Hydrogen Shift Research Articles

Late Eocene Record of Hydrology and Temperature From Prydz Bay, East Antarctica

AbstractThe Eocene‐Oligocene transition (EOT) marks the onset of Antarctic glaciation at 33.7 Ma. Although the benthic oxygen isotope record defines the major continental ice sheet expansion, recent sedimentary and geochemical evidence suggests the presence of earlier ephemeral ice sheets. Sediment cores from Ocean Drilling Program Legs 119 and 188 in Prydz Bay provide an archive of conditions in a major drainage system of East Antarctica. We study biomarker and microfossil evidence to discern how the vegetation and climate shifted between 36 and 33 Ma. Pollen was dominated by reworked Permian Glossopterid gymnosperms; however, penecontemporaneous Eocene pollen assemblages indicate that some vegetation survived the glacial advances. At the EOT, brGDGT soil biomarkers indicate abrupt cooling from 13°C to 8°C and soil pH increases from 6.0 to 6.7, suggesting drying which is further supported by plant wax hydrogen and carbon isotopic shifts of 20‰ and 1.1‰, respectively, and evidence for drying from weathering proxies. Although the terrestrial soil biomarker influx mostly precludes the use of TEX86, we find sea surface temperatures of 12°C in the late Eocene cooling to 8°C at the EOT. Marine productivity undergoes a sustained increase after the glacial advance, likely promoted by enhanced ocean circulation. Between the two glacial surge events of the Priabonian Oxygen Maximum at 37.3 Ma and the EOT at 33.7 Ma, we observe warming of 2–5°C at 35.7 and 34.7 Ma, with increase in penecontemporaneous pollen and enhanced marine productivity, capturing the last flickers of Antarctic warmth.

Non-Adiabatic Reaction Dynamics in the Gas-Phase Formation of Phosphinidenesilylene, the Isovalent Counterpart of Hydrogen Isocyanide, under Single-Collision Conditions.

The phosphinidenesilylene (HPSi; X1A') molecule was prepared via a directed gas-phase synthesis in the bimolecular reaction of ground-state atomic silicon (Si; 3P) with phosphine (PH3; X1A1) under single-collision conditions. The chemical dynamics are initiated on the triplet surface via addition of a silicon atom to the non-bonding electron pair of phosphine, followed by non-adiabatic dynamics and surface hopping to the singlet manifold, accompanied by isomerization via atomic hydrogen shift and decomposition to phosphinidenesilylene (HPSi, X1A') along with molecular hydrogen. Statistical calculations predict that silylidynephosphine (HSiP, X1Σ+) is also formed, albeit with lower yields. The barrier-less route to phosphinidenesilylene opens up a multipurpose mechanism to access the hitherto obscure class of phosphasilenylidenes through silicon-phosphorus coupling via reactions of atomic silicon with alkylphosphines under single-collision conditions in the absence of successive reactions of the reaction products, which are not feasible to prepare by traditional synthetic routes.

Synthesis and structural elucidation of a series of isoflavones-based on FPR antagonists

Synthesis and structural elucidation of a series of isoflavones-based on FPR antagonists

Molecular structures of nonvolatile components in the Haihong fruit wine and their free radical scavenging effect

In order to investigate the correlation between free radical scavenging effect and the related molecular structures of active substances in the Haihong fruit (Malus Micromalus Makino) wine, sixteen kinds of components were isolated from the fruit wine. The structures of thirteen components were identified by UV, FTIR, LC-MS, 1D-NMR and 2D-NMR. The scavenging abilities of the fruit wine on DPPH (2,2-Diphenyl-1 -picrylhydrazyl radical), OH, O2− and the protective effects on red blood cell, SOD (Superoxide Dismutase), CAT(Catalase) and GPX(glutathione peroxidases) in aging mice tissues were studied. Results showed that the structures of o-diphenol and m-diphenol play an important role in scavenging free radicals. A larger conjugation system in functional molecule is conducive to getting a higher scavenging rate of free radicals. When the chemical shift of phenol hydrogen is lower, the anti-oxygenation ability is stronger. The fruit wine exhibits a strong scavenging ability on free radicals. It can inhibit the damage of red blood cells caused by OH radical.

