scholarly journals Comparison of Structure and Local Dynamics of Two Peptide Dendrimers with the Same Backbone but with Different Side Groups in Their Spacers

Polymers ◽  
2020 ◽  
Vol 12 (8) ◽  
pp. 1657 ◽  
Author(s):  
Sofia Mikhtaniuk ◽  
Valeriy Bezrodnyi ◽  
Oleg Shavykin ◽  
Igor Neelov ◽  
Nadezhda Sheveleva ◽  
...  
Keyword(s):  
Ion Pairs ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
Peptide Dendrimers ◽  
Wide Range ◽  
Dynamics Method ◽  
Perform Computer Simulation ◽  
Good Agreement

In this paper, we perform computer simulation of two lysine-based dendrimers with Lys-2Lys and Lys-2Gly repeating units. These dendrimers were recently studied experimentally by NMR (Sci. Reports, 2018, 8, 8916) and tested as carriers for gene delivery (Bioorg. Chem., 2020, 95, 103504). Simulation was performed by molecular dynamics method in a wide range of temperatures. We have shown that the Lys-2Lys dendrimer has a larger size but smaller fluctuations as well as lower internal density in comparison with the Lys-2Gly dendrimer. The Lys-2Lys dendrimer has larger charge but counterions form more ion pairs with its NH 3 + groups and reduce the bare charge and zeta potential of the first dendrimer more strongly. It was demonstrated that these differences between dendrimers are due to the lower flexibility and the larger charge (+2) of each 2Lys spacers in comparison with 2Gly ones. The terminal CH2 groups in both dendrimers move faster than the inner CH2 groups. The calculated temperature dependencies of the spin-lattice relaxation times of these groups for both dendrimers are in a good agreement with the experimental results obtained by NMR.

Molecular Motion in Solid Tetraethyl -and Tetrapropylammonium Tetrafluoroborates

1995 ◽  
Vol 50 (6) ◽  
pp. 584-588 ◽  
Author(s):  
Barbara Szafrańska ◽  
Zdzisław Pająk
Keyword(s):  
Molecular Motion ◽  
Solid Phase ◽  
Complex Cation ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Fluorine Nmr ◽  
Spin Lattice ◽  
Second Moments ◽  
Wide Range

Abstract Proton and fluorine NMR second moments and spin-lattice relaxation times for polycrystalline tetraethyl-and tetrapropylammonium tetrafluoroborates have been measured over a wide range of temperatures. Solid-solid phase transitions were found for both compounds and confirmed by DSC. Methyl group C3 reorientation followed by more complex cation motions was evidenced in the low temperature phases. Overall cation reorientation characterises the high temperature phases of both compounds. Isotropic anion reorientation was found in both salts in both phases.

A133Cs NMR Spin-Lattice Relaxation Study in Incommensurate Cs2CdI4

2000 ◽  
Vol 55 (1-2) ◽  
pp. 339-342 ◽  
Author(s):  
Koh-ichi Suzuki ◽  
Shin'ichi Ishimaru ◽  
Ryuichi Ikeda
Keyword(s):  
Critical Exponent ◽  
Relaxation Times ◽  
Three Dimensional ◽  
Lattice Relaxation ◽  
Normal Phase ◽  
Incommensurate Phase ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
Relaxation Study ◽  
Good Agreement

133Cs NMR spin-lattice relaxation times(T1) in crystalline Cs2CdI4 were measured at 225 - 373 K. The critical exponent ( of T\ observed near the normal-incommensurate transition in the normal phase was determined to be 0.62 ± 0.03, in good agreement with the predicted value for three-dimensional XK-model. The frequency dependent T1 in the incommensurate phase could be explained by the fluctuation of amplitudon and small gap phason.

1H and 19 F NMR Study of Cation and Anion Motions in Guanidinium Hexafluorozirconate

1996 ◽  
Vol 51 (9) ◽  
pp. 991-996 ◽  
Author(s):  
M. Grottel ◽  
A. Kozak ◽  
Z. Pająk
Keyword(s):  
Solid Phase ◽  
Relaxation Times ◽  
High Mobility ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Fluorine Nmr ◽  
Spin Lattice ◽  
Nmr Study ◽  
Wide Range ◽  
Deuterated Analogue

Abstract Proton and fluorine NMR second moments and spin-lattice relaxation times of polycrystalline guanidinium hexafluorozirconate and its deuterated analogue were studied in laboratory (60 MHz) and rotating (H1 = 20 G) frames over a wide range of temperature. An analysis of the experimental results enabled us to reveal a dynamical inequivalence of two crystallographically independent cations and an unexpected high mobility of nonspherical anion dimers. A comparison of the ions dynamics in 2:1 complex studied with the guanidinium 1:1 and 3:1 complexes has shown a significant contribution of the hydrogen bonds to the potential barriers hindering the anion reorientations. At low temperatures a proton motion in the hydrogen bond and at 400 K a solid-solid phase transition have been discerned.

13C and 2H spin–lattice relaxation in solid adamantane

1980 ◽  
Vol 58 (7) ◽  
pp. 655-657 ◽  
Author(s):  
Roderick E. Wasylishen ◽  
Brian A. Pettitt
Keyword(s):  
Angular Correlation ◽  
Transition Point ◽  
Relaxation Times ◽  
Proton Nmr ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
Nmr Data ◽  
Plastic Phase ◽  
Good Agreement

Spin–lattice relaxation times for the 13C nuclei of adamantane and the 2H nuclei of adamantane-d16 are reported for most of the temperature range of the solid I (plastic) phase, and for the solid II phase just below the transition point. Angular correlation times are shown to be in good agreement with those previously obtained from proton nmr data by Resing.

