William P. Henry

Developing environmentally benign and effective organic wood preservatives by understanding the biocidal and non-biocidal properties of extractives in naturally durable heartwood

Abstract Wood products for exterior residential applications have long been protected with metallic preservatives. However, environmental and disposal concerns and governmental regulations have resulted in a growing trend to employ organic systems based on relatively benign and expensive agrochemicals. To develop organic preservatives that have increased efficacy and lower cost, various groups are studying the biocidal and non-biocidal properties of extractives present in naturally durable heartwoods. In this study, we determined the fungicidal, free radical scavenger/antioxidant, metal chelation and Fe3+ reducing properties of some flavones and flavonoid analogs and chromones. The results support our earlier hypothesis that the abiotic antioxidant, Fe3+ reduction and subsequent metal complexation properties, in combination with the extractives’ fungicidal properties, all have a role in natural durability. Consequently, it may be possible to employ non-biocidal additive(s) with the above abiotic properties to enhance the efficacy of the relatively expensive organic agrochemicals used to protect wood.

Iron binding of 3-hydroxychromone, 5-hydroxychromone, and sulfonated morin: Implications for the antioxidant activity of flavonols with competing metal binding sites

The iron binding properties and antioxidant activities of compounds with hydroxy-keto binding sites, 3-hydroxychromone, 5-hydroxychromone, and sulfonated morin were investigated. For these compounds, prevention of iron-mediated DNA damage and kinetics of Fe(II) oxidation were studied in aqueous solutions close to physiological pH (pH 6). 3-Hydroxychromone and sulfonated morin inhibit iron-mediated DNA damage at lower concentrations than 5-hydroxychromone. All three compounds bind iron, but 3-hydroxychromone and sulfonated morin promote Fe(II) oxidation much faster than 5-hydroxychromone. These results indicate that DNA damage inhibition by flavonols with competing hydroxy-keto binding sites is primarily due to iron binding at the 3-hydroxy-keto site. Iron oxidation rate also plays a significant role in antioxidant activity. In addition to iron binding and oxidation, reactive oxygen species scavenging occurs at high concentrations for the hydroxychromones. This study emphasizes the importance of iron binding in polyphenol antioxidant behavior and provides insights into the iron binding antioxidant activity of similar flavonols such as quercetin and myricetin.

Metal chelation studies relevant to wood preservation. 1. Complexation of propyl gallate with Fe2

Abstract We previously found that a combination of various organic biocides with low-cost non-biocidal antioxidants gave enhanced (synergistic) efficacy against wood-decaying fungi. The best laboratory results were obtained with propyl gallate, perhaps due to its dual antioxidant/metalchelating properties. In this study we report on potentiometric titration experiments for the complexation of Fe2+ with propyl gallate. The results suggest four coordination compounds are present in the pH range from 3 to 12. These are [(H2PG)Fe]+, (HPG)Fe, [(PG)Fe]−, and [(HPG)2Fe]2− {PG=O3C6H2CO2CH2CH2CH33−}. Equilibrium constants for the formation of all complexes are given. A plot of species present versus pH clearly indicates that propyl gallate strongly complexes with Fe2+ at the mildly acidic pH levels normally present in wood, with some complexing still possible in relatively acidic environments present in decaying wood. Propyl gallate complexes more strongly than catechol at the pH values of normal wood. Propyl gallate may also interfere with the proposed fungal redox cycles. Metal complexation may thus be an important part in the overall mechanism by which propyl gallate and organic biocides synergistically protect wood. Furthermore, the metal chelating properties of heartwood extractives, such as the hydrolysable tannins from which propyl gallate is made, may be an important factor in natural durability.

