Transitions Of Complexes Research Articles

Delocalization-to-Localization Charge Transition in Divinylthiophene-Bridged Biruthenium Complexes as a Function of Length of the Bridging Chain by Both IR Spectroscopy and Theoretical Investigations

A series of biruthenium complexes linked by oligothiophene bridges of variable lengths (4a–4d) have been prepared to probe intramolecular electronic delocalization as a function of the chain length of the bridging ligand. In going from monothiophene to quaterthiophene-bridged biruthenium-vinyl complex radical cations (4a+–4d+), the transition from a positive charge delocalized state to a localized state is clearly displayed by IR spectroscopy and density functional theory calculations and the bridge contributing to the charge and the unpaired spin density exhibits good linear correlation with the length of the bridging chain. The shortest member 4a+ displays a charge delocalized mixed-valence property as a result of the strong electronic coupling between two ruthenium termini. In the longest member 4d+, the charge is nearly fully localized at the bridge and the mixed-valence property disappears. Therefore, for even longer systems, the charge should be exclusively localized on the bridge.

Extension of the HCOOH and CO2 solid-state reaction network during the CO freeze-out stage: inclusion of H2CO

Context. Formic acid (HCOOH) and carbon dioxide (CO2) are simple species that have been detected in the interstellar medium. The solid-state formation pathways of these species under experimental conditions relevant to prestellar cores are primarily based off of weak infrared transitions of the HOCO complex and usually pertain to the H2O-rich ice phase, and therefore more experimental data are desired. Aims. Here, we present a new and additional solid-state reaction pathway that can form HCOOH and CO2 ice at 10 K “non-energetically” in the laboratory under conditions related to the “heavy” CO freeze-out stage in dense interstellar clouds, i.e., by the hydrogenation of an H2CO:O2 ice mixture. This pathway is used to piece together the HCOOH and CO2 formation routes when H2CO or CO reacts with H and OH radicals. Methods. Temperature programmed desorption – quadrupole mass spectrometry (TPD-QMS) is used to confirm the formation and pathways of newly synthesized ice species as well as to provide information on relative molecular abundances. Reflection absorption infrared spectroscopy (RAIRS) is additionally employed to characterize reaction products and determine relative molecular abundances. Results. We find that for the conditions investigated in conjunction with theoretical results from the literature, H + HOCO and HCO + OH lead to the formation of HCOOH ice in our experiments. Which reaction is more dominant can be determined if the H + HOCO branching ratio is more constrained by computational simulations, as the HCOOH:CO2 abundance ratio is experimentally measured to be around 1.8:1. H + HOCO is more likely than OH + CO (without HOCO formation) to form CO2. Isotope experiments presented here further validate that H + HOCO is the dominant route for HCOOH ice formation in a CO-rich CO:O2 ice mixture that is hydrogenated. These data will help in the search and positive identification of HCOOH ice in prestellar cores.

Synthesis and characterization of oxygen depleted tert-amine calix[4]arene ligands and study the effect on sigma non-opioid intracellular protein receptor

This study focuses on the biological prospects of oxygen-depleted calix[4]arene ligands on a protein target. Because of their extensive medical relevance, the oxygen-depleted bis(piperdine) (BPD) and bis(pyrazole) (BPZ) ligands were synthesized and characterized by NMR and mass spectrometry. Furthermore, molecular docking followed by molecular dynamics simulation was utilized to understand the behavior of ligands on selection of sigma non-opiod intracellular receptor (SigNOR) as a suitable protein target. The simulations were carried out by three level of complexity: (1) Apo SigNOR, (2) BPD: SigNOR, and (3) BPZ: SigNOR. The three complex systems were subjected to stability check before detail analysis. From the results of the estimation of binding free energy, it follows that both ligands possess the same free energy of binding which, in turn, suggests their similar role; however, energy components such as Van der waal and electrostatic potential recommend BPZ were identified as a competitive drug on SigNOR. In addition, temporal distribution of the clusters suggests that scattering of the cluster’s popularity is a measure of fast structural transitions in both complexes. Current study utilizes modern approach to synthesis, characterization, and simulation of our ligands. This study appropriately highlights the effect of our ligands on SigNOR Protein, which might further be extended to potential in vitro and in vivo bioassay.

