Coacervation of Cationic Gemini Surfactant with <i>N</i>‑Benzoylglutamic Acid in Aqueous Solution

Coacervation of cationic gemini surfactant hexamethylene-1,6-bis­(dodecyldimethylammonium bromide) (12–6–12) with pH-sensitive <i>N</i>-benzoylglutamic acid (H₂Bzglu) has been investigated by potentiometric pH-titration, turbidity titration, dynamic light scattering (DLS), isothermal titration calorimetry (ITC), TEM, ¹H NMR, and light microscopy. Phase boundaries of the 12–6–12/H₂Bzglu mixture were obtained over the pH range from 2 to 9 and in the H₂Bzglu concentration range from 30.0 to 50.0 mM at pH 4.5. When the H₂Bzglu concentration is beyond 30.0 mM, the 12–6–12/H₂Bzglu mixed solution undergoes the phase transitions from soluble aggregate, to precipitate, coacervate, and soluble aggregate again as pH increases. The results indicate that coacervation occurs at extremely low 12–6–12 concentration and lasts over a wide surfactant range, and can be enhanced or suppressed by changing pH, 12–6–12/H₂Bzglu molar ratio and H₂Bzglu concentration. The coacervates present a disorderly connected lay structure. Coacervation only takes place at pH 4–5, where the aggregates are nearly charge neutralized, and a minimum H₂Bzglu concentration of 30.0 mM is required for coacervation. In this pH range, H₂Bzglu mainly exist as HBzglu^–. The investigations on intermolecular interactions indicate that the aggregation of 12–6–12 is greatly promoted by the strong electrostatic and hydrophobic interactions with the HBzglu^– molecules, and the interaction also promotes the formation of dimers, trimers, and tetramers of HBzglu^– through hydrogen bonds. The double chains of 12–6–12 and the HBzglu^– oligomers can play the bridging roles connecting aggregates. These factors endow the mixed system with a very high efficiency in generating coacervation

Mass Measurement of Single Intact Nanoparticles in a Cylindrical Ion Trap

Accurate nanoparticle mass characterization is a challenging task, especially at a single particle level. To solve this problem, a strategy for the mass measurement of single intact nanoparticle was proposed. A microscopy-based ion trap mass spectrometer was built up. To improve the detection sensitivity, a cylindrical ion trap with transparent conductive end-caps was used to increase the transmission of scattered light, and a vacuum ultraviolet lamp was used to increase the charge state of the isolated nanoparticle. By detecting the scattered light of the isolated nanoparticle, a series of secular frequencies were obtained, from which the corresponding mass-to-charge ratio of the nanoparticle was calculated. Finally, a Labview program was used to help deduce the charge state and absolute mass of the individual nanoparticle. Masses of gold nanoparticles with different sizes were accurately examined, which are (5.08 ± 0.44) × 10⁷ Da for 20 nm, (3.55 ± 0.34) × 10⁸ Da for 40 nm, and (1.22 ± 0.14) × 10⁹ Da for 60 nm, respectively. The mass of MOFs with irregular shapes was also determined, which is (6.48 ± 1.08) × 10⁹ Da. This method can provide the mass information on nanomaterials, thus opens up new possibility of characterizing nanoparticles at the single particle level

Differentiation and Relative Quantitation of Disaccharide Isomers by MALDI-TOF/TOF Mass Spectrometry

Saccharide isomer differentiation has been a challenge in glycomics, as the lack of technology to decipher fully the diverse structures of compositions, linkages, and anomeric configurations. Several mass spectrometry-based methods have been applied to the discrimination of disaccharide isomers, but limited quantitative analyses have been reported. In the present study, MALDI-LIFT-TOF/TOF has been investigated to differentiate and relatively quantify underivatized glucose-containing disaccharide isomers that differ in composition, connectivity or configuration. <i>N</i>-(1-naphthyl)­ethylenediamine dihydrochloride (NEDC) was used as a highly sensitive matrix without matrix interferences in low mass range, thus yielding intense chloride-attached disaccharide ions [M + Cl]⁻, which could be fragmented to give diagnostic characteristic fragment patterns for distinguishing these isomers. Three different types of disaccharide isomers were successfully relatively quantified in a binary mixture using the specific product ion pairs. Finally, this method was utilized to identify and relatively quantify two disaccharide isomers in Medicago leaf (maltose and sucrose) without numerous preparation steps. In general, this method is a fast, effective, and robust method for rapid differentiation and quantitation of disaccharide isomers in complex medium

