Studies in Porphyrin Chemistry: A Synthetic Approach

1991 ◽  
Vol 44 (9) ◽  
pp. 1163 ◽  
Author(s):  
PS Clezy
Keyword(s):  
Oxidative Cyclization ◽  
Mechanistic Study ◽  
Synthetic Approach ◽  
General Strategy ◽  
Substitution Pattern ◽  
Synthetic Procedure ◽  
Wide Range ◽  
Porphyrin Synthesis ◽  
Broad Understanding

This review summarizes porphyrin synthesis in the author's laboratory, and deals mainly with the preparation of porphyrins substituted with electron-withdrawing groups. Oxidative cyclization of 1,19-dimethylbilenes-b has provided the most successful avenue to porphyrins of this class, and the procedure works best when the terminal rings of the bilene -b are substituted with electron-withdrawing groups. This methodology has yielded a wide range of porphyrins carrying this class of substituent on adjacent pyrrolic rings, and has led to the preparation of many biologically important molecules including porphyrin a and the chlorophylls c1 and c2. Also described are the necessary modifications which are required to adapt the general strategy to the synthesis of porphyrins carrying electron-withdrawing groups on opposite pyrrolic rings as well as for cases where only one such substituent occurs. All these procedures were designed specifically to handle the preparation of porphyrins which were unsymmetrically substituted. However, some biologically significant members of the porphyrin series have a symmetrical arrangement of substituents in part of the molecule, and an adaption of the general synthetic procedure allows advantage to be taken of this substitution pattern. A mechanistic study of the oxidative cyclization of bilenes -b, which has been the reaction central in all the above synthetic endeavours, has produced a broad understanding of the manner in which the cyclization proceeds. Very recent studies involving the synthesis of petroporphyrins, besides consolidating the structure of many of these compounds, have provided sufficient material to allow an investigation of the properties of these porphyrins to commence, and in some cases this had led to a clearer understanding of their orgin.

Microwave-Controlled Preparation of Alkenyl-(1H)-1,2,4-triazoles: First Heck Reaction on a (1H)-1,2,4-Triazole Moiety

2009 ◽  
Vol 62 (12) ◽  
pp. 1600 ◽  
Author(s):  
Ángel Díaz-Ortiz ◽  
Pilar Prieto ◽  
Abel de Cózar ◽  
Cristina Cebrián ◽  
Andrés Moreno ◽  
...  
Keyword(s):  
Heck Reaction ◽  
Cross Coupling ◽  
Synthetic Approach ◽  
Heck Reactions ◽  
Triazole Derivatives ◽  
Synthetic Procedure ◽  
Wide Range ◽  
Controlled Preparation

A new synthetic approach for the preparation of alkenyl-1,2,4-triazole derivatives based on microwave-induced C–C cross-coupling Heck reactions is described. To the best of our knowledge, this is the first application of the Heck reaction to a dihalogenated 1,2,4-triazole. This approach allows the introduction of a wide range of equivalent or different alkenyl substituents in the 5- and/or 3-positions, thus extending the possibilities for the preparation of these valuable derivatives. A similar microwave-induced synthetic procedure has also been applied to the Heck reaction of 4-vinyl-1,2,3-triazoles.

General Cyclopropane Assembly via Enantioselective Redox-Active Carbene Transfer to Aliphatic Olefins

2018 ◽  
Author(s):  
Marc Montesinos-Magraner ◽  
Matteo Costantini ◽  
Rodrigo Ramirez-Contreras ◽  
Michael E. Muratore ◽  
Magnus J. Johansson ◽  
...  
Keyword(s):  
Total Synthesis ◽  
Asymmetric Synthesis ◽  
Chemical Space ◽  
Synthetic Approach ◽  
Asymmetric Cyclopropanation ◽  
Redox Active ◽  
Wide Range ◽  
Leaving Group ◽  
Stereoelectronic Properties ◽  
Carbene Transfer

