Triclosan–lysozyme complex: A promising antimicrobial macromolecule stable against photooxidative damage

The oxidative stability of bioactive proteins is a critical issue in the food and drug development process. Recently, we explored a superior and multi-faceted antimicrobial compound by coupling the lytic enzyme lysozyme (LZ) to a phenolic antibiotic triclosan (TCS) via electrostatic and hydrophobic condensations at alkaline pH. To explore the candidacy of LZ–TCS complex (T–LZ) in food systems, its stability against photooxidative damage has been investigated in this study using riboflavin (RF) as a sensitizer. Electrophoretic and Tryptophan (Trp) fluorescence spectra revealed significant protection of LZ conformation in T–LZ complexes against mild or excessive photooxidative treatment using equivalent to variable mole ratios of RF over LZ. The promoted muramidase activity of T–LZ complexes, reported in our previous study, was markedly protected against both mild and excessive photooxidative treatments. However, LZ alone exhibited polymerization, fragmentation and quenching of Trp fluorescence upon photooxidation reaction. This suggests that in the complexes TCS binds with the tryptophan residues at LZ active site and thereby inhibits oxidation. Further, the complex retained its strong antimicrobial activity against several Gram-positive and Gram-negative bacteria even upon photooxidative treatment while causing a dramatic reduction in antimicrobial activity of TCS alone. The results indicate that accommodation of the TCS in the hydrophobic pocket of LZ does not only protect LZ from oxidation-induced loss of biological activities but also protect phenolic antimicrobial TCS from oxidative damage until its delivery to the bacterial cell. The finding, therefore, offers a new strategy in designing an oxidation-resistant microbicidal phenol–protein macromolecule with potential use in food and drug systems.     

Phosphorylation of proteins by dry-heating in the presence of pyrophosphate and some characteristics of introduced phosphate groups

Various proteins and dextrin were phosphorylated by dry-heating in the presence of pyrophosphate, and phosphate bonds characterised. The basic proteins were more highly phosphorylated than acidic proteins by dry-heating in the presence of pyrophosphate. The phosphorylated poly-l-lysine hydrobromide (PP-PLy) and lysozyme (PP-Lz) were more highly dephosphorylated than phosphorylated dextrin and ovalbumin (PP-OVA) by phosphatases, and the dephosphorylation of PP-PLy was much higher than that of PP-Lz. The phosphate bonds in all phosphorylated samples were stable during heating at 120 °C. The ³¹P NMR spectral data suggested that different types of phosphate bonds were introduced, and the N–P bond was suggested in PP-PLy. Some phosphorylated tryptic peptides from PP-Lz and PP-OVA were detected by mass spectrometry analysis. Furthermore, the introduced phosphate linkages in peptides from PP-Lz and PP-OVA were identified.     

Hyperbranched Polyglycerol‐Grafted Superparamagnetic Iron Oxide Nanoparticles: Synthesis,Characterization, Functionalization,Size Separation,Magnetic Properties,and Biological Applications

For biomedical application of nanoparticles, the surface chemical functionality is very important to impart additional functions, such as solubility and stability in a physiological environment, and targeting specificity as an imaging probe and a drug carrier. Although polyethylene glycol (PEG) has been used extensively, here, it is proposed that hyperbranched polyglycerol (PG) is a good or even better alternative to PEG. Superparamagnetic iron oxide nanoparticles (SPIONs) prepared using a polyol method are directly functionalized with PG through ring‐opening polymerization of glycidol. The resulting SPION‐PG is highly soluble in pure water (>40 mg mL^?1) and in a phosphate buffer solution (>25 mg mL^?1). Such high solubility enables separation of SPION‐PG according to size using size exclusion chromatography (SEC). The size‐separated SPION‐PG shows a gradual increase in transverse relaxivity (r₂) with increasing particle size. For biological application, SPION‐PG is functionalized through multistep organic transformations (–OH → –OTs (tosylate) → –N₃ → –RGD) including click chemistry as a key step to impart targeting specificity by immobilization of cyclic RGD peptide (Arg‐Gly‐Asp‐D ‐Tyr‐Lys) on the surface. The targeting effect is demonstrated by the cell experiments; SPION‐PG‐RGD is taken up by the cells overexpressing α_vβ₃‐integrin such as U87MG and A549.     

Involvement of β-Alkylation Machinery and Two Sets of Ketosynthase-Chain-Length Factors in the Biosynthesis of Fogacin Polyketides in Actinoplanes missouriensis

Fogacin and two novel fogacin derivatives, fogacins B and C, were isolated from the rare actinomycete Actinoplanes missouriensis. Biosynthesis of fogacin C apparently requires β alkylation of a polyketide chain. The fogacin biosynthetic type II polyketide synthase (PKS) gene cluster contains a hydroxymethylglutaryl-coenzyme A synthase (HCS) cassette, which is usually responsible for β alkylation in the type I PKS system. Another characteristic of the fog cluster is that it encodes two sets of ketosynthase (KS) and chain-length factor (CLF). Inactivation of either of the two KS genes in A. missouriensis and heterologous expression of the HCS cassette with either of the two KS-CLF genes in Streptomyces albus indicated that each KS-CLF had a different starter substrate specificity: one preferred an unusual β-alkylated starter and the other preferred a normal acetyl starter. This study expands knowledge of HCS cassette-dependent β alkylation into the type II PKS system and provides a natural example of combinatorial biosynthesis for producing diverse polyketides from different starter substrates.     

