Varying Chain Length Research Articles

Polyphosphate as an antithrombotic target and hemostatic agent.

Polyphosphate (PolyP) is a polymer comprised of linear phosphate units connected by phosphate anhydride bonds. PolyP exists in a diverse range of eukaryotes and prokaryotes with varied chain lengths ranging from six to thousands of phosphate units. Upon activation, human platelets and neutrophils release short-chain PolyP, along with other components, to initiate the coagulation pathway. Long-chain PolyP derived from cellular or bacterial organelles exhibits higher proinflammatory and procoagulant effects compared to short-chain PolyP. Notably, PolyP has been identified as a low-hemorrhagic antithrombotic target since neutralizing plasma PolyP suppresses the thrombotic process without impairing the hemostatic functions. As an inorganic polymer without uniform steric configuration, PolyP is typically targeted by cationic polymers or recombinant polyphosphatases rather than conventional antibodies, small-molecule compounds, or peptides. Additionally, because of its procoagulant property, PolyP has been incorporated in wound-dressing materials to facilitate blood hemostasis. This review summarizes current studies on PolyP as a low-hemorrhagic antithrombotic target and the development of hemostatic materials based on PolyP.

Synthesis of Deoxysugars from Aliphatic α‐Ketoacids and Aldoses Catalyzed by Thermostable Transketolase Variants from Geobacillus stearothermophilus

AbstractWe described a strategy for the enzymatic synthesis of 1‐deoxy and 1,2‐deoxyketoses from the aliphatic α‐ketoacids, pyruvate and 2‐oxobutyrate, as donors and natural aldoses of variable chain length as acceptors, catalyzed by thermostable transketolase variants from Geobacillus stearothermophilus (TKgst). Analytical studies have been carried out on a panel of TKgst variants with the appropriate substrates allowing to select the best combinations and to apply it to the preparative scale synthesis of 1‐deoxy and 1,2‐deoxyketoses obtained with good to excellent isolated yields (61%–86%). To optimize the strategy, and as a proof of principle, the α‐ketoacids pyruvate and 2‐oxobutyrate were generated in situ from the corresponding d‐amino acids d‐alanine and d‐homoalanine respectively, using a thermostable d‐amino acid oxidase dAAO4536 that was selected from a screening of 55 putative DAAOs provided by Prozomix Limited. Hence, a one‐pot one step procedure was performed at 50 °C by coupling dAAO4536 and the best TKgst variant H102L/L118I/H474S in the presence of d‐alanine or d‐homoalanine as α‐ketoacids precursors and d‐erythrose as acceptor substrate. The corresponding 1‐deoxy and 1,2‐dideoxyketoses were isolated with good yields (64% and 72% respectively, out of two steps).magnified image

Detecting renewal states in chains of variable length via intrinsic Bayes factors

Markov chains with variable length are useful parsimonious stochastic models able to generate most stationary sequence of discrete symbols. The idea is to identify the suffixes of the past, called contexts, that are relevant to predict the future symbol. Sometimes a single state is a context, and looking at the past and finding this specific state makes the further past irrelevant. States with such property are called renewal states and they can be used to split the chain into independent and identically distributed blocks. In order to identify renewal states for chains with variable length, we propose the use of Intrinsic Bayes Factor to evaluate the hypothesis that some particular state is a renewal state. In this case, the difficulty lies in integrating the marginal posterior distribution for the random context trees for general prior distribution on the space of context trees, with Dirichlet prior for the transition probabilities, and Monte Carlo methods are applied. To show the strength of our method, we analyzed artificial datasets generated from different models and one example coming from the field of Linguistics.

