Building Block Units Research Articles

Catalytic deNO x properties of novel vanadium oxide based open-framework materials

The deNO x catalytic properties of a new class of open-framework structure materials, Li6[Mn3(H2O)12V18O42(XO4)] · 24H2O (X = V, S) (1), [Fe3(H2O)12 V18O42(XO4)] · 24H2O (X = V, S) (2), [Co3(H2O)12V18O42(XO4)] · 24H2O (X = V, S) (3), and Li6[Ni 3 II (H2O)12V 16 VI V 2 V O42(SO4)] · 24H2O (4), have been studied. The crystal structures of these novel systems consist of three-dimensional arrays of vanadium oxide clusters {V18O42(XO4)} , as building block units, interlinked by {–O–M–O–} (M = Mn, 1; M = Fe, 2; M = Co, 3; M = Ni, 4) bridges. Their open-framework structures contain cavities, similar to those observed in conventional zeolites, which are occupied by exchangeable cations and/or readily removable water of hydration. The catalysts derived from these materials were tested for the selective catalytic reduction (SCR) of nitrogen oxides {NO x } into N2 using a hydrocarbon, propylene, as the reducing agent. The catalysts were ineffective under lean burn conditions. However, the new catalysts, especially the one derived from the cobalt derivative (3), showed intriguing deNO x activity under rich conditions. They remove up to ~ 99% of the toxic NO x emissions in 1.5% O2 with 100% selectivity to N2. The active phase of the catalysts exhibit good stability, can be readily regenerated, and are selective to the desired product-N2. The catalytic reactions occur at moderately low temperatures (400–500 °C). The catalysts were characterized by FT-IR, temperature programmed reactions (TPR and TPO), SEM, BET surface area measurements, elemental analysis, and X-ray diffraction (XRD). Additional advanced techniques were used to further characterize the catalyst phases that showed most promising deNO x activity and increased tolerance to oxygen.

A high-temperature structure for Ta 2O 5 with modulations by TiO 2 substitution

Solid solutions in the series (1− x)Ta 2O 5− xTiO 2 with x = 0.0 – 0.1 were prepared by high-temperature ceramic processing methods, and the crystal structure was determined at room temperature by transmission electron microscopy, electron diffraction and high-resolution lattice imaging. A structural model is proposed for the oxygen-deficient tantalum oxide (Ta 2O 5) phase with high TiO 2 doping level ( x = 0.08 ). The model is based on edge sharing of an oxygen octahedron–hexagonal bi-pyramid–octahedron molecular building block unit that repeats four times per unit cell. Electron diffraction reveals a monoclinic distortion from a pseudo-tetragonal model structure that is modulated primarily along 〈110〉. The modulation length varies with increasing TiO 2 content. Furthermore, by quantitative HREM analysis and matching of lattice images by simulation, it is shown that the modulation is associated with small ionic displacements in specific lattice planes that coincide with Ta ions in the model structure coordinated by oxygen hexagonal bi-pyramids. Based on this evidence, it is suggested that the modulation comes from a replacement of Ta with Ti ions, and the loss of inversion symmetry in the modulated structure is related to the dielectric properties of the material.

Abiotic Hydrolysis of Some Poly-D-glucaramides and Subsequent Microbial Utilization/Degradation

Carbohydrate acid amides, diamides and polyamides have been proposed to be utilized as nitrogen plant fertilizers or fertilizer components, and experiments with Brassica rapa demonstrated a positive biological response when these compounds were used as the only source of fixed nitrogen for plant growth. The present study was carried out with the aim of elucidating the mechanism of degradation of these polymers in both soil/compost and in liquid media and the role of microorganisms in this process. The results obtained suggest that a major route of degradation of polyglucaramides in the environment is their abiotic hydrolysis/release of the diacid and diamine building block units of these polymers, which are then utilized for growth by microorganisms. In cell-free crude extracts from enrichment cultures obtained with different poly-D-glucaramides, no enzyme activities catalyzing the release of diamines from these compounds were detected.

