Hydrogen Abstraction by Alkoxyl Radicals: Computational Studies of Thermodynamic and Polarity Effects on Reactivities and Selectivities.

Density functional theory calculations (ωB97X-D) are reported for the reactions of methoxy, tert-butoxy, trichloroethoxy, and trifluoroethoxy radicals with a series of 26 C-H bonds in different environments characteristic of a variety of hydrocarbons and substituted derivatives. The variations in activation barriers are analyzed with modified Evans-Polanyi treatments to account for polarity and unsaturation effects. The treatments by Roberts and Steel and by Mayer have inspired the development of a simple treatment involving the thermodynamics of reactions, the difference between the reactant radical and product radical electronegativities, and the absence or presence of α-unsaturation. The three-parameter equation (ΔH⧧ = 0.52ΔHrxn(1 - d) - 0.35ΔχAB2 + 10.0, where d = 0.44 when there is α-unsaturation to the reacting C-H bond), correlates well with quantum mechanically computed barriers and shows the quantitative importance of the thermodynamics of reactions (dictated by the reactant and the product bond dissociation energies) and polar effects.

Supramolecular Hydrogen Bonding Assembly from Non-Coplanar Aromatic Tetra-1H-Pyrazoles with Crystallization-Induced Emission (CIE).

Here, we report a design strategy for constructing supramolecular organic frameworks by introducing 1H-pyrazole groups to aromatic cores as non-coplanar molecules to form diverse supramolecular assemblies through multiple 1H-pyrazole [N-H···N] hydrogen bonds as well as other weak interactions. The new supramolecular organic frameworks displayed interesting crystallization-induced emission (CIE) behavior.

Deciphering Reactivity and Selectivity Patterns in Aliphatic C-H Bond Oxygenation of Cyclopentane and Cyclohexane Derivatives.

A kinetic, product, and computational study on the reactions of the cumyloxyl radical with monosubstituted cyclopentanes and cyclohexanes has been carried out. HAT rates, site-selectivities for C-H bond oxidation, and DFT computations provide quantitative information and theoretical models to explain the observed patterns. Cyclopentanes functionalize predominantly at C-1, and tertiary C-H bond activation barriers decrease on going from methyl- and tert-butylcyclopentane to phenylcyclopentane, in line with the computed C-H BDEs. With cyclohexanes, the relative importance of HAT from C-1 decreases on going from methyl- and phenylcyclohexane to ethyl-, isopropyl-, and tert-butylcyclohexane. Deactivation is also observed at C-2 with site-selectivity that progressively shifts to C-3 and C-4 with increasing substituent steric bulk. The site-selectivities observed in the corresponding oxidations promoted by ethyl(trifluoromethyl)dioxirane support this mechanistic picture. Comparison of these results with those obtained previously for C-H bond azidation and functionalizations promoted by the PINO radical of phenyl and tert-butylcyclohexane, together with new calculations, provides a mechanistic framework for understanding C-H bond functionalization of cycloalkanes. The nature of the HAT reagent, C-H bond strengths, and torsional effects are important determinants of site-selectivity, with the latter effects that play a major role in the reactions of oxygen-centered HAT reagents with monosubstituted cyclohexanes.

Adjuvant chemotherapy could not bring survival benefit to HR-positive, HER2-negative, pT1b-c/N0-1/M0 invasive lobular carcinoma of the breast: a propensity score matching study based on SEER database.

