Molekülstrukturen von Phosphorverbindungen, IV / Molecular Structures of Phosphorus Compounds, IV

The molecular structures of the two trifluoromethyl phosphoranes (CF3)2PCl3 and (CF3)3PCl2 have been determined by electron diffraction of gases. The structure of (CF3)2PCl3 was found to be a regular trigonal bipyramid with both CF3 groups in axial positions (D3h symmetry) and the fluorine atoms staggered to the equatorial chlorine atoms. The following geometric parameters (ra-values) were obtained: r(C-F) = 1.331(2) Å, r(P-C) = 1.950(II) Å, r(P-Cl) = 2.036(2) Å and ⦓ FCF = 108.3°(0.4). (CF3)3PCl2 possesses the structure of a distorted trigonal bipyramid with two CF3 groups in axial and one in equatorial position. Again the fluorine atoms of the axial CF3 groups are staggered to the equatorial atoms. The ra-values for the geometric parameters are: r(C-F)= 1.329(2) Å, r(P-C)eq= 1.938(31) Å, r(P-C)ax = 1.946(14) Å, r(P-Cl) = 2.053(6) Å, ⦓ FCF = 108.5°(0.3), ⦓ ClPCl = 133.0°(1.7) and ⦓ CaxPCeq = 95.5°(1.9). The average P-C bond length was found to be r(P-C)av = 1.943(5) A. The results for the mean square amplitudes are given in the article. It was shown that in both molecules the torsional amplitudes of the CF3 groups around the P-C bond directions are small, indicating high potential barriers to internal rotation.

Kernresonanz-Untersuchung am System (CH3)3P/BF3 / N.M.R. Study of the System (CH3)3P/BF3

The 2J (PH) coupling constant of mixtures of (CH3)3SiCH2CH2P(CH3)2 and BF3 depends on the ratio of the two components. During the investigation of the simpler system (CH3)3P/BF3the following results were obtained: 1. τH[P(CH3)3] and 2J(PH) vary steadily with the ratio (CH3)3P/BF3, 2. Only one doublet is observed even for mixtures with excess P(CH3)3, 3. 2J (PH) becomes zero for the given ratio BF3: P(CH3)3 = 0.4. The results can be explained by assuming a fast exchange according to equation (2) and opposite signs for the coupling constants of P(CH3)3 [2J (PH) = +2.5 Hz] and the adduct (CH3)3P →BF3[2J(PH) = -11.3 Hz].

Infrarot-Spektren und Struktur einiger Trifluormethyl-Element-Derivate des Mangancarbonyls

Infra-red data in the CO stretching region are recorded for a series of complexes having the formulae Mn2(CO)8E(CF3)2X [E = P, X = Cl, Br, I, SCF3, SeCF3, P(CF3)2, SCH3, P(CH3)2; E = As, X = I, SCF3, SeCF3] and Mn2(CO)8(ECF3)2 (E = S, Se). The spectra support the structural formula deduced from chemical and n.m.r. investigations. Considerations of frequency changes and intensities of the bands enable the four series observed to be assigned in pairs to the vibrations of CO groups that are coplanar with the bridge bonds, and those which are oriented perpendicular to this plane. Informations about the ligand properties of the bridging groups are obtained from the spectra.

Expression of VACM-1 protein in cultured rat adrenal endothelial cells is linked to the cell cycle

