scholarly journals Chiral Amphiphilic Secondary Amine-Porphyrin Hybrids for Aqueous Organocatalysis

Molecules ◽  
2020 ◽  
Vol 25 (15) ◽  
pp. 3420 ◽  
Author(s):  
Aitor Arlegui ◽  
Pol Torres ◽  
Victor Cuesta ◽  
Joaquim Crusats ◽  
Albert Moyano
Keyword(s):  
Catalytic Activity ◽  
High Yield ◽  
Aldol Reactions ◽  
Free Base ◽  
Reaction Products ◽  
Chirality Transfer ◽  
Base Form ◽  
Low Degree ◽  
Acidic Conditions ◽  
Ph Dependent

Two chiral proline-derived amphiphilic 5-substituted-10,15,20-tris(4-sulfonatophenyl)porphyrins were prepared, and their pH-dependent supramolecular behavior was studied. In neutral aqueous solutions, the free-base form of the hybrids is highly soluble, allowing enamine-based organocatalysis to take place, whereas under acidic conditions, the porphyrinic protonated core of the hybrid leads to the formation of self-assembled structures, so that the hybrids flocculate and their catalytic activity is fully suppressed. The low degree of chirality transfer observed for aqueous Michael and aldol reactions strongly suggests that these reactions take place under true “in water” organocatalytic conditions. The highly insoluble catalyst aggregates can easily be separated from the reaction products by centrifugation of the acidic reaction mixtures, and after neutralization and desalting, the sodium salts of the sulfonated amine-porphyrin hybrids, retaining their full catalytic activity, can be recovered in high yield.

Synthesis and Photophysical Properties of a Conformationally Flexible Mixed Porphyrin Star-Pentamer

2009 ◽  
Vol 62 (7) ◽  
pp. 692 ◽  
Author(s):  
Toby D. M. Bell ◽  
Sheshanath V. Bhosale ◽  
Kenneth P. Ghiggino ◽  
Steven J. Langford ◽  
Clint P. Woodward
Keyword(s):  
Energy Transfer ◽  
Photophysical Properties ◽  
Fluorescence Decay ◽  
High Yield ◽  
Free Base ◽  
Time Resolved ◽  
Zinc Porphyrin ◽  
Relative Contribution ◽  
Synthetic Strategy ◽  
Decay Times

The synthesis of a porphyrin star-pentamer bearing a free-base porphyrin core and four zinc(ii) metalloporphyrins, which are tethered by a conformationally flexible linker about the central porphyrin’s antipody, is described. The synthetic strategy is highlighted by the use of olefin cross metathesis to link the five chromophores together in a directed fashion in high yield. Photoexcitation into the Soret absorption band of the zinc porphyrin chromophores at 425 nm leads to a substantial enhancement of central free-base porphyrin fluorescence, indicating energy transfer from the photoexcited zinc porphyrin (outer periphery) to central free-base porphyrin. Time-resolved fluorescence decay profiles required three exponential decay components for satisfactory fitting. These are attributed to emission from the central free-base porphyrin and to two different rates of energy transfer from the zinc porphyrins to the free-base porphyrin. The faster of these decay components equates to an energy-transfer rate constant of 3.7 × 109 s–1 and an efficiency of 83%, whereas the other is essentially unquenched with respect to reported values for zinc porphyrin fluorescence decay times. The relative contribution of these two components to the initial fluorescence decay is ~3:2, similar to the 5:4 ratio of cis and trans geometric isomers present in the pentamer.

Highly Diastereoselective and Irreversible Aldol Reactions of N-Sulfonylimidates

Synthesis ◽  
2016 ◽  
Vol 48 (19) ◽  
pp. 3413-3419 ◽  
Author(s):  
Hannah Bartrum ◽  
Sébastien Carret ◽  
Jean-François Poisson
Keyword(s):  
Lewis Acid ◽  
High Yield ◽  
Aldol Reactions ◽  
Titanium Complex ◽  
Reaction Proceeds

A mild method for the aldolization of N-sulfonylimidates was developed. The reaction proceeds in excellent diastereoselectivity to provide a range of useful β-hydroxyimidates in high yield. The innate reversibility of the reaction is suppressed by the use of a titanium complex as a Lewis acid.