Hadronic vacuum-polarization contribution to various QED observables

Due to precision tests of quantum electrodynamics (QED), determination of accurate values of fundamental constants, and constraints on new physics, it is important in a consistent way to evaluate a number of QED observables such as the Lamb shift in hydrogen-like atomic systems. Even in a pure leptonic case, those QED variables are in fact not pure QED ones since hadronic effects are involved through intermediate states while accounting for higher-order effects. One of them is hadronic vacuum polarization (hVP). Complex evaluations often involve a number of QED quantities, for which treatment of hVP is not consistent. The highest accuracy for a calculation of the hVP term is required for the anomalous magnetic moment of a muon. However, a standard data-driven treatment of hVP, based on a dispersion integration of experimental data on electron-positron annihilation to hadrons and some other phenomena, leads to a contradiction with the experimental value of a_mu . This experimental value can be considered as an indirect determination of the hVP contribution to a_mu and the scatter of theory and experiment allows one to obtain a conservative estimation of the related hVP contribution. In this paper, we derive exact and approximate relations between the leading-order (LO) hVP contributions to various observables. Using those relations, we obtain for them a consistent set of the results, based on the scatter of a_mu values. While calculating the LO hVP term, we have to remember that next-to-LO (NLO) hVP corrections are often comparable with the uncertainty of the LO term. Special attention is payed to hVP contribution to simple atoms. In particular, we discuss the NLO contribution to the Lamb shift in ordinary and muonic hydrogen and other two-body atoms for Zle 10. We also consider the NLO contribution of the muonic vacuum polarization to the Lamb shift in hydrogen-like atoms. With the a_mu puzzle unresolved, one may still require present-days values of the hVP contributions to various observable for comparison to experiment etc. the presence of contradicting values and a lack of consistency means an additional uncertainty for a_mu and for key contributions to it, including the LO hVP one. We present here an estimation of such a propagated uncertainty in hVP contributions to different QED observables and recommend a consistent set of the related LO hVP contributions.Graphic

Hydrogen isotopic analysis of nuclear reactor materials using ultrafast laser-induced breakdown spectroscopy.

Laser-induced breakdown spectroscopy is a promising method for rapidly measuring hydrogen and its isotopes, critical to a wide range of disciplines (e.g. nuclear energy, hydrogen storage). However, line broadening can hinder the ability to detect finely spaced isotopic shifts. Here, the effects of varying plasma generation conditions (nanosecond versus femtosecond laser ablation) and ambient environments (argon versus helium gas) on spectral features generated from Zircaloy-4 targets with varying hydrogen isotopic compositions were studied. Time-resolved 2D spectral imaging was employed to detail the spatial distribution of species throughout plasma evolution. Results highlight that hydrogen and deuterium isotopic shifts can be measured with minimal spectral broadening in a ∼ 10 Torr helium gas environment using ultrafast laser-produced plasmas.

Significant bonding rearrangements triggered by Mg4 clusters.

The structure, stability, and bonding of the complexes formed by the interaction of Mg4 clusters and first row Lewis bases, namely, ammonia, water, and hydrogen fluoride, have been investigated through the use of high-level G4 single-reference and CASPT2 multireference formalisms. The adducts formed reflect the high electrophilicity of the Mg4 cluster through electron density holes in the neighborhood of each metallic center. After the adduct formation, the metallic bonding of the Mg4 moiety is not significantly altered so that the hydrogen shifts from the Lewis base toward the Mg atoms lead to new local minima with enhanced stability. For the particular case of ammonia and water, the global minima obtained when all the hydrogens of the Lewis base are shifted to the Mg4 moiety have in common a very stable scaffold with a N or an O center covalently tetracoordinated to the four Mg atoms, so the initial bonding arrangements of both reactants have completely disappeared. The reactivity features exhibited by these Mg4 clusters suggest that nanostructures of this metal might have an interesting catalytic behavior.

