Strong Bases Research Articles

Enantioselective α-Amination of Amides by One-Pot Organo-/Iodine Sequential Catalysis.

An one-pot organo- and iodine sequential catalysis strategy for reactions of amides with pyrazole-based primary amines was described to synthesize chiral α-amino amides with a quaternary stereocenter. This methodology exhibited strong asymmetric induction, resulting in a typical enantiomeric excess value exceeding 99% and diastereoselectivity up to >99:1 dr. Moreover, the reaction was conducted without the use of any metals or strong bases.

Evaluation of Phenyldiazenyl as a Protective/Activating Group in Lithiation–Substitution Reactions of Tetrahydroisoquinolines

AbstractPhenyldiazenyl moiety has been utilized both as a protective and activating group to synthesize C-1-substituted tetrahydroisoquinolines via lithiation–substitution strategy. This reaction sequence involves generation of α-amino carbanions, derived from N-phenyldiazenyl tetrahydroisoquinolines, followed by coupling with various electrophiles, e.g., aldehyde, ketones, alkyl halide, oxiranes, isocyanates, and with in situ generated arynes. Deprotection of the protecting group was carried out under acidic conditions to afford the desired α-substituted products in moderate to good yields. So, triazene as a protecting/directing group and its compatibility with strong bases provide a good synthetic utility for the synthesis of a variety of α-substituted secondary amines via lithiation substitution reaction.

Guided Acoustic Waves in Polymer Rods with Varying Immersion Depth in Liquid.

Monitoring tanks and vessels play an important part in public infrastructure and several industrial processes. The goal of this work is to propose a new kind of guided acoustic wave sensor for measuring immersion depth. Common sensor types such as pressure sensors and airborne ultrasonic sensors are often limited to non-corrosive media, and can fail to distinguish between the media they reflect on or are submerged in. Motivated by this limitation, we developed a guided acoustic wave sensor made from polyethylene using piezoceramics. In contrast to existing sensors, low-frequency Hanning-windowed sine bursts were used to excite the L(0,1) mode within a solid polyethylene rod. The acoustic velocity within these rods changes with the immersion depth in the surrounding fluid. Thus, it is possible to detect changes in the surrounding media by measuring the time shifts of zero crossings through the rod after being reflected on the opposite end. The change in time of zero crossings is monotonically related to the immersion depth. This relative measurement method can be used in different kinds of liquids, including strong acids or bases.

Layer-by-layer self-assembled liposomes prepared using sodium alginate and chitosan: Insights into vesicle characteristics and physicochemical stability

In this study, layer-by-layer self-assembled liposomes were prepared with different mixing ratios (3:7, 1:1, and 7:3) of sodium alginate (SA) and chitosan (CS), and the morphology, structure, and physicochemical properties of liposomes after layer-by-layer coating were investigated. After coating the liposomes with SA-CS layer-by-layer (S–C-L), the particle size of liposomes increased from 244.50 to 423.33 nm, the potential changed from negative to positive to 21.20 mV, and the PDI was only 0.393. In the S–C-L 7:3 formulation, the liposomes were uniformly distributed and spherical in size with a clear fingerprint structure. In addition, S–C-L reduced the number of hydrophobic regions within the molecule, allowing the phospholipid molecules to bind tightly into stacks, thus making the liposomes more stable. The S–C-L 7:3 formulation effectively improved the tolerance of liposomes to strong acids and bases, high-salt environments, and UV exposure, and maintained a constant particle size of 400 nm after 28 days of storage. The findings of this study might contribute to the development of polysaccharide layer-by-layer modification of liposomes for a more stable liposomal transport system.

Colorimetric pH-sensing core/shell beads designed for strong acid/base spill responses

Conventional pH sensors encounter obstacles when utilized in response to spill accidents involving highly acidic and basic chemicals, since the concentration of chemicals released in the accidents usually exceeds the detection limit of most pH sensors. Practical tools available for the chemical accidents are limited to pH papers and pH-indicating dyes; however, they also suffer from drawbacks such as difficulties in retrieval and removal, leading to secondary environmental contamination. In this study, colorimetric pH-sensing beads (CpH beads) with a core/shell structure were developed to have essential characteristics required for responding to chemical accidents. Magnetic Fe3O4 nanoparticles dispersed in the core allow the CpH bead to be readily recoverable from acidic or basic solutions using a magnet. The shell, which consists of an alginate-based composite with thymol blue-incorporated porous aluminum hydroxide, rapidly indicates the acidity or basicity of the solution by changing color. The response time for color change of the CpH bead decreases as the concentration of the acidic or basic solution increases. The color of CpH indicative of acidity or basicity changes within 5–60 s in 5 M solutions, and within 20–300 s in 0.5 M solutions. Moreover, the CpH bead has a leaching rate of dye approximately 33.5 times slower than the pH paper, and its easy retrieval via a magnet allows for six reuses, minimizing secondary environmental contamination. Therefore, the CpH bead demonstrates a significant potential for effectively responding to leakage accidents involving strong acids and bases in the field.

