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Vapor pressure ( p sat ) data are needed to assess the potential use of terpenes as breath markers of recent cannabis use. Herein, a recently introduced gas-saturation method for p sat measurements, known as dynamic vapor microextraction (DVME), was used to measure p sat for the terpene (±)-3,7-dimethylocta-1,6-dien-3-ol, commonly known as linalool. The DVME apparatus utilizes inexpensive and commercially available components, a low internal volume, and helium carrier gas to minimize nonideal mixture behavior. In the temperature range from 314 K to 354 K, DVME-based measurements of the p sat of linalool ranged from 81 Pa to 1250 Pa. With a measurement period of 30 min, the combined standard uncertainty of these measurements ranged from 0.0358· p sat to 0.0584· p sat , depending on temperature. The DVME-based measurements agree with a Wagner correlation of available literature data. We demonstrate that DVME produces accurate results for values of p sat that are 200 times higher than in the DVME validation study with n-eicosane (C 20 H 42 ). The oxidative stability of linalool was improved by the addition of 0.2 mass % of the antioxidant tert -butylhydroquinone., Competing Interests: The authors declare no competing financial interest.

A hydrophobic Schiff base catecholate vanadium complex was recently discovered to have anticancer properties superior to cisplatin and suited for intratumoral administration. This [VO(HSHED)(DTB)] complex, where HSHED is N -(salicylideneaminato)- N '-(2-hydroxyethyl)-1,2-ethanediamine and the non-innocent catecholato ligand is di- t -butylcatecholato (DTB), has higher stability compared to simpler catecholato complexes. Three new chloro-substituted Schiff base complexes of vanadium(V) with substituted catecholates as co-ligands were synthesized for comparison with their non-chlorinated Schiff base vanadium complexes, and their properties were characterized. Up to four geometric isomers for each complex were identified in organic solvents using 51 V and 1 H NMR spectroscopies. Spectroscopy was used to characterize the structure of the major isomer in solution and to demonstrate that the observed isomers are exchanged in solution. All three chloro-substituted Schiff base vanadium(V) complexes with substituted catecholates were also characterized by UV-vis spectroscopy, mass spectrometry, and electrochemistry. Upon testing in human glioblastoma multiforme (T98g) cells as an in vitro model of brain gliomas, the most sterically hindered, hydrophobic, and stable compound [ t 1/2 (298 K) = 15 min in cell medium] was better than the two other complexes (IC 50 = 4.1 ± 0.5 μM DTB, 34 ± 7 μM 3-MeCat, and 19 ± 2 μM Cat). Furthermore, upon aging, the complexes formed less toxic decomposition products (IC 50 = 9 ± 1 μM DTB, 18 ± 3 μM 3-MeCat, and 8.1 ± 0.6 μM Cat). The vanadium complexes with the chloro-substituted Schiff base were more hydrophobic, more hydrolytically stable, more easily reduced compared to their corresponding parent counterparts, and the most sterically hindered complex of this series is only the second non-innocent vanadium Schiff base complex with a potent in vitro anticancer activity that is an order of magnitude more potent than cisplatin under the same conditions.

The interpeptidic Cu II exchange rate constants were measured for two Cu amyloid-β complexes, Cu(Aβ 1-16 ) and Cu(Aβ 1-28 ), to fluorescent peptides GHW and DAHW using a quantitative tryptophan fluorescence quenching methodology. The second-order rate constants were determined at three pH values (6.8, 7.4, and 8.7) important to the two Cu(Aβ) coordination complexes, components Cu(Aβ) I and Cu(Aβ) II . The interpeptidic Cu II exchange rate constant is approximately 10 4 M -1 s -1 but varies in magnitude depending on many variables. These include pH, length of the Aβ peptide, location of the anchoring histidine ligand in the fluorescent peptide, number of amide deprotonations required in the tryptophan peptide to coordinate Cu II , and interconversion between Cu(Aβ) I and Cu(Aβ) II . We also present EPR data probing the Cu II exchange between peptides and the formation of ternary species between Cu(Aβ) and GHW. As the nonfluorescent GHK and DAHK peptides are important motifs found in the blood and serum, their ability to sequester Cu II ions from Cu(Aβ) complexes may be relevant for the metal homeostasis and its implication in Alzheimer's disease. Thus, their kinetic Cu II interpeptidic exchange rate constants are important chemical rate constants that can help elucidate the complex Cu II trafficking puzzle in the synaptic cleft.