Utilizing a Mini-Humidifier To Deposit Matrix for MALDI Imaging

MALDI mass spectrometry imaging (MALDI-MSI) is a powerful tool to study endogenous metabolites. The process of matrix deposition is crucial for a high-quality imaging result. Commercial instruments for matrix deposition are expensive. Low-cost methods like airbrushing will generate matrix crystals that are too large for high-spatial-resolution imaging. Sublimation may cause some compounds to go undetected because of the lack of solvent. Herein, we utilized a mini-humidifier, costing less than 5 dollars, to deposit matrix for MALDI-MSI. Compared with Imageprep, a commercialized instrument, our device based on the humidifier provided higher sensitivity and much smaller matrix crystals with diameters of less than 10 μm. High-quality ion images with 10 μm spatial resolution were obtained using our method. The enhancement of sensitivity by the humidifier could provide a sufficient amount of ions to perform tandem mass imaging. We also performed MALDI-MS/MS imaging to separate two lipids in mouse brain

<i>N</i>‑Phenyl-2-naphthylamine as a Novel MALDI Matrix for Analysis and in Situ Imaging of Small Molecules

Due to its strong ultraviolet absorption, low background interference in the small molecular range, and salt tolerance capacity, <i>N</i>-phenyl-2-naphthylamine (PNA) was developed as a novel matrix in the present study for analysis and imaging of small molecules by matrix-assisted laser desorption/ionization mass spectrometry time-of-fight (MALDI-TOF MS). The newly developed matrix displayed good performance in analysis of a wide range of small-molecule metabolites including free fatty acids, amino acids, peptides, antioxidants, and phospholipids. In addition, PNA-assisted LDI MS imaging of small molecules in brain tissue of rats subjected to middle cerebral artery occlusion (MCAO) revealed unique distributions and changes of 89 small-molecule metabolites including amino acids, antioxidants, free fatty acids, phospholipids, and sphingolipids in brain tissue 24 h postsurgery. Fifty-nine of the altered metabolites were identified, and all the changed metabolites were subject to relative quantitation and statistical analysis. The newly developed matrix has great potential application in the field of biomedical research

Laser Cleavable Probes-Based Cell Surface Engineering for <i>in Situ</i> Sialoglycoconjugates Profiling by Laser Desorption/Ionization Mass Spectrometry

Cell-surface sialoglycoconjugates (sialoglycoproteins and sialoglycolipids) play important roles in cell–cell interactions and related tumor metastasis process. Although there have been some analytical methods to evaluate the sialoglycoconjugates, an effective method providing both qualitative and quantitative information is still deficient. Here we establish an extraction-free, sensitive, and high-throughput platform to realize <i>in situ</i> detection of the cell-surface sialoglycoconjugates on various cell lines, e.g., cancer and normal cells by laser desorption/ionization mass spectrometry (LDI MS). In this proposal, azide groups were introduced into the ends of cell-surface sialoglycoconjugates by the biorthogonal method, and then the sialoglycoconjugates were armed with a laser-cleavable probe (Tphsene) through click chemistry. We can easily get the probes signal under laser irradiation, which reflected the presence of cell-surface sialoglycoconjugates. Different cell lines were discriminated simultaneously, and the LDI relative quantification agreed with fluorescent results. Besides, a linear quantitation relationship in the range of 100 fmol to 100 pmol was obtained with a designed and synthesized internal standard (phTsane) added. A detection limit of 5 fmol was obtained with good reproducibility. Based on the quantitative and high-throughput ability, we conducted pharmacodynamics study of drug (tunicamycin) on cancer cells. In addition, we found the tag was safe from sweet-spot effect of matrix adding. The simultaneous detection of sialoglycoconjugates and metabolites was therefore achieved. We believe that this laser cleavable probes-based cell-surface engineering for sialoglycoconjugates platform means great significance to diagnosis, prognosis, and therapeutic purposes. Besides, this strategy can be applied to other glycoconjugates which is hard to detect and the related disease processes when more corresponding chemically modified sugar substrates and exact biorthogonal reactions are developed

Quantitative Analysis of Oligosaccharides Derived from Sulfated Glycosaminoglycans by Nanodiamond-Based Affinity Purification and Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry

Degraded fragments of sulfated glycosaminoglycans (GAGs) are key reporters for profiling the burden of mucopolysaccharidosis (MPS) disease at baseline and during therapy. Here, we present a high-throughput assay, which combines microwave-assisted degradation, solid-phase affinity purification, and matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS), for quantitative analysis of sulfated oligosaccharides in biological samples. First, sulfated oligosaccharides such as chondroitin-4-sulfate (CS) were efficiently isolated from highly diluted solutions or spiked artificial cerebrospinal fluid (aCSF) using polyarginine-coated nanodiamonds (PA-coated NDs) as affinity sorbents. Next, they were degraded to disaccharides through microwave-assisted methanolysis or enzymatic digestion for subsequent MALDI-TOF MS analysis. The reaction times for GAG depolymerization were significantly reduced from a few hours to less than 7 min under the microwave irradiation. Deuterium-labeled internal standards were then mixed with the CS-derived disaccharides for quantitative analysis by MALDI-TOF MS using the <i>N</i>-(1-naphthyl) ethylenediamine dihydrochloride (NEDC) matrix. The new assay is facile, specific (with distinct chlorine-isotope trait markers), sensitive (with a detection limit of ∼70 pg), and potentially useful for clinical diagnosis of MPS

High-Salt-Tolerance Matrix for Facile Detection of Glucose in Rat Brain Microdialysates by MALDI Mass Spectrometry

Due to its strong ultraviolet absorption, high salt tolerance, and little interference in the low molecular weight region, <i>N</i>-(1-naphthyl) ethylenediamine dihydrochloride (NEDC) has been applied as a matrix to measure the level of glucose in rat brain microdialysates by matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) in combination with in vivo microdialysis. By monitoring the ion signals of (glucose + Cl)⁻ in the mass spectra, we achieved a low detection limit of ∼10 μM for glucose in 126 mM NaCl, which is a typical component in artificial cerebrospinal fluid, without prior sample purification. It is concluded that NEDC-assisted laser desorption/ionization (LDI) MS is a fast and general method for sensitive detection of small molecules (such as glucose and amino acids) in high ionic strength solutions

Carbon Nanodots As a Matrix for the Analysis of Low-Molecular-Weight Molecules in Both Positive- and Negative-Ion Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry and Quantification of Glucose and Uric Acid in Real Samples

Carbon nanodots were applied for the first time as a new matrix for the analysis of low-molecular-weight compounds by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) in both positive- and negative-ion modes. A wide range of small molecules including amino acids, peptides, fatty acids, as well as β-agonists and neutral oligosaccharides were analyzed by MALDI MS with carbon nanodots as the matrix, and the lowest 0.2 fmol limits-of-detection were obtained for octadecanoic acid. Clear sodium and potassium adducts and deprotonated signals were produced in positive- and negative-ion modes. Furthermore, the glucose and uric acid in real samples were quantitatively determined by the internal standard method with the linear range of 0.5–9 mM and 0.1–1.8 mM (<i>R</i>² > 0.999), respectively. This work gives new insight into the application of carbon nanodots and provides a general approach for rapid analysis of low-molecular-weight compounds

Quantitative Assessment of Protein Adsorption on Microparticles with Particle Mass Spectrometry

In this paper, particle mass spectrometry (PMS), which consists of an aerodynamic desorption/ionization (AD) source, a quadrupole ion trap (QIT) mass analyzer, and a charge detector, was exploited to characterize the protein adsorption on microparticles based on the mass variations of microparticles before and after protein adsorption. This method is simple and has low sample cost. Importantly, its mass resolution is good enough to distinguish the microparticles with and without protein. For the adsorption of bovine serum albumin (BSA) on 3 μm porous poly styrene-divinylbenzene (poly S-DVB), the minimum mass increase that can be resolved by PMS corresponds to 128 fg (1.8 ng/cm²) or 1.17 × 10⁶ BSA molecules on each poly S-DVB particle. With PMS, the adsorption process of BSA on poly S-DVB spheres was successfully characterized, and the obtained maximum adsorption capacity <i>q</i>_m and dissociation constant <i>K</i>_d were consistent with that determined by the conventional depletion method. In addition, the influence of surface modification of silica particles on the enzyme immobilization was evaluated. Compared with C₄ (propyldimethylsilane), C₈ (octyldimethylsilane), and Ph (phenyldimethylchlorosilane), the CN (cyanoethyldimethylchlorosilane) functionalized silica particles were screened to be most beneficial for the immobilization of both lysozyme and trypsin