Biocatalytic Modification of Naturally Occurring Iron Porphyrin

Hematin, a hydroxyferriprotoporphyrin, is the stable, oxidized form of heme. Heme has been reported to be the active catalytic center of naturally occurring peroxidases such as horseradish peroxidase (HRP). While there have been reports on the use of hematin as a catalyst for oxidative polymerization reactions, these reactions could be carried out only at high pH conditions due to limited aqueous solubility of hematin at lower pH conditions. We report here the biocatalytic modification of hematin using a lipase, Novozyme-435. Hematin has been modified by tethering monomethoxy polyethylene glycol (mPEG) chains which provide aqueous solubility over a fairly wide range of pH conditions. This pegylated Hematin (PEG-Hematin) is synthesized via a one-step solventless reaction and the products formed can be isolated with minimal purification. The PEG-Hematin synthesized serves as a robust alternative to HRP for the polymerization of aniline and phenol.     

Rose Oxides: A Facile Chemo and Chemo‐Enzymatic Approach

Nonracemic rose oxides were synthesized from racemic or nonracemic monoterpene alcohol citronellol by a novel chemo and chemo‐enzymatic route. After the key step of bromomethoxylation of citronellol, the intermediate was dehydrobrominated by a base, followed by an acid catalyzed demethoxylation along with cyclization to furnish rose oxides in high yield. The racemic dehydrobrominated precursor was also kinetically resolved using various lipases to produce nonracemic rose oxides.     

Solid‐State Structural Characterization of Cutinase–ECE‐Pincer–Metal Hybrids

Crystal‐clear structures : The first crystal structures of organometallic pincer–cutinase hybrids (see figure) provide insight into the 3D structural arrangement of both the protein and the organometallic pincer moiety, and reveal different binding modes for different pincers.

     

Lipase active-site-directed anchoring of organometallics: metallopincer/protein hybrids

The work described herein presents a strategy for the regioselective introduction of organometallic complexes into the active site of the lipase cutinase. Nitrophenol phosphonate esters, well known for their lipase inhibitory activity, are used as anchor functionalities and were found to be ideal tools to develop a single-site-directed immobilization method. A small series of phosphonate esters, covalently attached to ECE "pincer"-type d8-metal complexes through a propyl tether (ECE=[C6H3(CH2E)(2)-2,6]-; E=NR2 or SR), were designed and synthesized. Cutinase was treated with these organometallic phosphonate esters and the new metal-complex/protein hybrids were identified as containing exactly one organometallic unit per protein. The organometallic proteins were purified by membrane dialysis and analyzed by ESI-mass spectrometry. The major advantages of this strategy are: 1) one transition metal can be introduced regioselectively and, hence, the metal environment can potentially be fine-tuned; 2) purification procedures are facile due to the use of pre-synthesized metal complexes; and, most importantly, 3) the covalent attachment of robust organometallic pincer complexes to an enzyme is achieved, which will prevent metal leaching from these hybrids. The approach presented herein can be regarded as a tool in the development of regio- and enantioselective catalyst as well as analytical probes for studying enzyme properties (e.g., structure) and, hence, is a "proof-of-principle design" study in enzyme chemistry.     

Force-field parameters for the simulation of tetrahedral intermediates of serine hydrolases

CHARMM force-field parameters are reported for the tetrahedral intermediate of serine hydrolases. The fitting follows the standard protocol proposed for CHARMM22. The reference data include ab initio (RHF/6-31G*) interaction energies of complexes between water and the model compound 1,1-dimethoxyethoxide, torsional profiles of related model compounds from correlated ab initio (MP2/6-311+G*//B3LYP/6-31+G*) calculations, as well as molecular geometries and vibrational frequencies from density functional theory (B3LYP/6-31+G*). The optimized parameters reproduce the target data well. Their utility is demonstrated by a QM/MM study of the tetrahedral intermediate in Bacillus subtilis lipase A, and by classical molecular modeling of enantioselectivity in Pseudomonas aeruginosa lipase and its mutants.     

Bacteria‐Triggered Release of Antimicrobial Agents

Medical devices employed in healthcare practice are often susceptible to microbial contamination. Pathogenic bacteria may attach themselves to device surfaces of catheters or implants by formation of chemically complex biofilms, which may be the direct cause of device failure. Extracellular bacterial lipases are particularly abundant at sites of infection. Herein it is shown how active or proactive compounds attached to polymeric surfaces using lipase‐sensitive linkages, such as fatty acid esters or anhydrides, may be released in response to infection. Proof‐of‐concept of the responsive material is demonstrated by the bacteria‐triggered release of antibiotics to control bacterial populations and signaling molecules to modulate quorum sensing. The self‐regulating system provides the basis for the development of device‐relevant polymeric materials, which only release antibiotics in dependency of the titer of bacteria surrounding the medical device.     

酶法拆分(±)-N-(2,6-二甲苯基)-丙氨酸甲酯

用脂肪酶Candida rugosa lipase (CRL)拆分(±)-N-(2,6-二甲苯基)-丙氨酸甲酯, 并进一步优化反应条件. 结果表明, 在加入1 mmol N-(2,6-二甲苯基)-丙氨酸甲酯、100 mL的0.2 mol/L磷酸缓冲液中, CRL拆分该底物的最适反应条件为: pH 6.4, CRL脂酶250 mg, 聚乙二醇(PEG) 2 g, 转速160 r•min^－1, 温度 35 ℃. 其中酶量、温度对转化率影响较大. 反应后分离得R-(＋)-N-(2,6-二甲苯基)-丙氨酸甲酯. 它和酰氯反应可制备一系列旋光性N-酰基丙氨酸类杀菌剂.