Mechanochromic Luminescence and Aggregation Induced Emission of Dinaphthoylmethane ß-Diketones and Their Boronated Counterparts.

Mechanochromic luminescence has been observed in many boron coordinated ß-diketonate (BF2bdk) complexes. Recently, it was shown that the metal-free methoxy-substituted dinaphthoylmethane ß-diketone (dnmOMe) also displayed aggregation induced emission (AIE), solvatochromism, and high contrast mechanochromic luminescence (ML) that recovered rapidly at room temperature. In order to understand how substituents and boron coordination affect solution and solid-state optical properties, a series of methoxy- and bromo-substituted derivatives (dnm, dnmOMe, dnmBr, and dnmBrOMe) and their corresponding boron complexes (BF2dnm, BF2dnmOMe, BF2dnmBr, and BF2dnmBrOMe) were synthesized and their AIE, ML, and room temperature recovery properties were compared. All boron complexes exhibited red-shifted absorption and emission, in addition to larger solution and solid-state quantum yields than ß-diketones. While AIE studies show increased emission for dnmOMe and dnmBrOMe, the emission of corresponding boron complexes diminished upon aggregation. However, boron complexes were still strongly emissive in the solid state. ML properties were investigated using spin-cast films. Smearing resulted in the appearance of blue-green emission in ligands and a color change from green to yellow-orange in boron complexes. Bromide substituted derivatives showed increased room temperature recovery times compared to other dnm ligands, and boron complexes show only partial recovery over several days.

Oxygen Sensing Difluoroboron Dinaphthoylmethane Polylactide.

Dual emissive luminescence properties of solid-state difluoroboron ß-diketonate-poly(lactic acid) (BF2bdk-PLA) materials have been utilized as biological oxygen sensors. Dyes with red-shifted absorption and emission are important for multiplexing and in vivo imaging, thus hydroxyl-functionalized dinaphthoylmethane initiators and dye-PLA conjugates BF2dnm(X)PLA (X = H, Br, I) with extended conjugation were synthesized. The luminescent materials show red-shifted absorbance (~435 nm) and fluorescence tunability by molecular weight. Fluorescence colors range from yellow (~530 nm) in 10 - 12 kDa polymers to green (~490 nm) in 20 - 30 kDa polymers. Room-temperature phosphorescence (RTP) and thermally activated delayed fluorescence (TADF) are present under a nitrogen atmosphere. For the iodine-substituted derivative, BF2dnm(I)PLA, clearly distinguishable fluorescence (green) and phosphorescence (orange) peaks are present, making it ideal for ratiometric oxygen-sensing and imaging. Bromide and hydrogen analogues with weaker relative phosphorescence intensities and longer phosphorescence lifetimes can be used as highly sensitive, concentration independent, lifetime-based oxygen sensors or for gated emission detection. BF2dnm(I)PLA nanoparticles were taken up by T41 mouse mammary cells and successfully demonstrated differences in vitro ratiometric measurement of oxygen.

Luminescent difluoroboron ß-diketonate PEG-PLA oxygen nanosensors for tumor imaging.

Surface modification of nanoparticles and biosensors is a dynamic, expanding area of research for targeted delivery in vivo. For more efficient delivery, surfaces are PEGylated to impart stealth properties, long circulation, and enable enhanced permeability and retention (EPR) in tumor tissues. Previously, BF2 dbm(I)PLA was proven to be a good oxygen nanosensor material for tumor hypoxia imaging in vivo, though particles were applied directly to the tumor and surrounding region. Further surface modification is needed for this dual-emissive oxygen sensitive material for effective intravenous (IV) administration and passive and active delivery to tumors. In this paper, an efficient synthesis of a new dual-emissive material BF2 dbm(I)PLA-mPEG is presented and in vitro stability studies are conducted. It is found that fabricated nanoparticles are stable for 24 weeks as a suspension, while after 25 weeks the nanoparticles swell and both dye and polymer degradation escalates. Preliminary studies show BF2 dbm(I)PLA-mPEG nanoparticle accumulation in a window chamber mammary tumor 24 h after IV injection into mice (C57Bl/6 strain) enabling tumor oxygen imaging.