Structural, Magnetic, and Spectroscopic Comparative Studies on Four New Derivatives of DIMMAL (2-Di1H-2-imidazolylmethylmalonate): A Novel Generator of Multidimensional Networks

This paper reports the synthesis, structure solution, and magnetic characterization of four new DIMMAL-containing compounds (H2DIMMAL = 2-di1H-2-imidazolylmethylmalonic acid), H2DIMMAL x H2O (1), Na2(DIMMAL) x 5H2O (2), [Cu(HDIMMAL)2] (3), and [Cu2(DIMMAL)2(H2O)2] x 2H2O (4). Compound 1, containing two carboxylates and two protonated imidazole rings, adopts the dizwitterion configuration. These monohydrate MBBs pack together into a 3D array driven, as in the other three cases herein reported, by a combination of multiple-path H-bonds and aromatic-aromatic interactions. Compound 2 consists of centrosymmetric Na+ tetramers in which four NaO6 distorted octahedra are interconnected by carboxylate and water bridges. Compound 3 consists of mononuclear [Cu(HDIMMAL)2] units in which HDIMMAL- acts as a tridentate ligand through two imidazole N atoms and the deprotonated O from a carboxylate. Compound 4 consists of centrosymmetric cyclic dinuclear [Cu2(DIMMAL)2(H2O)2] x 2H2O units involving propionate-arm bridges. The building-block units described above, in each case, are interconnected into 3D networks by multiple H-bonding paths and aromatic-aromatic interactions. The EPR spectra are indicative of an essentially d(x2-y2) ground state for the copper(II) ions in 3 and 4 (CuN4O2 and CuN2O2O' chromophores, respectively). Magnetic susceptibility measurements in the range of 1.8-200 K for compound 4 show weak antiferromagnetic exchange between the copper(II) ions (2J = -1.6(1) cm(-1)). The effectiveness of the propionate-arm bridges, involving C-C sigma bonds, in propagating magnetic exchange between the copper(II) ions is discussed.

Synthesis, characterization and crystal structure of a Er III mono-substituted [α-SiW 11O 39] 8− polyoxotungstate containing one-dimensional zigzag chainlike structure

A Keggin-type monovacant silicotungstate derivative K 2H 2{Er(H 2O) 6[Er(H 2O) 3SiW 11O 39]} 2·22H 2O ( 1) has been synthesized by reaction of the polyoxometalate α-K 8SiW 11O 39·13H 2O ligands with erbium III cations in the aqueous solution under moderate condition, and characterized by elemental analyses, IR, UV-visible spectroscopy and X-ray single-crystal diffraction. Crystal data: K 2H 2{Er(H 2O) 6[Er(H 2O) 3SiW 11O 39]} 2·22H 2O, triclinic, P−1, a=12.463(3), b=14.849(3), c=16.772(3) Å, α=95.37(3), β=94.65(3), γ=106.76°, Z=1, R 1=0.0638, wR 2=0.1140. X-ray single-crystal diffraction reveals that the polyanion of crystalline 1 is made up of two crystallographically identical polyoxometalate-based {Er(H 2O) 6[Er(H 2O) 3SiW 11O 39]} 2− building block units, which are linked through erbium centers by means of the terminal oxygen atoms from the backbone of precursor [α-SiW 11O 39] 8−, generating a novel 1D chain-like structure. Variable-temperature magnetic susceptibility study indicates the presence of the relatively strong spin-orbital coupling in compound 1 in the wide temperature region of 70–300 K.

Synthesis, crystal structure and characterization of a praseodymiumIII-substituted silicotungstate with a novel 1D chain connection motif

The reaction of the mono-lacunary silicotungstate ligand α-K8SiW11O39·13H2O with praseodymiumIII cation results in a new Keggin-type derivative K3[(Pr(H2O)4SiW11O39)(NaPr2(H2O)12)(Pr(H2O)4SiW11O39)]·13.5H2O (1), whose polyanion consists of two crystallographically distinct [Pr(H2O)4SiW11O39]5− building block units and one [NaPr2(H2O)12]7+ subunit, which are connected by alternating praseodymium and sodium centers via the terminal and bridging oxygen atoms from the precursor [α-SiW11O39]8− to construct a 1D infinitely chainlike structure.

