Probing the photoinduced metal-nitrosyl linkage isomerism of sodium nitroprusside in solution using transient infrared spectroscopy

We study photoinduced metal-nitrosyl linkage isomerism in sodium nitroprusside (Na(2)[Fe(II)(CN)(5)NO]·2H(2)O, SNP) dissolved in methanol using picosecond transient infrared (IR) spectroscopy. The high sensitivity of this technique allows the simultaneous observation of two known metastable (MS) iron-nitrosyl linkage isomers of SNP, [Fe(II)(CN)(5)(η(1)-ON)](2-) (MS1) and [Fe(II)(CN)(5)(η(2)-NO)](2-) (MS2), at room temperature. The transient population of free nitrosyl radicals (NO·) is also measured in the sample solution. These three transient species are detected using their distinct nitrosyl stretching frequencies at 1794 cm(-1) (MS1), 1652 cm(-1) (MS2), and 1851 cm(-1) (NO·). The metastable isomers and NO· are formed on a subpicosecond time scale and have lifetimes greater than 100 ns. A UV (400 nm)-pump power dependence study reveals that MS1 can be formed with one photon, while MS2 requires two photons to be populated at room temperature in solution. Other photodissociation products including cyanide ion, Prussian blue, and [Fe(III)(CN)(5)(CH(3)OH)](2-) are observed. We develop a photochemical kinetic scheme to model our data, and the analysis reveals that photoisomerization and photodissociation of the metal-NO moiety are competing photochemical pathways in SNP dissolved in methanol at room temperature. Based on the analysis, the solvent-associated Fe(III) species and Prussian blue form on a 130 and 320 ps time scale, respectively. The simultaneous detection and characterization of photoinduced linkage isomerism (MS1 and MS2) and photodissociation of the metal-NO bond in SNP highlights the importance of understanding the role played by metastable metal-nitrosyl linkage isomers in the photochemistry of metal-nitrosyl compounds in chemistry and biology.     

Communication: Probing non-equilibrium vibrational relaxation pathways of highly excited C≡N stretching modes following ultrafast back-electron transfer

Fifth-order nonlinear visible-infrared spectroscopy is used to probe coherent and incoherent vibrational energy relaxation dynamics of highly excited vibrational modes indirectly populated via ultrafast photoinduced back-electron transfer in a trinuclear cyano-bridged mixed-valence complex. The flow of excess energy deposited into four C≡N stretching (ν(CN)) modes of the molecule is monitored by performing an IR pump-probe experiment as a function of the photochemical reaction (τ(vis)). Our results provide experimental evidence that the nuclear motions of the molecule are both coherently and incoherently coupled to the electronic charge transfer process. We observe that intramolecular vibrational relaxation dynamics among the highly excited ν(CN) modes change significantly en route to equilibrium. The experiment also measures a 7 cm(-1) shift in the frequency of a ～57 cm(-1) oscillation reflecting a modulation of the coupling between the probed high-frequency ν(CN) modes for τ(vis) < 500 fs.     

Picosecond X-ray absorption spectroscopy of a photoinduced iron(II) spin crossover reaction in solution

In this study, we perform steady-state and time-resolved X-ray absorption spectroscopy (XAS) on the iron K-edge of [Fe(tren(py)3)](PF6)2 dissolved in acetonitrile solution. Static XAS measurements on the low-spin parent compound and its high-spin analogue, [Fe(tren(6-Me-py)3)](PF6)2, reveal distinct spectroscopic signatures for the two spin states in the X-ray absorption near-edge structure (XANES) and in the X-ray absorption fine structure (EXAFS). For the time-resolved studies, 100 fs, 400 nm pump pulses initiate a charge-transfer transition in the low-spin complex. The subsequent electronic and geometric changes associated with the formation of the high-spin excited state are probed with 70 ps, 7.1 keV, tunable X-ray pulses derived from the Advanced Light Source (ALS). Modeling of the transient XAS data reveals that the average iron-nitrogen (Fe-N) bond is lengthened by 0.21+/-0.03 A in the high-spin excited state relative to the ground state within 70 ps. This structural modification causes a change in the metal-ligand interactions as reflected by the altered density of states of the unoccupied metal orbitals. Our results constitute the first direct measurements of the dynamic atomic and electronic structural rearrangements occurring during a photoinduced FeII spin crossover reaction in solution via picosecond X-ray absorption spectroscopy.     

Chitosan Nanoparticles-Insight into Properties,Functionalization and Applications in Drug Delivery and Theranostics

Nanotechnology-based development of drug delivery systems is an attractive area of research in formulation driven R&D laboratories that makes administration of new and complex drugs feasible. It plays a significant role in the design of novel dosage forms by attributing target specific drug delivery, controlled drug release, improved, patient friendly drug regimen and lower side effects. Polysaccharides, especially chitosan, occupy an important place and are widely used in nano drug delivery systems owing to their biocompatibility and biodegradability. This review focuses on chitosan nanoparticles and envisages to provide an insight into the chemistry, properties, drug release mechanisms, preparation techniques and the vast evolving landscape of diverse applications across disease categories leading to development of better therapeutics and superior clinical outcomes. It summarizes recent advancement in the development and utility of functionalized chitosan in anticancer therapeutics, cancer immunotherapy, theranostics and multistage delivery systems.     

