Syntheses, structures and luminescence of Europium α-thiophene carboxylates coordination polymer and supramolecular compound

Two europium α-thiophene carboxylic acid (HTPA) compounds, coordination polymer Eu(TPA)₃(HTPA)₂ (1) (TPA=α-thiophene carboxylate) and supramolecular compound Eu(TPA)₃(H₂O)₃ · 0.5H₂O (2) with luminescence and triboluminescence, have been synthesized and structurally characterized. In 1 each europium is bridged by six oxygen atoms from six carboxylates and coordinated with two carboxyl oxygen atoms from two α-thiophene carboxylic acid molecules, resulting in a coordination number of eight to Eu. For 2 each europium is chelated by six oxygen atoms from six carboxylates and coordinated with three oxygen atoms from three coordinated water generating a coordination number nine to Eu; A supramolecular compound is constructed through hydrogen bonds. Both 1 and 2 display strong characteristic emission of Eu³⁺ ion radiated by UV light and produce twinkling red light with an external force.     

Perception–action loops of multiple agents: informational aspects and the impact of coordination

Embodied agents can be conceived as entities perceiving and acting upon an external environment. Probabilistic models of this perception-action loop have paved the way to the investigation of information-theoretic aspects of embodied cognition. This formalism allows (i) to identify information flows and their limits under various scenarios and constraints, and (ii) to use informational quantities in order to induce the self-organization of the agent's behavior without any externally specified drives. This article extends the perception-action loop formalism to multiple agents. The multiple-access channel model is presented and used to identify the relationships between informational quantities of two agents interacting in the same environment. The central question investigated in this article is the impact of coordination. Information-theoretic limits on what can be achieved with and without coordination are identified. For this purpose, different abstract channels are studied, along with a concrete example of agents interacting in space. It is shown that, under some conditions, self-organizing systems based on information-theoretic quantities have a tendency to spontaneously generate coordinated behavior. Moreover, in the perspective of engineering such systems to achieve specific tasks, these information-theoretic limits put constraints on the amount of coordination that is required to perform the task, and consequently on the mechanisms that underlie self-organization in the system.     

Is coordination of leaf and root growth mediated by abscisic acid? Opinion

Leaf growth is more inhibited than root growth when the soil is nitrogen-deficient, dry, saline, compacted, or of restricted volume. Similar differential responses in leaf and root growth occur when ABA is applied to plants in well-watered and well-fertilised conditions, and opposite responses are often found in ABA-deficient mutants. ABA levels increase in plants in dry or saline soils, suggesting a regulating role in leaf and root growth in soils of low water potential. In nitrogen-deficient or compacted soils, or soils of restricted volume, ABA only sometimes increases, and in these situations its accumulation may be of secondary importance. Use of ABA-deficient mutants has so far indicated that ABA influences leaf and root growth in unstressed plants, and plants in dry soils, but not in soils that are compacted, of restricted volume, or are nitrogen-deficient.For ABA to determine the relationship between the rate of leaf growth and the rate of root growth, there must be long-distance transport of either ABA itself or a compound that controls ABA synthesis in the growing cells of leaves and roots. ABA invariably increases in xylem sap as the soil becomes dry or saline, and sometimes when it becomes nitrogen-deficient or compacted, however the ABA is of too low a concentration to affect leaf growth. There may be a compound in xylem sap that controls the synthesis of ABA in the leaf, but no such compound has been identified. ABA accumulates in phloem sap of plants in dry or saline soil, but its function in controlling root or leaf growth is unknown.We conclude that ABA affects the ratio of root growth to leaf growth via its independent effects on root and leaf growth, and may regulate the ratio of root to leaf growth via feedforward signals in xylem or phloem, but there is no satisfactory explanation of its mechanism of control.     

Cone packing model — a geometrical approach to coordination and organometallic chemistry of lanthanides and actinides

By projection of the ligands to a unit sphere centred at the metal ion, steric effects, both local and overall, can be studied quantitatively in terms of solid angle factor (SAF), fan angle (FA), coordination vector, gap and hole. The packing saturation rule and the packing centre rule have been determined by treatment of more than 400 structures of lanthanide and actinide coordination and organometallic compounds. A ligand packing model was thus adopted with cones joined at the same apex.‘Coordination Saturation’ in f-block chemistry was clarified to be saturation in coordination space, implying an equilibrium between bonding and steric effects. Molecular structures could be simulated on the basis of a uniform packing principle. The cone packing model has been applied to inorganic preparation, synergistic extraction and structure prediction. These predictions have been clearly substantiated experimentally, and the results are reported.A dynamic packing model was also suggested to study the reaction pathways by simulating the relative positions during the reaction process and the size and shape of holes, which correspond to the reaction areas in the coordination sphere. Lewis base association and dissociation, and the metal- carbon bond thermolysis of structural pattern MCp₃L were explained as examples.     

