Since an activated C-H group may take part in hydrogen bonding, the angles involved in the " short " interaction have been calculated for various compounds of known crystal structure containing activated C-H groups and " short " C -* * 0 distances. I n these compounds, the conditions for hydrogen bonding are satisfied by the methylidyne group and probably by the methylene and the methyl group. This type of hydrogen bond occurs rather widely and may be of importance in the structures of biological molecules.AN investigation of '' short '' intermolecular and intramolecular C --* 0 contacts has shown that many of these are due to C-H * --0 hydrogen bonds. Here the term '' short " implies that the distance between the carbon and the oxygen atom is less than the sum of their van der Waals radii plus some allowance for the hydrogen atom or atoms attached to the carbon. Thus C ---0 distances in the region of 3.1 A are considered.*The present work was prompted by the discovery of an intermolecular distance of 3 0 0 A between a methyl group and an oxygen atom in the crystal structure of 1,3,7,9tetramethyluric acid.l This value, obtained originalIy from a two-dimensional analysis of * This is necessary because of the range of values found for hydrogen bonds. The 0 --0 distance in an O -H . * * O hydrogen bond is usually less than the van der Waals distance. However the less electronegative nitrogen atom forms N-H * * -0 and N-H ---N bonds in which the N --0 and N -* -N distances are frequently greater than the van der Waals distance. Carbon which is less electronegative and has to be activated in order to participate in a hydrogen bond should behave similarly to nitrogen, forming even longer bonds.Sutor, Actn Cryst., in the press.

Caffeine crystallizes in the monoclinic space group P21/a with a = 14.8, b = 16.7, c = 3-97 A, fl = 97"0 °. The crystal structure was solved by an application of the isomorphous-replacement method and a consideration of the possible hydrogen bond system in the crystal. A comparison is made of the intramolecular distances with those in other purines and a pyrimidine, and indicates that steric hindrance must be allowed for in a theoretical calculation of bond lengths in relatively complicated molecules of this type. Evidence for and against the existence of a short hydrogen bond between water molecules is given.A C 11 32

Theophylline crystallizes in the monoclinic space group P21, nearly P2z/a, with unit-cell dimensions a = 13.3, b ----15.3, c = 4.50/~, fl ----99.5 °. The x and y coordinates were determined by an application of the isomorphous-replacement method and the z coordinates by a consideration of the hydrogen bond system possible in the crystal; these coordinates were refined by difference syntheses and difference generalized projections. The standard deviation in a bond length is 0.01 /~. The intramolecular distances are similar to those in other compounds containing a purine or pyrimidine group, but bond lengths of substituents attached to the purine ring are equivalent to the sum of the single-or double-bond radii.

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CALCIUM oxalate is important biologically because it is a major constituent of urinary calculi. Both calcium oxalate 1 HzO (whewellite) and calcium oxalate 2 to 23 HzO (weddellite) have been identified, but analyses of collections of stones have shown that the overall amount of whewellite present generally exceeds that of weddellite. Another form of hydrated calcium oxalate, usually referred to as the trihydrate, has been found in only one calculus (Prien, 1963). We have shown (Su1 or, unpublished work) that this hydrate contains only about two water molecules and belongs to the triclinic system. It is formed when " artificial stones " of calcium oxalate are grown in the presence of certain ions, e.g. citrate or pyrophosphate ions (Lyon and Vermeulen, 1965; and this paper).In a study of the composition of urinary calculi collected from many countries and dating from the eighteenth century to the present day, we have shown that calcium oxalate can occur in any of the nucleus, interior and surface layers of the stones and that frequently it is the major constituent of all layers (Lonsdale et al., 1968~1, b). If the nucleation of calcium oxalate could be prevented, or if, when once a nucleus had already formed, the continued deposition of calcium oxalate could be stopped or controlled in such a way that the stone was easily passed, the number of cases of oxalate stones requiring hospitalisation and surgery would be considerably diminished.There is as yet no satisfactory treatment for oxalate stone formers. Control of pH is neither practical nor effective in this case since calcium oxalate is equally insoluble in both acid and alkaline solutions and only at very high pH values is its formation slowed down (see below). We are therefore investigating the types of compounds and ions which are effective in preventing or slowing down its growth. These substances can be divided into the following groups: I, cheinicals claimed to be of therapeutic use in preventing growth of oxalate calculi; 11, synthetic polyelectrolytes; 111, compounds and ions which form complexes with either the calcium or the oxalate ion; IV, miscellaneous compounds; V, dyestuffs. So far, the work applies only to in vitro systems, but its development and extension to in vivo ones is planned.

The problem of urolithiasis is not a simple one for many kinds of stones are known which probably require different conditions for their nucleation and growth. Calculi are found in the kidneys, ureters, bladder and urethra and for those not resulting from any anatomical abnormality, there is no proven reason why growth should occur in say the upper urinary tract as opposed to the lower. Nevertheless, the results of many epidemiological studies (see, for example, references in review articles such as Andersen, 1969) have shown the existence of well-defined zones in the world in which either upper or lower urinary tract stones predominate. Bladder stones in children and adults are a problem in certain areas of technically developing countries like India and Thailand, while kidney stones in adults constitute most of the calculi from industrialised countries. Some possibly indirect connection between these 2 broad categories is, however, likely, for in certain countries of intermediate economic development, both varieties are found, usually but not always in different areas, and the distribution of upper and lower urinary tract stones in them is again dependent on the extent and duration of "industrialisation" present. There is also evidence that bladder stones were a problem in parts of Great Britain, Northern Ireland and Northern Europe prior to this century but they died out about 50 to 60 years ago and have been succeeded by kidney stones. Conditions which have led or are leading to the disappearance of one kind probably then favour the formation of the other.Stones also differ widely in composition. Many compounds can crystallise in them and frequently several are present in one calculus, but the importance of each constituent, as judged by its frequency of occurrence in collections of stones, varies considerably. In a geographical and historical investigation of the composition of urinary calculi, we have studied representative collections of stones from different countries and found that a few constituents, not always the same, predominate in each but that there is an overall similarity in the total amount of some of the constituents in collections comparable with respect to the variables already mentioned, namely the patient's age, the site of the stone in the urinary tract and the extent of economic development in the geographical area concerned (Sutor, 1972).We have now extended this work using a computer to group together comparable collections of stones and then to derive data on the patients and the calculi in each subdivision. This we hope will lead to a better understanding of the different types of urolithiasis as revealed by our study of stone composition, and demonstrate their distribution past and present on a geographical basis. Material and MethodsCollections of urinary calculi from the following countries, cities and institutions are included in this study: Czechoslovakia (99 stones), Eire (69) England (656 stones from 10 cities), India (176 stones from 2 centres), Kuwait (67) Northern Ireland (...

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