C-H Bond Research Articles

Citrate coated iron oxide nanoparticles: Synthesis, characterization, and performance in protein adsorption

<p>Magnetic nanoparticles (MNPs) are extensively utilized in biomedicine as part of controlled drug release systems, hyperthermia, and magnetic resonance imaging. Surface modification of MNPs not only enhances their stability and biocompatibility but also increases affinity with certain molecules, allowing them to be used in protein separation and adsorption processes. This article reports the synthesis and characterization of iron oxide MNPs functionalized with citric acid (IONPs@CA) to evaluate their performance in protein adsorption. The nanoparticles were characterized using various techniques such as transmission electron microscopy (TEM), X-ray diffraction (XRD), dynamic light scattering (DLS), thermogravimetric analysis (TGA), and Fourier-transform infrared spectroscopy (FT-IR). The percentage of lysozyme (Lyz) adsorbed by IONPs@CA was 84.9%, while the IONPs sample only adsorbed 5.9%. In silico evaluation results showed some repulsion bonds obtained in Lyz-IONPs and hydrogen bonds, carbon-hydrogen bonds, and van der Waals interactions in Lyz-IONPs@CA. These results may be novel since no previous research was found specifying this type of interaction between lysozyme and IONPs and/or IONPs@CA. The maximum adsorption efficiency obtained for the coated nanoparticles was 88.3%.</p>

Quantum effects in CH activation with [Cu2O2]2+ complexes.

We investigate the mechanism of primary alkane CH bond activation with dioxo-dicopper ([Cu2O2]2+) complexes, which serve as model catalysts for enzymes capable of activating CH bonds under mild conditions. As large H/D kinetic isotope effects (KIEs) are observed in enzymes and their synthetic mimics, we employ density functional theory along with variational transition-state theory with multidimensional tunneling to estimate reaction rate coefficients. By systematically varying ligand electrophilicity and substrate chain length, we examine trends in rate coefficients and kinetic isotope effects for the two proposed CH activation pathways - one-step oxo-insertion and two-step radical recombination. Although larger tunneling transmission coefficients are obtained for the radical pathway, the oxo-insertion mechanism yields higher rate coefficients on account of lower activation barriers. The question of the preferred CH activation mechanism, however, remains open: excellent agreement is observed between the predicted and known experimental KIE results for the radical pathway, while calculated Hammett slopes for the oxo-insertion pathway closely mirror experiments.

Localized surface plasmon resonance assisted photoredox catalysis using newly fabricated copper-nanorods: a decarboxylative approach towards carbon–hydrogen bond formation under visible light

Copper nanorods (Cu-NRs) exhibit significant plasmonic behavior, serving as efficient catalysts in an environmentally friendly decarboxylative process that converts alkyl carboxylic acids to alkane analogues under visible light.

Visible-light-induced direct C-H alkylation of polycyclic aromatic hydrocarbons with alkylsulfones.

Polycyclic aromatic hydrocarbons (PAHs) are fragments of graphene that have attracted considerable attention as a new class of carbon-based materials. The functionalization of edge positions in PAHs is important to enable the modulation of physical and chemical properties essential for various applications. However, straightforward methods that combine functional group tolerance and regioselectivity remain sought after. Here we report a photochemical approach for the direct alkylation of carbon-hydrogen bonds in PAHs that takes place in a regiospecific manner, an outcome that has never been achieved in related thermal reactions. A reaction mechanism involving a single electron transfer process from photo-excited PAHs to sulfones, and a rationale for the origin of regioselectivity are proposed on the basis of spectroscopic analyses and theoretical calculations.

Cooperative activation of carbon-hydrogen bonds by heterobimetallic systems.

The direct activation of C-H bonds has been a rich and active field of organometallic chemistry for many years. Recently, incredible progress has been made and important mechanistic insights have accelerated research. In particular, the use of heterobimetallic complexes to heterolytically activate C-H bonds across the two metal centers has seen a recent surge in interest. This perspective article aims to orient the reader in this fast moving field, highlight recent progress, give design considerations for further research and provide an optimistic outlook on the future of catalytic C-H functionalization with heterobimetallic complexes.

