New ferrocenyl-chalcones and bichalcones: Synthesis and characterization

Ferrocenyl-chalcones and their bichalcone analogues were characterized by IR and NMR spectroscopy, as well as electrochemically. Their UV–visible spectra were recorded, and the electronic transitions were assigned by time-dependent DFT calculations. The single-crystal X-ray structures were determined for two ferrocenyl bichalcones.     

Oxidative degradations of the side chain of unsaturated ent-labdanes. Part I

A selective route for the degradation of the unsaturated side chain of ent-labdanes has been devised, giving two useful synthons: 2beta-acetoxy-14,15,17-trinor-ent-labdane-8,13- dione (5) and 2beta-acetoxy-14,15-dinor-ent-labd-8(17)-en-13-one (7), the use of which for the preparation of terpenylquinone derivatives shall be reported elsewhere.     

Headspace solid-phase microextraction of cannabinoids in human head hair samples

A fast method was optimized and validated with the aim to detect cannabinoids (cannabidiol, cannabinol, and delta-9-tetrahydrocannabinol) in human head hair samples. The method was based on an initial procedure of external decontamination of hair samples (10 mg) with petroleum ether, followed by alkaline digestion and further extraction of cannabinoids by means of a headspace solid-phase microextraction technique (HS-SPME). GC-MS was used to identify and quantify the analytes in SIM mode. The LOQs and LODs obtained were 0.07 and 0.12 ng/mg, respectively, for all the studied cannabinoids. The method proved to be simple, rapid, and precise. By using the weighted least squares linear regression (weighting factor 1/x2), the accuracy of the analytical method was improved at the lower end of the calibration curve (from 0.12 to 12 ng/mg; r >0.98). Hair samples collected from eight volunteers (in-patients of a drug abuse rehabilitation clinic) were submitted to the proposed method. Detection of the drugs was observed in samples of the volunteers who reported frequent marijuana use (at least ten times a week).     

Neumann boundary conditions for a nonlocal nonlinear diffusion operator. Continuous and discrete models

Let be a nonnegative, smooth function with , supported in , symmetric, , and strictly increasing in . We consider the Neumann boundary value problem for a nonlocal, nonlinear operator that is similar to the porous medium, and we study the equation

We prove existence and uniqueness of solutions and a comparison principle. We find the asymptotic behaviour of the solutions as : they converge to the mean value of the initial data. Next, we consider a discrete version of the above problem. Under suitable hypotheses we prove that the discrete model has properties analogous to the continuous one. Moreover, solutions of the discrete problem converge to the continuous ones when the mesh parameter goes to zero. Finally, we perform some numerical experiments.

     

The Structure and Conformation of (CH3)3CSNO

The gas‐phase molecular structure of (CH₃)₃CSNO was investigated by using electron diffraction, allowing the first experimental geometrical parameters for an S‐nitrosothiol species to be elucidated. Depending on the orientation of the ?SNO group, two conformers (anti and syn) are identified in the vapor of (CH₃)₃CSNO at room temperature, the syn conformer being less abundant. The conformational landscape is further scrutinized by using vibrational spectroscopy techniques, including gas‐phase and matrix‐isolation IR spectroscopy, resulting in a contribution of ca. 80:20 for the anti:syn abundance ratio, in good agreement with the computed value at the MP2(full)/cc‐pVTZ level of approximation. The UV/Vis and resonance Raman spectra also show the occurrence of the conformational equilibrium in the liquid phase, with a moderate post‐resonance Raman signature associated with the 350 nm electronic absorption.     

