Co-C force constants from resonance Raman spectra of alkylcobalamins: insensitivity to dimethylbenzylimidazole coordination

The Co-C stretching vibration has been identified in resonance Raman spectra of alkyl-cobalamins, via isotope substitution, permitting estimation of the Co-C force constants, f = 1.85, 1.77 and 1.50 mdyn Å⁻¹ for methyl-, ethyl- and deoxyadenosyl-cobalamin, respectively (ν_Co-C = 506, 471 and 442/429 cm⁻¹). These values scale with the reported bond dissociation energies, and support the view that the Co-C bond weakens with increasing bulk of the alkyl group due to steric interaction with the corrin ring. However, the force constants are unaffected by dissociation of the dimethylbenzimidazole ligand at low pH, even though the bond dissociation energy rises significantly upon DMB dissociation in AdoCbl. This increase must therefore reflect destabilization of the Co^II product, rather than Co-C bond strengthening in the AdoCbl ground state. The insensitivity of the force constants to dimethylbenzimidazole dissociation implies that the steric effect of DMB coordination is not transmitted to the Co-C bond by the corrin ring. Consistent with this interpretation, the RR frequencies of the corrin ring modes are minimally perturbed by DMB dissociation, supporting earlier NMR results that indicated little change in the corrin conformation.     

Model energy landscapes and the force-induced dissociation of ligand-receptor bonds

We discuss models for the force-induced dissociation of a ligand-receptor bond, occurring in the context of cell adhesion or single molecule unbinding force measurements. We consider a bond with a structured energy landscape which is modeled by a network of force dependent transition rates between intermediate states. The behavior of a model with only one intermediate state and a model describing a molecular zipper is studied. We calculate the bond lifetime as a function of an applied force and unbinding forces under an increasing applied load and determine the relationship between both quantities. The dissociation via an intermediate state can lead to distinct functional relations of the bond lifetime on force. One possibility is the occurrence of three force regimes where the lifetime of the bond is determined by different transitions within the energy landscape. This case can be related to recent experimental observations of the force-induced dissociation of single avidin-biotin bonds.     

The optimum substrate to biomass ratio to reduce net biomass yields and inert compounds in biological leachate treatment under pure-oxygen conditions

To investigate the effect of both initially present soluble inert COD (S_I) and soluble inert COD formed by microbial activities (S_PM) on the effluent soluble residual COD (S_R) and to determine biokinetic constants, the pure-oxygen was employed for the batch assays of biological leachate treatment. The results of this work showed that the effluent residual soluble COD was entirely composed of S_I and S_PM, therefore, could not be reduced below 7-10% of total influent soluble COD (S_T0.inf), corresponding to the organics removal efficiency of 93-90%. The value of S_I of leachate, which is associated with the types of wastewaters, was determined as approximately 7.84% of S_T0.inf, and the soluble inert COD by microbial activities was assessed by means of the coefficient f_PM of 0.0474. These results mean that significant amount of feed leachate COD may pass the biological system without any change. On the basis of the concept that microorganisms must satisfy their maintenance energy requirements prior to synthesizing new biomass, a set of batch assays with various ratios of S_T0.inf /X₀ were carried out to evaluate their effects on the excess biomass production. Decreasing the supply of substrate per unit biomass resulted in gradual decrease in the biomass yields, but, at the same time, it resulted in gradual increase in the bacteria mediated inert COD as a side effect. The optimum ratios of S_T0.inf /X₀ were concluded as 0.2-0.6 according to the careful consideration of both aspects on the reduction of net sludge yields and inert COD from microbial activities.     

Prediction of electrocatalytic activity of some nitrogen-doped polyaromatic hydrocarbons by molecular modelling

Density function theory calculations of minimum energy structure of an oxygen molecule and oxygen atom bonded to the two dimensional molecules, C₂₃NH₁₂, coronene and C₂₁NH₁₄, pentacene doped with nitrogen, indicate the structures are at a minimum on the potential energy surface having no imaginary frequencies. Calculation of the bond dissociation energy (BDE) to remove an oxygen atom from nitrogen-doped pentacene to which is bonded O₂, (C₂₁NH₁₄O₂) shows it is less than that to dissociate O₂. However, this is not the case for nitrogen-doped coronene. This suggests that nitrogen-doped pentacene could be an effective catalyst for the oxygen reduction reaction in fuel cells assuming it is O₂ dissociation. It is also shown that O₂H can bond to nitrogen-doped coronene and pentacene and that the BDE to remove OH is less than that to remove OH from O₂H indicating that N-doped coronene and pentacene could also catalyse this reaction. The calculated adsorption energy for O₂ and O₂H on these molecules is negative indicating they can bond to N-doped coronene and pentacene.     

