ChemRxiv
Not a member yet
27047 research outputs found
Sort by
Iridium Complexes of a Bis(N-pyrrolyl)boryl/Bis(phosphine) PBP Pincer Ligand
No full textThis work reports the synthesis of a bis(pyrrolylphosphino)phenyl borane (PBP)Ph (2) and its incorporation of Ir by metal insertion into B–Ph to afford dipyrrolylboryl/bis(phosphine) pincer complex (PBP)Ir(Ph)Cl (3). Hydrogenolysis of 3 afforded (PBP)Ir(H)Cl (4). Compound 4 was converted into (PBP)IrCl2 (5a) via reaction with N-chlorosuccinimide, and exposure of 5a to CO produced (PBP)IrCl2(CO) (6a). Compounds 5a and 6a were converted into their analogs (PBP)IrI2 (5b) and (PBP)IrI2(CO) (6b) via metathesis with Me3SiI. Treatment of either 3 or 4 with Li[HAl(OBut)3] under H2 resulted in the formation of (PBP)IrH4 (7), with traces of 4 as a persistent impurity. Attempts to access 7 via the reaction of 4 with NaBH4 in isopropanol led to the loss of boron from the pincer and isolation of L2IrH5 (8, L = 2-diisopropylphosphinopyrrole). Compounds 4, 7, and 8 were examined as catalysts for alkane transfer dehydrogenation but displayed only modest activity. Solid-state structures of 6b and 7 were established by X-ray crystallography
Structural requirements of synthetic anionophores for inorganic phosphate and phosphate esters
No full textThe transmembrane transport of anions is a promising application of synthetic anion receptors. Numerous anionophores have been developed for chloride over the past decades. Despite the biological relevance of phosphate and phosphate esters, very few reports on their transport by synthetic systems exist. Here we report a systematic study on the transport of diphenyl phosphate, phenyl phosphate, and inorganic phosphate by five different anionophores. The transport of these phosphates into liposomes was monitored by fluorescence spectroscopy, 31P NMR spectroscopy, and an ion selective electrode. The results of these experiments showed that diphenyl phosphate is readily transported by most chloride ionophores. The transport of phenyl phosphate is more challenging, but can be enhanced by better shielding of the phosphate group. Inorganic phosphate is the most challenging to transport and was achieved using a macrocyclic anionophore with eight preorganised H-bond donors. These results pave the way for the development of anionophores for inorganic phosphate as well as phosphate esters
Synthesis of Os Hydride Complexes Supported by the Diarylamido/Bis(phosphine) PNP Ligand and Attempts at Using (PNP)Ru and (PNP)Os Complexes in C-H Borylation Catalysis
No full textThis manuscript describes the synthesis of Os complexes supported by the diarylamido/bis(phosphine) PNP pincer ligand. Compound (PNP)OsH(CO) (3-Os) was prepared by analogy with the previously reported 3-Ru. However, attempts to make (PNP)OsH3 (4-Os) analogously to 4-Ru resulted in the formation of an unexpected compound (5-Os) that is a product of addition of a BH3 unit across the Os-N bond in 4-Os. Nonetheless, 4-Os was prepared via an alternative route. Unlike 4-Ru, 4-Os appears to be a classical trihydride. Compounds 3-Ru, 3-Os, 4-Os, 4-Ru, and 5-Os were tested as potential catalysts for a) dehydrogenative borylation of terminal alkynes (DHBTA) and b) dehydrogenative borylation of benzene, but no catalyt-ic C-H borylation was observed for any of them
SynTemp: Efficient Extraction of Graph-Based Reaction Rules from Large-Scale Reaction Databases
No full textSynTemp is a framework designed to extract and hierarchically cluster reaction templates from large-scale reaction data repositories. Reaction templates are partial Imaginary Transition State graphs representing the reaction center as well as surrounding context. These graphs are equivalent to Double Pushout graph rewriting rules and thus can be applied directly to predict reaction outcomes at structural formula level. Rule inference is based on a consensus of multiple atom-atom mapping (AAM) tools integrating predictions RXNMapper, GraphormerMapper, and LocalMapper based on a robust graph-theoretic methodology for comparing partial atom-atom mappings. SynTemp achieves an exceptional accuracy of 99.5% and a success rate of 71.23% in obtaining AAMs on the Chemical Reaction Dataset. Reaction centers with surrounding contexts are extracted and completed with mechanistically relevant hydrogen atoms to obtain complete reaction templates. Subsequently, they were categorized into distinct groups based on topological features using hierarchical clustering, resulting in a library of 311 transformation rules that explains 86% of the reaction data set. A residual of 14% remained unresolved due to non-equivalent AAMs and ambiguous hydrogen placements. Despite these challenges, the coverage of our templates remains high at approximately 93.5-94.5%, surpassing that of RDChiral using SMARTS templates
