Experimental evidence supports early silica cementation of the Ediacara Biota

Abstract Casts and molds of soft-bodied organisms in Ediacaran sandstones (“Ediacara-style” fossilization) have played an important role in reconstruction of the emergence and radiation of early complex macroscopic life. However, the preservational processes responsible for the Ediacara fossil record are still vigorously debated. Whereas classic studies proposed fossilization via rapid sulfide mineralization of carcass and matground surfaces, a more recent view posits silica as the key mineral involved in their preservation. We performed experiments in which a variety of soft-bodied organisms were exposed to silica-rich solutions at concentrations considered characteristic of Ediacaran seawater (2 mM). Our results document continuous precipitation of amorphous silica onto the surfaces of these organic tissues under constant and normal marine pH values (7.8). Mineral formation was accompanied by a progressive decrease in the dissolved silica (DSi) concentration of the experimental solution to levels well below amorphous silica saturation. Additionally, we find that the magnitude of silica precipitation is correlated to each organism’s functional-group chemistry, as measured by potentiometric acid-base titrations. We suggest that a wide range of soft-bodied organisms were prone to silicification in Ediacaran marine environments characterized by anactualistically high DSi concentrations. This provides further support for the model that the extraordinary moldic preservation of the Ediacara Biota was promoted by early silica cementation and that this mode of preservation can offer an accurate glimpse into the composition of those early animal ecosystems.

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Synthesis, Characterization and Thermal studies of Novel Organomercury Driven from Sulfa Drugs Part 1

JOURNAL OF ADVANCES IN CHEMISTRY ◽

10.24297/jac.v7i2.2363 ◽

2011 ◽

Vol 7 (2) ◽

pp. 1338-1347

Author(s):

Tarek Ali Fahad ◽

Shaker.A.N. AL-Jadaan

Keyword(s):

Thermal Decomposition ◽

Thermal Behavior ◽

1H Nmr ◽

Elemental Analysis ◽

Thermal Studies ◽

Spectroscopic Techniques ◽

Sulfa Drugs ◽

Acid Base ◽

Ph Values ◽

Multi Stage

Two new heterocyclic Organmercury compounds were prepared from the reaction of Sulfamethaxazole and Sulfadiazine with 4-acetaminophenol as a coupler and separated as solids with characteristic colors. these compounds were characterized by F.T.IR-spectroscopy 1H-NMR , Micro-elemental Analysis and UV-Vis spectroscopic techniques . The work involves a study of acid – base properties compounds at different pH values, the ionization and protonation constants were calculated. The thermal behavior of these two compounds were investigated on the basis of thermogravimetric (TGA) and differential thermogravimetric (DTG) analyses, Thermal decomposition of these compounds is multi-stage processes.

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Nitrogen Removal from Anaerobically-Treated Leachate

Water Quality Research Journal ◽

10.2166/wqrj.1984.008 ◽

1984 ◽

Vol 19 (1) ◽

pp. 87-100

Author(s):

D. Prasad ◽

J.G. Henry ◽

P. Elefsiniotis

Keyword(s):

Nitrogen Removal ◽

Air Flow ◽

Operating Conditions ◽

Air Flow Rate ◽

Flow Rates ◽

Anaerobic Filter ◽

Ph Values ◽

Wide Range ◽

Ammonia Desorption ◽

Effects Of Ph

Abstract Laboratory studies were conducted to demonstrate the effectiveness of diffused aeration for the removal of ammonia from the effluent of an anaerobic filter treating leachate. The effects of pH, temperature and air flow on the process were studied. The coefficient of desorption of ammonia, KD for the anaerobic filter effluent (TKN 75 mg/L with NH3-N 88%) was determined at pH values of 9, 10 and 11, temperatures of 10, 15, 20, 30 and 35°C, and air flow rates of 50, 120, and 190 cm3/sec/L. Results indicated that nitrogen removal from the effluent of anaerobic filters by ammonia desorption was feasible. Removals exceeding 90% were obtained with 8 hours aeration at pH of 10, a temperature of 20°C, and an air flow rate of 190 cm3/sec/L. Ammonia desorption coefficients, KD, determined at other temperatures and air flow rates can be used to predict ammonia removals under a wide range of operating conditions.

