The role of ‘internal’ and ‘external’ Lewis bases in controlling the stereochemistry of highly active Ziegler–Natta catalysts

1987 ◽  
pp. 94-95 ◽  
Author(s):  
Francesco Ciardelli ◽  
Carlo Carlini ◽  
Angelina Altomare ◽  
Francesco Menconi
Keyword(s):  
Lewis Bases ◽  
Highly Active ◽  
Ziegler Natta Catalysts

scholarly journals The role of JrPPOs in the browning of walnut explants

2021 ◽  
Vol 21 (1) ◽  
Author(s):  
Shugang Zhao ◽  
Hongxia Wang ◽  
Kai Liu ◽  
Linqing Li ◽  
Jinbing Yang ◽  
...  
Keyword(s):  
Tissue Culture ◽  
Production Efficiency ◽  
Phenolic Content ◽  
Leaf Tissue ◽  
Limiting Factor ◽  
Mature Leaves ◽  
Survival Percentage ◽  
Highly Active ◽  
Young Leaves

Abstract Background Tissue culture is an effective method for the rapid breeding of seedlings and improving production efficiency, but explant browning is a key limiting factor of walnut tissue culture. Specifically, the polymerization of PPO-derived quinones that cause explant browning of walnut is not well understood. This study investigated explants of ‘Zanmei’ walnut shoot apices cultured in agar (A) or vermiculite (V) media, and the survival percentage, changes in phenolic content, POD and PPO activity, and JrPPO expression in explants were studied to determine the role of PPO in the browning of walnut explants. Results The results showed that the V media greatly reduced the death rate of explants, and 89.9 and 38.7% of the explants cultured in V media and A media survived, respectively. Compared with that of explants at 0 h, the PPO of explants cultured in A was highly active throughout the culture, but activity in those cultured in V remained low. The phenolic level of explants cultured in A increased significantly at 72 h but subsequently declined, and the content in the explants cultured in V increased to a high level only at 144 h. The POD in explants cultured in V showed high activity that did not cause browning. Gene expression assays showed that the expression of JrPPO1 was downregulated in explants cultured in both A and V. However, the expression of JrPPO2 was upregulated in explants cultured in A throughout the culture and upregulated in V at 144 h. JrPPO expression analyses in different tissues showed that JrPPO1 was highly expressed in stems, young leaves, mature leaves, catkins, pistils, and hulls, and JrPPO2 was highly expressed in mature leaves and pistils. Moreover, browning assays showed that both explants in A and leaf tissue exhibited high JrPPO2 activity. Conclusion The rapid increase in phenolic content caused the browning and death of explants. V media delayed the rapid accumulation of phenolic compounds in walnut explants in the short term, which significantly decreased explants mortality. The results suggest that JrPPO2 plays a key role in the oxidation of phenols in explants after branch injury.

scholarly journals A Mini Review on Doped Nickel-Based Electrocatalysts for Hydrogen Evolution Reaction

Energies ◽  
2020 ◽  
Vol 13 (18) ◽  
pp. 4651
Author(s):  
Yilin Deng ◽  
Wei Lai ◽  
Bin Xu
Keyword(s):  
Hydrogen Evolution ◽  
Hydrogen Evolution Reaction ◽  
Water Electrolysis ◽  
Energy Resources ◽  
Alkaline Media ◽  
Hydrogen Energy ◽  
Heteroatom Doping ◽  
Highly Active ◽  
Production Of Hydrogen

The energy crisis and environmental pollution have attracted much attention and have promoted researches on clean and sustainable hydrogen energy resources. With the help of highly active and stable transition metal nickel-based catalysts, the production of hydrogen from water electrolysis from electrolyzed water has become an inexpensive and efficient strategy for generating hydrogen energy. In recent years, heteroatom doping has been found to be an effective strategy to improve the electrocatalytic hydrogen evolution reaction (HER) performances of nickel-based catalysts in acidic, neutral, and alkaline media. This review will highlight many recent works of inexpensive and readily available heteroatom-doped nickel-based HER catalysts. The evaluation methods for the performances of HER catalyst will be briefly described, and the role of heteroatom doping and its application in nickel-based catalyst will be summarized. This article will also point out some heteroatom doping strategies, which may provide references and inspire the design of other catalysts with dopants.

