Adjacent Functional Groups Research Articles

C–H/C–H Aromative carbonylation of diarylalkynes enabled palladium-catalyzed by 6-endo-dig carbocyclization

Transition metal-catalyzed cycloaromatization reactions of diarylalkynes offer a swift and versatile approach to synthesizing a wide array of polycyclic aromatic compounds. However, the specific mechanism of Pd-catalyzed C–H/C–H aromative carbonylation of diarylalkynes, particularly those bearing adjacent functional groups, remains a relatively unexplored area. Herein, we present a palladium-catalyzed C–H/C–H aromative carbonylation of diarylalkynes, which proceeds through an exclusive 6-endo-dig carbocyclization pathway, followed by the incorporation of CO to yield carbonyl compounds. This methodology provides a novel and efficient route for generating complex aromatic structures, thus expanding the potential applications in organic synthesis.

The ortho-substituent effect regulating the separation of photogenerated carriers to efficiently photodegrade tetracycline on the surface of FeCo-based MOFs

It is feasible to improve the photodegradation efficiency of organic pollutants by metal-organic frameworks (MOF)-based semiconductors via ligand engineering. In this work, three (Fe/Co)-XBDC-based MOFs were synthesized by introducing different ortho-functional groups X (X = –H, –NO2, –NH2) next to the carboxyl group of the organic ligand (i.e., terephthalic acid). The analysis focused on the influence mechanism of the adjacent functional group effect of the ligand on the physicochemical properties of the material and the actual photodegradation activity of TC. Multiple pieces of evidences suggested that the differences in electron-induced and photocharge-transfer mechanisms of the above ortho functional groups affect the crystal morphology and photocatalytic activity of FeCo-MOF during pyrolysis. Interestingly, (Fe/Co)–NH2BDC exhibited the highest photocatalytic activity under neutral conditions. The results of density functional theory show that the introduction of a strong donor-NH2 group can enhance light absorption and act as an “electron pump” to supply electrons to the iron center, accelerating the separation and efficient transport of photogenerated carriers on the ligand-metal bridge. In conclusion, this study is a proposal for a strategy of structural regulation for the enhancement of the catalytic activity of (Fe/Co)-MOFs in the photodegradation of TC.

Evaluation of the Long-Term Stability of Select Phenylacetylindole, Cycloalkylindole, Quinolinyl, and Carboxamide Synthetic Cannabinoids using LC-MS/MS.

Forensic toxicology laboratories often encounter casework backlogs, which raise concerns for drug stability that can be affected by long storage times, temperature, and preservatives, or the lack thereof. The focus of this research was to evaluate the impact of these factors on the stability of 17 synthetic cannabinoids in human whole blood and 10 associated metabolites in human urine. The fortified biological specimens were stored under room temperature (20°C), refrigerator (4°C), and freezer (-20°C) conditions for a period of 52 weeks. Preservatives included potassium oxalate, sodium ethylenediaminetetraacetic acid, and sodium fluoride. Extraction of analytes was conducted using supported liquid extraction and analyzed using a liquid chromatograph-tandem mass spectrometer. Under all three storage conditions, the majority of urine metabolites were stable up to 9 weeks. All analytes in frozen sodium fluoride preserved blood were stable at 21 to 52 weeks with the exception of APP-PICA. Analytes in blood that were stable to 52 weeks in the freezer generally had a core structure of a carbonyl substituent on a pyrazole or pyrrole with surrounding nonpolar groups. In contrast, compounds with two adjacent polar carbonyl functional groups experienced degradation at 1 week or less under ambient temperature and refrigeration. 5-fluoropentyl analogs, XLR11 and 5-fluoro ADB-PINACA, in comparison to their counterpart analytes, UR144 and ADB-PINACA, were unstable at earlier time points under all temperatures. Based on these data, forensic blood evidence suggesting the presence of synthetic cannabinoid compounds are recommended to be frozen with sodium fluoride and potassium oxalate preservatives for optimal quantitative results.

