GONYAULACYSTA PARORTHOCERAS: A New Species of DINOFLAGELLATE CYST

Davey (1968 in press) emends the species Gonyaulacysta orthoceras Eisenack and also transfers it to the genus Cribroperidinium Neale and Sarjeant. By emending Eisenack's species the specimens described by Sarjeant (1966) as G. orthoceras, from the Lower Cretaceous of England, must now be excluded from this species. Hence, a new species is here erected to accommodate them

Some dinoflagellate cysts from the upper Cretaceous of northern Natal, South africa

Main articleFossil dinoflagellate cysts are for the first time described from South Africa and occur in sediments of Campanian, Maastrichtian and possibly Danian age. The sedimentary samples are from a borehole in northern Natal. The systematic section includes the erection of seven new species; these constitute only a few of the many species found in the assemblages.Non

Gonyaulacysta parorthoceras A new species if dinoflagellate cyst

Main articleDavey (1968 in press) emends the species Gonyaulacysta orthoceras Eisenack and also transfers it to the genus Cribroperidinium Neale and Sarjeant. By emending Eisenack's species the specimens described by Sarjeant (1966) as G. orthoceras, from the Lower Cretaceous of England, must now be excluded from this species. Hence, a new species is here erected to accommodate them.Non

THE EVOLUTION OF CERTAIN UPPER CRETACEOUS HYSTRICHOSPHERES FROM SOUTH AfRICA

This paper traces clearly, for the first time, an evolutionary sequence in dinoflagellate cysts. The sedimentary samples containing the cysts are from northern Natal, South Africa, and are of Upper Cretaceous age. The genera concerned in this study are Exochosphaeridium Davey et al. (1966), Cordosphaeridium Eisenack (1963b) and an intermediary genus Amphorosphaeridium nov. Morphological changes exhibited by the cysts are related to ecological considerations and are shown to be directional; their stratigraphic usefulness is also discussed. In all one genus, three species and two varieties are erected

Can molecular flexibility control crystallization? The case of <i>para</i> substituted benzoic acids.

From Europe PMC via Jisc Publications RouterHistory: ppub 2020-11-01, epub 2020-11-16Publication status: PublishedDespite the technological importance of crystallization from solutions almost nothing is known about the relationship between the kinetic process of nucleation and the molecular and crystal structures of a crystallizing solute. Nowhere is this more apparent than in our attempts to understand the behavior of increasingly large, flexible molecules developed as active components in the pharmaceutical arena. In our current contribution we develop a general protocol involving a combination of computation (conformation analysis, lattice energy), and experiment (measurement of nucleation rates), and show how significant advances can be made. We present the first systematic study aimed at quantifying the impact of molecular flexibility on nucleation kinetics. The nucleation rates of 4 para substituted benzoic acids are compared, two of which have substituents with flexible chains. In making this comparison, the importance of normalizing data to account for differing solubilities is highlighted. These data have allowed us to go beyond popular qualitative descriptors such 'crystallizability' or 'crystallization propensity' in favour of more precise nucleation rate data. Overall, this leads to definite conclusions as to the relative importance of solution chemistry, solid-state interactions and conformational flexibility in the crystallization of these molecules and confirms the key role of intermolecular stacking interactions in determining relative nucleation rates. In a more general sense, conclusions are drawn as to conditions under which conformational change may become rate determining during a crystallization process

Alcohol Intake and Blood Pressure: A Systematic Review Implementing a Mendelian Randomization Approach

Using a mendelian randomization approach Sarah Lewis and colleagues find strong support for the hypothesis that alcohol intake has a marked effect on blood pressure and the risk of hypertension

Polymorphism in p-Aminobenzoic Acid

We review the polymorphism of p-aminobenzoic acid (pABA), a model drugcompound whose crystallisation and polymorphic behaviour has been extensively studied in recent years. Beyond the well-known and characterised α and β forms, pABA also crystallises as a γ polymorph, which is structurally similar to the α form. In addition we also compare the newly reported δ form, obtained by high pressure crystallisation and through compression of the α-form. A structural analysis and comparison of all of the forms is presented, the conditions by which each of them is obtained summarised. Crystal structure prediction calculations have also been carried out in order to probe the solid form energy landscape of this compound. The overall picture of the polymorphism of pABA, reveals, surprisingly, the rarity of the β form

Do metastable polymorphs always grow faster? Measuring and comparing growth kinetics of three polymorphs of tolfenamic acid

The phenomenon of molecular crystal polymorphism is of central importance for all those industries that rely on crystallisation for the manufacturing of their products. Computational methods for the evaluation of thermodynamic properties of polymorphs have become incredibly accurate and a priori prediction of crystal structures is becoming routine. The computational study and prediction of the kinetics of crystallisation impacting polymorphism, however, have received considerably less attention despite their crucial role in directing crystallisation outcomes. This is mainly due to the lack of available experimental data, as nucleation and growth kinetics of polymorphs are generally difficult to measure. On the one hand, the determination of overall nucleation and growth kinetics through batch experiments suffers from unwanted polymorphic transformations or the absence of experimental conditions under which several polymorphs can be nucleated. On the other hand, growth rates of polymorphs obtained from measurements of single crystals are often only recorded along a few specific crystal dimensions, thus lacking information about overall growth and rendering an incomplete picture of the problem. In this work, we measure the crystal growth kinetics of three polymorphs (I, II and IX) of tolfenamic acid (TFA) in isopropanol solutions, with the intention of providing a meaningful comparison of their growth rates. First, we analyse the relation between the measured growth rates and the crystal structures of the TFA polymorphs. We then explore ways to compare their relative growth rates and discuss their significance when trying to determine which polymorph grows faster. Using approximations for describing the volume of TFA crystals, we show that while crystals of the metastable TFA-II grow the fastest at all solution concentrations, crystals of the metastable TFA-IX become kinetically competitive as the driving force for crystallisation increases. Overall, both metastable forms TFA-II and TFA-IX grow faster than the stable TFA-I

Open questions in organic crystal polymorphism

From Springer Nature via Jisc Publications RouterHistory: received 2020-09-17, accepted 2020-09-25, registration 2020-09-30, pub-electronic 2020-10-19, online 2020-10-19, collection 2020-12Publication status: PublishedFunder: The Royal Society, Industry Fellowship in AstraZenecaPolymorphs, crystals with different structure and properties but the same molecular composition, arise from the subtle interplay between thermodynamics and kinetics during crystallisation. In this opinion piece, the authors review the latest developments in the field of polymorphism and discuss standing open questions

Exploring the Developmental Overnutrition Hypothesis Using Parental–Offspring Associations and FTO as an Instrumental Variable

Using parental-offspring associations and theFTO gene as an instrumental variable for maternal adiposity, Debbie Lawlor and colleagues found that greater maternal BMI during offspring development does not appear to have a marked effect on offspring fat mass at age 9-11