scholarly journals Reviving the Coordination Chemistry of Sulfonium Cations

2021 ◽  
Author(s):  
Ruiping Li ◽  
Nitsan Barel ◽  
Vasudevan Subramaniyan ◽  
Orit Cohen ◽  
Francoise Tibika ◽  
...  
Keyword(s):  
Coordination Chemistry ◽  
Computational Analysis ◽  
Acid Catalysis ◽  
Phosphine Ligands ◽  
Pincer Complexes ◽  
Full Characterization ◽  
Sulfonium Ions ◽  
The Stability ◽  
First Time

ABSTRACT: More than a century old, sulfonium ions are still intriguing species in the landscape of organic chemistry. On one hand they have found broad applications in organic synthesis and material science, but on the other hand, while isoelectronic to the ubiquitous tertiary phosphine ligands, their own coordination chemistry has been neglected for the last three decades. Here we report the synthesis and full characterization of the first Rh(I) and Pt(II) complexes of sul-fonium. Moreover, for the first time, the coordinating ability of an aromatic sulfonium has been established. A thorough computational analysis of the exceptionally short S-Rh bonds obtained attests for the strongly π-accepting nature of sul-fonium cations and places them among the best π-acceptor ligands available today. Our calculations also show that when embedded within a pincer framework their π-acidity is enhanced. Therefore, in addition to the stability and modularity that these frameworks offer, our pincer complexes might open the way for sulfonium cations to become powerful tools in π-acid catalysis.

scholarly journals Terminal and Internal Alkyne Complexes and Azide-Alkyne Cycloaddition Chemistry of Copper(I) Supported by a Fluorinated Bis(pyrazolyl)borate

Molecules ◽  
2021 ◽  
Vol 27 (1) ◽  
pp. 16
Author(s):  
Anurag Noonikara-Poyil ◽  
Alvaro Muñoz-Castro ◽  
H. V. Rasika Dias
Keyword(s):  
Coordination Chemistry ◽  
Copper Complexes ◽  
Computational Analysis ◽  
Copper Catalyst ◽  
Dinuclear Complexes ◽  
Orbital Contribution ◽  
Full Characterization ◽  
Alkyne Complexes ◽  
Internal Alkyne

Copper plays an important role in alkyne coordination chemistry and transformations. This report describes the isolation and full characterization of a thermally stable, copper(I) acetylene complex using a highly fluorinated bis(pyrazolyl)borate ligand support. Details of the related copper(I) complex of HCºCSiMe3 are also reported. They are three-coordinate copper complexes featuring η2-bound alkynes. Raman data show significant red-shifts in CºC stretch of [H2B(3,5-(CF3)2Pz)2]Cu(HCºCH) and [H2B(3,5-(CF3)2Pz)2]Cu(HCºCSiMe3) relative to those of the corresponding alkynes. Computational analysis using DFT indicates that the Cu(I) alkyne interaction in these molecules is primarily of the electrostatic character. The π-backbonding is the larger component of the orbital contribution to the interaction. The dinuclear complexes such as Cu2(μ-[3,5-(CF3)2Pz])2(HCºCH)2 display similar Cu-alkyne bonding features. The mononuclear [H2B(3,5-(CF3)2Pz)2]Cu(NCMe) complex catalyzes [3+2] cycloadditions between tolyl azide and a variety of alkynes including acetylene. It is comparatively less effective than the related trinuclear copper catalyst {μ-[3,5-(CF3)2Pz]Cu}3 involving bridging pyrazolates.

scholarly journals A Versatile Approach to Access Trimetallic Complexes Based on Trisphosphinite Ligands

Molecules ◽  
2020 ◽  
Vol 25 (3) ◽  
pp. 593
Author(s):  
Juan Miranda-Pizarro ◽  
Macarena G. Alférez ◽  
M. Dolores Fernández-Martínez ◽  
Eleuterio Álvarez ◽  
Celia Maya ◽  
...  
Keyword(s):  
Coordination Chemistry ◽  
Late Transition Metal ◽  
X Ray Diffraction ◽  
X Ray ◽  
Full Characterization ◽  
Metal Precursors ◽  
Straightforward Method ◽  
One Step ◽  
Late Transition

