Interplay of strong and weak hydrogen bonding in molecular complexes of some 4,4'-disubstituted biphenyls with urea, thiourea and water

The crystal chemistry and engineering of a new family of host-guest complexes is described. 4,4'-Dicyanobiphenyl (DCBP) forms a 1:1 complex, 1 with urea wherein the DCBP host forms large hexagonal channels via C-H···N hydrogen bonds and the urea guest molecules are arranged in N-H···O ribbons which fit completely within the host channels. By analogy, 4,4'-bipyridine N,N'-dioxide (BPNO) was selected as a molecule that can form a corresponding C-H…O based channel. BPNO forms complexes with urea (2), thiourea (3) and water (4). Structures 2 and 3 provide some points of comparison with the structure of 1 but are not fully equivalent to it. In structure 4, the smaller guest water is able to fit neatly within the smaller hexagonal channel of BPNO and in this sense, the degree of structural predictability is satisfactory. To obtain another structure similar to that of 1, 4,4'-dinitrobiphenyl (DNBP) was identified as an alternative host compound. This choice was justified by the structure of its 1:1 complex, 5 with urea. In all cases, the guest molecules interact with each other via strong hydrogen bonds and form an essential template for the weak hydrogen bonded assembly of the host network structure but the latter is still of some significance. One finds consequently, in complexes 1-5, a constructive interplay of strong and weak hydrogen bonds

Molecular networks in the crystal structures of tetrakis(4-iodophenyl)methane and (4-iodophenyl)triphenylmethane

The crystal structure of tetrakis(4-iodophenyl)methane is analysed in terms of molecular networks wherein the tetraphenylmethane moieties and I4 synthons are considered as molecular and supramolecular nodes. This I4 cluster plays the same role in generating molecular networks as does the Br4 cluster in the isomorphous tetrakis(4-bromophenyl)methane derivative. (4-Iodophenyl)triphenylmethane crystallises in a lower symmetry space group but features an unusual I···Ph interaction. In this series of halo-substituted tetraphenylmethanes the molecules exhibit similar columnar packing in the solid state, accounting for their crystallisation in non-centrosymmetric space groups

Multiple novel prostate cancer susceptibility signals identified by fine-mapping of known risk loci among Europeans

Genome-wide association studies (GWAS) have identified numerous common prostate cancer (PrCa) susceptibility loci. We have fine-mapped 64 GWAS regions known at the conclusion of the iCOGS study using large-scale genotyping and imputation in 25 723 PrCa cases and 26 274 controls of European ancestry. We detected evidence for multiple independent signals at 16 regions, 12 of which contained additional newly identified significant associations. A single signal comprising a spectrum of correlated variation was observed at 39 regions; 35 of which are now described by a novel more significantly associated lead SNP, while the originally reported variant remained as the lead SNP only in 4 regions. We also confirmed two association signals in Europeans that had been previously reported only in East-Asian GWAS. Based on statistical evidence and linkage disequilibrium (LD) structure, we have curated and narrowed down the list of the most likely candidate causal variants for each region. Functional annotation using data from ENCODE filtered for PrCa cell lines and eQTL analysis demonstrated significant enrichment for overlap with bio-features within this set. By incorporating the novel risk variants identified here alongside the refined data for existing association signals, we estimate that these loci now explain ∼38.9% of the familial relative risk of PrCa, an 8.9% improvement over the previously reported GWAS tag SNPs. This suggests that a significant fraction of the heritability of PrCa may have been hidden during the discovery phase of GWAS, in particular due to the presence of multiple independent signals within the same regio

Organic alloys: diamondoid networks in crystalline complexes of 1,3,5,7-tetrabromoadamantane, hexamethylenetetramine and carbon tetrabromide

1,3,5,7-Tetrabromoadamantane and hexamethylenetetramine (hmt) co-crystalline to form a diamondoid-type 1 : 2 molecular complex but one of the two hmt molecules is disordered and can be substitutionally replaced by CBr4 to give the corresponding 1 : 1 : 1 Complex

Supramolecular synthons in crystal engineering. 4. Structure simplification and synthon interchangeability in some organic diamondoid solids

Any organic crystal structure can be simplified to a network wherein the molecules are the nodes and the supramolecular synthons are the node connections. This approach to crystal engineering is illustrated in this paper with reference to organic structures based on the diamond network. By introducing N···Br synthons into this network, a 2-fold-catenated structure is obtained for the 1:1 complex between hexamethylenetetramine (HMT) and CBr4. The use of C-H···N mediated synthons in the same network results in the 1:2 complex of 1,3,5,7-tetrabromoadamantane (AdBr4) with HMT. Further structural flexibility is achieved by the interchange of molecular and supramolecular synthons. Accordingly, the diamond-based crystal structures of tetrakis-(4-bromophenyl)methane and the 1:1 molecular complex of tetraphenylmethane and CBr4 are very similar. This near-identity arises because of the structural equivalence of the CBr4 molecular synthon and the Br4 supramolecular synthon and the ability of the CBr4 molecule to participate in Br···phenyl interactions. In general, there is much topological correspondence between organic and inorganic crystal structures, and this can be utilized in the description of organic crystal structures as networks. Such a depiction is of much practical utility and is different from Kitaigorodskii's model which distinguishes fundamentally between molecular and crystal structure. In the network model, molecular and supramolecular synthons are interchangeable within the same network structure

Molecular tapes based on C≡N···Cl interactions

Weak C≡N ··· Cl interactions may be used to design linear molecular tapes

N ··· Br mediated diamondoid network in the crystalline complex carbon tetrabromide: hexamethylenetetramine

CBr4 and hexamethylenetetramine cocrystallise to form a 1 : 1 molecular complex in which the component molecules are linked with N ··· Br interactions of 2.61(6)Å to form two non-connected but catenated diamondoid networks