Matrix-assisted laser desorption/ionization mass spectrometry of discrete mass poly(butylene glutarate) oligomers

Rapid screening of marine bacterial symbionts using MALDI-TOF MS

Matrix-Assisted Laser Desorption Ionization Time-Of-Flight Mass Spectrometry (MALDI-TOF MS) is a rapid, cost-effective and high-throughput method for bacteria characterization. However, most previous studies focused on clinical isolates. In this study, we evaluated the use of MALDI-TOF MS as a rapid screening tool for marine bacterial symbionts. A set of 255 isolates from different marine sources (corals, sponge, fish and seawater) was analyzed using cell lysates to obtain a rapid grouping. Cluster analysis of mass spectra and 16S rRNA showed 18 groups, including Vibrio, Bacillus, Pseudovibrio, Alteromonas and Ruegeria. MALDI-TOF distance similarity scores ≥ 60% and ≥ 70% correspond to ≥ 98.7% 16S rRNA gene sequence similarity and ≥ 95% pyrH gene sequence similarity, respectively. MALDI-TOF MS is a useful tool for Vibrio species groups' identification.

Mass Spectrometry of Polyurethanes

This review covers the applications of mass spectrometry (MS) and its hyphenated techniques to characterize polyurethane (PU) synthetic polymers and their respective hard and soft segments. PUs are commonly composed of hard segments including methylene bisphenyl diisocyanate (MDI) and toluene diisocyanate (TDI), and soft segments including polyester and polyether polyols. This literature review highlights MS techniques such as electrospray ionization (ESI), matrix assisted laser/desorption ionization (MALDI), ion mobility-mass spectrometry (IM-MS), and computational methods that have been used for the characterization of this polymer system. Here we review specific case studies where MS techniques have elucidated unique features pertaining to the makeup and structural integrity of complex PU materials and PU precursors.

Engineering a Microbial Consortium Based Whole-Cell System for Efficient Production of Glutarate From L-Lysine

Glutarate is an important C5 platform chemical produced during the catabolism of L-lysine through 5-aminovalerate (5-AMV) pathway. Here, we first established a whole-cell biocatalysis system for the glutarate production from L-lysine with the engineered Escherichia coli (E. coli) that co-expressed DavAB and GabDT. However, the accumulation of intermediate 5-AMV was identified as one important factor limiting glutarate production. Meanwhile, the negative interaction of co-expressing DavAB and GabDT in a single cell was also confirmed. Here, we solved these problems through engineering a microbial consortium composed of two engineered E. coli strains, BL21-22AB and BL21-YDT, as the whole-cell biocatalysts, each of which contains a part of the glutarate pathway. After the optimization of bioconversion conditions, including temperature, metal ion additives, pH, and cell ratio, 17.2 g/L glutarate was obtained from 20 g/L L-lysine with a yield of 95.1%, which was improved by 19.2% compared with that in a single cell. Little accumulation of 5-AMV was detected. Even at the high substrate concentration, the reduced 5-AMV accumulation and increased glutarate production were achieved. This synthetic consortium produced 43.8 g/L glutarate via a fed-batch strategy, the highest titer reported to date.

Consequences of Dispersity on the Self-Assembly of ABA-Type Amphiphilic Block Co-Oligomers

Intriguingly, little is known about the impact of dispersity on the crystallization driven self-assembly (CDSA) of amphiphilic block copolymers in aqueous media. Here, we investigate the influence of dispersity on the CDSA of ABA-type amphiphilic block co-oligomers (ABCOs). Two pairs of ABCOs are synthesized comprising discrete (Đ = 1.00) or disperse (Đ = 1.20) isotactic l-lactic acid 16-mers as the semicrystalline hydrophobic block and either oligo(ethylene glycol) methyl ether (MeOoEG) or oligo(tetraethylene glycol succinate) (oTEGSuc) as the discrete hydrophilic block. Self-assembly studies in water with 10% THF reveal uniform nanofibers/2D sheets for the discrete oligomers, but such structural regularity is largely compromised in the disperse oligomers. The results are corroborated by sharp melting transitions in both solution and bulk for the discrete ABCOs, unlike their disperse analogues that show a lack of crystallization. Interestingly, the discrete MeOoEG-LLA oligomer reveals crystallization driven gelation, illustrating the contrasting differences between the discrete oligomers and their disperse counterparts.

Scalable synthesis of sequence-defined, unimolecular macromolecules by Flow-IEG

We report a semiautomated synthesis of sequence and architecturally defined, unimolecular macromolecules through a marriage of multistep flow synthesis and iterative exponential growth (Flow-IEG). The Flow-IEG system performs three reactions and an in-line purification in a total residence time of under 10 min, effectively doubling the molecular weight of an oligomeric species in an uninterrupted reaction sequence. Further iterations using the Flow-IEG system enable an exponential increase in molecular weight. Incorporating a variety of monomer structures and branching units provides control over polymer sequence and architecture. The synthesis of a uniform macromolecule with a molecular weight of 4,023 g/mol is demonstrated. The user-friendly nature, scalability, and modularity of Flow-IEG provide a general strategy for the automated synthesis of sequence-defined, unimolecular macromolecules. Flow-IEG is thus an enabling tool for theory validation, structure-property studies, and advanced applications in biotechnology and materials science.