Exogenous passive heating during torpor arousal in free-ranging rock elephant shrews, <Emphasis Type="Italic">Elephantulus myurus</Emphasis>

In the laboratory rock elephant shrews (Elephantulus myurus; mean body mass 56.6 g) displayed the lowest torpor T_{b min} yet recorded (ca. 5°C) in a placental daily heterotherm. It was unknown whether these low T_bs were characteristic of daily heterothermy in free-ranging animals. It was also unclear how cost effective these low T_bs were since considerable energy is required to arouse from low T_bs on a daily basis. We continuously measured body temperature once every hour for 85 days in 13 free-ranging E. myurus from May to August 2001 (winter) in Weenen Game Reserve, KwaZulu-Natal, South Africa. We recorded a total of 412 torpor bouts. Free-ranging E. myurus had a high propensity for torpor with females displaying higher torpor frequency than males. The lowest T_b recorded was 7.5°C at T_a=2.7°C and the minimum torpor T_b was strongly correlated with ambient temperature. Torpor arousal was tightly coupled with ambient temperature cycles. Low torpor T_{b min} at low T_as was therefore cost-effective because the animals offset the high cost of arousal through exogenous passive heating. Laboratory studies under constant ambient temperatures may therefore underestimate the energetic benefits of torpor in free-ranging small mammals that inhabit regions where seasonality is moderate.     

Transmission of herbicide resistance from a monoecious to a dioecious weedy Amaranthus species

The genus Amaranthus includes several important monoecious and dioecious weed species, and several populations of these species have developed resistance to herbicides. These species are closely related and two or more species often coexist in agricultural settings. Collectively, these attributes raise the concern that herbicide resistance might transfer from one weedy Amaranthus species to another. We performed research to determine if a dominant allele encoding a herbicide-insensitive form of acetolactate synthase (ALS) could be transferred from a monoecious species, A. hybridus, to a dioecious species, A. rudis. Numerous F₁ hybrids were obtained from controlled crosses in a greenhouse between A. rudis and herbicide-resistant A. hybridus, and most (85%) of these hybrids were herbicide-resistant. Molecular analysis of the ALS gene was used to verify that herbicide-resistant hybrids contained both an A. rudis and an A. hybridus ALS allele. Although hybrids had greatly reduced fertility, 42 BC₁ plants were obtained by backcrossing 33 hybrids with male A. rudis. Fertility was greatly restored in BC₁ progeny, and numerous BC₂ progeny were obtained from a second backcross to A. rudis. The herbicide-resistance allele from A. hybridus was transmitted to 50% of the BC₁ progeny. The resistance allele was subsequently transmitted to and conferred herbicide resistance in 39 of 110 plants analyzed from four BC₂ families. Parental species, hybrids, and BC₂ progeny were compared for 2C nuclear DNA contents. The mean hybrid 2C nuclear DNA content, 1.27 pg, was equal to the average between A. rudis and A. hybridus, which had 2C DNA contents of 1.42 and 1.12 pg, respectively. The mean 2C DNA content of BC₂ plants, 1.40 pg, was significantly (! < 0.01) less than that of the recurring A. rudis parent and indicated that BC₂ plants were not polyploid. This report demonstrates that herbicide resistance can be acquired by A. rudis through a hybridization event with A. hybridus.     

Simulation of the mechanical strength of a single collagen molecule

We perform atomistic simulations on a single collagen molecule to determine its intrinsic molecular strength. A tensile pull simulation to determine the tensile strength and Young's modulus is performed, and a simulation that separates two of the three helices of collagen examines the internal strength of the molecule. The magnitude of the calculated tensile forces is consistent with the strong forces of bond stretching and angle bending that are involved in the tensile deformation. The triple helix unwinds with increasing tensile force. Pulling apart the triple helix has a smaller, oscillatory force. The oscillations are due to the sequential separation of the hydrogen-bonded helices. The force rises due to reorienting the residues in the direction of the separation force. The force drop occurs once the hydrogen bond between residues on different helices break and the residues separate.     