Development of Unactivated Bond Cleavage Reactions Under Mild Conditions Based on Stabilization of Addition Intermediates

Cleavage of unactivated bonds, such as amides, often requires challenging reaction conditions with strong acids and bases, and the tolerance of functional groups is limited. Therefore, the development of cleavage reactions for unactivated bonds under mild reaction conditions is essential. Herein, I report our recent developments in the cleavage of unactivated bonds under mild conditions. We achieved cleavage of unactivated amides, carbamates, ureas, and esters, as well as chemoselective cleavage of directing groups. Furthermore, we conducted mechanistic studies and found that these reactions proceed through the stabilization of addition intermediates.

Atomic layer deposition of magnetic thin films: Basic processes, engineering efforts, and road forward

Atomic layer deposition (ALD) is known as a key enabler of the continuous advances in device engineering for microelectronics. For instance, the state-of-the-art transistor technology depends entirely on ALD-grown high-κ materials. Another application branch where ALD could potentially play a similar important role in future is the magnetic thin film devices. Spin-based devices based on high-quality magnetic thin films are anticipated to provide high-efficiency operations with low power consumption. The strict quality demands the magnetic thin films must fulfill in the next-generation applications form the strong bases for the efforts to implement ALD in this application area. In this first comprehensive review on the topic, our aim is to provide an insightful account of the ALD processes so far developed for magnetic materials and to highlight the application-relevant magnetic properties of the thus fabricated thin films. Moreover, we discuss the various innovative engineering efforts made toward different multi-layered and nanostructured composite materials and complex architectures uniquely enabled by the sophisticated self-terminated film-growth mechanism of ALD. The review is finished with a brief outlook toward the future prospects and challenges in the field.

Facilely etching of superhydrophobic surface with regular mulriple hierarchical micro-nano structures for crowning wettability

Nowadays, achieving highly effective superhydrophobic surfaces on chemically active magnesium alloys via a straightforward and efficient etching method remains a formidable task. In this study, we have successfully fabricated regular mulriple hierarchical micro-nano structures on AZ91D substrates through a one-step etching process. The resultant nano-chrysanthemums exhibit remarkable biomimicry wherein the extended nanostructures and the protrusions on them further enhance the air–liquid interface contact area. Subsequent to the modification, the contact and sliding angles of the samples achieved exceptional performance surpassing that of previous etching techniques. Furthermore, this low adhesion surface demonstrates commendable chemical stability even when exposed to air, chemically aggressive solutions (including strong acids and bases), and cyclic icing/melting treatments. Moreover, this versatile superhydrophobic surface exhibits exceptional resistance to various forms of contamination. The method employed to generate such advantageous superhydrophobic surfaces necessitates minimal equipment complexity and boasts substantial advantages in terms of affordability and efficiency. These characteristics not only confer promising prospects for widespread application but also render it suitable for large-scale industrial production.

The strategic options of the United States of America in the Middle East during the Trump administration

Despite the geostrategic importance of the Middle East and the active participation of US forces in the Second Gulf War (Desert Storm). But the administration did not increase its military operations in the region until after the invasion of Iraq in 2003. Consistent with the idea of not losing the gains made to the United States after the occupation Iraq and trying to limit Iranian influence in Iraq and Syria, there was a need to redeploy US forces in Iraq and place them in strong and fortified bases in different parts of the country. This behavior was contrary to Obama's isolationist strategy. And boosted Trump's idea of maximizing US gains in the region, as well as restricting free rider access to any potential future gains in the region. The opposite direction that complicates the American options is the new Russian role in the region and the need to deal with Moscow to fight ISIS, especially at the intersection of interests between the two superpowers. As well as the growing Iranian influence on both the Iraqi and Syrian fronts, which Washington must strengthen its strategic objectives in cooperation with the regional allies. Despite the relatively realistic approach in his foreign policy. President Trump raised the slogan "make America great again".

