Relaxation Of Macromolecules Research Articles

In situ NMR Investigation of the Photoresponse of Perovskite Crystal

Summary Hybrid perovskites are outstanding candidates for use in optoelectronic devices. Nonetheless, hybrid perovskites present numerous fundamental issues that are not yet fully understood. This study seeks to address this problem by reporting on the occurrence of ultraslow dynamic orientation changes in the methylammonium (MA) cations and the corresponding changes in the inorganic lattice of MAPbI3 perovskite crystals occurring over a time scale of 100 s under continuous illumination based on in situ single-crystal 2H nuclear magnetic resonance and in situ X-ray diffraction results. The demonstrated ultraslow dynamic changes in MAPbI3 are far slower than elementary molecular motions typically having time scales of femtoseconds and picoseconds and have never been reported previously. The ultraslow dynamic changes have been correlated with the reduction of band gap and the increase of absorption coefficient of MAPbI3, providing the molecular origins of the stabilization process in the photoresponse of the MAPbI3 device.

High-frequency microwave diagnostics of of free and bound water content in biological objects

Most biomaterial molecules are electrically neutral. Electrophysical properties of a biomaterial molecule are acquired when water molecules having a pronounced dipole moment bind to them. Therefore, the solution to the problem of determining the relationship of water with biological macromolecules and creation of methods for monitoring the state of water in biological objects is a step in the general problem of diagnosing their state.The composition of biological macromolecules, proteins includes intramolecular water. This affects both the real and the imaginary part of the dielectric constant of biological objects. The study is based on the fact that water has the greatest effect on the dielectric constant of the media in which it is located. With complex molecules of a biological substance, water can have bonds various in nature. Therefore, there is a significant set of physical factors associated with obtaining information about the state of biological objects based on determining the amount and distribution of free and integrated water in macromolecules of biological substances using microwave sensors relative to biological objects in vivo and in vitro, as well as during external exposure to them.The main ideas are based on the fundamental principles of radio physical methods for obtaining values of the real and imaginary parts of the dielectric constant in the frequency range of relaxation of macro-molecules of biological media with bound and free water.Information on the content and changes in the distribution of free and bound water in biological objects makes it possible to diagnose their state. Microwave diagnostics of biological objects using resonator transducers with coaxial probe structures provide an opportunity for non-destructive analysis with millimeter and submillimeter spatial resolution. Analytical methods were used to study the nature of the interaction of electromagnetic fields created by coaxial apertures of various configurations with samples. Based on the results obtained, the directions for the implementation of microwave high-local diagnostics techniques are determined.

Identification of a New Interaction Mode between the Src Homology 2 Domain of C-terminal Src Kinase (Csk) and Csk-binding Protein/Phosphoprotein Associated with Glycosphingolipid Microdomains

Proteins with Src homology 2 (SH2) domains play major roles in tyrosine kinase signaling. Structures of many SH2 domains have been studied, and the regions involved in their interactions with ligands have been elucidated. However, these analyses have been performed using short peptides consisting of phosphotyrosine followed by a few amino acids, which are described as the canonical recognition sites. Here, we report the solution structure of the SH2 domain of C-terminal Src kinase (Csk) in complex with a longer phosphopeptide from the Csk-binding protein (Cbp). This structure, together with biochemical experiments, revealed the existence of a novel binding region in addition to the canonical phosphotyrosine 314-binding site of Cbp. Mutational analysis of this second region in cells showed that both canonical and novel binding sites are required for tumor suppression through the Cbp-Csk interaction. Furthermore, the data indicate an allosteric connection between Cbp binding and Csk activation that arises from residues in the βB/βC loop of the SH2 domain.

