Streamflow seasonality in a snow-dwindling world.

Climate warming induces shifts from snow to rain in cold regions1, altering snowpack dynamics with consequent impacts on streamflow that raise challenges to many aspects of ecosystem services2-4. A straightforward conceptual model states that as the fraction of precipitation falling as snow (snowfall fraction) declines, less solid water is stored over the winter and both snowmelt and streamflow shift earlier in season. Yet the responses of streamflow patterns to shifts in snowfall fraction remain uncertain5-9. Here we show that as snowfall fraction declines, the timing of the centre of streamflow mass may be advanced or delayed. Our results, based on analysis of 1950-2020 streamflow measurements across 3,049 snow-affected catchments over the Northern Hemisphere, show that mean snowfall fraction modulates the seasonal response to reductions in snowfall fraction. Specifically, temporal changes in streamflow timing with declining snowfall fraction reveal a gradient from earlier streamflow in snow-rich catchments to delayed streamflow in less snowy catchments. Furthermore, interannual variability of streamflow timing and seasonal variation increase as snowfall fraction decreases across both space and time. Our findings revise the 'less snow equals earlier streamflow' heuristic and instead point towards a complex evolution of seasonal streamflow regimes in a snow-dwindling world.

Characterising baseflow signature variability in the Yellow River Basin.

Baseflow is pivotal in maintaining catchment ecological health and improving sustainable economic development. The Yellow River Basin (YRB) is northern China's most important water supplier. However, it faces water shortage due to synergistic effects between natural conditions and anthropogenic activities. Investigating baseflow characteristics quantitively is, therefore, beneficial to promoting the sustainable development of the YRB. In this study, daily ensemble means baseflow data derived from four revised baseflow separation algorithms (i.e., the United Kingdom Institute of Hydrology (UKIH), Lyne-Hollick, Chapman-Maxwell, and Eckhardt methods) - was obtained from 2001 to 2020. Thirteen baseflow dynamics signatures were extracted to investigate baseflow spatiotemporal variations and their determinants across the YRB. The main findings were: (1) There were significant spatial distribution patterns of baseflow signatures, and most signatures had higher values in upstream and downstream reaches than in the middle reaches. There were also mixing patterns with higher values in middle and downstream reaches simultaneously. (2) The magnitude of temporal variation in baseflow signatures was most strongly correlated with catchment terrain (r = -0.4), vegetation growth (r > 0.3), and cropland coverage (r > 0.4). (3) There was a strong synergistic effect of multiple factors (e.g., soil textures, precipitation and vegetation conditions) on baseflow signature values. This study provided a heuristic evaluation of baseflow characteristics in the YRB, contributing to water resources management in the YRB and similar catchments.

The evolution of process-based hydrologic models: Historical challenges and the collective quest for physical realism.

The diversity in hydrologic models has historically led to great controversy on the "correct" approach to process-based hydrologic modeling, with debates centered on the adequacy of process parameterizations, data limitations and uncertainty, and computational constraints on model analysis. In this paper, we revisit key modeling challenges on requirements to (1) define suitable model equations, (2) define adequate model parameters, and (3) cope with limitations in computing power. We outline the historical modeling challenges, provide examples of modeling advances that address these challenges, and define outstanding research needs. We illustrate how modeling advances have been made by groups using models of different type and complexity, and we argue for the need to more effectively use our diversity of modeling approaches in order to advance our collective quest for physically realistic hydrologic models.

Gram Scale Conversion of R-BINAM to R-NOBIN.

A mild, operationally simple, and single-step transition-metal-free protocol for the synthesis of enantiomerically pure (R)-(+)-2'-amino-1,1'-binaphthalen-2-ol (R-NOBIN) from (R)-(+)-1,1'-binaphthyl-2,2'-diamine (R-BINAM) is reported. The one-pot conversion proceeds with good yield and shows no racemization. The hydroxyl on the R-NOBIN product was shown to have come from water in the reaction medium via an H2(18)O study. The correct value of the specific rotation of R-NOBIN was reported.

Reprint of: Enantiomeric separation of functionalized ethano-bridged Tröger bases using macrocyclic cyclofructan and cyclodextrin chiral selectors in high-performance liquid chromatography and capillary electrophoresis with application of principal component analysis.

