Transmission of electronic substituent effects through cage polycyclic alkanes: a computational study of diamantane derivatives based on structural variation

The transmission of long-range polar effects (field effects) across the diamantane cage has been investigated by analyzing the small structural changes induced by a variable substituent X in the phenyl group of 9-substituted 4-phenyldiamantane derivatives. The structures of many such molecules with charged or dipolar substituents have been determined from quantum chemical calculations at the HF/6-31G* and B3LYP/6-311++G** levels of theory. Comparison with the results of a similar study carried out on 4-substituted 1-phenylbicyclo[2.2.2]octane derivatives, where the distance between probe and substituent is substantially smaller, shows that the ability of the diamantane framework to transmit field effects is 45 % of that of the bicyclo[2.2.2]octane framework when X is a dipolar, uncharged substituent. This figure increases to 59 % in the case of charged groups. The structural results support the idea that the field effect of a dipolar substituent attenuates more rapidly with distance than that of a charged group. This makes it impossible to construct a single, universal scale of field parameters including both dipolar and charged groups. A single scale can only be set up for a fixed separation between substituent and probe. The presence of the variable substituent X has a pronounced effect on the geometry of the diamantane cage. The nonbonded distance between the bridgehead carbons C4 and C9 spans an interval about 0.20 Å wide and correlates quite well with the mean value of the three cage angles at C9. These geometric changes are closely similar to those of the corresponding parameters in 4-substituted 1-phenylbicyclo[2.2.2]octane derivatives. The concerted structural variation of the polycyclic cage is controlled primarily by the group electronegativity of X and does not correlate with the much smaller structural variation of the phenyl probe.     

Approximation of Piecewise Affine Homeomorphisms by Diffeomorphisms

We prove that any countably piecewise affine homeomorphism from an open set of ?² can be approximated, together with its inverse, by diffeomorphisms in the W ^1,p and the L ^∞ norms.     

On the principle of gyroscopic effect for self-excited rigid bodies

Summary A new method is described whereby the gyroscopic effect for self-excited rigid bodies is studied by means of a differential equation of the second order and the results of other Authors are generalized.

---

Sommario Si descrive un metodo di calcolo, che permette di ricondurre la discussione sulla validità dell'effetto giroscopico per i solidi autoeccitati allo studio di una equazione differenziale del secondo ordine e di generalizzare i risultati ottenuti da altri Autori.

---

---

This work has been done under the auspices of the Research Group no. 6 of C.N.R.     

Smooth approximation of bi-Lipschitz orientation-preserving homeomorphisms

We show that a planar bi-Lipschitz orientation-preserving homeomorphism can be approximated in the W^1,p$W^{1,p}$ norm, together with its inverse, with an orientation-preserving homeomorphism which is piecewise affine or smooth.     

Structure, electronic, and optical properties of TiO2 atomic clusters: an ab initio study

Atomic clusters of TiO(2) are modeled by means of state-of-the-art techniques to characterize their structural, electronic and optical properties. We combine ab initio molecular dynamics, static density functional theory, time-dependent density functional theory, and many body techniques, to provide a deep and comprehensive characterization of these systems. TiO(2) clusters can be considered as the starting seeds for the synthesis of larger nanostructures, which are of technological interest in photocatalysis and photovoltaics. In this work, we prove that clusters with anatase symmetry are energetically stable and can be considered as the starting seeds to growth much larger and complex nanostructures. The electronic gap of these inorganic molecules is investigated, and shown to be larger than the optical gap by almost 4 eV. Therefore, strong excitonic effects appear in these systems, much more than in the corresponding bulk phase. Moreover, the use of various levels of theory demonstrates that charge transfer effects play an important role under photon absorption, and therefore the use of adiabatic functionals in time dependent density functional theory has to be carefully evaluated.     

