Chiral zwitterionic stationary phases based on Cinchona alkaloids and dipeptides: Application in chiral separation of dipeptides under reversed phase conditions.

Chromatographic behavior of novel chiral stationary phases with bonded selectors based on Cinchona alkaloids modified with dipeptides was studied using dipeptides as probe molecules. Buffer-free and salt containing hydro-organic solutions were used as the mobile phases. The selectors exhibit pseudoenantiomeric behavior with respect to the L/D or LL/DD enantiomers and do not behave so with respect to the LD/DL enantiomers. The alkaloid part of the selectors is the driver of enantioselectivity, while the dipeptide substituent plays a modulating role. The quinidine-based selectors demonstrate stronger adsorption affinity and higher enantioselectivity as compared to the quinine-based selectors. The dipeptide analytes containing a glycyl fragment are weaker retained and their enantiomers are worse separated comparing to dipeptides with both units being larger amino acids. Moreover, a phenyl group in the structure of a dipeptide analyte facilitates enantioseparation. The effect of the mobile phase composition on retention depends on the hydrophobicity of an analyte. Hydrophobic dipeptides are better eluted by methanol-rich solvents, hydrophilic dipeptides are better eluted with water-rich solvents, and dipeptides with an intermediate hydrophobicity demonstrate a U-shaped or more complicated dependence of the retention factor on the percentage of methanol. Even a small buffer addition to the mobile phase decreases retention, but the ion-exchange mechanism was not confirmed. The effect of an electrolyte is rather due to the shielding of the charged groups of the selector reducing thereby electrostatic interaction between the selector and analyte. Efficiency of the novel columns is comparable to that of other brush-type chiral columns, the highest achieved number of the theoretical plates per 1 m varying between 30,000 and 40,000.

Anti-Quorum-Sensing Activity of Tryptophan-Containing Cyclic Dipeptides.

Quorum sensing (QS) can regulate the pathogenicity of bacteria and the production of some virulence factors. It is a promising target for screening to find anti-virulence agents in the coming post-antibiotics era. Cyclo (L-Trp-L-Ser), one variety of cyclic dipeptides (CDPs), isolated from a marine bacterium Rheinheimera aquimaris, exhibited anti-QS activity against Chromobacterium violaceum CV026 and Pseudomonas aeruginosa PAO1. Unlike the CDPs composed of phenylalanine or tyrosine, the anti-QS activity has been widely studied; however, cyclo (L-Trp-L-Ser) and derivatives, containing one tryptophan unit and one non-aromatic amino acid, have not been systematically explored. Herein, the cyclo (L-Trp-L-Ser) and seven derivatives were synthesized and evaluated. All tryptophane-contained CDPs were able to decrease the production of violacein in C.violaceum CV026 and predicted as binding within the same pocket of receptor protein CviR, but in lower binding energy compared with the natural ligand C6HSL. As for P. aeruginosa PAO1, owning more complicated QS systems, these CDPs also exhibited inhibitory effects on pyocyanin production, swimming motility, biofilm formation, and adhesion. These investigations suggested a promising way to keep the tryptophan untouched and make modifications on the non-aromatic unit to increase the anti-QS activity and decrease the cytotoxicity, thus developing a novel CDP-based anti-virulence agent.

Preparation of 177Lu-PSMA-617 in Hospital Radiopharmacy: Convenient Formulation of a Clinical Dose Using a Single-Vial Freeze-Dried PSMA-617 Kit Developed In-House.