14N Nuclear Magnetic Resonance Relaxation of the Nitrate Ion and Ion Pairing in Aqueous Solution

1995 ◽  
Vol 48 (2) ◽  
pp. 207 ◽  
Author(s):  
G Owens ◽  
P Guarilloff ◽  
BJ Steel ◽  
T Kurucsev
Keyword(s):  
Aqueous Solution ◽  
Ion Pairs ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Metal Nitrate ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
Fast Exchange ◽  
Resonance Relaxation ◽  
Two State Model

14 N n.m.r. spin-lattice relaxation times of four metal nitrate salts were measured as a function of concentration in aqueous solution. The concentration dependence of T1 was attributed to the formation of ion pairs with increasing concentration in these solutions. The T1 data, allowing for viscosity corrections, were treated by a two-state model of 'free' and 'bound' nitrate ions and to both possibilities of slow and fast exchange between the two states. In the equilibrium expressions estimates of the relevant activity coefficients were included. The slow nitrate exchange mechanism was favoured and the values obtained for this particular mechanism compared well with those derived from alternative measurements.

NH4+ Ion Motions in Some Ammonium Salts

1981 ◽  
Vol 36 (3) ◽  
pp. 205-209 ◽  
Author(s):  
Fevzi Köksal
Keyword(s):  
Hydrogen Bonding ◽  
Low Temperatures ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Experimental Results ◽  
Ammonium Salts ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
Unit Cells ◽  
Good Agreement

Spin-lattice relaxation times of protons in polycrystalline (NH4)2SO4, (NH3OH)2SO4, (NH4)2HPO4, NH4VO3, (NH4)2CrO4, (NH4)2C2O4 • H2O and NH4HF2 salts were measured over the temperature range 100-430 K. The double minima in T1 for the first three compounds were attributed to the nonequivalent NH4+ ions in the unit cells. In NH4VO3, the double minima were attributed to the reorientations about two and three fold axes. However only one minimum in T1 was observed for (NH4)2CrO4, (NH4)2C2O4 • H2O and NH4HF2 and the relaxation mechanisms for the first three compounds were attributed to random reorientations of NH4+ ions. The experimental results are in good agreement with the calculated values by using the existing theoretical expressions. The discrepancies between experimental and calculated values for (NH4)2HPO4 and NH4HF2 at low temperatures were attributed to the tightness of the hydrogen bonding at those temperatures

scholarly journals 81Br and 27Al NQR of AlBr3 · 2C5H5N, AlBr3 · 1.5CH3CN, and AlBr3 · 2CH3CN

1986 ◽  
Vol 41 (1-2) ◽  
pp. 230-235 ◽  
Author(s):  
Koji Yamada ◽  
Tsutomu Okuda ◽  
Hisao Negita
Keyword(s):  
Ion Pairs ◽  
Relaxation Times ◽  
Structural Models ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Reorientational Motion ◽  
Metal Ligands ◽  
Spin Lattice ◽  
Solid Compounds ◽  
Nqr Parameters

81Br NQR was studied in AlBr3 · 2C5H5N, AlBr3 · 1.5CH3CN, and AlBr3 · 2CH3CN. From the NQR spectra it is apparent that the solid compounds are build up by ion pairs [AlBr2(C5H5N )4+, AlBr4-], [Al(CH3CN)63+, 3AlBr4-], and [AlBr(CH3CN)52+, 2AlBr4-- CH3CN], respectively. 27Al NQR detected by SEDOR technique supports these structural models. Using these NQR parameters, the metal-ligands interactions in the six-coordinated complexes is discussed on the basis of the donor strength. In the case of AlBr3 ·2CH3CN two types of reorientational motion of the AlBr4- tetrahedra were detected from the spin lattice relaxation times and from fade-out phenomena of the 81Br NQR signals.

Molecular Motion in Solid Tetrabutylammonium Tetrafluoroborate

1991 ◽  
Vol 46 (6) ◽  
pp. 545-550 ◽  
Author(s):  
B. Szafranska ◽  
A. Kozak ◽  
Z. Pająk
Keyword(s):  
Relaxation Times ◽  
Activation Parameters ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Fluorine Nmr ◽  
Spin Lattice ◽  
Relaxation Effects ◽  
Second Moments ◽  
Wide Range ◽  
Tetrabutylammonium Tetrafluoroborate

Abstract Proton and fluorine NMR second moments and spin-lattice relaxation times for polycrystalline tetrabutylammonium tetrafluoroborate have been measured over a wide range of temperatures at several Larmor frequencies. An analysis of cross-relaxation effects results in a determination of activation parameters for anion and cation reorientations. Three solid phases characterized by different ion dynamics are evidence

35Cl NQR in Glassy Crystal of 2-chlorothiophene

2000 ◽  
Vol 55 (1-2) ◽  
pp. 183-185 ◽  
Author(s):  
Hiroki Fujimori ◽  
Tetsuo Asaji
Keyword(s):  
Activation Energy ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Half Maximum ◽  
Glass Transitions ◽  
Spin Lattice ◽  
Calorimetric Measurements ◽  
35Cl Nqr ◽  
Good Agreement

Stable crystalline 2-chlorothiophene has two glass transitions at 164 and 186 K. 35CI NQR measurements were carried out between 77 and 200 K. Two NQR signals with full widths of about 100 kHz at half maximum were observed in this temperature range. The spin-lattice relaxation times T1 were measured at the two peak frequencies. The activation energy obtained from the results of the T1 measurements showed a fairly good agreement with those estimated from calorimetric measurements.

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