Dynamic vapor microextraction (DVME) is a new method that enables rapid vapor pressure measurements on large molecules with state-of-the-art measurement uncertainty for vapor pressures near 1 Pa. Four key features of DVME that allow for the rapid collection of vapor samples under thermodynamic conditions are (1) the use of a miniature vapor-equilibration vessel (the "saturator") to minimize the temperature gradients and internal volume, (2) the use of a capillary vapor trap to minimize the internal volume, (3) the use of helium carrier gas to minimize nonideal mixture behavior, and (4) the direct measurement of pressure inside the saturator to accurately account for overpressure caused by viscous flow. The performance of DVME was validated with vapor pressure measurements of n -eicosane (C 20 H 42 ) at temperatures from 344 to 374 K. A thorough uncertainty analysis indicated a relative standard uncertainty of 2.03-2.82% for measurements in this temperature range. The measurements were compared to a reference correlation for the vapor pressures of n -alkanes; the deviation of the measurements from the correlation was ≤2.85%. The enthalpy of vaporization of n -eicosane at 359.0 K was calculated to be Δ vap H = 91.27 ± 0.28 kJ/mol compared to Δ vap H (corr) = 91.44 kJ/mol for the reference correlation. Total measurement periods as short as 15 min (3 min of thermal equilibration plus 12 min of carrier gas flow) were shown to be sufficient for high-quality vapor pressure measurements at 364 K.

The light-induced photolysis of [Zn(NTAdeCage)] - generates a temporally controlled burst of Zn 2+ , which is rapidly chelated in situ by the free ligand Zincon 2- . The [Zn(Zincon)] 2- coordination progress is monitored using absorption spectroscopy in bulk aqueous buffer and reverse micelle environments. The [Zn(NTAdeCage)] - photocage and free ligand Zincon 2- have different reverse micelle locations that affect the [Zn(Zincon)] 2- formation at the nanoscale compared to the bulk aqueous buffer. The formation of [Zn(Zincon)] 2- in a bulk aqueous buffer is more efficient despite the released Zn 2+ and Zincon 2- being physically closer within reverse micelles. The observed reduction of complex formation is attributed to the interfacial partitioning of Zincon 2- , distinct from the Zn 2+ photocage in the water pool, requiring diffusion for the species to meet to form [Zn(Zincon)] 2- . This work introduces a proof-of-concept methodology to experimentally measure fast chelation reactions in confined spaces and thus provides an approach to exploring cellular responses.

Menaquinones (MKs) are essential for electron transport in prokaryotes, and importantly, partially saturated MKs represent a novel virulence factor. However, little is known regarding how the degree of saturation in the isoprenyl side chain influences conformation or quinone redox potential. MenJ is an enzyme that selectively reduces the second isoprene unit on MK-9 and is contextually essential for the survival of Mycobacterium tuberculosis in J774A.1 macrophage-like cells, suggesting that MenJ may be a conditional drug target for pathogenic mycobacteria. Therefore, fundamental information about the properties of this system is important, and we synthesized the simplest MKs, unsaturated MK-1 and the saturated analogue, MK-1(H 2 ). Using two-dimensional nuclear magnetic resonance spectroscopy, we established that MK-1 and MK-1(H 2 ) adopted similar folded-extended conformations (i.e., the isoprenyl side chain folds upward) in each solvent examined but the folded-extended conformations differed slightly between organic solvents. Saturation of the isoprenyl side chain slightly altered the MK-1 analogue conformation in each solvent. We used molecular mechanics to illustrate the MK-1 analogue conformations. The measured quinone redox potentials of MK-1 and MK-1(H 2 ) differed between organic solvents (presumably due to differences in dielectric constants), and remarkably, an ∼20 mV semiquinone redox potential difference was observed between MK-1 and MK-1(H 2 ) in pyridine, acetonitrile, and dimethyl sulfoxide, demonstrating that the degree of saturation in the isoprenyl side chain of MK-1 influences the quinone redox potential. Finally, MK-1 and MK-1(H 2 ) interacted with Langmuir phospholipid monolayers and Aerosol-OT reverse micelle (RM) model membrane interfaces, where MK-1 adopted a slightly different folded conformation within the RM model membrane interface.

