Unveiling the hydrogen bonding network in liquid crystalline natural-based glycosides containing polymeric complexes: Experimental and theoretical assessment
Graphical abstract
Introduction
Hydrogen-bonding is a versatile technique to yield new supramolecular liquid crystals [1,2], thanks to the directional character of the hydrogen bonds that facilitates the arrangement of anisotropic structures. The typical strength of a hydrogen bond (1 60 kJ·mol−1) [3,4] can guarantee the stability of the new materials above their processing melting points, whilst providing some degree of “softness”. Some early examples of complexes with mesogenic character include the pyridine-benzoic assemblies, reported by Kato and co-workers [5,6], or the seminal works by Bruce and co-workers, using alkoxystilbazoles [[7], [8], [9]]. To date, a wide range of liquid crystals continues to be prepared by hydrogen-bonding, including, chiral bent-core with supramolecular induced chirality [10,11], photosensitive liquid crystals [12,13], modular assemblies showing broad blue phases [14], supramolecular dimers exhibiting the twist-bend nematic phase [[15], [16], [17]], or smectic networks for selective mass and ionic transport [[18], [19], [20]], among many others.
Carbohydrate liquid crystals can be considered as early precedents of supramolecular mesomorphic compounds, and were already reported in the first half of the 20th century [21,22]. More specifically, the different hydroxyl groups can form multiple hydrogen bonds between glycosides, resulting in microphase separation between polar and non-polar regions, ultimately favouring smectic behaviour [[23], [24], [25], [26], [27], [28], [29]]. We note, however, that the exhibition of liquid crystalline phases is not based in the formation of new “rod-like” or “disc-like” moieties by hydrogen-bonding, but instead on segregation due to the amphiphilic character of the glycosides, including hydrogen-bonding between the sugar heads. Carbohydrate liquid crystals experienced a fast development in the 1980′s and 1990′s [[26], [27], [28]], and the mesomorphic behaviour of new glycosides continues to be the object of systematic investigation by varying their composition and stereochemistry [[30], [31], [32], [33]].
Due to its important role on the formation of liquid crystal phases, in this work we investigate with detail the hydrogen-bonding network of a natural-based glycoside, a palm kernel oil-based mannoside, αManPKO, 1, and its complexes with different polymeric substrates,
The alkyl chains of αManPKO were obtained from palm kernel oil, and then added to a mannose head by glycosidation, resulting in a mixture containing different chain lengths, and the effect of composition of 1 is currently under investigation [34]. The formation of liquid crystalline structures and its non-toxicity, makes αManPKO a promising candidate for drug delivery applications [35]. αManPKO has been complexated to three different substrates: poly(ethylene oxide), PEG, 2; poly(4-vinyl pyridine), P4VP, 3; and a block copolymer with both PEG and P4VP segments, PEG45-b-P4VP18, 4,
Whilst PEG is considered as a polymer substrate of great interest for biological applications due to its bio-compatibility [36,37], P4VP has been widely applied as a building block to yield supramolecular polymers [13,[38], [39], [40], [41], [42], [43]]. Finally, block copolymers not only facilitate the introduction of new functionalities in different segments of the polymer chain, but they also offer further control over microphase separation by regulating their hydrophobic/hydrophilic ratios [[44], [45], [46]].
The materials are characterised by a combination of thermal, structural, spectroscopic and modelling techniques, in order to provide relevant insights into the role of the hydrogen-bonding network to assemble liquid crystalline glycosides [23]. Complexation of block-copolymers has been used for different applications and materials, including light-responsive materials studied in our lab [45]. More specifically, Ikkala and co-workers have reported several examples using P4VP as a polymeric matrix; and, for selected examples, they describe the self-assembly of P4VP block copolymers complexed with cholesteryl hemisuccinate [47] and with 3-pentadecylphenol [48]. These and other precedent works, however, focus on the structural and compositional analysis, whilst a detailed model of the hydrogen-bonding network is still crucial to describe and predict complexation. The assembly of glycosides, tackled in the present work, as well as other systems containing multiple and resonating hydrogen bonds [49], is particularly challenging, and requires accounting for several hydroxyl groups potentially acting as hydrogen-donors and hydrogen-acceptors. Our approach can then open new forefronts to prepare supramolecular liquid crystal polymers as drug-delivery and cosmetic formulations [[50], [51], [52], [53], [54]]. In the long-term, the use of amphiphilic polymers will be beneficial to provide nanocarriers stealth effects that suppress opsonisation, to reduce interactions with the reticular-endothelial system, and to ultimately prolong circulation lifetime in blood [[55], [56], [57]].
