Divergent self-assembly propensity of enantiomeric phenylalanine amphiphiles that undergo pH-induced nanofiber-to-nanoglobule conversion

This study presents the pathway diversity in the self-assembly of enantiomeric single phenylalanine derived amphiphiles (single F-PDAs), viz.L-NapF-EDA and D-NapF-EDA, that form supramolecular hydrogels at varied concentrations (≥1 mg mL-1 and ≥3 mg mL-1, respectively). By fitting the variable temperature circular dichroism (VT-CD) data to the isodesmic model, various thermodynamic parameters associated with their self-assembly, such as association constant (K), changes in enthalpy (ΔH), entropy (ΔS), and Gibbs free energy (ΔG), were extracted. The self-assembly of these single F-PDAs was found to be enthalpy-driven but entropically-disfavored. Although self-assembly of the D-isomer was slow, it also exhibited greater free energy of association than the L-isomer. Consequently, thermally and mechanically more robust self-assemblies were formed by the D-isomer than the L-isomer. We term these results as the "butterfly effect in self-assembly" wherein the difference in the stereochemical orientation of the residues at a single chiral center present in these molecules resulted in strong differences in the self-assembly propensity as well as in their thermal and mechanical stability. These single F-PDAs form helical nanofibers of opposite chirality upon self-assembly at basic pH (≥8) that produce intense CD signals. However, upon decreasing the pH, a gradual nanofiber-to-nanoglobular transformation was noticed due to protonation-induced structural changes in the PDAs.

Transition-metal ion-mediated morphological transformation of pyridine-based peptide nanostructures

Pyridine-mediated constitutionally isomeric artificial metallopeptides possess remarkable advantages over the natural counterparts mainly due to their tailor-made chemical structure.

Amphiphilic phenylalanine derivatives that temporally generate reactive oxygen species from water in the presence of Au(iii) ions

Amphiphilic derivatives of phenylalanine (ADFs) have strong self-assembling propensities and yield low molecular weight hydrogels on multiple occassions. The interaction of ADFs with metal ions can result in the morphological changes in the self-assemblies. Herein, we report the interesting consequences of the interaction between four N-protected ADFs with Au(iii) ions. In the case of ADF 1, the original nanofibrillar morphology of the self-assemblies spontaneously transformed into uniform nanoglobules of ∼80 nm in diameter upon addition of Au(iii) ions. A subsequent reduction of the Au(iii) ions to Au(0) nanoparticles (AuNPs) and the surface decoration of the nanoglobules with AuNPs were observed in the course of the next six to eight hours. Simultaneously, multiple reactive oxygen species (ROS) such as hydrogen peroxide (H₂O₂), hydroxyl radicals (˙OH), singlet oxygen and superoxide ions were also found to be present in the reaction medium. These ROS originate from water used as the reaction medium. The ROS production and the reduction of Au(iii) were inhibited upon deaeration of the reaction medium and the use of heavy water (D₂O) or organic solvents as the reaction medium, while an increase in the pH of the aqueous medium intensified both these processes. We exploited the temporal ROS generation using the mixture of 1 and Au(iii) ions towards anticancer therapy by enhancing the intracellular ROS levels. It is expected that this effort can be expanded into a viable anticancer therapy in the near future by modulating the amount and the rate of ROS-generation through judicious choice of the peptidic ligands and metal ions.

Peptide-Based Scaffold for Nitric Oxide Induced Differentiation of Neuroblastoma Cells

Nitric oxide is a gaseous messenger involved in neuronal differentiation, development and synaptogenesis, in addition to many other physiological functions. Therefore, it is imperative to maintain an optimal nitric oxide concentration to ensure its biochemical function. A sustained nitric oxide releasing scaffold, which supports neuronal cell differentiation, as determined by morphometric analysis of neurite outgrowth, is described. Moreover, the effect of nitric oxide on the neuroblastoma cell line was also confirmed by immunofluorescent analysis of neuronal nuclear protein (NeuN), specific neuronal marker and neurofilament (NF) protein, which revealed a significant increase in their expression levels, in comparison with undifferentiated cells.

Influence of size and surface capping on photoluminescence and cytotoxicity of gold nanoparticles

Hydrophilic and homogeneous sub-10 nm blue light-emitting gold nanoparticles (NPs) functionalized with different capping agents have been prepared by simple chemical routes. Structure, average, size, and surface characteristics of these NPs have been widely studied, and the stability of colloidal NP solutions at different pH values has been evaluated. Au NPs show blue PL emission, particularly in the GSH capped NPs, in which the thiol-metal core transference transitions considerably enhance the fluorescent emission. The influence of capping agent and NP size on cytotoxicity and on the fluorescent emission are analyzed and discussed in order to obtain Au NPs with suitable features for biomedical applications. Cytotoxicity of different types of gold NPs has been determined using NPs at high concentrations in both tumor cell lines and primary cells. All NPs used show high biocompatibility with low cytotoxicity even at high concentration, while Au-GSH NPs decrease viability and proliferation of both a tumor cell line and primary lymphocytes.

