Influence of Gold Nanoparticles of Varying Size in Improving the Lipase Activity within Cationic Reverse Micelles

Herein, we report the effect of gold nanoparticles (GNPs) in enhancing lipase activity in reverse micelles of cetyltrimethylammonium bromide (CTAB)/water/isooctane/n‐hexanol. The size and concentration of the nanoparticles were varied and their specific roles were assessed in detail. An overall enhancement of activity was observed in the GNP‐doped CTAB reverse micelles. The improvement in activity becomes more prominent with increasing concentration and size of the GNPs (0–52 μM and ca. 3–30 nm, respectively). The observed highest lipase activity (k₂=1070±12 cm³ g^?1 s^?1) in GNP‐doped CTAB reverse micelles ([GNP]: 52 μm, ca. 20 nm) is 2.5‐fold higher than in CTAB reverse micelles without GNPs. Improvement in the lipase activity is only specific to the GNP‐doped reverse micellar media, whereas GNP deactivates and structurally deforms the enzyme in aqueous media. The reason for this activation is probably due to the formation of larger‐sized reverse micelles in which the GNP acts as a polar core and the surfactants aggregate around the nanoparticle (‘GNP pool’) instead of only water. Lipase at the augmented interface of the GNP‐doped reverse micelle showed improved activity because of enhancement in both the substrate and enzyme concentrations and increased flexibility in the lipase conformation. The extent of the activation is greater in the case of the larger‐sized GNPs. A correlation has been established between the activity of lipase and its secondary structure by using circular dichroism and FTIR spectroscopic analysis. The generalized influence of GNP is verified in the reverse micelles of another surfactant, namely, cetyltripropylammonium bromide (CTPAB). TEM, dynamic light scattering (DLS), and UV/Vis spectroscopic analysis were utilized to characterize the GNPs and the organized aggregates. For the first time, CTAB‐based reverse micelles have been found to be an excellent host for lipase simply by doping with appropriately sized GNPs.     

Direct electrochemistry of cytochrome c on nanotextured diamond surface

Nanotextured diamond surfaces with geometrical properties close to protein dimensions were used for the realization of direct electron transfer of cytochrome c (cyt c) without any covalent bonding. The peroxidase activity of native and denatured cyt c was also investigated. Cyclic voltammograms of native cyt c show quasi-reversible electron transfer reactions, while no heme redox activity is detected for denatured cyt c. Unfolding (denaturation) of cyt c can be achieved in the presence of hydrogen peroxide. Partially or fully denatured cyt c showed higher peroxidase activity than native cyt c. This is because denatured cyt c loses its tertiary structure and hydrogen peroxide is easier to access the heme redox center. The apparent Michaelis–Menten constant K_m for native and denatured cyt c has been determined to be 0.23 mM and 0.08 mM.     

Hydrophobic Variations of N‐Oxide Amphiphiles for Membrane Protein Manipulation: Importance of Non‐hydrocarbon Groups in the Hydrophobic Portion

Amphipathic agents called detergents serve as membrane‐mimetic systems to maintain the native structures of membrane proteins during their manipulation. However, membrane proteins solubilized in conventional detergents tend to undergo denaturation and aggregation, necessitating the development of novel amphipathic agents with enhanced properties. Here we describe several new amphiphiles that contain an N‐oxide group as the hydrophilic portion. The new amphiphiles have been evaluated for the ability to solubilize and stabilize a fragile multi‐subunit assembly from biological membranes. We found that cholate‐based agents were promising in supporting retention of the native protein quaternary structure, while deoxycholate‐based amphiphiles were highly efficient in extracting/solubilizing the intact superassembly from the native membrane. Monitoring superassembly solubilization and stabilization as a function of variation in amphiphile structure led us to propose that a non‐hydrocarbon moiety such as an amide, ether, or a hydroxy group present in the lipophilic regions can manifest distinctive effects in the context of membrane protein manipulation.     

