Testing the Minimum System Entropy and the Quantum of Entropy.

Experimental and theoretical results about entropy limits for macroscopic and single-particle systems are reviewed. All experiments confirm the minimum system entropy S⩾kln2. We clarify in which cases it is possible to speak about a minimum system entropykln2 and in which cases about a quantum of entropy. Conceptual tensions with the third law of thermodynamics, with the additivity of entropy, with statistical calculations, and with entropy production are resolved. Black hole entropy is surveyed. Claims for smaller system entropy values are shown to contradict the requirement of observability, which, as possibly argued for the first time here, also implies the minimum system entropy kln2. The uncertainty relations involving the Boltzmann constant and the possibility of deriving thermodynamics from the existence of minimum system entropy enable one to speak about a general principle that is valid across nature.

Quantum Chemical Calculation and Evaluation of Partition Coefficients for Classical and Emerging Environmentally Relevant Organic Compounds.

Octanol/water (KOW), octanol/air (KOA), and hexadecane/air (KHdA) partition coefficients are calculated for 67 organic compounds of environmental concern using computational chemistry. The extended CRENSO workflow applied here includes the calculation of extensive conformer ensembles with semiempirical methods and refinement through density functional theory, taking into account solvation models, especially COSMO-RS, and thermostatistical contributions. This approach is particularly advantageous for describing large and nonrigid molecules. With regard to KOW and KHdA, one can refer to many experimental data from direct and indirect measurement methods, and very good matches with results from our quantum chemical workflow are evident. In the case of the KOA values, however, good matches are only obtained for the experimentally determined values. Larger systematic deviations between data computed here and available, nonexperimental quantitative structure-activity relationship literature data occur in particular for phthalic acid esters and organophosphate esters. From a critical analysis of the coefficients calculated in this work and comparison with available literature data, we conclude that the presented quantum chemical composite approach is the most powerful so far for calculating reliable partition coefficients because all physical contributions to the conformational free energy are considered and the structure ensembles for the two phases are generated independently and consistently.

Sensory Perception of Non-Deuterated and Deuterated Organic Compounds.

The chemical background of olfactory perception has been subject of intensive research, but no available model can fully explain the sense of smell. There are also inconsistent results on the role of the isotopology of molecules. In experiments with human subjects it was found that the isotope effect is weak with acetone and D6 -acetone. In contrast, clear differences were observed in the perception of octanoic acid and D15 -octanoic acid. Furthermore, a trained sniffer dog was initially able to distinguish between these isotopologues of octanoic acid. In chromatographic measurements, the respective deuterated molecule showed weaker interaction with a non-polar liquid phase. Quantum chemical calculations give evidence that deuterated octanoic acid binds more strongly to a model receptor than non-deuterated. In contrast, the binding of the non-deuterated molecule is stronger with acetone. The isotope effect is calculated in the framework of statistical mechanics. It results from a complicated interplay between various thermostatistical contributions to the non-covalent free binding energies and it turns out to be very molecule-specific. The vibrational terms including non-classical zero-point energies play about the same role as rotational/translational contributions and are larger than bond length effects for the differential isotope perception of odor for which general rules cannot be derived.

Proton-transfer rate constants for the determination of organic indoor air pollutants by online mass spectrometry.

Proton transfer reaction mass spectrometry (PTR-MS) has become an indispensable analytical tool for indoor related sciences. With high-resolution techniques not only is the online monitoring of the selected ions in the gas phase possible, but also, with some limitations, the identification of substance mixtures without chromatographic separation. The quantification is carried out with the help of kinetic laws, which require knowledge of the conditions in the reaction chamber, the reduced ion moblilities and the reaction rate constant kPT under these conditions. Ion-dipole collision theory can be used to calculate kPT. One approach is an extension of Langevin's equation and is known as average dipole orientation (ADO). In a further development, the analytical solution of ADO was replaced by trajectory analysis, which resulted in capture theory. The calculations according to ADO and capture theory require precise knowledge of the dipole moment and the polarizability of the respective target molecule. However, for many relevant indoor related substances, these data are insufficiently known or not known at all. Consequently, the dipole moment µD and polarizability α of 114 organic compounds that are frequently found in indoor air had to be determined using advanced quantum mechanical methods. This required the development of an automated workflow that performs conformer analysis before computing µD and α using density functional theory (DFT). Then the reaction rate constants with the H3O+ ion are calculated according to the ADO theory (kADO), capture theory (kcap) and advanced capture theory for different conditions in the reaction chamber. The kinetic parameters are evaluated with regard to their plausibility and critically discussed for their applicability in PTR-MS measurements.

