Johnslester3474

We characterize the Walden-inversion, front-side attack, and double-inversion SN2 pathways leading to Y- + CH3CN/CH3NC and the product channels of proton abstraction (HCN/HNC + CH2Y-), hydride-ion substitution (H- + YH2CCN/YH2CNC), halogen abstraction (YCN-/YNC- + CH3 and YCN/YNC + CH3-), and YHCN-/YHNC- complex formation (YHCN-/YHNC- + 1CH2) of the CN- + CH3Y [Y = F, Cl, Br, and I] reactions. Benchmark structures and frequencies are computed at the CCSD(T)-F12b/aug-cc-pVTZ level of theory, and a composite approach is employed to obtain relative energies with sub-chemical accuracy considering (a) basis-set effects up to aug-cc-pVQZ, (b) post-CCSD(T) correlation up to CCSDT(Q), (c) core correlation, (d) relativistic effects, and (e) zero-point energy corrections. C-C bond formation is both thermodynamically and kinetically more preferred than N-C bond formation, though the kinetic preference is less significant. Walden inversion proceeds via low or submerged barriers (12.1/17.9(F), 0.0/4.3(Cl), -3.9/0.1(Br), and -5.8/-1.8(I) kcal/mol for C-C/N-C bond formation), front-side attack and double inversion have high barriers (30-64 kcal/mol), the latter is the lower-energy retention pathway, and the non-SN2 electronic ground-state product channels are endothermic (ΔH0 = 31-92 kcal/mol).The role of excimer formation in inhibiting or enhancing the efficiency of the intramolecular singlet fission (iSF) process has been a subject of recent debate. Here, we investigated the effect of excimer formation on iSF dynamics by modifying its configuration by connecting pentacenes at various positions. Hence, pentacene dimers having slip-stacked (2,2' BP, J-type), oblique (2,6' BP), and facial (6,6' BP, H-type) configurations were synthesized by covalently linking pentacenes at positions 2,2', 2,6', and 6,6', respectively, with an ethynyl bridge, and their ultrafast excited-state relaxation dynamics were characterized. Femtosecond time-resolved transient absorption spectra revealed that the efficiency of iSF dynamics decreased from slip-stacked (182%) to oblique configuration (97%),whereas in the 6,6' BP with facial configuration, strong electronic coupling led to the formation of excimers that decayed nonradiatively without formation of correlated triplet pairs. These studies reveal the formation of excimers by strong intrapentacene electronic coupling upon ultrafast excitation, preventing the efficient iSF process.Dinaphthoporphycene (DNP) has emerged as a versatile ligand undergoing large out-of-plane distortion to form a cis-bimetallic complex with Pd(II) using Pd(OAc)2 and out-of-plane monometallic complexes with Pd(acac)2 and PtCl2(PhCN)2. Herein, we are finally able to synthesize the in-core complex with Pd(II) using PdCl2(PhCN)2 or PdCl2. The crystal structure shows the palladium ion resides slightly above the N4-core, with the Pd(II) dimensionally dissenting with the typical square planarity displayed by the reported in-core DNP complexes with Ni(II) and Cu(II) ions. The deformed complex displays a blue shift in the absorption spectra compared to DNP and its metallo-derivatives. PdDNP exhibits a moderate singlet oxygen generation ability (18%).A novel heptapeptide QEELISK derived from Antarctic krill was used to assemble a calcium delivery system, of which the calcium binding mechanism of QEELISK, in vitro digestion kinetics, and calcium absorption behaviors were explored. QEELISK with continuous Glu possessed higher calcium binding capacity than that of QELEISK and QAALISK. Ca2+ bound to the carboxyl oxygen of Glu at position 3 of the QEELISK peptide at a stoichiometric ratio of 11 through charge-charge interaction; the formed QEELISK-Ca showed superior stability. Moreover, QEELISK-Ca underwent disaggregation and self-assembly during in vitro digestion reflected by visualization of calcium ions and circular dichroism spectra. QELEISK was partially stable during gastrointestinal digestion, and calcium chelation improved the digestive stability of QELEISK. In addition, a significant enhancement of calcium absorption with QELEISK-Ca occurred in the duodenum and ileum when compared to CaCl2 absorption, which indicated that QEELISK might carry calcium ions through the gastrointestinal tract.Chaperonins are nanomachines that harness ATP hydrolysis to power and catalyze protein folding, a chemical action that is directly linked to the maintenance of cell function through protein folding/refolding and assembly. GroEL and the GroEL-GroES complex are archetypal examples of such protein folding machines. Here, variable-temperature electrospray ionization (vT-ESI) native mass spectrometry is used to delineate the effects of solution temperature and ATP concentrations on the stabilities of GroEL and GroEL-GroES complexes. The results show clear evidence for destabilization of both GroEL14 and GroES7 at temperatures of 50 and 45 °C, respectively, substantially below the previously reported melting temperature (Tm ∼ 70 °C). This destabilization is accompanied by temperature-dependent reaction products that have previously unreported stoichiometries, viz. GroEL14-GroESy-ATPn, where y = 1, 2, 8 and n = 0, 1, 2, 8, that are also dependent on Mg2+ and ATP concentrations. Variable-temperature native mass spectrometry reveals new insights about the stability of GroEL in response to temperature effects (i) temperature-dependent ATP binding to GroEL; (ii) effects of temperature as well as Mg2+ and ATP concentrations on the stoichiometry of the GroEL-GroES complex, with Mg2+ showing greater effects compared to ATP; and (iii) a change in the temperature-dependent stoichiometries of the GroEL-GroES complex (GroEL14-GroES7 vs GroEL14-GroES8) between 24 and 40 °C. The similarities between results obtained by using native MS and cryo-EM [Clare et al. An expanded protein folding cage in the GroEL-gp31 complex. J. Mol. Biol. 2006, 358, 905-911; Ranson et al. Allosteric signaling of ATP hydrolysis in