Organic carbon content determination in soils: challenges and opportunities of elemental analysis versus thermogravimetry

Sustainable soil management needs reliable and accurate monitoring of soil organic carbon (SOC) content. However, despite of the development of analytical techniques during last decades, the detection opportunities for short term and rather small changes in SOC induced by organic fertilization, organic amendments or land use changes are still limited with the available methods. This study aims to quantify the theoretical detection opportunities for changes in SOC content with elemental analysis (EA) as the standard method in comparing with thermogravimetry (TG) as an enhanced traditional approach derived from soil organic matter determination via mass losses on ignition. The carried out experiments consist of mixing soil samples from non-fertilized plots of three long-term agricultural experiments in Bad Lauchstaedt, Großbeeren and Muencheberg (silty loam, loamy sand and silty sand) with straw, farmyard manure, sheep faeces and charcoal in four quantities (3 t×ha-1, 20 t×ha-1, 60 t×ha-1 and 180 t×ha‑1fresh matter) under laboratory conditions.The quantities were based on fresh matter application in agricultural practice accepting different amounts of added organic carbon. The results confirm EA as a method of higher reliability and accuracy for carbon content determination. TG allows to distinguish the different types of added amendments with high sensitivity. This was achieved by using newly developed evaluation algorithms for the thermal decay dynamics. We conclude from these results that TG cannot substitute EA to determine organic carbon on a routine base. However, TG could be a supplementary fingerprinting technique for the detection of added organic carbon to soils from organic fertilizers and to distinguish sources of geological or anthropogenic origin enabling a future assessment of soil organic carbon quality

Overturning established chemoselectivities : selective reduction of arenes over malonates and cyanoacetates by photoactivated organic electron donors

The prevalence of metal-based reducing reagents, including metals, metal complexes, and metal salts, has produced an empirical order of reactivity that governs our approach to chemical synthesis. However, this reactivity may be influenced by stabilization of transition states, intermediates, and products through substrate-metal bonding. This article reports that in the absence of such stabilizing interactions, established chemoselectivities can be overthrown. Thus, photoactivation of the recently developed neutral organic superelectron donor 5 selectively reduces alkyl-substituted benzene rings in the presence of activated esters and nitriles, in direct contrast to metal-based reductions, opening a new perspective on reactivity. The altered outcomes arising from the organic electron donors are attributed to selective interactions between the neutral organic donors and the arene rings of the substrates

Impact of amendments on the physical properties of soil under tropical long-term no till conditions

Tropical regions have been considered the world's primary agricultural frontier; however, some physico-chemical deficiencies, such as low soil organic matter content, poor soil structure, high erodibility, soil acidity, and aluminum toxicity, have affected their productive capacity. Lime and gypsum are commonly used to improve soil chemical fertility, but no information exists about the long-term effects of these products on the physical attributes and C protection mechanisms of highly weathered Oxisols. A field trial was conducted in a sandy clay loam (kaolinitic, thermic Typic Haplorthox) under a no-tillage system for 12 years. The trial consisted of four treatments: a control with no soil amendment application, the application of 2.1 Mg ha-1 phosphogypsum, the application of 2.0 Mg ha-1 lime, and the application of lime + phosphogypsum (2.0 + 2.1 Mg ha-1, respectively). Since the experiment was established in 2002, the rates have been applied three times (2002, 2004, and 2010). Surface liming effectively increased water-stable aggregates > 2.0 mm at a depth of up to 0.2 m; however, the association with phosphogypsum was considered a good strategy to improve the macroaggregate stability in subsoil layers (0.20 to 0.40 m). Consequently, both soil amendments applied together increased the mean weight diameter (MWD) and geometric mean diameter (GMD) in all soil layers, with increases of up to 118 and 89%, respectively, according to the soil layer. The formation and stabilization of larger aggregates contributed to a higher accumulation of total organic carbon (TOC) on these structures. In addition to TOC, the MWD and aggregate stability index were positively correlated with Ca2+ and Mg2+ levels and base saturation. Consequently, the increase observed in the aggregate size class resulted in a better organization of soil particles, increasing the macroporosity and reducing the soil bulk density and penetration resistance. Therefore, adequate soil chemical management plays a fundamental role in improving the soil's physical attributes in tropical areas under conservative management and highly affected by compaction caused by intensive farming

