Tomasz S. Pawłowski

Acidity of Hydroxyl Groups: An Overlooked Influence on Antiradical Properties of Flavonoids

The reactions of 10 flavonoids with 2,2-diphenyl-1-picrylhydrazyl radical (dpph(*)) carried out in alcohols always occur significantly faster than in acidified alcohols or in dioxane. These fast kinetics benefit from the contribution of the electron transfer from a flavonoid anion to a radical, a mechanism known as Sequential Proton-Loss Electron-Transfer (SPLET), which adds to the kinetics of single-step Hydrogen Atom Transfer (HAT)/Proton Coupled Electron Transfer (PCET) processes (see Acc. Chem. Res. 2007, 40 , 222.). The domination of SPLET over HAT/PCET in case of a flavonoid reacting with electron-deficient radicals such as peroxyls or dpph(*) in polar solvents explains the enhancement of antioxidant activity of 3-hydroxyflavone. It also elucidates the great acceleration in the reactions of dpph(*) with quercetin, morin, galangin, and 7,8-dihydroxyflavone. The analysis of structure-acidity and structure-activity relationships for 10 flavonoids clearly indicates that hydroxyl group at position 7 is the most acidic site. Thus, in polar solvents this group can participate in radical reaction via SPLET. In nonpolar solvents the most active site in quercetin (a flavonoid antioxidant commonly found in plants) is 3,4-dihydroxyl moiety and HAT/PCET occurs. However, in ionization-supporting solvents an anion formed at position 7 is responsible for very fast kinetics of quercetin/dpph(*) reaction because both mechanisms participate: HAT (from catechol moiety in ring B) and SPLET (from ionized 7-hydroxyl in ring A). Because of conjugation of rings A, B, and C the final structure of the formed quercetin radical (or quercetin anion radical) is the same for the SPLET and HAT/PCET mechanisms.

Cosmic recall and the scattering picture of loop quantum cosmology

The global dynamics of a homogeneous Universe in loop quantum cosmology is viewed as a scattering process of its geometrodynamical equivalent. This picture is applied to build a flexible (easy to generalize) and not restricted just to exactly solvable models method of verifying the preservation of the semiclassicality through the bounce. The devised method is next applied to two simple examples: (i) the isotropic Friedmann-Robertson-Walker universe, and (ii) the isotropic sector of the Bianchi I model. For both of them we show that the dispersions in the logarithm of the volume ln(v) and scalar field momentum ln(p{sub {phi}}) in the distant future and past are related via strong triangle inequalities. This implies, in particular, a strict preservation of the semiclassicality (in considered degrees of freedom) in both the cases (i) and (ii). Derived inequalities are general: valid for all the physical states within the considered models.

Quantum constraints, Dirac observables and evolution: group averaging versus the Schrödinger picture in LQC

A general quantum constraint of the form (realized in particular in loop quantum cosmology models) is studied. Group averaging is applied to define the Hilbert space of solutions and the relational Dirac observables. Two cases are considered. In the first case, the spectrum of the operator is assumed to be discrete. The quantum theory defined by the constraint takes the form of a Schrodinger-like quantum mechanics with a generalized Hamiltonian . In the second case, the spectrum is absolutely continuous and some peculiar asymptotic properties of the eigenfunctions are assumed. The resulting Hilbert space and the dynamics are characterized by a continuous family of the Schrodinger-like quantum theories. However, the relational observables mix different members of the family. Our assumptions are motivated by new loop quantum cosmology models of quantum FRW spacetime. The two cases considered in this paper correspond to the negative and positive cosmological constant, respectively. Our results should also be applicable in many other general relativistic contexts.

Excess Molar Volumes for Binary Mixtures of 1-Alkanol and 1-Alkene. III. The System 1-Hexanol + 1-Alkene at 25°C

Excess molar volumes, VE, are reported for binary mixtures of 1-hexanol with the homologous C6, C7, C8, and C10 1-alkenes at 25°C. In this series of mixtures, the VE values vary as a function of mole fraction from positive–negative “sigmoid” shaped curves exhibiting a very small positive lobe in the dilute alkanol region for the shortest chain 1-alkene to positive values over the whole concentration range for the longer chain 1-alkene. The partial molar excess volumes, ViE, were calculated for the components over the whole concentration range. The partial molar volume of 1-hexanol in the 1-hexene system shows a large and sharp minimum and in the 1-decene system is positive over the whole concentration range. The modified model [Treszczanowicz et al., J. Solution Chem.31, 455 (2002) originally proposed by Treszczanowicz and Benson Fluid Phase Equilibr.23, 117 (1985)] was used for the interpretation and prediction of the reported data. The model describes qualitatively the variation of VE with the length of the molecule and concentration as a result of superposition of the contributions of association, free volume, and nonspecific interactions.

