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Novel simple and highly modular dipeptide-analogue ligands combined with [RuCl2(p-cymene)]2 were demonstrated to efficiently catalyze the reduction of ketones under hydrogen transfer conditions with enantioselectivities up to 96%.
This communication reports the preparation of a novel trans-chelating diphosphine, 1,5-bis(di-tert-butylphosphino)-2-(S)-dimethylaminopentane, that undergoes triple C-H activation in reaction with [RuCl2(p-cymene)]2 to give a chiral square-pyramidal 16-electron carbene complex of ruthenium.
The activation of 1,1-diphenyl-2-propyn-1-ol by complexes [RuCl(eta(6)-p-cymene)[eta(2)-P,N-Ph(2)PCH(2)P([=NR)Ph(2)]](+) results in the formation of the unusual tethered (eta(6)-arene)-ruthenium(ii) derivatives, via an unprecedented iminophosphorane-allenylidene coupling process.
The radical complexes [(micro-L)[Ru(bpy)(2)](2)]*(3+), [(micro-bmtz)[Ru(cym)Cl](2)]*(+) and [(micro-L)[Re(CO)(3)Cl](2)]*(-), where L are 3,6-disubstituted 1,2,4,5-tetrazines such as 3,6-bis(2-pyrimidyl)-1,2,4,5-tetrazine (bmtz) and cym =p-cymene, were studied by X-band EPR in fluid solution and by 285 GHz EPR in glassy frozen solution. A comparison with other transition metal complexes (Cu, Rh, Os, Ir, Pt) involving tetrazine radical ligands reveals that the g anisotropy reflects (i) the pi acceptor effect of the tetrazine substituents, (ii) the competition from ancillary pi acceptor ligands for back donation from the metal, and (iii) the spin-orbit coupling contributions from the transition metal.
The 1.6 [Angstrom] X-ray crystal structure of [(eta(6)-p-cymene)Ru(lysozyme)Cl(2)], the first of a half-sandwich complex of a protein, shows selective ruthenation of Nepsilon of the imidazole ring of His15.
Reduction of 4-(p-cymene)-4,1,12-closo-RuC2B10H12 followed by metallation with {M'} fragments (M' = {CpCo2+}, {(arene)Ru2+} or {(dppe)Ni2+}) affords 14-vertex bimetallic 1,14,2,10-RuM'C2B10 species having bicapped hexagonal antiprismatic structures.
A coordination cage with an elusive icosahedral geometry was obtained by K+-induced rearrangement of a hexanuclear [(cymene)Ru(pyridine-3,5-dicarboxylate)]6 complex.
The assembly of soluble, air-stable, binuclear structures, namely {(p-cymene)Ru[S(2)C(2)(B(10)H(10))]}(2)(micro-pyz), {Cp*Co[S(2)C(2)(B(10)H(10))]}(2)(micro-pyz), {Cp*Co[S(2)C(2)(B(10)H(10))]}(2)(micro-bpy), {Cp*Co[S(2)C(2)(B(10)H(10))]}(2)(micro-bpe) and {Cp*Ir[E(2)C(2)(B(10)H(10))]}(2)(micro-bpo) (E = S (), Se), in which organometallic units are bridged by pyridyl-based organic linkers, are synthesized. The complexes have been fully characterized by IR and NMR spectroscopy, as well as elemental analysis. The molecular structures are established through X-ray crystallography.
The activation of tris(dimethylamino)borane towards reaction with a chiral methimazole by N-methylimidazole has been used to prepare the first example of a chiral tris(methimazolyl)borate ligand. Coordination of this neutral ligand to Ru(II) has been achieved by reaction with [(p-cymene)RuCl(2)](2) to provide a single diastereomer complex in which the chirality of the methimazolyl substituents dictate the chirality of the bicyclo[3.3.3]cage formed by the ligand on coordination to the metal. The alternative approach to chiral tris(methimazolyl)borate ligands involving the introduction of a chiral group onto the boron atom has been explored by replacing N-methylimidazole in the above reaction by chiral oxazolines as activating bases in reaction with simple methimazole. However, although the B(NMe(2))(3) is activated to reaction with methimazole by these oxazolines, an intramolecular oxazoline ring-opening by a coordinated methimazolyl sulfur occurs and prevents the successful synthesis of these ligands.
AIMS: This study compared the antimicrobial activity of Melaleuca alternifolia (tea tree) oil with that of some of its components, both individually and in two-component combinations. METHODS AND RESULTS: Minimum inhibitory concentration and time-kill assays revealed that terpinen-4-ol, the principal active component of tea tree oil, was more active on its own than when present in tea tree oil. Combinations of terpinen-4-ol and either gamma-terpinene or p-cymene produced similar activities to tea tree oil. Concentration-dependent reductions in terpinen-4-ol activity and solubility also occurred in the presence of gamma-terpinene. CONCLUSION: Non-oxygenated terpenes in tea tree oil appear to reduce terpinen-4-ol efficacy by lowering its aqueous solubility. SIGNIFICANCE AND IMPACT OF THE STUDY: These findings explain why tea tree oil can be less active in vitro than terpinen-4-ol alone and further suggest that the presence of a non-aqueous phase in tea tree oil formulations may limit the microbial availability of its active components.
Pseudomonas aeruginosa is less susceptible to the antimicrobial properties of tea tree oil than many bacteria and its tolerance is considered to be due to its outer membrane. Polymyxin B nonapeptide (PMBN), which has no antibacterial action, was used to permeabilize the outer membrane. The addition of PMBN to Ps. aeruginosa NCTC 6749 markedly increased this organism's susceptibility to tea tree oil and to its normally inert hydrocarbons, p-cymene and gamma-terpinene.
