Cationic Reagents Research Articles

Lycium barbarum oligosaccharide-derived carbon quantum dots inhibit glial scar formation while promoting neuronal differentiation of neural stem cells

Overexpression of glial fibrillary acidic protein (GFAP) in activated astrocytes following spinal cord injury is closely associated with glial scar formation, which harms axonal regrowth. In this study, we prepared ultrasmall cationic carbon quantum dots (CQDs) via one-step hydrothermal carbonization. Lycium barbarum oligosaccharides were used as the carbon source for the first time, and polyetherimide (PEI) and ethylenediamine (ED) were used as cationic reagents. Interestingly, the resultant CQDs show the bioactivity of specifically inhibiting GFAP protein expression, while promoting neuronal marker expression in neural stem cells (NSCs). Furthermore, CQDs together with NSCs can remarkably improve the motor activity of animals after implantation into the transection lesion of the rat spinal cord. Histological analysis confirmed that CQDs can enhance neuronal differentiation of NSCs while inhibiting glial scar formation in vivo. Altogether, this study represents the first report of producing CQDs from oligosaccharides and investigating their impact on NSCs differentiation, thus providing a paradigm for exploring the bioactivity of quantum dots.

Assessing the sorption of uranium and thorium from simulated solutions using chemically treated biomass of Sargassum aquifolium macroalgae

This study aimed to investigate the potential application of activated Sargassum aquifolium macroalgae (ASAM) as a biosorbent for uranium(VI) and thorium(IV) ions, employing controlled experimental conditions. The parameters examined included pH, biosorbent mass, initial concentration, contact time, and temperature. To enhance sorption characteristics, the raw Sargassum aquifolium macroalgae (SAM) biomass underwent separate pre-treatments using phosphoric acid (H3PO4) and potassium hydroxide (KOH). Various models were employed to analyze the kinetic and sorption isotherm data, and thermodynamic parameters were determined to assess the sorption mechanism. The KOH-treated SAM demonstrated a higher capacity for biosorbing U(VI) and Th(IV) compared to the acid-treated biomass. The sorption mechanism was investigated through characterization techniques such as FTIR, SEM/EDS, XRD, Zeta-potential, and BET analysis. The desorption-sorption cycle efficiency of both sorbents was evaluated, indicating that 0.1 mol L-1 HNO3 exhibited the most efficient desorption reagent for both metal cations over five consecutive cycles. These findings suggest the potential of ASAM as a biosorbent for removing U(VI) and Th(IV) from aqueous solutions. Furthermore, the study demonstrated the remarkable effectiveness of the two activated sorbents in eliminating U(VI) and Th(IV) ions from real wastewater samples.

Quaternization of cassava starch and determination of antimicrobial activity against bacteria and coronavirus

This study describes the novel development of quaternized cassava starch (Q-CS) with antimicrobial and antiviral properties, particularly effective against the MHV-3 coronavirus. The preparation of Q-CS involved the reaction of cassava starch (CS) with glycidyltrimethylammonium chloride (GTMAC) in an alkaline solution. Q-CS physicochemical properties were determined by FTIR, NMR, elemental analysis, zeta potential, TGA, and moisture sorption. FTIR and NMR spectra confirmed the introduction of cationic groups in the CS structure. The elemental analysis revealed a degree of substitution (DS) of 0.552 of the cationic reagent on the hydroxyl groups of CS. Furthermore, Q-CS exhibited a positive zeta potential value (+28.6 ± 0.60 mV) attributed to the high positive charge density shown by the quaternary ammonium groups. Q-CS demonstrated lower thermal stability and higher moisture sorption compared to CS. The antimicrobial activity of Q-CS was confirmed against Escherichia coli (MIC = 0.156 mg mL−1) and Staphylococcus aureus (MIC = 0.312 mg mL−1), along with a remarkable ability to inactivate 99% of MHV-3 coronavirus after only 1 min of direct contact. Additionally, Q-CS showed high cell viability (close to 100%) and minimal cytotoxicity effects, guaranteeing its safe use. Therefore, these findings indicate the potential use of Q-CS as a raw material for antiseptic biomaterials.

