Die freien OH-Gruppen in konzentrierten wäßrigen Elektrolytlösungen — eine Infrarot-spektroskopische Untersuchung an Polyelektrolyten

1966 ◽  
Vol 21 (9) ◽  
pp. 1391-1394 ◽  
Author(s):  
G. Zundel ◽  
A. Murr
Keyword(s):  
Coordination Sphere ◽  
Rate Constants ◽  
Thermal Rearrangement ◽  
Hydrogen Bridge ◽  
Oh Groups ◽  
Water Of Hydration ◽  
Stretching Vibration

We have investigated the hydration of polyelectrolyt films 5 μ thick. A band sometimes observed at 3615 cm -1 is to be ascribed to the stretching vibration of the free OH groups in the network of the hydrate structures. The intensity of this band shows us that the number of free OH groups in the network of the hydrate structure is the smaller, firstly the more the hydrogen bridge donor affinity of the OH groups of the molecules of water of hydration is enhanced by the interaction of the cations with water, and secondly the larger the hydrogen bridge acceptor affinity of the anions is. Comparison with the rate constants of the rearrangement of the molecules of water of hydration in the inner coordination sphere shows that the free OH groups are those temporarily freed in the thermal rearrangement.

scholarly journals Beyond the Active Site: Mechanistic Investigations of the Role of the Secondary Coordination Sphere and Beyond on Multi-Electron Electrocatalytic Reactions and Their Relations Between Kinetics and Thermodynamics

2020 ◽  
Author(s):  
Vincent Wang
Keyword(s):  
Thermodynamic Parameters ◽  
Coordination Sphere ◽  
Active Site ◽  
Rate Constants ◽  
Reduction Reaction ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Secondary Coordination Sphere ◽  
Catalytic Rate ◽  
Rate Limiting

<p>The development of an electrocatalyst with a rapid turnover frequency, low overpotential and long-term stability is highly desired for fuel-forming reactions, such as water splitting and CO<sub>2</sub> reduction. The findings of the scaling relationships between the catalytic rate and thermodynamic parameters over a wide range of electrocatalysts in homogeneous and heterogeneous systems provide useful guidelines and predictions for designing better catalysts for those redox reactions. However, such relationships also suggest that a catalyst with a high catalytic rate is typically associated with a high overpotential for a given reaction. Inspired by enzymes, the introduction of additional interactions through the secondary coordination sphere beyond the active site, such as hydrogen-bonding or electrostatic interactions, have been shown to offer a promising avenue to disrupt these unfavorable relationships. Herein, we further investigate the influence of these cooperative interactions on the faster chemical steps, in addition to the rate-limiting step widely examined before, for molecular electrocatalysts with the structural and electronic modifications designed to facilitate the dioxygen reduction reaction, CO<sub>2</sub> reduction reaction and hydrogen evolving reaction. Based on the electrocatalytic kinetic analysis, the rate constants for faster chemical steps and their correlation with the corresponding thermodynamic parameters are evaluated. The results suggest that the effects of the secondary coordination sphere and beyond on these fuel-forming reactions are not necessarily beneficial for promoting all chemical steps and no apparent relation between rate constants and thermodynamic parameters are found in some cases studied here, which may implicate the design of electrocatalysts in the future. Finally, these analyses demonstrate that the characteristic features for voltammograms and foot-of-the-wave-analysis plots are associated with the specific kinetic phenomenon among these multi-electron electrocatalytic reactions, which provides a useful framework to probe the insights of chemical and electronic modifications on the catalytic steps quantitatively (i.e. kinetic rate constants) and to optimize some of critical steps beyond the rate-limiting step.</p>

scholarly journals Synthese und Eigenschaften unsymmetrischer Diketopiperazine des Cysteins / Synthesis and Properties of Unsymmetrical Diketopiperazines of Cysteine

