Interaction Constants Research Articles

Preparation and Construction of Chimeric Humanized Broadly Reactive Antibody 10H10 to Protein E of Tick-Borne Encephalitis Virus.

A full-length humanized chimeric antibody 10H10ch that specifically interacts with the surface glycoprotein E of flaviviruses was obtained. To construct it, we used variable fragments of the heavy and light chains of the monoclonal antibody 10H10 that form the active center of the antibody and a fragment of the constant part of the heavy chain of the human IgG1 antibody. The resulting full-length chimeric humanized antibody 10H10ch specifically interacted with the E protein of flaviviruses pathogenic to humans, such as tick-borne encephalitis, Zika, West Nile, and dengue viruses. An immunochemical assessment of the interaction constants of the 10H10ch antibody with a panel of native and recombinant flavivirus antigens by ELISA and biolayer interferometry showed that the dissociation constant (Kd) of the chimeric antibody is in the nanomolar region and is comparable to that of the high-affinity mouse monoclonal antibody 10H10. The possibility of using the resulting chimeric humanized antibody 10H10ch for the diagnosis, prevention, and treatment of various flavivirus infections is discussed.

Large Magnetic Anisotropy in van der Waals Ferromagnet Fe3GaTe2 above Room Temperature.

Discoveries of above-room-temperature intrinsic ferromagnetism in two-dimensional (2D) van der Waals (vdW) materials offer a platform for studying fundamental 2D magnetism and spintronic devices, especially the recently discovered above-room-temperature 2D vdW Fe3GaTe2 (FGaT). However, the magnetic mechanism in FGaT remains elusive. Here, a detailed investigation using magnetic force microscopy on the thickness-dependent magnetic behavior of FGaT single crystals is reported. The Heisenberg exchange interaction constant (J) at room temperature is determined to be 1.32836 × 10-12 J/m. Our study combining angle-resolved photoemission spectroscopy and density functional theory suggests that the high Curie temperature in FGaT is attributed to the shift of the localized Fe d band toward the Fermi level as well as the enhanced magnetic exchange effect due to the strong itinerant ability of Fe. This work sheds light on the understanding of magnetism in FGaT and provides a promising platform to investigate the mechanisms of 2D magnetic materials.

Theoretical Study of the Co‐doping Effects at Sr and Fe Sites on the Magnetic and Optical Properties of SrFe12O19

For the first time, the magnetic and optical (bandgap) properties of co‐doped Mg/Dy, Al/Dy, and Mn/Nd (SFO) at Sr and Fe sites are investigated using a microscopic model and the Green's function theory. It is shown that the co‐doping at both Sr and Fe sites can change the behavior of the magnetization which decreases by transition metal or nonmagnetic ion doping at the Fe site (with doping ions larger than the host Fe ions), but by additive co‐doping at the Sr site with rare‐earth ion (which ionic radius is smaller than that of Sr) the magnetization increases with increasing the co‐doping concentration. The bandgap energy decreases in the co‐doped SFO. The mechanism of this co‐doping effect is explained on microscopic level. It is due to the changes of the spin‐exchange interaction constants at the doped sites caused by the appearance of different strain by the doping with two ions. The theoretical results are compared with the existing experimental data and are in good qualitative agreement.

X-ray diffraction, luminescence, and electron paramagnetic resonance study of LaLuO3:Yb3+ nanopowders

The primary objective of materials science is the study of the properties of the existing materials and the development of new ones. In the present day, the use of solid-state lasers abroad has prompted material scientists globally to develop novel or enhance the properties of the existing active gain media. Materials comprising rare earth elements have historically proven effective in scintillation applications. The synthesis of LaLu1-xYbxO3 monodisperse nanopowders with a particle size of 50–62 nm via the Pechini complexing citrate method has been the subject of investigation using electron paramagnetic resonance (EPR) spectroscopy and photoluminescence (PL) measurements. The EPR data indicate that the Yb³⁺ ions predominantly create a single type of center, whereby the Yb³⁺ ion substitutes for the Lu³⁺ ion. The calculated EPR g-factors are estimated to be g1 = 3.85, g2 = 2.15, g3 = 1.55 and the 171Yb isotope hyperfine interaction constants are A1 = 600 × 10−4 cm−1, A2 = 700 × 10−4 cm−1, A3 ≈ 1800 × 10−4 cm−1. The principal values of the g factors and the hyperfine tensors indicate that the Yb site in LaLu1-xYbxO3 nanopowders exhibits orthorhombic symmetry. The PL measurements in the wavelength range of 350–1800 nm, with excitation provided by either a xenon lamp or a diode laser, indicate the presence of a broad emission band, centered at 404 nm, in addition to the well-known emission spectrum in the IR region (920–1100 nm) arising from Yb3+ ions.

