Carbon Footprints: The Wittig Reaction

Reactions ◽  
2011 ◽  
Author(s):  
Peter Atkins
Keyword(s):  
Wittig Reaction ◽  
Negative Charge ◽  
Positive Charge ◽  
Carbon Chain ◽  
Hydroxide Ion ◽  
Carbon Footprints ◽  
Proper Nouns ◽  
Partial Negative Charge ◽  
Growing Network ◽  
Positive Ion

As a molecular architect working on an atomic construction site you need to be able to build up the carbon skeleton of your project, not merely decorate it with foreign atoms. There are dozens of different ways of doing that, and in this and the next section I shall introduce you to just two of them to give you a taste of what is available. A secondary point is that throughout chemistry you will find reactions denoted by proper nouns, recognizing the chemists who have invented or developed them. One example is that of the ‘Wittig reaction’, which is named after the German chemist Georg Wittig (1897–1987; Nobel Prize 1979). The reaction is used to replace the oxygen atom of a CO group in a molecule by a carbon atom, so that what starts out as decoration becomes part of a growing network of carbon atoms. You need to know that phosphine, PH3, 1, the phosphorus cousin of ammonia, NH3, is a base (Reaction 2). When it accepts a proton it becomes the ion PH4+. The H atoms in that ion can be replaced with other groups of atoms. A replacement that will be of interest is when three of the H atoms have been replaced by benzene rings and the remaining H atom has been replaced by –CH3. The resulting ion is 2. In the presence of a base, such as the hydroxide ion, OH–, the –CH3 group can be induced to release one of its protons, so the positive ion becomes the neutral molecule, 3. Note that there is a partial positive charge on the P atom and a partial negative charge on the C atom of the CH2 group. The presence of that partial negative charge suggests that the species could act as a nucleophile (Reaction 15), a seeker out of positive charge, with the CH2 group the charge-seeking head of the missile. Let’s watch what happens when 3 attacks a molecule with a CO group, specifically 4: perhaps you want to sprout a carbon chain out from the ring and intend to begin by replacing the O atom with a C atom.

Two different products from the reaction of 1-aryl-5-chloro-3-methyl-1H-pyrazole-4-carbaldehyde with cyclohexylamine when the aryl substituent is phenyl or pyridin-2-yl: hydrogen-bonded sheetsversusdimers

2015 ◽  
Vol 71 (5) ◽  
pp. 363-368 ◽  
Author(s):  
Jessica Orrego Hernandez ◽  
Jaime Portilla ◽  
Justo Cobo ◽  
Christopher Glidewell
Keyword(s):  
Hydrogen Bond ◽  
Negative Charge ◽  
Positive Charge ◽  
Molecular Type ◽  
Aryl Substituent ◽  
Centrosymmetric Dimer ◽  
Partial Positive Charge ◽  
Partial Negative Charge ◽  
Independent Molecules ◽  
Compound Ii

Cyclohexylamine reacts with 5-chloro-3-methyl-1-(pyridin-2-yl)-1H-pyrazole-4-carbaldehyde to give 5-cyclohexylamino-3-methyl-1-(pyridin-2-yl)-1H-pyrazole-4-carbaldehyde, C16H20N4O, (I), formed by nucleophilic substitution, but with 5-chloro-3-methyl-1-phenyl-1H-pyrazole-4-carbaldehyde the product is (Z)-4-[(cyclohexylamino)methylidene]-3-methyl-1-phenyl-1H-pyrazol-5(4H)-one, C17H21N3O, (II), formed by condensation followed by hydrolysis. Compound (II) crystallizes withZ′ = 2, and in one of the two independent molecular types the cyclohexylamine unit is disordered over two sets of atomic sites having occupancies of 0.65 (3) and 0.35 (3). The vinylogous amide portion in each compound shows evidence of electronic polarization, such that in each the O atom carries a partial negative charge and the N atom of the cyclohexylamine portion carries a partial positive charge. The molecules of (I) contain an intramolecular N—H...N hydrogen bond, and they are linked by C—H...O hydrogen bonds to form sheets. Each of the two independent molecules of (II) contains an intramolecular N—H...O hydrogen bond and each molecular type forms a centrosymmetric dimer containing oneR22(4) ring and two inversion-relatedS(6) rings.