New relationships connecting the dipole polarizability, radius, and second ionization potential for atoms.

The atomic dipole polarizability α of the 101 elements from He to No is related to the second ionization potential I2 and the Waber-Cromer radius r(WC). Our recommended model is the function α = P1·I2⁻4 + P2·r(WC)(3) I2(y). With the parameters P1 = 2.26, P2 = 3.912, and y = 0.439, it reproduces the polarizabilities of all 101 elements with a mean absolute deviation of 7.5 au.

Quantum chemical calculation of the vapor pressure of volatile and semi volatile organic compounds.

The vapor pressure is a specific and temperature-dependent parameter that describes the volatility of a substance and thus its driving force for evaporation or sublimation into the gas phase. Depending on the magnitude of the vapor pressure, there are different methods for experimental determination. However, these are usually associated with a corresponding amount of effort and become less accurate as the vapor pressure decreases. For purposes of vapor pressure prediction, algorithms were developed that are usually based on quantitative structure-activity relationships (QSAR). The quantum mechanical (QM) approach followed here applies an alternative, much less empirical strategy, where the change in Gibbs free energy for the transition from the condensed to the gas phase is obtained from conformer ensembles computed for each phase separately. The results of this automatic, so-called CRENSO workflow are compared with experimentally determined vapor pressures for a large set of environmentally relevant compounds. In addition, comparisons are made with the single structure-based COSMO-RS QM approach, linear-free-energy relationships (LFER) as well as results from the SPARC program. We show that our CRENSO workflow is superior to conventional prediction models and provides reliable vapor pressures for liquids and sub-cooled liquids over a wide pressure range.

Experimental and theoretical determination of the dipole-quadrupole and dipole-octopole polarizabilities of the group IV tetrachlorides TiCl4, ZrCl4, and HfCl4.

The dipole-quadrupole and dipole-octopole polarizabilities A and E of TiCl4, ZrCl4, and HfCl4 have been determined from collision-induced light-scattering experiments. Our respective experimental results for /A/ are (165+/-10), (110+/-30), and (140+/-20) e2a0 3Eh (-1), whereas /E/ is determined to be (675+/-125), (750+/-200), and (670+/-400) e2a0 4Eh (-1). Theory predicts values convincingly close to experiment, as A=(181.4+/-9.1), (167.6+/-8.4), and (139.8+/-7.0) e2a0 3Eh (-1), and E=(-671+/-67), (-688+/-69), and (-574+/-57) e2a0 4Eh (-1). In addition our quantum chemical ab initio calculations give reliable values for the dipole polarizability alpha, as well as for the octopole and hexadecapole moments Omega and Phi for all three substances.

Dipole-quadrupole and dipole-octopole polarizability of OsO4 from depolarized collision-induced light scattering experiments, ab initio and density functional theory calculations.

The dipole-quadrupole and dipole-octopole polarizability of osmium tetroxide (OsO(4)) has been determined from collision-induced light-scattering experiments. Our final estimates for these properties are |A|=(84+/-5)e(2)a(3)(0)E(-1)(h) and |E|=(214+/-25)e(2)a(4)(0)E(-1)(h). We have also analyzed previous experimental data of the relative permittivity and refractivity of OsO(4) to propose the electronic part of the static dipole polarizability of alpha=51.0e(2)a(2)(0)E(-1)(h). To support our findings we have performed high-level ab initio and density functional theory calculations to obtain theoretical static estimates alpha=(50.2+/-1.6)e(2)a(2)(0)E(-1)(h), A=(84+/-10)e(2)a(3)(0)E(-1)(h), and E=(-252+/-32)e(2)a(4)(0)E(-1)(h), in essential agreement with the proposed experimental values.