Interaction between block copolymer micelles and azobenzene-containing surfactants: from coassembly in water to layer-by-layer assembly at the interface

In this paper, we describe the use of block copolymer micelles to incorporate Azo-AOT, an azobenzene-containing amphiphile having a structure suitable for reverse micelle formation and the fabrication of polyelectrolyte/micelle multilayer films. Interestingly, it is found that the PS21-PAA157 micelles can incorporate more Azo-AOT molecules than the PS115-PAA15 micelles, which is different from the case of incorporation of noncharged hydrophobic molecules. Moreover, Azo-AOT incorporated into the PS21-PAA157 micelles undergoes a faster photoisomerization than in the PS115-PAA15 micelles, which seems to be related to different aggregation states of Azo-AOT in the two micelles. From the data of UV-vis spectra, we can infer that Azo-AOT adopts a reverse micelle-like aggregation state in the PS115-PAA15 micelles and disperses in the interface between the core and corona of PS21-PAA157 micelles. These polyelectrolyte/micelle films incorporating functional amphiphiles have great potential in the field of functional thin films.     

Spectral properties and supramolecular inclusion complexes of β-cyclodextrin with flexible amphiphilic and rigid compounds

Spectral properties and inclusion complexes of β-cyclodextrin (β-CD) with nonionic amphiphiles and rigid 1-bromonaphthalene (BrN) was investigated in detail. Fluorescence and ¹H NMR measurements give new insights into inclusion of the hydrophobic moiety of amphiphiles into the cavity of β-CD. Their apparent stability constants were well correlated with the structure of the hydrophobic moiety of amphiphiles. The long and flexible hydrophobic moiety may occupy the cavity in the compressed manner. The phosphorescence quenching and the binding strength of BrN in ternary complexes indicate that the inclusion depth and the rigidity of BrN in the cavity of β-CD are predominant factors in determining its phosphorescence. Further inclusion of rigid BrN into the cavity drives the built-in phenyl group of amphiphiles to expose to bulk water phase to a greater extent. Comparative analyses of molecular sizes and models reveal that the flexible hydrocarbon chain of an amphiphile in supramolecular inclusion complexes was located inside the crowded cavity of β-CD due to the filling of rigid BrN into the cavity.     

Access to Different Nanostructures via Self‐Assembly of Thiourea‐Containing PEGylated Amphiphiles

Readily water‐soluble PEGylated amphiphiles containing bis‐thiourea‐based molecular recognition units at the interface of hydrophobic and hydrophilic blocks are developed. Self‐assembly of these amphiphiles is found to be dependent on the exact chemical composition of the hydrophobic component. Elongated, spherical, and disk‐like micelles are formed with the change in hydrophobic group from stearyl (2A), oleyl (2B), and dodecanol (2C), respectively. The length of the rod‐like elongated micelles formed by 2A could be tuned by thermal treatment as well. Synthesis and detailed structural characterization of these amphiphiles by TEM, DSC, synchrotron SAXS techniques are reported. Organic solvent‐free direct aqueous encapsulation of doxorubicin, an anticancer drug into these nanostructures is demonstrated.

     

Hydrogen‐Bonding‐Regulated Supramolecular Nanostructures and Impact on Multivalent Binding

Herein we describe the H‐bonding‐regulated nanostructure, thermodynamics, and multivalent binding of two bolaamphiphiles NDI‐1 and NDI‐2 consisting of a hydrophobic naphthalene diimide connected to a hydrophilic wedge by a H‐bonding group and a glucose moiety on its two arms. NDI‐1 and NDI‐2 differ by the single H‐bonding group, namely, hydrazide or amide, which triggers the formation of vesicles and cylindrical micelles, respectively. Although the extended H‐bonding ensures stacking with head‐to‐head orientation and the formation of an array of the appended glucose moieties in both systems, the adaptive cylindrical structure exhibited superior multivalent binding with concanavalin A (ConA) to that of the vesicle. A control amphiphile lacking a H‐bonding group assembled with a random lateral orientation to produce spherical micelles without any notable multivalent binding.     

Synthesis,physicochemical characterization,and self‐assembly of linear,dibranched, and miktoarm semifluorinated triphilic polymers

Linear, dibranched, and miktoarm amphiphiles containing both hydrophobic and fluorophilic moieties were synthesized and characterized in an attempt to elucidate the relationship between semifluorinated amphiphile structure and aggregate behavior in aqueous solution. For the linear and dibranched amphiphiles, there was an exponential decrease in critical aggregation concentration (CMC) and a logarithmic increase in core microviscosity with increasing length of the fluorocarbon segments; while the miktoarm architecture produced no notable trend in microviscosity or CMC. Furthermore, the linear and dibranched surfactants showed enhanced kinetic stability, dissociating more slowly in the presence of human serum than did either the dibranched or miktoarm amphiphiles. Finally, encapsulation studies with the hydrophobic drug paclitaxel (PTX) showed that the ability to solubilize and retain PTX increased with the presence and with the increasing size of the fluorocarbon moiety for both the linear and dibranched amphiphiles, while no such trend was observed for the miktoarm amphiphiles. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3324–3336     