Inflation from non-minimally coupled scalar field in loop quantum cosmology

The FRW model with non-minimally coupled massive scalar field has been investigated in LQC framework. Considered form of the potential and coupling allows applications to Higgs driven inflation. Out of two frames used in the literature to describe such systems: Jordan and Einstein frame, the latter one is applied. Specifically, we explore the idea of the Einstein frame being the natural environment for quantization and the Jordan picture having an emergent nature. The resulting dynamics qualitatively modifies the standard bounce paradigm in LQC in two ways: (i) the bounce point is no longer marked by critical matter energy density, (ii) the Planck scale physics features the mexican hat trajectory with two consecutive bounces and rapid expansion and recollapse between them. Furthermore, for physically viable coupling strength and initial data the subsequent inflation exceeds 60 e-foldings.

A new calix[4]arene derivative and its ionic recognition for silver(I) and mercury(II): the solvent effect

A new lower rim partially functionalized calix[4]arene, namely, 5,11,17,23-tetra-tert-butyl[25,27-bis(diethylthiocarbamoyl)oxy]calix[4]arene, 1 was synthesized and characterized by 1H NMR in different deuterated solvents to assess the degree of solvent–ligand interactions and the conformation of 1 in solution. 1H NMR, conductometric and thermodynamic investigations reveal that this receptor interacts only with silver(I) and mercury(II) in dipolar aprotic media. The complexation process has been thermodynamically characterized and the results are compared with the corresponding data (when available) involving analogous ligands and these metal cations in the appropriate solvent. Emphasis is made on the difference between ‘selective extraction’ and ‘selective ionic recognition’ by receptors. Final conclusions are given.

Singularity resolution from polymer quantum matter

We study the polymeric nature of quantum matter fields using the example of a Friedmann-Lemaitre-Robertson-Walker universe sourced by a minimally coupled massless scalar field. The model is treated in the symmetry reduced regime via deparametrization techniques, with the scale factor playing the role of time. Subsequently, the remaining dynamic degrees of freedom corresponding to the matter are polymer quantized. The analysis of the resulting genuine quantum dynamic shows that the big bang singularity is resolved, although with the form of the resolution differing significantly from that in the models with matter clocks: dynamically, the singularity is made passable rather than avoided. Furthermore, this analysis exposes crucial limitations to the so-called effective dynamic in loop quantum cosmology when applied outside of the most basic isotropic settings.

Observations on interfacing loop quantum gravity with cosmology

A simple idea of relating the loop quantum gravity (LQG) and loop quantum cosmology (LQC) degrees of freedom is introduced and used to define a relatively robust interface between these theories in context of toroidal Bianchi I model. The idea is an expansion of the construction originally introduced by Ashtekar and Wilson-Ewing and relies on explicit averaging of a certain subclass of spin networks over the subgroup of the diffeomorphisms remaining after the gauge fixing used in homogeneous LQC. It is based on the set of clearly defined principles and thus is a convenient tool to control the emergence and behavior of the cosmological degrees of freedom in studies of dynamics in canonical LQG. The constructed interface is further adapted to isotropic spacetimes. Relating the proposed LQG-LQC interface with some results on black hole entropy suggests a modification to the area gap value currently used in LQC.

A computable framework for Loop Quantum Gravity

We present a non-perturbative quantization of general relativity coupled to dust and other matter fields. The dust provides a natural time variable, leading to a physical Hamiltonian with spatial diffeomorphism symmetry. The methods of loop quantum gravity applied to this model lead to a physical Hilbert space and Hamiltonian. This provides a framework for physical calculations in the theory.

Dust time in quantum cosmology

We give a formulation of quantum cosmology with a pressureless dust and arbitrary additional matter fields. The dust provides a natural time gauge corresponding to a cosmic time, yielding a physical time independent Hamiltonian. The approach simplifies the analysis of both Wheeler-deWitt and loop quantum cosmology models, broadening the applicability of the latter.