OBJECTIVE: In the recent time, endoradionuclide therapy for metastatic castration-resistant prostate carcinoma employing 177Lu-PSMA-617 has yielded encouraging results and several clinical trials with the agent are currently ongoing. Routine preparation of 177Lu-PSMA-617 patient doses can be made simpler and convenient, if the ingredients essential for radiolabeling are made available in a ready-to-use lyophilized form. METHODS: PSMA-617 freeze-dried kit was formulated and used for the preparation of 177Lu-PSMA-617 clinical dose with high radiochemical purity using low/medium specific activity 177Lu. Detailed radiochemical studies were performed to determine the maximum activity and volume of 177LuCl3, which can be added in the kit for the formulation of 177Lu-PSMA-617. Studies were also performed to determine the shelf life of the kit to ensure its long-term usage. Studies were performed in buffer as well as human serum medium to determine the stability of the 177Lu-PSMA-617 complex after storing in respective media up to 7 days postpreparation. About ten patient doses of 177Lu-PSMA-617 were administered, and posttherapy scans were acquired. RESULTS: The formulated freeze-dried kit of PSMA-617 could be radiolabeled with an average percentage radiochemical purity > 98.53 ± 0.38. The freeze-dried kit was found suitable for tolerating up to 0.5 mL of 177LuCl3 (in 0.01 N HCl) and specific activity of 555 MBq/µg (15 mCi/µg) for the preparation of the patient dose of 177Lu-PSMA-617. The 177Lu-PSMA-617 complex prepared using the freeze-dried kit of PSMA-617 was observed to maintain % radiochemical purity (RCP) of 96.74 ± 0.87 and 94.81 ± 2.66, respectively, even after storing up to 7 days in buffer and human serum, respectively. 177Lu-PSMA-617 prepared using the in-house formulated freeze-dried kit of PSMA-617 exhibited accumulation in metastatic lesions picked up in a pretherapy PET scan. Reduction in number as well as size of lesions was observed in posttherapy scans acquired after two months of administering the first therapeutic dose of 177Lu-PSMA-617. CONCLUSIONS: The freeze-dried kit of PSMA-617 could be used for the preparation of 177Lu-PSMA-617 with high radiochemical purity (>98%) in a reproducible manner. 177Lu-PSMA-617 prepared using the developed kit was successfully evaluated in patients suffering from metastatic prostate cancer.

Application of Capillary and Free-Flow Zone Electrophoresis for Analysis and Purification of Antimicrobial ß-Alanyl-Tyrosine from Hemolymph of Fleshfly Neobellieria bullata.

The problem of a growing resistance of bacteria and other microorganisms to conventional antibiotics gave rise to a search for new potent antimicrobial agents. Insect antimicrobial peptides (AMPs) seem to be promising novel potential anti-infective therapeutics. The dipeptide ß-alanyl-tyrosine (ß-Ala-Tyr) is one of the endogenous insect toxins exhibiting antibacterial activity against both Gram-negative and Gram-positive bacteria. Prior to testing its other antimicrobial activities, it has to be prepared in a pure form. In this study, we have developed a capillary zone electrophoresis (CZE) method for analysis of ß-Ala-Tyr isolated from the extract of the hemolymph of larvae of the fleshfly Neobellieria bullata by reversed-phase high-performance liquid chromatography (RP-HPLC). Based on our previously described correlation between CZE and free-flow zone electrophoresis (FFZE), analytical CZE separation of ß-Ala-Tyr and its admixtures have been converted into preparative purification of ß-Ala-Tyr by FFZE with preparative capacity of 45.5 mg per hour. The high purity degree of the ß-Ala-Tyr obtained by FFZE fractionation was confirmed by its subsequent CZE analysis.

Isolation of balenine from opah (Lampris megalopsis) muscle and comparison of antioxidant and iron-chelating activities with other major imidazole dipeptides.

Balenine (Bal) in opah muscle was extracted using hot water and purified by ion-exchange chromatography and recrystallization to provide 41 g of over 95% pure Bal from 1 kg of opah muscle. The structure of purified Bal was identical to that of an authentic Bal standard by NMR analysis. The antioxidant (ORAC and HORAC values) and Fe(II) ion-chelating abilities of purified Bal were examined by comparison with two major imidazole dipeptides, carnosine (Car) and anserine (Ans). Opah-derived Bal showed significantly higher ORAC and HORAC values and Fe(II) ion-chelating ability at 0.3 mM. In silico molecular simulation revealed that Bal and Car formed hydrogen bonds between the hydrogen atom of the imidazole imino group and the carboxyl carbonyl oxygen, whereas Ans did not. The proposed method for extracting and purifying Bal from opah muscle suggests that opah can be utilized as a functional food or Bal resource.

