C1q is a versatile recognition protein that binds to an amazing variety of immune and non-immune ligands and triggers activation of the classical pathway of complement. The crystal structure of the C1q globular domain responsible for its recognition properties has now been solved and refined to 1.9 Å of resolution. The structure reveals a compact, almost spherical heterotrimeric assembly held together mainly by non-polar interactions, with a Ca 2؉ ion bound at the top. The heterotrimeric assembly of the C1q globular domain appears to be a key factor of the versatile recognition properties of this protein. Plausible three-dimensional models of the C1q globular domain in complex with two of its physiological ligands, C-reactive protein and IgG, are proposed, highlighting two of the possible recognition modes of C1q. The C1q/human IgG1 model suggests a critical role for the hinge region of IgG and for the relative orientation of its Fab domain in C1q binding.Innate immunity involves a combination of cell-surface receptors and soluble proteins with the ability to recognize microbial pathogens and thereby to generate signals that both orientate subsequent adaptive immune responses and trigger effector mechanisms (1, 2). Most of these molecules are oligomeric and recognize molecular patterns on microorganisms (3). An archetypal molecule of this type is C1q, the recognition subunit of C1, the complex that triggers activation of the classical pathway of complement, a major element of innate immunity. C1q is a 460-kDa protein with the overall shape of a bouquet of flowers, comprising six heterotrimeric collagen-like triple helices that associate in their N-terminal half to form a "stalk," then diverge to form individual "stems", each terminating in a C-terminal heterotrimeric globular domain (4). It is well documented that most of the C1 complex ligands are recognized by these peripheral globular domains, or heads, of C1q, thus triggering activation of C1r and C1s, the proteases associated with C1q (5). It is also established that C1q binds to immune complexes containing IgG or IgM, but not to those having IgA, IgD, or IgE (6). The major C1q binding site on IgG has been mapped to the CH2 domain of the Fc portion of the molecule (7-9). Although C1q shows marked differences in its reactivity toward IgG subclasses, the reason for this selectivity is not known.C1q is traditionally known for its ability to bind antibodies. However, it recognizes an amazing variety of other ligands. These include certain bacteria, viruses, parasites, and mycoplasma (6, 10 -12), underscoring its role as an antibody-independent defense protein. C1q also binds to C-reactive protein (CRP) 1 when complexed with exposed phosphocholine residues on bacteria, providing a further means of host defense (13). C1q is also capable of recognizing aberrant structures from self. Thus, in addition to cellular debris and sub-cellular membranes (14), it is established that C1q binds to, and induces clearance of, apoptotic cells (15), thereby playing a major role ...

Since fullerenes are available in macroscopic quantities from fullerene soot, large efforts have been geared toward designing efficient strategies to obtain highly pure fullerenes, which can be subsequently applied in multiple research fields. Here we present a supramolecular nanocage synthesized by metal-directed self-assembly, which encapsulates fullerenes of different sizes. Direct experimental evidence is provided for the 1:1 encapsulation of C 60 , C 70 , C 76 , C 78 and C 84 , and solid state structures for the host-guest adducts with C 60 and C 70 have been obtained using X-ray synchrotron radiation. Furthermore, we design a washingbased strategy to exclusively extract pure C 60 from a solid sample of cage charged with a mixture of fullerenes. These results showcase an attractive methodology to selectively extract C 60 from fullerene mixtures, providing a platform to design tuned cages for selective extraction of higher fullerenes. The solid-phase fullerene encapsulation and liberation represent a twist in host-guest chemistry for molecular nanocage structures.

The design, performance and first results of the new macromolecular crystallography beamline BL13-XALOC at the ALBA Synchrotron are described, including new developments in optics and control.

Metal-organic polyhedra (MOPs) are ultra-small (typically 1 nm to 4 nm) porous coordination cages made from the self-assembly of metal ions and organic linkers and amenable to the chemical functionalization of its periphery; however, it has been challenging to implement post-synthetic functionalization due to their chemical instability. Herein, we report the use of coordination chemistries and covalent chemistries to post-synthetically functionalize the external surface of 2.5 nm stable Rh(II)based cuboctahedra through their Rh-Rh paddlewheel units or organic linkers, respectively. We demonstrate that 12 N-donor ligands, including amino acids, can be coordinated on the periphery of Rh-MOPs. We used this reactivity to introduce new functionalities (e.g. chirality) to the MOPs and to tune their hydrophilicity/hydrophobic character, which allowed us to modulate their solubility in diverse solvents such as dichloromethane and water. We also demonstrate that all 24 organic linkers can be postsynthetically functionalized with esters via covalent chemistry. In addition, we anticipate that these two types of post-synthetic reactions can be combined to yield doubly-functionalized Rh-MOPs, in which a total of 36 new functional molecules can be incorporated on their surfaces. Likewise, these chemistries could be synergistically combined to enable covalent functionalization of MOPs through new linkages such as ethers. We believe that both reported post-synthetic pathways can potentially be used to engineer Rh-MOPs as scaffolds for applications in delivery, sorption and catalysis.

No abstract

No abstract

Herein we describe the topological influence of zigzag ligands in the assembly of Zr(IV) metal-organic frameworks (MOFs). Through a transversal design strategy using reticular chemistry, we were able to synthesize a family of isoreticular Zr(IV)-based MOFs exhibiting the bcu-rather than the fcu-topology. Our findings underscore the value of the transversal parameter in organic ligands for dictating MOF architectures.

The transfer of nanoparticles between immiscible phases can be driven by externally-triggered changes in their surface composition. Interestingly, phase transfers can enhance the processing of nanoparticles and enable their use as vehicles for transporting molecular cargo. Herein we report extension of such phase transfers to encompass porous Metal-Organic Polyhedra (MOPs). We report that a hydroxyl-functionalized, cuboctahedral Rh(II)-based MOP can be transferred between immiscible phases by pH changes or by cation-exchange reactions. We demonstrate use of this MOP to transport coordinatively-bound cargo between immiscible layers, including into solvents in which the cargo is insoluble. As proof-of-concept that our phase transfer approach could be used in chemical separation, we employed Rh(II)-based MOPs to separate a challenging mixture of structurally similar cyclic aliphatic (tetrahydrothiophene) and aromatic (thiophene) compounds. We anticipate that transport of coordinatively-bound molecules will open new avenues for molecular separation based on the relative coordination affinity that the molecules have for the Rh(II) sites of MOP.