The Characterization of the Inhibitory Substances Produced by Bacillus pumilus LYMC-3 and the Optimization of Fermentation Conditions

Bacillus pumilus plays a very important role in the biological control of plant diseases. In this study, we conducted indoor biocontrol experiments using the LYMC-3 strain of B. pumilus to assess its efficacy against poplar canker and tea gray blight. Simultaneously, we explored the optimal fermentation conditions for the production of inhibitory substances against Phomopsis macrospora and Pestalotiopsis vesicolor. Subsequently, the inhibitory substances were extracted crudely and subjected to a preliminary investigation of their properties. The results of the indoor biocontrol experiments showed that the LYMC-3 strain exhibited disease prevention rates of 44.12% and 48.59% against poplar canker and tea gray blight, respectively. The fermentation optimization experiment showed that a culture medium containing 10 g/L of glucose, 15 g/L of tryptone, and 5 g/L of sodium chloride favored the production of inhibitory substances via the LYMC-3 strain. Among the crude extracts obtained, the non-protein extracts demonstrated the most obvious inhibitory effects. Furthermore, the inhibitory substances exhibited high polarity, excellent thermal stability, and high sensitivity to strong acids and bases. This study establishes a theoretical foundation for the purification and identification of inhibitory substances using the LYMC-3 strain. Additionally, it contributes to elucidating biological control mechanisms and facilitates the application of the LYMC-3 strain in production.

Quantum-chemical study of the stability of solvents with respect to strong organic bases

The possibility of theoretical calculation of the ionization constants of strong organic bases in dimethyl sulfoxide and hexametapole was studied by the DLPNO-CCSD (T) and DFT methods. By comparison with the experimental data available in the literature, it has been established that the error of such calculations lies within 1–2 pKa units. The stability of some ionizing solvents against strong organic bases is investigated, the mechanisms of decomposition of solvent molecules in strongly basic media are predicted, and the corresponding energy barriers are estimated. According to the calculations, among ionizing solvents, hexamethylphosphoramide has the highest resistance to superbases, being able to maintain pH > 50 at room temperature. At the same time, 1,3-dimethyl-2-imidazolidinone gradually decomposes under these conditions, while tetrahydrofuran and pivalonitrile are even less stable.

Liquid Metal in Expired Artificial Kidneys: A Nanoporous Soft Conductive Wire Platform for Unconventional Interfacial Fluidic Studies

AbstractStrong chemical or voltage‐driven studies of gallium alloys (liquid metal, LM) show methods of altering the surface energy of the bare alloys by controlling Ga2O3 (Gallium Oxide)‐ a 3‐5 nm surface oxide that forms on LM. However, various fluids (i.e., water) interact weakly compared to strong acids or bases and do not etch Ga2O3. Specialized instruments are often required to study such interactions, which are not readily available. Herein, an LM‐based nanoporous conductive wire platform is demonstrated, which can effectively be utilized for real‐time weaker interfacial studies. The unconventional platform allows fluid transport and interfacial studies within the nanoporous domain, which is still foreign in the literature. Nanoporous conductive wires are fabricated by injecting eutectic gallium indium (eGaIn) into hollow microtubes collected from expired and unused artificial kidneys. These steps upcycle medical waste and confine Ga2O3 at the nanopores for an inexpensive metal‐oxide/metal framework. The platform for interfacial fluidics is harnessed, leveraging deionized (DI) water, 1 m hydrochloric acid (HCl), and 95% ethanol (EtOH). This study also demonstrates capacitive sensors that can be immediately implemented using nanoporous conducive wires. Advanced applications from this study suggest that future exploration of such soft systems can lead to more nano/bioanalyses harnessing LM alloys.

Harnessing triaryloxonium ions for aryne generation

Arynes are highly reactive and versatile intermediates for the functionalization of aromatic rings that are often generated using strong bases or fluoride sources, which, in some cases, can limit functional group tolerance. Here we demonstrate that triaryloxonium ions can be transformed into arynes through treatment with solid potassium phosphate at room temperature. A substantial range of functional group-bearing arynes, including 4,5-pyrimidynes, may be generated and trapped using cycloaddition reactions with high yields. Other arynophiles including nitrones, alkenes and azides are compatible with these conditions. Quantum computation in conjunction with an intramolecular kinetic isotope study is consistent with an elimination, unimolecular, conjugate base-like mechanism of elimination to form the aryne. These investigations demonstrate that the oxonium ion is a powerful electron-withdrawing group and a particularly effective leaving group. We anticipate that this study will stimulate further investigations into the synthetic utility of aryl oxonium ions.

