Oligomeric Fraction Research Articles

The domain swapping of human cystatin C induced by synchrotron radiation

Domain swapping is observed for many proteins with flexible conformations. This phenomenon is often associated with the development of conformational diseases. Importantly, domain swapping has been observed for human cystatin C (HCC), a protein capable of forming amyloid deposits in brain arteries. In this study, the ability of short exposure to high-intensity X-ray radiation to induce domain swapping in solutions of several HCC variants (wild-type HCC and V57G, V57D, V57N, V57P, and L68V mutants) was determined. The study was conducted using time-resolved small-angle X-ray scattering (TR-SAXS) synchrotron radiation. The protein samples were also analysed using small-angle neutron scattering and NMR diffusometry. Exposing HCC to synchrotron radiation (over 50 ms) led to a gradual increase in the dimeric fraction, and for exposures longer than 150 ms, the oligomer fraction was dominant. In contrast, the non-irradiated protein solutions, apart from the V57P variant, were predominantly monomeric (e.g., V57G) or in monomer/dimer equilibrium. This work might represent the first observation of domain swapping induced by high-intensity X-rays.

Preparative separation and bioactivity of oligomeric proanthocyanidins

Oligomeric proanthocyanidins are among the most widely distributed polyphenols in the plant kingdom, being endowed with antioxidant, anti-inflammatory, antimicrobial, immunomodulatory, antitumor and cardioprotective activities. Since oligomeric proanthocyanidins are found in limited amounts in plants and plant-derived products, there is a great need for efficient separation methodologies that can supply analytical quality standards or sufficient material for further bioassays. By efficiently providing a good molar mass distribution of oligomeric proanthocyanidins according to their degree of polymerization, Sephadex LH is the most used sorbent in column chromatography, together with other size exclusion polymers, such as Toyopearl, Diaion, MCI gel CHP or Amberlite. Combination of normal and reversed-phase high pressure liquid chromatography can significantly reduce the total number of chromatographic steps required to obtain high purity oligomeric proanthocyanidins, whereas hydrophilic interaction liquid chromatography on Diol phases can yield proanthocyanidins with a higher degree of polymerization. By lacking a solid support, countercurrent separations can solve issues related to irreversible adsorption, giving higher recoveries, low sample denaturation and a facile scale-up from analytical to industrial production. By taking advantage of the complementarity of all these chromatographic techniques, high-purity oligomeric proanthocyanidin fractions or individual compounds can be obtained on a large scale in a reduced number of separation steps.

Separation of linear and cyclic poly(dimethylsiloxanes) with polymer high-performance liquid chromatography

The growing importance of siloxanes in various industrial areas, e.g., health care, cosmetics, automotive and construction industries requires further method development of analysis techniques. In addition, and complementing gas chromatography analysis, a polymer liquid chromatography method for separation of linear and cyclic (poly)dimethylsiloxanes was developed and optimized. By an appropriate choice of mobile and stationary phase combinations, separations of up to 30 monomeric units were achieved. Therefore, various HPLC columns were investigated concerning physical and chemical properties, e.g., pore size, silica base material, and column functionality. Furthermore, solubility properties of siloxanes in adsorption- and desorption-promoting solvents were investigated and taking these results into account, the separation was optimized applying a mixture of methanol:water (75:25, v/v) and acetone. The findings indicate that precipitation/re-dissolution effects superimposed by adsorption chromatography play an important role for the efficient separationof a high number of monomer units. Besides method development on an analytical scale, linear poly(dimethylsiloxane) oligomers were separated with preparative polymer HPLC. These fractions of single oligomers allow further investigations of different material properties beyond polymer HPLC.

Lignin Modification Supported by DFT-Based Theoretical Study as a Way to Produce Competitive Natural Antioxidants.

The valorization of lignins as renewable aromatic feedstock is of utmost importance in terms of the use of sustainable resources. This study provides a deductive approach towards market-oriented lignin-derived antioxidants by ascertaining the direct effect of different structural features of lignin on the reactivity of its phenolic OH groups in the radical scavenging reactions. The antioxidant activity of a series of compounds, modeling lignin structural units, was experimentally characterized and rationalized, using thermodynamic descriptors. The calculated O–H bond dissociation enthalpies (BDE) of characteristic lignin subunits were used to predict the modification pathways of technical lignins. The last ones were isolated by soda delignification from different biomass sources and their oligomeric fractions were studied as a raw material for modification and production of optimized antioxidants. These were characterized in terms of chemical structure, molecular weight distribution, content of the functional groups, and the antioxidant activity. The developed approach for the targeted modification of lignins allowed the products competitive with two commercial synthetic phenolic antioxidants in both free radical scavenging and stabilization of thermooxidative destruction of polyurethane films.