Asymmetric cyclopropane synthesis currently requires bespoke strategies, methods, substrates and reagents, even when targeting similar compounds. This limits the speed and chemical space available for discovery campaigns. Here we introduce a practical and versatile diazocompound, and we demonstrate its performance in the first unified asymmetric synthesis of functionalized cyclopropanes. We found that the redox-active leaving group in this reagent enhances the reactivity and selectivity of geminal carbene transfer. This effect enabled the asymmetric cyclopropanation of a wide range of olefins including unactivated aliphatic alkenes, enabling the 3-step total synthesis of (–)-dictyopterene A. This unified synthetic approach delivers high enantioselectivities that are independent of the stereoelectronic properties of the functional groups transferred. Our results demonstrate that orthogonally-differentiated diazocompounds are viable and advantageous equivalents of single-carbon chirons<i>.</i>

Historical Dynamics

2018 ◽  
Author(s):  
Peter Turchin
Keyword(s):  
Religious Conversion ◽  
Synthetic Approach ◽  
Dynamical Processes ◽  
Factors Affecting ◽  
Historical Processes ◽  
Wide Range ◽  
Historical Dynamics ◽  
State Breakdown ◽  
Political Economic ◽  
High Degree

Many historical processes are dynamic. Populations grow and decline. Empires expand and collapse. Religions spread and wither. Natural scientists have made great strides in understanding dynamical processes in the physical and biological worlds using a synthetic approach that combines mathematical modeling with statistical analyses. Taking up the problem of territorial dynamics—why some polities at certain times expand and at other times contract—this book shows that a similar research program can advance our understanding of dynamical processes in history. The book develops hypotheses from a wide range of social, political, economic, and demographic factors: geopolitics, factors affecting collective solidarity, dynamics of ethnic assimilation/religious conversion, and the interaction between population dynamics and sociopolitical stability. It then translates these into a spectrum of mathematical models, investigates the dynamics predicted by the models, and contrasts model predictions with empirical patterns. The book's highly instructive empirical tests demonstrate that certain models predict empirical patterns with a very high degree of accuracy. For instance, one model accounts for the recurrent waves of state breakdown in medieval and early modern Europe. And historical data confirm that ethno-nationalist solidarity produces an aggressively expansive state under certain conditions (such as in locations where imperial frontiers coincide with religious divides). The strength of the book's results suggests that the synthetic approach advocated can significantly improve our understanding of historical dynamics.

Mechanistic Study on Gold(I)-Catalyzed Unsaturated Spiroketalization Reaction

2022 ◽  
Vol 19 ◽  
Author(s):  
Kamlesh Sharma
Keyword(s):  
Activation Barrier ◽  
Ring Formation ◽  
Hydroxyl Group ◽  
Mechanistic Study ◽  
Protecting Group ◽  
Wide Range ◽  
Oxocarbenium Ion ◽  
Metal Catalyzed ◽  
Insight Into ◽  
Mechanism Of The Reaction

Abstract: The mechanism of metal-catalyzed spiroketalization of propargyl acetonide is explored by employing DFT with the B3LYP/6-31+G(d) method. Acetonide is used as a regioselective regulator in the formation of monounsaturated spiroketal. The energies of transition states, intermediates, reactants and products are calculated to provide new insight into the mechanism of the reaction. The energetic features, validation of the observed trends in regioselectivity are conferred in terms of electronic indices via FMO analysis. The presence of acetonide facilitates a stepwise spiroketalization as it masks the competing nucleophile, and thus hydroxyl group present, exclusively acts as a nucleophile. The vinyl gold intermediate 3 is formed from 2 via activation barrier TS1. This is the first ring formation, which is 6-exo-dig cyclization. The intermediate 3 is converted into allenyl ether 4, which isomerizes to the intermediate oxocarbenium ion 5 via activation barrier TS2. The intermediate 5 cyclizes to 6 via TS3. This is the second ring formation. The intermediate 6 on protodeauration turns into 6,6-monounsaturated spiroketal 7. It is concluded that acetonide as a protecting group serves the purpose, and thus a wide range of spiroketals can be prepared, regioselectivity.

