Transitions Of Complexes Research Articles

Tunable from Blue to Red Emissive Composites and Solids of Silver Diphosphane Systems with Higher Quantum Yields than the Diphosphane Ligands.

PMMA composites and solids of complexes of formulas [AgX(P-P)]n [n = 1 and 2; X = Cl, NO3, ClO4, CF3COO, and OTf; P-P = dppb, xantphos, (PR2)2C2B10H10 (R = Ph and iPr)] display the whole palette of colors from blue to red upon selection of the anionic ligand (X) and the diphosphane (P-P). The diphosphane seems to play the most important role in tuning the emission energy and thermally activated delayed fluorescence (TADF) behavior. The PMMA composites of the complexes exhibit higher quantum yields than that of the diphosphane ligands and those with dppb are between 28 and 53%. Remarkably, instead of blue-green emissions which dominate the luminescence of silver diphosphane complexes in rigid phases, those with carborane diphosphanes are yellow-orange or orange-red emitters. Theoretical studies have been carried out for complexes with P-P = dppb, X = Cl; P-P = dppic, X = NO3; P-P = dppcc, X = Cl, NO3, and OTf and the mononuclear complexes [AgX(xantphos)] (X = Cl, Br). Optimization of the first excited triplet state was only possible for [AgX(xantphos)] (X = Cl and Br). A mixed MLCT and MC nature could be attributed to the S0 → T1 transition in these three-coordinated complexes.

Motifs and interface amino acid-mediated regulation of amyloid biogenesis in microbes to humans: potential targets for intervention.

Amyloids are linked to many debilitating diseases in mammals. Some organisms produce amyloids that have a functional role in the maintenance of their biological processes. Microbes utilize functional bacterial amyloids (FuBA) for pathogenicity and infections. Amyloid biogenesis is regulated differentially in various systems to avoid its toxic accumulation. A familiar feature in the process of amyloid biogenesis from humans to microbes is its regulation by protein-protein interactions (PPI). The spatial arrangement of amino acid residues in proteins generates topologies like flat interface and linear motif, which participate in protein interactions. Motifs and interface residue-mediated interactions have a direct or an indirect impact on amyloid secretion and assembly. Some motifs undergo post-translational modifications (PTM), which effects interactions and dynamics of the amyloid biogenesis cascade. Interaction-induced local changes stimulate global conformational transitions in the PPI complex, which indirectly affects amyloid formation. Perturbation of such motifs and interface residues results in amyloid abolishment. Interface residues, motifs and their respective interactive protein partners could serve as potential targets for intervention to inhibit amyloid biogenesis.

Development and Implementation of a Complex Health System Intervention Targeting Transitions of Care from Hospital to Post-acute Care.

Failure of effective transitions of care following hospitalization can lead to excess days in the hospital, readmissions, and adverse events. Evidence identifies both patient and system factors that influence poor care transitions, yet health systems struggle to translate evidence into complex interventions that have a meaningful impact on care transitions. We report on our experience developing, pilot testing, and evaluating a complex intervention (Addressing Complex Transitions program, or ACT program) that aims to improve care transitions for complex patients. Following the Medical Research Council (MRC) framework, we engaged in iterative, stakeholder-driven work to develop a complex care intervention, assess feasibility and pilot methods, evaluate the intervention in practice, and facilitate ongoing implementation monitoring and dissemination. Patients receiving care from UW Medicine's health system including 4 hospitals and 20-site Post-Acute Care network. Literature review and prospective data collection activities informed ACT program design. ACT program components include a tailored risk calculator that provides real-time scoring of transitions of care risk factors, a multidisciplinary team with the capacity to address complex barriers to safe transitions, and enhanced discharge workflows to improve care transitions for complex patients. Program evaluation metrics included estimated hospital days saved and program acceptance by care team members. During the 6-month pilot, 565 patients were screened and 97 enrolled in the ACT program. An estimated 664 hospital days were saved for the index admission of ACT program participants. Analysis of pre/post-hospital utilization for ACT program participants showed an estimated 3227 fewer hospital days after ACT program enrollment. Health systems need to address increasingly difficult challenges in care delivery. The use of evidence-based frameworks, such as the MRC framework, can guide systems to design complex interventions that respond to their local context and stakeholder needs.

