Structural Basis for Competitive Inhibition of 3,4-Dihydroxy-2-butanone-4-phosphate Synthase from Vibrio cholerae

The riboflavin biosynthesis pathway has been shown to be essential in many pathogens and is absent in humans. Therefore, enzymes involved in riboflavin synthesis are considered as potential antibacterial drug targets. The enzyme 3,4-dihydroxy-2-butanone-4-phosphate synthase (DHBPS) catalyzes one of the two committed steps in the riboflavin pathway and converts d-ribulose 5-phosphate (Ru5P) to l-3,4-dihydroxy-2-butanone 4-phosphate and formate. Moreover, DHBPS is shown to be indispensable for Mycobacterium, Salmonella, and Helicobacter species. Despite the essentiality of this enzyme in bacteria, no inhibitor has been identified hitherto. Here, we describe kinetic and crystal structure characterization of DHBPS from Vibrio cholerae (vDHBPS) with a competitive inhibitor 4-phospho-d-erythronohydroxamic acid (4PEH) at 1.86-Å resolution. In addition, we also report the structural characterization of vDHBPS in its apo form and in complex with its substrate and substrate plus metal ions at 1.96-, 1.59-, and 2.04-Å resolution, respectively. Comparison of these crystal structures suggests that 4PEH inhibits the catalytic activity of DHBPS as it is unable to form a proposed intermediate that is crucial for DHBPS activity. Furthermore, vDHBPS structures complexed with substrate and metal ions reveal that, unlike Candida albicans, binding of substrate to vDHBPS induces a conformational change from an open to closed conformation. Interestingly, the position of second metal ion, which is different from that of Methanococcus jannaschii, strongly supports an active role in the catalytic mechanism. Thus, the kinetic and structural characterization of vDHBPS reveals the molecular mechanism of inhibition shown by 4PEH and that it can be explored further for designing novel antibiotics.     

Dual 4‐ and 5‐phosphatase activities regulate SopB‐dependent phosphoinositide dynamics to promote bacterial entry

Salmonella are able to invade non‐phagocytic cells such as intestinal epithelial cells by modulating the host actin cytoskeleton to produce membrane ruffles. Two type III effector proteins SopB and SopE play key roles to this modulation. SopE is a known guanine nucleotide exchange factor (GEF) capable of activating Rac1 and CDC42. SopB is a phosphatidylinositol 4‐phosphatase and 5‐phosphatase promoting membrane ruffles and invasion of Salmonella through undefined mechanisms. Previous studies have demonstrated that the 4‐phosphatase activity of SopB is required for PtdIns‐3‐phosphate (PtdIns(3)P) accumulation and SopB‐mediated invasion. We show here that both the 4‐phosphatase as well as the 5‐phosphatase activities of SopB are essential in ruffle formation and subsequent invasion. We found that the 5‐phosphatase activity of SopB is likely responsible for generating PtdIns‐3,4‐bisphosphate (PtdIns(3,4)P₂) and subsequent recruitment of sorting nexin 9 (SNX9), an actin modulating protein. Intriguingly, the 4‐phosphatase activity is responsible for the dephosphorylation of PtdIns(3,4)P₂ into PtdIns(3)P. Alone, neither activity is sufficient for ruffling but when acting in conjunction with one another, the 4‐phosphatase and 5‐phosphatase activities led to SNX9‐mediated ruffling and Salmonella invasion. This work reveals the unique ability of bacterial effector protein SopB to utilize both its 4‐ and 5‐phosphatase activities to regulate phosphoinositide dynamics to promote bacterial entry.     

Enantioselective synthesis and antioxidant activity of 3‐(3,4‐dihydroxyphenyl)‐glyceric acid—Basic monomeric moiety of a biologically active polyether from Symphytum asperum and S. caucasicum