The coordination of copper(II) with β-casomorphin and its fragments

The synthesis of β-casomorphin-5 (Tyr-Pro-Phe-Pro-Gly, H₂L) and a number of its peptide fragments is described. Complexes formed between these peptides and Cu(II) have been investigated spectrophotometrically, using CD and EPR spectroscopy, and potentiometrically. Results show that, with tyrosine as the N-terminal residue, the major complex formed at physiological pH is the dimeric species, [Cu₂L₂], bonded through the phenolic O^? of the Tyr residue of one ligand and the N-terminal amine nitrogen of the second ligand molecule. There is no evidence for coordination through the peptide nitrogens unless the terminal Tyr group is removed.     

Importance of dynamical processes in the coordination chemistry and redox conversion of copper amyloid-β complexes

Interaction of Cu ions with the amyloid-β (Aβ) peptide is linked to the development of Alzheimer’s disease; hence, determining the coordination of Cu^I and Cu^II ions to Aβ and the pathway of the Cu^I(Aβ)/Cu^II(Aβ) redox conversion is of great interest. In the present report, we use the room temperature X-ray absorption near edge structure to show that the binding sites of the Cu^I and Cu^II complexes are similar to those previously determined from frozen-solution studies. More precisely, the Cu^I is coordinated by the imidazole groups of two histidine residues in a linear fashion. However, an NMR study unravels the involvement of all three histidine residues in the Cu^I binding due to dynamical exchange between several set of ligands. The presence of an equilibrium is also responsible for the complex redox process observed by cyclic voltammetry and evidenced by a concentration-dependent electrochemical response.     

Optimal coordination of maximal-effort horizontal and vertical jump motions – a computer simulation study

Background  

The purpose of this study was to investigate the coordination strategy of maximal-effort horizontal jumping in comparison with vertical jumping, using the methodology of computer simulation.     

Lumbar–pelvic range and coordination during lifting tasks

Spine motion has been described to have two regions, a neutral zone where lumbar rotation can occur with little resistance and an elastic zone where structures such as ligaments, facet joints and intervertebral disks resist rotation. In vivo, the passive musculature can contribute to further limiting the functional neutral range of lumbar motion. Movement out of this functional neutral range could potentially put greater loads on these structures. In this study, the range of lumbar curvature rotation was examined in twelve healthy, untrained volunteers at four torso inclination angles. The lumbar curvature during straight-leg lifting tasks was then defined as a percentage of this range of possible lumbar curvatures. Subjects were found to remain neutrally oriented during the flexion phase of a lifting task. During the extension phase of the lifting task, however, subjects were found to assume a more kyphotic posture, approaching the edge of the functional range of motion. This was found to be most pronounced for heavy lifting tasks. By allowing the lumbar curvature to go into a highly kyphotic posture, subjects may be taking advantage of stretch-shortening behavior in extensor musculature and associated tendons to reduce the energy required to raise the torso. Such a kyphotic posture during extension, however, may put excessive loading on the elastic structures of the spine and torso musculature increasing the risk of injury.     

Linear free energy relationships predict coordination and π-stacking interactions of small molecules with ferriprotoporphyrin IX

In order to better understand the interaction of antimalarial compounds with ferriprotoporphyrin IX (Fe(III)PPIX), association constants of pyridines, imidazoles, amines and phenolates with Fe(III)PPIX and protoporphyrin IX (PPIX) have been measured spectrophotometrically in 40% (v/v) aq. DMSO at pH 7.4. The pH independent log association constants for coordination of nitrogen donor ligands exhibit a linear free energy relationship (LFER) with the pK_a of the donor atom. Association through π-stacking interactions (log K_π) with PPIX and Fe(III)PPIX increases with the number of π-electrons in the aromatic ring system. These findings indicate that in the aqueous milieu of the malaria parasite digestive vacuole, coordination to the Fe(III) center of the porphyrin is necessarily very weak, while π-stacking interactions will be much stronger. On the other hand, in environments in which proton competition is absent, coordination will dominate, with the most basic donor atoms forming the strongest complexes with Fe(III)PPIX. The lipid nanospheres within the digestive vacuole which are now known to be the location of conversion of Fe(III)PPIX to hemozoin could possibly be such an environment, making both types of interaction relevant to the design of new hemozoin inhibitors.     

