A facile method to fabricate hydrogels from DMSO polymer gels via solvent exchange

2017 ◽  
Vol 41 (12) ◽  
pp. 4793-4796 ◽  
Author(s):  
Heekyoung Choi ◽  
Misun Go ◽  
Yubin Cha ◽  
Yeonweon Choi ◽  
Ki-Young Kwon ◽  
...  
Keyword(s):  
Polymer Gels ◽  
Building Blocks ◽  
Solvent Exchange ◽  
Acidic Conditions

A mixture of the bipyridine, phenyl and/or cyclohexanediamine-based building blocks 1, 2, and/or 3, having hydrazide, aldehyde or amine moieties, respectively, formed DMSO polymer gels by the hydrazone reaction under acidic conditions.

Iridium-catalyzed acid-assisted asymmetric hydrogenation of oximes to hydroxylamines

Science ◽  
2020 ◽  
Vol 368 (6495) ◽  
pp. 1098-1102 ◽  
Author(s):  
Josep Mas-Roselló ◽  
Tomas Smejkal ◽  
Nicolai Cramer
Keyword(s):  
Room Temperature ◽  
Asymmetric Hydrogenation ◽  
Selective Reduction ◽  
Building Blocks ◽  
Efficient Catalyst ◽  
Cyclopentadienyl Ligand ◽  
Acidic Conditions ◽  
Asymmetric Hydrogenations ◽  
Metal Catalyzed ◽  
Oxygen Bond

Asymmetric hydrogenations are among the most practical methods for the synthesis of chiral building blocks at industrial scale. The selective reduction of an oxime to the corresponding chiral hydroxylamine derivative remains a challenging variant because of undesired cleavage of the weak nitrogen-oxygen bond. We report a robust cyclometalated iridium(III) complex bearing a chiral cyclopentadienyl ligand as an efficient catalyst for this reaction operating under highly acidic conditions. Valuable N-alkoxy amines can be accessed at room temperature with nondetected overreduction of the N‒O bond. Catalyst turnover numbers up to 4000 and enantiomeric ratios up to 98:2 are observed. The findings serve as a blueprint for the development of metal-catalyzed enantioselective hydrogenations of challenging substrates.

Elastomers and Rubberlike Elasticity

2015 ◽  
Author(s):  
James E. Mark ◽  
Burak Erman
Keyword(s):  
Mechanical Properties ◽  
Liquid Crystalline ◽  
Random Network ◽  
Polymer Gels ◽  
Solvent Exchange ◽  
Specific Chemical ◽  
Functional Monomers ◽  
Elastomeric Materials ◽  
Deformed State ◽  
High Deformability

This article focuses on the rubberlike elasticity of elastomers, with particular emphasis on rubberlike materials that exhibit high deformability and recoverability. It begins with a discussion of the variety of practical ways to form and characterize a rubber-elastic network, including random chemical crosslinking, highly specific chemical end-linking, polymerizations with multi-functional monomers, physical aggregation, and crosslinking in solution and in the deformed state. It then considers the effects of network structure on elastomeric properties, along with the results of elasticity experiments regarding the mechanical properties of elastomeric materials. It also examines the evolution of theories of rubber elasticity describes the specific properties of swollen polymer gels where the possibility of solvent exchange leads to some dramatic transformations in the system. Finally, it evaluates new emerging classes of rubber-elastic materials, such as liquid crystalline elastomers, where the internal microstructure added to the random network leads to some unique mechanical properties.

Janus biocomposite aerogels constituted of cellulose nanofibrils and MXenes for application as single-module solar-driven interfacial evaporators

2021 ◽  
Author(s):  
Xinhong Han ◽  
Shaoqiu Ding ◽  
Liwu Fan ◽  
Yonghao Zhou ◽  
Shurong Wang
Keyword(s):  
Cellulose Nanofibrils ◽  
Building Blocks ◽  
Solvent Exchange ◽  
Functional Fillers

Novel biocomposite aerogels with Janus character are fabricated for application as interfacial evaporators, using cellulose nanofibrils (CNFs) as building blocks and Ti3C2Tx MXenes as functional fillers via pre-freezing, solvent exchange,...

scholarly journals Dehydration Enhances Prebiotic Lipid Remodeling and Vesicle Formation in Acidic Environments

2021 ◽  
Author(s):  
Luke H Steller ◽  
Martin J Van Kranendonk ◽  
Anna Wang
Keyword(s):  
Lipid Bilayer ◽  
Building Blocks ◽  
Selective Advantage ◽  
Physicochemical Process ◽  
Vesicle Formation ◽  
Acidic Conditions ◽  
Acidic Environments ◽  
Thin Walled ◽  
Lipid Aggregates