Criegee Intermediates in Autoxidation Reactions: Mechanistic Considerations.

Products of Criegee intermediate (CI) chemistry were recently detected in radical chain autoxidation reactions involving β-hydroxyperoxy radicals. Here, we demonstrate by means of accurate G4 computations that direct scission of the latter to CIs and radical byproducts is thermodynamically highly unfavorable. Instead, the reaction becomes possible through a hydrogen abstraction reaction that could proceed by reversible formation of a dimeric tetroxide and a subsequent [1,6] hydrogen shift of the hydroxy hydrogen.

A Theoretical Antioxidant Mechanism for Cytoprotective Effect of p-AcetamideSalicylate Derivatives against Free Radical Initiator AAPH in Human Erythrocytes

The molecular mechanism of cytoprotective effect on human erythrocytes of aminophenol and salicylates associated derivatives was related to their antioxidant capacity. The oxidative hemolysis induced by water-soluble free-radical initiator 2,2’-azobis-(2-amidine-propane)-dihydrochloride (AAPH) was inhibited by drug candidates named benzaminophen (BZL), salicytamide or 5-acetamide-salicylic acid (ASL), and salibenzamide or 5-benzamide-salicylic acid (BSL) when compared to their parents salicylic acid (SAC) and acetaminophen (ACP). Trolox (TLX) was the most powerful compound and used as positive control. BZL showed a potent effect followed by ACP > BSL > ASL. SAC did not show protective effect in any evaluated concentrations. These results are in accordance with the molecular mechanism by using theoretical calculation of single electron transfers (SET), hydrogen atom transfers (HAT), and sequential proton loss electron transfer (SPLET) by means of DFT/B3LYP/6-31++G(d,p) level of theory. [1,5] Hydrogen shift between carboxyl and phenol moieties and electronic properties related to pKa and other physicalchemical properties can be involved. The molecular association approach provides protective compounds more effective than SAC.

Understanding the sigmatropic shifts of cyclopenta-2,4-dien-1-yltrimethylsilane in its Diels-Alder addition.

To understand its dynamic processes in the Diels-Alder addition, temperature-dependent dynamic processes of cyclopenta-2,4-dien-1-yltrimethylsilane [1-(C5H5)Si(Me)3] are investigated by DFT computations. The degenerate sigmatropic migration of Si(Me)3 is found to be the dominant factor with a Gibbs free energy of activation of 13.2 kcal mol-1. The contribution from suprafacial hydrogen shifts is negligible, and the antarafacial sigmatropic hydrogen shifts are excluded due to their relatively high Gibbs barriers. Thermodynamically controlled Diels-Alder addition is obtained, which involves the critical interconversion between the 2,4-dienyl isomer 1 and 1,4-dienyl isomer 3.

The mechanism of conversion of substituted glycals to chiral acenes via Diels-Alder reaction: a computational study.

