Shapeshifting Nucleophiles HO^–(NH₃)_<i>n</i> React with Methyl Chloride

The microsolvated anions HO–(NH3)n were found to induce new nucleophile NH2–(H2O)­(NH3)n−1 via intramolecular proton transfer. Hence, the ion–molecule nucleophilic substitution (SN2) reaction between CH3Cl and these shapeshifting nucleophiles lead to both the HO– path and NH2– path, meaning that the respective attacking nucleophile is HO– or NH2–. The CCSD­(T) level of calculation was performed to characterize the potential energy surfaces. Calculations indicate that the HO– species are lower in energy than the NH2– species, and the SN2 reaction barriers are lower for the HO– path than the NH2–-path. Incremental solvation increases the barrier for both paths. Comparison between HO–(NH3)n and HOO–(NH3)n confirmed the existence of an α-effect under microsolvated conditions. Comparison between HO–(NH3)n and HO–(H2O)n indicated that the more polarized H2O stabilizes the nucleophiles more than NH3, and thus, the hydrated systems have higher SN2 reaction barriers. The aforementioned barrier changes can be explained by the differential stabilization of the nucleophile and HOMO levels upon solvation, thus affecting the HOMO–LUMO interaction between the nucleophile and substrate. For the same kind of nucleophilic attacking atom, O or N, the reaction barrier has a good linear correlation with the HOMO level of the nucleophiles. Hence, the HOMO level or the binding energy of microsolvated nucleophiles is a good indicator to evaluate the order of barrier heights. This work expands our understanding of the microsolvation effect on prototype SN2 reactions beyond the water solvent

Shapeshifting Nucleophile Singly Hydrated Hydroperoxide Anion Leads to the Occurrence of the Thermodynamically Unfavored S_N2 Product

Single water molecules alone may introduce unusual features into the kinetics and dynamics of chemical reactions. The singly hydrated hydroperoxide anion, HOO–(H2O), was found to be a shapeshifting nucleophile, which can be transformed to HO– solvated by hydrogen peroxide HO–(HOOH). Herein, we performed direct dynamics simulations of its reaction with methyl iodide to investigate the effect of individual water molecules. In addition to the normal SN2 product CH3OOH, the thermodynamically unfavored proton transfer-induced HO–-SN2 path (produces CH3OH) was also observed, contributing ∼4%. The simulated branching ratio of the HO–-SN2 path exceeded the statistical estimation (0.6%) based on the free energy barrier difference. The occurrence of the HO–-SN2 path was attributed to the shallow entrance channel well before a submerged saddle point, thus providing a region for extensive proton exchange and ultimately leading to the formation of CH3OH. In comparison, changing the leaving group from Cl to I increased the overall reaction rate as well as the proportion of the HO–-SN2 path because the CH3I system has a smaller internal barrier. This work elucidates the importance of the dynamic effect introduced by a single solvent molecule to alter the product channel and kinetics of typical ion–molecule SN2 reactions

Shapeshifting Nucleophile Singly Hydrated Hydroperoxide Anion Leads to the Occurrence of the Thermodynamically Unfavored S_N2 Product

Single water molecules alone may introduce unusual features into the kinetics and dynamics of chemical reactions. The singly hydrated hydroperoxide anion, HOO–(H2O), was found to be a shapeshifting nucleophile, which can be transformed to HO– solvated by hydrogen peroxide HO–(HOOH). Herein, we performed direct dynamics simulations of its reaction with methyl iodide to investigate the effect of individual water molecules. In addition to the normal SN2 product CH3OOH, the thermodynamically unfavored proton transfer-induced HO–-SN2 path (produces CH3OH) was also observed, contributing ∼4%. The simulated branching ratio of the HO–-SN2 path exceeded the statistical estimation (0.6%) based on the free energy barrier difference. The occurrence of the HO–-SN2 path was attributed to the shallow entrance channel well before a submerged saddle point, thus providing a region for extensive proton exchange and ultimately leading to the formation of CH3OH. In comparison, changing the leaving group from Cl to I increased the overall reaction rate as well as the proportion of the HO–-SN2 path because the CH3I system has a smaller internal barrier. This work elucidates the importance of the dynamic effect introduced by a single solvent molecule to alter the product channel and kinetics of typical ion–molecule SN2 reactions

Diastereo- and Enantioselective Formal [3 + 2] Cycloaddition of Cyclopropyl Ketones and Alkenes via Ti-Catalyzed Radical Redox Relay

