THE STRUCTURE OF HUMAN PANCREATIC LIPASE SUGGESTS A LOCALLY INVERTED, TRYPSIN-LIKE MECHANISM

Furthercrystallographic refinement of the structure of human pancreatic lipase hasled to an improved model which has been used for modelling studies of the hydrolysis of triglyceride substrates. In addition to the removalof the flap, further changesin the protein structure around the active site appear necessary to formulate a stereochemically plausible mechanism. A locally inverted trypsin-like mechanism is presently favoured and demands relatively modest changes of the X-ray structure. Additional new findings include the interpretation of the difference density for a butylboronic acid derivative and the location of a Ca2+ bindingsite

2,3-Bis(methylene)bicyclo[2.1.1]hexane and 3,4-Bis(methylene)tricyclo[3.1.0.02,6^{2,6}]hexane : Interaction between a π System and a Cyclobutane or Bicyclobutane Moiety

The He (I) photoelectron spectra of 2-bicyclo[2.1.l]hexene (1), 2,3-bis(methylene)bicyclo[2.1.l]hexane (3), and 3,4-bis(methylene)tricyclo[3.l.O.0$^{2.6}$]hexane (4) have been investigated. The assignment given is based on a ZDO model and semiempirical calculations. Tagether with the PE data of benzvalene (2), the reported data allow a comparison between 1-2 and 3-4. This yields a measure of the interactions between 8 cyclobutane or 8 bicyclobutane moiety and a double bond system within a ZDO model. The resonance integral found in the case of 1 and 3 amounts to -1.9 eV, that for 2 and 4, to -2.3 eV. The investigations furthermore reveal that the electronic factors which contribute to the higher reactivity of the bicyclobutane compounds amount to 5 kcal/mol

Preparation and X-ray crystal structures of two 1-amino-2,6-anhydro-1,3,4- trideoxy-D-erythro- and L-glycero-heptitol derivatives

The structures of the 1-amino-2,6-anhydro-hepitol derivatives (4) and (6), prepared from nitrile (3), were determined by X-ray crystallography

The Electronic Structure of Phenylene and Naphthylene Bicyclobutanes: Photoelectron spectroscopy and model calculations

The photoelectron (PE.) spectra of 1,2,3-methenoindane (2), 1,2,3-metheno-2,3-dihydro-1H-cyclopenta [b]naphthalene (3) and 1,2,3-metheno-2,3-dihydro-1H-phenalene (4) are investigated. The PE. spectrum of 1,3-methano-2,3-dihydrophenalene (7) is reported and compared with that of 4. The experimental results are analyzed in terms of empirical correlation diagrams and the results of semiempirical MINDO/3 and CNDO/S calculations. The analysis indicates that the strong impact of the bicyclobutylene group on the spectroscopic properties of the aromatic π-systems in 2, 3 and 4 is due to hyperconjugative interactions involving bicyclobutane Walsh orbitals

ChemInform Abstract: ELECTRONIC STATES OF PHENYLENE AND NAPHTHYLENE BICYCLOBUTANES. LINEAR DICHROISM IN STRETCHED POLYETHYLENE

Excited singlet states of bicyclobutylene-benzene (2), 1,2:4,5-bis (bicyclo-butylene)benzene (3), 2,3-bicyclobutylene-naphthalene (4), and 1,8-bicyclobutylene-naphthalene (5) are investigated by means of linear dichroic absorption spectroscopy of molecules oriented in stretched polyethylene films and by semiempirical model calculations. The results indicate a strong hyperconjugative impact of the bicyclobutylene group on the aromatic chromophores in these compounds. Valence isomerization to aromatic products is predicted as the preferred photochemical pathway