scholarly journals Improved control through a semi-batch process in RAFT-mediated polymerization utilizing relatively poor leaving groups

2015 ◽  
Vol 6 (46) ◽  
pp. 7945-7948 ◽  
Author(s):  
Alexander Ilchev ◽  
Rueben Pfukwa ◽  
Lebohang Hlalele ◽  
Marica Smit ◽  
Bert Klumperman
Keyword(s):  
Batch Process ◽  
Batch Mode ◽  
Leaving Group ◽  
Raft Agent ◽  
Negative Effect ◽  
Leaving Groups

The negative effect that a RAFT agent with a poor leaving group has on the evolution of molecular dispersity in a RAFT-mediated polymerization was shown to be mitigated by performing the polymerization in semi-batch mode.

The effect of steric size of leaving group on rates of the competing syn- and anti-pathways in biomolecular elimination

1980 ◽  
Vol 45 (8) ◽  
pp. 2171-2178
Author(s):  
Jiří Závada ◽  
Magdalena Pánková
Keyword(s):  
Comparative Analysis ◽  
Homologous Series ◽  
Leaving Group ◽  
Leaving Groups

Approximate rates of the competing syn- and anti-pathways have been determined in t-C4H9OK-t-C4H9OH promoted elimination from two homologous series of tosylates: I-OTs trans-III (R = H, CH3, C2H5, n-C3H7, i-C3H7, t-C4H9) and II-OTs trans-IV (R = CH3, C2H5, n-C3H7, i-C3H7, t-C4H9). A comparison has been made with rates of the same processes in the (+) elimination of the corresponding trimethylammonium salts I-N(CH3)3 trans-III and (+) II-N(CH3)3 trans-IV. The title effect is demonstrated by a comparative analysis of the rate patterns obtained for the two leaving groups.

Copper(II) complexes with tridentate halogen‐substituted Schiff base ligands: synthesis, crystal structures and investigating the effect of halogenation, leaving group and ligand flexibility on antiproliferative activities

2021 ◽  
Author(s):  
Nazanin Kordestani ◽  
Hadi Amiri Rudbari ◽  
Alexandra R Fernandes ◽  
Luís R Raposo ◽  
André Luz ◽  
...  
Keyword(s):  
Schiff Base ◽  
Anticancer Activity ◽  
Crystal Structures ◽  
Copper Complexes ◽  
Schiff Base Ligands ◽  
Leaving Group ◽  
Leaving Groups ◽  
Tridentate Schiff Base ◽  
Antiproliferative Activities

To investigate the effect of different halogen substituents, leaving groups and the flexibility of ligand on the anticancer activity of copper complexes, sixteen copper(II) complexes with eight different tridentate Schiff-base...

DENSITY FUNCTIONAL STUDY OF SELECTED MONO-ZINC AND GEM-DIZINC RADICAL CARBENOID CYCLOPROPANATION REACTIONS: OBSERVATION OF AN EFFICIENT RADICAL ZINC CARBENOID CYCLOPROPANATION REACTION AND THE INFLUENCE OF THE LEAVING GROUP ON RING CLOSURE

2003 ◽  
Vol 02 (03) ◽  
pp. 357-369 ◽  
Author(s):  
CUNYUAN ZHAO ◽  
DONG-QI WANG ◽  
DAVID LEE PHILLIPS
Keyword(s):  
Density Functional ◽  
Theoretical Study ◽  
Radical Reaction ◽  
Ring Closure ◽  
Functional Study ◽  
Reaction Step ◽  
Leaving Group ◽  
Reaction Barriers ◽  
Leaving Groups ◽  
Zinc Carbenoid

We report a theoretical study of the cyclopropanation reactions of EtZnCHI, (EtZn)2CH EtZnCHZnI, and EtZnCIZnI radicals with ethylene. The mono-zinc and gem-dizinc radical carbenoids can undergo cyclopropanation reactions with ethylene via a two-step reaction mechanism similar to that previously reported for the CH2I and IZnCH2 radicals. The barrier for the second reaction step (ring closure) was found to be highly dependent on the leaving group of the cyclopropanation reaction. In some cases, the (di)zinc carbenoid radical undergoes cyclopropanation via a low barrier of about 5–7 kcal/mol on the second reaction step and this is lower than the CH2I radical reaction which has a barrier of about 13.5 kcal/mol for the second reaction step. Our results suggest that in some cases, zinc radical carbenoid species have cyclopropanation reaction barriers that can be competitive with their related molecular Simmons-Smith carbenoid species reactions and produce somewhat different cyclopropanated products and leaving groups.

