Turning Tryptophanase into Odor‐Generating Biosensors

An odor‐based sensor system that exploits the metabolic enzyme tryptophanase (TPase) as the key component is reported. This enzyme is able to convert an odorless substrate like S‐methyl‐L ‐cysteine or L ‐tryptophan into the odorous products methyl mercaptan or indole. To make a biosensor, TPase was biotinylated so that it could be coupled with a molecular recognition element, such as an antibody, to develop an ELISA‐like assay. This method was used for the detection of an antibody present in nM concentrations by the human nose. TPase can also be combined with the enzyme pyridoxal kinase (PKase) for use in a coupled assay to detect adenosine 5′‐triphosphate (ATP). When ATP is present in the low μM concentration range, the coupled enzymatic system generates an odor that is easily detectable by the human nose. Biotinylated TPase can be combined with various biotin‐labeled molecular recognition elements, thereby enabling a broad range of applications for this odor‐based reporting system.     

Low temperature optical study of Gadolinium molybdate and influence of an external magnetic field

We describe the optical absorption spectrum of a single crystal of Gadolinium Molybdata (GMO) at the temperature of liquid helium. We observe a set of sharp lines in the near ultra violet region; we clasify the lines into three groups A, B, and C. We study the positions of the lines as functions of the orientation of the crystal relative to the polarization of the incident light and we investigate the Zeeman effect on the lines of the groups A and B. We suggest that the observed lines of all three groups are due to transitions between the ground ${}^8\text{S}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ state and the excited ${}^6\text{P}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$, ${}^6\text{P}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ and ${}^6\text{P}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ states of the Gd³⁺ ion in the crystal.     

Mass spectrometry guided in situ proteolysis to obtain crystals for X-ray structure determination

A strategy for increasing the efficiency of protein crystallization/structure determination with mass spectrometry has been developed. This approach combines insights from limited proteolysis/mass spectrometry and crystallization via in situ proteolysis. The procedure seeks to identify protease-resistant polypeptide chain segments from purified proteins on the time-scale of crystal formation, and subsequently crystallizing the target protein in the presence of the optimal protease at the right relative concentration. We report our experience with 10 proteins of unknown structure, two of which yielded high-resolution X-ray structures. The advantage of this approach comes from its ability to select only those structure determination candidates that are likely to benefit from application of in situ proteolysis, using conditions most likely to result in formation of a stable proteolytic digestion product suitable for crystallization.     

Fidelity of Cyber-Physical Empirical Methods

Experimental Techniques - Cyber-physical empirical methods enable to address problems that classical empirical methods alone, or models alone, cannot address in a satisfactory way. In CPEMs, the...     

Existence of charged excitons in CuCl

New experimental as well as theoretical results allow us to attribute the v₂ line (25,654 cm^?1at 4.2 K) of the copper chloride absorption spectra, to a direct optical transition between a Γ₇ free hole and a $\text{Γ}{}_{\mathrm{<mtext>6</mtext>}}$ positive X⁺₂ charged exciton.     

How Many Are Too Many? Managing OnLine Growing Pains

The Physical Chemistry OnLine Consortium (PCOL) is dedicated to enhancing undergraduate physical chemistry by encouraging faculty and challenging students to conduct short-term (~4 weeks) Webbased, mathematically sophisticated activities. PCOL projects involve students and faculty at geographically dispersed institutions. In the fall of 2000, PCOL sponsored three very different projects involving faculty and 175 students from 16 different institutions. This paper discusses strategies for dealing with the growing pains that our successful Web-based educational endeavor has encountered.Presented at the ACS Division of Chemical Education sponsored symposium on web-assisted learning in chemistry at its 221st national meeting in San Diego, CA April 1–5, 2001.     

On the Zeeman effect of the principal emission line of high purity CuI at very low temperatures

The strong emission line at 24346 cm^-1 (4.2 K) is attributed to the radiative recombination of excitons bound to neutral acceptors (A⁰, X).