BACKGROUND: The benefit of adjuvant chemotherapy in invasive lobular carcinoma (ILC) is still unclear. The objective of the current study was to elucidate the effectiveness of adjuvant chemotherapy in hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative, pT1b-c/N0-1/M0 ILC. METHODS: Based on Surveillance, Epidemiology, and End-Results (SEER) database, we identified original 12,334 HR-positive, HER2-negative, pT1b-c/N0-1/M0 ILC patients, who were then divided into adjuvant chemotherapy group and control group. End-points were overall survival (OS) and breast cancer-specific mortality (BCSM). Aiming to minimize the selection bias of baseline characteristics, Propensity Score Matching (PSM) method was used. RESULTS: In a total of 12,334 patients with HR-positive, HER2-negative, pT1b-c/N0-1/M0 ILC, 1785 patients (14.5%) were allocated into adjuvant chemotherapy group and 10,549 (85.5%) into control group. Used PSM, the 1785 patients in adjuvant chemotherapy group matched to the 1785 patients in control group. By Kaplan-Meier survival analyses, we observed no beneficial effect of adjuvant chemotherapy on OS in both original samples (P = 0.639) and matched samples (P = 0.962), however, ineffective or even contrary results of adjuvant chemotherapy on BCSM both in original samples (P = 0.001) and in matched samples (P = 0.002). In both original and matched multivariate Cox models, we observed ineffectiveness of adjuvant chemotherapy on OS (hazard ratio (HR) for overall survival = 0.82, 95% confidence interval (CI) [0.62-1.09]; P = 0.172 and HR = 0.90, 95%CI [0.65-1.26]; P = 0.553, respectively), unexpectedly promoting effect of adjuvant chemotherapy on BCSM (HR = 2.33, 95%CI [1.47-3.67]; P = 0.001 and HR = 2.41, 95%CI [1.32-4.39]; P = 0.004, respectively). Standard surgery was beneficial to the survival of patients. Lymph node metastasis was detrimental to survival and radiotherapy brought survival benefit in original samples, but two issues had unobvious effect in matched samples. CONCLUSION: In this study, adjuvant chemotherapy did not improve survival for patients with HR-positive, HER2-negative pT1b-c/N0-1/M0 ILC.

Relationships between Product Ratios in Ambimodal Pericyclic Reactions and Bond Lengths in Transition Structures.

Ambimodal reactions involve a single transition state leading to multiple products. In such reactions, transition state theory gives no information about the ratio of products that are formed, and molecular dynamics must be performed to predict this ratio. Understanding the relationship between the transition structure and the product ratio is a long-standing problem in molecular dynamics. We have studied 15 ambimodal pericyclic reactions and investigated the relationship between the TS bond lengths in the saddle points and the product ratios from trajectory simulations. A linear correlation, ln(B:A) = -9.4(Bond 3 - Bond 2), is found with R2 = 0.92, where A and B refer to the products formed upon formation of bonds 2 and 3, respectively. The correlation shows that the ratio of products formed after the bifurcation is related to the partial bond lengths, and corresponding bond orders, in the transition state.

Bimodal Evans-Polanyi Relationships in Dioxirane Oxidations of sp3 C-H: Non-perfect Synchronization in Generation of Delocalized Radical Intermediates.

The selectivities in C-H oxidations of a variety of compounds by DMDO have been explored with density functional theory. There is a linear Evans-Polanyi-type correlation for saturated substrates. Activation energies correlate with reaction energies or, equivalently, BDEs (ΔH‡sat = 0.91*BDE - 67.8). Unsaturated compounds, such as alkenes, aromatics, and carbonyls, exhibit a different correlation for allylic and benzylic C-H bonds (ΔH‡unsat = 0.35*BDE - 13.1). Bernasconi's Principle of Non-Perfect Synchronization (NPS) is found to operate here. The origins of this phenomenon were analyzed by a Distortion/Interaction model. Computations indicate early transition states for H-abstractions from allylic and benzylic C-H bonds, but later transition states for the saturated. The reactivities are mainly modulated by the distortion energy and the degree of dissociation of the C-H bond. While the increase in barrier with higher BDE is not unexpected from the Evans-Polanyi relationship, two separate correlations, one for saturated compounds, and one for unsaturated leading to delocalized radicals, were unexpected.

A monochromatic electrochemiluminescence sensing strategy for dopamine with dual-stabilizers-capped CdSe quantum dots as emitters.

A promising electrochemiluminescence (ECL) sensing strategy was proposed with dual-stabilizers-capped CdSe quantum dots (QDs) as ECL emitters. The dual-stabilizers-capped CdSe QDs were covalently immobilized onto p-aminobenzoic acid modified glass carbon electrode with ethylenediamine as a link molecule. This strategy can preserve the completely passivated surface states of dual-stabilizers-capped CdSe QDs, so that the sensor demonstrated eye-visible greenish, band gap engineering and monochromatic ECL emission at 546 nm with a fwhm of 35 nm. Moreover, the proposed sensor could accurately quantify dopamine from 10.0 nM to 3.0 µM with a detection limit of 3.0 nM in practical drug, human urine, and cerebrospinal fluid samples without any signal amplification techniques. This strategy is promising for developing ECL sensors with high sensitivity and spectral selectivity.

Vascular endothelial growth factor gene polymorphism (-634G/C) and breast cancer risk.