Thermochromism of Metal Exchange Reaction between Zinc(II) and Mercury(II) Porphyrins

1995 ◽  
Vol 50 (4) ◽  
pp. 545-550 ◽  
Author(s):  
Masaaki Tabata ◽  
Masahiro Ide ◽  
Kentaro Kaneko
Keyword(s):  
Aqueous Solution ◽  
Exchange Reaction ◽  
Thermodynamic Parameters ◽  
Distribution Curve ◽  
Equilibrium Constants ◽  
Metal Exchange ◽  
Free Base ◽  
Temperature Range ◽  
Base Form ◽  
Metal Exchange Reaction

Thermochromism was observed for an aqueous solution containing zinc(II) and mercury( II) cations and N-p-nitrobenzyl-5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin anion (NO2Bz(Htpps)4-) in the temperature range 10 to 70 °C. The equilibrium constants and the thermodynamic parameters of Zn(NO2Bztpps)3- and Hg(NO2Bztpps)3- have been determined spectrophotometrically to elucidate the thermochromism at 10, 15, 20, 25 and 30 °C in 0.1 mol dm-3 NaNO3. The protonation and metalation constants of NO2Bz(Htpps)4- are defined as K2 = [H2P][H+]-1[HP]-1, K3 = [H3P][H+]-1[H2P]-1 and KMP = [M P][H+][M2+]-1[HP]-1, where HP and MP denote the free base form of the prophyrin and the metalloporphyrins of zinc(II) and mercury(II), respectively. Charges of the prophyrin and metalloporphyrins are omitted for simplicity. The following values were found: logK2 = 7.75 ±0.02 (25 °C), ΔH°/kJmol-1 = -21.2±0.5 and ΔS°/Jmol-1K-1 = 77±1, logK3 = 2.55±0.02 (25 °C), ΔH°/kJmol-1 = -25±0.8 and ΔS°/Jmol-1K-1 = -35±3 and log KZnP = 0.63±0.03 (25 °C), ΔH°/kJmol-1 = 31.0±0.8 and ΔS°/Jmol-1K-1 = 116±3, logKHgP = 6.22±0.03 (25 °C), ΔH°/kJmol-1 = 4.5±0.7 and ΔS°/Jmol-1K-1 = 134±2. The distribution curve calculated from the thermodynamic parameters sufficiently agrees with the observed metal exchange reaction between the metalloporphyrins.

scholarly journals Effect of Fe Additives on the Catalytic Performance of Ion-Exchanged CsX Zeolites for Side-Chain Alkylation of Toluene with Methanol

Catalysts ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 829 ◽  
Author(s):  
Zhang ◽  
Yuan ◽  
Miao ◽  
Li ◽  
Shan ◽  
...  
Keyword(s):  
Catalytic Activity ◽  
Catalytic Performance ◽  
High Yield ◽  
Side Chain ◽  
Impregnation Method ◽  
Basic Sites ◽  
Lewis Acidic Sites ◽  
X Zeolite ◽  
Acidic Sites ◽  
Negative Effect

The side-chain alkylation of toluene with methanol was investigated over some Fe-modified Cs ion-exchanged X zeolite (CsX) catalysts prepared via the impregnation method using different iron sources. The absorption/activation behaviors of the reactants on the surface of the catalysts were studied by in situ Fourier-transform infrared (FT-IR) spectroscopy and temperature programmed desorption (TPD) mass measurements. Modification of CsX with a small amount of FeCl3 could result in a considerable decrease in catalytic activity, due mainly to the remarkable decrease in the density of acidic and basic sites of the catalysts. Interestingly, the Fe(NO3)3-modified CsX with an optimum Fe loading of 0.15 wt.% shows improved catalytic activity and high yield compared to the side-chain alkylation products. Modification of CsX with Fe(NO3)3 could also result in a decrease in basic sites of the catalyst. However, such a change does not bring an obvious negative effect on the adsorption/activation of toluene, while it could effectively inhibit the generation of the undesired bidentate formate. Furthermore, the introduced FeOx species (derived from the decomposition of Fe(NO3)3) may also act as new Lewis acidic sites to participate in the activation of methanol and to stabilize the formed active intermediates (i.e., unidentate formate). Therefore, modification of CsX with a suitable amount of Fe(NO3)3 may adjust its adsorption/activation ability for reagents by changing the acid–base properties of the catalyst, which can finally enhance the catalytic performance for the side-chain alkylation of toluene with methanol.