Effects of amino acid-derived chiral ionic liquids on cyclodextrin-mediated capillary electrophoresis enantioseparations of dipeptides.

The synergistic effect of chiral ionic liquids composed of tetraalkylammonium ions and the amino acids Asn, Asp or Pro on the enantioseparations of dipeptides mediated by ß-cyclodextrin and 2-hydroxypropyl-ß-cyclodextrin in capillary electrophoresis was studied. Addition of a chiral ionic liquid resulted in a concentration-dependent increase in the enantioresolutions compared to the sole presence of a cyclodextrin in the background electrolyte. The extent varied with the tetraalkylammonium cation (tetramethylammonium versus tetrabutylammonium) as well as the amino acid component of the ionic liquid. The presence of a chiral ionic liquid did not counteract the pH-dependent reversal of the enantiomer migration order of the dipeptides Ala-Phe, Ala-Tyr and Phe-Phe when increasing the pH of the background electrolyte from 2.5 to 3.5. Comparing the effect of a chiral ionic liquid based on Asp with the addition of equimolar concentrations of the individual components of the ionic liquid, a diverse picture was observed. In some cases, higher resolution values were obtained with the chiral ionic liquid, while for other cases superior enantioseparations were obtained upon separate addition of the amino acid component and a tetraalkylammonium chloride. With regard to the stereochemistry of the amino acid, a superior effect was typically observed using the l-configured amino acid, but in some cases higher resolution values were found in the presence of d-Asp. The rationale for the diverse observations is not obvious and may be due to the zwitterionic nature of analytes as well as the amino acid component of the chiral ionic liquid.

Biotechnological and Ecological Potential of Micromonospora provocatoris sp. nov., a Gifted Strain Isolated from the Challenger Deep of the Mariana Trench.

A Micromonospora strain, isolate MT25T, was recovered from a sediment collected from the Challenger Deep of the Mariana Trench using a selective isolation procedure. The isolate produced two major metabolites, n-acetylglutaminyl glutamine amide and desferrioxamine B, the chemical structures of which were determined using 1D and 2D-NMR, including 1H-15N HSQC and 1H-15N HMBC 2D-NMR, as well as high resolution MS. A whole genome sequence of the strain showed the presence of ten natural product-biosynthetic gene clusters, including one responsible for the biosynthesis of desferrioxamine B. Whilst 16S rRNA gene sequence analyses showed that the isolate was most closely related to the type strain of Micromonospora chalcea, a whole genome sequence analysis revealed it to be most closely related to Micromonospora tulbaghiae 45142T. The two strains were distinguished using a combination of genomic and phenotypic features. Based on these data, it is proposed that strain MT25T (NCIMB 15245T, TISTR 2834T) be classified as Micromonospora provocatoris sp. nov. Analysis of the genome sequence of strain MT25T (genome size 6.1 Mbp) revealed genes predicted to responsible for its adaptation to extreme environmental conditions that prevail in deep-sea sediments.

Serine-glycine-betaine, a novel dipeptide from an endophyte Macrophomina phaseolina: isolation, bioactivity and biosynthesis.

