Proton Magnetic Relaxation Dispersion Research Articles

Molecular Dynamics in the Lyophases of Copolymer P123 Investigated with FFC NMR Relaxometry.

Associative block copolymers of the type (EO) x(PO) y(EO) x (where EO and PO represent ethylene and propylene oxides, respectively) in aqueous solution have far reaching commercial applications such as solubilization, controlled-drug delivery, etc. The molecular dynamics of a self-associating triblock copolymer (EO)20(PO)70(EO)20 (known as P123 with a molecular weight of ∼5800), in aqueous solution (D2O), consisting of various lyotropic liquid crystalline phases such as isotropic micellar, cubic, hexagonal, and lamellar phases, is investigated using the fast field cycling nuclear magnetic resonance (FFC NMR) relaxometry technique in the Larmor frequency range from 5 kHz to 30 MHz. A nuclear spin-relaxation model consisting of chain modes (Rouse modes) and order fluctuation (OF) modes typical for polymers and liquid crystals, respectively, is considered to explain the observed proton magnetic relaxation dispersion (PMRD) data in the lyophases under investigation. The PMRD analysis in both isotropic micellar and cubic phases revealed a Rouse frequency dependence of spin-lattice relaxation rate ( R1), i.e., R1 ∝ -τs ln(ωτs), in the entire frequency range of study. Hexagonal and lamellar phase data show Rouse modes as well as OF modes, leaving the signature of the latter as R1 ∝ ω- p, where p ∼ 0.5 is typical for nematic mesogens. The activation energies were also determined from segmental correlation times in the lyophases of study. To the best of our knowledge, the present FFC NMR relaxometry study is unique and quantitative in unraveling molecular dynamics of the associative copolymer P123 in aqueous solution.

Influence of underlying local organisations in typical nematic phase of 6CHBT and induced nematic phase of bicomponent liquid crystalline systems 4DBT–12CB – a Fast Field Cycling NMR investigation

ABSTRACTVariable-temperature proton magnetic relaxation dispersion (PMRD) profiles are collected in the induced nematic phases of the binary liquid crystalline mixtures composed of smectic mesogens: 5-butyl-2-(4-isothiocyanatophenyl)-1,3-dioxane (4DBT) and 4′-dodecyl-4-cyanobiphenyl (12CB) and the low viscous nematogen 4-(trans-4′-n-hexylcyclohexyl)-isothiocyanatobenzene (6CHBT), with a view to assess the influence of local organisations on the power spectrum of director fluctuation modes. Two distinct compositions of the binary mixture i.e. 50 mol% of 12CB (without a smectic phase) and 70 mol% of 12CB (with a smectic phase) are used. Fast Field Cycling nuclear magnetic resonance relaxometry is employed to measure proton spin-lattice relaxation rates (R1) as a function of Larmor frequency (10 kHz–30 MHz). PMRD data analysis with the choice of a suitable model indicated nematic clusters of moderate size (~200 Å) found in the broad nematic region of 50 mol% 12CB, whose size is almost invariant with temperature. On the other hand, cybotactic clusters, i.e. local smectic organisations of relatively larger size (~2000–3000 Å), are observed near the nematic–smectic transition (T > TAN) of 70 mol% 12CB. Interestingly, the shape geometry of such local organisations accessed from PMRD analysis is weakly anisotropic near TAN, while being isotropic near TNI for 70 mol% 12CB.

Nuclear spin–lattice relaxation dispersion investigation of smectic order fluctuations in isotropic and nematic phases

Proton magnetic relaxation dispersion (PMRD) measurements are made with a view to investigating the influence of an underlying smectic phase, on the isotropic and nematic phases of the binary liquid crystalline mixture of 4DBT and 12CB, at two distinct concentrations, namely 50% 12CB (has no smectic phase) and 70% 12CB (retains S Ad phase of 12CB). Analyses of the data in terms of relevant molecular processes show that the influence of smectic clusters on the nematic order fluctuations persists even in the isotropic phase. Further, the molecular dynamics are qualitatively different in the respective nematic phases of the two mixtures.

Nonlinear Effect of GdnHCl on Hydration Dynamics of Proteins: A 1H Magnetic Relaxation Dispersion Study

Proton magnetic relaxation dispersion investigations with aqueous solutions of lysozyme and bovine serum albumin (BSA) in the 0-5 M range of guanidine hydrochloride (GdnHCl), pH 4.4, 27 degrees C, were taken up with the objective of examining the hydration dynamics of internal cavity waters as the protein is held under increasingly destabilizing conditions. Field cycling NMR and conventional pulsed NMR techniques were employed to cover a frequency range of 100 kHz to 50 MHz. Analyses of dispersion profiles at different concentrations of GdnHCl were carried out considering the contributions from internal and surface waters. The denaturant-dependent variation of internal water contribution indicates that the reorientational disorder of internal waters decreases with increments of the denaturant up to its subdenaturing limit. For both proteins, the variation of effective correlation time with GdnHCl apparently shows a marginal shrink in hydrodynamic volumes under the subdenaturing condition. These results suggest that subdenaturing amounts of GdnHCl restrict the motional freedom of the internal waters, and can have considerable influence on the surface hydration. On increasing the denaturant concentration further, the dispersion amplitude drops sharply, indicating that the chaotropic action of the denaturant now runs over its own cavity water-ordering effect operative in the subdenaturing limit. The results are fundamentally important for the understanding of the susceptibility of protein structure and hydration to denaturants.