Dual Pt atoms stabilized by an optimized coordination environment for propane dehydrogenation

Tailoring atomically dispersed catalysts by various methods has been the subject of intense current research in heterogeneous catalysis. In this work, the structural stability and propane dehydrogenation performance of Pt-TiO2 catalysts with single, dual, and triple Pt atoms doped on the reduced TiO2 surface have been examined. Experimental results indicate the atomically dispersed Pt is thermally very stable and shows exceptionally high activity (TOFpropane = 4.93 s−1) and selectivity (∼98.5 %) for the dehydrogenation reaction. The recently developed machine-learning-based SSW-NN method is then employed to explore the global potential energy surface of the atomically dispersed Pt atom-doped TiO2, which suggests that the single and dual Pt atoms can be tightly held by the vacancies created on the reduced transition-metal oxide, as confirmed by DFT + U calculated energetics. After that, advanced characterization techniques are used in conjunction with microkinetic analysis to establish the quantitative structure–activity relationships. It is found that the dual-Pt-atom structure with two Pt atoms embedded in adjacent Ti and O vacancies is the only active ensemble that dramatically promotes the CH bond activation and hydrogen recombination, as compared to single Pt atoms accommodated by either Ti or O vacancies. These results provide new and direct evidence in support of the idea that specific function can be imparted to specific active sites by tuning their coordination environments, which makes it possible to tailor the catalytic properties of metal oxides to a particular reaction such as propane dehydrogenation.

Hydration of biologically relevant tetramethylammonium cation by neutron scattering and molecular dynamics.

Neutron scattering and molecular dynamics studies were performed on a concentrated aqueous tetramethylammonium (TMA) chloride solution to gain insight into the hydration shell structure of TMA, which is relevant for understanding its behavior in biological contexts of, e.g., properties of phospholipid membrane headgroups or interactions between DNA and histones. Specifically, neutron diffraction with isotopic substitution experiments were performed on TMA and water hydrogens to extract the specific correlation between hydrogens in TMA (HTMA) and hydrogens in water (HW). Classical molecular dynamics simulations were performed to help interpret the experimental neutron scattering data. Comparison of the hydration structure and simulated neutron signals obtained with various force field flavors (e.g. overall charge, charge distribution, polarity of the CH bonds and geometry) allowed us to gain insight into how sensitive the TMA hydration structure is to such changes and how much the neutron signal can capture them. We show that certain aspects of the hydration, such as the correlation of the hydrogen on TMA to hydrogen on water, showed little dependence on the force field. In contrast, other correlations, such as the ion-ion interactions, showed more marked changes. Strikingly, the neutron scattering signal cannot discriminate between different hydration patterns. Finally, ab initio molecular dynamics was used to examine the three-dimensional hydration structure and thus to benchmark force field simulations. Overall, while neutron scattering has been previously successfully used to improve force fields, in the particular case of TMA we show that it has only limited value to fully determine the hydration structure, with other techniques such as ab initio MD being of a significant help.

An alternative catalytic cycle for selective methane oxidation to methanol with Cu clusters in zeolites.

The partial oxidation of methane to methanol catalyzed by Cu-exchanged zeolites involves at present a three-step procedure that requires changing reaction conditions along the catalytic cycle. In this work we present an alternative catalytic cycle for selective methane conversion to methanol using as active species small Cu5 clusters supported on CHA zeolite. Periodic DFT calculations show that molecular O2 is easily activated on Cu5 clusters producing bi-coordinated O atoms able to dissociate homolytically a CH bond from CH4 and to react with the radical-like non-adsorbed methyl intermediate formed producing methanol, while competitive overoxidation to CO2 is energetically disfavored. The present mechanistic study opens a new avenue to design catalytic materials based on their ability to stabilize radical species.

Heptanone isomers as biofuel: Reactivity with OH radicals

The reactions of heptanone isomers, namely diisopropyl ketone (DIPK, k1), isopropyl propyl ketone (IPPK, k2), and dipropyl ketone (DPK, k3), with OH radicals play a crucial role in predicting their combustion behavior. We conducted the first high-temperature measurements of these reactions over the temperature range of 876 to 1328 K at pressures near 1 bar. The determined overall rate coefficients may be described as (unit of cm3molecule−1s−1):k1=2.13×10−10e(−2684T)k2=2.42×10−10e(−2733T)k3=2.84×10−10e(−2808T)Over the investigated high temperature range, all three reactions exhibit a positive temperature dependence, with activation energies ranging 5.3 to 5.6 kcal mol−1. We did not observe discernible pressure dependence within the pressure range of 0.66 to 1.66 bar. At 1250 K, DPK reacts with OH radicals 11 % faster than IPPK and 21 % faster than DIPK. Interestingly, compared to heptane, which reacts twice as fast, the presence of the C=O group significantly hinders the reactivity of the normal chain heptanone (DPK) towards OH radicals. Furthermore, the rate coefficients of OH + DIPK reaction in literature models underestimate the measured activation energy and overpredict the overall rate coefficients. To enhance the accuracy of SAR prediction for OH + ketone reactions, a multiplicative factor of 0.6 - 0.75 is suggested. Additionally, this study provides a site-specific expression for the tertiary CH bonds adjacent to the C=O bond in ketone molecules, expanding the applicability of the NNN (next-nearest-neighbor) prediction scheme to encompass larger branched ketones.