AIMS: Endophytes are a rich source for structurally complex chemical scaffolds with interesting biological activities. Endophytes associated with Brugmansia aurea L. (family: Solanaceae), a medicinal plant, have not yet explored for the bioactive metabolites. METHOD AND RESULTS: Hence, Macrophomina phaseolina, a fungal endophyte, was isolated from the roots of the plant. Its methanolic extract was found active against human cancer cell lines with IC50 <20 µg ml-1 . Later, a di-peptide compound, serine-glycine-betaine, was isolated and characterized. Serine-glycine-betaine consists of a unit of an N-trimethyl glycine attached to serine. It exhibited potent activity against MIA PaCa-2 and HCT-116 cell lines with IC50 8·9 and 15·16 µmol l-1 , respectively. Furthermore, it induced apoptosis in MIA PaCa-2 cells confirmed by microscopy. The apoptotic cell death in MIA PaCa-2 cells was evidenced biochemically with the generation of intracellular reactive oxygen species level and leading to loss of mitochondrial membrane potential due to activation of the intrinsic pathway. This study describes the plausible biosynthesis of serine-glycine-betaine based on genomics (genome sequencing, annotation and genes alignment). CONCLUSIONS: A novel di-peptide, serine-glycine-betaine isolated from M. phaseolina induced apoptosis in MIA-Pa-Ca-2 cells. SIGNIFICANCE AND IMPACT OF THE STUDY: This study confirms that dipeptides like serine-glycine-betaine and tyrosine-betaine might be specific to fungal genera, hence being used for diagnostic purposes.

Enantioseparation of alanyl-phenylalanine analogs by capillary electrophoresis using negatively charged cyclodextrins as chiral selectors.

The separation of the ll- and dd-enantiomers of the dipeptides Ala-Phe, Ala-phenylglycine (Phg), Ala-homoPhe, Ala-ß-Phe, Gly-Phe and ß-Ala-Phe was studied by capillary electrophoresis in the presence of negatively charged α-, ß- and γ-cyclodextrin (CD) derivatives. Analysis was performed under standardized conditions in fused-silica capillaries at pH 2.5, 3.5 and 5.3. All analyte enantiomers could be separated at pH 2.5 under at least one of the experimental conditions. Especially ß-CD derivatives proved to be effective chiral selectors. The enantiomer migration order depended on CD cavity size and substituent type, while peptide structure had only a minor effect. Upon increasing the pH from 2.5 to 5.3, reversal of the enantiomer migration order was observed frequently. Investigation of the apparent and, in the case of randomly substituted CDs, averaged complexation constants and mobilities of the diastereomeric peptide enantiomer-CD complexes indicated that in most cases the migration order in the presence of sulfated α-, ß- and γ-CD and heptakis(6-O-sulfo)-ß-CD could be explained by the stronger binding of the second migrating analyte by the CD at pH 2.5. However, in few cases the weaker bound enantiomer migrated second, which could be attributed to the higher mobility of the respective CD complexes. At pH 5.3, similar data were obtained for sulfated ß-CD and heptakis(6-O-sulfo)-ß-CD, i.e. the strength of the complexes determined the migration order for some peptides, while the migration sequence was based on the apparent (and averaged) mobility of the diastereomeric analyte-CD complexes in other cases.

Anti-cancer Evaluation of Depsides Isolated from Indonesian Folious Lichens: Physcia millegrana, Parmelia dilatata and Parmelia aurulenta.

Cancer is a serious health burden on global societies. The discovery and development of new anti-cancer therapies remains a challenging objective. Although it has been shown that lichen secondary metabolites may be potent sources for new anti-cancer agents, the Indonesian- grown folious lichens, Physcia millegrana,Parmelia dilatata and Parmeila aurulenta, have not yet been explored. In this study exhaustive preparative high-performance liquid chromatography was employed to isolate the lichen constituents with spectroscopic and spectrometric protocols identifying nine depsides 9-17, including the new methyl 4-formyl-2,3-dihydroxy-6-methylbenzoate 13. The cytotoxicity of the depsides towards cancer cells was assessed using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The results indicated lowest toxicity of the depsides towards human A549 lung cancer cells. Importantly, the di-depsides (11, 12 and 17) showed greatest toxicity, indicating that these structures are biologically more active than the mono-depsides against the HepG2 liver cancer, A549 lung cancer and HL-60 leukemia cell lines.

Enantioseparation of analogs of the dipeptide alanyl-phenylalanine by capillary electrophoresis using neutral cyclodextrins as chiral selectors.