Potency of Biocoagulant from Cationic Modified Starch of Balbis Banana Blossom Waste for Palm Oil Wastewater Treatment: Literature Study

Lampung is one of the provinces producing Indonesia's second-largest banana crop. Operational activities at the Palm Oil Mill produce a by-product of Palm Oil Mill Effluent (POME), which can potentially be the most enormous environmental pollution. Communities often use chemicals to treat liquid waste, which causes health problems, cannot be decomposed, and can damage the environment. Therefore, treating liquid waste using organic materials that are more environmentally friendly, safe for health and easily degraded is necessary. By modifying cationic starch, natural polymers found in banana blossom waste may be utilized for producing natural biocoagulant that are more effective. This paper aims to review the potential of cationic-modified balbis banana blossom waste starch as a natural biocoagulant for processing palm oil waste. Starch was first modified into cationic starch by etherification method with the help of HMMAHC cationic reagents. The mechanism of cationic starch as a biocoagulant is the exchange of starch cation ions and waste anions to form bridges between colloidal particles and then form flocs that can precipitate. The implementation technique of this idea is by collaborating with several parties to ensure the successful use of banana hump starch as a biocoagulant material, providing support and facilities for the industry and promoting the use of biocoagulant, conducting literature studies related to the use of banana hump starch as a natural biocoagulant, testing the effectiveness of biocoagulant, implemented in the palm oil processing industry.

Rapid and efficient preparation of cationized lignin for downstream high value-added utilization of biodegradable antimicrobial nanofibrous membranes

Industrial lignin is underutilized as an abundant natural aromatic resource, resulting in a serious waste of biomass resources. In this study, a strategy was developed to efficiently achieve cationization of industrial lignin, which not only could increase the water solubility of the industrial lignin for good compatibility with polyvinyl alcohol (PVA), but also incorporated quaternary ammonium groups to improve the antimicrobial performance. The results showed that the cationized lignin products could be obtained by reacting at 75 °C for only 20 min and had good compatibility with PVA in aqueous systems, which not only shortened the lignin cationization time, but also reduced the amount of cationization reagent. By integrating the electrospinning technique, the nanofiber membranes with excellent antimicrobial performance can be produced for the field of medical dressing. With the addition of 7 wt% of the cationized lignin, the novel developed antimicrobial nano-medical dressing exhibited excellent breathability (61.08 mm/s), anti-UV properties, and compatibility with portable spinning technique. In addition, the cationized lignin-based nanofiber membranes had excellent antimicrobial performance, with an antimicrobial ratio of 100 % (Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli), as well as being biodegradable. In conclusion, this strategy could realize the cationization modification of industrial lignin while expanding the application in medical dressings and improving the economic sustainability of biorefinery strategies.

Selective flotation of ilmenite from titanaugite using 2-amino-1,3-propanediol as a novel depressant

In this investigation, micro-flotation, zeta potential measurements, adsorption tests, Fourier Transform Infrared Spectroscopy (FTIR), and X-ray Photoelectron Spectroscopy (XPS) were used to assess the separation mechanism of ilmenite and titanaugite using a novel cationic reagent, 2-amino-1,3-propanediol (APD). The micro-flotation results of single mineral and artificially mixed minerals demonstrated that APD had a negligible impact on ilmenite flotation, whereas it significantly reduced the recovery of titanaugite, resulting in the selective flotation of ilmenite from titanaugite. Zeta potential measurements indicated a significant positive shift in the titanaugite surface potential following interaction with APD, whereas the ilmenite surface potential exhibited a minimal change in the pH range between the isoelectric point (IEP) of the two minerals. The adsorption test demonstrated that a higher quantity of APD adsorbed onto the titanaugite surface than that of ilmenite. Moreover, APD adsorbed onto the titanaugite surface via chemical interaction with active sites containing Ca and Mg, which was confirmed by FTIR and XPS analysis. Overall, APD exhibits favorable adsorption characteristics on the surface of titanaugite through a combination of electrostatic attraction and chemical interaction, whereas its interaction with ilmenite is hindered by electrostatic repulsion. It is hoped that this study will contribute to the development of highly efficient flotation depressants targeting titanaugite in the field of ilmenite flotation.