PMRD investigations of molecular dynamics and phase transitions in the liquid crystal 6CHBT

Proton Magnetic Relaxation Dispersion (PMRD) measurements were carried out over a wide Larmor frequency range near the isotropic-nematic transition temperature (T NI) and in the mid nematic phase of a low viscous liquid crystal 4-(trans-4′-hexylcyclohexyl)-isothiocyanatobenzene (6CHBT), with a view to examining the pre-transitional effects just above isotropic-nematic transition (T > T NI) and the role of director fluctuations (DF) on the nematic phase stability of this system. The results near the transition indicate critical slowing down of the short-range nematic order modes just above T NI with a mean field critical exponent characterizing the coherence length (ξ). The observed temperature independence of the correlation time associated with the reorientations (τR) and the extension of DF mode spectrum, in the mid-nematic phase, to relatively higher resonance frequencies seem to suggest fairly low hindering barriers for the tumbling of the molecules about their short axes.

Paramagnetic relaxation of protons in rotationally immobilized proteins

The proton magnetic relaxation dispersion profiles are reported over the proton Larmor frequency range from 0.01 to 30 MHz for cross-linked gels and for the dry lyophilized bovine serum albumin covalently labeled at lysine with diethylenetriaminepentaacetic acid chelates of either Gd(III) or Mn(II) ions. The proton spin-lattice relaxation dispersion for the cross-linked paramagnetic protein gel is accurately represented as a sum of two major relaxation contributions. The diamagnetic term is a power law from the magnetic field dependence of the protein protons. The paramagnetic term is approximately described by the Solomon-Bloembergen-Morgan class of models. However, the paramagnetic relaxation mechanism in the dry lyophilized protein is fundamentally different and we develop a new quantitative description of the dispersion profile. In the dry case, no peak in the proton relaxation dispersion profile is detected from the field dependence of the electron spin relaxation times. The high-field paramagnetic relaxation dispersion is a power law in the Larmor frequency with an exponent of -0.8, which results from modulation of the electron-nuclear coupling by the intramolecular dynamics of the protein which primarily propagates along the primary structure of the protein. The low-field plateau is caused by the interruption of the electron-nuclear spin correlation by electron spin relaxation. This new quantitative description provides a simple approach to the measurement of electron spin-lattice relaxation times in paramagnetic protein systems at room temperature based on the magnetic field dependence of the proton spin-lattice relaxation rate constant.

Protein self‐association in solution: The bovine β ‐lactoglobulin dimer and octamer

We have used proton magnetic relaxation dispersion (MRD) to study the self-association of bovine beta-lactoglobulin variant A (BLG-A) as a function of temperature at pH 4.7 (dimer-octamer equilibrium) and as a function of NaCl concentration at pH 2.5 (monomer-dimer equilibrium). The MRD method identifies coexisting oligomers from their rotational correlation times and determines their relative populations from the associated dispersion amplitudes. From MRD-derived correlation times and hydrodynamic model calculations, we confirm that BLG-A dimers associate to octamers below room temperature. The tendency for BLG-A dimers to assemble into octamers is found to be considerably weaker than in previous light scattering studies in the presence of buffer salt. At pH 2.5, the MRD data are consistent with an essentially complete transition from monomers in the absence of salt to dimers in 1 M NaCl. Because of an interfering relaxation dispersion from nanosecond water exchange, we cannot determine the oligomer populations at intermediate salt concentrations. This nanosecond dispersion may reflect intersite exchange of water molecules trapped inside the large binding cavity of BLG-A.

