Modulation of Environmental Dynamics at the Active Site and Activity of an Enzyme under Nanoscopic Confinement: Subtilisin Carlsberg in Anionic AOT Reverse Micelle

Bioactives Promiscuity of Mucin: Insight from Multi-Spectroscopic, Thermodynamic, and Molecular Dynamic Simulation Analyses

Mucosal drug delivery plays an increasing role in the clinical setting owing to mucin's advantageous biochemical and pharmacological properties. However, how this transport system recognizes different substrates remains unclear. In this study, we explore the mechanism of bioactive (quercetin and berberine) promiscuity of mucin using various spectroscopic techniques and molecular dynamics simulations. The UV-visible spectroscopy results and the decreased fluorescence intensity of mucin in the presence of the bioactive compounds via a static quenching mechanism confirmed ground-state complex formation between the bioactives and mucin. The binding constants (K_b) were evaluated at different temperatures to afford K_b values of ∼10⁴ Lmol^-1, demonstrating the moderate and reasonable affinity of the bioactives for mucin, yielding greater diffusion into the tissues. Thermodynamic analysis and molecular dynamics (MD) simulations demonstrate that mucin-bioactive complex formation occurs primarily because of electrostatic/ionic interactions, while hydrophobic interactions were also crucial in stabilizing the complex. Far-UV circular dichroism spectroscopy showed that bioactive binding induced secondary structural changes in mucin. Sitemap and MD simulation indicated the principal binding site of mucin for the bioactives. This study also provides insight into the bioactives promiscuity of mucin in the presence of a crowded environment, which is relevant to the biological activity of mucin in vivo. An in vitro drug release study revealed that crowding assisted drug release in an enhanced burst manner compared with that in a dilute buffer system. This work thus provides fresh insight into drug absorption and distribution in the native cellular environment and helps direct new drug design and use in pharmaceutical and pharmacological fields.

Interfacial properties modulated by the water confinement in reverse micelles created by the ionic liquid-like surfactant bmim-AOT

The behavior of the interfacial water entrapped in reverse micelles (RMs) that were formed by the ionic liquid-like surfactant 1-butyl-3-methylimidazolium 1,4-bis-2-ethylhexylsulfosuccinate (bmim-AOT) was investigated with the use of UV-Vis absorption spectroscopy and nuclear magnetic resonance (NMR) relaxometry. The solvatochromism of two molecular probes, namely, 1-methyl-8-oxyquinolinium betaine (QB) and N,N,N',N'-tetramethylethylenediamine copper(ii)acetylacetonate tetraphenylborate ([Cu(acac)(tmen)][B(C6H5)4]), was investigated. As a comparison, the analog RMs formed by sodium 1,4-bis-2-ethylhexylsulfosuccinate (Na-AOT) were also explored. By varying the water content inside the RMs and consequently the different magnitude of the water-surfactant interactions at the interface, interesting properties were observed by comparing bmim-AOT and Na-AOT RMs. From the solvatochromic behavior of ([Cu(acac)(tmen)][B(C6H5)4]), we found that the interface in bmim-AOT RMs shows a smaller electron donating capacity than that in Na-AOT RMs. QB revealed that the interfacial region is a weaker hydrogen bond donor and less polar than the corresponding Na-AOT RMs. NMR experiments showed that the molecular motion of water in bmim-AOT RMs is less restricted than that of the water molecules confined in Na-AOT RMs. In summary, the results show how the nature of the bmim+ cation affects the interaction between the entrapped water and the RM interface, greatly modifying the interfacial water structure in comparison with the results known for Na-AOT.

Subtleties of catanionic surfactant reverse micelle assemblies revealed by a fluorescent molecular probe

In this work, the absorption and emission behavior of the cationic hemicyanine trans-4-[4-(dimethylamino)styryl]-N-methylpyridinium iodide (HC) in reverse micelles (RMs) formed by the catanionic surfactants benzyl-n-hexadecyldimethylammonium-1,4-bis-2-ethylhexylsulfosuccinate (AOT-BHD) and cetyltrimethylammonium-1,4-bis-2-ethylhexylsulfosuccinate (AOT-CTA) have been investigated. Our results show that the spectroscopic behavior of HC changes when the dye is dissolved in AOT-BHD or in AOT-CTA RMs. While HC undergoes an intramolecular charge-transfer process upon excitation in AOT-CTA RMs, in AOT-BHD RMs this process is inhibited due to a specific interaction between HC and the polar head group of the BHD⁺ cation. This implies that the chemical structure of CTA⁺ and BHD⁺ cations has a large impact on the excited stated from which HC emission occurs. Additionally, the structural difference between the two cations impacts on the water-RM interface interaction, which provides a way of controlling the solvation process in these RMs. Furthermore, differences in the interfacial fluidity between the two catanionic RMs is observed, a result that is particularly interesting with regard to these systems being used as nanoreactors.

