Search

Recent advances in experimental studies of nanoparticle-driven stabilization of chiral liquid-crystalline phases are highlighted. The stabilization is achieved via the nanoparticles’ assembly in the defect lattices of the soft liquid-crystalline hosts. This is of significant importance for understanding the interactions of nanoparticles with topological defects and for envisioned technological applications. We demonstrate that blue phases are stabilized and twist-grain boundary phases are induced by dispersing surface-functionalized CdSSe quantum dots, spherical Au nanoparticles, as well as MoS2 nanoplatelets and reduced-graphene oxide nanosheets in chiral liquid crystals. Phase diagrams are shown based on calorimetric and optical measurements. Our findings related to the role of the nanoparticle core composition, size, shape, and surface coating on the stabilization effect are presented, followed by an overview of and comparison with other related studies in the literature. Moreover, the key points of the underlying mechanisms are summarized and prospects in the field are briefly discussed. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.

We report on the effect of reduced-graphene oxide nanosheets decorated by CoPt nanoparticles on the blue phase range of a chiral liquid crystal. By means of high-resolution ac calorimetry and polarizing optical microscopy, it is demonstrated that a small concentration of these nanosheets induces the stabilization of a single blue phase structure in comparison to three blue phases existing in the pure compound. The results are compared with other liquid crystal-dispersed graphene studies, and, moreover, a short theoretical discussion of the stabilization effect is included. © 2020 Author(s).

Liquid crystals hosting nanoparticles comprise a fascinating research field, ranging from fundamental aspects of phase transitions to applications in optics and photonics. Liquid-crystalline phases exhibit topological defects that can be used for assembly of nanoparticles in periodical arrays, and at the same time, the nanoparticles can increase the stability range of liquid-crystalline phases. This has been experimentally demonstrated over the past few years in the case of blue phases that are present in some strongly chiral liquid crystals. Experimental results in quantum dot-driven blue phase stabilization are presented here by means of high-resolution calorimetry and polarizing optical microscopy. It is demonstrated that quantum dots essentially stabilize the macroscopically amorphous blue phase III. There are discussed similarities and differences between the effects of spherical and anisotropic nanoparticles on blue phase stabilization; moreover, future prospects and trends in the field are addressed. © Copyright © 2020 Cordoyiannis, Lavrič, Trček, Tzitzios, Lelidis, Nounesis, Daniel and Kutnjak.

We report on high-resolution calorimetry and small-angle X-ray scattering measurements along the Smectic-A to chiral Smectic-C* phase transition of the liquid crystal 4-(2-methyl butyl) phenyl 4-n-octylbiphenyl-4-carboxylate with dispersed, CoPt nanoparticle-coated reduced-graphene oxide nanosheets. The temperature dependence of heat capacity and smectic layer spacing are obtained in the vicinity of Smectic-A to chiral Smectic-C* phase transition. Though no remarkable pretransitional effects are present, the critical fits show a crossover from mean-field near a tricritical point to classical mean-field compared to pure liquid crystal. The X-ray data yield a dilation of smectic layer thickness, indicating the assembly of graphene oxide nanosheets between the smectic layers. © 2019, © 2019 Informa UK Limited, trading as Taylor & Francis Group.

A novel sulfur-based platelet derivative was synthesized by reacting elemental sulfur with oleyl amine. The sulfur-oleyl amine (S-OA) derivative has an ionic salt form, layered morphology and forms a highly lamellar structure. Polarized optical microscopy (POM) clearly shows the birefringent lyotropic liquid crystalline behavior of the S-OA platelets dispersions. © The Royal Society of Chemistry.

We report on the stabilisation of the liquid-crystalline, twist-grain boundary A (TGBA) phase in mixtures of a chiral liquid crystal and surface-functionalised spherical Au nanoparticles (NPs) of 10 nm diameter. The results, obtained by calorimetric, optical, small-angle X-ray and plasmon resonance measurements, demonstrate that a TGBA phase, which is metastable for the pure liquid crystal host, can be effectively stabilised for a 3 K range in the presence of NPs. Moreover, the role of NPs size on the TGBA stabilisation is briefly discussed. © 2017 Informa UK Limited, trading as Taylor & Francis Group.