Crystallographic and NMR Evidence for Flexibility in Oligosaccharyltransferases and Its Catalytic Significance

Oligosaccharyltransferase (OST) is a membrane-bound enzyme that catalyzes the transfer of an oligosaccharide to an asparagine residue in glycoproteins. It possesses a binding pocket that recognizes Ser and Thr residues at the+2 position in theN-glycosylation consensus, Asn-X-Ser/Thr. We determined the crystal structures of the C-terminal globular domains of the catalytic subunits of two archaeal OSTs. A comparison with previously determined structures identified a segment with remarkable conformational plasticity, induced by crystal contact effects. We characterized its dynamic properties in solution by (15)N NMR relaxation analyses. Intriguingly, the mobile region contains the+2 Ser/Thr-binding pocket. In agreement, the flexibility restriction forced by an engineered disulfide crosslink abolished the enzymatic activity, and its cleavage fully restored activity. These results suggest the necessity of multiple conformational states in the reaction. The dynamic nature of the Ser/Thr pocket could facilitate the efficient scanning of N-glycosylation sequons along nascent polypeptide chains.

Structural Dynamics of Bacterial Translation Initiation Factor IF2

Bacterial translation initiation factor IF2 promotes ribosomal subunit association, recruitment, and binding of fMet-tRNA to the ribosomal P-site and initiation dipeptide formation. Here, we present the solution structures of GDP-bound and apo-IF2-G2 of Bacillus stearothermophilus and provide evidence that this isolated domain binds the 50 S ribosomal subunit and hydrolyzes GTP. Differences between the free and GDP-bound structures of IF2-G2 suggest that domain reorganization within the G2-G3-C1 regions underlies the different structural requirements of IF2 during the initiation process. However, these structural signals are unlikely forwarded from IF2-G2 to the C-terminal fMet-tRNA binding domain (IF2-C2) because the connected IF2-C1 and IF2-C2 modules show completely independent mobility, indicating that the bacterial interdomain connector lacks the rigidity that was found in the archaeal IF2 homolog aIF5B.

Modulation of the distance dependence of paramagnetic relaxation enhancements by CSA × DSA cross-correlation

Paramagnetic metal ions with fast-relaxing electronic spin and anisotropic susceptibility tensor provide a rich source of structural information that can be derived from pseudo-contact shifts, residual dipolar couplings, dipole–dipole Curie spin cross-correlation, and paramagnetic relaxation enhancements. The present study draws attention to a cross-correlation effect between nuclear relaxation due to anisotropic chemical shielding (CSA) and due to the anisotropic dipolar shielding (DSA) caused by the electronic Curie spin. This CSA × DSA cross-correlation contribution seems to have been overlooked in previous interpretations of paramagnetic relaxation enhancements. It is shown to be sufficiently large to compromise the 1/ r 6 distance dependence usually assumed. The effect cannot experimentally be separated from auto-correlated DSA relaxation. It can increase or decrease the observed paramagnetic relaxation enhancement. Under certain conditions, the effect can dominate the entire paramagnetic relaxation, resulting in nuclear resonances narrower than in the absence of the paramagnetic center. CSA × DSA cross-correlation becomes important when paramagnetic relaxation is predominantly due to the Curie rather than the Solomon mechanism. Therefore the effect is most pronounced for relaxation by metal ions with large magnetic susceptibility and fast-relaxing electron spin. It most strongly affects paramagnetic enhancements of transverse relaxation in macromolecules and of longitudinal relaxation in small molecules.

Elucidation of cross relaxation in liquids by two-dimensional N.M.R. spectroscopy

Two-dimensional N.M.R. spectroscopy is applied to the elucidation of cross relaxation pathways in liquids. The theory underlying two dimensional studies of cross relaxation and of transient nuclear Overhauser effects is developed. The influence of the correlation time of the molecular random process is investigated. It is found that in the limit of short correlation times (extreme narrowing limit) weak negative cross-peaks are observed. However, for long correlation times (spin diffusion limit) strong positive cross-peaks can be obtained. The technique appears particularly promising for the study of cross relaxation in macromolecules. Examples of intra- and intermolecular cross relaxation in the extreme narrowing limit are presented.