Efficacy of a copper(II)/oxine copper wood preservative mixture after 69 months of outdoor ground-contact exposure and a proposed mechanism to explain the observed synergism

Abstract Ground-contact stakes, made from defect-free southern yellow pine sapwood, were treated with water-borne copper(II) [ammoniacal copper carbonate, ACC, Cu(II)] alone, oil-borne oxine copper (Cu-8) alone, or a dual treatment of ACC followed by drying and then Cu-8. The treated stakes were installed at two locations in Mississippi (Dorman Lake and Saucier) in high- or severe-deterioration hazard zones and inspected after 69 months of exposure. Stakes treated with Cu(II) alone at the highest retention of 5.1 kg m−3 [copper retention is based on the copper oxide (CuO) weight, as is standard in the US] performed moderately well at the Saucier test site, with decay and termite ratings of 8.0 out of 10.0, but unsatisfactory at the Dorman Lake test plot, with decay and termite ratings both below 7.0. Samples treated with Cu-8 alone at the highest retention of 1.92 kg m−3 had poor termite protection, with ratings below 7 at both sites, and only fair decay ratings of 7.0 (Dorman Lake) and 7.6 (Saucier). In contrast, all stakes treated with Cu(II)/Cu-8 combinations, with at least 2.4 kg m−3 Cu(II) and 0.2 kg m−3 Cu-8, performed satisfactorily, with average decay and termite ratings all above 8.0 at both locations. The addition of Cu(II) to Cu-8 likely causes the di-ligand form [bis(8-hydroxyquinolinolate)Cu(II)] to equilibrate principally to the mono form. Thus, the combination of Cu(II) and Cu-8 appears to form a new compound with greater efficacy than either of the two starting “reagents” and, consequently, this mixture is not literally synergistic. Possible advantages of mono Cu-8 include: (1) the mono form may be easier to formulate in a water- or solvent-borne system than the commercial bis-Cu-8 biocide; (2) the preservative would have a relatively low metal content, which may make future disposal of treated wood easier; (3) this system would likely have much fewer metal corrosion problems than preservative systems formulated with uncomplexed copper(II); and (4) the two copper coordination sites that are not complexed with the ligand could bind to the carboxylic or phenolic groups in wood to make the mono form relatively leach-resistant.

The crystal structure of the bis-tricarbonylchromium complex of dibenzo[a,e]cyclooctatetraene: Cr(CO)3 orientation controlled by short C–H⋯O hydrogen bonding

Abstract The structure of the title compound, 1, was determined by X-ray crystallography. One tricarbonylchromium [syn-Cr(CO)3] moiety is bound to the concave side of the dibenzo[a,e]cyclooctatetraene ligand while the other metal is bound to the convex side yielding an anti-Cr(CO)3. There are four independent molecules in the crystal with the main difference between them being the orientation of the anti-Cr(CO)3. Analysis of intermolecular interactions in the solid state confirms that the variable tripodal rotations are the result of short C–H···O(carbonyl) hydrogen bonds. In 1, the organic framework has flattened slightly relative to uncoordinated dibenzo[a,e]cyclooctatetraene.

Iron antagonism of MSMA herbicide applied to bermudagrass: characterization of the Fe2+-MAA complexation reaction

Abstract Discoloration of bermudagrass often results from application of MSMA herbicide used to control southern crabgrass and other weeds. However, when products containing iron sulfate (FeSO4) are tank-mixed with MSMA, this discoloration is reduced. Experiments investigated the effect of tank-mixing organic arsenical herbicides with FeSO4 or a chelated iron source (Sprint 330) in terms of southern crabgrass control and injury to bermudagrass. Tank-mixing MSMA with FeSO4 reduced bermudagrass injury. However, southern crabgrass control was also reduced by at least 50% with the addition of ≥0.38 kg Fe2+ ha−1. Neither antagonism nor safening of bermudagrass was observed when the chelated Fe2+ source was used. Applying FeSO4 as a separate treatment 1 to 4 d before or after MSMA application did not reduce visual burmudagrass injury 1 wk after treatment. Solution pH and FeSO4 concentration controlled the extent of complexation and level of antagonism observed in the field; inorganic Fe2+ reacted with MSMA to form a complex having reduced herbicidal activity. Potentiometric and spectrophotometric investigations found that methylarsonate, the parent acid of MSMA and other organic arsenical herbicides, reacts with inorganic Fe2+ to form a stable 1:1 Fe2+-methylarsonic acid chelate having two points of metal coordination and a stability constant log10 (β) = 2.77 ± 0.04. Tank-mixing MSMA with FeSO4 to protect against bermudagrass injury negates the benefit of applying the herbicide for weed control, and therefore is not a recommendable practice for turf managers. Nomenclature: MSMA; common bermudagrass, Cynodon dactylon (L.) Pers.; southern crabgrass, Digitaria sanguinalis (L.) Scop. DIGSP.

