The beta-carotene radical cation and deprotonated neutral radicals were studied at the density functional theory (DFT) level using different density functionals and basis sets: B3LYP/3-21G, SVWN5/6-31G*, BPW91/DGDZVP2, and B3LYP/6-31G**. The geometries, total energies, spin distributions, and isotropic and anisotropic hyperfine coupling constants of these species were calculated. Deprotonation of the methyl group at the double bond of the cyclohexene ring of the carotenoid radical cation at 5 or 5' produces the most stable neutral radical because of retention of the pi-conjugated system while less stable deprotonation at 9 or 9' and 13 or 13' of the chain methyl groups causes significant distortion of the conjugation. The predicted methyl hyperfine coupling constants of 13-16 MHz of the neutral radicals are in good agreement with the previous electron nuclear double resonance (ENDOR) spectrum of photolyzed beta-carotene on a solid support. DFT calculations on the beta-carotene radical cation in a polar water environment showed that the polar environment does not cause significant changes in the proton hyperfine constants from those in the isolated gas-phase molecule. DFT calculated methyl proton hyperfine coupling constants of less than 7.2 MHz are in agreement with those reported for the radical cation in photosystem II (PS II) and those found in the absence of UV light for the radical cation on a silica alumina matrix.
Photooxidation of β-carotene and canthaxanthin in mesoporous MCM-41, Ni-MCM-41, and Al-MCM-41 molecular sieves was studied by 9-220 GHz electron paramagnetic resonance (EPR) and 9 GHz electron nuclear double resonance (ENDOR). X-ray powder diffraction (XRD) measurements established that the MCM-41 pore size (33 Å) was large enough to accommodate carotenoids. Mesoporous MCM-41 molecular sieves are found to be promising hosts for long-lived photoinduced charge-separation between carotenoid radical cations (Car •+ ) and the MCM-41 framework. Incorporating metal ions into siliceous MCM-41 enhances efficiency of carotenoid oxidation. The photoyield and stability of generated carotenoid radical cations increased in the order MCM < Ni-MCM < Al-MCM. Formation of carotenoid radical cations within the Me-MCM-41 is due to electron transfer between incorporated carotenoid molecules and metal ions, which act as electron acceptor sites. Detected EPR signals of Ni(I) species provide direct evidence for the reduction of Ni(II) ions by carotenoids. The presence of Ni(II) ions in Ni-MCM-41 was verified by 220 GHz EPR spectroscopy. ENDOR measurements revealed that the central C13-CH 3 and C13′-CH 3 groups of both carotenoids in Al-MCM-41 are rapidly rotating, while mobility of the C9-CH 3 and C9′-CH 3 groups is restricted. We propose that carotenoids are bound to the MCM-41 pore walls via the ends of the polyene chain in close proximity to the C9,9′-CH 3 groups.
Contact-active antibacterial surfaces play a vital role in preventing bacterial contamination of artificial surfaces. In the past, numerous researches have been focused on antibacterial surfaces comprising of antifouling upper-layer and antibacterial sub-layer. In this work, we demonstrate a reversed surface structure which integrate antibacterial upper-layer and antifouling sub-layer. These surfaces are prepared by simply casting gemini quaternary ammonium salt waterborne polyurethanes (GWPU) and their blends. Due to the high interfacial energy of gemini quaternary ammonium salt (GQAS), chain segments containing GQAS can accumulate at polymer/air interface to form an antibacterial upper-layer spontaneously during the film formation. Meanwhile, the soft segments composed of polyethylene glycol (PEG) formed the antifouling sub-layer. Our findings indicate that the combination of antibacterial upper-layer and antifouling sub-layer endow these surfaces strong, long-lasting antifouling and contact-active antibacterial properties, with a more than 99.99% killing efficiency against both gram-positive and gram-negative bacteria attached to them.
We have prepared Langmuir−Blodgett monolayers of hexadecylquinolinium tricyanoquinodimethanide
(C16H33Q+-3CNQ-) on gold surfaces and characterized the structure by surface plasmon resonance (SPR),
X-ray photoelectron spectroscopy (XPS), reflection−absorption infrared spectroscopy (RAIRS), Raman
spectroscopy, and water contact angle measurements. We compare the IR and UV−vis spectra of C16H33Q+-3CNQ- to a series of compounds that contain the key functional groups in the titled compound to help assign
the spectral features. The surface spectroscopic measurements indicate that the molecules in the monolayer
are aligned such that the two terminal cyano groups are adsorbed on the Au surface, and that the aliphatic
chain is away from that surface. The thickness of the monolayer was measured by XPS to be ∼ 26 Å and
suggests that the molecules are tilted ∼40° away from the surface normal. High-resolution XPS and
spectroelectrochemical measurements of C16H33Q+-3CNQ- strongly suggest that it is a ground-state zwitterion
in both the adsorbed and solvated forms.
Carotenoids (Car), β-Carotene (I), 8′-apo-β-caroten-8′-al (II), and canthaxanthin (III), incorporated into activated Cu-MCM-41 were examined by UV/vis and EPR spectroscopies. A Cu 2+ -Car complex was formed for I and III but not for II. Formation of a complex results in distortion of the all-trans carotenoid geometry and a tetragonal geometry for Cu 2+ . The binding energies of Car and Cu 2+ , the changes in the maximum absorption, and the bond lengths of Car after the formation of the Cu 2+ -Car complex were examined by semiempirical ZINDO/1 and ZINDO/S calculations. Formation of a complex between Car and Cu 2+ favors both forward and back electron transfer (ET) reactions due to the short distance (∼2 Å) between Car and Cu 2+ , and reversible ET appears upon temperature cycling.
Fast
and easily distinguishable color change is the simplest sensor signal
recognized by naked eyes. Rapid color change has been done via filling
or removing liquid inside channels constructed by multilayered reflectors
in biological species for camouflage or signaling. By mimicking it,
a test paper for fast detection of similar organic solvents or water-content
in ethanol has been designed based on nanocomposite films composed
of cellulose nanocrystals (CNC) and polyvinylpyrrolidone (PVP) with
chiral nematic structure. The chiral nematic architecture and structural
color of CNC can be kept in CNC/PVP nanocomposites in a wide range
of PVP content, up to 70 wt %. Moreover, we have observed that the
nanocomposite containing higher weight percentage of PVP showed more
distinguishable color difference while dipping in similar solvents.
Owing to the wide solubility of PVP in organic solvents and the magnifying
effect via increasing content of PVP, CNC/PVP nanocomposite films
can work as discrimination sensors by presenting apparent color change
while being dipping in several groups of similar organic solvents,
such as homologues (methanol/ethanol), skeletal isomers (1-propanol/2-propanol),
halogenated hydrocarbons (choloroform/dichloromethane), and even ethanol
containing a small amount of water. The fast color change of CNC/PVP
has been induced by the sensitive response of its structural color
to the volume fraction change of CNC in the swollen state.
In this paper, polymer nanocapsules embedded with noble metal nanoparticles and showing a good catalytic activity were prepared by a novel and convenient method.
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