Computational Investigation of Substituent Effects on the Alcohol + Carbonyl Channel of Peroxy Radical Self- and Cross-Reactions

Organic peroxy radicals (RO2) are key intermediates in atmospheric chemistry and can undergo a large variety of both uni- and bimolecular reactions. One of the least understood reaction classes of RO2 are their self- and cross-reactions: RO2 + R'O2. In our previous work, we have investigated how RO2 + R'O2 reactions can lead to the formation of ROOR' accretion products through intersystem crossings and subsequent recombination of a triplet intermediate complex 3(RO···OR'). Accretion products can potentially have very low saturation vapor pressures, and may therefore participate in the formation of aerosol particles. In this work, we investigate the competing H-shift channel, which leads to the formation of more volatile carbonyl and alcohol products. This is one of the main, and sometimes the dominant, RO2 + R'O2 reaction channels for small RO2. We investigate how substituents (R and R' groups) affect the H-shift barriers and rates for a set of 3(RO···OR') complexes. The variation in barrier heights and rates is found to be surprisingly small, and most computed H-shift rates are fast: around 108-109 s-1. We find that the barrier height is affected by three competing factors: (1) the weakening of the breaking C-H bond due to interactions with adjacent functional groups; (2) the overall binding energy of the 3(RO···OR'), which tends to increase the barrier height; and (3) the thermodynamic stability of the reaction products. We also calculated intersystem crossing rate coefficients (ISC) for the same systems and found that most of them were of the same order of magnitude as the H-shift rates. This suggests that both studied channels are competitive for small and medium-sized RO2. However, for complex enough R or R' groups, the binding energy effect may render the H-shift channel uncompetitive with intersystem crossings (and thus ROOR' formation), as the rate of the latter, while variable, seems to be largely independent of system size. This may help explain the experimental observation that accretion product formation becomes highly effective for large and multifunctional RO2.

A computational investigation towards substitution effects on 8π electrocyclisation of conjugated 1,3,5,7-octatetraenes.

A computational investigation using M06-2X/6-31+G(d) method is reported for the substitution effects on 8π electrocyclisation of conjugated octatetraene. This systematic study describes the mono- and di-substitution effect across the 1,3,5,7-octatetraene skeleton. A general preference of the outward substitution over the inward, at C1 position of the monosubstituted system is observed. However, mesomerically electron donating group (-NH2 and -OH) display an opposite effect with respect to secondary orbital interaction (SOI) between the lone pair on the substituent and the orbital. A comparative evaluation on the computed activation energies for the 1-, 2-, 3-, and 4-monosubstituted system showed an insignificant impact on the rate of the reaction, in contrast to the electrocyclic ring closure of the unsubstituted compound. Computations of disubstituted system are more pronounced, where a remarkable acceleration is observed for 2-NO2-7-NO2 substituted octatetraene at 4.9 kcal mol-1, and a noticeable deceleration for 4-CH3-5-CH3 substituted octatetraene at 25.4 kcal mol-1 from the parent molecule, 17.0 kcal mol-1. A visible accelerated effects are commonly exhibited by the substitution on the terminal double bonds (C1, C2, C7, and C8), that are 1,2-, 1,7-, 1,8-, and 2,7-patterns, in regard to the greater orbital interaction for the new σ-bond formation. Despite the unfavourable steric clashes of the substituents in the 1,8-system, an apparent reduction in the energy barrier up to 7.4 kcal mol-1 is computed for 1-NH2-8-NO2 system from 17.0 kcal mol-1. This is due to the synergistic effect of the electron donor and electron acceptor, enhancing the stability of the transition structure. The electrocyclic ring closure involving vicinal substitution patterns, such as 1,2-, 2,3-, 3,4-, and 4,5-systems are critically dominated by steric crowding between the adjacent functional groups. In certain cases of the 1,2-substituted system, a noticeable accelerated effects are found for 1-NH2-2-NH2-substituted compound (9.7 kcal mol-1) due to an increased in electronic density on the substituted terminal double bond (C1-C2), hence favouring the formation of the new σ-bond.

Scalarane Sesterterpenoids Isolated from the Marine Sponge Hyrtios erectus and their Cytotoxicity.