Design of Luminescent, Heteroleptic, Cyclometalated PtII and PtIV Complexes: Photophysics and Effects of the Cyclometalated Ligands.

Neutral pentafluorophenyl benzoquinolinyl PtII [Pt(bzq)(HC^N-κN)(C6 F5 )] (1 a-g) complexes, bearing nonmetalated N-heterocyclic HC^N ligands [HC^N=2,5-diphenyl-1,3,4-oxadiazole (Hoxd) a, 2-(2,4-difluorophenyl)pyridine (dfppy) b, 2-phenylbenzo[d]thiazole (pbt) c, 2-(4-bromophenyl)benzo[d]thiazole (Br-pbt) d, 2-phenylquinoline (pq) e, 2-thienylpyridine (thpy) f, 1-(2-pyridyl)pyrene (pypy) g], and heteroleptic bis(cyclometalated) PtIV fac-[Pt(bzq)(C^N)(C6 F5 )Cl] (2 b-g, bzq: benzo[h]quinolinyl) derivatives, generated by oxidation of 1 b-g with PhICl2 , are reported. The oxidation reaction of 1 a evolved with formation of the bimetallic PtIV complex syn-[Pt(bzq)(C6 F5 )Cl(μ-OH)]2 3. The crystal structures of 1 a,d,f, 2 b,d,e and 3 were corroborated by X-ray crystallography. A comparative study of the absorption and photoluminescence properties of the two series of complexes PtII (1) and PtIV (2), supported by time-dependent DFT calculations (TD-DFT), is presented. The low-lying transitions (absorption and emission) of PtII complexes 1 a-e [solution and polystyrene (PS) films] were assigned to the IL/MLCT mixture located on the cyclometalated Pt(bzq) unit, with minor IL'/ML'CT/LL'CT contributions involving the non-metalated ligand. Complex 1 g, bearing the more delocalized pyridyl pyrene (Hpypy) as an ancillary ligand, shows dual 1 ππ* and 3 ππ* (Hpypy) emission in fluid CH2 Cl2 and dual 3 IL/3 MLCT [Pt(bzq)] and [3 ππ*, Hpypy] phosphorescence at 77 K. Upon oxidation, PtIV complexes 2 b-f display (solution, PS) ligand-based phosphorescence that arises from the bzq in 2 b (3 LC) or from the second C^N ligand in 2 c-f (3 L'C) with some 3 LL'CT in 2 f. Despite metalation of the pyrenyl group, 2 g exhibits dual emission 1 ππ*/3 ππ* located on the pypy chromophore.

Salt-induced swelling transitions of a lamellar amphiphile-Polyelectrolyte complex.

We report salt-induced swelling transitions of a lamellar complex of the anionic polyelectrolyte, poly(acrylic acid sodium salt) (PAANa), and the cationic amphiphile, didodecyldimethylammonium chloride (DDAC). Increasing the concentration of NaCl in the solution is found to lead to a collapsed → swollen → collapsed transition of the complex. The swelling transition is driven by an abrupt increase in PAANa adsorption on DDAC bilayers above a threshold salt concentration. The lamellar periodicity of the swollen phase is not determined by the thickness of the adsorption layer, and additional mechanisms have to be invoked to understand the extent of its swelling. The swelling transition is not observed for the highest molecular weight of PAANa used, but a gradual transformation between the two collapsed structures is seen on increasing the salt concentration. The polyelectrolyte chains desorb from the bilayers at a very high salt concentration, in a process similar to the well-known destabilization of complexes of oppositely charged polyelectrolytes. However, unlike the PAANa chains, the polymer-free bilayers do not disperse uniformly in the solution. Instead, they form a collapsed lamellar stack containing very little water due to the van der Waals attraction between them. The occurrence of an abrupt swelling transition at intermediate salt concentrations in this system contrasts sharply with the gradual swelling reported in other complexes with increasing salt concentration. Furthermore, this behavior does not seem to have been anticipated by theories of complexation of oppositely charged macroions. More experiments are required for a clear understanding of the interactions stabilizing the different phases observed in this system.

