Surfactant Structure-Dependent Interactions with Modified Starch Nanoparticles Probed by Fluorescence Spectroscopy

Location of a Hydrophobic Load in Poly(oligo(ethylene glycol) methyl ether methacrylate)s (PEGMAs) Dissolved in Water and Probed by Fluorescence

Two series of pyrene-labeled poly(oligo(ethylene glycol) methyl ether methacrylate)s referred to as PyEG5-PEGnMA and PyC4-PEGnMA were prepared to probe the region surrounding the polymethacrylate backbone by using the fluorescence of the dye pyrene. PyEG5-PEGnMA and PyC4-PEGnMA were prepared by copolymerizing the EGnMA methacrylate monomers with penta(ethylene glycol) 1-pyrenemethyl ether methacrylate or 1-pyrenebutyl methacrylate, respectively. In organic solvents, the much longer 18 non-hydrogen atom linker connecting the pyrene moieties to the polymethacrylate backbone in the PyEG5-PEGnMA samples enabled the deployment of the pyrenyl labels into the solution. In water, however, an excited pyrene for PyEG5-PEGnMA was found to probe a same volume as for the PyC4-PEGnMA samples where a much shorter 6 non-hydrogen atom spacer connected pyrene to the backbone. Another surprising observation, considering that the hydrophobicity of pyrene induces strong pyrene aggregation for many pyrene-labeled water-soluble polymers (Py-WSPs) in water, was the little pyrene aggregation found for the PyEG5-PEGnMA and PyC4-PEGnMA samples in water. These effects could be related to the organic-like domain (OLD) generated by the oligo(ethylene glycol) side chains densely arranged around the polymethacrylate backbone of the polymeric bottlebrush (PBB). Additional fluorescence experiments conducted with the penta(ethylene glycol) 1-pyrenemethyl ether derivative indicated that the cylindrical OLD surrounding the polymethacrylate backbone had a chemical composition similar to that of ethylene glycol. Binding of hydrophobic pyrene molecules to unlabeled PEGnMA bottlebrushes in water further supported the existence of the OLD. The demonstration, that PEGnMA samples form an OLD in water, which can host and protect hydrophobic cargoes like pyrene, should lead to the development of improved PEGnMA-based drug delivery systems.

Interior of glycogen probed by pyrene excimer fluorescence

A glycogen sample from oyster (O) and another from corn (C) were fluorescently labeled with 1-pyrenebutyric acid to yield two series of pyrene-labeled glycogen samples (Py-Glycogen(O/C)). Analysis of the time-resolved fluorescence (TRF) measurements of the Py-Glycogen(O/C) dispersions in dimethyl sulfoxide yielded the maximum number (<N_blob^exp>) of anhydroglucose units (AGUs), that could separate two pyrene-labeled AGUs and still allow efficient pyrene excimer formation (PEF) between an excited and a ground-state pyrene. Molecular mechanics optimizations (MMOs) were conducted on a lattice of hexagonally close packed oligosaccharide helices to determine how the theoretical N_blob^theo varied as a function of the lattice density. Comparing <N_blob^exp> and <N_blob^theo>, obtained after integrating N_blob^theo along the local density profile ρ(r) across the glycogen particles, led to the conclusion that ρ(r) took a maximum value at the center of the glycogen particles contrary to expectations based on the Tier Model.

Effect of Ionic and Non-Ionic Surfactants on the Pasting Characteristics and Digestive Properties of Regular and Frozen Starch for Oral Delivery

Starch is an ideal wall material for controlled release in oral delivery systems due to its non-allergic properties, availability, and cheap price. However, because of its poor mechanical behavior and high water permeability, it is necessary to modify the amphiphilic nature of starch. Surfactants are essential components to emulsify the lyophobic food ingredients. However, the interaction of starch with emulsifiers and how they affect the pasting behavior and digestion of starch are not well understood. In this paper, surfactants, such as non-ionic Tween (TW) and ionic sodium fatty acid (NaFA), with varying hydrophobic carbon chain lengths, were selected as model amphiphiles to investigate the structural, pasting, rheological properties and in vitro digestibility of regular and frozen starch samples. The results showed that, in most cases, the addition of TW reduced the viscosity of starch. However, saturated medium-chain NaFA increased the starch viscosity and rheological modulus greatly. Both surfactants inhibited starch digestion. This paper presents a comparative investigation on the effect of ionic and non-ionic surfactant on the structure and properties of corn starch, and therefore the information is useful for structural-based formulation with starch for developing colloidal delivery systems. It is also helpful for developing functional food with controllable digestion properties.