Effect of Polyvinyl Alcohol on Copper Leaching from Treated Wood

The new copper-based preservative systems leach a relatively high level of copper and, thus, generate some environmental concerns. Polyvinyl alcohol (PVOH) is known to complex with copper(II) and is water soluble. The effect of co-addition of fully hydrolyzed PVOH on the leaching of copper from wood treated with three different copper salts was examined. Southern pine sapwood wafers were treated with copper sulfate, copper acetate, and ammoniacal copper carbonate, all with 1 percent elemental copper in the waterborne solution, with and without 2 percent PVOH. The wafers were then dried and water leached for 2 weeks. PVOH co-addition greatly reduced the copper leached from wood treated with alkaline ammoniacal copper carbonate but not from wood treated with a slightly acidic solution of copper acetate or highly acidic copper sulfate.

Methanol Synthesis and Decomposition Reactions Catalyzed by a Model Catalyst Developed from Bis(1,5-diphenyl-1,3,5-pentanetrionato)dicopper(II)/Silica

Silica-supported model copper catalysts were prepared by supporting bis(1,5-diphenyl-1,3,5-pentanetrionato)dicopper(II), Cu2(dba)2, on Cab-O-Sil by a batch impregnation technique. This metal complex showed a strong affinity for the silica support, developing monolayer coverages near the value predicted from a consideration of the size and shape of the planar metal complex (2.6 wt % Cu). The supported catalysts were subsequently activated by decomposing the organic ligands at 400 °C in air followed by reduction with 2% H2/He at 250 °C. One sample was prepared having a loading of 3.70 wt % Cu2(dba)2/silica catalyst, and it was examined for the methanol synthesis reaction under the following conditions: 250 °C with an equimolar gas mixture of CO and H2 in a high-pressure batch reactor. Kinetic data over the model catalyst were fit to a rate equation, second order in the limiting reactant (H2), with a pseudo-second-order rate constant k2[CO]o[H2]o = 0.0957 [h-g total Cu]−1. A control experiment using a commercial catalyst, Cu/ZnO/Al2O3 with a copper loading of 41.20 wt %, showed a value of k2[CO]o[H2]o = 0.793 [h-g total Cu]−1. A fresh sample of Cu2(dba)2/silica was examined for methanol decomposition reaction at 220 °C. The model catalyst shows a methanol decomposition first-order rate constant greater than that of the commercial Cu/ZnO/Al2O3catalyst: 1.59 × 10–1 [min-g total Cu]−1 versus 9.6 × 10–3 [min-g total Cu]−1. X-ray diffraction analyzes confirm the presence of CuO particles in both catalysts after calcinations. Copper metal particles were found in both catalysts (fractional Cu dispersions were 0.11 and 0.16 on commercial and model catalysts, respectively) after the reduced catalysts were used in both the methanol synthesis and decomposition reactions. Using the values of copper dispersion found in these samples, we recalculated the rate constants for the two reactions per unit surface copper. These refined rate constants showed the same trends as those reported per total amount of Cu. One role of the promoter(s) in the commercial catalyst is the inhibition of the methanol decomposition reaction, thus allowing higher MeOH synthesis reaction rates in those regimes not controlled by thermodynamics.

CCDC 893855: Experimental Crystal Structure Determination

Related Article: Nilantha Bandara, Chinthaka N. Ratnaweera, Steven R. Gwaltney, William P. Henry|2013|J.Organomet.Chem.|745|86|doi:10.1016/j.jorganchem.2013.06.029