Analysis of polyisoprene oligomers via in situ silver nanoparticle formation on thin-layer chromatography plate using matrix-assisted laser-induced desorption/ionization mass spectrometry.

The direct mass spectrometry (MS) detection of polyisoprene (PI) oligomers on a thin-layer chromatography (TLC) plate using matrix-assisted laser-induced desorption/ionization (MALDI) with silver trifluoroacetate as the cationization reagent was investigated. The spots of PI oligomers and silver trifluoroacetate on the TLC plate resulted in brown materials after UV laser irradiation. It was suggested that silver trifluoroacetate yielded Ag nanoparticles as brown materials after heating via laser irradiation. The nanoparticles behaved as an inorganic matrix and a source of Ag+ adduct in the analysis of PI oligomers. The use of organic matrices together with silver trifluoroacetate reduced the signal intensity of PI oligomers on MALDI-MS on a TLC plate. The separation of PI oligomers (polymerization degree, n = 5-11) by TLC resulted in a single elliptical spot without a clear separation after the chromatographic procedure. However, in MS imaging, differences in migration lengths based on degrees of polymerization were clearly observed and the degrees of polymerization were identified without comparison with standards.

Dual-crosslinked starch/carboxymethyl cellulose blend film with ion-responsive dissolution properties

While the ability of quickly vanishing in water has made starch-based plastics a potential solution to the current marine plastic issue caused by discarded single-use plastics, this ability also translates into lack of water resistance in daily scenario. Here, we aim to improve the water resistance of starch-based blend films in daily scenarios while allowing them to disintegrate and vanish rapidly in marine environments via the introduction of ionic crosslinks. A dialdehyde starch (DAS)/carboxymethyl cellulose (CMC) blend film is prepared via a modified solution casting process, during which DAS is gradually rendered cationic by a cationizing reagent, Girard's reagent T, and interacts with CMC to form ionic crosslinks. Meanwhile, the aldehyde groups on DAS also form acetal bonds with the -OH groups on both DAS and CMC, which further increases the wet strength. In solutions of low ionic strength encountered in daily life, such as freshwater, the film remains stable for both types of crosslinks. In high-ionic-strength solutions, such as seawater, the film swells rapidly and disintegrates owing to the cleavage of ionic crosslinks. This study demonstrated ionic crosslink could be a potential solution for balancing the protection of marine ecosystem and ease of use of starch-based blend films, which is essential to the development of future marine ecosystem-friendly single-use plastics.

Recent developments and applications of selected ion flow tube mass spectrometry(SIFT-MS).

Selected ion flow tube mass spectrometry(SIFT-MS) is now recognized as the most versatile analytical technique for the identification and quantification of trace gases down to the parts-per-trillion by volume, pptv, range. This statement is supported by the wide reach of its applications, from real-time analysis, obviating sample collection of very humid exhaled breath, to its adoption in industrial scenarios for air quality monitoring. This review touches on the recent extensions to the underpinning ion chemistry kinetics library and the alternative challenge of using nitrogen carrier gas instead of helium. The addition of reagent anions in the Voice200 series of SIFT-MS instruments has enhanced the analytical capability, thus allowing analyses of volatile trace compounds in humid air that cannot be analyzed using reagent cations alone, as clarified by outlining the anion chemistry involved. Case studies are reviewed of breath analysis and bacterial culture volatile organic compound(VOC), emissions, environmental applications such as air, water, and soil analysis, workplace safety such as transport container fumigants, airborne contamination in semiconductor fabrication, food flavor and spoilage, drugs contamination and VOC emissions from packaging to demonstrate the stated qualities and uniqueness of the new generation SIFT-MS instrumentation. Finally, some advancements that can be made to improve the analytical capability and reach of SIFT-MS are mentioned.

