Search Results (55)

We synthesized seven carbocyclic nucleoside analogs featuring a cyclopentane ring in place of the (deoxy)ribose sugar, which serves as a linker in DNA/RNA nucleosides. We assessed the stability of cyclopentane nucleosides in 98% w/w sulfuric acid at room temperature via ¹H and ¹³C NMR spectroscopy. We observe that adenine (A1, A4), guanine (G1) and thymine (T1) cyclopentane nucleoside analogs remain stable for at least two weeks at room temperature, with only minor (~4%) degradation in A1. In contrast, the cytosine analog (C1) rapidly degrades to release a soluble cytosine. Methyl-substituted adenine analogs mimicking polymer backbone attachments at positions prone to tertiary carbocation formation (A2, A3) prove unstable and release soluble adenine. Only the 3,3-dimethylcyclopentyl adenine analog (A4) exhibits sufficient stability. Our findings reveal that cyclopentane serves as a viable stable linker in concentrated sulfuric acid for select nucleic acid bases, provided that the backbone connections avoid tertiary carbons susceptible to carbocation-mediated cleavage. We thus identify one potential key structural feature for engineering examples of genetic-like polymers that could potentially persist in Venus’s concentrated sulfuric acid cloud environment. Full article

The co-occurrence of rare terpenoid thiocyanates (R-SCN), structurally similar to their more common isothiocyanate isomers (R-NCS), poses an enigma: how does the accepted path, terpenyl cation R⁺ → R-NC → R-NCS, accommodate R-SCN? The mystery can now be rationalized by the consideration of three biosynthetic motifs: terpenoid carbocation (R⁺) capture by cyanoformate, NC-COOH (itself in equilibrium with NC⁻ and CO₂); co-localized rhodanese (a dual-function enzyme) that can both convert fugitive inorganic NC⁻ to thiocyanate ion, NCS⁻, and alkyl isonitriles to alkyl isothiocyanate (R-NC → R-NCS) and adventitious capture of the NCS⁻ by R⁺. The former two scenarios explain the preponderance of isothiocyanates, R-NCS, as products of a linear reaction path—the α-addition of S⁰ to R-NC—and the third scenario explains minor, less stable thiocyanates, R-SCN, as products of the adventitious capture of liberated NCS⁻ by the penultimate R⁺ precursor. DFT calculations support this proposal and eliminate other possibilities, e.g., the isomerization of R-NCS to R-SCN. Full article

As a core component of transportation fuels, clean gasoline plays a vital role in environmental protection. Alkylate, with its nearly zero sulfur, aromatic, and olefin contents, coupled with its superior research octane number, serves as an ideal blending component for clean gasoline. This study established a kinetic model for sulfuric-acid-catalyzed isobutane–butene alkylation based on the carbocation reaction mechanism, incorporating 20 lumped components and 37 reaction pathways. Reactor models were developed to reflect the design characteristics of STRATCO and SINOALKY technologies. The model parameters were estimated using industrial operational data via the non-linear least-squares method. The validation results demonstrated excellent agreement with industrial values, showing average relative deviation rates of 1.72% (STRATCO) and 1.73% (SINOALKY) for C₈ product prediction. A prediction analysis revealed that selectivity and alkylate octane number of C₈ exhibit positive correlations with the isobutane-to-olefin ratio, acid-to-hydrocarbon ratio, and space–time relationship. It was also found that the internal circulation in the STRATCO technology enables thorough contact between the acid and hydrocarbon phases, while the multi-stage feeding in the SINOALKY technology maintains a favorable isobutane-to-olefin ratio. Both features are conducive to the alkylation reaction, enhancing the selectivity and octane number of C₈. These trends align with the intrinsic reaction principles of sulfuric-acid-catalyzed alkylation systems, providing theoretical guidance for alkylate production optimization. Full article

Background: This study describes a novel biomaterial consisting of a mixture of biphasic bioceramic obtained from waste generated by the sugar industry (Carbocal) and a medical-grade epoxy resin adhesive called LOCTITE^® M31 CLTM. The objective was to demonstrate the possibility of coating non-bioactive and non-biodegradable metallic surfaces on implantable elements. Methods: After preparation, the mixture was applied to the surfaces of hip prostheses composed of two distinct materials: polyetherimide and grade 5 titanium. In both cases, adhesion tests produced favourable results. Additionally, cell cultures were conducted using human foetal osteoblastic cell lines (hFOB 1.19). Results: It was observed that the mixture did not affect the proliferation of bone cells. Conclusions: This composite material was found to promote the growth of bone cells, suggesting its potential for fostering bone tissue development. Full article

