Search Results (233)

The development of multifunctional smart packaging materials capable of simultaneously monitoring temperature and suppressing microbial contamination is critical for next-generation food and pharmaceutical safety systems. In this study, we report the design and characterization of a polymeric film integrating a spin crossover (SCO)-based thermochromic sensor with zinc oxide (ZnO) nanoparticles serving as an antimicrobial agent. Beyond the individual functionalities, we demonstrate a synergistic effect between SCO and ZnO components. Notably, the SCO transition of the pristine SCO complex is broadened, and the hysteresis width of the transition is decreased (i.e., from 6 K to 1.5 K, 2 K, and 1.5 K for ZnO loading of 0.5%, 1%, and 2%, respectively), in the polysulfone–SCO–ZnO composites. Migration studies reveal that the co-existence of SCO and ZnO does not disrupt the low release profile of active agents, which remains low across ZnO loadings. The polymeric film exhibited dose-dependent antiproliferative activity against MCF-7 breast cancer cells, with a significant reduction in cell viability observed only at the highest tested concentration, indicating cytotoxic potential. This multifunctional platform represents a promising advancement in smart packaging design, enabling real-time thermal indication combined with the integration of ZnO as a literature-established antimicrobial component, within a non-toxic, and visually transparent system. Collectively, the material’s properties offer promising scalability for both food and pharmaceutical packaging applications where visual clarity, antimicrobial integrity, and temperature monitoring are imperative. Full article

We present a fully controlled thermodynamic study of the two-dimensional dipolar Q-state clock model on small square lattices with free boundaries, combining exhaustive state enumeration with noise-free evaluation of canonical observables. We resolve the complete energy spectra and degeneracies $\{E_n,c_n\}$ for the Ising case ($Q=2$) on lattices of size $L=3,4,5$, and for clock symmetries $Q=4,6,8$ on a $3\times 3$ lattice, tracking how the competition between exchange and long-range dipolar interactions reorganizes the low-energy manifold as the ratio $\alpha =D/J$ is varied. Beyond a finite-size characterization, we identify several qualitatively new thermodynamic signatures induced solely by dipolar anisotropy. First, we demonstrate that ground-state level crossings generated by long-range interactions appear as exact zeros of the specific heat in the limit $C(T\to 0,\alpha )$, establishing an unambiguous correspondence between microscopic spectral rearrangements and macroscopic caloric response. Second, we show that the shape of the associated Schottky-like anomalies encodes detailed information about the degeneracy structure of the competing low-energy states: odd lattices ($L=3,5$) display strongly asymmetric peaks due to unbalanced multiplicities, whereas the even lattice ($L=4$) exhibits three critical values of $\alpha$ accompanied by nearly symmetric anomalies, reflecting paired degeneracies and revealing lattice parity as a key organizing principle. Third, we uncover a symmetry-driven crossover with increasing Q: while the $Q=2$ and $Q=4$ models retain sharp dipolar-induced critical points and pronounced low-temperature structure, for $Q\ge 6$, the energy landscape becomes sufficiently smooth to suppress ground-state crossings altogether, yielding purely thermal specific-heat maxima. Altogether, our results provide a unified, size- and symmetry-resolved picture of how long-range anisotropy, lattice parity, and discrete rotational symmetry shape the thermodynamics of mesoscopic magnetic systems. We show that dipolar interactions alone are sufficient to generate nontrivial critical-like caloric behavior in clusters as small as $3\times 3$, establishing exact finite-size benchmarks directly relevant for van der Waals nanomagnets, artificial spin-ice arrays, and dipolar-coupled nanomagnetic structures. Full article

