At elevated levels, homocysteine (Hcy, 1) is a risk factor for cardiovascular diseases, Alzheimer's disease, neural tube defects, and osteoporosis. Both 1 and cysteine (Cys, 3) are linked to neurotoxicity. The biochemical mechanisms by which 1 and 3 are involved in disease states are relatively unclear. Herein, we describe simple methods for detecting either Hcy or Cys in the visible spectral region with the highest selectivity reported to date without using biochemical techniques or preparative separations. Simple methods and readily available reagents allow for the detection of Cys and Hcy in the range of their physiologically relevant levels. New HPLC postcolumn detection methods for biological thiols are reported. The potential biomedical relevance of the chemical mechanisms involved in the detection of 1 is described.

Hydrogen-bonding interactions in DNA/RNA systems are a defining feature of double helical systems. They also play a critical role in stabilizing other higher-order structures, such as hairpin loops, and thus in the broadest sense can be considered as key requisites to the successful translation and replication of genetic information. This importance, coupled with the aesthetic appeal of nucleic acid base (nucleobase) hydrogen-bond interactions, has inspired the use of such motifs to stabilize a range of synthetic structures. This, in turn, has led to the formation of a number of novel ensembles. This tutorial review will discuss these structures, both from a synthetic perspective and in terms of their potential application in areas that include, but are not limited to, self-assembled macrocyclic and high-order ensemble synthesis, supramolecular polymer preparation, molecular cage construction, and energy and electron transfer modeling.

Homocysteine (Hcy) is a biomarker for significant disorders including Alzheimer's and cardiovascular disease. The monitoring of Hcy levels in plasma is of current concern. We describe highly selective colorimetric methods for the direct detection of Hcy. Inexpensive, commercially available materials are employed. The results show potential application for the detection of Hcy in human blood plasma.

Nonadiabatic electron transfer (ET) measures the rate of electron tunneling, often facilitated by intervening covalent and nonbonded interactions. [1][2][3][4] Bridge structure therefore influences the ET kinetics, and bridge thermal fluctuations are predicted to modulate the tunneling propensity. 4,5 Structure defines the coupling pathways, and thermal fluctuations enable the system to find configurations that enhance the interaction strength.6 An open and crucial question is whether or not bridge motion can be manipulated (driven) by an external field to control pathway interactions and ET kinetics. Here, we show that mid-IR driving of bridge vibrations produces ET kinetic slowing of a photoinduced charge separation reaction.Recent theoretical analysis indicates that ET kinetics can be changed by controlling the coherence of inelastic tunneling pathway interferences in a molecular analogue of the double-slit experiment. [1][2][3][4]7 In systems with two interfering ET pathways, the excitation of a pathway-specific bridge vibration, which may induce electron-vibration energy exchange, labels the ET pathway and therefore modifies pathway interferences. [1][2][3][4]7 Affecting ET rates using mid-IR radiation 3 is generally attractive because ultrashort laser pulses offer subpicosecond perturbation, and radiation in the mid-IR is chemically innocent. In addition to inelastic tunneling, excitation of bridge vibrations can perturb elastic-tunneling kinetics. The donor-acceptor (DA) coupling may be modulated by exciting a bridge vibrational mode without electron-phonon energy exchange. Related ideas for the control of currents in molecular wires are being addressed in the context of molecular electronics and inelastic-tunneling spectroscopy. 8 Here, we report the first real-time observation of ET rate modulation by mid-IR excitation in a donor-bridge-acceptor (DBA) ensemble. 9This ensemble consists of an anthracene-derived acceptor linked to a dimethylaniline-containing donor by guanosine-cytidine (GC) hydrogen bonding ( Figure 1A). The ET is probed in a 3-pulse experiment, performed with a sequence of UV, mid-IR, and visible pulses ( Figure 1B), each of ca. 100 fs duration. The first pulse at 400 nm creates the acceptor-localized electronic excited state (ES) that then "captures" an electron from the donor with an ET rate constant, k CS , of ca. (30 ps) -1 . 9 After a small time delay, τ, the second pulse centered at 1670 cm -1 (and ∼120 cm -1 in width) is applied, targeting vibrational modes in DBA labeled in Figure 1A. The third pulse in the visible spectral region probes the sample absorbance as a function of the probe's delay time, T ( Figure 1B).The absorbance changes in the 3-pulse measurements were calculated using the equation ∆abs ) D IR -D ) log(I/I IR ), where D IR and D are the optical densities and I IR and I are the probe signals with the IR pump on and off, respectively. Since the mid-IR pulses were chopped at half of the laser repetition rate, and the two consecutively recorded spectra were processed...