A Polyaromatic Gemini Amphiphile That Assembles into a Well‐Defined Aromatic Micelle with Higher Stability and Host Functions

A gemini‐type amphiphilic molecule, constituted of two V‐shaped polyaromatic amphiphiles linked by a linear acetylene spacer, was synthesized. The gemini amphiphile assembles into a well‐defined aromatic micelle (ca. 2 nm in core diameter), providing higher stability in water even at low concentration (0.09 mm ) and high temperature (>130 °C). Unlike common gemini amphiphiles with aliphatic chains, the present amphiphile and its micellar assembly emit green and orange fluorescence (Φ_F=33 and 9 %), respectively. Despite strong and multiple π‐stacks of the polyaromatic panels of the amphiphiles, the water‐soluble gemini aromatic micelle incorporates medium‐size to large hydrophobic compounds into the frameworks. Interestingly, the guest binding capability toward large planar molecules was enhanced by more than two times through the pre‐encapsulation of spherical molecules in the cavity.     

反相胶束对辣根过氧化物酶催化反应的影响

胶束体系是酶学研究比较理想的体系,因为它所具有的诸如热力学稳定、光学透明及能增溶亲水分子、亲油分子或两性分子等性质,使许多酶在胶束体系中的反应速率远远高于在水相中,即人们发现的所谓“超活性”［‘j．辣根过氧化物酶（HRP）是一种比较稳定的酶,且价廉易得,具备一般过氧化物酶的典型反应．在研究中人们发现,HRP在反相胶束体系中同样具有“超活性”,由于HRP能够催化大量底物进行反应,因此“超活性”对HRP的催化反应具有重要意义．已有研究者［’、’j对CTAB反相胶束体系中HRP的性质进行了探讨,但反相胶束对HRP的…     

Kinetic investigations on the alkaline hydrolysis of tris-(1,10-phenenthroline)Fe(II) with guar gum–surfactant interactions

The kinetic investigations on the alkaline hydrolysis of tris-(1,10–phenanthroline)iron(II) has been explored spectrophotometrically in microheterogeneous environment at 301?K and ionic strength of 0.13?mol?L^?1. Guar gum, cationic amphiphiles, and their mixtures are used as the reaction environments to carry out the reaction. Guar gum decreases the rate of reaction, which indicates that Fe(II) complex may be trapped in the hydrophobic region of gum. Cationic amphiphile decreases the rate in the presence of guar gum. The extent of interaction between guar gum and amphiphile increases with the hydrophobic carbon chain length. The critical aggregation concentration (CAC) and critical micelle concentration (CMC) of the amphiphiles (cetyl trimenthyl ammonium bromide (CTAB), tetradecyl trimenthyl ammonium bromide (TTAB), dodecyl trimenthyl ammonium bromide (DTAB)) in the presence of guar gum have been determined with conductometry and tensiometry. All observations support either weak or strong interaction of cationic amphiphiles with guar gum. Activation parameters of the reaction in different environments have been determined which corroborate the rate data.     

Graphene Nanoplatelets: Electrochemical Properties and Applications for Oxidation of Endocrine‐Disrupting Chemicals

In most graphene‐based electrochemical applications, graphene nanoplatelets (GNPs) have been applied. Now, for the first time, electrochemical properties of GNPs, namely, its electrochemical activity, potential window, and double‐layer capacitance, have been investigated. These properties are compared with those of carbon nanotubes (CNTs). GNP‐ and CNT‐coated electrodes were then applied for electrochemical oxidation of endocrine‐disrupting chemicals. The GNP‐coated electrode was characterized by atomic force microscopy and electrochemical techniques. Compared with the CNT‐coated electrode, higher peak current for the oxidation of 4‐nonylphenol is achieved on the GNP‐coated electrode, together with lower capacitive current. Electrochemical oxidation of 2,4‐dichlorophenol, bisphenol A, and octylphenol in the absence or presence of 4‐nonylphenol was studied on the GNP‐coated electrode. The results suggest that GNPs have better electrochemical performance than CNTs and are thus more promising for electrochemical applications, for example, electrochemical detection and removal of endocrine‐disrupting chemicals.     