We discuss the design, the analysis and the parallel implementation of a dynamic programming approach for the computation of the density of state in the simulation of spin-crossover nanoparticles. The motivation is the computation of a Hamiltonian, which is usually approximated using Monte Carlo techniques. However, physicists need better control of the accuracy of this approximation. An exact counting algorithm allows this error to be controlled, and also measures the impact on accuracy for the entire simulation. We propose an exact parallel counting algorithm and its two-level parallel implementation to tackle nanoscale problems on HPC architecture. We discuss its scalability and feasibility for $2D$ grids of n molecules. The new algorithm enables the exact computation for a three-variable density of state at nanoscale, which is seen as intractable. A comparison between the expectation of the model and implementation is proposed. The parallel complexity achieved is $O(n^{{\displaystyle \frac{5}{2}}}{2}^{\sqrt{n}})$ and the results allow the prediction of never-before-seen phenomena. Full article

Tailoring the spin crossover (SCO) effect in molecular materials remains a fundamental challenge, driven by the need to control critical parameters, such as the spin transition temperature (T₁/₂), hysteresis width, cooperativity, and switching kinetics for applications in sensing, memory, and actuation devices. SCO behavior is highly sensitive to small changes in the structure or crystal structure of the surrounding environment. In this context, achieving predictable and reproducible control remains elusive. Embedding SCO complexes into polymer matrices offers a more versatile and processable approach, but understanding how matrix–guest interactions affect spin-state behavior is still limited. In this study, we investigate a polymer-mediated strategy to tune SCO properties by incorporating the well-characterized Fe(II) complex [Fe(1,10-phenanthroline)₂(NCS)₂] into three polymers with distinct structural features: polylactic acid (PLA), polystyrene (PS), and polysulfone (PSF). In terms of potential electrostatic interaction between the complex and the polymeric matrixes, the polymers offer distinct features. Either there does not seem to be any specific interaction (PLA case) or, rather, there is π-π stacking between the aromatic rings of the SCO complex, and the corresponding ones present either in the backbone or in the side chain of the polymer (PSF and PS, respectively). The latter can potentially influence spin-state energetics and dynamics. Importantly, we also reveal and quantify the migration behavior of SCO particles within different polymer matrices, an aspect that has not been previously examined in SCO–polymer systems. Using magnetic susceptibility, spectroscopic, diffraction, and migration studies, we show that the polymer environment, PLA as well, actively modulates the SCO response. PSF yields lower T₁/₂, slower switching kinetics, and enhanced retention of the complex, indicative of strong matrix confinement and interaction. In contrast, PLA and PS composites exhibit sharper transitions and higher migration, suggesting weaker interactions and greater mobility. In addition, the semi-crystalline nature of PLA seems to induce the extension of the hysteresis width. These results highlight both the challenge and the opportunity in SCO polymer composites to tune SCO behavior, offering a scalable route toward functional hybrid materials for thermal sensing and responsive devices. Full article

We investigate the thermal evolution of fermionic pairings in a finite-size SU(2) × SU(2) complex model, drawing an analogy to the BCS-BEC crossover in interacting quantum gases. Unlike the conventional crossover, which is driven by tuning the interaction strength, our study suggests that temperature alone can induce a smooth transition from weakly bound Cooper pairs (BCS-like state) to tightly bound dimers (BEC-like state). Using an exactly solvable model with a finite number of fermions, we analyze the structure of eigenstates, pairing correlations, and thermodynamic response functions. We demonstrate that different multiplet structures, characterized by distinct quasi-spin quantum numbers, become thermally accessible, effectively mimicking the crossover behavior seen in ultracold Fermi gases. Our results provide new insights into the role of thermal fluctuations in quantum pairing phenomena and suggest alternative routes for exploring crossover physics in mesoscopic and strongly correlated systems. Full article