Mechanochemical activation of NHC–CS2 adducts for the generation of N‐heterocyclic carbenes

AbstractStable N‐heterocyclic carbenes (NHCs) have garnered significant attention in synthetic chemistry due to their versatile applications. In this study, we explored a novel mechanochemical method for the generation of free carbenes, which could be a good complement to traditional approaches that require strong bases or reductants. Ball milling of NHC–CS2 adducts at room temperature successfully resulted in the quantitative formation of free carbenes that can be subsequently trapped by sulfur or selenium. Importantly, heating NHC–CS2 adducts in solution phase did not lead to the successful generation of free carbenes, in agreement with the high activation energy required for NHC–CS2 dissociation. These findings underscore the potential of ball milling as a robust and versatile approach for generating NHCs from stable NHC‐small molecule adducts, and opens new avenues for developing mechanochemical strategies for generating valuable NHC‐derived compounds.

Novel BODIPY-Based Photobase Generators for Photoinduced Polymerization.

Photobase generators (PBGs) are compounds that utilize light-sensitive chemical-protecting groups to offer spatiotemporal control of releasing organic bases upon targeted light irradiation. PBGs can be implemented as an external control to initiate anionic polymerizations such as thiol-ene Michael addition reactions. However, there are limitations for common PBGs, including a short absorption wavelength and weak base release that lead to poor efficiency in photopolymerization. Therefore, there is a great need for visible-light-triggered PBGs that are capable of releasing strong bases efficiently. Here, we report two novel BODIPY-based visible-light-sensitive PBGs for light-induced activation of the thiol-ene Michael "click" reaction and polymerization. These PBGs were designed by connecting the BODIPY-based light-sensitive protecting group with tetramethylguanidine (TMG), a strong base. Moreover, we exploited the heavy atom effect to increase the efficiency of releasing TMG and the polymerization rate. These BODIPY-based PBGs exhibit extraordinary activity toward thiol-ene Michael addition-based polymerization, and they can be used in surface coating and polymer network formation of different thiol and vinyl monomers.

Photobase generators with AIE property used for visual observations of thiol–epoxy near‐UV/visible photopolymerization

AbstractPhotopolymerization of thiol–epoxy resins initiated by photobase generators (PBGs) is a very good way to prepare specific polymeric products. However, the lack of near‐UV or visible light emitting diode (LED) light‐sensitive PBGs that can release strong bases to effectively catalyze this reaction and synchronously monitor the polymerization progress still is a problem. In this work, a series of such PBGs are successfully synthesized by modifying common aggregation‐induced emission (AIE) molecules, including triphenylamine and tetraphenylethylene and then neutralizing them with strong bases like 1,8‐diazabicyclo[5.4.0]undec‐7‐ene, 1,5‐diazabicyclo[4.3.0]non‐5‐ene, and 1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene (TBD). The obtained PBGs show very good light absorption ability from 365 to 405 nm. They can generate free strong bases under near‐UV/visible LED light radiations as a result of photodecarboxylation reaction to catalyze the rapid thiol–epoxy photopolymerization. The TBD‐based PBGs have the best final monomer conversion above 60% due to their strongest alkalinity. Increasing viscosity during the polymerization process can trigger an AIE phenomenon of the PBGs. A linear correlation equation of the AIE intensity with the monomer conversion can be found, which is helpful for quantitatively monitoring the photopolymerization progress. More importantly, qualitative observations of the brightness changes of the resulting AIE lights are very useful to visualize the photopolymerization progress, which may find some applied potential in industry.