Linkage Isomerism Leading to Contrasting Carboboration Chemistry: Access to Three Constitutional Isomers of a Borylated Phosphaalkene

We describe the reactivity of two linkage isomers of a boryl-phosphaethynolate, [B]OCP and [B]PCO (where [B]=N,N’-bis(2,6-diisopropylphenyl)-2,3-dihydro-1H-1,3,2-diazaboryl), towards tris- (pentafluorophenyl)borane (BCF). These reactions afforded three constitutional isomers all of which contain a phosphaalkene core. [B]OCP reacts with BCF through a 1,2 carboboration reaction to afford a novel phosphaalkene, E-[B]O{(C₆F₅)₂B}C=P(C₆F₅), which subsequently undergoes a rearrangement process involving migration of both the boryloxy and pentafluorophenyl substituents to afford Z-{(C₆F₅)₂B}(C₆F₅)C=PO[B]. By contrast, [B]PCO undergoes a 1,3-carboboration process accompanied by migration of the N,N’-bis(2,6-diisopropylphenyl)-2,3-dihydro-1H-1,3,2-diazaboryl to the carbon centre.     

Undergraduate women empowering women in computational chemistry: Three perspectives

The undergraduate computational chemistry research group headed by Mauricio Cafiero at Rhodes College has a history of including, promoting, and supporting women in this predominantly male field. Alums of this research group from 2004 to 2019 include nine M.Ds, two science researchers, two Ph.D.s, one secondary teacher, two pharmacists, a physical therapist, two nurses, six current medical school students, and five current science graduate students. They have produced 18 peer-reviewed publications with female undergraduate first authors and over 100 conference presentations, including 9 international conference presentations. While Professor Cafiero does all he can to support these students, he attributes the continuous success of the group in recruiting, retaining, and supporting these women to the students themselves. The students' success and visibility on campus helps to recruit new students. The heavy presence of women in this group provides a strong support system for women who may otherwise feel isolated in a male-dominated field; and these support groups provide models and support for women to overcome common obstacles that women in science face. We will profile three recent graduates who will discuss how the above points affected them during their time in the research group and discuss their experience in the context of some literature on women in Science, Technology, Engineering and Mathematics.     

Gamma radiation effects on mechanical properties and morphology of a polyurethane derivate from castor oil

In this study, an adhesive of a polyurethane derivate from castor oil was irradiated with gamma radiation from a ⁶⁰Co source, at doses from 0.2 to 25 kGy. This adhesive polyurethane is considered for use in hospital furniture because it does not liberate dangerous solvents. Hardness and elastic modulus were measured by instrumented indentation with a pyramidal Berkovich indenter, using loads from 0.08–40 mN with a nanoindenter XP. The instrumented indentation hardness was 110 MPa for an untreated sample, increasing to 124 MPa after irradiation with 25 kGy, at penetration depths of about 5 μm. The increases in elastic modulus induced by radiation were less pronounced. This polyurethane is naturally cross-linked and the relative modifications in the hardness are attributed to an additional cross-linking process induced by radiation. X-ray diffraction indicates a slight increase in crystallinity. The roughness measured by atomic force microscopy increases after gamma irradiation.     

Analyticity and Smoothing Effect for the Coupled System of Equations of Korteweg-de Vries Type with a Single Point Singularity

Using Bourgain spaces and the generator of dilation P=3t ? _t +x ? _x , which almost commutes with the linear Korteweg-de Vries operator, we show that a solution of the initial value problem associated for the coupled system of equations of Korteweg-de Vries type which appears as a model to describe the strong interaction of weakly nonlinear long waves, has an analyticity in time and a smoothing effect up to real analyticity if the initial data only have a single point singularity at x=0.     

A biased random-key genetic algorithm for routing and wavelength assignment

The problem of routing and wavelength assignment in wavelength division multiplexing optical networks consists in routing a set of lightpaths and assigning a wavelength to each of them, such that lightpaths whose routes share a common fiber are assigned different wavelengths. This problem was shown to be NP-hard when the objective is to minimize the total number of wavelengths used. We propose a genetic algorithm with random keys for routing and wavelength assignment with the goal of minimizing the number of different wavelengths used in the assignment. This algorithm extends the best heuristic in the literature by embedding it into an evolutionary framework. Computational results show that the new heuristic improves the state-of-the-art algorithms in the literature.