On Raman optical activity sign-switching between the ground and excited states leading to an unusual resonance ROA induced chirality

Raman optical activity (ROA) spectra recorded for a chiral naphthalene diimide derivative (nBu-NDI–BINAM) dissolved in a series of solvents exhibit strong solute to solvent induced chirality with: (1) dominating bands of solvents, (2) nBu-NDI–BINAM resonance ROA (RROA) bands which are barely visible, (3) monosignate RROA Solvent spectra with an unexpected sign concordant with that of the ECD band of the resonant electronic state, (4) bisignate RROA bands for a few solvents, and (5) superposition of non-resonant and resonant ROA bands of the chiral solvents. The unusual ROA enhancement was explained in terms of resonance energy transfer with resonant Raman emission. The surprising RROA sign-switching was found to be due to specific conformational equilibria where one solute conformer dominates in the ground and the other in the first excited singlet state, and, the signs of the related ECD bands of these two conformers are opposite.

Unusual solute to solvent induced chirality in ROA comes from specific conformer equilibria in the ground and the excited states.     

Synthesis and Characterization of Rhenium(V) Oxo Complexes with a New Thiol-Amide-Thiourea Ligand System. X-ray Crystal Structure of [1-Phenyl-3-[2-((2-thioacetyl)amino)ethyl]thioureato]oxorhenium(V)

General methods for preparing Re(V)O complexes with a novel series of thiol-amide-thiourea (TATU) ligands, a new class of N(2)S(2) chelates, were developed. The TATU ligands, the first multidentate systems designed with a bidentate thiourea moiety, have been used to prepare the first high-valent transition metal complexes with bidentate thiourea coordination. Direct reaction of N-(2-aminoethyl)-2-((triphenylmethyl)thio)acetamide (1) with phenyl, 4-methoxyphenyl, 4-chlorophenyl, and methyl isothiocyanate afforded ready access to the corresponding S-protected TATU ligands in one step. A two-step preparation of the N,N-dimethylthiourea TATU ligand derived from 1 was also developed. Deprotection of thiols in trifluoroacetic acid with triethylsilane followed by a ligand exchange reaction with Re(V)O precursors yielded neutral ReO(TATU) complexes. The structure of [1-phenyl-3-[2-((2-thioacetyl)amino)ethyl]thioureato]oxorhenium(V) (6a) was determined by X-ray diffraction methods. Crystal data for 6a: C(11)H(12)N(3)O(2)ReS(2), fw 468.6, orthorhombic, Pca2(1); a = 22.605(5) ?, b = 13.029(3) ?, c= 9.698(2) ?; V = 2856.3(11) ?(3); Z = 8. The coordination environment of 6a was pseudo-square-pyramidal with a deprotonated thiol S, deprotonated amide N, deprotonated thiourea N, and thiocarbonyl S coordinated in the basal plane and the oxo ligand in the apical position. The thiourea function forms a four-membered chelate ring in the multidentate TATU ligands. The two N-C and the S-C bond distances within the monodeprotonated thiourea moiety were typical of bonds with multiple-bond character. Solution (1)H NMR data for all five complexes were consistent with the solid-state structure of 6a. A broad singlet attributable to the uncoordinated NH group of thiourea was observed for the monosubstituted thiourea complexes but was not present for the N,N-dimethylthiourea derivative. Instead, two singlets of equal intensity were observed for the two methyl groups, indicating that there is restricted rotation around the C-N(CH(3))(2) bond and an extended pi system in the thiourea moiety. The four-membered ring might cause difficulty because the M-S distance would be relatively long in an undistorted ligand. This may be the reason such chelate ligands have not been previously investigated. However, the N-C-S angle narrows to approximately 105 degrees, permitting a Re-S bond with a typical bond length to be formed. We conclude that such a ring represents a versatile new building block to create multidentate ligands.     

New Near-Infrared Cyanine Dyes for Labelling of Proteins

Isothiocyanato-functionalized cyanine dyes 7 and 11 for labelling of proteins at amino groups have been synthesized. The dyes and their adducts with amines show strong absorbance and fluorescence in the near-infrared region of 750-850 nm.     