Ex-situ SIMS characterization of plasma-deposited polystyrene near atmospheric pressure

Polystyrene-like coatings are synthesized by plasma near atmospheric pressure. Elucidating their chemical structure after exposure to ambient air could be very challenging because of the interference of surface-related phenomena, mainly post-polymerization oxidation and contamination. In this paper, we propose secondary ion mass spectrometry (SIMS) in molecular depth-profiling mode, combined to multivariate analysis, as a more reliable tool for their investigation as a function of the injected power. Indeed, the information provided by the inner layers is more representative of the film in growth. The SIMS approach is validated by complementary, surface-sensitive and bulk techniques: X-rays photoelectron spectroscopy (XPS) and infrared spectroscopy (IR). The SIMS results suggest that the high concentration of -CH3 groups in the polymer matrix, pointed out by IR, is due to branching and/or grafting of CH3· radicals to active sites (prevalently in position α, β, γ) along the aliphatic backbone, in addition to a significant fraction of trapped oligomers. The oligomer contribution is supported by an original study based on the molecular weight dependence of the sputtering efficiency. The overall experimental evidences indicate a milder fragmentation of the precursor at lower powers, leading to a higher conservation of the aromaticity and a lesser branched and/or cross-linked content.

Oligomerization mechanism of tea catechins during tea roasting

Roasting of green tea causes oligomerization of tea catechins, which decreases the astringency. The aim of this study was to elucidate the oligomerization mechanism. The 13C NMR spectrum of the oligomer fraction showed signals arising from catechin and sugar residues. Heating of epigallocatechin-3-O-gallate with 13C-labeled glucose (150 °C for 2 h) suggested that condensation of sugars with catechin A-rings caused the oligomerization. The dimeric product obtained by heating for a shorter period (30 min) suggested cross-linking occurred between sugars and catechin A-rings. Furthermore, heating of phloroglucinol, a catechin A-ring mimic, with glucose, methylglyoxal, and dihydroxyacetone, confirmed that the basic mechanism included reaction of the catechin A-ring methine carbons with carbonyl carbons of glucose and their pyrolysis products.

Understanding the Role of Aggregation in the Broad Absorption Bands of Eumelanin.

In this work, we investigate the relationship between the complex hierarchical assembly structure of eumelanin, its characteristic broad absorption band, and the highly unusual nonlinear dynamics revealed by pump-probe or transient absorption microscopy. Melanin-like nanoparticles (MelNPs), generated by spontaneous oxidation of dopamine, were created with uniform but adjustable size distributions, and kinetically controlled oxidation was probed with a wide range of characterization methods. This lets us explore the broad absorption bands of eumelanin models at different assembly levels, such as small subunit fractions (single monomeric and oligomeric units and small oligomer stacks), stacked oligomer fractions (protomolecules), and large-scale aggregates of protomolecules (parental particles). Both the absorption and pump-probe dynamics are very sensitive to these structural differences or to the size of intact particles (a surprising result for an organic polymer). We show that the geometric packing order of protomolecules in long-range aggregation is key secondary interactions to extend the absorption band of eumelanin to the low energy spectrum and produce drastic changes in the transient absorption spectrum.

Modeling the Synthesis of Butyl Methacrylate Macromonomer by Sequential ATRP‐CCTP

AbstractThe atom transfer radical polymerization of butyl methacrylate mediated by Cu(I)Br/N,N,N′,N″,N″‐pentamethyldiethylenetriamine in anisole at 70 °C with the subsequent addition of bis(difluoroboryldiphenylglyoximato)cobalt(II) after 2 h is modeled using Predici software, to gain additional insight to the system used experimentally to produce macromonomer chains with narrow dispersity. The mechanistic model, using kinetic coefficients from the literature and activation and deactivation rate coefficients estimated from this work, provides a good representation of experimental results. The simulations demonstrate that the time (conversion) at which cobalt chain transfer agent is added to the system is critical to control the number‐average molar mass of the final product and also confirm that chains of higher length in the final product are more likely to be nonfunctionalized, in agreement with experimental observations. The model predicts the production of a significant fraction of macromonomer oligomers with lengths of 1–3 units, also consistent with experiments.

