Systems of oblate molecules. Monte Carlo study

Monte Carlo (MC) simulations were performed for systems of hard oblate spherocylinders with breadth-to-height ratios φ = 0.5–3.5 and packing fractions y = 0.25–0.45 and for Kihara oblate molecule systems of φ = 1 at reduced temperatures T* = 0.75 and 1.0 and y = 0.05–0.45. The compression factors and the dependence of the average correlation functions on the shortest surface-to-surface distance were determined for the case of hard oblate spherocylinders and the compression factors, residual internal energies and average correlation functions for the case of the generalized Kihara molecule systems. In addition, values of the third virial coefficient of the hard oblate spherocylinders were evaluated in the range of φ = 1–3. Results of the MC simulations for the hard oblate spherocylinders compare well with the available data in the literature and theoretical values; thermodynamic functions of the Kihara molecule systems were determined from the second-order perturbation theory. They agree well with our MC values at lower densities and higher reduced temperatures.     

ON THE TYROSINATE INVOLVEMENT IN THE SCHIFF BASE DEPROTONATION IN THE PROTON PUMP CYCLE OF BACTERIORHODOPSIN

Abstract— The ultraviolet transient absorption assigned to the tyrosinate species in bacteriorhodopsin is followed in time and as a function of pH. Both its rise time and titration curve closely resemble those observed for the production of the M₄₁₂ intermediate. These results may support a recently proposed mechanism that couples tyrosinate production to the Schiff base deprotonation in the proton pump of bacteriorhodopsin.     

TRYPTOPHAN PHOSPHORESCENCE AT ROOM TEMPERATURE AS A TOOL TO STUDY PROTEIN STRUCTURE AND DYNAMICS

Fluorescence and phosphorescence resemble each other and in many ways can give the same type of information. Both originate from a dipolar interaction between light and the molecule. In this regard, both are polarized and subject to the same type of quenching phenomena. In other respects the information which they divulge are complementary. The fluorescence quantum yield is higher for exposed tryptophans and this is expressed in longer lifetime (Grinvald and Steinberg, 1976); in contrast long lifetime of phosphorescence appears to correlate with burial. Phosphorescence, spin-disallowed, is much longer lived than fluorescence. This allows the structural/dynamic characterization of proteins to be studied on a new time regime. A really remarkable finding of studies of protein phosphorescence is that there is such variability both in phosphorescence lifetime and quenchability. We would interpret this to indicate that the tryptophan environment can range from essentially a crystal, almost comparable in rigidity as found at 77 K, to tryptophans in a flexible environment, almost as flexible as free in solution. An interesting task will be to examine the relationship between the yield and lifetime of phosphorescence and details of the tryptophan environment in terms of rigidity and adjacent amino acids among the proteins with known three dimensional structure.     

Using Natural and Artificial Light Sources to Illustrate Quantum Mechanical Concepts

We present here a discovery-based laboratory project that introduces elementary quantum mechanical concepts using the spectral distributions of natural and artificial light sources. The measured emission spectra of sunlight and interior/exterior lighting are explained using the electromagnetic spectrum, the phenomenon of blackbody radiation, and the quantization of light. This 4–5 week experiment is appropriate for the general chemistry laboratory or can be expanded for use in upper-division chemistry laboratories, and it uses modern spectroradiometric equipment that is readily available and increasingly used in the physical and biological sciences.     

Critical properties of non-spherical molecule fluids from the virial expansion

Critical constants of pure fluids (as important reference data in constructing vapour-liquid phase diagrams and basic input of various estimation methods) were determined for systems of non-spherical Kihara molecules; values of the critical temperature, density, compression factor and pressure of fluids composed of prolate and oblate molecules were evaluated from the fourth-order virial expansion. The second and third virial coefficients of the Kihara molecules were determined by applying the recently proposed method in which the effect of molecular core geometry and functional dependence of a pair interaction on the surface-surface distance are factorized and the former contribution determined from a formula for the corresponding hard convex body virial coefficient. The virial expansion for non-spherical Kihara molecules is applied to determine the critical constants of n-alkanes (methane to octane) and cyclic hydrocarbons (cyclopentane, cyclohexane, benzene and naphthalene); a fair agreement with experimental data was found.     

Critical properties of non-spherical molecule fluids from virial expansion

For systems of Kihara molecules with circular cores, the values of the reduced critical constants were determined from the fourth-order virial expansion as functions of the core diameter/thickness ratio. From expressions for the reduced functions both for the oblate and prolate shapes, the values of critical constants of four cyclic hydrocarbons and four branched alkanes were evaluated and compared with the experimental data and values obtained from the perturbation theory.     

CONTINGENT VALUATION OF MARINE PROTECTED AREAS: SOUTHERN CALIFORNIA ROCKY INTERTIDAL ECOSYSTEMS

ABSTRACT. Designation as Marine Protected Areas (MPAs) can protect coastal ecosystems, but apparently has not effectively protected the rocky intertidal zone in urban Southern California. Here, illegal collecting and habitat disturbance harm coastal marine life. We surveyed day visitors to sandy beaches or adjacent rocky habitats in Orange County. Using the close‐ended, double‐bounded contingent valuation method, we estimate the benefit of more effective enforcement and management of MPAs designed to avoid coastal ecosystem decay. We solve the problem of sample selection bias, introduced by the likelihood that the sample disproportionately includes respondents who visit more frequently and who may have a higher willingness to pay (WTP). We estimate the WTP for enacting policies to reduce illegal collecting and on‐site habitat disturbance to average $6 per family‐visit. Our estimate is consistent with other studies that estimate consumer surplus at $15 per person‐trip for nearby, lower quality beaches, and extrapolates from other studies to $3.6 $4.8 million per mile of coastline.