Spin Resonance Research Articles

Data-based analysis of the forward-backward asymmetry in B±→K±K∓K±

An analysis of the Forward-Backward Asymmetry (FBA) in the decay $B^\pm \to K^\pm K^\mp K^\pm$ is carried out based on the LHCb data. It is found that the large FBA observed for the invariant mass of the $K^+ K^-$ pair around 1.5 GeV can be explained by the interference of the amplitudes between the resonances with even and odd spins, where the former can be the spin-0 $f_0(1500)$ resonance plus a non-resonance $s$-wave, while the latter is a spin-1 resonance which is probably $\rho^0 (1450)$. The analysis shows the existence of the decay channel $B^\pm\to \rho^0(1450) K^\pm$, with $C\!P$ asymmetry of $A_{CP}(B^\pm\to \rho^0(1450) K^\pm)=(-3.4\pm3.0)\%$. This is in contradiction with the conclusion of BaBar in Phys. Rev. D 85, 112010, according to which the analysis showed no signal of the spin-1 resonance $\rho^0(1450)$. We suggest our experimental colleagues to perform a closer analysis to this channel. We also suggest to perform the measurements of the FBAs (as well as the FB-$C\!P$As) in other three-body decay channels of beauty and charmed mesons, as it is helpful for resonance analysis.

Improved Mo95 neutron resonance parameters and astrophysical reaction rates

Background: Improved $^{95}\mathrm{Mo}$ neutron resonance parameters and reaction rates are important for nuclear astrophysics, testing nuclear models, and nuclear criticality safety. However, despite many previous neutron-capture and total cross-section measurements on this nuclide, there still is much room for improvement as well as several discrepancies. For example, there are very few firm resonance spin and parity assignments; average resonance parameters are available only for each parity, the currently recommended astrophysical reaction rate results in disagreements between stellar models and meteoric isotopic anomalies, and there are substantial disagreements in the neutron-capture cross section at low energies important for nuclear criticality safety.Purpose: To obtain an improved set of neutron resonance parameters and astrophysical reaction rates for $^{95}\mathrm{Mo}$.Method: High-resolution neutron-capture and transmission data were measured at the Oak Ridge Electron Linear Accelerator (ORELA) using highly isotopically enriched $^{95}\mathrm{Mo}$ samples. The neutron-capture apparatus, data reduction, and analysis were improved so that information contained in the $\ensuremath{\gamma}$-ray cascade following neutron capture were used to assign resonance ${J}^{\ensuremath{\pi}}$ values. Following this, simultaneous analysis of the new neutron-capture and transmission data was used to obtain resonance energies, gamma widths, and neutron widths and their uncertainties to a maximum energy of 10 keV. Accurate neutron-capture cross sections also were obtained for the unresolved resonance region to a maximum energy of 500 keV and, together with the new resonance parameters, used to calculate the astrophysical reaction rates in the temperature range from 5 to 30 keV.Results: A vastly improved set of $^{95}\mathrm{Mo}$ neutron resonance parameters and an astrophysical reaction rate accurate to about 3% were obtained. Firm ${J}^{\ensuremath{\pi}}$ assignments were determined for 261 of the 314 observed resonances. This is a very large improvement over the previously published 32 firm ${J}^{\ensuremath{\pi}}$ assignments for 108 resonances. Also, the number of resonances having both firm ${J}^{\ensuremath{\pi}}$ assignments and ${\mathrm{\ensuremath{\Gamma}}}_{\ensuremath{\gamma}}$ values was increased by almost a factor of 24---from 11 to 261. Neutron- and total-radiation-width distributions and average resonance spacings, average total radiation widths, and neutron strength functions were obtained for the six different $s$- and $p$-wave possibilities. Parameters for the lowest $s$-wave resonance, which is most important for criticality benchmarks, were obtained with high accuracy.Conclusions: Simple modification of the neutron-capture apparatus and expansion and improvement of data analysis techniques led to a large increase in firm ${J}^{\ensuremath{\pi}}$ assignments for $^{95}\mathrm{Mo}$ neutron resonances. The resulting astrophysical reaction rate is 20%--30% larger than the currently recommended rate at $s$-process temperatures, which should lead to better agreement between stellar models and meteoric isotopic anomalies. The neutron-capture cross section at low energies is substantially larger than recommended in the latest evaluation, which is problematical for criticality benchmarks. The average resonance spacing as a function of spin and parity is significantly different from current models. The total-radiation-width distributions are significantly broader than predicted by theory and show significant departures from the expected Gaussian shapes.

