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Density functional theory (DFT) was used to study the mechanism of Diels–Alder (DA) reaction between 2‐Methyl‐ 1,3 Butadiene (MBD) with B12N12, B6N6C12 and B6C12N6 fullerens in the gas phase. In this mechanism, B‐N bonds of four‐membered and six‐membered rings of nanocages were chosen to react with MBD. Due to the existence of two types of B‐N bonds, two competitive pathways (a and b) were investigated. The effect of the substitution of carbon atoms instead of boron and nitrogen atoms on the stability of the structures and the regioselectivity of the DA reaction was examined. The potential energy of all structures and the activation barrier for all reaction pathways was evaluated. The chemical reactivity of fullerens using the molecular quantum descriptors was assessed. To evaluate the global electron density transfer in transition states (TS) structures, the natural bond orbital (NBO) analysis was performed. [ABSTRACT FROM AUTHOR]

A potentiometric method was used to determine the autoprotolysis constant for aqueous solutions containing 0, 20 and 40 weight percent of methanol in wide range of NaCl concentration at 25°C. Ionic strength was ranged between 0.25 and 2.00 mol L-1 by intervals of 0.25 units. Osmotic and activity coefficient of mixed solvents were calculated as a function of ionic strength. Dependence on ionic strength was analyzed by using the original Specific ion Interaction Theory. The specific ion interaction parameters were extracted associated with the thermodynamic autoprotolysis constant. Results indicate that interaction between ions increases with the increasing of the methanol content in mixture.

We have applied DFT calculations to investigate the effect of the adjacent pentagons (APs) on the geometries, stabilities, and electronic structures of the non-IPR isomers of Si60 and Si70 fullerenes containing three adjacent pentagon pairs, Si60(D3) and Si70(C2v), and the SW defective Si60 and Si70 fullerenes with four AP pairs. These non-IPR isomers of Si60 and Si70 cages are more stable than their IPR ones. Natural bond orbital analyses and electrostatic potential surfaces indicate the charge densities are more localized at the pentagon-pentagon edges of the non-IPR fullerenes, which increase by going to the charged ones. Based on our results, the SW rearrangement process in the Si60 and Si70 silicon fullerenes is exothermic. A silylene-like transition state along a stepwise reaction path is characterized at the B3LYP/6-311 + G* level of theory. The barrier for the SW rearrangement of Si60 fullerene is obtained to be 5.36 eV which is smaller than that reported for SW rearrangement of C60 fullerene. [ABSTRACT FROM AUTHOR]

Density functional theory calculations have been carried out to investigate the [2 + x] x = 1, 2, and 3 cycloaddition reactions (paths A, B, and C) of triatomic sulfur (S3) with the C70 fullerene in terms of geometry, energies, and electronic structures. The thiozonation (S3) on the hexagon-hexagon and hexagon-pentagon bonds of the C70 fullerene through 1,3-dipolar reaction, i.e., [2 + 3] cycloaddition, is generally exothermic, while through the chelotrope additions, i.e., [2 + 1] cycloaddition, are endothermic. The results indicate that the 1,3-dipolar cycloaddition is the most preferable path. Having more negative values of reaction energies Er together with the lower barrier heights, thiozonation of the hexagon-hexagon bonds is thermodynamically and kinetically more favorable than hexagon-pentagon ones. Moreover, the addition of thiozone to the hexagon-hexagon bonds near the pole area of the C70 leads to more negative reaction energies. Therefore, it is established that the arrangement and position of C=C bonds play an important role in the thiozonation of C70 fullerene. Thiozonolysis of triatomic sulfur (S3) indicates that S-S bond cleavage has not occurred, instead a sulfur bridge over a C-C bond or a four-membered ring of 1,2-dithietane-1-sulfide is preferred to be formed. [ABSTRACT FROM AUTHOR]

We have applied density functional theory calculations to study polarizability of the Si60H60 derivatives with epoxide moieties (Si60H60−2nOn with n up to 30). The results show that mean polarizability, α, of oxygen-containing silicon fullerene derivatives is higher than that of Si60H60. The mean polarizabilities of the isomers slightly depend on the positional relationship of the epoxide moieties, and are determined mainly by the number of epoxide moieties. Mean polarizabilities of Si60H60−2nOn linearly increase with n, and are characterized by the depression of polarizability. The formula describing the mean polarizability as a function of the number of epoxide groups has been obtained, which may be important for the design of silicon-containing nanostructures with regulated polar parameters. [ABSTRACT FROM AUTHOR]

An efficient multicomponent reaction of nitroalkanes and elemental sulfur with oxiranes was developed with the aid of silver salt. This reaction procedure provides a novel and practical strategy for the rapid assembly of 1,3-oxathiolane skeletons. The reaction exhibited remarkable functional group tolerability and regio-selectivity so that only one regio-isomer formed during the ring opening of oxiranes. Graphical abstract: [ABSTRACT FROM AUTHOR]

Chronic subdural hematoma (CSDH) is a curable entity frequently encountered by neurosurgeons. The present study was conducted to explore expert opinion and common practice in Iran. Besides, a Review of randomized clinical trials in literature was performed. A questionnaire including six questions discussing major aspects of practice on CSDH, with multiple choices was designed. A pilot study was performed for reliability analysis of the questionnaire. A total of 100 neurosurgeons were selected randomly from the members of Iranian Association of Neurological Surgeons. Frequency of answers to each item, differences in response rates and correlation of various categories were analyzed using Chi-square statistics. The mean duration of experience was 15.4 ± 5 years, with a range of 10 to 37 years. The most common initial procedure of choice was burr-hole drainage (64%). At recurrent cases, surgical approach was changed to craniotomy at one-third of those treated initially with burr-hole drainage. The participants believed that surgical technique was predictive of outcome and recurrence. Burr-hole without drainage was used by less expert neurosurgeons (mean 12.5 ± 6), however, burr-hole drainage was the dominant technique at more than 15 years of experience and craniectomy was used only by participants with more than 30 years of experience (10%). Irrigation was used by most of the neurosurgeons (87.5%) in combination with drainage and burr-hole. The majority of participants used flat position at the postoperative period. At the current study, the pattern of management for CSDH was similar to other reports at literature suggesting the burr-hole drainage and irrigation as optimal treatment. Individualized decision-making could be made at challenging cases. [ABSTRACT FROM AUTHOR]

