Novel high-performance ingredients based on functionalized polysaccharides – The role of enzymatic catalysis.

Polysaccharides are interesting starting materials in the design of high-performance cosmetic ingredients, not only because of their generally low toxicity and “green” profile, but also because of their wide and exciting propensity to form complex self-aggregated structures. These structures have direct relevance for formulation science, since they provide us with the means to tailor and optimize rheological characteristics, solubilization efficiency, emulsification and other critical attributes of a formulation. However, in order to fully exploit this potential of polysaccharide-based materials we need not only the ability to extract, purify and refine them on an industrial scale. We also need cost-efficient tools that allow us to optimize their performance and enable new functionalities. The present talk will focus on the role of industrial enzymatic catalysis in this context. Because of their natural origin, polysaccharides obviously lend themselves to enzymatic modification, and many carbohydrate-specific enzymes are available in bulk quantities, including well-known examples from the amylase and cellulase families. In the presentation, sugar-based surfactants will be used as the prime example of how enzymes can help us create tomorrow’s polysaccharide-based ingredients. Today, sugar-based surfactants are used in manifold cosmetic and personal care products, in the form of “alkylpolyglucosides” (or “APGs” for short). However, this term is a misnomer in the sense that the hydrophilic head-groups in these surfactants are by no means polymeric. Rather, APGs consist of a mixture of species, in which the head-groups comprise merely one to three repeating hexose units. This constraint severely inhibits the full exploitation of alkylglycoside functionality, and many attempts to increase the head-group size have therefore been performed over the years. However, synthesis of alkylglycosides with longer head-groups by conventional means has proved prohibitively difficult, for reasons of physical incompatibility of the starting materials (glucose and fatty alcohols). Over the last couple of years, Enza Biotech AB has developed an enzymatic technology that allows us to circumvent the limitations of conventional APG synthesis. This technology allows for synthesis of alkylglycosides with longer head-groups, which are truly oligomeric, or even polymeric. As will be discussed in the talk, this opens up vast new possibilities for sugar-based surfactants, in areas that have so far been reserved for ethoxylated non-ionic surfactants. In the talk, the novel alkylglycosides will also be used to illustrate the more general observation that new materials based on sustainable starting materials not only allow us to mimic existing functionalities, but also to identify entirely new ones. For polysaccharides these opportunities generally have their origins in their complex self-aggregation behavior, which involves both the carbohydrate backbone and its substituents

Surfactants modify the release from tablets made of hydrophobically modified poly (acrylic acid)

AbstractMany novel pharmaceutically active substances are characterized by a high hydrophobicity and a low water solubility, which present challenges for their delivery as drugs. Tablets made from cross-linked hydrophobically modified poly (acrylic acid) (CLHMPAA), commercially available as Pemulen™, have previously shown promising abilities to control the release of hydrophobic model substances. This study further investigates the possibility to use CLHMPAA in tablet formulations using ibuprofen as a model substance. Furthermore, surfactants were added to the dissolution medium in order to simulate the presence of bile salts in the intestine.The release of ibuprofen is strongly affected by the presence of surfactant and/or buffer in the dissolution medium, which affect both the behaviour of CLHMPAA and the swelling of the gel layer that surrounds the disintegrating tablets. Two mechanisms of tablet disintegration were observed under shear, namely conventional dissolution of a soluble tablet matrix and erosion of swollen insoluble gel particles from the tablet. The effects of surfactant in the surrounding medium can be circumvented by addition of surfactant to the tablet. With added surfactant, tablets that may be insusceptible to the differences in bile salt level between fasted or fed states have been produced, thus addressing a central problem in controlled delivery of hydrophobic drugs. In other words CLHMPAA is a potential candidate to be used in tablet formulations for controlled release with poorly soluble drugs