In the present study, the enantioseparation of the ll- and dd-enantiomers of the dipeptides Ala-Phe, Ala-phenylglycine (Phg), Ala-homoPhe, Ala-ß-Phe, Gly-Phe and ß-Ala-Phe was studied by capillary electrophoresis in the presence of native α-, ß- and γ-cyclodextrin (CD) as well as their methyl and hydroxypropyl derivatives. Separations were performed under standardized conditions in fused-silica capillaries at pH 2.5, 3.5 and 9.5. All analyte enantiomers could be separated at acidic pH under at least one of the experimental conditions. ß-CDs proved to be more universal chiral selectors than α- and γ-CDs. Only few alkaline conditions led to an enantioseparation. For a given dipeptide, the enantiomer migration order depended on the type of CD with regard to cavity size and degree of substitution. Little effect was found with regard to the structure of the dipeptides. pH-dependent reversal of the enantiomer migration order upon increasing the pH from 2.5 to 3.5 was observed for all dipeptides with at least one of the ß-CD derivatives. In the case of ß-CD, analysis of the complexation constants and the apparent limiting mobilities of the diastereomeric peptide enantiomer-CD complexes revealed, that the enantiomer migration order of Ala-Phe, Ala-homoPhe and Ala-ß-Phe was determined by the stereoselective complexation by ß-CD at pH 2.5. At pH 3.5 opposite chiral recognition of the enantiomers by ß-CD was found for Ala-Phe and Ala-ß-Phe resulting in the reversed migration order. In contrast, chiral recognition did not change in the case of Ala-homoPhe, but reversal of the enantiomer migration order was based on the apparent mobility of the diastereomeric analyte-CD complexes.

A cyclic dipeptide from the Chilean hazelnut cotyledons (Gevuina avellana Mol., Proteaceae).

The Chilean hazelnut (Gevuina avellana Mol., Proteaceae) is a southern South American nut consumed as a snack and included in different preparations of traditional Chilean cuisine. Recently we described the fatty acid profile, oxylipins, phenolic compounds, as well as the antioxidant capacity. The main compounds of the phenolic-enriched extract were only tentatively identified by spectrometric means. In the present work, we describe the isolation and full characterization of a cyclic dipeptide cyclo(Arg-Trp) and other compounds from the phenolic enriched extracts of the G. avellana cotyledons. Compounds were isolated by means of counter-current chromatography and structures were established by spectroscopic and spectrometric methods. This is the first report on small peptides in G. avellana and adds evidence on the possible beneficial effects of this nut in human health.

Four pairs of proline-containing cyclic dipeptides from Nocardiopsis sp. HT88, an endophytic bacterium of Mallotus nudiflorus L.

Strain HT88 was isolated from the fresh stems of Mallotus nudiflorus L, and it was identified as Nocardiopsis sp. by analyzing its morphology and the 16S rRNA sequence. The extracts of fermented HT88 showed potent antimicrobial activities. Bioassay guided separation of extracts led to eight proline (or hydroxyproline, Hyp)-containing cyclic dipeptides. Their structures were determined by 1D and 2D NMR spectroscopy and ESI mass spectrometry and further comparison with existing 1H and 13C NMR, melting points and specific rotation data. The eight 2,5-diketopiperazines (DKPs) were identified as cyclo(L-Pro-L-Leu) (1), cyclo(Pro-Leu) (2), cyclo(L-trans-Hyp-L-Leu) (3), cyclo(D-trans-Hyp-D-Leu) (4), and cyclo(D-Pro-L-Phe) (5), cyclo(L-Pro-L-Phe) (6), and cyclo(D-cis-Hyp-L-Phe) (7), cyclo(L-trans-Hyp-L-Phe) (8), respectively. Up to date, this is the first isolation of four pairs of proline based DKPs from Nocardiopsis sp.

A peculiar chromatographic selectivity of porous graphitic carbon during the separation of dileucine isomers.