Heme enzymes that bind and reduce O₂ are susceptible to poisoning by NO. The high reactivity and affinity of NO for ferrous heme produces stable ferrous-NO complexes, which in theory should preclude O₂ binding and turnover. However, NO inhibition is often competitive with respect to O₂ and rapidly reversible, thus providing cellular and organismal survival advantages. This kinetic paradox has prompted a search for mechanisms for reversal and hence resistance. Here, I critically review proposed resistance mechanisms for NO dioxygenase (NOD) and cytochrome c oxidase (CcO), which substantiate reduction or oxidation of the tightly bound NO but nevertheless fail to provide kinetically viable solutions. A ferrous heme intermediate is clearly not available during rapid steady-state turnover. Reversible inhibition can be attributed to NO competing with O₂ in transient low-affinity interactions with either the ferric heme in NOD or the ferric heme-cupric center in CcO. Toward resolution, I review the underlying principles and evidence for kinetic control of ferric heme reduction via an O₂-triggered ferric heme spin crossover and an electronically-forced motion of the heme and structurally-linked protein side chains that elicit electron transfer and activate O₂ in the flavohemoglobin-type NOD. For CcO, kinetics, structures, and density functional theory point to the existence of an analogous O₂ and reduced oxygen intermediate-controlled electron-transfer gate with a linked proton pump function. A catalytic cycle and mechanism for CcO is finally at hand that links each of the four O₂-reducing electrons to each of the four pumped protons in time and space. A novel proton-conducting tunnel and channel, electron path, and pump mechanism, most notably first hypothesized by Mårten Wikström in 1977 and pursued since, are laid out for further scrutiny. In both models, low-energy spin-orbit couplings or ‘spintronic’ interactions with O₂ and NO or copper trigger the electronic motions within heme that activate electron transfer to O₂, and the exergonic reactions of transient reactive oxygen intermediates ultimately drive all enzyme, electron, and proton motions. Full article

M-edge X-ray absorption spectroscopy (XAS), which probes 3p→3d transitions in first-row transition metals, provides detailed insights into oxidation states, spin-states, and local electronic structure with high element and orbital specificity. Operating in the extreme ultraviolet (XUV) region, this technique provides sharp multiplet-resolved features with high sensitivity to ligand field and covalency effects. Compared to K- and L-edge XAS, M-edge spectra exhibit significantly narrower full widths at half maximum (typically 0.3–0.5 eV versus >1 eV at the L-edge and >1.5–2 eV at the K-edge), owing to longer 3p core-hole lifetimes. M-edge measurements are also more surface-sensitive due to the lower photon energy range, making them particularly well-suited for probing thin films, interfaces, and surface-bound species. The advent of tabletop high-harmonic generation (HHG) sources has enabled femtosecond time-resolved M-edge measurements, allowing direct observation of ultrafast photoinduced processes such as charge transfer and spin crossover dynamics. This review presents an overview of the fundamental principles, experimental advances, and current theoretical approaches for interpreting M-edge spectra. We further discuss a range of applications in catalysis, materials science, and coordination chemistry, highlighting the technique’s growing impact and potential for future studies. Full article

We present an alternative to the classical SQUID magnetometric measurements for the First-Order Reversal Curve (FORC) diagram approach by employing differential scanning calorimetry (DSC) experiments. After discussing the main results, the advantages and limitations of the magnetometric FORCs, we introduce the calorimetric method. We argue that, while the results are comparable to those obtained via magnetometry, the calorimetric method not only significantly simplifies the required mathematical computations but also detects subtle or overlapping phase transitions that might be hard to distinguish magnetically. The methodology is illustrated through both experimental data and mean-field simulations. Full article

The pressure dependence of structural behavior in the orthorhombic (Pccn, PI) and monoclinic (P2₁/c, PII) polymorphs of the compound [Fe(PM-BiA)₂(NCS)₂], where PM–BiA = (N–(2′–pyridylmethylene)–4-amino–bi–pheynyl), is studied with synchrotron single-crystal X-ray diffraction and vibrational spectroscopy. Both polymorphs are stable up to ∼1.5 GPa, with a spin state transition occurring only in polymorph PII under hydrostatic conditions as documented by single-crystal synchrotron diffraction. The diffraction data also provide evidence of the formation of superstructures for both PI, with a doubled c axis, and PII, with a doubled b axis, on applying pressures above 2 GPa. The LS and HS states seem to coexist at high-pressures for both polymorphs studied with synchrotron infrared spectroscopy at quasi-hydrostatic conditions. Such results indicate that the occurrence of spin-crossover transformations in [Fe(PM-BiA)₂(NCS)₂] might strongly depend on the stress in the sample. Full article