The racemic and enantioselective synthesis of a novel glyceric acid derivative, namely, 2,3‐dihydroxy‐3‐(3,4‐dihydroxyphenyl)‐propionic acid as well as the antioxidant activities is described. The virtually pure enantiomers, (+)‐(2R,3S)‐2,3‐dihydroxy‐3‐(3,4‐dihydroxyphenyl)‐propionic acid and (?)‐(2S,3R)‐2,3‐dihydroxy‐3‐(3,4‐dihydroxyphenyl)‐propionic acid were synthesized for the first time via Sharpless asymmetric dihydroxylation of trans‐caffeic acid derivatives using the enantiocomplementary catalysts, (DHQD)₂‐PHAL and (DHQ)₂‐PHAL. The determination of enantiomeric purity of the novel chiral glyceric acid derivatives was performed by high‐performance liquid chromatographic techniques on the stage of their alkylated precursors. The novel glyceric acid derivatives show strong antioxidant activity against hypochlorite and N,N‐diphenyl‐N‐picryl‐hydrazyl free radical. Their antioxidant activity is about 40‐fold higher than that of the corresponding natural polyether and three‐fold higher of trans‐caffeic acid itself. Chirality, 2010. © 2010 Wiley‐Liss, Inc.     

Quaternary variations in the structural assembly of N‐acetylglucosamine‐6‐phosphate deacetylase from Pasteurella multocida

N‐acetylglucosamine 6‐phosphate deacetylase (NagA) catalyzes the conversion of N‐acetylglucosamine‐6‐phosphate to glucosamine‐6‐phosphate in amino sugar catabolism. This conversion is an essential step in the catabolism of sialic acid in several pathogenic bacteria, including Pasteurella multocida, and thus NagA is identified as a potential drug target. Here, we report the unique structural features of NagA from P. multocida (PmNagA) resolved to 1.95 Å. PmNagA displays an altered quaternary architecture with unique interface interactions compared to its close homolog, the Escherichia coli NagA (EcNagA). We confirmed that the altered quaternary structure is not a crystallographic artifact using single particle electron cryo‐microscopy. Analysis of the determined crystal structure reveals a set of hot‐spot residues involved in novel interactions at the dimer‐dimer interface. PmNagA binds to one Zn²⁺ ion in the active site and demonstrates kinetic parameters comparable to other bacterial homologs. Kinetic studies reveal that at high substrate concentrations (~10‐fold the K_M), the tetrameric PmNagA displays hysteresis similar to its distant neighbor, the dimeric Staphylococcus aureus NagA (SaNagA). Our findings provide key information on structural and functional properties of NagA in P. multocida that could be utilized to design novel antibacterials.     

Identification and analysis of residues contained on β → α loops of the dual‐substrate (βα)8 phosphoribosyl isomerase A specific for its phosphoribosyl anthranilate isomerase activity

A good model to experimentally explore evolutionary hypothesis related to enzyme function is the ancient‐like dual‐substrate (βα)₈ phosphoribosyl isomerase A (PriA), which takes part in both histidine and tryptophan biosynthesis in Streptomyces coelicolor and related organisms. In this study, we determined the Michaelis–Menten enzyme kinetics for both isomerase activities in wild‐type PriA from S. coelicolor and in selected single‐residue monofunctional mutants, identified after Escherichia coli in vivo complementation experiments. Structural and functional analyses of a hitherto unnoticed residue contained on the functionally important β → α loop 5, namely, Arg¹³⁹, which was postulated on structural grounds to be important for the dual‐substrate specificity of PriA, is presented for the first time. Indeed, enzyme kinetics analyses done on the mutant variants PriA_Ser⁸¹Thr and PriA_Arg¹³⁹Asn showed that these residues, which are contained on β → α loops and in close proximity to the N‐terminal phosphate‐binding site, are essential solely for the phosphoribosyl anthranilate isomerase activity of PriA. Moreover, analysis of the X‐ray crystallographic structure of PriA_Arg¹³⁹Asn elucidated at 1.95 Å herein strongly implicates the occurrence of conformational changes in this β → α loop as a major structural feature related to the evolution of the dual‐substrate specificity of PriA. It is suggested that PriA has evolved by tuning a fine energetic balance that allows the sufficient degree of structural flexibility needed for accommodating two topologically dissimilar substrates—within a bifunctional and thus highly constrained active site—without compromising its structural stability.     