Porous graphitic carbon is a versatile stationary phase for high-performance liquid chromatography which performs especially well for isomeric separations. Shape-sensitivity of the stationary phase is caused by a steric effect when a molecule interacts with a flat carbon surface. It follows that branched, non-flat molecules are eluted much earlier than flat or linear molecules. In this short communication we show that if a molecule has a highly ionizable group, the "shape" of a molecule part which is farther from the ionizable group affects retention much more than the "shape" of a molecule part which is closer to the ionizable group. Dipeptides which consist of tert-leucine and norleucine were used as an example. Basic and acidic eluents were used. Retention strongly depends on whether a norleucine or tert-leucine residual is located near the non-ionized side in an eluent for both basic and acidic eluents. A residual located on the opposite side is less important. To investigate the possible causes of this peculiar retention behavior we compared the retention behavior of these dipeptides for porous graphitic carbon with the behavior for other types of stationary phases and with the calculated physicochemical properties. Strong and complex dependence of elution order on a mobile phase composition is demonstrated. The separation of other dileucine isomers is also considered. The applicability of porous graphitic carbon for the separation of complex mixtures of isomeric peptides is discussed.

Tryptophan-related dipeptides in fermented dairy products suppress microglial activation and prevent cognitive decline.

The rapid growth in aging populations has made prevention of age-related memory decline and dementia a high priority. Several epidemiological and clinical studies have concluded that fermented dairy products can help prevent cognitive decline; furthermore, intake of Camembert cheese prevents microglial inflammation and Alzheimer's pathology in mouse models. To elucidate the molecular mechanisms underlying the preventive effects of fermented dairy products, we screened peptides from digested milk protein for their potential to regulate the activation of microglia. We identified dipeptides of tryptophan-tyrosine (WY) and tryptophan-methionine that suppressed the microglial inflammatory response and enhanced the phagocytosis of amyloid-ß (Aß). Various fermented dairy products and food materials contain the WY peptide. Orally administered WY peptide was smoothly absorbed into blood, delivered to the brain, and improved the cognitive decline induced by lipopolysaccharide via the suppression of inflammation. Intake of the WY peptide prevented microglial inflammation, hippocampal long-term potential deficit, and memory impairment in aged mice. In an Alzheimer's model using 5×FAD mice, intake of the WY peptide also suppressed microglial inflammation and accumulation of Aß, which improved cognitive decline. The identified dipeptides regulating microglial activity could potentially be used to prevent cognitive decline and dementia related to inflammation.

Enantioseparations by High-Performance Liquid Chromatography Based on Chiral Ligand Exchange.

Although the first application of chiral ligand-exchange chromatography (CLEC) in HPLC dates back to late 1960s, this enantioselective strategy still represents the elective choice for the direct analysis of compounds endowed with chelating moieties. As a specific feature of the CLEC mechanism, the interaction between the chiral selector and the enantiomer does not take place in direct contact. Indeed, it is mediated by a central metal ion that, acting as a Lewis acid, simultaneously coordinates the two species, selector and analyte, through the activation of dative bonds. As a consequence, two diastereomeric mixed ternary complexes are generated in the column, ultimately leading to the stereoisomeric discrimination. CLEC applications can be carried out both with the chiral selector included in the mobile phase (chiral mobile phase, CMP), or as a part of the stationary phase. In the latter case, the chiral selector can be either covalently immobilized onto a solid support (bonded CSP, B-CSP) or physically adsorbed onto a conventional packing material, coated chiral stationary phase (C-CSP).In this chapter, a selection of CLEC applications with CMP- and C-CSP-based chiral systems is presented.

Peptides and polyketides isolated from the marine sponge-derived fungus Aspergillus terreus SCSIO 41008.

Two new isomeric modified tripeptides, aspergillamides C and D (compounds 1 and 2), together with fifteen known compounds (compounds 3-17), were obtained from the marine sponge-derived fungus Aspergillus terreus SCSIO 41008. The structures of the new compounds, including absolute configurations, were determined by extensive analyses of spectroscopic data (NMR, MS, UV, and IR) and comparisons between the calculated and experimental electronic circular dichroism (ECD) spectra. Butyrolactone I (compound 11) exhibited strong inhibitory effects against Mycobacterium tuberculosis protein tyrosine phosphatase B (MptpB) with the IC50 being 5.11 ± 0.53 µmol·L-1, and acted as a noncompetitive inhibitor based on kinetic analysis.

