Chieu D. Tran

Analytical thermal lens instrumentation

This review describes recent instrumentation developments of the thermal lens techniques. It will begin with a brief discussion of the theory of the techniques. Its main focus is, however, on the detail description of various instruments. Specifically, the discussion will begin with the description of single beam instruments which were initially developed following by dual beam instruments. Elaboration will be focused on some of the most sophisticated instruments which were developed recently. These include differential thermal lens instruments, multiwavelength and spectral tunable instruments, circular dichroism spectropolarimeters, rotoreflecting instruments, and miniaturized thermal lens instruments. Selection of lasers, focusing, modulation, sample position, sample cells, data acquisition, noise reduction, and applications of acousto‐optic tunable filters will also be discussed. The future of the techniques in terms of instrumentation will be finally forecasted.

Absorption of Water by Room-Temperature Ionic Liquids: Effect of Anions on Concentration and State of Water

Near-infrared (NIR) spectrometry was successfully used for the noninvasive and in situ determination of concentrations and structure of water absorbed by room-temperature ionic liquids (RTILs). It was found that RTILs based on 1-butyl-3-methylimidazolium, namely, [BuMIm]+[BF4]−, [BuMIm]+[bis((trifluoromethyl)sulfonyl)amide, or Tf2N]− and [BuMIm]+[PF6]−, are hydroscopic and can quickly absorb water when they are exposed to air. Absorbed water interacts with the anions of the RTILs, and these interactions lead to changes in the structure of water. Among the RTILs studied, [BF4]− provides the strongest interactions and [PF6]− the weakest. In 24 hours, [BuMIm]+[BF4]− can absorb up to 0.320 M of water, whereas [BuMIm]+[PF6]− can only absorb 8.3 × 10−2 M of water. It seems that higher amounts of water can be absorbed when the anion of the RTIL can strongly interact and hence stabilize absorbed water molecules by forming hydrogen bonds with them or inducing hydrogen bonds among water molecules. More importantly, the NIR technique can be sensitively used for the noninvasive, in situ determination of absorbed water in RTILs, without any pretreatment, and at limits of detection as low as 3.20 × 10−3 M.

Chiral ionic liquids for enantioseparation of pharmaceutical products by capillary electrophoresis

A chiral ionic liquid (IL), S-[3-(chloro-2-hydroxypropyl)trimethylammonium] [bis((trifluoromethyl)sulfonyl)amide] (S-[CHTA](+)[Tf(2)N](-)), which can be easily and readily synthesized in a one-step process from commercially available reagents, can be successfully used both as co-electrolyte and as a chiral selector for CE. A variety of pharmaceutical products including atenolol, propranolol, warfarin, indoprofen, ketoprofen, ibuprofen and flurbiprofen, can be successfully and baseline separated with the use of this IL as electrolyte. Interestingly, while S-[CHTA](+)[Tf(2)N](-) can also serve as a chiral selector, enantioseparation cannot be successfully achieved with S-[CHTA](+)[Tf(2)N](-) as the only chiral selector. In the case of ibuprofen, a second chiral selector, namely a chiral anion (sodium cholate), is needed for the chiral separation. For furbiprofen, in addition to S-[CHTA](+)[Tf(2)N](-) and sodium cholate, a third and neutral chiral selector, 1-S-octyl-beta-d-thioglucopyranoside (OTG), is also needed. Due to the fact that the chirality of this chiral IL resides on the cation (i.e., -[CHTA](+)), and that needed additional chiral selector(s) are either chiral anion (i.e., cholate) or chiral neutral compound (OTG), the results obtained seem to suggest that additional chiral selector(s) are needed to provide the three-point interactions needed for chiral separations.

Chitosan-cellulose composite materials: preparation, characterization and application for removal of microcystin.