We report on wide-angle X-ray scattering measurements along the smectic-A to chiral ferroelectric smectic-C* phase transition of the liquid crystal SCE9 and its mixture with maghemite magnetic nanoparticles of typical dimension 20 nm. The temperature profiles of the tilt angle are fitted by an extended mean-field model. Neither pre-transitional order effects nor variations in the SmA layer thickness are observed, indicating a rather negligible influence of these nanoparticles upon the molecular orientation at the smectic-A to smectic-C* phase transition of SCE9. These results are very different from what was observed for smaller CdSe nanoparticles (3.5 nm) where both a dilation of the smectic layers in the SmA phase and a crossover behaviour for the smectic-A to smectic-C* transition away from tricriticality have been observed for analogous concentrations. © 2015 Taylor & Francis.

The histone-like DNA-binding proteins (HU) serve as model molecules for protein thermostability studies, as they function in different bacteria that grow in a wide range of temperatures and show sequence diversity under a common fold. In this work, we report the cloning of the hutth gene from Thermus thermophilus, the purification and crystallization of the recombinant HUTth protein, as well as its X-ray structure determination at 1.7 Å. Detailed structural and thermodynamic analyses were performed towards the understanding of the thermostability mechanism. The interaction of HUTth protein with plasmid DNA in solution has been determined for the first time with MST. Sequence conservation of an exclusively thermophilic order like Thermales, when compared to a predominantly mesophilic order (Deinococcales), should be subject, to some extent, to thermostability-related evolutionary pressure. This hypothesis was used to guide our bioinformatics and evolutionary studies. We discuss the impact of thermostability adaptation on the structure of HU proteins, based on the detailed evolutionary analysis of the Deinococcus–Thermus phylum, where HUTth belongs. Furthermore, we propose a novel method of engineering thermostable proteins, by combining consensus-based design with ancestral sequence reconstruction. Finally, through the structure of HUTth, we are able to examine the validity of these predictions. Our approach represents a significant advancement, as it explores for the first time the potential of ancestral sequence reconstruction in the divergence between a thermophilic and a mainly mesophilic taxon, combined with consensus-based engineering. © 2016, Springer Japan.

We report on the appearance and stabilisation of twist-grain-boundary-A A* (TGB A*) phase in confined geometry samples of the liquid-crystalline compound CE8, by means of polarised optical microscopy. The chiral liquid crystal (LC) compound was chosen such as to undergo a cholesteric–smectic-A* transition with temperature (type-I smectic), and to be close to the triple point between the cholesteric, TGB A* , and smectic-A A* phases. We used several types of anchoring conditions and various effective anchoring strengths. The results reveal that (i) the TGB A* phase exists as a metastable phase with strong fluctuations in the bulk, and (ii) it can be stabilised by the sample boundaries for adequate anchoring conditions. This means that we probably observed a type-I to type-II smectic transition induced by the substrate. Some dependence of the stabilisation on the surface-anchoring conditions and on the cell thickness is reported. © 2016 Informa UK Limited, trading as Taylor & Francis Group.

Chitinase 60 from the psychrophilic bacterium Moritella marina (MmChi60) is a four-domain protein whose structure revealed flexible hinge regions between the domains, yielding conformations in solution that range from fully extended to compact. The catalytic domain is a shallow-grooved TIM-barrel. Heat-induced denaturation experiments of the wild-type and mutants resulting from the deletions of the two-Ig-like domains and the chitin binding domain reveal calorimetric profiles that are consistent with non-collaborative thermal unfolding of the individual domains, a property that must be associated to the "hinge-regions". The calorimetric measurements of the (β/α)8 catalytic domain reveal that the thermal unfolding is a slow-relaxation transition exhibiting a stable, partially structured intermediate state. Circular dichroism provides evidence that the intermediate exhibits features of a molten globule i.e., loss of tertiary structure while maintaining the secondary structural elements of the native. GdnHCl-induced denaturation studies of the TIM-barrel demonstrate an extraordinarily high resistance to the denaturant. Slow-relaxation kinetics characterize the unfolding with equilibration times exceeding six days, a property that is for the first time observed for a psychrophilic TIM barrel. On the other hand, the thermodynamic stability is δG=6.75±1.3kcal/mol, considerably lower than for structural-insertions-containing barrels. The mutant E153Q used for the crystallographic studies of MmChi60 complexes with NAG ligands has a much lower stability than the wild-type. © 2015.

