Relaxation In Dilute Solutions Research Articles

Sizes and Conformation of the Molecules of DNA–Surfactant Complexes in Dilute Solutions and on the Atomic Smooth Substrates

The conformations of the molecules of DNA–surfactant complexes in dilute solutions and on the atomic smooth surfaces of mica and highly oriented pyrolytic graphite were comparatively studied by the methods of isothermal diffusion, electric birefringence, and atomic force microscopy. The DNA–surfactant complexes were deposited onto the substrates from a chloroform solution. The number of particles of the DNA–surfactant complex on the substrate was changed by varying the concentration of the initial solution within three orders of magnitude. The particles of a shape close to ellipsoidal, 25–70 nm in diameter and 2–4 nm high, were observed at the lowest concentration of DNA–surfactant solution on the mica substrate. The shape and size of these particles correspond to those of a single DNA–surfactant complex, calculated from its translational diffusion coefficient and the time of orientational relaxation in dilute solutions. An increase in the number of molecules deposited onto the substrate leads to an increase in the characteristic sizes of DNA–surfactant complex particles observed by the atomic force microscopy. This may be associated with the aggregation of DNA–surfactant complexes.

Frequency dependence of the nonlinear dielectric effect in diluted dipolar solutions

The nonlinear dielectric relaxation in dilute solutions of strongly polar molecules (4,4′- n-hexylcyanobiphenyl) in nonpolar medium (benzene) has been investigated. The nonlinear dielectric increment, induced by a d.c. electric field of high intensity (Eo ≈ 10 7 V/m), was detected with an a.c. field of small intensity and variable frequency (1 MHz-3 GHz). The relaxational behavior of the increment is discussed in the framework of the theory proposed by Coffey et al.

Dielectric relaxation in dilute solutions of poly(organophosphazenes): evidence of the localized electronic structure of the P:N double bonds

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTDielectric relaxation in dilute solutions of poly(organophosphazenes): evidence of the localized electronic structure of the P:N double bondsShunsuke Uzaki, Keiichiro Adachi, and Tadao KotakaCite this: Macromolecules 1988, 21, 1, 153–156Publication Date (Print):January 1, 1988Publication History Published online1 May 2002Published inissue 1 January 1988https://doi.org/10.1021/ma00179a031RIGHTS & PERMISSIONSArticle Views48Altmetric-Citations19LEARN 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 (475 KB) Get e-Alerts Get e-Alerts

Models for spin relaxation in dilute solutions of randomly coiled polymers

AbstractModels for the interpretation of magnetic relaxation in a randomly coiled macromolecule in dilute solution are considered. Expressions are given for the spin‐lattice relaxation time and the nuclear Overhauser enhancement resulting from modulation of the dipole–dipole interaction by three specific independent and mutually competitive types of macromolecular motion. Overall molecular rotation is characterized by a single exponential correlation time and internal anisotropic rotation by the well‐known Woessner theory. A simple description of backbone motion is presented based upon a three‐bond crankshaft motion and the concept of limited coupling among backbone bonds. The resulting correlation function is numerically similar to that recently proposed by Valeur, Jarry, Gény, and Monnerie from a somewhat different standpoint. Representative calculations for appropriate ranges of the model parameters are made for a 13C nucleus relaxing by heteronuclear dipole–dipole interaction with a single 1H nucleus.

Ultrasonic and viscoelastic relaxation in solutions of poly (2,6-dimethyl-p-phenylene oxide)

Acoustic relaxation in dilute solutions of poly (2,6-dimethyl-p-phenylene oxide) in toluene is due to conformational change between states which are not exactly isoenergetic, but for which ΔH°= 400 ± 100 J mol–1 and –6 × 10–7 < ΔV° < –5 × 10–8 m3 mol–1. The relaxation frequencies are rather low, being ∼ 3 MHz at 313 and 333 K, with a temperature dependence less than the experimental error (± 0.3 MHz over 20 K).

Dielectric and viscoelastic relaxation in dilute solutions of some non-Gaussian chains

Dielectric and viscoelastic measurements have been made on dilute solutions of poly(butylisocyanate). The measurements confirm that the molecules are predominantly rod-like in hydrodynamic behaviour. The end-over-end rotation times obtained from both sets of observations have been analyzed by three methods. The monomer projection length along the major axis cannot be evaluated independently of the value chosen for the length-to-thickness ratio, but it is probably less than 1.1 Å and greater than 0.6 Å. Application of the Kratky-Porod model to molecules for which the chain length is less than the persistence length must be treated with caution. For poly(butylisocyanate) the persistence length obtained from dilute solutions is 230 monomer units, although extrapolation of a wider concentration range to infinite dilution yields a value of 400 monomer units. Concentration has a marked effect on chain stiffness parameters (increasing apparent cylinder radii or decreasing persistence lengths) which is explained in terms of side-by-side dipole association.