CDF run IIb silicon detector: electrical performance and deadtime-less operation

The main building block and readout unit of the planned CDF Run IIb silicon detector is a stave, a highly integrated mechanical, thermal, and electrical structure. One of its characteristic features is a copper-on-Kapton flexible cable for power, high voltage, data transmission, and control signals that is placed directly below the silicon microstrip sensors. The dense packaging makes deadtime-less operation of the stave a challenge since coupling of bus cable activity into the silicon sensors must be suppressed efficiently. The stave design features relevant for deadtime-less operation are discussed. The electrical performance achieved with stave prototypes is presented.

Survival Strategy of Photosynthetic Organisms. 2. Experimental Proof of the Size Variability of the Unit Building Block of Light-Harvesting Oligomeric Antenna

The present series of papers is part of an integrated research program to understand the effective functional strategy of native light-harvesting molecular antennae in photosynthetic organisms. This work tackles the problem of the structural optimization of light-harvesting antennae of variable size. In vivo, the size responds to the illumination intensity, thus implying more sophisticated optimization strategies, since larger antenna size demands finer structural tuning. Earlier modeling experiments showed that the aggregation of the antenna pigments, apart from being itself a universal structural factor of functional antenna optimization with any (!) spatial lattice of light-harvesting molecules, determines the antenna performance provided that the degree of aggregation varies: the larger the unit building block, the higher the efficacy of the whole structure. It means that altering the degree of pigment aggregation in response to the antenna size is biologically expedient. In the case of the oligomeric chlorosomal antenna of green bacteria, the strategy of variable antenna structural optimization in response to the illumination intensity was demonstrated to take place in vivo and facilitate high antenna performance regardless of its size, thus allowing bacteria to survive in diverse illumination conditions.

The Model of Pigment Aggregation in the Chlorosomal Antenna of the Green Bacterium Chloroflexus aurantiacus

Independent experimental and theoretical evaluation was performed for the adequacy of our previously proposed general molecular model of the structural organization of light-harvesting pigments in chlorosomal bacteriochlorophyll (BChl) с/d/e-containing superantennae of different green bacteria. Measurement of the temperature dependence of steady-state fluorescence spectra of BChl c was accomplished in intact cells of a photosynthetic green bacterium Chloroflexus aurantiacus; this allows in vivodetermination of the structure of exciton levels of BChl c oligomers in this natural antenna. Experimental data confirm our model of organization of oligomeric pigments in chlorosomal BChl c antenna of green bacterium Chloroflexus aurantiacus. This model implies that the unit building block of the antenna is a cylindrical assembly containing six excitonically coupled linear pigment chains, whose exciton structure with intense upper levels provides for the optimal spectral properties of the light-harvesting antenna.

Quantitative self-assembly of a hetero-bimetallic trinuclear square-shaped macrocycle

A new hetero-bimetallic trinuclear macrocycle has been self-assembled quantitatively, in one step, by means of axial Zn II–N and 90° angular Pt II–N binding, with the metallated angular bisporphyrin, the cis-square-planar platinum bistriflate complex and the linear 4,4 ′-bipyridine, as building block units.

Formation, growth mechanism and packing sequences of binary alloy cluster anions from laser ablation of mixtures of lead and transition metals.

By using laser ablation of the mixtures of a transition metal (M: Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Pd, Ag) plus lead, M/Pb binary cluster anions were observed except for Zn, and the number of transition metal atoms contained in the binary clusters is at most 4. This behavior is different from that reported previously for M/Ge binary clusters. The experiments indicate that it is also very difficult to form Al/Pb clusters. The distribution patterns of M/Pb binary alloy cluster anions are remarkably similar to those of pure Pb clusters, consistent with a formation mechanism in which transition metal atoms are sequentially attached to [M(x-1)Pb(y)](-) clusters and thus form [M(x)Pb(y)](-) clusters by a simple condensation process. As the number of transition metal atoms increases, the intensities of binary clusters gradually decrease. It is proposed that [MPb(4)](-) and [MPb(5)](-) cluster anions might be the unit building blocks of M/Pb binary cluster anions, and the layer packing sequences for magic clusters are predicted on this basis. The [M(x)Pb(y)](-) binary clusters containing 13 atoms (x + y = 13; x not equal 0) are proposed to have an icosahedral structure.

