Unraveling the nanostructure of supramolecular assemblies of hydrogen-bonded rosettes on graphite: an atomic force microscopy study

AFM evaluation of a humanized recombinant antibody affecting C. auris cell wall and stability

Fungal infections are increasingly impacting on the health of the population and particularly on subjects with a compromised immune system. The resistance phenomenon and the rise of new species carrying sometimes intrinsic and multi-drug resistance to the most commonly used antifungal drugs are greatly concerning healthcare organizations. As a result of this situation, there is growing interest in the development of therapeutic agents against pathogenic fungi. In particular, the Candida genus is responsible for severe life-threatening infections and among its species, C. auris is considered an urgent threat by the Center for Disease Control and Prevention, and is one of the three leading causes of morbidity and mortality worldwide. H5K1 is a humanized monoclonal antibody (hmAb) that selectively binds to β-1,3-glucans, vital components of the fungal cell wall. It has been previously demonstrated that it is active against Candida species, especially against C. auris, reaching its greatest potential when combined with commercially available antifungal drugs. Here we used atomic force microscopy (AFM) to assess the effects of H5K1, alone and in combination with fluconazole, caspofungin and amphotericin B, on C. auris cells. Through an extensive exploration we found that H5K1 has a significant role in the perturbation and remodeling of the fungal cell wall that is reflected in the loss of whole cell integrity. Moreover, it contributes substantially to the alterations in terms of chemical composition, stiffness and roughness induced specifically by caspofungin and amphotericin B. In addition to this, we demonstrated that AFM is a valuable technique to evaluate drug-microorganism interaction.

Photoinduced charge carrier dynamics in a ZnSe quantum dot-attached CdTe system

A new nanohybrid material is prepared by attaching CdTe nanoneedles (NNs) to surface-modified ZnSe quantum dots (QDs). The NNs and QDs are prepared by a colloidal synthesis method in an aqueous alkaline medium. The surface modification and the attachment of nanostructures are achieved by a bifunctional ligand 3-mercaptopropionic acid (3-MPA). The band gap of the ZnSe QDs is varied by controlling the size of the QDs in order to get the maximum overlap between the absorption band of the CdTe NNs and the emission band of the ZnSe QDs, which is a prerequisite for effective charge/energy transfer. The possibility of photoinduced charge transfer (PCT) and Förster resonance energy transfer (FRET) from the donor (QDs) to the acceptor (NNs) has been assessed. Very fast (less than 800 ps) PCT and FRET from QDs to NNs occur because the emission band of QDs overlaps with the absorption band of NNs. The calculated large value of the overlapping integral, J(λ) ∼4.5 × 10¹⁹M^-1cm^-1nm⁴, of the donor and the acceptor bands proves the feasibility of energy transfer. These findings suggest that the ZnSe QDs can exchange photoinduced energy with the CdTe NNs effectively over a wide distance in a CdTe-ZnSe nanohybrid.

In vitro effects on calcium oxalate crystallization kinetics and crystal morphology of an aqueous extract from Ceterach officinarum: Analysis of a potential antilithiatic mechanism

Ceterach officinarum Willd is a plant widespread throughout Europe and used in southern Italy as a diuretic. Beliefs in the benefits of C. officinarum aqueous extract in the treatment of calcium oxalate kidney stones are widely held. Little is known, however, about the actual mechanism of its antilithiatic action. Our results in this in vitro study corroborate C. officinarum aqueous extract as a good source of antioxidants with a high antioxidant effects. Our results also demonstrate a major impact of C. officinarum aqueous extract on in vitro induced calcium oxalate crystallization kinetics and crystal morphology, showing its critical role in kidney stone formation and/or elimination. We show that progressively increasing doses of C. officinarum aqueous extract cause a sequence of effects. A powerful inhibitory action on calcium oxalate monohydrate (COM) growth and aggregation is first observed. C. officinarum aqueous extract also appears highly effective in stimulating nucleation increasing the number and reducing the size of COM crystals, which become progressively thinner, rounded and concave in a dose-dependent manner. These shape-modified COM crystals are known to be less adherent to renal tubular cells and more easily excreted through the urinary tract preventing kidney stone formation. Further, C. officinarum aqueous extract promotes the formation of calcium oxalate dihydrate (COD) rather than the monohydrate so that, at the highest concentrations used, only COD crystals are observed, in significant greater numbers with a clear reduction in their size, in a dose-dependent manner. Furthermore, AFM analyses allowed us to reveal the presence of C. officinarum component(s) on the surfaces of COD and modified COM crystals. The crystal surface adsorbed component(s) are shown to be similarly active as the total aqueous extract, suggesting a trigger factor which may direct crystal modification towards COD forms. In urolithiasis pathogenesis COD crystals are less dangerous than the COM forms due to their lower affinity for renal tubular cells. Our results are important in understanding the mechanisms which guide the modification induced by C. officinarum on the crystallization process. Based on these data, together with no adverse toxic effect being observed on the in vitro model of human intestinal enterocytes, C. officinarum aqueous extract could represent an attractive natural therapy for the treatment of urolithiasis.

