Organic Modification and Subsequent Biofunctionalization of Porous Anodic Alumina Using Terminal Alkynes

Abstract

Porous anodic alumina (PAA) is a well-defined material that has found many applications. The range of applications toward sensing and recognition can be greatly expanded if the alumina surface is covalently modified with an organic monolayer. Here, we present a new method for the organic modification of PAA based on the reaction of terminal alkynes with the alumina surface. The reaction results in the the formation of a monolayer within several hours at 80 °C and is dependent on both oxygen and light. Characterization with X-ray photoelectron spectroscopy and infrared spectroscopy indicates formation of a well-defined monolayer in which the adsorbed species is an oxidation product of the 1-alkyne, namely, its α-hydroxy carboxylate. The obtained monolayers are fairly stable in water and at elevated temperatures, as was shown by monitoring the water contact angle. Modification with 1,15-hexadecadiyne resulted in a surface that has alkyne end groups available for further reaction, as was demonstrated by the subsequent reaction of N-(11-azido-3,6,9-trioxaundecyl)trifluoroacetamide with the modified surface. Biofunctionalization was explored by coupling 11-azidoundecyl lactoside to the surface and studying the subsequent adsorption of the lectin peanut agglutinin (PNA) and the yeast Candida albicans, respectively. Selective and reversible binding of PNA to the lactosylated surfaces was demonstrated. Moreover, PNA adsorption was higher on surfaces that exposed the β-lactoside than on those that displayed the α anomer, which was attributed to surface-associated steric hindrance. Likewise, the lactosylated surfaces showed increased colonization of C. albicans compared to unmodified surfaces, presumably due to interactions involving the cell wall β-glucan. Thus, this study provides a new modification method for PAA surfaces and shows that it can be used to induce selective adsorption of proteins and microorganisms.

Organic Monolayers from 1-Alkynes Covalently Attached to Chromium Nitride: Alkyl and Fluoroalkyl Termination

“…This finding is strongly supported by the analogous reaction of 1-alkynes on the η-alumina surface, which also displays surfacebound carbonyl groups. 29 In contrast, alkynes were shown to bind to the silicon carbide surface via a double Markovnikov addition, 19 but that bonding situation yields significantly different spectra.…”

“…To circumvent such hydrolytic reactivity and to obtain a wider access to surface-modified substrates, our group has recently shown the potential of the modification with 1-alkenes or 1-alkynes of hydroxyl-terminated surfaces such as silica, 28 indium tin oxide (ITO), 3 alumina, 29 and silicon carbide (SiC). 19 On such surfaces, the surface properties (wettability and surface dipole/band bending) can be tuned in great detail via modification of the top group.…”

“…29 In this case, after plasma activation the samples were rinsed in ethanol and immersed in a 1 mM solution of 2-hydroxyhexadecanoic acid in ethanol at 65°C for 16 h. This same procedure was used to prepare palmitic acid (PMA)-derived monolayers.…”

Covalent Surface Modification of Oxide Surfaces

“…Accurately benchmarked DFT simulations (based on B3LYP/6‐311G(d,p) level calculation) of C1s XPS spectra,148 showed that a CO signal is to be expected at 289.5 eV, while ‐ C ‐CO carbon atom should give rise to a signal at 287.6 eV, in close to agreement with the experiment. The mechanism for such an oxidation reaction is not fully clear yet, also in view of the heterogeneity of the surface, but such reactions have also been observed for the analogous attachment of 1‐alkynes onto porous aluminum oxide 149. For 1‐alkenes oxidative attachment to yield 1‐carboxylic acids has been observed both on CrN and Al 2 O 3 .…”

Ambient Surface Analysis of Organic Monolayers using Direct Analysis in Real Time Orbitrap Mass Spectrometry

“…29 In all cases, upon ambient plasma ionization, either with direct analysis in real time (DART) 28 or with low-temperature plasma (LTP), 29 the desorption of monomeric and dimeric thiolate molecules from the gold surfaces was observed, which is consistent with previous surface MS studies. 9,13,14,17 However, little is known about the fragmentation of monolayers with stronger interfacial bonds tethering the monolayer, that is, covalently bound monolayers on glass, 30 silicon nitride (Si 3 N 4 ), 31 silicon (Si), 32 alumina (Al 2 O 3 ), 33 etc.…”