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Thermo- and Photoresponsive Behaviors of Dual-Stimuli-Responsive Organogels Consisting of Homopolymers of Coumarin-Containing Methacrylate

Polymers ◽

10.3390/polym13030329 ◽

2021 ◽

Vol 13 (3) ◽

pp. 329

Author(s):

Seidai Okada ◽

Eriko Sato

Keyword(s):

Functional Group ◽

Solution Temperature ◽

Stimuli Responsive ◽

Critical Solution Temperature ◽

Equilibrium Degree ◽

Stimuli Responsive Polymers ◽

Responsive Polymers ◽

Dual Functional ◽

Wide Range ◽

Increasing Temperature

Coumarin-containing vinyl homopolymers, such as poly(7-methacryloyloxycoumarin) (P1a) and poly(7-(2′-methacryloyloxyethoxy)coumarin) (P1b), show a lower critical solution temperature (LCST) in chloroform, which can be controlled by the [2 + 2] photochemical cycloaddition of the coumarin moiety, and they are recognized as monofunctional dual-stimuli-responsive polymers. A single functional group of monofunctional dual-stimuli-responsive polymers responds to dual stimuli and can be introduced more uniformly and densely than those of dual-functional dual-stimuli-responsive polymers. In this study, considering a wide range of applications, organogels consisting of P1a and P1b, i.e., P1a-gel and P1b-gel, respectively, were synthesized, and their thermo- and photoresponsive behaviors in chloroform were investigated in detail. P1a-gel and P1b-gel in a swollen state (transparent) exhibited phase separation (turbid) through a temperature jump and reached a shrunken state (transparent), i.e., an equilibrium state, over time. Moreover, the equilibrium degree of swelling decreased non-linearly with increasing temperature. Furthermore, different thermoresponsive sites were photopatterned on the organogel through the photodimerization of the coumarin unit. The organogels consisting of homopolymers of coumarin-containing methacrylate exhibited unique thermo- and photoresponsivities and behaved as monofunctional dual-stimuli-responsive organogels.

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Modern Synthetic Methods for the Stereoselective Construction of 1,3-Dienes

Molecules ◽

10.3390/molecules26020249 ◽

2021 ◽

Vol 26 (2) ◽

pp. 249

Author(s):

Raquel G. Soengas ◽

Humberto Rodríguez-Solla

Keyword(s):

Organic Chemistry ◽

Natural Products ◽

Functional Group ◽

Biological Activities ◽

Synthetic Methods ◽

Bond Forming ◽

Drug Candidates ◽

The Past ◽

Wide Range

The 1,3-butadiene motif is widely found in many natural products and drug candidates with relevant biological activities. Moreover, dienes are important targets for synthetic chemists, due to their ability to give access to a wide range of functional group transformations, including a broad range of C-C bond-forming processes. Therefore, the stereoselective preparation of dienes have attracted much attention over the past decades, and the search for new synthetic protocols continues unabated. The aim of this review is to give an overview of the diverse methodologies that have emerged in the last decade, with a focus on the synthetic processes that meet the requirements of efficiency and sustainability of modern organic chemistry.

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Lewis acid / Base-free Strategy for the Synthesis of 2-Arylthio and Selenyl Benzothiazole / Thiazole and Imidazole

Heterocyclic Communications ◽

10.1515/hc-2020-0119 ◽

2021 ◽

Vol 27 (1) ◽

pp. 17-23

Author(s):

Guniganti Balakishan ◽

Gullapalli Kumaraswamy ◽

Vykunthapu Narayanarao ◽

Pagilla Shankaraiah

Keyword(s):

Lewis Acid ◽

Bond Formation ◽

Acid Base ◽

Mechanistic Pathway ◽

Wide Range ◽

Acid And Base ◽

Lewis Acid And Base ◽

Sulfur Bond

Abstract A Cu(II)-catalyzed Csp2-Se and Csp2-Sulfur bond formation was achieved with moderate to good yields without the aid of Lewis acid and base. The reaction is compatible with a wide range of heterocycles such as benzothiazole, thiazole, and imidazole. Also, this typical protocol is found to be active in thio-selenation via S-H activation. Additionally, we proposed a plausible mechanistic pathway involving Cu(III) putative intermediate.

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Hybrid Acrylated Chitosan and Thiolated Pectin Cross-Linked Hydrogels with Tunable Properties

Polymers ◽

10.3390/polym13020266 ◽

2021 ◽

Vol 13 (2) ◽

pp. 266

Author(s):

Shaked Eliyahu ◽

Alexandra Galitsky ◽

Esther Ritov ◽

Havazelet Bianco-Peled

Keyword(s):

Electrostatic Interactions ◽

Profile Analysis ◽

Hybrid Hydrogel ◽

Texture Profile ◽

Ph Values ◽

X Ray Scattering ◽

Wide Range ◽

Michael Type Addition ◽

Physical And Chemical ◽

Hydrogel System

We developed and characterized a new hydrogel system based on the physical and chemical interactions of pectin partially modified with thiol groups and chitosan modified with acrylate end groups. Gelation occurred at high pectin thiol ratios, indicating that a low acrylated chitosan concentration in the hydrogel had a profound effect on the cross-linking. Turbidity, Fourier transform infrared spectroscopy, and free thiol determination analyses were performed to determine the relationships of the different bonds inside the gel. At low pH values below the pKa of chitosan, more electrostatic interactions were formed between opposite charges, but at high pH values, the Michael-type addition reaction between acrylate and thiol took place, creating harder hydrogels. Swelling experiments and Young’s modulus measurements were performed to study the structure and properties of the resultant hydrogels. The nanostructure was examined using small-angle X-ray scattering. The texture profile analysis showed a unique property of hydrogel adhesiveness. By implementing changes in the preparation procedure, we controlled the hydrogel properties. This hybrid hydrogel system can be a good candidate for a wide range of biomedical applications, such as a mucosal biomimetic surface for mucoadhesive testing.

