Synthetical Applications of Activated Metal Catalysts. XVI. The Role of Hydrogen in the Formation of 2,2'-Bipyridyl from Pyridine under the Influence of Degassed Raney Nickel

1963 ◽  
Vol 16 (1) ◽  
pp. 14 ◽  
Author(s):  
WHF Sasse ◽  
CP Whittle
Keyword(s):  
Raney Nickel ◽  
Nickel Catalysts ◽  
Nickel Atom ◽  
Metal Catalysts ◽  
Published Data ◽  
Hydrogen Atoms ◽  
Adsorbed Pyridine

The efficiency of W7 Raney nickel catalysts degassed between 30 and 400�C in the preparation of 2,2'-bipyridyl has been examined. The highest activities are observed with catalysts which have been degassed at 200�C, and these catalysts arc up to 20% more efficient than catalysts previously used and degassed at 100�C. The results obtained are compared with published data concerning the hydrogen contents of degassed Raney nickel catalysts (Kokes and Emmett 1959, 1960). This shows that catalysts which are virtually free of hydrogen are only 25% less efficient than catalysts degassed at l00�C (containing 65 to 70% of their original hydrogen). Because of this finding a new mechanism is proposed in which the adsorbed pyridine is activated by the transfer of an electron from the catalyst. On stereochemical grounds it is proposed that meso-2,2'-dihydro-2,2'-bipyridyl with axially disposed hydrogen atoms at the 2,2'-positions and bonded via both nitrogen atoms to one nickel atom is the energetically most favoured intermediate.

Synthetical applications of activated metal catalysts. XXV. The hydrogenolysis of some phenyl derivatives of silicon by Raney nickel

1966 ◽  
Vol 19 (10) ◽  
pp. 1897 ◽  
Author(s):  
WHF Sasse ◽  
KO Wade
Keyword(s):  
Raney Nickel ◽  
Silicon Atom ◽  
Atmospheric Pressure ◽  
Nickel Catalysts ◽  
Metal Catalysts ◽  
Derivatives Of ◽  
Related Compounds ◽  
Raney Cobalt

Tetraphenylsilane and 11 related compounds have been cleaved by treatment at atmospheric pressure with Raney nickel catalysts to give mixtures of benzene and cyclohexane. Yields exceeding 90% are obtained with degassed Raney nickel and silanes. Silanols and siloxanes are less readily spilt. The presence of methanol in the reaction mixtures retards the fission of silicon-phenyl bonds. Tetracyclo-hexylsilane, cyclohexyltrimethylsilane, and hexa(n-hexyl)disiloxane did not react detectably with Raney nickel. Raney cobalt had no effect on tetraphenylsilane. A mechanism for the new reaction is discussed which involves chemisorption via the silicon atom, ejection of a phenyl anion, and hydrogenolysis of the absorbed triphenylsilyl species.

The Role of Hydrogen in Raney Nickel Catalysts

1959 ◽  
Vol 81 (19) ◽  
pp. 5032-5037 ◽  
Author(s):  
R. J. Kokes ◽  
P. H. Emmett
Keyword(s):  
Raney Nickel ◽  
Nickel Catalysts

Geometric Factor in Skeletal Reactions of 2-Methylpentane on Stepped Surfaces of Platinum Catalyst

1992 ◽  
Vol 57 (10) ◽  
pp. 2012-2020
Author(s):  
Vladimír Hejtmánek
Keyword(s):  
Active Sites ◽  
Platinum Catalyst ◽  
Point Of View ◽  
Geometric Factor ◽  
Published Data ◽  
Stepped Surfaces ◽  
Geometric Conditions ◽  
Surface Intermediates ◽  
Isomerization Mechanism

The role of geometric factor in the course of skeletal reactions (isomerization, hydrogenolysis) of 2-methylpentane on stepped (119), (557) and reconstructed R(557) surfaces of single crystals of platinum was evaluated with computer designed models. These calculations were compared with reported experimental data. It was found by analysis of geometric conditions that there are accessible active ensembles on double step of the reconstructed R(557) surface. In addition, these active sites are unsaturated in their coordination sphere and thus catalytically effective. This finding is consistent with published data, confirming higher catalytic activity of this surface. The various pathways of Bond Shift isomerization mechanism of 2-methylpentane from the point of view of steric demands of surface intermediates on differently located ensembles are discussed, too.