Heterogeneous Nucleation Effects of Neodymium Oxide on Polyamide-1010

In this paper microcrystalline structures of polyamide-1010 (PA1010) mixed with neodymium oxide (Nd2O3) were studied by Wide Angle X-ray Diffraction (WAXD) and Small Angle X-ray Scattering (SAXS). Crystallization behavior was investigated by DSC. The transition and relaxation of macromolecules in the crystalline phase were explored by Differential Scanning Calorimetry (DSC). It was revealed that neodymium oxide plays an important role in PA1010 crystallization as a heterogeneous nucleating agent. It can improve the crystallization rate, reduce crystallite size and introduce crystal imperfections. The microcrystalline structure was imposed by the addition of Nd2O3 However, the heterogeneous nucleation effect obviously does not exert its influence on the transition and relaxation of macromolecules in the crystalline phase.

Segmental relaxation in macromolecules

Segmental relaxation in macromolecules

Relaxation and nonradiative decay in disordered systems. II. Two-fracton inelastic scattering.

The two localized-vibrational quanta (Raman) relaxation process is calculated for a localized electronic state. The calculation is expected to be relevant to relaxation at elevated temperatures where the principal vibrational excitations are of high energy (and hence of short length scale). Localization of the vibrational eigenstates is most likely for this regime. Vibrational localization can be geometrical in origin (as on a fractal network, with the quantized vibrational states fractons), or as a consequence of scattering (analogous to Anderson localization, with the quantized vibrational states localized phonons). The relaxation rate is characterized by a probability density which is calculated for both classes of localization under the assumption that the electronic and vibrational energy widths are larger than the maximum electronic relaxation rate. The time profile of the initial elec- tronic state population is calculated. The long-time behavior begins as ${t}^{[1/2(a\mathrm{\ensuremath{-}}1)]}$exp[-${c}_{1}$(t${)}^{1\phantom{\rule{0ex}{0ex}}/(a\mathrm{\ensuremath{-}}1)}$], where a=4q+2d\ifmmode\bar\else\textasciimacron\fi{}\ifmmode\bar\else\textasciimacron\fi{} and 4q+2d\ifmmode\bar\else\textasciimacron\fi{}\ifmmode\bar\else\textasciimacron\fi{}-2 for Kramers and non-Kramers transitions, respectively. Here, d\ifmmode\bar\else\textasciimacron\fi{}\ifmmode\bar\else\textasciimacron\fi{} is the fracton dimensionality and q=d\ifmmode\bar\else\textasciimacron\fi{}\ifmmode\bar\else\textasciimacron\fi{}${d}_{\ensuremath{\varphi}}$/D. The fractal dimensionality is D, and ${d}_{\ensuremath{\varphi}}$ is defined by the range dependence of the fracton wave ). The long-time behavior thus begins as a stretched exponential. After a crossover time, the long-time behavior varies as (lnt${)}^{\ensuremath{\eta}\mathrm{\ensuremath{-}}1/2}$${t}^{\mathrm{\ensuremath{-}}{c}_{1}}$(ln t${)}^{2\ensuremath{\eta}}$ where ${c}_{1}$ is a constant and \ensuremath{\eta}=D/${d}_{\ensuremath{\varphi}}$. This portion of the time decay is faster than any power law but slower than exponential or stretched exponential.In the presence of rapid electronic cross relaxation, the time profile is exponential, with a low-temperature relaxation time 1/${T}_{1}^{\mathrm{ave}}$ proportional to ${T}^{2d\ifmmode\bar\else\textasciimacron\fi{}\ifmmode\bar\else\textasciimacron\fi{}[1+2({d}_{\ensuremath{\varphi}}/D)]\mathrm{\ensuremath{-}}1}$ and ${T}^{2d\ifmmode\bar\else\textasciimacron\fi{}\ifmmode\bar\else\textasciimacron\fi{}[1+2({d}_{\ensuremath{\varphi}}/D)]\mathrm{\ensuremath{-}}3}$ for Kramers and non-Kramers transitions, respectively. These results may explain recent fractional temperature exponents found for electronic spin-lattice relaxation in macromolecules and nuclear spin-lattice relaxation in glasses.