Pressure drop, mechanic deformation, stabilization and scale-up of wheat straw fixed-beds during hydrothermal pretreatment: Experiments and modeling

Fixed-bed reactors for liquid hot water pretreatment (LHW) are a promising approach for profitable lignocellulose pretreatment. The flow-through treatment in a tightly packed biomass bed enables high solids loadings and recovery of a considerable hemicellulose oligomer fraction in the liquid product stream. However, the dense biomass packing, as well as the elevated hydrolysate viscosity, cause a significant pressure drop over the bed length, which is likely to compress the fixed-bed irreversibly. This is expected to lead to fluid maldistribution or in the worst case to complete blocking of the reactor. Fixed-bed scale-up, in this case, is therefore not possible without a detailed understanding of the processes inside the bed. This work investigates the pressure drop, fixed-bed mechanics, scale-up as well as possible stabilization techniques of a perfused wheat straw bed during LHW pretreatment experimentally and based on a comprehensive process model. The results show that it is possible to predict the behavior of a fixed-bed with changing bed and fluid properties with the developed model, including heat and mass transfer, reaction kinetics as well as fluid mechanics and bed compression at 3 L lab and 40 L pilot scale. Further, it could be shown that the pressure drop and bed compressibility strongly limit the scale-up potential of the investigated lignocellulose fixed-bed and elaborate stabilization internals are required.

Microwave-assisted recovery of monomeric sugars from an acidic steam treated wood hydrolysate

Fractionation of components from bio-refinery wastes streams is complicated by the presence of both oligomer and lignin fractions. Microwave-assisted acid hydrolysis was used in this study to convert oligomer sugars in an industrial prehydrolysis liquor (PHL) to monomeric sugars. A total of 19.6 g/L monomeric sugars was obtained at a combined severity factor (CSF) of 3.2. Furthermore, it was found that xylan linked to lignin in a lignin-carbohydrate complex (LCC) could be liberated, resulting in lignin with a relatively low dispersity (3.12) and average molecular weight (1718 g/mol) that has high commercial value in the phenol–formaldehyde resin industry. This study presents for the first time a relatively inexpensive method for recovery of 100% of available sugars in the PHL without apparent loss in monomeric sugar as well as 50% removal of lignin as a valuable by-product. Application of this method can significantly improve the economic sustainability of forest-based biorefineries.

Isolation of chemically well-defined semipreparative liquid chromatography fractions from complex mixtures of proanthocyanidin oligomers and polymers

In this study, a semipreparative liquid chromatography method was developed for the isolation of chemically well-defined proanthocyanidin (PA) oligomer and polymer fractions. The aim was to achieve better separation than traditionally achieved for the PAs with other chromatographic methods. The method was tested with eleven PA rich Sephadex LH-20 fractions, which originated from eleven different plant species. The resulting semipreparative fractions were analyzed by both triple quadrupole and high-resolution mass spectrometry assisted by ultrahigh-performance liquid chromatography (UPLC) separation. The results showed remarkable differences in the procyanidin to prodelphinidin ratio, mean degree of polymerization, and specific oligomeric and polymeric content. However, some of these features indicated consistent patterns between species as the function of UPLC retention time. The developed method enables the production of tens of well-defined fractions of PA oligomers and polymers from the unresolved chromatographic PA hump. Accordingly, this allows researchers to explore the most bioactive parts of the complex PA humps of any plant species, which have not been possible earlier.

