Reactive scattering of alkali dimers: Product K atoms from K2+Br2, IBr,BrCN, SnCl4

Approximate angular distribution measurements of reactively scattered K atoms from a potassium dimer K₂ beam by cross beam molecules Br₂, IBr, BrCN, SnCl₄ are reported. Forward peaking in the centre of mass differential cross section for K₂+Br₂, IBr, BrCN unambiguously confirms that the reaction path at large impact parameters yields K + KX + Y products. Differential cross sections at wide angles for K compared with KX products, suggest that the reaction path yielding KX + KY products becomes important at small impact parameters. Comparison of the reactive K atom scattering with the KX scattering lends further support to a schematic mechanism of the reaction dynamics suggested previously. The K₂ + SnCl₄ reaction does not yield reactively scattered K atoms.     

Reactive scattering of oxygen atoms: O+I2, ICl,Br2

Angular and velocity distribution measurements of IO reactive scattering from crossed beams of O atoms and halogen molecules I₂, ICl are reported. Angular distribution measurements are reported for BrO from O + Br₂. The O atom beam was generated at ～350 K from a microwave discharge source and the halogen molecule beam from a supersonic nozzle source at ～380 K. The product time-of-flight distribution was recorded at each laboratory scattering angle by a mini-computer. The scattering data are found to be in excellent agreement with the RRKM-AM model of reactive scattering via a long-lived collision complex. The observation of IO product from O + ICl identifies the complex with a bound O-I-Cl triplet state, previously observed for O-Cl-Cl in matrix isolation studies, as proposed by Herschbach. The maximum centrifugal barrier B _m′ for dissociation of the long-lived complex can be accurately determined, particularly for O + I₂. The B _m′ values indicate that both the entrance and exit valleys of the potential energy surface are governed by centrifugal barriers in the region of long-range van der Waals potentials. The comparatively small reaction cross section (e.g. Q ～ 2 Ų for O + Br₂ from discharge flow measurements) is attributed primarily to an orientation requirement for reaction. The RRKM-AM model indicates a ‘tight linear’ transition state for dissociation of the O-I-I complex, corresponding to significant long-range IO orienting forces in the exit valley of the potential energy surface.     

Reactive scattering of alkali dimers K2 + I2, CH2I2, CHI3, CBr4

Angular distribution measurements of KX reactive scattering of a potassium dimer K₂ beam by I₂ and by a series of halomethane molecules are reported. The K₂ + I₂ reactive scattering is similar to that previously observed for K₂ + Br₂. The predominant reaction path yields K + KI + I with the K and KI product recoiling in the forward direction. However, the forward peak of the KI differential cross section is lower than that for K from K₂ + I₂ and is broader than that observed for KBr from K₂ + Br₂. This is attributed to slow dissociation of the I ₂ ^- ion formed in the electron jump mechanism previously proposed for K₂ + Br₂. In the halomethane reactions, both alkali atoms of the K₂ dimer become bound alkali halide molecules in all reactive collisions, despite the direct dynamics of the corresponding supersonic K atom reactions. Thus, these reactions provide compelling evidence for a second electron jump mechanism, previously proposed for the reactions of K₂ dimers with polyhalide molecules. The differential cross sections for the K₂ dimer plus halomethane reactions indicate an osculating collision complex with a lifetime at least comparable to its rotational period, perhaps much longer. This reaction complex is identified with the doubly ionic state formed by the second electron jump transition.     

A new cytotoxic diterpenoid glycoside from the leaves of Blumea lacera and its effects on apoptosis and cell cycle

A new diterpenoid glycoside, 6E,10E,14Z-(3S)-17-hydroxygeranyllinalool-17-O-β-d-glucopyranosyl-(1?→?2)-[α-l-rhamnopyranosyl-(1?→?6)]-β-d-glucopyranoside (1) together with the known diterpenoid glycoside (2) and two known flavonoid glycosides (3, 4) were isolated from the methanol extract of Blumea lacera leaves. The structures were determined by the interpretation of their spectroscopic data and comparison with the literature. All compounds were isolated for the first time from B. lacera and evaluated for their cytotoxic activity. Only the new compound (1) showed strong cytotoxic activity with the lowest IC₅₀ value (8.3 μM) being displayed against MCF-7 breast cancer cells. In apoptosis and cell cycle analysis, 1 revealed strong apoptotic activity against MCF-7 cells (45.5% AV⁺/PI^?) after 24 h, but showed no arresting of any of the cell cycle phases in MCF-7.     

