acetylene molecules add to a σ-radical in the six-membered ring adjacent to the five-membered ring via a low entrance barrier. The predominant product of R2 + C2H2 is predicted to be 3-ethynyl-4H-cyclopenta[def]phenanthrene Pr5 via immediate H elimination from the initial addition complex. Next, Pr5 undergoes H-assisted isomerization to 4aH-pentaleno[4,3,2,1-cdef]phenanthrene Pr4, and the latter adds a H-atom eventually forming the 1-pyrenylmethyl radical Pr3: R2 + C2H2 ⇆ 3-ethynyl-4H-cyclopenta[def]phenanthrene (Pr5) + H or 4aH-pentaleno[4,3,2,1-cdef]phenanthrene (Pr4) + H; Pr5 + H ⇆ Pr4 + H; Pr4 + H → 1-pyrenylmethyl (Pr3). This HACA sequence may be competitive with the methyl radical addition to the R1 radical formed by H abstraction from the CH2 group in the five-membered ring of cyclopenta[d,e,f]phenanthrene, which provides a pathway to pyrene following two H-atom losses. Relative contributions of the two mechanisms of the five- to six-membered ring transformation would strongly depend on the branching ratios of the R1 and R2 radicals produced by the H abstractions and the available concentration of C2H2 versus CH3 and hence differ in different flames.

Markers of muscle damage and strength performance in professional football (soccer) players during the competitive period.

BACKGROUND: The present study investigated the impact of competitive soccer on the short-term changes in isometric strength of the adductor muscle group during the competitive season. METHODS: In this cohort study we evaluated the association between a serum marker of muscle damage [creatine phosphokinase (CPK)] and isometric strength of the adductor muscles of the hip in 30 professional football players (age: 26.7±2.9 years) during two seasons of the national top-level championship. Serum CPK level was determined the day before the match, 12-20, 36-48, 60-72 h after the match. The maximum voluntary isometric contraction force of the adductor muscles complex was determined immediately after having taken blood samples. RESULTS: There was evidence of a statistically significant positive association between age, body mass index (BMI), percentage of body fat, and muscle strength, and between weight and muscle strength. There was evidence of a statistically significant negative association between the level of CPK and the maximum isometric strength of the adductors of soccer players. Changes in CPK levels were associated with the muscle strength recovery trend (P<0.001). The strength/CPK ratio at different time points had a U-shaped curve. CONCLUSIONS: Exercise induced muscle damage significantly affects the strength of the adductor muscle group of professional soccer players during the competitive period. The lower the CPK level, the greater the athletes' strength at a given time point. Also, the greater the decrease in CPK level, the greater the rate of strength restoration.

Swirlonic state of active matter.

We report a novel state of active matter-a swirlonic state. It is comprised of swirlons, formed by groups of active particles orbiting their common center of mass. These quasi-particles demonstrate a surprising behavior: In response to an external load they move with a constant velocity proportional to the applied force, just as objects in viscous media. The swirlons attract each other and coalesce forming a larger, joint swirlon. The coalescence is extremely slow, decelerating process, resulting in a rarified state of immobile quasi-particles. In addition to the swirlonic state, we observe gaseous, liquid and solid states, depending on the inter-particle and self-driving forces. Interestingly, in contrast to molecular systems, liquid and gaseous states of active matter do not coexist. We explain this unusual phenomenon by the lack of fast particles in active matter. We perform extensive numerical simulations and theoretical analysis. The predictions of the theory agree qualitatively and quantitatively with the simulation results.

Ultrafast dynamics in LMCT and intraconfigurational excited states in hexahaloiridates(iv), models for heavy transition metal complexes and building blocks of quantum correlated materials.

