A high-resolution infrared spectroscopic investigation of the halogen atom-HCN entrance channel complexes solvated in superfluid helium droplets

Rotationally resolved infrared spectra are reported for the X-HCN (X = Cl, Br, I) binary complexes solvated in helium nanodroplets. These results are directly compared with that obtained previously for the corresponding X-HF complexes [J. M. Merritt, J. K\"upper, and R. E. Miller, PCCP, 7, 67 (2005)]. For bromine and iodine atoms complexed with HCN, two linear structures are observed and assigned to the $^{2}\Sigma_{1/2}$ and $^{2}\Pi_{3/2}$ ground electronic states of the nitrogen and hydrogen bound geometries, respectively. Experiments for HCN + chlorine atoms give rise to only a single band which is attributed to the nitrogen bound isomer. That the hydrogen bound isomer is not stabilized is rationalized in terms of a lowering of the isomerization barrier by spin-orbit coupling. Theoretical calculations with and without spin-orbit coupling have also been performed and are compared with our experimental results. The possibility of stabilizing high-energy structures containing multiple radicals is discussed, motivated by preliminary spectroscopic evidence for the di-radical Br-HCCCN-Br complex. Spectra for the corresponding molecular halogen HCN-X$_{2}$ complexes are also presented.Comment: 20 pages, 15 figures, 6 tables, RevTe

Hybrid Quantum and Classical Mechanical Monte Carlo Simulations of the Interaction of Hydrogen Chloride with Solid Water Clusters

Monte Carlo simulations using a hybrid quantum and classical mechanical potential were performed for crystal and amorphous-like HCl-water(n) clusters The subsystem composed by HCl and one water molecule was treated within Density Functional Theory, and a classical force field was used for the rest of the system. Simulations performed at 200 K suggest that the energetic feasibility of HCl dissociation strongly depends on its initial placement within the cluster. An important degree of ionization occurs only if HCl is incorporated into the surface. We observe that local melting does not play a crucial role in the ionization process.Comment: 14 Latex pages with 4 postscript figures, to appear in Chem. Phys. Let

Halogen Bonding with Phosphine: Evidence for Mulliken Inner Complexes and the Importance of Relaxation Energy

Intermolecular halogen bonding in complexes of phosphine and dihalogens has been theoretically investigated using explicitly correlated coupled cluster methods and symmetry adapted perturbation theory. The complexes H3P· · · ClF, H3P· · · BrF and H3P· · ·IF are demonstrated to possess unusually strong interactions that are accompanied by an increase in the induction component of the interaction energy and significant elongation of the X–Y halogen distance on complex formation. The combination of these factors is indicative of Mulliken inner complexes and criteria for identifying this classification are further developed. The importance of choosing an electronic structure method that describes both dispersion and longer range interactions is demonstrated, along with the need to account for the change in geometry on complexation formation via relaxation energy and overall stabilisation energies

The Hydrogen Bond, the Halogen Bond and Rotational Spectroscopy:A Personal Retrospective

This article is a personal, chronological account of experimental work carried out on the hydrogen bond, the halogen bond and other non-covalent interactions by my research group using (mainly) rotational spectroscopy since 1974. It is not intended to be comprehensive, and therefore does not include contributions made by many groups in the last 40 years or so.</p

Stimulation of soil native microflora to stabilize soils after wildfires

Stimulation of soil native microflora to stabilize soils after wildfires In nature ureolytic bacteria will use Urea as a carbon source. In the presence of Calcium, the ureolytic reaction will form Calcium Carbonate. This pathway is of interest because Calcium Carbonate will function as a bio-cementing molecule, stabilizing the soil in a process known as Microbial-Induced Calcite Precipitation (MICP). This study hypothesizes that amendment of soil with Urea will enrich the natural population of ureolytic bacteria which upon the addition of Calcium Chloride will result in the stabilization of the soil. For this purpose, burned and unburned soil will be treated with microbiological media to promote the growth of native ureolytic populations. We will then measure the enriched soil urease activity using a colorimetric assay, calcite precipitation with a gravimetric method after the acid dissolution of the calcite, and the compaction and stabilization of soil using ASTM standard methods. We will also isolate and identify ureolytic bacteria to be applied in future MICP experiments. This is a collaborative effort between students and faculty of the Aerospace Physiology and Civil Engineering programs

