α- and β-Cyclodextrin [2]rotaxanes with (diethylenetriamine)platinum(II) stoppers

2005 ◽  
Vol 83 (12) ◽  
pp. 2091-2097 ◽  
Author(s):  
Victor X Jin ◽  
Donal H Macartney ◽  
Erwin Buncel
Keyword(s):  
Self Assembly ◽  
Electrospray Mass Spectrometry ◽  
Platinum Complexes ◽  
H Nmr ◽  
Bridging Ligand ◽  
Dinuclear Platinum ◽  
End Groups ◽  
Group A ◽  
Kinetics Of ◽  
End Group

A series of dinuclear platinum(II) complexes, [(dien)Pt(NH2(CH2)nNH2)Pt(dien)]Cl4 (dien = diethylenetriamine, n = 8, 9, 10, and 12) and their corresponding [2]rotaxanes with α-cyclodextrin (α-CD), [(dien)Pt{NH2(CH2)nNH2·α-CD}Pt(dien)]Cl4, have been synthesized and characterized by 1H, 13C, and 195Pt NMR spectroscopy and electrospray mass spectrometry. The rotaxanes were prepared by reacting the {NH2(CH2)nNH2·α-CD} pseudorotaxanes with [Pt(dien)]Cl, to stopper the included linear α,ω-diaminoalkane chains with the inert Pt(II) end groups. The kinetics of the self-assembly and dissociation of the β-CD rotaxane, [(dien)Pt{NH2(CH2)10NH2·β-CD}Pt(dien)]4+, were investigated by using 1H NMR and are indicative of a slippage mechanism, owing to the comparable sizes of the β-CD cavity and the [Pt(dien)]+ end group. A relatively weak inclusion of the end group in the β-CD cavity precedes a thermally promoted passage of the β-CD over the [Pt(dien)]+ end group onto the hydrophobic polymethylene chain of the bridging ligand of the thread. Key words: rotaxanes, pseudorotaxanes, cyclodextrin, platinum complexes, slippage mechanism.

scholarly journals Kinetics of radical telomerization of acrylic acid in the presence of 1-octadecanethiol

2018 ◽  
Vol 90 (11) ◽  
pp. 1743-1754 ◽  
Author(s):  
Yaroslav O. Mezhuev ◽  
Oksana Y. Sizova ◽  
Yuri V. Korshak ◽  
Anna L. Luss ◽  
Ivan V. Plyushchii ◽  
...  
Keyword(s):  
Critical Micelle Concentration ◽  
Acrylic Acid ◽  
Monomer Concentration ◽  
Atom Economy ◽  
Exponential Factor ◽  
H Nmr ◽  
Radical Telomerization ◽  
Kinetics Of ◽  
End Group ◽  
C Nmr

AbstractThe oligomer of acrylic acid with a thiooctadecyl end-group was obtained by using octadecyl mercaptan as the chain-transfer agent. The resulting oligomer was characterized by 1H NMR and 13C NMR spectroscopy and critical micelle concentration was determined in aqueous solution. The order with respect to the initiator concentration was 0.5 and 1.6 with respect to the monomer concentration. The abnormal reaction order with respect to the monomer concentration was explained by participation in the chain propagation of unassociated and associated forms of acrylic acid, which were stabilized by formation of hydrogen bonds. The kinetic parameters of telomerization were determined. Telomerization with acrylic acid in the non-associated form had lower activation energy and lower pre-exponential factor than in the case of associated forms. The synthesis of the acrylic acid oligomer with a thiooctadecyl end-group having a low critical micelle concentration in water was carried out in one stage and corresponds to the concept of atom economy.

Kinetic and spectroscopic studies on α- and β-cyclodextrin rotaxanes with (µ-N,N′- bis(4-pyridinylmethylene)-α,ω-alkanediimine)bis[pentacyanoferrate(II)] threads

2005 ◽  
Vol 83 (3) ◽  
pp. 195-201 ◽  
Author(s):  
Victor X Jin ◽  
Donal H Macartney ◽  
Erwin Buncel
Keyword(s):  
Chemical Shift ◽  
Metal Complexes ◽  
Key Words ◽  
Rate Constants ◽  
Self Assembly ◽  
Spectroscopic Studies ◽  
Ligand Substitution ◽  
H Nmr ◽  
End Groups ◽  
The Stability