反相胶束中辣根过氧化物酶的停流光谱研究

用停流光谱法研究了HRP在AOT、CTAB和SDS反相胶束中的吸收光谱和反应动力学，实验结果显示在AOT反相胶束中，HRP的吸收峰位置与水相中相同；而另外两种反相胶束对HRP的分子结构产生了较大影响，快速反应动力学研究显示在反相胶束中HRP形成化合物Ⅰ的速率常数远远高于化合物Ⅰ形成HRP—Ⅱ的反应速率常数，推测这是反相胶束的特殊性质造成的结果。     

Protein Unfolding: 1H‐NMR Studies of Paramagnetic Ferricytochrome c‐550 from Horse Heart

Electronic transfer protein cytochrome c‐550 from horse heart is studied in the unfolded state by means of paramagnetic ¹H NMR. The protein contains 104 aminoacid residues and a heme group with low spin Fe^III ion in the oxidized form of protein. The global secondary structure is of the α‐helix type as occurs in the case of very other cytochromes c investigated such as cyt c‐550 from Thiobacillus versutus or cyt c‐551 from Pseudomonas aeruginosa. We have studied the coordination characteristic and electronic properties of heme iron horse heart ferricytochrome c‐550 at increasing denaturing conditions (up to 3.1 M GuHCl and 288‐323 K). The ¹H T₁ values of the signals were measured and some resonance assignments made based on EXSY experiments. The electronic structure of the iron(III) is discussed on the basis of the temperature dependence of the isotropic shifts and relaxation times. These results show that it is produced a change of spin, from low‐spin iron(III) (²T₂, S=1/2) in the folded state to high‐spin iron(III) (⁶A₁, S=5/2) in the unfolded state. It seems to be possible that in the opened structure the ferricyt c‐550 loses one axial ligand (His/‐) appearing the spin transition.     

Chemical Synthesis of the 20 kDa Heme Protein Nitrophorin 4 by α‐Ketoacid‐Hydroxylamine (KAHA) Ligation

The chemical synthesis of the 184‐residue ferric heme‐binding protein nitrophorin 4 was accomplished by sequential couplings of five unprotected peptide segments using α‐ketoacid‐hydroxylamine (KAHA) ligation reactions. The fully assembled protein was folded to its native structure and coordinated to the ferric heme b cofactor. The synthetic holoprotein, despite four homoserine residues at the ligation sites, showed identical properties to the wild‐type protein in nitric oxide binding and nitrite dismutase reactivity. This work establishes the KAHA ligation as a valuable and viable approach for the chemical synthesis of proteins up to 20 kDa and demonstrates that it is well‐suited for the preparation of hydrophobic protein targets.     

Correlation between catalytic activity and surface ligands of monolayer protected gold nanoparticles

Gold nanoparticles (GNPs) are known to be a very good catalyst. Also, the anchoring of GNPs with stabilizing ligands is essential for surface modification, tuning of size and shapes, and to prevent from aggregation in suspension. But the effect of ligand on the catalytic property of ligand-capped GNP is yet to be explored in detail. In this paper, we perform an in-depth study of effect of ligands on the catalytic activity of monolayer protected GNPs. For this study, a series of different ligand functionalized GNPs in suspension as well as functionalized GNPs' thin film on glass substrate are prepared and used as catalysts in two model reactions, viz. borohydride reduction of 4-nitrophenol and redox reaction between potassium ferricyanide and sodium thiosulfate. The functionalization of GNPs with any ligand reduces its virgin catalytic activity, no matter whether the GNPs are suspended or supported as thin film. An increase in alkyl chain length of alkanethiols and alkylamines ligands and their graft density to the surface of GNP reduces its catalytic activity. Interestingly, the capping of GNPs with 11-mercaptoundecanoic acid and 11-mercaptoundecanol ligands completely destroys its catalytic activity. The effect of anchoring group of ligand molecules on the catalytic activity of ligand-protected GNPs is also discussed.     