Self-Association of Lysozyme as Seen by Magnetic Relaxation Dispersion

The pH and salt dependent self-association of hen egg-white lysozyme (HEWL) has been studied extensively, mainly by scattering techniques, but it has proven difficult to distinguish oligomerization from long-range interactions. Because HEWL is the principal model system in studies of protein crystallization, it is important to establish its oligomerization behavior unambiguously. Here, we address this problem with the aid of proton magnetic relaxation dispersion (MRD), which can determine the sizes and populations of coexisting oligomers with minimal influence of long-range interactions. We find that HEWL is monomeric at pH 4 and dimeric at pH 9. Dimers as well as a higher oligomer are formed also at pH 4 in the presence of K2SO4. The dimer observed in solution has the same rotational correlation time as a dimer present in tetragonal HEWL crystals. The higher oligomer, consisting of about 16 HEWL monomers, is more abundant as the saturation limit is approached, but is suppressed by addition of sulfobetaine. It is also promoted by contaminating proteins, present in commercial HEWL preparations. These findings can explain why HEWL tends to form amorphous precipitates in the presence of sulfate and why crystallization of HEWL is facilitated by sulfobetaine. The MRD data also yield a residence time of 2 ns for several protein-associated water molecules, probably including the four-molecule cluster buried between the α and β subunits of HEWL.

Molecular oxygen spin-lattice relaxation in solutions measured by proton magnetic relaxation dispersion.

Proton spin-lattice relaxation rate constants have been measured as a function of magnetic field strength for water, water-glycerol solution, cyclohexane, methanol, benzene, acetone, acetonitrile, and dimethyl sulfoxide. The magnetic relaxation dispersion is well approximated by a Lorentzian shape. The origin of the relaxation dispersion is identified with the paramagnetic contribution from molecular oxygen. In the small molecule cases studied here, the effective correlation time for the electron-nuclear coupling may include contributions from both translational diffusion and the electron T(1). The electron T(1) for molecular oxygen dissolved in several solvents was found to be approximately 7.5 ps and nearly independent of solvent or viscosity.

ChemInform Abstract: Azide and Fluoride Binding to E. coli Iron Superoxide Dismutase as Studied by Solvent Proton Magnetic Relaxation Dispersion.

ChemInformVolume 18, Issue 23 Physical Organic Chemistry ChemInform Abstract: Azide and Fluoride Binding to E. coli Iron Superoxide Dismutase as Studied by Solvent Proton Magnetic Relaxation Dispersion. D. M. DOOLEY, D. M. DOOLEY Dep. Chem., City Univ., London EC1V 0HB, UKSearch for more papers by this authorT. F. JONES, T. F. JONES Dep. Chem., City Univ., London EC1V 0HB, UKSearch for more papers by this authorJ. L. KARAS, J. L. KARAS Dep. Chem., City Univ., London EC1V 0HB, UKSearch for more papers by this authorM. A. MCGUIRL, M. A. MCGUIRL Dep. Chem., City Univ., London EC1V 0HB, UKSearch for more papers by this authorR. D. III BROWN, R. D. III BROWN Dep. Chem., City Univ., London EC1V 0HB, UKSearch for more papers by this authorS. H. KOENIG, S. H. KOENIG Dep. Chem., City Univ., London EC1V 0HB, UKSearch for more papers by this author D. M. DOOLEY, D. M. DOOLEY Dep. Chem., City Univ., London EC1V 0HB, UKSearch for more papers by this authorT. F. JONES, T. F. JONES Dep. Chem., City Univ., London EC1V 0HB, UKSearch for more papers by this authorJ. L. KARAS, J. L. KARAS Dep. Chem., City Univ., London EC1V 0HB, UKSearch for more papers by this authorM. A. MCGUIRL, M. A. MCGUIRL Dep. Chem., City Univ., London EC1V 0HB, UKSearch for more papers by this authorR. D. III BROWN, R. D. III BROWN Dep. Chem., City Univ., London EC1V 0HB, UKSearch for more papers by this authorS. H. KOENIG, S. H. KOENIG Dep. Chem., City Univ., London EC1V 0HB, UKSearch for more papers by this author First published: June 9, 1987 https://doi.org/10.1002/chin.198723042AboutPDF 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. Volume18, Issue23June 9, 1987 RelatedInformation

Azide and fluoride binding to E. coli iron superoxide dismutase as studied by solvent proton magnetic relaxation dispersion

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAzide and fluoride binding to E. coli iron superoxide dismutase as studied by solvent proton magnetic relaxation dispersionDavid M. Dooley, Timothy F. Jones, Jennifer L. Karas, Michele A. McGuirl, Rodney D. Brown III, and Seymour H. KoenigCite this: J. Am. Chem. Soc. 1987, 109, 3, 721–725Publication Date (Print):February 1, 1987Publication History Published online1 May 2002Published inissue 1 February 1987https://doi.org/10.1021/ja00237a014RIGHTS & PERMISSIONSArticle Views104Altmetric-Citations8LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (680 KB) Get e-Alerts Get e-Alerts

Proton magnetic relaxation dispersion in aqueous biopolymer systems

Measurements of the proton spin-lattice relaxation rates for Larmor frequencies between 200 Hz and 60 MHz and of the spin-spin relaxation rates at 2 kHz and 25 MHz have been performed in three types of polymerized fibrin. The influence of aggregation-induced macromolecular dynamical hindrance on the relaxation behaviour is analysed and discussed. Special attention is given to the relaxation behaviour at low magnetic field, which results from a combined effect of macromolecular reorientation, hydration and chemical exchange between free and bound water. Further support is given to an overall relaxation scheme involving slow exchanging protein protons as well as slightly anisotropically bound water molecules. Bound water protons appear to relax mainly by intramolecular interaction and to exchange with free water protons through a thermally activated process with activation energy of ca 7·5 kJ mol-1.