Eighteen scalarane sesterterpenoids (1–18), including eight new derivatives (1–8), were isolated from the sponge Hyrtios erectus (family Thorectidae), the extract of which showed cytotoxicity against the HeLa and MCF-7 cell lines. Of the new derivatives, six compounds (1–6) were found to contain a γ-hydroxybutenolide moiety capable of reversible stereoinversion at the hydroxylated carbon center. Under the influence of other adjacent functional groups, each derivative exhibited a different stereochemical behavior, which was fully deduced by ROESY experiments. All the isolated compounds were examined for their cytotoxicity by MTS assay using staurosporine as a positive control (IC50 0.18 and 0.13 μΜ against HeLa and MCF-7 cells, respectively), and they were found to show weak growth inhibitory activities against HeLa and MCF-7 cells, with a minimal IC50 value of 20.0 μΜ. The compounds containing a γ-hydroxybutenolide moiety (1–3, 10, 12) showed cytotoxicity, with IC50 values ranging from 24.3 to 29.9 μΜ, and the most potent derivative was heteronemin (16). Although the cytotoxicities of isolated compounds were insufficient to discuss the structure–activity relationship, this research could contribute to expanding the structural diversity of scalaranes and understanding the stereochemical behavior of γ-hydroxybutenolides.

Azo-Integrated Covalent Organic Frameworks As Electrodes for Lithium-Ion Batteries

Covalent Organic Frameworks (COFs) are two-dimensional, porous, and crystalline organic structures. The well-established frameworks provide ordered mesopores, structural stability, high density, and negligible solubility, which are particularly attractive for battery electrodes. By integrating a redox-active azo group to COFs, we designed positive organic electrodes and applied these electrodes for nonaqueous Li-ion batteries. The azo group can undergo two electrons transfer, whereas its reversibility and stability are highly dependent on adjacent functional groups [1,2]. We developed three azo-integrated COFs with three different linkages, -ketoenamine, imine, and thiazole-fused ring. These azo-COFs had identical hexagonal P6/m space groups, ~3 nm of pore size, and 600~1000 m2 g–1 of surface area. However, the redox chemistries of azo groups were remarkably distinct from the linkages. The-ketoenamine and imine based azo-COFs showed irreversible azo reactions, resulting in poor capacity retention. In contrast, the fully conjugated COF containing the thiazole-fused ring rendered excellent cycling stability showing 5000 cycles at 10 C. The reversible azo reaction was also demonstrated by using operando Raman spectroscopy. This result corresponded to the single and sharp redox wave at a formal potential of ~1.7 V vs. Li/Li+, suggesting the one-step two electrons transfer. The solid electrolyte interphase (SEI) was formed at the initial cycles only, which could protect the COF surface and inhibit the continuous decomposition of the electrolyte solution. Electrochemical impedance spectroscopy (EIS) revealed the low charge transfer resistance (~18 Ω), which decreased further after 20 cycles (~6 Ω). The mass transport region in the EIS curve was retained, indicating the access of Li+ to the bulk COF structure through mesopores for cycling. In the presentation, I will discuss the details of COF designs and the role of linkages enhancing the reversible and stable redox reactions in Li-ion cells.

Nucleation of water clusters on functionalised graphite with kinetic Monte Carlo scheme

ABSTRACT Although activated carbon is generally hydrophobic, water can adsorb on its surface due to the presence of functional groups. During the initial interactions between functional groups and water molecules, atoms of the functional groups rotate around the sigma bonds to maximise the electrostatic interactions. This physical process was simulated within the framework of kinetic Monte Carlo (kMC). We extended kMC to account for the rotation of the atoms of functional groups around the sigma bonds by entropic sampling of the orientation space, and tested the modified kMC scheme for adsorption of water on graphite functionalised with either hydroxyl groups or carboxyl groups. Results show that the amount adsorbed is greater when the rotation of atoms around the sigma bonds is allowed. The interspacing of functional groups also affects the adsorbed density. It was found that the optimum distances between hydroxyl groups and carboxyl groups to initiate water cluster are 0.4 and 0.7 nm, respectively, because of the synergistic effect of electrostatic interactions between water molecule and adjacent functional groups. This effect is reduced when the spatial distance is either decreased (because of the increasing importance of the repulsion) or increased (because of the loss of the synergetic effect).

