Colorimetric transition of polydiacetylene/cyclodextrin supramolecular assemblies and implications as colorimetric sensors for food phenolic antioxidants

Molecular self-assembly has significant potential in the field of sensing. Polydiacetylenes (PDAs) are conjugated polymers possessing peculiar optical properties obtained by photopolymerization of self-assembled diacetylene monomers. Herein, the blue-to-red phase transition upon either thermal stimulus or interaction with cyclodextrins (CDs) of two PDAs, bearing either carboxylic (PCDA) or amino (PCDA-NH2) polar heads, is investigated to develop a colorimetric sensor for food phenolic antioxidants. The change in the PDA polar head does not affect significantly thermo-chromatic transition. Upon thermal stimulus, in both PDAs, color transition occurs straightforward between two distinct stable states and does not involve the disordering of the PDA crystal phase, as revealed by UV-vis spectroscopy and SAXS analysis. Contrarily, PDA/alpha-CD interaction is influenced by intermolecular forces among PDA polar heads and is more efficient for PCDA. alpha-CDs presumably cause changes in both PDA backbone conformation and local environment surrounding the individual PDA chains. The PCDA/alpha-CD assemblies are investigated as colorimetric sensors for the detection of Tyrosol (Ty) and caffeic acid (CAF), by using the principle of competitive inclusion complex formation. The system results to be more sensitive to CAF than Ty and may permit the determination of CAF in concentration ranges suitable for different food products

Thymol-functionalized hyaluronic acid as promising preservative biomaterial for the Inhibition of Candida albicans biofilm formation

Hyaluronic acid (HA) is a naturally occurring biopolymer that has been employed for a plethora of medicinal applications. Nevertheless, as HA is a natural polysaccharide, it can be a substrate able to promote microbial growth and proliferation. Biopolymer–drug conjugates have gained attention over the years to overcome drawbacks of each single component. Within this context, thymol (Thy), a phenolic compound occurring in essential oils (EOs) extracted from Thymus and Origanum, has been largely studied for its antimycotic applications. However, it is characterized by a low water solubility and moderate cytotoxicity. Herein, we report an innovative HA–thymol conjugate (HA-Thy) biomaterial to circumvent the drawbacks of free thymol use by providing the polymer conjugate with the beneficial properties of both components. Preliminary biological tests evidenced the decrease of thymol cytotoxicity for the HA-Thy conjugate, paired with a promising antibiofilm formation activity against Candida albicans, similar to pure thymol, highlighting its potential application as a preservative biomaterial in formulations

Targeting the antifungal activity of carbon dots against Candida albicans biofilm formation by tailoring their surface functional groups

Carbon dots (CDs) are an emerging class of carbon nanoparticles, which for their characteristics have found applications in many fields such as catalysis, materials and biomedicine. Within this context, the application of CDs as antibacterial agents has received much attention in very recent years, while their use as antifungal nanoparticles has been scarcely investigated. Here we report a systematic investigation of the surface functional groups of CDs to study their influence on these nanoparticles' against Candida albicans. Three classes of CDs have been synthesised and fully characterized. A thorough in vitro and in vivo biological screening against C. albicans was performed to test their antifungal, antiadhesion and antibiofilm formation activities. Moreover, the interaction with C. albicans cells was investigated by microscopic analysis. Our results evidence how the presence of a positively polarised surface results crucial for the internalization into COS-7 cells. Positively charged nanoparticles were also able to inhibit adhesion and biofilm formation, to interact with the cellular membrane of C. albicans, and to increase the survival of G. mellonella infected larvae after the injection with positive nanoparticles. The antifungal activity of CDs and their extremely low toxicity may represent a new strategy to combat infections sustained by C.albicans

Functionalization of hyaluronic acid with a chondroprotective molecule and preparation of sulfonated HA-based materials

In the work of thesis, several aspects of hyaluronic acid chemical modification have been explored. In particular, the polysaccharide has been functionalized with NAPA, an amino acidic derivative of D-glucosamine and N-Acetyl-L-phenylalanine with chondroprotective properties, by means of esterification of the glucuronic unit. Preliminary biological studies on human primary chondrocytes (HPCs) has also been presented. The procedure discussed so far represents an innovative and fascinating method for the linkage of a glucosamine derivative to hyaluronic acid that could be useful also in the case of other GlcN-based products. The new HA bioconjugates could gain high relevance as injectable treatments against osteoarthritic disorders. An insight on racemization mechanism that occurs for N-acetylated amino acid was also conducted. In addition, hyaluronic acid was subjected to sulfonation in water. Two sulfonating agents, such as Tau and Bes, were reacted in order to synthetized soluble HA-SO3H derivatives and 3D hydrogels enriched in polar sulfonic groups. Sulfonated polymer demonstrated to have tunable properties depending upon reaction conditions and showed to be promising HA-based materials for biomedical applications