Experimental and Theoretical Studies of the Corrosion Inhibition Performance of Fatty Acid-based Ionic Liquids for Mild Steel in 1 M HCl: Effects of the Varied Alkyl Chain Length in the Anionic Group

Five fatty acid-based ionic liquids (FAILs) with various anionic alkyl chain lengths are synthesized, namely methyltrioctylammonium butyrate ([N8881][C4:0]), methyltrioctylammonium caproate ([N8881][C6:0]), methyltrioctylammonium octanoate ([N8881][C8:0]), methyltrioctylammonium laurate ([N8881][C12:0]), and methyltrioctylammonium palmitate ([N8881][C16:0]), to investigate the potential effects of anionic alkyl chains on their corrosion inhibition property for mild steel in 1 M HCl solution via X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, contact angle measurements, electrochemical measurements, and weight loss measurements. The results reflect that the FAIL inhibitor can adsorb on the surface of mild steel to form a protective film and effectively inhibit the corrosion. [N8881][C8:0] exhibits the optimal inhibition efficiency (96.94%) in comparison to [N8881][C4:0] (80.73%), [N8881][C6:0] (89.34%), [N8881][C12:0] (90.69%), and [N8881][C16:0] (74.42%). It is speculated that the varied anionic alkyl chain length may change the intensity of the protective film to affect the inhibition efficiency. The in-depth analysis by molecular dynamic simulation confirms that [N8881][C8:0] with the same anionic and cationic alkyl chain lengths shows the most ordered and compact film on the mild steel surface. The present study focuses on the effects of the anionic alkyl chain on the corrosion inhibition performance and provides novel insights into the design and development of effective and eco-friendly ionic liquids as corrosion inhibitors.

Sublethal Exposure of Per- and Polyfluoroalkyl Substances of Varying Chain Length and Polar Functionality Results in Distinct Metabolic Responses in Daphnia magna.

Per- and polyfluoroalkyl substances (PFAS) are a class of persistent organic pollutants used in industrial applications because of their physicochemical properties, which results in their ubiquitous presence across environmental matrices. To date, legacy PFAS have been well studied; however, the concentration of alternative PFAS may exceed the concentration of legacy pollutants, and more information is needed regarding the sublethal toxicity at the molecular level of aquatic model organisms, such as Daphnia magna. Perfluorobutanoic acid (PFBA), perfluorohexanoic acid (PFHxA), perfluorohexanesulfonic acid (PFHxS), and perfluorononanoic acid (PFNA) are four widely detected PFAS alternatives of varying chain length and polar functionality that are quantified in aquatic environments. The present study examines the metabolic perturbations of PFAS with varying chemistries to D. magna using targeted mass spectrometry-based metabolomics. Daphnia were acutely exposed to sublethal concentrations of PFBA, PFHxA, PFHxS, and PFNA before the polar metabolite profile was extracted from single organisms. Multivariate analysis demonstrated significant separation between the sublethal concentrations of PFHxA, PFHxS, and PFNA relative to the controls; in sum, longer chain lengths demonstrated greater overall perturbations to the extracted metabolic profiles. Univariate statistics revealed significant perturbations in the concentrations of several amino acids, nucleotides/nucleosides, and neurotransmitters with exposure to PFAS. These metabolic perturbations are consistent with disruptions in energy metabolism (pantothenate and coenzyme A metabolism, histidine metabolism) and protein synthesis (aminoacyl-transfer RNA biosynthesis and amino acid metabolism), which were identified through biochemical pathway analysis. These results provide evidence that although PFAS chemistry (chain length and polar functional group) invokes unique metabolic responses, there is also an underlying toxic mode of action that is common with select PFAS exposure. Overall, the present study highlights the capabilities of environmental metabolomics to elucidate the molecular-level perturbations of pollutants within the same chemical class to model aquatic organisms, which can be used to prioritize risk assessment of substituted PFAS alternatives. Environ Toxicol Chem 2023;42:242-256. © 2022 SETAC.

Loose Semirigid Aromatic Polyester Bottle Brushes at Poly(2-isopropyl-2-oxazoline) Side Chains of Various Lengths: Behavior in Solutions and Thermoresponsiveness.