Interaction of β‐cyclodextrin‐capped CdSe quantum dots with inorganic anions and cations

A facile method was developed for the preparation of water soluble β‐Cyclodextrin (β‐CD)‐modified CdSe quantum dots (QDs) (β‐CD‐QDs) by directly replacing the oleic acid ligands on the QDs surface with β‐CD in an alkaline aqueous solution. The as‐prepared QDs show good stability in aqueous solution for several months. Oxoanions, including phosphoric acid ion, sulphite acid ion and carbonic acid ion, affect the fluorescence of β‐CD‐QDs. Among them, H₂PO₄^– exhibited the largest quenching effect. For the polyprotic acids (HO)₃AO, the effect of acidic anions on the fluorescence of β‐CD‐QDs was in the order: monoanion (HO)₂AO₂^– > dianion (HO)AO₃^2– >> trianion AO₄^3–. After photoactivation for several days in the presence of anions at alkaline pH, the β‐CD‐QDs exhibited strong fluorescence emission. The effect of various heavy and transition metal ions on the fluorescence properties of the β‐CD‐QDs was investigated further. It was found that Ag⁺, Hg²⁺ and Co²⁺ have significant quenching effect on the fluorescence of the β‐CD‐QDs. The Stern–Volmer quenching constants increased in the order: Hg²⁺ < Co²⁺ <Ag⁺. The adsorption model of metal ions on β‐CD‐QDs was explored. Copyright © 2011 John Wiley & Sons, Ltd.     

Resolution of 1‐n‐Butyl‐3‐Methyl‐3‐Phospholene 1‐Oxide With TADDOL Derivatives and Calcium Salts of O,O'‐Dibenzoyl‐(2R,3R)‐ or O,O'‐di‐p‐Toluoyl‐(2R,3R)‐tartaric Acid

The resolution methods applying (?)‐(4R,5R)‐4,5‐bis(diphenylhydroxymethyl)‐2,2‐dimethyldioxolane (“TADDOL”), (?)‐(2R,3R)‐α,α,α',α'‐tetraphenyl‐1,4‐dioxaspiro[4.5]decan‐2,3‐dimethanol (“spiro‐TADDOL”), as well as the acidic and neutral Ca²⁺ salts of (?)‐O,O'‐dibenzoyl‐ and (?)‐O,O'‐di‐p‐toluoyl‐(2R,3R)‐tartaric acid were extended for the preparation of 1‐n‐butyl‐3‐methyl‐3‐phospholene 1‐oxide in optically active form. In one case, the intermediate diastereomeric complex could be identified by single‐crystal X‐ray analysis. The absolute P‐configuration of the enantiomers of the phospholene oxide was also determined by comparing the experimentally obtained and calculated CD spectra. Chirality 26:174–182, 2014. © 2014 Wiley Periodicals, Inc.     

Mobile loop mutations in an archaeal inositol monophosphatase: Modulating three‐metal ion assisted catalysis and lithium inhibition

The inositol monophosphatase (IMPase) enzyme from the hyperthermophilic archaeon Methanocaldococcus jannaschii requires Mg²⁺ for activity and binds three to four ions tightly in the absence of ligands: K_D = 0.8 μM for one ion with a K_D of 38 μM for the other Mg²⁺ ions. However, the enzyme requires 5–10 mM Mg²⁺ for optimum catalysis, suggesting substrate alters the metal ion affinity. In crystal structures of this archaeal IMPase with products, one of the three metal ions is coordinated by only one protein contact, Asp38. The importance of this and three other acidic residues in a mobile loop that approaches the active site was probed with mutational studies. Only D38A exhibited an increased kinetic K_D for Mg²⁺; D26A, E39A, and E41A showed no significant change in the Mg²⁺ requirement for optimal activity. D38A also showed an increased K_m, but little effect on k_cat. This behavior is consistent with this side chain coordinating the third metal ion in the substrate complex, but with sufficient flexibility in the loop such that other acidic residues could position the Mg²⁺ in the active site in the absence of Asp38. While lithium ion inhibition of the archaeal IMPase is very poor (IC₅₀～250 mM), the D38A enzyme has a dramatically enhanced sensitivity to Li⁺ with an IC₅₀ of 12 mM. These results constitute additional evidence for three metal ion assisted catalysis with substrate and product binding reducing affinity of the third necessary metal ion. They also suggest a specific mode of action for lithium inhibition in the IMPase superfamily.     