Host-guest interactions and confinement effects in HZSM-5 and chabazite zeolites studied by low-field NMR spin relaxation

The characterization of fluid/solid interactions in porous materials is crucial for their design and optimization, most notably in applications such as adsorption and catalysis. Yet, probing interfacial phenomena of fluids confined in porous systems is particularly challenging. Nuclear magnetic resonance (NMR) spin relaxation has emerged in recent years as a rapid, non-invasive experimental technique to probe adsorbate/adsorbent interactions in mesoporous catalytic materials. More recently, NMR relaxation measurements performed on high-field (300 MHz) superconducting magnets have been successfully validated as a robust method to characterize acidity in HZSM-5 zeolites. Expanding such techniques in the context of low-field, bench-top NMR instruments would be highly beneficial as it would make NMR relaxation a much more appealing and accessible tool for non-invasive, rapid characterization of adsorbate/adsorbent interactions in zeolites and microporous materials. Herein, we validate the use of low-field, bench-top NMR spin relaxation as an indicator for characterizing host-guest interactions in microporous zeolitic materials, using water as guest molecules confined within two different zeolite frameworks, HZSM-5 and chabazite, with varying silica/alumina ratio. The results reported here demonstrate the robustness and sensitivity of low-field NMR relaxation measurements as a rapid screening tool for characterizing adsorption and molecular dynamics in microporous materials, with important implications for both academics and industrialists in terms of making the method more widely accessible, hence expanding the set of tools for materials chemistry and characterization.

Molecular motion of imidazolium cations and phase transitions in (ImH)2KCo(CN)6 with double perovskite structure

Temperature dependence of 1H nuclear magnetic resonance spin–lattice relaxation time T1 of (ImH)2KCo(CN)6, ImH+: imidazolium cation, is reported. The asymmetric T1 minimum observed in intermediate-temperature phase between 198 and 112 K is analyzed assuming the Cole-Davidson distribution of correlation time. Temperature dependences of 14N nuclear quadrupole resonance frequencies and spin–lattice relaxation times are also reported. The phase transitions at 198 and 112 K are shown to be of second and first order, respectively. The 14N relaxation is shown to be governed by the electric field gradient fluctuation due to the in-plane reorientational motion of the imidazolium cations.

Reactive oxygen species scavenging capacities of oil palm trunk sap evaluated using the electron spin resonance spin trapping method

Oil palm waste is a potential source of renewable energy and also of bioactive compounds. In the present study, we analysed oil palm trunk sap (OPTS) squeezed from different parts of the trunk stored for different times and measured the reactive oxygen species (ROS) scavenging capacity using the electron spin resonance (ESR) spin trapping method using 5-(2,2-dimethyl-1,3-propoxycyclophosphoryl)−5-methyl-1-pyrroline-N-oxide (CYPMPO) as the spin trapping reagent. The highest alkoxyl radical (RO•), hydroxyl radical (•OH) and singlet oxygen (1O2) scavenging capacities were found in OPTS squeezed from the middle and top parts of the oil palm trunk. OPTS from the bottom part exhibited a lower ROS scavenging capacity than the other parts. The highest scavenging capacity for RO• was found in OPTS from the middle part of the trunk (10.38 mM Trolox eq./mL), similar to that of green tea (12.42 mM Trolox eq./mL). The scavenging capacities for •OH of OPTS from the middle, top, and bottom parts of the trunk were 4779, 3729 and 1920 mM mannitol eq./mL, respectively, compared with 6594 mM mannitol eq./mL for blackberry. The highest 1O2 scavenging capacity of 228 mM GSH eq./mL was exhibited by OPTS from the top part of the trunk, which was higher than that of the green tea, blackberry, black tea, aloe and cucumber used as standards. The ROS scavenging capacity of OPTS measured by ESR was correlated with the corresponding values from the oxygen radical absorbance capacity (ORAC) assay. The antioxidant activity of OPTS decreased with storage time after the OPT was felled. The strong ROS scavenging capacity of OPTS makes it a potential source of bioactive compounds for use in pharmacological, cosmetic, chemical and functional food applications.