Muscarinic receptor subtypes - search for selective agonists and antagonists

Since the late eighties five muscarinic receptor subtypes (m1 - m5) have been cloned and four of them (M1 - M4) have also been pharmacologically characterized. However, there is still a lack of potent muscarinic agonists and antagonists, which are highly selective for one muscarinic receptor subtype over all other subtypes. For the treatment of Alzheimer's disease, M1-selective agonists capable of penetrating into the CNS are needed. It is hypothezised that such substances would not only improve memory and cognitive ability, but also delay the progression of the disease. In our laboratory, the functionally M1-selective quaternary ammonium compound McN-A-343 has been used as a starting point for the design of such CNS active muscarinic ligands. Structure-activity relationship studies led to the tertiary amine 4-(4-fluorophenylcarbamoyloxy)-2-butynylpyrrolidine (4-F-PyMcN), which was found to stimulate M1 receptors with some functional selectivity. In order to increase the potency and selectivity of 4-F-PyMcN several new derivatives were synthezised and pharmacologically characterized in different functional assays as well as in binding and biochemical (PI turnover) studies. The most promising results were obtained with (S)-4-(4-fluorophenylcarbamoyloxy)-1-methyl-2-butynylpyrrolidine (4-F-MePyMcN). Due to its potent partial agonistic activity at M1 receptors and its M2-antagonistic properties leading to an increase of acetylcholine release by blockade of M2 autoreceptors, this compound may be considered as an important tool for future drug research of cognitive disorders. M2 receptor antagonists may also be used for the treatment of Alzheimer's disease, furthermore in the therapy of supraventricular bradycardia and for quantifying M2 receptors in the CNS with PET imaging. In the search for antagonists which clearly differentiate M2 from other muscarinic receptors, we investigated the two enantiomers of the widely used H1-antihistaminic drug dimethindene. (S)-Dimethindene proved to be a potent M2-selective antagonist with lower affinities for the M1, M3 and M4 receptors. In addition, the (S)-enantiomer was more potent than the (R)-enantiomer in all muscarinic assays. Interestingly, the stereoselectivity was inverse at histamine H1 receptors, the (R)-enantiomer being the eutomer. M3 receptor antagonists may be useful in the treatment of spastic disorders of the gastrointestinal, urogenital and respiratory tract as well as for the relief of glandular hypersecretion. In previous studies, hexahydro-difenidol (HHD) and its sila-analogue, hexahydro-sila-difenidol (HHSiD), as well as the antiparkinsonian drug trihexyphenidyl (THP) were found to be valuable tools for the discrimination of M3 and M2 receptors. In order to further assess the structural requirements (including stereochemical aspects) of the above-mentioned compounds for potency and selectivity, a series of HHD and THP analogues as well as of the corresponding silicon and germanium derivatives (sila- and germa-substitution) were studied. The (R)-enantiomers displayed higher affinities and selectivities than the corresponding (S)-isomers. The enantioselectivity of some of these analogues is best explained by the concept of the four-binding-subsite model suggesting that the differences in affinity of the (R)- and (S)-enantiomers at muscarinic receptors are due to opposite binding of the phenyl and the cyclohexyl ring to the preferring subsites. Surprisingly, there was no significant difference between the Si and Ge analogues indicating a strongly pronounced Si/Ge bioisosterism in this series of compounds. The related carbon derivatives, however, showed higher receptor affinities as well as greater stereoselectivities at all muscarinic receptors studied compared with the silicon and germanium analogues. © 1996 Elsevier B.V. All rights reserved.SCOPUS: ar.kinfo:eu-repo/semantics/publishe