Synthesis of linearly fused aromatic systems using a glycal-based diene with an aryne is a long-standing topic of interest in glycal chemistry. We have examined the mechanistic pathways for the transformation of substituted glycals to chiral fused aromatic cores via Diels-Alder (DA) reaction using the SMDACN-M06-2X/6-31G(d) level of theory. The DA reactions of E (1a) and Z (1a') forms of C-2 alkenyl glycal and an aryl glycal (1b) as a diene were examined with a benzyne intermediate generated as a dienophile. The computational results reveal that 1a and 1b can only be transformed into the fused aromatic cores by the base-catalyzed reaction because a [1,5] sigmatropic hydrogen shift is not feasible. The activation free energy barrier for the base-catalyzed proton abstraction process is 4.2 kcal mol-1 and there is almost no barrier for stereoisomeric 1a DA-complexes. The activation free energy barrier values for stereoisomeric 1b DA-complexes for the base-catalyzed proton abstraction process are 10.8 and 12.4 kcal mol-1. The appropriate orientation of glycal-ring-oxygen and hydrogen at the 5th position of Z (1a') forms of C-2 alkenyl glycal facilitates the [1,5] sigmatropic hydrogen shift; however, the base-catalyzed reaction is energetically more favored than the former case. The rate-determining step for 1a and 1a' is the ring-opening step (18.2 and 19.5 kcal mol-1 for the S-stereoisomer), whereas the DA adduct formation step is the rate-determining step for 1b (16.1 kcal mol-1 for the S-stereoisomer). The structural analysis reveals the formation of the preferred S-stereoisomer over the R-stereoisomer with the respective dienes.

Thermochemistry and Reaction Kinetics of Secondary Ethyl Radical of Methyl Ethyl Sulfide, CH<sub>3</sub>SCH•CH<sub>3</sub>, with <sup>3</sup>O<sub>2</sub> to CH<sub>2</sub>SCH(OO•)CH<sub>3</sub>

The quantum Rice-Ramsperger-Kassel (QRRK) theory is used to analyze the reaction between the activated CH₃S CH•CH₃ and molecular oxygen to account for further reaction and collisional and deactivation. hydroxyl radicals initiate the oxidation of Methyl ethyl sulfide (CH₃SCH₂CH₃) and MES (methylthioethane) under combustion conditions. The CBS-QB3 and G3MP2B3 composite and M062X/6-311+G(2d, p) DFT methods was used to study the thermochemical properties of reactants, products and transition states. These thermochemical properties are used for the calculations for kinetic and thermochemical parameters. Under high pressure and low temperature, isomerization and stabilization of the CH₃SCH(OO•)CH₃ adduct is of importance. Under atmospheric pressure and at temperatures between above 600 ~ 800 K reactions of the chemically activated peroxy adduct become important relative to stabilization. The reaction between CH₃SCH•CH₃ and O₂ forms an energized peroxy adduct CH₃SCH(OO•)CH₃ with a calculated well depth of 30.2 kcal/mol at the CBS-QB3 level of theory. Kinetic parameters are calculated using the thermochemical properties of products, reactants and transition states obtained using under CBS-QB3 method of calculation. At temperature below 500 K, Stabilization of CH₃SCH(OO•)CH₃ adduct is of importance. Temperature of 500-900 K, is optimal for intramolecular hydrogen shift and the isomerization of CH₃SCH(OO•)CH₃ adduct. At temperature above 800 K, all of the subsequent reaction paths are of importance. For a reaction to move forward under pressure 1-4 atm, the recommended optimal temperature is between 600-800 K. A new pathway for the CH₃SCH(OO•)CH₃ adduct is observed, the attachment of peroxyl oxygen radical to sulfur followed by carbon-sulfur bond dissociation and formation of oxygen-sulfur and oxygen-carbon double bonds.

Energy profile, structure, spectroscopic and quantum chemical investigations of trans–3,4–(methylenedioxy)cinnamic acid

Abstract The molecular structural parameters and thermodynamic properties of trans–3,4–(methylenedioxy)cinnamic acid have been determined by B3LYP method by using 6–311++G** and cc–pVTZ basis sets. The vibrational frequencies of the compound have been precisely assigned, analysed and the theoretical results are compared with FT-IR and FT-Raman data. The energies of important MOs of the compound are also evaluated from DFT method. The frontier orbital energy gap (ELUMO–EHOMO) is found to be 4.1032 eV. The hydrogen and carbon chemical shifts are elaborately discussed. The dual descriptors Δfk, Δsk and Δωk reveals that the order of reactivity towards nucleophilic attack is C1 > O13 > O12 > C3 > C8 > C6. The minimum and maximum limits of the electrostatic potential observed in MDCA is –1.448e × 10–2(red) and +1.448e × 10–2 (blue). Thus, the present investigation provides complete structural, vibrational and reactivity characteristics of the compound .

