Controlling the crystal polymorph by exploiting the time dependence of nucleation rates

Most substances can crystallise into two or more different crystal lattices, called polymorphs. Despite this, there are no systems in which we can quantitatively predict the probability of one competing polymorph forming, instead of the other. We address this problem using large scale (hundreds of events) studies of the competing nucleation of the alpha and gamma polymorphs of glycine. In situ Raman spectroscopy is used to identify the polymorph of each crystal. We find that the nucleation kinetics of the two polymorphs is very different. Nucleation of the alpha polymorph starts off slowly but accelerates, while nucleation of the gamma polymorph starts off fast but then slows. We exploit this difference to increase the purity with which we obtain the gamma polymorph by a factor of ten. The statistics of the nucleation of crystals is analogous to that of human mortality, and using a result from medical statistics we show that conventional nucleation data can say nothing about what, if any, are the correlations between competing nucleation processes. Thus we can show that, with data of our form, it is impossible to disentangle the competing nucleation processes. We also find that the growth rate and the shape of a crystal depends on when it nucleated. This is new evidence that nucleation and growth are linked.Comment: 8 pages, plus 17 pages of supplementary materia

Evidence of gene-environment interaction for two genes on chromosome 4 and environmental tobacco smoke in controlling the risk of nonsyndromic cleft palate

Nonsyndromic cleft palate (CP) is one of the most common human birth defects and both genetic and environmental risk factors contribute to its etiology. We conducted a genome-wide association study (GWAS) using 550 CP case-parent trios ascertained in an international consortium. Stratified analysis among trios with different ancestries was performed to test for GxE interactions with common maternal exposures using conditional logistic regression models. While no single nucleotide polymorphism (SNP) achieved genome-wide significance when considered alone, markers in SLC2A9 and the neighboring WDR1 on chromosome 4p16.1 gave suggestive evidence of gene-environment interaction with environmental tobacco smoke (ETS) among 259 Asian trios when the models included a term for GxE interaction. Multiple SNPs in these two genes were associated with increased risk of nonsyndromic CP if the mother was exposed to ETS during the peri-conceptual period (3 months prior to conception through the first trimester). When maternal ETS was considered, fifteen of 135 SNPs mapping to SLC2A9 and 9 of 59 SNPs in WDR1 gave P values approaching genome-wide significance (10-6<P<10-4) in a test for GxETS interaction. SNPs rs3733585 and rs12508991 in SLC2A9 yielded P = 2.26×10-7 in a test for GxETS interaction. SNPs rs6820756 and rs7699512 in WDR1 also yielded P = 1.79×10-7 and P = 1.98×10-7 in a 1 df test for GxE interaction. Although further replication studies are critical to confirming these findings, these results illustrate how genetic associations for nonsyndromic CP can be missed if potential GxE interaction is not taken into account, and this study suggest SLC2A9 and WDR1 should be considered as candidate genes for CP. © 2014 Wu et al

Whole genome sequence analysis of platelet traits in the NHLBI Trans-Omics for Precision Medicine (TOPMed) initiative

Platelets play a key role in thrombosis and hemostasis. Platelet count (PLT) and mean platelet volume (MPV) are highly heritable quantitative traits, with hundreds of genetic signals previously identified, mostly in European ancestry populations. We here utilize whole genome sequencing (WGS) from NHLBI's Trans-Omics for Precision Medicine initiative (TOPMed) in a large multi-ethnic sample to further explore common and rare variation contributing to PLT (n = 61 200) and MPV (n = 23 485). We identified and replicated secondary signals at MPL (rs532784633) and PECAM1 (rs73345162), both more common in African ancestry populations. We also observed rare variation in Mendelian platelet-related disorder genes influencing variation in platelet traits in TOPMed cohorts (not enriched for blood disorders). For example, association of GP9 with lower PLT and higher MPV was partly driven by a pathogenic Bernard-Soulier syndrome variant (rs5030764, p.Asn61Ser), and the signals at TUBB1 and CD36 were partly driven by loss of function variants not annotated as pathogenic in ClinVar (rs199948010 and rs571975065). However, residual signal remained for these gene-based signals after adjusting for lead variants, suggesting that additional variants in Mendelian genes with impacts in general population cohorts remain to be identified. Gene-based signals were also identified at several genome-wide association study identified loci for genes not annotated for Mendelian platelet disorders (PTPRH, TET2, CHEK2), with somatic variation driving the result at TET2. These results highlight the value of WGS in populations of diverse genetic ancestry to identify novel regulatory and coding signals, even for well-studied traits like platelet traits

