D. V. Soldatov

Unusual sculpting of dipeptide particles by ultrasound induces gelation.

A readily synthesized dipeptide shows unprecedented gelation behavior when dispersed and submitted to ultrasound in nonsolvents. SEM and FFEM revealed spectacular shape changes from a sheet-like material into a highly interconnected fiber network and ribbons while the dipeptide maintains an anti conformation inside β-sheets at the molecular scale.

Novel structural features in Candida albicans hyphal glucan provide a basis for differential innate immune recognition of hyphae versus yeast

Background: The human innate immune system can discriminate between Candida albicans yeast and hyphal forms. Results: C. albicans hyphae possess glucan structures that are unique to the hyphae and are not found in yeast. Conclusion: Hyphal glucan elicits robust immune responses. Significance: These data provide a structural basis for differential immune recognition of C. albicans yeast versus hyphae. The innate immune system differentially recognizes Candida albicans yeast and hyphae. It is not clear how the innate immune system effectively discriminates between yeast and hyphal forms of C. albicans. Glucans are major components of the fungal cell wall and key fungal pathogen-associated molecular patterns. C. albicans yeast glucan has been characterized; however, little is known about glucan structure in C. albicans hyphae. Using an extraction procedure that minimizes degradation of the native structure, we extracted glucans from C. albicans hyphal cell walls. 1H NMR data analysis revealed that, when compared with reference (1→3,1→6) β-linked glucans and C. albicans yeast glucan, hyphal glucan has a unique cyclical or “closed chain” structure that is not found in yeast glucan. GC/MS analyses showed a high abundance of 3- and 6-linked glucose units when compared with yeast β-glucan. In addition to the expected (1→3), (1→6), and 3,6 linkages, we also identified a 2,3 linkage that has not been reported previously in C. albicans. Hyphal glucan induced robust immune responses in human peripheral blood mononuclear cells and macrophages via a Dectin-1-dependent mechanism. In contrast, C. albicans yeast glucan was a much less potent stimulus. We also demonstrated the capacity of C. albicans hyphal glucan, but not yeast glucan, to induce IL-1β processing and secretion. This finding provides important evidence for understanding the immune discrimination between colonization and invasion at the mucosal level. When taken together, these data provide a structural basis for differential innate immune recognition of C. albicans yeast versus hyphae.

Xe NMR lineshapes in channels of peptide molecular crystals.

To further an understanding of the nature of information available from Xe chemical shifts in cavities in biological systems, it would be advantageous to start with Xe in regular nanochannels that have well known ordered structures built from amino acid units. In this paper, we report the experimental observation of Xe NMR lineshapes in peptide channels, specifically the self-assembled nanochannels of the dipeptide l-Val-l-Ala and its retroanalog l-Ala-l-Val in the crystalline state. We carry out grand canonical Monte Carlo simulations of Xe in these channels to provide a physical understanding of the observed Xe lineshapes in these two systems.

Impact on molecular organization of amylopectin in starch granules upon annealing

This study investigated the influence of the internal structure of amylopectin on annealing (3h, 24h) of starches from four different types of amylopectin (Bertoft, Koch, & Aman, 2012; Bertoft, Piyachomkwan, Chatakanonda, & Sriroth, 2008). Regardless of the starch source and incubation time, annealing significantly increased the onset gelatinization temperature (To) and narrowed and deepened the amylopectin endotherm. However, the extent of the change in the melting temperature (Tm) and the enthalpy of gelatinization (ΔH) differed among the types. In terms of the To and Tm, starches from type 1 (oat, rye, barley, and waxy barley) showed the most significant response to annealing. The Tm of starches belonging to type 2 (waxy maize, rice, waxy rice, and sago) remained unchanged after 3h of annealing. Type 1 and type 2 starches with the lowest gelatinization temperatures showed the greatest increase in melting temperature after annealing. However, type 3 (tapioca, mung bean, and arrowroot) and type 4 (potato, waxy potato, canna, and yam) starches were not in line with these observations. Instead, starches from type 3 and type 4 showed a pronounced increase in the ΔH. The inter-block chain length (IB-CL) (distance between tightly branched units within a cluster) correlated positively (r=0.93, p<0.01) with the change in enthalpy after 24h of annealing. These data indicate that a short IB-CL affects the optimum registration of double helices within the crystalline lamellae. The relationship between the gelatinization parameters before and after annealing suggests that type 1 and 2 starches might possess a high number of unpacked double helices (type 1>type 2) compared to other types. Longer IB-CLs, which facilitate the parallel packing of splayed double helices, and the lengthening of double helices likely increased the ΔH in type 3 and type 4 starches. It is concluded that annealing can be used as a probe for visualizing the organization of glucan chains (alignment of double helices/degree of perfection) within crystalline lamellae.