Maximizing the applicability of continuous wave (CW) Electron Paramagnetic Resonance (EPR): what more can we do after a century?

Electron Paramagnetic Resonance/Electron Spin Resonance (EPR/ESR) spectroscopy is a powerful experimental approach solving challenging problems that are inaccessible to other experimental techniques. While pulsed EPR techniques and their applications have been the central focus of the field nowadays, methodology development and application of continuous wave (CW) EPR have never been undervalued. Although the importance of EPR in research has been recognized in many areas as indicated by the increasing number of EPR research articles published every year, the growth in the number of EPR research teams seems to not match the former, likely caused by the relatively high cost of modern pulsed EPR spectrometers. In this perspective, we aim to discuss the new areas and new directions of the application of CW EPR in combination with spin labeling that are slightly different from the classic/traditional applications of the CW EPR technique. Based on our experience, we show example applications of CW EPR on the interfaces of protein-confinement materials, protein-inorganic crystal lattices, protein-nanoparticles, and protein-polymers. Various structure and dynamics information can be resolved from the data analysis of CW EPR, leading to enhanced understanding of protein biophysics upon interaction with the synthetic nanostructures as well as possible guidance of hybrid materials development based on the combination of proteins and nanostructures. We also discussed the possibilities of even broadening the application spectrum of EPR spectroscopy. The relatively high affordability of CW EPR spectrometers (as compared to the pulsed ones) also facilitates the growth in EPR research groups worldwide.

Search for heavy resonances decaying to ZZ or ZW and axion-like particles mediating nonresonant ZZ or ZH production at sqrt{s} = 13 TeV

A search has been performed for heavy resonances decaying to ZZ or ZW and for axion-like particles (ALPs) mediating nonresonant ZZ or ZH production, in final states with two charged leptons (ℓ = e, μ) produced by the decay of a Z boson, and two quarks produced by the decay of a Z, W, or Higgs boson H. The analysis is sensitive to resonances with masses in the range 450 to 2000 GeV. Two categories are defined corresponding to the merged or resolved reconstruction of the hadronically decaying boson. The search is based on data collected during 2016–2018 by the CMS experiment at the LHC in proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 138 fb−1. No significant excess is observed in the data above the standard model background expectation. Upper limits on the production cross section of heavy, narrow spin-2 and spin-1 resonances are derived as functions of the resonance mass, and exclusion limits on the production of bulk graviton particles and W′ bosons are calculated in the framework of the warped extra dimensions and heavy vector triplet models, respectively. In addition, upper limits on the ALP-mediated diboson production cross section and ALP couplings to standard model particles are obtained in the framework of linear and chiral effective field theories. These are the first limits on nonresonant ALP-mediated ZZ and ZH production obtained by the LHC experiments.

Hopfion dynamics in chiral magnets

Resonant spin dynamics of topological spin textures are correlated with their topological nature, which can be employed to understand this nature. In this study, we present resonant spin dynamics of three-dimensional topological spin texture, i.e., Neel and Bloch hopfions. Using micromagnetic simulations, we stabilize Bloch and Neel hopfions with bulk and interfacial Dzyaloshinskii–Moriya interaction, respectively. We identify the ground state spin configuration of both hopfions, effects of anisotropies, geometric confinements, and demagnetizing fields. To confirm topological nature, Hopf number is calculated for each spin texture. Then, we calculate the resonance frequencies and spin-wave modes of spin precessions under multiple magnetic fields. Unique resonance frequencies and specific magnetic field dependence can help to guide experimental studies to identify the three-dimensional topological spin texture of hopfions in functioning chiral magnets when imaging is not possible.