scholarly journals Overview on the Different Patterns of Tumor Vascularization

Cells ◽  
2021 ◽  
Vol 10 (3) ◽  
pp. 639
Author(s):  
Domenico Ribatti ◽  
Francesco Pezzella
Keyword(s):  
Vasculogenic Mimicry ◽  
Endothelial Cell Proliferation ◽  
Published Data ◽  
Alternative Mechanism ◽  
Tumor Vascularization ◽  
Angiogenic Therapy ◽  
Physiological Processes ◽  
Inhibition Of Angiogenesis ◽  
Therapeutic Development

Angiogenesis is a crucial event in the physiological processes of embryogenesis and wound healing. During malignant transformation, dysregulation of angiogenesis leads to the formation of a vascular network of tumor-associated capillaries promoting survival and proliferation of the tumor cells. Starting with the hypothesis formulated by Judah Folkman that tumor growth is angiogenesis-dependent, this area of research has a solid scientific foundation and inhibition of angiogenesis is a major area of therapeutic development for the treatment of cancer. Over this period numerous authors published data of vascularization of tumors, which attributed the cause of neo-vascularization to various factors including inflammation, release of angiogenic cytokines, vasodilatation, and increased tumor metabolism. More recently, it has been demonstrated that tumor vasculature is not necessarily derived by endothelial cell proliferation and sprouting of new capillaries, but alternative vascularization mechanisms have been described, namely vascular co-option and vasculogenic mimicry. In this article, we have analyzed the mechanisms involved in tumor vascularization in association with classical angiogenesis, including post-natal vasculogenesis, intussusceptive microvascular growth, vascular co-option, and vasculogenic mimicry. We have also discussed the role of these alternative mechanism in resistance to anti-angiogenic therapy and potential therapeutic approaches to overcome resistance.

The Need for Consensus About Liver Transplantation For Patients With Neuropsychiatric Wilson’s Disease

2021 ◽  
pp. 152692482110028
Author(s):  
Alberto Ferrarese ◽  
Patrizia Burra
Keyword(s):  
Liver Transplantation ◽  
Patient Outcomes ◽  
Wilson’S Disease ◽  
Therapeutic Option ◽  
Copper Metabolism ◽  
Wilson's Disease ◽  
Published Data ◽  
Neurological Improvement ◽  
Effective Therapeutic Option

Liver transplantation is considered an effective therapeutic option for Wilson’s disease (WD) patients with hepatic phenotype, since it removes the inherited defects of copper metabolism, and is associated with excellent graft and patient outcomes. The role of liver transplantation in WD patients with mixed hepatic and neuropsychiatric phenotype has remained controversial over time, mainly because of high post-operative complications, reduced survival and a variable, unpredictable rate of neurological improvement. This article critically discusses the recently published data in this field, focussing in more detail on isolated neuropsychiatric phenotype as a potential indication for liver transplantation in WD patients.

scholarly journals Novel Insights on the Role of Nitric Oxide in the Ovary: A Review of the Literature

2021 ◽  
Vol 18 (3) ◽  
pp. 980
Author(s):  
Maria Cristina Budani ◽  
Gian Mario Tiboni
Keyword(s):  
Nitric Oxide ◽  
In Vivo Studies ◽  
Published Data ◽  
Vitro Fertilization ◽  
Peripheral Neurons ◽  
Relevant Role ◽  
Oocyte Meiotic Maturation

Nitric oxide (NO) is formed during the oxidation of L-arginine to L-citrulline by the action of multiple isoenzymes of NO synthase (NOS): neuronal NOS (nNOS), endotelial NOS (eNOS), and inducible NOS (iNOS). NO plays a relevant role in the vascular endothelium, in central and peripheral neurons, and in immunity and inflammatory systems. In addition, several authors showed a consistent contribution of NO to different aspects of the reproductive physiology. The aim of the present review is to analyse the published data on the role of NO within the ovary. It has been demonstrated that the multiple isoenzymes of NOS are expressed and localized in the ovary of different species. More to the point, a consistent role was ascribed to NO in the processes of steroidogenesis, folliculogenesis, and oocyte meiotic maturation in in vitro and in vivo studies using animal models. Unfortunately, there are few nitric oxide data for humans; there are preliminary data on the implication of nitric oxide for oocyte/embryo quality and in-vitro fertilization/embryo transfer (IVF/ET) parameters. NO plays a remarkable role in the ovary, but more investigation is needed, in particular in the context of human ovarian physiology.