A novel S = 1/2 paramagnetic chelating ligand tert-butyl 5-(p-biphenylyl)-2-pyridyl nitroxide (bppyNO) and its S = 1 nickel(II) ion complex [Ni(bppyNO)₂Br₂] were synthesized. X-ray crystallography revealed a 2p–3d–2p heterospin triad, with half of the molecule being crystallographically independent. A relatively planar chelate geometry with the torsion angle ϕ(Ni-O-N-C_2py) = −10.6(5)° at 300 K becomes significantly out-of-plane distorted with ϕ = −46.9(8) and 26.1(11)° at 90 K accompanied by disorder at the oxygen site. The torsion angle changes, Δϕ = 36° and 37°, are among the largest reported for related compounds. Magnetic measurements indicate gradual and incomplete spin transition-like behavior around 143(2) K. A three-state model involving an intermediate-spin (S_total = 1) state is proposed to explain non-zero χ_mT plateau in a low-temperature region. Density functional theory calculations using the determined structures support the proposed mechanism. Furthermore, geometry optimizations assuming S_total = 0, 1, and 2 are in good agreement with the present model. Full article

The increasing demand for real-time multimedia communications has driven the need for highly secure and computationally efficient encryption schemes. In this work, we present a novel chaos-based encryption system that provides remarkable levels of security and performance. It leverages the benefits of applying fast-to-evaluate chaotic maps, along with a 2-Dimensional Look-Up Table approach (2D-LUT), and simple but powerful periodic perturbations. The foundation of our encryption system is a Pseudo-Random Number Generator (PRNG) that consists of a fully connected random graph with M vertices representing chaotic maps that populate the 2D-LUT. In every iteration of the system, one of the M chaotic maps in the graph and the corresponding trajectories are randomly selected from the 2D-LUT using an emulated spin-wheel picker game. This approach exacerbates the complexity in the event of an attack, since the trajectories may come from the same or totally different maps in a non-sequential time order. We additionally perform two levels of perturbation, at the map and trajectory level. The first perturbation (map level) produces new trajectories that are retrieved from the 2D-LUT in non-sequential order and with different initial conditions. The second perturbation applies a p-point crossover scheme to combine a pair of trajectories retrieved from the 2D-LUT and used in the ciphering process, providing higher levels of security. As a final process in our methodology, we implemented a simple packet-based data integrity scheme that detects with high probability if the received information has been modified (for example, by a man-in-the-middle attack). Our results show that our proposed encryption scheme is robust to common cryptanalysis attacks, providing high levels of security and confidentiality while supporting high processing speeds on the order of gigabits per second. To the best of our knowledge, our chaotic cipher implementation is the fastest reported in the literature. Full article

The purpose of this study was to investigate the benefits of a 12-week plyometric training program intervention on lower limb joint mobility, explosive strength, advanced layup success rates, and injury rates. The study recruited 15 collegiate male basketball players as participants. They underwent basketball training five times per week, each lasting two hours, and additionally received plyometric training twice a week. The study utilized image processing software (ImageJ, version 1.54f, National Institutes of Health, Bethesda, MD, USA) to measure the lower limb joint mobility during the take-off phase of a layup and employed a force plate to assess the explosive strength of the lower limbs during the jump. Furthermore, the study examined the success rate and injury rate of advanced layups—including crossover layups, spin layups, and straight-line layups—as well as the sports injury rate. The results demonstrated that plyometric training significantly enhanced the hip, knee, and ankle joint mobility as well as lower limb explosive strength, with a strong positive correlation between these variables. Furthermore, plyometric training improved joint mobility and lower limb explosive strength. The success rate of advanced layups increased from 50% to 72%, while the sports injury rate decreased from 18% to 8%. In conclusion, plyometric training significantly improved participants’ lower limb joint mobility and explosive strength, which in turn enhanced advanced layup performance and reduced the sports injury rate. Although this study provided preliminary evidence supporting the effectiveness of plyometric training, further research is needed to examine its long-term effects and other influencing factors. Full article