Metal ion size and coordination mode in complexes of a β-diketiminate ligand with pendant quinoline arms

A suite of late first row transition metal complexes has been synthesized using a monoanionic nitrogen donor β-diketiminate ligand with quinolyl pendant arms, BDI^QQH (1). BDI^QQNiOTf (2), BDI^QQCuCl (4), BDI^QQZnCl (5) were prepared from the reaction of 1 with Ni(OTf)₂, CuCl₂·2H₂O and ZnCl₂, respectively. BDI^QQNiCl (3) was synthesized from an anion exchange of 2 with ⁿBu₄NCl. Reaction of 1 and CoI₂ afforded the unexpected [(BDI^QQ)₂Co]⁺I⁻ (6). Through density functional theory (DFT) calculations, ligand geometries in BDI^QQ complexes were investigated and it was found that smaller ionic radius and higher charge destabilize 1:1 metal-ligand complexes relative to alternative 1:2 complexes like 6 owing to significant conformational strain in 1:1 complexes involving metals with small ionic radii. Synthesis and characterization of these complexes, including crystal structures of 4 and 5, are reported, in addition to the results of DFT calculations.     

Conformational change and human cytochrome c function: mutation of residue 41 modulates caspase activation and destabilizes Met-80 coordination

Cytochrome c is a highly conserved protein, with 20 residues identical in all eukaryotic cytochromes c. Gly-41 is one of these invariant residues, and is the position of the only reported naturally occurring mutation in cytochrome c (human G41S). The basis, if any, for the conservation of Gly-41 is unknown. The mutation of Gly-41 to Ser enhances the apoptotic activity of cytochrome c without altering its role in mitochondrial electron transport. Here we have studied additional residue 41 variants and determined their effects on cytochrome c functions and conformation. A G41T mutation decreased the ability of cytochrome c to induce caspase activation and decreased the redox potential, whereas a G41A mutation had no impact on caspase induction but the redox potential increased. All residue 41 variants decreased the pK _a of a structural transition of oxidized cytochrome c to the alkaline conformation, and this correlated with a destabilization of the interaction of Met-80 with the heme iron(III) at physiological pH. In reduced cytochrome c the G41T and G41S mutations had distinct effects on a network of hydrogen bonds involving Met-80, and in G41T the conformational mobility of two Ω-loops was altered. These results suggest the impact of residue 41 on the conformation of cytochrome c influences its ability to act in both of its physiological roles, electron transport and caspase activation.     

Structure and coordination of CuB in the Acidianus ambivalens aa 3 quinol oxidase heme–copper center

The coordination environment of the Cu_B center of the quinol oxidase from Acidianus ambivalens, a type B heme–copper oxygen reductase, was investigated by Fourier transform (FT) IR and extended X-ray absorption fine structure (EXAFS) spectroscopy. The comparative structural chemistry of dinuclear Fe–Cu sites of the different types of oxygen reductases is of great interest. Fully reduced A. ambivalens quinol oxidase binds CO at the heme a ₃ center, with ν(CO)=1,973 cm⁻¹. On photolysis, the CO migrated to the Cu_B center, forming a Cu_B^I–CO complex with ν(CO)=2,047 cm⁻¹. Raising the temperature of the samples to 25°C did not result in a total loss of signal in the FTIR difference spectrum although the intensity of these signals was reduced sevenfold. This observation is consistent with a large energy barrier against the geminate rebinding of CO to the heme iron from Cu_B, a restricted limited access at the active-site pocket for a second binding, and a kinetically stable Cu_B–CO complex in A. ambivalens aa ₃. The Cu_B center was probed in a number of different states using EXAFS spectroscopy. The oxidized state was best simulated by three histidines and a solvent O scatterer. On reduction, the site became three-coordinate, but in contrast to the bo ₃ enzyme, there was no evidence for heterogeneity of binding of the coordinated histidines. The Cu_B centers in both the oxidized and the reduced enzymes also appeared to contain substoichiometric amounts (0.2 mol equiv) of nonlabile chloride ion. EXAFS data of the reduced carbonylated enzyme showed no difference between dark and photolyzed forms. The spectra could be well fit by 2.5 imidazoles, 0.5 Cl⁻ and 0.5 CO ligands. This arrangement of scatterers would be consistent with about half the sites remaining as unligated Cu(his)₃ and half being converted to Cu(his)₂Cl⁻CO, a 50/50 ratio of Cu(his)₂Cl⁻ and Cu(his)₃CO, or some combination of these formulations. Electronic Supplementary Material Supplementary material is available for this article at .     