Molecular Understanding for Motion Modes of Oil Droplets in Aqueous Solutions of Ester- and Amide-Containing Cationic Surfactants
No full textThe study of self-propelled motion in soft matter systems has garnered significant interest due to its potential applications in microfluidics, soft robotics, and the design of autonomous systems. Understanding the molecular mechanisms behind such motility is crucial for advancing these applications. This study investigates the self-propelled motion of lauronitrile oil droplets in aqueous surfactant solutions, focusing on the impact of different surfactant molecular structures on droplet dynamics. The research compares surfactants containing ester and amide linkages, which play a critical role in modulating interfacial tension and influencing Marangoni convection—a key factor of droplet movement. surfactants with ester linkages exhibit a higher affinity for lauronitrile and adsorb more rapidly at the oil-water interface, resulting in stronger Marangoni flows and faster droplet motion. In contrast, amide-containing surfactants show slower adsorption and weaker interactions with lauronitrile, leading to reduced or absent motion. These findings provide new insights into the molecular mechanisms underlying self-propelled droplet behavior in non-equilibrium systems, and contribute to a deeper understanding of self-organising phenomena
Supramolecular Self-assembly of Galactose-Based Reversed N-Nucleosides for Removal of Disperse Dyes from Aqueous Solutions
No full textThis paper describes the design and synthesis of an efficient galactose-triazole based reversed N-nucleoside as a thermoreversible, low molecular weight organogelator (8a). The gelator 8a showed a phase-selective behavior toward ethyl acetate with respect to water. XRD, SEM, FTIR, and UV results showed that the xerogel has a multilamellar structure due to supramolecular forces identified as H-bonding, van der Waals interactions and stacking. The viscoelastic behavior of 8a was examined through rheology experiments, suggesting a dominant viscoelastic structure. The dye adsorption studies and desorption characteristics of 8a were explored against disperse dyes, including Foron Red RD-RBLS, Foron Blue SE-2R and Foron Black S-2B2S via UV and FTIR and SEM. The data revealed that H-bonding between dye molecules and 8a is the main force responsible for dye adsorption. Adsorption kinetics studies showed that physisorption resulted in dye adsorption. Dye removal efficiency was found to be in the range of 80%-90% in 1 h without agitation. The dyes and 8a could be recycled in excellent yields (98% and 92 %, respectively) in their pure forms
Functionalized Cyclic Olefin Copolymers: Chemoselective Polymerization of Cyclopropane-Containing Norbornadiene Dimer using Titanium Catalyst and Post-Polymerization Modification
No full textThe synthesis of functionalized polyolefins is important for turning their properties and expanding their application range. However, the copolymerization of olefins with polar monomers using early transition-metal catalysts remains a formidable challenge. Here, we demonstrate a synthesis strategy through the Ti-catalyzed addition polymerization of a cyclopropane-containing norbornadiene dimer (1) followed by post-polymerization modification (PPM). The polymerization of 1 using a constrained-geometry Ti catalyst afforded poly1 with narrow molecular weight distributions (Đ < 1.3), wherein the molecular weight linearly increased against the monomer conversion. Additionally, the copolymerization of 1 with 1-octene proceeded rapidly, and 1 was consumed faster than 1-octene to form gradient copolymers. Further, the 13C nuclear magnetic resonance (NMR) spectroscopies indicated the 2,3-addition structure of poly1 and no side reaction at the cyclopropane moiety. The polymerizations were highly controlled and chemoselective owing to the lack of cyclopropane coordination to the active polymerization Ti species. The PPM of poly(1-co-1-octene) via the protic acid-catalyzed ring-opening reaction of the cyclopropane introduced aromatic, acyloxyl, and alkoxy groups in high incorporation ratios without cross-linking reactions. Thus, this work demonstrates a promising procedure for the modification of cyclic olefin copolymers using specific cyclopropane reactivity
