Abdalla H. Karoyo

Tunable macromolecular-based materials for the adsorption of perfluorooctanoic and octanoic acid anions

The sorption properties of tunable urethane-based copolymer materials containing β-cyclodextrin (β-CD) were evaluated with perfluorooctanoic acid (PFOA) and octanoic acid (OA) anions in aqueous solutions, respectively. The copolymer materials are herein referred to as macromolecular imprinted materials (MIMs) since their design strategy incorporates a porogen macromolecule (β-CD) within a cross-linked hexamethylene diisocyanate (HDI) framework. We report the tunable uptake of OA and PFOA anions from aqueous solution with variable adsorption modes, in accordance with the composition of the MIMs. The sorption results with granular activated carbon (GAC) were compared at 295 K and pH values exceeding the pKa values of each adsorbate. The BET and Sips models provided estimates of the monolayer sorption capacity (Qm) and related equilibrium sorption parameters. The Qm value for GAC with PFOA was ~1.4 mmol/g; whereas, a greater Qm value for PFOA (up to 2.6 mmol/g) was observed with the MIMs. GAC displays greater sorption capacity toward PFOA at relatively low Ce values and saturation of the monolayer occurs at Ce~0.5 mM. The MIMs/PFOA system displays monolayer completion at values of Ce~1 mM and multilayer sorption when Ce>1mM. Equilibrium sorption of PFOA onto MIMs occurs at the inclusion sites of β-CD and interstitial binding sites of the polymeric framework. Surface adsorption of the PFOA anion occurs between the PFOA carboxylate head group and dipolar interstitial domains of the cross-linker framework. The MIMs sorbents display tunable and favorable binding with PFOA and OA anions where the uptake (per mg MIMs) with PFOA was ~5-33% (5 μM-5 mM) and with OA was ~0.5-5% (1-20 mM). The overall sorptive uptake of OA and PFOA anions by the MIMs sorbents meets or exceeds those observed for GAC.

Physicochemical Properties and the Gelation Process of Supramolecular Hydrogels: A Review

Supramolecular polysaccharide-based hydrogels have attracted considerable research interest recently due to their high structural functionality, low toxicity, and potential applications in foods, cosmetics, catalysis, drug delivery, tissue engineering and the environment. Modulation of the stability of hydrogels is of paramount importance, especially in the case of stimuli-responsive systems. This review will update the recent progress related to the rational design of supramolecular hydrogels with the objective of understanding the gelation process and improving their physical gelation properties for tailored applications. Emphasis will be given to supramolecular host–guest systems with reference to conventional gels in describing general aspects of gel formation. A brief account of the structural characterization of various supramolecular hydrogels is also provided in order to gain a better understanding of the design of such materials relevant to the nature of the intermolecular interactions, thermodynamic properties of the gelation process, and the critical concentration values of the precursors and the solvent components. This mini-review contributes to greater knowledge of the rational design of supramolecular hydrogels with tailored applications in diverse fields ranging from the environment to biomedicine.

A 1H NMR Study of Host/Guest Supramolecular Complexes of a Curcumin Analogue with β-Cyclodextrin and a β-Cyclodextrin-Conjugated Gemini Surfactant

Host systems based on β-cyclodextrin (βCD) were employed as pharmaceutical carriers to encapsulate a poorly soluble drug, curcumin analogue (NC 2067), in order to increase its water solubility. βCD was chemically conjugated with an amphiphilic gemini surfactant with the ability to self-assemble and to form nanoscale supramolecular structures. The conjugated molecule, βCDgemini surfactant (βCDg), was shown to be a promising drug delivery agent. In this report, its physicochemical properties were assessed in aqueous solution using 1D and 2D 1H NMR spectroscopy. The results showed that the apolar hydrocarbon domain of the gemini surfactant was self-included within the βCD internal cavity. The host/guest complexes composed of native βCD or βCDg with NC 2067 were examined using 1D/2D ROESY NMR methods. The stoichiometry of βCD/NC 2067 complex was estimated using Jobs method via 1H NMR spectroscopy. The binding geometry of NC 2067 within βCD was proposed using molecular docking and further supported by 1D and 2D ROESY NMR results. Addition of NC 2067 to βCDg revealed minimal changes to the overall structure of the βCDg system, in agreement with the formation of a βCDg/NC 2067 ternary complex.

Raman and DRIFT spectra, vibrational assignments and quantum mechanical calculations of centrosymmetric meso-2,3-Dimercaptosuccinic acid

