Antioxidant activity of propofol and related monomeric and dimeric compounds

This study was carried out to investigate the antioxidant activity of propofol (2,6-diisopropylphenol) and its related compounds, butylated hydroxyanisole (BHA), 2,6-dimethylphenol, 2,6-di-t-butylphenol, and their dimeric compounds. The degree of antioxidant activity was evaluated based on the degree of peroxidation induced with Fe-ascorbic acid in egg phosphatidylcholine through the determination of thiobarbituric acid-reactive substances (TBARS) formed during peroxidation. Their antioxidant activities were in the order of dipropofol>di(2,6-di-t-butylphenol)>diBHA>di(2,6-dimethylphenol). Dipropofol, a dimeric compound of propofol, showed the highest antioxidant activities. Dimeric compounds had higher activities than monomeric compounds, and the 1,1-diphenyl-p-picryhydrazyl-trapping ability of dimeric compounds was also greater than those of monomeric compounds (4-10-fold). These results suggest that dimeric phenols may increase their antioxidant activities along with increments in the conjugation system and play a inhibitory role in the propagation of free radical chain reactions.     

Antioxidant activity and kinetics studies of eugenol and 6-bromoeugenol

In this work, we report the antioxidant and free radical scavenging activity of 6-bromoeugenol and eugenol. EC₅₀, the concentration providing 50% inhibition, is calculated and the antioxidant activity index (AAI) is evaluated. The antioxidant activity was evaluated using 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging method. EC₅₀ values of 6-bromoeugenol, ascorbic acid and eugenol were 34.270 μg/mL, 54.888 μg/mL and 130.485 μg/mL, respectively. 6-Bromoeugenol showed higher AAI value (1.122) followed by ascorbic acid (0.700), then by eugenol (0.295). We also investigate the kinetics of DPPH radical scavenging activity of our products to determine the useful parameter TEC₅₀ to evaluate their antiradical efficiency (ARE). Our results have shown high ARE. This study has provided the following ARE ( × 10^? 3) order for the tested antioxidants: ascorbic acid (70.119)>6-bromoeugenol (34.842) > eugenol (21.313). Finally, we classify ascorbic acid and eugenol as fast kinetics reaction (TEC₅₀ 8.82 and 11.38 min, respectively) and 6-bromoeugenol as medium kinetics reaction (TEC₅₀ 39.24 min).     

Unusual fluorescent monomeric and dimeric dialkynyl dipyrromethene-borane complexes

Novel monomeric and dimeric dialkynyl borondipyrromethene dyes (E-Bodipy) have been prepared in two different ways, providing systems in which the boron center is attached to either two similar or two dissimilar acetylenic units incorporating chromophores such as pyrene or anthracene. Both families exhibit interesting fluorescence and redox properties in which almost quantitative intramolecular energy transfer occurs.     

Dimethylalkoxygallanes: monomeric versus dimeric gas-phase structures

The molecular structures of the vapors produced on heating dimethylalkoxygallanes of the type [Me(2)Ga(OR)](2) have been determined by gas electron diffraction and ab initio molecular orbital calculations. In the solid state [Me(2)Ga(OCH(2)CH(2)NMe(2))](2) (1) and [Me(2)Ga(OCH(2)CH(2)OMe)](2) (2) adopt dimeric structures, although only the monomeric forms [Me(2)Ga(OCH(2)CH(2)NMe(2))] (1a) and [Me(2)Ga(OCH(2)CH(2)OMe)] (2a) were observed in the gas phase. For comparison the structure of the vapor produced on heating [Me(2)Ga(O(t)Bu)](2) (3) was also studied by gas electron diffraction. In contrast to 1 and 2, compound 3 is dimeric in the gas phase, as well as in the solid state. The gas-phase structures of 1a and 2a exhibit five-membered rings formed by a dative bond between Ga and the donor atom (N or O) from the donor-functionalized alkoxide. In 3 there is no possibility of a monomeric structure being stabilized by the formation of such a dative bond since only a monofunctional alkoxide is present in the molecule.     