A polycondensation aromatic polyester with an oxygen spacer was synthesized and used as a macroinitiator for the grafting of linear poly(2-isopropyl-2-oxazoline) (PiPrOx) by the cationic polymerization method. The length of the thermosensitive side chains was varied by the initiator:monomer ratio. Using methods of molecular hydrodynamics, light scattering and turbidimetry, the copolymers were studied in organic solvents and in water. The molecular characteristics of the main chain and graft copolymers, the polymerization degree of side chains and their grafting density have been determined. The equilibrium rigidity of the macroinitiator and the conformations of grafted macromolecules were evaluated. In selective solvents, they take on a star-like conformation or aggregate depending on the degree of shielding of the main chain by side chains. The thermoresponsiveness of graft copolymers in aqueous solutions was studied, and their LCST were estimated. The results are compared with data for graft copolymers composed of PiPrOx side chains and flexible or rigid chain backbones of aromatic polyester type.

Recyclable polymeric ionic liquids applied as metal-free transfer hydrogenation catalysts

A new methodology for immobilizing a triazolium salt onto polyethylene glycols (PEG) was developed. The immobilization is a two-step reaction, involving the tosylation of PEGs followed by a neat reaction between the PEG tosylates and the triazole. It is a high-yielding reaction conducted under mild conditions with a simple workup procedure. Hence, the salt 1-benzyl-4-phenyl-1H-1,2,3-triazolium iodide was immobilised onto PEGs of varying chain lengths (PEG300_8000) to yield various polymeric ionic liquids (PILs). All the PIL compounds were characterised by spectroscopic analysis and utilised as homogeneous metal-free organocatalysts for the transfer hydrogenation of ketones to alcohols in isopropanol as solvent and hydrogen source. The metal-free PIL catalysts showed activity for transforming acetophenone to 1-phenyl alcohol at up to 87% conversion. The representative PEG600 system was recycled three times with minimal loss in activity. The mechanism of a possible catalyst leaching was investigated using computational calculations. The results reveal that the promoter, isopropanol, also promotes the leaching of the triazole from the PEG backbone.

Macrochain Transfer Agents for Catalytic Ring-Opening Metathesis Polymerization.

A monosubstituted 1,3-diene derivative attached to a polymer is demonstrated to act as a macrochain transfer agent in catalytic ring-opening metathesis polymerization. PEG- and PLA-based macrochain transfer agents were synthesized in a few steps and were characterized using NMR spectroscopy, size exclusion chromatography (SEC) and matrix-assisted laser desorption/ionization-time-of-flight (MALDI-ToF) mass spectrometry. Poly(l-lactide) based diblock copolymer, poly(ethylene glycol)-based diblock, and triblock (ABA type) copolymers of varied chain lengths were prepared catalytically in a one-pot approach via metathesis polymerization. Block copolymers were characterized by SEC and showed monomodal molecular weight distributions. Moreover, DOSY NMR spectroscopy further proved the block microstructures of the synthesized polymers.

Modified polybenzoxazine and carbon fiber surface with improved mechanical properties by introducing hydrogen bonds

While both polybenzoxazine and carbon fiber are attractive due to their excellent mechanical properties, polybenzoxazine suffers from low toughness, and carbon fiber has an inert surface. By incorporating newly designed and synthesized curcumin-based polyurethanes with varying chain lengths into polybenzoxazine (PU1.2 and PU2.0) and the surface of carbon fiber, we were able to introduce variable amounts of hydrogen bonds. Our modified polybenzoxazine exhibited enhanced mechanical properties, such as higher toughness and flexural strength of up to 16.0 kJ/m2 and 147 MPa, respectively. In comparison, the flexural strength of our surface-modified carbon fiber reinforced benzoxazine composites was up to 537 MPa. Additionally, the improved mechanical properties of surface-modified carbon fiber reinforced polybenzoxazine are because curcumin-based polyurethanes can significantly improve the interfacial adhesion between the matrix and resin by introducing a soft layer with a high concentration of hydrogen bonds. Our study not only improved the mechanical properties of polybenzoxazine and carbon fibers reinforced polymer composites, but also revealed a novel method for enhancing the mechanical properties of thermosetting resins and interface adhesion of carbon fiber by regulating the hydrogen bonding content.

How does Poly(ethylene glycol) with varied chain length affect the thermo-responsive behavior of methyl cellulose in aqueous solutions?