Two iron(III) spin crossover complexes [Fe(⁵Cl-L)(NCS)] (1) and [Fe(⁵Cl-L)(NCSe)] (2) were synthesized with the pentadentate Schiff base ligand ⁵Cl-L and thiocyanato and selenocyanato as coligands. ⁵Cl-L, as an asymmetric {N₃O₂} donor Schiff base, was synthesized by a condensation reaction of 5-chlorosalicyladehyde using the asymmetric N-(2-aminoethyl)-1,3-propanediamine. The complexes exhibited a spin crossover at 280 (1) and 293 K (2), respectively, and were subjected to electron spin resonance (ESR) and Mössbauer spectroscopy at 77, 295 and 325 K. Ab initio CASSCF calculations followed by the NEVPT2 method were applied for predicting the g-tensor components as well as Mössbauer parameters. Full article

The heteroleptic halogen-substituted Fe³⁺ complex of formula [FeL₂Bipy]Cl, where L is 1-(4-fluoro-phenyl)-3-(4-bromo-phenyl)-propane-1,3-dione and Bipy is 2,2′-bipyridine, was synthesized, and its optic and magnetic properties were studied. Magnetic measurements showed that the complex at high temperatures (T > 75 K) is predominantly in the high-spin (HS) state of Fe³⁺ ions (S = 5/2, γ_HS¹ = 93%) with a small admixture of low-spin (LS) state (S = 1/2, γ_LS¹ = 7%). At T* ≈ 46 K, a partial spin-crossover transition (SCO, 5/2↔1/2) occurs. This process is accompanied not only by a change in the magnetic state (γ_HS² = 76%, γ_LS² = 24%), but also by the appearance of AFM interactions (θ_II = −2.3 K) between neighboring Fe³⁺ ions. A theoretical model was proposed to describe magnetic susceptibility, χ(T). As a result of the analysis of the ground spin state M(H) at 2.0 K, it was established that the majority of the LS states, as well as part of the HS states of Fe³⁺ ions (γ_HS ~ 53%), do not participate in exchange interactions. EPR studies confirmed the presence of HS and LS Fe³⁺ centers and made it possible to isolate I-type and II-type HS centers, corresponding to strong low-symmetry and weak distorted octahedral fields. SCO was also detected and the temperature dependences of the EPR intensities, I(T), of the HS and LS centers were analyzed. Full article

The 2,6-bis(pyrazol-1-yl)pyridine (bpp) ligand family is widely recognized for its versatile coordination abilities and broad functionalization potential. This review examines bpp and its modifications at the pyridine ring’s 4-position, focusing on their influence on magnetic, optical, and electronic properties. Key applications discussed include spin crossover (SCO), single-ion and single-molecule magnetism (SIM and SMM), luminescence, redox flow batteries (RFBs), and photonic devices. We provide a comprehensive overview of ligand modifications involving carboxylates, extended aromatic systems, radicals, and redox-active units such as tetrathiafulvalene (TTF), alongside supramolecular architectures. The review highlights fundamental design principles, particularly the role of substituents in tuning the SCO behavior, photophysical properties, and self-assembly into functional nanostructures. Notable advancements include SCO-driven conductivity modulation, reversible luminescent switching, and amphiphilic bpp-based vesicles for multicolor emission. By analyzing the interplay between ligand structure and magnetic, optical, and electronic functions, we provide insights into the potential of bpp derivatives for advanced materials design. This review presents recent experimental and theoretical developments, offering a foundation for future exploration of bpp-based compounds in multifunctional devices. Full article