Combined Experimental and Theoretical Studies on Electron Transfer in Potassium Collisions with CCl4

Negative ion formation in electron transfer experiments from fast neutral potassium (K) atom collisions with neutral tetrachloromethane (CCl₄) molecules has been investigated in the laboratory frame range of 8-1000 eV. Comprehensive calculations on the electronic structure were performed for CCl₄ in the presence of a potassium atom and used to help analyze the lowest unoccupied molecular orbitals participating in the collision process. Additionally, K⁺ energy loss produced in the forward direction has served to further our knowledge on the electronic state spectroscopy of CCl₄. A vertical electron affinity of -0.79 ± 0.20 eV has been obtained and assigned to a purely repulsive transition from CCl₄ ground state to the ²T₂ state of the temporary negative ion yielding Cl^- formation. Other features in the energy loss spectrum were observed for the first time and related to Cl₂^-, CCl₂^-, and CCl₃^- formation. Special attention is also given to the unresolved feature corresponding to a positive electron affinity of 0.24 ± 0.2 eV, assigned to a vibrationally hot transition from CCl₄ ground state into the triply degenerate ²T₂ excited state of the negative ion. The combined time-of-flight mass spectrometry together with K⁺ energy loss data represents the most comprehensive assignment of the tetrachloromethane anion yields and the role of CCl₄ electronic states in collision induced dissociation to date.

Communication: Site-selective bond excision of adenine upon electron transfer

This work demonstrates that selective excision of hydrogen atoms at a particular site of the DNA base adenine can be achieved in collisions with electronegative atoms by controlling the impact energy. The result is based on analysing the time-of-flight mass spectra yields of potassium collisions with a series of labeled adenine derivatives. The production of dehydrogenated parent anions is consistent with neutral H loss either from selective breaking of C-H or N-H bonds. These unprecedented results open up a new methodology in charge transfer collisions that can initiate selective reactivity as a key process in chemical reactions that are dominant in different areas of science and technology.

Electron transfer driven decomposition of adenine and selected analogs as probed by experimental and theoretical methods

We report on a combined experimental and theoretical study of electron-transfer-induced decomposition of adenine (Ad) and a selection of analog molecules in collisions with potassium (K) atoms. Time-of-flight negative ion mass spectra have been obtained in a wide collision energy range (6-68 eV in the centre-of-mass frame), providing a comprehensive investigation of the fragmentation patterns of purine (Pu), adenine (Ad), 9-methyl adenine (9-mAd), 6-dimethyl adenine (6-dimAd), and 2-D adenine (2-DAd). Following our recent communication about selective hydrogen loss from the transient negative ions (TNIs) produced in these collisions [T. Cunha et al., J. Chem. Phys. 148, 021101 (2018)], this work focuses on the production of smaller fragment anions. In the low-energy part of the present range, several dissociation channels that are accessible in free electron attachment experiments are absent from the present mass spectra, notably NH₂ loss from adenine and 9-methyl adenine. This can be understood in terms of a relatively long transit time of the K⁺ cation in the vicinity of the TNI tending to enhance the likelihood of intramolecular electron transfer. In this case, the excess energy can be redistributed through the available degrees of freedom inhibiting fragmentation pathways. Ab initio theoretical calculations were performed for 9-methyl adenine (9-mAd) and adenine (Ad) in the presence of a potassium atom and provided a strong basis for the assignment of the lowest unoccupied molecular orbitals accessed in the collision process.

Unravelling the dissociation pathways of acetic acid upon electron transfer in potassium collisions: experimental and theoretical studies

Electron transfer in alkali-molecule collisions with gas phase acetic acid and its deuterated analogues resulting in OH^- formation requires considerable internal rearrangement in the temporary negative ion. At a collision energy well above the threshold of negative ion formation, electron transfer from potassium to CH₃COOH/CH₃COOD and CD₃COOH results not only in H transfer from CH₃ to COOH/COOD, but also in H release from COOH and subsequent rearrangement to eliminate OH^-. These processes are also investigated by theoretical post-Hartree-Fock and DFT calculations. The combination of both studies reveals that the most favourable intermediate mechanism occurs via diol formation. Such intramolecular H transfer is reported here for the first time in the context of electron transfer induced dissociation experiments in alkali-molecule collisions. A comprehensive fragmentation study is presented and dissociation mechanisms are suggested.

