Yaroslav Khimyak | University of East Anglia (original) (raw)

Papers by Yaroslav Khimyak

European Polymer Journal, 2018

Hybrid polymer coated silica nanoparticles (NPs) were synthesized using low temperature graft (co... more Hybrid polymer coated silica nanoparticles (NPs) were synthesized using low temperature graft (co)polymerization of trimethoxysilane propyl methacrylate (MPTS) initiated by surface-active oligoperoxide metal complex (OMC) in aqueous media. These NPs were characterized by means of kinetic, solid-state NMR, TEM and FTIR techniques. Two processes, namely the radical graftcopolymerization due to presence of double bonds and 3D polycondensation provided by the intra-or/and intermolecular interaction of organosilicic fragments, occurred simultaneously. The relative contribution of the reactions depending on initiator concentration and pH value leading to the formation of low cured polydisperse microparticles or OMC coated SiO 2 NPs of controlled curing degree was studied. The availability of free-radical forming peroxide fragments on the surface of SiO 2 NPs provides an opportunity for seeded polymerization leading to the formation of the functional polymer coated NPs with controlled particle structure, size, and functionality. Encapsulation of the luminescent dye (Rhodamine 6G) in SiO 2 core of functionalized NPs provided a noticeable increase in their resistance to photobleaching and improved biocompatibility. These luminescent NPs were not only attached to murine leukemia L1210 cells but also tolerated by the mammalian cells. Their potential use for labeling of the mammalian cells is considered.

Journal of the American Chemical Society, Oct 31, 2006

Co-intercalation of methylamine molecules into the cubic K3C60 lattice affords the fulleride (CH3... more Co-intercalation of methylamine molecules into the cubic K3C60 lattice affords the fulleride (CH3NH2)K3C60, which was characterized by Raman and MAS 13C and 1H NMR spectroscopy. The high-resolution synchrotron X-ray powder diffraction technique was employed to determine its crystal structure at ambient temperature. We find that CH3NH2 bonds to K+ ions residing in the pseudo-octahedral interstices, thereby providing an efficient and facile route to hyperexpanded close-packed strongly anisotropic fulleride lattices, while retaining the electronic contact between the C603- anions. Preliminary evidence for the occurrence of a transition to an antiferromagnetic state at low temperature is also presented, consistent with the proximity of the present system to the metal-insulator boundary of the electronic phase diagram of C603- fullerides.

Angewandte Chemie, Nov 19, 2007

Chemistry – A European Journal, 2020

Understanding the fine details of the self‐assembly of building blocks into complex hierarchical ... more Understanding the fine details of the self‐assembly of building blocks into complex hierarchical structures represents a major challenge en route to the design and preparation of soft‐matter materials with specific properties. Enzymatically synthesised cellodextrins are known to have limited water solubility beyond DP9, a point at which they self‐assemble into particles resembling the antiparallel cellulose II crystalline packing. We have prepared and characterised a series of site‐selectively fluorinated cellodextrins with different degrees of fluorination and substitution patterns by chemoenzymatic synthesis. Bearing in mind the potential disruption of the hydrogen‐bond network of cellulose II, we have prepared and characterised a multiply 6‐fluorinated cellodextrin. In addition, a series of single site‐selectively fluorinated cellodextrins was synthesised to assess the structural impact upon the addition of one fluorine atom per chain. The structural characterisation of these mat...

Saturation transfer difference (STD) NMR spectroscopy is a well‑known ligand‑based solution NMR t... more Saturation transfer difference (STD) NMR spectroscopy is a well‑known ligand‑based solution NMR technique used extensively for ligand epitope mapping, the identification of the nature of ligand binding sites, and the determination of ligand binding affinity. Recently, we have shown that STD NMR can be also applied to monitor changes in bound water during gelation of particulate dispersions. However, this technique is strongly dependent on gelator and solvent concentrations and does not report on the degree of organisation of the solvent within the particle network. This obscures the detailed understanding of the role of the solvent on gelation and precludes the comparison of solvation properties between dispersions prepared under different experimental conditions. In this work we report a novel STD NMR method to characterise the degree of solvent structuration in carbohydrate-based particulate dispersions by demonstrating for the first time that, for solvents interacting with large ...