Improvement of functional properties of whey soy protein phosphorylated by dry-heating in the presence of pyrophosphate

The physicochemical and functional properties of a whey soyprotein (WSP), which was phosphorylated by dry heating, were investigated. The phosphorus content of WSP was 0.85 g/100 g by dry-heating at pH 4.0 for 5 days in the presence of pyrophosphate. ³¹P NMR spectral data suggested that the serine and sugar of WSP were phosphorylated. Although changes in the random coil structure of WSP measured by circular dichroism were mild, increased surface hydrophobicity and decreased tryptophan fluorescence intensity were observed following phosphorylation. Phosphorylation improved the stability against heat-induced insolubility, emulsifying properties, foaming properties, water absorption capacity, and oil absorption capacity of WSP. These results suggested that dry-heating phosphorylation is a useful method for improving the functional properties of WSP.     

Submillimetre-wave lines of H2D+ and D2H+ as probes into chemistry in cold dark clouds

We discuss past and recent progress of our continuing project of submillimetre-wave spectroscopic investigations of H2D+ and D2H+. Three new lines of H2D+ in the 2.5-3.5 THz range are measured with a tunable far-infrared laser system. Since these molecules are very light asymmetric molecules, analysis based on a conventional effective Hamiltonian is not very useful in predicting the transition frequencies to the accuracy of the order of several MHz or better. In this respect, any addition of new accurate measurements of transition frequencies is important. In this paper, some discussions will be made on H5+ and its deuterated species as probable interstellar species in cold dark clouds. In particular, D3+, which is predicted to be abundant in cold dark clouds, can be (indirectly) detected by observing D3+ x H2.     

Surface pressure induced charge transfer between fullerene and tetrathiafulvalene derivative in Langmuir-Blodgett films

Structures and electronic states of a 1:1 mixture of bis-tetrathiafulvalene annulated macrocycle (1) and C60 in Langmuir films at the air-water interface and Langmuir-Blodgett (LB) films on solid substrates were examined. Compression of the Langmuir films induced for the first time a phase transition from a weakly interacting state without charge transfer (CT) to a neutral CT state. The scanning force microscope images of LB films transferred onto mica by a single withdrawal showed quite different spatial patterns depending on the CT states. When deposited at around 1 mNm(-1), a domain structure with 3 nm height was obtained, which corresponded to the state without CT interaction. Contrastingly, once the CT interaction was induced by applying surface pressure, a network structure was observed with a height of 6 nm. The CT band, whose transition moment was almost parallel to the substrate surface, was observed at 11.5 x 10(3) cm(-1) in the polarized UV-VIS-NIR spectra of the films deposited at 9 mNm(-1). The phase transition was irreversible, although the surface pressure-area isotherm showed a reversible behavior below 9 mNm(-1). The morphology and electronic state of the film was controllable merely by changing the surface pressure at the air-water interface.     

Two-dimensional dielectric nanosheets: novel nanoelectronics from nanocrystal building blocks

Two-dimensional (2D) nanosheets, which possess atomic or molecular thickness and infinite planar lengths, are regarded as the thinnest functional nanomaterials. The recent development of methods for manipulating graphene (carbon nanosheet) has provided new possibilities and applications for 2D systems; many amazing functionalities such as high electron mobility and quantum Hall effects have been discovered. However, graphene is a conductor, and electronic technology also requires insulators, which are essential for many devices such as memories, capacitors, and gate dielectrics. Along with graphene, inorganic nanosheets have thus increasingly attracted fundamental research interest because they have the potential to be used as dielectric alternatives in next-generation nanoelectronics. Here, we review the progress made in the properties of dielectric nanosheets, highlighting emerging functionalities in electronic applications. We also present a perspective on the advantages offered by this class of materials for future nanoelectronics.     

Phosphorylation of ovalbumin by dry-heating in the presence of pyrophosphate: Effect of carbohydrate chain on the phosphorylation level and heat stability

Ovalbumin (OVA) derived from egg white (N-OVA) and recombinant OVA (Re-OVA), which was essentially carbohydrate-free, expressed by Escherichia coli, were phosphorylated by dry-heating for 1 day in the presence of pyrophosphate (PP-N- and PP-Re-OVA). The phosphorus contents of N- and Re-OVA were 0.79% and 0.46%, respectively, after phosphorylation. The secondary structural change of both OVAs was small, and the midpoint temperature of both OVAs determined from the thermal unfolding curve was decreased by phosphorylation. In addition, the differential scanning calorimetry thermograms of both OVAs showed a lowering of denaturation temperature by phosphorylation. The stability of both OVA solutions after heating at pH 7.0 was improved, and the degree of stabilization was higher for PP-N-OVA than for PP-Re-OVA. This suggests that the phosphate groups introduced to the carbohydrate chain also play an important role in the heat stability of OVA.