Seasonal and inter-annual variation in the chlorophyll content of three co-existing Sphagnum species exceeds the effect of solar UV reduction in a subarctic peatland.

We measured chlorophyll (chl) concentration and chl a/b ratio in Sphagnum balticum, S. jensenii, and S. lindbergii, sampled after 7 and 8 years of ultraviolet-B (UVB) and temperature manipulation in an open field experiment in Finnish Lapland (68°N). We used plastic filters with different transmittance of UVB radiation to manipulate the environmental conditions. The plants were exposed to (1) attenuated UVB and increased temperature, (2) ambient UVB and increased temperature and (3) ambient conditions. Chlorophyll was extracted from the capitula of the mosses and the content and a/b ratio were measured spectrophotometrically. Seasonal variation of chlorophyll concentration in the mosses was species specific. Temperature increase to 0.5-1 °C and/or attenuation of solar UVB radiation to ca. one fifth of the ambient (on average 12 vs. 59 uW/cm(2)) had little effect on the chlorophyll concentration or its seasonal variation. In the dominant S. lindbergii, UVB attenuation under increased temperature led to a transient decrease in chlorophyll concentration. Altogether, species-specific patterns of seasonal chlorophyll variation in the studied Sphagna were more pronounced than temperature and UVB treatment effects.

Lessons from look-back in acute liver failure? A single centre experience of 3300 patients.

BACKGROUND & AIMS: Acute liver failure (ALF) is a rapidly progressive critical illness with high mortality. Complex intensive care unit (ICU) protocols and emergency liver transplantation (ELT) are now often available, but rarity and severity of illness have limited its study and evidence-base for care. We reviewed patients treated over a 35-year period at a specialist high-volume ICU, quantifying changes in disease aetiology, severity and evolution of ICU support and ELT use and outcome. METHODS: Review of adult patients admitted during the period 1973-2008, with acute liver dysfunction and coagulopathy with overt hepatic encephalopathy (ALF) and those without (acute liver injury; ALI). RESULTS: 3305 patients fulfilled inclusion criteria, 2095 with ALF. Overall hospital survival increased from 30% in 1973-78 to 76% in 2004-08; in ALF from 17% to 62% (both p<0.0001). In ALF patients treated without ELT, survival rose from 17% to 48% (p<0.0001); in those undergoing ELT (n=387) from 56% in 1984-88 to 86% in 2004-08 (p<0.01). Coincident with drug sales-restriction, paracetamol-related admissions fell significantly. Viral admissions fell from 56% to 17% of non-paracetamol cases (p<0.0001). Admission markers of liver injury severity fell significantly and the proportion of patients with intracranial hypertension (ICH) fell from 76% in 1984-88 to 20% in 2004-08 (p<0.0001). In those with ICH, mortality fell from 95% to 55% (p<0.0001). CONCLUSIONS: The nature and outcome of ALF have transformed over 35 years, with major improvements in survival and a fall in prevalence of cerebral oedema and ICH, likely consequent upon earlier illness recognition, improved ICU care, and use of ELT.

Chiral discrimination of ß-3-homo-amino acids using the kinetic method.

Chiral discrimination of seven enantiomeric pairs of ß-3-homo-amino acids was studied by using the kinetic method and trimeric metal-bound complexes, with natural and unnatural α-amino acids as chiral reference compounds and divalent metal ions (Cu(2+) and Ni(2+) ) as the center ions. The ß-3-homo-amino acids were selected for this study because, first of all, chiral discrimination of ß-amino acids has not been extensively studied by mass spectrometry. Moreover, these ß-3-homo-amino acids studied have different aromatic side chains. Thus, the emphasis was to study the effect of the side chain (electron density of the phenyl ring, as well as the difference between phenyl and benzyl side chains) for the chiral discrimination. The results showed that by the proper choice of a metal ion and a chiral reference compound, all seven enantiomeric pairs of ß-3-homo-amino acids could be differentiated. Moreover, it was noted that the ß-3-homo-amino acids with benzyl side chains provided higher enantioselectivity than the corresponding phenyl ones. However, increasing or decreasing the electron density of the aromatic ring by different substituents in both the phenyl and benzyl side chains had practically no role for chiral discrimination of ß-3-homo-amino acids studied. When copper was used as the central metal, the phenyl side chain containing reference molecules (S)-2-amino-2-phenylacetic acid (L-Phg) and (S)-2-amino-2-(4-hydroxyphenyl)-acetic acid (L-4'-OHPhg) gave rise to an additional copper-reduced dimeric fragment ion, [Cu(I) (ref)(A)](+) . The inclusion of this ion improved noticeably the enantioselectivity values obtained.

Chiral differentiation of some cyclic beta-amino acids by kinetic and fixed ligand methods.

Differentiation of beta-amino acid enantiomers with two chiral centres was investigated by kinetic method with trimeric metal-bound complexes. Four enantiomeric pairs of beta-amino acids were studied: cis-(1R,2S)-, cis-(1S,2R)-, trans-(1R,2R)- and trans-(1S,2S)-2-aminocyclopentanecarboxylic acids (cyclopentane beta-amino acids), and cis-(1R,2S)-, cis-(1S,2R)-, trans-(1R,2R)-, and trans-(1S,2S)-2-aminocyclohexanecarboxylic acids (cyclohexane beta-amino acids). The results showed that the choice of metal ion (Cu(2+), Ni(2+)) and chiral reference compound (alpha- and beta-amino acids) had an effect on the enantioselectivity. Especially, aromaticity of the reference compound was noted to enhance the enantioselectivity. The fixed-ligand kinetic method, a modification of the kinetic method, was then applied to the same beta-amino acids, with dipeptides used as fixed ligands. With this method, dipeptide containing an aromatic side chain enhanced the enantioselectivity.