In this study, by using a set of narrowly distributed polyethylene glycol (PEG) samples with varied average molar mass (PEGn, 9 <n < 454), we have systematically studied how PEG molar mass and solution concentration influence the thermal response behavior of methyl cellulose (MC) aqueous solutions (Mw = 4.3 × 105 g/mol, <Rg> = 71 nm) by a combination of isothermal titration calorimetry (ITC), rheometer, UV–vis spectroscopy, laser light scattering (LLS) and atomic force microscopy (AFM). At room temperature, ITC result clarifies the existence of extremely weak hydrophobic interactions between MC and PEG chains. In addition, for MC/PEG mixed solution with shorter PEGs (PEG22 and PEG90), experimentally measured zero-shear viscosity (ηexp) is confirmed to be 5–10% higher than the theoretical values (ηcalc), further supporting the interchain association. Whereas for MC/PEG454, insoluble aggregates are formed, which results in ηexp < ηcalc. Further, dynamic laser scattering (DLS) results further reveal how the percentage of peak area of aggregates depends on the chain length of PEG. During the heating process from T = 20 to 70 °C, a combination of UV, LLS and AFM results clearly illustrates that the shorter PEG chains can effectively stabilize the formed MC fibers and prevent the fiber extension; whereas for longer PEG chains, they can not only promote the nucleation process, but also destabilize the formed fibers and promote the fiber extension. Our result unambiguously reveals the macromolecular effect of PEGs on the thermal response behavior of MC in solutions.

Designing monovalent selective anion exchange membranes for the simultaneous separation of chloride and fluoride from sulfate in an equimolar ternary mixture

Selective removal of multiple counter-ions in a single mixture is highly desirable for many industrial applications but also very challenging. This study focuses on designing monovalent selective anion exchange membranes (AEMs) for the simultaneous separation of F− and Cl− from SO42− using electrodialysis (ED). A series of brominated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO) polymers with adjusted bromination degrees at benzyl and aryl positions were synthesized, and quaternized with different tertiary amines of varying chain lengths to produce optimized AEMs. Differences in bromination degrees and the chain lengths of the tertiary amines alter the microstructure of AEMs, which influences the anion transport through the developed membranes. Selected AEMs were modified via layer-by-layer (LbL) deposition of poly (sodium 4-styrenesulfonate) (PSS) and poly(allylamine hydrochloride) (PAH) polyelectrolytes to enhance their monovalent selectivity. ED tests were carried out with an equimolar ternary mixture. When 5 layers of deposition were applied, the achieved Cl−/ SO42− and F−/ SO42− selectivities were 11.7 ± 0.2 and 8.3 ± 0.3, respectively, showing significant improvement compared to a commercial monovalent selective ASVN membrane. Experimental results confirm that simultaneously optimizing membrane microstructure and surface can be an effective strategy for the separation of similar counter-ions in an ED process.

Rack-gear structures in columnar liquid crystal phases of trialkoxybenzyl pentafluorobenzoates and their influences on intercolumnar interdigitation and macroscopic morphologies

ABSTRACT In this study, 3,4,5-trialkoxybenzyl pentafluorbenzoates with alkyl chains of various lengths were synthesised, and the phase transition behaviours, liquid crystallinities, and molecular packing structures of their columnar phases were investigated. The results showed that discs comprising two half-discoid molecules stack up to form columns with rack-gear structures, generating columnar liquid crystal phases. From powder and single crystal X-ray diffraction investigation, the mechanism of the self-assembly of molecules into columns and their intercolumnar interdigitation was postulated. Furthermore, it was revealed that the combination of alkyl groups of the benzyl groups was closely related to the type of columnar liquid crystal phases generated and the macroscopic morphologies of the liquid crystal domains.