Endohedral alkali cations promote charge transfer transitions in complexes of C60 with [10]cycloparaphenylenes.

[10]cycloparaphenylene ([10]CPP) effectively encapsulates ionic endofullerenes M+C60 (M = Li+, Na+, K+) as revealed by dispersion-corrected density functional theory methods. The interaction between [10]CPP and these fullerenes is dominated by dispersion, though it is stronger than with pristine C60 due to a reinforcement of electrostatic and induction contributions to the stability. The C60 carbon cage effectively shields the cations and distributes the charge among all carbon atoms, so the nature of the endohedral cation has no noticeable effect upon the final stability of the complexes. However, the presence of the cation induces important changes in the absorption spectra of the complexes, and new absorption bands near the infrared region appear. These bands are associated with charge transfer transitions from [10]CPP to the fullerene, suggesting the suitability of these complexes for use in organic photovoltaic devices.

Near-infrared circularly polarized luminescence from chiral Yb(iii)-diketonates

We report a rare example of near infrared circularly polarized luminescence (NIR-CPL) in the 920-1050 nm region associated with the f-f transitions of Yb diketonate complexes bearing chiral ancillary ligands. Developing NIR-CPL emitters may have implications from CPL-based (bio)-assays to chiral optoelectronics.

The Zinc-Metallothionein Redox System Reduces Oxidative Stress in Retinal Pigment Epithelial Cells.

Oxidative stress affects all the structures of the human eye, particularly the retina and its retinal pigment epithelium (RPE). The RPE limits oxidative damage by several protective mechanisms, including the non-enzymatic antioxidant system zinc-metallothionein (Zn-MT). This work aimed to investigate the role of Zn-MT in the protection of RPE from the oxidative damage of reactive oxygen intermediates by analytical and biochemical-based techniques. The Zn-MT system was induced in an in vitro model of RPE cells and determined by elemental mass spectrometry with enriched isotopes and mathematical calculations. Induced-oxidative stress was quantified using fluorescent probes. We observed that 25, 50 or 100 μM of zinc induced Zn-MT synthesis (1.6-, 3.6- and 11.9-fold, respectively), while pre-treated cells with zinc (25, 50, and 100 μM) and subsequent 2,2′-Azobis(2-methylpropionamidine) dihydrochloride (AAPH) treatment increased Zn-MT levels in a lesser extent (0.8-, 2.1-, 6.1-fold, respectively), exerting a stoichiometric transition in the Zn-MT complex. Moreover, AAPH treatment decreased MT levels (0.4-fold), while the stoichiometry remained constant or slightly higher when compared to non-treated cells. Convincingly, induction of Zn-MT significantly attenuated oxidative stress produced by free radicals’ generators. We conclude that the stoichiometry of Zn-MT plays an important role in oxidative stress response, related with cellular metal homeostasis.

Fractional-order two-component oscillator: stability and network synchronization using a reduced number of control signals

In this paper, a fractional-order version of a chaotic circuit made simply of two non-idealized components operating at high frequency is presented. The fractional-order version of the Hopf bifurcation is found when the bias voltage source and the fractional-order of the system increase. Using Adams–Bashforth–Moulton predictor–corrector scheme, dynamic behaviors are displayed in two complementary types of stability diagrams, namely the two-parameter Lyapunov exponents and the isospike diagrams. The latest being a more fruitful type of stability diagrams based on counting the number of spikes contained in one period of the periodic oscillations. These two complementary types of stability diagrams are reported for the first time in the fractional-order dynamical systems. Furthermore, a new fractional-order adaptive sliding mode controller using a reduced number of control signals was built for the stabilization of a fractional-order complex dynamical network. Two examples are shown on a fractional-order complex dynamical network where the nodes are made of fractional-order two-component circuits. Firstly, we consider an ideal channel, and secondly, a non ideal one. In each case, increasing of the coupling strength leads to the phase transition in the fractional-order complex network.Graphical abstract