Asymmetric Synthesis of (S)‐4‐Oxopipecolic Acid by a 3+3 Atom‐Unit Assembly Strategy

Abstract(S)‐4‐Oxopipecolic acid has been prepared in enantiomerically pure form from two readily accessible starting materials, (R)‐N‐(cyanomethyl)‐4‐phenyloxazolidine (2) and 2‐(methoxymethoxy)allyl chloride, (3, MOM‐allyl chloride). This strategy exploits the complementary electrophile/nucleophile reactivity at each end of this pair of 3‐atom unit building blocks. Thus, alkylation of the anion of 2 with 3 (creation of the piperidine C‐2−C‐3 bond) followed by Lewis acid induced cyclisation (creation of the C‐5−C‐6 bond), leads principally to a bicyclic intermediate 5 which incorporates a protected form of the title compound. Subsequent chemical transformations lead to the target molecule in an overall yield of 20% for the five‐step sequence. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Pure Photoorientation of Azo Dye in Polyurethanes and Quantification of Orientation of Spectrally Overlapping Isomers

We show that the occurrence of pure photoorientation by photoisomerization of azo dye in polymers is influenced by the polymer molecular structure, as well as by the photoisomerization quantum yields and the cis → trans thermal isomerization rate. These findings are rationalized by the study of the photoorientation of azo dye in a series of polyurethane polymers, each with distinct differences in the molecular structure of the unit building blocks. It will be shown that the thermally activated chromophore movement in these polymers is dictated by the polymer backbone. We also show how to quantify coupled photoisomerization and photoorientation of spectrally overlapping isomers in polymers, and we determine the photoisomerization quantum yields and the photoorientation movement of the chromophores in azo-polyurethanes.

A structure for the yeast prohibitin complex: Structure prediction and evidence from chemical crosslinking and mass spectrometry.

The mitochondrial prohibitin complex consists of two subunits (PHB1 of 32 kD and PHB2 of 34 kD), assembled into a membrane-associated supercomplex of approximately 1 MD. A chaperone-like function in holding and assembling newly synthesized mitochondrial polypeptide chains has been proposed. To further elucidate the function of this complex, structural information is necessary. In this study we use chemical crosslinking, connecting lysine side chains, which are well scattered along the sequence. Crosslinked peptides from protease digested prohibitin complexes were identified with mass spectrometry. From these results, spatial restraints for possible protein conformation were obtained. Many interaction sites between PHB1 and PHB2 were found, whereas no homodimeric interactions were observed. Secondary and tertiary structural predictions were made using several algorithms and the models best fitting the spatial restraints were selected for further evaluation. From the structure predictions and the crosslink data we derived a structural building block of one PHB1 and one PHB2 subunit, strongly intertwined along most of their length. The size of the complex implies that approximately 14 of these building blocks are present. Each unit contains a putative transmembrane helix in PHB2. Taken together with the unit building block we postulate a circular palisade-like arrangement of the building blocks projecting into the intermembrane space.

Theoretical Study of Structural and Electronic Properties of Methyl Silsesquioxanes

Calculations based on density functional theory (DFT) were performed on various structural isomers of methyl silsesquioxanes, [MeSiO3/2]n where n = 4, 6, 8, 10, 12, 14, and 16, to study their structural and electronic properties. The calculated results find the stability of methyl silsesquioxanes, except [MeSiO3/2]4, against fragmentation and hydrolysis, and of one isomer of [MeSiO3/2]14 against hydrolysis. The deformation density plots show that chemical bonding in methyl silsesquioxanes is mainly determined by the building block unit, (MeSiO3/2) as also seen in hydridosilsesquioxanes (HSQ). However, unlike HSQ, the large cages of methyl silsesquioxanes do not develop a localized electronic state in the HOMO−LUMO gap.

Light control over the size of an antenna unit building block as an efficient strategy for light harvesting in photosynthesis

It was shown that an increase in the bacteriochlorophyll (BChl) c antenna size observed upon lowering growth light intensities led to enhancement of the hyperchromism of the BChl c Q y absorption band of the green photosynthetic bacterium Chloroflexus aurantiacus. With femtosecond difference absorption spectroscopy, it was shown that the amplitude of bleaching of the oligomeric BChl c Q y band (as compared to that for monomeric BChl a) increased with increasing BChl c content in chlorosomes. This BChl c bleaching amplitude was about doubled as the chlorosomal antenna size was about trebled. Both sets of findings clearly show that a unit BChl c aggregate in the chlorosomal antenna is variable in size and governed by the grow light intensity, thus ensuring the high efficiency of energy transfer within the BChl c antenna regardless of its size.

