Analytical Currents Synopses of significant analytical articles from other publications Observing deposit ELECTROANALYTICAL growth a t the
nanoscale Understanding the role that additives play in electrodeposition has been hampered by problems in observing the early stages of deposit growth. Researchers have traditionally used electrochemical measurements cou pled with observations of deposit mor phology, made optically at low magnifica tion or ex situ at high magnification. The advent of scanning tunneling microscopy and related techniques, such as atomic force microscopy (AFM), has made it feasible to study these processes in situ. Rebecca M. Rynders and Richard C. Alkire of the University of Illinois at Urbana-Champaign have investigated the ini tial stages of copper electrodeposition on platinum from a purified acidic cupric sul fate solution containing benzonitriazole (BTA), which is known to inhibit copper electrodeposition and to influence deposit morphology. Platinum crystals were misoriented to form terraces for deposition. AFM reveals that deposits form on the larger terraces from a solution that contains no BTA. From a solution containing 10 μηι BTA the copper deposits in clumps along the terraces; and in a 100-pm BTA solution, deposition occurs without regard to the structure of the terrace. (J. Electrochem. Soc. 1994,141,1166-73)
provides unique experimental evidence of the position, shape, and movement of the ECL reaction layer through the course of reactant generation. (J. Am. Ckem. Soc. 1994,116, 4095-96)
5
C-G3' or 5G-C:!' base pairs in the oligonucleotides. Noncovalent actinomycin D and single-stranded DNA complexes disappeared at low pH. (Bio. Mass Spectrom. 1994,23,272-76)
Temperature -
Combinatorial libraries MASS SPECTROMETRY Combinatory methnear-IR "ϊζ, ods can provide spectroscopy " large repertoires of of g l u c o s e compounds with Near-IR spectroextensive molecu scopic analysis of lar variation— aqueous solutions libraries with more than 1 million mem is problematic because the position of the bers can be created through synthesis on three major water absorption bands is afsolid supports. Stephen J. Benkovic, Ni fected by temperature. Noninvasive measurements of clinical samples, which con- cholas Winograd, and colleagues at The Pennsylvania State University have used tain large quantities of water, are difficult to obtain because it is not easy to control imaging time-of-flight secondary ion MS to identify the molecular weights of mole temperature. Kevin H. Hazen and Mark cules bound to polystyrene beads. A. Arnold of the University of Iowa and Gary W. Small of Ohio University have deThe analysis is made possible by the veloped a temperature-insensitive specselective clipping of the bond linking the tral processing scheme for measuring clin- peptide to the bead with trifluoracetic acid ically relevant levels of aqueous glucose vapor before secondary ion MS analysis. by near-IR spectroscopy. The approach can be applied to large num A digital Fourier filter is combined with bers of polystyrene beads, 30-60 pm in diameter, and does not depend on the syn partial least-squares regression to generate a calibration model insensitive to tem- thesis of a tagging molecule or the attach ment of sets of tagging molecules. Al perature over the range 32-41 °C. The model was created using spectra collected though the method is illustrated for tri over the range 5000-4000 cnT1 with sam- mer peptides, the researchers believe it ples maintained at 37 °C. The best model should prove useful for identifying a vari provides a mean standard error of predic- ety of pharmaceutically active agents. (Sci ence 1994,264,399-402) tion across all temperatures of 0.14 mM (2.52 mg/dL). (Appl. Spectrosc. 1994,48, 477-83) Perfusion LC/ESI ion trap MS of neuropeptides Binding of actinomycin D Because neuropeptides are involved in in ECL interferometry tracellular communication in a variety of Electrochemiluminescence (ECL), the Recent advances in gentle ionization and production of light from electrochemically sensitive detection methods have made biologically important functions, there is considerable interest in developing both generated reagents, has been used ex MS an important technique in bioanalytitensively for a variety of applications, in cal chemistry. A wide variety of biologi- quantitative and qualitative methods for the determination of neuropeptides and cluding obtaining information about cally important noncovalent association their metabolites. Robert D. Voyksner highly energetic electron-transfer reac complexes, including enzyme-substrate, tions. Applying a rapidly alternating receptor-ligand, duplex DNA, heme- and Hung-Yu Lin of the Research