中空纤维三相液相微萃取-薄层色谱分离同步荧光法测定酱油中的色胺含量

以三相中空纤维液相微萃取(HF-LPME)作为样品前处理方法,结合薄层色谱分离,同步荧光光谱法测定酱油中色胺的含量。通过单因素实验确立的萃取最优条件为:样品溶液p H值为12.0,正辛醇为萃取溶剂,0.1 mol/L的HCl为接受相,搅拌速度为590 r/min,萃取时间为60 min;取20μL接受相进行TLC分析,样品点用异丙醇溶解后离心分离;采用同步荧光在λem=350.4 nm处进行定量分析。在最佳萃取条件下,方法的线性范围为0.32~50 mg/L(r0.978 0),检出限(S/N=3)为0.32 mg/L。酱油样品的加标回收率为87.5%~107.7%,相对标准偏差(RSD)不大于6.6%。该方法操作简单、绿色高效、灵敏度高,可用于酱油中色胺的快速准确测定。     

Simulating picosecond iron K-edge X-ray absorption spectra by ab initio methods to study photoinduced changes in the electronic structure of Fe(II) spin crossover complexes

Recent time-resolved X-ray absorption experiments probing the low-spin to high-spin photoconversion in Fe(II) complexes have monitored the complex interplay between electronic and structural degrees of freedom on an ultrafast time scale. In this study, we use transition potential (TP) and time-dependent (TD) DFT to simulate the picosecond time-resolved iron K-edge X-ray absorption spectrum of the spin crossover (SCO) complex, [Fe(tren(py)(3))](2+). This is achieved by simulating the X-ray absorption spectrum of [Fe(tren(py)(3))](2+) in its low-spin (LS), (1)A(1), ground state and its high-spin (HS), (5)T(2), excited state. These results are compared with the X-ray absorption spectrum of the high-spin analogue (HSA), [Fe(tren(6-Me-py)(3))](2+), which has a (5)T(2) ground state. We show that the TP-DFT methodology can simulate a 40 eV range of the iron K-edge XANES spectrum reproducing all of the major features observed in the static and transient spectra of the LS, HS, and HSA complexes. The pre-edge region of the K-edge spectrum, simulated by TD-DFT, is shown to be highly sensitive to metal-ligand bonding. Changes in the intensity of the pre-edge region are shown to be sensitive to both symmetry and π-backbonding by analysis of relative electric dipole and quadrupole contributions to the transition moments. We generate a spectroscopic map of the iron 3d orbitals from our TD-DFT results and determine ligand field splitting energies of 1.55 and 1.35 eV for the HS and HSA complexes, respectively. We investigate the use of different functionals finding that hybrid functionals (such as PBE0) produce the best results. Finally, we provide a detailed comparison of our results with theoretical methods that have been previously used to interpret Fe K-edge spectroscopy of equilibrium and time-resolved SCO complexes.     

Two-dimensional infrared spectroscopy of antiparallel beta-sheet secondary structure

We investigate the sensitivity of femtosecond Fourier transform two-dimensional infrared spectroscopy to protein secondary structure with a study of antiparallel beta-sheets. The results show that 2D IR spectroscopy is more sensitive to structural differences between proteins than traditional infrared spectroscopy, providing an observable that allows comparison to quantitative models of protein vibrational spectroscopy. 2D IR correlation spectra of the amide I region of poly-l-lysine, concanavalin A, ribonuclease A, and lysozyme show cross-peaks between the IR-active transitions that are characteristic of amide I couplings for polypeptides in antiparallel hydrogen-bonding registry. For poly-l-lysine, the 2D IR spectrum contains the eight-peak structure expected for two dominant vibrations of an extended, ordered antiparallel beta-sheet. In the proteins with antiparallel beta-sheets, interference effects between the diagonal and cross-peaks arising from the sheets, combined with diagonally elongated resonances from additional amide transitions, lead to a characteristic "Z"-shaped pattern for the amide I region in the 2D IR spectrum. We discuss in detail how the number of strands in the sheet, the local configurational disorder in the sheet, the delocalization of the vibrational excitation, and the angle between transition dipole moments affect the position, splitting, amplitude, and line shape of the cross-peaks and diagonal peaks.     

Revealing the bonding of solvated Ru complexes with valence-to-core resonant inelastic X-ray scattering

Ru-complexes are widely studied because of their use in biological applications and photoconversion technologies. We reveal novel insights into the chemical bonding of a series of Ru(ii)- and Ru(iii)-complexes by leveraging recent advances in high-energy-resolution tender X-ray spectroscopy and theoretical calculations. We perform Ru 2p4d resonant inelastic X-ray scattering (RIXS) to probe the valence excitations in dilute solvated Ru-complexes. Combining these experiments with a newly developed theoretical approach based on time-dependent density functional theory, we assign the spectral features and quantify the metal–ligand bonding interactions. The valence-to-core RIXS features uniquely identify the metal-centered and charge transfer states and allow extracting the ligand-field splitting for all the complexes. The combined experimental and theoretical approach described here is shown to reliably characterize the ground and excited valence states of Ru complexes, and serve as a basis for future investigations of ruthenium, or other 4d metals active sites, in biological and chemical applications.

Combined experimental and theoretical Ru 2p4d resonant inelastic X-ray scattering study probes the chemical bonding and the valence excited states of solvated Ru complexes.