1971 ◽  
Vol 26 (11) ◽  
pp. 1144-1151 ◽  
Author(s):  
V. Rossbach, ◽  
H. Wenck
Keyword(s):  
Ir Spectra ◽  
Functional Groups ◽  
Hydrogen Bridge ◽  
Subsequent Reduction ◽  
Oh Groups ◽  
Nucleophilic Reactivity ◽  
Kinetics Of

The synthesis of cyclo (c)-cys-ser, c-cys-asp and c-cys-try via cyclisation of the corresponding cystin-dipeptidesters and subsequent reduction of the disulfides of the diketopiperazines with mercapto-ethanole is described. The ir-spectra of the cyclo-dipeptides and their disulfides were studied with regard to interactions of the functional groups. The spectra indicate a strong hydrogen bridge between the OH-groups of c-cys-ser-disulfide and interactions between the SH and other functional groups of the above mentioned diketopiperazines. The kinetics of the reaction of cysdiketopiperazines with N-ethylmaleimide and p-nitro-phenylacetate were studied. The SH-groug of cys-diketopiperazines has a greater nucleophilic reactivity towards p-nitro-phenylacetate than was expected on the basis of the pKSH-values.

scholarly journals Darstellung und Struktur dreier verschiedener Bis(ethylendiamin)-kupfer(II)-tetraborate / Preparation and Structure of Three Different Bis(ethylenediamine) Copper(II) Tetraborates

1994 ◽  
Vol 49 (5) ◽  
pp. 627-634 ◽  
Author(s):  
Mahmood Shakibaie-Moghadam ◽  
Ulrich Timper ◽  
Gert Heller
Keyword(s):  
Crystal Structure ◽  
Boric Acid ◽  
Coordination Sphere ◽  
Oh Groups ◽  
Jahn Teller

Three different bis(ethylenediamine) Copper(II) tetraborates have been prepared: Cu(en)2[B4O5(OH)4] · 2B(OH)3 (A), 2{Cu(en)2B(OH)3 · H2O[B4O5(OH)4]} · H2O (B) and {Cu(H2O)2[B4O5(OH)4]2}(μ-H2O){Ag(en)2} · (μ-H2O){Na(H2O)2) (C). The crystal structure analyses of A (monoclinic, P21/c, a = 1282.5(1), b = 1020.8(1), c = 1510.5(2) pm; β = 96.66(1)°, Z = 4), B (monoclinic, Pc, a = 1254.4(1), b = 914.1(1), c = 1594.2(2) pm; β = 94.79(1)°, Z = 2) and C (triclinic, P1, a = 846.3(3), b = 917.9(3), c = 928.1(7) pm; α = 93.71(6)°, β = 104.79(3)°, γ = 103.23(2)°; Z = 1) show that all compounds contain the tetraborate ion [B4O5(OH)4]2-. In A and B, there are tetraborate ions and boric acid molecules. The coordination sphere of the Cu2+ ion is Jahn-Teller distorted, coordinated by 2 en groups with 4 Cu-N distances between 196 and 206 pm, as well as by 2 OH groups with Cu-O distances of 251 to 274 pm. In C, the Cu2+ ion is surrounded by 6 OH groups, and the Ag+ ion by 2 en and 2μ-H2O molecules.

Influence of Second Coordination Sphere on the Kinetics of Electrode Reactions in Molten Salts

2002 ◽  
Vol 57 (9-10) ◽  
pp. 85-88 ◽  
Author(s):  
S. A. Kuznetsov ◽  
M. Gaune-Escarda
Keyword(s):  
Coordination Sphere ◽  
Rate Constants ◽  
Diffusion Coefficients ◽  
Redox Reaction ◽  
Alkali Halide ◽  
Molten Salts ◽  
Electrode Reactions ◽  
Standard Rate ◽  
Second Coordination Sphere ◽  
Kinetics Of

The influence of the second coordination sphere on the electroreduction of hafnium complexes to hafnium metal, and the redox reaction Eu(III) + e⇔ ,Eu(II) in alkali halide melts was studied. It is shown that the large caesium cations in the melt reduce the transfer and the diffusion coefficients as well as the heterogeneous rate constants for charge transfer of hafnium complexes. The standard rate constants for the europium redox reaction increase when going from NaCl-KCl to CsCl. The different influence of the second coordination sphere on the electrode reactions is explained by different limitation stages for electron transfer.

