Noureen Siraj

Virtual Colorimetric Sensor Array: Single Ionic Liquid for Solvent Discrimination

There is a continuing need to develop high-performance sensors for monitoring organic solvents, primarily due to the environmental impact of such compounds. In this regard, colorimetric sensors have been a subject of intense research for such applications. Herein, we report a unique virtual colorimetric sensor array based on a single ionic liquid (IL) for accurate detection and identification of similar organic solvents and mixtures of such solvents. In this study, we employ eight alcohols and seven binary mixtures of ethanol and methanol as analytes to provide a stringent test for assessing the capabilities of this array. The UV-visible spectra of alcoholic solutions of the IL used in this study show two absorption bands. Interestingly, the ratio of absorbance for these two bands is found to be extremely sensitive to alcohol polarity. A virtual sensor array is created by using four different concentrations of IL sensor, which allowed identification of these analytes with 96.4-100% accuracy. Overall, this virtual sensor array is found to be very promising for discrimination of closely related organic solvents.

Fluorescence, Phosphorescence, and Chemiluminescence

Noureen Siraj,† Bilal El-Zahab,‡ Suzana Hamdan,† Tony E. Karam,† Louis H. Haber,† Min Li, Sayo O. Fakayode, Susmita Das, Bertha Valle, Robert M. Strongin, Gabor Patonay, Herman O. Sintim, Gary A. Baker, Aleeta Powe, Mark Lowry, Jan O. Karolin, Chris D. Geddes, and Isiah M. Warner*,† †Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, United States ‡Department of Mechanical and Materials Engineering, Florida International University, Miami, Florida 33174, United States Process Development Center, Albemarle Corporation, Baton Rouge, Louisiana 70805, United States Department of Chemistry, Winston-Salem State University, Winston-Salem, North Carolina 27110, United States Department of Civil Engineering, Adamas Institute of Technology, Barasat, Kolkata 700126, West Bengal India Department of Chemistry, Texas Southern University, Houston, Texas 77004, United States Department of Chemistry, Portland State University, Portland, Oregon 97207, United States Department of Chemistry, Georgia State University, Atlanta, Georgia 30302-4098, United States Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, United States Department of Chemistry, University of Missouri Columbia, Columbia, Missouri 65211-7600, United States Department of Chemistry, University of Louisville, Louisville, Kentucky 40208, United States Institute of Fluorescence, University of Maryland Baltimore County, Baltimore, Maryland 21202, United States

Perspectives on Moving Ionic Liquid Chemistry into the Solid Phase

Ionic liquid (IL) chemistry has evolved over the past century, such that these organic salts have impacted virtually every area of science and engineering. In the area of chemistry, initial applications of these salts were primarily the domain of chemists or chemical engineers who desired to manipulate the properties of IL solvents for a variety of applications including tuning various chemical processes. Since then, the chemistry of these organic salts has progressed such that changing an important property of a solvent (e.g., melting point or hydrophobicity) often involves simply altering the counterion of the organic salt. It is with this simplicity in mind that we have recently embarked upon the use of such chemistry to manipulate important properties of solid-phase ionic organic materials. To differentiate this chemistry from ionic liquid chemistry, we have coined the acronym GUMBOS (group of uniform materials based on organic salts). In this perspective article, we describe and demonstrate how ionic liquid chemistry can provide distinct and sometimes unique chemistry for solid-phase applications. Solid phase properties which can be manipulated via this chemistry include, but are not limited to, magnetism, melting point, hydrophobicity, fluorescence quantum yields, nanoformulations, material aggregation, viscosity, viscoelasticity, and cytotoxicity. In addition, we discuss a few examples to demonstrate how GUMBOS chemistry, until now, has been beneficial to the general area of materials chemistry and, more broadly, to the field of analytical chemistry. We also project future applications of this technology.