Loss and Increase of the Electron Exchange Capacity of Natural Organic Matter during Its Reduction and Reoxidation: The Role of Quinone and Nonquinone Moieties

Redox-active quinone and nonquinone moieties represent the electron exchange capacity (EEC) of natural organic matter (NOM), playing an important role in the electron transfer link of microbes and transformation of contaminants/metal minerals. However, the corresponding transformation of quinone/phenol and their respective influence on the EECs during reduction and reoxidation remain poorly characterized. Besides, it is still controversial whether nonquinones donate or accept electrons. Herein, we demonstrated that reoxidation of NOM after reduction can form new phenolic/quinone moieties, thus increasing the EEC. The assessment for the EEC, including the electron-donating capacity (EDC) and electron-accepting capacity (EAC), of nonquinones reflects the contribution of sulfur-containing moieties with considerable EDCs and EACs. In contrast, nitrogen-containing moieties donate negligible electrons even at Eh = +0.73 V. The contributions of both thiol and amine moieties to the EEC are greatly affected by adjacent functional groups. Meanwhile, aldehydes/ketones did not display an EAC during the electron transfer process of NOM. Furthermore, substantially increased EDC at Eh from +0.61 to +0.73 V could not be fully explained using thiol and phenolic moieties, suggesting the contribution of unknown moieties with high oxidation potential. The overall findings suggest that the roles of new quinones/phenol (derived from the addition of oxygen to condensed aromatic/lignin-like components) during redox dynamic cycling and thiol species should be considered in assessing the electron transfer processes of NOM.

Highly efficient and selective electrocatalytic hydrogen peroxide production on Co-O-C active centers on graphene oxide

Electrochemical oxygen reduction provides an eco-friendly synthetic route to hydrogen peroxide (H2O2), a widely used green chemical. However, the kinetically sluggish and low-selectivity oxygen reduction reaction (ORR) is a key challenge to electrochemical production of H2O2 for practical applications. Herein, we demonstrate that single cobalt atoms anchored on oxygen functionalized graphene oxide form Co-O-C@GO active centres (abbreviated as Co1@GO for simplicity) that act as an efficient and durable electrocatalyst for H2O2 production. This Co1@GO electrocatalyst shows excellent electrochemical performance in O2-saturated 0.1 M KOH, exhibiting high reactivity with an onset potential of 0.91 V and H2O2 production of 1.0 mg cm−2 h−1 while affording high selectivity of 81.4% for H2O2. Our combined experimental observations and theoretical calculations indicate that the high reactivity and selectivity of Co1@GO for H2O2 electrogeneration arises from a synergistic effect between the O-bonded single Co atoms and adjacent oxygen functional groups (C-O bonds) of the GO present in the Co-O-C active centres.

Dendrimers and their applications

Dendrimers are symmetric molecules; their size is within the nanoscale. Its structure is usually homogeneous and monodisperse; they are composed of a nucleus and several layers 1. The number of layers that the dendrimer has defines its generation. There are different types of dendrimers. The synthesis of these macromolecules is carried out following steps of growth and activation, and organic reactions are required to obtain their branched structure2. Although size is essential, the determining factor of toxicity in dendrimers is the charge of the surface; it has been found that the higher generation dendrimers and the cationic ones are the most toxic compared to the lower generation anionics that evaluated at low concentrations did not show any toxicity 3. The dendrimers will favor the pharmacokinetics of a drug through the dendritic structure, the generation of the dendrimer to be used, the intramolecular interaction force between the adjacent functional groups in the dendrimer, the conditions of the environment such as pH, solvent polarity, strength ionic, saline concentration or presence of counterions, among others 4. Due to dendrimers' size and surface composition, the use of dendrimers in drug delivery has been increasingly studied. There are different interaction mechanisms between drugs in dendrimers, and these can be broadly divided into simple encapsulation, electrostatic interaction, and covalent bonds 5. The use of dendrimers in ocular administration has greatly impacted the complexity of this administration route. Gene therapy has also benefited from the emergence of these molecules as it facilitates targeted therapy.
 Keywords: Dendrimers, Drug delivery, Gene therapy, Pharmacokinetic, Transport System

Transition metal catalyzed P–C(sp2) constructing couplings

Phosphorous compounds are one of most important class of ligands that are used in synthesis, catalysis and other processes. The coarse adjustment of electrodonative character of phosphorous can be done by switching to phosphonates or phosphinates with consecutive transformation. However fine tuning of phosphorous atom by variation of adjacent functional groups might be a serious problem due to reactivity of those. An alternative introduction of aromatic and vinylic groups can be done by P–C coupling reactions. Here I'd like to present a brief overview of published catalytic systems.