Double benzylidene ketones as photoinitiators for visible light photopolymerization

In this work, four novel double benzylidene ketone dyes (TPA-H, CZ-H, TPA-C, and CZ-C) with D–A structure were synthesized and showed good charge transfer characteristics and high absorption capability in the visible light range. The double benzylidene ketone dyes can be used as type II photoinitiators to initiate free radical photopolymerization (FRP) or as charge transfer sensitizers to sensitize diaryliodonium salt (ONI) synergistically for the initiation of FRP and cationic photopolymerization (CP) together with aromatic amine groups under 460 and 532 nm LED light sources. FRP and CP experiments revealed that TPA-C and CZ-C with polyarylamine groups had high sensitization and initiation activities under 460 and 532 nm LED light sources. The photochemical properties of the initiator system were investigated by means of steady-state photolysis, fluorescence quenching, cyclic voltammetry, and electron spin resonance spin trapping experiments.

Transient quantum beatings of trions in hybrid organic tri-iodine perovskite single crystal

Utilizing the spin degree of freedom of photoexcitations in hybrid organic inorganic perovskites for quantum information science applications has been recently proposed and explored. However, it is still unclear whether the stable photoexcitations in these compounds correspond to excitons, free/trapped electron-hole pairs, or charged exciton complexes such as trions. Here we investigate quantum beating oscillations in the picosecond time-resolved circularly polarized photoinduced reflection of single crystal methyl-ammonium tri-iodine perovskite (MAPbI3) measured at cryogenic temperatures. We observe two quantum beating oscillations (fast and slow) whose frequencies increase linearly with B with slopes that depend on the crystal orientation with respect to the applied magnetic field. We assign the quantum beatings to positive and negative trions whose Landé g-factors are determined by those of the electron and hole, respectively, or by the carriers left behind after trion recombination. These are {g}_{[001]}^{e} = 2.52 and {g}_{[1bar{1}0]}^{e},= 2.63 for electrons, whereas big|{g}_{[001]}^{h}big|,= 0.28 and big|{g}_{[1bar{1}0]}^{h}big|,= 0.57 for holes. The obtained g-values are in excellent agreement with an 8-band K.P calculation for orthorhombic MAPbI3. Using the technique of resonant spin amplification of the quantum beatings we measure a relatively long spin coherence time of ~ 11 (6) nanoseconds for electrons (holes) at 4 K.

In Situ EPR Spin Trapping and Competition Kinetics Demonstrate Temperature-Dependent Mechanisms of Synergistic Radical Production by Ultrasonically Activated Persulfate.

Ultrasound coupled with activated persulfate can synergistically degrade aqueous organic contaminants. Here, in situ electron paramagnetic resonance spin trapping was used to compare radicals produced by ultrasonically activated persulfate (US-PS) and its individual technologies, ultrasound alone (US) and heat-activated persulfate (PS), with respect to temperature. Radicals were trapped using 5,5-dimethyl-1-pyrroline-N-oxide, DMPO, to form detectable nitroxide adducts. Using initial rates of radical adduct formation, and compared to US and PS, US-PS at 40 and 50 °C resulted in the largest synergistic production of radicals. Radicals generated from US were reasonably consistent from 40 to 70 °C, indicating that temperature had little effect on cavitational bubble collapse over this range. However, synergy indexes calculated from initial rates showed that ultrasonic activation of persulfate at the bubble interface changes with temperature. From these results, we speculate that higher temperatures enhance persulfate uptake into cavitation bubbles via nanodroplet injection. DMPO-OH was the predominant adduct detected for all conditions. However, competition modeling and spin trapping in the presence of nitrobenzene and atrazine probes showed that SO4•- predominated. Therefore, the DMPO-OH signal is derived from SO4•- trapping with subsequent DMPO-SO4- hydrolysis to DMPO-OH. Spin trapping is effective in quantifying total radical adduct formation but limited in measuring primary radical speciation in this case.