We report on the widening of blue phase range induced by surface-functionalised laponite nanoplatelets dispersed in a chiral liquid crystal. The results are obtained by means of high-resolution ac calorimetry and optical microscopy and they are reproducible upon heating and cooling, identifying thermodynamically stable blue phases. It is shown that nanoplatelets target mostly the cubic structure of blue phase I and increase its temperature stability range by a factor of two. The present results are in agreement with recent findings that anisotropic nanoparticles tend to effectively stabilise blue phase I. © 2015 Copyright © Taylor & Francis Group, LLC.

By means of high-resolution ac calorimetry and polarizing optical microscopy, it is demonstrated that surface-functionalized spherical CdSSe nanoparticles induce a twist-grain boundary phase when dispersed in a chiral liquid crystal. These nanoparticles can effectively stabilize the one-dimensional lattice of screw dislocations, thus establishing the twist-grain boundary order between the cholesteric and the smectic-A phases. A Landau-de Gennes-Ginzburg model is used to analyze the impact of nanoparticles on widening the temperature range of molecular organizations possessing a lattice of screw dislocations. We show that in addition to the defect-core-replacement mechanism, the saddle-splay elasticity may also play a significant role. © 2014 American Physical Society.

It is demonstrated that interactions between nanoparticles and topological defects induce a twist-grain boundary phase in a chiral liquid crystal. The occurrence of this phase, the analogue of the Shubnikov phase in type-II superconductors, is driven by direct interactions between surface-functionalized CdSe quantum dots and screw dislocations. It is shown that, within an adaptive-defect-core-targeting mechanism, nanoparticles of appropriate size and functionalization adapt to qualitatively different cores of topological defects such as disclination lines and screw dislocations. This mechanism enables the effective reduction of the energetically costly, singular defect core volume, while the surrounding phase ordering remains relatively weakly affected. The findings suggest new pathways towards the controlled assembly of superstructures in diverse, symmetry-broken, condensed-matter systems, ranging from nanoparticle-decorated liquid crystals to superconductors. © The Royal Society of Chemistry 2013.

The stabilization of liquid-crystalline blue phases is recently attracting considerable interest because of the envisioned applications in fast optical displays and tunable photonic crystals. We report on the effect of surface-functionalized graphene nanosheets on the blue phase range of a chiral liquid crystal. Calorimetric and optical measurements, reproducible on heating and cooling, demonstrate that the resulting soft nanocomposite exhibits an increased blue phase temperature stability range for a minute concentration of dispersed graphene. The impact is stronger on the ordered, cubic structured blue phase I. These findings suggest that anisotropic nanoparticles may be of great usefulness for stabilizing blue phases. © 2013 AIP Publishing LLC.

Spherical CdSe nanoparticles, surface-treated with oleylamine and tri-octylphosphine, dispersed in ferroelectric liquid crystals, can efficiently target disclination lines, substantially altering the macroscopic properties of the host compound. Here we present an ac calorimetry and x-ray diffraction study demonstrating that for a large range of nanoparticle concentrations the smectic-A layer thickness increases monotonically. This provides evidence for enhanced accumulation of nanoparticles at the smectic layers. Our results for the Smectic-A (SmA) to chiral smectic-C (SmC*) phase transition of the liquid crystal S-(+)4-(2′-methylbutyl)phenyl-4 ′-n-octylbiphenyl-4-carboxylate (CE8) reveal that the character of the transition is profoundly changed as a function of the nanoparticle concentration. Large transition temperature shifts are recorded. Moreover, the heat-capacity peaks exhibit a crossover trend to a step-like anomaly. This behavior may be linked to the weakening of the SmA and SmC* order parameter coupling responsible for the observed near-tricritical, mean-field character of the transition in bulk CE8. At lower temperatures, the presence of nanoparticles disrupts the phase sequence involving the tilted hexatic phases most likely by obstructing the establishment of long-range bond-orientational order. © 2013 American Physical Society.