ChemInform Abstract: MODEL‐FREE APPROACH TO THE INTERPRETATION OF NUCLEAR MAGNETIC RESONANCE RELAXATION IN MACROMOLECULES. 2. ANALYSIS OF EXPERIMENTAL RESULTS

Chemischer InformationsdienstVolume 13, Issue 47 Physical Organic Chemistry ChemInform Abstract: MODEL-FREE APPROACH TO THE INTERPRETATION OF NUCLEAR MAGNETIC RESONANCE RELAXATION IN MACROMOLECULES. 2. ANALYSIS OF EXPERIMENTAL RESULTS G. LIPARI, G. LIPARISearch for more papers by this authorA. SZABO, A. SZABOSearch for more papers by this author G. LIPARI, G. LIPARISearch for more papers by this authorA. SZABO, A. SZABOSearch for more papers by this author First published: November 23, 1982 https://doi.org/10.1002/chin.198247061AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume13, Issue47November 23, 1982 RelatedInformation

ChemInform Abstract: MODEL‐FREE APPROACH TO THE INTERPRETATION OF NUCLEAR MAGNETIC RESONANCE RELAXATION IN MACROMOLECULES. 1. THEORY AND RANGE OF VALIDITY

Chemischer InformationsdienstVolume 13, Issue 47 Physical Organic Chemistry ChemInform Abstract: MODEL-FREE APPROACH TO THE INTERPRETATION OF NUCLEAR MAGNETIC RESONANCE RELAXATION IN MACROMOLECULES. 1. THEORY AND RANGE OF VALIDITY G. LIPARI, G. LIPARISearch for more papers by this authorA. SZABO, A. SZABOSearch for more papers by this author G. LIPARI, G. LIPARISearch for more papers by this authorA. SZABO, A. SZABOSearch for more papers by this author First published: November 23, 1982 https://doi.org/10.1002/chin.198247060Citations: 3AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article.Citing Literature Volume13, Issue47November 23, 1982 RelatedInformation

Model-free approach to the interpretation of nuclear magnetic resonance relaxation in macromolecules. 2. Analysis of experimental results

Model-free approach to the interpretation of nuclear magnetic resonance relaxation in macromolecules. 2. Analysis of experimental results

Model-free approach to the interpretation of nuclear magnetic resonance relaxation in macromolecules. 1. Theory and range of validity

A new approach to the interpretation of nuclear magnetic resonance relaxation experiments on macromolecules in solution is presented. This paper deals with the theoretical foundations and establishes the range of validity of this approach, and the accompanying paper demonstrates how a wide variety of experimental relaxation data can be successfully analyzed by using this approach. For both isotropic and anisotropic overall motion, it is shown that the unique imformation on fast internal motions contained in relaxation experiments can be completely specified by two model-independent quantities; (1) a generalized order parameter, S, which is a measure of the spatial restriction of the motion, and (2) an effective correlation time, T/sub e/, which is a measure of the rate of motion. A simple expression for the spectral density involving these two parameters is derived and is shown to be exact when the internal (but not overall) motions are in the extreme narrowing limit. The model-free approach (so called because S/sup 2/ and T/sub e/ have model-independent significance) consists of using the above spectral density to least-squares fit relaxation data by treating S/sup 2/ and T/sub e/ as adjustable parameters. The range of validity of this approach is illustrated by analyzing error-free relaxationmore » data generated by using sophisticated dynamical models. Empirical rules are presented that allow one to estimate the of S/sup 2/ and T/sub e/ extracted by using the model-free approach by considering their numerical values, the resonance frequencies, and the parameters for the overall motion. For fast internal motions, it is unnecessary to use approaches based on complicated spectral densities derived within the framework of a model because all models that can give the correct value of S/sup 2/ work equally well.« less

Elucidation of cross relaxation in liquids by two-dimensional N.M.R. spectroscopy

Two-dimensional N.M.R. spectroscopy is applied to the elucidation of cross relaxation pathways in liquids. The theory underlying two dimensional studies of cross relaxation and of transient nuclear Overhauser effects is developed. The influence of the correlation time of the molecular random process is investigated. It is found that in the limit of short correlation times (extreme narrowing limit) weak negative cross-peaks are observed. However, for long correlation times (spin diffusion limit) strong positive cross-peaks can be obtained. The technique appears particularly promising for the study of cross relaxation in macromolecules. Examples of intra- and intermolecular cross relaxation in the extreme narrowing limit are presented.