The Raman spectrum (3700-100cm-1) of meso-2,3-Dimercaptosuccinic acid (meso-DMSA; C4H6O4S2) was recorded in the solid phase using 514.5 and 785nm excitation lines. Whereas, the DRIFT spectrum (4000-400cm-1) of the sample powdered in KBr was obtained. Moreover, DFT-B3LYP/6-31G(d) geometry optimization and frequency calculations were carried out for centrosymmetric trans (Ci), gauche (C1; G+/G-) and eclipsed (Cs; Ef and C1; E+/E-) rotational isomers in favor of a trans conformation, the least energy with real frequencies. However, other conformers were found at either local minima or local maxima as a result of the rotation of carboxyl, hydroxyl and thiol groups according to a potential energy surface scan. Moreover, an imaginary wavenumber was predicted; therefore, they are considered transition states. On the other hand, the mass spectrum of the sample dissolved in an acetonitrile/methanol mixture reveal 4-6% dimer through intermolecular hydrogen bonding interactions via the dicarboxylic groups. Therefore, we have modeled the complex structure obeying Ci restricted symmetry for an isolated dimer unit using DFT-B3LYP/6-31G(d) and for two molecules per unit cell in the solid phase implementing DFT-PBE functional. Thus, the meso-DMSA forms long strands in which individual molecules are bonded together at each termini through hydrogen bonding. Aided by normal coordinate analysis, complete vibrational assignments were provided herein which support Ci configuration of meso-DMSA in the solid state which found consistent with the observed broadening, composite, split bands, and the mutual exclusion rule.

Cyclodextrin-Based Polymer-Supported Bacterium for the Adsorption and in-situ Biodegradation of Phenolic Compounds

Dual function polymer materials with immobilized Sphingobium Chorophenolicum (SpC) bacterium cells are reported herein that undergo tandem adsorption and biodegradation of phenolic compounds. The cross-linked polymer materials contain β-cyclodextrin (β-CD) with incremental hexamethylene diisocyanate (HDI) cross-linker at variable mole ratios (X = 1, 3, or 6), denoted as HDI-X systems. The adsorptive uptake properties of the insoluble HDI-X polymers (X = 3 and 6) with various phenolic compounds [pentachlorophenol (PCP), 2,4,6-trichlorophenol (TCP), and 2,4,6-trimethylphenol (TMP)] were studied using batch adsorption isotherms. The molecular selective phenol removal (SR) capacity of the HDI-3 and HDI-6 materials was evaluated by electrospray ionization mass spectrometry (ESI-MS). The results were compared against granular activated carbon (GAC) and native β-CD, where 1D/2D 1H NMR spectral characterization of the complexes formed between phenolic guests and a soluble polymer (HDI-1) in aqueous solution provide insight on the intermolecular interactions and the role of cross-linking effects. Immobilization of SpC onto HDI-3 was shown to form a composite polymer/bacterium material. The composite system displays synergistic removal effects due to tandem PCP adsorption and SpC biodegradation to yield by-products such as 2,6-dichloro-1,4-hydroquinone (DCHQ). Apoptosis and cytotoxicity of DCHQ were evaluated using three breast cancer cell lines.

Starch Particles, Energy Harvesting, and the “Goldilocks Effect”

This study reports on the unique water vapor adsorption properties of biomass-derived starch particles (SPs). SPs offer an alternative desiccant for air-to-air energy exchangers in heating, ventilation, and air conditioning systems because of their remarkable adsorption–desorption performance. SP15 has a particle diameter (dp) of 15 μm with a surface area (SA) of 2.89 m2/g and a pore width (Pw) of 80 Å. Microporous starch particles (SP15) were compared with high amylose starch (HAS15; SA = 0.56 m2/g, dp = 15 μm, Pw = 46 Å) and silica gel (SG13; SA = 478 m2/g, dp = 13 μm, Pw = 62 Å). Transient water vapor tests were performed using a customized small-scale energy exchanger coated with SP15, HAS15, and SG13. The water swelling (%) for SP15 was ca. 2 orders of magnitude greater with markedly higher (ca. three- and six-fold) water vapor uptake compared to HAS15 and SG13, respectively. At similar desiccant coating levels on the energy exchanger, the latent effectiveness of the SP15 system was much improved (4–31%) over the HAS15 and SG13 systems at controlled operating conditions. SP15 is a unique desiccant material with high affinity for water vapor and superior adsorption properties where ca. 98% regeneration was achieved under mild conditions. Therefore, SPs display unique adsorption–desorption properties, herein referred to as the “Goldilocks effect”. This contribution reports on the utility of SPs as promising desiccant coatings in air-to-air energy exchangers for ventilation systems or as advanced materials for potential water/energy harvesting applications.

Smart polymer materials - Tuning the physicochemical properties of polysaccharides via crosslinking conditions

B utilizing Localized Surface Plasmon Resonance (LSPR) offers relatively inexpensive, label-free, facile detection that is amenable to on-chip devices. Such devices can provide exquisite sensitivity at a low cost and should prove extremely useful in resource limited environments. However, several challenges remain, such as: sensitivity to small molecule binding, specificity in complex biological solutions, detection of membrane-associated species and integration into on-chip devices. This presentation will highlight recent advances in LSPR-based biosensing devices developed in the Sagle group to overcome these limitations. One study we have done to increase sensitivity is an assay in which gold nanostars are aggregated upon addition of an analyte. Due to increased surface area of contact, a large decrease in Kd and limit of detection in the attomolar range was observed with this simple aggregation assay. In addressing the second challenge, we have incorporated shape complementarity on the nanoparticle surface to carry out size-selective biosensing with improved selectivity. The third challenge is tackled through the development of a novel plasmonic platform containing a solid supported lipid bilayer so that label-free measurements of membrane associated species can be carried out. This device is shown to have improved sensitivity over existing platforms. Lastly, large-scale patterning of the nanoparticle arrays enabling the interfacing of these arrays with microfluidic on-chip devices are also presented.