Solvent Effect on Organogel Formation by Low Molecular Weight Molecules

Solvent−gelator interactions play a key role in mediating organogel formation and ultimately determine the properties of the gel. The effect of solvent on organogel formation was investigated in selected ester, ketone, and alcoholic solvents using unique symmetrical trehalose diesters as gelators. In solvents of the same class the gelation number (defined as the ratio of solvent molecules that gel per gelator molecule) decreased for trehalose 6,6‘-diacetate and 6,6‘-dibutyrate as the solvent Hildebrand solubility parameter increased. The opposite was observed for trehalose 6,6‘-didecanoate and 6,6‘-dimyristate. In general, the gelation numbers for all the gelators studied decreased in the order of esters > ketones > alcohols. Alcohols, which are capable of hydrogen bonding and can make substantial contribution to the total solvent−gelator interaction, significantly compromise gel formation. Optical microscopy and scanning electron microscopy revealed that for systems with high gelation numbers, such as trehalose 6,6‘-diacetate and 6,6‘-dibutyrate in ethyl acetate and trehalose 6,6‘-didecanoate and 6,6‘-dimyristate in acetonitrile, thin, flexible, and highly entangled nanofibers were formed. Conversely, thick, rigid, and often highly clustered fibers accompanied systems with poor gelation, such as gels formed from trehalose 6,6‘-diacetate and 6,6‘-dibutyrate in acetonitrile. Understanding the role of solvent in organogel formation is crucial in designing gels with desired structure and physicochemical properties. Such designed gels may provide controlled gelation by fine-tuning the solvent or the chemical environment of the gelator

Highly Enantioselective Oxidation of <i>cis</i>-Cyclopropylmethanols to Corresponding Aldehydes Catalyzed by Chloroperoxidase

Chloroperoxidase (CPO) catalyzes the enantioselective oxidation of cyclopropylmethanols, such as 2-methylcyclopropylmethanol, to cyclopropyl aldehydes using tert-butyl hydroperoxide as the terminal oxidant. In all cases, CPO oxidation of cis-cyclopropanes shows much higher enantioselectivity than with the trans isomers, although CPO gives similar catalytic activity on both isomers. This presents the first example for a heme enzyme that catalyzes the enantioselective oxidation of cyclopropylmethanols. This finding enables a novel route to the synthesis of optically active cyclopropane derivatives, which occur widely in natural products and compounds of pharmaceutical interest. In addition, chiral cyclopropane molecules may be useful model substrates to investigate reaction mechanisms of CPO and the related cytochromes P450

Solvent Effect on Organogel Formation by Low Molecular Weight Molecules

Solvent−gelator interactions play a key role in mediating organogel formation and ultimately determine the properties of the gel. The effect of solvent on organogel formation was investigated in selected ester, ketone, and alcoholic solvents using unique symmetrical trehalose diesters as gelators. In solvents of the same class the gelation number (defined as the ratio of solvent molecules that gel per gelator molecule) decreased for trehalose 6,6‘-diacetate and 6,6‘-dibutyrate as the solvent Hildebrand solubility parameter increased. The opposite was observed for trehalose 6,6‘-didecanoate and 6,6‘-dimyristate. In general, the gelation numbers for all the gelators studied decreased in the order of esters > ketones > alcohols. Alcohols, which are capable of hydrogen bonding and can make substantial contribution to the total solvent−gelator interaction, significantly compromise gel formation. Optical microscopy and scanning electron microscopy revealed that for systems with high gelation numbers, such as trehalose 6,6‘-diacetate and 6,6‘-dibutyrate in ethyl acetate and trehalose 6,6‘-didecanoate and 6,6‘-dimyristate in acetonitrile, thin, flexible, and highly entangled nanofibers were formed. Conversely, thick, rigid, and often highly clustered fibers accompanied systems with poor gelation, such as gels formed from trehalose 6,6‘-diacetate and 6,6‘-dibutyrate in acetonitrile. Understanding the role of solvent in organogel formation is crucial in designing gels with desired structure and physicochemical properties. Such designed gels may provide controlled gelation by fine-tuning the solvent or the chemical environment of the gelator