Yielding of double-network hydrogels with systematically controlled Tetra-PEG first networks
No full textMechanical yielding of double-network (DN) hydrogels is a distinctive feature out of the classical polymer networks, which links to the toughening of the DN gels. Previous studies have focused on the effect of swelling on yield point; however, yield strain and yield stress could not be decoupled from each other which restricted the solid understanding of the micromechanical model of the yielding. In this study, we investigated the yield point of various DN gels where the first network parameters (preparation concentration, strand arm length and network connectivity) have been systematically varied using the well-established Tetra-PEG networks. This experimental approach clarified the universal relations of (1) yield elongation ratio to the finite extensibility of the first network and (2) yield stress to the number density of the first network strands regardless of the strand length, network connectivity and orientation. This research will lead to unveiling the true physical criterion of the yielding of double-network materials
Benchtop 19F NMR Spectroscopy optimized Knorr pyrazole synthesis of Celecoxib and Mavacoxib, 3-(trifluoromethyl) pyrazolyl benzenesulfonamides Non-Steroidal Anti-Inflammatory Drugs (NSAIDs)
No full textFluorinated organic compounds have demonstrated remarkable utility in medicinal chemistry due to their enhanced metabolic stability and potent therapeutic efficacy. Several examples exist of fluorinated non-steroidal anti-inflammatory drugs (NSAIDs) including diflunisal, flurbiprofen, and trifluoromethylated pyrazoles celecoxib and mavacoxib. These trifluoromethylated pyrazoles, which are most commonly constructed through cyclocondensation of a trifluorinated 1,3-dicarbonyl and an aryl hydrazine, are also found in numerous other drug candidates. Here, we interrogate the effects of solvent and the presence of Brønsted or Lewis acid catalysts on catalyzing this process. We highlight the utility of benchtop 19F NMR spectroscopy in enabling real-time quantification of reaction progress and identification of fluorinated species present in crude reaction mixtures without the need for cost-prohibitive deuterated solvents. Ultimately, we find that the reaction solvent has the greatest impact on rate and product yield, and also found that the relationship between keto-enol equilibrium of the dicarbonyl starting material pyrazole formation rate is highly solvent dependent. More broadly, we describe the optimization of the yield and kinetics of trifluoromethylpyrazole formation in the synthesis of celecoxib and mavacoxib, which is made possible through high-throughput reaction screening on benchtop NMR
Electrostatic Embedding Machine Learning for Ground and Excited State Molecular Dynamics of Solvated Molecules
No full textThe application of quantum mechanics (QM) / molecular mechanics (MM) models for studying dynamics in complex systems is nowadays well established. However, their significant limitation is the high computational cost, which restricts their use for larger systems and long-timescale processes. We propose a machine-learning (ML) based approach to study the dynamics of solvated molecules on the ground- and excited-state potential energy surfaces. Our ML model is trained on QM/MM calculations and is designed to predict energies and forces within an electrostatic embedding framework. We built a socket-based interface of our machinery with AMBER to run ML/MM molecular dynamics simulations. As an application, we investigated the excited state intramolecular proton transfer of 3-hydroxyflavone in two different solvents: methanol and methylcyclohexane. Our ML/MM simulations accurately distinguished between the two solvents, effectively reproducing the solvent effects on proton transfer dynamics