Kryptoracemates

Racemic crystals normally crystallise in centrosymmetric spacegroups containing equal numbers of enantiomers. More rarely, racemates may crystallise in non-centrosymmetric space-groups having glide symmetry or, even more rarely, in space-groups devoid of a centre of inversion, having no rotary-inversion axes nor glide plane. The latter class of crystals form the subject of the present bibliographic review – a survey of kryptoracemic behaviour. The term kryptoracemic alludes to the presence of a hidden or non-crystallographic centre of inversion between two molecules that might otherwise be expected to crystallise in an achiral space-group, often about a centre of inversion. Herein, examples of molecules with stereogenic centres crystallising in one of the 65 Sohncke space-groups are described. Genuine kryptoracemates, i.e. crystals comprising only enantiomorphous pairs are described followed by an overview of non-genuine kryptoracemates whereby the crystal also contains other species such as solvent and/or counterions. A full range, i.e. one to six, stereogenic centres are noted in genuine kryptoracemates. Examples will also be described whereby there are more that one enantiomeric pair of molecules in the crystallographic asymmetric unit. A more diverse range of examples are available for non-genuine kryptoracemates. There are unbalanced species where in addition to the enantiomeric pair of molecules, there is another enantiomeric molecule present. There are examples of genuine co-crystals, solvated species and of salts. Finally, special examples will be highlighted where the counterions are chiral and where they are disparate, both circumstances promoting kryptoracemic behaviour

Highly regioselective monothionation of squaric and semisquaric acid derivatives

An efficient synthesis of 4-thioxocyclobut-2-enones by the action of 0.5 molar equivalents of Lawesson's reagent on the corresponding diones is reported

Highly regioselective monothionation of squaric and semisquaric acid derivatives

An efficient synthesis of 4-thioxocyclobut-2-enones by the action of 0.5 molar equivalents of Lawesson's reagent on the corresponding diones is reported

Energy Allocation in Juveniles of a Warm-temperate Reef Fish

During the first year of life, organisms are faced with competing demands for energy between growth and storage. Most research on energy allocation in young fishes has focused on cold-temperate species which are subjected to strong seasonal fluctuations in productivity, while few studies have considered those at lower latitudes where seasonality is less pronounced. Gag (Mycteroperca microlepis) of the northeastern Gulf of Mexico settle in coastal seagrass beds in the spring as juveniles and emigrate to offshore reefs in the fall. Upon settlement, these young fish grow at remarkably fast rates, but their growth slows considerably before emigration. Slowed growth can be explained by one of three hypotheses: (1) size-specific emigration times; (2) reduced feeding efficiency associated with declines in primary and secondary productivity; or (3) energetic shifts in allocation from growth to storage. Gag emigrate essentially as a cohort, so slowed growth does not result from differential emigration patterns based on fish size. They also emigrate before seasonal declines in primary and secondary productivity; thus, food remains abundant and feeding efficiency constant. The more plausible hypothesis is that there is an energetic shift from growth to storage. The liver serves as the primary site of lipid storage and the hepatosomatic index of juvenile gag increases coincident with reduced growth. The overall effect of increased energy stores is presumably for use during offshore migration and/or for overwinter survival

Electricity for Fluidics and Bio-Devices

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