Characterization of Braun's lipoprotein and determination of its attachment sites to peptidoglycan by 252Cf-PD and MALDI time-of-flight mass spectrometry

A strategy for the characterization of bacterial lipoprotein-in this case Braun's lipoprotein (an outer membrane 7-ku lipoprotein) isolated from Escherichia coli —is described by time-of-flight mass spectrometric (TOF/MS) techniques [252Cf plasma desorption (PD) TOF/MS and matrix-assisted laser desorption-ionization (MALDI) TOF/MS]. Covalent linkage of lipid at the N-terminal cysteine (posttranslationally modified to a S-[2,3-bis(acyloxy)-propyl]-N-acylcysteine) and, therefore, strict insolubility in aqueous solution constitute common features for this class of proteins. Relative molecular mass determination of the major molecular species of Braun's lipoprotein was obtained by selection of an appropriate mixture of organic solvents compatible with matrix/support materials useful for the mass spectrometric techniques applied. Minor components of this lipoprotein that differ only in the fatty acid composition of the lipid anchor were detected by PD TOF/MS after enzymatic release of the extremely hydrophobic N-terminal amino acid followed by selective extraction with chloroform. Part of the primary sequence of this lipoprotein was confirmed based on peptide fragment ions observed in the positive ion PD mass spectra of cyanogen bromide-generated peptide fragments that had been isolated previously by reverse phase high-performance liquid chromatography (HPLC). Peptidoglycan fragments that represent the attachment sites of lipoprotein to peptidoglycan were enzymatically released, separated by reverse phase HPLC, and finally characterized by time-of-flight mass spectrometric techniques (252Cf-PD TOF/MS, MALDI TOF/MS). The results obtained with both techniques differed only in the better sensitivity obtained with MALDI TOF/MS, which consumed a factor of 100 to 1000 less material than with PD TOF/MS

Directing Intrinsic Chirality in Gold Nanoclusters: Preferential Formation of Stable Enantiopure Clusters in High Yield and Experimentally Unveiling the “Super” Chirality of Au144_{144}

Chiral gold nanoclusters offer significant potential for exploring chirality at a fundamental level and for exploiting their applications in sensing and catalysis. However, their widespread use is impeded by low yields in synthesis, tedious separation procedures of their enantiomeric forms, and limited thermal stability. In this study, we investigated the direct synthesis of enantiopure chiral nanoclusters using the chiral ligand 2-MeBuSH in the fabrication of Au$_{25}$, Au$_{38}$, and Au$_{144}$ nanoclusters. Notably, this approach leads to the unexpected formation of intrinsically chiral clusters with high yields for chiral Au$_{38}$ and Au$_{144}$ nanoclusters. Experimental evaluation of chiral activity by circular dichroism (CD) spectroscopy corroborates previous theoretical calculations, highlighting the stronger CD signal exhibited by Au$_{144}$ compared to Au$_{38}$ or Au$_{25}$. Furthermore, the formation of a single enantiomeric form is experimentally confirmed by comparing it with intrinsically chiral Au$_{38}$(2-PET)$_{24}$ (2-PET: 2-phenylethanethiol) and is supported theoretically for both Au$_{38}$ and Au$_{144}$. Moreover, the prepared chiral clusters show stability against diastereoisomerization, up to temperatures of 80°C. Thus, our findings not only demonstrate the selective preparation of enantiopure, intrinsically chiral, and highly stable thiolate-protected Au nanoclusters through careful ligand design but also support the predicted “super” chirality in the Au$_{144}$ cluster, encompassing hierarchical chirality in ligands, staple configuration, and core structure

Investigations of the generality of quaternary ammonium salts as alkylating agents in direct C-H alkylation reactions: solid alternatives for gaseous olefins

C–H alkylation reactions using short chain olefins as alkylating agents could be operationally simplified on the lab scale by using quaternary ammonium salts as precursors for these gaseous reagents: Hofmann elimination delivers in situ the desired alkenes with the advantage that the alkene concentration in the liquid phase is high. In case a catalytic system did not tolerate the conditions for Hofmann elimination, a very simple spatial separation of both reactions, Hofmann elimination and direct alkylation, was achieved to circumvent possible side reactions or catalyst deactivation. Additionally, the truly catalytically active species of a rhodium(I) mediated alkylation reaction could be identified by using this approach.ISSN:1477-0520ISSN:1477-053

Molecular weight-determination of biosynthetically modified monomeric and oligomeric muropeptides from Escherichia coli by plasma desorption-mass spectrometry

AbstractThe presence of certain d-amino acids in the growth media of Escherichia coli results in the accumulation of 2 major and 3–5 minor new muropeptides in the murein sacculus. Preliminary data suggested that the major muropeptides correspond to a monomer and a cross-linked dimer with one residue of d-amino acid per molecule. We have analyzed several d-amino acid-modified muropeptides by plasma desorption-mass spectrometry. Our results confirmed that the general structures of the major modified muropeptides are: GlucNAc-MurNAc-l-Ala-d-Glu-m-A2pm-d-X, and GlucNAc-MurNAc-l-Ala-d-Glu-m-A2pm-d-Ala; GlucNAc-MurNAc-l-Ala-d-Glu-m-A2pm-d-X, being X a residue of the d-amino acid. These results corroborate the usefulness of this technique for the structural analysis of muropeptides