The population and structural dynamics of IrCl62- is studied in acetonitrile and aqueous solutions in comparison to isoelectronic IrBr62- using ultrafast broadband, dispersed transient absorption, with both octahedra excited with 85 fs pulses at four different wavelengths, encompassing the first seven t2g-based electronic states. Ligand-to-metal charge transfer (LMCT) 420 or 490 nm excitation of IrCl62- into Uu'(2T2u) + Eu''(2T2u) states, superimposed due to Ham effect, or Uu'(2T1u), respectively, leads to symmetry lowering due to Jahn-Teller effect in these excited states with the subsequent 100 fs decay into Ug'(2T1g). This first LMCT state is formed vibrationally coherent in the 104 cm-1 t2g (scissor) or 243 cm-1 eg (out-of-phase-stretch) Jahn-Teller modes for the respective excitation wavelength. Direct excitation into Ug'(2T1g) at 600 nm and the intraconfigurational lowest excited Ug'(2T2g) state at 1900 nm helped to establish that Ug'(2T1g) decays via back electron transfer into Ug'(2T2g) (time constants, 3.55 ps in acetonitrile and 0.9 ps in water), and the decay of Ug'(2T2g) into the ground state is the rate-limiting relaxation step. The relaxation cascade of IrBr62- is similar with short-lived (≤100 fs) higher LMCT states, but the vibrational coherence is only observed in the Jahn-Teller t2g mode. Faster back electron transfer for IrBr62- is explained by the energy gap law. The intraconfigurational Ug'(2T2g) states, which are ∼5100 cm-1 above the ground state for both complexes, have a sub-nanosecond lifetime largely independent of the ligand nature (∼350 ps, acetonitrile).

On the mechanism of soot nucleation. II. E-bridge formation at the PAH bay.

A recently proposed mechanism of soot nucleation (M. Frenklach and A. M. Mebel, Phys. Chem. Chem. Phys., 2020, 22, 5314-5331) based upon the formation of a rotationally-activated dimer in the collision of an aromatic molecule and a radical leading to a stable, doubly-bonded E-bridge between them, rooted in the existence of a five-membered ring on the molecule edge, has been further investigated with a focus on the 5-6 E-bridge forming in the reaction of a PAH cyclopenta group with a bay site of another PAH. As a prototype reaction of this kind, we examined the reaction between 4-phenanthrenyl and acenaphthylene and, to project these results to larger aromatic structures, we also explored the size effect of the E-bridge forming reactions by computing the 1-naphthyl + acenaphthylene system and comparing these results with the prior results for pyrenyl + acepyrene. The two systems have been studied through high-level G3(MP2,CC)//B3LYP/6-311G(d,p) ab initio calculations of their potential energy surfaces combined with the RRKM/Master Equation calculations of reaction rate constants. With PAH monomers of similar sizes involved, the formation of E-bridge structures at the bay radical sites appeared to be faster and lead to increased nucleation rates as compared to the zigzag-forming ones. A model combining both the bay and zigzag rotationally-induced formation of E-bridges successfully reaches the level of nucleation fluxes comparable to those of the irreversible pyrene dimerization, thus affirming the rotationally-activated dimerization as a feasible mechanism for soot particle nucleation.

Femtosecond dynamics of metal-centered and ligand-to-metal charge-transfer (t2g-based) electronic excited states in various solvents: A comprehensive study of IrBr6 2.

The photophysical properties of intraconfigurational metal-centered (MC) and ligand-to-metal charge transfer (LMCT) states were studied in a prototype low spin heavy d5 transition metal complex, IrBr6 2-. The femtosecond-to-picosecond dynamics of this complex was investigated in solutions of drastically different polarity (acetonitrile, chloroform, and water) by means of ultrafast broadband transient absorption spectroscopy. We observed that the system, when excited into the third excited [second LMCT, 2Uu'(T1u)] state, undergoes distortion from the Franck-Condon geometry along the t2g vibrational mode as a result of the Jahn-Teller effect, followed by rapid internal conversion to populate (90 fs) the second excited [first LMCT, 2Ug'(T1g)] state. Vibrational decoherence and vibrational relaxation (∼400 fs) in 2Ug'(T1g) precede the decay of this state via internal conversion (time constants, 2.8 and 3 ps in CH3CN and CHCl3 and 0.76 ps in water), which can also be viewed as back electron transfer and which leads into the intraconfigurational MC 2Ug'(T2g) state. This is the lowest-excited state, from which the system returns to the ground state. This MC state is metastable in both CH3CN and CHCl3 (lifetime, ∼360 ps), but is quenched via OH-mediated energy transfer in aqueous environments, with the lifetime shortening up to 21 ps in aqueous solutions. The cascade relaxation mechanism is the same upon excitation into the second excited state. Excitation of IrBr6 2- in chloroform into higher 2Uu'(T2u), 2Eu″(T2u), and 2Eg'(T1g) states is observed to populate the third excited 2Uu'(T1u) state within 100 fs. These experiments allow us to resolve the ultrafast relaxation coordinate and emphasize that the excited-state Jahn-Teller effect is a driving force in the ultrafast dynamics, even for heavy transition metal complexes with very significant spin-orbit interactions.