Search for heavy resonances decaying to WW , WZ , or WH boson pairs in a final state consisting of a lepton and a large-radius jet in proton-proton collisions at s=13 TeV

A search for new heavy resonances decaying to pairs of bosons (WW, WZ, or WH) is presented. The analysis uses data from proton-proton collisions collected with the CMS detector at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 137 fb$^{-1}$. One of the bosons is required to be a W boson decaying to an electron or muon and a neutrino, while the other boson is required to be reconstructed as a single jet with mass and substructure compatible with a quark pair from a W, Z, or Higgs boson decay. The search is performed in the resonance mass range between 1.0 and 4.5 TeV and includes a specific search for resonances produced via vector boson fusion. The signal is extracted using a two-dimensional maximum likelihood fit to the jet mass and the diboson invariant mass distributions. No significant excess is observed above the estimated background. Model-independent upper limits on the production cross sections of spin-0, spin-1, and spin-2 heavy resonances are derived as functions of the resonance mass and are interpreted in the context of bulk radion, heavy vector triplet, and bulk graviton models. The reported bounds are the most stringent to date.

Understanding nanomedicine treatment in an aggressive spontaneous brain cancer model at the stage of early blood brain barrier disruption

Personalised nanomedicine is an advancing field which has developed significant improvements for targeting therapeutics to aggressive cancer and with fewer side effects. The treatment of gliomas such as glioblastoma (or other brain tumours), with nanomedicine is complicated by a commonly poor accumulation of drugs in tumour tissue owing to the partially intact blood-brain barrier (BBB). Nonetheless, the BBB becomes compromised following surgical intervention, and gradually with disease progression. Increased vasculature permeability generated by a tumour, combined with decreased BBB integrity, offers a mechanism to enhance therapeutic outcomes. We monitored a spontaneous glioma tumour model in immunocompetent mice with ongoing T2-weighted and contrast-enhanced T1-weighted magnetic resonance imaging gradient echo and spin echo sequences to predict an optimal “leakiness” stage for nanomedicine injections. To ascertain the effectiveness of targeted nanomedicines in treating brain tumours, subsequent systemic administration of targeted hyperbranched polymers was then utislised, to deliver the therapeutic payload when both the tumour and brain vascularity had become sufficiently susceptible to allow drug accumulation. Treatment with either doxorubicin-loaded hyperbranched polymer, or the same nanomedicine targeted to an ephrin receptor (EphA2) using a bispecific antibody, resulted in uptake of chemotherapeutic doxorubicin in the tumour and in reduced tumour growth. Compared to vehicle and doxorubicin only, nanoparticle delivered doxorubicin resulted in increased tumour apoptosis, while averting cardiotoxicity. This suggests that polyethylene based (PEGylated)-nanoparticle delivered doxorubicin could provide a more efficient treatment in tumours with a disrupted BBB, and that treatment should commence immediately following detection of gadolinium permeability, with early detection and ongoing ‘leakiness’ monitoring in susceptible patients being a key factor.

True oxygen reduction capacity during photosynthetic electron transfer in thylakoids and intact leaves.

Reactive oxygen species (ROS) are generated in electron transport processes of living organisms in oxygenic environments. Chloroplasts are plant bioenergetics hubs where imbalances between photosynthetic inputs and outputs drive ROS generation upon changing environmental conditions. Plants have harnessed various site-specific thylakoid membrane ROS products into environmental sensory signals. Our current understanding of ROS production in thylakoids suggests that oxygen (O2) reduction takes place at numerous components of the photosynthetic electron transfer chain (PETC). To refine models of site-specific O2 reduction capacity of various PETC components in isolated thylakoids of Arabidopsis thaliana, we quantified the stoichiometry of oxygen production and consumption reactions associated with hydrogen peroxide (H2O2) accumulation using membrane inlet mass spectrometry and specific inhibitors. Combined with P700 spectroscopy and electron paramagnetic resonance spin trapping, we demonstrate that electron flow to photosystem I (PSI) is essential for H2O2 accumulation during the photosynthetic linear electron transport process. Further leaf disc measurements provided clues that H2O2 from PETC has a potential of increasing mitochondrial respiration and CO2 release. Based on gas exchange analyses in control, site-specific inhibitor-, methyl viologen-, and catalase-treated thylakoids, we provide compelling evidence of no contribution of plastoquinone pool or cytochrome b6f to chloroplastic H2O2 accumulation. The putative production of H2O2 in any PETC location other than PSI is rapidly quenched and therefore cannot function in H2O2 translocation to another cellular location or in signaling.