[2]Pseudorotaxanes have been prepared by threading N,N′-bis(4-pyridinylmethylene)-1,2-ethanediimine (L2), -1,4-butanediimine (L4), and -1,6-hexanediimine (L6) ligands through α-cyclodextrin (α-CD) and β-cyclodextrin (β-CD), and have subsequently been converted to the corresponding [2]rotaxane species by coordinating bulky [Fe(CN)5]3– end groups. The stability constants for the [2]pseudorotaxanes were determined by 1H NMR chemical shift titrations and increase with the polymethylene chain length n. The rate constants for both the formation of the [Fe(CN)5(Ln)]3– complexes from the [Fe(CN)5OH2]3– ion and Ln, and the rate constants for the dissociation of Ln from the metal complexes, exhibit significant diminutions in the presence of α- and β-CD, owing to inclusions of the free and coordinated ligands, respectively. The lability of the iron(II)–pyridine bonds also permits the spontaneous self-assembly of the [2]rotaxane upon the addition of cyclodextrin to the iron dimer complexes. The mechanism for this process involves the rate-determining dissociation of a [Fe(CN)5]3– unit from [(NC)5Fe(Ln)Fe(CN)5]6–, followed by CD inclusion of the Ln ligand to form a semirotaxane, and subsequent recomplexation by the [Fe(CN)5OH2]3– ion. Key words: cyclodextrins, rotaxanes, pentacyanoferrate(II), ligand substitution, kinetics.

Kinetics of the self-assembly of bold alpha -cyclodextrin [2]pseudorotaxanes with polymethylene threads bearing quaternary ammonium and phosphonium end groups

1998 ◽  
Vol 76 (6) ◽  
pp. 843-850
Author(s):  
Angela P Lyon ◽  
Nicola J Banton ◽  
Donal H Macartney
Keyword(s):  
Rate Constant ◽  
Self Assembly ◽  
Elevated Temperatures ◽  
Formation Rate ◽  
Minor Effect ◽  
Prolonged Heating ◽  
End Groups ◽  
A Minor ◽  
Kinetics Of

The kinetics and mechanism of the formation and dissociation of a series of [2]pseudorotaxanes, comprised of α -cyclodextrin (α -CD) as the cyclic component and the ([Me3N(CH2)nNMe3]2+ (n = 8-12), [Me2EtN(CH2)10NEtMe2]2+, and [Me3P(CH2)10PMe3]2+) dications as the threads, were determined by means of 1H and 31P NMR in aqueous solution. The length of the polymethylene chain (n) of the thread, which has a minor effect on the rate constant for pseudorotaxane formation, is important in the kinetics of the dissociation reactions, with the longer, more hydrophobic chains resulting in slower pseudorotaxane dissociation. The replacement of one methyl substitutent by an ethyl group in each of the end groups on the [Me3N(CH2)10NMe3]2+ thread results in a 30-fold decrease in the formation rate constant. Replacements, by ethyls, of two or all of the methyl substitutents prevent the formation of the pseudorotaxane, even after prolonged heating. The pseudorotaxane containing the {Me3P(CH2)10PMe3.; α-CD}2+ thread forms only at elevated temperatures by a slippage mechanism, and the rate constant for its self-assembly at 75°C (8 x 10-5 M-1 s-1) is more than 106 smaller than the rate constant at 75°C (200 M-1 s-1) extrapolated for the corresponding {Me3N(CH2)10NMe3 . α -CD}2+complex. The enthalpies and entropies of activation for the formation and dissociation of the [2]pseudorotaxanes decrease with an increase in the size and hydrophobicity of the end groups, suggesting a reduced role of desolvation of the quaternized atoms in the threading or dethreading processes.Key words: pseudorotaxane, α -cyclodextrin, kinetics, self-assembly, slippage, supramolecular.

pH-sensitivity and Conformation Change of the N-terminal Methacrylated Peptide VK20

MRS Advances ◽  
2017 ◽  
Vol 2 (47) ◽  
pp. 2571-2579 ◽  
Author(s):  
Zewang You ◽  
Marc Behl ◽  
Candy Löwenberg ◽  
Andreas Lendlein
Keyword(s):  
Conformational Changes ◽  
Self Assembly ◽  
Terminal Group ◽  
Random Coil ◽  
Coupling Reactions ◽  
End Group Functionalization ◽  
Physically Crosslinked ◽  
Influence Of Ph ◽  
Kinetics Of ◽  
End Group

