Exchange Speed of Four-Component Nanorotors Correlates with Hammett Substituent Constants

Three distinct four-component supramolecular nanorotors were prepared, using, for the first time, bipyridine instead of phenanthroline stations in the stator. Following our established self-sorting protocol to multicomponent nanodevices, the nanorotors were self-assembled by mixing the stator, rotators with various pyridine head groups, copper(I) ions and 1,4-diazabicyclo[2.2.2]octane (DABCO). Whereas the exchange of a phenanthroline vs. a bipyridine station did not entail significant changes in the rotational exchange frequency, the para-substituents at the pyridine head group of the rotator had drastic consequences on the speed: 4-OMe (k298 = 35 kHz), 4-H (k298 = 77 kHz) and 4-NO2 (k298 = 843 kHz). The exchange frequency (log k) showed an excellent linear correlation with both the Hammett substituent constants and log K of the copper(I)–ligand interaction, proving that rotator–copper(I) bond cleavage is the key determining factor in the rate-determining step.

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Notable Substituent Effects on the Rate Constant of Thermal Denitrogenation of Cyclic Azoalkanes: Strong Evidence for a Stepwise Denitrogenation Mechanism

Australian Journal of Chemistry ◽

10.1071/ch10281 ◽

2010 ◽

Vol 63 (12) ◽

pp. 1615 ◽

Cited By ~ 10

Author(s):

Chizuko Ishihara ◽

Manabu Abe

Keyword(s):

Rate Constant ◽

Linear Correlation ◽

Strong Evidence ◽

Bond Cleavage ◽

Relative Rate ◽

Substituent Effects ◽

Relative Rate Constant ◽

Rate Determining Step ◽

Singlet Diradicals ◽

Type Radical

The thermal denitrogenation rates (k) of a series of 7,7-dimethoxy-1,4-diaryl-2,3-diazabicyclo[2.2.1]hept-2-ene derivatives 2 with a variety of aryl groups (p-CNC6H4, C6H5, p-MeC6H4, p-MeOC6H4) were determined to investigate the denitrogenation mechanism. A linear correlation (r = 0.988) between the relative rate-constant (log krel) of the denitrogenation reaction and Arnold’s σα• parameter for benzylic-type radical-stabilization was observed. However, the relative rate-constant was not correlated with the substituent effect on the lifetime of the resulting singlet diradicals DR2. These results indicate that the rate-determining step of denitrogenation of 7,7-dimethoxy-2,3-diazabicyclo[2.2.1]hept-2-ene derivatives involves stepwise C–N bond cleavage.

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Electron Donation by Low-Crystalline Ba-La-Ce Oxygen-Deficient Composite Oxide Accumulating on Ru Nanoparticles for Ammonia Synthesis under Mild Conditions

10.26434/chemrxiv.7763657.v1 ◽

2019 ◽

Author(s):

Katsutoshi Sato ◽

Shin-ichiro Miyahara ◽

Yuta Ogura ◽

Kotoko Tsujimaru ◽

Yuichiro Wada ◽

...

Keyword(s):

Ammonia Synthesis ◽

Bond Cleavage ◽

Synthesis Process ◽

Strong Electron ◽

Mild Conditions ◽

Ru Nanoparticles ◽

Rate Determining Step ◽

Highly Active ◽

Composite Oxides ◽

Low Crystalline

To mitigate global problems related to energy and global warming, it is helpful to develop an ammonia synthesis process using catalysts that are highly active under mild conditions. Here we show that the ammonia synthesis activity of Ru/Ba/LaCeOx pre-reduced at 700 °C is the highest reported among oxide-supported Ru catalysts. Our results indicate that low crystalline oxygen-deficient composite oxides, which include Ba2+, Ce3+ and La3+, with strong electron-donating ability, accumulate on Ru particles and thus promote N≡N bond cleavage, which is the rate determining step for ammonia synthesis.

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Electron Donation by Low-Crystalline Ba-La-Ce Oxygen-Deficient Composite Oxide Accumulating on Ru Nanoparticles for Ammonia Synthesis under Mild Conditions

10.26434/chemrxiv.7763657 ◽

2019 ◽

Author(s):

Katsutoshi Sato ◽

Shin-ichiro Miyahara ◽

Yuta Ogura ◽

Kotoko Tsujimaru ◽

Yuichiro Wada ◽

...

Keyword(s):

Ammonia Synthesis ◽

Bond Cleavage ◽

Synthesis Process ◽

Strong Electron ◽

Mild Conditions ◽

Ru Nanoparticles ◽

Rate Determining Step ◽

Highly Active ◽

Composite Oxides ◽

Low Crystalline

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Host density predicts the probability of parasitism by avian brood parasites

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.2018.0204 ◽

2019 ◽

Vol 374 (1769) ◽

pp. 20180204 ◽

Cited By ~ 3

Author(s):

Iliana Medina ◽

Naomi E. Langmore

Keyword(s):