Novel synthesized anionic gemini and monomeric surfactants bearing sulphonate group as petro-dispersing/collecting agents: Design, characterization and surface-active properties

Conventional and gemini anionic sulphonate surfactants of variable alkyl chain length (8, 10, and 12 carbon atoms), were synthesized by three steps reactions using ethylenediamine, alkyl halides and sodium 3-chloro-2-hydroxypropane-1-sulfonate. Various spectroscopic tools (i.e., 1H and 13C NMR and IR spectra) were used to clarify the structures of synthesized surfactants. The solution surface properties of synthesized surfactants were studied by critical micelle concentration (CMC). Both maximum surface excess and minimum surface area per surfactant molecule were measured. Besides, the adsorption and micellization performance of the synthesized surfactants, which were estimated by the parameter of free adsorption energy (ΔGads0) and micellization (ΔGmic0) were measured. Moreover, the behavior of the synthesized surfactants as petroleum-collecting or dispersing agents has been studied in solid and diluted forms in water with different salinity. The results indicate that the synthesized surfactants possess superior petroleum-dispersing properties in water solutions of different salinity. Whereas the dispersing effect was improved by rising the hydrophobicity of these compounds. Furthermore, all the synthesized conventional and gemini anionic surfactants have a high ability to adsorb at the surface than micellized in the solution.

Synthesis, Self‐Aggregation, Interfacial Behavior and Interaction Studies of Non‐ Cytotoxic Caffeinium‐Based Surface Active Ionic Liquids with Sodium Dodecyl Sulfate

Caffeinium-based surface-active ionic liquids (SAILs), (1-(2-alkanoyl oxy) ethylcaffeinium bromide), [CnEcaf]Br with variable chain length (n=12, 14, 16) were synthesized and their molecular structures were explored by multiple spectral techniques. The critical micelle concentration (CMC) of pure SAILs and their mixtures with sodium dodecyl sulfate (SAIL-DS) in aqueous solution was determined by employing various techniques at 298 K. The tensiometry and dynamic light scattering (DLS) techniques have been employed to gain insight about the interfacial behavior and aggregate size of cat-anionic mixtures in aqueous solution. Interestingly, the interaction parameters ( ) showed strong synergism between these two oppositely charged molecules. Further, it was found that SAIL-DS cat-anionic mixtures exhibit excellent adsorption efficacy and are more effective in lowering the surface tension of water as compared to pure SAILs. The DLS results showed the formation of mixed-size aggregates in SAIL-DS systems. The contact angle and wetting properties of pure SAILs over the parafilm surface were also determined using a static sessile drop method. Further, MTT assay was used to determine the biocompatibility of SAILs on Human embryonic kidney (HEK-293) cell line and in-vitro anti-cancer activity on Lung cancer cells (A549). These SAILs displayed substantial cytotoxicity against cancerous cells, indicating that they could be useful in a variety of biological applications.

Diversity-Oriented Synthesis of a Molecular Library of Immunomodulatory α-Galactosylceramides with Fluorous-Tag-Assisted Purification and Evaluation of Their Bioactivities in Regard to IL-2 Secretion.

Structural variants of α-galactosylceramide (α-GalCer) that stimulate invariant natural killer T (iNKT) cells constitute an emerging class of immunomodulatory agents in development for numerous biological applications. Variations in lipid chain length and/or fatty acids in these glycoceramides selectively trigger specific pro-inflammatory responses. Studies that would link a specific function to a structurally distinct α-GalCer rely heavily on the availability of homogeneous and pure materials. To address this need, we report herein a general route to the diversification of the ceramide portion of α-GalCer glycolipids. Our convergent synthesis commences from common building blocks and relies on the Julia-Kocienski olefination as a key step. A cleavable fluorous tag is introduced at the non-reducing end of the sugar that facilitates quick purification of products by standard fluorous solid-phase extraction. The strategy enabled the rapid generation of a focused library of 61 α-GalCer analogs by efficiently assembling various lipids and fatty acids. Furthermore, when compared against parent α-GalCer in murine cells, many of these glycolipid variants were found to have iNKT cell stimulating activity similar to or greater than KRN7000. ELISA assaying indicated that glycolipids carrying short fatty N-acyl chains (1fc and 1ga), an unsubstituted (1fh and 1fi) or CF3-substituted phenyl ring at the lipid tail, and a flexible, shorter fatty acyl chain with an aromatic ring (1ge, 1gf, and 1gg) strongly affected the activation of iNKT cells by the glycolipid-loaded antigen-presenting molecule, CD1d. This indicates that the method may benefit the design of structural modifications to potent iNKT cell-binding glycolipids.