Influence of decomposition temperature of aromatic sulfonic acid catalysts on the molecular weight and thermal stability of poly(l-lactic acid) prepared by melt/solid state polycondenstaion

Melt/solid polycondensation (MP/SSP) of poly(l-lactic acid) (PLLA) was conducted by using several aromatic sulfonic acids as the catalysts. It was clarified that the increase in molecular weight and the thermal stability of the obtained polymer are correlated with the 5% weight loss temperatures (Td,5%) of the sulfonic acids determined by thermal gravimetric analysis. When 2,5-dimethyl-, 2,4-dimethyl- and 4-methyl-benzenesulfonic acids showing Td,5% around 150 °C were used as the catalysts, PLLA polymers with high molecular weight and excellent thermal stability could be obtained. On the other hand, 2,4,6-trimethylbenzenesulfonic acid showing Td,5% around 100 °C and 4-dodecylbenzenesulfonic acid with Td,5% above 200 °C gave PLLA polymers with remarkably low thermal stability. The residual catalyst involved in the product polymer or SO3 generated during the polymerization decreased the thermal stability of the polymer. The oligomeric fractions of the PLLA products were extracted with acetone and analyzed by 1H NMR and mass spectra. It was verified that the catalyst had efficiently been removed by thermal annealing while it remained active during the SSP to produce a thermally stable PLLA with high molecular weight.

Stepwise pyrolysis of mixed plastics and paper for separation of oxygenated and hydrocarbon condensates

Mixed plastics and papers are two of the main fractions in municipal solid waste which is a critical environmental issue today. Recovering energy and chemicals from this waste stream by pyrolysis is one of the favorable options to achieve a circular economy. While pyrolysis products from plastics are mainly hydrocarbons, pyrolysis products from paper/biomass are highly oxygenated. The different nature of the two pyrolysis products results in different treatments and applications as well as economic values. Therefore, separation of these two products by multi-step pyrolysis based on their different decomposition temperatures could be beneficial for downstream processes to recover materials, chemicals and/or energy. In this work, stepwise pyrolysis of mixed plastics and paper waste was performed in a batch type fixed bed reactor using two different pyrolysis temperatures. Neat plastic materials (polystyrene, polyethylene) and cellulose mixtures were used as starting materials. Then, the same conditions were applied to a mixed plastics and paper residue stream derived from paper recycling process. The condensable products were analyzed by GC/MS. It was found that pyrolysis temperatures during the first and second step of 350 and 500 °C resulted in a better separation of the oxygenated and hydrocarbon condensates than when a lower pyrolysis temperature (300 °C) was used in the first step. The products from the first step were derived from cellulose with some heavy fraction of styrene oligomers, while the products from the second step were mainly hydrocarbons derived from polystyrene and polyethylene. This thus shows that stepwise pyrolysis can separate the products from these materials, although with some degree of overlapping products. Indications of interaction between PS and cellulose during stepwise pyrolysis were observed including an increase in char yield, a decrease in liquid yield from the first temperature step and changes in liquid composition, compared to stepwise pyrolysis of the two materials separately. A longer vapor residence time in the second step was found to help reducing the amount of wax derived from polyethylene. Results from stepwise pyrolysis of a real waste showed that oxygenated and acidic products were concentrated in the liquid from the first step, while the product from the second step contained a high portion of hydrocarbons and had a low acid number.

Laccase Activity as an Essential Factor in the Oligomerization of Rutin

The enzyme-mediated polymerization of bioactive phenolic compounds, such as the flavonoid rutin, has gained interest due to the enhanced physico-chemical and biological properties of the products, which increases their potential application as a nutraceutical. In this work, the influence of enzyme activity on rutin oligomerization was evaluated in reactions with low (1000 U/L) and high (10,000 U/L) initial laccase activities. For both reactions, high molecular weight oligomer fractions showed better properties compared to lower weight oligomers. Products of the reaction with low laccase activity exhibited thermal stability and antioxidant potential similar to control reaction, but led to higher inhibitory activity of xanthine oxidase and apparent aqueous solubility. Oligomers obtained in the reaction with high laccase activity showed better apparent aqueous solubility but decreased biological activities and stability. Their low antioxidant activity was correlated with a decreased phenolic content, which could be attributed to the formation of several bonds between rutin molecules.