A straightforward method for the preparation of trisphosphinite ligands in one step, using only commercially available reagents (1,1,1-tris(4-hydroxyphenyl)ethane and chlorophosphines) is described. We have made use of this approach to prepare a small family of four trisphosphinite ligands of formula [CH3C{(C6H4OR2)3], where R stands for Ph (1a), Xyl (1b, Xyl = 2,6-Me2-C6H3), iPr (1c), and Cy (1d). These polyfunctional phosphinites allowed us to investigate their coordination chemistry towards a range of late transition metal precursors. As such, we report here the isolation and full characterization of a number of Au(I), Ag(I), Cu(I), Ir(III), Rh(III) and Ru(II) homotrimetallic complexes, including the structural characterization by X-ray diffraction studies of six of these compounds. We have observed that the flexibility of these trisphosphinites enables a variety of conformations for the different trimetallic species.

scholarly journals Characterization of Cocycle Attractors for Nonautonomous Reaction–Diffusion Equations

2016 ◽  
Vol 26 (08) ◽  
pp. 1650135 ◽  
Author(s):  
C. A. Cardoso ◽  
J. A. Langa ◽  
R. Obaya
Keyword(s):  
Chaotic Dynamics ◽  
Linear Part ◽  
Reaction Diffusion ◽  
Positive Cone ◽  
Reaction Diffusion Equations ◽  
Diffusion Equations ◽  
Minimal Set ◽  
Full Characterization ◽  
The Stability

In this paper, we describe in detail the global and cocycle attractors related to nonautonomous scalar differential equations with diffusion. In particular, we investigate reaction–diffusion equations with almost-periodic coefficients. The associated semiflows are strongly monotone which allow us to give a full characterization of the cocycle attractor. We prove that, when the upper Lyapunov exponent associated to the linear part of the equations is positive, the flow is persistent in the positive cone, and we study the stability and the set of continuity points of the section of each minimal set in the global attractor for the skew product semiflow. We illustrate our result with some nontrivial examples showing the richness of the dynamics on this attractor, which in some situations shows internal chaotic dynamics in the Li–Yorke sense. We also include the sublinear and concave cases in order to go further in the characterization of the attractors, including, for instance, a nonautonomous version of the Chafee–Infante equation. In this last case we can show exponentially forward attraction to the cocycle (pullback) attractors in the positive cone of solutions.

scholarly journals Immobilization of Eversa Lipase on Octyl Agarose Beads and Preliminary Characterization of Stability and Activity Features

Catalysts ◽  
2018 ◽  
Vol 8 (11) ◽  
pp. 511 ◽  
Author(s):  
Sara Arana-Peña ◽  
Yuliya Lokha ◽  
Roberto Fernández-Lafuente
Keyword(s):  
Immobilized Enzyme ◽  
Biodiesel Production ◽  
Free Form ◽  
Enzyme Specificity ◽  
Agarose Beads ◽  
The Stability ◽  
Isoform B ◽  
First Time ◽  
Commercial Lipase

Eversa is an enzyme recently launched by Novozymes to be used in a free form as biocatalyst in biodiesel production. This paper shows for first time the immobilization of Eversa (a commercial lipase) on octyl and aminated agarose beads and the comparison of the enzyme properties to those of the most used lipase, the isoform B from Candida antarctica (CALB) immobilized on octyl agarose beads. Immobilization on octyl and aminated supports of Eversa has not had a significant effect on enzyme activity versus p-nitrophenyl butyrate (pNPB) under standard conditions (pH 7), but immobilization on octyl agarose beads greatly enhanced the stability of the enzyme under all studied conditions, much more than immobilization on aminated support. Octyl-Eversa was much more stable than octyl-CALB at pH 9, but it was less stable at pH 5. In the presence of 90% acetonitrile or dioxane, octyl-Eversa maintained the activity (even increased the activity) after 45 days of incubation in a similar way to octyl-CALB, but in 90% of methanol, results are much worse, and octyl-CALB became much more stable than Eversa. Coating with PEI has not a clear effect on octyl-Eversa stability, although it affected enzyme specificity and activity response to the changes in the pH. Eversa immobilized octyl supports was more active than CALB versus triacetin or pNPB, but much less active versus methyl mandelate esters. On the other hand, Eversa specificity and response to changes in the medium were greatly modulated by the immobilization protocol or by the coating of the immobilized enzyme with PEI. Thus, Eversa may be a promising biocatalyst for many processes different to the biodiesel production and its properties may be greatly improved following a suitable immobilization protocol, and in some cases is more stable and active than CALB.

scholarly journals Full Characterization of Act-and-wait Control for First-order Unstable Lag Processes