Dynamics of α-Hb chain binding to its chaperone AHSP depends on heme coordination and redox state

Background

AHSP is an erythroid molecular chaperone of the α-hemoglobin chains (α-Hb). Upon AHSP binding, native ferric α-Hb undergoes an unprecedented structural rearrangement at the heme site giving rise to a 6th coordination bond with His(E7).

Methods

Recombinant AHSP, WT α-Hb:AHSP and α-Hb^HE7Q:AHSP complexes were expressed in Escherichia coli. Thermal denaturation curves were measured by circular dichroism for the isolated α-Hb and bound to AHSP. Kinetics of ligand binding and redox reactions of α-Hb bound to AHSP as well as α-Hb release from the α-Hb:AHSP complex were measured by time-resolved absorption spectroscopy.

Results

AHSP binding to α-Hb is kinetically controlled to prevail over direct binding with β-chains and is also thermodynamically controlled by the α-Hb redox state and not the liganded state of the ferrous α-Hb. The dramatic instability of isolated ferric α-Hb is greatly decreased upon AHSP binding. Removing the bis-histidyl hexacoordination in α-HbH58(E7)Q:AHSP complex reduces the stabilizing effect of AHSP binding. Once the ferric α-Hb is bound to AHSP, the globin can be more easily reduced by several chemical and enzymatic systems compared to α-Hb within the Hb-tetramer.

Conclusion

α-Hb reduction could trigger its release from AHSP toward its final Hb β-chain partner producing functional ferrous Hb-tetramers. This work indicates a preferred kinetic pathway for Hb-synthesis.

General significance

The cellular redox balance in Hb-synthesis should be considered as important as the relative proportional synthesis of both Hb-subunits and their heme cofactor. The in vivo role of AHSP is discussed in the context of the molecular disorders observed in thalassemia.     

How do load carriage and walking speed influence trunk coordination and stride parameters?

To determine the effects of load carriage and walking speed on stride parameters and the coordination of trunk movements, 12 subjects walked on a treadmill at a range of walking speeds (0.6-1.6 m s(-1)) with and without a backpack containing 40% of their body mass. It was hypothesized that compared to unloaded walking, load carriage decreases transverse pelvic and thoracic rotation, the mean relative phase between pelvic and thoracic rotations, and increases hip excursion. In addition, it was hypothesized that these changes would coincide with a decreased stride length and increased stride frequency. The findings supported the hypotheses. Dimensionless analyses indicated that there was a significantly larger contribution of hip excursion and smaller contribution of transverse plane pelvic rotation to increases in stride length during load carriage. In addition, there was a significant effect of load carriage on the amplitudes of transverse pelvic and thoracic rotation and the relative phase of pelvic and thoracic rotation. It was concluded that the shorter stride length and higher stride frequency observed when carrying a backpack is the result of decreased pelvic rotation. During unloaded walking, increases in pelvic rotation contribute to increases in stride length with increasing walking speed. The decreased pelvic rotation during load carriage requires an increased hip excursion to compensate. However, the increase in hip excursion is insufficient to fully compensate for the observed decrease in pelvis rotation, requiring an increase in stride frequency during load carriage to maintain a constant walking speed.     

Synthesis and exploratory coordination chemistry of the new ditertiary carbinamine ligand 2,6-bis(α-aminoisopropyl)pyridine

The new pyridine-based N∩N∩N tridentate ligand 2,6-C₅H₃N(CMe₂NH₂)₂ (1) was synthesized by the treatment of 2,6-pyridinedicarbonitrile with an excess of the organocerium reagent in situ generated from CeCl₃ and methyllithium in THF. The reaction of 1 with [RuCl₂(PPh₃)₃] in THF at ambient conditions afforded (OC-6-23)-[RuCl{2,6-C₅H₃N(CMe₂NH₂)₂}(PPh₃)₂]Cl (2). The corresponding dimethyl sulfoxide complex [RuCl{2,6-C₅H₃N(CMe₂NH₂)₂}{S(O)Me₂}₂]Cl (3) was isolated as a mixture of the (OC-6-23) and (OC-6-32) stereoisomers 3a and 3b from the reaction between 1 and (OC-6-22)-[RuCl₂{S(O)Me₂}₃(OSMe₂)] in toluene at 80 °C. A prolonged interaction in toluene at reflux temperature gave isomerically pure 3a. The metal trichloride hydrates MCl₃ · xH₂O (M = Ru, Rh, Ir; x ≅ 2-4) produced mer-[RuCl₃{2,6-C₅H₃N(CMe₂NH₂)₂}] (M = Ru: 4; Rh: 5; Ir: 6), when combined with 1 in refluxing ethanol. The crystal structures of the following compounds were determined: ligand 1 and complexes 2-5 as addition compounds 2 · CH₂Cl₂, 3a · C₇H₈, 4 · EtOH and .     