Multifunctional polyelectrolyte microcapsules as a contrast agent for photoacoustic imaging in blood

The polyelectrolyte microcapsules that can be accurate either visualized in biological media or in tissue would enhance their further in vivo application both as a carrier of active payloads and as a specific sensor. The immobilization of active species, for instance fluorescent dyes, quantum dots, metal nanoparticles, in polymeric shell enables visualization of capsules by optical imaging techniques in aqueous solution. However, for visualization of capsules in complex media an instrument with high contrast modality requires. Herein, we show for the first time photoacoustic imaging (PAI) of multifunctional microcapsules in water and in blood. The microcapsules exhibit greater photoacoustic intensity compare to microparticles with the same composition of polymeric shell presumably their higher thermal expansion. Photoacoustic intensity form microcapsules dispersed in blood displays an enhancement (2-fold) of signal compare to blood. Photoacoustic imaging of microcapsules might contribute to non-invasive carrier visualization and further their in vivo distribution.

Can natural fibers be a silver bullet? Antibacterial cellulose fibers through the covalent bonding of silver nanoparticles to electrospun fibers

Natural cotton was dissolved in a room-temperature ionic liquid 1-ethyl-3-methyl acetate and wet-jet electrospun to obtain nanoscale cotton fibers with a substantially reduced diameter-and therefore an increased surface area-relative to natural cotton fibers. The resulting nano-cotton fibers were esterified with trityl-3-mercaptopropionic acid, which after selective de-tritylation afforded nano-cotton fibers containing reactive thiol functionality. Silver nanoparticles that were covalently attached to these sulfhydryl groups were assembled next. The microstructure of the resulting nanocomposite was characterized, and the antibacterial activity of the resulting nano-cotton Ag-nanoparticle composite was also studied. This nanocomposite showed significant activity against both Gram-negative and Gram-positive bacteria.

Thermoplasmonic effect of silver nanoparticles modulates peptide amphiphile fiber into nanowreath-like assembly

This study demonstrates the beneficial role of di-tryptophan containing short peptide amphiphiles (sPA), for the synthesis and stabilization of AgNPs in the presence of sunlight followed by garlanding of AgNPs along the fibrous network of sPA. Such hybrid structures were precisely and selectively moulded into a nanowreath-type morphology due to the thermoplasmonic effect of AgNPs, and can be used for several bio-nanotechnological applications.

Adenosine Triphosphate-Triggered Release of Macromolecular and Nanoparticle Loads from Aptamer/DNA-Cross-Linked Microcapsules

The synthesis of stimuli-responsive DNA microcapsules acting as carriers for different payloads, and being dissociated through the formation of aptamer-ligand complexes is described. Specifically, stimuli-responsive anti-adenosine triphosphate (ATP) aptamer-cross-linked DNA-stabilized microcapsules loaded with tetramethylrhodamine-modified dextran (TMR-D), CdSe/ZnS quantum dots (QDs), or microperoxidase-11 (MP-11) are presented. In the presence of ATP as trigger, the microcapsules are dissociated through the formation of aptamer-ATP complexes, resulting in the release of the respective loads. Selective unlocking of the capsules is demonstrated, and CTP, GTP, or TTP do not unlock the pores. The ATP-triggered release of MP-11 from the microcapsules enables the MP-11-catalyzed oxidation of Amplex UltraRed by H2O2 to the fluorescent product resorufin.

Label-free, optical sensing of the supramolecular assembly into fibrils of a ditryptophan-DNA hybrid

The grafting of a short nucleic acid strand to ditryptophan dipeptide (WW) results in a peptide-DNA hybrid, which assembles into fibrils under controlled aggregation conditions as evidenced by label free optical sensing owing to the intrinsic fluorescence of the dipeptide.

Soft structure formation and cancer cell transport mechanisms of a folic acid-dipeptide conjugate

Folic acid (FA) is a low-molecular-weight micronutrient, which plays a critical role in the prevention of birth defects and cancers. It is also essential for biochemical pathways responsible for DNA synthesis and maintenance and for the generation of new red blood cells. Cellular trafficking of FA and folate is based on its high-affinity binding to cognate folate receptor, a protein commonly expressed in several human cancers. Thus, folate conjugates of drugs, plasmids, biosensors, contrast, and radiodiagnostic imaging agents have been used for assisted delivery in folate receptor-positive cancer cells, via endocytosis pathways. This report describes morphologies of soft structures from a fully characterized FA-dipeptide conjugate and detailed mechanistic studies of its cancer cell uptake, as tracked by the inherent fluorescence of the conjugate.

Microstructure manipulation and guest release from cation responsive peptide microspheres

A thiolated C₃-symmetric dihistidine conjugate and its self-assembly to yield nanospheres. Doughnut shaped, porous microspheres formed upon co-incubation with ATP that can be triggered to release cargo in response to cationic stimulus.

Fabrication of gold nanoparticles on biotin-di-tryptophan scaffold for plausible biomedical applications

AuNPs were synthesized and encapsulated by spherical scaffold of biotinylated di-tryptophan and such devices can be used for plausible biomedical applications.

Assembly, postsynthetic modification and hepatocyte targeting by multiantennary, galactosylated soft structures

Enzyme modifiable, hollow self-assembled structures offer an excellent scope for multiantennary delivery vectors.