Section snippets
Materials preparation
The mannoside αManPKO, 1, was synthesised according to the process described in detail in [34], and can be reviewed as electronic supplementary information (ESI, section A). D(+)-mannose monohydrate and boron trifluoride, BF3, were purchased from Sigma Aldrich and used without further purification. The palm kernel oil, PKO, was obtained from Golden Jomalina Food Industries Sdn. Bhd. (Malaysia), and the main components after reduction were lauryl (49 %), myristyl (16 %) and oleyl (7 %) alcohols,
Phase behaviour and structure, POM, DSC and SWAXS
The phase behaviour of αManPKO and its complexes was assessed by polarised optical microscopy, POM, and confirmed by differential scanning calorimetry, DSC. αManPKO forms a monotropic smectic A phase below ca. 146 °C, assessed by the appearance of battonêtes under the polarised microscope, which further coalesce into a focal conic fan texture, in coexistence with homeotropic regions. The PEG⋅αManPKO, P4VP⋅αManPKO and PEG45-b-P4VP18⋅αManPKO complexes, also develop battonêtes on cooling from the
Conclusions
We have prepared complexes of the so-called αManPKO mannoside with different polymeric substrates, resulting in three new supramolecular polymers with smectic A mesomorphism, following a facile method to yield new formulations containing natural-based liquid crystal carbohydrates, and their lyotropic properties in water solutions are under current evaluation. The polymeric segments are located at the interface of the glycoside bilayers, stabilised by specific interactions with the αManPKO
CRediT authorship contribution statement
Nurul Fadhilah Kamalul Aripin: Conceptualization, Data curation, Writing - original draft, Writing - review & editing, Funding acquisition. Jonathan Maclean Heap: Data curation, Formal analysis. Rafael Piñol: Data curation, Methodology. Vijayan Manickam-Achari: Data curation, Formal analysis, Writing - original draft. Alfonso Martinez-Felipe: Conceptualization, Investigation, Writing - original draft, Writing - review & editing, Funding acquisition.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This work was supported by the Ministry of Education of Malaysia [FRGS/1/2019/TK05/UITM/02/9, 2019]; Royal Academy of Engineering, U.K., and Academy of Science, Malaysia [NRCP1516/4/61, 2016]; University of Aberdeen [SF10192, 2018] and University Malaya [UMRG grant RP038B-17AFR].
References (75)
- et al.
The role of hydrogen bonding in the phase behaviour of supramolecular liquid crystal dimers
J. Mol. Struct.
(2015) - et al.
Ionically conducting and photoresponsive liquid crystalline terpolymers: towards multifunctional polymer electrolytes
Eur. Polym. J.
(2018) - et al.
Carbohydrate liquid crystals: synthesis and characterisation of the methyl-6-O-(n-acyl)-alpha-D-glucopyranosides
Chem. Phys. Lipids
(2011) - et al.
Non-symmetric liquid crystal dimer containing a carbohydrate-based moiety
Carbohydr. Res.
(2012) - et al.
Carbohydrate liquid-crystals .2. Carbohydr Res
(1983) - et al.
Branched chain glycosides: enhanced diversity for phase behavior of easily accessible synthetic glycolipids
Thin Solid Films
(2006) - et al.
Thermosensitive sol-gel reversible hydrogels
Adv. Drug Deliv. Rev.
(2002) - et al.
Polycaprolactone-b-poly(ethylene oxide) copolymer micelles as a delivery vehicle for dihydrotestosterone
J. Control. Release
(2000) - et al.
Synthesis and characterization of spin-labelled and spin-probed side-chain liquid crystal polymers
Polymer
(1996) - et al.
Towards supramolecular side-chain liquid crystal polymers .4. Blends of low molar mass mesogens with amorphous polymers
Eur. Polym. J.