2010 ◽  
Vol 16 (7-8) ◽  
pp. 1209-1233 ◽  
Author(s):  
T. Insperger ◽  
P. Wahi ◽  
A. Colombo ◽  
G. Stépán ◽  
M. Di Bernardo ◽  
...  
Keyword(s):  
Time Delay ◽  
Feedback Systems ◽  
Periodic Control ◽  
First Order ◽  
Full Characterization ◽  
The Stability ◽  
And Control ◽  
Time Periodic ◽  
Special Case

Act-and-wait control is a special case of time-periodic control for systems with feedback delay, where the control gains are periodically switched on and off in order to stabilize otherwise unstable systems. The stability of feedback systems in the presence of time delay is a challenging problem. In this paper, we show that the act-and-wait type time-periodic control can always provide deadbeat control for first-order unstable lag processes with any (large but) fixed value of the time delay in the feedback loop. A full characterization of this act-and-wait controller with respect to the system and control parameters is given based on performance and robustness against disturbances.

Acidolysis of intermediates used in the preparation of core-modified porphyrinic macrocycles

2002 ◽  
Vol 06 (03) ◽  
pp. 186-197 ◽  
Author(s):  
Fabien Chevalier ◽  
G. Richard Geier ◽  
Jonathan S. Lindsey
Keyword(s):  
Mass Spectrometry ◽  
Acid Catalysis ◽  
Pyrrole Ring ◽  
Laser Desorption ◽  
Laser Desorption Mass Spectrometry ◽  
Desorption Mass Spectrometry ◽  
Gc Analysis ◽  
The Stability

The stability towards acidolysis of intermediates used in the preparation of core-modified porphyrinic macrocycles was examined. Experiments were performed using analogs of 5-phenyldipyrromethane in which one of the two pyrrole rings was modified (XPM). The XPMs utilized in these studies had X = 2-furyl (OPM), 2-thienyl (SPM), 2-selenyl (SePM), or 3-pyrrolyl (NCPPM). The XPMs possess a potentially labile linkage to a heteroatom-modified ring as well as a potentially labile linkage to a pyrrole ring. The stability of the two types of linkages was examined under acid catalysis conditions commonly used in the preparation of porphyrinic macrocycles. The methodology employed enabled characterization of the stability of the XPM (GC analysis), the yield of porphyrin (UV-vis absorption), and the composition of porphyrinic species (laser-desorption mass spectrometry, LD-MS) formed upon acidolysis of the XPM. These experiments showed that (1) the linkage to the heteroatom-modified ring is fairly stable in the presence of a linkage to pyrrole, and (2) the linkage to pyrrole is much more stable in the XPMs than is the case in 5-phenyldipyrromethane. Additional experiments with analogs of 5-phenyldipyrromethane having both rings modified ( X 2 M ), where X = 2- furyl ( O 2 M ), 2- thienyl ( S 2 M ), or 2- selenyl ( Se 2 M ) confirmed that linkages to furyl, thienyl, and selenyl rings are stable towards acidolysis. Taken together, the observations concerning stability of various linkages provide a foundation for understanding the types and yields of core-modified porphyrinic macrocycles formed in reactions with reactants that are not direct precursors to the isolated products.

Synopsis and lectotypification of Distimake rhyncorhiza (Dalzell) Simões & Staples (Convolvulaceae): a little known species from the Western Ghats (India)

Phytotaxa ◽  
2018 ◽  
Vol 336 (3) ◽  
pp. 293
Author(s):  
ANA RITA SIMÕES ◽  
SUSHANT MORE
Keyword(s):  
Western Ghats ◽  
Conservation Status ◽  
Distinct Species ◽  
Morphological Evidence ◽  
Morphological Description ◽  
Western India ◽  
Full Characterization ◽  
First Time ◽  
The Western Ghats

We present a synopsis of a rare and little-known species of Distimake from Western India: a complete morphological description based on recent collections is provided, and nomenclature and typification issues are resolved. The fruit and seeds are described for the first time. With new morphological evidence and a full characterization of D. rhyncorhiza, the present study corroborates its placement in Distimake and supports its identity as a distinct species. The conservation status is assessed as Endangered but its distribution range is not yet fully documented and this assessment might be reviewed if more collections are made.

scholarly journals Protoflavanones from the Wood Stem of Salvertia convallariodora