Molecular mechanisms of plant growth promotion for methylotrophic Bacillus aryabhattai LAD

Plant growth-promoting rhizobacteria (PGPR) can produce hormone-like substances, promote plant nutrient uptake, enhance plant resistance, inhibit the growth of pathogenic bacteria, and induce plant resistance to biotic and abiotic stresses. Bacillus is one of the most studied genera that promote plant root development. Since its discovery in 2009, B. aryabhattai has shown promising properties such as promoting plant growth and improving crop yield. However, the mechanisms of B. aryabhattai promoting plant growth remain to be investigated. In this study, the chromosome of B. aryabhattai strain LAD and five plasmids within the cell were sequenced and annotated. The genome, with a length of 5,194,589 bp and 38.12% GC content, contains 5,288 putative protein-coding genes, 39 rRNA, and 112 tRNA. The length of the five plasmids ranged from 116,519 to 212,484 bp, and a total of 810 putative protein-coding genes, 4 rRNA, and 32 tRNA were predicted in the plasmids. Functional annotation of the predicted genes revealed numerous genes associated with indole-3 acetic acid (IAA) and exopolysaccharides (EPSs) biosynthesis, membrane transport, nitrogen cycle metabolism, signal transduction, cell mobility, stress response, and antibiotic resistance on the genome which benefits the plants. Genes of carbohydrate-active enzymes were detected in both the genome and plasmids suggesting that LAD has the capacity of synthesizing saccharides and utilizing organic materials like root exudates. LAD can utilize different carbon sources of varied carbon chain length, i.e., methanol, acetate, glycerol, glucose, sucrose, and starch for growth and temperature adaptation suggesting a high versatility of LAD for thriving in fluctuating environments. LAD produced the most EPSs with sucrose as sole carbon source, and high concentration of IAA was produced when the maize plant was cultivated with LAD, which may enhance plant growth. LAD significantly stimulated the development of the maize root. The genome-based information and experimental evidence demonstrated that LAD with diverse metabolic capabilities and positive interactions with plants has tremendous potential for adaptation to the dynamic soil environments and promoting plant growth.

Volume Overlap Variation within Hyperbranched Polymer Brushes Resolves Topology Effects against Protein Fouling.

Hyperbranched polymer brushes with a three-dimensional dendritic structure are used in antifouling applications to obtain bioinert and compact dendritic structures. Though hyperbranched polyglycerol (HPG) is extensively utilized in the antifouling layer, there is still a lack of direct studies on the relationship between the interfacial properties and topology effect of hyperbranched polymer brushes. Here, we established the degree of chain volume overlap (Dv) to characterize the spatial shielding efficiency generated by HPG brushes and investigated the impact mechanism of the variable chain length on the interfacial physicochemical properties. The results revealed the Dv-relevant feature of performance that the most densely packed HPG brushes for a medium-length LHPG3.07 enable the functional surface to display optimal antifouling performance toward protein adsorption by forming the most effective space barrier and hydrated layer in appropriate molecular weights and graft density. Moreover, we clarified the advance of hyperbranched polymer brushes exhibited in topology effects for imparting surface-enhanced resistance to biofouling relies on the generable higher steric hindrance as compared with linear analogs. This study established a Dv-relevant evaluation model for acquiring an optimized antifouling surface based on the appropriate choice of polymer structure, topology morphologies, and grafting parameters.

Frequency dynamics of a chain of magnetized rotors: dumbbell model vs Landau–Lifshitz equation

During the past decades magnetic materials and structures that span several length scales have been of interest mainly due to their application in data storage and processing, flexible electronics, medicine, between others. From a microscopic point of view, these systems are typically studied using the Landau–Lifshitz equation (LLE), while approaches such as the dumbbell model are used to study macroscopic magnetic structures. In this work we use both the LLE and the dumbbell model to study spin chains of various lengths under the effect of a time dependent-magnetic field, allowing us to compare qualitatively the results obtained by both approaches. This has allowed us to identify and describe in detail several frequency modes that appear, with additional modes arising as the chain length increases. Moreover, we find that high frequency modes tend to be absorbed by lower frequency ones as the amplitude of the field increases. The results obtained in this work are of interest not only to better understand the behavior of the macroscopic spins chains, but also expands the available tools for qualitative studies of both macroscopic and microscopic versions of the studied system, or more complex structures such as junctions or lattices. This would allow to study the qualitative behavior of microscopic systems (e.g. nanoparticles) using macroscopic arrays of magnets, and vice versa.