Mechanism and rate constants of the CH2 + CH2 CO reactions in triplet and singlet states: A theoretical study.

Ab initio and density functional CCSD(T)-F12/cc-pVQZ-f12//B2PLYPD3/6-311G** calculations have been performed to unravel the reaction mechanism of triplet and singlet methylene CH2 with ketene CH2 CO. The computed potential energy diagrams and molecular properties have been then utilized in Rice-Ramsperger-Kassel-Marcus-Master Equation (RRKM-ME) calculations of the reaction rate constants and product branching ratios combined with the use of nonadiabatic transition state theory for spin-forbidden triplet-singlet isomerization. The results indicate that the most important channels of the reaction of ketene with triplet methylene lead to the formation of the HCCO + CH3 and C2 H4 + CO products, where the former channel is preferable at higher temperatures from 1000 K and above. In the C2 H4 + CO product pair, the ethylene molecule can be formed either adiabatically in the triplet electronic state or via triplet-singlet intersystem crossing in the singlet electronic state occurring in the vicinity of the CH2 COCH2 intermediate or along the pathway of CO elimination from the initial CH2 CH2 CO complex. The predominant products of the reaction of ketene with singlet methylene have been shown to be C2 H4 + CO. The formation of these products mostly proceeds via a well-skipping mechanism but at high pressures may to some extent involve collisional stabilization of the CH3 CHCO and cyclic CH2 COCH2 intermediates followed by their thermal unimolecular decomposition. The calculated rate constants at different pressures from 0.01 to 100 atm have been fitted by the modified Arrhenius expressions in the temperature range of 300-3000 K, which are proposed for kinetic modeling of ketene reactions in combustion. © 2018 Wiley Periodicals, Inc.

Ultrafast Excited-State Dynamics of Ligand-Field and Ligand-to-Metal Charge-Transfer States of CuCl42- in Solution: A Detailed Transient Absorption Study.

Ultrafast excited-state dynamics of CuCl42- in acetonitrile is studied by femtosecond broadband transient absorption spectroscopy following excitation of the complex into all ligand-field (LF or d-d) states and into the two ligand-to-metal charge transfer (LMCT) states corresponding to the most intense steady-state absorption bands. The LF excited states are found to be nonreactive. The lowest-lying 2E LF excited state has a lifetime less than 150 fs, and the lifetimes of the second (2B1) and the third (2A1) LF excited states are 1 and 5 ps, respectively. All three LF states decay directly into the ground 2B2 state. Such significant differences in excited-state decay time constants were rationalized computationally through time-dependent density functional theory (TD-DFT) computations. TD-DFT mapping of the relaxation pathway along the symmetric Cl-Cu-Cl umbrella bending vibration gives evidence for a conical intersection between the 2E excited state and the ground 2B2 state. The LMCT states decay within 200 fs with the primary deactivation mode consistent to be Cu-Cl stretch. A fraction of the CuCl42- complexes excited into the LMCT states undergoes ionic dissociation to form products that survive longer than 1 ns. The remaining fraction undergoes internal conversion, which can be viewed as back electron transfer, populating the lower vibrationally hot LF states. The LF states populated from the LMCT states exhibit the same lifetimes as the Franck-Condon LF states and likewise decay directly into the ground state.

Down syndrome: age-dependence of PiB binding in postmortem frontal cortex across the lifespan.

