Calculation Of Free Energy Changes Research Articles

Exploring the underlying oxygen reduction reaction electrocatalytic activities of pyridinic-N and pyrrolic-N doped graphene quantum dots

In this study, density functional theory was used to investigate the differences of oxygen reduction reaction catalytic activities between pyridinic-N and pyrrolic-N doped graphene quantum dots (GQDs) and the influence of four ions/groups: OH–, H3O+, OH and H3O on their electronic properties. Free energy change calculations show that pyridinic-N doped GQDs (pN-GQDs) have better catalytic activities than pyrrolic-N doped GQDs (prN-GQDs). Moreover, the catalytic activity of both pN-GQDs and prN-GQDs can be enhanced via the functionalization of OH and H3O groups, which greatly alters electronic structures of the GQDs and thereby the adsorption strength of reactants can be effectively controlled. The findings can shed light on the effects of different N doping configurations and adsorbed species on electrocatalytic activities and provide theoretical guidelines for design and development of carbon-based oxygen reduction reaction electrocatalysts for fuel cells and metal-air batteries.

Potential dual inhibition of SE and CYP51 by eugenol conferring inhibition of Candida albicans: Computationally curated study with experimental validation

Ergosterol is the key sterol component in the cell membrane of fungi including moulds and yeasts. Any decrease in the levels of ergosterol in the cell membrane of fungi render them venerable to cell membrane damage and even its death. Majority of antifungal drug targets the key enzymes involved in ergosterol biosynthesis pathway. The biochemical pathway for the synthesis of Ergosterol is a complex one, though the reactions carried by Squalene Epoxidase (SE) and 14α-demethylase (CYP51- a member of Cytochrome P450 family) serves to the key rate limiting reactions that can impact the overall production of Ergosterol. Allylamines class of antifungal drug target SE while Azoles target the CYP51. Currently advancement in the drug development is focused to introduce newer drugs that can simultaneously inhibit both this rate limiting enzymes. However, natural compounds established to possess antifungal activity but the major loophole about their understanding lies in the fact that their mode of action are severely unstudied. One such well-established antifungal natural phytochemical is Eugenol, and in current manuscript we investigated its efficacy to interact with both, SE and CYP51 of Candida albicans using molecular Docking, Free energy change calculations and Molecular Dynamics (MD) simulation, showing promising outcomes. For experimental studies, terbinafine, clotrimazole and eugenol showed 4 μg/ml, 2 μg/ml, and 512 μg/ml MIC90 values, respectively against C. albicans and also showed reduction in Ergosterol production at sub-MIC levels. The obtained result indicates the involvement of eugenol in the inhibition of enzymes require in the ergosterol biosynthesis pathway.

Benzylidene ketones as visible light radical photoinitiator: The effects of electron-donating group and co-initiator

Benzylidene ketones (BK) are promising visible photoinitiator due to their facile synthesis and photochemical hydrogen atom transfer (HAT) reaction between tertiary amines. However, the effect of electron donating (ED) groups on their photophysical, electrochemical properties, and initiation efficiency were not fully disclosed. Moreover, it is not clear which co-initiator is suitable for BK. In this work, four benzylidene ketones bearing hydrogen (C3PH), methoxy (C3PO), methylthio (C3PS), and dimethylamine (C3PN) substitution were synthesized and characterized. BK’s maximum light absorption wavelengths increase following the order of C3PH < C3PO < C3PS < C3PN. Photopolymerization and steady state photolysis show that only C3PO and C3PS display higher HAT efficiency than C3PH, which is highly relating to the free energy change calculations results. Overall, C3PO is the most efficient one because good polymerization rate and final monomer conversion can be achieved. Triethanolamine is the best co-initiator because of its low oxidation potential and the lowest energy barrier to form a complex with C3PO.