Developing bifunctional β‐lactamase molecules with built‐in target‐recognizing module for prodrug therapy: identification of Enterobacter Cloacae P99 cephalosporinase loops suitable for randomization and phage‐display selection

This study was focused on developing catalytically active β‐lactamase enzyme molecules that have target‐recognizing sites built within their scaffold. Using phage‐display approach, nine libraries were constructed by inserting the randomized linear or cysteine‐constrained heptapeptides in the five different loops on the outer surface of P99 β‐lactamase molecule. The pIII signal peptide of Sec‐pathway was employed for a periplasmic translocation of the β‐lactamase fusion protein, which we found more efficient than the DsbA signal peptide of SRP‐pathway. The randomized heptapeptide loops replaced native amino acids between positions ³⁴Y‐³⁷K, ²³⁸M‐²⁴⁶A, ²⁷⁵N‐²⁸⁰A, ³⁰⁵A‐³¹¹S, or ³²⁹I‐³³⁴I of the P99 β‐lactamase molecules for generating the loop‐1 to ‐5 libraries, respectively. The diversity of each loop library was judged by counting the primary and β‐lactamase‐active clones. The linear peptide inserts in the loop‐2 library showed the maximum number of the β‐lactamase‐active clones, followed by the loop‐5, loop‐3, and loop‐4. The insertion of the cysteine‐constrained loops exhibited a dramatic loss of the enzyme‐active β‐lactamase clones. The complexity of the loop‐2 linear library, as determined by the frequency and diversity of amino acid distributions in the randomized region, appears consistent with the standards of other types of phage display library systems. The selection of the loop‐2 linear library on streptavidin protein as a test target identified several β‐lactamase clones that specifically bound to streptavidin. In conclusion, this study identified the suitability of the loop‐2 of P99 β‐lactamase for constructing a phage‐display library of the β‐lactamase enzyme‐active molecules that can be selected against a target. This is an enabling step in our long‐term goal of developing bifunctional β‐lactamase molecules against cancer‐specific targets for enzyme prodrug therapy of cancer. Copyright © 2009 John Wiley & Sons, Ltd.     

Acidic residues and a predicted,highly conserved α‐helix are critical for the endonuclease/strand separation functions of bacteriophage λ’s TerL

Complementation, endonuclease, strand separation, and packaging assays using mutant TerL^λ’s, coupled with bioinformatic information and modeling of its endonuclease, identified five residues, D401, E408, D465, E563, and E586, as critical acidic residues of TerL^λ’s endonuclease. Studies of phage and viral TerL nucleases indicate acidic residues participate in metal ion‐binding, part of a two‐ion metal catalysis mechanism, where metal ion A activates a water for DNA backbone hydrolysis. Modeling places D401, D465, and E586 in locations analogous to those of the metal‐binding residues of many phage and viral TerLs. Our work leads to a model of TerL^λ’s endonuclease domain where at least three acidic residues from a ~185 residue segment (D401 to E586) are near each other in the structure, forming the endonuclease catalytic center at cosN, the nicking site. DNA interactions required to bring the rotationally symmetric cosN precisely to the catalytic center are proposed to rely on an ~60 residue region that includes a conserved α‐helix for dimerization. Metal ion A, positioned by TerL^λ’s acidic D401 and E586, would be placed at cosN for water activation, ensuring high accuracy for DNA backbone hydrolysis.     

Structural and mechanistic insights into homocysteine degradation by a mutant of methionine γ‐lyase based on substrate‐assisted catalysis

Methionine γ‐lyse (MGL) catalyzes the α, γ‐elimination of l ‐methionine and its derivatives as well as the α, β‐elimination of l ‐cysteine and its derivatives to produce α‐keto acids, volatile thiols, and ammonia. The reaction mechanism of MGL has been characterized by enzymological studies using several site‐directed mutants. The Pseudomonas putida MGL C116H mutant showed drastically reduced degradation activity toward methionine while retaining activity toward homocysteine. To understand the underlying mechanism and to discern the subtle differences between these substrates, we analyzed the crystal structures of the reaction intermediates. The complex formed between the C116H mutant and methionine demonstrated that a loop structure (Ala51–Asn64) in the adjacent subunit of the catalytic dimer cannot approach the cofactor pyridoxal 5′‐phosphate (PLP) because His116 disrupts the interaction of Asp241 with Lys240, and the liberated side chain of Lys240 causes steric hindrance with this loop. Conversely, in the complex formed between C116H mutant and homocysteine, the thiol moiety of the substrate conjugated with PLP offsets the imidazole ring of His116 via a water molecule, disrupting the interaction of His116 and Asp241 and restoring the interaction of Asp241 with Lys240. These structural data suggest that the Cys116 to His mutation renders the enzyme inactive toward the original substrate, but activity is restored when the substrate is homocysteine due to substrate‐assisted catalysis.     