The aim of this meta-analysis was to assess if the -634G/C polymorphism represents a predisposition factor for the risk of breast cancer. We included eight published case-control studies, in which a total of 6,175 cancer cases and 6,421 cancer-free controls were included. Pooled ORs and 95 % CIs were calculated by the fixed effects model to evaluate the association of the -634G/C polymorphism and breast cancer risk. When all studies were pooled, we did not find statistical evidence of any significant association with overall breast cancer risk (ORBB vs. bb = 1.00, 95 % CI = 0.93-1.07, P = 0.999; ORBB + Bb vs. bb = 1.00, 95 % CI = 0.95-1.05, P = 0.999; ORBB vs. Bb + bb = 1.03, 95 % CI = 0.96-1.09, P = 0.984; ORallele B vs. allele b = 1.01, 95 % CI = 0.97-1.05, P = 0.998; ORBb vs. bb = 0.99, 95 % CI = 0.92-1.06, P = 0.992). In further stratified analyses by ethnicity and control source, no significant association was revealed. This study suggests that the -634G/C polymorphism does not appear to represent a risk factor for breast cancer.

CD243 gene polymorphism significantly associated with breast cancer susceptibility.

We aimed to obtain a summary risk estimate for CD243 gene polymorphism associated with breast cancer. A total of nine case-control studies, including 5,073 cancer patients and 7,498 control subjects, were pooled in our fixed effects meta-analysis of the association between CD243 gene polymorphism and risk of breast cancer. All data were analyzed by using Stata software (version 12.0). We found significant risk effects under TT vs. TC + CC genetic model [odds ratio (OR) = 1.09, 95 % confidence interval (CI) = 1.01-1.18, P = 0.516], but not in other comparisons. Stratifying the pooled data by ethnicity and source of controls revealed that the association between the T allele and an increased risk of breast cancer was more pronounced among Asians (TT vs. CC: OR = 1.26, 95 % CI = 1.02-1.57, P = 0.720; TT vs. TC + CC: OR = 1.31, 95 % CI = 1.07-1.61, P = 0.708) and hospital-based studies (TT vs. CC: OR = 1.25, 95 % CI = 1.02-1.53, P = 0.877; TT vs. TC + CC: OR = 1.27, 95 % CI = 1.05-1.53, P = 0.540). No notable heterogeneity was indicated across studies. Our meta-analysis demonstrates that CD243 gene polymorphism may act as a predisposition factor for breast cancer, particularly in Asian populations.

MWCNTs Alleviated saline-alkali stress by optimizing photosynthesis and sucrose metabolism in rice seedling.

Saline and alkali stress affects the growth and development, survival rate, and final yield of rice, while new nano materials can have a positive effect on rice growth. In order to investing the effects of carboxymethyl multi walled carbon nanotubes (MWCNTs) on the growth and development of rice seedlings under salt alkali stress, rice seedlings were cultured using rice variety "Songjing 3" using nutrient solution water culture method. The effects of MWCNTs on water absorption capacity, leaf photosynthesis, and sucrose metabolism of rice seedlings under 50 mmol/L saline-alkali stress (1NaCl: 9Na2SO4: 9NaHCO3: 1Na2CO3) conditions were investigated. The results showed that MWCNTs can improve the water use ability of roots and leaves, especially the water absorption ability of roots, which provides a guarantee for the improvement of rice biomass and the enhancement of leaf photosynthetic capacity under adverse conditions. After treatment with MWCNTs, the photosynthetic rate (Pn), stomatal conductance (gs), and transpiration rate (Tr) of leaves increased significantly, and the photochemical quenching value (qP), photochemical quantum efficiency value (Fv/Fm), and electron transfer rate value (ETR) of chlorophyll fluorescence parameters increased significantly, which is beneficial to the improvement of the PSII photosynthetic system. MWCNTs treatment promoted the increase of photosynthetic pigment content in leaves under salt and alkali stress, improved the ratio of Chla and Chlb parameters, increased the activities of key photosynthetic enzymes (RUBPCase and PEPCase) in leaves, increased the value of total lutein cycle pool (VAZ), and significantly enhanced the deepoxidation effect of lutein cycle (DEPS), which can effectively alleviate the stomatal and non stomatal constraints on leaf photosynthesis caused by salt and alkali stress. MWCNTs treatment significantly enhanced the activities of sucrose phosphate synthase (SPS) and sucrose synthase (SS) under salt and alkali stress, and decreased the activities of soluble acid invertase (SAInv) and alkaline/neutral invertase (A/N-Inv), indicating that MWCNTs promoted sucrose synthesis while inhibiting sucrose decomposition, thereby promoting sucrose accumulation in rice leaves. This study can provide theoretical and experimental basis for the application of MWCNTs to the production of rice under salt and alkali stress, and can find a new way for rice production in saline and alkaline lands.