The vasopressin-activated calcium-mobilizing (VACM-1) protein is a unique arginine vasopressin (AVP) receptor which shares sequence homology with the cullins, genes involved in the regulation of cell cycle transitions. Unlike either cullins or AVP receptors, however, VACM-1 is expressed exclusively in the vascular endothelial cells and in the renal collecting tubule cells. In order to test the hypothesis that the expression of VACM-1 might be correlated with the cell cycle, and to establish an endothelial cell model for the VACM-1 receptor, we examined VACM-1 expression in rat adrenal medulla endothelial cells (RAMEC). Northern and Western blot analyses of mRNA and protein from RAMEC identified presence of 6.4 kb mRNA and a Mr 81 kDa protein, respectively. Immunostaining of RAMEC with anti-VACM-1 antibodies and Western blot analyses indicated that in RAMEC, VACM-1 protein expression is dependent on the cell cycle. VACM-1 protein virtually disappears during the S phase and localizes to the cytosol during cell division and to the cell membrane at the completion of cytokinesis. Furthermore, pretreatment of RAMEC with anti-VACM-1 specific antibodies increased basal levels of Ca2+and attenuated the AVP-dependent increase in cytosolic Ca2+. In summary, these results indicate that VACM-1 protein expression in RAMEC membrane is linked to the cell cycle, and consequently, VACM-1 may be involved in the regulation of cell division.

Quitting cigarette smoking produces minimal loss of chronic tolerance to nicotine

RATIONALE

Long-term exposure to nicotine is associated with chronic tolerance to its acute effects, adaptation that may lead to tobacco dependence. The time course for loss of this tolerance after cessation of exposure is not known in humans but could relate to risk of smoking relapse.

OBJECTIVES

We examined changes in responses to nicotine as a function of days, weeks, or years of smoking cessation in formerly dependent smokers to determine at what point sensitivity to nicotine is reinstated (i.e., loss of tolerance).

METHODS

Acute subjective, cardiovascular, performance, and reinforcing (self-administration) effects of nicotine nasal spray (0-20 microg/kg) were assessed prospectively in men and women smokers before and then day-by-day (study 1) or 3 weeks (study 2) after stopping smoking. A smoking resumption period (study 1) and a group of non-quitting smokers (study 2) were included to control for the passage of time. These effects were also compared cross-sectionally between those who had quit for 1-4 years and those who had for 6-19 years in a separate sample of long-time ex-smokers to determine whether lengthier abstinence causes greater loss of tolerance (study 3).

RESULTS

No clear loss of tolerance was observed on any measure in studies 1 or 2, suggesting that chronic tolerance is fully maintained for at least weeks after quitting smoking. Sensitivity to nicotine's effects was also not different as a function of years quit in study 3.

CONCLUSIONS

Chronic tolerance to nicotine is not lost within several weeks of quitting smoking and may not change even after years of abstinence from tobacco use.

Sex differences in the subjective and reinforcing effects of visual and olfactory cigarette smoke stimuli

Although nicotine intake clearly reinforces cigarette smoking behavior, non-nicotine smoke stimuli may become conditioned reinforcers of smoking. In Study 1, we compared the acute subjective and reinforcing effects of cigarette smoking in men and women under two conditions: blockade of visual and olfactory/taste smoke stimuli vs. no blockade. Subjective hedonic ratings of 'like puffs' and 'satisfying', but not 'strength', 'high in nicotine', or CO boost, were significantly reduced under the blockade vs. no blockade conditions. During subsequent ad lib puffing, significantly fewer puffs were self-administered under the blockade condition, particularly among women. In Study 2, we examined the influences of these stimuli separately and found that olfactory/taste stimuli, but not visual stimuli, reduced hedonic ratings and puff self-administration in women but not in men. In Study 3, procedures similar to those in Study 1 were used to examine whether this sex difference in responses to conditioned stimuli generalizes to a non-drug consummatory behavior, eating (pizza). However, hedonic ratings and ad lib consumption of pizza were substantially reduced in both men and women following blockade of visual and olfactory/taste food stimuli. These results indicate that the presumably conditioned stimuli of olfactory/taste from cigarette smoke may influence subjective hedonic ratings and reinforcement from smoking more in women than in men. However, this sex difference may not generalize beyond smoking or other drug reinforcement.