Sugar-containing Polyamines Prepared Using Galactose Oxidase Coupled with Chemical Reduction

Sugar-containing Polyamines Prepared Using Galactose Oxidase Coupled with Chemical Reductio

In Vitro Precursor-Directed Synthesis of Polyketide Analogues with Coenzyme A Regeneration for the Development of Antiangiogenic Agents

Polyketide analogues are produced via in vitro reconstruction of a precursor-directed polyketide biosynthetic pathway. Malonyl-CoA synthetase (MCS) was used in conjunction with chalcone synthase (CHS), thereby allowing efficient use of synthetic starter molecules and malonate as extender. Coenzyme-A was recycled up to 50 times. The use of a simple immobilization procedure resulted in up to a 30-fold higher yield of pyrone CHS products than that obtained with the free enzyme solutions

Dramatic Solvent and Hydration Effects on the Transition State of Soybean Peroxidase

Enzymes are shown to function in nonaqueous media; however, relatively little information is available on the influence of the organic solvent as well as its associated water content on the properties of the enzymatic transition states. A better understanding of these effects will be useful in developing kinetic models that can then be used to predict optimal solvent and substrate choices for enzymatic reactions in organic media. The influence of the reaction media on soybean peroxidase-catalyzed oxidation of para-substituted phenols was studied using Hammett analysis for several organic solvent systems. The catalytic activity and substrate specificity of the enzyme are influenced by the nature of the solvent and its associated hydration. These findings may allow one to draw conclusions about the reaction mechanism and the roles of solvent and solvent hydration on enzyme function

Nonaqueous Biocatalytic Synthesis of New Cytotoxic Doxorubicin Derivatives: Exploiting Unexpected Differences in the Regioselectivity of Salt-Activated and Solubilized Subtilisin

Two enzymes, Mucor javanicus lipase and subtilisin Carlsberg (SC), catalyzed the nonaqueous acylation of doxorubicin (DOX). Compared to the untreated enzyme the rate of DOX acylation at the C-14 position with vinyl butyrate in toluene was 25-fold higher by lipase ion-paired with Aerosol OT (AOT) and 5-fold higher by lipase activated by 98% (w/w) KCl co-lyophilization (3.21 and 0.67 μmol/min g-lipase, respectively, vs 0.13 μmol/min g-lipase). Particulate subtilisin Carlsberg (SC) was nearly incapable of DOX acylation, but ion-paired SC (AOT-SC) catalyzed acylation at a rate of 2.85 μmol/min g-protease. The M. javanicus formulations, AOT-SC, and SC exclusively acylated the C14 primary hydroxyl group of DOX. Co-lyophilization of SC with 98% (w/w) KCl expanded the enzyme's regiospecificity such that KCl-SC additionally acylated the C4‘ hydroxyl and C3‘ amine groups. The total rate of DOX conversion with KCl-SC was 56.7 μmol/min g-protease. The altered specificity of KCl-SC is a new property of the enzyme imparted by the salt activation, and represents the first report of unnatural regioselectivity exhibited by a salt-activated enzyme. Using AOT-SC catalysis, four unique selectively acylated DOX analogues were generated, and KCl-SC was used to prepare DOX derivatives acylated at the alternative sites. Cytotoxicities of select derivatives were evaluated against the MCF7 breast cancer cell line (DOX IC50 = 27 nM) and its multidrug-resistant sub-line, MCF7-ADR (DOX IC50 = 27 μM). The novel derivative 14-(2-thiophene acetate) DOX was relatively potent against both cell lines (IC50 of 65 nM and 8 μM, respectively) and the 14-(benzyl carbonate) DOX analogue was as potent as DOX against the MCF7 line (25 nM). Activated biocatalysts and their novel regioselectivity differences thus enabled single-step reaction pathways to an effective collection of doxorubicin analogues