Adsorption of water on carbon materials: The formation of “water bridge” and its effect on water adsorption

Water adsorption is very important for the modifications and applications of carbon materials. Some interesting phenomena in the process of water adsorption are still difficult to explain, and this necessitated our study. X-ray diffraction and X-ray photoelectron spectroscopies were used to characterize the structure and surface chemical properties of the carbon materials (namely graphite, activated carbon and coal). The water adsorption on carbon materials was analyzed by adsorption isotherms, and molecular simulation was used to explore the adsorption mechanisms. The results indicate that different structures and surface chemical properties of the carbon materials led to different adsorption isotherms. Graphite exhibited a Type III adsorption isotherm due to its compact structure and fewer oxygen-containing functional groups. The adsorption isotherms of activated carbon and coal conformed to the Type IV adsorption isotherm, but they presented dissimilar hysteresis loops. The “water bridge” was one of the important factors that affected water adsorption, and it was generated from the adsorption and charge transfer of water molecules induced by adjacent oxygen-containing functional groups on the surface. The strong hydrogen bond network formed by the interconnection of “water bridge” enhanced the water adsorption, capillary condensation, “ink bottle” effect, and adsorption/desorption hysteresis.

Some Surprising Transformations of Colchicone and Other Colchicine‐Derived Tropolones

AbstractThe alkaloid colchicine represents a prominent lead structure for the development of tubulin‐binding chemotherapeutics. In the course of explorative research into semi‐synthetic colchicinoids we stumbled upon a number of unexpected and mechanistically surprising transformations which reflect the very particular reactivity of the tropolone ether unit and its interplay with adjacent functional groups. Examples are the selective C‐8‐methylation of colchicone upon reaction with the Wittig reagent triphenylphosphonium methylide, the AlMe3‐mediated isomerization of colchicone to a tetracyclic lactone, and the cyanide‐induced reaction of the colchicol‐derived mesylate to a rearranged and ring B‐defunctionalized cyano‐allo‐colchicinoid. Finally, the fragmenting rearrangement of a tetracyclic colchicinoid with BF3⋅OEt2 in the presence of vinyl‐MgBr afforded a tropolonyl difluoroborate under concomitant transfer of an O‐methyl group from ring C to ring A.

DFT study on the effect of functional groups of carbonaceous surface on ammonium adsorption from water

Density functional theory (DFT) was used to study the adsorption of ammonium ion on carbon materials. The effects of single and multiple adjacent functional groups of carbon structures on ammonium ion adsorption were emphasized. The electrostatic potential, adsorption energy, charge transfer, molecular orbital, and dipole moment of different configurations were analyzed. Results showed that the carbonyl group was more likely to adsorb ammonium ion than lactone, carboxyl, and hydroxyl. When the carbon material contained multiple adjacent functional groups at the same time, the adsorption of ammonium ion can be promoted or inhibited due to the interaction among functional groups. The effect of functional groups on the adsorption of π bond in carbon materials was related to the electronegativity of functional groups, i.e., greater electronegativity led to smaller adsorption energy of π bond. Carbon material itself is nonpolar and hydrophobic, so adding oxygen-containing functional groups can increase the dipole moment of carbon material molecules, thereby enhancing its polarity and adsorption capacity.

Influence of salinity on the heterogeneous catalytic ozonation process: Implications to treatment of high salinity wastewater

The heterogeneous catalytic ozonation process is a promising treatment option for high salinity reverse osmosis concentrate (ROC) however the influence of salts on the catalyst performance is not well understood. In this work, we investigate the effect of salts on the performance of the catalytic ozonation process for treatment of synthetic ROC using a commercially available Fe-loaded Al2O3 catalyst. Our results show that the presence of salts influences the rate and extent of degradation of organic compounds present in the synthetic ROC when subjected to the heterogeneous catalytic ozonation process. Scavenging of aqueous O3 by chloride ions and/or transformation of organics (particularly humics) to more hydrophobic form as a result of charge shielding between adjacent functional groups and/or intramolecular binding by cations inhibits the bulk oxidation of organics to a measurable extent. While the scavenging of aqueous hydroxyl radicals at the salt concentrations investigated here was minimal, the accumulation of chloride ions in the electric double layer near the catalyst surface, particularly when pH< pHpzc, results in more significant scavenging of surface associated hydroxyl radicals. Overall, the presence of salts (particularly chloride ions) has a significant influence on the performance of both conventional and catalytic ozonation processes with some scope to mitigate this effect through appropriate choice of catalyst.