Proceedings of the Shevchenko Scientific Society. Series Сhemical Sciences, 2018

A series of multi-component aluminium containing-CH 2 CH 2-/-CH=CH-periodic mesoporous organosili... more A series of multi-component aluminium containing-CH 2 CH 2-/-CH=CH-periodic mesoporous organosilica (PMO) has been prepared via cationic templating. The influence of pre-hydrolysis on the distribution of the organic and inorganic moieties has been investigated using a variety of complementary solid-state NMR techniques.

Biomacromolecules, 2020

Surface hydrophobization of cellulose nanomaterials has been used in the development of nanofille... more Surface hydrophobization of cellulose nanomaterials has been used in the development of nanofiller-reinforced polymer composites and formulations based on Pickering emulsions. Despite well-known effect of hydrophobic domains on self-assembly or association of water-soluble polymer amphiphiles, very few studies have addressed the behavior of hydrophobized cellulose nanomaterials in aqueous media. In this study, we investigate the properties of hydrophobized cellulose nanocrystals (CNCs) and their self-assembly and amphiphilic properties in suspensions and gels. CNCs of different hydrophobicity were synthesized from sulfated CNCs by coupling primary alkylamines of different alkyl chain lengths (6, 8 and 12 carbon atoms). The synthetic route permitted the retention of surface charge, ensuring good colloidal stability of hydrohobized CNCs in aqueous suspensions. We compare surface properties (surface charge, Zeta-potential), hydrophobicity (water contact angle, microenvironment probing using pyrene fluorescence emission) and surface activity (tensiometry) of different hydrophobized CNCs and hydrophilic CNCs. Association of hydrophobized CNCs driven by hydrophobic effects is confirmed by X-ray scattering (SAXS) and autofluorescent spectroscopy experiments. As a result of CNC association, CNCs suspensions/gels can be produced with a wide range of rheological properties depending on the hydrophobic/hydrophilic balance. In particular, sol-gel transitions for hydrophobized CNCs occur at lower concentrations then hydrophilic CNCs and more robust gels are formed by hydrophobized CNCs. Our work illustrates that amphiphilic CNCs can complement associative polymers as modifiers of rheological properties of water-based systems.

Understanding the fine details of self-assembly of building blocks into complex hierarchical stru... more Understanding the fine details of self-assembly of building blocks into complex hierarchical structures represents a major challenge en route to the design and preparation of soft matter materials with specific properties. Enzymatically-synthesised cellodextrins are known to have limited water solubility beyond DP9, a point at which they self-assemble into particles resembling the anti-parallel cellulose II crystalline packing. We have prepared and characterized a series of site-selectively fluorinated cellodextrins of different degrees of fluorination and substitution patterns by chemoenzymatic synthesis. The structural characterization of these materials at different length scales, combining advanced NMR and microscopy methods, showed that multiply 6-fluorinated cellodextrin chains assembled into particles presenting morphological and crystallinity features that are unprecedented for cellulose-like materials. In contrast, the introduction of a single fluorine atom per cellodextrin...