A Novel Synthetic Approach to Asymmetric Salen, Dihydrosalen, and Tetrahydrosalen Ligands: Structures and O2-Activating Properties of their Nickel(II) and Cobalt(II) Complexes

1994 ◽  
Vol 49 (8) ◽  
pp. 1089-1100 ◽  
Author(s):  
Arnd Böttcher ◽  
Horst Elias ◽  
Brigitte Eisenmann ◽  
Elke Hilms ◽  
Andreas Huber ◽  
...  
Keyword(s):  
Equilibrium Constants ◽  
Spectrophotometric Titration ◽  
Acetone Solution ◽  
Synthetic Approach ◽  
Coordination Core ◽  
Type Complex ◽  
Square Planar ◽  
Synthetic Procedure ◽  
Derivatives Of ◽  
Methyl Phenyl

A synthetic procedure is described for the preparation of the tetradentate N2O2 ligands H2[H4]L1=6-(2-hydroxyphenyl)-2,5-diaza-3,3-dimethyl-1-(2-hydroxy-3-t-butyl-5-methyl- phenyl)heptane, H2[H2]L1 = 6-(2-hydroxyphenyl)-2,5-diaza-3,3-dimethyl-1-(2-hydroxy-3-t-butyl-5-methylphenyl)-1-heptene, and H2L1 = 6-(2-hydroxyphenyl)-2,5-diaza-3,3-dimethyl-1-(2- hydroxy-3-t-butyl-5-methylphenyl)-1,5-heptadiene, which are asymmetric derivatives of the ligands tetrahydrosalen, dihydrosalen, and salen. Complexes Ni[H4]L1, Ni[H2]L1, NiL1, CoL1, Ni[H4]L2 (([H4]L2)2- = anion of H2[H4]L2 = N,N'-bis(2-hydroxy-3-t-butyl-5-methylbenzyl)- trans-(S,S)-1,2-diaminocyclohexane), and NiL2 were prepared, characterized (VIS and IR ab­sorption, magnetic moment) and subjected to spectrophotometric titration with pyridine, to determine the equilibrium constants for adduct formation. Single crystal X-ray structure analy­ses were carried out for Ni[H2]L1 (monoclinic, P21/n; a = 8.926(4), b = 29.324(7), c = 8.411(4) Å; β = 95.3(1)°; Z = 4), CoL1 (monoclinic, C2/c; a = 25.389(2), b = 18.139(2), c = 10.179(1) Å; β = 112.227(6); Z = 8), and Ni[H4]L2·acetone (tetragonal, P41212; a = 13.928(3), c = 33.698(5) Å; Z = 8). In all of the three complexes, the N2O2-metal coordination core is square-planar. The skeleton of the tetradentate ligand is more or less twisted. The planar cobalt(II) complex CoL1 is a low spin d7 system with μexp = 2.02 BM at 298 K, whereas the planar complexes NiL1, Ni[H2]L1 and Ni[H4]L2 are diamagnetic (μexp = 0.28-0.64 BM). The blue solvate Ni[H4]L1- 3EtOH · H2O is paramagnetic (μexp = 3.04 BM), which points to octahedral coordination. In aerated acetone solution, the tetrahydrosalen-type complex Ni[H4]L1 activates dioxygen and one C-N bond is oxidatively dehydrogenated. The VIS spectrum of the dihydrosalen-type complex formed is virtually identical with that of the aldimine complex Ni[H2]L1. In the pres­ence of dioxygen, Co[H4]L1 and Co[H2]L1 are readily oxidized to CoL1 in acetone solution.

scholarly journals The 3-O-sulfation of heparan sulfate modulates protein binding and lyase degradation

2021 ◽  
Vol 118 (3) ◽  
pp. e2012935118
Author(s):  
Pradeep Chopra ◽  
Apoorva Joshi ◽  
Jiandong Wu ◽  
Weigang Lu ◽  
Tejabhiram Yadavalli ◽  
...  
Keyword(s):  
Heparan Sulfate ◽  
Binding Proteins ◽  
Factor Xa ◽  
Tissue Expression ◽  
Cell Entry ◽  
Synthetic Approach ◽  
Array Technology ◽  
Wide Range ◽  
Simplex Virus