Thieno[3,4‐c]Pyrrole‐4,6‐Dione‐Based Polymer Acceptors for High Open‐Circuit Voltage All‐Polymer Solar Cells

While polymer acceptors are promising fullerene alternatives in the fabrication of efficient bulk heterojunction (BHJ) solar cells, the range of efficient material systems relevant to the “all‐polymer” BHJ concept remains narrow, and currently limits the perspectives to meet the 10% efficiency threshold in all‐polymer solar cells. This report examines two polymer acceptor analogs composed of thieno[3,4‐c ]pyrrole‐4,6‐dione (TPD) and 3,4‐difluorothiophene ([2F]T) motifs, and their BHJ solar cell performance pattern with a low‐bandgap polymer donor commonly used with fullerenes (PBDT‐TS1; taken as a model system). In this material set, the introduction of a third electron‐deficient motif, namely 2,1,3‐benzothiadiazole (BT), is shown to (i) significantly narrow the optical gap (E _opt) of the corresponding polymer (by ≈0.2 eV) and (ii) improve the electron mobility of the polymer by over two orders of magnitude in BHJ solar cells. In turn, the narrow‐gap P2TPDBT[2F]T analog (E _opt = 1.7 eV) used as fullerene alternative yields high open‐circuit voltages (V _OC) of ≈1.0 V, notable short‐circuit current values (J _SC) of ≈11.0 mA cm⁻², and power conversion efficiencies (PCEs) nearing 5% in all‐polymer BHJ solar cells. P2TPDBT[2F]T paves the way to a new, promising class of polymer acceptor candidates.     

Crystal structure of Saccharomyces cerevisiae Aro8, a putative α‐aminoadipate aminotransferase

α‐Aminoadipate aminotransferase (AAA‐AT) catalyzes the amination of 2‐oxoadipate to α‐aminoadipate in the fourth step of the α‐aminoadipate pathway of lysine biosynthesis in fungi. The aromatic aminotransferase Aro8 has recently been identified as an AAA‐AT in Saccharomyces cerevisiae. This enzyme displays broad substrate selectivity, utilizing several amino acids and 2‐oxo acids as substrates. Here we report the 1.91Å resolution crystal structure of Aro8 and compare it to AAA‐AT LysN from Thermus thermophilus and human kynurenine aminotransferase II. Inspection of the active site of Aro8 reveals asymmetric cofactor binding with lysine‐pyridoxal‐5‐phosphate bound within the active site of one subunit in the Aro8 homodimer and pyridoxamine phosphate and a HEPES molecule bound to the other subunit. The HEPES buffer molecule binds within the substrate‐binding site of Aro8, yielding insights into the mechanism by which it recognizes multiple substrates and how this recognition differs from other AAA‐AT/kynurenine aminotransferases.     

Synthesis,crystal structure and fluorescence properties of terbium complexes with phenoxyacetic acid and 2,4,6‐tris‐(2‐pyridyl)‐s–triazine

Two complexes of Tb³⁺, Gd³⁺/Tb³⁺ and one heteronuclear crystal Gd³⁺/Tb³⁺ with phenoxyacetic acid (HPOA) and 2,4,6‐tris‐(2‐pyridyl)‐s–triazine (TPTZ) have been synthesized. Elemental analysis, rare earth coordination titration, inductively coupled plasma atomic emission spectrometry (ICP‐AES) and thermogravimetric analysis‐differential scanning calorimetry (TG‐DSC) analysis show that the two complexes are Tb₂(POA)₆(TPTZ)₂·6H₂O and TbGd(POA)₆(TPTZ)₂·6H₂O, respectively. The crystal structure of TbGd(POA)₆(TPTZ)₂·2CH₃OH was determined using single‐crystal X‐ray diffraction. The monocrystal belongs to the triclinic system with the P‐1 space group. In particular, each metal ion is coordinately bonded to three nitrogen atoms of one TPTZ and seven oxygen atoms of three phenoxyacetic ions. Furthermore, there exist two coordinate forms between C₆H₅OCH₂COO^– and the metal ions in the crystal. One is a chelating bidentate, the other is chelating and bridge coordinating. Fluorescence determination shows that the two complexes possess strong fluorescence emissions. Furthermore, the fluorescence intensity of the Gd³⁺/Tb³⁺ complex is much stronger than that of the undoped complex, which may result from a decrease in the concentration quench of Tb³⁺ ions, and intramolecular energy transfer from the ligands coordinated with Gd³⁺ ions to Tb³⁺ ions. Copyright © 2015 John Wiley & Sons, Ltd.     