Comparative Computational Study on Molecular Structure, Electronic and Vibrational Analysis of Vinyl Bromide based on HF and DFT Approach

In this study, we have used the Hartree-Fock and Density Functional Theory method of calculation and compared the equilibrium configuration, electronic and vibrational mode of Vinyl Bromide molecule. The molecule is geometrically optimized initially by using 6-31G basis set with B3LYP functional and then bond angles, bond lengths, dihedral angles and IR spectra are compared respectively. Various groups of atoms in Vinyl Bromide molecule by DFT has more accurate bond length, bond angle values rather than by HF computation when comparing with the experimental values. The ground state energies are found at angle 10° or 180° or 360° using HF and DFT method of calculation for the H4-C1-C2-Br6 position. Values of the carbon-hydrogen, carbon-carbon and carbon-bromine bond lengths and bond angles for optimization state of C2H3Br molecule using Hartree-Fock and Density Functional Theory methods with respect to the basis set 6-31G have been analyzed. The C−H in-plane bending vibration and C−H out-of-plane bending vibrations occur in the region 1400–1050 cm-1 and 1000–675 cm-1 respectively. The electronic properties, such as Highest Occupied Molecular Orbital and Lowest Unoccupied Molecular Orbital energies are performed by HF and DFT approach and the difference in Highest Occupied Molecular Orbital and Lowest Unoccupied Molecular Orbital energy gap for HF and DFT method are 14.0847 eV and 6.8994 eV respectively

Transition of characteristic explosion limits: From hydrogen to diethyl ether

In this work, the explosion limits of three different fuels: hydrogen (H2), propane (C3H8, C3), and diethyl ether (DEE, C2H5OC2H5, C4), are investigated based on detailed chemical kinetics. The results reveal that the explosion limit of H2O2 exhibits the typical Z-shape, while C3H8O2 exhibits a single-NTC response, and DEE-O2 displays a double-NTC response. Sensitivity analysis indicates that the appearance of the NTC response in both the C3 and DEE fuels is intricately linked to low-temperature reaction paths. Moreover, the extents of the NTC responses are comparable for these two fuels with similar low-temperature reaction paths, but operate under different temperature conditions. Specifically, the double-NTC response observed in DEE is attributed to its primary CH and CO bonds, generating C4 and C2 radicals. The oxygen addition and the subsequent pathways of these radicals dominate in distinct temperature ranges. In contrast, C3H8 only possesses the CH bond, resulting in a single-NTC response, as OH radicals are mainly released by C3 radicals through oxygen addition, isomerization, and decomposition reactions. The results of binary fuel mixtures with H2 addition indicate that the reactivity of H2 controls the low-pressure and high-temperature regime, while the C3 and DEE fuels dominate the high-pressure and low-temperature regime. Additionally, a triangular crossover regime is identified between these two regimes due to the switchover of the reactivity. Sensitivity analysis further reveals the transition of the dominating reactions related to different fuels at various pressure-temperature regimes. Finally, based on the explosion limits of the multi-component mixtures, a detailed explosion regime diagram is proposed for carbon-free fuel (H2), alkane fuel (C3H8), and oxygenated ether fuel (DEE). This new regime diagram provides valuable insights for the investigation and utilization of ether fuels and the mixture of different fuels.

Investigation and drug design for novel molecules from natural products as inhibitors for controlling multiple myeloma disease using in-silico tools