Proton magnetic relaxation dispersion in aqueous biopolymer systems

Proton magnetic relaxation dispersion in aqueous biopolymer systems

Comparison of the spectroscopic and saccharide binding properties of lentil and pea isolectins

The lentil isolectins, CMLcH A and CMLcH B, and pea isolectins, CMPSA A and CMPSA B, are compared in terms of their spectroscopic and saccharide binding properties. The paramagnetic contribution to the solvent proton magnetic relaxation dispersion profiles of solutions of the isolectins of each protein are found to be essentially identical. Electron paramagnetic resonance spectra suggest a high degree of octahedral symmetry at the Mn 2+ site for both pairs of isolectins. The near-ultraviolet absorption spectra of CMLcH A and CMLcH B are identical, as are the spectra of CMPSA A and CMPSA B. Carbohydrate binding activities of the isolectins of each protein are compared using hemagglutination, precipitation, and precipitation-inhibition assays, and are found to be identical, although the activities of CMLcH and CMPSA differ somewhat. These results demonstrate that the spectroscopic and saccharide binding properties of the isolectins of CMLcH are essentially identical, as are those of the isolectins of CMPSA, and suggest that native mixtures of the isolectins may be treated as single proteins in further studies.

Proton magnetic relaxation dispersion in solutions of the cuproprotein diamine oxidase

Proton nuclear magnetic resonance relaxation measurements were made over the range 4.7--220 MHz for aqueous solutions of hog kidney diamine oxidase. The values of 1/T1 give rise in two distinct dispersions, at 16 and 75 MHz, whereas 1/T2 displays a minimum at 20 MHz. The temperature dependence of relaxation rates in all cases yield apparent activation energies less than 0.6 kcal/mol. These data indicate to us that the two Cu(II) ions of diamine oxidase are intrinsically different in terms of their electronic relaxation characteristics and hence, chemical environments. Low field limits of the two electronic relaxation times are 2 and 10 ns, with one of these correlation times being frequency dependent. The value of the frequency-dependent electronic relaxation time is governed by interactions that are modulated by a process having a correlation time of 5 ps.

Mechanism of binding of mono- and oligosaccharides to concanavalin A: a solvent proton magnetic relaxation dispersion study

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMechanism of binding of mono- and oligosaccharides to concanavalin A: a solvent proton magnetic relaxation dispersion studyCurtis F. Brewer and Rodney D. Brown, IIICite this: Biochemistry 1979, 18, 12, 2555–2562Publication Date (Print):June 12, 1979Publication History Published online1 May 2002Published inissue 12 June 1979https://doi.org/10.1021/bi00579a019RIGHTS & PERMISSIONSArticle Views113Altmetric-Citations61LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts Get e-Alerts

Solvent proton magnetic relaxation dispersion in solutions of concanavalin A.

Concanavalin A, a protein isolated from jack beans, exhibits several important biological properties, all of which are related to its ability to bind and precipitate specific polysaccharides. Concanavalin A is a dimer at pH 5.6, and has one transition-metal and one calcium-ion binding site per monomer unit of molecular weight 27,000. Both metal-ion sites must be occupied for the protein to be active. It is of interest to determine the role of the transition metal ion in Concanavalin A and its relationship to the sugar binding activity of the protein. We report the magnetic field and temperature dependences of the spin-lattice magnetic relaxation rates of solvent protons in aqueous solutions of zinc and manganese derivatives of Concanavalin A, and the influence of monosaccharide binding on these rates. The results of a leastsquares fit of the data to the theory, with five adjustable parameters, indicate that there is one rapidly exchanging water molecule ligand on the Mn(2+) ion, with a residence lifetime of 2.5 musec at 25 degrees , and with its protons 0.27 nm (2.7 A) from the Mn(2+) ion. We find that at low magnetic fields (proton Larmor frequencies below about 10 MHz), the correlation time for the dipolar interaction between the Mn(2+) electronic spin moment and the protons on the water ligand is the spin-lattice relaxation time tau(S) of the Mn(2+) moment, but that at higher magnetic fields the correlation time for the dipolar interaction is determined by the Brownian rotational tumbling of the protein, because of the substantial variation of tau(S) with magnetic field. Monosaccharide binding to manganese Concanavalin A has little effect on the relaxation rates of solvent protons, a result that indicates that the sugars do not bind directly to the transition metal in the protein.