Identification and Characterization of the Isomeric Impurity of the Fungicide "Cyazofamid".

Identification and characterization of biproducts/ impurities present in agrochemicals are critical in view of their efficacy and safety towards public health. We herein present our study on identification and characterization of an impurity, 5-chloro-2-cyano-N,N-dimethyl-4-p-tolylimidazole-1-sulfonamide (2) present in the fungicide, "cyazofamid". Intermittent HPLC analysis of the reaction of substituted imidazole (1) with N,N-dimethylsulfamoyl chloride suggested that 2 is formed during the reaction. Isolation by preparative HPLC and characterization by NMR, LC/HRMS, MS/MS and single crystal XRD analysis confirmed 2 as an isomer of cyazofamid, wherein the N,N-dimethyl sulfonamide group was positioned on the other nitrogen of imidazole in close proximity to chloride group. Computational studies further supported the formation of 2 and ruled out the other possible isomeric structures.

Exploring the potential of iron to replace ruthenium in photosensitizers: a computational study.

In an effort to replace the widely used ruthenium metal complexes with low-cost, earth abundant iron complexes as photosensitizers for dye-sensitized solar cell (DSSC) applications, herein we report the computational design of heteroleptic iron complexes (FC1-3) coordinated with benzimidazole-phenylcarbene (C^N) ligands. DFT and TDDFT calculations predicted the stronger σ-donating and π-accepting nature of phenyl carbene ligands substituted with electron-withdrawing CF3, donating -N(CH3)2, and benzothiazine annulation than the imidazole carbene ligands (FC4); consequently, the metal-ligand bond distances and interactions that influence the ordering of charge transfer states with respect to metal centered states are altered in FC1-3 complexes. Detailed analysis based on energy decomposition analysis, spin density distribution analysis, and ab initio ligand field theory parameters were enabled to understand the nature of heteroleptic ligand interactions with the rest of the metal complex. The results from the study shed light on the judicious choice of ligands, as the same non-innocent ligand that is experimentally proven as favorable for Ru-dyes (TC1) is found to be detrimental for Fe-dyes (FC1). Among the complexes studied, the FC3 complex is a promising sensitizer for DSSC with 1,3MLCT energy level well separated from 3,5MC, thereby preventing the deactivation of MLCT. The outcome of the study is therefore an important step toward the development of photosensitizers based on iron metal. Graphical abstract Potential photosensitzers based on earth-abundant, low cost iron metal have been designed for dye sensitized solar cell applications.

Oxidative difunctionalization of 2-amino-4H-pyrans in iodobenzene diacetate and N-chlorosuccinimide: reactivity, mechanistic insights, and DFT calculations.

Oxidative difunctionalization of 2-amino-4H-pyrans was accomplished with iodobenzene diacetate (IBD) and N-chlorosuccinimide (NCS) reagents in alcoholic medium. 2-Amino-4H-pyrans undergo geminal dialkoxylation with the migration of an amino group (1a,b, 2a-i, 3a,b, and 4) in IBD, whereas with NCS addition of both chlorine and alkoxy groups takes place across the chromene double bond (6a-i).

Initial excited-state structural dynamics of uracil from resonance Raman spectroscopy are different from those of thymine (5-methyluracil).

To explore the origin of the differences in UV photochemistry of uracil (RNA) and thymine (DNA) nucleobases, we have measured the UV resonance Raman spectra of uracil in aqueous solution at wavelengths throughout the lowest-energy absorption band and analyzed the resulting resonance Raman excitation profiles and absorption spectra using a time-dependent wave-packet formalism to obtain the initial excited-state structural changes. In contrast to thymine, which differs from uracil only by the presence of a methyl group at C(5), most of the resonance Raman intensity and resulting initial excited-state structural dynamics for uracil occur along in-plane hydrogen-bond angle deformation, ring stretching, and carbonyl vibrational modes. Weaker intensities and less significant structural dynamics are observed along the C=C stretching mode. These results suggest that the initial excited-state structural dynamics of uracil occur along a carbon pyramidalization coordinate. These dynamics are different from those of thymine, which distorts primarily along a C(5)=C(6) bond lengthening coordinate. These differences in initial excited-state structural dynamics can explain the different primary photoproducts observed for these two pyrimidine nucleobases.

Initial excited-state structural dynamics of thymine are coincident with the expected photochemical dynamics.

To explore the excited-state structural dynamics of thymine, a DNA nucleobase, we measured the resonance Raman spectra of thymine in aqueous solution at wavelengths throughout the lowest-energy absorption band. Self-consistent analysis of the resulting resonance Raman excitation profiles and absorption spectrum using a time-dependent wave packet formalism yielded the excited-state structural dynamics. The photochemically relevant C=C stretching and C-H deformation vibrational modes were found to exhibit maximum resonance Raman intensity and structural change upon photoexcitation for thymine, suggesting that the initial dynamics of thymine lie along the photochemical reaction coordinate.

Molecular beacon probes of photodamage in thymine and uracil oligonucleotides.

Molecular beacons (MB) are becoming more common as sequence-selective detectors of nucleic acids. Although they can easily detect single-base mismatches, they have never been used to directly detect DNA or RNA damage. To measure the degree of ultraviolet (UV) light damage in oligonucleotides, we report a novel MB approach for general detection of photoproducts in UV-irradiated rU17 and dT17 oligonucleotides. With monochromatic UV light irradiation at ca 280 nm under anoxic conditions, the oligonucleotide absorption decays with a single-exponential time constant of 123+/-1 min for rU17 and with double-exponential time constants of 78+/-0.5 min (99%) and 180+/-5 min (0.05%) for dT17 oligonucleotides. Under the same conditions, the MB fluorescence decays more quickly, with single-exponential time constants of 19+/-2 and 26+/-3 min for rU17 and dT17, respectively. Similar kinetics were observed with broadband UV light irradiation of oligonucleotides. The differences in the UV damage kinetics of dT17 and rU17 and their detection by absorption and fluorescence techniques will be discussed in the context of differential instabilities introduced in the nucleic acid-MB duplex by the different photoproducts formed.