Self-assembly of cis- and trans-cyclic-1,2-diols. Supramolecular synthon equivalence between cis-1,2-diols and primary amides

Inspite of the fact that the self-assembly of compounds containing hydroxyl group has been enormously documented in the literature, our studies with aliphatic cyclic diols have offered the unique opportunity to examine the self-assembly of gauche and anti forms of ethylene glycol. Whereas the cis-diols are found to form dimers that infinitely assemble further to yield tapes, the anti-diols are found to form linear chains that link up further to yield molecular tapes. Notably, both the isomers lead to molecular tapes, which have attracted immense attention since the inception of self-assembly for controlling molecular organization. Quite remarkably, the self-assembly observed with cis-diols establish a formal equivalence between supramolecular synthons associated with cis-1,2-diols and primary amides. Although the assembly of diols is akin to the tape structure adopted by primary amides, we prefer to view the association of diols as a ladder. The structures of 5-cis and 8-cis are both step-ladder assemblies. That formed by 5-trans is a new variant termed as rope-ladder assembly. The ring motifs observed in the crystal packing suggest for further scope in exploiting the polyhydroxyl compounds for self-assembly in a predictive manner

Addition of NOCl to cyclic vinylsilanes: An unexpected reversal of regiochemistry

NOCl adds to cyclic vinylsilanes in a syn manner with NO+ bonding to the β-carbon and Cl- to the α-carbon, which is a reversal of the regiochemistry expected from the β-silicon effect. The adducts dimerize to a single diastereomer containing enantiomeric pairs and/or give secondary products on further reaction. © 2001 Elsevier Science Ltd

The global burden of cancer attributable to risk factors, 2010–19: a systematic analysis for the Global Burden of Disease Study 2019

BACKGROUND: Understanding the magnitude of cancer burden attributable to potentially modifiable risk factors is crucial for development of effective prevention and mitigation strategies. We analysed results from the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2019 to inform cancer control planning efforts globally. METHODS: The GBD 2019 comparative risk assessment framework was used to estimate cancer burden attributable to behavioural, environmental and occupational, and metabolic risk factors. A total of 82 risk–outcome pairs were included on the basis of the World Cancer Research Fund criteria. Estimated cancer deaths and disability-adjusted life-years (DALYs) in 2019 and change in these measures between 2010 and 2019 are presented. FINDINGS: Globally, in 2019, the risk factors included in this analysis accounted for 4·45 million (95% uncertainty interval 4·01–4·94) deaths and 105 million (95·0–116) DALYs for both sexes combined, representing 44·4% (41·3–48·4) of all cancer deaths and 42·0% (39·1–45·6) of all DALYs. There were 2·88 million (2·60–3·18) risk-attributable cancer deaths in males (50·6% [47·8–54·1] of all male cancer deaths) and 1·58 million (1·36–1·84) risk-attributable cancer deaths in females (36·3% [32·5–41·3] of all female cancer deaths). The leading risk factors at the most detailed level globally for risk-attributable cancer deaths and DALYs in 2019 for both sexes combined were smoking, followed by alcohol use and high BMI. Risk-attributable cancer burden varied by world region and Socio-demographic Index (SDI), with smoking, unsafe sex, and alcohol use being the three leading risk factors for risk-attributable cancer DALYs in low SDI locations in 2019, whereas DALYs in high SDI locations mirrored the top three global risk factor rankings. From 2010 to 2019, global risk-attributable cancer deaths increased by 20·4% (12·6–28·4) and DALYs by 16·8% (8·8–25·0), with the greatest percentage increase in metabolic risks (34·7% [27·9–42·8] and 33·3% [25·8–42·0]). INTERPRETATION: The leading risk factors contributing to global cancer burden in 2019 were behavioural, whereas metabolic risk factors saw the largest increases between 2010 and 2019. Reducing exposure to these modifiable risk factors would decrease cancer mortality and DALY rates worldwide, and policies should be tailored appropriately to local cancer risk factor burden

cis-Hydroxylation of cyclic vinylsilanes using cetyltrimethylammonium permanganate

Cetyltrimethylammonium permanganate (CTAP) effects cis-hydroxylation of cyclic vinylsilanes smoothly under mild conditions both in aqueous and nonaqueous solvents. cis-1-Trimethylsilylcycloalkane-1,2-diols 7-12 were prepared in good yields. The oxidation occurs at 20°C and takes a much shorter time in comparison with OsO4 oxidation reported in the literature

Stereoelectronic requirement and effect of ring size on silanol elimination: A kinetic study

Acid catalyzed elimination of silanol from the cyclic cis-αβ-dihydroxysilanes 3-8 to cycloalkanones was studied at three different temperatures (298, 313 and 328 K). Silyldiols 3-7 hydrolyzed smoothly, while 8 was resistant to hydrolysis. The observed ease of elimination (reflected in the rate constants) was found to be related to the conformational flexibility of the ring and intramolecular hydrogen bonding. The results have confirmed the requirement of perfect antiperiplanar geometry of the eliminating groups, SiMe3 and β-OH. The quantitation of the hydrolysis products, the cycloalkanones, was done using the gas chromatographic peak area normalization method using an internal standard. The rate data obtained at three different temperatures were employed to calculate ΔH‡, ΔS‡, and ΔG‡. The rate constants and thermodynamic parameters increase with the ring size. There is an interesting demarcation between these two values for common ring silyldiols and the larger ring silyldiols

Hydrogen bonded channel formation in a molecular complex: Cis-1-chloro-2-ammonium-1-trimethylsilylcycloheptane picrate

The crystal and molecular structure of cis-1-chloro-2-amino-1- trimethylsilylcycloheptane picrate (cis-CATP) is determined and discussed along with its spectroscopy. The crystal structure of this compound (C 10H23SiClN+ C6H2N 3O 7 - ) consists of ammonium cycloheptane cation and picrate anion stabilized by interionic N-H⠢⢠⠢O and C-Hâ ¢ â¢â¢O interactions leading to extended hydrogen bonded network structure. Apart from the less common syn addition of nitrosylchloride to 1-trimethylsilylcycloheptene ring, an interesting and unexpected reversal of regiochemistry of addition is revealed. The preparation of cis-1-chloro-2- ammonium-1-trimethylsilylcycloheptane picrate is described and its crystal structure is determined and discussed. Figure not available: see fulltext. © 2008 Springer Science+Business Media, LLC