DFT calculations are applied to evaluate the effects of atomic arrangements of dopant atoms on electronic features of the most stable structures of C60−nNn(n = 1–12) fullerenes. Our study reveals that 13C isotropic chemical shifts (δiso) of the nuclei at C–N pentagon–hexagon (ph) junctions appear at downfield values while there are no tangible values of δiso for the nuclei at C–N hexagon–hexagon (hh) junctions; the carbon sites attached to the first neighbors of nitrogen at hh junctions (the second neighboring effect) yield upfield values of δiso. Moreover, compensation between diatropic and paratropic ring currents leads to slightly less negative NICS value in C59N heterofullerene (-3.6) compared to the parent fullerene C60 (-4.25). However, with incorporating more nitrogen atoms into the cage the aromaticity first increases, up to the 66π-system C54N6 and C53N7, yielding the most negative NICS values of -26.3 and -26.8, respectively, and then decreases so that NICS finally reaches the value of -6.6 ppm for C48N12 heterofullerene. On the basis of distinct value predicted for each heterofullerene, one expects that NICS values may also be useful for identification of the molecules through their endohedral 3He NMR chemical shifts. [ABSTRACT FROM AUTHOR]

Abstract: DFT calculations are applied to evaluate the effects of atomic arrangements of dopant atoms on electronic features of the most stable structures of (BC2N)6 including both C24 fullerene doped with six BN units (C12B6N6; model 1–7) and B12N12 nanocage doped with six CC units (B6N6C12; model 8–15). Our study reveals a relation between local structures, C α , C β , C γ , and Cδ within the molecules and 13C NMR signals. This is also observed with natural charges, so that the increase of negative charge on carbon is along with more shielding of corresponding carbon. All BN-substituted species (model 1–7) with the negative calculated NICS at their cage center are predicted to be aromatic, in contrast to C24 (NICS=±37). The predicted NICS values may be useful for the identification of the heterofullerenes through their endohedral 3He NMR chemical shifts. [Copyright &y& Elsevier]

Background: Intrathecal injection of fluorescein is a useful adjuvant method for localization of fistulas in endoscopic endonasal repair of cerebrospinal fluid (CSF) leakage. Although being neurotoxic in commercial doses, a low dose of diluted fluorescein seems to be safe on the basis the existing data in the literature. Objectives: The purpose of this study was to investigate the role of a low-dose intrathecal fluorescein injection in detection of CSF fistula and potential adverse effects of this technique. Materials and Methods: CSF rhinorrhea was repaired in 20 patients with an endoscopic endonasal technique. Intraoperative intrathecal fluorescein injection was used for localization of the site of the CSF leak. The accuracy rate of leakage site identification and the incidence of complications and recurrences were recorded. Results: Intrathecal administration of fluorescein demonstrated CSF leakage in 18 of the 20 patients (90%). There were no intraoperative complications. Definitive closure of the CSF leakage site was achieved in 16 patients (80%) after the initial reconstruction. Recurrence occurred in four cases and all patients were free of CSF leakage after the second surgical attempt. Conclusions: The present study suggested that a low dose of intraoperative intrathecal fluorescein administration is a safe and sensitive method for localization of CSF leakage sites. [ABSTRACT FROM AUTHOR]

The limitation of Liquid-liquid micro-extraction (LLME) procedures can be the need for the use of a dispersive solvent which should be soluble in both of aqueous and organic phases. In this research, a new method named SUPRA-based LLME, is introduced which uses supra molecular solvent (SUPRA), as an environmentally friendly solvent, for quantitative and selective extraction of Co 2+ ions from its aqueous solution via liquid-liquid micro-extraction process. The aqueous immiscible SUPRA phase, composed of vesicles of decanoic acid was synthesized via ex-situ procedure and used as a single liquid phase. In order to make the SUPRA phase selective, N, N'-disalicylidene-3, 4-diaminotoluene (H 2 dst) was synthesized and completely dissolved in the SUPRA phase. Then the lipophilic and selective prepared liquid sorbent, as liquid SUPRA phase, was used for the facile and selective LLME of Cobalt (II) ions from aqueous samples. Experimental studies showed that there was not any need of dispersing solvent and so liquid SUPRA phase could easily dispersed in the aqueous phase and then separated by centrifugation as the supernatant phase. Then the effects of some important variables on the extraction efficiency were also investigated and optimized. The results showed that under optimal conditions, efficient extraction of Cobalt (II) ions was achieved, about 99 % ± 2.7 (n = 10) , in a short time of extraction (10 min), and the linear range of calibration curve was from 500 to 2500 μg L -1 of Cobalt(II) with correlation coefficient of 0.999. Also detection limit and pre-concentration factor were 150 μg L -1 and 35.2, respectively. Although the experimental conditions were optimized for extraction of only Co 2+ ions, the selectivity study showed a high tendency of selective liquid SUPRA phase toward extraction of both of Co 2+ and Ni 2+ ions. The matrix effects on the SUPRA-based LLME of Co 2+ ions from matrix samples, factory wastewater and sea-water, were studied and least matrix effects were observed., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier B.V.)