Semisynthesis of dimeric proteins by expressed protein ligation

A one-pot synthesis of homodimeric proteins is described. The synthetic strategy is based on a double expressed protein ligation reaction between thioester peptides and a new bis-cysteinyl linker. The protocol was also applied to the synthesis of heterodimers.     

Rotamer stability in cis-[Pt(diA)G2] complexes (diA = diamine derivative and G = guanine derivative) mediated by carrier-ligand amine stereochemistry as revealed by circular dichroism spectroscopy

Extensive investigations of cis-[Pt(diA)G2] complexes (in which G = a guanine ligand; diA = a single diamine ligand) revealed the types of interactions between the two G ligands and between the G and the cis-amine substituents when diA is a diamine ligand with substituents on each nitrogen atom being a small hydrogen atom and a bulky group able to slow the rotation about the Pt-G bond. All these interactions are shown to apply also when diA = dach (1,2-diaminocyclohexane), even though this chiral primary diamine has only small N-H atoms on each side of the coordination plane. However, a slight difference in the stereochemistry of the two protons (one N-H has "quasi axial" and the other "quasi equatorial" character) is sufficient to induce a significant change in the relative stabilities of the [Pt(dach)G2] deltaHT and lambdaHT rotamers (HT = head-to-tail). The new results show that at acidic and neutral pH the induction of asymmetry from the dach ligand to the HT rotamers is governed by the G-to-G dipole-dipole interaction, which is greater for the six-membered ring of each guanine leaning towards the cis-G. Such a "six-in" canting of the two guanine ligands can be hampered by the steric interaction between the H8 of each guanine and the substituent on the cis-amine that is on the same side of the coordination plane. Such a repulsion is greater for a "quasi equatorial" N-H than for a "quasi axial" N-H. Under basic pH conditions, deprotonation of the guanine N1-H renders the O6 atom a much better hydrogen-bond acceptor; therefore, the stability of the HT rotamers is governed by the hydrogen-bond interaction of guanine O6 and the cis-amine N-H group. Such a guanine O6/N-H cis-amine interaction is stronger for a "quasi axial" than for a "quasi equatorial" N-H group. In the head-to-head (HH) rotamer, in which the electrostatic repulsion between electron-rich O6 atoms, both on the same side of the platinum coordination plane, tends to place the six-membered rings of each guanine further from the cis-guanine and closer to the cis-amine, we can expect better N-H...O6 hydrogen bonding for the "quasi equatorial" N-H groups.     

Conformational study of isotactic poly[(S)-5-methyl-1-heptene] and poly[(S)-2-methylbutyl vinyl ether] by IR spectroscopy

Infrared (IR) investigation of structurally analogous optically active polymers such as poly[(S)-5-methyl-1-heptene (1)] and poly[(S)-2-methylbutyl vinyl ether (2)] was carried out in the solid state, in the molten state, and in solution. Vibrational data are in accordance with the existence of helical conformations in solution and in the molten state for both polymers, confirming the previous suggestions based on optical rotation measurements. In particular, an accurate examination of the spectral region between 850 and 700 cm^?1, where characteristic absorptions of the sec-butyl group occur, enables us to assign the medium intensity band at 827 cm^?1 (present in both polymers in the solid state) to the GTTG^?T conformation of the side chains.     

Structural and spectral study of 7-bromo-1,3-dihydro-5-(2-pyridyl)-2H-1,4-benzodiazepin-2-one (bromazepam) platinum(II) dichloride bisdimethylsulfoxide

The synthesis and crystal and molecular structure of the title compound are reported. It belongs to the monoclinic space groupC2/c, witha=17.889(2),b=13.511(1),c=19.912(2) Å,=99.841(4)°, andZ=8. The structure was refined to a finalR of 2.77% (R _w =2.88%) for 3617 observed reflections. Vibrational spectra are recorded and discussed.     

Restricted rotation in amides—VI : Configurations and conformations of unsymmetrical tertiary benzamides

Configurational assignments in a series of N-alkyl-N-benzylbenzamides using a variety of NMR techniques lead to consistent assignments in amides with two isomers but are inconclusive for amides with single isomers. Single crystal X-ray structure determination shows the configuration of o-bromo-N-benzyl-N-t-butyl-benzamide to have the t-Bu group syn to the carbonyl oxygen. Surprisingly, the major isomer of o-chloro-N-benzyl-N-i-propylbenzamide, appears to have the opposite configuration, i.e., the i-Pr group is anti to the carbonyl oxygen. The structural details of o-bromo-N-benzyl-N-t-butylbenzamide reveal slight deviation from planarity for the amide group and chirality of the benzoyl group.     