scholarly journals AUTOMATED SYSTEM FOR CONTINUOUS MICROALGAE CULTIVATION IN PHOTOBIOREACTORS

2017 ◽  
Vol 16 (2) ◽  
pp. 03
Author(s):  
D. A. L. D’Agostin ◽  
G. M. Domene ◽  
A. S. Oliveira ◽  
M. J. C. Bonfim ◽  
A. B. Mariano
Keyword(s):  
Continuous Production ◽  
Batch Process ◽  
Automated System ◽  
Control Mode ◽  
Raspberry Pi ◽  
Percentage Error ◽  
Monitoring And Control ◽  
Microalgae Cultivation ◽  
Batch Mode ◽  
Continuous Regime

The objective of this work was to design a automate system for microalgae cultivation on a continuous modes in laboratory scale and allow its remote monitoring and control. For this, a sensor were developed is able to measure biomass concentration. The concentration sensor used the principle of light scattering, that is, by measuring the turbidity of the culture medium by the use of a set of phototransistor and green led. It presented an mean absolute percentage error of 8.46% during the experiment. A pH, temperature and light sensor were also installed. The control of all the sensors was accomplished by means of an microcontroller. For remote control and monitoring of the controller, a database was designed and implemented on a Raspberry Pi connected to the network. The graphics and data collected are available on an HTML page that allows changes in the control mode of the photobioreactor, for example by changing the dilution rates. The controller was able to operate the photobioreactor in batch mode, as well as to maintain the culture operating in continuous regime. The continuous production of microalgae biomass in a continuous regime showed productivity 74.5% higher than the traditional batch process and 28.2% higher than semicontinuous cultivation.

scholarly journals Improvement in hydrolytic antibody activity by change in haptenic structure from phosphate to phosphonate with retention of a common leaving-group determinant: evidence for the ‘flexibility’ hypothesis

2003 ◽  
Vol 376 (3) ◽  
pp. 813-821 ◽  
Author(s):  
Sheraz GUL ◽  
Sanjiv SONKARIA ◽  
Surapong PINITGLANG ◽  
José FLOREZ-ALVAREZ ◽  
Syeed HUSSAIN ◽  
...  
Keyword(s):  
Structural Motif ◽  
Catalytic Antibody ◽  
Antibody Activity ◽  
Reaction Centre ◽  
Binding Characteristics ◽  
Leaving Group ◽  
Catalytic Mechanisms ◽  
Leaving Groups ◽  
Antibody Preparations ◽  
Ester Substrate

To investigate the hypothesis that decreased hapten flexibility may lead to increased catalytic antibody activity, we used two closely related immunogens differing only in the flexibility of the atomic framework around the structural motif of the haptens, analogous to the reaction centre of the corresponding substrates. Identical leaving-group determinants in the haptens and identical leaving groups in the substrates removed the ambiguity inherent in some data reported in the literature. Anti-phosphate and anti-phosphonate kinetically homogeneous polyclonal catalytic antibody preparations were compared by using carbonate and ester substrates respectively, each containing a 4-nitrophenolate leaving group. Synthetic routes to a new phosphonate hapten and new ester substrate were developed. The kinetic advantage of the more rigid anti-phosphonate/ester system was demonstrated at pH 8.0 by a 13-fold advantage in kcat/knon-cat and a 100-fold advantage in the proficiency constant, kcat/knon-cat·Km. Despite these differences, the pH-dependences of the kinetic and binding characteristics and the results of chemical modification studies suggest closely similar catalytic mechanisms. The possible origin of the kinetic advantage of the more rigid hapten/substrate system is discussed.

The Formation of Alkenes by the Thermal Elimination Reaction of N-Methyl-4-alkoxypyridinium Iodides. II. An Investigation of the Mechanism

1972 ◽  
Vol 50 (8) ◽  
pp. 1188-1191
Author(s):  
George H. Schmid ◽  
Aaron W. Wolkoff
Keyword(s):  
Elimination Reaction ◽  
Product Composition ◽  
Thermal Elimination ◽  
Leaving Group ◽  
Elimination Reactions ◽  
Leaving Groups

A comparison of the products from elimination reactions of a number of compounds containing various leaving groups with those containing the N-methyl oxypyridinium leaving group suggests that the elimination is not occurring by means of a simple E1 mechanism. Changing the anion of the salt from iodide to methyl-sulphate and tetrafluoroborate affects the product composition indicating that the anion is taking part in the reaction. The mechanism of this reaction appears to be on the E1-E2 borderline.