Structure determination of 2,5-difluorophenol by microwave spectroscopy

The Fourier transform microwave spectrum of 2,5-difluorophenol has been obtained in the centimeter wave range, revealing only one conformer stabilized by an intramolecular interaction where the hydrogen atom of the OH group is in a syn orientation to the fluorine atom at the 2-ring position. The heavy atom backbone structure was obtained from the rotational constants of the 13C and 18O isotopologues whose spectra were measured in natural abundance. The spectrum of the OD isotopologue obtained by deuterium enrichment was also measured, and the nuclear quadrupole hyperfine structures arising from deuterium were analyzed. The semi-experimental equilibrium structure (reSE) was determined by correcting the experimental rotational constants with the vibration-rotation interaction constants obtained via an anharmonic force field. Quantum chemical calculations at various levels of theory were used to support results from the experiments.

Theoretical Study of Co-Doping Effects with Different Ions on the Multiferroic Properties of BiFeO3 Nanoparticles.

Using a microscopic model and the Green's function theory, the size and co-doping effects on the multiferroic and optical (band gap) properties of BiFeO3 (BFO) nanoparticles are investigated. The magnetization increases, whereas the band gap energy decreases with decreasing nanoparticle size. The substitution with Co/Mn, Nd/Sm, Ce/Ni, and Cd/Ni is discussed and explained on a microscopic level. By the ion co-doping appear different strains due to the difference between the doping and host ionic radii, which leads to changes in the exchange interaction constants for tuning all properties. It is observed that by co-doping with Nd/Sm at the Bi site or with Co/Mn at the Fe site, the multiferroic properties are larger than those by doping with one ion. Moreover, by doping with Ni, the multiferroic properties are reduced. But by adding another ion (for example Ce or Cd), an increase in these properties is obtained. This shows the advantages of the co-doping, its flexibility, and its greater possibility of tuning the multiferroic properties compared to single ion substitution. The band gap energy decreases for all co-dopants. The polarization increases with increasing magnetic field. This is evidence of magnetoelectric coupling, which is enhanced by co-doping with Co/Mn. The observed theoretical results are in good qualitative agreement with the existing experimental data.

How do mirror charge radii constrain density dependence of the symmetry energy?

It has recently been suggested that differences in the charge radii of mirror nuclei (ΔRchmirr) are strongly correlated with the neutron-skin thickness (Rskin) of neutron-rich nuclei and with the slope of the symmetry energy (L). To test this assumption, we present ab initio calculations of Rskin in 48Ca and 208Pb, ΔRchmirr in 36Ca−36S, 38Ca−38Ar, 41Sc−41Ca, 48Ni−48Ca, 52Ni−52Cr, and 54Ni−54Fe mirror pairs, and L. Employing the recently developed 34 chiral interaction samples, identified by the history matching approach, we conduct rigorous statistical analysis of correlations among ΔRchmirr, Rskin and L, accounting for quantified uncertainties from low-energy constants of chiral interaction, chiral effective field theory truncation and many-body method approximation. The ab initio results reveal an appreciable ΔRchmirr−L correlation in fp-shell mirror pairs. However, contrary to previous studies, the present calculation finds that the studied sd-shell mirror pairs do not exhibit any ΔRchmirr−L correlation.

Methods for monitoring protein-membrane binding. Comparison based on the interactions between amyloidogenic protein human cystatin C and phospholipid liposomes

A cell membrane is an essential cellular component providing protection against the outer environment. It is also a host for proteins and carbohydrates responsible for, e.g. transporter, receptor, or enzymatic functions. In parallel, the membrane may also be implicated in pathological processes leading, e.g. to the oligomerization of amyloid-forming proteins, a hallmark of i.a. Alzheimer's disease. The increasing need for detailed information on mechanisms driving the amyloid formation and the potential role of cell membranes in the process proves the research on protein-membrane interactions biologically relevant. Considering the potential and limitations of the relatively well established and newly developed methods, this study focused on selecting methods that allow a broad and comprehensive description of interactions between amyloidogenic protein human cystatin C and lipid bilayers. In the first step, dot-blot and ELISA tests were selected as techniques allowing fast screening for protein-ligand interactions. Next, surface plasmon resonance, spectral shift, biolayer interferometry, and switchSENSE® technology were used to determine kinetic parameters and binding constants for interactions between human cystatin C and the selected lipid bilayers. Based on the obtained results we have proposed the most promising candidates for monitoring of interactions and determining affinity between amyloidogenic proteins and membrane mimetics.