The breast cancer tumor suppressor protein BRCA1 is involved in DNA repair and cell cycle control. Mutations at the two C-terminal tandem (BRCT) repeats of BRCA1 detected in breast tumor patients were identified either to lower the stability of the BRCT domain and/or to disrupt the interaction of BRCT with phoshpopeptides. The aim of this study was to analyze five BRCT pathogenic mutations for their effect on structural integrity and protein stability. For this purpose, the five cancer-associated BRCT mutants: V1696L, M1775K, M1783T, V1809F, and P1812A were cloned in suitable prokaryotic protein production vectors, and the recombinant proteins were purified in soluble and stable form for further biophysical studies. The biophysical analysis of the secondary structure and the thermodynamic stability of the wild-type, wt, and the five mutants of the BRCT domain were performed by Circular Dichroism Spectroscopy (CD) and Differential Scanning Microcalorimetry (DSC), respectively. The binding capacity of the wt and mutant BRCT with (pBACH1/BRIP1) and pCtIP were measured by Isothermal Titration Calorimetry (ITC). The experimental results demonstrated that the five mutations of the BRCT domain: (i) affected the thermal unfolding temperature as well as the unfolding enthalpy of the domain, to a varying degree depending upon the induced destabilization and (ii) altered and/or abolished their affinity to synthetic pBACH1/BRIP1 and pCtIP phosphopeptides by affecting the structural integrity of the BRCT active sites. The presented experimental results are one step towards the elucidation of the effect of various missense mutations on the structure and function of BRCA1-BRCT. © 2009 Wiley-Liss, Inc.

127 Greek breast/ovarian cancer families were screened for germline BRCA1/2 mutations by dHPLC followed by direct sequencing. Our results indicated 16 and 5 breast/ovarian cancer families bearing deleterious mutations in the BRCA1 and BRCA2 genes, respectively. Two novel BRCA2 germline mutations (G4X and 3783del10) are reported here for the first time. Subsequent compilation of our present findings with previously reported mutation data reveals that in a total of 287 Greek breast/ovarian cancer families, 46 and 13 carry a deleterious mutation in BRCA1 and BRCA2, respectively. It should be noted that two BRCA1 mutations, 5382insC and G1738R, both located in exon 20, account for 46% of the families found to carry a mutation. Based on our mutation analysis results, we propose here a hierarchical, cost-effective BRCA1/2 mutation screening protocol for individuals of Greek ethnic origin. The suggested protocol can impact on the clinical management of breast-ovarian cancer families on a national healthcare system level. © 2007 Springer Science+Business Media, LLC.

Missense mutations at the BRCT domain of human BRCA1 protein have been associated with an elevated risk for hereditary breast/ovarian cancer. They have been shown to affect the binding site and they have also been proposed to affect domain stability, severely hampering the protein's tumor suppressor function. In order to assess the impact of various such mutations upon the stability and the function of the BRCT domain, heat-induced denaturation has been employed to study the thermal unfolding of variants M1775R and R1699W, which have been linked with the disease, as well as of V1833M, which has been reported for patients with a family history. Calorimetric and circular dichroism results reveal that in pH 9.0, 5 mM borate buffer, 200 mM NaCl, analogously to wild type BRCT, all three variants undergo partial thermal unfolding to a denatured state, which retains most of the native's structural characteristics. With respect to wild-type BRCT, the mutation M1775R induces the most severe effects especially upon the thermostability, while R1699W also has a strong impact. On the other hand, the thermal unfolding of variant V1833M is only moderately affected relative to wild-type BRCT. Moreover, isothermal titration calorimetric measurements reveal that contrary to M1775R and R1699W variants, V1833M binds to BACH1 and CtIP phosphopeptides. © 2007 Elsevier B.V. All rights reserved.

High-precision differential scanning calorimetry (DSC) and circular dichroism (CD) have been employed to study the thermal unfolding of chitinase 40 (Chi40) from Streptomyces thermoviolaceus. Chi40 belongs to family 18 of glycosyl hydrolase superfamily bearing a catalytic domain with a "TIM barrel"-like fold, which exhibits deviations from the (β/α) 8 fold. The thermal unfolding is reversible at pH = 8.0 and 9.0. The denatured state is characterized by extensive structural changes with respect to the native. The process is characterized by slow relaxation kinetics. Even slower refolding rates are recorded upon cooling. It is shown that the denaturation calorimetric data obtained at slow heating rate (0.17 K/min) are in excellent agreement with equilibrium data obtained by extrapolation of the experimental results to zero scanning rate. Analysis of the DSC results reveals that the experimental data can be successfully fitted using either a nontwo-state sequential model involving one equilibrium intermediate, or an independent transitions model involving the unfolding of two Chi40 energetic domains to intermediate states. The stability of the native state with respect to the final denatured state is estimated, ΔG = 24.0 kcal/mol at 25°C. The thermal results are in agreement with previous findings from chemical denaturation studies of a wide variety of (β/α)8 barrel proteins, that their unfolding is a nontwo-state process, always involving at least one unfolding intermediate. © 2006 Wiley-Liss, Inc.