Spatial Distribution ◽

Reproductive Success ◽

Host Species ◽

Field Data ◽

Host Density ◽

Brood Parasites ◽

Parasitism Rates ◽

Analyse Data ◽

First Time ◽

Determining Factor

The spatial distribution of hosts can be a determining factor in the reproductive success of parasites. Highly aggregated hosts may offer more opportunities for reproduction but can have better defences than isolated hosts. Here we connect macro- and micro-evolutionary processes to understand the link between host density and parasitism, using avian brood parasites as a model system. We analyse data across more than 200 host species using phylogenetic comparative analyses and quantify parasitism rate and host reproductive success in relation to spatial distribution using field data collected on one host species over 6 years. Our comparative analysis reveals that hosts occurring at intermediate densities are more likely to be parasitized than colonial or widely dispersed hosts. Correspondingly, our intraspecific field data show that individuals living at moderate densities experience higher parasitism rates than individuals at either low or high densities. Moreover, we show for the first time that the effect of host density on host reproductive success varies according to the intensity of parasitism; hosts have greater reproductive success when living at high densities if parasitism rates are high, but fare better at low densities when parasitism rates are low. We provide the first evidence of the trade-off between host density and parasitism at both macro- and micro-evolutionary scales in brood parasites. This article is part of the theme issue ‘The coevolutionary biology of brood parasitism: from mechanism to pattern’.

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Benzene solvent induced shifts of the proton magnetic resonance spectra of some benzene derivatives. Importance of charge effects

Canadian Journal of Chemistry ◽

10.1139/v70-485 ◽

1970 ◽

Vol 48 (18) ◽

pp. 2885-2895 ◽

Cited By ~ 12

Author(s):

R. Wasylishen ◽

T. Schaefer ◽

R. Schwenk

Keyword(s):

Magnetic Resonance ◽

Linear Correlation ◽

Proton Magnetic Resonance ◽

Steric Effects ◽

Benzene Derivatives ◽

Charge Effects ◽

Solvent Shift ◽

Solvent Shifts ◽

Substituent Constants ◽

Magnetic Resonance Spectra

The benzene solvent shifts of the proton magnetic resonance spectra of numerous polysubstituted benzene derivatives are measured with respect to cyclohexane as reference solvent. For many of these compounds, an additive scheme can be devised in which the effect of a substituent, X, on the solvent shift, Δ, of a proton is given by Δix so that Δ = Σx, Σi Δix where i = ortho, meta, or para. There is a linear correlation of Δmx or Δpx with Taft's substituent constants σm0 and σp0. It is suggested that charge effects are much more important than steric effects in determining both the magnitude and sign of Δ.

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A highly sensitive naked-eye fluorescent probe for trace hydrazine based on ‘C-CN’ bond cleavage

The Analyst ◽

10.1039/c8an01161c ◽

2018 ◽

Vol 143 (18) ◽

pp. 4354-4358 ◽

Cited By ~ 15

Author(s):

Hai Xu ◽

Zhen Huang ◽

Yaqian Li ◽

Biao Gu ◽

Zile Zhou ◽

...

Keyword(s):

Detection Limit ◽

Fluorescent Probe ◽

Water Samples ◽

Bond Cleavage ◽

Eye Detection ◽

Naked Eye ◽

Real Water Samples ◽

Highly Sensitive ◽

First Time ◽

Naked Eye Detection

The ‘C–CN’ bond cleavage was applied to the recognition of N2H4 for the first time; the obvious change in color could be used for “naked-eye” detection; the corresponding detection limit was found to be 5.81 × 10−8 M (1.65 ppb); the probe could be applied for N2H4 detection in real water samples.

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Inductive Effects on Molecular Ionization Potentials, XVIII Alkylpyridines and Alkylthiophenes. Molecular Orbital Calculations on Alkylbenzenes and Alkylpyridines

Zeitschrift für Naturforschung B ◽

10.1515/znb-1977-1013 ◽

1977 ◽

Vol 32 (10) ◽

pp. 1160-1164 ◽

Cited By ~ 5

Author(s):

Cyril Párkányi ◽

Leonard S. Levitt

Keyword(s):

Molecular Orbital ◽

Linear Correlation ◽

Molecular Orbitals ◽

Ionization Potentials ◽

Molecular Orbital Calculations ◽

Alkyl Groups ◽

Inductive Effects ◽

Substituent Constants ◽

Linear Correlations ◽

Molecular Ionization

Models of alkylbenzenes were treated by the HMO and SCF—MO methods and excellent linear correlations were found between the experimental ionization potentials, EI, and the energies of the highest occupied π-molecular orbitals calculated by the above-mentioned methods. A similar linear correlation was obtained for a group of methylpyridines. Also, the experimental ionization potentials of methylpyridines and alkylthiophenes have been linearly correlated with the sum of TAFT'S inductive substituent constants, ΣσI of the alkyl groups.