Finishing the euchromatic sequence of the human genome

The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead

A "tortoise and the hare" story : the relationship between induction time and polymorphism in glycine crystallisation.

Crystal polymorphism, where a molecule forms several different crystal lattices, is common, and often needs to be controlled. For example, crystalline drugs must be manufactured as one specified polymorph, so polymorph purity is essential to the pharmaceutical industry. This thesis is a quantitative study of the crystallization of glycine from aqueous solution, which focuses particularly on polymorphism. Crystallization is observed within a 96-well microplate, where each well is filled with 0.1 mL of supersaturated solution. We address the difficulty of obtaining reproducible nucleation data. This problem is difficult because induction times are extremely sensitive to factors such as how the crystallizing system is prepared, and small variations in the supersaturation. The appropriate statistical tests needed to show reproducibility are discussed. Glycine has two common polymorphs, alpha and gamma, the competition between these polymorphs is studied. We obtain data at multiple NaCl concentrations. Addition of NaCl is known to favour nucleation of the gamma polymorph. The polymorph of crystals are individually identified in-situ using Raman spectroscopy. At high salt concentrations, nucleation kinetics of the alpha and gamma polymorphs are qualitatively different. The gamma polymorph behaves like the hare in Aesop's story of the tortoise and the hare: Nucleation start off rapidly, but slows, while for the alpha polymorph, nucleation starts off slow but at later times almost overtakes that of the gamma polymorph. The opposite time dependencies of the nucleation of the competing polymorphs, allows optimisation of polymorph purity using time-dependent supersaturation. Growth of the two polymorphs is analysed. The alpha polymorph is observed to grow faster than the gamma polymorph. Growth rates were variable, so they were also analysed in relation to induction times and crystal habits. We show that crystals with long induction times tend to be needle-like, and needle-like morphologies tend to grow faster than non needle-like morphologies

A "tortoise and the hare" story : the relationship between induction time and polymorphism in glycine crystallisation.

Crystal polymorphism, where a molecule forms several different crystal lattices, is common, and often needs to be controlled. For example, crystalline drugs must be manufactured as one specified polymorph, so polymorph purity is essential to the pharmaceutical industry. This thesis is a quantitative study of the crystallization of glycine from aqueous solution, which focuses particularly on polymorphism. Crystallization is observed within a 96-well microplate, where each well is filled with 0.1 mL of supersaturated solution. We address the difficulty of obtaining reproducible nucleation data. This problem is difficult because induction times are extremely sensitive to factors such as how the crystallizing system is prepared, and small variations in the supersaturation. The appropriate statistical tests needed to show reproducibility are discussed. Glycine has two common polymorphs, alpha and gamma, the competition between these polymorphs is studied. We obtain data at multiple NaCl concentrations. Addition of NaCl is known to favour nucleation of the gamma polymorph. The polymorph of crystals are individually identified in-situ using Raman spectroscopy. At high salt concentrations, nucleation kinetics of the alpha and gamma polymorphs are qualitatively different. The gamma polymorph behaves like the hare in Aesop's story of the tortoise and the hare: Nucleation start off rapidly, but slows, while for the alpha polymorph, nucleation starts off slow but at later times almost overtakes that of the gamma polymorph. The opposite time dependencies of the nucleation of the competing polymorphs, allows optimisation of polymorph purity using time-dependent supersaturation. Growth of the two polymorphs is analysed. The alpha polymorph is observed to grow faster than the gamma polymorph. Growth rates were variable, so they were also analysed in relation to induction times and crystal habits. We show that crystals with long induction times tend to be needle-like, and needle-like morphologies tend to grow faster than non needle-like morphologies