The enantiomeric separation of a series of racemic functionalized ethano-bridged Tröger base compounds was examined by high performance liquid chromatography (HPLC) and capillary electrophoresis (CE). Using HPLC and CE the entire set of 14 derivatives was separated by chiral stationary phases (CSPs) and chiral additives composed of cyclodextrin (native and derivatized) and cyclofructan (derivatized). Baseline separations (Rs ≥ 1.5) in HPLC were achieved for 13 of the 14 compounds with resolution values as high as 5.0. CE produced 2 baseline separations. The separations on the cyclodextrin CSPs showed optimum results in the reversed phase mode, and the LARIHC cyclofructan CSPs separations showed optimum results in the normal phase mode. HPLC separation data of the compounds was analyzed using principal component analysis (PCA). The PCA biplot analysis showed that retention is governed by the size of the R1 substituent in the case of derivatized cyclofructan and cyclodextrin CSPs, and enantiomeric resolution closely correlated with the size of the R2 group in the case of non-derivatized γ-cyclodextrin CSP. It is clearly shown that chromatographic retention is necessary but not sufficient for the enantiomeric separations of these compounds.

Enantiomeric separation of biaryl atropisomers using cyclofructan based chiral stationary phases.

Normal phase chiral HPLC methods are presented for the enantiomeric separation of 30 biaryl atropisomers including 18 new compounds recently produced via a novel synthetic approach. Three new cyclofructan based chiral stationary phases were evaluated. Separations were achieved for all but six analytes and the LARIHC™ CF6-P alone provided 15 baseline separations. Effects of polar modifiers and temperature effects also were studied. Apparent thermodynamic parameters were determined by van't Hoff plots. Preparative scale methods were developed and employed resulting in the first ever isolation of these novel atropisomers in their pure enantiomeric form. Insights into the mechanism of retention and chiral discrimination are presented.

Enantiomeric separation of functionalized ethano-bridged Tröger bases using macrocyclic cyclofructan and cyclodextrin chiral selectors in high-performance liquid chromatography and capillary electrophoresis with application of principal component analysis.

The enantiomeric separation of a series of racemic functionalized ethano-bridged Tröger base compounds was examined by high performance liquid chromatography (HPLC) and capillary electrophoresis (CE). Using HPLC and CE the entire set of 14 derivatives was separated by chiral stationary phases (CSPs) and chiral additives composed of cyclodextrin (native and derivatized) and cyclofructan (derivatized). Baseline separations (Rs≥1.5) in HPLC were achieved for 13 of the 14 compounds with resolution values as high as 5.0. CE produced 2 baseline separations. The separations on the cyclodextrin CSPs showed optimum results in the reversed phase mode, and the LARIHC™ cyclofructan CSPs separations showed optimum results in the normal phase mode. HPLC separation data of the compounds was analyzed using principal component analysis (PCA). The PCA biplot analysis showed that retention is governed by the size of the R1 substituent in the case of derivatized cyclofructan and cyclodextrin CSPs, and enantiomeric resolution closely correlated with the size of the R2 group in the case of non-derivatized γ-cyclodextrin CSP. It is clearly shown that chromatographic retention is necessary but not sufficient for the enantiomeric separations of these compounds.

Rapid analysis of ethanol and water in commercial products using ionic liquid capillary gas chromatography with thermal conductivity detection and/or barrier discharge ionization detection.

Analysis of ethanol and water in consumer products is important in a variety of processes and often is mandated by regulating agencies. A method for the simultaneous quantitation of ethanol and water that is simple, accurate, precise, rapid, and cost-effective is demonstrated. This approach requires no internal standard for the quantitation of both ethanol and water at any/all levels in commercial products. Ionic liquid based gas chromatography (GC) capillary columns are used to obtain a fast analysis with high selectivity and resolution of water and ethanol. Typical run times are just over 3 min. Examination of the response range of water and ethanol with GC, thermal conductivity detection (TCD), and barrier ionization detection (BID) is performed. Quantitation of both ethanol and water in consumer products is accomplished with both TCD and BID GC detectors using a nonlinear calibration. Validation of method accuracy is accomplished by using standard reference materials.

Development and evaluation of gas and liquid chromatographic methods for the analysis of fatty amines.