Synthesis, structure and magnetic properties of two μ-oxo and thiocyanato-bridged manganese(II)-mercury(II) coordination polymers

Mixed-metal thiocyanate complexes [MnHg(SCN)₄(NOP)] (1) and [MnHg(SCN)₄(DMSO)] (2) (NOP = 3-methyl-4-nitropyridine-N-oxide, DMSO = dimethylsulfoxide) have been synthesized and structurally characterized by single crystal X-ray analysis. Complex 1 and 2 both contain a [Mn₂(μ₂-O)₂] lozenge, which is bridged to Hg(II) ions by end-to-end thiocyanate groups to form a 2-D and 3-D polymeric network, respectively. Magnetic studies indicate that both complexes are anti-ferromagnets, with 1 showing anti-ferrimagnetic ordering below 8.0 K.     

How do neural connectivity and time delays influence bimanual coordination?

Multilevel crosstalk as a neural basis for motor control has been widely discussed in the literature. Since no natural process is instantaneous, any crosstalk model should incorporate time delays, which are known to induce temporal coupling between functional elements and stabilize or destabilize a particular mode of coordination. In this article, we systematically study the dynamics of rhythmic bimanual coordination under the influence of varying connection topology as realized by callosal fibers, cortico-thalamic projections, and crossing peripheral fibers. Such connectivity contributes to various degrees of neural crosstalk between the effectors which we continuously parameterize in a mathematical model. We identify the stability regimes of bimanual coordination as a function of the degree of neural crosstalk, movement amplitude and the time delays involved due to signal processing. Prominent examples include explanations of the decreased stability of the antiphase mode of coordination in split brain patients and the role of coupling in mediating bimanual coordination.     

Interaction between the premotor processes of eye and hand movements: Possible mechanism underlying eye–hand coordination

Interaction between the execution process of eye movement and that of hand movement must be indispensable for eye–hand coordination. The present study investigated corticospinal excitability in the hand muscles during the premotor processes of eye and/or hand movement to elucidate interaction between these processes. Healthy humans performed a precued reaction task of eye and/or finger movement and motor-evoked potentials in the hand muscles were evoked in the reaction time. Leftward eye movement suppressed corticospinal excitability in the right abductor digiti minimi muscle only when little finger abduction was simultaneously executed. Corticospinal excitability in the first dorsal interosseous muscle was not suppressed by eye movement regardless of whether or not it was accompanied by finger movement. Suppression of corticospinal excitability in the hand muscles induced by eye movement in the premotor period depends on the direction of eye movement, the muscle tested, and the premotor process of the tested muscle. The suppression may reflect interaction between the motor process of eye movement and that of hand movement particularly active during eye–hand coordination tasks during which both processes proceed.     

Is there coordination of leaf and fine root traits at local scales? A test in temperate forest swamps

Examining the coordination of leaf and fine root traits not only aids a better understanding of plant ecological strategies from a whole‐plant perspective, but also helps improve the prediction of belowground properties from aboveground traits. The relationships between leaf and fine root traits have been extensively explored at global and regional scales, but remain unclear at local scales. Here, we measured six pairs of analogous leaf and fine root traits related to resource economy and organ size for coexisting dominant and subordinate vascular plants at three successional stages of temperate forest swamps in Lingfeng National Nature Reserve in the Greater Hinggan Mountains, NE China. Leaf and fine root traits related to resource acquisition (e.g., specific leaf area [SLA], leaf N, leaf P, root water content, and root P) decreased with succession. Overall, we found strong linear relationships between leaf dry matter content (LDMC) and root water content, and between leaf and root C, N, and P concentrations, but only weak correlations were observed between leaf area and root diameter, and between SLA and specific root length (SRL). The strong relationships between LDMC and root water content and between leaf and root C, N, and P held at the early and late stages, but disappeared at the middle stage. Besides, C and P of leaves were significantly correlated with those of roots for woody plants, while strong linkages existed between LDMC and root water content and between leaf N and root N for herbaceous species. These results provided evidence for the existence of strong coordination between leaf and root traits at the local scale. Meanwhile, the leaf–root trait relationships could be modulated by successional stage and growth form, indicating the complexity of coordination of aboveground and belowground traits at the local scale.