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New Sensitizers Developed on a Methylpheophorbide a Platform for Photodynamic Therapy: Synthesis, Singlet Oxygen Generation and Modeling of Passive Membrane Transport
摘要： This study focuses on the behavior of new potential sensitizers for photodynamic therapy of cancer developed on a chlorophyll a platform. Pheophorbide a 17-(3) methylester and its two glycol derivatives have been synthesized from chlorophyll and identified via visible, UV-, NMR- and MS-spectra. The behavior of photosensitizers in solutions has been studied with various experimental techniques. They are found to generate singlet oxygen with a sufficient quantum yield and reveal a tendency to effectively penetrate into cell membranes due to high lipophilicity. Thermodynamic analysis indicates that the sensitizer transfer from a water-like to a lipid-like medium is controlled by a large and negative enthalpic term excepting the case of the most polar solute, where for phosphate saline buffer the favorable entropic term dominates. Our study highlights the important feature dealing with the temperature dependence of partition coefficients between saline buffer and 1-octanol which is found to be surprisingly strong for hydrophobic solutes and temperature independent for the species containing both H-donor and H-acceptor groups.
关键词： Hydrophobicity,Photosensitizers,Photodynamic therapy,Thermodynamics of solvation,Partition coefficients,Reactive oxygen species
更新于2025-09-09 09:28:46
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Three in one: Mesogenic aromatic acid as a liquid crystal matrix, a chiral dopant in liquid crystals and a stabilizer for nanoparticles
摘要： Studies of thermodynamics of the N*-I phase transitions and optical properties of the new liquid crystal - (R)-2-[4”-(trans-4-butylcyclohexyl)-2’-chloro-p-terphenyl-4-oxy) propanoic acid are carried out. The aim of these studies is to analyse the capabilities of that liquid crystal to simultaneously serve as a matrix for inorganic semiconductor nanoparticles (NP) as well as a chiral dopant for liquid crystals and a chiral ligand stabilizing the surface of CdSe NPs. The chiral doping of a nematic liquid crystal was proven by the measurements of selective transmittance of the visible light. The embedding of NPs in a nematic liquid crystal leads to the increase in TN*I, which is explained by the shape anisotropy of the NPs. The anisotropy of the ligand shell may result from the interaction between the ligand and LC matrix inducing the change of the spherical shape of the shell toward the ellipsoidal one. TN*I of the liquid crystal matrix of (R)-2-[4”-(trans-4-butylcyclohexyl)-2’-chloro-p-terphenyl-4-oxy) propanoic acid (R-MPA) decreases with the embedding of NPs stabilized by the same ligands, which is in a good agreement with prior experimental results and theory, but there exists a considerable quantitative difference.
关键词： optical properties,liquid crystal,thermodynamics,nanoparticles,chiral dopant
更新于2025-09-09 09:28:46
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Phonon thermodynamics and elastic behavior of GaN at high temperatures and pressures
摘要： The effects of temperature and pressure on the phonons of GaN were calculated for both the wurtzite and zinc-blende structures. The quasiharmonic approximation (QHA) gave reasonable results for the temperature dependence of the phonon DOS at zero pressure but unreliably predicted the combined effects of temperature and pressure. Pressure was found to change the explicit anharmonicity, altering the thermal shifts of phonons and more notably qualitatively changing the evolution of phonon lifetimes with increasing temperature. These effects were largest for the optical modes, and phonon frequencies below approximately 5 THz were adequately predicted with the QHA. The elastic anisotropies of GaN in both wurtzite and zinc-blende structures were calculated from the elastic constants as a function of pressure at 0 K. The elastic anisotropy increased with pressure until reaching elastic instabilities at 40 GPa (zinc blende) and 65 GPa (wurtzite). The calculated instabilities are consistent with proposed transformation pathways to rocksalt GaN and place upper bounds on the pressures at which wurtzite and zinc-blende GaN can be metastable.