We report a stereoselective formal [3 + 2] cycloaddition of cyclopropyl ketones and radical-acceptor alkenes to form polysubstituted cyclopentane derivatives. Catalyzed by a chiral Ti­(salen) complex, the cycloaddition occurs via a radical redox-relay mechanism and constructs two C–C bonds and two contiguous stereogenic centers with generally excellent diastereo- and enantioselectivity

Diastereo- and Enantioselective Formal [3 + 2] Cycloaddition of Cyclopropyl Ketones and Alkenes via Ti-Catalyzed Radical Redox Relay

We report a stereoselective formal [3 + 2] cycloaddition of cyclopropyl ketones and radical-acceptor alkenes to form polysubstituted cyclopentane derivatives. Catalyzed by a chiral Ti­(salen) complex, the cycloaddition occurs via a radical redox-relay mechanism and constructs two C–C bonds and two contiguous stereogenic centers with generally excellent diastereo- and enantioselectivity

Video1_Laparoscopic extraction of a urethral self-inflicted needle from pelvis in a boy: a case report.mp4

IntroductionSelf-insertion of foreign bodies in the urethra is an infrequent occurrence in children, and their management aims to minimize urethral morbidity. Endoscopic removal presents a significant challenge, particularly in boys. Currently, there are few reports on laparoscopic management of urethral foreign bodies that have migrated to the pelvic cavity.Case descriptionAn 11-year-old boy presented to the emergency department with complaints of increased frequency of micturition and dysuria. A sharp sewing needle was discovered lodged in the posterior urethra mucosa during cystoscopy. Attempts to remove the needle using an endoscopic grasping forceps were unsuccessful due to the forceps' weak biting power. During a digital rectal examination, the needle migrated into the pelvic region, wedged between the prostatic urethra and the rectal ampulla. After careful inspection of the peritoneal reflection over the fundus of the bladder, the needle was identified and successfully removed through laparoscopy without any complications. Psychiatric counseling was advised for this patient, who was in good condition during an 8-week follow-up.ConclusionsOur case demonstrates the first recorded use of laparoscopy to remove a self-inserted urethral needle that had migrated into the pelvic region, after failed attempts at endoscopic extraction. Future cases may benefit from considering laparoscopic interventions for similar circumstances.</p

Enhanced solidification/stabilization of lead in MSWI fly ash treatment and disposal by gelatinized sticky rice

Recently, innocent treatment of heavy metals in hazardous waste has become a hot topic in China. In particular, lead (Pb) as a typical heavy metal, is one of the easiest leaching heavy metal elements for municipal solid waste incineration (MSWI) fly ash. In this paper, different dosages of gelatinized sticky rice (SR) as green additives were added into the mixture of MSWI fly ash (FA) and ordinary Portland cement (OPC) to solidify/stabilize Pb in an attempt to optimize cement solidification. The leaching behaviour of Pb, hydration phases and hydration microstructure were determined by Toxicity Characteristic Leaching Procedures (TCLP) leaching test, Tessier sequential extraction method, XRD, BET and SEM. The results showed that Pb leaching concentration significantly decreased when adding 10% OPC and 30% gelatinized SR solution compared to only OPC treatment, and increasing dosage of SR also reduced Pb leaching concentration and met the criteria of landfill after curing 28 days. Additionally, increase of gelatinized SR dosage made Pb in fraction of Fe–Mn oxides more easily transformed into the stable crystal and organic matter structure of FA solidified products, and the growth of hydration products were restricted and particle size became finer. The addition of gelatinized SR also reduced initial/final setting times and increased compressive strength. The data suggest that the addition of gelatinized SR provides a new and clean approach to enhance the FA/OPC solidification/stabilization and reduce the leaching concentration of heavy metals in MSWI fly ash.</p

Diastereo- and Enantioselective Formal [3 + 2] Cycloaddition of Cyclopropyl Ketones and Alkenes via Ti-Catalyzed Radical Redox Relay

We report a stereoselective formal [3 + 2] cycloaddition of cyclopropyl ketones and radical-acceptor alkenes to form polysubstituted cyclopentane derivatives. Catalyzed by a chiral Ti­(salen) complex, the cycloaddition occurs via a radical redox-relay mechanism and constructs two C–C bonds and two contiguous stereogenic centers with generally excellent diastereo- and enantioselectivity