2017 ◽  
Vol 12 (4) ◽  
pp. 1934578X1701200
Author(s):  
Mariana L. de Mesquita ◽  
José E. de Paula ◽  
Laila S. Espindola ◽  
Luiz A. L. Soares ◽  
Tania M. G. da Silva ◽  
...  
Keyword(s):  
Ethyl Acetate ◽  
Ethyl Acetate Extract ◽  
2D Nmr ◽  
Phytochemical Analysis ◽  
Brazilian Cerrado ◽  
Stem Wood ◽  
Full Characterization ◽  
Glucosyl Ester ◽  
First Time

Phytochemical analysis of the ethyl acetate extract of stem wood of Salvertia convallariodora A. St.-Hil. (Vochysiaceae), a Brazilian Cerrado species, led to the isolation and full characterization of three new non-aromatic B-ring flavanones (1-3) as well as the terpene mixture of sericic acid (4), 24-hydroxytormentic acid (5), 24-hydroxytormentic acid glucosyl ester (6), and sericoside (7), all identified for the first time from S. convallariodora. The structures of the new flavanones (1-3) were established from IR, LC-PDA-qTOF-MS, and NMR spectral data, including 2D NMR experiments.

scholarly journals A two-dimensional waveguide beam for X-ray nanodiffraction

2011 ◽  
Vol 45 (1) ◽  
pp. 85-92 ◽  
Author(s):  
Christina Krywka ◽  
Henrike Neubauer ◽  
Marius Priebe ◽  
Tim Salditt ◽  
Jozef Keckes ◽  
...  
Keyword(s):  
Cross Sections ◽  
Main Concern ◽  
Tin Coating ◽  
Silicon Waveguides ◽  
X Ray ◽  
Full Characterization ◽  
X Ray Scattering ◽  
Beam Commissioning ◽  
First Time

The micro- and nanofocus X-ray scattering (MINAXS) beamline of PETRA III is equipped with two consecutively arranged endstations, the last of which is the nanofocus endstation. The first in-beam commissioning of the experimental equipment was successfully performed at the end of 2010, using two-dimensionally confining hard X-ray silicon waveguides with cross sections of 50 nm × 50 µm to 50 nm × 2 µm for nanobeam generation. A full characterization of the waveguide-generated beams was performed, giving values for the beam geometries, the transmission efficiencies of the waveguides and absolute fluxes. Along with these results a detailed description of the setup is presented in this paper. A first high-resolution nanodiffraction experiment on a nanocrystalline TiN hard coating was performed to verify the resolution of the nanodiffraction setup and to reveal the local gradients across the blasted TiN coating. In conclusion, the main concern is the availability of the nanobeam, how it was generated and the fact that a beam out of a two-dimensionally confining waveguide was used for diffraction experiments for the first time.

scholarly journals Computational studies on eukaryotic transmembrane β-barrel proteins

2018 ◽  
Author(s):  
Ahmed F. Roumia ◽  
Margarita C. Theodoropoulou ◽  
Konstantinos D. Tsirigos ◽  
Pantelis G. Bagos
Keyword(s):  
Computational Analysis ◽  
Markov Models ◽  
Outer Membrane Proteins ◽  
Computational Studies ◽  
Cellular Functions ◽  
Pfam Database ◽  
Eukaryotic Proteins ◽  
Transport Of Ions ◽  
First Time

Transmembrane β-barrel proteins perform multiple cellular functions such as passive transport of ions and allowing the flux of molecules. Also, they act as enzymes, transporters, receptors and virulence factors. Even though, in the last few years, several families of eukaryotic β-barrel outer membrane proteins (OMPs) have been discovered, the computational characterization of these families is far from complete. The PFAM database includes only very few characteristic profiles for these families and, in most cases, the profile Hidden Markov Models where trained using both prokaryotic and eukaryotic proteins. Here, we present, for the first time, a comprehensive computational analysis of eukaryotic transmembrane β- barrels. Ten characteristic pHMMs were build that can discriminate eukaryotic β-barrels from other classes of β-barrel proteins (globular and bacterial) and are, also, capable of discriminating between mitochondrial and chloroplastic ones. Specifically, we built six new pHMMs for the chloroplastic β-barrel families not included in the PFAM database and, also, updated the profile for MDM10 family (PF12519) and divided the porin family (PF01459) into two separated families VDAC and TOM40. We hope that all the pHMMs presented here will be used for the detection and characterization of eukaryotic OMPs in newly discovered proteomes.

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