Manganese-Catalyzed Dehydrogenative Silylation of Alkenes Following Two Paral-lel Pathways

We report on an additive-free Mn(I)-catalyzed dehydrogenative silylation of terminal alkenes. The most active pre-catalyst is the bench-stable alkyl bisphosphine Mn(I) complex fac-[Mn(dippe)(CO)3(CH2CH2CH3)]. The catalytic pro-cess is initiated by migratory insertion of a CO ligand into the Mn-alkyl bond to yield an acyl intermediate which un-dergoes rapid Si-H bond cleavage of the silane HSiR3 forming the active 16e- Mn(I) silyl catalyst [Mn(dippe)(CO)2(SiR3)] together with liberated butanal. A broad variety of aromatic and aliphatic alkenes was efficient-ly and selectively converted into E-vinylsilanes and allylsilanes, respectively, at room temperature. Mechanistic insights are provided based on experimental data revealing that two parallel reaction pathways are operative: an acceptorless reaction pathway involving dihydrogen release and a pathway requiring an alkene as sacrificial hydrogen acceptor

Manganese-Catalyzed Aminomethylation of Aromatic Compounds with Methanol as a Sustainable C1 Building Block

This study represents the first example of a manganese-catalyzed environmentally benign, practical three-component aminomethylation of activated aromatic compounds including naphtols, phenols, pyridines, indoles, carbazoles, and thiophenes in combination with amines and MeOH as a C1 source. These reactions proceed with high atom efficiency via a sequence of dehydrogenation and condensation steps which give rise to selective C–C and C–N bond formations, thereby releasing hydrogen and water. A well-defined hydride Mn­(I) PNP pincer complex, recently developed in our laboratory, catalyzes this process in a very efficient way, and a total of 28 different aminomethylated products were synthesized and isolated yields of up to 91%. In a preliminary study, a related Fe­(II) PNP pincer complex was shown to catalyze the methylation of 2-naphtol rather than its aminomethylation displaying again the divergent behavior of isoelectronic Mn­(I) and Fe­(II) PNP pincer systems

Efficient Hydrogenation of Ketones and Aldehydes Catalyzed by Well-Defined Iron(II) PNP Pincer Complexes: Evidence for an Insertion Mechanism

Nokian kunnassa Kolmenkulman alueelle on rakentunut kiertotalouden yrityspuisto, jossa hyödynnetään alustatalouden mallia liiketoiminnan ohjaamisessa. Puiston nimi on ECO3. Yhtenä alueen ankkuriyrityksenä on Pirkanmaan Jätehuolto Oy ja alustaa hallinnoi Nokian kaupungin kehitysyhtiö Verte Oy. Alueen tarkoituksena on ollut kerätä kierrätysliiketoimintaa samalle alueelle, jossa jokainen yritys saa samanlaisen taloudellisen sekä neuvoa-antavan tuen. Aineisto koostui kolmesta asiantuntijahaastattelusta, jotka toteutettiin puolistrukturoituina teemahaastatteluina. Haastatteluaineiston sisällönanalyysin kautta tutkielmani tuo esille, niitä seikkoja mitkä ovat saaneet julkisen jätehuoltoyhtiön lähtemään mukaan kehittämään uudenlaista ja innovatiivista ajatusta jätteiden käsittelyssä. Haastatteluaineisto tuo esille, millaisia haasteita julkinen toimija voi kohdata kehittäessään kiertotalouden alustaa. Tutkimus toteutettiin laadullisena tapaustutkimuksena. Tarkasteltavan ilmiön määrittelemiseksi rakennettiin ensin teoreettinen viitekehys, joka valottaa kiertotalouden ja alustatalouden perusajatuksia. Tutkielma tuo esille millaiset motivaatiotekijät julkisella jätehuoltoyhtiöllä on kehittää kiertotaloustoimintaa Pirkanmaalla. Tutkimuksen tavoite on myös luoda ymmärrystä kiertotaloudesta ja sen kehittämisestä julkisten toimijoiden, etenkin julkisen jätehuollon, kautta. Kiertotalouden ohella tärkeänä selvittämiskohteena tutkimuksessa on alustatalouden periaatteet, joiden kautta kiertotalouspuisto ECO3 on muodostunut Nokian Kolmenkulman alueelle. Tutkimuksessa havaittiin, että alati muuttuva toimintaympäristö vaatii julkista jätehuoltoyhtiötä kehittämään toimintaansa kestävämpään suuntaan. Julkisen jätehuollon motiiveita kehittää kiertotaloustoimintoja on lainsäädännön tuomat kiristykset ja sitä kautta oman liiketoiminnan kehittäminen