Unveiling the Mode of Interaction of Berberine Alkaloid in Different Supramolecular Confined Environments: Interplay of Surface Charge between Nano-Confined Charged Layer and DNA

In this Article, we demonstrate a detailed characterization of binding interaction of berberine chloride (BBCl) with calf-thymus DNA (CT-DNA) in buffer solution as well as in two differently charged reverse micelles (RMs). The photophyscial properties of this alkaloid have been modulated within these microheterogeneous bioassemblies. The mode of binding of this alkaloid with DNA is of debate to date. However, fluorescence spectroscopic measurements, circular dichroism (CD) measurement, and temperature-dependent study unambiguously establish that BBCl partially intercalates into the DNA base pairs. The nonplanarity imposed by partial saturation in their structure causes the nonclassical types of intercalation into DNA. Besides the intercalation, electrostatic interactions also play a significant role in the binding between BBCl and DNA. DNA structure turns into a condensed form after encapsulation into RMs, which is followed by the CD spectra and microscopy study. The probe location and dynamics in the nanopool of the RMs depended on the electrostatic interaction between the charged surfactants and cationic berberine. The structural alteration of CT-DNA from B form to condensed form and the interplay of surface charge between RMs and DNA determine the interaction between the alkaloid and DNA in RMs. Time-resolved study and fluorescence anisotropy measurements successfully provide the binding interaction of BBCl in the nanopool of the RMs in the absence and in the presence of DNA. This study motivates us to judge further the potential applicability of this alkaloid in other biological systems or other biomimicking organized assemblies.

How the cation 1-butyl-3-methylimidazolium impacts the interaction between the entrapped water and the reverse micelle interface created with an ionic liquid-like surfactant

The behavior of the interfacial water entrapped in reverse micelles (RMs) formed by the ionic liquid-like surfactant 1-butyl-3-methylimidazolium 1,4-bis-2-ethylhexylsulfosuccinate (bmim-AOT) dissolved in benzene (or chlorobenzene) was investigated using noninvasive techniques such as dynamic light scattering (DLS), static light scattering (SLS), FT-IR and (1)H NMR. The DLS and SLS results reveal the formation of discrete spherical and non-interacting water droplets stabilized by the bmim-AOT surfactant. Moreover, since the droplet size increases as the W0 (W0 = [water]/[surfactant]) value increases, water interacts with the RM interface. From FT-IR and (1)H NMR data, a weaker water-surfactant interaction in bmim-AOT RMs in comparison with the RMs created by sodium 1,4-bis-2-ethylhexylsulfosuccinate (Na-AOT) is detected. Consequently, there are less water molecules interacting with the interface in bmim-AOT RMs, and their hydrogen bond network is not completely disrupted as they are in Na-AOT RMs. The results show how the nature of the new cation impacts the interaction between the entrapped water and the RM interface, modifying the interfacial water structure in comparison with the results known for Na-AOT.

Startling temperature effect on proteins when confined: single molecular level behaviour of human serum albumin in a reverse micelle

The present work reports the effect of confinement, and temperature therein, on the conformational fluctuation dynamics of domain-I of human serum albumin (HSA) by fluorescence correlation spectroscopy (FCS).

Effect of the cationic surfactant moiety on the structure of water entrapped in two catanionic reverse micelles created from ionic liquid-like surfactants

The behavior of water entrapped in reverse micelles (RMs) formed by two catanionic ionic liquid-like surfactants, benzyl-n-hexadecyldimethylammonium 1,4-bis-2-ethylhexylsulfosuccinate (AOT-BHD) and cetyltrimethylammonium 1,4-bis-2-ethylhexylsulfosuccinate (AOT-CTA), was investigated by using dynamic (DLS) and static (SLS) light scattering, FTIR, and (1)H NMR spectroscopy techniques. To the best of our knowledge, this is the first report in which AOT-CTA has been used to create RMs and encapsulate water. DLS and SLS results revealed the formation of RMs in benzene and the interaction of water with the RM interface. From FTIR and (1)H NMR spectroscopy data, a difference in the magnitude of the water-catanionic surfactant interaction at the interface is observed. For the AOT-BHD RMs, a strong water-surfactant interaction can be invoked whereas for AOT-CTA this interaction seems to be weaker. Consequently, more water molecules interact with the interface in AOT-BHD RMs with a completely disrupted hydrogen-bond network, than in AOT-CTA RMs in which the water structure is partially preserved. We suggest that the benzyl group present in the BHD(+) moiety in AOT-BHD is responsible for the behavior of the catanionic interface in comparison with the interface created in AOT-CTA. These results show that a simple change in the cationic component in the catanionic surfactant promotes remarkable changes in the RMs interface with interesting consequences, in particular when using the systems as nanoreactors.