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Nickel-Catalyzed Electronically-Reversed Enantioselective Hydrocarbofunctionalizations of Acrylamides

Synlett ◽

10.1055/a-1478-2280 ◽

2021 ◽

Author(s):

Lou Shi ◽

Wei Shu

Keyword(s):

Nickel Catalyst ◽

Functional Group ◽

Optically Active ◽

Forming Process ◽

Carbon Bond ◽

Bond Forming ◽

Synthetic Strategy ◽

Carbon Carbon Bond ◽

Wide Range ◽

Simple Protocol

Asymmetric hydrocarbofunctionalizations of alkenes has emerged as an efficient synthetic strategy for accessing optically active molecules via carbon-carbon bond-forming process from readily available alkenes and carbo-electrophiles. Herein, we present a summary of the efforts from our group to control the regio- and enantioselectivity of hydrocarbofunctionalizations of electron-deficient alkenes with a nickel catalyst and chiral bisoxazolidine ligand. The reaction undergoes electron-reversed hydrocarbofunctionalizations acrylamides with excellent enantioselectivity. This operationally simple protocol enables the asymmetric hydroalkylation, hydrobenzylation and hydropropargylation of acrylamides. This reaction is useful for preparing a wide range of α-branched chiral amides with broad functional group tolerance.

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Site-specific Umpolung amidation of carboxylic acids via triplet synergistic catalysis

Nature Communications ◽

10.1038/s41467-021-24908-w ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Yunyun Ning ◽

Shuaishuai Wang ◽

Muzi Li ◽

Jie Han ◽

Chengjian Zhu ◽

...

Keyword(s):

Carboxylic Acids ◽

Functional Group ◽

Amide Bond ◽

Coupling Reagents ◽

Complex Molecules ◽

Bond Forming ◽

Synergistic Catalysis ◽

Wide Range ◽

Amidation Reaction ◽

Forming Methods

AbstractDevelopment of catalytic amide bond-forming methods is important because they could potentially address the existing limitations of classical methods using superstoichiometric activating reagents. In this paper, we disclose an Umpolung amidation reaction of carboxylic acids with nitroarenes and nitroalkanes enabled by the triplet synergistic catalysis of FeI2, P(V)/P(III) and photoredox catalysis, which avoids the production of byproducts from stoichiometric coupling reagents. A wide range of carboxylic acids, including aliphatic, aromatic and alkenyl acids participate smoothly in such reactions, generating structurally diverse amides in good yields (86 examples, up to 97% yield). This Umpolung amidation strategy opens a method to address challenging regioselectivity issues between nucleophilic functional groups, and complements the functional group compatibility of the classical amidation protocols. The synthetic robustness of the reaction is demonstrated by late-stage modification of complex molecules and gram-scale applications.

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In Vitro Incorporation of Helicobacter pylori into Candida albicans Caused by Acidic pH Stress

Pathogens ◽

10.3390/pathogens9060489 ◽

2020 ◽

Vol 9 (6) ◽

pp. 489 ◽

Cited By ~ 1

Author(s):

Kimberly Sánchez-Alonzo ◽

Cristian Parra-Sepúlveda ◽

Samuel Vega ◽

Humberto Bernasconi ◽

Víctor L. Campos ◽

...

Keyword(s):

Helicobacter Pylori ◽

Candida Albicans ◽

Pcr Amplification ◽

Growth Curves ◽

Acidic Ph ◽

Ph Values ◽

16S Gene ◽

Wide Range ◽

H Pylori

Yeasts can adapt to a wide range of pH fluctuations (2 to 10), while Helicobacter pylori, a facultative intracellular bacterium, can adapt to a range from pH 6 to 8. This work analyzed if H. pylori J99 can protect itself from acidic pH by entering into Candida albicans ATCC 90028. Growth curves were determined for H. pylori and C. albicans at pH 3, 4, and 7. Both microorganisms were co-incubated at the same pH values, and the presence of intra-yeast bacteria was evaluated. Intra-yeast bacteria-like bodies were detected using wet mounting, and intra-yeast binding of anti-H. pylori antibodies was detected using immunofluorescence. The presence of the H. pylori rDNA 16S gene in total DNA from yeasts was demonstrated after PCR amplification. H. pylori showed larger death percentages at pH 3 and 4 than at pH 7. On the contrary, the viability of the yeast was not affected by any of the pHs evaluated. H. pylori entered into C. albicans at all the pH values assayed but to a greater extent at unfavorable pH values (pH 3 or 4, p = 0.014 and p = 0.001, respectively). In conclusion, it is possible to suggest that H. pylori can shelter itself within C. albicans under unfavorable pH conditions.

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