The dynamic landscape of transcription initiation in yeast mitochondria

Controlling efficiency and fidelity in the early stage of mitochondrial DNA transcription is crucial for regulating cellular energy metabolism. Conformational transitions of the transcription initiation complex must be central for such control, but how the conformational dynamics progress throughout transcription initiation remains unknown. Here, we use single-molecule fluorescence resonance energy transfer techniques to examine the conformational dynamics of the transcriptional system of yeast mitochondria with single-base resolution. We show that the yeast mitochondrial transcriptional complex dynamically transitions among closed, open, and scrunched states throughout the initiation stage. Then abruptly at position +8, the dynamic states of initiation make a sharp irreversible transition to an unbent conformation with associated promoter release. Remarkably, stalled initiation complexes remain in dynamic scrunching and unscrunching states without dissociating the RNA transcript, implying the existence of backtracking transitions with possible regulatory roles. The dynamic landscape of transcription initiation suggests a kinetically driven regulation of mitochondrial transcription.

Solid-to-Liquid Phase Transition in Polyelectrolyte Complexes

Strongly interacting polyelectrolyte complexes (PECs) are known to form solid precipitates that can transform into liquid droplets upon the addition of salt to break intrinsic ionic associations. H...

LUMINESCENCE OF Α-WILLEMITE IN THE CATALYTIC OXIDATION OF CARBON MONOXIDE

The interaction of neutral gas particles of thermal energies (molecules and atoms) with the surface of a solid is accompanied by radiation in the visible and I.R. parts of the spectrum. In this case, the surface of a solid body acts as a catalyst for the recombination reactions of gas particles. In this connection, the possibility of exciting luminescence during the catalytic oxidation of carbon monoxide directly by the atomic form of oxygen pre-adsorbed on the surface of a solid is of interest. Kinetic and spectral methods were used to study the luminescence arising from the catalytic oxidation of carbon monoxide by the atomic form of oxygen preadsorbed on the surface of a solid – a sample of α-willemite Zn2SiO4:Mn2+. The main stages in the mechanisms of recombination between adsorbate particles are established. Electronic transitions in adsorption complexes and the activator ion have been identified. During the filling process, the sample temperature was maintained by a constant high-speed electronic control system of the heater current. This made it possible to avoid thermal side effects. The main stages in the mechanisms of recombination between adsorbate particles are established. Electronic transitions in adsorption complexes and the activator ion have been identified. It was found that luminescence excitation proceeds in two main stages, somewhat time-shifted. The two-stage mechanism for the catalytic oxidation of carbon monoxide on the surface of α-willemite with pre-adsorbed atomic oxygen allows a consistent description of the luminescence observed in this case. This type of luminescence has the prospect of using for studying the mechanisms of catalytic oxidation of carbon monoxide.

Water and Ion Transport through the Glass Transition in Polyelectrolyte Complexes

Polyelectrolyte complexes or coacervates, PECs, represent one of the many families of ion-containing polymers proposed or in use for applications requiring mobile ions, including fuel cells, water ...

Lactate Attenuates Synaptic Transmission and Affects Brain Rhythms Featuring High Energy Expenditure.

SummaryLactate shuttled from blood, astrocytes, and/or oligodendrocytes may serve as the major glucose alternative in brain energy metabolism. However, its effectiveness in fueling neuronal information processing underlying complex cortex functions like perception and memory is unclear. We show that sole lactate disturbs electrical gamma and theta-gamma oscillations in hippocampal networks by either attenuation or neural bursts. Bursting is suppressed by elevating the glucose fraction in substrate supply. By contrast, lactate does not affect electrical sharp wave-ripple activity featuring lower energy use. Lactate increases the oxygen consumption during the network states, reflecting enhanced oxidative ATP synthesis in mitochondria. Finally, lactate attenuates synaptic transmission in excitatory pyramidal cells and fast-spiking, inhibitory interneurons by reduced neurotransmitter release from presynaptic terminals, whereas action potential generation in the axon is regular. In conclusion, sole lactate is less effective and potentially harmful during gamma-band rhythms by omitting obligatory ATP delivery through fast glycolysis at the synapse.

Ab initio potential energy surface and microwave spectrum of the NH3-N2 van der Waals complex.