Thermodynamics of iron reduction from oxides by hydrogen at different ratio of the oxide and reducing agent

The results of calculation of the standard Gibbs free energy of the reactions of iron oxides reduction by hydrogen at different oxide to reductant ratios in the temperature range of 900-1600 K are presented in this paper. The calculation is based on the principle of independence of the reactions in the system. It is shown that if iron (III) oxide is taken, then at 1:3 oxide to hydrogen ratio the equilibrium position in the indicated temperature range is shifted to the right, and the reaction product is iron. The production of iron from iron (II, III) oxide is possible at 1:4 oxide to hydrogen ratio and temperatures above 1200 K. Iron can be obtained from oxygen-rich w&uuml;stite at temperatures higher than 1400 K. The standard Gibbs free energy change calculations of oxygen-poor w&uuml;stite with hydrogen reaction show that the equilibrium position is shifted to the left, to the reactant side. A shift of the equilibrium position to the right can be achieved at high hydrogen to water ratio in the gas phase. Iron can interact with iron oxides Fe2O3, Fe3O4, FeO(1+x"), as a result, the reaction products are Fe3O4, FeO(1+x"), FeO(1+x'). Thermodynamic calculations indicate that iron oxides FeO(1+x") and FeO(1+x'), in turn, can interact with Fe2O3 to form Fe3O4, and Fe3O4 can interact with FeO(1+x') to form FeO(1+x"). Thus, the overall process of the reduction of iron from oxides by hydrogen is proposed to be considered as a sequential reduction of iron from oxides containing iron of different oxidation states, from Fe (III) to Fe (II).

An arginine residue in the outer segment of hASIC1a TM1 affects both proton affinity and channel desensitization.

Acid-sensing ion channels (ASICs) respond to changes in pH in the central and peripheral nervous systems and participate in synaptic plasticity and pain perception. Understanding the proton-mediated gating mechanism remains elusive despite the of their structures in various conformational states. We report here that R64, an arginine located in the outer segment of the first transmembrane domain of all three isoforms of mammalian ASICs, markedly impacts the apparent proton affinity of activation and the degree of desensitization from the open and preopen states. Rosetta calculations of free energy changes predict that substitutions of R64 in hASIC1a by aromatic residues destabilize the closed conformation while stabilizing the open conformation. Accordingly, F64 enhances the efficacy of proton-mediated gating of hASIC1a, which increases the apparent pH50 and facilitates channel opening when only one or two subunits are activated. F64 also lengthens the duration of opening events, thus keeping channels open for extended periods of time and diminishing low pH-induced desensitization. Our results indicate that activation of a proton sensor(s) with pH50 equal to or greater than pH 7.2-7.1 opens F64hASIC1a, whereas it induces steady-state desensitization in wildtype channels due to the high energy of activation imposed by R64, which prevents opening of the pore. Together, these findings suggest that activation of a high-affinity proton-sensor(s) and a common gating mechanism may mediate the processes of activation and steady-state desensitization of hASIC1a.

Free Radical Photopolymerization and 3D Printing Using Newly Developed Dyes: Indane-1,3-Dione and 1H-Cyclopentanaphthalene-1,3-Dione Derivatives as Photoinitiators in Three-Component Systems

The design of photoinitiating systems with excellent photochemical reactivities at 405nm LED is one of the obstacles to efficiently promote free radical polymerization in mild conditions (e.g., low light intensity, under air). Here, our actual search for new multicomponent photoinitiating systems at 405nm LED prompts us to develop new dyes based on push–pull structures. In the present paper, we chose two series of new dyes which possess indane-1,3-dione and 1H-cyclopenta naphthalene-1,3-dione groups as the electron-withdrawing groups, since they have the great potential to behave as sensitive and remarkable photoinitiators in vat photopolymerization/3D printing. When incorporated with a tertiary amine (ethyl dimethylaminobenzoate EDB, used as electron/hydrogen donor) and an iodonium salt (used as electron acceptor) as the three-component photoinitiating systems (PISs), and among a series of 21 dyes, 10 of them could efficiently promote the free radical photopolymerization of acrylates. Interestingly, steady state photolysis experiments revealed different behaviors of the dyes. Fluorescence experiments and free energy change calculations for redox processes were also carried out to investigate the relevant chemical mechanisms. Additionally, the formation of radicals from the investigated PISs was clearly observed by electron spin resonance (ESR) spin-trapping experiments. Finally, stereoscopic 3D patterns were successfully fabricated by the laser writing technique. In this work, the use of push–pull dyes based on the naphthalene scaffold as photoinitiators of polymerization is reported for the first time in a systematic study aiming at investigating the structure–performance relationship for irradiation carried out at 405 nm. By carefully selecting the electron donors used in the two series of push–pull dyes, novel and high-performance photoinitiating systems operating at 405 nm are thus proposed.

Mineralization versus fermentation: evidence for two distinct anaerobic bacterial degradation pathways for dichloromethane.