Synthesis of semicrystalline poly(guanamine)s based on 2-substituted-4,6-dichloro-1,3,5-triazine with α, ω-alkylene diamines, and the formation of cyclic tetramers

Polycondensation of various 2-substituted-4,6-dichloro-1,3,5-triazine such as N,N-diphenylamino (DCPT), benzylamino (BnDCT) substituents with α, ω - alkylene diamines including hexamethylene (HMDA), octamethylene (OcDA), decamethylene (DcDA), and dodecamethylene diamine (DdDA) was performed, and the resultant polymers were analyzed. Two-phase polymerization in nitrobenzene/aqueous NaHCO3 at 100 °C resulted in a high molecular weight (MW) polymer (Mn = 12,400) with a small fraction (26.7 wt%) of low MW oligomer, whose main component was confirmed as a 4-membered cyclic compound. Polymers prepared with HMDA were crystalline with poor solubility, whereas those with OcDA, DcDA, and DdDA were all amorphous with high MWs (Mn = 40,000–60,000) and good solubility enough to prepare the self-standing transparent films. The polymers show moderate glass transition temperatures from 76 °C to 159 °C. In differential scanning calorimetry measurements, only poly(BnDCT-HMDA) showed a clear endothermic peak (ΔH = 119 J/g), which corresponds to melting at 220 °C.

Pressurized hot water extraction of β-glucans from Cantharellus tubaeformis.

Cantharellus tubaeformis was processed by pressurized hot water extraction (80-240°C) with the aim of maximizing the extraction of oligomeric fractions, β-glucans, and the in vitro antioxidant properties of the extracts. Increased severity of treatment enhanced the extraction yields above 62% at temperatures of 210ºC or higher, corresponding to the maximum β-glucan yields. The highest antioxidant capacity was obtained at 170ºC, although the highest content of phenolic compounds was obtained at the highest severity studied. This hydrothermal treatment can be considered a suitable process to obtain extracts with antioxidant properties and rich in β-glucans.

A multidimensional fractionation protocol for the oligomer analysis of oxidized waxes

Oxidized waxes possess far superior properties as compared to the alkanes they are derived from. The separation of alkane oligomers via gas chromatography (GC) becomes a challenge when polar oxygen-containing functional groups are introduced or when higher molar masses are targeted. In the present study, the separation and analysis of oligomers in oxidized and non-oxidized waxes using different liquid chromatographic techniques are investigated. Oligomers in two oxidized waxes and a non-oxidized wax from which they are derived, are separated using high-temperature solvent gradient interaction chromatography (HT-SGIC) and high-temperature two-dimensional liquid chromatography (HT-2D-LC). Evaporative light scattering detector conditions are tailored to provide the best detection with the solvent system at use. It is shown that oligomers in oxidized and non-oxidized waxes can be separated and identified using the mentioned techniques. It has been found that the ELSD detector response systematically decreases as the oxidation levels of the waxes increase. Coupling of HT-HPLC and high-temperature size exclusion chromatography (HT-SEC) in a comprehensive 2D-LC setup shows a broadening of the molar mass distributions of the lower oligomer fractions as a consequence of the modification indicating changes in the oligomer chain microstructures. A preparative fractionation technique is utilized to collect specific oligomer fractions from the bulk waxes followed by hyphenation to HT-HPLC and other techniques. HPLC is shown to provide more detailed information on the oligomer composition of waxes when coupled to a pre-fractionation technique.

Effect of relative humidity on the composition of secondary organic aerosol from the oxidation of toluene

Abstract. The effect of relative humidity (RH) on the chemical composition of secondary organic aerosol (SOA) formed from low-NOx toluene oxidation in the absence of seed particles was investigated. SOA samples were prepared in an aerosol smog chamber at < 2 % RH and 75 % RH, collected on Teflon filters, and analyzed with nanospray desorption electrospray ionization high-resolution mass spectrometry (nano-DESI–HRMS). Measurements revealed a significant reduction in the fraction of oligomers present in the SOA generated at 75 % RH compared to SOA generated under dry conditions. In a separate set of experiments, the particle mass concentrations were measured with a scanning mobility particle sizer (SMPS) at RHs ranging from < 2 to 90 %. It was found that the particle mass loading decreased by nearly an order of magnitude when RH increased from < 2 to 75–90 % for low-NOx toluene SOA. The volatility distributions of the SOA compounds, estimated from the distribution of molecular formulas using the “molecular corridor” approach, confirmed that low-NOx toluene SOA became more volatile on average under high-RH conditions. In contrast, the effect of RH on SOA mass loading was found to be much smaller for high-NOx toluene SOA. The observed increase in the oligomer fraction and particle mass loading under dry conditions were attributed to the enhancement of condensation reactions, which produce water and oligomers from smaller compounds in low-NOx toluene SOA. The reduction in the fraction of oligomeric compounds under humid conditions is predicted to partly counteract the previously observed enhancement in the toluene SOA yield driven by the aerosol liquid water chemistry in deliquesced inorganic seed particles.