We developed a simple and one-step method to prepare biocompatible composites from cellulose (CEL) and chitosan (CS). [BMIm(+)Cl(-)], an ionic liquid (IL), was used as a green solvent to dissolve and prepare the [CEL+CS] composites. Since majority (>88%) of IL used was recovered for reuse by distilling the aqueous washings of [CEL+CS], the method is recyclable. XRD, FTIR, NIR, (13)C CP-MAS-NMR and SEM were used to monitor the dissolution and to characterize the composites. The composite was found to have combined advantages of their components: superior mechanical strength (from CEL) and excellent adsorption capability for microcystin-LR, a deadly toxin produced by cyanobacteria (from CS). Specifically, the mechanical strength of the composites increased with CEL loading; e.g., up to 5× increase in tensile strength was achieved by adding 80% of CEL into CS. Kinetic results of adsorption confirm that unique properties of CS remain intact in the composite, i.e., it is not only a very good adsorbent for microcystin but also is better than all other available adsorbents. For example, it can adsorb 4× times more microcystin than the best reported adsorbent. Importantly, the microcystin adsorbed can be quantitatively desorbed to enable the composite to be reused with similar adsorption efficiency.

Chitosan–cellulose composite for wound dressing material. Part 2. Antimicrobial activity, blood absorption ability, and biocompatibility

Chitosan (CS), a polysaccharide derived from chitin, the second most abundant polysaccharide, is widely used in the medical world because of its natural and nontoxic properties and its innate ability for antibacterial and hemostasis effects. In this study, the novel composites containing CS and cellulose (CEL) (i.e., [CEL + CS]), which we have previously synthesized using a green and totally recyclable method, were investigated for their antimicrobial activity, absorption of anticoagulated whole blood, anti-inflammatory activity through the reduction of tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6), and the biocompatibility with human fibroblasts. The [CEL + CS] composites were found to inhibit the growth of both Gram positive and negative micro-organisms. For examples, the regenerated 100% lyophilized chitosan material was found to reduce growth of Escherichia coli (ATCC 8739 and vancomycin resistant Enterococcus faecalis (ATCC 51299) by 78, 36, and 64%, respectively. The composites are nontoxic to fibroblasts; that is, fibroblasts, which are critical to the formation of connective tissue matrix were found to grow and proliferate in the presence of the composites. They effectively absorb blood, and at the same rate and volume as commercially available wound dressings. The composites, in both air-dried and lyophilized forms, significantly inhibit the production of TNF-α and IL-6 by stimulated macrophages. These results clearly indicate that the biodegradable, biocompatible and nontoxic [CEL + CS] composites, particularly those dried by lyophilizing, can be effectively used as a material in wound dressings.

Synergistic adsorption of heavy metal ions and organic pollutants by supramolecular polysaccharide composite materials from cellulose, chitosan and crown ether

We have developed a simple one-step method to synthesize novel supramolecular polysaccharide composites from cellulose (CEL), chitosan (CS) and benzo-15-crown 5 (B15C5). Butylmethylimidazolium chloride [BMIm(+)Cl(-)], an ionic liquid (IL), was used as a sole solvent for dissolution and preparation of the composites. Since majority of [BMIm(+)Cl(-)] used was recovered for reuse, the method is recyclable. The [CEL/CS+B15C5] composites obtained retain properties of their components, namely superior mechanical strength (from CEL), excellent adsorption capability for heavy metal ions and organic pollutants (from B15C5 and CS). More importantly, the [CEL/CS+B15C5] composites exhibit truly supramolecular properties. By itself CS, CEL and B15C5 can effectively adsorb Cd(2+), Zn(2+) and 2,4,5-trichlorophenol. However, adsorption capability of the composite was substantially and synergistically enhanced by adding B15C5 to either CEL and/or CS. That is, the adsorption capacity (qe values) for Cd(2+) and Zn(2+) by [CS+B15C5], [CEL+B15C5] and [CEL+CS+B15C5] composites are much higher than combined qe values of individual CS, CEL and B15C5 composites. It seems that B15C5 synergistically interact with CS (or CEL) to form more stable complexes with Cd(2+) (or Zn(2+)), and as a consequence, the [CS+B15C5] (or the [CEL+B15C5]) composite can adsorb relatively larger amount Cd(2+) (or Zn(2+)). Moreover, the pollutants adsorbed on the composites can be quantitatively desorbed to enable the [CS+CEL+B15C5] composites to be reused with similar adsorption efficiency.