Optimization of kappa-carrageenan cationization using experimental design for model-drug release and investigation of biological properties

Cationization is a promising chemical modification technique that improves properties by attaching permanent positive charges to the backbone of biopolymers. Carrageenan is a widely available and non-toxic polysaccharide, commonly used in food industry but with low solubility in cold water. We performed a central composite design experiment to check the parameters that most influence the degree of cationic substitution and the film solubility. Hydrophilic quaternary ammonium groups on the carrageenan backbone enhance interaction in drug delivery systems and create active surfaces. Statistical analysis indicated that within the studied range, only the molar ratio between the cationizing reagent and the repeating disaccharide unit of carrageenan had a significant effect. Optimized parameters using 0.086 g of sodium hydroxide and glycidyltrimethylammonium/disaccharide repeating unit of 6.83 achieved 65.47 % degree of substitution and 4.03 % solubility. Characterizations confirmed the effective incorporation of cationic groups into the commercial structure of carrageenan and thermal stability improvement of the derivatives.

A SIFT-MS study of positive and negative ion chemistry of the ortho-, meta- and para-isomers of cymene, cresol, and ethylphenol.

Selected Ion Flow Tube Mass Spectrometry (SIFT-MS) is a soft ionisation technique based on gas phase ion-molecule reaction kinetics for the quantification of trace amounts of volatile organic compound vapours. One of its previous limitations is difficulty in resolving isomers, although this can now be overcome using different reactivities of several available reagent cations and anions (H3O+, NO+, O2+˙, O-˙, OH-, O2-˙, NO2-, NO3-). Thus, the ion-molecule reactions of these eight ions with all isomers of the aromatic compounds cymene, cresol and ethylphenol were studied to explore the possibility of their immediate identification and quantification without chromatographic separation. Rate coefficients and product ion branching ratios determined experimentally for the 72 reactions are reported. DFT calculations of their energetics confirmed the feasibility of the suggested reaction pathways. All positive ion reactions proceeded fast but largely did not discriminate between the isomers. The reactivity of the anions was much more varied. In all cases, OH- reacts by proton transfer forming (M-H); NO2- and NO3- were unreactive. The differences observed for product ion branching ratios can be used to identify isomers approximately.

Efficient Cationization of Cotton for Salt-Free Dyeing by Adjusting Fiber Crystallinity through Alcohol-Water-NaOH Pretreatment.

Cationization of cotton is considered to be an effective way to realize salt-free dyeing of reactive dyes. However, applying cotton modified with glycidyltrimethylammonium chloride (GTA) suffers from large consumption of the cationic reagent. One of the reasons is that high crystallinity of cotton fibers hinders the penetration of the reagents into the cellulose interior and limits the reaction between them. This paper designed to use alcohol-water-NaOH system to pretreat the fibers before cationization. With this method, crystallinity of the cotton fibers is decreased and more reactive -OH is exposed, resulting in much higher fiber-reagent reactivity and increased GTA utilization. Influence of alcohol type, alcohol-to-water ratio, and quantity of NaOH on fiber crystallinity and GTA dosage for cationization are all examined. It is found that for achieving 96.0% fixation of C.I. Reactive Black 5 in the absence of salt, GTA dosage can be reduced by half when the fibers are pretreated by alcohol-water-NaOH. Compared with ethanol, n-propanol and isopropanol, tert-butyl alcohol incorporated system shows better performance in increasing fiber reactivity due to their weaker ability to dissolve ions. In this study, XRD and FT-IR are used to demonstrate changes in crystallinity of the fibers after pretreatment. The alteration in micromorphology and hydrophilicity of the pretreated fibers is observed by SEM and water contact angle test, respectively. Furthermore, the alcohol-water-NaOH system can be recycled to show very good repeatability. Notably, all dyed samples pretreated with the system present high color saturation and satisfactory color fastness, especially that the wet rub fastness reaches 4-5 grade, which is one grade higher than that obtained from the conventional dyeing with salt. The above findings prove that alcohol-water-NaOH pretreatment is effective in enhancing reactivity of the cotton fibers and penetrability of the agent, and it shows promising prospects in real application.