We present a five-dimensional intermolecular potential energy surface (PES) of the NH3-N2 complex, bound state calculations, and new microwave (MW) measurements that provide information on the structure of this complex and a critical test of the potential. Ab initio calculations were carried out using the explicitly correlated coupled cluster [CCSD(T)-F12a] approach with the augmented correlation-consistent aug-cc-pVTZ basis set. The global minimum of the PES corresponds to a configuration in which the angle between the NH3 symmetry axis and the intermolecular axis is 58.7° with the N atom of the NH3 unit closest to the N2 unit, which is nearly parallel to the NH3 symmetry axis. The intermolecular distance is 7.01 a0, and the binding energy De is 250.6 cm-1. The bound rovibrational levels of the four nuclear spin isomers of the complex, which are formed when ortho/para (o/p)-NH3 combines with (o/p)-N2, were calculated on this intermolecular potential surface. The computed dissociation energies D0 are 144.91 cm-1, 146.50 cm-1, 152.29 cm-1, and 154.64 cm-1 for (o)-NH3-(o)-N2, (o)-NH3-(p)-N2, (p)-NH3-(o)-N2, and (p)-NH3-(p)-N2, respectively. Guided by these calculations, the pure rotational transitions of the NH3-N2 van der Waals complex were observed in the frequency range of 13-27 GHz using the chirped-pulse Fourier-transform MW technique. A complicated hyperfine structure due to three quadrupole 14N nuclei was partly resolved and examined for all four nuclear spin isomers of the complex. Newly obtained data definitively established the K values (the projection of the angular momentum J on the intermolecular axis) for the lowest states of the different NH3-N2 nuclear spin isomers.

Highly Emissive Dinuclear Platinum(III) Complexes.

Dinuclear Pt(III) complexes were commonly reported to have short-lived lowest-lying triplet states, resulting in extremely weak or no photoluminescence. To overcome this obstacle, a new series of dinuclear Pt(III) complexes, named Pt2a-Pt2c, were strategically designed and synthesized using donor (D)-acceptor (A)-type oxadiazole-thiol chelates as bridging ligands. These dinuclear Pt(III) complexes possess a d7-d7 electronic configuration and exhibit intense phosphorescence under ambient conditions. Among them, Pt2a exhibits orange phosphorescence maximized at 618 nm in degassed dichloromethane solution (Φp ≈ 8.2%, τp ≈ 0.10 μs) and near-infrared (NIR) emission at 749 nm (Φp ≈ 10.1% τp ≈ 0.66 μs) in the crystalline powder and at 704 nm (Φp ≈ 33.1%, τp ≈ 0.34 μs) in the spin-coated neat film. An emission blue-shifted by more than 3343 cm-1 is observed under mechanically ground crystalline Pt2a, affirming intermolecular interactions in the solid states. Time-dependent density functional theory (TD-DFT) discloses the lowest-lying electronic transition of Pt2a-Pt2c complexes to be a bridging ligand-metal-metal charge transfer (LMMCT) transition. The long-lived triplet states of these dinuclear platinum(III) complexes may find potential use in lighting. Employing Pt2a as an emitter, high-performance organic light-emitting diodes (OLEDs) were fabricated with NIR emission at 716 nm (η = 5.1%), red emission at 614 nm (η = 8.7%), and white-light emission (η = 11.6%) in nondoped, doped (in mCP), and hybrid (in CzACSF) devices, respectively.

Correlation between the C-C Cross-Coupling Activity and C-to-Ni Charge Transfer Transition of High-Valent Ni Complexes.

High-valent Ni complexes have proven to be good platforms for diverse cross-coupling reactions that are otherwise difficult to be achieved with conventional low-valent catalysts. However, their reductive elimination (RE) activities are still significantly variable by up to 5 orders of magnitude, depending on the supporting ligand and oxidation state of the Ni center. To elucidate frontier molecular orbitals (FMOs) that determine the RE activity of the Ni center, the electronic structures of cycloneophyl (CH2C(CH3)2-o-C6H4) NiIII and NiIV complexes have been characterized by utilizing various transition metal-based spectroscopic techniques such as electronic absorption, magnetic circular dichroism, electron paramagnetic resonance, resonance Raman, and X-ray absorption spectroscopies. In combination with density functional theory computations, the spectroscopic analyses have shown that the energies of the C-to-Ni charge-transfer (CT) electronic transitions are strongly correlated to the rates of C-C bond-forming RE reaction. This correlation suggests that the kinetic barrier of the RE reaction is determined by energy cost for internal CT (ICT) from the coordinated carbon moiety to the Ni center, and that FMOs involved in the RE reaction and the C-to-Ni CT electronic transitions are essentially identical. This FMO determination has led us to discover that photoexcitation to the C-to-Ni CT excited states accelerates the C-C cross-coupling reaction by up to 105 times, as the CT electronic transition can substitute for the rate-determining ICT step of the RE reaction at the ground electronic state.