Enantioselective Cyclopropanation/[1,5]-Hydrogen Shift to Access Rauhut-Currier Product.

A Michael addition initiated cyclopropanation/[1,5]-hydrogen shift has been developed for the enantioselective synthesis of Rauhut-Currier products. The reaction of α-alkyl diazoesters and in situ generated o-quinone methides proceeds in the presence of chiral oxazaborolidinium ion, providing Z-stereocontrolled Rauhut-Currier products in high yields (up to 96%) with excellent Z/E selectivities (>20:1) and enantioselectivities (up to >99% ee). The synthetic utility was illustrated by conversion of the product to 3,4-dihydrocoumarins with two adjacent chiral stereocenters.

Directed Gas Phase Formation of the Elusive Silylgermylidyne Radical (H3 SiGe, X2 A'').

The previously unknown silylgermylidyne radical (H3 SiGe; X2 A'') was prepared via the bimolecular gas phase reaction of ground state silylidyne radicals (SiH; X2 Π) with germane (GeH4 ; X1 A1 ) under single collision conditions in crossed molecular beams experiments. This reaction begins with the formation of a van der Waals complex followed by insertion of silylidyne into a germanium-hydrogen bond forming the germylsilyl radical (H3 GeSiH2 ). A hydrogen migration isomerizes this intermediate to the silylgermyl radical (H2 GeSiH3 ), which undergoes a hydrogen shift to an exotic, hydrogen-bridged germylidynesilane intermediate (H3 Si(μ-H)GeH); this species emits molecular hydrogen forming the silylgermylidyne radical (H3 SiGe). Our study offers a remarkable glance at the complex reaction dynamics and inherent isomerization processes of the silicon-germanium system, which are quite distinct from those of the isovalent hydrocarbon system (ethyl radical; C2 H5 ) eventually affording detailed insights into an exotic chemistry and intriguing chemical bonding of silicon-germanium species at the microscopic level exploiting crossed molecular beams.

P.725 ACC neurometabolites in Bipolar Disorder are influenced by mood state and medication: a systematic review and meta-analysis of 1H-MRS studies

Local anesthetics promote analgesia by interacting with excitable membranes. Articaine (ATC) has a unique composition among local anesthetics as it possesses a thiophene instead of the typical phenyl ring. Aiming to characterize the interaction of neutral articaine (nATC) with phospholipid membranes, we have employed a synergistic approach of experimental and computational techniques. Fluorescence measurements supported nATC partitioning into the membranes, since its intrinsic fluorescence anisotropy increased from 0.03 in water to 0.29 in the presence of egg phosphatidylcholine (EPC) liposomes, and the fluorescence of AHBA, a probe that monitors the water-membrane interface, was quenched by nATC. 1H NMR experiments revealed changes in the chemical shifts of articaine and EPC hydrogens after partitioning, and shorter T1 values of nATC hydrogens when inserted into the EPC vesicles. Contacts of nATC and the phospholipid polar head group were inferred from 2D-NOE. Taken together, these results indicate a superficial insertion of the nATC molecules inside EPC bilayers. This conclusion was confirmed by molecular dynamics simulations, which allowed the identification of the key interactions underlying the preferential location of nATC in the bilayer. Contrary to what is often stated (that articaine is a high lipophilic local anesthetic agent) our results place ATC among the hydrophilic ones, such as lidocaine, prilocaine, and mepivacaine, for which the water/membrane interface is the preferred location.

