Frustrated Helicity: Joining the Diverging Ends of a Stable Aromatic Amide Helix to Form a Fluxional Macrocycle

Macrocyclization of a stable two‐turn helical aromatic pentamide, that is, an object with diverging ends that are not prone to cyclization, was made possible by the transient introduction of disruptors of helicity in the form of acid‐labile dimethoxybenzyl tertiary amide substituents. After removal of the helicity disruptors, NMR, X‐ray crystallography, and computational studies show that the macrocycle possesses a strained structure that tries to gain as high a helical content as possible despite being cyclic. Two points of disruption of helicity remain, in particular a cis amide bond. This point of disruption of helicity can propagate along the cycle in a fluxional manner according to defined trajectories to produce ten degenerate conformations.     

A General Approach Towards Triazole‐Linked Adenosine Diphosphate Ribosylated Peptides and Proteins

Current methods to prepare adenosine diphosphate ribosylated (ADPr) peptides are not generally applicable due to the labile nature of this post‐translational modification and its incompatibility with strong acidic conditions used in standard solid‐phase peptide synthesis. A general strategy is presented to prepare ADPr peptide analogues based on a copper‐catalyzed click reaction between an azide‐modified peptide and an alkyne‐modified ADPr counterpart. The scope of this approach was expanded to proteins by preparing two ubiquitin ADPr analogues carrying the biological relevant α‐glycosidic linkage. Biochemical validation using Legionella effector enzyme SdeA shows that clicked ubiquitin ADPr is well‐tolerated and highlights the potential of this strategy to prepare ADPr proteins.     

Asymptotic properties of the growth curve model with covariance components

We consider a multivariate regression (growth curve) model of the form , where and are unknown scalar covariance components. In the case of replicated observations, we derive the explicit form of the locally best estimators of the covariance components under normality and asymptotic confidence ellipsoids for certain linear functions of the first order parameters {B _ij} estimating simultaneously the first and the second order parameters.     

On Conjugations for Functions with Values in Extensions of Ordered Groups

We continue our study of generalized conjugations for functions with values in the canonical enlargement of a complete ordered group, started in [10], which encompass various kinds of known conjugations and polarities. We obtain extensions, to this framework, of some results on d.c. duality theory and subdifferentials, and we give some applications to conjugations and subdifferentials for functions with values in .     

Generalized Cohomologies and the Physical Subspace of the SU(2) WZNW Model

The zero modes of the monodromy extended SU(2) WZNW model give rise to a gauge theory with a finite-dimensional state space. A generalized BRS operator A such that being the height of the current algebra representation) acts in -dimensional indefinite metric space of quantum group invariant vectors. The generalized cohomologies Ker are 1-dimensional. Their direct sum spans the physical subquotient of .     

Structure of a novel fluxional molecule: 1,2,3-trithia-[3]-ferrocenophane

The crystal and molecular structure of 1,2,3-trithia-[3]-ferrocenophane has been determined from three-dimensional X-ray data collected by counter techniques. The molecule consists of two nearly parallel, eclipsed cyclopentadienyl rings linked by an S₃ bridge. The material crystallizes in the monoclinic space groupP2₁/c with unit cell parametersa = 9·628(3),b = 9·347(4),c= 11·408(4) Å, = 96·70(3) °. The structure was solved by standard techniques and the least-squares refinement converged to a conventionalR factor of 9·6 %.We wish to thank A. Davison for the gift of the crystals and the U.S. Atomic Energy Commission for financial support.     

The x-ray crystal and molecular structure of glechomafuran

The X-ray crystal structure of glechomafuran (1,10,4,5-diepoxy-7,8-furanogermacrane), a natural product obtained from seeds ofSmyrnium olusatrum L., has been determined in order to establish the correct relative configuration of the molecule. Crystals are monoclinic, space groupP2₁ witha=6.785(4),b=12.325(9),c=16.390(6) Å,=97.89(4)°, and four molecules in the unit cell. The two epoxides are found to be ,-attached, and the associated methyl groups are positionedsyn to each other. The furan ring is essentially flat, and shows no evidence of any double bond delocalization.     

The effect of the secondary structure on dissociation of peptide radical cations: fragmentation of angiotensin III and its analogues

Fragmentation of protonated RVYIHPF and RVYIHPF-OMe and the corresponding radical cations was studied using time- and collision energy-resolved surface-induced dissociation (SID) in a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS) specially equipped to perform SID experiments. Peptide radical cations were produced by gas-phase fragmentation of Co (III)(salen)-peptide complexes. Both the energetics and the mechanisms of dissociation of even-electron and odd-electron angiotensin III ions are quite different. Protonated molecules are much more stable toward fragmentation than the corresponding radical cations. RRKM modeling of the experimental data suggests that this stability is largely attributed to differences in threshold energies for dissociation, while activation entropies are very similar. Detailed analysis of the experimental data obtained for radical cations demonstrated the presence of two distinct structures separated by a high free-energy barrier. The two families of structures were ascribed to the canonical and zwitterionic forms of the radical cations produced in our experiments.