The chemistry of thujone. VIII. Thujone as a chiral synthon for the synthesis of optically active steroid analogues. The enol lactone route

The thujone-derived enone 1 is converted via enol lactone intermediates 4 and 5 to the optically active steroidal analogue 13 and the corresponding 19-norsteroid analogue 14 . The structure of 13 was determined by X-ray diffraction analysis. The acid-catalyzed cyclopropane-ring opening of 13 and ozonolysis of the resulting olefin provided the 16-keto-steroid analogue 18 .     

Nonlocal density functional calculation of gas phase heats of formation

A general procedure is presented for computing the gas phase heats of formation of a wide variety of organic compounds. ΔE for the formation of the molecule from its elements at 0 K is obtained from density functional calculations (Gaussian 92/DFT) for optimized geometries. This result is converted to ΔH at 298 K by assuming ideal behavior and adding the translational, rotational, and vibrational energies. Additive correction terms corresponding to the various coordination states of the carbons, nitrogens, and oxygens were developed using a database of 54 compounds. The experimental ΔH values of these compounds are then reproduced with an average absolute error of 3 kcal/mol and a standard deviation of 4 kcal/mol. For a group of 10 test cases that were not part of the database, the average absolute error is 3.5 kcal/mol and the standard deviation is 4.1 kcal/mol. © 1995 by John Wiley & Sons, Inc.     

Neither in vivo MRI nor behavioural assessment indicate therapeutic efficacy for a novel 5HT1A agonist in rat models of ischaemic stroke

Background  

5HT_1A agonists have previously been shown to promote recovery in animal models of stroke using ex vivo outcome measures which have raised the hopes for a potential clinical implementation. The purpose of this study was to evaluate the potential neuroprotective properties of a novel 5HT_1A agonist DU123015 in 2 different models of transient focal ischaemic stroke of varying severities using both in vivo neuroimaging and behavioural techniques as primary outcome measures. For these studies, the NMDA receptor antagonist MK-801 was also utilized as a positive control to further assess the effectiveness of the stroke models and techniques used.     

Translational energy threshold functions for oxygen atom reactions

The similarities between core and valence Rydberg series observed in inert-gas atoms are explained by the electron density relaxation which extends up to the outer atomic shell, regardless of the localization of the hole.     

δD and δ13C analyses of atmospheric volatile organic compounds by thermal desorption gas chromatography isotope ratio mass spectrometry

This paper describes the establishment of a robust method to determine compound specific δD and δ(13)C values of volatile organic compounds (VOCs) in a standard mixture ranging between C(6) and C(10) and was applied to various complex emission samples, e.g. from biomass combustion and car exhaust. A thermal desorption (TD) unit was linked to a gas chromatography isotope ratio mass spectrometer (GC-irMS) to enable compound specific isotope analysis (CSIA) of gaseous samples. TenaxTA was used as an adsorbent material in stainless steel TD tubes. We determined instrument settings to achieve a minimal water background level for reliable δD analysis and investigated the impact of storage time on δD and δ(13)C values of collected VOCs (176 days and 40 days of storage, respectively). Most of the standard compounds investigated showed standard deviations (SD)<6‰ (δD) when stored for 148 days at 4 °C. However, benzene revealed occasionally D depleted values (21‰ SD) for unknown reasons. δ(13)C analysis demonstrated that storage of 40 days had no effect on VOCs investigated. We also showed that breakthrough (benzene and toluene, 37% and 7%, respectively) had only a negligible effect (0.7‰ and 0.4‰, respectively) on δ(13)C values of VOCs on the sample tube. We established that the sample portion collected at the split flow effluent of the TD unit can be used as a replicate sample for isotope analysis saving valuable sampling time and resources. We also applied TD-GC-irMS to different emission samples (biomass combustion, petrol and diesel car engines exhaust) and for the first time δD values of atmospheric VOCs in the above range are reported. Significant differences in δD of up to 130‰ were observed between VOCs in emissions from petrol car engine exhaust and biomass combustion (Karri tree). However, diesel car emissions showed a high content of highly complex unresolved mixtures thus a baseline separation of VOCs was not achieved for stable hydrogen isotope analysis. The ability to analyse δD by TD-GC-irMS complements the characterisation of atmospheric VOCs and is maybe used for establishing further source(s).