The oil from the aerial parts of Lippia laxibracteata Herzog (Verbenaceae) was obtained by hydrodistillation and analyzed by GC and GC/MS. The major component of the oil was thymol (67%) with minor amounts of p-cymene (10%), cis-beta-ocimene (7%) and carvacrol (4.5%).
The composition and the antimicrobial activity of the bark oil of Croton stellulifer, an endemic and rare species of these islands (S. Tomé and Príncipe) are reported. Analysis was carried out by GC, GC/MS and 13C-NMR. The major constituents were alpha-phellandrene (15.4-18.6%), p-cymene (14.4-17.7%), linalool (12.0-12.6%) and alpha-pinene (8.1-9.1%). Kessane, a sesquiterpenoid oxide, not yet reported in the genus Croton, was identified by NMR. The essential oil of C. stellulifer was active against both bacterial and fungal strains, except Aspergillus niger.
The volatile fraction of Tambourissa leptophylla fruit skin was extracted by petrol ether, purified by adsorption chromatography (LPC) and analysed by gas chromatographic-spectroscopic methods. 27 non-oxygenated terpene hydrocarbons and 10 oxygenated derivatives were identified. The most abundant components were: limonene (24.0%), cis-alpha-bergamotene (23.2%), delta-3-carene (8.2%), alpha-curcumene (6.0%), trans-alpha-bergamotene (5.1%), alpha-copaene (4.1%), alpha-pinene (4.0%), p-cymene (4.0%) and bicyclogermacrene (3.3%). The crude volatile fraction was tested in vitro against Cladosporium cucumerinum in direct bioautography on TLC plates on the basis of the antifungal use of fruit skin. Activity of petrol ether extract against this micro-organism was demonstrated.
The chemical composition of the essential oils of Calea clematidea Baker obtained by hydrodistillation of the leaves and flowers was analysed by GC and GC/MS and the oils were assayed for their antifungal activities. The essential oil of the leaves showed a high content of a new natural epoxy terpenoid, named clemateol (ca. 70 %), with minor amounts of o-vanillin (6.5 %), spathulenol (4.2 %), alpha-terpinene (4.0 %), germacrene B (2.9 %), yomogi alcohol (1.8 %), ( E)-caryophylene (1.7 %), m-cymenene (1.6 %), and alpha-gurjunene (1.5 %), while the essential oil of the flowers was characterized by a higher content of thymol methyl ether (ca. 80 %), with minor amounts of clemateol (4.8 %) and o-cymene (4.7 %). The antimicrobial activity of the oils was also evaluated against dermatophytes for their possible use in pharmaceutical preparations for topical applications. The oil of the leaves (MIC > 3.57 mg/ml), clemateol (MIC > 1.52 mg/ml), and the alcohol 2 (MIC > 2.82 mg/ml) showed a moderate antifungal activity against Trichophyton tonsurans, Trichophyton rubrum, Trichophyton menthagrophytes var. i nterdigitale, Epidermophyton floccosum, Microsporum gypseum, Microsporum canis and Microsporum nanum.
The composition and the antimicrobial activity of the essential oil of Lippia graveolens H.B.K. collected in Guatemala were studied. Two samples of essential oils were obtained from the aerial parts of the plant by hydrodistillation and analyzed by GC and GC-MS. The oils were characterized by their high content of monoterpenes (70.0-87.2 %). Important differences between the major constituents were found, particularly for carvacrol (0.2 vs. 44.8 %), thymol (18.1 vs. 7.4 %) and p-cymene (6.8 vs. 21.8 %). Both oils showed significant activity against all tested Gram-positive and Gram-negative bacteria, as well as against fungi. Nevertheless, the oil with the higher carvacrol content was found to be more active than the thymol type, with MICs ranging from 0.25 to 0.83 microL/mL and 0.12 to 0.27 microL/mL for bacteria and fungi, respectively.
The essential oils of Satureja parnassica subsp. parnassica (samples A and B), were analyzed by means of GC/MS. From the fifty-seven identified constituents representing 98.5 % and 99.35 % of the oils respectively, ( E)-caryophyllene, carvacrol and caryophyllene oxide were the major components of sample A (flowering stage), whereas in sample B (vegetative stage) major components were spathulenol, p-cymene and linalool. The oils were tested against Helicobacter pylori (HP), as well as against six aerobically growing bacteria. Both samples showed a moderate activity against Gram-positive bacteria; sample A oil showed greater anti-HP activity than sample B.
The composition and the antifungal activity of the essential oil of Origanum virens on Candida species were studied. The essential oil was obtained from the aerial parts of the plant by hydrodistillation and analyzed by GC and GC-MS. The oil was characterized by its high content of carvacrol (68.1 %) and its biogenetic precursors, gamma-terpinene (9.9 %) and p-cymene (4.5 %). The minimal inhibitory concentration (MIC) and the minimal lethal concentration (MLC) were used to evaluate the antifungal activity against Candida strains (7 clinical isolates and 3 ATCC type strains). The inhibition of germ tube formation and flow cytometry, using the fluorescent probe propidium iodide (PI), were used to evaluate their mechanisms of action. MIC and MLC values were similar for most tested strains, ranging from 0.16 to 0.32 microL/mL. Concentrations lower than MIC values strongly prevent germ tube formation. The fungicidal effect is primarily due to an extensive lesion of the membrane.