Chaperone-like Activity of Tubulin: BINDING AND REACTIVATION OF UNFOLDED SUBSTRATE ENZYMES

The eukaryotic cytoskeletal protein tubulin is a heterodimer of two subunits, alpha and beta, and is a building block unit of microtubules. In a previous communication we demonstrated that tubulin possesses chaperone-like activities by preventing the stress-induced aggregation of various proteins (Guha, S., Manna, T. K., Das, K. P., and Bhattacharyya, B. (1998) J. Biol. Chem. 273, 30077-30080). As an extension of this observation, we explored whether tubulin, like other known chaperones, also protected biological activity of proteins against thermal stress or increased the yields of active proteins during refolding from a denatured state. We show here that tubulin not only prevents the thermal aggregation of alcohol dehydrogenase and malic dehydrogenase but also protects them from loss of activity. We also show that tubulin prevents the aggregation of substrates during their refolding from a denatured state and forms a stable complex with denatured substrate. The activity of malic dehydrogenase, alpha-glucosidase, and lactate dehydrogenase during their refolding from urea or guanidium hydrochloride denatured states increased significantly in presence of tubulin compared with that without tubulin. These results suggest that tubulin, in addition to its role in mitosis, cell motility, and other cellular events, might be implicated in protein folding and protection from stress.

Unit building block of the oligomeric chlorosomal antenna of the green photosynthetic bacterium Chloroflexus aurantiacus: modeling of nonlinear optical spectra

The size of a unit BChl c aggregate of the chlorosomal antenna of the green photosynthetic bacterium Chloroflexus aurantiacus was estimated by using the relative difference absorption measurements of the oligomeric BChl c and monomeric BChl a bands [S. Savikhin et al., FEBS Lett. 430 (1998) 323]. A quantitative fit of the data was obtained within the framework of the exciton model proposed before [Z.G. Fetisova et al., Biophys. J. 71 (1996) 995]. The model assumes that a unit building block of the antenna has a form of a tubular aggregate of L=6 linear chains, containing N BChl c molecules each. The simultaneous fit of the linear and nonlinear (pump-probe) absorption gave the intrachain interaction energy of 400 cm −1 , the site inhomogeneity value of 280 cm −1 , and the number of pigments in each individual linear chain N=4. The size of the antenna unit was found to be L× N=24 exciton-coupled BChl c molecules.

Diastereofacial selection in the 1,2-addition of MeMgX and McLi to 4-oxo sugar:Efficient synthesis of 4-C-methyl-l-S-β-D-gluco- and galactopyranoside building blocks of moenomycin

The stereochemical course of the 1,2-addition upon treatment of various 1-thio-4-oxo sugars with McMgXand McLi has been determined. The effects of reagent, solvent, and neighboring functionalities in the gluco/galacto (non-chelation/chelation controlled) product distribution are detailed. Stereocontrolled 1,2-addition to these 4-oxo sugars provide access to a number of differently functionalized F unit building blocks of the moenomycin family, and demonstrate the versatility of this transformation.

Expeditious route to F unit building block of moenomycin A

Synthesis of the versatile F sugar unit building block of moenomycin A, Phenyl 2-O-levulinoyl-4-C-methyl-1-thio-β-D-glucopyranosiduronic acid is described starting from phenyl 1-thio-β-D-galactopyranoside. The key synthetic steps included: (I) Regioselective protection of the 3-OH group of phenyl 6-O-trityl-1-thio-β-D-galactopyranoside as its TBDMS ether, (ii) TBAF mediated TBDMS group migration from the C-3 to C-2 position of phenyl 3-O-TBDMS-4-C-methyl-6-O-trityl-1-thio-β-D-galactopyranoside, and (iii) Selective deprotection of TBDMS and trityl groups in phenyl 2-O-levulinoyl-3-O-TBDMS-4-C-methyl-6-O-trityl-1-thio-β-D-glucopyranoside by DDQ.