scholarly journals Zerumbone Inhibits Helicobacter pylori Urease Activity

Molecules ◽  
2021 ◽  
Vol 26 (9) ◽  
pp. 2663
Author(s):  
Hyun Jun Woo ◽  
Ji Yeong Yang ◽  
Pyeongjae Lee ◽  
Jong-Bae Kim ◽  
Sa-Hyun Kim
Keyword(s):  
Helicobacter Pylori ◽  
Carbon Atom ◽  
Natural Compound ◽  
Urease Activity ◽  
Negative Charge ◽  
Positive Charge ◽  
Gastric Epithelium ◽  
Functional Inhibition ◽  
Electrical Gradient ◽  
H Pylori

Helicobacter pylori (H. pylori) produces urease in order to improve its settlement and growth in the human gastric epithelium. Urease inhibitors likely represent potentially powerful therapeutics for treating H. pylori; however, their instability and toxicity have proven problematic in human clinical trials. In this study, we investigate the ability of a natural compound extracted from Zingiber zerumbet Smith, zerumbone, to inhibit the urease activity of H. pylori by formation of urease dimers, trimers, or tetramers. As an oxygen atom possesses stronger electronegativity than the first carbon atom bonded to it, in the zerumbone structure, the neighboring second carbon atom shows a relatively negative charge (δ−) and the next carbon atom shows a positive charge (δ+), sequentially. Due to this electrical gradient, it is possible that H. pylori urease with its negative charges (such as thiol radicals) might bind to the β-position carbon of zerumbone. Our results show that zerumbone dimerized, trimerized, or tetramerized with both H. pylori urease A and urease B molecules, and that this formation of complex inhibited H. pylori urease activity. Although zerumbone did not affect either gene transcription or the protein expression of urease A and urease B, our study demonstrated that zerumbone could effectively dimerize with both urease molecules and caused significant functional inhibition of urease activity. In short, our findings suggest that zerumbone may be an effective H. pylori urease inhibitor that may be suitable for therapeutic use in humans.

scholarly journals Indication of the Coronavirus Model Using a Nanowire Biosensor

Proceedings ◽  
2020 ◽  
Vol 60 (1) ◽  
pp. 50
Author(s):  
Vladimir Generalov ◽  
Olga Naumova ◽  
Dmitry Shcherbakov ◽  
Alexander Safatov ◽  
Boris Zaitsev ◽  
...  
Keyword(s):  
Field Effect ◽  
Field Effect Transistor ◽  
Negative Charge ◽  
Positive Charge ◽  
Silicon On Insulator ◽  
Nanowire Surface ◽  
Before And After ◽  
Effect Transistor ◽  
Current Value ◽  
Silicon On Insulator Technology

The presented results indicate virus-like particles of the coronavirus (CVP) using a nanowire (NW) biosensor based on silicon-on-insulator technology. In the experiment, we used suspensions of CVP and of specific antibodies to the virus. Measurements of the current value of the field-effect transistor before and after the introduction of the CVP on the surface of the nanowire were performed. Results showed antibody + CVP complexes on the phase section with the surface of the nanowire modulate the current of the field-effect transistor; CVP has an electrically positive charge on the phase section “nanowire surface-viral suspension»; antibody + CVP complexes have an electrically negative charge on the phase section “nanowire surface-viral suspension”; the sensitivity of the biosensor is made up of 10−18 M; the time display was 200–300 s.

scholarly journals The mechanism of spray electrification: the waterfall effect

2016 ◽  
Author(s):  
James K. Beattie
Keyword(s):  
Negative Charge ◽  
Positive Charge ◽  
Hydrophobic Hydration ◽  
General Phenomenon ◽  
Aqueous Interfaces ◽  
Preferential Adsorption ◽  
Negative Surface ◽  
Negative Surface Charge ◽  
Low Permittivity ◽  
Net Positive Charge

Abstract. The waterfall effect describes the separation of charge by splashing at the base of a waterfall. Smaller drops that have a net negative charge are created, while larger drops and/or the bulk maintain overall charge neutrality with a net positive charge. Since it was first described by Lenard (1892) the effect has been confirmed many times, but a molecular explanation has not been available. Application of our fluctuation-correlation model of hydrophobic hydration accounts for the negative charge observed at aqueous interfaces with low permittivity materials. The negative surface charge observed in the waterfall effect is created by the preferential adsorption of hydroxide ions generated from the autolysis of water. On splashing, shear forces generate small negative drops from the surface, leaving a positive charge on the remaining large fragment. The waterfall effect is a manifestation of the general phenomenon of the negative charge at the interface between water and hydrophobic surfaces that is created by the preferential adsorption of hydroxide ions.