Synthesis and biological activity of fluorescent neonicotinoid insecticide thiamethoxam

Here, we describe the synthesis of two new fluorescent derivatives of thiamethoxam and compared their toxicity on aphid Acyrthosiphon pisum and their mode of action on insect nicotinic acetylcholine receptors expressed on the sixth abdominal ganglion. The compound 3 with two 2-chlorothiazole moieties was found to be more toxic using toxicological bioassays 24 h and 48 h after exposure while compound 4 appeared more active using cockroach ganglionic depolarization. Interestingly, thiamethoxam appeared more effective than component 3 and 4, respectively. Our results demonstrated that component 3 and 4 act as agonists of insect nicotinic acetylcholine receptors.

Effect of light activation on tooth sensitivity after in-office bleaching

This clinical study evaluated the effects of light-emitting diode (LED)/laser activation on bleaching effectiveness (BE) and tooth sensitivity (TS) during in-office bleaching. Thirty caries-free patients were divided into two groups: light-activated (LA) and non-activated (NA) groups. A 35% hydrogen peroxide gel (Whiteness HP Maxx, FGM Dental Products, Joinville SC, Brazil) was used in three 15-minute applications for both groups. For the LA group, LED/laser energy (Whitening Lase Light Plus, DMC Odontológica, São Carlos SP, Brazil) was used, in accordance with the manufacturer's directions. Two sessions of bleaching were performed at one-week intervals. Color was registered at baseline and after the first and second bleaching sessions using a Vita shade guide. Patients recorded TS on a 0 to 4 scale during bleaching and within the next 24 and 48 hours of each session. BE at recall each week and intensity of TS were evaluated by repeated measures analysis of variance (ANOVA) and Tukey tests (α=0.05). Tooth sensitivity was compared using the Friedman repeated measures analysis of variance by rank and the Wilcoxon sign-ranked test. Faster bleaching was observed for the LA group than for the NA group after the first session (4.8 and 3.8 shade guide units [SGUs]; p=0.0001). However, both techniques were capable of bleaching the same number of SGUs after the second bleaching session (p=0.52). Most of the LA group (53.3%) had sensitivity even 24 hours after each bleaching session, but only 26.6% from the NA group reported TS. The intensity of TS was similar for both groups immediately after bleaching but significantly higher for the LA group 24 hours after each bleaching session (p=0.001). After two bleaching sessions, the use of LED/laser light activation did not improve bleaching speed. Persistent tooth sensitivity and higher tooth sensitivity after 24 hours of bleaching were observed when light activation was used.

Mandibular ramus-related Stafne's bone cavity

Mandibular bone depressions located on the lingual/buccal aspect of the mandibular ramus are the rarest variants of the so-called Stafne's bone cavities, or major salivary gland-related depressions, with only 17 cases reported in the literature including both clinical cases and archaeological specimens. We report the case of a 14-year-old male patient who sought clinical assistance complaining of a hard expansion on the lower left premolar-molar region. Apart from a unilocular radiolucent lesion between the lower left second premolar and first molar, a panoramic radiograph showed another radiolucent lesion located in the right mandibular ramus, at the level of the mandibular foramen. Computed tomography (CT) revealed an expansile lesion in the left mandibular body, later diagnosed as a simple bone cyst through surgical exploration. The three-dimensional CT volume rendering reconstructed image showed that the second lesion, located on the lingual aspect of the ascending ramus, was an actual cortical bone defect, which was diagnosed as a mandibular ramus-related Stafne's bone cavity. Considering the young age of the patient, the size of the defect, the recognizedly slow development of mandibular bone defects and, above all, the location of the bone defect under discussion, we believe it to have a congenital rather than a developmental origin (i.e. it was caused by a focal failure during intramembranous ossification of the mandible). If this is the case, mandibular bone depressions should not be seen exclusively as salivary gland-related bone defects.

Sarcomatoid squamous cell carcinoma of the uterine cervix: case report

Sarcomatoid squamous cell carcinoma (SSCC) is a recognized entity, usually involving the upper aerodigestive tract and skin. Location in the lower female genital tract is rare. Only 11 cases have been previously reported, four of which arose in the uterine cervix. The authors describe the case of a 39-years-old woman with SSCC of the uterine cervix in Stage I of the International Federation of Gynecology and Obstetrics (F.I.G.O.) classification. The patient died of disease 12 months after diagnosis. Similar cases described in the literature are also reviewed.