A First‐Principles and Experimental Investigation of Nickel Solubility into the P2 NaxCoO2 Sodium‐Ion Cathode

The difficulty in finding positive electrode materials for sodium‐ion (Na‐ion) batteries with a large specific energy has slowed down their commercialization. Layered transition metal (M) oxides Na_xMO₂ with a two‐layer oxygen stacking (P2, 0.6 ≤ x ≤ 0.75), are promising candidates. However, the high average metal oxidation state needed during synthesis means that P2 Na_xMO₂ cathodes often require the introduction of high‐valent cations (Mn⁴⁺, Ti⁴⁺, Sn⁵⁺, or Te⁶⁺), limiting the cathode's performance. Using a combination of first‐principles calculations and experiments, the feasibility of P2 cathodes containing only electrochemically active nickel and cobalt cations is investigated. It is found that P2 Na_xNi_yCo_1–yO₂ materials with x = 0.66, 0.75, and 0 ≤ y ≤ 0.33 are either thermodynamically stable or metastable yet close to the convex hull at typical P2 synthesis temperatures (≈1000 K). It is demonstrated that a novel P2 compound with y = 0.22 and both Ni^3+/4+ and Co^3+/4+ can be successfully synthesized. It is studied electrochemically and structurally, using in situ and ex situ X‐ray diffraction. It is demonstrated that the chemical space of P2 layered compounds is not fully explored yet and that ab initio phase diagrams allow the determination of new high‐specific energy positive electrodes to be targeted experimentally.     

Purification of glucose‐6‐phosphate dehydrogenase from rat (Rattus norvegicus) erythrocytes and inhibition effects of some metal ions on enzyme activity

Glucose‐6‐phosphate dehydrogenase (G6PD) is the first enzyme on which the pentose phosphate pathway was checked. In this study, purification of a G6PD enzyme was carried out by using rat erythrocytes with a specific activity of 13.7 EU/mg and a yield of 67.7 and 155.6‐fold by using 2′,5′‐ADP Sepharose‐4B affinity column chromatography. For the purpose of identifying the purity of enzyme and molecular mass of the subunit, a sodium dodecyl sulfate‐polyacrylamide gel electrophoresis was carried out. The molecular mass of subunit was calculated 56.5 kDa approximately. Then, an investigation was carried out regarding the inhibitory effects caused by various metal ions (Fe²⁺, Pb²⁺, Cd²⁺, Ag⁺, and Zn²⁺) on G6PD enzyme activities, as per Beutler method at 340 nm under in vitro conditions. Lineweaver–Burk diagrams were used for estimation of the IC₅₀ and K_i values for the metals. K_i values for Pb⁺², Cd⁺², Ag⁺, and Zn⁺² were 113.3, 215.2, 19.4, and 474.7 μM, respectively.     

Synthesis and Deprotection of Biodegradably and Thermally Protected Dinucleoside‐2′,5′‐Monophosphate Prodrug Model of 2‐5A

Protected dinucleoside‐2′,5′‐monophosphate has been prepared to develop a prodrug strategy for 2‐5A. The removal of enzymatically and thermally labile 4‐(acetylthio)‐2‐(ethoxycarbonyl)‐3‐oxo‐2‐methylbutyl phosphate protecting group and enzymatically labile 3′‐O‐pivaloyloxymethyl group was followed at pH 7.5 and 37 °C by HPLC from the fully protected dimeric adenosine‐2′,5′‐monophosphate 1 used as a model compound for 2‐5A. The desired unprotected 2′,3′‐O‐isopropylideneadenosine‐2′,5′‐monophosphate ( 9 ) was observed to accumulate as a major product. Neither the competitive isomerization of 2′,5′‐ to a 3′,5′‐linkage nor the P–O5′ bond cleavage was detected. The phosphate protecting group was removed faster than the 3′‐O‐protection and, hence, the attack of the neighbouring 3′‐OH on phosphotriester moiety did not take place.     