Reduced stability of the tandem BRCT domains of human BReast CAncer 1 (BRCA1) due to missense mutations may be critical for loss of function in DNA repair and damage-induced checkpoint control. In the present thermal denaturation study of the BRCA1 BRCT region, high-precision differential scanning calorimetry (DSC) and circular dichroism (CD) spectroscopy provide evidence for the existence of a denatured state that is structurally very similar to the native. Consistency between theoretical structure-based estimates of the enthalpy (ΔH) and heat capacity change (ΔCp) and the calorimetric results is obtained when considering partial thermal unfolding contained in the region of the conserved hydrophobic pocket formed at the interface of the two BRCT repeats. The structural integrity of this region has been shown to be crucial for the interaction of BRCA1 with phosphorylated peptides. In addition, cancer-causing missense mutations located at the inter-BRCT-repeat interface have been linked to the destabilization of the tandem BRCT structure. © 2004 Elsevier B.V. All rights reserved.

lt has been shown that the partitioning of vinblastine in 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) single and multiple bilayer dispersions induces partial interdigitation of the lipid alkyl chains. Similar behavior has been observed for abietic and ursodeoxycholic acids and may well be generalized for the partitioning of bulky amphoteric molecules, which tend to localize in the vicinity of the polar heads. For the present study, differential scanning calorimetry (DSC) has been employed to investigate the role of lipid molecular characteristics such as the alkyl chain length and the polarity of the head-group, as well as the impact of cholesterol upon vinblastine-induced interdigitation. It is found that vinblastine does not induce interdigitation in lipids with either shorter or longer alkyl chains than DPPC, or having head-groups of different polarity. In addition, it is shown that the presence of cholesterol in the lipid bilayer tends to modulate the phase behavior of the lipid/vinblastine bilayer system. Preliminary studies show that such properties directly affect the encapsulation efficiency and the pharmacokinetics of liposomes. (C) 2003 Elsevier B.V. All rights reserved.

Differential scanning calorimetry has been employed to study the thermal effects of vinblastine sulfate upon aqueous, single and multiple bilayer dispersions of 1,2-dipaimitoyl-3-sn-phosphatidylcholine (DPPC). The calorimetric results summarized to an increase in the gel to liquid-crystalline phase transition enthalpy and the abolishment of the L’(beta) (gel phase) to P’(beta) (ripple phase) pretransition for the uni- and multilamellar dispersions, as well as an increase in the transition temperature T-m and the transition cooperativity for single bilayer DPPC/vinblastine mixed vesicles, are consistent with an induced, partially interdigitated, gel phase. Computational analysis has been successfully applied to clarify the intermolecular effects and verify the feasibility of the proposed interdigitation for the vinblastine sulfate molecules and also for the ursodeoxycholic acid (UDCAH) and bromocylated taxanes, which have been shown to induce an interdigitated gel phase in DPPC bilayers. (C) 2002 Elsevier Science B.V. All rights reserved.

A series of oxorhenium(V) SNS/S mixed ligand complexes [ReO(Ln/L)] carrying different types of tridentate ligand [L1: C2H5N(CH2CH2S)2, L2: (C2H5)2NCH2CH2N(CH2CH2S)2, L3: C2H5SCH2CH2N(CH2CH2S)2 and L4: 2,6-(SCH2)2NC5H3] and the same monodentate coligand (L: C6H5S) have been synthesized and characterized by spectroscopic methods and elemental analyses. X-ray structure determination was performed for complexes 3 and 4. Complex 3 adopts the expected distorted trigonal bipyramidal geometry around the metal in a syn configuration, while complex 4, due to the aromatic character of the nitrogen of the SNS donor-atom set, exhibits a distorted square pyramidal geometry. The interaction of complexes 1 - 4 with glutathione (GSH) was studied by high performance liquid chromatography (HPLC), revealing the rapid formation of the respective daughter complexes 5 - 8, wherein the L coligand has been substituted by GS. The daughter complexes 5 - 8 have been characterized by ES-MS and a battery of NMR measurements involving HETCOR, COSY and NOESY procedures. Kinetic aspects of the interaction of complexes 1 ¾ 3 with GSH have been studied by isothermal titration microcalorimetry providing direct measurements of the interaction rate constants as well as the total enthalpy change. The reaction of complex 1 is characterized by the slowest and that of complex 2 by the fastest rate. This is in agreement with previously reported trends for analogous 99mTc complexes.