Dichloromethane (DCM) is an anthropogenic pollutant with ozone destruction potential that is also formed naturally. Under anoxic conditions, fermentation of DCM to acetate and formate has been reported in axenic culture Dehalobacterium formicoaceticum, and to acetate, H2 and CO2 in mixed culture RM, which harbors the DCM degrader 'Candidatus Dichloromethanomonas elyunquensis'. RM cultures produced 28.1 ± 2.3 μmol of acetate from 155.6 ± 9.3 μmol DCM, far less than the one third (i.e., about 51.9 µmol) predicted based on the assumed fermentation model, and observed in cultures of Dehalobacterium formicoaceticum. Temporal metabolite analyses using gas chromatography-mass spectrometry (GC-MS) and nuclear magnetic resonance (NMR) spectroscopy revealed that no 13C-labeled acetate was formed in 13C-DCM-grown RM cultures, indicating acetate was not a direct product of DCM metabolism. The data were reconciled with DCM mineralization and H2 consumption via CO2 reduction to acetate and methane by homoacetogenic and methanogenic partner populations, respectively. In contrast, Dehalobacterium formicoaceticum produced 13C-labeled acetate and formate from 13C-DCM, consistent with a fermentation pathway. Free energy change calculations predicted that organisms with the mineralization pathway are the dominant DCM consumers in environments with H2 <100 ppmv. These findings have implications for carbon and electron flow in environments where DCM is introduced through natural production processes or anthropogenic activities.

Accurate Calculation of Free Energy Changes upon Amino Acid Mutation.

Molecular dynamics based free energy calculations allow for a robust and accurate evaluation of free energy changes upon amino acid mutation in proteins. In this chapter we cover the basic theoretical concepts important for the use of calculations utilizing the non-equilibrium alchemical switching methodology. We further provide a detailed step-by-step protocol for estimating the effect of a single amino acid mutation on protein thermostability. In addition, the potential caveats and solutions to some frequently encountered issues concerning the non-equilibrium alchemical free energy calculations are discussed. The protocol comprises details for the hybrid structure/topology generation required for alchemical transitions, equilibrium simulation setup, and description of the fast non-equilibrium switching. Subsequently, the analysis of the obtained results is described. The steps in the protocol are complemented with an illustrative practical application: a destabilizing mutation in the Trp cage mini protein. The concepts that are described are generally applicable. The shown example makes use of the pmx software package for the free energy calculations using Gromacs as a molecular dynamics engine. Finally,we discuss how the current protocol can readily be adapted to carry out charge-changing or multiple mutations at once, as well aslarge-scale mutational scans.

Calculation of free energy changes due to mutations from alchemical free energy simulations

How a mutation affects the binding free energy of a ligand is a fundamental problem in molecular biology/biochemistry with many applications in pharmacology and biotechnology, e.g. design of drugs and enzymes. Free energy change due to a mutation can be determined most accurately by performing alchemical free energy calculations in molecular dynamics (MD) simulations. Here we discuss the necessary conditions for success of free energy calculations using toxin peptides that bind to ion channels as examples. We show that preservation of the binding mode is an essential requirement but this condition is not always satisfied, especially when the mutation involves a charged residue. Otherwise problems with accuracy of results encountered in mutation of charged residues can be overcome by performing the mutation on the ligand in the binding site and bulk simultaneously and in the same system. The proposed method will be useful in improving the affinity and selectivity profiles of drug leads and enzymes via computational design and protein engineering.

Combine umbrella sampling with integrated tempering method for efficient and accurate calculation of free energy changes of complex energy surface.

Umbrella sampling is an efficient method for the calculation of free energy changes of a system along well-defined reaction coordinates. However, when there exist multiple parallel channels along the reaction coordinate or hidden barriers in directions perpendicular to the reaction coordinate, it is difficult for conventional umbrella sampling to reach convergent sampling within limited simulation time. Here, we propose an approach to combine umbrella sampling with the integrated tempering sampling method. The umbrella sampling method is applied to chemically more relevant degrees of freedom that possess significant barriers. The integrated tempering sampling method is used to facilitate the sampling of other degrees of freedom which may possess statistically non-negligible barriers. The combined method is applied to two model systems, butane and ACE-NME molecules, and shows significantly improved sampling efficiencies as compared to standalone conventional umbrella sampling or integrated tempering sampling approaches. Further analyses suggest that the enhanced performance of the new method come from the complemented advantages of umbrella sampling with a well-defined reaction coordinate and integrated tempering sampling in orthogonal space. Therefore, the combined approach could be useful in the simulation of biomolecular processes, which often involves sampling of complex rugged energy landscapes.