Photoactive N-hydroxysulfonamides photocaged with the (6-bromo-7-hydroxycoumarin-4-yl)methyl chromophore have been successfully synthesized, and the mechanisms of photodecomposition investigated for two of the compounds. Upon irradiation up to 97% of a diagnostic marker for (H)NO release, sulfinate was observed for the trifluoromethanesulfonamide system. In the absence of a species that reacts rapidly with (H)NO, (H)NO instead reacts with the carbocation intermediate to ultimately generate (E)-BHC-oxime and (Z)-BHC-oxime. Alternatively, the carbocation intermediate reacts with solvent water to give a diol. Deprotonation of the N(H) proton is required for HNO generation via concerted C-O/N-S bond cleavage, whereas the protonation state of the O(H) does not affect the observed photoproducts. If the N(H) is protonated, C-O bond cleavage to generate the parent N-hydroxysulfonamide will occur, and/or O-N bond cleavage to generate a sulfonamide. The undesired competing O-N bond cleavage pathway increases when the volume percentage of water in acetonitrile/water solvent mixtures is increased. Full article

The chiral H₈-BINOL derivatives R-1 and R-2 were efficiently synthesized via a Suzuki coupling reaction, and they can be used as novel dialdehyde fluorescent probes for the enantioselective recognition of R/S-2-amino-1-phenylethanol. In addition, R-1 is much more effective than R-2. Scanning electron microscope images and X-ray analyses show that R-1 can form supramolecular vesicles through the self-assembly effect of the π-π force and strong hydrogen bonding. As determined via analysis, the fluorescence of the probe was significantly enhanced by mixing a small amount of S-2-amino-1-phenylethanol into R-1, with a redshift of 38 nm, whereas no significant fluorescence response was observed in R-2-amino-1-phenylethanol. The enantioselective identification of S-2-amino-1-phenylethanol by the probe R-1 was further investigated through nuclear magnetic titration and fluorescence kinetic experiments and DFT calculations. The results showed that this mechanism was not only a simple reactive probe but also realized object recognition through an ICT mechanism. As the intramolecular hydrogen bond activated the carbonyl group on the probe R-1, the carbonyl carbon atom became positively charged. As a strong nucleophile, the amino group of S-2-amino-1-phenylethanol first transferred the amino electrons to a carbonyl carbocation, resulting in a significantly enhanced fluorescence of the probe R-1 and a 38 nm redshift. Similarly, S-2-amino-1-phenylethanol alone caused severe damage to the self-assembled vesicle structure of the probe molecule itself due to its spatial structure, which made R-1 highly enantioselective towards it. Full article

The basic hydrolysis of Malachite Green (MG) in the presence of β-Cyclodextrin (β-CD) has been studied using UV-Vis spectroscopic techniques and at 20 °C. β-CD was found to catalyze the basic hydrolysis. Indeed, this basic hydrolysis is catalyzed by the interaction cyclodextrin hydroxyl group, in its deprotonated form with the carbocation in the host-guest complex. The proposed model has been successfully applied to a reaction catalyzed by CD. It considers two simultaneous pathways in the aqueous medium involving free hydroxyl ions and the substrate-CD complex. The model allows us to obtain the kinetic parameters including the bimolecular rate constant between MG and HO⁻ in bulk water (k_w = 1.47 ± 0.01 mol⁻¹s⁻¹), the rate constant between MG and the deprotonated hydroxyl group of β-CD inside the host-guest complex (k_CD = 0.25 ± 0.03 s⁻¹) and the binding constant of MG inside the β-CD (K_S = 2500 ± 50). This behavior is like the hydrolysis of Cristal Violet (CV) in the same reaction media. Full article