Applicability of density functional and wave function theories combined with the three-dimensional reference interaction site model self-consistent field method to the d–d transitions of a transition metal aqua complex

The applicability of density functional theory (DFT) and wave function theory combined with the three-dimensional reference interaction site model self-consistent field method to the d–d transitions of transition metal aqua complexes was examined using [Cr(H2O)6]3+ in aqueous solution as an example. DFTs with hybrid functionals, multiconfigurational self-consistent field followed by perturbation theory, and coupled-cluster singles and doubles (CCSD) followed by the equation of motion CCSD, gave reasonable d–d transition energies.

Pinning of energy transitions of defects, complexes, and surface states in AlGaN alloys

In this work, we determine the dependence of the defect transition energies, electronic bands, and surface charge neutrality levels in AlGaN. With Vacuum level as reference, we show that energy transitions of localized defects and the surface Fermi level are independent of the alloy composition as electronic bands diverge with the increase in the bandgap as a function of alloy composition. The invariance of localized states on the alloy composition creates a convenient internal reference energy with respect to which other energy states may be measured. We demonstrate a higher generality to the universality rule with the independence of deep transition states of otherwise shallow donor type defects [(+1/+3) transition for VN] and defect complexes (CN+SiIII) in addition to the earlier predicted independent nature of mid-gap states when they are either the antibonding state between cationic impurities and host anion or acceptors at anion sites.

Chain length effect on the structure and thermotropic phase transitions of solid catanionic complexes built of cetyltrimethylammonium bromide and saturated n-fatty acids

Chain length effect on the structure and thermotropic properties of asymmetric solid catanionic complexes (CAC) built of cetyltrimethylammonium bromide (C16TABr) and saturated n-fatty acids (CnSFA, CnH2nO2, n = 12, 18, 20, and 22) was investigated by XRD, DSC, and FTIR spectroscopy. All CAC show a lamellar crystalline structure and a series of solid–solid phase transitions below the melting point. The phase transitions are suggested to be caused by sequential melting of the methylene chains in the hydrophobic layer followed by a change in the crystalline structure. C16TABr stabilizes the bilayer structure of CAC and raises its melting point compared to initial CnSFA.

Spin transition in a ferrous chloride complex supported by a pentapyridine ligand.

Ferrous chloride complexes [FeIILxCl] commonly attain a high-spin state independently of the supporting ligand(s) and temperature. Herein, we present the first report of a complete spin crossover with T1/2 = 80 K in [FeII(Py5OH)Cl]+ (Py5OH = pyridine-2,6-diylbis[di(pyridin-2-yl)methanol]). Both spin forms of the complex are analyzed by X-ray spectroscopy and DFT calculations.

Фосфоресценция жидкого кислорода при возбуждении на кооперативных переходах в видимой области спектра

The phosphorescence of liquid oxygen were studied upon its excitation at the cooperative transitions of O2-O2 molecular oxygen complexes with using for direct optical excitation of LED matrices with radiation in the near UV and visible spectral regions with wavelengths partially or completely coinciding with the absorption lines of molecular complexes

Changes in the Electronic Transitions of Polyethylene Glycol upon the Formation of a Coordinate Bond with Li+, Studied by ATR Far-Ultraviolet Spectroscopy.

This study investigates the electronic transitions of complexes of lithium with polyethylene glycol (PEG) by the absorption bands of solvent molecules via attenuated total reflectance spectroscopy in the far-UV region (ATR-FUV). Alkali-metal complexes are interesting materials because of their functional characteristics such as good ionic conductivity. These complexes are used as polymer electrolytes for Li batteries and as one of the new types of room-temperature ionic liquids, termed solvation ionic liquids. Considering these applications, alkali-metal complexes have been studied mainly for their electrochemical characteristics; there is no fundamental study providing a clear understanding of electronic states in terms of electronic structures for the ground and excitation states near the highest occupied molecular orbital-lowest occupied molecular orbital transitions. This study explores the electronic transitions of ligand molecules in alkali-metal complexes. In the ATR-FUV spectra of the Li-PEG complex, a decrease in intensity and a large blue shift (over 4 nm) were observed to result from an increase in the concentration of Li salts. This observation suggests the formation of a complex, with coordinate bonding between Li+ and the O atoms in PEG. Comparison of the experimental spectrum with a simulated spectrum of the Li-PEG complex calculated by time-dependent density functional theory indicated that changes in the intensities and peak positions of bands at approximately 155 and 177 nm (pure PEG shows bands at 155, 163, and 177 nm) are due to the formation of coordinate bonding between Li+ and the O atoms in the ether molecule. The intensity of the 177 nm band depends on the number of residual free O atoms in the ether, and the peak wavelength at approximately 177 nm changes with the expansion of the electron clouds of PEG. We assign a band in the 145-155 nm region to the alkali-metal complex because we observed a new band at approximately 150 nm in the ATR-FUV spectra of very highly concentrated binary mixtures.