A computational study of 4-substituted biphenyls in their minimum energy conformation: twist angles, structural variation, and substituent effects

The role of electronic substituent effects in determining the twist angle of 4-substituted biphenyls and the mechanism of their propagation through the biphenyl frame have been studied by quantum chemical calculations at the HF/6-31G* and B3LYP/6-311++G** levels of theory, carried out on 41 p-Ph–C₆H₄–X molecules in their equilibrium conformation. The twist angle φ about the C–C bond connecting the two benzene rings, ca 45° in unsubstituted biphenyl, almost invariably decreases when a para substituent is present. In the majority of cases the difference ?φ = φ(X) ? φ(H) is small, less than a couple of degrees; the decrease of φ becomes substantial only when the substituent is a charged π-donor or π-acceptor. Multiple regression analysis using appropriate explanatory variables indicates a quadratic dependence of ?φ on the π-donor/acceptor ability of the substituent, and, to a lesser extent, on its field effect. The propagation of substituent effects through the biphenyl frame has been studied from the structural variation of the Ph group acting as a probe (ring B). This is best measured by a linear combination of the internal ring angles, termed S _F ^BIPH(e) . Multiple regression analysis of S _F ^BIPH(e) reveals a composite field effect, a substantial proportion of which is originated by resonance- and polarization-induced π-charges on the carbon atoms of the –C₆H₄– spacer (ring A). Extended conjugation between ring A and ring B, caused by resonance and polarization effects, gives rise to quadratic terms in the regression. The reliability of S _F ^BIPH(e) as a measure of long-range polar effects is supported by correlations with various experimental parameters.     

Dual-color bioluminescent bioreporter for forensic analysis: evidence of androgenic and anti-androgenic activity of illicit drugs

Bioassays represent promising complementary techniques to conventional analytical approaches used in doping analysis to detect illicit drugs like anabolic-androgenic steroids (AAS). The fact that all AAS share a common mechanism of action via the human androgen receptor (hAR) enables the use of bioassays, relying on the activation of hAR as antidoping screening tools. Previously, we developed a dual-color bioreporter based on yeast cells engineered to express hAR and androgen response elements driving the expression of the bioluminescent (BL) reporter protein Photinus pyralis luciferase. A second reporter protein, the red-emitting luciferase PpyRE8, was introduced in the bioreporter as internal viability control. Here, we report the first forensic application of a straightforward, accurate, and cost-effective bioassay, relying on spectral resolution of the two BL signals, in 96-microwell format. The bioreporter responds to dihydrotestosterone as reference androgen in a concentration-dependent manner from 0.08 to 1,000 nM with intra- and inter-assay variation coefficients of 11.4 % and 13.1 %, respectively. We also demonstrated the suitability of this dual-color bioreporter to assess (anti)-androgenic activity of pure AAS, mixtures of AAS, and other illicit drugs provided by the Scientific Police. Significant anti-androgenic activity was observed in samples labeled as marijuana and hashish, containing Δ⁹-tetrahydrocannabinol as major constituent.

The effect of the intermolecular potential formulation on the state‐selected energy exchange rate coefficients in N2–N2 collisions

The rate coefficients for N₂–N₂ collision‐induced vibrational energy exchange (important for the enhancement of several modern innovative technologies) have been computed over a wide range of temperature. Potential energy surfaces based on different formulations of the intramolecular and intermolecular components of the interaction have been used to compute quasiclassically and semiclassically some vibrational to vibrational energy transfer rate coefficients. Related outcomes have been rationalized in terms of state‐to‐state probabilities and cross sections for quasi‐resonant transitions and deexcitations from the first excited vibrational level (for which experimental information are available). On this ground, it has been possible to spot critical differences on the vibrational energy exchange mechanisms supported by the different surfaces (mainly by their intermolecular components) in the low collision energy regime, though still effective for temperatures as high as 10,000 K. It was found, in particular, that the most recently proposed intermolecular potential becomes the most effective in promoting vibrational energy exchange near threshold temperatures and has a behavior opposite to the previously proposed one when varying the coupling of vibration with the other degrees of freedom. © 2014 Wiley Periodicals, Inc.