The encapsulation of genetic polymers inside lipid bilayer compartments is a vital step in the emergence of cell-based life. However, even though acidic conditions promote many reactions required for generating prebiotic building blocks, prebiotically-relevant lipids tend to form denser aggregates at acidic pHs rather than prebiotically useful vesicles that exhibit sufficient solute encapsulation. Here we describe how dehydration/rehydration (DR) events, a prebiotically-relevant physicochemical process known to promote polymerization reactions, can remodel dense lipid aggregates into thin-walled vesicles capable of RNA encapsulation even at acidic pHs. Furthermore, DR events appears to favor the encapsulation of RNA within thin-walled vesicles over more lipid-rich vesicles, thus conferring such vesicles a selective advantage.

scholarly journals pH-Dependent Adsorption of Peptides on Montmorillonite for Resisting UV Irradiation

Life ◽  
2020 ◽  
Vol 10 (4) ◽  
pp. 45
Author(s):  
Rongcan Lin ◽  
Yueqiao Wang ◽  
Xin Li ◽  
Yan Liu ◽  
Yufen Zhao
Keyword(s):  
Aqueous Solution ◽  
Uv Irradiation ◽  
Building Blocks ◽  
Ph Effects ◽  
Uv Degradation ◽  
Prebiotic Chemical ◽  
Peptide Adsorption ◽  
Concentration Step ◽  
Acidic Conditions ◽  
Ph Conditions

Ultraviolet (UV) irradiation is considered an energy source for the prebiotic chemical synthesis of life’s building blocks. However, it also results in photodegradation of biology-related organic compounds on early Earth. Thus, it is important to find a process to protect these compounds from decomposition by UV irradiation. Herein, pH effects on both the adsorption of peptides on montmorillonite (MMT) and the abilities of peptides to resist UV irradiation due to this adsorption were systematically studied. We found that montmorillonite (MMT) can adsorb peptides effectively under acidic conditions, while MMT-adsorbed peptides can be released under basic conditions. Peptide adsorption is positively correlated with the length of the peptide chains. MMT’s adsorption of peptides and MMT-adsorbed peptide desorption are both rapid-equilibrium, and it takes less than 30 min to reach the equilibrium in both cases. Furthermore, compared to free peptides, MMT-adsorbed peptides under acidic conditions are well protected from UV degradation even after prolonged irradiation. These results indicate amino acid/peptides are able to concentrate from aqueous solution by MMT adsorption under low-pH conditions (concentration step). The MMT-adsorbed peptides survive under UV irradiation among other unprotected species (storage step). Then, the MMT-adsorbed peptides can be released to the aqueous solution if the environment becomes more basic (releasing step), and these free peptides are ready for polymerization to polypeptides. Hence, a plausible prebiotic concentration–storage–release cycle of amino acids/peptides for further polypeptide synthesis is established.

3,3'-Dipyrrolyl sulfides, useful building blocks for the syntheses of macrocycles containing dipyrromethene units

2003 ◽  
Vol 81 (9) ◽  
pp. 988-991 ◽  
Author(s):  
Qingqi Chen ◽  
David Dolphin
Keyword(s):  
Key Words ◽  
Building Blocks ◽  
Acidic Conditions ◽  
High Yields

5,5'-Dicarboxy-3,3'-dipyrrolyl sulfide was condensed with 5,5'-diformyl-3,3'-dipyrrolyl sulfide or 5,5'-diformyldipyrromethane under acidic conditions to produce, in high yields, macrocycles containing four dipyrromethene units. Key words: 3,3-dipyrrolyl sulfide, cyclopolypyrrole, dipyrromethene, macrocycle.

Efficient synthesis of free-base 2-formyl-5,10,15,20-tetraarylporphyrins, their reduction and conversion to [(porphyrin-2-yl)methyl]phosphonium salts

2002 ◽  
Vol 06 (11) ◽  
pp. 708-719 ◽  
Author(s):  
Edia E. Bonfantini ◽  
Anthony K. Burrell ◽  
Wayne M. Campbell ◽  
Maxwell J. Crossley ◽  
Jeffrey J. Gosper ◽  
...  
Keyword(s):  
Catalytic Reduction ◽  
Building Blocks ◽  
Phosphonium Salts ◽  
Free Base ◽  
Efficient Synthesis ◽  
Acidic Conditions ◽  
Key Steps ◽  
Hydrolysis Of ◽  
By Products ◽  
Porphyrin Dimers