Multiple myeloma (MM) is a disease that causes plasma cell growth in the bone marrow and immune globulin buildup in blood and urine. Despite recent advances in MM therapy, many still die due to its high mortality rate. A study using computational simulations analyzed 100 natural ingredients from the SANC database to determine if they inhibited the IgH domain, a known cause of multiple myeloma. Natural component Diospyrin inhibited the IgH enzyme with the best binding energy of −10.3 kcal/mol and three carbon-hydrogen bonds, followed by Parviflorone F complex with a binding energy of −10.1 kcal/mol and two conventional-hydrogen bonds. As a result, the Molecular Dynamic simulation was used to test the stability of the two complexes. During the simulation, the Diospyrin molecule dissociated from the protein at roughly 67.5 ns, whereas the Parviflorone F molecule stayed attached to the protein throughout. The latter was the subject of the investigation. The analysis of the production run data revealed that the Parviflorone F molecule exhibits a variety of conformations within the binding pocket while keeping a relatively constant distance from the protein’s center of mass. The analysis of the production run data revealed that the Parviflorone F molecule exhibited a variety of conformations within the binding pocket while keeping a relatively constant distance from the protein’s center of mass. The root mean square deviation (RMSD) plots for both the protein and complex showed a stable and steady average value of 4.4 Å for the first 82 nanoseconds of manufacture. As a result, the average value increased to 8.3 Å. Furthermore, the components of the binding free energy, as computed by MM-GBSA, revealed that the mean binding energy of the Parviflorone F molecule was −23.88 kcal/mol. Finally, after analyzing all of the examination data, Parviflorone F was identified as a powerful inhibitor of the IgH domain and hence of the MM disease, which requires further in-vivo conformation. Communicated by Ramaswamy H. Sarma

Aliphatic C[sbnd]H azidation by Mn based mimics of α-ketoglutarate dependent enzymes

α-Ketoglutarate dependent nonheme halogenases catalyze regioselective functionalization of aliphatic CH bonds via H abstraction by the ferryl site of the [X−FeIV=O] intermediate, followed by radical rebound to an adjacent halogen ligand X at the same Fe center. Herein we report biomimetic nonheme Mn complexes, possessing two labile cis-α coordination sites and capable of catalyzing the enantioselective azidation of C(sp3)−H groups. Proper ligand environment of the active sites imposes steric constraints on HO−Mn rebound, thus accounting for preferential C-radical rebound to the adjacent N3−Mn ligand. Such mechanism of selectivity control is analogous to that operating in the prototypical α-ketoglutarate-dependent nonheme iron halogenases.

Evaluation of in silico anticancer activity of some striazine derivatives as VEGFR2 inhibitors

The s-triazine derivatives have been shown to have diverse biological activities, especially anticancer activity. Fifty s-triazine derivatives were screened for anticancer activity through inhibition of VEGFR2 (vascular endothelial growth factor receptor-2) by molecular docking method using AutoDock Vina software. Compounds 20 and 40 showed the strongest interactions among all tested compounds with the binding affinity values of -10.8 and -10.5 Kcal/mol, respectively compared to reference drugs Gedatolisib (-9.1 Kcal/mol) and Paclitaxel (-7.8 Kcal/mol) at the active site of VEGFR2. These compounds established one carbon-hydrogen bond at amino acid HIS1026, specifically exhibiting better electrostatic and hydrophobic interactions than the reference drugs Gedatolisib and Paclitaxel. Moreover, compounds 20 and 40 also showed interactions with the VEGFR2 receptor that resemble the reference drug Gedatolisib at amino acids such as ARG1027, ASP1046, and HIS1026. Therefore, these compounds could be a potential lead molecule for anticancer activity.

Biocatalytic hydroxylation tertiary C-H bonds for synthesis of chiral tertiary alcohols by cytochrome P450

In view of the importance and beneficial characteristics of enantioenriched tertiary alcohols in pharmaceutical chemistry, efficient and green strategies for their synthesis are highly sought after. Here, we report a simple synthesis of the elusive chiral tertiary alcohols. A cytochrome P450 monooxygenase called P450PL2 was developed to enable chiral tertiary alcohols by the benzylic CH bonds asymmetric hydroxylation of the racemic tertiary carbon substrates. This P450-catalyzed protocol provides various chiral tertiary alcohols with unexpectedly functional group tolerance and excellent enantioselectivities (up to >99 % ee). The method features mild reaction and employs molecular oxygen as an oxidant, avoids the use of pre-oxygen functionalized substrates. Preliminary molecular dynamics simulation studies were carried out to reveal the possible reasons for the exceptional selective hydroxylation of substrate during P450PL2 catalysis.

Peptidomics Screening and Molecular Docking with Umami Receptors T1R1/T1R3 of Novel Umami Peptides from Oyster (Crassostrea gigas) Hydrolysates.