Structures of highly flexible intracellular domain of human \u03b17 nicotinic acetylcholine receptor

The intracellular domain (ICD) of Cys-loop receptors mediates diverse functions. To date, no structure of a full-length ICD is available due to challenges stemming from its dynamic nature. Here, combining nuclear magnetic resonance (NMR) and electron spin resonance experiments with Rosetta computations, we determine full-length ICD structures of the human α7 nicotinic acetylcholine receptor in a resting state. We show that ~57% of the ICD residues are in highly flexible regions, primarily in a large loop (loop L) with the most mobile segment spanning ~50 Å from the central channel axis. Loop L is anchored onto the MA helix and virtually forms two smaller loops, thereby increasing its stability. Previously known motifs for cytoplasmic binding, regulation, and signaling are found in both the helices and disordered flexible regions, supporting the essential role of the ICD conformational plasticity in orchestrating a broad range of biological processes.

Search for heavy resonances decaying into a pair of Z bosons using 139 fb−1 of p–p collisions at s=13 TeV with the ATLAS detector

This paper presents the search for heavy resonances decaying into a pair of [Formula: see text] bosons leading to the [Formula: see text] and [Formula: see text] final states, where [Formula: see text] stands for either an electron or a muon. The search uses proton–proton collision data at a center-of-mass energy of 13 TeV collected with the ATLAS detector from 2015 to 2018 corresponding to an integrated luminosity of 139 [Formula: see text], which is the full data statistics collected during the Run 2 of the Large Hadron Collider (LHC). The mass range for the hypothetical resonances considered spans from 200 GeV to 2000 GeV. In the absence of an observed significant excess, the results are interpreted as upper limits on the production cross-section of a spin-0 or spin-2 resonance. The upper limits for the spin-0 resonance are interpreted to exclusion contours in the context of Type-I and Type-II two-Higgs-doublet models (2HDM), while those for the spin-2 resonance are used to constrain the Randall–Sundrum (RS) model with an extra dimension giving rise to spin-2 graviton excitations.

Electric field effect on electron gas spins in two-dimensional magnets with strong spin-orbit coupling

The recent rise of material platforms combining magnetism and two-dimensionality of mobile carriers reveals a diverse spectrum of spin-orbit phenomena and stimulates its ongoing theoretical discussions. In this paper, we use the density matrix approach to provide a unified description of subtle microscopic effects governing the electron gas spin behavior in the clean limit upon electric perturbations in two-dimensional magnets with strong spin-orbit coupling. We discuss that an inhomogeneity of electrostatic potential generally leads to the electron gas spin tilting with the subsequent formation of equilibrium skyrmionlike spin textures and demonstrate that several microscopic mechanisms of two-dimensional electron gas (2DEG) spin response are equally important for this effect. We analyze the dynamics of 2DEG spin upon an oscillating electric field with a specific focus on the emergent electric dipole spin resonance. We address the resonant enhancement of magneto-optical phenomena from the spin precession equation perspective and discuss it in terms of the resonant spin generation. We also clarify the connection of both static and dynamic spin phenomena arising in response to a scalar perturbation with the electronic band Berry curvature.