Triangle Institute have combined perfusion LC square wave to a microelectrode allows protein, and protein-protein, have been with electrospray ion trap MS for the de the measurement time scale to approach detected with ion spray MS. Jack D. Hethat of the kinetics of the light-producing nion and co-workers at Cornell University termination of neuropeptides in plasma. The method allows analysis of 8-10 se reaction. R. Mark Wightman and co-work have used ion spray MS in conjunction rum extract samples per hour, with subers at the University of North Carolinawith MS/MS to study the binding of actiChapel Hill and at the Université di Padova nomycin D, which is currently used for picomole detection of neuropeptides in the 1000-5000 molecular weight range. Al (Italy) have described the presence of chemotherapy, to single-stranded DNA though commercial instruments that cou distinct interference patterns in the ECL The researchers found that hydrogen curves obtained at high frequencies due to bonding interactions between actinomycin ple electrospray with ion trap MS are not yet available, such combinations can be the reflection of light from the electrode D and single-stranded DNA are strongly used to increase sensitivity relative to surface. The presence of these patterns influenced by the presence or absence of BIOANALYTICALinsensitive
Analytical Chemistry, Vol. 66, No. 13, July 1, 1994 6 8 3 A
Analytical
Currents
mass analyzers with lower ion-sampling peak was verified by subjecting a !Hecycles. Optimization of parameters (such labeled fullerene mixture to an addition re as pressure, ionization time, and qz for action. They found that adding to just one trapping) is critical for achieving optimal of the 30 double bonds produced a 3-ppm sensitivity. (Rapid Commun. Mass Spec- shift of the helium peak upfield. (/. Am. trom. 1994,8, 333-38) Chem. Soc. 1994,116,3621-22)
partitioning process depends primarily on the atmospheric gas-phase (rather than airborne particulate-adsorbed) PAH concentration as well as on ambient temperature. (Environ. Sci. Technol. 1994, 28, 939-43)
Cyclodextrin Thermal energy recovery nanotubes Thermal lens spectrometry, a convenient SPECTROSCOPYInterest in supermethod for directly observing the nonradiative relaxation processes that occur fol molecular assem lowing absorption of radiation, is often ap blies such as mo plied for the determination of fluores lecular necklaces cence quantum yields. J. Georges and and nanotubes is growing because of J. M. Mermet of the Université Claude Bernard-Lyon have investigated the thertheir possible use as molecular devices. Linda McGown and Guang Li of Duke Uni mal energy recovery of thermal lens spectrometry in fluorescence quenching exversity have used dynamic fluorescence anisotropy, scatter light intensity measure periments. ments, and scanning tunneling micros Simultaneous measurement of the fluocopy to confirm the formation of rigid mo rescence intensity and the thermal lens lecular nanotube aggregates of β- and signal were made for fluorescein dianion f cyclodextrin (CD) through linkage by in water and perylene in ethanol. Georges the rodlike molecule of all-trans-\,6-diphe- and Mermet found that the thermal signyl-l,3,5-hexatriene (DPH). nal is not fully recovered during complete fluorescence quenching of fluorescein Molecular modeling shows that CD (by potassium iodide) and perylene (by nicavity size and rodlike DPH structure are key factors in nanotube formation. Spectra tromethane). Deviation from the exgenerated by proton NMR indicate the in pected thermal signal depends on the operating mode (continuous wave or pulsed) clusion of DPH in the interior of the CDs and the formation of nanotubes in β- and of the excitation laser and the solvent composition. (Spectrochim. Acta 1994, γ-CDs only. The photophysical properties of DPH are affected by its arrangement in a 50A, 953-59) one-dimensional array within the CD nanotube, possibly because of exciton for PAH cycling SEPARATIONS through the mation. (Science 1994,264,249-51) seasons 3 H e NMR for fullerenes What affects the seasonal partitionFullerenes react readily with a variety of ing of polycyclic arreagents. Although the ,3C NMR spectra omatic hydrocarof C60 and C70 are simple, spectra of the re bons (PAHs) beaction products are not, because the at tachment of groups to the fullerene skele tween the atmosphere and the Earth's surface? Staci Simonich and Ronald Hites ton reduces the high symmetry. After of Indiana University have investigated chemical modification, long data acquisi tion times are needed to obtain spectra of the factors leading to increased PAH levels in vegetation by extracting air and plant such products. Using l:
