Phenol Oligomers Research Articles

Voltammetric techniques for low-cost on-site routine analysis of thymol in the medicinal plant Ocimum gratissimum

The composition of essential oils varies according to culture conditions and climate, which induces a need for simple and inexpensive characterization methods close to the place of extraction. This appears particularly important for developing countries. Herein, we develop an analytical strategy to determine the thymol content in Ocimum Gratissimum, a medicinal plant from Benin. The protocol is based on electrochemical techniques (cyclic and square wave voltammetry) implemented with a low cost potentiostat. Thymol is a phenol derivative and was directly oxidized at the electrode surface. We had to resort to submillimolar concentrations (25–300 μM) in order to minimize production of phenol oligomers that passivate the electrode. We worked first on two essential oils and realized that in one of them the thymol concentration was below our detection method. These results were confirmed by gas chromatography – mass spectrometry. Furthermore, we optimized the detection protocol to analyze an infusion made directly from the leaves of the plant. Finally, we studied whether the cost of the electrochemical cell may also be minimized by using pencil lead as working and counter electrodes.

Upcycling of polyphenylene ether waste products to hypercrosslinked organic porous materials

Dimethyl phenol (DMP) oligomers are a side product of industrial poly(phenylethyl ether) (PPE) fabrication and significantly contribute to the environmental burden associated with PPE application. Here, a new process for the upcycling of waste-derived DMP into hyper-crosslinked porous polymer networks through Friedel-Crafts alkylation with p- dichloroxylene as an external crosslink agent is presented. The resulting hypercrosslinked porous polymers exhibited a maximum BET surface area of 740 m2/g and displayed and adsorption capacity of 5.9 wt% and 0.85 wt% towards CO2 (at 1.0 bar, 298 K) and H2 (at 1.0 bar, 77.3 K), respectively. Form stability of micro- and mesopores was attributed to the rigidity of the aromatic network structure. The results suggest new opportunities for the upcycling of DMP-waste components for applications such as carbon capture that could reduce the negative environmental const associated with the fabrication and application of PPE and related engineering polymers.

Quantitative Measurement of Cooperativity in H-Bonded Networks.

Cooperative H-bonding interactions are a feature of supramolecular networks involving alcohols. A family of phenol oligomers, in which the hydroxyl groups form intramolecular H-bonds, was used to investigate this phenomenon. Chains of intramolecular H-bonds were characterized using nuclear magnetic resonance (NMR) spectroscopy in solution and X-ray crystallography in the solid state. The phenol oligomers were used to make quantitative measurements of the effects of the intramolecular interactions on the strengths of intermolecular H-bonding interactions between the H-bond donor on the end of the chain and a series of H-bond acceptors. Intramolecular H-bonding interactions in the chain increase the strength of a single intermolecular H-bond between the terminal phenol and quinuclidine by up to 14 kJ mol-1 in the n-octane solution. Although the magnitude of the effect increases with the length of the H-bonded chain, the first intramolecular H-bond has a much larger effect than subsequent interactions. H-bond cooperativity is dominated by pairwise interactions between nearest neighbors, and longer range effects are negligible. The results were used to develop a simple model for cooperativity in H-bond networks using an empirical parameter κ to quantify the sensitivity of the H-bond properties of a functional group to polarization. The value of κ measured in these systems was 0.33, which means that formation of the first H-bond increases the polarity of the next H-bond donor in the chain by 33%. The cumulative cooperative effect in longer H-bonded chains reaches an asymptotic value, which corresponds to a maximum increase in the polarity of the terminal H-bond donor of 50%.

Penetration depth of phenol-formaldehyde (PF) resin into beech wood studied by light microscopy

Using light microscopy (LM), the distribution and penetration depth of phenol–formaldehyde (PF) resin into wood specimens were examined after the seventh dry–wet cycle following the anti-swelling efficiency method. PF resins with the average molecular weights (Mw) of 297, 421, 655 and 854 g/mol at concentrations of 9, 18 and 27 wt% in water were vacuum-impregnated into beech wood (Fagus sylvatica) blocks (25 × 25 × 10 mm3). The measurements of the increase in cell wall thickness (bulking) showed that the 297 and 421 g/mol oligomers resulted in greater cell wall bulking (14.9 and 15.4%, respectively) than the 655 and 854 g/mol oligomers (11 and 9.9% bulking, respectively). The presence of chemical agents in the wood was detected based on the safranin staining intensity of the specimen’s transverse sections. The amount of safranin adsorbed on the beech wood sections decreased as the amount of resin incorporated into the cell walls increased, apparently due to a decrease in the number of free microvoids available for safranin adsorption. Less intense dye staining was observed in treated sample sections compared with untreated transverse sections. The lowest amount of safranin was found in wood that was treated with phenol oligomers of 297 and 421 g/mol; wood treated with oligomers of 655 and 854 g/mol adsorbed greater amounts of safranin. Thus, high-molecular-weight PF resins were more uniformly distributed in the specimen and mainly located in the fiber lumens. The results show that safranin staining and visual evaluation by LM is a simple and reliable method to determine the location of PF resin in treated wood.

A Simple One-Step Ultrasonic Route To Synthesize Antioxidant Molecules and Fluorescent Nanoparticles from Phenol and Phenol-Like Molecules

Fluorescent oligomeric structures were synthesized from the phenolic moieties by a simple one-step sonochemical approach without the use of enzymes, metal catalyst, or other toxic reagents. The formation of phenol dimers, trimers, and oligomers was confirmed by absorption spectroscopy, fluorescence spectroscopy, HPLC, and mass spectroscopy. We have demonstrated that the cavitation bubble surface acted as a catalytic binding site to generate such oligomers, and the ultrasonic frequency, concentration, and other physicochemical properties (surface activity) of phenolic building blocks can affect the formation of these oligomers. The sonochemically produced phenolic oligomers showed antioxidant activity which was determined by DPPH assay. The study suggests that acoustic cavitation could promote polymerization of simple phenolic molecules to generate bioactive oligomers and nanostructures with varying functional properties.

Hot water extraction of Norway spruce (Picea abies [Karst.]) bark: analyses of the influence of bark aging and process parameters on the extract composition

Abstract The hot water (HW) extraction of Norway spruce (Picea abies [Karst.]) delivers condensed tannins and considerable amounts of other compounds. Yield and composition of the HW extracts were investigated as a function of natural weathering for up to 15 months. Total phenol monomers and oligomers were detected by Folin-Ciocaltau assay after fractionation by solid phase extraction (SPE). Procyanidins (PC) were determined by HPLC-UV after acid thiolysis and carbohydrates by HPLC combined with acid hydrolysis. Topochemistry of the bark before and after extraction was investigated by UV-microspectrometry (UMSP) and non-extractable PC analyzed by direct thiolysis on the bark. The influence of the parameters on the yield and composition of the extracts were evaluated, such as the extraction temperature, time and the addition of sodium sulfate and urea. Prolonged weathering resulted in a considerable decrease of the total extraction yield, partly because of leaching of phenolic monomers, mono- and oligosaccharides. The yield of phenolic oligomers also decreased at a moderate rate, while the yield of polysaccharides (pectins) was almost stable. Non-extractable and non-leachable compounds deposited in the cell lumens represent the majority of the phenolic extractives in spruce bark. Sequential extractions performed at increasing temperature proved to be a suitable method for the recovery of tannin-rich extracts.

Computational assessment of the fluorescence emission of phenol oligomers: A possible insight into the fluorescence properties of humic-like substances (HULIS)

Abstract Compounds with fluorescence in the humic-like substances (HULIS) region are known to be formed under conditions where the oxidation (which could lead to the oligomerization) of phenolic compounds is operational, because of the formation of phenoxy radicals. However, there was no evidence to date that such fluorescence emission was really due to phenol oligomers. In this work, the fluorescence of phenol and some of its oligomers was studied by computational methods and it was compared with experimental data, when allowed by the availability of commercial standards. The oligomer fluorescence depends on the contribution of different stable conformers, which differ from one another for the dihedral angles between the aromatic rings. Differences in the dihedral angles are also observed between the ground states and the corresponding excited singlet states. The predicted wavelengths of fluorescence emission increase with increasing the number of aromatic rings, up to a plateau at around 450 nm. Compounds with more than three-four aromatic rings are not expected to show emission in a different range, because the transitions causing fluorescence involve only three consecutive rings. These results support the hypothesis that oligomers account for the fluorescence emission in the HULIS region, which has been observed under the photochemical and photosensitized transformation of phenolic compounds.

Nitrogen-Containing Oxypropylates of Phenol and its Derivatives as Oxidation and Corrosion Inhibiting Additives to Engine Oils

Oxidation and corrosion inhibiting properties of nitrogen-containing phenol oligomers in base engine oil are investigated. It is shown that in the presence of benzoguanamine and benzoguanamine oxypropylates, the basic matrix containing products of oxypropylation of phenol and monoalkyl phenols (C8-C12 alkyl radical) has a higher thermal stability and a lower corrosivity. The results obtained are substantiated.

Calixarene methylene bisphosphonic acids as promising effectors of biochemical processes

this interdisciplinary study, performed with participation of research workers of Palladin Institute of Biochemistry and Institute of organic chemist ry of NaS of ukraine, is devoted to analysis of biochemical effects of some calixarene methylene bisphosphonic acids (cyclic phenol oligomers) on two well-known biological phenomenons – mg2+-dependent atP hydrolysis (myosin subfragment-1 of myometrium smooth muscle was used as an example) and fibrin polymerization. calix[4]arene С-97 (calix[4]arene methylene bisphosphonic acids) is a macrocyclic substance, which contains intramolecular highly ordered lipophilic cavity formed by four aromatic rings, one of which is functionalized at the upper rim with methylene bisphosphonic group. at concentration of 100 μm, this substance was shown to effectively inhibit atPase activity of pig myometrium myosin subfragment-1 (inhibition coefficient І0.5 = 83 ± 7 μm). at the same time, this calix[4]arene causes significant (vs. control) increase of myosin subfragment-1 hydrodynamic diameter, which may indicate formation of an intermolecular complex between calixarene and myosin head. computer simulation methods (docking and molecular dynamics with addition of grid technologies) enabled to elucidate the grounds of intermolecular interactions between calix[4]arene С-97 and myometrium myosin subfragment-1, that involve hydrophobic, electrostatic and π-π-stacking interactions, some of which are close to the atPase active centre. In view of the ability of calixarenes to penetrate into the cell and their low toxicity, the results obtained may be used as a basis for further development of a new generation of supramolecular effectors (starting from the above mentioned substances, in particular calix[4]arene С-97) for regulation of smooth muscle contractile activity at the level of atP dependent actin-myosin interaction. calix[4]arenes bearing two or four methylenebisphosphonic acid groups at the macrocyclic upper rim have been studied with respect to their effects on fibrin polymerization. the most potent inhibitor proved to be calix[4]arene tetrakis-methylene-bis-phosphonic acid (c-192), in which case the maximum rate of fibrin polymerization in the fibrinogen + thrombin reaction decreased by 50% at concentrations of 0.52·10-6 m (Ic50 ). at this concentration, the molar ratio of the compound to fibrinogen was 1.7 : 1. For the case of desaB fibrin polymerization, the Ic50 was 1.26·10 -6 m at a molar ratio of c-192 to fibrin monomer of 4 : 1. Dipropoxycalix[4]-arene bis-methylene-bis-phosphonic acid (c-98) inhibited fibrin desaB polymerization with an Ic50 = 1.31·10 -4 m. We hypothesized that c-192 blocks fibrin formation by combining with polymerization site ‘a’ (aa17–19), which ordinarily initiates protofibril formation in a ‘knob-hole’ manner. this suggestion was confirmed by an hPLc assay, which showed a host–guest inclusion complex of c-192 with the synthetic peptide gly-Pro-arg-Pro, an analogue of site ‘a’. Further confirmation that the inhibitor was acting at the initial step of the reaction was obtained by electron microscopy, with no evidence of protofibril formation being evident. calixarene c-192 also doubled both the prothrombin time and the activated partial thromboplastin time in normal human blood plasma at concentrations of 7.13·10-5 and 1.10·10-5 m, respectively. these experiments demonstrate that c-192 is a specific inhibitor of fibrin polymerization and blood coagulation and can be used for the design of a new class of antithrombotic agents.

Effect of nitogen-containing phenol oligomers on the viscosity-temperature properties of base motor oil

The effect of nitrogen-containing phenol oligomers on the viscosity-temperature properties of base motor oil is studied. It is found that the products of oxypropylation of phenol and monoalkylphenols (alkyl chain length – C8-C12) in the presence of benzoguanamine, as well as oxypropylated benzoguanamine have a positive effect on these properties. It is also found and scientifically validated that the viscosity –temperature properties of base-oil compositions are affected by the concentration, component composition, and thickening power of oligomers in oil.

Synthesis of Azacalixarenes through Dihydrobenzoxazine Derivatives of Phenols

AbstractA new series of azacalix[n]arenes were synthesized by the reaction between the benzoxazine derivatives of phenols and the phenol oligomers. The reaction should be carried out at 40–80 °C, because scrambling of the phenol units occurs at higher temperatures. The appropriate reaction conditions afforded the desired azacalixarene which was asymmetrical along the N···N′ or N···CH2 axis.

Vibrational Dynamics of Hydrogen-Bonded Complexes in Solutions Studied with Ultrafast Infrared Pump−Probe Spectroscopy

In aqueous solution, the basis of all living processes, hydrogen bonding exerts a powerful effect on chemical reactivity. The vibrational energy relaxation (VER) process in hydrogen-bonded complexes in solution is sensitive to the microscopic environment around the oscillator and to the geometrical configuration of the hydrogen-bonded complexes. In this Account, we describe the use of time-resolved infrared (IR) pump-probe spectroscopy to study the vibrational dynamics of (i) the carbonyl CO stretching modes in protic solvents and (ii) the OH stretching modes of phenol and carboxylic acid. In these cases, the carbonyl group acts as a hydrogen-bond acceptor, whereas the hydroxyl group acts as a hydrogen-bond donor. These vibrational modes have different properties depending on their respective chemical bonds, suggesting that hydrogen bonding may have different mechanisms and effects on the VER of the CO and OH modes than previously understood. The IR pump-probe signals of the CO stretching mode of 9-fluorenone and methyl acetate in alcohol, as well as that of acetic acid in water, include several components with different time constants. Quantum chemical calculations indicate that the dynamical components are the result of various hydrogen-bonded complexes that form between solute and solvent molecules. The acceleration of the VER is due to the increasing vibrational density of states caused by the formation of hydrogen bonds. The vibrational dynamics of the OH stretching mode in hydrogen-bonded complexes were studied in several systems. For phenol-base complexes, the decay time constant of the pump-probe signal decreases as the band peak of the IR absorption spectrum shifts to lower wavenumbers (the result of changing the proton acceptor). For phenol oligomers, the decay time constant of the pump-probe signal decreases as the probe wavenumber decreases. These observations show that the VER time strongly correlates with the strength of hydrogen bonding. This acceleration may be due to increased coupling between the OH stretching mode and the accepting mode of the VER, because the low-frequency shift caused by hydrogen bond formation is very large. Unlike phenol oligomers, however, the pump-probe signals of phenol-base complexes did not exhibit probe frequency dependence. For these complexes, rapid interconversion between different conformations causes rapid fluctuations in the vibrational frequency of the OH stretching modes, and these fluctuations level the VER times of different conformations. For the benzoic acid dimer, a quantum beat at a frequency of around 100 cm(-1) is superimposed on the pump-probe signal. This result indicates the presence of strong anharmonic coupling between the intramolecular OH stretching and the intermolecular stretching modes. From a two-dimensional plot of the OH stretching wavenumber and the low-frequency wavenumber, the wavenumber of the low-frequency mode is found to increase monotonically as the probe wavenumber is shifted toward lower wavenumbers. Our results represent a quantitative determination of the acceleration of VER by the formation of hydrogen bonds. Our studies merit further evaluation and raise fundamental questions about the current theory of vibrational dynamics in the condensed phase.