CONTACT STABILIZATION OF HOST COMPLEX MOLECULES DURING CLATHRATE FORMATION: THE PYRIDINE-ZINC NITRATE AND THE PYRIDINE-CADMIUM NITRATE SYSTEMS

Abstract Clathrate formation ranges of the phase diagrams of two binary systems Py-Zn(NO3)2 and Py-Cd(NO3)2 (Py = pyridine) were studied. A clathrate of composition [MPy4(NO3)2]·2Py (M = Zn, Cd) was observed in each of the systems. The space group Ccca (orthorhombic system) and the parameters of the unit cells of both clathrates were determined by X-ray analysis of their single crystals. The data obtained show them to be isostructural with the clathrate [NiPy4(NO3)2]·2Py whose structure is known and suggest the actual presence of the host molecules trans-[MPy4(NO3)2] (M = Zn,Cd) inside the clathrate phases. Host complexes do not form as separate compounds but can only arise in clathrate phases due to contact stabilization by the guest molecules. Both Zn- and Cd-clathrates are of constant composition and melt incongruently at 62.3(6) and 106.0(5)°C, respectively, yielding the complexes [ZnPy3(NO3)2] and [CdPy3(NO3)2], these melting congruently at 131.4(5) and 169.5(5)°C, respectively. During thermal decomp...

Modified Metal Dibenzoylmethanates and their Clathrates. Part I. Clathration Ability of dipyridinebis(dibenzoylmethanato)nickel(II), a Novel Metal-Complex Host [1]

Abstract The title complex, [NiPy2(DBM)2] (DBM = C6H5CO CHCOC6H5, dibenzoylmethanate), entraps solvent molecules upon crystallization. Six clathrates of four structural types have been studied by single-crystal X-ray diffraction (guest, host:guest molar ratio, crystal system, space group, formula units per unit cell): (I) carbon tetrachloride, 1:2, orthorhombic, P212121, Z = 4; (II) pyridine, 1:2, monoclinic, C2/c, Z = 8; (III) benzene, 1:1, monoclinic, C2/c, Z = 8; (IV) chlorobenzene, 1:1, monoclinic, C2/c, Z = 8; (V) chloroform, 1:2, monoclinic, P21/n, Z = 2; (VI) tetra-hydrofuran, 1:2, monoclinic, P21/n, Z = 2. A non-clathrate form of the complex (VII) was obtained from acetone; it is triclinic, P1, Z = 1. The compounds I-VII are consistent with van der Waals type of packing. The complex unit is formed by octahedral coordination to nickel of four oxygen and two nitrogen atoms from two chelate DBM and two pyridine molecules, respectively. In all seven compounds the host complex is trans-configured. Comp...

4-Vinylpyridine-Modified Nickel and Cobalt Dibenzoylmethanates as New Hosts: Inclusions with Carbon Tetrachloride and Chlorobenzene

Abstract Bis(4-vinylpyridine)bis(dibenzoylmethanato)metal(II), [M(ViPy)2(DBM)2] (M = Ni(II), Co(II); ViPy = 4-Vinylpyridine; DBM = C6H5COCHCOC6H5 −, dibenzoylmethanate) is a new metal-complex host. Its inclusions with carbon tetrachloride (host:guest = 1:2; triclinic, P 1, Z = 1) and chlorobenzene (host:guest = 1:1; monoclinic, P2 1 /c, Z = 4) are consistent with the van der Waals packing of neutral complex (host) and solvent (guest) molecules. In the host unit, four oxygens from two chelate DBM-units provide a square-planar environment around the metal center that is extended to octahedral coordination by two apical nitrogens from two vinylpyridine moieties in the trans-position. In the carbon tetrachloride inclusions, the host traps two guest molecules in large prolate spheroidal cavities. In the chlorobenzene inclusions, guest species are located inside 8-shaped serpentine channels along the y-axis. The nickel and cobalt versions of the inclusion compounds were found to be very similar.