A highly efficient synthesis of 2-formyl-5,10,15,20-tetraarylporphyrins, 1 and 2, that can be carried out on multi-gram scales is reported. The key steps in the sequence involve use of copper(II) chelation to ensure very efficient electrophilic substitution, and the demetalation of the intermediate iminium salt that results from Vilsmeier-Haack formylation of the copper(II) porphyrins prior to base-catalyzed hydrolysis of the salt to the corresponding free-base 2-formylporphyrin. This sequence avoids the formation of by-products that inevitably result when the formyl group is subjected to acidic conditions. Borohydride reduction of (metallo)-2-formylporphyrins give the corresponding 2-hydroxymethyl-porphyrins in quantitative yield. Catalytic reduction of copper(II) 2-hydroxymethyl-5,10,15,20-tetraphenylporphyrin 15 with hydrogen under acidic conditions affords 2-methyl-5,10,15,20-tetraphenylporphyrin 20 in 60% yield. Treatment of 2-hydroxymethyl-porphyrins with thionyl chloride in dry pyridine yields the corresponding 2-chloromethyl-porphyrins in good yields. The 2-chloromethyl-porphyrins give the corresponding triphenyl[(porphyrin-2-yl)methyl]phosphonium chlorides in 90% yield on treatment with PPh 3 in boiling chloroform. These salts are useful building blocks for the synthesis of conjugated porphyrin dimers and higher oligomers.

Photochemical Evolution of Interstellar/Precometary Organic Material

1997 ◽  
Vol 161 ◽  
pp. 23-47 ◽  
Author(s):  
Louis J. Allamandola ◽  
Max P. Bernstein ◽  
Scott A. Sandford
Keyword(s):  
Origin Of Life ◽  
Building Blocks ◽  
Complex Species ◽  
Infrared Observations ◽  
Interstellar Ice ◽  
Polycyclic Aromatic ◽  
Ultraviolet Photolysis ◽  
The Origin Of Life ◽  
Simple Molecules ◽  
Complex Organic

AbstractInfrared observations, combined with realistic laboratory simulations, have revolutionized our understanding of interstellar ice and dust, the building blocks of comets. Since comets are thought to be a major source of the volatiles on the primative earth, their organic inventory is of central importance to questions concerning the origin of life. Ices in molecular clouds contain the very simple molecules H2O, CH3OH, CO, CO2, CH4, H2, and probably some NH3and H2CO, as well as more complex species including nitriles, ketones, and esters. The evidence for these, as well as carbonrich materials such as polycyclic aromatic hydrocarbons (PAHs), microdiamonds, and amorphous carbon is briefly reviewed. This is followed by a detailed summary of interstellar/precometary ice photochemical evolution based on laboratory studies of realistic polar ice analogs. Ultraviolet photolysis of these ices produces H2, H2CO, CO2, CO, CH4, HCO, and the moderately complex organic molecules: CH3CH2OH (ethanol), HC(= O)NH2(formamide), CH3C(= O)NH2(acetamide), R-CN (nitriles), and hexamethylenetetramine (HMT, C6H12N4), as well as more complex species including polyoxymethylene and related species (POMs), amides, and ketones. The ready formation of these organic species from simple starting mixtures, the ice chemistry that ensues when these ices are mildly warmed, plus the observation that the more complex refractory photoproducts show lipid-like behavior and readily self organize into droplets upon exposure to liquid water suggest that comets may have played an important role in the origin of life.

Laboratory and in-situ analysis of comet dust

1988 ◽  
Vol 46 ◽  
pp. 8-9
Author(s):  
D.E. Brownlee ◽  
A.L. Albee
Keyword(s):  
Electron Microscopy ◽  
Solar System ◽  
Laboratory Study ◽  
Isotopic Analysis ◽  
Building Blocks ◽  
Sem Analysis ◽  
Early Solar System ◽  
Cometary Material ◽  
Comet Dust

Comets are primitive, kilometer-sized bodies that formed in the outer regions of the solar system. Composed of ice and dust, comets are generally believed to be relic building blocks of the outer solar system that have been preserved at cryogenic temperatures since the formation of the Sun and planets. The analysis of cometary material is particularly important because the properties of cometary material provide direct information on the processes and environments that formed and influenced solid matter both in the early solar system and in the interstellar environments that preceded it.The first direct analyses of proven comet dust were made during the Soviet and European spacecraft encounters with Comet Halley in 1986. These missions carried time-of-flight mass spectrometers that measured mass spectra of individual micron and smaller particles. The Halley measurements were semi-quantitative but they showed that comet dust is a complex fine-grained mixture of silicates and organic material. A full understanding of comet dust will require detailed morphological, mineralogical, elemental and isotopic analysis at the finest possible scale. Electron microscopy and related microbeam techniques will play key roles in the analysis. The present and future of electron microscopy of comet samples involves laboratory study of micrometeorites collected in the stratosphere, in-situ SEM analysis of particles collected at a comet and laboratory study of samples collected from a comet and returned to the Earth for detailed study.

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