Catch Bond Interaction between Cell-Surface Sulfatase Sulf1 and Glycosaminoglycans

In biological adhesion, the biophysical mechanism of specific biomolecular interaction can be divided in slip and catch bonds, respectively. Conceptually, slip bonds exhibit a reduced bond lifetime under increased external force and catch bonds, in contrast, exhibit an increased lifetime (for a certain force interval). Since 2003, a handful of biological systems have been identified to display catch bond properties. Upon investigating the specific interaction between the unique hydrophilic domain (HD) of the human cell-surface sulfatase Sulf1 against its physiological glycosaminoglycan (GAG) target heparan sulfate (HS) by single molecule force spectroscopy (SMFS), we found clear evidence of catch bond behavior in this system. The HD, ∼320 amino acids long with dominant positive charge, and its interaction with sulfated GAG-polymers were quantitatively investigated using atomic force microscopy (AFM) based force clamp spectroscopy (FCS) and dynamic force spectroscopy (DFS). In FCS experiments, we found that the catch bond character of HD against GAGs could be attributed to the GAG 6-O-sulfation site whereas only slip bond interaction can be observed in a GAG system where this site is explicitly lacking. We interpreted the binding data within the theoretical framework of a two state two path model, where two slip bonds are coupled forming a double-well interaction potential with an energy difference of ΔE ≈ 9 k_BT and a compliance length of Δx ≈ 3.2 nm. Additional DFS experiments support this assumption and allow identification of these two coupled slip-bond states that behave consistently within the Kramers-Bell-Evans model of force-mediated dissociation.     

Ab Initio Calculations of Vibrational Frequencies,Potential Functions of Internal Rotations and Vibrational Infrared and Raman Spectra for 3,3,3-Trifluoropropanal

The conformational behavior and structure of 3,3,3,-trifluoropropal have been investigated by utilizing ab initio calculations with the 6-31G^** basis set (valence double zeta basis with polarization functions on all atoms) at the restricted Hartree Fock (RHF), second-order Møller-Plesset perturbation (MP2), and Density Functional (B3LYP) levels. The molecule is predicted to have a cis Û gauche conformational equilibrium. Full optimization of the transition states was performed and the rotational barriers of both the CHO and CF₃ rotors were calculated. Vibrational frequencies were computed at the three levels and the zero-point corrections were included into the calculated asymmetric CHO rotational barrier. Complete vibrational assignments were made on the basis of normal coordinate calculations for both stable conformers of the molecule.     

Lactate dehydrogenase from the Antarctic eelpout, Lycodichthys dearborni

As part of our studies to examine the molecular basis of cold-adaptation, we have determined the kinetic properties, thermal stability and deduced amino acid sequence of the enzyme lactate dehydrogenase (LDH) from an Antarctic zoarcid fish, Lycodichthys dearborni. Unlike Antarctic notothenioid fish which are endemic to the Southern Ocean, zoarcid fish are cosmopolitan and have a substantially longer evolutionary history as a sub-order. The A₄-LDH isoform was isolated and purified from the white muscle of L. dearborni. The kinetic parameters K_m^PYR and k_cat were determined at temperatures from 0 to 25°C. K_m^PYR was substantially higher at low temperatures than those from Antarctic and temperate notothenioid fish, whereas k_cat at these temperatures was essentially the same as those of the other fish LDH in this study. The sequence of L. dearborni A₄-LDH was determined from cDNA derived from white muscle RNA and found to be similar to, but distinct from, the A₄-LDH sequences of Antarctic notothenioid fish. Molecular modelling based on the structure of the A₄-LDH from Pagothenia borchgrevinki suggested that three conservative amino acid changes within the core of the protein that are not directly part of the active site but which might nonetheless influence the active site, may be important in cold-adaptation in L. dearborni A₄-LDH, and that several other changes on the surface of the protein might also play a role in cold-adaptation.     