Rational Design of QCM-D Virtual Sensor Arrays Based on Film Thickness, Viscoelasticity, and Harmonics for Vapor Discrimination

Herein, we demonstrate an alternative strategy for creating QCM-based sensor arrays by use of a single sensor to provide multiple responses per analyte. The sensor, which simulates a virtual sensor array (VSA), was developed by depositing a thin film of ionic liquid, either 1-octyl-3-methylimidazolium bromide ([OMIm][Br]) or 1-octyl-3-methylimidazolium thiocyanate ([OMIm][SCN]), onto the surface of a QCM-D transducer. The sensor was exposed to 18 different organic vapors (alcohols, hydrocarbons, chlorohydrocarbons, nitriles) belonging to the same or different homologous series. The resulting frequency shifts (Δf) were measured at multiple harmonics and evaluated using principal component analysis (PCA) and discriminant analysis (DA) which revealed that analytes can be classified with extremely high accuracy. In almost all cases, the accuracy for identification of a member of the same class, that is, intraclass discrimination, was 100% as determined by use of quadratic discriminant analysis (QDA). Impressively, some VSAs allowed classification of all 18 analytes tested with nearly 100% accuracy. Such results underscore the importance of utilizing lesser exploited properties that influence signal transduction. Overall, these results demonstrate excellent potential of the virtual sensor array strategy for detection and discrimination of vapor phase analytes utilizing the QCM. To the best of our knowledge, this is the first report on QCM VSAs, as well as an experimental sensor array, that is based primarily on viscoelasticity, film thickness, and harmonics.

Sodium Deoxycholate Hydrogels: Effects of Modifications on Gelation, Drug Release, and Nanotemplating.

In the present study, sodium deoxycholate (NaDC) was used to produce gelation of tris(hydroxymethyl)amino-methane (TRIS) solutions above, below, and near the pKa of NaDC, respectively, which yielded a neutral gelator, a charged gelator, and a mixture of each. Impacts of ionic interactions on gel formation were studied in detail and showed that pH can be used to modify many hydrogel properties including sol-gel temperature, crystallinity, and mechanical strength. Several formulations yielded a unique rheological finding of two stable regions of elastic modulus. The release of a small molecule has been investigated under different hydrogel conditions and at variable shear rate, suggesting utility as a drug-delivery vehicle. It was also observed that pH modification of the hydrogels affected nanoparticle formation. Nanoparticles derived from a Group of Uniform Materials Based on Organic Salts (nanoGUMBOS), specifically cyanine-based NIR dyes, were templated within the hydrogel network for potential applications in tissue imaging. These nanoGUMBOS were found to be size-tunable, although material-dependent. Further understanding of NaDC/TRIS gelation has broadened the tunability and multidimensional applications of these tailored hydrogel systems.

Surfactant-based ionic liquids for extraction of phenolic compounds combined with rapid quantification using capillary electrophoresis

A rapid liquid phase extraction employing a novel hydrophobic surfactant‐based room temperature ionic liquid (RTIL), tetrabutylphosphonium dioctyl sulfosuccinate ([4C4P][AOT]), coupled with capillary electrophoretic‐UV (CE‐UV) detection is developed for removal and determination of phenolic compounds. The long‐carbon‐chain RTIL used is sparingly soluble in most solvents and can be used to replace volatile organic solvents. This fact, in combination with functional‐surfactant‐anions, is proposed to reduce the interfacial energy of the two immiscible liquid phases, resulting in highly efficient extraction of analytes. Several parameters that influence the extraction efficiencies, such as extraction time, RTIL type, pH value, and ionic strength of aqueous solutions, were investigated. It was found that, under acidic conditions, most of the investigated phenols were extracted from aqueous solution into the RTIL phase within 12 min. Good linearity was observed over the concentration range of 0.1–80.0 μg/mL for all phenols investigated. The precision of this method, expressed as RSD, was determined to be within 3.4–5.3% range. The LODs (S/N = 3) of the method were in the range of 0.047–0.257 μg/mL. The proposed methodology was successfully applied to determination of phenols in real water samples.

Spectral and physicochemical characterization of dysprosium-based multifunctional ionic liquid crystals.

We report on the synthesis and characterization of multifunctional ionic liquid crystals (melting points below 100 °C) which possess chirality and fluorescent behavior as well as mesomorphic and magnetic properties. In this regard, (1R,2S)-(-)-N-methylephedrine ((-)MeEph), containing a chiral center, is linked with variable alkyl chain lengths (e.g., 14, 16, and 18 carbons) to yield liquid crystalline properties in the cations of these compounds. A complex counteranion consisting of trivalent dysprosium (Dy(3+)) and thiocyanate ligand (SCN(-)) is employed, where Dy(3+) provides fluorescent and magnetic properties. Examination of differential scanning calorimetry (DSC) and hot-stage polarizing optical microscopy (POM) data confirmed liquid crystalline characteristics in these materials. We further report on phase transitions from solid to liquid crystal states, followed by isotropic liquid states with increasing temperature. These compounds exhibited two characteristic emission peaks in acetonitrile solution and the solid state when excited at λex = 366 nm, which are attributed to transitions from (4)F9/2 to (6)H15/2 and (4)F9/2 to (6)H13/2. The emission intensities of these compounds were found to be very sensitive to the phase.

