Second Dissociation Constant of Two Substituted Aminomethanesulfonic Acids in Water from 5 to 55°C

The equilibrium constants for the dissociation steps of (4-morpholineethanesulfonic acid) (MES) and (2-{[tris(hydroxymethyl)methyl]-1-ethanesulfonic acid (TES) have been determined at 12 and 7 different temperatures, respectively, from 5 to 55°C. The emf measurements were carried out by using a cell without liquid junction of the type:Pt; H₂ (g, 1 atm) | buffer(m₁), Na salt of buffer(m₂), NaCl(m₃) | AgCl, Ag.The pK ₂ values of MES and TES at 25°C are 6.269 and 7.550. The thermodynamic quantities for the dissociation process have been calculated. These zwitterionic compounds are useful for pH control as standard buffers in the physiological region of pH 5.50 to 6.50 for MES, 6.5 to 7.5 for TES, respectively. Reliable measurements of the pH at isotonic saline solution (I = 0.16m) such as blood and plasma are important for clinical diagnosis.     

Singlet oxygen reactions of 3-methoxy-2-pyrrole carboxylic acid tert-butyl esters. A route to 5-substituted pyrrole precursors of prodigiosin and analogs

Reaction of the tert-butyl ester of 3-methoxy-2-pyrrole carboxylic acid with singlet oxygen yields a peroxidic intermediate which undergoes coupling with a range of nucleophiles to yield 5-substituted pyrroles. Among these products are α,α′-bipyrroles which serve as precursors of prodigiosin, including A-ring substituted analogues.     

Nitrogen configuration determined by X-ray analysis on an homogeneous series of 3-Indolinones

The X-ray diffraction analyses of 2-methyl-2-phenylindolin-3-one 1 , 1,2-dimethyl-2-phenylindolin-3-one 2 , 1-hydroxy-2-methyl-2-phenylindolin-3-one 3 and 1-methoxy-2-methyl-2-phenylindolin-3-one 4 have been carried out and the structural data were compared with those of 1-oxyl-2-methyl-2-phenylindolin-3-one 5 . The results demonstrate that only compounds 2 and 5 show planar trigonal geometry which is coplanar with the conjugated benzene ring of the indolinic nucleus, whereas compounds 3 and 4 show a marked pyramidality of the nitrogen. Even if compound 1 shows a certain pyramidality of the nitrogen, it has been considered similar to compound 2 . The reactivity of all studied compounds fit the structural data.     

Plants and Natural Products with Activity against Various Types of Coronaviruses: A Review with Focus on SARS-CoV-2

COVID-19 is a pandemic disease caused by the SARS-CoV-2 virus, which is potentially fatal for vulnerable individuals. Disease management represents a challenge for many countries, given the shortage of medicines and hospital resources. The objective of this work was to review the medicinal plants, foods and natural products showing scientific evidence for host protection against various types of coronaviruses, with a focus on SARS-CoV-2. Natural products that mitigate the symptoms caused by various coronaviruses are also presented. Particular attention was placed on natural products that stabilize the Renin–Angiotensin–Aldosterone System (RAAS), which has been associated with the entry of the SARS-CoV-2 into human cells.     

Chemical and biological evaluation of essential oils from two species of Myrtaceae - Eugenia uniflora L. and Plinia trunciflora (O. Berg) Kausel

The chemical composition and antimicrobial activity of essential oils obtained from leaves of two Myrtaceae species-Eugenia uniflora L. and Plinia trunciflora (O. Berg) Kausel-were determined. Analysis by GC/MS as well as determination of Kovatz indexes indicated atractylone (26.78%) and curzerene (17.96%) as major constituents of E. uniflora oil and α-cadinol (19.15%), apiole (11.15%) and cubenol (5.43%) as main components in P. trunciflora oil. Both essential oils were tested for antimicrobial activity against yeasts and bacteria. E. uniflora and P. trunciflora essential oils were active towards two Gram-positive bacteria, Streptococcus equi and Staphylococcus epidermis. In addition, biological activity of both essential oils was detected for pathogenic yeasts of the genus Candida and Cryptococcus. E. uniflora was active towards all yeast tested and exhibited interesting minimal inhibitory concentrations (0.11 to 3.75 mg/mL) across a broad spectrum of activity.     

Antibacterial activity of Aristolochia brevipes against multidrug-resistant Mycobacterium tuberculosis

The increased incidence of Multidrug-Resistant Mycobacterium tuberculosis (MDR-MT) requires the search for alternative antimycobacterial drugs. The main aim of this study was to evaluate the dichloromethane extract from Aristolochia brevipes (Rhizoma) and the compounds isolated from this extract against several mycobacterial strains, sensitive, resistant (monoresistant), and clinical isolates (multidrug-resistant), using the alamarBlue? microassay. The extract was fractionated by column chromatography, yielding the following eight major compounds: (1) 6α-7-dehydro-N-formylnornantenine; (2) E/Z-N-formylnornantenine; (3) 7,9-dimethoxytariacuripyrone; (4) 9-methoxy-tariacuripyrone; (5) aristololactam I; (6) β-sitosterol; (7) stigmasterol; and (8) 3-hydroxy-α-terpineol. The structures of these compounds were elucidated by 1H- and 13C- (1D and 2D) Nuclear Magnetic Resonance (NMR) spectroscopy. This study demonstrates that the dichloromethane extract (rhizome) of A. brevipes possesses strong in vitro antimycobacterial activity against Mycobacterium tuberculosis H37Rv (Minimum Inhibitory Concentration value [MIC], 12.5 μg/mL). The most active compound against all mycobacterial strains tested was the compound aristolactam I (5), with MIC values ranging between 12.5 and 25 μg/mL. To our knowledge, this the first report of antimycobacterial activity in this plant.     

Conformational behaviour, hydrogen bond competition and intramolecular dynamics in vanillin derivatives: acetovanillone and 6-hydroxy-3-methoxyacetophenone

The conformational landscape of the structural isomers acetovanillone (apocynin, AV) and 6-hydroxy-3-methoxyacetophenone (HMAP) has been investigated in a supersonic jet using Fourier transform microwave spectroscopy. Two conformers have been detected in the jet-cooled expansion for each molecule (s-cis and s-trans in AV; s-trans and a-trans for HMAP), differing in the relative orientation of the acetyl and methoxy groups. Both molecules are stabilized by O-H···O or O-H···O=C hydroxyl intramolecular hydrogen bonds, either constraining the local conformations of the methoxy group in AV, or that of the acetyl group in HMAP. Internal rotation splittings have been observed in both conformers of each molecule, originated by the acetyl group, that yield information on the influence of the intramolecular hydrogen bonds on the methyl torsion. The similar internal rotation barriers in both molecules (6.6 and 7.4 kJ mol(-1) in AV; 7.3 and 7.0 kJ mol(-1) in HMAP) suggest that the acetyl torsion is only slightly affected by intramolecular hydrogen bonding. The absence of torsional tunnellings due to the methoxy group indicates torsional barriers above 10.2 and 8.9 kJ mol(-1) for AV conformers, 10.1 and 10.4 kJ mol(-1) for HMAP. Conformational ratios and relative free energies have been estimated from relative intensity measurements of the spectral lines. Ab initio (MP2) and density functional calculations using the recent M05-2X empirical functional have been used to aid the experimental work in describing the structures, internal rotation barriers and isomerization potentials.