Quinoline, Indole, and Isogranatanine Alkaloids from Malayan Leuconotis eugeniifolia.

Nine new alkaloids, eugeniinalines A-H (1-8) and (+)-eburnamenine N-oxide (9), comprising one quinoline, six indole, and two isogranatanine alkaloids, were isolated from the stem-bark extract of the Malayan Leuconotis eugeniifolia. The structures and absolute configurations of these alkaloids were established based on the analysis of the spectroscopic data, GIAO NMR calculations, DP4+ probability analysis, TDDFT-ECD method, and X-ray diffraction analysis. Eugeniinaline A (1) represents a new pentacyclic quinoline alkaloid with a 6/6/5/6/7 ring system. Eugeniinaline G (7) and its seco-derivative, eugeniinaline H (8), were the first isogranatanine alkaloids isolated as natural products. The known alkaloids leucolusine (10) and melokhanine A (11) were found to be the same compound, based on comparison of the spectroscopic data of both compounds, with the absolute configuration of (7R, 20R, 21S). Eugeniinalines A and G (1 and 7) showed cytotoxic activity against the HT-29 cancer cell line with IC50 values of 7.1 and 7.2 µM, respectively.

Highly effective ashless and non-corrosive dimercaptobenzothiadiazole as multifunctional lubricant additives in naphthenic base oil.

The conventional medium chain chlorinated paraffin (MCCP) and zinc dialkyl dithiophosphate (ZDDP) additives have greatly enhanced the extreme pressure (EP) and anti-wear (AW) performance of the metalworking fluids. However, chlorine- and zinc-containing additives are restricted in use due to eco-toxicity issue. Herein, ashless and non-corrosive dimercaptobenzothiadiazole derivatives, namely bis-2,5-benzylsulfanyl-[1,3,4]thiadiazole (BBST) and bis-2,5-octylsulfanyl-[1,3,4]thiadiazole (BOST) consist of three sulfur atoms have been synthesized and evaluated. The performance of BBST shows a weld load (PD) of 3089 N and AW value of 5 mm2, which represents an improvement of 3.1 and 7.4 folds over naphthenic base oil (NBO). In addition, BBST also outperformed BOST, MCCP, and ZDDP in terms of its weld load and AW properties. Based on XPS analysis and molecular electrostatic potential maps (MEPS), BBST exhibits superior tribology performance due to the interaction between the sulfur (S), nitrogen (N), and π-electrons of the benzene ring with the metal surface. The formation of FeS, Fe2O3 and Fe⋯N coordinate bonds contributes to the creation of an excellent tribofilm.

Enhancing operational stability of OLEDs based on subatomic modified thermally activated delayed fluorescence compounds.

The realization of operationally stable blue organic light-emitting diodes is a challenging issue across the field. While device optimization has been a focus to effectively prolong device lifetime, strategies based on molecular engineering of chemical structures, particularly at the subatomic level, remains little. Herein, we explore the effect of targeted deuteration on donor and/or acceptor units of thermally activated delayed fluorescence emitters and investigate the structure-property relationship between intrinsic molecular stability, based on isotopic effect, and device operational stability. We show that the deuteration of the acceptor unit is critical to enhance the photostability of thermally activated delayed fluorescence compounds and hence device lifetime in addition to that of the donor units, which is commonly neglected due to the limited availability and synthetic complexity of deuterated acceptors. Based on these isotopic analogues, we observe a gradual increase in the device operational stability and achieve the long-lifetime time to 90% of the initial luminance of 23.4 h at the luminance of 1000 cd m-2 for thermally activated delayed fluorescence-sensitized organic light-emitting diodes. We anticipate our strategic deuteration approach provides insights and demonstrates the importance on structural modification materials at a subatomic level towards prolonging the device operational stability.

Tetradentate C∧C∧N∧N Ligand-Containing Gold(III) Complexes with Orange to Deep-Red Thermally Activated Delayed Fluorescence (TADF) and Their Application in Organic Light-Emitting Devices.