Photoinduced electron transfer between cytochrome c and a novel 1,4,5,8-naphthalenetetracarboxylic diimide with amphiphilic character

N-dodecyl-N'-(2-phosphonoethyl)-1,4,5,8-naphthalenetetracarboxylic diimide (DNDI) is a novel naphthalenic diimide with amphiphilic character. DNDI was synthesized through the sequential reaction of 1,4,5,8-naphthalenetetracarboxylic dianhydride, first with dodecylamine and then with 2-aminoethylphosphonic acid. Fluorescence measurements showed that DNDI forms excimers in water at sufficiently high concentrations. The fluorescence quantum yield of DNDI in diluted solutions is sensitive to the polarity of the microenvironment, decreasing as going from water to less polar solvents. This property allowed to monitor the incorporation of DNDI into cetyl trimethyl ammonium bromide (CTAB) micelles, with a binding constant of 1.2x10(4) M-1. UV irradiation (365 nm) of solutions containing DNDI and the redox protein cytochrome c (cyt c) resulted in the reduction of the heme iron from the Fe(III) to the Fe(II) state, a reaction that was inhibited by the incorporation of DNDI into CTAB micelles. DNDI formed host-guest complexes with alpha-cyclodextrin (alpha-CD) through the inclusion of the dodecyl group, resulting in an increased aqueous solubility of the compound.     

Properties of ABA and BA polysiloxane amphiphiles modified by polyether

To investigate the effect of content of polyether (F400) grafted on the properties of polysiloxane amphiphiles, polyether was grafted on the polysiloxane by hydrosilylation reaction with H₂PtCl₆ catalyst. The modified polysiloxanes were divided into two types; moreover, the ratio of polyether and polysiloxane was 1:1 or 1:2. The first one was similar to the conventional surfactant structure that is BA polysiloxane amphiphile, which own one hydrophobic chain and one hydrophilic group. Another one was ABA polysiloxane amphiphile, which possess one hydrophobic chain and two hydrophilic groups at the terminal. In our work, we compared the property of modified polysiloxanes with various contents of polyether in aqueous solution at room temperature to analyze the impact of polyether content on siloxane surfactants. The conclusion was that siloxane amphiphiles possess good solubility, high surface activity, and excellent spreading property.     

Amphiphilic Nanoparticles Control the Growth and Stability of Lipid Bilayers with Open Edges

Molecular amphiphiles self‐assemble in polar media to form ordered structures such as micelles and vesicles essential to a broad range of industrial and biological processes. Some of these architectures such as bilayer sheets, helical ribbons, and hollow tubules are potentially useful but inherently unstable owing to the presence of open edges that expose the hydrophobic bilayer core. Here, we describe a strategy to stabilize open bilayer structures using amphiphilic nanoparticle surfactants that present mixtures of hydrophilic and hydrophobic ligands on their surface. We observe that these particles bind selectively to the open edge of bilayer membranes to stabilize otherwise transient amphiphile assemblies. We show how such particles can precisely control the size of lipid tubules, how they can inhibit the formation of undesirable assemblies such as gallstone precursors, and how they can stabilize free‐floating lipid microdiscs.     

Amphiphilic β‐cyclodextrin‐based star‐like block copolymer unimolecular micelles for facile in situ preparation of gold nanoparticles

Multifunctional polymer unimolecular micelles, which are used as templates to fabricate stable gold nanoparticles (GNPs) in one‐step without external reductant, have been designed and prepared. Amphiphilic 21‐arm star‐like block copolymers β‐cyclodextrin‐{poly(lactide)‐poly(2‐(dimethylamino) ethyl methacrylate)‐poly[oligo(2‐ethyl‐2‐oxazoline)methacrylate]}₂₁ [β‐CD‐(PLA‐PDMAEMA‐PEtOxMA)₂₁] and the precursors are synthesized by the combination of ring‐opening polymerization (ROP) and activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP). The tertiary amine groups of PDMAEMA block reduce the counterion to zerovalent gold in situ, and these gold atoms combine mutually to form final GNPs. GNPs with relatively small size and narrow size distribution can be obtained in longer DMAEMA block copolymer, larger molar ratio of DMAEMA to HAuCl₄ and smaller absolute concentrations of both polymer and HAuCl₄. These results showed that the unimolecular micelles can be used as templates for preparing and stabilizing GNPs in situ without any external reducing agents and organic solvents, suggesting that the nanocomposite systems are latent nanocarriers for further biomedical application. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 186–196