Rapid Electrophilic Cysteine Arylation with Pyridinium Salts.

Here, we present a series of fluorinated cationic reagents that enable rapid arylation of cysteine under mild conditions compatible with proteins and peptides. The highly polarized C-F bond and attractive nucleophile-electrophile Coulombic interactions substantially accelerate cysteine arylation, leading to unusually high rate constants on the order of 100 M-1·s-1 and allowing for equimolar labeling of substrates at micromolar concentrations. The synthetic modularity of this approach promotes the direct coupling of structurally diverse phenol-containing functional motifs to cysteine residues of biomacromolecules with high efficiency. This user-friendly chemistry enables fast bond formation between commonly used bioconjugation partners, thus greatly streamlining the synthetic chemistry workflow, and can be easily developed as convenient kits for chemical biology and medicinal chemistry applications.

Nonaqueous Capillary Zone Electrophoresis for Polyesters and Polyamides Using Hexafluoroisopropyl Alcohol as Electrophoretic Medium

Nonaqueous capillary zone electrophoresis (NACZE) utilizing cationic reagents as an electrophoresis promoter has the potential for separating water-insoluble synthetic polymers and that with tetrahydrofuran based electrophoretic media containing cationic reagents has been reported. In this study, NACZE using hexafluoroisopropyl alcohol (HFIP)-based media was developed for separating polyesters and polyamides, which were insoluble in tetrahydrofuran. Nonaqueous media of HFIP containing 400 mM cetyltrimethylammonium chloride (CTAC) and 50 mM trihexyl(tetradecyl)phosphonium chloride (P66614Cl) were used, and it was found that hydrophobic P66614 cation enhanced the electrophoresis of both polyesters and polyamides compared with cetyltrimethylammonium cation. The media containing CTAC resulted in partially separated poly(ethylene terephthalate)/poly(hexamethylene terephthalate) and poly(ethylene terephthalate)/poly(ethylene naphthalate), but P66614Cl failed to separate them. By contrast, nylon 6I and nylon 6/6I were separated with the P66614Cl media, whereas they were co-eluted in the media with CTAC.

Amine-Modified Chitosan Flocculant Synthesized via Single-Mode Microwave Method for Laundry Wastewater Treatment.

In this study, an effective and environmentally friendly polyaminated cross-linked chitosan (M-PACTS) flocculant was successfully synthesized via circular focus single-mode microwave synthesizer irradiation. Epichlorohydrin and tetraethylenepentamine were used as the cross-linking agent and active cationic reagent, respectively. The same formation was used to prepare cationic lightly cross-linked chitosan (C-PACTS) via the conventional heating method. The flocculant was characterized using Fourier transform infrared spectroscopy, X-ray diffraction analysis, and scanning electron microscopy. The flocculation capability of C-PACTS and M-PACTS was compared using laundry wastewater as a model pollutant. The pH, PACTS dosage, temperature, stirring rate, stirring time, and setting time were systematically investigated. The experimental results showed that circular focus single-mode microwave synthesizer irradiation was a more efficient method to modify chitosan. M-PACTS exhibited a higher capacity for turbidity and chemical oxygen demand (CODCr) removal. Under optimal conditions, the removal rate values of M-PACTS were up to 96% (turbidity) and 78% (CODCr). The proposed PACTS is suitable for treatment of polluted wastewater in an eco-friendly manner without causing secondary pollution.