A CASE OF THYROTOXIC PERIODIC PARALYSIS IN AN AFRICAN AMERICAN MALE REQUIRING MECHANICAL VENTILATION AND HEMODIALYSIS

SESSION TITLE: Medical Student/Resident Critical Care SESSION TYPE: Med Student/Res Case Report PRESENTED ON: October 18-21, 2020 INTRODUCTION: Thyrotoxic periodic paralysis (TPP) represents a rare, acquired form of hypokalemic periodic paralysis characterized by acute onset muscle weakness and hypokalemia. We report a severe presentation requiring mechanical ventilation and hemodialysis (HD). CASE PRESENTATION: A 25 year old African American male presented with bilateral lower extremity weakness and hypokalemia at 1.6 mmol/L with characteristic hypokalemic ECG changes. After receiving 40 mEq IV potassium chloride, his hypokalemia worsened to 1.1. Given acute progression of ascending paralysis to complete paraplegia, 3/5 strength in upper extremities and concern for impending diaphragmatic weakness, he was intubated. Despite an additional 170 mEq of potassium, his repeat K+ was 1.5 with progressive EKG changes. He also had a metabolic acidosis with pH of 7.208 and a lactic acid of 8.7. Given refractory hypokalemia and concern that bicarbonate therapy for acidosis would worsen the hypokalemia, the patient was initiated on HD with a high potassium bath. The team confirmed suspicion of TPP upon return of TSH level <0.015 mU/L and administered 3 doses of 1 mg IV Propranolol during which he exhibited spontaneous extremity movements. Serial labs then revealed a rebound hyperkalemia up to 7.4 mmol/L with characteristic hyperkalemic ECG changes. He received usual stabilizing treatments and a second session of emergent HD to correct the up trending hyperkalemia. Diagnosis and recovery was confirmed after stable potassium levels, resolved acidosis, complete recovery of his neurological exam and notably elevated T4 and T3 levels. He was extubated without complication and discharged home on Propylthiouracil with instructions to follow-up with endocrinology for further evaluation of his hyperthyroidism. DISCUSSION: As compared to prior published cases of TPP most often amongst Asian males, management of this African American patient differed with the use of mechanical ventilation for airway protection due to rapidly progressive ascending paralysis and down trending negative inspiratory forces and vital capacities. It also necessitated the use of hemodialysis to correct both the refractory hypokalemia and concomitant acidosis. It is believed that a thyrotoxic-mediated beta-adrenergic response drives potassium into cells hyperpolarizing muscle fibers, causes an extracellular shift of hydrogen and increases conversion of pyruvate to lactate resulting in acidosis. The concern with addressing this with a bicarbonate drip was that a secondary alkalosis would further intracellularly shift potassium. Fortunately, already having a HD catheter in place allowed for more rapid treatment of the severe rebound hyperkalemia. CONCLUSIONS: Initial suspicion of TPP on the differential for ascending paralysis and earlier use of IV propranolol can prevent progression of paralysis, rebound hyperkalemia, lactic acidosis and life-threatening cardiac arrhythmias. Reference #1: Younis AA. Thyrotoxic Periodic Paralysis as a Presentation of Thyrotoxicosis: A Case Report and review of the literature. Mediterr J Rheumatol. 2018;29(1):46–48. Reference #2: Wong P. Hypokalemic thyrotoxic periodic paralysis: a case series. CJEM. 2003;5(5):353–355. Reference #3: Tassone H, Moulin A, Henderson SO. The pitfalls of potassium replacement in thyrotoxic periodic paralysis: a case report and review of the literature. J Emerg Med. 2004;26(2):157–161. DISCLOSURES: No relevant relationships by Firth Bowden, source=Web Response No relevant relationships by Uday Gulati, source=Web Response No relevant relationships by Asma Qayyum, source=Web Response No relevant relationships by samson zarbiv, source=Admin input

Lessons from Fitting the Lowest Order Energy Independent Chiral Based bar{K}N Potential to Experimental Data