A new class of thermally activated delayed fluorescence (TADF) tetradentate C∧C∧N∧N ligand-containing gold(III) complexes containing acridinyl moieties has been designed and synthesized. These complexes exhibit orange-red to deep-red emission with photoluminescence quantum yields (PLQYs) of up to 0.76 in solid-state thin films. Short excited-state lifetimes of ≤2.0 µs and large radiative decay rate constants (kr) in the order of 105 s-1 have also been found in the complexes. High-performance solution-processed and vacuum-deposited organic light-emitting devices (OLEDs) based on these complexes have been fabricated, demonstrating high maximum external quantum efficiencies (EQEs) of 12.2 and 12.7%, respectively, which are among the best values ever reported for red-emitting gold(III)-based OLEDs. In addition, satisfactory operational half-lifetime (LT50) values of up to 34,058 h have been attained in these red-emitting devices. It is found that the operational stability is strongly dependent on the choice of functional groups on the acridinyl moieties, of which the incorporation of -O- and -S- linkers can effectively prolong the LT50 value by an order of magnitude. The TADF properties of the complexes are substantiated by the hypsochromic shift in emission energies and the remarkable enhancement in the emission intensity upon increasing temperature. The TADF properties have also been supported by temperature-dependent ultrafast transient absorption studies, with the direct observation of reverse intersystem crossing (RISC) and the determination of the activation parameters for the very first time, together with their excited-state dynamics.

Surface or Internal Hydration - Does It Really Matter?

The precise location of an ion or electron, whether it is internally solvated or residing on the surface of a water cluster, remains an intriguing question. Subtle differences in the hydrogen bonding network may lead to a preference for one or the other. Here we discuss spectroscopic probes of the structure of gas-phase hydrated ions in combination with quantum chemistry, as well as H/D exchange as a means of structure elucidation. With the help of nanocalorimetry, we look for thermochemical signatures of surface vs internal solvation. Examples of strongly size-dependent reactivity are reviewed which illustrate the influence of surface vs internal solvation on unimolecular rearrangements of the cluster, as well as on the rate and product distribution of ion-molecule reactions.

Synthesis, Electrochemistry, Photophysics, and Photochemistry of a Discrete Tetranuclear Copper(I) Sulfido Cluster.

A tetranuclear copper(I) complex, [Cu4{µ-(Ph2P)2NH}4(µ4-S)](PF6)2 (1), was synthesized. It was found to display intense and long-lived phosphorescence in the solid and solution states. The lowest-energy excited state was assigned as ligand-to-metal charge transfer (LMCT) [S2- → Cu4] mixed with some metal-centered (ds/dp) character. In addition, the phosphorescent state of this complex was found to be quenched by pyridinium acceptors via an oxidative electron-transfer quenching process. An excited-state reduction potential of -1.74 V versus saturated salt calomel electrode was estimated through oxidative quenching studies with a series of structurally related pyridinium acceptors, indicative of its strong reducing power in the excited state. From the transient absorption difference spectrum of the tetranuclear copper(I) sulfido complex and 4-(methoxycarbonyl)-N-methylpyridinium hexafluorophosphate, in addition to the characteristic absorption of the pyridinyl radical at ca. 395 nm, two absorption bands at ca. 500 and 660 nm were also observed. The former was assigned as an LMCT absorption [S2- → Cu4] and the latter as an intervalence charge-transfer transition, associated with the mixed-valence species CuI/CuI/CuI/CuII.

Stimuli-Induced Reversible Transformation between Decanuclear and Pentanuclear Gold(I) Sulfido Complexes.

Decanuclear and pentanuclear gold(I) sulfido complexes of phenanthrene- and dibenzothiophene-based diphosphine ligands were synthesized and characterized. Unprecedented stimuli-induced reversible transformation between decanuclear and pentanuclear gold(I) sulfido complexes was observed, which could be readily monitored by NMR and UV-vis absorption spectroscopy in solution. Remarkably, the decanuclear gold(I) sulfido complex (Au10-LPh) was found to show a highly reversible transformation process, which is stable for over 10 successive cycles in solution. The stimuli-induced reversible transformation behavior of the gold(I) sulfido complexes was found to depend on the P-P bite distance of the bidentate phosphine ligands.

Carbazolylgold(iii) complexes with thermally activated delayed fluorescence switched on by ligand manipulation as high efficiency organic light-emitting devices with small efficiency roll-offs.

A series of carbazolyl ligands has been designed and synthesized through the integration of various electron-donating and electron-accepting motifs, including electron-donating 4-(diphenylamino)aryl and electron-accepting cyano and diphenylphosphine oxide moieties, for the development of a new class of gold(iii) complexes, where the energies of their triplet intraligand and ligand-to-ligand charge transfer excited states can be manipulated for the activation of thermally activated delayed fluorescence (TADF). Upon excitation, these complexes show high photoluminescence quantum yields of up to 80% in solid-state thin films, with short excited state lifetimes down to 1 µs. Vacuum-deposited and solution-processed organic light-emitting devices based on these complexes demonstrate promising electroluminescence (EL) performance with maximum external quantum efficiencies of 15.0% and 11.7%, respectively, and notably small efficiency roll-off values of less than 1% at the practical luminance brightness level of 1000 cd m-2. These distinct EL performances are believed to be due to the occurrence of multichannel radiative decay pathways via both phosphorescence and TADF that significantly shorten the emission lifetimes and hence reduce the occurrence of the detrimental triplet-triplet annihilation in the gold(iii) complexes.