Multi-spectroscopic characterization of bitumen and its polarity-based fractions

• Insights on H/C-ratio, aromatic systems and average molecular sizes are obtained. • NMR reveals varying chain lengths of aliphatic substituents throughout the fractions. • Characteristic NMR shifts in the resins suggest presence of some esters or amides. • 31 P NMR after derivatization, shows minor amounts of alcohols and carboxylic acids. Bitumen contains a complex mixture of molecules, ranging from simple linear alkanes to complex polyaromatic systems. Used in road construction, those structures are permanently influenced by atmospheric processes, which result in oxidation, degradation, loss of volatiles and structural rearrangements. In order to understand those molecular changes, a profound description of the unaltered system is needed. In this study, structural and chemical peculiarities of bitumen and its polarity-based fractions were analysed using nuclear magnetic resonance (NMR) techniques in combination with infrared/fluorescence spectroscopy and elemental analysis. The bitumen sample was separated into saturates, aromatics, resins and asphaltenes. Elemental analysis provided insights into variations of heteroatom content and hydrogen-carbon ratio among the fractions. Fluorescence spectroscopy showed an increase in the aromatic condensation degree with rising polarity. The combination of heteronuclear single quantum coherence (HSQC) and elemental analysis facilitated the assessment of length and branching extent of aliphatic side chains, throughout the fractions. Another 2D NMR technique, heteronuclear multiple bond coherence (HMBC) found evidence for minor contributions of carboxylic esters or amides within the resins. Hydroxyl and amino groups were analysed by 31 P NMR after derivatization, revealing minor amounts of alcohols, amides and carboxylic acids in the most polar fractions. Additionally, diffusion ordered spectroscopy was carried out to obtain estimations on average molecular sizes and weights. Applying in-depth NMR analysis to bitumen and combining it with complementary analytical techniques, this study provides a unique basis for future ageing studies and demonstrates how multi-spectroscopy can give new insights into bitumen structure and chemistry.

Effect of Surfactant Chain Length on Emulsification Dynamics of Self Emulsifying Formulation of Poorly Soluble Drug.

In this work, the aim was to study the effect of the chain length of surfactant on the self emulsifying system of a poorly soluble drug, aceclofenac. The selection of almond oil as a lipid vehicle was done on the basis of solubility and compatibility of the vehicle with the drug. The effect of varying chain length of different surfactants of Tween series, namely Tween 20, Tween 40, Tween 60 and Tween 80, was evaluated on self emulsifying efficiency by constructing the pseudoternary diagrams. PEG-400 was used as a co-surfactant in a definite ratio with all the surfactants to minimize their concentration. The best self emulsifying ability was exhibited by Tween 80: PEG-400 combination followed by Tween 60: PEG-400, Tween 40: PEG-400, Tween 20: PEG-400. This observation indicates that as the chain length of Tweens increases, their ability to form a good microemulsion increases if the same co-surfactant is used. However, it has also been found that the presence of unsaturated bond in Tween 80 provides it an elasticity which supports good intermixing of oil and water, leading to formation of a fine microemulsion. Six different formulations were prepared using a combination of almond oil, Tween 80, PEG-400 and the drug aceclofenac. The formulations were subjected to various evaluation parameters, such as dispersibility, transmittance, pH, globule size, polydispersibility, zeta potential, viscosity, refractive index and in vitro dissolution. The best formulation was found to have globule size of less than 100 nm and zeta potential of -3.35 ± 0.60 mV, indicating the formation of a microemulsion of aceclofenac with good stability.