A bronze matryoshka: the discrete intermetalloid cluster [Sn@Cu12@Sn20](12-) in the ternary phases A12Cu12Sn21 (A = Na, K)

The synthesis and crystal structure of the first ternary A-Cu-Sn intermetallic phases for the heavier alkali metals A = Na to Cs is reported. The title compounds A(12)Cu(12)Sn(21) show discrete 33-atom intermetalloid Cu-Sn clusters {Sn@Cu(12)@Sn(20)}, which are composed of {Sn(20)} pentagonal dodecahedra surrounding {Cu(12)} icosahedra with single Sn atoms at the center. Na(12)Cu(12)Sn(21) and K(12)Cu(12)Sn(21) were characterized by single-crystal XRD studies, and the successful synthesis of analogous A-Cu-Sn compounds with A = Rb and Cs is deduced from powder XRD data. The isotypic A(12)Cu(12)Sn(21) phases crystallize in the cubic space group Pn ?3m (No. 224), with the Cu-Sn clusters adopting a face centered cubic arrangement. A formal charge of 12- can be assigned to the {Sn@Cu(12)@Sn(20)} cluster unit, and the interpretation of the title compounds as salt-like intermetallic phases featuring discrete anionic intermetalloid [Sn@Cu(12)@Sn(20)](12-) clusters separated by alkali metal cations is supported by electronic structure calculations. For both Na(12)Cu(12)Sn(21) and K(12)Cu(12)Sn(21), DFT band structure calculations (TB-LMTO-ASA) reveal a band gap. The discrete [Sn@Cu(12)@Sn(20)](12-) cluster is analyzed in consideration of the molecular orbitals obtained from hybrid DFT calculations (Gaussian 09) for the cluster anion. The [Sn@Cu(12)@Sn(20)](12-) cluster MOs can be classified with labels indicating the numbers of radial and angular nodes, in the style of spherical shell models of cluster bonding.     

Total Synthesis of Berkelic Acid

A productive total synthesis of both enantiomers of berkelic acid ( 1 ) is outlined that takes the structure revision of this bioactive fungal metabolite previously proposed by our group into account. The successful route relies on a fully optimized triple‐deprotection/1,4‐addition/spiroacetalization cascade reaction sequence, which delivers the tetracyclic core 32 of the target as a single isomer in excellent yield. The required cyclization precursor 31 is assembled from the polysubstituted benzaldehyde derivative 20 and methyl ketone 25 by an aldol condensation, in which the acetyl residue in 20 transforms from a passive protecting group into an active participant. Access to fragment 25 takes advantage of the Collum–Godenschwager variant of the ester enolate Claisen rearrangement, which clearly surpasses the classical Ireland–Claisen procedure in terms of diastereoselectivity. Although it is possible to elaborate 32 into the target without any additional manipulations of protecting groups, a short detour consisting in the conversion of the phenolic ? OH into the corresponding TBS‐ether is beneficial. It tempers the sensitivity of the compound toward oxidation and hence improves the efficiency and reliability of the final stages. Orthogonal ester groups for the benzoate and the aliphatic carboxylate terminus of the side chain secure an efficient liberation of free berkelic acid in the final step of the route.     

Gas chromatography-olfactometry analysis of the volatile compounds of two commercial Irish beef meats

The volatile flavour compounds of two commercial Irish beef meats (labelled as conventional and organic) were evaluated by gas chromatography-olfactometry and were identified by gas chromatography-mass spectrometry. The volatile compounds were isolated in a model mouth system. Gas chromatography-olfactometry was performed by a group of eight assessors using the detection frequency methodology. The odours of the detected compounds were described as well. Eighty-one volatile compounds were identified, 11 compounds of which possessed odour activity in the first beef sample and 14 of which in the second meat sample. Ten volatile flavour compounds were common to both: methanethiol, dimethyl sulphide, 2-butanone, ethyl acetate, 2- and 3-methylbutanal, an unknown compound, 2-octanone, decanal and benzothiazole. Two unknown compounds were only detected in the first sample while 2,3-pentanedione, 4-methyl-3-penten-2-one, 2-heptanone, dimethyl trisulphide and nonanal were only perceived in the second beef. Significant differences in terms of detection frequency, odour characteristics and in nature of the volatile flavour compounds were emphasised between the two samples.     

Hexamerization of the bacteriophage T4 capsid protein gp23 and its W13V mutant studied by time-resolved tryptophan fluorescence

The bacteriophage T4 capsid protein gp23 was studied using time-resolved and steady-state fluorescence of the intrinsic protein fluorophore tryptophan. In-vitro gp23 consists mostly of monomers at low temperature but forms hexamers at room temperature. To extend our knowledge of the structure and hexamerization characteristics of gp23, the temperature-dependent fluorescence properties of a tryptophan mutant (W13V) were compared to those of wild-type gp23. The W13V mutation is located in the N-terminal part of the protein, which is cleaved off after prohead formation in the live bacteriophage. Results show that W13 plays a role in the hexamerization process but is not needed to stabilize the hexamer once it is formed. Furthermore, besides the monomer-to-hexamer temperature transition (15-23 degrees C and 12-43 degrees C for wild-type and W13V gp23, respectively), we were able to observe denaturation of the N-terminus in hexameric wild-type gp23 around 40 degrees C. In addition, with the aid of a recently published homology model of gp23, the lifetimes obtained from time-resolved fluorescence measurements could tentatively be assigned to specific tryptophan residues.     

Polycondensations of Substituted Maleic Anhydrides and 1,6-Hexanediol Catalyzed by Metal Triflates

Polycondensations of methylmaleic anhydride (citraconic anhydride, CiAh), bromomaleic anhydride (BMaAh), and dichloromaleic anhydride (DCMaAh) with 1,6-hexanediol were conducted in bulk. For polycondensations of CiAh, the triflates of aluminum, bismuth, lanthanum, magnesium, samarium, and scandium were used as catalysts and the best results were obtained with Bismuth triflate. MALDI-TOF mass spectra indicated that the chain growth was limited by cyclization and incomplete conversion, but temperatures above 100°C were not advantageous due to side reactions. Bismuth and samarium triflate catalyzed polycondfensations of BMaAh and DCMaAh were less successful than polycondensations of CiAh. For polycondensations of CiAh, BMaAh, and DCMaAh, only a low extent of isomerization to trans isomers (1–3%) was observed at 100°C, but considerably higher extent at 140°C.     

Synthesis of rhamnosylated diosgenyl glucosides as mimetics of cytostatic steroidal saponins from Ornithogalum saindersiae and Galtonia candicans

The synthesis of mimetic of the steroid saponins 1 and 2 was investigated. As a substitute for the complex 22-homo-23-nor-steroid moieties A and B in 1 and 2 diosgenin was introduced. The silyl protected thioorthoester 20 was successfully employed for glucosylation. After selective 2--deacetylation, the glucosylated diosgenyl acceptor 23 was rhamnosylated. The 4---methoxybenzoylated donor 12 gave only minor yields. By using the tri--benzoyl protected donor 15 the [small alpha]--rhamnopyranosyl-(1[rightward arrow]2)-[small beta]--glucopyranosyl-(1[rightward arrow]3[small beta])-diosgenin derivative 25 was obtained.