Practical and efficient applications of novel dioxaborolanes and dioxaborinanes in the synthesis of corresponding boronates and their use in the palladium-catalyzed cross coupling reactions

The syntheses of boronates derived from the reaction of dioxaborolanes and dioxaborinanes with either organolithium or organomagnesium reagents are investigated along with their subsequent use in the palladium cross coupling reaction. The intrinsic stability of these cyclic esters contributes to their facile reaction with both lithium and magnesium nucleophiles at mild and safe conditions. We have found that many of the reactions proceed at room temperature which is a significant improvement over the traditional routes which require cryogenic temperatures. The scope of these reactions and their practical application to large scale process synthesis is described.     

Determination of Bismuth by Adsorptive Stripping Voltammetry Using Aluminum Oxide for Elimination of Environmental Sample Matrix Interferences

The aim of this work was to find a fast new and simple method for efficient elimination of negative influence of humic substances and synthetic surfactants in the voltammetric determination of bismuth. The negative influence of the organic matrix present in environmental water samples due to their adsorption on aluminum oxide was successfully evaluated. The organic compounds such as humic substances and surface active compounds were removed by adsorption on the surface of aluminum oxide from the water samples. The application of this method was the recovery of Bi(III) from spiked water samples.     

Simultaneous determination of terpenes and cannabidiol in hemp (Cannabis sativa L.) by fast gas chromatography with flame ionization detection

Hemp (Cannabis sativa L.) has become widely used in several sectors due to the presence of various bioactive compounds such as terpenes and cannabidiol. In general, terpenes and cannabidiol content is determined separately, which is time consuming. Thus, a fast gas chromatography with flame ionization detection method was validated for simultaneous determination of both terpenes and cannabidiol in hemp. The method enabled a rapid detection of 29 different terpenes and cannabidiol within a total analysis time of 16 min, with satisfactory sensitivity (limit of detection = 0.03–0.27 µg/mL, limit of quantitation = 0.10–0.89 µg/mL). The inter‐ and intraday precision (RSD) was <7.82 and <3.59%, respectively. Recoveries at two spiked concentration levels (low, 3.15 µg/mL; high, 20.0 µg/mL) were determined on both apical leaves (78.55–101.52%) and inflorescences (77.52–107.10%). The reproducibility (RSD) was <5.94 and <5.51% in apical leaves and inflorescences, respectively. The proposed and validated method is highly sensitive, robust, fast, and accurate for determination of the main terpenes and cannabidiol in hemp and could be routinely used for quality control.     

Behavior of a nickel electrode in the presence of carbon monoxide

The electrochemical behavior of a nickel electrode with limited volume (LVE) electrodeposited as a thin layer on gold has been studied. The influence of the gold matrix on the electrochemical Ni electrode behavior has been considered. The electrosorption and oxidation of carbon monoxide on the Ni surface and its influence on hydrogen sorption has also been demonstrated. Received: 21 May 1997 / Accepted: 9 June 1997     

The Influence of Polyols on the Process Kinetics and Bioactive Substance Content in Osmotic Dehydrated Organic Strawberries

In recent years, an increasing interest in reducing sugar consumption has been observed and many studies are conducted on the use of polyols in the osmotic dehydration process to obtain candied or dried fruits. The studies in the literature have focused on the kinetics of the process as well as the basic physical properties. In the scientific literature, there is a lack of investigation of the influence of such polyol solutions such as sorbitol and mannitol used as osmotic substances during the osmotic dehydration process on the contents of bioactive components, including natural colourants. Thus, the aim of the study was to evaluate the impact of polyols (mannitol and sorbitol) in different concentrations on the process kinetics and on chosen physical (colour and structural changes) as well as chemical (sugars and polyol content, total anthocyanin content, total polyphenol content, vitamin C, antioxidant activity) properties of osmotic-dehydrated organic strawberries. Generally, the results showed that the best solution for osmotic dehydration is 30% or 40% sorbitol solutions, while mannitol solution is not recommended due to difficulties with preparing a high-concentration solution and its crystallization in the tissue. In the case of sorbitol, the changes of bioactive compounds, as well as colour change, were similar to the sucrose solution. However, the profile of the sugar changed significantly, in which sucrose, glucose, and fructose were reduced in organic strawberries and were partially replaced by polyols.