High Photocatalytic Activity of g-C3N4/La-N-TiO2 Composite with Nanoscale Heterojunctions for Degradation of Ciprofloxacin.

Ciprofloxacin (CIP) in natural waters has been taken as a serious pollutant because of its hazardous biological and ecotoxicological effects. Here, a 3D nanocomposite photocatalyst g-C3N4/La-N-TiO2 (CN/La-N-TiO2) was successfully synthesized by a simple and reproducible in-situ synthetic method. The obtained composite was characterized by XRD, SEM, BET, TEM, mapping, IR, and UV-vis spectra. The photocatalytic degradation of ciprofloxacin was investigated by using CN/La-N-TiO2 nanocomposite. The main influential factors such as pH of the solution, initial CIP concentration, catalyst dosage, and coexisting ions were investigated in detail. The fastest degradation of CIP occurred at a pH of about 6.5, and CIP (5 mg/L starting concentration) was completely degraded in about 60 min after exposure to the simulated solar light. The removal rates were rarely affected by Na+ (10 mg·L-1), Ca2+ (10 mg·L-1), Mg2+ (10 mg·L-1), and urea (5 mg·L-1), but decreased in the presence of NO3- (10 mg·L-1). The findings indicate that CN/La-N-TiO2 nanocomposite is a green and promising photocatalyst for large-scale applications and would be a candidate for the removal of the emerging antibiotics present in the water environment.

[Determination of the ofloxacin in the biologic samples by fluorescence microscopic imaging technique].

The method of CTMAB-Al(3+)-OFLX ternary complex fluorescence microscopic imaging technique was established for the determination of ofloxacin based on the capillary effect of solvent on solid supports, and the concentration in the serum after the chicken was burdened with ofloxacin tablet, the concentration in the human urines and the percentage composition in the honeies, ofloxacin tablets and eye-drops were measured with satisfaction, respectively. In the presence of pH 9. 50 NH3-NH4Cl buffer solution and PVA-124, CTMAB-Al(3+)-OFLX ternary complex can form a self-ordered ring on the hydrophobic supports with the diameter of 1.63 mm and its ring belt width of 50 microm. When a 0.20 microL droplet was spotted, the fluorescence intensity of the ring had a favorable linear relation (r = 0.999 2) with the drug concentration in the range of 3.30 x 10(-13) - 1.65 x 10(-12) mol x ring(-1) (0.60-2.98 mg x L(-1)) and the limit of detection can reach 4.10 x 10(-15) mol x ring(-1) (7.41 microg x L(-1)) with three times of signal to noise ratio. This method has been applied to the average concentration of ofloxacin in the chicken serum with the recovery of 96.4%-101.2% after two hours of being burdened with ofloxacin tablet. Then the technique was applied to the determination of ofloxacin in the three healthy volunteer's urines after oral administration with recovery of 98.2% - 106.%. It was found that the concentrations of ofloxacin in urines were the highest after three hours of taking medicine; the result was similar to reports in the literature. The residues of ofloxacin in three different honey samples were satisfactorily determined with the recoveries of 98.2% - 106.1%, and RSD was less than 2.3%. The contents of active constituent in tablet samples and eye-drops sample were determined with recoveries of 93.5%-101.5% and 95.8%-104.2%, and RSD was 3.5% and 3.6%, respectively, which were similar to marked values.

Enhancing the Photoelectric Properties of Zinc Porphyrin Dyes by Introducing Five-Membered Heterocyclic Rings into the Electron Donor: A Density Functional Theory and Time-Dependent Density Functional Theory Study.