Preparation and Drug-Loading Properties of Amphoteric Cassava Starch Nanoparticles.

Based on the characteristics of charge reversal around the isoelectric point (pI) of amphoteric starch-containing anionic and cationic groups, amphoteric cassava starch nanoparticles (CA-CANPs) are prepared by a W/O microemulsion crosslinking method using (3-chloro-2-hydroxypropyl) trimethyl ammonium chloride as a cationic reagent and POCl3 as an anionic reagent, and the effects of preparation conditions on the particle size of the CA-CANPs are studied in detail in the present study. CA-CANPs with a smooth surface and an average diameter of 252 nm are successfully prepared at the following optimised conditions: a crosslinking agent amount of 15 wt%, an aqueous starch concentration of 6.0 wt%, an oil–water ratio of 10:1, a total surfactant amount of 0.20 g·mL−1, and a CHPTAC amount of 4.05 wt%. The pH-responsive value of the CA-CANPs can be regulated by adjusting the nitrogen–phosphorus molar ratio in the CA-CANPs. By using CA-CANPs with a pI of 6.89 as drug carriers and the paclitaxel (PTX) as a model drug, the maximum loading rate of 36.14 mg·g−1 is achieved, and the loading process is consistent with the Langmuir isotherm adsorption, with the calculated thermodynamic parameters of ΔH° = −37.91 kJ·mol−1, ΔS° = −10.96 J·mol−1·K−1 and ΔG° < 0. By testing the release rate in vitro, it is noted that the release rates of PTX in a neutral environment (37.6% after 96 h) and a slightly acidic environment (58.65% after 96 h) are quite different, suggesting that the CA-CANPs have the possibility of being a targeted controlled-release carrier with pH responsiveness for antitumor drugs.

Ternary association reactions of H3O+, NO+ and O2+• with N2, O2, CO2 and H2O; implications for selected ion flow tube mass spectrometry analyses of air and breath

The reactions of the reagent ions used for trace gas analysis in selected ion flow tube mass spectrometry (SIFT-MS), R+ , viz. H3 O+ , NO+ and O2 + , with the major gases in air and breath samples, M, viz. N2 , O2 , CO2 and H2 O, are investigated. These reactions are seen to form weakly-bound adduct ions, R+ M, by ternary association reactions that must not be mistaken for genuine volatile organic compound (VOC) analyte ions. The ternary association rate coefficients mediated by helium (He) carrier gas atoms, k3a , have been determined for all combinations of R+ and M, which form R+ M adduct ions ranging in m/z from 47 (H3 O+ N2 ) to 76 (O2 +• CO2 ). This was achieved by adding variable amounts of M (up to 0.5mbar pressure) into the He carrier gas (pressure of 1.33 mbar) in a SIFT-MS flow tube at 300 K. Parabolic curvature was observed on some of the semi-logarithmic decay curves that allowed the rate coefficients mediated by M molecules, k3b , to be estimated. Values of k3a were found to range from 1 × 10-31 cm6 s-1 to 5 × 10-29 cm6 s-1 , which form mass spectral R+ M "ghost peaks" of significant strength when analysing VOCs at parts-per-billion concentrations. It was seen that the R+ M adduct ions (except when M is H2 O) react with H2 O molecules by ligand switching forming the readily recognised monohydrates of the initial reagent cations R+ H2 O. Whilst this ligand switching diminishes the R+ M adduct ghost peaks, it does not eliminate them entirely. The significance of these adduct ions for trace gas analysis by SIFT-MS in the low m/z region is alluded to, and some examples are given of m/z spectral overlaps of the R+ M and R+ H2 O adduct cations with analyte cations of VOCs formed by analysis of complex media like exhaled breath, warning that ghost peaks will be enhanced using nitrogen carrier gas in SIFT-MS.