Humans express seven heparan sulfate (HS) 3-O-sulfotransferases that differ in substrate specificity and tissue expression. Although genetic studies have indicated that 3-O-sulfated HS modulates many biological processes, ligand requirements for proteins engaging with HS modified by 3-O-sulfate (3-OS) have been difficult to determine. In particular, the context in which the 3-OS group needs to be presented for binding is largely unknown. We describe herein a modular synthetic approach that can provide structurally diverse HS oligosaccharides with and without 3-OS. The methodology was employed to prepare 27 hexasaccharides that were printed as a glycan microarray to examine ligand requirements of a wide range of HS-binding proteins. The binding selectivity of antithrombin-III (AT-III) compared well with anti-Factor Xa activity supporting robustness of the array technology. Many of the other examined HS-binding proteins required an IdoA2S-GlcNS3S6S sequon for binding but exhibited variable dependence for the 2-OS and 6-OS moieties, and a GlcA or IdoA2S residue neighboring the central GlcNS3S. The HS oligosaccharides were also examined as inhibitors of cell entry by herpes simplex virus type 1, which, surprisingly, showed a lack of dependence of 3-OS, indicating that, instead of glycoprotein D (gD), they competitively bind to gB and gC. The compounds were also used to examine substrate specificities of heparin lyases, which are enzymes used for depolymerization of HS/heparin for sequence determination and production of therapeutic heparins. It was found that cleavage by lyase II is influenced by 3-OS, while digestion by lyase I is only affected by 2-OS. Lyase III exhibited sensitivity to both 3-OS and 2-OS.

Recent Developments in Ride Control

2015 ◽  
Author(s):  
Alan J. Haywood ◽  
Benton H. Schaub ◽  
Chris M. Pappas
Keyword(s):  
Control Systems ◽  
High Speed ◽  
New Technologies ◽  
Early Adoption ◽  
Wide Range ◽  
Ride Control ◽  
Recent Developments ◽  
Material Choice ◽  
Maintenance Requirements ◽  
Broad Understanding

The use of ride control systems on high speed vessels has become the norm within many industries, producing better seakeeping that in turn provides a more comfortable and operationally effective vessel. Commercial ferry designers have been at the forefront of adoption of new technologies notably with early adoption of T-foils and interceptors. These devices have been taken up by others, for example offshore crew boats and frontline naval warships. The range of vessel types has also expanded with more industries adopting different hull designs including catamarans and trimarans. Ride control systems have developed alongside innovative designers producing for example combined lifting foil and ride control systems, lifting T-foil systems, retractable T-foils. This paper will review the different ride control devices including fins, trim tabs, interceptors, T-foils (including retractable T-foils) and lifting foils. As well as technical aspects, the discussion will consider costs, ease of installation, operational and maintenance requirements and material choice. Extensive examples from a wide range of industries will be presented. By the end of the talk, delegates will have a broad understanding of the options available to them in improving the seakeeping of their vessels.

scholarly journals A novel three-component reaction between isocyanides, alcohols or thiols and elemental sulfur: a mild, catalyst-free approach towards O-thiocarbamates and dithiocarbamates

2019 ◽  
Vol 15 ◽  
pp. 1523-1533 ◽  
Author(s):  
András György Németh ◽  
György Miklós Keserű ◽  
Péter Ábrányi-Balogh
Keyword(s):  
Elemental Sulfur ◽  
Building Blocks ◽  
Reaction Conditions ◽  
One Pot ◽  
Catalyst Free ◽  
Synthetic Procedure ◽  
Three Component Reaction ◽  
Wide Range ◽  
Organic Chemist ◽  
The One

A new multicomponent reaction has been developed between isocyanides, sulfur and alcohols or thiols under mild reaction conditions to afford O-thiocarbamates and dithiocarbamates in moderate to good yields. The one-pot reaction cascade involves the formation of an isothiocyanate intermediate, thus a catalyst-free synthesis of isothiocyanates, as valuable building blocks from isocyanides and sulfur is proposed, as well. The synthetic procedure suits the demand of a modern organic chemist, as it tolerates a wide range of functional groups, it is atom economic and easily scalable.

scholarly journals Kinetic and Mechanistic Study of Rhodamine B Degradation by H2O2 and Cu/Al2O3/g-C3N4 Composite