Photosynthetic characteristics in canopies of Quercus rubra, Quercus prinus and Acer rubrum differ in response to soil water availability

Photosynthesis and related leaf characteristics were measured in canopies of co-occurring Quercus rubra L. (red oak), Quercus prinus L. (chestnut oak) and Acer rubrum L. (red maple) trees. Mature (20+ m tall) trees were investigated at sites of differing soil water availability within a catchment (a drier upper site and a wetter lower site). Leaf photosynthetic characteristics differed significantly between species and in response to site and position in the canopy. Photosynthetic capacity (A_max) was significantly greater at the wetter site in all canopy strata in A. rubrum but not in Q. rubra or Q. prinus. Our findings for A. rubrum are generally consistent with those predicting that species with higher specific leaf area (SLA) will have higher A_max per unit leaf nitrogen (N) and that species with leaves with lower SLA (e.g. Q. rubra and Q. prinus) will have shallower slopes of the A_max-N relationship. Importantly, the relationships between A_max and N_area (and by implication photosynthetic nitrogen-use efficiency, PNUE) differed in A. rubrum between the sites, with PNUE significantly lower at the drier site. The lower photosynthetic capacity and PNUE must substantially reduce carbon acquisition capacity in A. rubrum under these field conditions. Maximum stomatal conductance (g_smax) differed significantly between species, with g_smax greatest in Q. rubra and Q. prinus. In Q. rubra and Q. prinus, g_smax was significantly lower at the upper site than the lower site. There was no significant response of g_smax to site in A. rubrum. These stomatal responses were consistent with the C_i/C_a ratio, which was significantly lower in leaves of Q. rubra and Q. prinus at the upper site, but did not differ between sites in A. rubrum. Leaf '¹³C was significantly lower in A. rubrum than in either Q. rubra or Q. prinus at both sites. These findings indicate differences in stomatal behaviour in A. rubrum which are likely to contribute to lower water use efficiency at both sites. Our results support the hypothesis that the two Quercus species, in contrast to A. rubrum, maintain photosynthetic capacity at the drier site whilst minimising transpirational water loss. They also suggest, based primarily on physiological evidence, that the ability of A. rubrum to compete with other species of these deciduous forests may be limited, particularly in sites of low moisture availability and during low rainfall years.     

Robust multiple-input-multiple-output control of non-linear continuous fermentation processes

In this study, the removal of nitrate (NO₃^m) ions from aqueous streams with liquid membrane technique has been investigated. Among the other parameters (temperature, pH, acceptor phase type and medium concentration), the stirring speed was chosen as process parameter. From the experimental results, it has been determined that the reaction was diffusion controlled. The transport efficiency of nitrate ions increased with increasing stirring speed. The membrane entrance and exit rate constants (k_1d, k_2m and k_2a respectively) were linearly dependent on the stirring speed ratios of 100 to 250 rpm. Coupled transport of nitrate ions through a liquid membrane in 85% n-hexane-15% tricloromethane as diluent, containing tetraoctyl ammonium chloride (TOACl) as a carrier was examined at various stirring speeds. Membrane entrance (k_1d) and exit rates (k_2m and k_2a) increase with increasing the stirring speeds. The diffusion of the nitrate ion-carrier complex through the narrow stagnant layers was found to be rate determining step. The membrane was stable during the transport experiments. There is no leakage of carrier or nitrate ion-carrier complex to both aqueous phases and also, no supplementary water penetration into the membrane. This favours interfacial reaction of nitrate ion and carrier.     

Seedling herbivory by slugs in a willow hybrid system: developmental changes in damage, chemical defense, and plant performance

We evaluated feeding preference and damage by the slug, Arion subfuscus, on seedlings of two willow species, Salix sericea and S. eriocephala, and their F₁ interspecific hybrids. Trays of seedlings were placed in the field and excised leaves were presented to slugs in choice tests. Slugs preferred feeding on and caused the most damage to S. eriocephala seedlings. S. sericea seedlings were least preferred and least damaged. F₁ hybrid seedlings were intermediate in preference and damage. Slug preference of and damage to these seedlings decreased over time, suggesting developmental changes in resistance. Seedlings were sampled for phenolic glycoside and tannin chemistry weekly to coincide with the field and laboratory experiments. Concentrations of phenolic glycosides and tannins increased linearly with seedling age, coincident with changes in slug preference and damage, indicating a developmental change in defense. Slug deterrence was not detected at low concentrations of salicortin when painted on leaves or discs, but both salicortin and condensed tannins deterred slug feeding at concentrations between 50 and 100 mg/g, levels found in adult willows. Seedling performance was related to damage inflicted by slugs. Due to lower levels of damage when exposed to slugs in the field, S. sericea plants had significantly greater biomass than S. eriocephala plants. Biomass of F₁ hybrids was equal to S. sericea when damaged. However, undamaged S. eriocephala and F₁ hybrid plants had the greatest biomass. Because F₁ hybrid seedlings performed as well as the most fit parent in all cases, slugs could be an important selective factor favoring introgression of defensive traits between these willow species.     

