The alteration of intra-ligand donor-acceptor interactions through torsional connectivity in substituted Re-dppz complexes

The ground and excited properties of a series of [ReCl(CO)3(dppz)] complexes with substituted donor groups have been investigated. Alteration of donor-acceptor communication through modulation of torsional angle and the number and nature of the donor substituent allowed the effects on the photophysical properties to be characterized though both computational and spectroscopic techniques, including TD-DFT, resonance Raman and time resolved infrared. The ground state optical properties show significant variation as a result of donor group modulation, with increased angle between the donor and acceptor blue-shifting and depleting the intensity of the lowest energy transition, which was consistently ILCT in nature. However, across all complexes studied there was minimal perturbation to the excited state properties and dynamics. Three excited states on the picosecond, nanosecond and microsecond time scales were observed in all cases, corresponding to 1ILCT, ππ* and 3ILCT respectively

Computational and Spectroscopic Analysis of β‑Indandione Modified Zinc Porphyrins

Porphyrins have characteristic optical properties which give them the potential to be used in a range of applications. In this study, a series of β-indandione modified zinc porphyrins, systematically changed in terms of linker length and substituent, resulted in absorption spectra that are dramatically different than that observed for the parent zinc porphyrin (ZnTXP, 5,10,15,20-tetrakis­(3,5-dimethylphenyl)­porphyrinato zinc­(II)). These changes include strong absorptions at 420, 541, and 681 nm (110.2, 57.5, and 29.2 mM^–1 cm^–1, respectively) for the most perturbed compound. Computational studies were conducted and showed the different optical effects are due to a reorganization of molecular orbitals (MOs) away from Gouterman’s four-orbital model. The substituent effects alter both unoccupied and occupied MOs. An increased length of linker group raised the energy of the HOMO–2 such that it plays a significant role in the observed transitions. The degenerate LUMO (e_g) set are split by substitution, and this splitting may be increased by use of a propylidenodinitrile group, which shows the lowest-energy transitions and the greatest spectral perturbation from the parent zinc porphyrin complex. These data are supported by resonance Raman spectroscopy studies which show distinct enhancement of phenyl modes for high-energy transitions and indandione modes for lower-energy transitions

Controlled Formation of Heteroleptic [Pd₂(L_a)₂(L_b)₂]⁴⁺ Cages

Metallo­supra­molecular architectures are beginning to be exploited for a range of applications including drug delivery, catalysis, molecular recognition, and sensing. For the most part these achievements have been made with high-symmetry metallo­supra­molecular architectures composed of just one type of ligand and metal ion. Recently, considerable efforts have been made to generate metallo­supra­molecular architectures that are made up of multiple different ligands and/or metals ions in order to obtain more complex systems with new properties. Herein we show that the addition of an electron-rich 2-amino-substituted tripyridyl ligand, 2,6-bis­(pyridin-3-ylethynyl)­pyridine (<b>2A-tripy</b>), to a solution of the [Pd₂(<b>tripy</b>)₄]⁴⁺ cage resulted in the clean generation of a hetero­leptic [Pd₂(<b>tripy</b>)₂­(<b>2A-tripy</b>)₂]⁴⁺ architecture. The formation of the mixed-ligand cage [Pd₂(<b>tripy</b>)₂­(<b>2A-tripy</b>)₂]⁴⁺ was confirmed using ¹H NMR spectroscopy, diffusion-ordered spectroscopy, and rotating-frame nuclear Overhauser effect spectroscopy and high-resolution electrospray ionization mass spectrometry. Density functional theory calculations suggested the <i>cis</i> isomer was more stable that the <i>trans</i> isomer. Additionally, the calculations indicated that the hetero­leptic palladium­(II) cages are kinetically metastable intermediates rather than the thermodynamic product of the reaction. Competition experiments supported that finding and showed the cages are long-lived in solution at room temperature. Finally, it was shown that the addition of <b>2A-tripy</b> to a range of preformed [Pd₂(<b>L</b>_<b>tripy</b>)₄]⁴⁺ cages cleanly generated the mixed-ligand systems. Three other systems displaying different <i>exo</i> and <i>endo</i> functionalities within the cage assembly were generated, suggesting that this method could be applied to synthesize a range of highly functionalized hetero­leptic <i>cis</i>-[Pd₂(<b>L</b>_<b>a</b>)₂­(<b>L</b>_<b>b</b>)₂]⁴⁺ cages

Percentage of nitrogen content (w/w) versus the organic-phosphate (<i>ν</i>₁) ratio.