THE EFFECT OF PROCOAGULANT PHOSPHOLIPID VESICLES WITH NET POSITIVE CHARGE ON THE ACTIVITY OF PROTHROMBINASE

1987 ◽  
Author(s):  
J Rosing ◽  
H Speijer ◽  
J W P Govers-Riemslag ◽  
R F A Zwaal
Keyword(s):  
Vitamin K ◽  
Negative Charge ◽  
Positive Charge ◽  
Coagulation Factor ◽  
Phospholipid Vesicles ◽  
Electrostatic Model ◽  
Acidic Phospholipid ◽  
Positively Charged ◽  
Net Positive Charge ◽  
Prothrombin Activation

It is generally thought that procoagulant phospholipid surfaces that promote the activation of vitamin K-dependent coagulation factors should have a net negative charge in order to promote calcium-dependent binding of the enzymes (FVIIa, FIXa and FXa) and substrates (prothrombin and FX) of the coagulation factor-activating complexes. Two models have been proposed to explain calcium-mediated association of vitamin K-dependent proteins with phospholipid: a) an electrostatic model, in which a positively-charged protein-calcium complex is attracted by a negatively-charged phospholipid surface and b) a chelation model in which a coordination complex is formed between calcium ions, γ-carboxyglutamic acids of the proteins and negatively-charged membrane phospholipids. To study the effect of the electrostatic potential of phospholipid vesicles on their activity in the pro-thrombinase complex the net charge of vesicles was varied by introduction of varying amounts of positively-charged stearylamine in the membrane surface. Introduction of 0-15 mole% stearylamine in phospholipid vesicles that contained 5 mole% phosphatidylseri-ne (PS) hardly affected their activity in prothrombin activation. Electrophoretic analysis showed that vesicles with > 5 mole% stearylamine had a net positive charge. The procoagulant activity of vesicles that contained phosphatidic acid, phosphatidylglyce-rol, phosphatidylinositol or phosphatidyl-glactate (PLac) as acidic phospholipid was much more effected by incorporation of stearylamine. Amounts of stearylamine that compensated the negative charge of acidic phospholipid caused considerable inhibition of the activity of the latter vesicles in prothrombin activation. The comparison of vesicles containing PS and PLac as acidic phospholipid is of special interest. PS and PLac only differ by the presence of NH+ 3-group in the serine moiety of PS. Thus, in spite of the fact that vesicles with PLac are more negatively charged than vesicles with PS, they are less procoagulant. Our results show that a) although procoagulant membranes have to contain acidic phospholipids there is no requirement for a net negative charge, b) the amino group of phosphatidylserine has an important function in the interaction of procoagulant membranes with vitamin K-dependent proteins and c) the chelation model can satisfactorily explain calcium-mediated lipid-protein association.

Electrokinetic properties of Cassiterite

1953 ◽  
Vol 6 (3) ◽  
pp. 278 ◽  
Author(s):  
DJ O'Connor ◽  
AS Buchanan
Keyword(s):  
Negative Charge ◽  
Positive Charge ◽  
Weak Acid ◽  
Surface Conductivity ◽  
Surface Ionization ◽  
Conductivity Measurements ◽  
The Third ◽  
Three Samples ◽  
Negative Surface ◽  
Flotation Collector

Simultaneous ζ-potential and surface conductivity measurements have been made on three samples of cassiterite (SnO2) in water, in solutions of HCl, alkalis, inorganic salts, and the flotation collector reagent sodium cetyl sulphate. It is probable that the intrinsic surface charge of cassiterite in water is negative and that it is due to surface ionization as a very weak acid. Two of the solids possessed a negative surface whilst the positive charge of the third seemed to be due to ionization of a strongly basic impurity. Those samples having a negative charge showed little reaction with sodium cetyl sulphate alone, but appreciable adsorption of cetyl sulphate ion took place in acid solution. On the other hand, the sample with the positive surface reacted with cetyl sulphate ion even in the absence of acid. In all cases adsorption of cetyl sulphate was completely reversible.

