| Van Slyke apparatus | An apparatus for determining the amounts of respiratory gases in the blood. (05 Mar 2000) |
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| Van Slyke's formula | The value obtained when the square root of the urine flow (when below 2 ml/min) is multiplied by the urine urea concentration and divided by the whole blood urea concentration; represents an old empirical adjustment for the effect of low urine flow on urea excretion; sometimes corrected for body size by dividing by some function of body weight or surface area. Later, plasma concentration was substituted for blood concentration in the calculation. The normal value is about 54 ml/min per 1.73 m2 in an adult person. Synonym: Van Slyke's formula. (05 Mar 2000) |
| Van Slyke, Donald | <person> U.S. Biochemist, 1883-1971. See: slyke, Van Slyke apparatus, Van Slyke's formula. (05 Mar 2000) |
| van't Hoff's equation | Equation for osmotic pressure of dilute solutions. See: van't Hoff's law. For any reaction, d(ln Keq/d(1/T) equals -dH/R where Keq is the equilibrium constant, T the absolute temperature, R is the universal gas constant, and dH is the change in enthalpy; thus, plotting ln Keq vs. 1/T allows the determination of dH. (05 Mar 2000) |
| van't Hoff's law | In stereochemistry, all optically active substances have one or more multivalent atoms united to four different atoms or radicals so as to form in space an unsymmetrical arrangement, the osmotic pressure exerted by any substance in very dilute solution is the same that it would exert if present as gas in the same volume as that of the solution; or, at constant temperature, the osmotic pressure of dilute solutions is proportional to the concentration (number of molecules) of the dissolved substance; i.e., the osmotic pressure, π, in dilute solutions is π = RTσci, where R is the universal gas constant, T is the absolute temperature, and ci is the molar concentration of solute i, the rate of chemical reactions increases between two-and three-fold for each 10캜 rise in temperature. (05 Mar 2000) |
| van't Hoff's theory | That substances in dilute solution obey the gas laws. Compare: van't Hoff's law. (05 Mar 2000) |
| van't Hoff, Jacobus | <person> Dutch chemist and Nobel laureate, 1852-1911. See: van't Hoff's equation, van't Hoff's law, van't Hoff's theory, Le Bel-van't Hoff rule. (05 Mar 2000) |
| vanadate | VO4(3) Powerful inhibitor of many, but not all enzymes that cleave the terminal phosphate bond of ATP. The vanadate ion is believed to act as an analogue of the transition state of the cleavage reaction. Dynein is very sensitive to inhibition by vanadate, whereas kinesin is relatively insensitive. Similarly tyrosine kinases are sensitive to vanadate, but threonine/serine protein kinases are insensitive. (18 Nov 1997) |
| vanadates | Oxyvanadium ions in various states of oxidation. They act primarily as ion transport inhibitors due to their inhibition of sodium-, potassium-, and calcium-atpase transport systems. They also have insulin-like action, positive inotropic action on cardiac ventricular muscle, and other metabolic effects. (12 Dec 1998) |
| vanadic | <chemistry> Pertaining to, or obtained from, vanadium; containing vanadium; specifically distinguished those compounds in which vanadium has a relatively higher valence as contrasted with the vanadious compounds; as, vanadic oxide. <chemistry> Vanadic acid, an acid analogous to phosphoric acid, not known in the free state but forming a well-known series of salts. Source: Websters Dictionary (01 Mar 1998) |
| vanadic acid | An acid, H3VO4, derived from vanadium, forming salts with various bases. (05 Mar 2000) |
| vanadinite | <chemical> A mineral occurring in yellowish, and ruby-red hexagonal crystals. It consist of lead vanadate with a small proportion of lead chloride. Source: Websters Dictionary (01 Mar 1998) |
| vanadious | <chemistry> Pertaining to, or containing, vanadium; specifically, designating those compounds in which vanadium has a lower valence as contrasted with the vanadic compounds; as, vanadious acid. [Sometimes written also vanadous. Source: Websters Dictionary (01 Mar 1998) |
| vanadite | <chemistry> A salt of vanadious acid, analogous to a nitrite or a phosphite. Source: Websters Dictionary (01 Mar 1998) |
| vanadium | <chemistry, element> A rare element of the nitrogen-phosphorus group, found combined, in vanadates, in certain minerals, and reduced as an infusible, grayish-white metallic powder. It is intermediate between the metals and the non-metals, having both basic and acid properties. Atomic weight: 51.2 Abbreviation: V Origin: NL, fr. Icel. Vanadis, a surname of the Scandinavian goddess Freya. (30 Mar 1998) |