Potential Relationship Between Vascular Depression and Autobiographical Memory Specificity in an Older Adult Population According to the CaR-FA-X Model

Vascular depression is a type of depression that has its onset later in life, and it has been associated with cardiovascular or metabolic diseases. Depression can be costly and associated with other health problems, which is why it becomes imperative to uncover the multiple mechanisms of action for depression symptomatology. A proposed mechanism of action for the emergence of depressive symptomatology is poor autobiographical memory specificity according to the CaR-FA-X model. However, it remains unclear whether this mechanism contributes somehow to the vascular depression specific type. The purpose of this research was to determine the potential relationship between the mechanisms proposed by the CaR-FA-X model and the presence of vascular depression, which has not been addressed by previous literature or research. Forty three older adults over the age of seventy from the Orlando area completed multiple measures including the Geriatric Depression Scale, Autobiographical Memory Test, and physiological measures. Results showed no support for a relationship between CaR-FA-X model elements and vascular depression; however, support was found for the relationship between cerebrovascular burden and depression as proposed by the vascular depression theory with rumination serving as a moderator. To our knowledge, this is the first time a study finds the moderating effect of rumination in the development of vascular depression. Further studies will need to address other potential mechanisms that increase risk for this specific type of depression as well as investigate the reasons under which, if any, autobiographical memory specificity might be related to vascular depression by using other measures that might be more sensitive to a non-clinical population

Nonbonding pairs in cyclic thioethers: Electrostatic modelling and ab initio calculations for complexes of 2,5-dihydrothiophene, thietane and thiirane with hydrogen fluoride

Electrostatic potential energies V(ϕ) of a non‐perturbing, protonic charge at fixed distances r from the S atom in three cyclic thioethers were examined as functions of the angles ϕ made by the r‐vector with the C2 axis (thiirane and 2,5‐dihydrothiophene) or the local C2 axis (thietane). The electrostatic PE VHF(ϕ) of HF (HF modelled as an extended electric dipole) was also calculated and the results compared with geometries of the thioether⋯HF complexes calculated at the CCSD(T)‐F12c/cc‐pVTZ‐F12 level. The latter reveal angular deviations θ ∼10‐20° of the S⋯H-F nuclei from collinearity in directions suggesting secondary interactions of F with H atom(s) of the rings. Angles ϕ made by the S⋯H hydrogen bond with the C2 (or local C2) axes in the complexes are systematically larger (∼4‐9°) than indicated by the VHF(ϕ) functions. Minima in the simple V(ϕ) versus ϕ functions occur at values smaller (∼5‐10°) than those in the VHF(ϕ) curves

Bacterial antibiotic resistance in space

Antimicrobial resistance poses a serious threat to public health and is a growing concern for space exploration missions. Recent studies suggest that microorganisms express higher levels of resistance to antibiotics under microgravity conditions due to the decrease in molecular collisions. Determining the minimum inhibitory concentration (MIC) of antimicrobial agents against microorganisms is an important tool in antimicrobial susceptibility testing and can help clinicians to determine the appropriate dosage and duration of antimicrobial therapy for a given infection. However, the effects of microgravity on MIC remain largely unknown. To address this, a team of researchers used the Kirby Bauer assay to screen the effectiveness of different antibiotics against three bacterial species, Escherichia coli, Staphylococcus epidermidis, and Vibrio fischeri. The assay involved placing filter paper disks containing known concentrations of antibiotics onto a culture of the target bacteria and measuring the diameter of the zone of inhibition around each disk. The results indicated that Tetracycline was the most effective antibiotic to target E. coli, while Chloramphenicol was most effective against V. fischeri and S. epidermidis. The team is now working to establish MIC under Earth\u27s gravity for each species-antibiotic pair to serve as a control and to re-calculate the results for comparison once the pairs are subjected to simulated microgravity using a 2D clinostat. These findings will help inform future research on antimicrobial resistance and space exploration