Investigation into the Initialization Behaviour of RAFT-Mediated Styrene–Maleic Anhydride Copolymerizations

2006 ◽  
Vol 59 (10) ◽  
pp. 742 ◽  
Author(s):  
Eric T. A. van den Dungen ◽  
Jacques Rinquest ◽  
Nadine O. Pretorius ◽  
Jean M. McKenzie ◽  
James B. McLeary ◽  
...  
Keyword(s):  
Maleic Anhydride ◽  
Raft Polymerization ◽  
Polymerization Process ◽  
Unit Model ◽  
Reversible Addition ◽  
Raft Agent ◽  
Addition Rate ◽  
Leaving Groups ◽  
Chain Lengths ◽  
Alternating Copolymerization

The living radical alternating copolymerization of styrene and maleic anhydride mediated by the reversible addition–fragmentation chain transfer (RAFT) polymerization process has been studied at short chain lengths using two different dithiobenzoate RAFT agents. The results indicate specificity of addition of the RAFT-agent leaving groups for either styrene or maleic anhydride. The addition rate of the monomers and the fact that monomers are added individually favour the penultimate unit model of polymer propagation.

Addition and Elimination

2007 ◽  
Author(s):  
Perry A. Frey ◽  
Adrian D. Hegeman
Keyword(s):  
Carboxylic Acid ◽  
Tricarboxylic Acid Cycle ◽  
The Body ◽  
Addition Reactions ◽  
Divalent Metal Ions ◽  
Major Barrier ◽  
Body Of Knowledge ◽  
Leaving Group ◽  
Leaving Groups ◽  
The Many

Most elimination and addition reactions in biochemistry proceed by α,β-elimination/addition mechanisms. In the case of elimination, the leaving group is β to an activating functional group in the substrate. The activating group may be the carbonyl group of a ketone or aldehyde, the iminium group derived from an aldehyde or ketone, or the acyl-carbonyl of a carboxylic acid or ester, and the proton is α to the activating group. Addition reactions in this class are the same reactions in reverse, and they follow the course of the Michael addition in organic chemistry. The generic process is illustrated in scheme 9-1. Substituents among the activating and leaving groups are diverse and are presumed to account for the significant variations among enzymes in the class. A few enzymes in this class catalyze elimination/addition without the assistance of a coenzyme or cofactor. They presumably incorporate sufficiently acidic (A—H) or basic (:B) amino acid side chains to catalyze the proton transfer processes, or they may stabilize carbanionic intermediates by low-barrier hydrogen bonding. Others employ divalent metal ions, pyridoxal-5'-phosphate (PLP), [4Fe–4S] centers, or NAD+ to facilitate the reactions. Cofactors and coenzymes increase the acidity of Cα—H or improve the propensity of the leaving group Y to depart. In most cases, the major barrier consists of increasing the acidity of the Cα—H group, which decreases the pKa. In a few cases, as when the leaving group is a carboxylic acid or a phosphate, no catalysis is required for it to depart. Limited space prevents discussion of the many enzymes that catalyze cofactor-independent α, β-eliminations. We address the actions of fumarase and crotonase because of the historic emphasis on the biochemical significance of these enzymes. Many other dehydratases and ammonia lyases also belong in this group. In the tricarboxylic acid cycle, fumarate arises from the action of succinate dehydrogenase, and fumarase (EC 4.2.1.2) catalyzes the addition of water to form S-malate. The reaction can be monitored in either direction, and in various studies, the kinetic parameters may be quoted as such (e.g., fumarate formation, or malate formation). The body of knowledge about the action of fumarase is surprisingly incomplete, given the importance of the enzyme in metabolism.

Homolytic versus heterolytic cleavage for the photochemistry of 1-naphthylmethyl derivatives

1985 ◽  
Vol 63 (11) ◽  
pp. 3140-3146 ◽  
Author(s):  
B. Arnold ◽  
L. Donald ◽  
A. Jurgens ◽  
J. A. Pincock
Keyword(s):  
Excited Singlet ◽  
Triplet Energy ◽  
Heterolytic Cleavage ◽  
Exciplex Formation ◽  
Singlet States ◽  
Leaving Group ◽  
Excited Singlet States ◽  
Leaving Groups ◽  
Triplet Energy Transfer ◽  
Photochemical Cleavage

The photochemical cleavage of the 1-naphthylmethyl derivatives, 1–7, has been examined in methanol solvent under both direct and sensitized conditions. The competitition between homolytic and heterolytic cleavage as a function of multiplicity and leaving group has been studied in detail. Only substrates 1, 2, 3, and 7 react on sensitization with xanthone but evidence is presented that the resulting reactivity of 1, 2, and 3 may not be triplet energy transfer but rather exciplex formation. A semi-quantitative scale for photofugacities of the leaving groups from the excited singlet states has been established.

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