Modeling water exchange on monomeric and dimeric Mn centers

Water exchange on Mn centers in proteins has been modeled with density functional theory using the B3LYP functional. The reaction barrier for dissociative water exchange on [Mn^IV(H₂O)₂(OH)₄] is only 9.6 kcal mol^–1, corresponding to a rate of 6×10⁵ s^–1. It has also been investigated how modifications of the model complex change the exchange rate. Three cases of water exchange on Mn dimers have been modeled. The reaction barrier for dissociative exchange of a terminal water ligand on [(H₂O)₂(OH)₂Mn^IV(-O)₂Mn^IV(H₂O)₂(OH)₂] is 8.6 kcal mol^–1, while the bridging oxo group exchange with a ring-opening mechanism has a barrier of 19.2 kcal mol^–1. These results are intended for interpretations of measurements of water exchange for the oxygen evolving complex of photosystem II. Finally, a tautomerization mechanism for exchange of a terminal oxyl radical has been modeled for the synthetic O₂ catalyst [(terpy)(H₂O)Mn^IV(-O)₂Mn^IV(O)(terpy)]³⁺ (terpy=2,2:6,2-terpyridine). The calculated reaction barrier is 14.7 kcal mol^–1.Contribution to the Björn Roos Honorary Issue     

Mass spectral fragmentation studies in monomeric and dimeric coumarins

A study on the behavior of a large number of monomeric and dimeric coumarins in the mass spectrometer is reported and discussed. The results illustrate that the observed characteristic fragmentation patterns are of considerable utility in the application of mass spectrometry to structure elucidation in this series.     

Comparative study of planar motion in monomeric and dimeric discotics

Deuterium NMR spectra are reported in powder samples of discotic monomer and dimer as a function of temperature in their column Col(ho) phases. To simulate the observed powder patterns, a threefold jump model is used in the monomer, while in the related dimer the libration motion of the monomeric core is described using the infinitesimal jump method under a restricting potential due to the spacer. By comparing the diffusive rates for the two samples, it is concluded that the planar motion in the dimer is at least 30 times smaller than that of the monomer. This could lead to an enhancement of charge and energy transport in discotic dimer systems.     

Binding of monomeric and dimeric Concanavalin A to mannose-functionalized dendrimers

Because of the central role of Concanavalin A (Con A) in the study of protein-carbohydrate interactions, a thorough understanding of the multivalent functions of Con A is imperative. Here, the association of monomeric and dimeric derivatives of Con A with mannose-functionalized generation two through six PAMAM dendrimers is reported. Hemagglutination assay results indicate relatively low activity of the dendrimers for monomeric Con A, with small increases as the dendrimer generation increases. Isothermal titration microcalorimetry experiments indicate monovalent binding by the dendrimers with monomeric Con A and divalent binding by the dendrimers with dimeric Con A. Continuous (and comparable) but narrowing increases in enthalpy and entropy and the slight increase in association constants with monomeric Con A as the dendrimer generation increases suggest favorable proximity effects on binding. Both the hemagglutination assay and the calorimetry experiments suggest that statistical binding enhancements can be observed with monomeric Con A. The results described here should allow for a more quantitative evaluation of the enhancements that are often observed in protein-carbohydrate interactions for glycosylated frameworks binding to Con A.     

Photosynthesis of dimeric cinnamaldehyde,eugenol, and safrole as antimicrobial agents

It has been reported that trans-cinnamaldehyde, eugenol and safrole inhibited bacteria and fungi growth in vivo mode. In order to improve their biological activity, dimeric cinnamaldehyde, eugenol and safrole have been photosynthesized. The photosynthesis compounds were 4,6-diphenyl-1,2-dioxane-3,5-dicarboxaldehyde, 4,4-(cyclobutone-1,3-diyl bis(methylene))bis(2-methoxyphenal), and 3,6-bis(benzo[d][1,3]dioxol-5-ylmethyl)-1,2-dioxane. These new dimeric compounds strongly inhibited Candida albicans growth more than the monomers.     

