A computational investigation of the activation of allene (H2C = C = CHR; R = H, CH3, CN) by a frustrated phosphorous/boron Lewis pair

Capecitabine loaded potato starch-chitosan nanoparticles: A novel approach for targeted therapy and improved outcomes in aggressive colon cancer

Aggressive colon cancer treatment poses significant challenges. This study investigates the potential of innovative carbohydrate-based nanoparticles for targeted Capecitabine (CTB) delivery. CTB nanoparticles were synthesized by conjugating CTB with potato starch and chitosan using ultrasonication, hydrolysis, and ionotropic gelation. Characterization included drug loading, rheology, Surface-Enhanced Raman Spectroscopy (SERS), Fourier-Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), X-ray Diffraction (XRD), and Thermogravimetric Analysis (TGA). In vitro and in vivo antitumor activity was evaluated using HT-29 cells and N, N-dimethylhydrazine-induced Balb/c mice, respectively. Cellular assays assessed angiogenesis, migration, proliferation, and apoptosis. Nanoparticles exhibited a mean size of 245 nm, positive zeta potential (+30 mV), high loading efficacy (76 %), and sustained drug release (92 % over 100 h). CTB-loaded nanoparticles displayed superior colon histology, reduced tumour scores, and inhibited VEGD and CD31 expression compared to free CTB. Cellular assays confirmed significant antitumor effects, including reduced tube formation, migration, and proliferation, and increased apoptosis. This study demonstrates the promise of CTB-loaded potato starch-chitosan nanoparticles for aggressive colon cancer treatment. These findings highlight the potential of these nanoparticles for further evaluation in diverse cancer models.

Frustrated Lewis pair-mediated hydro-dehalogenation: crucial role of non-covalent interactions

CONTEXT

Organic halides stand as invaluable reagents with diverse applications in synthetic chemistry and various industrial processes. Despite their utility, concerns arise due to their inherent toxicity. Addressing these apprehensions, hydro-dehalogenation has emerged as a promising strategy involving the replacement of halogen atoms with hydrogen atoms to transform toxic organic halides into hydrocarbons. This study delves into the computational exploration of hydro-dehalogenation reactions of benzyl halide, mediated by frustrated Lewis pairs (FLPs), using density functional theory (DFT). The reactions entail the formation of FLP1 or FLP2 in the presence of TMP or lutidine with B(C6F5)3, respectively. This is followed by heterolytic cleavage of dihydrogen and subsequent reaction with benzyl halides. Non-covalent interaction analysis underscores the significance of π-π stacking and CH-π interactions in stabilizing transition states. Additionally, the activation strain model (ASM) dissects activation energies, revealing the substantial impact of strain energy on reaction barriers. Energy decomposition analysis (EDA) offers insights into the contributions of electrostatic, orbital, and dispersion energies to the overall attractive interaction energy. The investigation extends to hydro-dehalogenation reactions of ethyl halides, uncovering distinct mechanisms and activation barriers. This comprehensive analysis illuminates the intricacies of hydro-dehalogenation reactions, providing valuable insights into their mechanisms and paving the way for future studies in this field.

METHODS

Geometry optimizations were carried out at the M06-2X/def2-SVP level of theory, which was performed using the Gaussian 16 program. Solvent-corrected single-point energies were also calculated using the polarizable continuum model (PCM) at the PCM(chloroform)-M06-2X/def2-TZVP//M06-2X/def2-SVP level of theory. The Gibbs free energy correction was determined from computations performed at the M06-2X/def2-SVP level of theory. Principal interacting orbital (PIO) analysis was conducted using the NBO 6.0 software. The nature of bonding in the respective transition state (TS) structures was analyzed using atoms-in-molecules (AIM) analyses. Additionally, the presence of non-covalent interactions (NCI) was exemplified using Multiwfn software.

CO2 reduction using aluminum hydride: Generation of in-situ frustrated Lewis pairs and small molecule activation therein

CO2 reduction is appealing for the long-term production of high-value fuels and chemicals. Herein, using density functional theory (DFT) based calculations, we study the CO2 reduction pathway to formic acid using aluminum hydride and phosphine derivatives. Our primary focus is on aluminum hydride derivatives, aimed at improving the efficiency of the CO2 reduction process. Substituents with σ-donating properties at the aluminum center are discovered to lower the activation barriers. We demonstrate how di-tert-butylphosphine oxide (LB-O)/di-tert-butylphosphine sulfide (LB-S)/di-tert-butylphosphanimine (LB-N) work together with aluminum hydride to facilitate CO2 reduction process and generate in-situ frustrated Lewis pairs (FLPs), such as FLP-O, FLP-S, and FLP-N. The activation strain model (ASM) analysis reveals the significance of strain energy in determining activation barriers. EDA-NOCV and PIO analyses elucidate the orbital interactions at the corresponding transition states. Furthermore, the study delves into the activation of various small molecules, such as dihydrogen, acetylene, ethylene, carbon dioxide, nitrous oxide, and acetonitrile, using those in-situ generated FLPs. The study highlights the low activation barriers and emphasizes the potential for small molecule activation in this context.