Transition metal centers with anharmonic elastic interactions in one-dimensional spin-crossover solids

An exact examination of a one-dimensional (1D) anharmonic elastic model describing the thermodynamic properties of spin-crossover (SCO) solids is presented. This elastic model incorporates both intra-chain and mean field inter-chain interactions, providing a more understanding of 1D SCO materials. Numerical findings for a linear chain of spins unveil intriguing features, such as a two-step-like transition. Extending the model to interacting chains leads to an additional term in the effective ligand field of the system’s Hamiltonian, thereby enhancing its predictive power by accounting for more elastic constants of interactions. This augmentation reinforces the model’s validity in capturing the spin-crossover phenomenon. Numerical results in this extended framework elucidate clearer two-step-like spin crossover transitions, with the HS_LS fraction of spins approaching maximum values at equilibrium temperature Teq.

High precision in a Fourier-transform spectrum of protactinium: extensive weighted least-squares fits of peak wavenumbers for analysis of fine and hyperfine structure

A Fourier-transform recording of protactinium in the infrared range is reanalysed with high precision in order to determine the hyperfine interaction constants A and B. Starting with a selection of best lines and least-squares fits of hyperfine structure intervals, large systems of linear equations compare experimental hyperfine peak wavenumbers with a theoretical representation. The theoretical representation is based on Ritz’s combination principle and Casimir’s formula according to the existing classification. Weighted least-squares fits allow a discrimination between unperturbed and perturbed data such as blended hyperfine structure components. For the first time, the wavenumbers of the hyperfine components of more than 600 lines are fitted using the characteristics of about 250 levels as parameters. 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Representative examples illustrate extensive results obtained for atomic protactinium. This high precision facilitates further search for new energy levels, and 20 new levels were presented. Foreword The data presented here are the results of a study carried out at the Laboratoire Aimé Cotton (LAC) at Paris-Orsay in the years 2003 and 2004, when I was there for a research stay. At this time, I worked together with Jean-François Wyart and Annie Ginibre on the re-examination of protactinium spectra that have been measured about 30 years earlier and that were available in the form of a printed list of peak wavenumbers and a printed paper chart of the intensity profile. The spectra had already been analysed, but there was still a lot of additional information that could be extracted from the spectra with time and effort. The review of the data, the selection of the data and the step-by-step optimization of the data set took a lot of time. When I returned to Berlin in 2004, we had made good progress, but in principle, it is like a bottomless pit. We continued together to optimize the data and tried to the finishing touches to it. At some point, we decided that we had reached a ‘level of maturity’ where the data could be published. We have discussed a lot about how detailed the text should be. This discussion has dragged on over the years and this project has repeatedly been lost in the stream of other everyday tasks. Every now and then there was a small attempt to return to this topic, but it quickly got lost in the daily hustle and bustle. In 2012, we presented the results at a conference. The death of both of them within two years hit me hard. I very much regret that this work was not published earlier. This special volume was the right motivation for me to finally publish this data. I no longer have access neither to the computer programs used at the time, which ran on large computer systems, nor to the original measurement data. I have not been able to find out what happened to the large quantity of paper (printed list of peak wavenumbers anda printed paper chart of spectra). But I have a bunch of input and output files of the calculations that have become a bit jumbled over the years, which contain a lot of information, as well as our unfinished manuscript. The resulting data contain important information for posterity – particularly since the element is radioactive and the experiments to collect laboratory data are unlikely to be repeated any time soon. I think it is worth publishing these data.Graphic abstractHigh precision FT spectra of Pa: analysis of fine and hyperfine structure

An automated protocol to construct flexibility parameters for classical forcefields: applications to metal-organic frameworks.

