Sensitive Detection of Various Forms of Hydrogen Sulfide via Highly Selective Naphthalimide-Based Fluorescent Probe.

Hydrogen sulfide (H2S) is an important gasotransmitter, but only a few methods are available for real-time detection. Fluorescent probes are attractive tools for biological applications because of their high sensitivity, convenience, rapid implementation, noninvasive monitoring capability, and simplicity in fluorescent imaging of living cells and tissues. Herein, we report on a pro-fluorescent probe, NAP-Py-N3 based on naphthalimide derivative, which was found to show high selectivity toward H2S over various other analytes, including biothiols, making it feasible to detect H2S. After reaction with H2S, this probe showed rapid and significant turn-on green fluorescent enhancement at 553 nm (about 54-fold, k2 = 9.62 M-1s-1), high sensitivity (LOD: 15.5 nM), significant Stokes shift (118 nm), and it was found that the fluorescence quantum yield of fluorescence product can reach 0.36. Moreover, the probe has also been successfully applied to detect the gaseous H2S and to confirm the presence of H2S released from modern organic donors, which in recent years have been commonly used to investigate the role of H2S in biological systems. All the results indicate that this probe is excellent and highly valuable.

A New and Fast-Response Fluorescent Probe for Monitoring Hypochlorous Acid Derived from Myeloperoxidase.

Hypochlorous acid (HOCl) has been implicated in numerous pathologies associated with an inflammatory component, but its selective and sensitive detection in biological settings remains a challenge. In this report, imaging of HOCl was realized with a thiomorpholine-based probe as derivative of nitrobenzothiadiazole (NBD-S-TM). The fluorescence is based on photoinduced electron transfer by using nitrobenzothiadiazole core as a donor and thiomorpholine substituent as an acceptor. NBD-S-TM showed high sensitivity and a fast response to HOCl k = (2.6 ± 0.2) × 107 M-1s-1 with a 1:1 stoichiometry. The detection limit for HOCl was determined to be 60 nM. Furthermore, the desirable features of NBD-S-TM for the detection of HOCl in aqueous solutions, such as its reliability at physiological pH, rapid fluorescence response, and biocompatibility, enabled its application in the detection of HOCl in myeloperoxidase enzymatic system. Moreover, NBD-S-TM exhibited excellent selectivity and sensitivity for HOCl over other biologically relevant species, such as hydrogen peroxide and peroxynitrite. The fluorescent S-oxidized product (NBD-S-TSO) is only formed in the presence of HOCl. Probing with NBD-S-TM may be helpful to further the development of high throughput screening assays to monitor the activity of myeloperoxidase.

A thiomorpholine-based fluorescent probe for the far-red hypochlorous acid monitoring.

A simple thiomorpholine-based fluorescent probe was designed and synthesized by combining thiomorpholine (TM) and nitrobenzenoselenadiazoles fluorophore (NBD-Se). The thiomorpholine group quenches the fluorescence of NBD-Se efficiently through the photoinduced electron transfer (PET) effect. Hypochlorous acid (HOCl) oxidizes the NBD-Se-TM probe to its fluorescent S-oxide (NBD-Se-TSO) with a 1:1 stoichiometry. The desirable features of NBD-Se-TM for detecting HOCl in aqueous solutions, such as its high sensitivity and selectivity, reliability at physiological pH, and rapid fluorescence response, enabled its application in the detection of HOCl produced by myeloperoxidase. The results proved that NBD-Se-TM is a promising fluorescent probe that can be used in screening assays for MPO inhibitors. Its high reaction rate constant with HOCl (2k = 2.0 × 107M-1s-1) indicates the possibility of application in more complex biological systems.

HPLC Study of Product Formed in the Reaction of NBD-Derived Fluorescent Probe with Hydrogen Sulfide, Cysteine, N-acetylcysteine, and Glutathione.

Hydrogen sulfide (H2S) and its bioderivatives analogs, such as L-cysteine (L-Cys) and glutathione (GSH), are ubiquitous biological thiols in the physiological and pathological processes of living systems. Their aberrant concentration levels are associated with many diseases. Although several NBD-based fluorescence probes have been developed to detect biological thiols, the HPLC-detection of H2S, GSH, L-Cys, and N-acetylcysteine-specific products has not been described. Herein, a novel NBD-derived pro-coumarin probe has been synthesized and used to develop a new strategy for the triple mode detection of H2S and such thiols as GSH, L-Cys, and NAC. Hydrogen sulfide and those biothiols at physiological pH release fluorescent coumarin from the probe and cause a significant fluorescence enhancement at 473 nm. The appropriate NBD-derived product for H2S, L-Cys, GSH, and NAC has a different color and retention time that allows distinguishing these biological thiols meaning the probe has a great possibility in the biological application. Fluorescent imaging combined with colorimetric and HPLC detection of H2S/biothiol-specific product(s) brings a potential tool for confirming the presence of biological thiols and determining concentrations in various aqueous biological samples.

In Memoriam: Professor Jaroslaw Lewkowski (1966-2019).