Spectroscopic techniques to characterize the spin state: Vibrational, optical, Mössbauer, NMR, and X-ray spectroscopy

Basic principles and recent work using probes including Mössbauer, optical, X-ray, and vibrational spectroscopies to follow the transitions in spin crossover complexes are reviewed. X-ray spectroscopy, being a relatively lesser-known probe, is discussed in more detail. X-ray spectroscopic methods have been used in the spin crossover field mostly to elucidate surface phenomena, ultrafast dynamics, and high pressure effects, but recent technical developments provide perspectives for a more widespread use of these powerful techniques in home laboratories.

Design of Luminescent Isocyano Rhenium(I) Complexes: Photophysics and Effects of the Ancillary Ligands.

Despite the well-reported MLCT [dπ(M) → π*(CNR)] transitions in the isocyano transition metal complexes, emissive complexes with phosphorescence derived from MLCT [dπ(M) → π*(CNR)] were not extensively studied. To provide insights into the design strategy of phosphorescent rhenium(I) complexes with an emissive 3MLCT [dπ(Re) → π*(CNR)] excited state, a series of pentaisocyano rhenium(I) complexes have been synthesized. In contrast to most of the reported penta- or hexaisocyano rhenium(I) complexes with unsubstituted or alkyl- or monohalo-substituted phenylisocyanide ligands, which only exhibit photoluminescence in 77 K glassy medium, the solutions of all of these complexes were found to show phosphorescence at room temperature. Detailed study on their emission properties revealed that they are derived from the 3MLCT [dπ(Re) → π*(CNR)] excited state mixed with LL'CT character. It has been shown that the strong electron-withdrawing substituents on the isocyanide ligands can lower the energy of the MLCT [dπ(Re) → π*(CNR)] state and raise the deactivating ligand-field state. These effects are the crucial criteria to render the pentaisocyano rhenium(I) complexes emissive. Moreover, the emission properties in terms of energy, lifetime, and quantum yields can also be enhanced by the ancillary ligand.

Creating a sustainable assessment tool and follow-up plan to improve care transitions for the frail elderly patient population: The TPRAS project

Abstract A variety of health care professionals effectively collaborating is often required to successfully coordinate care transitions of complex, frail older adult patients who are experiencing co-morbidities and cognitive decline. This paper describes an interprofessional approach using quality improvement methodology to iteratively develop and improve an acute geriatric medical unit's discharge planning and care transitions processes. The approach has shown early signs of positive outcomes at the patient, provider, and organizational levels. Health care leaders may use a similar approach in their efforts to improve patient, family and provider experiences and outcomes associated with discharge and care transitions planning for the older complex adult patient population.

Metallo-Supramolecular Polymers Made of Cobalt and 3,4-Propylenedioxythiophene-Bisterpyridine Complexes for Electrochromic Applications

In this study, a series of organometallic hybrid polymers were synthesized through the complexation of cobalt metal ions with bisterpyridine derivatives bearing substituted 3,4-propylenedioxythiophene. The prepared polymers exhibited specific color changes from orange to dark green based on the metal-to-ligand charge transfer transitions. Cyclic voltammograms of the polymers showed a reversible redox wave according to the redox reaction of the cobalt metal ions. In addition, the electrochromic devices containing the polymer film cast on an indium-tin-oxide electrode exhibited good electrochromic properties, with reversible and stable spectral transitions of the cobalt-bisterpyridine complexes.

Long-Range Corrected DFT Calculations of First Hyperpolarizabilities and Excitation Energies of Metal Alkynyl Complexes.