Near-threshold scaling of resonant inelastic collisions at ultralow temperatures

We show that the cross sections for a broad range of resonant {\it inelastic} processes accompanied by excitation exchange (such as spin-exchange, F\"orster resonant, or angular momentum exchange) exhibit an unconventional near-threshold scaling $E^{\Delta m_{12}}$, where $E$ is the collision energy, $\Delta m_{12}=m_1'+m_2'-m_1-m_2$, and $m_i$ and $m_i'$ are the initial and final angular momentum projections of the colliding species ($i=1,\,2$). In particular, the inelastic cross sections for $\Delta m_{12}=0$ transitions display an unconventional $E^0$ scaling similar to that of elastic cross sections, and their rates vanish as $T^{\Delta m_{12}+1/2}$. For collisions dominated by even partial waves (such as those of identical bosons in the same internal state) the scaling is modified to $\sigma_\text{inel}\propto E^{\Delta m_{12} +1} $ if $\Delta m_{12}$ is odd. We present accurate quantum scattering calculations that illustrate these modified threshold laws for resonant spin exchange in ultracold Rb+Rb and O$_2$+O$_2$ collisions. Our results illustrate that the threshold scaling of collision cross sections is determined only by the energetics of the underlying process (resonant vs. exothermic) rather than by whether the internal states of colliding particles is changed in the collision.

Confinement dependence of protein-associated solvent dynamics around different classes of proteins, from the EPR spin probe perspective.

Protein function is modulated by coupled solvent fluctuations, subject to the degree of confinement from the surroundings. To identify universal features of the external confinement effect, the temperature dependence of the dynamics of protein-associated solvent over 200-265 K for proteins representative of different classes and sizes is characterized by using the rotational correlation time (detection bandwidth, 10-10-10-7 s) of the electron paramagnetic resonance (EPR, X-band) spin probe, TEMPOL, which is restricted to regions vicinal to protein in frozen aqueous solution. Weak (protein surrounded by aqueous-dimethylsulfoxide cryosolvent mesodomain) and strong (no added crysolvent) conditions of ice boundary confinement are imposed. The panel of soluble proteins represents large and small oligomeric (ethanolamine ammonia-lyase, 488 kDa; streptavidin, 52.8 kDa) and monomeric (myoglobin, 16.7 kDa) globular proteins, an intrinsically disordered protein (IDP, β-casein, 24.0 kDa), an unstructured peptide (protamine, 4.38 kDa) and a small peptide with partial backbone order (amyloid-β residues 1-16, 1.96 kDa). Expanded and condensate structures of β-casein and protamine are resolved by the spin probe under weak and strong confinement, respectively. At each confinement condition, the soluble globular proteins display common T-dependences of rotational correlation times and normalized weights, for two mobility components, protein-associated domain, PAD, and surrounding mesodomain. Strong confinement induces a detectable PAD component and emulation of globular protein T-dependence by the amyloid-β peptide. Confinement uniformly impacts soluble globular protein PAD dynamics, and is therefore a generic control parameter for modulation of soluble globular protein function.

Realtime, continuous assessment of complex-mixture protease and protease inhibitor activity

Recently the treatment PAXLOVID™ (nirmatrelvir co-packaged with ritonavir) was authorized for use as a treatment for COVID-19. The presumed mechanism of action of the treatment, an inhibitor of a Sars-Cov-2 “3CL” protease, continues decades-long interest in viral protease inhibition in the fight against pathogenic viruses (e.g., HIV protease inhibitors). Proteolysis assay methods vary widely, roughly bounded by interrogation of basic biochemistry and high-throughput, early-stage drug screening. Reported here are methods that provide unique and biologically relevant characterization of proteolysis and protease inhibition. A companion report provides evidence that these methods show promise for drug and basic biological discovery, especially for early detection of potential side effects. Electron spin resonance spectroscopy and spin labeling (ESRSL) of whole proteins are leveraged to monitor reactants and products of whole-protein digestion through differentiation of angular mobility of those products and reactants. These proof-of-concept data demonstrate consistency with prior art for all possible combinations of four proteases, two whole-protein substrates and three inhibitors. Thus, ESRSL is shown to uniquely and widely interrogate proteolysis of natural, whole-protein, substrates insuring the biological relevance of results.