Beta-amyloid (Aß) deposition in brain accumulates as a function of age in people with Down syndrome (DS) with subsequent development into Alzheimer disease neuropathology, typically by 40 years of age. In vivo imaging using the Pittsburgh compound B (PiB) ligand has facilitated studies linking Aß, cognition, and dementia in DS. However, there are no studies of PiB binding across the lifespan in DS. The current study describes in vitro 3H-PiB binding in the frontal cortex of autopsy cases with DS compared to non-DS controls. Tissue from 64 cases included controls (n = 25) and DS (n = 39). In DS, 3H-PiB binding was significantly associated with age. After age 40 years in DS, 3H-PiB binding rose dramatically along with increasing individual variability. 3H-PiB binding correlated with the amount of Aß42. Using fixed frontal tissue and fluorescent 6-CN-PiB, neuritic and cored plaques along with extensive cerebral amyloid angiopathy showed 6-CN-PiB binding. These results suggest that cortical PiB binding as shown by positron emission tomography imaging reflects plaques and cerebral amyloid angiopathy in DS brain.

Direct photoisomerization of CH2I2vs. CHBr3 in the gas phase: a joint 50 fs experimental and multireference resonance-theoretical study.

Femtosecond transient absorption measurements powered by 40 fs laser pulses reveal that ultrafast isomerization takes place upon S1 excitation of both CH2I2 and CHBr3 in the gas phase. The photochemical conversion process is direct and intramolecular, i.e., it proceeds without caging media that have long been implicated in the photo-induced isomerization of polyhalogenated alkanes in condensed phases. Using multistate complete active space second order perturbation theory (MS-CASPT2) calculations, we investigate the structure of the photochemical reaction paths connecting the photoexcited species to their corresponding isomeric forms. Unconstrained minimum energy paths computed starting from the S1 Franck-Condon points lead to S1/S0 conical intersections, which directly connect the parent CHBr3 and CH2I2 molecules to their isomeric forms. Changes in the chemical bonding picture along the S1/S0 isomerization reaction path are described using multireference average coupled pair functional (MRACPF) calculations in conjunction with natural resonance theory (NRT) analysis. These calculations reveal a complex interplay between covalent, radical, ylidic, and ion-pair dominant resonance structures throughout the nonadiabatic photochemical isomerization processes described in this work.

Solution-state photophysics of N-carbazolyl benzoate esters: dual emission and order of states in twisted push-pull chromophores.

The stepwise photoinduced charge transfer in a series of N-carbazolyl benzoate ester push-pull chromophores has been studied in solution. Dual emission from the locally excited (LE, the lowest-energy singlet excited state of 1Lb nature localized on the carbazole donor) and the highly polarized, intramolecular charge-transfer states of (pre)-twisted type (TICT states) is observed in non-polar and polar solvents. Ultrafast transient spectroscopy reveals that the excitation into the 1Lb LE state is followed by rapid (∼ps) charge separation into an emissive TICT state. Excitation into the second singlet excited state localized on the carbazole (S2) with 1La nature results in sub-100 fs population of both 1Lb and TICT states.

Extraction and coordination studies of a carbonyl-phosphine oxide scorpionate ligand with uranyl and lanthanide(III) nitrates: structural, spectroscopic and DFT characterization of the complexes.

Hybrid scorpionate ligand (OPPh2)2CHCH2C(O)Me (L) was synthesized and characterized by spectroscopic methods and X-ray diffraction. The selected coordination chemistry of L with UO2(NO3)2 and Ln(NO3)3 (Ln = La, Nd, Lu) has been evaluated. The isolated mono- and binuclear complexes, namely, [UO2(NO3)2L] (1), [{UO2(NO3)L}2(µ2-O2)]·EtOH (2), [La(NO3)3L2]·2.33MeCN (3), [Nd(NO3)3L2]·3MeCN (4), [Nd(NO3)2L2]+·(NO3)−·EtOH (5) and [Lu(NO3)3L2] (6) have been characterized by IR spectroscopy and elemental analysis. Single-crystal X-ray structures have been determined for complexes 1-5. Intramolecular intraligand π-stacking interactions between two phenyl fragments of the coordinated ligand(s) were observed in all complexes 1-5. The π-stacking interaction energy was estimated from Bader's AIM theory calculations performed at the DFT level. Solution properties have been examined using IR and multinuclear ((1)H, (13)C, and (31)P) NMR spectroscopy in CD3CN and CDCl3. Coordination modes of L vary with the coordination polyhedron of the metal and solvent nature showing many coordination modes: P(O),P(O), P(O),P(O),C(O), P(O),C(O), and P(O). Preliminary extraction studies of U(VI) and Ln(III) (Ln = La, Nd, Ho, Yb) from 3.75 M HNO3 into CHCl3 show that scorpionate L extracts f-block elements (especially uranium) better than its unmodified prototype (OPPh2)2CH2.