Structural consequences of metal complexation of cyclo[Pro-Phe-Phe-Ala-Xaa]2 decapeptides

The conformational features of both free and Ca2+-complexed cyclo[Pro-Phe-Phe-Ala-Xaa]2 (with Xaa= Glu(OtBu), Lys(CIZ), Leu, and Ala) in solution have been determined by NMR spectroscopy and extensive distance-geometry calculations. The decapeptides are conformationally homogeneous in solution and show common structural features in their free and complexed forms. The structures of the free form contain only trans peptide bonds and are topologically similar to the structure of gramicidin-S, folded up in two antiparallel extended structures, stabilized by interstrand hydrogen bonds, and closed at both ends by two beta-turns. In contrast, the Ca2+-complexed peptides present two cis peptide bonds and are generally similar to those observed for the metal-complexed forms of antamanide and related analogues, folded into a saddle shape with two beta-turns. The Glu(OtBu)-, Leu-, and Lys(ClZ)-containing peptides examined here maintain the biological activity of the cyclolinopeptide A in their ability to competitively inhibit cholate uptake. The natural antamanide and cyclolinopeptide A are both able to inhibit the uptake of bile salts into hepatocytes. They share the same postulated active sequence Pro-Phe-Phe. Based on our structural results, we conclude that the ability to adopt a global conformation, characterized by a clear amphipathic separation of hydrophobic and hydrophilic surfaces, is an important feature for the functioning of this class of peptides.     

Solid-state structure and conformation of (Z)-2-(phenylbenzylidene)-3-quinuclidinone,an intermediate in the synthesis of quinuclidine derivatives

(Z)-2-(2-phenylbenzylidene)-3-quinuclidinone, C₂₀H₁₉NO,M _r =300.47D crystallizes in the monoclinicP2₁/c space group witha = 6.9809(2) Å,b=19.0523(2) Å,c = 11.7733(1) Å,=100.92(2)°,V=1537.5(3) ų,Z=4,D _c = 1.298 g/cm³,D _x =1.29 g/cm³ (flotation). Diffractometric data, using CuK radiation,=1.54178 Å, were collected on plate-like crystals. The structure, solved by direct methods was refined to a final R value of 0.037 for the 2645 observed reflections withF _o >3.0(F _o ). The molecule shows a trans conformation around the double bond. The quinuclidine and the diphenyl moieties present deformations in their geometric and conformational parameters due to the need of releasing intramolecular strains and/or nonbonded interactions.     

On the quantum Teichmüller invariants of fibred cusped 3-manifolds

This paper defines the pressure metric on the Moduli space of Margulis spacetimes without cusps and shows that it is positive definite on the constant entropy sections. It also demonstrates an identity regarding the variation of the cross-ratios.     

A fast 3D dual boundary element method based on hierarchical matrices

In this paper a fast solver for three-dimensional BEM and DBEM is developed. The technique is based on the use of hierarchical matrices for the representation of the collocation matrix and uses a preconditioned GMRES for the solution of the algebraic system of equations. The preconditioner is built exploiting the hierarchical arithmetic and taking full advantage of the hierarchical format. Special algorithms are developed to deal with crack problems within the context of DBEM. The structure of DBEM matrices has been efficiently exploited and it has been demonstrated that, since the cracks form only small parts of the whole structure, the use of hierarchical matrices can be particularly advantageous. Test examples presented show that, with the proposed technique, substantial increase in number of elements over the crack surfaces leads only to moderate increases in memory storage and solution time.     

A New Perspective in Adhesion Science and Technology: Testing Dynamic Failure of Adhesive Junctions for Space Applications

Under micro-gravity conditions, typical of the space environment, adhesion forces may play a relevant role in the manipulation of objects, especially when they must be released into free-fall under controlled residual velocity conditions. When only contact forces may be applied to the body that must be released to free-fall, no solution different from inertia is available to detach it from the manipulating device. If the manipulator is retracted from the body quickly enough, any adhesive bond existing between them is brought to failure, being loaded by the inertia force. The body acquires a residual momentum equal to the impulse developed by the adhesion force upon its failure. An experimental technique has been developed to characterize the impulse that adhesive junctions between two metallic rough surfaces develop upon dynamic failure, as part of the qualification of a system (the Caging Mechanism) designed for this specific function in the frame of the LISA Pathfinder space mission by the European Space Agency (ESA). This paper reports on the recent results obtained through the experimental campaigns performed in the LISA Pathfinder ground testing activities of the Caging Mechanism.