Crystal and molecular structure of 1,4-S,S′-bis-isothiosemicarbazidebutane dihydrobromide

The synthesis and crystal structure of 1,4-S,S-isothiosemicarbazidebutane dihydrobromide have been presented. The crystals are monoclinic:P2₁/n, a=7.9910(10),b=10.979(2),c=8.9240(10)Å, =111.450(10)°,Z=2, room temp. The structure was solved by direct methods. and refined to R=0.0297 for 846 reflections. The title compound consists of the centrosymmetric [C₆H₁₈N₆S₂]²⁺ dication and two Br^– anions. Intramolecular N–H...N and intermolecular N–H...Br hydrogen bonds stabilizetrans conformation of the thiosemicarbazide moiety.     

Polynomial symplectomorphisms

Let be the field of real or complex numbers. Let (X ²ⁿ, )be a symplectic affine space. We study the group of polynomialsymplectomorphisms of X. We show that for an arbitrary k thegroup of polynomial symplectomorphisms acts k-transitively onX. Moreover, if 2 l 2n – 2 then elements of this groupcan be characterized by polynomial automorphisms which preservethe symplectic type of all algebraic l-dimensional subvarietiesof X.     

The exact asymptotic of the collision time tail distribution for independent Brownian particles with different drifts

In this note we consider the time of the collision τ for n independent Brownian motions X ¹ _t ,...,X _t ⁿ with drifts a ₁,...,a _n , each starting from x = (x ₁,...,x _n ), where x ₁ < ... < x _n . We show the exact asymptotics of ${\mathbb{P}}_{\bf x}(\tau > t) = Ch({\bf x})t^{-\alpha} {\rm e}^{-\gamma t}(1 + o(1))$ as t → ∞ and identify C, h(x), α, γ in terms of the drifts.     

Structural features of the Cu(II) complex with the rat Abeta(1-28) fragment

The interaction between Cu(II) and the rat amyloid beta (1-28) fragment in micellar solutions at pH 7.5 was investigated by CD and NMR spectroscopy; the proton-copper distances were used in restrained molecular dynamics simulations to obtain a structural model of the Cu(II) complex.     

Zn(II) ions bind very efficiently to tandem repeat region of "prion related protein" (PrP-rel-2) of zebra-fish. MS and potentiometric evidence

Multi-histidine peptide fragments of zebra-fish prion protein are effective ligands for Zn(II) ions. Moreover the formation of a dinuclear complex species with a longer peptide can suggest the existence of the cooperative effect in the metal ion binding.     

Enantioselective synthesis of (+)-trypargine and (+)-crispine E

Asymmetric transfer hydrogenation was used as a key step in the synthesis of two guanidine-derived alkaloids (+)-trypargine and (+)-crispine E. The enantiomeric compositions of key intermediates were established on the basis of ¹H NMR spectra with chiral solvating agents. The absolute stereochemistry was proven by X-ray crystallography.     

Competition between the albumin and three histidine fragment of amyloid precursor protein sites to bind Cu(II)

The aim of this work was to check experimentally the relationship between the five-nitrogen donor system {3 × N_imid, 2 × N⁻} seen e.g. in the peptide fragments of the cysteine-rich amyloid precursor protein (APP) region and the albumin-like {NH₂, 2 × N⁻, N_imid} coordination site. The protected and unprotected octadecapeptides DAHQERMDVSETHLHWHT and Ac-DAHQERMDVSETHLHWHT-NH₂ were synthesized and potentiometric and spectroscopic studies were performed. A comparison of both metal-binding sites that occur in both peptides clearly shows that in the unprotected ligand albumin-like binding is much more efficient than the three His site, although around pH 5 both sites have a comparable ability to bind the Cu(II) ion. However, a comparison of the protected and unprotected peptides with their metal binding sites clearly shows that the three His site is very efficient in binding Cu(II) although less effective than the albumin-like motif.     

"Chemical ligation": a versatile method for nucleoside modification with boron clusters

A general approach to the synthesis of nucleoside conjugates containing carborane and metallocarborane complexes, based on Huisgen 1,3-dipolar cycloaddition ("chemical ligation"), is described. Boron-cluster-donors bearing terminal azide or ethynyl groups were prepared in the ring-opening reaction of dioxane-boron-cluster adducts and an azide anion or suitable alkynol-derived alcoholate nucleophile. Analogous derivatives bearing terminal sulfhydryl groups were also prepared. Nucleosides with various spacers containing terminal azide or ethynyl groups, located within nucleobases or sugar residues, were used as boron-cluster acceptors. The proposed methodology provides a convenient way to synthesize libraries of boron-cluster-modified nucleosides for various applications.     

Universal Cycle Packings and Coverings for <Emphasis Type="Italic">k</Emphasis>-Subsets of an <Emphasis Type="Italic">n</Emphasis>-Set

A cyclic sequence of elements of [n] is an (n, k)-Ucycle packing (respectively, (n, k)-Ucycle covering) if every k-subset of [n] appears in this sequence at most once (resp. at least once) as a subsequence of consecutive terms. Let \(p_{n,k}\) be the length of a longest (n, k)-Ucycle packing and \(c_{n,k}\) the length of a shortest (n, k)-Ucycle covering. We show that, for a fixed \(k,p_{n,k}={n\atopwithdelims ()k}-O(n^{\lfloor k/2\rfloor })\). Moreover, when k is not fixed, we prove that if \(k=k(n)\le n^{\alpha }\), where \(0<\alpha <1/3\), then \(p_{n,k}={n\atopwithdelims ()k}-o({n\atopwithdelims ()k}^\beta )\) and \(c_{n,k}={n\atopwithdelims ()k}+o({n\atopwithdelims ()k}^\beta )\), for some \(\beta <1\). Finally, we show that if \(k=o(n)\), then \(p_{n,k}={n\atopwithdelims ()k}(1-o(1))\).