To fabricate highly efficient dye sensitizers for dye-sensitized solar cells, new zinc porphyrin dye sensitizers were designed based on one of the most efficient dyes, YD2-o-C8, by introducing electron-rich heterocyclic rings into the electron donor. Five potentially efficient dyes, Dye1-5, were obtained by replacing the phenyl group of the donor in YD2-o-C8 with pyrrolyl, furyl, and thienyl groups. The electronic structures, absorption spectra, intramolecular charge-transfer characteristics, and excited-state lifetimes of the designed dyes were investigated using the density functional theory and time-dependent density functional theory methods. All the designed dyes exhibit better photoelectric properties than those of YD2-o-C8. Compared with YD2-o-C8, the designed new dyes have smaller frontier molecular orbital energy gaps and obvious red-shifting absorption spectra in the Q band. The analyses of charge density difference plots and intramolecular charge-transfer characteristics indicated that the designed dyes can better promote intramolecular charge transfer and electron-hole separation. Among the five designed dyes, Dye1 with a pyrrolyl group exhibits the best performance. Dye3 and Dye5 with methyl-furyl and methyl-thienyl groups, respectively, exhibit the next best performance. Dye2 and Dye4 with furyl and thienyl groups, respectively, are the worst performers. The introduced methyl group can further improve the electron-donating ability of heterocyclic rings and promote the red shift of the Q bands and intramolecular charge transfer of dyes. The excited-state lifetimes of the new dyes were in the following order: YD2-o-C8 < Dye4 < Dye2 < Dye5 < Dye3 < Dye1, which shows their stronger abilities to inject electrons into semiconductor films.

Synthesis and nitric oxide releasing properties of novel fluoro S-nitrosothiols.

A series of new fluoro S-nitrosothiols is reported as potential nitric oxide (NO) donors. A three-step synthesis and the NO releasing kinetic profiles of these species are presented. The stoichiometric release of NO, with the clean formation of corresponding disulfides, confirms that these new species can facilitate their application as NO donors for various applications including creating novel antimicrobial and thromboresistant fluoropolymer-based medical devices.

Spatial arrangement of alpha-cyclodextrins in a rotaxane. Insights from free-energy calculations.

The rotaxane formed by alpha-cyclodextrins (alpha-CDs) threaded onto a poly(ethylene glycol) (PEG) chain was investigated in the gas phase and in an aqueous solution by means of molecular dynamics simulations. The free-energy difference between the three possible spatial arrangements of consecutive alpha-CD--viz.. head-to-head (HH), head-to-tail (HT), and tail-to-tail, was determined using free-energy perturbation calculations. These simulations reveal that the interaction of alpha-CD with the PEG chain is very similar in the two surroundings, whereas the mutual interaction of the macrocycles is stronger in the gas phase than in the aqueous solution. Moreover, difference in the overall interaction appears to stem primarily from changes in the electrostatic contribution. Analysis of intermolecular hydrogen bonds indicates that hydrogen bonds created between alpha-CD and water molecules weaken the hydrogen-bonding interaction of adjacent alpha-CDs. Comparison of the free-energy differences characteristic of the three possible spatial arrangements of contiguous alpha-CDs reveals that the HH motif of the rotaxane is the most stable in the gas phase due to the hydrogen-bond formation between the secondary hydroxyl groups of the two alpha-CDs, and the slight preference for the HT motif in aqueous solution, which can be related to the directionality of the dipole moment borne by the macrocycles in these two motifs.

Catalytic Asymmetric Chlorocyclization of 2-Vinylphenylcarbamates for Synthesis of 1,4-Dihydro-2H-3,1-benzoxazin-2-one Derivatives.

A facile synthetic approach to a series of chiral 4-chloromethyl-1,4-dihydro-2H-3,1-benzoxazin-2-one derivatives has been described. This transformation is achieved through the catalytic asymmetric chlorocyclization of 2-vinylphenylcarbamates using a newly developed organocatalyst. Furthermore, the resulting products can be easily converted into diverse bioactive agents.

Pico-HPLC system integrating an equal inner diameter femtopipette into a 900 nm I.D. porous layer open tubular column.

A picoflow high performance liquid chromatography (pico-HPLC) system was developed, which could directly pipette femtoliter samples using a separation column tip driven by an electroosmotic pump. Amino acid enantiomers were separated in the 900 nm I.D. porous layer open tubular column at a flow rate of 13.50 pL min-1.

Molecular dynamics study of the inclusion of cholesterol into cyclodextrins.