scholarly journals Electrical and Polarimetric Radar Observations of a Multicell Storm in TELEX

2007 ◽  
Vol 135 (7) ◽  
pp. 2525-2544 ◽  
Author(s):  
Eric C. Bruning ◽  
W. David Rust ◽  
Terry J. Schuur ◽  
Donald R. MacGorman ◽  
Paul R. Krehbiel ◽  
...  
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Negative Charge ◽  
Positive Charge ◽  
Three Dimensional ◽  
Phase Region ◽  
Polarimetric Radar ◽  
Radar Observations ◽  
Mapping Array ◽  
Lightning Initiation

Abstract On 28–29 June 2004 a multicellular thunderstorm west of Oklahoma City, Oklahoma, was probed as part of the Thunderstorm Electrification and Lightning Experiment field program. This study makes use of radar observations from the Norman, Oklahoma, polarimetric Weather Surveillance Radar-1988 Doppler, three-dimensional lightning mapping data from the Oklahoma Lightning Mapping Array (LMA), and balloon-borne vector electric field meter (EFM) measurements. The storm had a low flash rate (30 flashes in 40 min). Four charge regions were inferred from a combination of LMA and EFM data. Lower positive charge near 4 km and midlevel negative charge from 4.5 to 6 km MSL (from 0° to −6.5°C) were generated in and adjacent to a vigorous updraft pulse. Further midlevel negative charge from 4.5 to 6 km MSL and upper positive charge from 6 to 8 km (from −6.5° to −19°C) were generated later in quantity sufficient to initiate lightning as the updraft decayed. A negative screening layer was present near the storm top (8.5 km MSL, −25°C). Initial lightning flashes were between lower positive and midlevel negative charge and started occurring shortly after a cell began lofting hydrometeors into the mixed phase region, where graupel was formed. A leader from the storm’s first flash avoided a region where polarimetric radar suggested wet growth and the resultant absence of noninductive charging of those hydrometeors. Initiation locations of later flashes that propagated into the upper positive charge tracked the descending location of a polarimetric signature of graupel. As the storm decayed, electric fields greater than 160 kV m−1 exceeded the minimum threshold for lightning initiation suggested by the hypothesized runaway breakdown process at 5.5 km MSL, but lightning did not occur. The small spatial extent (≈100 m) of the large electric field may not have been sufficient to allow runaway breakdown to fully develop and initiate lightning.

The influence of organic matter extracted from humified clover on the properties of amorphous aluminosilicates. I. Surface charge

Soil Research ◽  
1978 ◽  
Vol 16 (3) ◽  
pp. 327 ◽  
Author(s):  
KW Perrott
Keyword(s):  
Surface Charge ◽  
Negative Charge ◽  
Positive Charge ◽  
Degree Of Polymerization ◽  
Aqueous Extracts ◽  
Hydrous Oxides ◽  
Soil Clays ◽  
Charge Balancing ◽  
Inorganic Components ◽  
Allophanic Soil

A series of synthetic amorphous aluminosilicates, hydrous oxides and allophanic soil clays were treated with aqueous extracts of humified clover. The resulting changes in surface charge due to organic treatment were determined by comparing the charge characteristics of these organic treated samples and samples treated with a synthetic mixture of the inorganic components of the humified clover extract. Organic treatment caused a change of net surface charge to more negative values. The change in surface charge varied with the mole ratio Al/(Al+Si) of the aluminosilicate, being largest at low values of Al/(Al+Si). Where the aluminosilicates contain positive charges these are reduced by the organic treatment. This is a major contributor to the alteration of net surface charge in the more aluminous samples. The effect of organic treatment on the charge characteristics of allophanic soil clays was similar to that for the synthetic aluminosilicates of intermediate composition. The inorganic treatments also caused an increase in negative charge, and this is attributed to the neutralization of positive charge by the adsorption of phosphate and the removal of charge-balancing aluminium-hydroxy material. The effect of the organic and inorganic treatments on the positive and negative charge components of amorphous aluminosilicates is discussed in terms of the degree of polymerization of chargebalancing hydroxy-aluminium as envisaged in current models of the structure of amorphous aluminosilicates.

scholarly journals C5-Substituted 2-Selenouridines Ensure Efficient Base Pairing with Guanosine; Consequences for Reading the NNG-3′ Synonymous mRNA Codons