Chiral differentiation of some cyclopentane and cyclohexane beta-amino acid enantiomers through ion/molecule reactions.

Chiral differentiation of four enantiomeric pairs of beta-amino acids, cis-(1R,2S)-, cis-(1S,2R)-, trans-(1R,2R)-, and trans-(1S,2S)-2-aminocyclopentanecarboxylic acids (cyclopentane beta-amino acids), and cis-(1R,2S)-, cis-(1S,2R)-, trans-(1R,2R)-, and trans-(1S,2S)-2-aminocyclohexanecarboxylic acids (cyclohexane beta-amino acids) was performed successfully by using host-guest complexes and ion/molecule reactions. The experiments were conducted by using electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. The effect of a chiral host molecule was tested by using three different host compounds; (+)-(18-Crown-6)-2,3,11,12-tetracarboxylic acid, (-)-(18-Crown-6)-2,3,11,12-tetracarboxylic acid, and beta-cyclodextrin. This is the first time that small enantiomeric pairs with two chiral centers have been differentiated using ion/molecule reactions and host-guest complexes.

Diastereochemical differentiation of some cyclic and bicyclic beta-amino acids, via the kinetic method.

Stereochemical differentiation of five diastereomeric pairs of beta-amino acids, di-endo- and di-exo-2,3-disubstituted norbornane and norbornene amino acids, cis- and trans-2-aminocyclohexane-, 2-amino-4-cyclohexene-, and 2-aminocyclopentanecarboxylic acids, was investigated via the kinetic method with metal-bound trimeric complexes. This is the first time that diastereomers (di-endo/di-exo and cis/trans) have been differentiated with metal-bound trimeric complexes and the kinetic method. Moreover, determination of diastereochemical excess by the kinetic method was applied to norbornane beta-amino acids and cyclopentane beta-amino acids. Experiments showed that a remarkable differentiation of the studied diastereomers was achieved. It was observed that better selectivity values correlated to more rigid structures. The reference compounds for the studied beta-amino acids varied from alpha-amino acids to some beta-amino acids. In addition, variation of the metal ion (Cu(2+) and Ni(2+)) had some role in the selectivity values obtained. Ab initio and hybrid density functional theory calculations were performed to clarify the results obtained by mass spectrometry.

Differentiation of diastereomeric cyclic beta-amino acids by varying the neutral reagent in ion/molecule reactions studied by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry.

Stereochemical differentiation of diasteromeric pairs of cis- and trans-2-aminocyclohexane-, -2-amino-4-cyclohexene-, and -2-aminocyclopentanecarboxylic acids was investigated with host-guest complexes where tetraethyl resorcarene was the host molecule. Diastereoselectivity was evaluated by ion/molecule reactions and collision-induced dissociation with electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICRMS). The effect of varying the neutral reagent (n-propylamine, i-propylamine, diethylamine, and triethylamine) in ion/molecule reactions was evaluated. Both steric interactions and proton affinity of the neutral reagents influenced the reaction rates. High proton affinity of the neutral reagent apparently had a twofold effect. If the proton affinity of the neutral reagent was too high, the reaction tended to become too exothermic and part of the host-guest complex decomposed instead of transforming to a new host-guest complex, effecting a decrease in the reaction rate. The remaining portion of the host-guest complexes meanwhile reacted very fast with the neutral reagent due to high proton affinity causing an increase in the reaction rate. n-Propylamine and i-propylamine proved to be the best neutral reagents, providing clear diastereoselectivity for beta-amino acids in ion/molecule reactions. Interestingly, diastereoselectivity was better for flexible cyclohexane beta-amino acids (2 and 3) than for more rigid cyclopentane beta-amino acids (6 and 7). The results of ab initio and hybrid density functional theory calculations on the structures of the host-guest complexes of saturated beta-amino acids were in good agreement with the experimental results.

Diastereochemical differentiation of beta-amino acids using host-guest complexes studied by Fourier transform ion cyclotron resonance mass spectrometry.

Host-guest complexes where tetraethyl resorcarene was the host molecule were used to study the stereoselectivity of diasteromeric pairs of di-endo- and di-exo-2,3-disubstituted norbornane and norbornene amino acids by ion-molecule reactions and collision-induced dissociation with electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS). Both methods showed stereoselectivity for the diastereomeric pairs. Particularly high selectivity was achieved for di-endo- and di-exo-2,3-disubstituted norbornane amino acids with ion-molecule reactions. Also, ab initio and hybrid density functional theory calculations were performed to study the different structures of the host-guest complexes. Hydrogen bonding was crucial for the calculated lowest energy structures, and sterical considerations satisfactorily explained the ion-molecule reaction results.

Complex formation between a tetramesityl sulfonated resorcarene and alkylammonium ions: a mass spectrometric study of noncovalent interactions.

Noncovalent complex formation between a tetramesityl sulfonated tetramethyl resorcarene and primary, secondary, and tertiary alkylammonium ions was investigated by electrospray ionization (ESI) Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. Competition measurements, collision-induced dissociation, and gas-phase hydrogen/deuterium (H/D)-exchange reactions were employed to elucidate the interactions involved in complexation, the stability of the complexes, and the position of the guest with relation to the resorcarene. The complex formation ability of tetramesityl sulfonated resorcarene and the stability of the compexes were compared with the corresponding properties of tetratosylium tetraethyl resorcarene, which has been studied previously. Complex formation and the properties of the complexes were most strongly determined by the steric properties of the guests and their ability to form hydrogen bonds. Comparison of the two host molecules revealed the impact of steric hindrance in tetramesityl sulfonated tetramethyl resorcarene.