Modified Amber Force Field Correctly Models the Conformational Preference for Tandem GA pairs in RNA.

Molecular mechanics with all-atom models was used to understand the conformational preference of tandem guanine-adenine (GA) noncanonical pairs in RNA. These tandem GA pairs play important roles in determining stability, flexibility, and structural dynamics of RNA tertiary structures. Previous solution structures showed that these tandem GA pairs adopt either imino (cis Watson–Crick/Watson–Crick A-G) or sheared (trans Hoogsteen/sugar edge A-G) conformations depending on the sequence and orientation of the adjacent closing base pairs. The solution structures (GCGGACGC)2 [Biochemistry, 1996, 35, 9677–9689] and (GCGGAUGC)2 [Biochemistry, 2007, 46, 1511–1522] demonstrate imino and sheared conformations for the two central GA pairs, respectively. These systems were studied using molecular dynamics and free energy change calculations for conformational changes, using umbrella sampling. For the structures to maintain their native conformations during molecular dynamics simulations, a modification to the standard Amber ff10 force field was required, which allowed the amino group of guanine to leave the plane of the base [J. Chem. Theory Comput., 2009, 5, 2088–2100] and form out-of-plane hydrogen bonds with a cross-strand cytosine or uracil. The requirement for this modification suggests the importance of out-of-plane hydrogen bonds in stabilizing the native structures. Free energy change calculations for each sequence demonstrated the correct conformational preference when the force field modification was used, but the extent of the preference is underestimated.

3P110 Calculation of free energy changes due to charged residues mutation from alchemical free energy calculations:Improving toxins selectivity(03. Membrane proteins,Poster,The 52nd Annual Meeting of the Biophysical Society of Japan(BSJ2014))

3P110 Calculation of free energy changes due to charged residues mutation from alchemical free energy calculations:Improving toxins selectivity(03. Membrane proteins,Poster,The 52nd Annual Meeting of the Biophysical Society of Japan(BSJ2014))

DFT-based inhibitor and promoter selection criteria for pentagonal dodecahedron methane hydrate cage

Density functional theory (DFT)-based simulations have been performed to provide electronic structure property correlation based reasoning for conceptualizing the effect of encapsulated methane molecule on the formation of methane hydrate cages, the role of methanol and ethylene glycol as inhibitor and the role of tetra-hydro-furan (THF) and cyclopentane as promoter of methane hydrate. Geometry optimization of 512 cage, 51262 cage and 51264 cage with and without encapsulated methane and the cluster of 512 cage with ethylene glycol, methanol, cyclopentane have been performed by density functional theory using ωB97X-D/6-31+ +G(d,p) method. Methane hydrate formation inhibition by methanol and ethylene glycol as well as methane hydrate stabilization by cyclopentane and tetrahydrofuran are critically analysed based on the interaction energy, free energy change, dipole moment and infrared frequency calculation. Calculation of free energy change for formation of methane hydrate with/without reagents at various temperature and pressure using optimized structure is reported here. It is observed that hydrogen bond between water molecules of clathrate 512 cages become stronger in the presence of cyclopentane and tetrahydrofuran but weaker/broken in the presence of ethylene glycol and methanol. Simulated results correspond well with experimental findings and can be useful for designing new inhibitor and promoter molecules for gas hydrate formation. DFT studies have been performed to show the effect of some inhibitor and promoter molecules on pentagonal dodecahedron methane hydrate cage (1CH4@512) structures and electronic properties. It illustrates scientifically the role of promoter (e.g., cyclopentane) and inhibitor (e.g., methanol) on stability and formation possibility of (1CH4@512).

Structures and Free Energy Landscapes of the Wild-Type and A30P Mutant-Type α-Synuclein Proteins with Dynamics