Metal–Organic Framework-Based Composite for Photocatalytic Detection of Prevalent Pollutant

Photocatalytic properties of 2,5-furandicarboxylic acid (FDCA), a model organic molecule used for biopolymer production, are reported for the first time. Further integration of FDCA into metal–organic framework (MOF) structures and subsequent silver-based photoactivation leads to the next generation of hybrids with controlled morphologies, capable of forming sensorial platforms for prevalent phenol contaminant detection. The mechanisms that allow photocatalytic functionality are driven by the charge carrier generation in the organic molecule (either in its alone or integrated form) and depend on sample’s physical and chemical properties as confirmed by scanning and transmission electron microscopy, Fourier transform infrared and X-ray photoelectron spectroscopy, and X-ray diffraction, respectively. Electrochemical analysis using cyclic voltammetry confirmed high sensitivity for p-nitrophenol (p-NP) detection as dictated by the selective electron migration at a user-controlled electrode interface. Considering the wide usage of p-NP and its increased discharge shown to lead to harmful effects on both the environment and biosystems, this new detection method is envisioned to allow effective control and regulation of such compound release, all under low-cost and environmentally friendly conditions

Flexible Peptide Linkers Enhance the Antimicrobial Activity of Surface-Immobilized Bacteriolytic Enzymes

Chemical linkers are frequently used in enzyme immobilization to improve enzyme flexibility and activity, whereas peptide linkers, although ubiquitous in protein engineering, are much less explored in enzyme immobilization. Here, we report peptide-linker-assisted noncovalent immobilization of the bacteriolytic enzyme lysostaphin (Lst) to generate anti-Staphylococcus aureus surfaces. Lst was immobilized through affinity tags onto a silica surface (glass slides) and nickel nitrilotriacetic acid (NiNTA) agarose beads via silica-binding peptides (SiBPs) or a hexahistidine tag (His-tag) fused at the C-terminus of Lst, respectively. By inserting specific peptide linkers upstream of the SiBP or His-tag, the immobilized enzymes killed >99.5% of S. aureus ATCC 6538 cells (108 CFU/mL) within 3 h in buffer and could be reused multiple times without significant loss of activity. In contrast, immobilized Lst without a peptide linker was less active/stable. Molecular modeling of Lst–linker–affinity tag constructs illustrated that the presence of the peptide linkers enhanced the molecular flexibility of the proximal Lst binding domain, which interacts with the bacterial substrate, and such increased flexibility correlated with increased antimicrobial activity. We further show that Lst immobilized onto NiNTA beads retained the ability to kill ∼99% of a 108 CFU/mL microbial challenge even in the presence of 1% of a commercial anionic surfactant, C12-14 alcohol EO 3:1 sodium sulfate, when the Lst construct contained a decapeptide linker containing glycine, serine, and alanine residues. This linker-assisted immobilization strategy could be extended to an unrelated lytic enzyme, the endolysin PlyPH, to target Bacillus anthracis Sterne cells either in buffer or in the presence of anionic surfactants. Our approach, therefore, provides a facile route to the use of antimicrobial enzymes on surfaces

Directed Assembly of Carbon Nanotubes at Liquid−Liquid Interfaces: Nanoscale Conveyors for Interfacial Biocatalysis

We report that single-walled carbon nanotubes (SWNTs) can be directed to aqueous−organic interfaces with the aid of surfactants. This phenomenon can also be used to transport enzymes to the interface to effect biphasic biotransformations. Consequently, SWNT−enzyme conjugates enhance the rate of catalysis by up to 3 orders of magnitude relative to the rates obtained with native enzymes in similar biphasic systems. Furthermore, we demonstrate that this concept can be extended to other nanomaterials and other enzymes, thereby providing a general strategy for efficient interfacial biocatalysis. The ability to direct the assembly of nanotubes at the interface also provides an attractive route to organizing these nanomaterials into 2D architectures