ABSTRACT
The light-driven activation of halophosphines R2PX (R = alkyl- or aryl, X = Cl, Br) by an IrIII-based photocatalyst is described. It is shown that initially formed secondary phosphines R2PH react readily with the remaining R2PX in a parent-child reaction to form diphosphines R2P-PR2. Aryl-containing diphosphines can be further reduced to secondary phosphines RAr2PH under identical photoredox conditions. Dihalophosphines RPX2 are also activated by the photoredox protocol, giving rise to unusual 3-, 4-, and 5-membered cyclophosphines. Transient absorption studies show that the excited state of the Ir photocatalyst is reductively quenched by the DIPEA (N,N-di-iso-propylethylamine) electron donor. Electron transfer to R2PX is however unexpectedly slow and cannot compete with recombination with the oxidized donor DIPEAâ¢+. As DIPEA is not a perfectly reversible donor, a small proportion of the total IrII population escapes recombination, providing the reductant for the observed transformations.
ABSTRACT
A new version of the double cross-polarization MAS NMR experiment, which transfers polarization Forth and Back (FBCP) between high- and low-γ spin nuclei, is presented. The pulse sequence is demonstrated by ¹9F-{²9Si}-¹9F and ¹9F-{¹³C}-¹9F FBCP NMR spectra of a mixture of cuspidine (Ca4Si2O7F2) and Teflon (-CF2-)(n). The experiment is useful for assignment of the high-γ spin resonances, as demonstrated by ¹9F-{²9Si}-¹9F FBCP NMR of a fluoride-containing calcium-silicate-hydrate (C-S-H) phase, where the ¹9F resonance from fluoride ions incorporated in the interlayer structure of the C-S-H phase is identified.
ABSTRACT
A reduction in CO(2) emission from Portland cement production can be achieved by energy savings associated with a lowering of the temperature at which the high temperature alite (Ca(3)SiO(5)) and belite (Ca(2)SiO(4)) silicates form. This can be accomplished by fluoride mineralization where a small amount of fluorine (e.g., CaF(2)) is added to the raw mix of starting materials. This work provides the mechanism for incorporation of fluoride ions in the calcium silicate phases of Portland cements which is important in the optimization of the fluoride mineralization. It is demonstrated by double-resonance (29)Si{(19)F} CP/MAS NMR experiments that the fluoride ions are exclusively incorporated into the alite phase of the two calcium silicates. The fluoride ions substitute for oxygen by a coupled mechanism that also involves replacement of Si(4+) by Al(3+) to achieve charge balance. Most importantly, (29)Si{(19)F} REDOR NMR experiments reveal that the fluoride ions are incorporated in alite with a site preference for the "interstitial" oxygen sites and thus not the covalently bonded oxygens of the SiO(4) units. This implies that only one-fifth of the oxygen sites in alite are available for substitution by fluoride ions which limits the gain in entropy of mixing that is a key factor for the reduction in upper temperature of the cement kiln.
ABSTRACT
The purpose of the present descriptive study was to determine the risks associated with hypertension in Vietnamese communities around Ho Chi Minh City, Vietnam. The 357 volunteers for this health promotion screening consisted of 125 men and 232 women, 19-85 years of age. Participants completed surveys on their cardiovascular health history, health practices and hypertension knowledge. Nearly one-third of the sample was found to have systolic blood pressure (SBP) above 139 mmHg and/or diastolic blood pressure (DBP) above 89 mmHg. Fifteen participants had either SBP over 180 mmHg or DBP over 108 mmHg, nine of these 15 participants were taking antihypertensive drugs and 76 were taking other cardiac medications. The majority (98%) cooked with salt and 75% added salt when eating. Drinking alcohol (21%) and smoking (23%) were more common in male participants. Knowledge of cardiovascular risks was very low, indicating a need for community health promotion activities with educational campaigns and further screenings.