Open‐Structured V2O5·nH2O Nanoflakes as Highly Reversible Cathode Material for Monovalent and Multivalent Intercalation Batteries

The high‐capacity cathode material V₂O₅·n H₂O has attracted considerable attention for metal ion batteries due to the multielectron redox reaction during electrochemical processes. It has an expanded layer structure, which can host large ions or multivalent ions. However, structural instability and poor electronic and ionic conductivities greatly handicap its application. Here, in cell tests, self‐assembly V₂O₅·n H₂O nanoflakes shows excellent electrochemical performance with either monovalent or multivalent cation intercalation. They are directly grown on a 3D conductive stainless steel mesh substrate via a simple and green hydrothermal method. Well‐layered nanoflakes are obtained after heat treatment at 300 °C (V₂O₅·0.3H₂O). Nanoflakes with ultrathin flower petals deliver a stable capacity of 250 mA h g^?1 in a Li‐ion cell, 110 mA h g^?1 in a Na‐ion cell, and 80 mA h g^?1 in an Al‐ion cell in their respective potential ranges (2.0–4.0 V for Li and Na‐ion batteries and 0.1–2.5 V for Al‐ion battery) after 100 cycles.     

HS‐SPME‐GC‐FID method for detection and quantification of Bacillus cereus ATCC 10702 mediated 2‐acetyl‐1‐pyrroline

A rapid micro‐scale solid‐phase micro‐extraction (SPME) procedure coupled with gas‐chromatography with flame ionized detector (GC‐FID) was used to extract parts per billion levels of a principle basmati aroma compound “2‐acetyl‐1‐pyrroline” (2‐AP) from bacterial samples. In present investigation, optimization parameters of bacterial incubation period, sample weight, pre‐incubation time, adsorption time, and temperature, precursors and their concentrations has been studied. In the optimized conditions, detection of 2‐AP produced by Bacillus cereus ATCC10702 using only 0.5 g of sample volume was 85 μg/kg. Along with 2‐AP, 15 other compounds produced by B. cereus were also reported out of which 14 were reported for the first time consisting mainly of (E)?2‐hexenal, pentadecanal, 4‐hydroxy‐2‐butanone, n‐hexanal, 2–6‐nonadienal, 3‐methoxy‐2(5H) furanone and 2‐acetyl‐1‐pyridine and octanal. High recovery of 2‐AP (87 %) from very less amount of B. cereus samples was observed. The method is reproducible fast and can be used for detection of 2‐AP production by B. cereus. © 2014 American Institute of Chemical Engineers Biotechnol. Prog., 30:1356–1363, 2014     

Thieno,Furo, and Selenopheno[3,4‐c]pyrrole‐4,6‐dione Copolymers: Air‐Processed Polymer Solar Cells with Power Conversion Efficiency up to 7.1%

Polymers based on thieno[3,4‐c]pyrrole‐4,6‐dione derivatives are interesting and promising candidates for organic bulk heterojunction solar cells. Herein, a series of push–pull conjugated polymers based on thieno[3,4‐c]pyrrole‐4,6‐dione (TPD), furo[3,4‐c]pyrrole‐4,6‐dione (FPD), and selenopheno[3,4‐c]‐pyrrole‐4,6‐dione (SePD) have been synthesized by direct heteroarylation polymerization and fully characterized. The impacts of both the heteroatom (sulfur, oxygen, and selenium) and the side chain (branched or linear) of [3,4‐c]pyrrole‐4,6‐dione unit on the electro‐optical properties have been investigated. Among polymers developed, two new highly processable terthiophene–SePD ( P4 ) and dithienosilole–SePD ( P9 ) copolymers led to air‐processed polymer solar cells with power conversion efficiencies of 5.1% and 7.1% using the following inverted configuration: ITO/ZnO/Polymer:PCBM/MoO₃/Ag. These promising results make P4 and P9 good candidates for further upscaling and device optimization.