Asymmetric catalysis by chiral FLPs: A computational mini-review

Steric hindrance in Lewis acid (LA) and Lewis base (LB) obstruct the Lewis acid-base adduct formation, and the pair was termed as frustrated Lewis pair (FLP). In the past 16 years, the field of enantioselective catalysis by chiral FLPs has been slowly growing. It was shown that chiral LAs are significant as they are involved in the hydrogen transfer (HT) step to the imine, resulting in enantioselectivity. After H2 activation, the borohydride can exist in a number of plausible conformations and their stability is governed by the presence of noncovalent interaction through C-H····π and π····π interactions. However, LBs are not ideal for asymmetric induction as they compete with the imine substrate as a counter LB. Further, the proton transfer from chiral LB to the imine does not induce any chirality as chirality develops in the HT step. However, intramolecular FLPs with chiral scaffold are very efficient as they possess an optimum distance between LA and LB, which facilitates the H2 activation but precludes the adduct formation of the small molecules substrate with the LA component. This mini-review summarizes computational investigation involving chiral LA and LB, and discusses intramolecular FLPs in the enantioselective catalysis.

Unraveling Reactivity Pathways: Dihydrogen Activation and Hydrogenation of Multiple Bonds by Pyramidalized Boron-Based Frustrated Lewis Pairs

The activation of H2 by pyramidalized boron-based frustrated Lewis Pairs (FLPs) (B/E-FLP systems where "E" refers to N, P, As, Sb, and Bi) have been explored using density functional theory (DFT) based computational study. The activation pathway for the entire process is accurately characterized through the utilization of the activation strain model (ASM) of reactivity, shedding light on the underlying physical factors governing the process. The study also explores the hydrogenation process of multiple bonds with the help of B/N-FLP. The research findings demonstrate that the liberation of activated dihydrogen occurs in a synchronized, albeit noticeably asynchronous, fashion. The transformation is extensively elucidated using the activation strain model and the energy decomposition analysis. This approach suggests a co-operative double hydrogen-transfer mechanism, where the B-H hydride triggers a nucleophilic attack on the carbon atom of the multiple bonds, succeeded by the migration of the protic N-H.

In Silico Investigation of the Mechanism of Disulfide Bond Dissociation by New Frustrated Lewis Pairs

Understanding the mechanism of disulfide bond cleavage is important in various scientific disciplines including organic synthesis, catalysis, and biochemistry. In this study, an in silico investigation has been carried out for the dissociation of disulfide bonds using newly designed frustrated Lewis pairs (FLPs). The study revealed that the cleavage of the disulfide bond by the FLP P(tBu)3/B(C2NBSHF2)3 can also be used like the conventional FLP (tBu)3P/B(C6F5)3. It has been observed that the reaction is almost thermoneutral in the gas phase but exothermic in nonpolar solvents, such as toluene, heptane, and hexane. Furthermore, the natural bond orbital (NBO) describes insights into the role of FLPs in facilitating this reaction. Additionally, reaction force and force constant studies shed light on the energy requirements for completing the reaction and the synchronous nature of the dissociation process, respectively. Reaction electronic flux (REF) and its separations give the pattern of electronic activity during the chemical reaction. Extended transition state-natural orbitals for chemical valence (ETS-NOCV) and principal interacting orbital (PIO) analysis provide valuable information about the orbital interactions during the chemical reaction.

Frustrated Lewis Pairs: Bonding, Reactivity, and Applications

The outstanding capability of Frustrated Lewis Pair (FLP) catalysts to activate small molecules has gained significant attention in recent times. Reactivity of FLP is further extended toward the hydrogenation of various unsaturated species. Over the past decade, this unique catalysis concept has been successfully expanded to heterogeneous catalysis as well. The present review article gives a brief survey on several studies on this field. A thorough discussion on quantum chemical studies concerning the activation of H₂ is provided. The role of aromaticity and boron-ligand cooperation on the reactivity of FLP is discussed in the Review. How FLP can activate other small molecules by cooperative action of its Lewis centers is also discussed. Further, the discussion is shifted to the hydrogenation of various unsaturated species and the mechanism regarding this process. It also discusses the latest theoretical advancements in the application of FLP in heterogeneous catalysis across various domains, such as two-dimensional materials, functionalized surfaces, and metal oxides. A deeper understanding of the catalytic process may assist in devising new heterogeneous FLP catalysts through experimental design.