In this work, forcefield flexibility parameters were constructed and validated for more than 100 metal-organic frameworks (MOFs). We used atom typing to identify bond types, angle types, and dihedral types associated with bond stretches, angle bends, dihedral torsions, and other flexibility interactions. Our work used Manz's angle-bending and dihedral-torsion model potentials. For a crystal structure containing N atoms in its unit cell, the number of independent flexibility interactions is 3(N atoms - 1). Because the number of bonds, angles, and dihedrals is normally much larger than 3(N atoms - 1), these internal coordinates are redundant. To reduce (but not eliminate) this redundancy, our protocol prunes dihedral types in a way that preserves symmetry equivalency. Next, each dihedral type is classified as non-rotatable, hindered, rotatable, or linear. We introduce a smart selection method that identifies which particular torsion modes are important for each rotatable dihedral type. Then, we computed the force constants for all flexibility interactions together via LASSO regression (i.e., regularized linear least-squares fitting) of the training dataset. LASSO automatically identifies and removes unimportant forcefield interactions. For each MOF, the reference dataset was quantum-mechanically-computed in VASP via DFT with dispersion and included: (i) finite-displacement calculations along every independent atom translation mode, (ii) geometries randomly sampled via ab initio molecular dynamics (AIMD), (iii) the optimized ground-state geometry using experimental lattice parameters, and (iv) rigid torsion scans for each rotatable dihedral type. After training, the flexibility model was validated across geometries that were not part of the training dataset. For each MOF, we computed the goodness of fit (R-squared value) and the root-mean-squared error (RMSE) separately for the training and validation datasets. We compared flexibility models with and without bond-bond cross terms. Even without cross terms, the model yielded R-squared values of 0.910 (avg across all MOFs) ± 0.018 (st. dev.) for atom-in-material forces in the validation datasets. Our SAVESTEPS protocol should find widespread applications to parameterize flexible forcefields for material datasets. We performed molecular dynamics simulations using these flexibility parameters to compute heat capacities and thermal expansion coefficients for two MOFs.

Implementation of ICRU report 90 to re-evaluate the dosimetry standards in Taiwan

The purpose of this investigation is to re-evaluate primary dosimetry standards at the National Radiation Standard Laboratory (NRSL/INER) according to the recommendation of the International Commission on Radiation Units and Measurements Report 90 (ICRU Report 90). These standards are air kerma (Kair) in X-rays, 60Co and 137Cs beams, absorbed dose to water (DW) in 60Co beam, as well as reference air kerma (RAKR) in 192Ir beam for brachytherapy in Taiwan.However, the Consultative Committee for Ionizing Radiation (CCRI) summarized the expected changes in ICRU Report 90 to primary standards. These include modifications to the mean excitation energy of water (Iw) and graphite (Ig), the application of the density effect correction for graphite, new combined correction factors and the uncertainty related to the average energy required to create an ion pair in air (Wair), improved calculations of the stopping power, and the adoption of renormalized photoeffect cross-section. The recommendations of the CCRI were adopted for recalculation regarding correction factors and radiation-matter interaction constants for NRSL/INER primary standards. Furthermore, a newer version of Monte Carlo software and the alternative measurements with new ionization chambers (ICs) of a similar design were used to reassess the impact on the NRSL/INER standards. Consequently, the impact of the new ICRU recommendation on dosimetry standards ranged from -0.8% to 0.1%. The changes to the primary standards are in good correlation with similar changes implemented for the BIPM primary standards. For international comparisons of these standards, adoption of the ICRU Report 90 would not change significantly the degree of equivalence stated in the Asia-Pacific Metrology Programme (APMP) key and supplementary comparison database considering the impacts of the BIPM standards in the comparisons of APMP.RI(I)-K3, APMP.RI(I)-K1.1, APMP.RI(I)-K4, APMP.RI(I)-K8 and APMP.RI(I)-S3. Therefore, the NRSL/INER has formally implemented the re-evaluation standards on the 1st January 2024.

A Divalent Metal Cation-Metabolite Interaction Model Reveals Cation Buffering and Speciation.