In this study, novel umami peptides were prepared from oyster (Crassostrea gigas) hydrolysates, and their umami mechanisms were investigated. Umami fractions G2 and G3 were isolated by gel filtration chromatography (GFC) and sensory evaluation. The umami scores of the G2 and G3 fractions were 7.8 ± 0.12 and 7.5 ± 0.18, respectively. 36 potential umami peptides with molecular weights below 1500 Da, E and D accounting for >30% of the peptides and iUmami-SCM > 588 were screened by peptidomics. Peptide source analysis revealed that myosin, paramyosin, and sarcoplasmic were the major precursor proteins for these peptides. The electronic tongue results demonstrated that the synthetic peptides DPNDPDMKY and NARIEELEEE possessed an umami characteristic, whereas SIEDVEESRNK and ISIEDVEESRNK possessed a saltiness characteristic. Additionally, molecular docking results indicated that the umami peptide (DPNDPDMKY, NARIEELEEE, SIEDVEESRNK, and ISIEDVEESRNK) binds to H145, S276, H388, T305, Y218, D216, and Q389 residues in the T1R3 taste receptor via a conventional hydrogen bond and a carbon-hydrogen bond. This research provides a new strategy for the screening of umami peptides.

Pyrolysis and combustion reaction mechanisms of methyl palmitate with ReaxFF-MD method

As a substitute for fossil fuel, methyl palmitate (C17H34O2) has important scientific and practical significance to study its pyrolysis and combustion mechanism. In this paper, the ReaxFF-MD method is used to research the reaction mechanism and main products of C17H34O2. The effects of temperature and O2 on the decomposition, main products and reaction paths of C17H34O2 are analyzed to determine its reaction mechanism. The results show that the reaction activation energies of C17H34O2 in pyrolysis and combustion are 201.76 kJ/mol and 139.07 kJ/mol, respectively. The effect of temperature on C17H34O2 is greater than O2 on C17H34O2 at higher temperature. The basic reaction paths for the initial decomposition of C17H34O2 is that the CC, CO, and CH bonds are broken into smaller intermediates. In addition, the detailed distribution and generation paths of the main products C2H4, H2, H2O, CH2O, and so on are depicted to construct the reaction mechanism of C17H34O2.

Intramolecular C-H bond amination catalyzed by myoglobin reconstituted with iron porphycene

C−H bond amination is an effective way to obtain nitrogen-containing products. In this work, we demonstrate that myoglobin reconstituted with iron porphycene (rMb(FePc)) catalyzes intramolecular C(sp3)−H bond amination of arylsulfonyl azides to yield corresponding sultam analogs. The total turnover number of rMb(FePc) is up to 5.7 × 104 for the C−H bond amination of 2,4,6-triisopropylbenzenesulfonyl azide. Moreover, rMb(FePc) exhibits higher selectivity for the desired C-H bond amination than the competing azide reduction compared to native myoglobin. Kinetic studies reveal that the kcat value of rMb(FePc) is 4-fold higher than that of native myoglobin. Furthermore, H64A, H64V and H64I mutants of rMb(FePc) enhance the turnover number (TON) and enantioselectivity for the C−H bond amination of 2,4,6-triethylbenzenesulfonyl azide. The present findings indicate that iron porphycene is an attractive artificial cofactor for myoglobin toward the C−H bond amination reaction.

Influence of operating parameters on the yield of micro-plastics from plastics incineration

Plastics account for a large proportion of domestic waste. However, micro-plastics will be produced after the plastic is incinerated. The purpose of this study is to find out the change rule of micro-plastics produced during incineration under different conditions. Combining micro-FTIR and PCA algorithm is a good tool to identify the micro-plastics. The PE, PP and PVC micro-plastics are distinguished using PCA-FTIR spectra. The results show different incineration conditions significantly affect the output of micro-plastics. The yield of micro-plastics increases with increasing temperature for both PP and PVC. And the yield of micro-plastics decreases with the increase in flow rate. The maximum amount of micro-plastics is produced by PE, which is 6.62 × 103 after 1 g PE incineration. The yield of micro-plastics in the co-incineration of PE and PP, as well as PE and PVC, significantly increased to 1.42 and 1.89 times of the calculated values, respectively. The nano-particles are also observed. The FTIR and EDS results show that the nano-particles are the products of incineration of plastics, including partly CH bond and unburned carbon, tar and ash.

Trinuclear ruthenium clusters supported by piconol ligands: Application in catalytic C(sp3)-H bond oxidation in CH3CN/H2O

Trinuclear ruthenium clusters supported by piconol ligands [6-C8H6N-PyCR1R2O](μ2H)Ru3(CO)9 (R1 = R2 = CH3 (1); R1 = R2 = CH2CH3 (2); R1, R2 = -(CH2)4- (3); R1 = CH3, R2 = Ph (4)) have been proved to be efficient catalysts for the oxidation of saturated CH bonds. Cluster 1 was found to be the most active of the four, which can catalyze the oxidation of various hydrocarbons, with tert‑butyl hydroperoxide as the oxidant in CH3CN/H2O at room temperature, to afford the corresponding ketones in excellent yields.