Three-state combinatorial switch models as applied to the binding of oxygen by human hemoglobin.

Uncovering mechanism of excessive copper ion-activated depressed-sphalerite under moderate alkaline conditions: A combined experimental and DFT investigation

In this paper, we delve into the intricate interplay between optical fields with varying relative phases in a closed-loop configuration semiconductor quantum well waveguide with four distinct energy levels, and how it impacts the Fraunhofer diffraction patterns obtained via four-wave mixing. By harnessing a strong control field, a standing wave driving field, and two weak probe and signal fields, we drive the waveguide to generate these patterns with maximum efficiency. To achieve this, we consider three distinct light-matter interaction scenarios, where the system is first set up in either a lower electromagnetically induced transparency or a coherent population trapping state, followed by a final state that enables electron spin coherence (ESC) induction. Our results reveal that the efficiency of Fraunhofer diffraction in the quantum well waveguide can be enhanced significantly under specific parameter regimes via the spin coherence effect. Further investigation of the light-matter interaction in the ESC zone, where only one of the control fields is a standing wave field, demonstrates that spin coherence facilitates more efficient transfer of energy from the probe light to the third and fourth orders, highlighting its crucial role in shaping the diffraction patterns.

The well known increase of the Hall coefficient with temperature in SnTe is usually explained bythe double valence band model. SnTe is synthesized and crystallized by various methods. In the concentration interval of carriers of 4 × 1019 to 5 × 1020 cm−3 it is often found, that the curves RH(T) are crossed, a fact, which cannot be explained with the model above mentioned. A model of thermally generated Frenkel-type defects of Te-atoms is proposed. As result of the generation hole traps occur with two distinct energy levels. The low-temperature level depends on carrier concentration (on the concentration differences between the vacancies of Sn and Te). The high temperature level is connected with the dopands. The exponent a in the temperature dependence of mobility, μ ∽ T−a in the range. RH = const depends elementarily on the compensation coefficient (ratio of the concentrations of the tellur and tin vacancies). [Russian Text Ignored].

We discuss adiabatic quantum phenomena at a level crossing. Given a path in the parameter space which passes through a degeneracy point, we find a criterion which determines whether the adiabaticity condition can be satisfied. For paths that can be traversed adiabatically we also derive a differential equation which specifies the time dependence of the system parameters, for which transitions between distinct energy levels can be neglected. We also generalize the well-known geometric connections to the case of adiabatic paths containing arbitrarily many level-crossing points and degenerate levels.

Harnessing optical supermode interaction to construct artificial photonic molecules has uncovered a series of fundamental optical phenomena analogous to atomic physics. Previously, the distinct energy levels and interactions in such two-level systems were provided by coupled microresonators. The reconfigurability is limited, as they often require delicate external field stimuli or mechanically altering the geometric factors. These highly specific approaches also limit potential applications. Here, we propose a versatile on-chip photonic molecule in a multimode microring, utilizing a flexible regulation methodology to dynamically control the existence and interaction strength of spatial modes. The transition between single/multi-mode states enables the “switched-off/on” functionality of the photonic molecule, supporting wider generalized applications scenarios. In particular, “switched-on” state shows flexible and multidimensional mode splitting control in aspects of both coupling strength and phase difference, equivalent to the a.c. and d.c. Stark effect. “Switched-off” state allows for perfect low-loss single-mode transition (Qi ~ 10 million) under an ultra-compact bend size (FSR ~ 115 GHz) in a foundry-based silicon microring. It breaks the stereotyped image of the FSR-Q factor trade-off, enabling ultra-wideband and high-resolution millimeter-wave photonic operations. Our demonstration provides a flexible and portable solution for the integrated photonic molecule system, extending its research scope from fundamental physics to real-world applications such as nonlinear optical signal processing and sixth-generation wireless communication.