Topological dynamics of micelles formed by geometrically varied surfactants

The molecular architecture of sugar-based surfactants strongly affects their self-assembled structure, i.e., the type of micelles they form, which in turn controls both the dynamics and rheological properties of the system. Here, we report the segmental and mesoscopic structure and dynamics of a series of C16 maltosides with differences in the anomeric configuration and degree of tail unsaturation. Neutron spin-echo measurements showed that the segmental dynamics can be modeled as a one-dimensional array of segments where the dynamics increase with inefficient monomer packing. The network dynamics as characterized by dynamic light scattering show different relaxation modes that can be associated with the micelle structure. Hindered dynamics are observed for arrested networks of worm-like micelles, connected to their shear-thinning rheology, while nonentangled diffusing rods relate to Newtonian rheological behavior. While the design of novel surfactants with controlled properties poses a challenge for synthetic chemistry, we demonstrate how simple variations in the monomer structure can significantly influence the behavior of surfactantsThe authors thank the Swedish Research Council Formas (Grant 2015-666) for funding J.L. The research was performed with financial support from the Vinnova─Swedish Governmental Agency for Innovation Systems within the NextBioForm Competence Centre. The authors also thank the Institut Laue-Langevin, France, for the awarded beamtime (Proposal No. 9-10-1652). NSE data is openly available at doi: 10.5291/ILL-DATA.9-10-1652S

Comparison of the helix-coil transition of a titrating polypeptide in aqueous solutions and at the air-water interface

The transition from a-helix to random coil of the titrating polyamino acid Co-poly-L-(lysine, phenylalanine), (p-(Lys,Phe)), has been investigated as a function of pH and ionic strength in aqueous solution and at the air water interface by means of circular dichroism (CD) spectroscopy and the Langmuir surface film balance technique. The results strongly suggest that the helix-coil transition for peptides at the air-water interface can be determined by using the two-dimensional Flory exponent, v, to express the pH dependent peptide surface conformation. The helix-coil titration curve of p-(Lys,Phe) shifts approximately 2.5 pH units towards lower pH at the air-water interface, as compared with the bulk solution. This finding is of relevance for the understanding of conformation and conformational changes of membrane-tran sporting and membrane penetrating peptides as well as for the use of peptides in molecular devices. (c) 2005 Elsevier B.V All rights reserved

Effects of pH, ionic strength, calcium, and molecular mass on the arrangement of hydrophobic peptide helices at the air-water interface

The influence of subphase characteristics (ionic strength, pH, and the presence of bridging cations) on the conformation and lateral orientation of the hydrophobic polypeptide poly-(L)-leucine (p-leu) has been investigated at the air-water interface with the surface film balance technique as well as with Brewster angle microscopy (BAM). In addition, Langmuir-Blodgett films of p-leu deposited on quartz and mica from different subphases have been studied by circular dichroism (CD) spectroscopy and atomic force microscopy (AFM). P-leu forms alpha-helices at the interface regardless of subphase characteristics. Long-range lateral orientation of the alpha-helical strands in the p-leu monolayer was obtained under conditions where attractive interpeptide end-group interactions prevail. These interactions were obtained under conditions where (1) end-group charges lend a zwitterionic character to the peptide, thus enabling strong electrostatic attraction between adjacent strands, (2) there is a possibility for formation of carboxylic acid dimers, or (3) calcium bridges form between carboxylate end groups. These three cases correspond to an increase of the effective molecular mass of the peptide. It was concluded that such an increase, and thereby an increased long-range lateral orientation, can be obtained by enabling peptide end group attraction, but not by screening peptide end group repulsion. Kinetic studies of monolayer relaxation strongly suggest that the end-group effects influence the thermodynamic, as well as the kinetic, properties of peptide monolayers

Aggregate morphology and flow behaviour of micellar alkylglycoside solutions

Solutions of n-nonyl-beta-D-glucoside (C(9)G(1)), n-decyl-beta-D-glucoside (C(10)G(1)), n-dodecyl-beta-D-maltoside (C(12)G(2)) n-tetradecyl-beta-D-maltoside (C(14)G(2)) and C(9)G(1)/C(10)G(1) mixtures have been characterised by capillary viscometry and rheology in H2O and D2O, in order to map the influence of surfactant characteristics on micellisation over a wide concentration range. For the maltosides, the micellar solutions are shear thinning with a zero-shear viscosity that scales with concentration according to a power law with an exponent of about 5.8. In contrast, solutions of the glucosides C(9)G(1), C(10)G(1) and their mixtures show Newtonian flow behaviour and a much lower scaling exponent (< 2.4). In C(9)G(1)/C(10)G(1) mixtures, the scaling exponent decreases monotonously with increasing C(10)G(1) content. The flow behaviour correlates with the packing requirements of the various surfactants, and are compatible with the idea that the maltosides form worm-like micelles, whereas the glucosides form branched, interconnected micelles (C(9)G(1)) and space-filling micellar networks (C(10)G(1))