Molecular Alignment of Alkynylplatinum(II) 2,6-Bis(benzimidazol-2-yl)pyridine Double Complex Salts and the Formation of Well-Ordered Nanostructures Directed by Pt···Pt and Donor-Acceptor Interactions.

A new class of alkynylplatinum(II) bzimpy (bzimpy = bis(benzimidazol-2-yl)pyridine) double complex salts (DCSs) containing dialkoxynaphthalene or pyromellitic diimide moieties on the alkynyl ligand has been reported to display distinct morphological properties compared to their precursor alkynylplatinum(II) complexes, with the capability of being aligned by the directional Pt···Pt and/or π-π stacking interactions. The incorporation of donor and acceptor units on the alkynyl ligands has been found to significantly perturb the alignment of the oppositely charged complex ions in the DCSs to stack in a twisted head-to-head manner, attributed to the additional driving forces of electrostatic and donor-acceptor interactions. The modulation of the Pt···Pt distances and the extent of aggregate formation have been demonstrated by altering the charge matching between the platinum(II) bzimpy moieties and the donor or acceptor moieties on the alkynyl ligand.

Photochromic dithienylethene-containing four-coordinate boron(III) compounds with a spirocyclic scaffold.

A new series of four-coordinate boron compounds bearing a photochromic dithienylethene-containing C^C ligand and an ancillary N^C ligand have been successfully designed and synthesised. These compounds exhibit reversible photochromism upon photoexcitation with percentage conversions of 71-96% and readily tuneable photocycloreversion quantum yields by convenient modification of the ancillary ligand to turn on the thermally activated upconversion from the lower-lying unreactive excited state to the higher-lying photoreactive excited state.

Decomposition of nitrous oxide in hydrated cobalt(I) clusters: a theoretical insight into the mechanistic roles of ligand-binding modes.

Hydrated cobalt(i) cluster ions, [Co(H2O)n]+, can decompose the inert nitrous oxide molecule, N2O. Density functional theory suggests that N2O can anchor to Co+ of [Co(N2O)(H2O)n]+ through either O end-on (η1-OL) or N end-on (η1-NL) coordinate mode. The latter is thermodynamically more favorable resulting from a subtle π backdonation from Co+ to N2O. N2O decomposition involves two major processes: (1) redox reaction and (2) N-O bond dissociation. The initial activation of N2O through an electron transfer from Co+ to N2O yields anionic N2O-, which binds to the metal center of [Co2+(N2O-)(H2O)n] also through either O end-on (η1-O) or N end-on (η1-N) mode and is stabilized by water molecules through hydrogen bonding. From η1-O, subsequent N-O bond dissociation to liberate N2, producing [CoO(H2O)n]+, is straightforward via a mechanism that is commonplace for typical metal-catalyzed N2O decompositions. Unexpectedly, the N-O bond dissociation directly from η1-N is also possible and eliminates both N2 and OH, explaining the formation of [CoOH(H2O)n]+ as observed in a previous experimental study. Interestingly, formation of [CoO(H2O)n]+ is kinetically controlled by the initial redox process between Co+ and the O-bound N2O, the activation barriers of which in large water clusters (n ≥ 14) are higher than that of the unexpected N-O bond dissociation from the N-bound structure forming [CoOH(H2O)n]+. This theoretical discovery implies that in the present of water molecules, the metal-catalyzed N2O decomposition starting from an O-bound metal complex is not mandatory.

Getting Ready for the Hydrogen Evolution Reaction: The Infrared Spectrum of Hydrated Aluminum Hydride-Hydroxide HAlOH+ (H2 O)n-1 , n=9-14.

Hydrated singly charged aluminum ions eliminate molecular hydrogen in a size regime from 11 to 24 water molecules. Here we probe the structure of HAlOH+ (H2 O)n-1 , n=9-14, by infrared multiple photon spectroscopy in the region of 1400-2250 cm-1 . Based on quantum chemical calculations, we assign the features at 1940 cm-1 and 1850 cm-1 to the Al-H stretch in five- and six-coordinate aluminum(III) complexes, respectively. Hydrogen bonding towards the hydride is observed, starting at n=12. The frequency of the Al-H stretch is very sensitive to the structure of the hydrogen bonding network, and the large number of isomers leads to significant broadening and red-shifting of the absorption of the hydrogen-bonded Al-H stretch. The hydride can even act as a double hydrogen bond acceptor, shifting the Al-H stretch to frequencies below those of the water bending mode. The onset of hydrogen bonding and disappearance of the free Al-H stretch coincides with the onset of hydrogen evolution.