<p>Percentage of nitrogen content (w/w) versus the organic-phosphate (<i>ν</i>₁) ratio.</p

Effect of Bridge Alteration on Ground- and Excited-State Properties of Ruthenium(II) Complexes with Electron-Donor-Substituted Dipyrido[3,2‑<i>a</i>:2′,3′‑<i>c</i>]phenazine Ligands

A series of Ru­(II) 2,2′-bipyridine (bpy) complexes with an electron-accepting dipyrido­[3,2-<i>a</i>:2′,3′-<i>c</i>]­phenazine (dppz) ligand coupled to an electron-donating triarylamine (TAA) group have been investigated. Systematic alteration of a bridging unit between the dppz and TAA allowed exploration into how communication between the donor and acceptor is perturbed by distance, as well as by steric and electronic effects. The effect of the bridging group on the electronic properties of the systems was characterized using a variety of spectroscopic methods, including Fourier transform–Raman (FT-Raman) spectroscopy, resonance Raman spectroscopy, and transient resonance Raman (TR²) spectroscopy. These methods were used in conjunction with ground- and excited-state absorption spectroscopy, electrochemical studies, and DFT calculations. The ground-state electronic absorption spectra show distinct variation with the bridging group, with the wavelength observed for the lowest energy electronic transition ranging from 449 nm to 522 nm, accompanied by large changes in the molar absorptivity. The lowest-energy Franck–Condon state was determined to be intra-ligand charge transfer (ILCT) in nature for most compounds. The presence of higher-energy metal-to-ligand charge transfer (MLCT) Ru­(II) → bpy and Ru­(II) → dppz transitions was also confirmed via resonance Raman spectroscopy. The TR² spectra showed characteristic dppz^• – and TAA^• + vibrations, indicating that the THEXI state formed was also ILCT in nature. Excited-state lifetime measurements reveal that the rate of decay is in accordance with the energy gap law and is not otherwise affected by the nature of the bridging unit

Raman Spectroscopy of Fish Oil Capsules: Polyunsaturated Fatty Acid Quantitation Plus Detection of Ethyl Esters and Oxidation

Fish oils are the primary dietary source of ω-3 polyunsaturated fatty acids (PUFA), but these compounds are prone to oxidation, and commercial fish oil supplements sometimes contain less PUFA than claimed. These supplements are predominantly sold in softgel capsules. In this work, we show that Fourier transform (FT)–Raman spectra of fish oils (<i>n</i> = 5) and ω-3 PUFA concentrates (<i>n</i> = 6) can be acquired directly through intact softgel (gelatin) capsules. These spectra could be used to rapidly distinguish supplements containing ethyl esters from those containing triacylglyceride oils. Raman spectroscopy calibrated with partial least-squares regression against traditional fatty acid methyl ester analyses by gas chromatography–mass spectrometry could be used to rapidly and nondestructively quantitate PUFA and other fatty acid classes directly though capsules. We also show that FT–Raman spectroscopy can noninvasively detect oxidation with high sensitivity. Oils with peroxide values of as low as 10 mequiv kg^–1, which are on the cusp of falling outside of specification, could be readily distinguished from oils that were within specification (7 mequiv kg^–1)

The FT-Raman spectrum of the bone sample from Burial 511 from Ban Non Wat (Raman ID 41), one of the 6 bones that displayed high protein content relative to the other Ban Non Wat specimens.

<p>Inset is of the C-H stretch region.</p

Percentage of carbon content (w/w) versus the organic-phosphate (<i>ν</i>₁) ratio.

<p>Percentage of carbon content (w/w) versus the organic-phosphate (<i>ν</i>₁) ratio.</p

Weight % nitrogen (%N), weight % carbon (%C), % yield of gelatin relative to undemineralised bone starting weight (% collagen), and Raman organic-phosphate ratio [C-H/PO₄³⁻ (<i>ν</i>₁)] for 31 Ban Non Wat skeletal samples.

<p>The %N, %C, and the atomic CN ratio [Atomic C:N  =  (%C/%N) ×1.1666] from stable isotope analysis are provided to illustrate mass spectrometry indicators of protein survival. The % collagen yield is calculated from bone weight before demineralisation.</p

The location of the site of Ban Non Wat in present-day northeast Thailand, and other important archaeological sites (from [38].

<p>The location of the site of Ban Non Wat in present-day northeast Thailand, and other important archaeological sites (from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0098462#pone.0098462-Higham2" target="_blank">[38]</a>.</p