Limitation of stomatal conductance by hydraulic traits: sensing or preventing xylem cavitation?

We tested the hypothesis that hydraulic conductance per unit leaf surface area of plant shoots (K_SL) determines the maximum diurnal stomatal conductance (g_L) that can be reached by plants growing in the field. A second hypothesis was tested that some xylem cavitation cannot be avoided by transpiring plants and might act as a signal for regulating g_L. Eleven woody species were studied, differing from each other with respect to taxonomy, wood anatomy and leaf habit. Maximum diurnal g_L, transpiration rate (E_L), pre-dawn and minimum diurnal leaf water potential (O_pd and O_min, respectively) were measured in the field. The critical O level at which stem cavitation was triggered (O_cav) was measured on detached branches, using the acoustic method. A high-pressure flow meter was used to measure maximum K_SL of 1-year-old shoots. Both g_L and E_L were positively related to K_SL. The whole-plant hydraulic conductance per unit leaf area (K_WL) of all the species studied, calculated as the ratio of E_L to (O (=O_pd-O_min) was closely related to K_SL. In every case, O_min (ranging between -0.85 and -1.35 MPa in the different species) dropped to the O_cav range or was <O_cav (ranging between -0.71 and -1.23 MPa), thus suggesting that some cavitation-induced embolism could not be avoided. The possibility is discussed that some cavitation-induced reduction in K_SL is the signal for stomatal closure preventing runaway embolism. The lack of correlation of g_L to O_cav is discussed in terms of the inconsistency of O_cav as an indicator of the vulnerability of plants to cavitation. No differences in hydraulic traits were observed between evergreen and deciduous species.     

Growth, photosynthesis and ozone uptake of young beech (Fagus sylvatica L.) in response to different ozone exposures

Beech seedlings (Fagus sylvatica L.) were exposed to episodes of O₃ in environmentally controlled growth chambers during one growing season. Three treatments were applied: charcoal-filtered air, charcoal-filtered air with the addition of 40 ppb O₃ for seven episodes of 5 days' duration (9000-1700 hours), and charcoal-filtered air with the addition of 100 ppb O₃ for seven episodes of 5 days' duration (9000-1700 hours). The accumulated exposure over a threshold of 40 ppb in the last treatment reached 13,911 ppb h. Throughout the growing season we measured growth as well as photosynthetic properties and related effects to external and calculated internal doses of O₃, using stomatal conductance (g_s) data. Growth, measured as diameter increment and biomass, was not significantly affected by the O₃ treatments. In the 100-ppb treatment, light-saturated CO₂ assimilation rates and chlorophyll content were significantly reduced, and the chlorophyll fluorescence parameter F_v/F_m was significantly reduced at times of high uptake rates and coincided with strong reductions of assimilation rates. O₃ uptake was lowered in the 100-ppb treatment due to reduced g_s. There was serious visible damage by the end of the exposure period in the 100-ppb treatment, while the treatment with 40 ppb O₃ did not seem to cause any significant changes.     

Identification of novel low M(r) glutenin subunits in the high quality bread wheat cv Salmone and their effects on gluten quality

Southern-blot hybridization with a probe specific for genes encoding for low M_r glutenin subunits showed that the high quality bread wheat cv Salmone contains two DNA fragments designated as SF720 and SF750. These fragments were found to occur on the chromosome-1B satellite, and to be associated with the presence of two strongly staining low M_r glutenin subunits in the two-dimensional A-PAGE 2 SDS-PAGE pattern of cv Salmone. Comparison of 65 F₆ random lines derived from the cross between cv Salmone and the medium quality line FAP74809 revealed that the presence of fragments SF720 and SF750 had significant positive effects on several quality related parameters such as SDS sedimentation volume, Farinograph stability and Alveograph strength (W), tenacity (P) and elasticity (L). Additive effects of high M_r glutenin subunits 1 and 7+9 on gluten quality were found as well. Fragments SF720 and SF750 were suggested to occur at a locus other than Glu-B3, as indicated by their relatively high frequency of recombination with the Gli-B1 locus.     