INVESTIGATION THE OLIGOMERIZATION PROCESS OF HEXENE-1

In article for oligomerization and alkylation processes, to obtain a useful and highly stable active catalyst, New Catalytic Complex (NCC) synthesized which is based on aluminum metal using C2H4Cl2 and this complex has shown high stability in alkylation, oligomerization processes compared to other aluminum-containing catalysts. It is difficult to regulate the molecular mass distribution of received products during oligomerization, either Intensificate the oligomerization process of olefins that is why this process take place in presence of obtaining of bimetal catalytic complex with a highly stable activity from the modification of the New Catalytic Complex(NCC) with transition metal chloride. Comparatively studied oligomerization of Hexen-1 in present of new bimetallic catalytic complex which was modified by NCC and chromium salt (NCC/CrCl3), effect of temperature, reaction time, concentration of the catalyst and the proportion of catalyst components (Al:Cr) in the process was investigated.It was determined that at the initial time (10 min) conversion hexene-1 and the yield of purposeful oil fraction were low. Increasing time, conversion rate of Hexen-1 increases and the optimal time for the process is considered as 60 minutes. In low concentrations of catalyst (0,1-0,3) oligomerization of hexene-1 is low but in high concentrations(>1%) reaction goes with high rate, at optimal concentration 0,5% mass both the yield of oil fraction and its chemical-physical properties were high.In oligomerization process investigated ratio effect of catalyst components Al: Cr that was used Al: Cr=(4-32):1 mol.It has been revealed that oligomerization of Hexen-1, at low mol ratio of components (4:1), received yield of oligomer fraction decreases while mol ratio increases (16:1, 32:1).Studies determined that bimetallic complex at 8:1 mole has shown the maximal activity in oligomerization process of Hexen-1.The effect of the temperature on the oligomerization process was studied in the range of 30-60ºC, increasing the temperature up to 50 °C has a positive effect on the course of the process and despite providing complete oligomerization of hexene-1 its also providing increasing the amount of oil fractions with high viscosity. According to the researches, the optimal conditions for the oligomerization process of hexene-1 with the participation of the bimetallic catalytic complex: reaction time – 60 min., concentration of catalyst – 0,5 % by wt., mol ration of components Al:Cr = 8:1, temperature – 50 °C. In known optimal condition its possible to obtain oligomers with physical indications, characterized by narrow molecular mass distribution, by new catalytic complex that was modified by chromium salt.Such products have special importance, as low-freezing, high viscosity index qualitative engine oils.Synthesis of bimetallic catalytic complexes, with their presence in oligomerization of olefins and fractions, opens wide range perspectives in synthesis of different high-molecular compounds in industry

Enzymatic production of all fourteen partially acetylated chitosan tetramers using different chitin deacetylases acting in forward or reverse mode

Some of the most abundant biomolecules on earth are the polysaccharides chitin and chitosan of which especially the oligomeric fractions have been extensively studied regarding their biological activities. However, most of these studies have not been able to assess the activity of a single, defined, partially acetylated chitosan oligosaccharide (paCOS). Instead, they have typically analyzed chemically produced, rather poorly characterized mixtures, at best with a single, defined degree of polymerization (DP) and a known average degree of acetylation (DA), as no pure and well-defined paCOS are currently available. We here present data on the enzymatic production of all 14 possible partially acetylated chitosan tetramers, out of which four were purified (>95%) regarding DP, DA, and pattern of acetylation (PA). We used bacterial, fungal, and viral chitin deacetylases (CDAs), either to partially deacetylate the chitin tetramer; or to partially re-N-acetylate the glucosamine tetramer. Both reactions proceeded with surprisingly strong and enzyme-specific regio-specificity. These pure and fully defined chitosans will allow to investigate the particular influence of DP, DA, and PA on the biological activities of chitosans, improving our basic understanding of their modes of action, e.g. their molecular perception by patter recognition receptors, but also increasing their usefulness in industrial applications.