Does the γ Polymorph of Glycine Nucleate Faster? A Quantitative Study of Nucleation from Aqueous Solution

We quantitatively study the crystallization of glycine from solution by following the crystallization of a plate with 96 wells, each with 0.1 mL of supersaturated solution. Our first aim is to address the difficult problem of obtaining nucleation data that is reproducible. This problem is difficult because of the extreme sensitivity of nucleation times. Nucleation is sensitive to factors that include how the crystallizing system is prepared and even small (1%) variations in the supersaturation. We discuss the appropriate statistical tests needed to show reproducibility. Our second aim is to study the competition between the nucleation of the alpha and gamma polymorphs of glycine. We find that nucleation appears to be heterogeneous: Some samples crystallize in minutes, whereas others do not crystallize after days, which indicates that there is no well-defined nucleation rate for the set of samples. Homogeneous nucleation gives a well-defined rate. Those samples that crystallize in minutes mostly yield the metastable alpha polymorph. We speculate that these crystals may be the result of seed crystals formed by transient local increases in supersaturation in pipette tips during sample preparation. However, those that crystallize in hours are largely the equilibrium gamma polymorph. This is perhaps surprising because typically the alpha polymorph is obtained from crystallization from aqueous solutions near neutral pH. We speculate that the nucleation rate of the gamma polymorph may be higher than that of the alpha form but that in earlier work with larger solution volumes (increasing the probability of seeding) and with stirring the alpha polymorph dominates because of its much faster growth rate

Perspectives on Deprescribing in long-term care: qualitative findings from nurses, aides, residents, and proxies

Abstract Background Deprescribing initiatives in the long-term care (LTC) setting are often unsuccessful or not sustained. Prior research has considered how physicians and pharmacists feel about deprescribing, yet little is known about the perspectives of frontline nursing staff and residents. Our aim was to elicit perspectives from LTC nursing staff, patients, and proxies regarding their experiences and preferences for deprescribing in order to inform future deprescribing efforts in LTC. Methods This study was a qualitative analysis of interviews with nurses, nurse aides, a nurse practitioner, residents, and proxies (family member and/or responsible party) from three LTC facilities. The research team used semi-structured interviews. Guides were designed to inform an injury prevention intervention. Interviews were recorded and transcribed. A qualitative framework analysis was used to summarize themes related to deprescribing. The full study team reviewed the summary to identify actionable, clinical implications. Results Twenty-six interviews with 28 participants were completed, including 11 nurse aides, three residents, seven proxies, one nurse practitioner, and six nurses. Three themes emerged that were consistent across facilities: 1) build trust with team members, including residents and proxies; 2) identify motivating factors that lead to resident, proxy, nurse practitioner, and staff acceptance of deprescribing; 3) standardize supportive processes to encourage deprescribing. These themes suggest several actionable steps to improve deprescribing initiatives including: 1) tell stories about successful deprescribing, 2) provide deprescribing education to frontline staff, 3) align medication risk/benefit discussions with what matters most to the resident, 4) standardize deprescribing monitoring protocols, 5) standardize interprofessional team huddles and care plan meetings to include deprescribing conversations, and 6) strengthen non-pharmacologic treatment programs. Conclusions By interviewing LTC stakeholders, we identified three important themes regarding successful deprescribing: Trust, Motivating Factors, and Supportive Processes. These themes may translate into actionable steps for clinicians and researchers to improve and sustain person-centered deprescribing initiatives. Trial registration NCT0424218