Metal-directed formation of three-dimensional M(3)L(2) trigonal-bipyramidal cages.

[reaction: see text] The simple combination of two angular tritopic pyridine donor linkers (109 degrees bond angle) with three ditopic platinum acceptors (90 degrees bond angle) leads to essentially quantitative formation of self-assembled M(3)L(2) trigonal-bipyramidal (TBP) supramolecular species.

Palladium-catalyzed highly chemo- and regioselective formal [2+2+2] sequential cycloaddition of alkynes: a renaissance of the well known trimerization reaction?

A new concept of highly chemo- and regioselective formation of the benzene ring by a palladium-catalyzed formal [2 + 2 + 2] sequential intermolecular trimerization of alkynes is proposed. Homodimerization of terminal alkynes and subsequent [4 + 2] benzannulation with diynes gives tetrasubstituted benzenes in moderate to good yields. The introduction of two different alkynes (terminal and internal) in the first step of the sequence allows for construction of pentasubstituted benzenes from three different acyclic acetylenic units. In all cases the tetra- and pentasubstituted benzenes are formed as a single reaction product without being accompanied by any of regio- or chemoisomers. A significant acceleration of the sequential trimerization reaction in the presence of Lewis acid/phosphine combined system was observed. Mechanistic studies reveal that the Lewis acid assisted isomerization of the E-enyne formed in the first step of the sequence to the more reactive Z-isomer is responsible for the observed acceleration effect. The proposed methodology provides a conceptually new and synthetically useful route to multifunctional aromatic compounds.

Palladium-catalyzed arylation of enynes and electron-deficient alkynes using diaryliodonium salts.

A new single-pot procedure for the synthesis of aryl alkynes is described. Palladium catalyzes the coupling reaction of diaryliodonium compounds with enynes and electron-deficient alkynes to give aryl alkynes in good yields.

Hereditary protein C deficiency--the first symptomatic family in Singapore.

Protein C is an important physiological inhibitor of coagulation. A deficiency of this protein is a recognised cause of recurrent venous thromboembolism. The assay for protein C was not locally available until recently. Our investigation of a young Malay woman who had sustained two previous pulmonary emboli led us to identify the first family in Singapore with this familial disorder. The definitive diagnosis of symptomatic protein C deficiency justifies longterm anticoagulant therapy in two members of this family. We now systematically screen all young adults who present with the first episode of deep venous thrombosis or pulmonary embolism irrespective of whether the event is spontaneous or seemingly precipitated.

Effect of restricted potassium intake on its excretion and on physiological responses during heat stress.

The effect of low potassium (K+) intake on its excretion, concentration in sweat and on physiological responses during heat stress was evaluated on eight Indian male soldiers in winter months at Delhi. After a stabilization period of 3 days on each diet, i.e., 85 mEq of K+/d (diet I, normal), 55 mEq of K+/d (diet II), and 45 mEq of K+/d (diet III), the physiological responses and the sodium and potassium concentrations in sweat, plasma, RBC, and urine were measured when the subjects were exposed to heat for 3 h daily in a climatic chamber maintained at 40 degrees C DB and 32 degrees C WB. The subjects worked in the chamber at the rate of 465 W/h for 20 min periods with 40 min rest between each period of exercise. The whole body sweat was collected after the spell of work and was analysed for sodium and potassium levels. Throughout the study the subjects remained on positive sodium balance except on day 4 in diet III. Fluid balance also remained positive while potassium balance was negative in subjects on diet II and diet III. There was no significant change in heart rate, sweat volume, oral temperature, sodium, and potassium concentrations in plasma and RBC during the entire period of the study. Even in the subjects with negative potassium balance there was no change in the sodium and potassium concentrations in sweat during exercise in heat. The only evidence of potassium conservation was a reduced excretion in urine. Out of the eight subjects, in one subject there was a flattening of the 'T' wave in the ECG and reduction in amplitude of the 'T' wave in two more subjects. As there is no reduction in sweat potassium concentration and the urine volume is low, the marginal level of reduced excretion of potassium in urine with a high rate of sweating (7-81) in subjects doing work in the tropics, there is every likelihood of potassium deficiency if a liberal intake is not ensured. In our earlier studies (Malhotra et al. 1976) we found that the concentration of potassium (K+) in sweat is much higher than in plasma even in acclimatised subjects. A large amount of K+ is therefore likely to be lost in sweat during exposure to heat. In that study there was no evidence of a reduction in K+ concentration in the sweat or urine upon repeated exposure of the subjects to heat, indicative of a compensatory mechanism for conservation of K+ losses. However, these earlier studies were done on subjects who were on a normal diet which contained 75-80 mEq of K+ per day. Since a compensatory mechanism may be triggered only when the body K+ becomes dificient and not earlier, as is the case with sodium (Malhotra et al. 1959), we have now investigated the effects of a sequential reduction of reduced dietary K+ on the dermal and urinary losses of K+. The effects of K+ deficiency on the physiological responses to heat have also been studied. The results of these studies are reported here.

Electrolyte changes at 3500 m in males with and without high-altitude pulmonary edema.

Ten normal healthy male subjects between 20-30 years of age were initially examined at Delhi (200 m) and thereafter air-lifted to an altitude of 3,500 m. Excretion of sodium, potassium and chloride in urine and their plasma level were determined at sea level (SL) and daily at high altitude (HA) for 4 d. At HA, four subjects developed high-altitude pulmonary edema (HAPE), four remained normal, and two suffered from acute mountain sickness. The results on normals and HAPE are presented. There was increased excretion of potassium at HA in both groups resulting in reduction of plasma level. The sodium and chloride excretion was also increased in normals at HA irrespective of urine volume. In HAPE cases, the sodium and chloride excretion was related to urine output. With the retention of fluid, the excretion of these ions in urine was diminished without a parallel change in plasma levels.