The link between low-frequency time-dependent variability and the existence of multiple unstable steady-state solutions in a reduced gravity quasigeostrophic ocean model for the midlatitude wind-driven circulation is investigated. It is shown that a sequence of successive symmetry-breaking pitchfork bifurcations lead to multiple equilibria that differ from each other primarily in the elongation of the recirculation cell, in the amount of meandering present in the intergyre jet, and in a north–south shift in the eastward jet. The elongation of the recirculation cells and the meandering of the jet play compensating roles in the establishment of the global energy and vorticity balance. The solutions also have distinct energy levels, but general agreement between them and the bumps in a histogram of the total energy obtained from a 1200-yr time-dependent simulation is not found. Nevertheless, a substantial fraction of the variance (30%) can be accounted for by four coherent structures that capture th...

Self-trapped exciton (STE) luminescence, typically associated with structural deformation of excited states, has attracted significant attention in metal halide materials recently. However, the mechanism of multiexciton STE emissions in certain metal halide crystals remains largely unexplored. This study investigates dual luminescence emissions in HCOO- doped Cs3Cu2I5 single crystals using transient and steady-state spectroscopy. The dual emissions are attributed to intrinsic STE luminescence originating from the host lattice and extrinsic STE luminescence induced by external dopants, respectively, each of which can be triggered independently at distinct energy levels. Theoretical calculations reveal that multiexciton emission originates from structural distortion of the host and dopant STEs within the 0D lattice in their respective excited states. By meticulously tuning the excitation wavelength and selectively exciting different STEs, the dynamic alteration of color change in Cs3Cu2I5:HCOO- crystals is demonstrated. Ultimately, owing to an extraordinarily high photoluminescence quantum yield (99.01%) and a diminished degree of self-absorption in Cs3Cu2I5:HCOO- crystals, they exhibit remarkable X-ray scintillation characteristics with light yield being improved by 5.4 times as compared to that of pristine Cs3Cu2I5 crystals, opening up exciting avenues for achieving low-dose X-ray detection and imaging.

Distinct luminescent properties between thiophene-S-oxide and Thiophene-S, S-dioxides incorporated ladder-type molecules

Binding of triethyllead chloride by hemoglobin

Concentration Dependence of the Self-Diffusion of Human and Lumbricus terrestris Hemoglobin

Oxygen isotherms of human hemoglobin measured in distilled water and in solutions of sodium chloride in the concentration range from 0.02 to 3.0 M indicate that the oxygen affinity decreases up to about 1 M salt and then begins to increase. The isotherms obtained in the range from 0.02 to 0.6 M sodium chloride, at 37 degrees and pH 7.4, have been analyzed in terms of changes in Gibbs free energy of heme ligation, resulting from the differential interaction between the chloride ion and the two forms of hemoglobin. The maximal theoretical change in Gibbs free energy that chloride ion can exert on the oxygen binding of hemoglobin amounts to 4.9 +/- 0.2 kcal/mol (21 +/- 0.8 kJ/mol) of hemoglobin tetramer. A plot of the logarithm of oxygen concentration at half saturation versus the logarithm of the chloride concentration has a slope of 0.40, suggesting 1.6 apparent chloride sites per hemoglobin tetramer. Because the interaction between chloride and hemoglobin is dependent on pH, the apparent thermodynamic linkage between chloride and oxygen binding will also include the salt dependence of the Bohr effect at pH 7.4. The fractional change in Gibbs free energy, measured as a function of the chloride concentration, can be approximated by the binding isotherm between a protein and a ligand, using an association constant of 11 M(-1). Thus, if the number of oxygen-linked chloride sites is more than one per hemoglobin tetramer, these sites must be considered independent.

