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Mycobacterium tuberculosis, the causative agent of tuberculosis (TB), is a major pathogen responsible for 1.5 million deaths annually. This bacterium is characterized by a highly unusual and impermeable cell envelope, which plays a key role in mycobacterial survival and virulence. Although many studies have focused on the composition and functioning of the mycobacterial cell envelope, the capsular α-glucan has received relatively minor attention. Here we show that a murine monoclonal antibody (Mab) directed against glycogen cross-reacts with mycobacterial α-glucans, polymers of α(1-4)-linked glucose residues with α(1-6)-branch points. We identified the Mab epitope specificity by saturation transfer difference NMR and show that the α(1-4)-linked glucose residues are important in glucan-Mab interaction. The minimal epitope is formed by (linear) maltotriose. Notably, a Mycobacterium mutant lacking the branching enzyme GlgB does not react with the Mab; this suggests that the α(1-6)-branches form part of the epitope. These seemingly conflicting data can be explained by the fact that in the mutant the linear form of the α-glucan (amylose) is insoluble. This Mab was subsequently used to develop several techniques helpful in capsular α-glucan research. By using a capsular glucan-screening methodology based on this Mab we were able to identify several unknown genes involved in capsular α-glucan biogenesis. Additionally, we developed two methods for the detection of capsular α-glucan levels. This study therefore opens new ways to study capsular α-glucan and to identify possible targets for further research.

The mixed valence dodecanuclear complex [Mn12O12(O2CEt) 16(H2O)3 may be reduced by one electron to give (PPh4)[Mn12O12(O2CEt)16(H2O)4. Reduction of the complex occurs at one MnIII ion to give an unusual trapped-valence MnIIMnIII 7MnIV 4 complex. This formulation is supported by X-ray crystallography at both low temperature and room temperature. DC (2.0–4.0K, 20–50 kG fields) and AC (2.0–30 K, 1.0 and 0.0050G fields, 25–1000 Hz frequencies) magnetic susceptibility measurements indicate ground states of S=9 and S=19/2 for the neutral and reduced species, respectively. (PPh4)[Mn12O122(O2CEt)16(H2O)4 exhibits an out-of-phase component of the AC magnetic susceptibility (X M) which has a frequency dependent maximum. This is a very unusual property for a discrete molecular species to display. The neutral analog shows two peaks in the X M vs. T plot. DC measurements also show the presence of prominent hysteresis loops, and field-cooled and zero-field-cooled magnetization data are not superimposed at low ...

Tris(o-mercaptophenyl) phosphinate (PS3) binds to Tc(III) as a tetradentate ligand to form the formally 14-electron complex Tc(PS3)(CNMe). An x-ray single-crystal structure determination of the isopropyl isocyanide derivative Tc(PS3)(CN-i-Pr) shows sulfurs bound in the equatorial plane. The crystal data for MF = C{sub 22}H{sub 19}NPS{sub 3}Tc is presented. In the presence of a large excess of isonitrile, these electron-deficient complexes bind a sixth ligand. The six-coordinate complex Tc(PS3)(CN-i-Pr){sub 2}, was also structurally characterized and the crystal data is presented. 8 refs., 2 figs., 4 tabs.

A methanol solution of the Tc(VI) complex (Ph 4 As)[TcNCl 4 ] is reduced in the presence of pyridine to give the orange Tc(V) complex [TcN(OH)(py) 4 ](Ph 4 B) (1); the pyridine ligands are labile and undergo exchange with free pyridine in solution. The TcO 2 + and TcN(OH) + cores also appear to be similar electronically, since the 99 Tc NMR chemical shifts for these two compounds are not significantly different. Compound 1 reacts with 2,3,5,6-tetramethylbenzenethiolate (tmbt) to give quantitative yields of the robust compound trans-TcN(tmbt) 2 (py) 2

As a means of varying the electron count of complexes [Mn12O12(O2CR)16(H2O)4](1; R = Me or Ph), the aggregates [Mn8Fe4O12(O2CMe)16(H2O)4]2 and [NPrn4][Mn12O12(O2CPh)16(H2O)4]3 have been prepared; magnetochemical measurements confirm that the unusual of properties 1 can be significantly altered by ‘conversion’ to 2 and 3.

Reduction of the 8MnIII,4MnIV complex [Mn12O12(O2CEt)16(H2O)3] with PPh4l in CH2Cl2 leads to isolation of (PPh4)[Mn12O12(O2CEt)16(H2O)4](3) whose crystal structure shows that the added electron is localized on a formerly MnIII ion to give a trapped-valence MnII,7MnIII,4MnIV situation; DC and AC magnetic susceptibility studies show that 3 has an S= 19/2 ground state and that it displays a superparamagnet-like non-zero, frequency-dependent, out-of-phase response in the AC susceptibility behaviour that is extremely unusual for a molecular species and unique for an ionic species.

Both Tc(III) compounds Tc(tmbt){sub 3}(MeCN){sub 2} (6) and Tc(tmbt){sub 3}(py){sub 2} (7) an be oxidized to Tc(V) oxo species by oxygen atom transfer. The initial product of the reaction of 6 with DMSO was characterized by x-ray crystallography and found to be Tc(tmbt){sub 3}(DMSO)(MeCN), the product of ligand substitution, not oxygen atom transfer. However, compound 6 is oxidized to TcO(tmbt){sub 3}(py) (1) by pyridine N-oxide, and 7 reacts with a number of other oxygen atom transfer reagents as well to produce the oxotechnetium(V) complex 1. The Tc(V) oxo compound TcO(SC{sub 15}H{sub 23}){sub 3}(NC{sub 5}H{sub 5}) (1) was also characterized by x-ray cyrstallography. Addition of excess thiolate to 1 yields (Ph{sub 4}As) (TcO(tmbt){sub 4}) (3), which can also be prepared directly from (Ph{sub 4}As)(TcOCl{sub 4}). Both 1 and 3 can be reduced by oxygen atom abstraction to restore the Tc(III) tris(thiolate) core. Reaction of 3 with PEt{sub 3} requires much more vigorous conditions than 1 does, but both materials are reduced to Tc(tmbt){sub 3}(PEt{sub 3}){sub 2}. The oxidative and reductive oxo-transfer reactions can be coupled to complete a catalytic cycle. In the oxidation of PPh{sub 3} by DMSO, the catalyst is still fully active after 500 turnovers. 31 refs., 5 figs.,more » 6 tabs.« less

Preparation et structure cristalline de complexes Tc(SC 10 H 13 ) 3 (CH 3 CN) 2 , Tc(SC 10 H 13 ) 3 (CO)(CH 3 CN) et Tc(SC 10 H 13 ) 3 (CO)(C 5 H 5 N)