Vibrational population relaxation of hydrogen-bonded phenol complexes in solution: Investigation by ultrafast infrared pump–probe spectroscopy

We investigated the vibrational population relaxation of the OH stretching mode of hydrogen-bonded phenol complexes in solution by ultrafast infrared spectroscopy. For a phenol–benzonitrile complex, vibrational population relaxation takes place at around 5 ps. The decay time constants of the pump–probe signals do not depend on the probe frequency. We also measured the pump–probe signals of the OH stretching vibrations for phenol–acetone, phenol–diethylether and phenol–tetrahydrofuran complexes. We found that the time scales of vibrational population relaxation for these complexes are correlated with hydrogen bond strength; i.e., stronger hydrogen bonding leads to faster vibrational population relaxation. We did not observe a clear probe frequency dependence in relaxation rates. For these complexes, rapid evolution between different conformations causes fast fluctuation in the vibrational frequency of the OH stretching modes. This fluctuation averages out the vibrational population relaxation times of different conformations. In contrast, the decay time constants of pump–probe signals for hydrogen-bonded phenol oligomers were found to depend significantly on probe frequency. The decay time constant at the blue side (3521 cm −1) was 2.1 ps, while that at the red side (3320 cm −1) was 0.7 ps. We discuss the probe frequency dependence of vibrational population relaxation times for hydrogen-bonded phenol oligomers in solution.

Tert-Butylation of Phenol over Ordered Solid Acid Catalysts in Supercritical Carbon Dioxide: Efficient Synthesis of 2,4-Di-tert-butylphenol and 2,4,6-Tri-tert-butylphenol

The tert-butylation of phenol was carried out over ordered solid acid catalysts (zeolites and MCM-41-supported heteropolyacids and rare-earth-metal triflates) in supercritical CO2. The catalytic performances in supercritical CO2 were superior to those in other reaction media such as liquid-phase and N2 atmosphere conditions. The tert-butylation of phenol gave 2,4-di-tert-butylphenol (2,4-DTBP) in 65% yield over H−Y zeolites and 2,4,6-tri-tert-butylphenol (2,4,6-TTBP) in 40% yield over Sc(OTf)3 supported on MCM-41 [Sc(OTf)3/MCM-41]. The coke formation in supercritical CO2 was much lower than that in other reaction media. These high performances are due to the high solubilities of reactants and products and to the minimal coke formation: supercritical CO2 works as the reaction medium; removes coke precursors, which are heavy aromatics from phenol and/or isobutene oligomers, before they convert to coke materials; and keeps the catalytic sites clean during the catalysis. The spatial requirement for catalytic...

Inhibition of Heme Peroxidase During Phenol Derivatives Oxidation. Possible Molecular Cloaking of the Active Center

Ab initio quantum chemical calculations have been applied to the study of the molecular structure of phenol derivatives and oligomers produced during peroxidasecatalyzed oxidation. The interaction of substrates and oligomers with Arthromyces ramosus peroxidase was analyzed by docking methods. The most possible interaction site of oligomers is an active center of the peroxidase. The complexation energy increases with increasing oligomer length. However, the complexed oligomers do not form a precise (for the reaction) hydrogen bonding network in the active center of the enzyme. It seems likely that strong but non productive docking of the oligomers determines peroxidase inhibition during the reaction.