(1997)
Polyethylene glycol (PEG)-dendron phospholipids as innovative constructs for the preparation of super stealth liposomes for anticancer therapy
J. Control. Release
PEO-b-PCL grafted niosomes: the cooperativilty of amphiphilic components and their properties in vitro and in vivo
Colloids and Surfaces B-Biointerfaces
Synthesis of alkyl and cycloalkyl alpha-D-mannopyranosides and derivatives thereof and their evaluation in the mycobacterial mannosyltransferase assay
Carbohydr. Res.
Automatic atom type and bond type perception in molecular mechanical calculations
J. Mol. Graph. Model.
A fourier-transform infrared spectroscopy study of sugar glasses
Carbohydr. Res.
Relaxation in liquids, polymers and plastic crystals - strong fragile patterns and problems
J. Non. Solids
An FT-IR spectroscopic study of the role of hydrogen bonding in the formation of liquid crystallinity for mixtures containing bipyridines and 4-pentyloxybenzoic acid
RSC Adv.
Molecular tectonics: design of hybrid networks and crystals based on charge-assisted hydrogen bonds
Molecular recognition via hydrogen bonding in supramolecular complexes: a fourier transform infrared spectroscopy study
Molecules
New approach to mesophase stabilization through hydrogen-bonding molecular-interactions in binary-mixtures
J. Am. Chem. Soc.
Hydrogen-bonded liquid-crystals - a novel mesogen incorporating nonmesogenic 4,4’-bipyridine through selective recognition between hydrogen-bonding donor and acceptor
Chem. Lett.
Hydrogen-bonded liquid crystals from alkoxystilbazoles and 3-cyanophenols: structural control of mesomorphism. Molecular structure of the complex between 4-cyanophenol and 4-octyloxystilbazole
J. Mater. Chem.
Hydrogen bonded liquid crystals from nitrophenols and alkoxystilbazoles
J. Mater. Chem.
Hydrogen-bonded complexes between 4-alkoxystilbazoles and fluorophenols: solid-state structures and liquid crystallinity
Chem. Eur. J.
Hydrogen-bonded banana liquid crystals
Angewandte Chemie-International Edition
New H-bonded complexes and their supramolecular liquid-crystalline organizations
European J. Org. Chem.
Supramolecular design principles for efficient photoresponsive polymer-azobenzene complexes
J. Mater. Chem. C
Polymer-dye complexes: a facile method for high doping level and aggregation control of dye molecules
Chem. Mater.
Hydrogen-bonded liquid crystals with broad-range blue phases
J. Mater. Chem. C
Spontaneous chirality through mixing achiral components: a twist-bend nematic phase driven by hydrogen-bonding between unlike components
Chem. Commun.
New insights into the liquid crystal behaviour of hydrogen-bonded mixtures provided by temperature-dependent FTIR spectroscopy
Liq. Cryst.
A twist-bend nematic phase driven by hydrogen bonding
Angewandte Chemie-International Edition
Proton conductive cationic nanoporous polymers based on smectic liquid crystal hydrogen-bonded heterodimers
J. Mater. Chem. C
Study of structure formation in side-chain liquid crystal copolymers by variable temperature fourier transform infrared spectroscopy
Ind. Eng. Chem. Res.
New synthetic glucoside
Justus Liebigs Ann. Chem.
The preparation of some higher alkylglucosides
J. Am. Chem. Soc.
New insights into the transitional behaviour of methyl-6-O-(n-dodecanoyl)-alpha-D-glucopyranoside using variable temperature FTIR spectroscopy and X-ray diffraction
Liq. Cryst.
Cited by (2)
Incommensurate lamellar phase from long chain Mannosides: Investigation by X-Ray scattering and replica exchange molecular dynamics (REMD)
2022, Journal of Molecular LiquidsCitation Excerpt :Each sugar head is covalently linked to a hydrophobic hydrocarbon chain. The combination of hydrogen-bonding and non-polar interactions yields both rich thermotropic (in bulk) and lyotropic (in the presence of solvents) liquid crystalline behaviour, including lamellar, hexagonal, or complex three-dimensional cubic phases [8–21]. Molecular dynamics (MD) simulations can unveil complex phenomena of lipids and glycolipids, such as, raft formation [22–24], self-assembly [25], and interactions with membrane components [26–28].
Surface Properties and Liquid Crystal Properties of Alkyltetra(oxyethyl) β-D-Glucopyranoside
2021, Journal of Agricultural and Food Chemistry