The genetic missense A30P mutation of the wild-type α-synuclein protein results in the replacement of the 30th amino acid residue from alanine (Ala) to proline (Pro) and was initially found in the members of a German family who developed Parkinson's disease. Even though the structures of these proteins have been measured before, detailed understanding about the structures and their relationships with free energy landscapes is lacking, which is of interest to provide insights into the pathogenic mechanism of Parkinson's disease. We report the secondary and tertiary structures and conformational free energy landscapes of the wild-type and A30P mutant-type α-synuclein proteins in an aqueous solution environment via extensive parallel tempering molecular dynamics simulations along with thermodynamic calculations. In addition, we present the residual secondary structure component transition stabilities at the atomic level with dynamics in terms of free energy change calculations using a new strategy that we reported most recently. Our studies yield new interesting results; for instance, we find that the A30P mutation has local as well as long-range effects on the structural properties of the wild-type α-synuclein protein. The helical content at Ala18-Gly31 is less prominent in comparison to the wild-type α-synuclein protein. The β-sheet structure abundance decreases in the N-terminal region upon A30P mutation of the wild-type α-synuclein, whereas the NAC and C-terminal regions possess larger tendencies for β-sheet structure formation. Long-range intramolecular protein interactions are less abundant upon A30P mutation, especially between the NAC and C-terminal regions, which is linked to the less compact and less stable structures of the A30P mutant-type rather than the wild-type α-synuclein protein. Results including the usage of our new strategy for secondary structure transition stabilities show that the A30P mutant-type α-synuclein tendency toward aggregation is higher than the wild-type α-synuclein but we also find that the C-terminal and NAC regions of the A30P mutant-type α-synuclein are reactive toward fibrillzation and aggregation based on atomic level studies with dynamics in an aqueous solution environment. Therefore, we propose that small molecules or drugs blocking the specific residues, which we report herein, located in the NAC- and C-terminal regions of the A30P mutant-type α-synuclein protein might help to reduce the toxicity of the A30P mutant-type α-synuclein protein.

Identification of Novel Targets for miR-29a Using miRNA Proteomics

MicroRNAs (miRNAs) are short regulatory RNA molecules that interfere with the expression of target mRNA by binding to complementary sequences. Currently, the most common method for identification of targets of miRNAs is computational prediction based on free energy change calculations, target site accessibility and conservation. Such algorithms predict hundreds of targets for each miRNA, necessitating tedious experimentation to identify the few functional targets. Here we explore the utility of miRNA-proteomics as an approach to identifying functional miRNA targets. We used Stable Isotope Labeling by amino acids in cell culture (SILAC) based proteomics to detect differences in protein expression induced by the over-expression of miR-34a and miR-29a. Over-expression of miR-29a, a miRNA expressed in the brain and in cells of the blood lineage, resulted in the differential expression of a set of proteins. Gene Ontology based classification showed that a significant sub-set of these targets, including Voltage Dependent Anion Channel 1 and 2 (VDAC1 and VDAC2) and ATP synthetase, were mitochondrial proteins involved in apoptosis. Using reporter assays, we established that miR-29a targets the 3′ Untranslated Regions (3′ UTR) of VDAC1 and VDAC2. However, due to the limited number of proteins identified using this approach and the inability to differentiate between primary and secondary effects we conclude that miRNA-proteomics is of limited utility as a high-throughput alternative for sensitive and unbiased miRNA target identification. However, this approach was valuable for rapid assessment of the impact of the miRNAs on the cellular proteome and its biological role in apoptosis.

The Synthesis of Eu3+Doped with TiO2Nano-Powder and Application as a Pesticide Sensor

Using tetrabutyl titanate as precursor, <TEX>$Eu^{3+}$</TEX> doped <TEX>$TiO_2$</TEX> nano-powder was prepared by sol-gel method, the nature of luminescence of nano-powder was studied. The interaction of chlorpyrifos with <TEX>$Eu^{3+}$</TEX> doped <TEX>$TiO_2$</TEX> was studied by absorption and fluorescence spectroscopy. The results indicated the fluorescence intensity of <TEX>$Eu^{3+}$</TEX> doped <TEX>$TiO_2$</TEX> was quenched by chlorpyrifos and the quenching rate constant (<TEX>$k_q$</TEX>) was <TEX>$1.24{\times}10^{11}\;L/mol{\cdot}s$</TEX> according to the Stern-Volmer equation. The dynamics of photoinduced electron transfer from chlorpyrifos to conduction band of <TEX>$TiO_2$</TEX> nanoparticle was observed and the mechanism of electron transfer had been confirmed by the calculation of free energy change (<TEX>${\Delta}G_{et}$</TEX>) by applying Rehm-Weller equation as well as energy level diagram. A new rapid method for detection of chlorpyrifos was established according to the fluorescence intensity of <TEX>$Eu^{3+}$</TEX> doped <TEX>$TiO_2$</TEX> was proportional to chlorpyrifos concentration. The range of detection was <TEX>$5.0{\times}10^{-10}-2.5{\times}10^{-7}mol/L$</TEX> and the election limit (<TEX>$3{\sigma}$</TEX>) was <TEX>$3.2{\times}10^{-11}$</TEX> mol/L.

