SIRIUS

Analysis of the electromagnetic radiation spectrum emanating from the star Sirius shows that = 260 nm. Estimate the surface temperature of Sirius. 

A White 7500-11000 H lines very strong Sirius, Vega... 

The blue book compilations [154-158] are probably the most comprehensive sources of ionization constants collected from the literature (up to the end of 1970s). These are recommended for experts in the field. On the other hand, the red books contain critically selected values [159]. The six-volume set has been put into electronic form in cooperation with NIST (National Institute of Standards and Technology), and is available at a very reasonable price [160]. A two-volume set of critically determined constants is available from Sirius Analytical Instalments Ltd., and covers molecules of particular interest to the pharmaceutical community [161,162]. In Section 3.8 at the end of this chapter, a list of gold standard pKa values of mostly drug-like molecules is presented (see Table 3.1), with many of the values determined by the author since the early 1970s. 

About 250 experimentally determined pKa values of drugs and some agrochemicals are listed in Table 3.1. These have been critically selected to represent high-quality results. Most of these constants have been determined either at Sirius or pION since 1990, with many personally determined by the author. 

HPLC log P techniques, first described by Mirrlees et al. [374] and Unger et al., [375], are probably the most frequently used methods for determining log/1. The directly measured retention parameters are hydrophobicity indices, and need to be converted to a log P scale through the use of standards. The newest variants, breadths of scope, and limitations have been described in the literature [292-298]. A commercial automated HPLC system based on an extension of the approach described by Slater et al. [150] has just introduced by Sirius (www. sirius-analytical. com). 

Temperature 25°C, unless otherwise stated. Sirius Analytical Instrument Ltd. 

Avdeef, A., Applications and Theory Guide to pH-Metric pKa and log P Measurement, Sirius Analytical Instruments Ltd. Forest Row, UK, 1993. 

Another source of high-quality measurement of log D values, though only for ion-izable drugs, is the pH-metric method. In this method, log P is calculated from the difference between the apparent pKa (p0Ka) measured in a dual-phase system, the volume ratio of the phases and the aqueous pKa. First described 50 years ago [8], this method was overlooked until the early 1990s, when it was developed at Sirius as the basis for log P measurement in the GLpKa instrument. The pH-metric method has been extensively described [9-13]. 

At Sirius, a dedicated instmment (Profiler LDA) has been developed for the rapid measurement of log D by liquid-liquid partition chromatography. In this instrument the column is coated with a layer of octanol, and the retention times are therefore tmly related to octanol/water partitioning. Although the method used was first described 25 years ago [29], it has been difficult to apply in an automated system because of the tendency of octanol to be flushed from the column by the eluent, thus requiring frequent renewals of the octanol coating. In our method, the octanol coating is kept in place by reversing the direction of the eluent after each... 

I could not have completed this chapter without the help of colleagues and collaborators. Among my colleagues at Sirius I particularly thank Steve Elliott for his... 

Sirius Technical Application Notes, 2. Sirius Analytical Instruments Ltd., Forest Row, RH18 5DW, UK, 1995. 

Absolv, Sirius Analytical Instruments, Ltd., Riverside, Forest Row Business Park, Forest Row, East Sussex, RH18 5DW, UK, Tel. +44 (0)1342 820720, Fax +44 (0)1342 820725, e-mail sirius sirius-analytical.com, website www. siriur-analytical. com. 

Absolv solute property prediction version 1.2. For further information, visit http //www.sirius-analytical.com/ absolv.htm. 

Sirius A Canis Major (Great Dog) Main sequence 9 2.3 2.5 16000 35 -1.47... 

Note Mass, radius and brightness are given in solar units. For example, Sirius A has 2.3 solar masses, is 2.5 times the size of the Sun and is intrinsically 35 times brighter than the Sun. 1 Solar mass = 2 x 1030 kg = 330000 Earth masses 1 solar radius = 700000 km = 110 Earth radii. 

To explain this, we must consider that, from the known velocity of light, it may be proved, that when we look at Sirius, the rays which enter the eye cannot have been less than 6 years and 4 months coming from that star to the observer. Hence it follows, that when we see an object of the calculated distance at which one of these very remote nebulae may still be perceived, the rays of light which convey its image to the eye, must have been more than nineteen hundred and ten thousand, that is, almost two millions of years on their way and that, consequently, so many years ago, this object must already have had an existence in the sidereal heavens, in order to send out those rays by which we now perceive it. 

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