Effect of librational motion on fluorescence depolarization and nuclear magnetic resonance relaxation in macromolecules and membranes

The theory of fluorescent emission anisotropy [r(t)] of a cylindrical probe in a membrane suspension is developed. It is shown, independent of any model, that the limiting anisotropy [r(infinity)] is proportional to the square to the order parameter of the probe. The order parameter determines the first nontrivial term in the expansion of the equilibrium orientational distribution function of the probe in a series of Legendre polynomials. Following Kinosita, Kawato, and Ikegami, the motion of the probe is described as diffusion ("wobbling") within a cone of semiangle theta 0. Within the framework of this model, an accurate single-exponential approximation for r(t) is considered. An analytic expression relating the effective relaxation time, which appears in the above approximation, to theta 0 and the diffusion coefficient for wobbling is derived. The model is generalized to the situation where the probe is attached to a macromolecule whose motion cannot be neglected on the time scale of the fluorescence experiment. Finally, by exploiting the formal similarity between the theory of fluorescence depolarization and 13C-NMR dipolar relaxation, expressions for T1, T2, and the nuclear Overhauser enhancement are derived for a protonated carbon which is nonrigidly attached to a macromolecule and undergoes librational motion described as diffusion on a spherical "cap" of semiangle theta 0.

Carbon-13 Nuclear Magnetic Relaxation in Macromolecules with Side Chains Undergoing Multiple Internal Rotations. Effects of the Distribution of Correlation Times and Overall Anisotropic Motion

Carbon-13 Nuclear Magnetic Relaxation in Macromolecules with Side Chains Undergoing Multiple Internal Rotations. Effects of the Distribution of Correlation Times and Overall Anisotropic Motion

Theory of NMR relaxation in macromolecules: Restricted diffusion and jump models for multiple internal rotations in amino acid side chains

The theory required to extract detailed motional information from NMR relaxation times of nuclei in an amino acid side chain containing multiple internal rotation axes attached to a large macromolecule of at least cylindrical symmetry is developed. Emphasis is placed on the analysis of 13C-NMR of protonated carbons where dipolar relaxation is predominant. Extension to other relaxation processes is straightforward. The spectral density from which the relaxation times can be calculated is obtained for various models for the motion of the side chain. The existing theory which assumes that internal rotations are both independent and free is generalized to incorporate excluded volume effects in a heuristic way by restricting the amplitude of the internal rotations. It is found that small amplitude motions are ineffective in causing relaxation. Thus jump models involving a relatively small number of configurations are appropriate to describe the motion of the side chain. The advantage of jump models is twofold: (1) excluded volume effects can be handled simply by including only sterically allowed configurations, and (2) the unrealistic assumption of diffusional models that rotations about different bonds are independent can be removed by considering concerted motions in which the positions of only a small number of atoms are altered. An explicit expression for the spectral density, which is computationally practical when the number of configurations is less than 200, is obtained for a class of jump models in which the dynamics is described by a master equation. A detailed application of the general formalism is made to the case of a lysine side chain whose carbon–carbon backbone is constrained to lie on a tetrahedral lattice. Finally, numerical calculations are presented to illustrate some of the qualitative features of the different models, and the strategy that can be used to obtain motional information from experiment within the framework of these models is discussed.

Nuclear relaxation in macromolecules by paramagnetic ions: a novel mechanism

The magnetic dipolar interaction of a nuclear spin with the thermal average of an electronic spin (“Curie spin”) is modulated by molecular motion but not by the electronic spin relaxation. In high fields, where the Curie spin becomes large; and for large molecules, which rotate slowly, nuclear transverse relaxation may be dominated by interaction with the Curie spin. The effect is studied for heme protons of hemoglobin. It is proposed as a new approach to the method of relaxation enhancement where it has the advantage that it does not require knowledge of the electron spin relaxation time.

Dielectric properties of long chains with one short dipole

We study theoretically dielectric relaxation of macromolecules with one single electric dipole in the center of the chain.