GroEL-GroES complexes.Nat. Struct. Mol. Biol. 2006, 13, 147-152] underscore the utility of native MS for investigations of molecular machines as well as identification of key intermediates involved in the chaperonin-assisted protein folding cycle.To enable the further exploration of structure-activity relationships (SARs) of proanthocyanidins (PACs) with dentin biomodification abilities, Cinnamomum verum was selected for scaled-up purification of mixed A-/B-type, medium-size PAC oligomers. Sequential purification by centrifugal partition chromatography (CPC), Sephadex LH-20, and semiprep HPLC chromatography yielded four underivatized tetrameric (5-8) and two pentameric (9-10) PACs. Their unambiguous structural characterization involved extensive spectral and chemical degradation approaches to show that epicatechin units are connected by plant-specific combinations of doubly linked A- and singly linked B-type interflavanyl bonds. The biomechanical properties (via dynamic mechanical analysis) and physicochemical structure (via infrared spectroscopy) were assessed to evaluate the biomodification potency of PAC-treated collagen in a preclinical dentin model. This study revealed that (4→8) versus (4→6) bonds in PAC interflavan linkages have limited influence on biomechanical outcomes of dentin. By exhibiting a 25-fold increase in the complex modulus of treated dentin compared to control, aesculitannin E (5) was found to be the most potent PAC known to date for enhancing the mechanical properties of dentin in this preclinical model.The selective recognition of caffeine in water among structurally related xanthines and purine or pyrimidine bases was achieved by a simple tweezer-shaped receptor featuring sulfonate hydrosolubilizing groups. The remarkable affinity for caffeine, among the highest reported thus far in the literature and larger than that shown by adenosine receptors of all subtypes, stems from a synergistic combination of hydrogen bonding, CH-π, and π-stacking interactions.Phosphatidylserine (PS) improves learning and memory capacity. OG-L002 supplier In this study, PS formulation was optimized by a response surface methodology. Moreover, we found that PS not only functions as a biologically active component in food preparations but also improves the emulsion's physical stability. Our results showed that the PS emulsions are characterized by a smaller particle size, higher ζ-potential (negative), higher viscosity, and lower surface tension and centrifugal stability constants than the emulsion without PS. Furthermore, we explored the neuroprotective effects of PS emulsion and its underlying mechanisms. Treatment with 2% (w/w) PS emulsion for three months enhanced spatial learning and memory in 5- and 12-week old mice in the Morris water maze test. Western-blotting analysis displayed that the 2% (w/w) PS emulsion treated group upregulated BDNF, TrkB, PSD95, mTOR, MBP, and ErbB4 expression in the hippocampus of 5- and 12-week old mice. Reverse transcription polymerase chain reaction (RT-PCR) analysis revealed elevated Nrg-1 and ErbB4 mRNA expression in the 2% (w/w) PS emulsion treated groups, and high Nrg-1 and ErbB4 expression levels were associated with better myelination. In conclusion, we reported PS emulsions with high stability and high bioavailability. Meanwhile, 2% (w/w) PS emulsion enhances learning, memory, and myelination in mice by activating the BDNF/TrkB and Nrg-1/ErbB4 signaling.Ammonia (NH3) is an important precursor of secondary inorganic aerosols and greatly impacts nitrogen deposition and acid rain. Previous studies have mainly focused on the agricultural NH3 emissions, while recent research has noted that industrial sources could be significant in China. However, detailed estimates of NH3 emitted from industrial sectors in China are lacking. Here, we established an unprecedented high-spatial-resolution data set of China's industrial NH3 emissions using up-to-date measurements of NH3 and point source-level information covering eight major industries and 27 subdivided process categories. We found that China emitted 798 (90% confidence interval 668-933) gigagrams of industrial NH3 into the atmosphere in 2019, equivalent to 44 ± 20% of the industrial emissions worldwide; this flux is 3-fold larger than that in 1998 and has fluctuated since 2014. Furthermore, although fertilizer production is responsible for approximately half of the emissions in China, the emissions from cement production and coal-fired power plants increased dramatically from near zero to 164 and 41 gigagrams, respectively, in the past two decades, primarily due to the NH3 escape caused by the large-scale application of the denitration process. Our results reveal that, unlike other major air pollutants, China's industrial NH3 emission control is still in a critical period, and stricter NH3 emission standards and innovation in pollution control technologies are highly desirable.Liquid crystal monomers (LCMs) in liquid crystal displays (LCDs) may be released into the environment, especially in electronic waste (e-waste) recycling industrial parks with a high pollution risk. However, little has been known about the environmental release and human exposure to LCMs until now. Herein, a total of 45 LCMs were detected in LCDs of commonly used smartphones and computers by high-resolution mass spectrometry with suspect screening analysis. Fluorinated biphenyls and their analogs were the dominant LCMs. Based on available standards of the screening results and previous studies, 55 LCMs were quantified in samples from an e-waste recycling industrial park in Central China. The LCMs were frequently detected in outdoor dust (n = 43), workshop #1 indoor dust (n = 53), and hand (n = 43) and forehead wipes (n = 43), with median concentrations of 6950 ng/g, 67,400 ng/g, 46,100 ng/m2, and 62,100 ng/m2, respectively. The median estimated daily intake values of the LCMs via dust ingestion and dermal absorption were 48.