Infrared Multispectral Imaging: Principles and Instrumentation

Abstract A multispectral imaging spectrometer is an instrument that can simultaneously record spectral and spatial information of a samples. Chemical and physical properties of the sample can be elucidated from such images. In a multispectral imaging instrument, a camera is used to record the spatial distribution of the sample, and the spectral information is gained by scanning a dispersive device to record spectra for each image. This overview article describes operational principles and recent development of various components used in infrared multispectral imaging instruments including the electronic dispersive devices (acousto-optic tunable filter and liquid crystal tunable filter) and IR cameras (InGaAs, InSb, HgCdTe and QWIP cameras).

Electronic Tuning, Amplitude Modulation of Lasers by a Computer-Controlled Acousto-optic Tunable Filter

A novel, compact, all-solid-state, computer-controlled acousto-optic tunable filter (AOTF) which has no moving parts has been developed. The filter can be successfully used not only for the rapid tuning and amplitude-modulation of the multiwavelength laser beam but also for the stabilization of the power of the diffracted beam regardless of whether it is a continuous single wavelength or a modulated multiwavelength beam. The potential applications of this filter to the spectrochemical methods of analyses are discussed.

Principles and analytical applications of acousto-optic tunable filters, an overview

Advantages of acousto-optic tunable filters have been exploited to develop novel analytical instruments which are not feasible otherwise. The instrumentation development and unique features of such AOTF based instruments including the multidimensional fluorimeter, the multiwavelength thermal lens spectrometer, the near-infrared spectrometer based on erbium doped fiber amplifier (EDFA), and detectors for high performance liquid chromatography (HPLC) and flow injection analysis (FIA), will be described.

Cellulose, Chitosan, and Keratin Composite Materials. Controlled Drug Release

A method was developed in which cellulose (CEL) and/or chitosan (CS) were added to keratin (KER) to enable [CEL/CS+KER] composites to have better mechanical strength and wider utilization. Butylmethylimmidazolium chloride ([BMIm+Cl–]), an ionic liquid, was used as the sole solvent, and because the [BMIm+Cl–] used was recovered, the method is green and recyclable. Fourier transform infrared spectroscopy results confirm that KER, CS, and CEL remain chemically intact in the composites. Tensile strength results expectedly show that adding CEL or CS into KER substantially increases the mechanical strength of the composites. We found that CEL, CS, and KER can encapsulate drugs such as ciprofloxacin (CPX) and then release the drug either as a single or as two- or three-component composites. Interestingly, release rates of CPX by CEL and CS either as a single or as [CEL+CS] composite are faster and independent of concentration of CS and CEL. Conversely, the release rate by KER is much slower, and when incorporated into CEL, CS, or CEL+CS, it substantially slows the rate as well. Furthermore, the reducing rate was found to correlate with the concentration of KER in the composites. KER, a protein, is known to have secondary structure, whereas CEL and CS exist only in random form. This makes KER structurally denser than CEL and CS; hence, KER releases the drug slower than CEL and CS. The results clearly indicate that drug release can be controlled and adjusted at any rate by judiciously selecting the concentration of KER in the composites. Furthermore, the fact that the [CEL+CS+KER] composite has combined properties of its components, namely, superior mechanical strength (CEL), hemostasis and bactericide (CS), and controlled drug release (KER), indicates that this novel composite can be used in ways which hitherto were not possible, e.g., as a high-performance bandage to treat chronic and ulcerous wounds.