The performance of the CAM-B3LYP, ωB97X and LC-BLYP long-range corrected density functional theory methods in the calculation of molecular first hyperpolarizabilities (β) and low-lying charge transfer (CT) excitation energies of the metal alkynyl complexes M(C≡C-4-C6 H4 -1-NO2 )(κ2 -dppe)(η5 -C5 H5 ) [M=Fe (1), Ru (2), Os (3)] and trans-[Ru{C≡C-(1,4-C6 H4 C≡C)n -4-C6 H4 -1-NO2 }Cl(κ2 -dppm)2 ] [n=0 (4), 1 (5), 2 (6)] was assessed. The BLYP, B3LYP and PBE0 standard exchange-correlation functionals and the Hartree-Fock method were also examined. The BLYP functional was shown to perform poorly in the calculation of β and low-energy CT transitions. The hybrid functionals (B3LYP and PBE0) showed significant improvement over the pure functional BLYP, but overestimated the hyperpolarizability ratios and the wavelengths of the lowest energy metal-to-ligand CT transitions for 5 and 6. The effect of long-range corrections is noteworthy, particularly for the larger complexes, improving the calculation of β ratios for 4-6. However, CAM-B3LYP, ωB97X, and LC-BLYP considerably overestimated the low-lying CT energies. PBE0 was found to give the best transition energy match for 4. The influence of the phenylene ring orientation in the alkynyl ligand on the calculated properties is substantial, particularly for the larger complexes. For these types of calculations, a basis set with diffuse functions (at least 6-31+G(d)) for the heavy elements is recommended.

Syntheses, structures, photoluminescence and semiconductor properties of two novel mercury-lanthanide complexes with a three-dimensional open framework

Two novel mercury-lanthanide complexes [Hg3Cl6(u-IA)3Ln(H2O)2]n (IA = isonicotinic acid anion; Ln = Pr (1) and Sm (2)) have been synthesized under hydrothermal conditions and structurally determined by single crystal X-ray diffraction. Complexes 1 and 2 are isostructure and feature a three-dimensional (3-D) open framework with two types of one-dimensional (1-D) chains. Based on the condensed 3-D open framework, there is a large void space being 1010.3 Å3 and 1018.1 Å3 which occupy 27.2% and 27.4% of the unit-cell volume for complexes 1 and 2, respectively. Solid-state UV/Vis diffuse reflectance spectroscopy reveals that there is a wide optical band gap of 3.51 eV and 3.54 eV for complexes 1 and 2, respectively. Photoluminescence measurements using solid-state samples discover that both complexes display red light emission. The emission bands can be ascribed to the characteristic emission of the 4f electron intrashell transitions of the Ln3+ ions, i.e. 1D2 → 3H4 and 3P0 → 3F3 transitions for complex 1, as well as 4G5/2 → 6H5/2, 4G5/2 → 6H7/2 and 4G5/2 → 6H9/2 transitions for complex 2.

Complex Coacervation of Milk Proteins with Sodium Alginate

Beta-lactoglobulin (BLG) and bovine serum albumin (BSA) coacervate formation with sodium alginate (ALG) was investigated by turbidimetric analysis, zeta potential, particle size, viscosity, transmission electron microscopy (TEM) and isothermal titration calorimetric (ITC) measurements as a function of pH (1.0-7.0) and protein/alginate mixing ratio (1:1, 1.5:1, 2:1, 1:0, and 0:1 wt.). Critical pH values of phase transitions for BSA-ALG complexes (pHC, pHφ1, and pHφφ2) representing the formation of soluble and insoluble complexes of a protein-ALG mixture (2:1) at pH 4.8, 4.2, and 1.8, respectively. In the case of BLG-ALG, critical pH values (pHC, pHφ1, and pHφ2) were found to be 4.8, 4.2, and 1.6, respectively. The pHopt values, expressed by the highest optical density, were pH 2.8 for BSA-ALG and 2.4 for BLG-ALG. TEM and zeta-potential results showed that maximum coacervate formation occurred at pH 4.2 for both protein-polysaccharide solutions. The interaction between BLG-ALG and BSA-ALG was spontaneously exothermic at pH 4.2 according to ITC measurements. The findings of this study provide insights to a thorough understanding about the nature of interactions between milk proteins and ALG and formulate new applications for food, pharmaceutical, nutraceutical, and cosmetics applications.