Comparison of two matrix-assisted laser desorption ionization-time of flight mass spectrometry methods with conventional phenotypic identification for routine identification of bacteria to the species level

Bacterial identification relies primarily on culture-based methodologies requiring 24 h for isolation and an additional 24 to 48 h for species identification. Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) is an emerging technology newly applied to the problem of bacterial species identification. We evaluated two MALDI-TOF MS systems with 720 consecutively isolated bacterial colonies under routine clinical laboratory conditions. Isolates were analyzed in parallel on both devices, using the manufacturers' default recommendations. We compared MS with conventional biochemical test system identifications. Discordant results were resolved with "gold standard" 16S rRNA gene sequencing. The first MS system (Bruker) gave high-confidence identifications for 680 isolates, of which 674 (99.1%) were correct; the second MS system (Shimadzu) gave high-confidence identifications for 639 isolates, of which 635 (99.4%) were correct. Had MS been used for initial testing and biochemical identification used only in the absence of high-confidence MS identifications, the laboratory would have saved approximately US$5 per isolate in marginal costs and reduced average turnaround time by more than an 8-h shift, with no loss in accuracy. Our data suggest that implementation of MS as a first test strategy for one-step species identification would improve timeliness and reduce isolate identification costs in clinical bacteriology laboratories now.

Versatile strategy for the synthesis of dendronlike polypeptide/linear poly(epsilon-caprolactone) block copolymers via click chemistry

A new class of dendron-like polypeptide/linear poly(epsilon-caprolactone) block copolymers with asymmetrical topology (i.e., dendron-like poly(gamma-benzyl-l-glutamate)/linear PCL copolymers having 2(m) PBLG branches, m = 0, 1, 2, and 3; denoted as PCL-Dm-PBLG) was for the first time synthesized via the combination of controlled ring-opening polymerization (ROP) of epsilon-caprolactone, click chemistry, and the ROP of gamma-benzyl-l-glutamate N-carboxyanhydride (BLG-NCA). The linear hydroxyl-terminated PCL (PCL-OH) was synthesized by controlled ROP of epsilon-caprolactone and then transformed into clickable azide-terminated PCL (PCL-N(3)). The PCL-N(3) precursor was further click conjugated with propargyl focal point PAMAM-typed dendrons (i.e., Dm having 2(m) primary amine groups) to generate PCL-dendrons (PCL-Dm) using CuBr/PMDETA as catalyst in dimethylformamide solution at 35 degrees C. Finally, PCL-Dm was used as macroinitiator for the ROP of BLG-NCA monomer to produce the targeted PCL-Dm-PBLG block copolymers. Their molecular structures and physical properties were characterized in detail by FT-IR, NMR, matrix assisted laser desorption ionization time-of-flight mass spectrometry, gel permeation chromatography, differential scanning calorimetry, and wide-angle X-ray diffraction. To the best of our knowledge, this is the first report that describes the synthesis of dendron-like polypeptide/linear PCL block copolymers with asymmetrical topology via the combination of ROP and click chemistry. Consequently, this provides a versatile strategy for the synthesis of biodegradable and biomimetic dendron-like polypeptide-based biohybrids.

Interpretation of Reversible Addition−Fragmentation Chain-Transfer Polymerization Mechanism by MALDI-TOF-MS

Several polystyrene polymers were prepared by reversible addition-fragmentation chain-transfer (RAFT) polymerization of styrene, using two different RAFT agent-initiator systems, and then further characterized by NMR and SEC as well as MALDI-TOF-MS techniques. The data indicate that most of the polymer chains are terminated by the active groups (Ph-C(=S)-S-) derived from RAFT agents, and few of the polymer chains bear initiator fragments at one end. Most importantly, the structures arising from the intermediate RAFT radicals and their cross-termination adducts were detected. Also, the MALDI-TOF-MS analysis shows that the combination termination between two macromolecular radicals is minor, and the amount of dead chains is quite low. Thus, narrow molecular weight distribution is obtained. This analysis confirms the operation of the Rizzardo mechanism including the Monteiro intermediate radical termination model for the RAFT polymerization.

Molar mass of main-chain bile acid-based oligo-esters measured by SEC, MALDI-TOF spectrometry and NMR spectroscopy: A comparative study

Bile acid-based polymers are promising new materials for biomedical applications. The determination of their molar mass, as for other novel polymers, has been difficult, due to the lack of suitable standards for size exclusion chromatography (SEC). In order to solve this problem, a family of main-chain bile acid-based oligo-esters has been synthesized by acyclic diene metathesis to be used as analogues in such analysis. These oligomers have been characterized by SEC, MALDI-TOF mass spectrometry and NMR spectroscopy. The results show that SEC with polystyrene standards tends to overestimate the molar mass of these materials and that a correction factor between 0.50 and 0.60 should be used for more accuracy.

Effect of delay time and grid voltage changes on the average molecular mass of polydisperse polymers and polymeric blends determined by delayed extraction matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

The dependence of the calculated average molecular mass of a polyethylene glycol with a large polydispersity on the instrumental parameters adopted in the acquisition of mass spectra using delayed extraction matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (DE MALDI-TOFMS) was investigated. It has been shown that a combined effect of delay times and potential gradients can act on the ion cloud in the source chamber affecting both mass resolution and average molecular mass value of the analyzed polymeric sample. Also examined was a blend of two different polymers (a PEG and a PMMA commercial sample having a similar average molecular mass), which presents an additional problem concerning the discrimination among the different polymer species as a function of the experimental conditions. In this work, the best instrumental conditions to obtain both good resolution and a correct average molecular mass for the examined polydisperse sample are reported.