Reactivity and chemical synthesis of L-pyrrolysine- the 22(nd) genetically encoded amino acid

L-pyrrolysine, the 22(nd) genetically encoded amino acid, was previously deduced to be (4R, 5R)-4-substituted-pyrroline-5-carboxylate attached to the epsilon-nitrogen of lysine based on the crystal structure of the M. barkeri monomethylamine methyltransferase (MtmB). To confirm L-pyrrolysine's identity, structures of MtmB have been determined following treatment with hydroxylamine, N-methylhydroxylamine, or dithionite. Analysis of these structures has provided additional support for the presence of the pyrroline ring and, together with previous mass spectroscopy data, has led us to assign the C(4)-substituent to a methyl group. Based on this assignment, synthetic L-pyrrolysine was prepared by chemical methods. Detailed study of this chemically synthesized L-pyrrolysine has allowed us to characterize its physical properties, to study its chemical stability, and to elucidate the role of its C(4) substituent. Future applications of this synthetic L-pyrrolysine include its in vivo incorporation into recombinant proteins.     

Preparation and structural characterisation of methoxybis(trimethylsilyl)silyl potassium and its condensation product

Depending on the conditions the reaction of tris(trimethylsilyl)methoxysilane (1) with potassium tert-butoxide either in benzene and in the presence of 18-crown-6 or in THF gives either the crown ether adduct of potassium-methoxybis(trimethylsilyl)silane (2), or 2-methoxytetrakis(trimethylsilyl)disilanyl potassium (3).     

Synthesis and characterization of model compounds of the lysine tyrosyl quinone cofactor of lysyl oxidase

4-n-Butylamino-5-ethyl-1,2-benzoquinone (1(ox)) has been synthesized as a model compound for the LTQ (lysine tyrosyl quinone) cofactor of lysyl oxidase (LOX). At pH 7, 1(ox) has a lambda(max) at 504 nm and exists as a neutral o-quinone in contrast to a TPQ (2,4,5-trihydroxyphenylalanine quinone) model compound, 4, which is a resonance-stabilized monoanion. Despite these structural differences 1(ox) and 4 have the same redox potential (ca. -180 mV vs SCE). The structure of the phenylhydrazine adduct of 1(ox) (2) is reported, and 2D NMR spectroscopy has been used to show that the position of nucleophilic addition is at C(1). UV-vis spectroscopic pH titration of phenylhydrazine adducts of 1(ox) and 4, 2, and 11, respectively, reveals a similar red shift in lambda(max) at alkaline pH with the same pK(a) (approximately 11.8). In contrast, the red shift in lambda(max) at acidic pH conditions yields different pK(a) values (2.12 for 2 vs -0.28 for 11), providing a means to distinguish LTQ from TPQ. Reactions between in situ generated 4-ethyl-1,2-benzoquinone and primary amines give a mixture of products, indicating that the protein environment must play an essential role in LTQ biogenesis by directing the nucleophilic addition of the epsilon-amino group of a lysine residue to the C(4) position of a putative dopaquinone intermediate. Characterization of a 1,6-adduct between an o-quinone and butylamine (3-n-butylamino-5-ethyl-1,2-benzoquinone, 13) confirms the assignment of LTQ as a 1,4-addition product.     

A Conversation with Lee Alvin DuBridge - Part II

Physicist Lee A. DuBridge became president of the California Institute of Technology in 1946. In this interview he recalls his dealings at Caltech with Linus Pauling; his memories of George W. Beadle, Theodore von Kármán, and J. Robert Oppenheimer; the military Vista Project at Caltech; and the difficulties surrounding the deportation of Hsue-Shen Tsien, Caltech's Goddard Professor of Jet Propulsion.     

trans‐1,2,3‐Tris(1‐hydroxycyclo­propyl)cyclopropane

The central three‐membered ring in the title compound, trans‐1,1′,1′′‐cyclo­propane‐1,2,3‐triyl­tris­(cyclo­propanol), C₁₂H₁₈O₃, shows pronounced asymmetry of the bond lengths, which is induced by the different orientations of the substituents. A network of hydrogen bonds links the mol­ecules into sheets.     

An integrated experimental and theoretical investigation of the vibrational modes and molecular structure of a new Cu(II)–phosphocreatine complex

A new complex of Cu(II) of stoichiometry [Cu(PCr)(H₂O)] was prepared from aqueous solution at pH 6. Its synthesis, characterization, thermogravimetric, vibrational spectroscopy, and electron paramagnetic resonance analyses were described and suggest that phosphocreatine (PCr) in solid state is acting as a tridentate ligand (the nitrogen atom of the guanidine group and the oxygen atoms of the phosphate group and the carboxylate group being the donor atoms). The fourth position is occupied by a water molecule. These results were confirmed through computational calculations (DFT/B3LYP:6-311G theoretical procedure). The tetra coordination of Cu(II) arranged in a quadratic planar geometry was found to be more stable in the DFT calculations. The calculated vibrational spectrum agrees well with the FT-IR experimental spectrum.     

Proficiency testing scheme for the harmonization and comparability of analytical measurements

According to the experience of the successful implementation of proficiency tests (PT) by using the certified reference value as the assigned value, a new scheme of evaluation is presented by suggesting the use of the uncertainty associated with the certified value. The technical performance of laboratories is evaluated by the parameter quadratic mean error (QME), which is the square root of the sum of the square of the bias and that of the standard deviation of the laboratory. This parameter is considered as the estimate of the measurement uncertainty of the laboratory and is compared to the uncertainty (U) associated with the certified value provided by an NMI. Considering that the calibration and measurement capability, known as the CMC, is recognized among NMIs, the ratio QME/U enables us to compare the PT relative to the CMC of an NMI, and, consequently, to any other comparison results based on the CMC of signatories of the mutual recognition arrangement (MRA) of the International Committee of Weights and Measure (CIPM). Presented at BERM-11, October 2007, Tsukuba, Japan.