Biomacromolecules, 2019

Bacterial cellulose (BC) consists of a complex threedimensional organization of ultrafine fibers ... more Bacterial cellulose (BC) consists of a complex threedimensional organization of ultrafine fibers which provide unique material properties such as softness, biocompatibility, and water-retention ability, of key importance for biomedical applications. However, there is a poor understanding of the molecular features modulating the macroscopic properties of BC gels. We have examined chemically pure BC hydrogels and composites with arabinoxylan (BC−AX), xyloglucan (BC−XG), and high molecular weight mixed-linkage glucan (BC−MLG). Atomic force microscopy showed that MLG greatly reduced the mechanical stiffness of BC gels, while XG and AX did not exert a significant effect. A combination of advanced solid-state NMR methods allowed us to characterize the structure of BC ribbons at ultra-high resolution and to monitor local mobility and water interactions. This has enabled us to unravel the effect of AX, XG, and MLG on the short-range order, mobility, and hydration of BC fibers. Results show that BC−XG hydrogels present BC fibrils of increased surface area, which allows BC−XG gels to hold higher amounts of bound water. We report for the first time that the presence of high molecular weight MLG reduces the density of clusters of BC fibrils and dramatically increases water interactions with BC. Our data supports two key molecular features determining the reduced stiffness of BC−MLG hydrogels, that is, (i) the adsorption of MLG on the surface of BC fibrils precluding the formation of a dense network and (ii) the preorganization of bound water by MLG. Hence, we have produced and fully characterized BC−MLG hydrogels with novel properties which could be potentially employed as renewable materials for applications requiring high water retention capacity (e.g. personal hygiene products).

Cellulose, 2019

Utilization of reversible non-covalent interactions is a versatile design strategy for the develo... more Utilization of reversible non-covalent interactions is a versatile design strategy for the development of stimuli responsive soft materials. In this study, hydrophobic interactions were harnessed to assemble water-soluble macromolecules and nanoparticles into a transient hybrid network forming thermosensitive hydrogels with tunable rheological properties. Hybrid hydrogels were built of biopolymer derived components: cellulose nanocrystals (CNCs), nanoparticles of high aspect ratio, and hydroxypropyl methylcellulose (HPMC). To enable polymer/CNC assembly via hydrophobic interactions, the surface of highly hydrophilic CNCs was modified by binding octyl moieties (octyl-CNCs). The amphiphilicity of Electronic supplementary material The online version of this article (

ACS Applied Materials & Interfaces, 2018

Cellulose nanocrystals (CNCs) that bind to each other through associative hydrophobic interaction... more Cellulose nanocrystals (CNCs) that bind to each other through associative hydrophobic interactions have been synthesized by modifying sulfated CNCs (sCNCs) with hydrophobic moieties. These octyl-CNCs form gels at significantly lower concentrations than parent sCNCs, producing extremely strong hydrogels. Unlike sCNCs, these octyl-CNCs do not form ordered liquid crystalline phases indicating a random association into a robust network driven by hydrophobic interactions. Furthermore, involvement of the octyl-CNCs into multicomponent supramolecular assembly was demonstrated in combination with starch. AFM studies confirm favorable interactions between starch and octyl-CNCs, which is thought to be the source of the dramatic increase in gel strength.

Journal of colloid and interface science, Jan 25, 2018

A novel mechanism of heat-triggered gelation for oxidised cellulose nanofibrils (OCNF) is reporte... more A novel mechanism of heat-triggered gelation for oxidised cellulose nanofibrils (OCNF) is reported. We demonstrate that a synergistic approach combining rheology, small-angle X-ray scattering (SAXS) and saturation transfer difference NMR (STD NMR) experiments enables a detailed characterisation of gelation at different length scales. OCNF dispersions experience an increase in solid-like behaviour upon heating as evidenced by rheological studies, associated with enhanced interfibrillar interactions measured using SAXS. Interactions result in an increased fibrillar overlap and increased population of confined water molecules monitored by STD NMR. In comparison, cationic cellulose nanofibrils (produced by reaction of cellulose with trimethylglycidylammonium chloride) were found to be heat-unresponsive.

Soft matter, Jan 15, 2018

Zwitterionic cellulose nanofibrils (ZCNFs) with an isoelectric point of 3.4 were obtained by graf... more Zwitterionic cellulose nanofibrils (ZCNFs) with an isoelectric point of 3.4 were obtained by grafting glycidyltrimethylammonium chloride onto TEMPO/NaBr/NaOCl-oxidised cellulose nanofibrils. The ZCNF aqueous dispersions were characterized via transmission electron microscopy, rheology and small angle neutron scattering, revealing a fibril-bundle structure with pronounced aggregation at pH 7. Surfactants were successfully employed to tune the stability of the ZCNF dispersions. Upon addition of the anionic surfactant, sodium dodecyl sulfate, the ZCNF dispersion shows individualized fibrils due to electrostatic stabilization. In contrast, upon addition of the cationic species dodecyltrimethylammonium bromide, the dispersion undergoes charge neutralization, leading to more pronounced flocculation.

