Direct spectrophotometric determination of thiocyanate in serum and urine with a continuous-flow analyzer

A spectrophotometric method for the rapid measurement of thiocyanate in serum and urine without separation from interfering substances is described. Thiocyanate reacts immediately with chloramine-T in presence of iron(III) chloride catalyst to give cyanogen chloride, which reacts with a mixture of γ-picoline (4-methylpyridine) and barbituric acid to form a soluble violet—blue product, which is measured at 605 nm. Other components of physiological fluids react more slowly and do not interfere if the reaction time of the chlorinating step is kept very short. The proposed procedure is compared with a highly selective method, based on the oxidation of thiocyanate to cyanide, and good agreement was obtained for both serum and urine. The method is readily adapted to a continuous-flow procedure with a Technicon AutoAnalyzer.     

Ditocopheryl Sulfides and Disulfides: Synthesis and Antioxidant Profile

Symmetrical ditocopheryl disulfides ( Toc ) ₂ S₂ and symmetrical and unsymmetrical ditocopheryl sulfides ( Toc )₂ S were simply prepared under remarkably mild conditions with complete control of the regiochemistry by using δ-, γ-, and β-tocopheryl-N-thiophthalimides ( Toc-NSPht ) as common starting materials. The roles of sulfur atom(s), H-bond and aryl ring substitution pattern on the antioxidant profile of these new compounds, which were assembled by linking together two tocopheryl units, are also discussed.     

Continued Progress towards Efficient Functionalization of Natural and Non-natural Targets under Mild Conditions: Oxygenation by C−H Bond Activation with Dioxirane

The successful isolation and characterization of a dioxirane species in 1988 opened up one of the most attractive methods for the efficient oxidation of simple and/or structurally complex molecules. Dioxirane today rank among the most powerful tools in organic chemistry, with numerous applications in commercially important processes. They were quickly recognized as efficient oxygen transfer agents, especially for epoxidations and for a wide range of O-insertion reactions into C−H bonds. Dioxirane possess catalytic activity and appear as highly (chemo-, regio-, and stereo-) selective oxidants, despite their reactivity under mild and strictly neutral conditions being controlled by a combination of steric and electronic factors. In this review, we discuss some of the most recent and significant developments in the selective homogeneous and heterogeneous oxyfunctionalization of non-activated C−H bonds in hydrocarbons of natural and non-natural targets by using isolated dioxirane or, more generally, by using the ketones (i.e., the dioxirane precursors) as organocatalysts.     

A test case for time-dependent density functional theory calculations of electronic circular dichroism: 2-chloro-4-methoxy-6- [(R)-1-phenylethylamino]-1,3,5- triazine

The three-dimensional structure of an optically active substituted s-triazine derivative, 2-chloro-4-methoxy-6-[(R)-1-phenylethylamino]-1,3,5-triazine, has been studied by conformational analysis using density functional theory (DFT) both in vacuo and in acetonitrile solution in the polarizable continuum model integral equation formalism framework. Time-dependent DFT methods have been used to investigate the molecular electronic CD and absorption UV spectra. Comparison with experimental results allowed the reliability of the theoretical predictions to be enhanced and suggested a possible interpretation of the measured data. Electronic Supplementary Material The online version of this article doi:contains supplementary material, which is available to authorized users.     

Structural characterization of Cu2+, Ni2+ and Zn2+ binding sites of model peptides associated with neurodegenerative diseases

Metal ions, especially redox active copper, are thought to play critical roles in neurodegenerative disorders. As a matter of fact, metal binding may result into severe conformational changes of proteins involved in neurodegeneration. The present review describes the interactions of metal ions with model peptides mimicking metal binding sites of such proteins, including the prion protein, the β-amyloid and the α-synuclein that have been related to the pathological onset of spongiform encephalopathies, Alzheimer's disease and Parkinson's disease, respectively. Using short protein fragments provides successful tools for characterizing the metal ion interaction with protein domains devoid of any defined secondary structure, and allows one to gain structural information on the metal ion binding properties of the corresponding proteins. Moreover, such an approach based on simplified models yields a multidimensional knowledge that would be never accessible for the natural systems, thus providing a significant and powerful tool for biochemical studies.     

Bio-Guided Fractionation of Stem Bark Extracts from Phyllanthus muellarianus: Identification of Phytocomponents with Anti-Cholinesterase Activity

A combination of flash chromatography, solid phase extraction, high-performance liquid chromatography, and in vitro bioassays was used to isolate phytocomponents endowed with anticholinesterase activity in extract from Phyllanthus muellarianus. Phytocomponents responsible for the anti-cholinesterase activity of subfractions PMF1 and PMF4 were identified and re-assayed to confirm their activity. Magnoflorine was identified as an active phytocomponent from PMF1 while nitidine was isolated from PMF4. Magnoflorine was shown to be a selective inhibitor of human butyrylcholinesterase—hBChE (IC₅₀ = 131 ± 9 μM and IC₅₀ = 1120 ± 83 μM, for hBuChE and human acetylcholinesterase—hAChE, respectively), while nitidine showed comparable inhibitory potencies against both enzymes (IC₅₀ = 6.68 ± 0.13 μM and IC₅₀ = 5.31 ± 0.50 μM, for hBChE and hAChE, respectively). When compared with the commercial anti-Alzheimer drug galanthamine, nitidine was as potent as galanthamine against hAChE and one order of magnitude more potent against hBuChE. Furthermore, nitidine also showed significant, although weak, antiaggregating activity towards amyloid-β self-aggregation.     