The interaction of three cyclodextrins (CDs), viz. beta-CD, heptakis (2,6-di-O-methyl)-beta-CD (DM-beta-CD), and 2-hydroxypropyl-beta-CD (HP-beta-CD), with cholesterol was investigated using molecular dynamics (MD) simulations. The free energy along the reaction pathway delineating the inclusion of cholesterol into each CD was computed using the adaptive biasing force method. The association constant and the corresponding association free energy were derived by integrating the potential of mean force (PMF) over a representative ordering parameter. The results show that the free energy profiles possess two local minima corresponding to roughly equally probable binding modes. Among the three CDs, DM-beta-CD exhibits the highest propensity to associate with cholesterol. Ranking for binding cholesterol, viz. DM-beta-CD > HP-beta-CD > beta-CD, agrees nicely with experiment. Partitioning of the PMF into free energy components illuminates that entering of cholesterol into the CD cavity is driven mainly by electrostatic interactions, whereas deeper inclusion results from van der Waals forces and solvation effects. Additional MD simulations were performed to investigate the structural stability of the host-guest complexes near the free energy minima. The present results demonstrate that association of cholesterol and CDs follows two possible binding modes. Although the latter are thermodynamically favorable for all CDs, one of the two inclusion complexes appears to be preferred kinetically in the case of DM-beta-CD.

Cod skin peptide reduces chemotherapy-induced toxicity in gastric cancer patients.

BACKGROUND AND OBJECTIVES: The present study was conducted to evaluate the effect of cod skin peptide (CSPE) on chemotherapy-induced toxicity in gastric cancer patients. METHODS AND STUDY DESIGN: A cohort of 60 gastric cancer patients for chemotherapy was randomly divided into two groups (n=30 per group), who were orally treated with either supplemental CSPE or placebo apart from chemotherapy. The hematologic and gastrointestinal toxicities experienced by the patients, as well as their Karnofsky Performance Status (KPS) as an index of quality of life was evaluated. RESULTS: Leukocyte counts and haemoglobin levels were significantly reduced in the group treated with peptide (p<0.05), while gastrointestinal toxicity was not affected (p>0.05). KPS consists of 11 categories of quality of life, and the score denoted in deciles ranges from 100 (asymptomatic, normal function) to 0 (death). The KPS score is used to evaluate a cancer patient's ability to function at work and home, the severity of symptoms, and the patient's need for personal and medical care. Treatment with CSPE significantly improved the quality of life of patients, as indicated by increased KPS scores (p<0.05). CONCLUSIONS: CSPE can potentially be considered as a food supplement that can be used to improve the quality of life of cancer patients.

Electronic effects of the substituent on the dioxygen-activating abilities of substituted iron tetraphenylporphyrins: a theoretical study.

A density functional theoretical (DFT) method was applied to understand the effects of the substituent on dioxygen activation by a series of substituted iron tetraphenylporphyrins [FeT(o/p-R)PP (o = ortho-substituted, p = para-substituted; R = -H, -Cl, -NO2, -CH3, -OCH3)]. The ground states (GS) of the dioxygen adducts of the substituted iron tetraphenylporphyrins [FeT(o/p-R)PPO2] were determined at the B3LYP/6-31G(d) level without any symmetry constraints. Binding energy calculations indicated that the presence of electron-withdrawing substituents at the para position favors O2 binding. Calculations of the O-O bond length of the adsorbed dioxygen revealed that the influence of the p-substituent on the activation of dioxygen decreases in the order p-CH3 > p-Cl > p-OCH3 > -H > p-NO2, while the influence of the o-substituent decreases in the order o-NO2 > o-CH3 > o-Cl > o-OCH3 > -H. The low-lying excited states (LLES) of the FeT(o/p-R)PPO2 adducts suggest that the ability to activate dioxygen decreases in the order o-CH3 > o-OCH3 = -H > o-NO2 > o-Cl for o-substituents and p-CH3 > p-Cl > -H > p-NO2 > p-OCH3 for p-substituents. NBO charge population analysis and spin density analysis showed that substitution caused more ß-electrons to be transferred from the iron tetraphenylporphyrin to the dioxygen, which enhanced dioxygen activation. Spin density analysis confirmed that the ß-electron population at the adsorbed dioxygen is an accurate indicator of the degree of dioxygen activation. The trend observed in porphyrin catalytic activity as the substituent on the dioxygen adduct was varied is consistent with the trend in the binding energy. It is clear that substituents at the ortho and para positions in these dioxygen adducts play different roles in dioxygen activation.