Polyethylene (PE) is the most widely used plastic, known for its high mechanical strength and affordability, rendering it responsible for ~70% of packaging waste and contributing to microplastic pollution. The cleavage of the carbon chain can induce the conversion of PE wastes into low-molecular-weight hydrocarbons, such as petroleum oils, waxes, and natural gases, but the thermal degradation of PE is challenging and requires high temperatures exceeding 400 °C due to its lack of specific chemical groups. Herein, we prepare metal/zeolite nanocatalysts by incorporating small-sized nickel nanoparticles into zeolite to lower the degradation temperature of PE. With the use of nanocatalysts, the degradation temperature can be lowered to 350 °C under hydrogen conditions, compared to the 400 °C required for non-catalytic pyrolysis. The metal components of the catalysts facilitate hydrogen adsorption, while the zeolite components stabilize the intermediate radicals or carbocations formed during the degradation process. The successful pyrolysis of PE at low temperatures yields valuable low-molecular-weight oil products, offering a promising pathway for the upcycling of PE into higher value-added products. Full article

Ester compounds, widely found in pharmaceutical and natural products, play a crucial role in organic synthesis, prompting the development of numerous methods for their synthesis. An important chemical approach in synthesizing esters from carboxylic acids involves the activation of the carboxyl function, requiring the conversion of the hydroxyl group into a suitable leaving group. This paper presents the findings of our investigations into an efficient method for producing esters from carboxylic acids and alcohols, using the Lewis acid titanium tetrachloride. Titanium tetrachloride has proven highly effective as a coupling reagent for the one-pot formation of esters from carboxylic acids and alcohols operating under mild and neutral conditions. Notably, the reaction eliminates the need for bases, yielding carboxylic esters in high purity and yields. The method is efficient, even with long-chain carboxylic acids, and operates well with primary alcohols in dichloromethane. Steric hindrance, potentially present in carboxylic acids, has a moderate effect on the reaction. Alcohol substrates that easily form stable carbocations require, instead, the use of non-polar solvents like hexane for the reaction. Full article

This study focuses on the competition reaction rules of a system containing resorcinol (as a tannin model compound) and dimethylol urea (as a urea–formaldehyde resin model compound) under various alkaline and acidic environments. The aim is to investigate the crosslinked modification mechanism of urea–formaldehyde resin with tannin adhesive. The study delves into the competitive relationship between self-condensation polymerization reactions and co-condensation polymerization reactions. It specifically highlights the conditions for the copolycondensation reaction of dimethylolurea and resorcinol and validates its rationality through an examination of the resorcinol–urea–formaldehyde system’s reaction rules. The results show that (1) under strongly acidic conditions, the activity of carbocation intermediates produced by hydroxymethyl resorcinol for the resorcinol phenol ring is higher than the electrophilic reactivity of nitrogen atoms on hydroxymethyl urea, which is more beneficial for the resorcinol–formaldehyde self-polycondensation reaction, and the co-polycondensation structures do not play a dominant role. (2) Under weakly acidic conditions, the co-polycondensation structures are evidently advantageous over self-polycondensation structures, and the degree of the co-polycondensation reaction is positively correlated with pH below the neutral point of resorcinol. (3) Under alkaline conditions, the self-polycondensation between resorcinol and formaldehyde is dominant in the system. (4) The concentration of hydroxymethyl urea carbocation is the key factor to determine the degree of the co-polycondensation reaction. Full article

Due to the electronic configuration of the atom and charge of the nucleus, the chlorine in organic molecules can exert a variety of effects. It can depart as a chloride anion in the process of substitution and elimination, facilitates the abstraction of protons and stabilizes generated carbanions, exerts moderate stabilizing effect of carbenes, carbocations and radicals. There are frequent cases where chlorine substituent promotes more than one transformation. These rich effects of chlorine substituent will be illustrated by examples of our work. Full article