In contrast to the plethora of publications on the separation of fatty acids, analogous studies involving fatty amines are scarce. A recently introduced ionic-liquid-based capillary column for GC was used to separate trifluoroacetylated fatty amines focusing on the analysis of a commercial sample. Using the ionic liquid column (isothermal mode at 200 °C) it was possible to separate linear primary fatty amines from C12 to C22 chain length in less 25 min with MS identification. The log of the amine retention factors are linearly related to the alkyl chain length with a methylene selectivity of 0.117 kcal/mol for the saturated amines and 0.128 kcal/mol for the mono-unsaturated amines. The sp2 selectivity for unsaturated fatty amines also could be calculated as 0.107 kcal/mol for the ionic liquid column. The commercial sample was quantified by GC with flame ionization detection (FID). An LC method also was developed with a reversed phase gradient separation using acetonitrile/formate buffer mobile phases and ESI-MS detection. Native amines could be detected and identified by their single ion monitoring chromatograms even when partial coelution was observed. The analysis of the commercial sample returned results coherent with those obtained by GC-FID and with the manufacturer's data.

Enantiomeric separation of isochromene derivatives by high-performance liquid chromatography using cyclodextrin based stationary phases and principal component analysis of the separation data.

Isochromene derivatives are very important precursors in the natural products industry. Hence the enantiomeric separations of chiral isochromenes are important in the pharmaceutical industry and for organic asymmetric synthesis. Here we report enantiomeric separations of 21 different chiral isochromene derivatives, which were synthesized using alkynylbenzaldehyde cyclization catalyzed by chiral gold(I) acyclic diaminocarbene complexes. All separations were achieved by high-performance liquid chromatography with cyclodextrin based (Cyclobond) chiral stationary phases. Retention data of 21 chiral compounds and 14 other previously separated isochromene derivatives were analyzed using principal component analysis. The effect of the structure of the substituents on the isochromene ring on enantiomeric resolution as well as the other separation properties was analyzed in detail. Using principal component analysis it can be shown that the structural features that contribute to increased retention are different from those that enhance enantiomeric resolution. In addition, principal component analysis is useful for eliminating redundant factors from consideration when analyzing the effect of various chromatographic parameters. It was found that the chiral recognition mechanism is different for the larger γ-cyclodextrin as compared to the smaller ß-cyclodextrin derivatives. Finally this specific system of chiral analytes and cyclodextrin based chiral selectors provides an effective format to examine the application of principal component analysis to enantiomeric separations using basic retention data and structural features.

1,3-Dimethylamylamine (DMAA) in supplements and geranium products: natural or synthetic?

1,3-Dimethylamylamine (DMAA) is a stimulant existing in various pre-workout supplements and often labelled as part of geranium plants. The safety and origin of DMAA in these supplements is the subject of intense debate. In this study, the enantiomeric and diastereomeric ratios of two different known synthetic DMAA compounds, as well as the total concentrations of DMAA and its stereoisomeric ratios in 13 different supplements, were determined by gas chromatography. The stereoisomeric ratios of DMAA in the synthetic standards and in all the commercial supplements were indistinguishable. Eight different commercial geranium extracts of different geographical origins (China and the Middle East) were examined for the presence of DMAA by high performance liquid chromatography coupled with mass spectrometry (HPLC-MS). No DMAA was detected in any of the eight geranium products with a limit of detection of 10 parts per billion (w/w).

Structural and anticancer properties of hydrogen bonded diphenyl phosphate adducts of Pt(IV) complexes: the importance of pKa matching.

Co-crystallisation of diphenyl phosphate (Hdpp) with anticancer active Pt(IV) complexes of the type cis,trans,cis-[PtCl(2)(OH)(2)(am(m)ine)(2)] has produced a new type of supramolecular adduct with short hydrogen bonds from the Hdpp molecules to the hydroxide ligands in all cases. X-ray crystallographic analysis showed within the adduct cis,trans-[PtCl(2)(en)(OH(2))(2)](dpp)(2) (1) a hydrogen bond length of 2.341(6) Å; the shortest O ··· O distance reported in the literature. Similar, though longer hydrogen bonds were observed in three other complexes: [PtCl(2)(OH)(NH(3))(2)(OH(2))]dpp·3H(2)O (2), trans-[Pt(mal)(OH)(OH(2))(S,S-chxn)]dpp·3H(2)O (3), and trans-[Pt(ox)(OH)(OH(2))(S,S-chxn)]dpp·2H(2)O (4). Co-crystallisation with Hdpp leads to higher aqueous solubility than the parent complexes indicating the potential of the adducts for use as active pharmaceutical ingredients. Anticancer testing of [Pt(mal)(OH)(OH(2))(S,S-chxn)]dpp·3H(2)O (3) showed in vitro cytotoxicity is low, as expected for Pt(IV) prodrugs, yet substantial tumour growth inhibition was observed in an in vivo ADJ/PC6 tumour model, with activity retained at maximum tolerated dose (MTD)/2 and MTD/4.