Comparison of dielectric and viscoelastic relaxation in dilute solutions of some acrylic polymers

Measurements of dielectric relaxation and viscoelastic relaxation at audio- and radio-frequencies have been made on dilute solutions of polymethyl acrylate, polymethyl methacrylate, methyl methacrylate citraconic anhydride copolymers, poly n-butyl methacrylate and poly nonyl methacrylate (3,3,5-trimethyl hexyl). For polymers of molecular weight about 5 × 105 the viscoelastic relaxation occurs at a reduced frequency below about 102 to 103 Hz, and is slightly dependent on polymer structure.

Proton magnetic relaxation in dilute solutions of paramagnetic ions

The influence of hyperfine interaction on proton magnetic relaxation in dilute solutions of paramagnetic ions was investigated. Theoretical and experimental results were compared with the theory of Solomon and Bloembergen.

Proton Relaxation in Dilute Solutions of Cobalt(II) and Nickel(II) Ions in Methanol and the Rate of Methanol Exchange of the Solvation Sphere

The nuclear relaxation of the hydroxyl and methyl protons in methanol containing low concentrations of Co++ and Ni++ ions has been investigated between —80°C and +80°C. This work complements previous studies of the NMR spectra of the solvation complexes in similar solutions. Over the temperature range studied, the relaxation due to the dissolved paramagnetic ions changes over two or three orders of magnitude. This dependence, as well as a corresponding temperature dependence of the chemical shift of the methanol peaks, can be quantitatively interpreted in terms of chemical exchange of methanol molecules between the coordination sphere of the paramagnetic ions and the bulk methanol. It is found that the dominant exchange process involves whole methanol molecules, i.e., proton transfer is relatively unimportant. The exchange rate is characterized by ΔH‡=13.8 kcal mole—1 and ΔS‡=+7.2 eu for Co++ ions; and ΔH‡=15.8 kcal per mole and ΔS‡=+8.0 eu for Ni++ ions. The hyperfine interaction between the paramagnetic ion and a methanol molecule in the coordination sphere is for Co++:+4.1×105 cps for the CH3 protons, and +80×105 cps for the OH proton; the corresponding numbers for Ni++ are: +5.7×105 cps and +6.8×105 cps. Proton relaxation times of the methanol in the coordination sphere are also obtained.

Electron Spin Relaxation in Metal—Ammonia Solutions

The pulsed magnetic resonance technique was employed to measure the electron spin relaxation times T1 and T2 in solutions of sodium and potassium in liquid ammonia. Measurements were carried out over a range of temperatures from —50°C to +30°C, and for the concentration range of 10—4 to 10—2 mole metal per mole NH3. It was found that T1 and T2 are equal at all measured concentrations and temperatures, these times ranging from 1 to 3 μsec. For dilute solutions, the data are shown to be quantitatively consistent with the assumption that the relaxation is owing to the contact hyperfine interaction of the electrons with the N14 nuclei of ammonia. This interaction is modulated by the relative motion of the electrons and the ammonia molecules, the spin relaxation time being proportional to the modulation rate, as is typical in cases of extreme motional narrowing. An electron tunneling mechanism is proposed as a possible source of the modulation. That the electron-nitrogen hyperfine interaction is largely responsible for the spin relaxation in dilute solutions is verified by measurements on a sample prepared from isotopically substituted ammonia (N15H3). A qualitative explanation of the variation of the electron spin relaxation time with concentration is proposed.

Dielectric Relaxation of Dilute Solutions in the Millimeter Wave Region

The dielectric losses of benzophenone, diphenylether, diphenylamine, chlorobenzene, and aniline, measured at 12.33, 6.19, 3.08, and 2.47 mm wavelength in dilute benzene solutions, have been found to fit Debye type relaxation curves within the limits of experimental error. The distinctly lower relaxation time of diphenylether and of diphenylamine, compared to the one for benzophenone, can be explained by a high internal mobility of the phenyl rings in these two molecules. Similarly, the mobility of the amino group in aniline results in a decrease of the relaxation time, compared to the rigid chlorobenzene molecule.

Dielectric relaxation in dilute solutions of polar chain molecules

AbstractThe dielectric properties of polymer solutions are calculated on the assumption that each polymer molecule may be divided in N submolecules whose end‐to‐end distance shows Gaussian distribution. Electrical charges of alternating sign are attributed to the ends of these submolecules. The equations of motion are given for free‐drained structures. From these equations of motion the diffusion equation in configuration space is constructed. The average dipole moment can be calculated by a simple integration procedure. It is found that there should be two dispersion regions, one at low frequencies proportional to 1/N2 and one at high frequencies independent of N. The high frequency maximum in the loss curve has a shape which is very nearly that for a process with a single relaxation time.