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Kinetics and Correlation Analysis of Reactivity in the Oxidation of Some α-Hydroxy Acids by Benzimidazolium Dichromate

Progress in Reaction Kinetics and Mechanism ◽

10.3184/146867818x15319903829236 ◽

2018 ◽

Vol 43 (3-4) ◽

pp. 300-314

Author(s):

Dinesh Panday ◽

Teena Kachawa ◽

Seema Kothari

Keyword(s):

Solvent Effect ◽

Mandelic Acid ◽

Bond Cleavage ◽

Hydroxy Acids ◽

Cyclic Transition ◽

Hydride Ion ◽

Rate Determining Step ◽

Reaction Constant ◽

Cyclic Transition State ◽

Hydride Ion Transfer

Kinetic and mechanistic studies of the oxidation of mandelic acid and nine monosubstituted mandelic acids by benzimidazolium dichromate (BIDC) in dimethyl sulfoxide are discussed with an emphasis on correlation of structure and reactivity. The reactions were of first order with respect to BIDC. However, Michaelis-Menten type kinetics were observed with respect to hydroxy acids. The reactions are catalysed by protons. The deuterium isotope effect for the oxidation of mandelic acid ( kH/ kD = 5.91 at 298 K) indicated an α-C-H bond cleavage in the rate-determining step. An analysis of the solvent effect showed that the role of cationsolvation is major. The reaction showed an excellent correlation with the Hammett σ values, the reaction constant being negative. Based on the kinetic data, analysis of the solvent effect and results of structure-reactivity correlation along with some non-kinetic parameters, a mechanism involving rate-determining oxidative decomposition of the complex through hydride-ion transfer via a cyclic transition state to give the corresponding oxoacid is suggested.

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Graptolites from the Lower–Middle Ordovician St. George and Table Head groups, western Newfoundland, and their correlation with trilobite, brachiopod, and conodont zones

Canadian Journal of Earth Sciences ◽

10.1139/e87-047 ◽

1987 ◽

Vol 24 (3) ◽

pp. 456-470 ◽

Cited By ~ 16

Author(s):

S. Henry Williams ◽

W. Douglas Boyce ◽

Noel P. James

Keyword(s):

Head Group ◽

Middle Ordovician ◽

Faunal Assemblages ◽

Head Groups ◽

Brachiopod Fauna ◽

Lower Slope

Faunal assemblages of the autochthonous, shelf carbonate sequences belonging to the St. George and Table Head groups are dominated by shelly macrofossils and conodonts. Rare, usually monotypic graptolitic horizons enable correlation with the allochthonous Cow Head Group, which was deposited on the middle to lower slope, and the shelly, conodont, and graptolitic zonal schemes elsewhere in North America.The Catoche Formation of the St. George Group is of Ibexian (Canadian) age and yields graptolites indicative of the Tetragraptus approximatus and Tetragraptus akzharensis zones (early Arenig). The basal Aguathuna Formation belongs to the Pendeograptus fruticosus Zone, whereas higher parts span the Ibexian–Whiterock boundary. Graptolites suggest that the Table Head Group entirely postdates the Cow Head Group. This is supported by a Whiterock (early Llanvirn) trilobite, conodont, and brachiopod fauna.

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Biosynthesis of Ether-Type Polar Lipids in Archaea and Evolutionary Considerations

Microbiology and Molecular Biology Reviews ◽

10.1128/mmbr.00033-06 ◽

2007 ◽

Vol 71 (1) ◽

pp. 97-120 ◽

Cited By ~ 212

Author(s):

Yosuke Koga ◽

Hiroyuki Morii

Keyword(s):

Mevalonate Pathway ◽

Polar Lipids ◽

In Vivo Studies ◽

Head Group ◽

Polar Head Group ◽

Phospholipid Synthesis ◽

Polar Head ◽

Head Groups

SUMMARY This review deals with the in vitro biosynthesis of the characteristics of polar lipids in archaea along with preceding in vivo studies. Isoprenoid chains are synthesized through the classical mevalonate pathway, as in eucarya, with minor modifications in some archaeal species. Most enzymes involved in the pathway have been identified enzymatically and/or genomically. Three of the relevant enzymes are found in enzyme families different from the known enzymes. The order of reactions in the phospholipid synthesis pathway (glycerophosphate backbone formation, linking of glycerophosphate with two radyl chains, activation by CDP, and attachment of common polar head groups) is analogous to that of bacteria. sn-Glycerol-1-phosphate dehydrogenase is responsible for the formation of the sn-glycerol-1-phosphate backbone of phospholipids in all archaea. After the formation of two ether bonds, CDP-archaeol acts as a common precursor of various archaeal phospholipid syntheses. Various phospholipid-synthesizing enzymes from archaea and bacteria belong to the same large CDP-alcohol phosphatidyltransferase family. In short, the first halves of the phospholipid synthesis pathways play a role in synthesis of the characteristic structures of archaeal and bacterial phospholipids, respectively. In the second halves of the pathways, the polar head group-attaching reactions and enzymes are homologous in both domains. These are regarded as revealing the hybrid nature of phospholipid biosynthesis. Precells proposed by Wächtershäuser are differentiated into archaea and bacteria by spontaneous segregation of enantiomeric phospholipid membranes (with sn-glycerol-1-phosphate and sn-glycerol-3-phosphate backbones) and the fusion and fission of precells. Considering the nature of the phospholipid synthesis pathways, we here propose that common phospholipid polar head groups were present in precells before the differentiation into archaea and bacteria.

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