Concerning the influence of inert gas adsorption on the infrared spectrum of OH groups on powdered silica

1976 ◽  
Vol 54 (9) ◽  
pp. 1388-1393 ◽  
Author(s):  
J. G. Roth ◽  
M. J. Dignam
Keyword(s):  
Optical Model ◽  
Gas Adsorption ◽  
Inert Gas ◽  
Center Frequency ◽  
Hydroxyl Groups ◽  
Oh Groups ◽  
Band Area ◽  
Stretching Vibration ◽  
Orientational Distribution ◽  
Measured Change

McDonald's study of the absorption band at 3749 cm−1, due to the O—H stretching vibration of hydroxyl groups on outgassed powdered silica, revealed substantial changes in center frequency and band area upon adsorption of Ar. The main features of these changes are accounted for here using an optical model for porous adsorbent–adsorbate systems due to Dignam, Rao, and Roth. The possibility of using the measured change in band intensity on adsorbing an inert gas, as a general indicator of the orientational distribution of the adsorbed species responsible for the band, is noted.

scholarly journals Double Proton Tautomerism via Intra- or Intermolecular Pathways? The Case of Tetramethyl Reductic Acid Studied by Dynamic NMR: Hydrogen Bond Association, Solvent and Kinetic H/D Isotope Effects

Molecules ◽  
2021 ◽  
Vol 26 (14) ◽  
pp. 4373
Author(s):  
Hans-Heinrich Limbach ◽  
Simone Baumgärtner ◽  
Roland Franke ◽  
Ferdinand Männle ◽  
Gerd Scherer ◽  
...  
Keyword(s):  
Rate Constants ◽  
Chemical Shifts ◽  
Isotope Effects ◽  
Intrinsic Rate ◽  
Tunneling Model ◽  
Oh Groups ◽  
First Order ◽  
Order Rate ◽  
Pseudo First Order ◽  
Hydrogen Bonded

Using dynamic liquid-state NMR spectroscopy a degenerate double proton tautomerism was detected in tetramethyl reductic acid (TMRA) dissolved in toluene-d8 and in CD2Cl2. Similar to vitamin C, TMRA belongs to the class of reductones of biologically important compounds. The tautomerism involves an intramolecular HH transfer that interconverts the peripheric and the central positions of the two OH groups. It is slow in the NMR time scale around 200 K and fast at room temperature. Pseudo-first-order rate constants of the HH transfer and of the HD transfer after suitable deuteration were obtained by line shape analyses. Interestingly, the chemical shifts were found to be temperature dependent carrying information about an equilibrium between a hydrogen bonded dimer and a monomer forming two weak intramolecular hydrogen bonds. The structures of the monomer and the dimer are discussed. The latter may consist of several rapidly interconverting hydrogen-bonded associates. A way was found to obtain the enthalpies and entropies of dissociation, which allowed us to convert the pseudo-first-order rate constants of the reaction mixture into first-order rate constants of the tautomerization of the monomer. Surprisingly, these intrinsic rate constants were the same for toluene-d8 and CD2Cl2, but in the latter solvent more monomer is formed. This finding is attributed to the dipole moment of the TMRA monomer, compensated in the dimer, and to the larger dielectric constant of CD2Cl2. Within the margin of error, the kinetic HH/HD isotope effects were found to be of the order of 3 but independent of temperature. That finding indicates a stepwise HH transfer involving a tunnel mechanism along a double barrier pathway. The Arrhenius curves were described in terms of the Bell–Limbach tunneling model.

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