Macro and micro thermal investigation of nanoarchitectonics-based coatings on cotton fabric using new quaternized starch.

Implementation of a new cationizing reagent and its incorporation onto the backbone of starch was performed successfully, confirmed from the remarkable micro- and macro anti-flammable properties. The morphologies and localized compositional analysis of the modified starch-based LBL coatings on the cotton surface were carried out using LV-SEM and EDX: highly uniform coating layers and uptake of solution species for intermediate implant reagent concentrations were confirmed. The subject samples were further analyzed through thermogravimetric analysis (TGA), microcombustion experiments (MCC), flame testing (VFT) and afterburn measurements. The peak range of the degradation was highly improved from the lower range to the higher range (329.92–394.48 °C), together with significant mass residue for TBAB-0.7–17.02%. Moreover, a significant decrease in the absolute heat loss (THR ∼ 30%), heat dissipation competence (HRC ∼ 27.86%), and peak heat output (PHRR ∼ 23%) was achieved for a TBAB loading of ∼0.7 g. The results were further confirmed from the increase in the limiting oxygen index (LOI) to a higher rate of ∼23.2, improved structural integrity and higher quality of char obtained in the VFT and after-burn analysis.

A green approach to starch modification by solvent-free method with betaine hydrochloride

In this study, a novel simple and eco-efficient, semi-dry method with a spray system for starch modification has been developed. Compared to conventional semi-dry methods, this method does not use solvents so that no slurry or semi-liquid mixture is obtained, the material is in a moisted/semi-moisted state. The modification of starch was performed using betaine hydrochloride (BHC) as the cationic reagent, and the characteristics of such starch derivates were compared with cationic starches obtained using glycidyltrimethylammonium chloride (GTMAC). Due to the instability, toxicity, and high cost of the most commonly used GTMAC, it should be replaced with more eco-friendly reagents, such as BHC, which is derived from betaine found in most green plants (e.g., spinach - Spinacia oleracea, beets - Beta vulgaris). The influence of processing conditions such as temperature, concentration of cationic reagents, presence and concentration of natural plasticizers/catalyst on physico-chemical and structural properties of cationic starches have also been studied. The cationic degree varied from 0.045–0.204 for the starch–BHC samples and within the range of 0.066–0.245 for the starch–GTMAC samples. The modification of starch with cationic reagents resulted in an increased solubility and swelling capacity, followed by decreased viscosity of the modified starches.

Carbocation Footprinting of Soluble and Transmembrane Proteins

Here, we introduce carbocations (R3C+) as laser-initiated footprinting reagents for proteins. We screened seven candidates and selected trifluomethoxy benzyl bromide (TFBB) as an effective precursor for the electrophilic trifluomethoxy benzyl carbocation (TFB+) under laser (248 nm) irradiation on the fast photochemical oxidation of proteins (FPOP) platform. Initial results demonstrate that this electrophilic cation reagent affords residue coverage of nucleophilic amino acids including H, W, M, and S. Further, the addition of TFB+ increases the hydrophobicity of the peptides so that separation of isomeric peptide products by reversed-phase LC is improved, suggesting opportunities for subresidue footprinting. Comparison of apo- and holo-myoglobin footprints shows that the TFB+ footprinting is sensitive to protein conformational change and solvent accessibility. Interestingly, because the TFB+ is amphiphilic, the reagent can potentially footprint membrane proteins as demonstrated for vitamin K epoxide reductase (VKOR) stabilized in a micelle. Not only does footprinting of the extra-membrane domain occur, but also some footprinting of the hydrophobic transmembrane domain is achieved owing to the interaction of TFB+ with the micelle. Carbocation precursors are stable and amenable for tailoring their properties and those of the incipient carbocation, enabling targeting their soluble or membrane-associated or embedded regions and distinguishing between the extra- and trans-membrane domains of membrane proteins.