Structural Perturbations due to Mutation (H1047R) in Phosphoinositide-3-kinase (PI3Kα) and Its Involvement in Oncogenesis: An in Silico Insight.

PI3Kα is a heterodimer protein consisting of two subunits (p110α and p85α) which promotes various signaling pathways. Oncogenic mutation in the catalytic subunit p110α of PI3Kα at the 1047 position in the kinase domain substitutes the histidine with arginine. This mutation brings about conformational transitions in the protein complex. These transitions expose the membrane binding region of PI3Kα, and then it independently binds to the cell membrane through its kinase domain without the involvement of the membrane-bound protein RAS. We observed notable changes between the protein complexes (p110α–p85α) of native and mutant structures at the atomic level using molecular dynamics simulations. Simulation results revealed formation of a less number of hydrogen bonds between the two subunits in the mutant protein complex which led the two subunits to move away from each other. This increase in distance between the subunits led to an expanded structure, thereby increasing the flexibility of the protein complex. Furthermore, a study of secondary structure elements and the electrostatic potential of the protein also gave a molecular insight into the change in interaction patterns of the protein with the plasma membrane. Our finding clearly indicates the role of mutation in oncogenesis and provides an insight into considering the structural aspects to handle this mutation.

Reversible On-Off Switching of the Hysteretic Spin Crossover in a Cobalt(II) Complex via Crystal to Crystal Transformation.

Reversible controlling and switching of magnetic bistability remains relatively difficult. Here, reversible on-off switching of a hysteretic spin transition in a CoII complex via a single-crystal to single-crystal (SC-SC) transformation during dehydration and rehydration was reported. Upon dehydration, a switching from a basically low spin state to an abrupt and hysteretic spin crossover (SCO) with broad hysteresis loops was achieved. Hysteretic and anisotropic crystal lattice expansion or contraction in the spin transition temperature range was also observed in the dehydrated complex. The magneto-structural relationship in this system was established on the basis of detailed structure analyses on both the hydrated and dehydrated examples over a wide range of temperatures. The elimination of guest internal pressure, the tuning of the supramolecular interactions, and the strong electron-lattice coupling should be responsible for the hysteretic SCO in the dehydrated complex.

Absorption properties of a BODIPY-curved graphene nanoflake system: A theoretical investigation.

Modifications in the electronic transitions of a popular 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (boron dipyrromethene, BODIPY) dye caused by quasi-parallel stacking with corannulene (C) were studied by means of time-dependent density functional theory (TD-DFT) with the CAM-B3LYP functional. The effects of the electron-withdrawing (CN) and electron-donating (NH2) substituents at the meso (8) position in the BODIPY core and the corannulene rim position on the character, location, and oscillator strengths (f) of some transitions of complexes were also discussed. To understand better the nature of the transitions, their occupied and virtual orbitals involved into the first electronic transitions as well as the electron density difference plots between excited and ground states of the complexes were investigated. The S0 → S1 transitions of 8H-B/C and 8NH2-B/C complexes have a small admixture of the charge transfer (CT) character in direction from BODIPY to corannulene (B → C). They located at 2.80 and 3.11 eV, respectively, and have f of ∼0.15. The 8CN-B/C complex with a stronger acceptor BODIPY part has the S0 → S1 transition with a higher degree of CT (B → C) at 2.32 eV with f = 0.08. The 8H-B/2NH2-C complex with a stronger donor corannulene part has the S0 → S1 transition with an expressed CT(B → C)-character at 2.58 eV with f = 0.003, whereas the S0 → S2 transition acquires in a some extent the features of the LE(B → B) character. A much interesting situation exists in the case of the 8NH2-B/2CN-C complex. Here we can find both CT (B → C) and CT (C → B) among the first five states. Besides this, different, higher in energy CT states and states delocalized on both molecules were observed.