ABSTRACTN-terminal methacrylation of peptide MAX1, which is capable of conformational changes by variation of the pH, results in a peptide, named VK20. Increasing the reactivity of this terminal group enables further coupling reactions or chemical modifications of the peptide. However, this end group functionalization may influence the ability of conformational changes of VK20, as well as its properties. In this paper, the influence of pH on the transition between random coil and ß-sheet conformation of VK20, including the transition kinetics, were investigated. At pH values of 9 and higher, the kinetics of ß-sheet formation increased for VK20, compared to MAX1. The self-assembly into ß-sheets recognized by the formation of a physically crosslinked gel was furthermore indicated by a significant increase of G’. An increase in pH (from 9 to 9.5) led to a faster gelation of the peptide VK20. Simultaneously, G’ was increased from 460 ± 70 Pa (at pH 9) to 1520 ± 180 Pa (at pH 9.5). At the nanoscale, the gel showed a highly interconnected fibrillary network structure with uniform fibril widths of approximately 3.4 ± 0.5 nm (N=30). The recovery of the peptide conformation back to random coil resulted in the dissolution of the gel, whereby the kinetics of the recovery depended on the pH. Conclusively, the ability of MAX1 to undergo conformational changes was not affected by N-terminal methacrylation whereas the kinetics of pH-sensitive ß-sheet formations has been increased.

scholarly journals Chimeric Platinum-Polyamines and DNA Binding. Kinetics of DNA Interstrand Cross-Link Formation by Dinuclear Platinum Complexes with Polyamine Linkers

2012 ◽  
Vol 134 (16) ◽  
pp. 7135-7146 ◽  
Author(s):  
Rasha A. Ruhayel ◽  
Janina S. Langner ◽  
Matilda-Jane Oke ◽  
Susan J. Berners-Price ◽  
Ibrahim Zgani ◽  
...  
Keyword(s):  
Dna Binding ◽  
Platinum Complexes ◽  
Binding Kinetics ◽  
Cross Link ◽  
Dinuclear Platinum ◽  
Kinetics Of ◽  
Dinuclear Platinum Complexes ◽  
Link Formation

In situ Time-Resolved Small-Angle X-ray Scattering Reveals the Formation Kinetics of Polyelectrolyte Complex Micelles

2019 ◽  
Author(s):  
Hao Wu ◽  
Jeffrey Ting ◽  
Siqi Meng ◽  
Matthew Tirrell
Keyword(s):  
Small Angle ◽  
Self Assembly ◽  
Electrostatic Interactions ◽  
Polyelectrolyte Complex ◽  
Time Resolved ◽  
X Ray ◽  
X Ray Scattering ◽  
Kinetics Of ◽  
Ray Scattering

We have directly observed the <i>in situ</i> self-assembly kinetics of polyelectrolyte complex (PEC) micelles by synchrotron time-resolved small-angle X-ray scattering, equipped with a stopped-flow device that provides millisecond temporal resolution. This work has elucidated one general kinetic pathway for the process of PEC micelle formation, which provides useful physical insights for increasing our fundamental understanding of complexation and self-assembly dynamics driven by electrostatic interactions that occur on ultrafast timescales.

Rotationsbarriere der Endgruppen bei Poly- methinoxonolen verschiedener Kettenlänge / Rotation Barrier of the End Groups of Polymethine Oxonols with Different Chain Lengths

1976 ◽  
Vol 31 (8) ◽  
pp. 1017-1018 ◽  
Author(s):  
H. Oehling ◽  
F. Baer
Keyword(s):  
Nmr Spectra ◽  
Rotation Barrier ◽  
Free Enthalpy ◽  
Temperature Dependent ◽  
Restricted Rotation ◽  
H Nmr ◽  
Enthalpy Of Activation ◽  
End Groups ◽  
Electron Contribution ◽  
Chain Lengths

Abstract Polymethine oxonols show temperature dependent 1H-NMR-spectra because of restricted rotation of the end groups. The dependence of the value of the corresponding free enthalpy of activation AGt on the length of the poly-methine chain can be explained by the change of the π-electron contribution to ⊿G≠.

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