Isolation and characterization of collagen type I crosslink from skin: high-resolution NMR reveals diastereomers of hydroxylysinonorleucine crosslink.

Skin is made up of mainly collagen type I and its structure is stabilised by the formation of covalent immature and mature crosslinks. In this study, collagen immature crosslink hydroxylysinonorleucine (HLNL) was isolated from bovine skin in high purity using two sequential purification steps. These consisted of preparative fibrous cellulose and size exclusion chromatography. The purified crosslink was then analysed using tandem mass spectrometry and high-resolution nuclear magnetic resonance (NMR) spectroscopy. The mass of singly and doubly charged ions of HLNL was 292.1865 and 146.5970 m/z and their optimised fragmentation energy was 17 keV and 5 keV, respectively. The 13C NMR of HLNL showed a doubled-up peak at 67.84 and 67.91 ppm which corroborated a diastereomeric form of collagen immature crosslink HLNL and both are chiroptically indistinguishable. The chemical structure was fully resolved using 1H, 13C and DEPT-135 high-resolution NMR spectroscopy and compared with other previous studies. We also obtained for the first time the 2D NMR spectra COSY and HSQC of HLNL. We therefore suggested that collagen organization into specific fibrils' orientation may be affected by the different configuration of these diastereomers of HLNL.

Silica Monolith Nested in Sponge (SiMNS): A Composite Monolith as a New Solid Phase Extraction Material for Environmental Analysis.

We report a new material of a composite silica monolith nested in sponge (SiMNS) and demonstrate an application in the trace analysis of environmental contaminants in water. SiMNS is prepared through sponge absorption of a hydrolyzed mixture of siloxanes and in situ gel formation within the pores. Images obtained using scanning electron microscopy show that the silica and sponge skeletons are mutually nested in SiMNS. This nested composite structure of SiMNS enhances the mechanical flexibility of the material, allowing for reproducible production of desirable sizes and shapes for solid phase extraction (SPE) cartridges without the need to use frits. Functionalization of SiMNS provides appropriate SPE options for selective and efficient extraction of specific contaminants. SPE cartridges packed with functionalized SiMNS-SO3Na have high extraction capacity, good stability in the pH range of 2 to 11, and efficient enrichment of dipeptides in water. Extraction of six dipeptides from water using these new SiMNS-SO3Na SPE cartridges followed by HPLC-MS/MS analysis results in improved method detection limits (MDLs) of 0.02-1.3 ng/L and method quantification limits (MQLs) of 0.05-4.3 ng/L. Successful identification and quantification of three dipeptides, Tyr-Gly, Phe-Gly, and Tyr-Ala, from raw water demonstrates a useful application of the new SPE materials for environmental analysis of trace contaminants. On the basis of this work, a range of functionalized SiMNS materials can be produced and tailored for various environmental and exposomic analyses.

Significantly improved production of Welan gum by Sphingomonas sp. WG through a novel quorum-sensing-interfering dipeptide cyclo(L-Pro-L-Phe).

A variety of physiological functions such as exopolysaccharide synthesis, antibiotic production, and primary metabolism are tightly controlled by quorum sensing in microorganisms. In this study, a marine-derived bacterium Sphingomonas sp. WG was found to possess a cyclo(L-Pro-L-Phe)-mediated quorum sensing mechanism. The cyclo(L-Pro-L-Phe) produced by Sphingomonas sp. WG functions as a signalling molecule in this quorum sensing system. It is the first attempt to characterize cyclic dipeptides as quorum sensing signalling molecules in Sphingomonas sp. and the results effectively make the classical quorum sensing theory more perfect. Furthermore, the supplementation with isolated cyclo(L-Pro-L-Phe) resulted in a 15% increase in the production of welan gum secreted by Sphingomonas sp. WG in the submerged fermentation. The data presented in this study will provide evidences for exploring the role of cyclic dipeptides in regulating the production of welan gum.