Tyrosyl Radical in the W164Y Mutant of P. eryngii Versatile Peroxidase: an EPR and DFT/PCM Study

Versatile peroxidases (VP) constitute a new class of high redox potential fungal enzymes that are able to degrade lignin and large substrate molecules. These enzymes catalyze the oxidation of substrates at an exposed tryptophan radical formed by a long-range electron transfer mechanism to heme following the activation by H₂O₂. In a previous paper, it was demonstrated using electron paramagnetic resonance (EPR) and electron-nuclear double resonance experiments on wild-type VP that Trp164 was the radical site and that it was in a hydrogen-bonded neutral form. In this paper, the W164Y variant is analyzed and it is shown that also the variant is able to form the so-called Compound I (VPI) in the form of protein radical, although in different yields with respect to the wild type. The X-band EPR experiments in combination with density functional theory/polarizable continuum model calculations show that the W164Y mutant is able to form a neutral radical on Tyr164 residue, after activation by H₂O₂, but in contrast to Trp164, tyrosine is not expected to be hydrogen bonded.     

Substituent effects on the stereochemistry of gas-phase intracomplex nucleophilic substitutions

The mechanism and stereochemistry of the intracomplex solvolysis of proton-bound complexes [Y...H...M]+ between M = CH3 (18)OH and Y = 1-arylethanol [(S)-1-(para-tolyl)ethanol (1S), (S)-1-(para-chlorophenyl)ethanol (2S), (S)-1-(meta-alpha,alpha,alpha-trifluoromethylphenyl)ethanol (3S), (S)-1-(para-alpha,alpha,alpha-trifluoromethylphenyl)ethanol (4S), (R)-1-(pentafluorophenyl)ethanol (5R), (R)-alpha-(trifluoromethyl)benzyl alcohol (6R), and (R)-1-phenylethanol (7R)] have been investigated in the gas phase (CH3F; 720 Torr) in the 25-140 degrees C temperature range. Gas-phase solvolysis of [Y...H...M]+ (Y=2S, 3S, 4S, and 7R) leads to extensive racemization above a characteristic temperature t(#) (e.g. at t(#)>60 degrees C for 7R), whereas below that temperature the reaction displays a preferential retention of configuration. Predominant retention of configuration is instead observed in the intracomplex solvolysis of [Y...H...M]+ (Y=1S, 4S, 5R, and 6R) with the temperature range investigated (25 相似文献   

Conformational landscape of (R,R)-pterocarpans with biological activity in vacuo and in aqueous solution (PCM and/or water clusters)

All possible combinations of stable dihedral values have been considered in vacuo at the B3LYP/6-31G level for 3,9-dihydroxy-4,8-diprenylpterocarpan (erybraedin C), whose hydroxy out-out conformation had been examined earlier together with the conformational preferences of 3,9-dimethoxy-4-prenylpterocarpan (bitucarpin A) at the same level (Phys. Chem. Chem. Phys. 2004, 6, 2849). The structure with O5 trans with respect to H6a (O(t)) is about 2 kcal/mol less stable in vacuo than that with one of the H6 trans to it (H(t)); in aqueous solution its energy gap is nearly conserved. The in-in arrangement of the hydroxyl groups of erybraedin turns out to be preferred in vacuo (even considering zero point and thermal effects), where pseudo H-bonds are formed between hydroxy hydrogens and pi electron distributions of prenyl groups. The continuum solvent effect (water) at the IEF-PCM/B3LYP/6-31G level on the relative stability of the various rotamers is very limited both on bitucarpin and erybraedin. Considering the dihydrated derivatives, significant differences in the solvation energy are found between the distinct hydration sites, increasing in the order: methoxy O, ring O, hydroxy O, and hydroxy H. In hydroxy-water interactions, in fact, water prefers to behave as an H-bond acceptor unless nearby bulky groups prevent its approach. Interestingly enough, a bridging water molecule between the hydroxy H of erybraedin and the prenyl group can be found. The inclusion of BSSE corrections in hydroxy-water interactions decidedly favors out-out hydrated arrangements, followed by out-in and in-out ones. Bulk solvent effects with IEF-PCM about the dihydrated systems almost invert the stability order found in vacuo. When a four-water cluster is considered using QM methods, waters gather in H-bonded pairs around the solute OH groups. MD simulations, carried out on a pterocarpan solute (J. Phys. Chem. B 2005, 109, 16918), supply water adducts consistent with a liquid state that have also been embedded in the continuum solvent.