It is shown, that fitting parameters of a bar{K}N interaction model to different sets of experimental data can lead to physical conclusions which might provide a deeper insight into the physics of this multichannel system. The available experimental data are divided into three parts: the “classical” set consisting of the low-energy K^-p cross sections and the threshold branching ratios, the SIDDHARTA 1s level shift in kaonic hydrogen and the CLAS photoproduction data. We have fitted the parameters of the potential to different combinations of these data. We found, that the two poles corresponding to the I=0 nuclear quasi-bound state (Lambda (1405)) and to the K^-p 1s atomic level seem to resist to their simultaneous reproduction at the right place, though a more or less satisfactory compromise can be achieved. Potentials with the Lambda (1405) pole pinned down close to the PDG value fail to reproduce the classical two-body data with an acceptable accuracy. We also added comments on two papers criticizing the potential used in the fits.

Comparing Reaction Routes for 3(RO···OR') Intermediates Formed in Peroxy Radical Self- and Cross-Reactions.

Organic peroxy radicals (RO2) are key intermediates in the chemistry of the atmosphere. One of the main sink reactions of RO2 is the recombination reaction RO2 + R'O2, which has three main channels (all with O2 as a coproduct): (1) R-H═O + R'OH, (2) RO + R'O, and (3) ROOR'. The RO + R'O "alkoxy" channel promotes radical and oxidant recycling, while the ROOR' "dimer" channel leads to low-volatility products relevant to aerosol processes. The ROOR' channel has only recently been discovered to play a role in the gas phase. Recent computational studies indicate that all of these channels first go through an intermediate complex 1(RO···3O2···OR'). Here, 3O2 is very weakly bound and will likely evaporate from the system, giving a triplet cluster of two alkoxy radicals: 3(RO···OR'). In this study, we systematically investigate the three reaction channels for an atmospherically representative set of RO + R'O radicals formed in the corresponding RO2 + R'O2 reaction. First, we systematically sample the possible conformations of the RO···OR' clusters on the triplet potential energy surface. Next, we compute energetic parameters and attempt to estimate reaction rate coefficients for the three channels: evaporation/dissociation to RO + R'O, a hydrogen shift leading to the formation of R'-H═O + ROH, and "spin-flip" (intersystem crossing) leading to, or at least allowing, the formation of ROOR' dimers. While large uncertainties in the computed energetics prevent a quantitative comparison of reaction rates, all three channels were found to be very fast (with typical rates greater than 106 s-1). This qualitatively demonstrates that the computationally proposed novel RO2 + R'O2 reaction mechanism is compatible with experimental data showing non-negligible branching ratios for all three channels, at least for sufficiently complex RO2.

Absolute Stereochemistry of Antifungal Limonene-1,2-diols from Lippia rubella

From the active dichloromethane-soluble extract of Lippia rubella (Moldenke) T.R.S. Silva & Salimena, Verbenaceae (MIC = 78 μg/ml against Cryptococcus neoformans), two diastereomers of limonene-1,2-diol were isolated by countercurrent chromatography. An extensive NMR exploration to address the problem of distinguishing and evaluating the stereochemical influences of the C-2 hydroxy substituent on hydrogen and carbon chemical shifts of the natural products confirmed that these natural antifungal monoterpenes are derived from R-(+)-limonene. The absolute stereochemistry for both isolated diols was confirmed by the application of Mosher esters methodology. For the novel synclinal 1,2-diol, its structure was confirmed as (−)-(1S,2R,4R)-1-methyl-4-(prop-1-en-2-yl)cyclohexane-1,2-diol, which displayed a stronger antifungal activity against Crytococcus neoformans (MIC = 31.25 μg/ml; 184 μM) than the trans-diaxial 1,2-diol (2) which corresponded to the (+)-(1S,2S,4R) isomer (MIC = 250 μg/ml; 1470 μM) probably the most frequently distributed stereoisomer in volatile oils. The natural occurrence of 1 and 2 is being reported for the first time.