Probing the fate of lowest-energy near-infrared metal-centered electronic excited states: CuCl(4)(2-) and IrBr(6)(2-).

Ultrafast transient absorption spectroscopy is used to investigate the radiationless relaxation dynamics of CuCl4(2-) and IrBr6(2-) complexes directly promoted into their lowest-energy excited metal-centered states upon near-infrared femtosecond excitation at 2000 nm. Both the excited CuCl4(2-) (2)E and IrBr6(2-) (2)Ug'(T2g) states undergo internal conversion to the ground electronic states, yet with significantly different lifetimes (55 fs and 360 ps, respectively) despite the fact that the (2)E and (2)Ug'(T2g) states are separated by the same energy gap (∼5000 cm(-1)) from the respective ground state. This difference likely arises from the predominance of the Jahn-Teller effect in a Cu(2+) ion and the spin-orbit coupling effect in an Ir(4+) ion. The approach documented in this work may be used for elucidating the role of low-energy metal-centered states in relaxation cascades of a number of coordination compounds, allowing for design of efficient light-triggered metal complexes.

Tritium-labeled (E,E)-2,5-bis(4'-hydroxy-3'-carboxystyryl)benzene as a probe for ß-amyloid fibrils.

Accumulation of Aß in the brains of Alzheimer disease (AD) patients reflects an imbalance between Aß production and clearance from their brains. Alternative cleavage of amyloid precursor protein (APP) by processing proteases generates soluble APP fragments including the neurotoxic amyloid Aß40 and Aß42 peptides that assemble into fibrils and form plaques. Plaque-buildup occurs over an extended time-frame, and the early detection and modulation of plaque formation are areas of active research. Radiolabeled probes for the detection of amyloid plaques and fibrils in living subjects are important for noninvasive evaluation of AD diagnosis, progression, and differentiation of AD from other neurodegenerative diseases and age-related cognitive decline. Tritium-labeled (E,E)-1-[(3)H]-2,5-bis(4'-hydroxy-3'-carbomethoxystyryl)benzene possesses an improved level of chemical stability relative to a previously reported radioiodinated analog for radiometric quantification of Aß plaque and tau pathology in brain tissue and in vitro studies with synthetic Aß and tau fibrils.

A distinct subfraction of Aß is responsible for the high-affinity Pittsburgh compound B-binding site in Alzheimer's disease brain.

The positron emission tomography (PET) ligand (11) C-labeled Pittsburgh compound B (PIB) is used to image ß-amyloid (Aß) deposits in the brains of living subjects with the intent of detecting early stages of Alzheimer's disease (AD). However, deposits of human-sequence Aß in amyloid precursor protein transgenic mice and non-human primates bind very little PIB. The high stoichiometry of PIB:Aß binding in human AD suggests that the PIB-binding site may represent a particularly pathogenic entity and/or report local pathologic conditions. In this study, (3) H-PIB was employed to track purification of the PIB-binding site in > 90% yield from frontal cortical tissue of autopsy-diagnosed AD subjects. The purified PIB-binding site comprises a distinct, highly insoluble subfraction of the Aß in AD brain with low buoyant density because of the sodium dodecyl sulfate-resistant association with a limited subset of brain proteins and lipids with physical properties similar to lipid rafts and to a ganglioside:Aß complex in AD and Down syndrome brain. Both the protein and lipid components are required for PIB binding. Elucidation of human-specific biological components and pathways will be important in guiding improvement of the animal models for AD and in identifying new potential therapeutic avenues. A lipid-associated subpopulation of Aß accounts for the high-affinity binding of Pittsburgh compound B (PIB) in Alzheimer's disease brain. Mass spectrometry of the isolated PIB-binding site from frontal cortex identified Aß peptides and a set of plaque-associated proteins in AD but not age-matched normal brain. The PIB-binding site may represent a particularly pathogenic entity and/or report local pathologic conditions.