Niraikulam Ayyadurai

In Vivo Residue‐Specific Dopa‐Incorporated Engineered Mussel Bioglue with Enhanced Adhesion and Water Resistance

Misaminoacylation of 3,4-dihydroxyphenylalanine (Dopa) molecules to tRNA(Tyr) by endogenous tyrosyl-tRNA synthetase allowed the quantitative replacement of tyrosine residues with a yield of over 90 % by an in vivo residue-specific incorporation strategy, to create, for the first time, engineered mussel adhesive proteins (MAPs) in Escherichia coli with a very high Dopa content, close to that of natural MAPs. The Dopa-incorporated MAPs exhibited a superior surface adhesion and water resistance ability by assistance of Dopa-mediated interactions including the oxidative Dopa cross-linking, and furthermore, showed underwater adhesive properties comparable to those of natural MAPs. These results propose promising use of Dopa-incorporated engineered MAPs as bioglues or adhesive hydrogels for practical underwater applications.

Photoswitchable azobenzene–rhodamine tweezers for biosensing of Al3+ ions

Dominant excited state photochemical deactivation over the radiative decay pathway of azobenzene enables this molecule to be non-fluorescent despite its rich π-conjugation. Partial or complete control over the photoisomerization reaction is indispensable in making this molecule fluorescent. To control the excited state properties of azobenzene, we have covalently coupled it with a spirocyclic rhodamine unit through a p-phenylmethanimine bridge. While the characteristic weak fluorescence and trans → cis photoisomerization of azobenzene have not been affected by spirocyclic rhodamine, selective Al3+ ion induced spirocyclic ring opening prevents the photoisomerization with a concomitant enhancement in fluorescence. This process is reversed by the addition of a F− ion. The occurrence of fluorescence resonance energy transfer (FRET) from azobenzene to rhodamine and light catalyzed spirocyclic ring opening reactions underscore that the azobenzene excited state can be altered without affecting its core structure. Indeed, the light catalyzed ring opening reaction helps to enhance the signal intensity, which would be advantageous in detecting Al3+ ions at lower concentrations. The applicability of the probe has been tested in prokaryotic and eukaryotic cell lines, where turn-on, intense fluorescence in the presence of Al3+ ions was observed.

A Low-Molecular-Weight Gelator Composed of Pyrene and Fluorene Moieties for Effective Charge Transfer in Supramolecular Ambidextrous Gel

Charge-transfer (CT) gel materials obtained from low-molecular-weight (LMW) compounds through a supramolecular self-assembly approach have received fascinating attention by many researchers because of their interesting material property and potential applications. However, most of the CT gel materials constructed were of organogels while the construction of CT gels in the form of a hydrogel is a challenge because of the solubility issue in water, which considerably limits the use of CT hydrogels. Herein, for the first time, we report a new LMW gelator [Nα-(fluorenylmethoxycarbonyl)-Nε-(δ-butyric-1-pyrenyl)-l-lysine, (FmKPy)], composed of two functional moieties such as fluorenylmethoxycarbonyl and pyrene, which not only parade both hydro and organo (ambidextrous) supramolecular gel formation but also exhibit CT ambidextrous gels when mixed with an electron acceptor such as 2,4,7-trinitro-9-fluorenone (TNF). This finding is significant as the established CT organogelator in the literature did not form an organogel in the absence of an electron acceptor or lose their gelation property upon the addition of the acceptor. CT between pyrene and TNF was confirmed by the color change as well as the appearance of the CT band in the visible region of the absorption spectrum. CT between FmKPy and TNF was supported by the solvent dilution method using tetrahydrofuran as the gel breaker and pyrene fluorescence quenching in the case compound containing pyrene and TNF. The morphology of FmKPy ambidextrous gels indicates the fibrous nature while the self-assembled structure is primarily stabilized by π-π stacking among fluorenyl and pyrenyl moieties and hydrogen bonding between amide groups. The FmKPy-TNF CT ambidextrous gel retains the fibrous nature; however, the size of the fibers changed. In FmKPy-TNF CT gels, TNF is intercalated between pyrene moieties in the self-assembled structure as confirmed by fluorescence quenching and powder X-ray diffraction. The FmKPy ambidextrous gel exhibits significant properties such as low minimum gelation concentration (MGC), thixotropic nature, pH stimuli response, and high thermal stability. Upon the addition of TNF, the FmKPy-TNF CT ambidextrous gel maintains all these properties except MGC which increased for FmKPy-TNF. Because pyrene-based LMW organogels have been developed widely for many applications while their hydrogels were limited, the current finding of the pyrene-based ambidextrous fluorescent gel with the CT property provides a wide opportunity to use FmKPy as a soft material maker and also for potential applications in fields like surface coating, three-dimensional printing, and so forth.

Psychrosphaera aquimarina sp. nov., a marine bacterium isolated from seawater collected from Asan Bay, Republic of Korea

Cells of strain SW33T, isolated from the seawater of Asan Bay, Republic of Korea, were characterized as Gram-stain-negative, aerobic, rod-shaped, motile and non-spore-forming. Phylogenetic analysis revealed that strain SW33T belonged to the genus Psychrosphaera and clustered distantly with the other genera in the family Pseudoalteromonadaceae in the phylogenetic tree. The 16S rRNA sequences of strain SW33T revealed high similarities to Psychrosphaera saromensis SA4-48T (98.7 %), Psychrosphaera haliotis KDW4T (97.4 %) and Psychrosphaera aestuarii PSC101T (97.3 %). The major fatty acids were C16 : 0 (27.9 %), summed feature 3 (32.2 %) and summed feature 8 (17.2 %). The predominant quinone was Q-8, and the polar lipid profile consisted of diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol and an unidentified amino lipid. The DNA G+C content was 38.3 mol%. The DNA-DNA relatedness values with the three species of Psychrosphaera saromensis KCTC 23240T, Psychrosphaera haliotis KCTC 22500T and Psychrosphaera aestuarii KCTC 32274T were 22, 23 and 18 %, respectively. Based on the phenotypic characteristics and taxonomic analyses, we propose that strain SW33T represents a novel species within the genus Psychrosphaera, for which the name Psychrosphaera aquimarina sp. nov. with the type strain SW33T (=KCTC 52743T=CICC 24249T) is proposed.

Gated photochromism in azobenzene-appended rhodamine cassette: through-bond energy transfer – a universal strategy towards “Lock and Unlock” system

A dyad 1 comprising fluorescent rhodamine and photochromic azobenzene covalently linked through a phenylene bridge, which still retains their individual electronic properties, was synthesized. Gating between the fluorescent and photochromic properties of the dyad in the presence of external stimuli such as light or cations/anions or both paved the way for the development of new stimuli-responsive molecular materials. Among the several metal ions, Fe3+ ion was found to be selective in inducing the spirocyclic ring opening reaction of rhodamine, which can be witnessed through turn-on fluorescence. Fe3+-bound dyad 1 precluded the traditional trans → cis isomerization of remotely connected azobenzene and catalysed the spirocyclic ring opening reaction, which led to fluorescence enhancement by a factor of 640. The fluorescence enhancement originated from through-bond energy transfer upon excitation of azobenzene. Indeed, the turn-on fluorescence and optical changes upon UV irradiation indicated that this material can be used as a probe to monitor harmful UV radiation. The distinctly different responses of 1 concerning physical stimuli (light) and chemical stimuli (Fe3+ and F− ions) make this molecule a multi-addressable functional material.