This paper will discuss the design and construction of BESIII [1], which is designed to study physics in the τ-charm energy region utilizing the new high luminosity BEPCII double ring e + ecollider [2]. The expected performance will be given based on Monte Carlo simulations and results of cosmic ray and beam tests. In BESIII, tracking and momentum measurements for charged particles are made by a cylindrical multilayer drift chamber in a 1 T superconducting solenoid. Charged particles are identified with a time-of-flight system based on plastic scintillators in conjunction with dE/dx (energy loss per unit pathlength) measurements in the drift chamber. Energies of electromagnetic showers are measured by a CsI(Tl) crystal calorimeter located inside the solenoid magnet. Muons are identified by arrays of resistive plate chambers in the steel magnetic flux return. The level 1 trigger system, Data Acquisition system and the event filter system based on networked computers will also be described.

Conformational properties of a 12-residue tryptophan zipper (trpzip) -hairpin peptide (AWAWENGKWAWK-NH 2 , a modification of the original trpzip2 sequence) are analyzed under equilibrium conditions using ECD and IR spectra of a series of variants, singly and doubly C 1 -labeled with 13 C on the amide CdO. The characteristic features of the 13 CdO component of the amide I′ IR band and their sensitivity to the local structure of the peptide are used to differentiate stabilities for parts of the hairpin structure. Doubly labeled peptide spectra indicate that the ends of the -strands are frayed and that the center part is more stable as would be expected from formation of a stable hydrophobic core consisting of four tryptophan residues, and supported by MD simulations. NMR analyses were used to determine a best fit solution structure that is in close agreement with that of trpzip2, except for a small variation in the turn geometry. The distinct vibrational coupling patterns of the labeled sites based on this structure are also well matched by ab initio DFT-level calculations of their IR spectral patterns. Thermal unfolding of the peptides as studied with CD spectra could be fit with an apparent two-state transition model. ECD senses only the tryptophan interactions (tertiary-like) and their overall environment, as shown by TD-DFT modeling of the Trp-Trp π-π* ECD. However, variation of the amide I IR spectra of 13 C-isotopomers showed that the thermal unfolding process is not cooperative in terms of the peptide backbone (secondary structure), since the transition temperatures sensed for labeled modes differ from those for the whole peptide. The thermal data also evidence dependence on concentration and pH but these cause little spectral variation. This study illustrates the consequences of multistate conformational change at the residue-or sequence-specific level in a system whose structure is dominated by hydrophobic collapse.

Two antiparallel beta-strands connected by a turn make beta-hairpins an ideal model system to analyze the interactions and dynamics of beta-sheets. Site-specific conformational dynamics were studied by temperature-jump IR spectroscopy and isotopic labeling in a model based on the tryptophan zipper peptide, Trpzip2, developed by Cochran et al. (Proc. Natl. Acad. Sci. U.S.A. 2001, 98, 5578). The modified Trpzip2C peptides have nearly identical equilibrium spectral behavior as Trpzip2 showing that they also form well-characterized beta-hairpin conformations in aqueous solution. Selective introduction of 13C=O groups on opposite strands lead to distinguishable cross-strand coupling of the labeled residues as monitored in the amide I' band. These frequency patterns reflect theoretical predictions, and the coupled 13C=O band loses intensity with increase in temperature and unfolding of the hairpin. Thermal relaxation kinetics were analyzed for unlabeled and cross-strand isotopically labeled variants. T-jumps of approximately 10 degrees C induce relaxation times of a few microseconds that decrease with increase of the peptide temperature. Differences in kinetic behavior for the loss of beta-strand and gain of disordered structure can be used to distinguish localized structure dynamics by comparison of nonlabeled and labeled amide I' components. Analysis of the data supports multistate dynamic and equilibrium behavior, but because of this process it is not possible to clearly define a folding and unfolding rate. Nonetheless, site-specific relaxation kinetics could be seen to be consistent with a hydrophobic collapse hypothesis for hairpin folding.