scholarly journals The essential role of physiotherapists in providing rehabilitation services to people living with HIV in South Africa

2013 ◽  
Vol 69 (1) ◽  
Author(s):  
S. Cobbing ◽  
V. Chetty ◽  
J. Hanass-Hancock ◽  
J. Jelsma ◽  
H. Myezwa ◽  
...  
Keyword(s):  
South Africa ◽  
South African ◽  
Policy Formulation ◽  
People Living With Hiv ◽  
Highly Active ◽  
Hiv Epidemic ◽  
Wide Range ◽  
Living With Hiv ◽  
Education Courses

Despite increased access to highly active anti-retroviral therapy (HAART) in South Africa, there remains a high risk of people living with HIV (PLHIV) developing a wide range of disabilities. Physiotherapists are trained to rehabilitate individuals with the disabilities related to HIV. Not only can South African physiotherapists play a significant role in improving the lives of PLHIV, but by responding proactively to the HIV epidemic they can reinforce the relevance and value of the profession in this country at a time when many newly qualified therapists are unable to secure employment. This paper offers recommendations that may help to fuel this response. These ideas include enhancing HIV curricula at a tertiary level, designing and attending continuing education courses on HIV and researching Southern African rehabilitation interventions for HIV at all levels of practice. furthermore, it is vital that physiotherapists are at the forefront of directing multi-disciplinary responses to the rehabilitation of PLHIV in order to influence stakeholders who are responsible for health policy formulation. it is hoped that this paper stimulates discussion and further ideas amongst physiotherapists and other health professionals in order to improve the quality and access to care available to PLHIV in South Africa.

scholarly journals Engineering Mesoporous NiO with Enriched Electrophilic Ni3+ and O− toward Efficient Oxygen Evolution

Catalysts ◽  
2018 ◽  
Vol 8 (8) ◽  
pp. 310 ◽  
Author(s):  
Xiu Liu ◽  
Zhi-Yuan Zhai ◽  
Zhou Chen ◽  
Li-Zhong Zhang ◽  
Xiu-Feng Zhao ◽  
...  
Keyword(s):  
Surface Area ◽  
Oxygen Evolution ◽  
Low Cost ◽  
Large Surface Area ◽  
Nucleophilic Attack ◽  
Title Reaction ◽  
Highly Active ◽  
Decomposition Of Water ◽  
Uniform Mesopores

Tremendous efforts have been devoted to develop low-cost and highly active electrocatalysts for oxygen evolution reaction (OER). Here, we report the synthesis of mesoporous nickel oxide by the template method and its application in the title reaction. The as-prepared mesoporous NiO possesses a large surface area, uniform mesopores, and rich surface electrophilic Ni3+ and O− species. The overpotential of meso-NiO in alkaline medium is 132 mV at 10 mA cm−1 and 410 mV at 50 mA cm−1, which is much smaller than that of the other types of NiO samples. The improvement in the OER activity can be ascribed to the synergy of the large surface area and uniform mesopores for better mass transfer and high density of Ni3+ and O− species favoring the nucleophilic attack by OH− to form a NiOOH intermediate. The reaction process and the role of electrophilic Ni3+ and O− were discussed in detail. This results are more conducive to the electrochemical decomposition of water to produce hydrogen fuel as a clean and renewable energy.