Carbon dots as bioactive antifungal nanomaterials

Nowadays, the widespread diffusion of infections caused by opportunistic fungi represents a demanding threat for global health security. This phenomenon has also worsened by the emergence of contagious events in hospitalisation environments and by the fact that many fungi have developed harsh and serious resistance mechanisms to the traditional antimycotic drugs. Hence, the design of novel antifungal agents is a key factor to counteract mycotic infections and resistance. Within this context, nanomaterials are gaining increasing attention thanks to their biocidal character. Among these, carbon dots (CDs) represent a class of zero-dimensional, photoluminescent and quasi-spherical nanoparticles which, for their great and tuneable features, have found applications in catalysis, sensing and biomedicine. Nevertheless, only a few works define and recapitulate their antifungal properties. Therefore, we aim to give an overview about the recent advances in the synthesis of CDs active against infective fungi. We described the general features of CDs and fungal cells, by highlighting some of the most common antimycotic mechanisms. Then, we evaluated the effects of CDs, antimicrobial drugs-loaded CDs and CDs-incorporated packaging systems on different fungi and analysed the use of CDs as fluorescent nano-trackers for bioimaging, showing, to all effects, their promising application as antifungal agents

Surface functionalized PLLA for scaffold preparation

Biocompatible and degradable poly(alpha-hydroxy acids) are among the more widely used materials in scaffolds for tissue engineering, although they often need surface modification to improve their interaction with the cells. In the present research Poly(L-lactide) 3D scaffold were prepared by salt-leaching method, with a porosity of 80 % and interconnected pores. In order to increase the hydrophilicity of the PLLA scaffolds surface, taurine was grafted through aminolysis reaction. The reaction enriched the surface with sulfonate groups increasing PLLA hydrophilicity and electrostatic interaction with collagen. In vitro biological tests with chondrocytes or fibroblasts showed that taurine grafting and collagen absorption improved cell viability and adhesion compared to the unmodified scaffold, suggesting that these modifications make PLLA substrate suitable for cartilage repair

Chiral Carbon Dots as nano-organocatalysts to promote Michael Reactions

Chiral Carbon Dots (CCDs) are carbon nanoparticles easily synthetized from small and readily available organic molecules, with an active surface which retains the molecular features of the starting materials, including chiral properites.1 Recent studies demonstrate the low toxicity of this promising and bio-compatible materials, underling widespread applications in chemistry.2 High solubility in water, in addition to others organic solvents, together with the possibility of an efficient functionalization of the active surface allow the use of CCD as nano-organocatalyst in several organic reactions.3 In fact, the presence of characteristic and tunable functional groups on the surface, paired with the chiral informations, could lead to a strong interaction with substrates, aiming to promote stereoselective transformations. Herein, an innovative synthetic approach to activate Michael donors is reported, exploring the potentiality of CCDs as green catalysts with two different types of activations. The reaction between 3-Methyl-1-phenyl-2-pyrazoline-5-one (1) and β-Nitrostyrene (3) was investigated relying on a non-covalent activation by L-phenylalanine-derived CCDs, while L-proline-functionalised CCDs were prepared to promote the Michael reaction between cyclohexanone (4) and 2. The desired products were isolated with high yields and moderate to good stereoselectivity under operationally simple and sustainable conditions, allowing for the efficient recovering and recycle of the nano-catalysts

Nano-organocatalytic Michael reactions promoted by Chiral Carbon Dots

Chiral Carbon Dots (CCDs) are carbon nanoparticles easily synthetized from small and readily available organic molecules, with an active surface which retains the molecular features of the starting materials, including chiral properites.1 Recent studies demonstrate the low toxicity of this promising and bio- compatible materials, underling widespread applications in chemistry.2 High solubility in water, in addition to others organic solvents, together with the possibility of an efficient functionalization of the active surface allow the use of CCD as nano-organocatalyst in several organic reactions.3 In fact, the presence of characteristic and tunable functional groups on the surface, paired with the chiral information, could lead to a strong interaction with substrates, aiming to promote stereoselective transformations. Herein, an innovative synthetic approach to activate Michael donors is reported, exploring the potentiality of CCDs as green catalysts with two different types of activations. The reaction between 3-Methyl-1- phenyl-2-pyrazoline-5-one (1) and β-Nitrostyrene (2) was investigated relying on a non-covalent activation by L-phenylalanine-derived CCDs, while L-proline-functionalised CCDs were prepared to promote the Michael reaction between cyclohexanone (4) and 2. The desired products were isolated with high yields and moderate to good stereoselectivity under operationally simple and sustainable conditions, allowing for the efficient recovering and recycle of the nano-catalysts

Isotactic polypropylene reversible crystallization investigated by modulated temperature and quasi‐isothermal FTIR

Modulated temperature techniques allow to separatethe reversing and non-reversing contributions of material transitions. To investigate reversible crystallization and melting of isotactic polypropylene (iPP) at microstructural level, in this research, modulated temperature Fourier transform infrared (MTFTIR) and quasi-isothermal FTIR (QIFTIR) analyses are used.By following the intensity variation of iPP regularity bands, associated with 31 helix structures of different lengths (n repeating units), MTFTIR evidences that, independently from helix length, a reversing coil–helix transition takes place few degrees below the non-reversing crystallization onset. By comparing spectroscopicand differential scanning calorimetry experiments performed inquasi-isothermal conditions, the reversing transition was found to be associated with the reversible melting-crystallization phenomenon. Moreover, QIFTIR evidences that helices of different lengths contribute differently to the reversible transition: the helices composed of n=10 and n= 12 are active into all the explored temperature range (30–130°C) whereas the shortest (n= 6) and the longest (n> 15) helices contribute to reversibility atT>100°C