Ultrafast Rechargeable Aqueous Zinc‐Ion Batteries Based on Stable Radical Chemistry

AbstractAqueous zinc‐ion batteries (ZIBs) are a promising candidate for fast‐charging energy‐storage systems due to its attractive ionic conductivity of water‐based electrolyte, high theoretical energy density, and low cost. Current strategies toward high‐rate ZIBs mainly focus on the improvement of ionic or electron conductivity within cathodes. However, enhancing intrinsic electrochemical reaction kinetics of active materials to achieve fast Zn2+ storage has been greatly omitted. Herein, for the first time, stable radical intermediate generation is demonstrated in a typical organic electrode material (methylene blue [MB]), which effectively decreases the reaction energy barrier and enhances the intrinsic kinetics of MB cathode, enabling ultrafast Zn2+ storage. Meanwhile, anionic co‐intercalation essentially avoids MB molecules rearranging their configuration and sharing Zn2+ with adjacent functional groups, thus keeps the structure stable. As a result, Zn–MB batteries exhibit an excellent rate capability up to 500C and ultralong life of 20 000 cycles with a negligible 0.07% capacity decay per cycle at 100C, which is superior to that of most reported aqueous ZIBs batteries. This work provides a novel strategy of stable radical chemistry for ultrafast‐charging aqueous ZIBs, which can be introduced to other appropriate organic materials and multivalent ion battery systems.

Adjacent functional group effects on the assembly of columnar liquid crystals

Although the impact of individual functional groups on the self-assembly of columnar liquid crystal phases has been widely studied, the effect of varying multiple substituents has received much less attention. Herein, we report a series of dibenzo[a,c]phenazines containing an alcohol or ether adjacent to an electron-withdrawing ester or acid. With one exception, these difunctional mesogens form columnar phases. The phase behavior appeared to be dominated by the electron-withdrawing substituent; transition temperatures were similar to derivatives with these groups in isolation. In most instances, the addition of an electron-donating group ortho to an ester or acid suppressed the melting temperature and elevated the clearing temperature, leading to broader liquid crystal thermal ranges. This effect was more pronounced for derivatives functionalized with longer chain hexyloxy groups. These results suggest a potential strategy for controlling the phase ranges of columnar liquid crystals and achieving room temperature mesophases.

Stability and structural aspects of complexes forming between aluminum(III) and D-heptagluconate in acidic to strongly alkaline media: An unexpected diversity

In the current contribution, the complex formation equilibria between Al3+ and α-D–heptagluconate (Hpgl−) ions, which is of relevance in, e.g., the Bayer process for obtaining alumina from bauxitic ores, has been investigated. Potentiometric titrations and polarimetric measurements performed at 25 °C and 4 M ionic strength uncovered the formation of several complexes forming in the hyperalkaline (pH ≥ 13) pH range: Al(OH)4Hpgl2−, Al(OH)5Hpgl3−, Al(OH)5Hpgl42−, Al3(OH)13Hpgl62− and Al4(OH)15Hpgl63−. NMR spectroscopy measurements revealed that diverse complexation processes took place in the hyperalkaline region. In the 9 to 7 pH range, ligand–stabilized aluminum hydroxides were formed. In acidic medium, the binding sites of the ligand could be identified as C2H(OH), C3H(OH), C4H(OH) and C5H(OH). Freezing point depression (FPD) measurements indicated, that association occurred to a large extent. ESI–MS measurements confirmed the predominant formation of Al2(OH)6Hpgl− at pH = 7, and implied the coordination via the carboxylate and the adjacent OH functional groups of the ligand.

Direct Copper‐Catalyzed C‐H Monofluoroalkylation of Benzoxazoles with 1‐Fluoro‐1‐haloalkanes

The first example of direct C–H bond monofluoroalkylation with 1‐fluoro‐1‐haloalkanes with no adjacent functional groups and with β‐hydrogens has been developed. This transformation offers a straightforward route for the synthesis of a series of monofluoroalkylated benzoxazoles.