Enzymatic route to alkyl glycosides having oligomeric head groups

Cyclodextrin glycosyl transferase (CGTase) from Bacillus macerans was used to catalyse the coupling of alpha-cyclodextrin to alkyl beta-glycosides. The acceptor substrate dodecyl beta-maltoside was thus converted to dodecyl beta-D-maltooctaoside. Further coupling steps and disproportionation reactions occurred, but by optimisation of the reaction time, a yield of 50% of the primary coupling product was obtained. The method worked well for a range of acceptors with different length of the carbohydrate part (1-3 glucose residues) and the hydrocarbon chain (10-14 carbon atoms). With respect to the principles of green chemistry, the method is superior to previously used methods involving protection/deprotection reactions

Efficient synthesis of a long carbohydrate chain alkyl glycoside catalysed by cyclodextrin glycosyltransferase (CGTase).

Alkyl glycosides with long carbohydrate groups are surfactants with attractive properties but they are very difficult to synthesize. Here, a method for extension of the carbohydrate group of commercially available dodecyl-beta-D-maltoside (DDM) is presented. (DDM) was converted to dodecyl-beta-D-maltooctaoside (DDMO) in a single step by using a CGTase as catalyst and alpha-cyclodextrin (alpha-CD) as glycosyl donor. The coupling reaction is under kinetic control and the maximum yield depends on the selectivity of the enzyme. The B. macerans CGTase favoured the coupling reaction while the Thermoanaerobacter enzyme also catalysed disproportionation reactions leading to a broader product range. A high ratio alpha-CD/DDM favoured a high yield of DDMO and yields up to 80 % were obtained using the B. macerans enzyme as catalyst. (c) 2009 Wiley Periodicals, Inc

Solid-state phase behaviour of dodecylglycosides

The solid-state phase behaviour of lyophilised n-dodecyl-beta-D-glucoside (beta-C(12)G(1)), n-dodecyl-beta-D-maltoside (beta-C(12)G(2)) and n-dodecyl-beta-D-maltotrioside (beta-C(12)G(3)) has been investigated by differential scanning calorimetry (DSC) and X-ray techniques. For beta-C(12)G(1), lyophilisation results in a formation of a crystalline anhydrate. The lamellar spacing (37 angstrom) is consistent with an alkyl chain packing in which the chains are not interdigitated. At 80 degrees C, the material melts into a lamellar liquid crystal with a lamellar spacing of 32 angstrom, which suggests that the non-interdigitated chain packing of the crystalline state is retained in the liquid crystal. In contrast, lyophilisation of beta-C(12)G(2) and beta-C(12)G(3) results in the formation of a glassy state, best described as a frozen version of the lamellar liquid crystal. For beta-C(12)G(2), the lamellar spacing in the glass and liquid crystal suggests interdigitation of the alkyl chains. The glass transition temperature was found to be 65 degrees C for beta-C(12)G(3), and 100 degrees C for K12G3, which compares favourably with the glass transition of the parent carbohydrates. A second crystalline modification of beta-C(12)G(1) was prepared by precipitation from an aqueous solution at temperatures below the Krafft point (38 degrees C). For this modification, the lamellar distance (24 angstrom) is consistent with interdigitated alkyl chains. At 50 degrees C, the crystalline material melts into a liquid crystalline phase. The material also readily loses water and rapidly re-crystallises to the anhydrate. The amount of water lost upon drying is consistent with the idea that the material is a monohydrate of beta-C(12)G(1). The drying and re-crystallisation processes give rise to 'pre-transitions' in the DSC thermograms and illustrate the importance of careful control of water in any analysis of the phase behaviour of alkylglycosides. (c) 2005 Elsevier Ltd. All rights reserved