Mechanochromic luminescence and aggregation induced emission for a metal-free ß-diketone.

Reversible mechanochromic luminescence (ML) is known for difluoroboron ß-diketonates (BF2bdks). Here, we report ML for the methoxy-substituted dinaphthoylmethane (dnmOMe) ligand even without coordination to boron. In addition, dnmOMe shows solvatochromism and aggregation-induced emission (AIE). Diketone thin films showed high contrast emission when smeared, and rapid recovery of the pre-smeared state at room temperature.

Dual-Emissive Difluoroboron Naphthyl-Phenyl ß-Diketonate Polylactide Materials: Effects of Heavy Atom Placement and Polymer Molecular Weight.

Luminescent materials are important for imaging and sensing. Aromatic difluoroboron ß-diketonate complexes (BF2bdks) are classic fluorescent molecules that have been explored as photochemical reagents, two-photon dyes, and oxygen sensors. A series of BF2bdks with naphthyl and phenyl groups was synthesized, and photophysical properties were investigated in both methylene chloride and poly(lactic acid) (PLA). Polymer molecular weight and dye attachment site along with bromide heavy atom placement were varied to tune optical properties of dye-PLA materials. Systems without heavy atoms have long phosphorescence lifetimes, which is useful for lifetime-based oxygen sensing. Bromine substitution on the naphthyl ring resulted in intense, clearly distinguishable fluorescence and phosphorescence peaks important for ratiometric oxygen sensing and imaging.

Mechanistic studies of reactions catalysed by diamine oxidase using isotope effects.

Diamine oxidase (DAO), the enzyme that is responsible for amine biodegradation in animals, plants and humans, catalyses the biotransformation of amines such as histamine (HA), putrescine, 1-phenylethylamine, tyrosine, tryptamine, serotonine and spermine. The kinetic and solvent isotope effects (SIEs) were applied to study the mechanism of the biotransformation using HA and its methylderivatives. The SIE for the biotransformation of HA, N(τ)-methylhistamine and N(π)-methylhistamine was found to be 3.58, 2.22 and 5.70 on Vmax, and 1.58, 1.06 and 1.14 on Vmax/KM, respectively. On the other hand, the kinetic isotope effect for oxidation of stereospecifically deuterium-labelled [(α R)-(2)H]-N(τ)-methylhistamine and [(α R)-(2)H]-N(π)-methylhistamine was 0.69 and 0.62 on Vmax, and 15.06 and 7.50 on Vmax/K(M), respectively. These results demonstrate that DAO catalyses amine biotransformation by stereospecifically cleaving the αC-H bond in the pro-S position. Moreover, the oxidation of amine to aldehyde involves several transition states, including hybridisation change from sp(3) (Schiff base) to sp(2) (imine), then back again to sp(3) to give a final product with hybridisation sp(2) (aldehyde).

Synthesis of a new class of ribose functionalized dinucleotide cap analogues for biophysical studies on interaction of cap-binding proteins with the 5' end of mRNA.

mRNAs of primitive eukaryotes such as Caenorhabditis elegans and Ascaris summ possess two different caps at their 5' terminus. They have either a typical cap which consists of 7-methylguanosine linked via a 5',5'-triphosphate bridge to the first transcribed nucleotide (MMG cap) or an atypical hypermethylated form with two additional methyl groups at the N2 position (TMG cap). Studies on interaction between the 5' end of mRNA and proteins that specifically recognize its structure have been carried out for several years and they often require chemically modified cap analogues. Here, we present the synthesis of five novel dinucleotide MMG and TMG cap analogues designed for binding studies using biophysical methods such as electron spin resonance (ESR) and surface plasmon resonance (SPR). New analogues were prepared by derivatization of the 2',3'-cis diol of the second nucleotide in the cap structure with levulinic acid, and coupling of the obtained acetal through its carboxylic group with 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl (4-amino TEMPO), ethylenediamine (EDA) or (+)-biotinyl-3,6,9-trioxaundecanediamine (amine-PEO(3)-biotin).