Lithium aminoborohydrides 16. Synthesis and reactions of monomeric and dimeric aminoboranes

Aminoboranes are synthesized in situ from the reaction of the corresponding lithium aminoborohydrides (LABs) with methyl iodide, trimethylsilylchloride (TMS-Cl), or benzyl chloride under ambient conditions. In hexanes, the reaction using methyl iodide produces aminoborane and methane, whereas in tetrahydro-furan (THF) this reaction produces amine-boranes (R1R2HN:BH3) as the major product. The reaction of iPr-LAB with TMS-Cl or benzyl chloride yields exclusively diisopropylaminoborane [BH2-N(iPr)2] in THF as well as in hexanes at 25 degrees C. Diisopropylaminoborane and dicyclohexylaminoborane exist as monomers due to the steric requirement of the alkyl group. All other aminoboranes studied are not sterically hindered enough to be monomers in solution, but instead exist as a mixture of monomers and dimers. The dimers are four-membered rings formed through boron-nitrogen coordination. In general aminoboranes are not hydroborating reagents. However, monomeric aminoboranes, such as BH2-N(iPr)2, can reduce nitriles in the presence of catalytic amounts of LiBH4. This BH2-N(iPr)2/LiBH4 reducing system also re-duces ketones, aldehydes, and esters. Diisopropylaminoborane, synthesized from iPr-LAB, can be converted into boronic acids by a palladium-catalyzed reaction with aryl bromides. Aminoboranes derived from heterocyclic amines, such as pyrrole, pyrazole, and imidazole, can be prepared by the direct reaction of borane/tetrahydrofuran (BH3:THF) with these heterocyclic amines. It has been reported that pyrazole-derived aminoborane forms a six-membered dimer through boron-nitrogen coordination, where as, pyrrolylborane forms a dimer through boron-hydrogen coordination. Pyrrolylborane monohydroborates both alkenes and alkynes at ambient temperatures. Hydroboration of styrene with pyrrolylborane followed by hydrolysis gives the corresponding boronic acid, 2-phenylethylboronic acid, in 40% yield. Similarly phenylacetylene is mono-hydroborated by pyrrolylborane, to give E-2-phenylethenylboronic acid in 50% yield.     

A monomeric selenium(IV) diimide and a dimeric seleninylamine

The selenium(IV) diimide AdN=Se=NAd (Ad = 1-adamantyl) adopts a monomeric structure with a Z,E configuration in the solid state whereas the seleninylamine OSe(mu-NBut)2SeO crystallizes as the cis-dimer.     

Ab initio calculations on the structure of monomeric and dimeric formic acid

Experiments show changes in the carbon-oxygen bond lengths when a carboxylic acid dimerizes. To see how these changes are depicted in the electronic structure, a series of ab initio calculations have been made on monomeric and dimeric formic acid. Both systems have been examined through energy optimalization and through a Mulliken population analysis.The experimental changes can be qualitatively explained by the calculations, however, the quantitative agreement is not as good as desired.The calculations on monomeric formic acid give valuable information on the possibility of separately computing the different structural parameters.     

Spatial and electronic structure of monomeric and dimeric complexes of carnosine with zinc

A molecular mechanics method in the MM⁺ semi-empirical field potentials and a quantum chemical method in the PM3 approximation are used to calculate the geometric and energy parameters of a biocarnosine molecule in two tautomeric forms of the imidazole ring. The electronic structures of monomeric and dimeric complexes of both carnosine forms with zinc are investigated     

Synthesis and antitumor activity of puupehedione and related compounds

The first enantiospecific synthesis of bioactive marine puupehedione (2) and related compounds from (−)-sclareol (11) is reported. The antitumor activity of these compounds was assayed and compared with that of the natural products.     

Synthesis and structural characterization of functionalized dimeric aluminophosphonates and a monomeric gallophosphonate anion

Reaction of t-BuP(O)(OSiMe(3))(OH) with Me(3)Al leads to the formation of [Me(2)Al(mu-O)(2)P(OSiMe(3))(t-Bu)](2) (1) whereas Me(2)AlCl reacts with Ph(2)P(O)(OH) to yield [(Cl)(Me)Al(mu-O)(2)PPh(2)](2) (2). These compounds represent the first examples of functionalized dimeric four-ring type aluminophosphonate systems. The double four-ring type gallophosphonate, namely, [t-BuPO(3)GaMe](4), reacts with n-Bu(4)NHF(2) under ambient conditions, resulting in the formation of a monomeric gallophosphonate [n-Bu(4)N][MeGa[t-BuPO(2)(OH)](3)] (3). These derivatives have been adequately characterized using various spectroscopic techniques and X-ray diffraction studies.     