Catalysts ◽  
2020 ◽  
Vol 10 (3) ◽  
pp. 317 ◽  
Author(s):  
Chunsun Zhou ◽  
Zhongda Liu ◽  
Lijuan Fang ◽  
Yulian Guo ◽  
Yanpeng Feng ◽  
...  
Keyword(s):  
Rate Constant ◽  
Rhodamine B ◽  
Active Sites ◽  
Reaction Rate ◽  
Reaction Rate Constant ◽  
Mechanistic Study ◽  
Al2o3 Composite ◽  
Degradation Rates ◽  
Wide Range ◽  
Alkaline Conditions

The classic Fenton reaction, which is driven by iron species, has been widely explored for pollutant degradation, but is strictly limited to acidic conditions. In this work, a copper-based Fenton-like catalyst Cu/Al2O3/g-C3N4 was proposed that achieves high degradation efficiencies for Rhodamine B (Rh B) in a wide range of pH 4.9–11.0. The Cu/Al2O3 composite was first prepared via a hydrothermal method followed by a calcination process. The obtained Cu/Al2O3 composite was subsequently stabilized on graphitic carbon nitride (g-C3N4) by the formation of C−O−Cu bonds. The obtained composites were characterized through FT-IR, XRD, TEM, XPS, and N2 adsorption/desorption isotherms, and the immobilized Cu+ was proven to be active sites. The effects of Cu content, g-C3N4 content, H2O2 concentration, and pH on Rh B degradation were systematically investigated. The effect of the catalyst dose was confirmed with a specific reaction rate constant of (5.9 ± 0.07) × 10−9 m·s−1 and the activation energy was calculated to be 71.0 kJ/mol. In 100 min 96.4% of Rh B (initial concentration 20 mg/L, unadjusted pH (4.9)) was removed in the presence of 1 g/L of catalyst and 10 mM of H2O2 at 25 °C, with an observed reaction rate constant of 6.47 × 10−4 s−1. High degradation rates are achieved at neutral and alkaline conditions and a low copper leaching (0.55 mg/L) was observed even after four reaction cycles. Hydroxyl radical (HO·) was identified as the reactive oxygen species by using isopropanol as a radical scavenger and by ESR analysis. HPLC-MS revealed that the degradation of Rh B on Cu/Al2O3/CN composite involves N-de-ethylation, hydroxylation, de-carboxylation, chromophore cleavage, ring opening, and the mineralization process. Based on the results above, a tentative mechanism for the catalytic performance of the Cu/Al2O3/g-C3N4 composite was proposed. In summary, the characteristics of high degradation rate constants, low ion leaching, and the excellent applicability in neutral and alkaline conditions prove the Cu/Al2O3/g-C3N4 composite to be a superior Fenton-like catalyst compared to many conventional ones.

scholarly journals Combinatorial microfluidic droplet engineering for biomimetic material synthesis

2016 ◽  
Vol 2 (10) ◽  
pp. e1600567 ◽  
Author(s):  
Lukmaan A. Bawazer ◽  
Ciara S. McNally ◽  
Christopher J. Empson ◽  
William J. Marchant ◽  
Tim P. Comyn ◽  
...  
Keyword(s):  
General Strategy ◽  
Emulsion Droplet ◽  
Material Synthesis ◽  
Widespread Application ◽  
Carrier Fluid ◽  
Wide Range ◽  
In Vitro Protein Expression ◽  
Selection Of ◽  
Vitro Protein

Although droplet-based systems are used in a wide range of technologies, opportunities for systematically customizing their interface chemistries remain relatively unexplored. This article describes a new microfluidic strategy for rapidly tailoring emulsion droplet compositions and properties. The approach uses a simple platform for screening arrays of droplet-based microfluidic devices and couples this with combinatorial selection of the droplet compositions. Through the application of genetic algorithms over multiple screening rounds, droplets with target properties can be rapidly generated. The potential of this method is demonstrated by creating droplets with enhanced stability, where this is achieved by selecting carrier fluid chemistries that promote titanium dioxide formation at the droplet interfaces. The interface is a mixture of amorphous and crystalline phases, and the resulting composite droplets are biocompatible, supporting in vitro protein expression in their interiors. This general strategy will find widespread application in advancing emulsion properties for use in chemistry, biology, materials, and medicine.

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