Crystal Growth & Design, 2017

Phenylalanine (Phe) is an amino acid of great interest as coupling of an aromatic group with a ch... more Phenylalanine (Phe) is an amino acid of great interest as coupling of an aromatic group with a chiral hydrophilic region imparts a number of unique properties. Recently there has been an increased interest in the crystalline and gel forms of this compound, part as a result of the 2 complex and undetermined structures of the resulting materials and the relationship of the solid forms of Phe with the disease phenylketonuria. In this report, we highlight the relationship between gelation, crystallisation and the dynamics of self-assembly processes of Phe. We do this by describing the gelation of the amino acid, the gel to crystal relationship, crystal structure predictions for this relatively simple compound and the dynamics of assembly as determined by NMR in both water and dimethyl sulfoxide. This will provide guidance to future research into Phe assemblies, possible treatments for phenylketonuria and diseases related to formation of amyloidlike fibres.

Langmuir : the ACS journal of surfaces and colloids, Jan 13, 2016

This study aims at investigating the molecular level organization and molecular mobility in montm... more This study aims at investigating the molecular level organization and molecular mobility in montmorillonite nanocomposites with the uncharged organic low-molecular-weight compound lactose commonly used in pharmaceutical drug delivery, food technology, and flavoring. Nanocomposites were prepared under slow and fast drying conditions, attained by drying at ambient conditions and by spray-drying, respectively. A detailed structural investigation was performed with modulated differential scanning calorimetry, powder X-ray diffraction, solid-state nuclear magnetic resonance spectroscopy, scanning electron microscopy, microcalorimetry, and molecular dynamics simulations. The lactose was intercalated in the sodium montmorillonite interlayer space regardless of the clay content, drying rate, or humidity exposure. Although, the spray-drying resulted in higher proportion of intercalated lactose compared with the drying under ambient conditions, nonintercalated lactose was present at 20 wt % l...

Faraday discussions, Jan 24, 2017

Phenylalanine is an important amino acid both biologically, essential to human health, and indust... more Phenylalanine is an important amino acid both biologically, essential to human health, and industrially, as a building block of artificial sweeteners. Our interest in this particular amino acid and its derivatives lies with its ability to form gels in a number of solvents. We present here the studies of the influence of halogen addition to the aromatic ring on the gelation properties and we analyse the crystal structures of a number of these materials to elucidate the trends in their behaviour based on the halogen addition to the aromatic group and the interactions that result.

Soft matter, May 29, 2016

Eighteen N-aryl-N'-alkyl urea gelators were synthesised in order to understand the effect of ... more Eighteen N-aryl-N'-alkyl urea gelators were synthesised in order to understand the effect of head substituents on gelation performance. Minimum gelation concentration values obtained from gel formation studies were used to rank the compounds and revealed the remarkable performance of 4-methoxyphenyl urea gelator in comparison to 4-nitrophenyl analogue , which could not be simply ascribed to substituent effects on the hydrogen bonding capabilities of the urea protons. Crystal structure prediction calculations indicated alternative low energy hydrogen bonding arrangements between the nitro group and urea protons in gelator , which were supported experimentally by NMR spectroscopy. As a consequence, it was possible to relate the observed differences to interference of the head substituents with the urea tape motif, disrupting the order of supramolecular packing. The combination of unbiased structure prediction calculations with NMR is proposed as a powerful approach to investigate ...

CrystEngComm, 2016

It has previously been reported that the caffeine : malonic acid co-crystal system forms spontane... more It has previously been reported that the caffeine : malonic acid co-crystal system forms spontaneously upon the contact of the two materials, here we explore the mechanism of this formation and control the kinetics to enable us to monitor the conversion.