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Determining the mechanism of metal–organic framework (MOF) crystal growth is important for the development of more efficient and reliable synthetic methods. Resonance Raman spectroscopy has been used for the first time to detect interactions in solution between metal ions and bridging ligands as MOFs form. UV excitation (229 nm) produced strong resonance enhancement of 4,4′-bipyridine (bpy) vibrational bands and showed that soluble Co2+-bpy species formed in solution prior to the growth of MOF crystals from bpy and Co(NO3)2. The results of the Raman experiments informed the development of faster methods for synthesizing [Co2(bpy)3(NO3)4]n 2D bilayer and [Co(bpy)(NO3)2(H2O)2]n 1D chain MOFs. [ABSTRACT FROM AUTHOR]

Calmodulin (CaM) is a ubiquitous moderator protein for calcium signaling in all eukaryotic cells. This small calcium-binding protein exhibits a broad range of structural transitions, including domain opening and folding-unfolding, that allow it to recognize a wide variety of binding partners in vivo. While the static structures of CaM associated with its various binding activities are fairly well-known, it has been challenging to examine the dynamics of transition between these structures in real-time, due to a lack of suitable spectroscopic probes of CaM structure. In this article, we examine the potential of ultraviolet resonance Raman (UVRR) spectroscopy for clarifying the nature of structural transitions in CaM. We find that the UVRR spectral change (with 229 nm excitation) due to thermal unfolding of CaM is qualitatively different from that associated with opening of the C-terminal domain in response to Ca2+ binding. This spectral difference is entirely due to differences in tertiary contacts at the interdomain tyrosine residue Tyr138, toward which other spectroscopic methods are not sensitive. We conclude that UVRR is ideally suited to identifying the different types of structural transitions in CaM and other proteins with conformation-sensitive tyrosine residues, opening a path to time-resolved studies of CaM dynamics using Raman spectroscopy. [ABSTRACT FROM AUTHOR]

Time-resolved resonance Raman (RR) spectra are reported for hemoglobin (Hb) tetramers, in which the α and β chains are selectively substituted with mesoheme. The Soret absorption band shift in mesoheme relative to protoheme permits chain-selective recording of heme RR spectra. The evolution of these spectra following HbCO photolysis shows that the geminate recombination rates and the yields are the same for the two chains, consistent with recent results on 15N-heme isotopomer hybrids. The spectra also reveal systematic shifts in the deoxyheme ν4 and νFe–His RR bands, which are anticorrelated. These shifts are resolved for the successive intermediates in the protein structure, which have previously been determined from time-resolved UV RR spectra. Both chains show Fe–His bond compression in the immediate photoproduct, which relaxes during the formation of the first intermediate, Rdeoxy (0.07 μs), in which the proximal F-helix is proposed to move away from the heme. Subsequently, the Fe–His bond weakens, more so for the α chains than for the β chains. The weakening is gradual for the β chains, but is abrupt for the α chains, coinciding with completion of the R–T quaternary transition, at 20 μs. Since the transition from fast- to slow-rebinding Hb also occurs at 20 μs, the drop in the α chain νFe–His supports the localization of ligation restraint to tension in the Fe–His bond, at least in the α chains. The mechanism is more complex in the β chains. [ABSTRACT FROM AUTHOR]

Methionine-rich motifs have an important role in copper trafficking factors, including the CusF protein. Here we show that CusF uses a new metal recognition site wherein Cu(I) is tetragonally displaced from a Met2His ligand plane toward a conserved tryptophan. Spectroscopic studies demonstrate that both thioether ligation and strong cation-π interactions with tryptophan stabilize metal binding. This novel active site chemistry affords mechanisms for control of adventitious metal redox and substitution chemistry. [ABSTRACT FROM AUTHOR]