Insights into the Reactivity of the Ring-Opening Reaction of Tetrahydrofuran by Intramolecular Group-13/P- and Al/Group-15-Based Frustrated Lewis Pairs

A theoretical study concerning key factors affecting activation energies for ring-opening reactions of tetrahydrofuran (THF) by G13/P-based (G13 = B, Al, Ga, In, and Tl) and Al/G15-based (G15 = N, P, As, Sb, and Bi) frustrated Lewis pairs (FLPs) featuring the dimethylxanthene scaffold was performed using density functional theory. Our theoretical findings indicate that only dimethylxanthene backbone Al/P-Rea (Rea = reactant) FLP-type molecules can be energetically favorable to undergo the ring-opening reaction with THF. Our theoretical evidence reveals that the shorter the separating distance between Lewis acidic (LA) and Lewis basic (LB) centers of the dimethylxanthene backbone FLP-type molecules, the greater the orbital overlaps between the FLP and THF and the lower the activation barrier for such a ring-opening reaction. Energy decomposition analysis (EDA) evidence suggests that the bonding interaction for such a ring-opening reaction is predominated by the donor-acceptor interaction (singlet-singlet interaction) compared to the electron-sharing interaction (triplet-triplet interaction). In addition, the natural orbitals for chemical valence (NOCV) evidence demonstrate that the bonding situations of such ring-opening reactions can be best described as FLP-to-THF forward bonding (the lone pair (G15) → the empty σ*(C-O)) and THF-to-FLP back bonding (the empty σ*(G13) ← filled p-π(O)). The EDA-NOCV observations show that the former plays a predominant role and the latter plays a minor role in such bonding conditions. The activation strain model reveals that the deformation energy of THF is the key factor in determining the activation energy of their ring-opening reactions. Comparing the geometrical structures of the transition states with their corresponding reactants, a linear relationship between them can be rationally explained by the Hammond postulate combined with the respective activation barriers calculated in this work.

A strained intramolecular P/Al-FLP and its reactivity toward allene

FLPs featuring aluminum-phosphane interactions, spring-loaded by a rigid biphenylene linker, have been accessed through a route where trimethyltin units at phosphane-functionalized organic backbones are exchanged by an AlCl₂ moiety. Upon contact with substrates like CO₂ these are readily bound by the Al/P site with release of strain. The system could also be utilized for a unique reactivity, namely the activation of allene.

Significant Insight into the Origin of Reaction Barriers Determining Dihydrogen Activation by G13-P-P (G13 = Group 13 Element) and G15-P-Ga (G15 = Group 15 Element) Frustrated Lewis Pairs

The heterolytic cleavage of H₂ by multiply bonded phosphorus-bridged G13-P-P-Rea (G13 = B, Al, Ga, In, and Tl) and G15-P-Ga-Rea (G15 = N, P, As, Sb, and Bi) frustrated Lewis pairs (FLPs) has been theoretically investigated using density functional theory calculations. For the above nine FLP-type molecules, our theoretical findings suggest that only Al-P-P-Rea, Ga-P-P-Rea, and In-P-P-Rea can undergo the energetically feasible H₂ activation reaction from kinetic and thermodynamic viewpoints. Our study based on the activation strain model (ASM) reveals that gaining a better orbital overlap between G13-P-P-Rea and G15-P-Ga-Rea molecules and H₂ affected the reaction barriers through the atomic radius of G13 and G15. According to our energy decomposition analysis-natural orbitals for chemical valence (EDA-NOCV) results, the bonding of these H₂ activation reactions involving G13-P-P-Rea and G15-P-Ga-Rea is dominated by the donor-acceptor interaction (singlet-singlet interaction) rather than the electron-sharing interaction (triplet-triplet interaction). Moreover, our EDA-NOCV evidence reveals that the best description for the above bonding situations is the lone pair(G15) → σ*(H₂) interaction rather than the empty p-π-orbital(G13) ← σ(H₂) interaction. In particular, the findings in this work based on theoretically calculated geometries and the corresponding relative free energies of the stationary points combined with the results from the above sophisticated methods nicely agree with the famous Hammond postulate.