EXTRACTION AND APPLICATION OF SOME NATURAL FLOWER PIGMENTS AS ACID-BASE INDICATORS

In this study, the pigments of Ixora coccinea, Lantana camara, Moringa oleifera, Nerium oleander, and Sensevieria trifasciata were used to identify the natural indicators for acid-base titrations using 0.1% acidified ethanolic solvent. The Potiskum Vetenary, biological gardens of Federal University Gashua and Umar Suleiman College of Education Gashua were used to collect the samples. All three types of acid-base titrations—strong acids against strong bases, strong acids against weak bases, and weak acids against strong bases—were studied. Calculations were made for the indicator's color change, the pH at the relevant point and the average titre values for each type of acid-base titration. According to the data, there was no appreciable difference between the mean titre values of methyl orange and Ixora c. flower extract in strong acid against weak base. Moringa o. flower extract can be used in place of methyl orange and phenolphthalein for strong acid against strong base, strong acid against weak base and weak acid against strong base titrations. Nerium o. flower extract can be used in place of phenolphthalein in weak acid against strong base titrations. Sensevieria t. flower extract can be used in place of methyl orange in strong acid against weak base titrations and phenolphthalein for strong acid against strong base and weak acid against strong base titrations. In all acid-base titrations, lantana c. flower extract had no discernible reaction. Most of the extracts proved to be a good substitute for synthetic acid-base indicators. Using these harmless and readily available flowers is recommended.

Simple preparation superhydrophobic melamine sponge via one-step emulsion polymerization for continuous oil/water separation in harsh environment

The oil spill and industrial oily wastewater in large quantities has caused severe harm to the environment and human health, which make an urgent requirement to develop low-cost, eco-friendly, stable performance and highly efficient oil/water separation materials. Herein, a superhydrophobic/superlipophilic melamine sponge with excellent hydrophobic stability was successfully fabricated via one-step emulsion polymerization. During polymerization, trimethylolpropane triacrylate (TMPTA) and polyethylene imine (PEI) form robust microspheres, and polydimethylsilane (PDMS) cross-links to form hydrophobic coating on the original sponge skeleton. The modified sponge could continuously separate various immiscible oil/water mixtures under harsh conditions (including strong acids, strong bases, salts). Even after 10 consecutive cycles, the separation efficiency for toluene and petroleum ether exceeds 99.87%. In addition, the as-prepared sponge exhibited extraordinarily high oil absorption capacities (with a maximum saturated oil absorption of 107.31 g/g for chloroform) and excellent reversible compressibility (up to 100 compression cycles). More importantly, the pore size of modified sponge was adjusted through a simple mechanical compression strategy so that the compressed sponge met the particle size screening requirements to effectively separate the surfactant-stabilized water-in-oil emulsions. Based on the simple preparation protocol, fluorine-free raw materials, and excellent properties, the MS-TMPTA/PEI-PDMS sponge presented here have extremely promising application potential in oil/water separation.

Atomically dispersed calcium as solid strong base catalyst with high activity and stability

Solid strong base catalysts are highly attractive for diverse reactions owing to their advantages of neglectable corrosion, facile separation, and environmental friendliness. However, their widespread applications are impeded by basic components aggregation and low stability. In this work, we fabricate single calcium atoms on graphene (denoted as Ca1/G) by use of a redox strategy for the first time, producing solid strong base catalyst with high activity and stability. The precursor Ca(NO3)2 is first reduced to CaO at 400 °C by the support graphene, forming CaO/G with conventional basic sites, and the subsequent reduction at 850 °C results in the generation of Ca1/G with atomically dispersed Ca. Various characterizations reveal that Ca single atoms are anchored on graphene in tetra-coordination (Ca–C2–N2) where N is in situ doped from Ca(NO3)2. The atomically dispersed Ca, along with their anchoring on the support, endow Ca1/G with high activity and stability toward the transesterification reaction of ethylene carbonate with methanol. The turnover frequency value reaches 128.0 h−1 on Ca1/G, which is much higher than the traditional counterpart CaO/G and various reported solid strong bases (2.9–46.2 h−1). Moreover, the activity of Ca1/G is well maintained during 5 cycles, while 60% of activity is lost for the conventional analogue CaO/G due to the leaching of Ca.

Probing Catalyst Degradation in Metathesis of Internal Olefins: Expanding Access to Amine-Tagged ROMP Polymers.

Ruthenium-promoted ring-opening metathesis polymerization (ROMP) offers potentially powerful routes to amine-functionalized polymers with antimicrobial, adhesive, and self-healing properties. However, amines readily degrade the methylidene and unsubstituted ruthenacyclobutane intermediates formed in metathesis of terminal olefins. Examined herein is the relevance of these decomposition pathways to ROMP (i.e., metathesis of internal olefins) by the third-generation Grubbs catalyst. Primary alkylamines rapidly quench polymerization via fast adduct formation, followed by nucleophilic abstraction of the propagating alkylidene. Bulkier, Brønsted-basic amines are less aggressive: attack competes only for slow polymerization or strong bases (e.g., DBU). Added HCl limits degradation, as demonstrated by the successful ROMP of an otherwise intractable methylamine monomer.