A simultaneous TG–DTA study of the thermal decomposition of 2-hydroxybenzoic acid, 2-carboxyphenyl ester (salsalate)

Simultaneous thermogravimetry–differential thermal analysis (TG–DTA) and gas and liquid chromatography with mass spectrometry detection have been used to study the kinetics and decomposition of 2-hydroxybenzoic acid, 2-carboxyphenyl ester, commercially known as salsalate. Samples of salsalate were heated in the TG–DTA apparatus in an inert atmosphere (100 ml min −1 nitrogen) in the temperature range 30–500 °C. The data indicated that the decomposition of salsalate is a two-stage process. The first decomposition stage (150–250 °C) had a best fit with second-order kinetics with E a=191–198 kJ/mol. The second decomposition stage (300–400 °C) is described as a zero-order process with E a=72–80 kJ/mol. The products of the decomposition were investigated in two ways: (a) Salsalate was heated in a gas chromatograph at various isothermal temperatures in the range 150–280 °C, and the exit gas stream analyzed by mass spectrometry (GC–MS). This approach suggested that salsalate decomposes with the formation of salicylic acid, phenol, phenyl salicylate, and cyclic oligomers of salicylic acid di- and tri-salicylides. (b) One gram samples of salsalate were heated in a vessel under nitrogen to 150 °C, and the residues were analyzed by liquid chromatography–mass spectrometry (LC–MS). The major compound detected was a linear tetrameric salicylate ester.

Detecting hydrogen bonding by NMR relaxation of the acceptor nuclei

The formation of hydrogen bonds (HB) between phenol or N-methyltrifluoroacetamide and several acceptors (pyridine, carbonyl compounds, nitriles, amides) in CCl4 or CHCl3 been investigated through the analysis of NMR relaxation times (T1) of the heteronuclei (14N and 17O) directly involved in the HB interaction. Thus, a comparison is made between such T1 values (corrected for changes in molecular dynamics and motional anisotropy) and electric field gradients calculated by ab initio methods for the acceptor molecules, both isolated and in 1:1 or 2:1 hydrogen-bonded complexes. When other effects are properly accounted for, there is a good agreement between theoretical and experimental electric field gradient (efg) changes. The noticeable difference found between CCl4 or CHCl3 as solvents is discussed in relation to the presence of phenol oligomers, and the non-negligible HB donor power of CHCl3.

Crystal structure and inclusion property of p-tert-butylthiacalix[6]arene

Although the reaction of p-tert-butylphenol with elemental sulfur in the presence of CsOH as a base catalyst yielded a complex mixture comprised of sulfur-bridged phenol oligomers, p-tert-butylthiacalix[6]arene (TC6A) could be isolated in an appreciable yield (0.8%). The X-ray analysis revealed that TC6A adopted a distorted cone conformation stabilized by two sets of hydrogen bondings comprising three phenolic OH groups. The recrystallization from various solvents showed that TC6A had higher inclusion ability toward more guests than TC4A did, suggesting that the expanded central cavity and/or the crystal lattice of the former allowed a more comfortable accommodation of the guest molecules.

Polymeric Antioxidants. I.

Phenolic oligomers directly linked to aromatic rings were prepared by horseradish peroxidase catalyzed oxidation of phenol derivatives by hydrogen peroxide. The phenols used were p-cresol, p-ethylphenol, p-s-butylphenol, p-t-butylphenol, p-methoxyphenol, p-nonylphenol, m-cresol, m-t-butyl-phenol, m-methoxyphenol, and 3, 4-xylenol. p-Nonylphenol and m-t-butylphenol were not polymerized by oxidation. Number-average molecular weights (Mn) of para alkyl substituted phenolic oligomers were about 800 and bulky substituted groups prevented decrease in the number of hydroxyl groups during polymerization. Mn of p-methoxyphenol oligomer was almost 1700. Meta substituted oligomers had lower Mn and a greater number of remaining hydroxyl groups (D.R.H.) than the corresponding para substituted phenol oligomers. Antioxidant effects of the phenolic oligomers on the autoxidation of lard were evaluated. Improvement of this effect for lard could hardly be detected by polymerization. That of the oligomers on the autoxidation of tetralin was much more pronounced than for the corresponding monomers, except for p-methoxyphenol. Higher reactivity of phenolic oligomers toward peroxyl radicals and the formation of stable phenoxyl radicals may possibly have been the cause for this. Phenolic oligomers having higher D.R.H. exhibited the better antioxidant effect. The antioxidant effects of meta substituted oligomers were greater than those of the corresponding para substituted oligomers.