Formation of n → π+ interaction facilitating dissociative electron transfer in isolated tyrosine-containing molecular peptide radical cations.

Long-range electron transfer in proteins can be rationalized as a sequential short-distance electron-hopping processes via amino acid residues having low ionization energy as relay stations. Tyrosine residues can serve as such redox-active intermediates through one-electron oxidation to form a π-radical cation at its phenol side chain. An electron transfer from a vicinal functional group to this π-electron hole completes an elementary step of charge migration. However, transient oxidized/reduced intermediates formed at those relay stations during electron transfer processes have not been observed. In this study, formation of analog reactive intermediates via electron donor-acceptor coupling is observed by using IRMPD action spectroscopy. An elementary charge migration at the molecular level in model tyrosine-containing peptide radical cations [M]˙+ in the gas phase is revealed with its unusual Cα-Cß bond cleavage at the side chain of the N-terminal residue. This reaction is induced by the radical character of the N-terminal amino group (-NH2˙+) resulting from an n → π+ interaction between the nonbonding electron pair of NH2 (n) and the π-electron hole at the Tyr side chain (π+). The formation of -NH2˙+ is supported by the IRMPD spectrum showing a characteristic NH2 scissor vibration coupled with Tyr side-chain stretches at 1577 cm-1. This n → π+ interaction facilitates a dissociative electron transfer with NH2 as the relay station. The occurrence of this side-chain cleavage may be an indicator of the formation of reactive conformers featuring the n → π+ interaction.

Evidence for the Prerequisite Formation of Phenoxyl Radicals in Radical-Mediated Peptide Tyrosine Nitration In Vacuo.

The elementary mechanism of radical-mediated peptide tyrosine nitration, which is a hallmark of post-translational modification of proteins under nitrative stress in vivo, has been elucidated in detail by using an integrated approach that combines the gas-phase synthesis of prototypical molecular tyrosine-containing peptide radical cations, ion-molecule reactions, and isotopic labeling experiments with DFT calculations. This reaction first involves the radical recombination of . NO2 towards the prerequisite phenoxyl radical tautomer of a tyrosine residue, followed by proton rearrangements, finally yielding the stable and regioselective 3-nitrotyrosyl residue product. In contrast, nitration with the π-phenolic radical cation tautomer is inefficient. This first direct experimental evidence for the elementary steps of the radical-mediated tyrosine nitration mechanism in the gas phase provides a fundamental insight into the regioselectivity of biological tyrosine ortho-nitration.

Infrared Spectroscopy of Size-Selected Hydrated Carbon Dioxide Radical Anions CO2 .- (H2 O)n (n=2-61) in the C-O Stretch Region.

Understanding the intrinsic properties of the hydrated carbon dioxide radical anions CO2 .- (H2 O)n is relevant for electrochemical carbon dioxide functionalization. CO2 .- (H2 O)n (n=2-61) is investigated by using infrared action spectroscopy in the 1150-2220 cm-1 region in an ICR (ion cyclotron resonance) cell cooled to T=80 K. The spectra show an absorption band around 1280 cm-1 , which is assigned to the symmetric C-O stretching vibration νs . It blueshifts with increasing cluster size, reaching the bulk value, within the experimental linewidth, for n=20. The antisymmetric C-O vibration νas is strongly coupled with the water bending mode ν2 , causing a broad feature at approximately 1650 cm-1 . For larger clusters, an additional broad and weak band appears above 1900 cm-1 similar to bulk water, which is assigned to a combination band of water bending and libration modes. Quantum chemical calculations provide insight into the interaction of CO2 .- with the hydrogen-bonding network.

The experience of mindful yoga for older adults with depression.