I present the perspective that the divalent metalome and the metabolome can be modeled as a network of chelating interactions instead of separate entities. I review progress in understanding the complex cellular environment, in particular recent contributions to modeling metabolite-Mg2+ interactions. I then demonstrate a simple extension of these strategies based approximately on intracellular Escherichia coli concentrations. This model is composed of four divalent metal cations with a range of cellular concentrations and physical properties (Mg2+, Ca2+, Mn2+, and Zn2+), eight representative metabolites, and interaction constants. I applied this model to predict the speciation of divalent metal cations between free and metabolite-chelated species. This approach reveals potentially beneficial properties, including maintenance of free divalent metal cations at biologically relevant concentrations, buffering of free divalent metal cations, and enrichment of functional metabolite-chelated species. While currently limited by available interaction coefficients, this modeling strategy can be generalized to more complex systems. In summary, biochemists should consider the potential of cellular metabolites to form chelating interactions with divalent metal cations.

Modeling public opinion control by a charismatic leader

We study the average long-time behavior of the binary opinions of a social group with peer-to-peer interactions under the influence of an external bias and a persuadable leader, a strongly-biased agent with a dynamic opinion with the intention of spreading it across the system. We use a generalized, fully-connected Ising model, with each spin representing the binary opinion of an agent at a given time and a single, super spin representing the opinion of the leader. External fields and interaction constants model the opinion bias and peer-to-peer interactions, respectively, while the temperature T models an idealized social climate, representing an authoritarian regime if T is low or a liberal one if T is high. We derive a mean-field solution for the average magnetization m, the “social mood”, and investigate how m and the super spin magnetization vary as a function of T. We find that, depending on the initial conditions, due to the presence of metastable states, the sign of the average magnetization depends on the temperature. Finally, we verify that this effect is also present even if we consider only nearest-neighbor interactions within the social group.

Migdal-type effect in the dark matter absorption process

We propose a new mechanism of absorption of dark matter particles in atoms which resembles the Migdal effect of inelastic dark matter scattering. In this process, atoms may be ionized upon absorption of a scalar particle through the scalar-nucleon Yukawa-type interaction. The crucial difference from the inelastic dark matter scattering on atoms is that the total energy of the particle, including its rest mass mc2 term, is transferred to the electron. As a result, the emitted electron kinetic energy is about 6 orders in magnitude bigger than that in the dark matter scattering process. This absorption process allows one to probe dark matter particles with a relatively small mass, in the range from 1 to 100 keV, that cannot be detected in the scattering process. It is also possible to detect hypothetical scalar particles emitted from the Sun. We calculate absorption cross sections of this process in Na, Si, Ar, Ge, I, Xe, and Tl target atoms and extract limits on the scalar-nucleon interaction constant from null results of the XENONnT experiment. Published by the American Physical Society 2024

Emulating ab initio computations of infinite nucleonic matter

We construct efficient emulators for the computation of the infinite nuclear matter equation of state. These emulators are based on the subspace-projected coupled-cluster method for which we here develop a new algorithm called small-batch voting to eliminate spurious states that might appear when emulating quantum many-body methods based on a non-Hermitian Hamiltonian. The efficiency and accuracy of these emulators facilitate a rigorous statistical analysis within which we explore nuclear matter predictions for >106 different parametrizations of a chiral interaction model with explicit Δ-isobars at next-to-next-to leading order. Constrained by nucleon-nucleon scattering phase shifts and bound-state observables of light nuclei up to He4, we use history matching to identify nonimplausible domains for the low-energy coupling constants of the chiral interaction. Within these domains we perform a Bayesian analysis using sampling and importance resampling with different likelihood calibrations and study correlations between interaction parameters, calibration observables in light nuclei, and nuclear matter saturation properties. Published by the American Physical Society 2024

Theoretical Study of the Phonon Energy and Specific Heat of Ion-Doped LiCsSO4-Bulk and Nanoparticles.

Using a microscopic model, the temperature dependence of two phonon modes, ω0 = 32 cm-1 and 72 cm-1, and their damping of the ferroelastic LiCsSO4 compound, are calculated within Green's function technique. It is observed that the first mode increases whereas the second one decreases with increasing temperature T. This different behavior is explained with different sign of the anharmonic spin-phonon interaction constant. At the ferroelastic phase transition temperature TC, there is a kink in both modes due to the spin-phonon interaction. The phonon damping increases with T, and again shows an anomaly at TC. The contributions of the spin-phonon and phonon-phonon interactions are discussed. TC is reduced by decreasing the nanoparticle size, and can be enhanced by doping with K, Rb and NH4 ions at the Cs site. TC decreases by doping with Na, K or Rb on the Li site. The specific heat Cp also shows a kink at TC. Cp decreases with decreasing nanoparticle size and the peak disappears, whereas Cp increases with increasing K ion doping concentration.