2020 ◽  
Vol 21 (8) ◽  
pp. 2882 ◽  
Author(s):  
Grazyna Leszczynska ◽  
Marek Cypryk ◽  
Bartlomiej Gostynski ◽  
Klaudia Sadowska ◽  
Paulina Herman ◽  
...  
Keyword(s):  
Gene Expression ◽  
Density Functional ◽  
Negative Charge ◽  
Positive Charge ◽  
Dominant Role ◽  
Regulation Of Gene Expression ◽  
Side Chain ◽  
Functional Theory ◽  
Physiological Conditions ◽  
Synonymous Codons

5-Substituted 2-selenouridines (R5Se2U) are post-transcriptional modifications present in the first anticodon position of transfer RNA. Their functional role in the regulation of gene expression is elusive. Here, we present efficient syntheses of 5-methylaminomethyl-2-selenouridine (1, mnm5Se2U), 5-carboxymethylaminomethyl-2-selenouridine (2, cmnm5Se2U), and Se2U (3) alongside the crystal structure of the latter nucleoside. By using pH-dependent potentiometric titration, pKa values for the N3H groups of 1–3 were assessed to be significantly lower compared to their 2-thio- and 2-oxo-congeners. At physiological conditions (pH 7.4), Se2-uridines 1 and 2 preferentially adopted the zwitterionic form (ZI, ca. 90%), with the positive charge located at the amino alkyl side chain and the negative charge at the Se2-N3-O4 edge. As shown by density functional theory (DFT) calculations, this ZI form efficiently bound to guanine, forming the so-called “new wobble base pair”, which was accepted by the ribosome architecture. These data suggest that the tRNA anticodons with wobble R5Se2Us may preferentially read the 5′-NNG-3′ synonymous codons, unlike their 2-thio- and 2-oxo-precursors, which preferentially read the 5′-NNA-3′ codons. Thus, the interplay between the levels of U-, S2U- and Se2U-tRNA may have a dominant role in the epitranscriptomic regulation of gene expression via reading of the synonymous 3′-A- and 3′-G-ending codons.

scholarly journals Interactions between apo-(d-β-hydroxybutyrate dehydrogenase) and phospholipids studied by intrinsic and extrinsic fluorescence

1986 ◽  
Vol 237 (2) ◽  
pp. 359-364 ◽  
Author(s):  
M S el Kebbaj ◽  
N Latruffe ◽  
M Monsigny ◽  
A Obrenovitch
Keyword(s):  
Conformational Changes ◽  
Negative Charge ◽  
Positive Charge ◽  
Tryptophan Residue ◽  
Fluorescence Energy Transfer ◽  
Hydrophobic Region ◽  
Phospholipid Liposomes ◽  
Tryptophan Residues ◽  
Beta Hydroxybutyrate ◽  
Fluorescence Energy

Interactions of D-beta-hydroxybutyrate dehydrogenase with phospholipids were investigated by both intrinsic- and extrinsic-fluorescence approaches. The intrinsic fluorescence, mainly caused by tryptophan residues, increased upon re-activation in the presence of phospholipids bearing a positive charge, i.e. phosphatidylcholine, but decreased in the presence of non-re-activating phospholipids with a negative charge. This indicates either that the environment of tryptophan residues is affected by charges rather than by hydrophobic chains of phospholipids, or that the enzyme undergoes different conformational changes depending on the nature of the phospholipids. On the other hand, the graph of the temperature-dependence of the fluorescence intensities of the enzyme embedded in dimyristoylphosphatidylcholine liposomes exhibits a break around 21 degrees C. This indicates either that at least one tryptophan residue is closely in contact with the hydrophobic chains of phospholipids or that there is a change in the environment of tryptophan residues owing to the physical state of the phospholipids. The addition of D-beta-hydroxybutyrate apo-dehydrogenase to phospholipid liposomes containing diphenylhexatriene (a fluorescent probe) increased the diphenylhexatriene fluorescence polarization. Moreover, there was a partial fluorescence energy transfer from tryptophan to diphenylhexatriene. These results strongly favour the possibility that there is a portion of the enzyme polypeptide chain inserted into the phospholipid hydrophobic region. All these results demonstrate that D-beta-hydroxybutyrate apo-dehydrogenase interacts with both polar and hydrophobic parts of phospholipids and leads to small, but essential, conformational changes of the enzyme.

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