Strategy for tuning the photophysical properties of photosensitizers for use in photodynamic therapy.

A novel approach for tuning spectral properties, as well as minimizing aggregation, in zinc porphyrin and zinc phthalocyanine-based compounds is presented. Particular emphasis is placed on use of these compounds as photosensitizers in photodynamic therapy (PDT). To accomplish this aim, a bulky hydrophobic cation, trihexyltetradecylphosphonium, is paired with anionic porphyrin and phthalocyanine dyes to produce a group of uniform materials based on organic salts (GUMBOS) that absorb at longer wavelengths with high molar absorptivity and high photostability. Nanoparticles derived from these GUMBOS possess positively charged surfaces with high zeta potential values, which are highly desirable for PDT. Upon irradiation at longer wavelengths, these GUMBOS produced singlet oxygen with greater efficiency as compared to the respective parent dyes.

GUMBOS matrices of variable hydrophobicity for matrix-assisted laser desorption/ionization mass spectrometry

RATIONALE Detection of hydrophobic peptides remains a major obstacle for matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). This stems from the fact that most matrices for MALDI are hydrophilic and therefore have low affinities for hydrophobic peptides. Herein, 1-aminopyrene (AP) and AP-derived group of uniform materials based on organic salts (GUMBOS) as novel matrices for MALDI-MS analyses of peptides were investigated for hydrophobic and hydrophilic peptides. METHODS A number of solid-phase AP-based GUMBOS are synthesized with variable hydrophobicity simply by changing the counterions. Structures were confirmed by use of (1)H NMR and electrospray ionization mass spectrometry (ESI-MS). 1-Octanol/water partition coefficients (Ko/w) were used to measure the hydrophobicity of the matrices. A dried-droplet method was used for sample preparation. All spectra were obtained using a MALDI-TOF mass spectrometer in positive ion reflectron mode. RESULTS A series of AP-based GUMBOS was synthesized including [AP][chloride] ([AP][Cl]), [AP][ascorbate] ([AP][Asc]) and [AP][bis(trifluoromethane)sulfonimide] ([AP][NTf2]). The relative hydrophobicities of these compounds and α-cyano-4-hydroxycinnamic acid (CHCA, a common MALDI matrix) indicated that AP-based GUMBOS can be tuned to be much more hydrophobic than CHCA. A clear trend is observed between the signal intensities of hydrophobic peptides and hydrophobicity of the matrix. CONCLUSIONS MALDI matrices of GUMBOS with tunable hydrophobicities are easily obtained simply by varying the counterion. We have found that hydrophobic matrix materials are very effective for MALDI determination of hydrophobic peptides and, similarly, the more hydrophilic peptides displayed greater intensity in the more hydrophilic matrix.

Tunable near-infrared emission of binary nano- and mesoscale GUMBOS

Tuning the emission spectra of organic nanomaterials is of great interest due to possible use in sensing, optoelectronics, and light harvesting applications. Herein, we report the tunable emission of binary organic nanomaterials derived from a group of uniform materials based on organic salts (GUMBOS). In these studies, the cations of cyanine-based GUMBOS are altered by increasing the number of alkyl groups on an attached methine chain. Mixtures of these GUMBOS are used to form binary nanomaterials, which are then characterized by use of UV-vis absorption spectroscopy, fluorescence spectroscopy, and cyclic voltammetry. Based on these studies, it is determined that these binary nanomaterials exhibit broad absorption spectra, as well as tunable emission spectra due to the presence of Forster resonance energy transfer (FRET). This tunable emission of binary nanomaterials suggests potential applications as sensitizers in the visible to near-infrared region of the electromagnetic spectrum. Furthermore, examination of electrochemical properties indicates possible utility for light harvesting and optoelectronic applications.