Fourier transform microwave spectroscopy of the 13C- and 18O-substituted tropolone. Proton tunneling effect for the isotopic species with the asymmetric potential wells.

Fourier-transform microwave spectroscopy has been applied for the 13C/18O-substituted tropolone to observe tunneling-rotation transitions as well as pure rotational transitions. The tunneling-rotation transitions were observed between the 13C-4 and -6 forms as well as between 13C-3 and -7, between 13C-1 and -2, and between 18O-8 and -9 (we denote these tunneling pairs as 13C-46, etc., below) although they have an asymmetric tunneling potential due to the difference in the zero point energy (ZPE). From the observed tunneling splittings ΔEij (0.9800-1.6824 cm-1), the differences in ZPE Δij for the 13C-46, -37, -12, and 18O-89 species are derived to be -0.1104, 0.5652, -1.3682, and 1.3897 cm-1 to agree well with the DFT calculation. The state mixing ratio of the tunneling states decreases drastically from (44%:56%) to (8.7%:91.3%) for 13C-46 and 18O-89 with an increase in the asymmetry Δij of the tunneling potential function. The observed tunneling-rotation interaction constants Fij decrease from 16.001 to 9.224 cm-1 as the differences in ZPE Δij increase, while the diagonal tunneling-rotation interaction constants Fu increase from 1.767 to 13.70 cm-1, explained well by the mixing ratio of the tunneling states.

Theoretical Study of the Multiferroic Properties of Ion-Doped CaBaCo4O7

Using a microscopic model and Green’s function theory, we investigated the magnetization, specific heat, and polarization properties of CaBaCo4O7 (CBCO), scrutinizing their variations with temperature, magnetic field strength, and doping effects. Our analysis revealed a conspicuous kink in the specific heat curve near the critical temperature (TC), indicative of a phase transition. Additionally, the observed increase in polarization, P with escalating magnetic field strength serves as compelling evidence for the multiferroic nature of CBCO. Substituting Co ions with Fe ions resulted in an augmentation of the CBCO magnetization, M, while doping with Zn, Mn, or Ni ions led to a decline. Similarly, doping CBCO with Y or Sr ions at the Ca site exhibited divergent effects on magnetization, M, with an increase in the former and a decrease in the latter case. This modulation of the magnetization, M, can be attributed to the varying strains induced by the doping ions, thereby altering the exchange interaction constants within the system. The polarization, P, increases by Ni, Mn, or Zn substitution on the kagome layer Co sites. It can be concluded that Ni, Mn, or Zn doping enhances the magnetoelectric effect of CBCO. Notably, our findings align qualitatively well with experimental observations, reinforcing the validity of our theoretical framework.

Structure and Stability of Ago2 MID-Nucleotide Complexes: All-in-One (Drop) His6-SUMO Tag Removal, Nucleotide Binding, and Crystal Growth.

The middle (MID) domain of eukaryotic Argonaute (Ago) proteins and archaeal and bacterial homologues mediates the interaction with the 5'-terminal nucleotide of miRNA and siRNA guide strands. The MID domain of human Ago2 (hAgo2) is comprised of 139 amino acids with a molecular weight of 15.56 kDa. MID adopts a Rossman-like beta1-alpha1-beta2-alpha2-beta3-alpha3-beta4-alpha4 fold with a nucleotide specificity loop between beta3 and alpha3. Multiple crystal structures of nucleotides bound to hAgo2 MID have been reported, whereby complexes were obtained by soaking ligands into crystals of MID domain alone. This protocol describes a simplified one-step approach to grow well-diffracting crystals of hAgo2 MID-nucleotide complexes by mixing purified His6-SUMO-MID fusion protein, Ulp1 protease, and excess nucleotide in the presence of buffer and precipitant. The crystal structures of MID complexes with UMP, UTP and 2'-3' linked α-L-threofuranosyl thymidine-3'-triphosphate (tTTP) are presented. This article also describes fluorescence-based assays to measure dissociation constants (Kd) of MID-nucleotide interactions for nucleoside 5'-monophosphates and nucleoside 3',5'-bisphosphates. © 2024 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Crystallization of Ago2 MID-nucleotide complexes Basic Protocol 2: Measurement of dissociation constant Kd between Ago2 MID and nucleotides.