A short review and an empirical method for estimating the absorbed enthalpy of formation and the absolute enthalpy of dried microbial biomass for use in studies on the thermodynamics of microbial growth

The equation DrX = DrH - DrQ represents a calculated free-energy change when the exchange of absor- bed thermal energy in a chemical system represented by TDrS in the Gibbs free-energy equation is replaced by DrQ. The symbol Q is used in place of H (enthalpy = HT - H0 = HT) to represent absorbed thermal energy. Acquiring the experimental data for determining both S and Q requires the use of a low-temperature calorimeter to measure Cp as a function of T/K and these are not generally available. In a previous study it was demonstrated that for one unit-carbon formula dry weight of cells, DfSbiomass =- 0.813 P Satoms and Sbiomass = 0.187 P Satoms, where P Satoms represents the sum of the entropies of the numbers and kinds of atoms in the biomass. Using similar techniques, it is shown here that DfQbiomass =- 0.648 P Qatoms and that Qbiomass = 0.352 P Qatoms, where P Qatoms represents the sum of the absorbed thermal energies of the numbers and kinds of atoms in the biomass. Because mathematically the value of TS for solid substances is twice that of Q for the same T/K (usually ref- erenced at 298.15 K), one of these values must be physically incorrect. There cannot be two different values for the quantity of thermal energy which must be absorbed to raise the temperature of the same quantity of the same substance from 0 K to a given temperature. The argument is made that the use of Q is preferable to the use of S in the calculation of free-energy changes.

Single Ion and Dimerization Studies of the Al(III) Ion in Aqueous Solution

Aqueous trivalent aluminum (Al) ions and their oligomers play important roles in diverse areas, such as environmental sciences and medicine. The geometries of octahedral Al(H(2)O)(6)(3+) and tetrahedral Al(OH)(4)(-) species have been studied extensively. However, structures of intermediate hydrolysis products of the Al(III) ion, such as the penta-coordinated Al(OH)(2+) species, which exists at pH values ranging from 3.0 to 4.3, and their mode of formation have been poorly understood. Here, we present that a trigonal bipyramidal Al(OH)(H(2)O)(4)(2+) structure is formed in aqueous solution and how this monomeric species dimerizes to a dinuclear [(H(2)O)(4)Al(OH)(2)Al(H(2)O)(4)](4+) complex in aqueous solution. The Gibbs free energy change calculations indicate that the formation of the dinuclear complex is preferred over the existence of two single trigonal bipyramidal Al(OH)(H(2)O)(4)(2+) species in aqueous solution. This study captures the solution dynamics and proton transfer in the oligomerization reactions of penta-coordinated Al(OH)(2+) species in aqueous solution.

Fluorescence Quenching of Phycoerythrin by Anthraquinone Dyes

Abstract Fluorescence quenching of phycoerythrin (PE) by a series of anthraquinone dyes has been investigated using steady state fluorescence technique in water medium. The dyes used were Uniblue, Acid blue 129, Alizarin and Alizarin red S. The quenching of PE was found to obey the Stern-Volmer equation and the corresponding Stern-Volmer plots were linear indicating the dynamic quenching. The quenching rate constants (k q) were calculated by using fluorescence data. The mechanism of quenching is discussed on the basis of quenching rate constants as well as the reduction potential of dyes. The electron transfer mechanism has been proved by the calculation of free energy change (ΔGet) by applying Rehm-Weller equation.

Studies on the Photoinduced Interaction between Zn(II) Porphyrin and Colloidal TiO2

The interaction of Zn(II) porphyrin (ZnPP) with colloidal TiO2was studied by absorption and fluorescence spectroscopy. The fluorescence emission of ZnPP was quenched by colloidal TiO2upon excitation of its absorption band. The quenching rate constant (kq) is1.24×1011 M−1 s−1. These data indicate that there is an interaction between ZnPP and colloidal TiO2nanoparticle surface. The quenching mechanism is discussed on the basis of the quenching rate constant as well as the reduction potential of the colloidal TiO2. And the mechanism of electron transfer has been confirmed by the calculation of free energy change(ΔGet)by applying Rehm-Weller equation as well as energy level diagram.