Comprehensive SummaryKasha's exciton model proposes that T1 energy levels of organic compounds are insensitive to molecular aggregation and microenvironment change because of negligible small transition dipole moments of T1 states. This model holds true in most organic systems till now. Here we report the fabrication of twisted organic phosphors with intramolecular charge transfer characters and flexible molecular structures. When doped into different organic matrices, the twisted phosphor adopts different conformation, exhibits distinct phosphorescence colors and T1 energy levels, which violates Kasha's exciton model in organic system. Given that the change of phosphorescence colors and maxima can be readily distinguished by human eyes and conventional instrument, the twisted phosphors would be exploited as a new type of molecular probe, which would exhibit potential application in optical sensing and stimuli‐responsive systems.

The mechanism of cooperativity in the human hemoglobin tetramer (a dimer of alpha beta dimers) has historically been modeled as a simple two-state system in which a low-affinity structural form (T) switches, on ligation, to a high-affinity form (R), yielding a net loss of hydrogen bonds and salt bridges in the dimer-dimer interface. Modifications that weaken these cross-dimer contacts destabilize the quaternary T tetramer, leading to decreased cooperativity and enhanced ligand affinity, as demonstrated in many studies on symmetric double modifications, i.e., a residue site modified in both alpha- or both beta-subunits. In this work, hybrid tetramers have been prepared with only one modified residue, yielding molecules composed of a wild-type dimer and a modified dimer. It is observed that the cooperative free energy of ligation to the modified dimer is perturbed to the same extent whether in the hybrid tetramer or in the doubly modified tetramer. The cooperative free energy of ligation to the wild-type dimer is unperturbed, even in the hybrid tetramer, and despite the overall destabilization of the T tetramer by the modification. This asymmetric response by the two dimers within the same tetramer shows that loss of dimer-dimer contacts is not communicated across the dimer-dimer interface, but is transmitted through the dimer that bears the modified residue. These observations are interpreted in terms of a previously proposed dimer-based model of cooperativity with an additional quaternary (T/R) component.

Molecular oxygen migration through the xenon docking sites of human hemoglobin in the R-state

The binding of inositol hexaphosphate (IHP) to oxyhemoglobin (oxy-Hb) was investigated by gel filtration and stopped flow kinetic methods. The stoichiometry of the complex is 1 IHP per hemoglobin tetramer in 0.05 m 2,2-bis(hydroxymethyl)-2,2',2''-nitrilotriethanol (pH 7.0) containing 0.11 m NaCl and appears to approach 2 IHP per tetramer when the ionic strength is reduced to 0.01. The dissociation constant for the IHP-oxy-Hb complex is of the order of 10-6 m. Kinetic experiments conducted over a wide range of concentrations of oxy-Hb suggest, in addition, that the liganded hemoglobin dimer does not bind IHP. The complex of IHP with deoxyhemoglobin also exhibits a stoichiometry of 1 organic phosphate molecule per hemoglobin tetramer; the dissociation constant was not measured but must be less than 10-8 m based on the large inhibitory effect of IHP on oxygen binding and the high affinity of oxy-Hb for IHP. The kinetics of oxygen and carbon monoxide binding were examined in the presence of IHP; the rate constant for the dissociation of oxygen from fully saturated oxy-Hb was doubled from about 50 sec-1 to 100 sec-1 when IHP was added to phosphate-free hemoglobin, whereas in the case of carbon monoxide, the comparable dissociation rate constant increased from 0.019 sec-1 to 0.032 sec-1. Partial photodecomposition of oxy-Hb and carbon monoxide hemoglobin in the presence and absence of IHP demonstrated that the intermediate species Hb4X3 binds ligand with rate constants of 5 x 106 m-1 sec-1 and 33 x 106 m-1 sec-1, respectively (X = oxygen), whereas the corresponding rate constants for carbon monoxide are 1.4 x 106 m-1 and 7.4 x 106 m-1 sec-1. IHP was also found to induce kinetic heterogeneity in the reaction of deoxyhemoglobin with carbon monoxide which was not present in hemoglobin free of phosphates. This heterogeneity is most prominent at wave lengths near the Soret isosbestic region of the deoxy and carbon monoxide spectra and presumably reflects phosphate-induced kinetic differences between the α and β chains of hemoglobin.