关键词： phonon thermodynamics,high pressures,elastic anisotropy,anharmonicity,high temperatures,GaN,elastic behavior,quasiharmonic approximation
更新于2025-09-09 09:28:46
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Solar plant with short diffuser concept: Further improvement of numerical model by included influence of guide vane topology on shape and stability of gravitational vortex
摘要： An alternative renewable energy concept, i.e. the concept of a solar power plant with short diffuser (SPD), was numerically investigated by more advanced computational fluid dynamics (CFD) model. Developed model is characterized by a more sophisticated and streamlined guide vane topology. The main novelty of this work is conducted optimization of the guide vane topology, for a specific novel application related to the alternative renewable energy concept (SPD). Optimization involved determining the required guide vane topology using minimal number of geometry influencing parameters. The objective was to result in vortex genesis and stabilization with respect to the desired circumferential velocity and to minimize the required pressure potential that is necessary for stable operation of the SDP plant. Provided numerical investigation was necessary, and for sure a step forward towards consideration of the experimental plant (which will assume introduction of the turbines). It needs to be taken into account that we deal with complex flow structure that requires gradual numerical investigation, in order to be able to get detail insight in the various influences and processes that can strongly affect SPD operating parameters. The guide vane topology was altered to develop an SPD capable of establishing and maintaining a stable gravitational vortex in pressure ranges which resemble atmospheric vortex phenomena (feasible for development of a compact system, and with maximal velocities in chimney throat regions below 20 m s?1). The study outlines nine cases, each representing the altered guide vane design, where the best case is determined and compared with the available experimental data from other research groups. The comparison indicates that the numerical model, although quite simple, is accurate and robust in predicting the distribution of local velocity and pressure profiles and fit for implementation on wind turbines in order to determine the influence of the installed turbines on the vortex shape and stability in a future study. An important finding is that the swirl ratio can be manipulated by altering the guide vane shape, and it is independent of the Reynolds number (which will be important during the design phase since it can be used as a control strategy for vortex genesis and as a prevention of unintentional genesis regarding additional multiple vortices). The gained numerical results revealed specific operating conditions that will ensure a safer environment around the SPD and that will enable a carbon free electricity production.
关键词： Solar power plant,Numerical modelling,Carbon-free electricity production,Thermodynamics,Vortices,Solar energy
更新于2025-09-04 15:30:14
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Ab initio-Based Approach to N-pair Formation on GaAs(001)-(2^|^times;4) Surfaces
摘要： Nitrogen{pair formation processes on the GaAs(001)-(2×4) surfaces found experimentally are systematically investigated using ab initio-based approach incorporating beam equivalent pressure p (pAs = 3:0 × 10?6 Torr, pN = 7:0 × 10?6 Torr) and temperature T = 830 K. The calculated surface phase diagrams elucidates that the (2×4)α1 and (2×4)α2 surfaces are stable at the growth conditions under As2 and As4, respectively. The Monte Carlo simulations reveal that the N incorporation on the (2×4)α1 and (2×4)α2 surfaces proceeds with increase of energetically favorable Ga{N bonds in the third layer via series of events such as adsorption of N{As dimer, substitution of N for As located in the third layer, and As dimer desorption to form the N{pair in the third layer. It is also found that the probability of the N{pair formation on the (2×4)α1 surface is much larger than that on the (2×4)α2 surface. This is because the strain around the N{pair on the (2×4)α1 surface is smaller than that on the (2×4)α2 surface where N{As surface dimer is formed to relax the larger strain. Furthermore, the N{pair formation probabilities P under As2 and As4 are estimated as a function of temperature including (2×4)β1. N atoms incorporated on the GaAs(001) surface can form N{pair along [110] with P ～ 0:8 on the surface with two phase mixture of (2×4)α1 and (2×4)α2 at T = 830 K under As2 and As4.
关键词： Gallium arsenide,Surface thermodynamics,Nitrogen molecule,Ab initio quantum chemical methods and calculations
更新于2025-09-04 15:30:14