SynopsisOriented fibers drawn from aqueous gels of calf-thymus DNA were maintained at constant relative humidities of 75 and 92% to yield canonical A-DNA and B-DNA structures, respectively. Raman spectra of the two forms of DNA were recorded over the spectral range KKL4OOO cm-l. The authenticated DNA fibers were deuterated in hygrostatic cells containing DzO at appropriate relative humidities, and the corresponding spectra of deuterated DNAs were also obtained. The spectra reveal all of the Raman scattering frequencies and intensities characteristic of A-and B-DNA structures in both nondeuterated and deuterated forms, as well as the frequencies and intensities of adsorbed solvent molecules from which the hydration content of DNA fibers can be calculated. Numerous conformation-sensitive vibrational modes of DNA bases and phosphate groups have been identified throughout the 300-1700-~m-~ interval. Evidence has also been obtained for conformation sensitivity of deoxyribosyl CH stretching modes in the 2800-3000-~m-~ region. Raman lines of both the backbone and the bases are proposed as convenient indicators of A-and B-DNA structures. The results are extended to Z-DNA models investigated previously. Some implications of these findings for the determination of DNA or RNA structure from Raman spectra of nucleoproteins and viruses are considered.

General X-ray Crystallographic Data for Cyclic Peptide 8. Clear, colorless crystals of cyclic peptide 8 were obtained by slow diffusion from CH 2 Cl 2 /hexane at room temperature (20-25°C). The dimensions of the crystal analyzed were: 0.3 x 0.5 x 0.5 mm. The crystals belong to the orthorhombic system with unit cell parameters at 156 K: a = 19.30(1) Å, b = 24.73(2) Å, c = 12.134(7) Å, and V = 5791(6) Å 3 . The space group is P2 1 2 1 2 1 with Z = 4 formula units/unit cell and ρ (calcd) = 1.246 g/cm 3 . Intensity data (4698 total) was collected on a Picker (Crystal Logic) diffractometer system using monchromatized MoK α radiation (λ = 0.7107 Å) via an θ-2θ

NMR spectroscopy and computer modeling were used to characterize tiopronin monolayer-protected gold clusters (MPCs). These MPCs contain gold cores with a distribution of radii ranging from 0.4 to 2.6 nm. NOESY and HMQC spectra yielded assignments for all NMR sensitive nuclei in the tiopronin ligands. DOSY and T 2 experiments provided information about the particle size distribution as a function of proton frequency shift. Further information was obtained from hole-burning and amide-exchange experiments. The spectroscopic data reveal two classes of ligands, a network of hydrogen bonds, and considerable inhomogeneous and homogeneous line broadening. The methyl and methine protons clearly exhibit two components with separations that decrease strongly with the number of bonds separating the proton from the gold core. Spin−echo experiments clearly show that a range of T 2 values is associated with each resonance frequency in both the upfield and downfield components for each type of proton but that the most probable value is larger for the upfield component. Various models that may be consistent with the NMR data and the properties of reported crystal structures were considered. It is suggested that bimodal frequency distributions result from chemical shifts that are associated with a mixture of primarily two gold cluster structure types that differ in the mode of core packing. It is suggested that the Knight shift contributes to the large downfield shift observed for the methine protons in the larger particles.

Supporting Information Experimental procedures and characterization data (1 H and 13 C and 2D NMR, IR, HRMS, GPC) for all compounds and their precursors. General Information. NMR spectra were obtained on either a Mercury 300 MHz spectrometer, an INOVA 500 MHz spectrometer equipped with an AutoX broadband probe with z-gradients, or an INOVA 600 MHz spectrometer equipped with an inverse HCN triple resonance probe with x,y,and z-gradients. All spectrometers were running Varian VNMRJ software. Chemical shifts for both 1 H and 13 C spectra are reported in per million (ppm) relative to Si(CH3)4 (δ=0) and referenced internally to the proteo solvent resonance. Multiplicities are abbreviated as follows: singlet (s), doublet (d), triplet (t), quartet (q), quintet (qt), septuptlet (sp), multiplet (m), and broad (br). MestReNova NMR 5.3.2 software was used to analyze all NMR spectra. Molecular mass calculations were performed with ChemBioDraw Ultra 11.0.1 (Cambridge Scientific). Mass spectrometry measurements (FAB, EI, and MALDI) were performed by the California Institute of Technology Mass Spectrometry Facility. Analytical thin-layer chromatography (TLC) was performed using silica gel 60 F254 precoated plates (0.25 mm thickness) with a fluorescent indicator. Visualization was performed using UV and iodine stain. Flash column chromatography was performed using silica gel 60 (230-400 mesh) from EM Science. Gel permeation chromatography (GPC) was carried in THF out on two PLgel 10 μm mixed-B LS columns (Polymer Labs) connected in series with a DAWN EOS multiangle laser light scattering (MALLS) detector and an Optilab DSP differential refractometer (both from Wyatt Technology). No calibration standards were used, and dn/dc values were obtained for each injection assuming 100% mass elution from the columns. IR was obtained on a Perkin-Elmer BX-II FTIR spectrometer using thin-film techniques on NaCl plates.