Time-spliced X-ray diffraction imaging of magnetism dynamics in a NdNiO3 thin film

Diffraction imaging of nonequilibrium dynamics at atomic resolution is becoming possible with X-ray free-electron lasers. However, there are unresolved problems with applying this method to objects that are confined in only one dimension. Here I show that reliable one-dimensional coherent diffraction imaging is possible by splicing together images recovered from different time delays in an optical pump X-ray probe experiment. The time and space evolution of antiferromagnetic order in a vibrationally excited complex oxide heterostructure is recovered from time-resolved measurements of a resonant soft X-ray diffraction peak. Midinfrared excitation of the substrate is shown to lead to a demagnetization front that propagates at a velocity exceeding the speed of sound, a critical observation for the understanding of driven phase transitions in complex condensed matter.

Temperature-dependent vibrational spectroscopy to study order-disorder transitions in charge transfer complexes

Charge-transfer (CT) complexes are a promising class of materials for the semiconductor industry because of their versatile properties. This class of compounds shows a variety of phase transitions, which are of interest because of their potential impact on the electronic characteristics. Here temperature-dependent vibrational spectroscopy is used to study structural phase transitions in a set of organic CT complexes. Splitting and broadening of infrared-active phonons in the complex formed between pyrene and pyromellitic dianhydride (PMDA) confirm the structural transition is of the order-disorder type and complement previous x-ray diffraction (XRD) results. We show that this technique is a powerful tool to characterize transitions, and apply it to a range of binary CT complexes composed of polyaromatic hyrdocarbons (anthracene, perylene, phenanthrene, pyrene, and stilbene) and PMDA. We extend the understanding of transitions in perylene-PMDA and pyrene-PMDA, and show that there are no order-disorder transitions present in anthracene-PMDA, stilbene-PMDA and phenanthrene-PMDA in the temperature range investigated here.

A high temperature reversible phase transition in a supramolecular complex of 15-crown-5 with tetraphenylboron sodium

High temperature (391 K) reversible phase transition and large thermal hysteresis (19 K) was observed in 15-crown-5 clathrates: [Na(15-crown-5)][BPh4] (15-crown-5 = 1,4,7,10,13-pentaoxacyclopentadecane, NaBPh4 = sodium tetraphenylboron).

Низкотемпературная люминесценция и термостимулированная люминесценция монокристаллов BeO : Mg

AbstractLuminescence and thermally stimulated luminescence (TL) of BeO: Mg crystals are studied at T = 6–380 K. The TL glow curves and the spectra of luminescence (1.2–6.5 eV), luminescence excitation, and reflection (3.7–20 eV) are obtained. It is found that the introduction of an isovalent magnesium impurity into BeO leads to the appearance of three new broad luminescence bands at 6.2–6.3, 4.3–4.4, and 1.9–2.6 eV. The first two are attributed to the radiative annihilation of a relaxed near-impurity (Mg) exciton, the excited state of which is formed as a result of energy transfer by free excitons. The impurity VUV and UV bands are compared with those for the intrinsic luminescence of BeO caused by the radiative annihilation of self-trapped excitons (STE) of two kinds: the band at 6.2–6.3 eV of BeO: Mg is compared with the band at 6.7 eV (STE_1) of BeO, and the band at 4.3–4.4 eV is compared with the band at 4.9 eV (STE^2) of BeO. In the visible region, the luminescence spectrum is due to a superposition of intracenter transitions in an impurity complex including a magnesium ion. The manifestation of X-ray-induced luminescence bands at T = 6 K in BeO: Mg indicates their excitation during band-to-band transitions and in recombination processes. The energy characteristics of the impurity states in BeO: Mg are determined; the effect of the isovalent impurity on the fluctuation rearrangement of the BeO: Mg structure in the thermal transformation region of STE_1 → STE_2 is revealed.