scholarly journals Distribution of Methanol-Water and Ethanol-Water Mixtures in Strongly Basic Polystyrene Anion Exchangers in Free Base Form.

1962 ◽  
Vol 16 ◽  
pp. 392-402 ◽  
Author(s):  
Eero Sjöström ◽  
Lalli Nykänen ◽  
Pekka Laitinen ◽  
G. A. Sim ◽  
Olof Theander ◽  
...  
Keyword(s):  
Free Base ◽  
Anion Exchangers ◽  
Base Form

Na+/NH4+, Na+/H+ Exchanges and NH3 Movement Across the Gill of Carassius Auratus

1973 ◽  
Vol 58 (1) ◽  
pp. 255-275 ◽  
Author(s):  
J. MAETZ
Keyword(s):  
Carassius Auratus ◽  
External Medium ◽  
Ammonia Excretion ◽  
Alkaline Media ◽  
Ionic Balance ◽  
Free Base ◽  
Acid Media ◽  
Base Form ◽  
Monovalent Ions ◽  
The Law

1. Sodium exchange, ammonia excretion and H+ ion movement across the gill were measured in sodium-depleted Carassius auratus. Sodium uptake and ammonia excretion are considerably enhanced by sodium depletion. In this respect sodium-depleted fish behave as ammonia-loaded fish. 2. A decrease of the external pH by one unit results in a 50-60% decrease in both influx and efflux of sodium. A transient augmentation of the rate of ammonia excretion is observed upon acidification, suggesting an increased permeability of the gill to the free-base form of ammonia. 3. The ionic balance sheet of the movements of the monovalent ions across the gill was drawn up when a permeant co-ion for sodium was absent from the external medium. In both acid and alkaline media the ionic balance was achieved in accordance with the law of electroneutrality of external and internal solutions. 4. Net Na+ uptake was only found to be correlated to NH4+ excretion if H+ ion movements across the gill were taken into account. 5. Ammonia-gradient experiments were performed to test the ability of the gill to excrete ammonia against a gradient of ammonia partial pressure. Ammonia excretion is independent of this gradient in alkaline media when sodium ions are present. In these conditions ammonia moves in the ionic form. In acid media, with Na present in the external medium, ammonia movement is correlated with the pNH3 gradient but uphill movement still occurs. Ammonia moves in both the free-base and the ionized forms. In the absence of external sodium, movements of ammonia obey the law for passive transfer and ammonia moves exclusively in the free-base form, even though the external medium is alkaline.

scholarly journals A New pH-Dependent Macrocyclic Rhodamine B-Based Fluorescent Probe for Copper Detection in White Wine

Sensors ◽  
2019 ◽  
Vol 19 (20) ◽  
pp. 4514 ◽  
Author(s):  
Nour Doumani ◽  
Elias Bou-Maroun ◽  
Jacqueline Maalouly ◽  
Maya Tueni ◽  
Adrien Dubois ◽  
...  
Keyword(s):  
Rhodamine B ◽  
White Wine ◽  
Green Solvent ◽  
Acidic Media ◽  
One Pot ◽  
Acidic Conditions ◽  
Ph Conditions ◽  
Ph Dependent ◽  
Copper Detection ◽  
Color Emission

For efficiently measuring copper (II) ions in the acidic media of white wine, a new chemosensor based on rhodamine B coupled to a tetraazamacrocyclic ring (13aneN4CH2NH2) was designed and synthesized by a one-pot reaction using ethanol as a green solvent. The obtained chemosensor was characterized via NMR, UV and fluorescent spectra. It was marked with no color emission under neutral pH conditions, with a pink color emission under acidic conditions, and a magenta color emission under acidic conditions where copper (II) ions were present. The sensitivity towards copper (II) ions was tested and verified over Ca2+, Ag+, Zn2+, Mg2+, Co2+, Ni2+, Fe2+, Pb2+, Cd2+, Fe3+, and Mn2+, with a detection limit of 4.38 × 10−8 M in the fluorescence spectrum.