WHAT IS KNOWN ON THE SUBJECT?: Mindful yoga combines yoga techniques with the mindfulness-based stress reduction approach. Previous studies on mindful yoga have reported improvements in depression for working-age adults, but no studies have been conducted with older people. WHAT THE PAPER ADDS TO EXISTING KNOWLEDGE?: Mindful yoga may be a safe and acceptable intervention to improve the mental and physical health of older adults with depression. The beneficial therapeutic ingredients of mindful yoga, included calmness, being non-judgmental, letting go and seizing the day. WHAT ARE THE IMPLICATIONS FOR PRACTICE?: Single-sex mindful yoga groups may be more acceptable for some people. Well-conducted feasibility studies comparing mindful yoga with an alternative group-based approach are necessary. Abstract Introduction Mindful yoga combines yoga techniques with the mindfulness-based stress reduction approach. Previous studies on mindful yoga have reported improvements in depression for working-age adults, but no studies have been conducted with older people. Aims To explore the experiences of older adults with depression participating in a mindful yoga group to establish whether the approach has potential as a future intervention for this client group. Method This study adopted a qualitative descriptive method and used inductive content analysis. Eighteen in-depth individual interviews were conducted with nine participants (each participant had one interview following the programme and another four weeks later). Results Six main themes emerged: "improved physical status," "actively involved in the community," "positive psychological effects," "perceived therapeutic ingredients," "facilitators of practising mindful yoga" and "barriers to practising mindful yoga.". Discussion Most participants reported benefitting from the programme. Two male participants expressed that exercises were too challenging and more suited to women, suggesting single-sex groups may be more acceptable. Implications for practice Mindful yoga may be an acceptable/useful intervention for older adults with depression, but future studies are required to establish its feasibility and potential efficacy.

Self-Assembled Binuclear Cu(II)-Histidine Complex for Absolute Configuration and Enantiomeric Excess Determination of Naproxen by Tandem Mass Spectrometry.

Naproxen is one of the most consumed nonsteroidal anti-inflammatory drugs and marketed as S-naproxen since R-naproxen is hepatotoxic. In this study, chiral recognition of naproxen has been investigated by tandem mass spectrometry (MS/MS). Among all diastereomeric complexes formed between naproxen and the examined chiral selectors, including cyclodextrins (α/ß/γ-CD), modified phenylalanines ( N-acetyl-phenylalanine, N-t-butoxycarbonyl-phenylalanine, N-9-fluorenylmethyloxycarbonyl-phenylalanine), amino acids (Trp, Phe, Tyr, His), glucose, tartaric acid, and vancomycin, a novel binuclear metal bound diastereomeric complexes [(M(II))2( S/ R-naproxen)(l-His)2-3H]+ (M = Cu, Ni, or Co with Cu being the best) could allow effective identification of the absolute configuration of naproxen and determination of its enantiomeric excess ( ee) through MS/MS analysis. The key candidate structure of [(Cu(II))2( S/ R-naproxen)(l-His)2-3H]+ has been revealed by means of collision-induced dissociation, ion mobility mass spectrometry and density functional theory calculations, indicating an interesting and unusual self-assembled compact geometry with the two Cu(II) ions bridged closely together (Cu-Cu distance is 3.04 Å) by the carboxylate groups of the two histidines. It was shown that the difference in dissociation efficiency between the two diastereomers was attributed to the interaction between the NH2 bond of the amino group of one histidine and the naphthyl ring of naproxen. The present report is the first to observe and characterize the complex of (Cu(II))2(His)2 with aromatic acid, which could contribute to the chiral recognition of other chiral aromatic acids, design of catalysts based on binuclear copper bound complex, as well as the better understanding of metal ion complexation by His or His-containing ligands.

Kinetics of the reaction of CO3˙-(H2O)n, n = 0, 1, 2, with nitric acid, a key reaction in tropospheric negative ion chemistry.

A significant fraction of nitrate in the troposphere is formed in the reactions of HNO3 with the carbonate radical anion CO3˙- and the mono- and dihydrated species CO3˙-(H2O)1,2. A reaction mechanism was proposed in earlier flow reactor studies, which is investigated here in more detail by quantum chemical calculations and experimental reactivity studies of mass selected ions under ultra-high vacuum conditions. Bare CO3˙- forms NO3-(OH˙) as well as NO3-, with a total rate coefficient of 1.0 × 10-10 cm3 s-1. CO3˙-(H2O) in addition affords stabilization of the NO3-(HCO3˙) collision complex, and thermalized CO3˙-(H2O) reacts with a total rate coefficient of 6.3 × 10-10 cm3 s-1. A second solvent molecule quenches the reaction, and only black-body radiation induced dissociation is observed for CO3˙-(H2O)2, with an upper limit of 6.0 × 10-11 cm3 s-1 for any potential bimolecular reaction channel. The rate coefficients obtained under ultra-high vacuum conditions are smaller than in the earlier flow reactor studies, due to the absence of stabilizing collisions, which also has a strong effect on the product branching ratio. Quantum chemical calculations corroborate the mechanism proposed by Möhler and Arnold. The reaction proceeds through a proton-transferred NO3-(HCO3˙) collision complex, which can rearrange to NO3-(OH˙)(CO2). The weakly bound CO2 easily evaporates, followed by evaporation of the more strongly attached OH˙, if sufficient energy is available.