Synthesis, characteristics, and applications of modified starch nanoparticles: A review

Nowadays, starch nanoparticles (SNPs) are drawing attention to the scientific community due to their versatility and wide range of applications. Although several works have extensively addressed the SNP production routes, not much is discussed about the SNPs modification techniques, as well as the use of modified SNPs in typical and unconventional applications. Here, we focused on the SNP modification strategies and characteristics and performance of the resulting products, as well as their practical applications, while pointing out the main limitations and recommendations. We aim to guide researchers by identifying the next steps in this emerging line of research. SNPs esterification and oxidation are preferred chemical modifications, which result in changes in the functional groups. Moreover, additional polymers are incorporated into the SNP surface through copolymer grafting. Physical modification of starch has demonstrated similar changes in the functional groups without the need for toxic chemicals. Modified SNPs rendered differentiated properties, such as size, shape, crystallinity, hydrophobicity, and Zeta-potential. For multiple applications, tailoring the aforementioned properties is key to the performance of nanoparticle-based systems. However, the number of studies focusing on emerging applications is fairly limited, while their applications as drug delivery systems lack in vivo studies. The main challenges and prospects were discussed.

Protein-like particles through nanoprecipitation of mixtures of polymers of opposite charge

HYPOTHESIS

Polymer nanoparticles (NPs) have a very high potential for applications notably in the biomedical field. However, synthetic polymer NPs cannot yet concurrence the functionalities of proteins, their natural counterparts, notably in terms of size, control over internal structure and interactions with biological environments. We hypothesize that kinetic trapping of polymers bearing oppositely charged groups in NPs could bring a new level of control and allow mimicking the surfaces of proteins.

EXPERIMENTS

Here, the assembly of mixed-charge polymer NPs through nanoprecipitation of mixtures of oppositely charged polymers is studied. Two series of copolymers made of ethyl methacrylate and 1 to 25 mol% of either methacrylic acid or a trimethylammonium bearing methacrylate are synthesized. These carboxylic acid or trimethylammonium bearing polymers are then mixed in different ratios and nanoprecipitated. The influence of the charge fraction, mixing ratio of the polymers, and precipitation conditions on NP size and surface charge is studied.

FINDINGS

Using this approach, NPs of less than 25 nm with tunable surface charge from +40 mV to -40 mV are assembled. The resulting NPs are sensitive to pH and certain NP formulations have an isoelectric point allowing repeated charge reversal. Encapsulation of fluorescent dyes yields very bright fluorescent NPs, whose interactions with cells are studied through fluorescence microscopy. The obtained results show the potential of nanoprecipitation of oppositely charged polymers for the design of NPs with precisely tuned surface properties.

Superparamagnetic iron oxide-gold nanoparticles conjugated with porous coordination cages: Towards controlled drug release for non-invasive neuroregeneration

This paper reports a smart intracellular nanocarrier for sustainable and controlled drug release in non-invasive neuroregeneration. The nanocarrier is composed by superparamagnetic iron oxide-gold (SPIO-Au) core-shell nanoparticles (NPs) conjugated with porous coordination cages (PCCs) through the thiol-containing molecules as bridges. The negatively charged PCC-2 and positively charged PCC-3 are compared for intracellular targeting. Both types result in intracellular targeting via direct penetration across cellular membranes. However, the pyrene (Py)-PEG-SH bridge enabled functionalization of SPIO-Au NPs with PCC-3 exhibits higher interaction with PC-12 neuron-like cells, compared with the rhodamine B (RhB)-PEG-SH bridge enabled case and the stand-alone SPIO-Au NPs. With neglectable toxicities to PC-12 cells, the proposed SPIO-Au-RhB(Py)-PCC-2(3) nanocarriers exhibit effective drug loading capacity of retinoic acid (RA) at 13.505 μg/mg of RA/NPs within 24 h. A controlled release of RA is achieved by using a low-intensity 525 nm LED light (100% compared to 40% for control group within 96 h).

Fluorescence Study of the Influence of the Structure and Hydrophobicity of Fluorescent Dyes and Cationic Surfactants on their Association in Aqueous Solutions

The statistical characteristics of the dependences of the fluorescence signal of analytical systems as a function of the integral parameters of the structure of fluorescent reagents and cationic surfactants on their association in aqueous solutions has been investigated. Molecular weight, surface area, and their first-order molecular connectivity index have been taken as parameters of the structure of the reagents and cationic surfactants. The influence of the hydrophobicity of the reagent and cationic surfactants, such as the octanol–water distribution constant and octanol–water partition coefficient, on the fluorescence signal of the reagent–cationic surfactant associates have also been investigated. It is shown that the associates of anionic reagents with cationic surfactant counter ions are characterised by high stability and a higher analytical signal compared with associates in which there is no electrostatic attraction between the reagent and the surfactant ion. The effect of hydrophobicity of the reagent and cationic surfactant in the absence of electrostatic attraction between the interacting particles is similar. The increase in the role of the influence of the structure of cationic reagents in their association with cationic surfactants, when the electrostatic attraction is absent and the stability of the associates is due mainly to hydrophobic interactions, is noticeable. The regularities of the influence of the colloid-chemical state on the analytical signal of associated cationic surfactants in solutions have been investigated. The study made it possible to formulate a rational basis for the search and design of analytical systems for the determination of large cations by the fluorescence method.