Role of solid-state structure in propene hydrogenation with nickel catalysts

1990 ◽  
Vol 86 (4) ◽  
pp. 739 ◽  
Author(s):  
Giovanni Carturan ◽  
Stefano Enzo ◽  
Renzo Ganzerla ◽  
Maurizio Lenarda ◽  
Roberto Zanoni
Keyword(s):  
Solid State ◽  
Nickel Catalysts ◽  
State Structure ◽  
Solid State Structure

scholarly journals The Biochemical Diagnosis of Acromegaly

2021 ◽  
Vol 10 (5) ◽  
pp. 1147
Author(s):  
Amit Akirov ◽  
Hiba Masri-Iraqi ◽  
Idit Dotan ◽  
Ilan Shimon
Keyword(s):  
English Language ◽  
Diagnostic Delay ◽  
Tolerance Test ◽  
Oral Glucose ◽  
Published Data ◽  
Biochemical Diagnosis ◽  
Key Factor ◽  
Assay Methods ◽  
Serum Gh

Background: The diagnosis of acromegaly still poses a clinical challenge, and prolonged diagnostic delay is common. The most important assays for the biochemical diagnosis and management of acromegaly are growth hormone (GH) and insulin-like growth factor-1 (IGF-1). Objective: Discuss the role of IGF-1, basal serum GH, and nadir GH after oral glucose tolerance test (OGTT) for the diagnosis, management, and treatment of patients with acromegaly. Methods: We performed a narrative review of the published data on the biochemical diagnosis and monitoring of acromegaly. An English-language search for relevant studies was conducted on PubMed from inception to 1 January 2021. The reference lists of relevant studies were also reviewed. Results: Serum IGF-1 levels, basal GH values, and nadir GH after OGTT play a major role in the diagnosis, management, and treatment of patients with acromegaly. Measurement of IGF-1 levels is the key factor in the diagnosis and monitoring of acromegaly, but basal and nadir GH following OGTT are also important. However, several factors may significantly influence the concentrations of these hormones, including assay methods, physiologic and pathologic factors. In some cases, discordant GH and IGF-1 levels may be challenging and usually requires additional data and monitoring. Conclusion: New GH and IGF-1 standards are much more precise and provide more accurate tools to diagnose and monitor patients with acromegaly. However, all these biochemical tools have their limitations, and these should be taken under consideration, along with the history, clinical features and imaging studies, when assessing patients for acromegaly.

Platelet Glycoprotein Receptor IIIa Polymorphism PlA1/PlA2 and Coronary Risk: a Meta-Analysis

2001 ◽  
Vol 85 (04) ◽  
pp. 626-633 ◽  
Author(s):  
Augusto Di Castelnuovo ◽  
Giovanni de Gaetano ◽  
Maria Benedetta Donati ◽  
Licia Iacoviello
Keyword(s):  
Odds Ratio ◽  
Meta Analysis ◽  
Platelet Glycoprotein ◽  
Published Data ◽  
Coronary Risk ◽  
Gene Encoding ◽  
Glycoprotein Iiia ◽  
Artery Disease ◽  
Revascularization Procedures

SummaryMembrane glycoprotein IIb/IIIa plays a major role in platelet function. The gene encoding the glycoprotein IIIa shows a common polymorphism PlA1/PlA2 that was variably associated with vascular disease. To clarify the role of PlA1/PlA2 polymorphism in coronary risk, a meta-analysis of published data was conducted. Studies were identified both by MEDLINE searches, and hand searching of journals and abstract books.A total of 34 studies for coronary artery disease (CAD), and 6 for restenosis after revascularization were identified, for a total of 9,095 cases and 12,508 controls. In CAD, the overall odds ratio for carriers of the PlA2 allele was 1.10 (95% CI: 1.03 to 1.18), and it was 1.21 (95% CI: 1.05 to 1.38) in subjects younger than 60. Overall odds ratio was 1.31 (95% CI: 1.10 to 1.56) after revascularization procedures.The association of PlA2 status with overall cardiovascular disease in the general population is significant but weak; higher risk has been identified in less heterogeneous subgroups as in the younger cohorts and in the restenosis subset with stents.

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