Photochemical and photosensitizing properties of monomeric and dimeric Sn(IV)-protoporphyrin

Sn(IV)-protoporphyrin IX (Sn-Pp) in aqueous media exists as a mixture of monomeric and dimeric species, which can be readily distinguished on the basis of their absorption maxima at around 410 and 386 nm respectively. Sn-Pp dimers prevail as the pH is decreased and are characterized by a lower fluorescence quantum yield, a larger tendency to undergo photobleaching and a reduced photosensitizing efficiency compared with the Sn-Pp monomer. The photosensitizing action of Sn-Pp appears to involve the intermediacy of singlet oxygen (1O2) as shown by photo-oxidation studies with N-acetyl-tryptophanamide in light and deuterated water solutions. Using 1,3-diphenyl-isobenzofuran as a substrate, the quantum yield of 1O2 generation by monomeric Sn-Pp was found to be about 0.6.     

Synthesis and electrical properties of monomeric and dimeric iron-1,5-disubstituted 2,4-dithiobiurets

The synthesis of monomeric and polymeric iron-1,5-disubstituted 2,4-dithiobiurets having the general empirical formula (FeCl₃·L) where L = 1,5-diphenyl-2,4-dithiobiuret (DPDTB); 1,5-diparatelyl 2,4-dithiobiuret (DpTDTB); 1,5-diorthotolyl 2,4-dithiobiuret (DoTDTB); 1-phenyl 5-paratolyl-2,4-dithiobiuret (PpTDTB); 1-phenyl 5-orthotolyl 2,4-dithiobiuret (PoTDTB) is described. The complexes were characterized by elemental analysis, molar conductance, magnetic susceptibility, IR and UV spectra. The dielectric constant and resistivity of characterized samples were studied as a function of temperature. The data indicate possible transitions at 90 and 185°C for monomeric iron-complexes whereas polymeric iron-1,5-disubstituted-2,4-dithiobiuret shows no breaks.     

Role of dimeric and monomeric aluminum chlorides as catalysts is aromatic electrophilic substitution

Aromatic electrophilic substitution reactions were simulated by ab initio calculations of the intermediate complexes and transition states involving the dimeric and monomeric forms of aluminum chloride. With the monomeric form, breaking of the catalytic cycle should be expected due to formation of a stable intermediate complex. With the dimeric form, no such complex was revealed, implying a key role this form plays in the catalysis.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 9, 2004, pp. 1498–1503.Original Russian Text Copyright © 2004 by Volkov, Timoshkin, Suvorov.This revised version was published online in April 2005 with a corrected cover date.     

Micellization of monomeric and dimeric (gemini) surfactants in polar nonaqueous-water-mixed solvents

Dimeric or gemini surfactants are novel surfactants that are finding a great deal of discussion in the academic and industrial arena. They consist of two hydrophobic chains and two polar head groups covalently linked by a spacer. Data on critical micelle concentration (cmc) and degree of counterion dissociation (α) are reported on bis-cationic C₁₆H₃₃N⁺(CH₃)₂–(CH₂)_s–N⁺(CH₃)₂C₁₆H₃₃, 2Br⁻, referred to as 16-s-16, for spacer lengths s=4, 5, 6 in aqueous and in polar nonaqueous (1-propanol, 2-methoxyethanol or methyl cellosolve, dimethyl sulfoxide, acetonitrile)-water-mixed solvents. The behavior is compared with conventional monomeric surfactant cetyltrimethylammonium bromide (CTAB). Thermodynamic parameters are obtained from the temperature dependence of the cmc values. It is observed that micellization tendency of the surfactants decreases in the presence of polar nonaqueous solvents. However, detailed studies with dimethylsulfoxide (DMSO) show that the geminis nearly outclass the micellization-arresting property of this solvent. Also, within geminis, higher spacer length is found suitable for showing micellization even with high DMSO content (50% v/v). The implications of these results of gemini micellization may be useful in micellar catalysis in polar nonaqueous solvents.     

Synthesis and analgetic activity of sulfur-containing morphinans and related compounds

3-Acylthiomorphinans, 3-carbamoylthio-3-deoxydihydromorphine and 3-benzoylthio-9-aza-17-carbamorphinan were synthesized by Newman-Kwart rearrangement of the corresponding O-thiocarbamates. The analgetic activities were lower than that of pentazocine, and the opioid receptor binding affinities were very weak. These acylthiomorphinans showed low antinociceptive activity compared with corresponding sulfur-containing benzomorphans. 3-Carbamoylthio-deoxydihydromorphine had no significant analgetic activity.