Effect of Structure on Polypeptide Blobs: A Model Study Using Poly(l-lysine)

The conformation of a series of pyrene-labeled poly(l-lysine)s (Py-PLLs) in 60:40 and 90:10 (v/v) acetonitrile:water mixtures was determined by comparing the results obtained from the fluorescence blob model (FBM) analysis of their fluorescence decays with those obtained from molecular mechanics optimizations (MMOs). PLL aggregates formed in both solutions as demonstrated by FRET experiments between naphthalene- and pyrene-labeled PLLs. Addition of an excess of unlabeled PLL allowed the conformational study of isolated Py-PLL embedded in a matrix of unlabeled PLLs. By varying the acetonitrile (ACN) content of the solution from 60 to 90 vol % ACN, Py-PLL was found to undergo a conformational change from a random coil to an α-helix. The conformational change induced an increase in the maximum number of lysines (N_blob) separating two pyrene-labeled lysines that could still form an excimer between an excited- and a ground-state pyrene. N_blob obtained from the FBM analysis increased from 15.2 ± 2.1 to 25.2 ± 1.2 lysines as PLL changed its conformation from a random coil to an α-helix. AFM revealed that the α-helical PLLs organized themselves into structured bundles ∼22 nm in diameter. The FBM analysis of the decays acquired with a solution of aggregated Py-PLLs in a 90:10 ACN:water mixture yielded a larger N_blob value of 36.6 ± 3.4. The increase in N_blob indicated that the Py-PLL constructs could now interact with one another in the helical bundles. This increase in N_blob was then used in conjunction with MMOs to determine an interhelical spacing of 2.9 ± 0.1 nm for Py-PLLs in a bundle. This interhelical spacing resulted in a local density of 0.25 ± 0.01 g·cm^-3 for the bundles of PLL α-helices, which was a reasonable density for a protein in solution. This study describes an experimental means to probe the number of amino acids that interact with each other as the conformation of a polypeptide evolves from that of a random coil to that of an α-helix to finally that of a bundle of α-helices.

Detection of Nitroaromatics by Pyrene-Labeled Starch Nanoparticles

Starch nanoparticles (SNPs) were hydrophobically modified by using 1-pyrenebutyric acid (PyBA) with degrees of substitution (DS) between 0.0006 and 0.11. Fluorescence quenching studies were conducted on the pyrene-labeled starch nanoparticles (Py-SNPs) in dimethyl sulfoxide (DMSO) and water with nitromethane (NM), 4-mononitrotoluene (MNT), 2,6-dinitrotoluene (DNT), and 2,4,6-trinitrotoluene (TNT) to assess the mode of quenching of the pyrene labels in the two solvents. In DMSO where pyrene, starch, and the quenchers were soluble, a decrease in fluorescence signal was the result of dynamic encounters between the excited pyrene labels and the nitrated quenchers. In water where starch could be dispersed but pyrene and the nitroaromatic compounds (NACs) were sparingly soluble, quenching took place through the binding of NACs to pyrene aggregates. Py(11)-SNPs (Py-SNPs with a DS of 0.11)-coated filter papers (Py-CFPs) were prepared as fluorescence sensors. The fluorescence emitted by Py-CFPs was quenched to 25% of its original value within 10 ± 2, 72 ± 20, and 23 ± 4 s upon exposure to vapors of MNT, DNT, and TNT, respectively. When known amounts of NACs were deposited onto Py-CFPs, their limit of detection (LOD) when the fluorescence decreased by more than 3 standard deviations (3σ) from its original value equaled 9.2 ± 0.8, 3.3 ± 0.5, and 0.20 ± 0.02 ng/mm² for MNT, DNT, and TNT, respectively. These response times and LODs were among the best values reported to date in the scientific literature for fluorescence sensors. The selectivity of the Py-CFPs toward NACs was also investigated by comparing their response to the presence of non-nitrated aromatics, amines, and aromatic ketones. Quenching was only observed with the latter family of chemicals tested, but with much lower efficiency compared to TNT, thus reflecting some level of selectivity toward this specific NAC.