Chirality-Regulated Clusteroluminescence in Polypeptides.

The low emission efficiency of clusteroluminogens restricts their practical applications in the fields of sensors and biological imaging. In this work, the clusteroluminescence of ordered/disordered polypeptides was observed, and the photoluminescence (PL) intensity of polypeptides can be modulated by the chirality of amino acid residues. Polyglutamates with different chiral compositions were synthesized, and the racemic polypeptides exhibited a significantly higher PL intensity than the enantiopure ones. This emission originates from the n-π* transition between C═O groups of polypeptides and is enhanced by clusterization of polypeptides. CD and Fourier transform infrared spectra demonstrated that the enantiopure and racemic polypeptides form α-helix and random coil structures, respectively. The disordered polypeptides can form more chain entanglements and interchain interactions because of their high flexibility, leading to more clusterizations and stronger PL intensity. The rigidity of ordered helical structures restrains the chain entanglements, and the formation of intrachain hydrogen bonds between amide groups of the backbone impairs the interchain interaction between polypeptides, resulting in lower PL intensity. The PL intensity of the polypeptides can also be manipulated by the addition of urea or trifluoroacetic acid. Our study not only elucidates the chirality/order-based structure-property relationship of clusteroluminescence in peptide-based polymers but also offers implications for the rational design of fluorescent peptides/proteins.

Syntheses, Crystal Structures and Antimicrobial Property of Schiff Base Copper(II) Complexes.

Four new copper(II) complexes, [CuL1(?1,1-N3)]n (1), [CuL1(?1,3-NCS)]n (2), [Cu(HL2)2](SCN)2 (3) and [Cu(L2)2] (4), where L1 and L2 are 2-((2-(dimethylamino)ethylimino)methyl-4,6-difluorophenolate and 2,4-difluoro-6-((3-morpholinopropylimino) methyl)phenolate, respectively, and HL2 is 2-((2-(dimethylammonio)ethylimino)methyl-4,6-difluorophenolate, were synthesized and characterized by elemental analysis, IR and UV-vis spectroscopy. The structures for the complexes were further confirmed by single crystal X-ray structure determination. Complexes 1 and 2 are polymeric copper(II) complexes, with the Cu atoms in square pyramidal coordination. Complexes 3 and 4 are mononuclear copper(II) complexes, with the Cu atoms in square planar coordination. The complexes were assayed for their antimicrobial properties.

Two Vanadium(V) Complexes Derived from Bromo and Chloro-Substituted Hydrazone Ligands: Syntheses, Crystal Structures and Antimicrobial Property.

Two vanadium(V) complexes derived from the bromo and chloro-substituted hydrazones N'-(4-bromo-2-hydroxybenzylidene)- 2-chlorobenzohydrazide (H2L1) and N'-(3-bromo-5-chloro-2-hydroxybenzylidene)-3-methylbenzohydrazide (H2L2) with the formula [VOL1(OCH3)(CH3OH)] (1) and [VOL2(OCH3)(CH3OH)] (2) were newly synthesized and characterized by IR, UV-Vis and 1H NMR spectroscopy. The structures of H2L1 and the complexes were further confirmed by single crystal X-ray diffraction. Both vanadium complexes are mononuclear, with the metal atoms coordinated by the hydrazone ligands, methanol ligands, and methanolate ligands, and the oxo groups, forming octahedral geometry. The hydrazones and the vanadium complexes were assayed for the antimicrobial activities on Bacillus subtilis, Staphylococcus aureus, Escherichia coli, and Pseudomonas fluorescence, and the fungi Candida albicans and Aspergillus niger. The existence of the bromo and chloro groups in the hydrazone ligands may improve the antimicrobial property.