The interpeptidic exchange of Cu(II) between biologically relevant peptides like Gly-His-Lys (GHK) was measured through proximity static fluorescence quenching of a noncoordinating tryptophan residue by Cu(II). The inability to spectrally distinguish between starting and final Cu(H -1 GHK) + complexes by the current methods was solved by the replacement of noncoordinating lysine for tryptophan in the starting complex, Cu(H -1 GHW). Because the apoGHW is the only fluorescent species, the recovered fluorescence is directly proportional to the [Cu(II)] exchanged between GHW and GHK. The apparent second-order rate constants of the exchanges from Cu(H -1 GHW) to GHK and DAHK are 1.6 (±0.2) × 10 2 and 5.0 (±0.7) × 10 1 M -1 s -1 , respectively. The easy-to-implement kinetic fluorescent method described here for Cu(II) interpeptidic exchange can be expanded to other biological systems.

Menaquinones (naphthoquinones, MK) are isoprenoids that play key roles in the respiratory electron transport system of some prokaryotes by shuttling electrons between membrane-bound protein complexes acting as electron acceptors and donors. Menaquinone-2 (MK-2), a truncated MK, was synthesized, and the studies presented herein characterize the conformational and chemical properties of the hydrophobic MK-2 molecule. Using 2D NMR spectroscopy, we established for the first time that MK-2 has a folded conformation defined by the isoprenyl side-chain folding back over the napthoquinone in a U-shape, which depends on the specific environmental conditions found in different solvents. We used molecular mechanics to illustrate conformations found by the NMR experiments. The measured redox potentials of MK-2 differed in three organic solvents, where MK-2 was most easily reduced in DMSO, which may suggest a combination of solvent effect (presumably in part because of differences in dielectric constants) and/or conformational differences of MK-2 in different organic solvents. Furthermore, MK-2 was found to associate with the interface of model membranes represented by Langmuir phospholipid monolayers and Aerosol-OT (AOT) reverse micelles. MK-2 adopts a slightly different U-shaped conformation within reverse micelles compared to within solution, which is in sharp contrast to the extended conformations illustrated in literature for MKs.

Since membrane penetration is important for drug efficacy, how antimalarial precursor material 1-phenylbiguanide (PBG) interacts with an interface was characterized using a reverse micelle (RM) model system. (1)H NMR studies show that PBG partitions across the membrane interface. Specifically, the (1)H NMR studies showed that the 1-phenylbiguanide compound in an aqueous environment changed when placed near an interface. PBG is known to affect hydrogen bonding in water, and as the size of the RMs changes, the water organization in the water pool is changed. The NOESY spectrum of PBG in AOT RM contains cross-peak signals between the PBG protons and AOT protons, which is consistent with the penetration of the PBG into the interface. At the same time, there is a cross peak between the biguanide moiety and the HOD signal. This shows that these NH protons are near the HOD protons, placing the biguanide functional group in the water pool. Preliminary differential FTIR spectroscopic studies confirmed this location. In summary, we found that PBG interacts with different regions of the interface, with the phenyl group penetrating the hydrophobic interface while the biguanide remains in the water pool.