Polypseudorotaxane architecture of poly-bis[4-(N-benzyl- pyridinium)]piperazine-hexa-thiocyanato-di-cadmium(II) with 2-D honeycomb-like [Cd(SCN)3]nn− anionic polymeric framework

An unusual, honeycomb-like cadmium-tri-thiocyanate polymeric framework was found in the studied hybrid material of general formula (L2+)n[Cd(SCN)3]2n2n− (3), where L2+ is bis[4-(N-benzylpyridinium)]piperazine dication. The perforated coordination net forms due to a template effect of the organic dications which reside in the holes penetrating the net in a polyrotaxane-like manner. The salt (L2+)(SCN)2·2H2O (4) was studied for comparison.

Vapour pressure of 4-methylpyridine (MePy) over [Ni(MePy)4(NCS)2]·y(MePy) and [Cu(MePy)4(NCS)2]·2/3(MePy) clathrates during their dissociation

Strain measurement and quasiequilibrium thermogravimetry were used to study the dissociation processes of two clathrates, [Ni(MePy)4(NCS)2]·(MePy) and [Cu(MePy)4(NCS)2]·2/3(MePy), accompanied by the liberation of MePy into the gaseous phase. In the Ni clathrate dissociation process in the temperature range 298–368 K the liberated MePy was redistributed between the solid clathrate and gaseous phases; the MePy vapour pressure over the clathrate is a function of temperature and the guest contenty, which agrees with the presence in the MePy-[Ni(MePy)4(NCS)2] system of a wide range of β-clathrate solutions, [Ni(MePy)4(NCS)2]·y(MePy). The same methods used to study the Cu clathrate dissociation resulted in conclusions different from those obtained for the dissociation process of the above clathrate: the process is described by the equation [Cu(MePy)4(NCS)2]·2/3(MePy)solid =[Cu(MePy)2(NCS)2]solid+22/3(MePy)gas; the temperature dependence of the Mepy vapour pressure over the solid sample does not depend on its composition, which points to the absence from the system of solid solutions based on the clathrate. Standard changes of the enthalpy, entropy, and isobaric-isothermal reaction potential for the temperature range 292–325 K are equal to 178.6±1.7 kJ (mole of clathrate)−1, 463±5.6 J (mole of clathrate)−1 K−1, and 40.4±2.4 kJ (mole of clathrate)−1, respectively.

High-Spin Ribbons and Antiferromagnetic Ordering of a Mn II - Biradical-Mn II Complex

A binuclear metal coordination complex of the first thiazyl-based biradical ligand 1 is reported (1 = 4,6-bis(1,2,3,5-dithiadiazolyl)pyrimidine; hfac =1,1,1,5,5,5,-hexafluoroacetylacetonato-). The Mn(hfac)2-biradical-Mn(hfac)2 complex 2 is a rare example of a discrete, molecular species employing a neutral bridging biradical ligand. It is soluble in common organic solvents and can be easily sublimed as a crystalline solid. Complex 2 has a spin ground state of S(T) = 4 resulting from antiferromagnetic coupling between the S(birad) = 1 biradical bridging ligand and two S(Mn) = 5/2 Mn(II) ions. Electrostatic contacts between atoms with large spin density promote a ferromagnetic arrangement of the moments of neighboring complexes in ribbon-like arrays. Weak antiferromagnetic coupling between these high-spin ribbons stabilizes an ordered antiferromagnetic ground state below 4.5 K. This is an unusual example of magnetic ordering in a molecular metal-radical complex, wherein the electrostatic contacts that direct the crystal packing are also responsible for providing an efficient exchange coupling pathway between molecules.