The role of the Lewis acid−base properties in the supramolecular association of 1,2,5-chalcogenadiazoles

2013 ◽  
Vol 91 (5) ◽  
pp. 338-347 ◽  
Author(s):  
Anthony F. Cozzolino ◽  
Philip J.W. Elder ◽  
Lucia Myongwon Lee ◽  
Ignacio Vargas-Baca
Keyword(s):  
Topological Analysis ◽  
Structural Features ◽  
Lewis Acidity ◽  
Electron Localization ◽  
Dispersion Forces ◽  
Acid Base ◽  
Lewis Bases ◽  
The Individual ◽  
Secondary Bonding

The secondary bonding interactions that link the supramolecular structures assembled by 1,2,5-chalcogenadiazoles were analyzed through explicit orthogonalization of molecular orbitals (NBO), topological analysis of the electron density (AIM), and the electron localization function (ELF). The results of these analyses are consistent with a bonding description that attributes important covalent and electrostatic character to these interactions. Application of these analyses to the individual molecules highlighted the structural features from which each of those contributions originates, namely the polarity and modest strength of the E–N bond. Both of these effects increase along the series S, Se, Te. Perturbations to the heterocycle electronic structure that result in a weaker and more polar E–N bond cause an increase in the Lewis acidity at the chalcogen centre, which in turn leads to stronger secondary bonding interactions with Lewis bases. Additionally, the contribution of dispersion forces is not negligible and is most important in the case of sulfur.

Spectroscopic Investigation of Heterogeneous Ziegler-Natta Catalysts: Ti and Mg Chloride Tetrahydrofuranates, Their Interaction Compound, and the Role of the Activator

2011 ◽  
Vol 17 (31) ◽  
pp. 8648-8656 ◽  
Author(s):  
Kalaivani Seenivasan ◽  
Anna Sommazzi ◽  
Francesca Bonino ◽  
Silvia Bordiga ◽  
Elena Groppo
Keyword(s):  
Spectroscopic Investigation ◽  
Ziegler Natta Catalysts

scholarly journals Extending the Definition of the GyrB Quinolone Resistance-Determining Region in Mycobacterium tuberculosis DNA Gyrase for Assessing Fluoroquinolone Resistance in M. tuberculosis

2012 ◽  
Vol 56 (4) ◽  
pp. 1990-1996 ◽  
Author(s):  
Alix Pantel ◽  
Stéphanie Petrella ◽  
Nicolas Veziris ◽  
Florence Brossier ◽  
Sylvaine Bastian ◽  
...  
Keyword(s):  
Mycobacterium Tuberculosis ◽  
Hot Spot ◽  
Dna Gyrase ◽  
Quinolone Resistance ◽  
Fluoroquinolone Resistance ◽  
Wild Type ◽  
Content Type ◽  
Highly Active ◽  
Definition Of

ABSTRACTFluoroquinolone (FQ) resistance is emerging inMycobacterium tuberculosis. The main mechanism of FQ resistance is amino acid substitution within the quinolone resistance-determining region (QRDR) of the GyrA subunit of DNA gyrase, the sole FQ target inM. tuberculosis. However, substitutions in GyrB whose implication in FQ resistance is unknown are increasingly being reported. The present study clarified the role of four GyrB substitutions identified inM. tuberculosisclinical strains, two located in the QRDR (D500A and N538T) and two outside the QRDR (T539P and E540V), in FQ resistance. We measured FQ MICs and also DNA gyrase inhibition by FQs in order to unequivocally clarify the role of these mutations in FQ resistance. Wild-type GyrA, wild-type GyrB, and mutant GyrB subunits produced from engineeredgyrBalleles by mutagenesis were overexpressed inEscherichia coli, purified to homogeneity, and used to reconstitute highly active gyrase complexes. MICs and DNA gyrase inhibition were determined for moxifloxacin, gatifloxacin, ofloxacin, levofloxacin, and enoxacin. All these substitutions are clearly implicated in FQ resistance, underlining the presence of a hot spot region housing most of the GyrB substitutions implicated in FQ resistance (residues NTE, 538 to 540). These findings help us to refine the definition of GyrB QRDR, which is extended to positions 500 to 540.

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