Ginsenoside Rg5, a relatively uncommon secondary ginsenoside, exhibits notable pharmacological activity and is commonly hypothesized to originate from the dehydration of Rg3. In this work, we compared different conversion pathways using Rb1, R-Rg3 and S-Rg3 as the raw material under simple acid catalysis. Interestingly, the results indicate that the conversion follows this reaction activity order Rb1 > S-Rg3 > R-Rg3, which is contrary to the common understanding of Rg5 obtained from Rg3 by dehydration. Our experimental results have been fully confirmed by theoretical calculations and a NOESY analysis. The DFT analysis reveals that the free energies of S-Rg3 and R-Rg3 in generating carbocation are 7.56 mol/L and 7.57 mol/L, respectively, which are significantly higher than the free energy of 1.81 mol/L when Rb1 generates the same carbocation. This finding aligns with experimental evidence suggesting that Rb1 is more prone to generating Rg5 than Rg3. The findings from the nuclear magnetic resonance (NMR) analysis suggest that the fatty chains (C22–C27) in R-Rg3 and S-Rg3 adopt a Gauche conformation and an anti conformation with C16–C17 and C13–C17, respectively, due to the relatively weak repulsive van der Waals force. Therefore, the configuration of R-Rg3 is more conducive to the formation of intramolecular hydrogen bonds between 20C–OH and 12C–OH, whereas S-Rg3 lacks this capability. Consequently, this also explains the fact that S-Rg3 is more prone to dehydration to generate Rg5 than R-Rg3. Additionally, our research reveals that the synthetic route of Rg5 derived from protopanaxadiol (PPD)-type ginsenosides (including Rb1, Rb2, Rb3, Rc and Rd) exhibits notable advantages in terms of efficacy, purity and yield when compared to the pathway originating from Rg3. Moreover, this study presents a highly effective and practical approach for the extensive synthesis of Rg5, thereby facilitating the exploration of its pharmacological properties and potential application in drug discovery. Full article

This study focuses on developing hydroxyapatite synthesized from a CaCO₃-rich byproduct of sugar beet processing called Carbocal^® using a hydrothermal reactor. The purpose of this biomaterial is to enhance the osteoinductivity of implantable surfaces and serve as a bone filler, providing a sustainable and economically more affordable alternative. This research involved compositional analysis and micro- and macrostructural physicochemical characterization, complemented with bioactivity and live/dead assays. The biphasic nature of the Carbocal^®-derived sample was significant within the context of the bioactivity concept previously proposed in the literature. The bioactivity of the biomaterial was demonstrated through a viability test, where the cell growth was nearly equivalent to that of the positive control. For comparison purposes, the same tests were conducted with two additional samples: hydroxyapatite obtained from CaCO₃ and commercial hydroxyapatite. The resulting product of this process is biocompatible and possesses properties similar to natural hydroxyapatite. Consequently, this biomaterial shows potential as a scaffold in tissue engineering and as an adhesive filler to promote bone regeneration within the context of the circular bioeconomy in the geographical area proposed. Full article

Aldehyde condensation is a reaction step in the oxidization of a lubricant base stock into high-molecular-weight products, forming sludge and a paint film, which lead to the failure of lubricating oil. Calculations on the basis of the density functional theory (DFT) were employed to investigate the reaction mechanism of the acid-catalyzed aldol condensation of a lubricant base stock. Carbonyl compounds could be converted into their resonant enol structures. However, the activation energy of the process was relatively high, and it was difficult to initiate. The existence of the acid could obviously decrease the activation energy of the reaction from 269.17–287.82 kJ/mol to 177.10–177.63 kJ/mol, and it significantly reduced the difficulty of initiating this reaction. The carbocation formed by the carbonyl compounds and acid could further react with the enol and produce an intermediate reaction product in which the chain of molecules grew longer. This process was not difficult to initiate, with a reaction activation energy of 65.10 kJ/mol. The intermediate product with a larger molecular weight could be converted into carbonyl compounds containing a β-hydroxy by removing a hydrogen proton from it. The energy barrier for this process was 193.15 kJ/mol, and it was not easy to initiate the reaction. Full article

Introduction of Cl and O atoms into C₄-vinyl carbocations was studied by X-ray diffraction analysis and IR spectroscopy. Chlorine atoms are weak electron acceptors in ordinary molecules but, within vinyl carbocations, manifest themselves as strong electron donors that accept a positive charge. The attachment of a Cl atom directly to a C=C bond leads to an increase in the e-density on it, exceeding that of the common double bond. The positive charge should be concentrated on the Cl atom, and weak δ⁻ may appear on the C=C bond. More distant attachment of the Cl atom, e.g., to a C atom adjacent to the C=C bond, has a weaker effect on it. If two Cl atoms are attached to the C_γ atom of the vinyl cation, as in Cl₂C_γC_δHC_αHCH₃, then the cation switches to the allyl type with two practically equivalent and almost uncharged C_γC_δC_α bonds. When such a strong nucleophile as the O atom is introduced into the carbocation, a protonated ester molecule with a C–O(H⁺)–C group and a C=C bond forms. Nonetheless, in the future, there is still a possibility of obtaining carbocations with a non-protonated C–O–C group. Full article