Obtaining the Morse parameter for large bond-stretching using Murrell-Sorbie parameters

Although the second derivative approach has been shown to provide good parameter relationships between any two interatomic potential functions, these relations are valid only at and near the equilibrium point. Arising from the significant discrepancy between connected potential functions for large stretching of covalent bonds by the second derivative approach, an integral approach is developed herein. By equating interatomic energy integral from equilibrium to bond dissociation, the overall discrepancy is minimized for that range between the Morse and Murrell-Sorbie potential functions. Plotted results reveal two observations. First of all, the second derivative approach is appropriate for bond compression and infinitesimal bond stretching, while the integral approach is more suitable when the extent of bond stretching is significant. Secondly, the Morse function exactly fits the Murrell-Sorbie curve when the Morse shape parameters based on the second derivative and integral approaches are equal. Hence a criterion for determining the accuracy level of Murrell-Sorbie parameters for conversion to Morse parameter is established. Finally, a demonstration was made for cases where a clear discrepancy was observed in the potential energy curves. It was found that the integral approach gives a more conservative and more realistic interatomic force curve than those of derivative approach. Figure Morse potential force using Murrell-Sorbie parameters     

Petiole mechanics, leaf inclination, morphology, and investment in support in relation to light availability in the canopy of Liriodendron tulipifera

To determine the role of leaf mechanical properties in altering foliar inclination angles, and the nutrient and carbon costs of specific foliar angle variation patterns along the canopy, leaf structural and biomechanical characteristics, biomass partitioning into support, and foliar nitrogen and carbon concentrations were studied in the temperate deciduous species Liriodendron tulipifera L., which possesses large leaves on long petioles. We used beam theory to model leaf lamina as a uniform load, and estimated both the lamina and petiole flexural stiffness, which characterizes the resistance to bending of foliar elements at a common load and length. Petiole and lamina vertical inclination angles with respect to horizontal increased with increasing average daily integrated photon flux density (Q_int). Yet, the light effects on lamina inclination angle were primary determined by the petiole inclination angle. Although the petioles and laminas became longer, and the lamina loads increased with increasing Q_int, the flexural stiffness of both lamina and petiole increased to compensate for this, such that the lamina vertical displacement was only weakly related to Q_int. In addition, increases and decreases in the petiole inclination angle with respect to the horizontal effectively reduced the distance of lamina load from the axis of rotation, thereby reducing the bending moments and lamina inclination due to gravity. We demonstrate that large investments, up to 30% of total leaf biomass, in petiole and large veins are necessary to maintain the lamina at a specific position, but also that light has no direct effect on the fractional biomass investment in support. However, we provide evidence that apart from light availability, structural and chemical characteristics of the foliage may also be affected by water stress, magnitude of which scales positively with Q_int.     

Computation of the bond dissociation enthalpies and free energies of hydroxylic antioxidants using the ab initio Hartree–Fock method

Abstract

Introduction

A new method for calculating theoretical bond dissociation enthalpy (BDE) and bond dissociation free energy (BDFE) of hydroxylic antioxidants is forwarded. BDE and BDFE may be understood as activation energies accompanying the formation of transition states, which may undergo downhill homolytic dissociation. The new method does not involve the complete fission of O–H bonds.

Method

Theoretical gas phase BDE values were calculated with the ab initio unrestricted Hartree–Fock (UHF) method, as changes in enthalpy between ground singlet states (GS) and triplet dissociative states (DS). Similarly, gas phase BDFEs were estimated from the corresponding changes in Gibbs free energy. The results were then compared with reliable experimental reports.

Results

The proposed theoretical approach of BDE and BDFE determination was tested using 10 simple phenols, 5 flavonoids, and l-ascorbic acid derivatives. The agreement between our calculated gas phase results and the adopted experimental values were generally within 0.5 kcal mol^?1, with a very few exceptions.

Discussion

Generally, steric interactions as well as intramolecular hydrogen bonding involving the dissociating OH group should be minimized in the GS. The DS are both electronically and vibrationally exited transition states. They have one unpaired electron on the carbon atom, which bears the homolytically dissociating OH group and are second order saddle points with a fixed <C–O–H bond angel of 180°.

Conclusion

It was concluded that ab initio UHF was well suited for the estimation of gas phase BDE and BDFE. The method presented has a good potential for application across a range of hydroxylic antioxidants. Currently, work is underway to extend its application in other class of antioxidants.