Trimethylsilyl- and trimethylstannyldimethylphosphane--convenient and versatile reagents for the synthesis of polyfluoroaryldimethylphosphanes

Trimethylsilyldimethylphosphane (Me3SiPMe2) and the corresponding tin compound (Me3SnPMe2) were used as reagents for the substitution of fluorine by the Me2P group in polyfluoroarenes C6F5X (X = F, H, Cl, CF3) and C5NF5. The reactions occur even under mild conditions (T = 0-20 C), either in benzene or without solvent, to give as a rule 4-X-1-(dimethylphosphano)tetrafluorobenzenes (XC6F4PMe2, 1-4) and 4-(dimethylphosphano)tetrafluoropyridine (C5NF4PMe2, 5), respectively, in yields between 75 and 95%. In the case of C6F6, double substitution is also observed, which affords 1,4-bis(dimethylphosphano)tetrafluorobenzene (6). A very efficient route to the compounds XC6F4PMe2 (X = F, H, Cl, CF3) and C5NF4PMe2 was developed as a one-pot reaction of the corresponding fluoroarenes with tetramethyldiphosphane (P2Me4) and trimethyltin hydride (Me3SnH) at moderate temperatures. This process was tested for C6F6 and perfluorobiphenyl which gave C6F5PMe2 (1) and 4,4'-bis(dimethylphosphano)octafluorobiphenyl (7), respectively. The results, which included kinetic measurements that used the intensities of the 31P signals, revealed the influence of the substrate type on the rate of reaction in the sequence: C5NF5>C6F5CF3> C6F5Cl, C6F5PMe2>C6F5H>C6F6>> C6H5F. Ab initio calculations were carried out on the model reactions of pentafluoropyridine with silylphosphane, phosphane or phosphide to discriminate between possible reaction mechanisms. The novel phosphanes were characterised by spectroscopic investigations (NMR, MS), by preparation of the related thiophosphanes ArFP(=S)Me2 (8-14), their spectroscopic and analytic data and single crystal X-ray diffraction studies on five of these derivatives.

Influence of acute smoking exposure on the subsequent reinforcing value of smoking

The reinforcing value of smoking (i.e., the degree to which a smoker will work to obtain smoking) after varying the magnitude of prior smoke exposure in smokers not trying to quit was examined. Eight men and 8 women participated in 5 sessions involving manipulation of prior exposure to smoking: 0, 2, 6, or 12 puffs after overnight smoking abstinence or ad-lib smoking before the session. After exposure, participants engaged in a computer task involving concurrent schedules of reinforcement for smoke puffs (16% all trials) versus money (4-64%). Only the greatest amount of prior exposure (ad lib) produced a significant reduction in subsequent responding for smoke puffs. No exposure condition significantly increased responding above that for 0 puffs, indicating no priming effect. By contrast, self-report measures of desire to smoke and amount of money participants would pay for a cigarette declined sharply with greater prior exposure. These measures were correlated only weakly with smoke-reinforced responding on the behavioral task, suggesting that subjective versus behavioral measures assess different dimensions of smoking's reward value.

Tobacco abstinence, smoking cues, and the reinforcing value of smoking

One definition of the reinforcing value of a drug is the degree to which an organism will work to obtain it. Male and female smokers (n = 8 each) engaged in a task involving concurrent schedules of reinforcement for responding to receive cigarette puffs versus money on four occasions, following overnight abstinence versus no abstinence and in the presence of a lit cigarette (smoking "cue") or with no cigarette (2 x 2 design). Reinforcement schedule for puffs ranged from variable ratio 4 (VR4) to VR32, with schedule order during the first five trials (VR4 first, VR32 first) counterbalanced and repeated in reverse sequence during the second five trials. Schedule for money remained at VR4 during all trials. Results indicated significantly greater responding for puffs after overnight abstinence and in the presence of the smoking cue, although effect of the cue was specific to the "leaner" VR schedules (VR16, VR32). Unexpectedly, not only was reinforcement schedule for puffs a significant determinant of responding, but the order of these schedules (i.e., VR4 first vs. VR32 first) produced a significant overall difference in responding for puffs, especially in the presence of the cue. There was no difference in responding between males and females. These findings indicate that the reinforcing value of smoking is increased by overnight abstinence, the presence of a lit cigarette under lean reinforcement conditions, and the order in which reinforcement schedules are presented.