Synthesis of 1,2-Diamine Bifunctional Catalysts for the Direct Aldol Reaction Through Probing the Remote Amide Hydrogen

2019 ◽  
Vol 6 (2) ◽  
pp. 171-176
Author(s):  
Rajasekhar Dodda ◽  
Sampak Samanta ◽  
Matthew Su ◽  
John Cong-Gui Zhao
Keyword(s):  
Hydrogen Bonding ◽  
Catalytic Activity ◽  
Aldol Reaction ◽  
Catalytic Efficiency ◽  
Aldol Reactions ◽  
Catalyst Loading ◽  
Bifunctional Catalysts ◽  
Amide Hydrogen ◽  
Highly Efficient ◽  
Direct Aldol Reaction

Background: While proline can catalyze the asymmetric direct aldol reactions, its catalytic activity and catalyst turnover are both low. To improve the catalytic efficiency, many prolinebased organocatalysts have been developed. In this regard, prolinamide-based bifunctional catalysts have been demonstrated by us and others to be highly efficient catalysts for the direct aldol reactions. Results: Using the β-acetamido- and β-tosylamidoprolinamide catalysts, the highly enantio- and diastereoselective direct aldol reactions between enolizable ketones and aldehydes were achieved (up to >99% ee, 98:2 dr). A low catalyst loading of only 2-5 mol % of the β-tosylamidoprolinamide catalyst was needed to obtain the desired aldol products in good to high yields and high stereoselectivities. Methods: By carefully adjusting the hydrogen bonding ability of the remote β-amide hydrogen of the 1,2-diamine-based prolinamide bifunctional catalysts, the catalytic activity and the asymmetric induction of these catalysts were significantly improved for the direct aldol reaction between aldehydes and enolizable ketones. Conclusion: Some highly efficient 1,2-diamine-based bifunctional prolinamide catalysts have been developed through probing the remote β-amide hydrogen for its hydrogen bonding capability. These catalysts are easy to synthesize and high enantioselectivities may be achieved at very low catalyst loadings.

Photodegradation of Cationic and Anioic Dyes by pH-Dependent Dispersion of Amphoteric g-C3N4 Nanosheets

2020 ◽  
Vol 20 (10) ◽  
pp. 6215-6221
Author(s):  
Qingmei Zhang ◽  
Aoli Wen ◽  
Guoliang Chen ◽  
Juan Huang ◽  
Xu Zhou ◽  
...  
Keyword(s):  
Ph Value ◽  
Cationic Dye ◽  
Amino Groups ◽  
Anionic Dye ◽  
Chromotrope 2R ◽  
Different Types ◽  
Acidic Conditions ◽  
Ph Dependent

g-C3N4 nanosheets (NSs) were prepared via H2SO4 exfoliation from the bulky g-C3N4 and the photocatalytic (PC) activities were investigated comprehensively using Rodamine B (RhB) and Chromotrope 2R (Ch2R) as candidate pollutants. The results showed that the pH value have important functions in the improvement of photodegradation performance of C3N4 NSs. RhB as cationic dye could be photodegraded more efficiently under acidic conditions while Ch2R as anionic dye was degraded easily in pH ≥ 11 solution. In particular, the Ch2R could be degraded completely within only 30 min in pH = 11 solution. It might be because the amphoteric C3N4 NSs surface with carboxyl and amino groups possessed negative and positive charges in alkaline and acidic conditions, respectively. These results presumably provided a new idea to enhance the pH-dependent photodegradation activity and degrade different types of pollutants selectively by adjusting the pH of amphoteric nanocatalyts.

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