Effect of monomer structure and solvent on the growth of supramolecular nanoassemblies on a graphite surface

The self-assembly of high aspect ratio hierarchical surface assemblies, as observed by fluid tapping mode AFM, can be achieved through careful design of the supramolecular interactions between low-molecular-weight adsorbates. Needlelike assemblies of monotopic guanine end-capped alkanes grow on a graphite surface when deposited from a water/DMSO solution. The growth of these assemblies can be monitored by AFM in real time, and the growth rate along the two different axes can be understood (through molecular modeling) in terms of the specific adsorbate-adsorbate interactions along those axes. Additionally, through judicious solvent selection (e.g., use of non-H-bonding solvents such as o-dichlorobenzene), which allows the formation of hydrogen-bonding aggregates in solution and influences the surface-adsorbate interactions, dramatically different surface assemblies of these guanine derivatives are obtained.

Superperiodic assembly of 2,6-diethynylpyridine through weak hydrogen bonds at the 1-phenyloctane/HOPG interface

Regardless of the absence of alkyl chains and conventional hydrogen bonding sites as well as its small size, 2,6-diethynylpyridine forms an ordered array at the interface between 1-phenyloctane and highly oriented pyrolytic graphite (HOPG) under room temperature conditions, as revealed by scanning tunneling microscopy. We propose a model for the superperiodic molecular arrangement with reference to the bulk crystal structure, in which the surface pattern is governed by weak C-H...N and C-H...pi hydrogen bonds as well as the periodic potential of the underlying graphite surface.

Molecular engineering of supramolecular scaffold coatings that can reduce static platelet adhesion

Novel supramolecular coatings that make use of low-molecular weight ditopic monomers with guanine end groups are studied using fluid tapping AFM. These molecules assemble on highly oriented pyrolytic graphite (HOPG) from aqueous solutions to form nanosized banding structures whose sizes can be systematically tuned at the nanoscale by tailoring the molecular structure of the monomers. The nature of the self-assembly in these systems has been studied through a combination of the self-assembly of structural derivatives and molecular modeling. Furthermore, we introduce the concept of using these molecular assemblies as scaffolds to organize functional groups on the surface. As a first demonstration of this concept, scaffold monomers that contain a monomethyl triethyleneglycol branch were used to organize these "functional" units on a HOPG surface. These supramolecular grafted assemblies have been shown to be stable at biologically relevant temperatures and even have the ability to significantly reduce static platelet adhesion.

Self-organization of gold-containing hydrogen-bonded rosette assemblies on graphite surface

The self-organization of supramolecular structures, in particular gold-containing hydrogen-bonded rosettes, on highly oriented pyrolytic graphite (HOPG) surfaces was investigated by tapping-mode atomic force microscopy (TM-AFM) and scanning tunneling microscopy (STM). TM-AFM and high-resolution STM results show that these hydrogen-bonded assemblies self-organize to form highly ordered domains on HOPG surfaces. We find that a subtle change in one of the building blocks induces two different orientations of the assembly with respect to the surface. These results provide information on the control over the construction of supramolecular nanoarchitectures in 2D with the potential for the manufacturing of functional materials based on structural manipulation of molecular components.

Macroscopic 2D networks self-assembled from nanometer-sized protein/DNA complexes

We demonstrate the self-assembly of DNA and DNA binding proteins into two-dimensional networks that are then addressable by sending a second protein to a specific recognition site on the DNA network. These networks cover centimeters in area but can be addressed with nanometer precision. This hierarchical self-assembly of specific DNA protein complexes will be the basis for complex positioning of single molecules in two and three dimensions.

Programmed hyperhelical supramolecular assembly of nickel phthalocyanine bearing enantiopure 1-(p-tolyl)ethylaminocarbonyl groups

The present paper reports uniqueness of a simple, programmed design of disk-shaped homochiral nickel phthalocyanine (Pc) molecules bearing four enantiomerically pure 1-(p-tolyl)ethylaminocarbonyl groups at their peripheral positions, (Pc-(R) and Pc-(S)), and their controlled self-organization into mesoscopic supramolecular helical fibers with a preferential handedness in solution and onto solid surfaces. A combination of four fundamental intermolecular interactions, including quadruple hydrogen bonding, pi-pi stacking, homochiral interactions of the enantiopure bulky aralkyl entities, and noncoordinating nature of nickel ion of the Pc molecules afforded a high thermal stability of the Pc self-assembly in chloroform (CHCl(3)), tetrahydrofuran, and o-dichlorobenzene and onto hydrophilic mica and hydrophobic HOPG surfaces. A higher-ordered helical self-assembly of Pc disks was observed in these solutions (approximately 200 Pc molecules), while the self-assembly was completely dissociated into monomeric species in N,N-dimethylformamide due to a loss of hydrogen-bonding interactions between Pc molecules. Supramolecular chirality in the hierarchical self-assembly of Pc molecules originated from the presence of (R)- or (S)-chiral centers in the peripheral tails, which rotate noncovalently linked molecular building blocks to effectively form the helical architectures. The helical Pc nanofibers dissolved in CHCl(3), estimated to be ca. 70 nm from peak molecular weight obtained by SEC analysis, acts as a building block for higher-order helical fibers (ca. 1 microm) at single molecular level on the solid surfaces, as demonstrated by the dynamic force mode atomic force microscopy. Regardless of hydrophilic and hydrophobic substrates, the interaction between these Pc molecules and the solid surfaces could not affect the morphology of helical assemblies, indicating a unique robustness of these assemblies.