Most oceanic dissolved organic matter (DOM) is still not fully molecularly characterized. We combined high-field nuclear magnetic resonance (NMR) and ultrahigh-resolution mass spectrometry (Fourier-transform ion cyclotron resonance mass spectrometry, FT-ICR-MS) for the structural and molecular formula-level characterization of solid-phase extracted (SPE) DOM from surface, mesopelagic, and bathypelagic Atlantic and Pacific Ocean samples. Using a MicroCryoProbe, unprecedented low amounts of SPE-DOM (∼1 mg carbon) were sufficient for two-dimensional NMR analysis. Low proportions of olefinic and aromatic relative to aliphatic and carboxylated structures (NMR) at the sea surface were likely related to photochemical transformations. This was consistent with lower molecular masses and higher degrees of saturation and oxygenation (FT-ICR-MS) compared to those of the deep sea. Carbohydrate structures in the mesopelagic North Pacific Ocean suggest export and release from sinking particles. In our sample set, the universal molecular DOM composition, as captured by FT-ICR-MS, appears to be structurally more diverse when analyzed by NMR, suggesting DOM variability across oceanic provinces to be more pronounced than previously assumed. As a proof of concept, our study takes advantage of new complementary approaches resolving thousands of structural and molecular DOM features while applying reasonable instrument times, allowing for the analysis of large oceanic data sets to increase our understanding of marine DOM biogeochemistry.

No abstract

Unambiguous identification and precise quantification of enantiomers in chiral mixtures is crucial for enantiomer specific synthesis as well as chemical analysis. The task is often challenging for mixtures with high enantiomeric excess and for complex molecules with strong (1)H-(1)H scalar (J) coupling network. The recent advancements in (1)H-(1)H decoupling strategies to suppress the J-interactions offered new possibilities for NMR based unambiguous discrimination and quantification enantiomers. Herein, we discuss a high resolution two-dimensional pure-shift zCOSY NMR method with homonuclear band-selective decoupling in both the F1 and F2 dimensions (F1F2-HOBS-zCOSY). This advanced method shows a sharp improvement in resolution over the other COSY methods and also eliminates the problems associated with the overlapping decoupling sidebands. The efficacy of this method has been exploited for precise quantification of enantiomeric excess (ee) ratio (R/S) up to 99:1 in the presence of very low concentrations of chiral lanthanide shift reagents (CLSR) or chiral solvating agents (CSA). The F1F2-HOBS-zCOSY is simple and can be easily implemented on any modern NMR spectrometers, as a routine analytical tool.

In a wide spectrum of neurodegenerative diseases, self-assembly of pathogenic proteins to cytotoxic intermediates is accelerated by the presence of metal ions such as Cu2+. Only low concentrations of these...

Cryopreservation and subsequent thawing of semen for assisted reproductive procedures decreases sperm motility; motility further reduces when the cryoprotectant medium is removed because of the osmotic shock and centrifugation done to prepare the sperm. To compare motility and thus pregnancy rates, this study examined the effects of adding an additional refrigeration medium and three different centrifugation speeds for sperm preparation. Semen samples from 16 healthy normal volunteers were obtained by masturbation after 48 h of abstinence. Sperm motility and other motion characteristics were analyzed with a computer-assisted semen analyzer before freezing, after thawing, and after centrifugation. Each sample was divided into 6 aliquots and frozen using the liquid nitrogen vapor method. After thawing, human tubal fluid (HTF) with 5% human serum albumin was added to 3 aliquots, and refrigeration medium (identical to freezing medium without glycerol) was added to the remaining 3 tubes for each specimen. The tubes containing the two media were then washed by centrifugation at 100 g, 300 g, and 500 g for 10 min. Aliquots with refrigeration medium did not significantly differ from those with HTF for percent motility, curvilinear velocity, straight-line velocity, and amplitude of lateral head displacement at any centrifugation speed. Motile sperm count was significantly greater only at 100 g and 300 g for refrigeration medium (p = .02 and .01) and HTF (p = 0.001); at 300 g, average path velocity in refrigeration medium aliquots (p = .01) and linearity in HTF (p = .01) were greater. The results indicated that the reduction in motility and other motion characteristics probably cannot be overcome by changing factors such as the sperm preparation medium or centrifugation speed. More effective cryopreservation techniques or preparation methods that eliminate centrifugation need to be developed.