In the investigation presented here the synthesis of new lariat ether derivative obtained from the modification of tetrapyrrolidinyl-PNP-crown ether macrocycle is described. The polyheterotopic molecular coreceptor consisted of the replacement of chlorine atoms with an optically active (S)-(1-benzylpyrrolidin-2-yl) methanamine. The structure was confirmed by using elemental analysis, mass spectrometry, and NMR spectroscopy. This work covers results concerning the complexing properties of the new ligand towards Ag+, Cu2+, Co2+, Ni2+, and Zn2+ ions. The formation of non-covalent complexes of 1:1 stoichiometry with the Cu2+, Co2+, Ni2+, and Zn2+ ions have been confirmed by mass spectrometry. Due to the previous work and application possibilities, a large emphasis was put on the investigation of the complexation ability of lariat ether with silver (I) cation to determine stability constants by direct potentiometric method. In this case, the formation of four different forms of complexes AgL, Ag2L, Ag3L, and Ag4L has been proved. The observed unusual binding through the nitrogen atoms from the exocyclic substituents may provide the structural unit to build a new coordination polymers.

The atmospherically highly relevant methylsulfinyl radical (CH3(O)S˙) readily reacts with molecular triplet oxygen in cryogenic argon matrices containing small amounts of (3)O2. Comparison of experimental and computed IR- and UV/Vis spectra, including isotope exchange, show that the initially formed (3)O2 adduct has the structure of a peroxyl radical (CH3(O)SOO˙), which upon irradiation with UV light isomerizes to the methylsulfonoxyl radical (CH3SO3˙). The latter transforms into the methansulfonic acid radical (˙CH2SO3H) by irradiation with visible light. During the matrix photolysis small amounts of SO3 and the methyl radical were detected indicating competitive direct photodissociation.

The atmospherically highly relevant methylsulfonyl radical (CH3SO2(•)) was generated by high-vacuum flash pyrolysis (HVFP) of allylmethylsulfone and isolated in an argon matrix at 10 K; the allyl radical formed as the cofragment. Upon thermolysis, the methylsulfonyl radical undergoes partial decomposition, leading to substantial amounts of sulfur dioxide in the matrix. The title compound was characterized through the assignment of eight fundamental IR bands of its CD3 and (13)CH3 isotopologues and the excellent agreement with the B3LYP/6-311+G(3df,3pd) computed harmonic vibrational frequencies. The two most intense absorptions were found at 1267.1 and 1067.6 cm(-1). In extension of this study S-methyl methanethiosulfonate was found to be another suitable, although less efficient, precursor for the gas-phase generation of the methylsulfonyl radical.

The atmospherically highly relevant methylsulfinyl radical CH3(O)S˙ was generated thermally under flash pyrolysis conditions and isolated in Ar matrices at 10 K; the allyl radical is a byproduct. CH3(O)S˙ and its D3- and (13)C-isotopologues were characterized through the excellent agreement between experimental and computed IR and UV/Vis spectra.

Transformations of functional groups, such as OCH2Ph, OCOPh, NO2 and I, in 1,3,5-triphenyl-6-oxoverdazyls 1a-1e were investigated in order to expand the range of synthetic tools for incorporation of the verdazyl system into more complex molecular architectures and to increase spin delocalization. Thus, Pd-catalyzed debenzylation of the OCH2Ph group or basic hydrolysis of the OCOPh group gave the phenol functionality, which was acylated, but could not be alkylated. Orthogonal deprotection of diphenol functionality was also demonstrated in radical 1c. Pt-catalyzed reduction of the NO2 group led to the aniline derivative, which was acylated. Attempted C-C coupling reactions to iodophenyl derivatives 1e and 5e were unsuccessful. Selected verdazyl radicals were characterized by EPR and electronic absorption spectroscopy, and results were analyzed with the aid of DFT computational methods.

We describe the first preparation of the long-sought parent oxathiirane from sulfine through photochemical rearrangement with light at lambda = 313 +/- 10 nm in an Ar matrix at 11 K. Oxathiirane was characterized by the extraordinarily good agreement of experimentally measured and (unscaled) CCSD(T)/cc-pVTZ computed vibrational frequencies for both the perhydrogenated and perdeuterated species. The title molecule is ca. 10 kcal mol(-1) less stable than sulfine, in marked contrast to the isomer energy difference of dioxirane vs carbonyl oxide (ca. -25 kcal mol(-1)). This is due to the strong positive polarization (blue potential) versus the highly electronegative oxygen atom (red). The stability ordering and the relative energy differences of carbonyl versus thiocarbonyl groups underline the likely role oxathiiranes play in sulfur transfer reactions.

The current case study focuses on the generation, identification, and characterization of two representative mono- and disubstituted alkyl phosphonatocarbenes by means of matrix isolation techniques in conjunction with density functional theory [B3LYP/6-311++G(d,p)] and coupled cluster [CCSD(T)/cc-pVXZ, X = D, T] computations. The EPR measurements identify both carbenes as triplet ground-state species with D values of 0.660 and 0.623 cm(-1), respectively, exhibiting persistency toward intramolecular reactions (the EPR signal observable in perfluoromethylcyclohexane up to around 70 K for the disubstituted molecule). While the reaction of the carbene center of the conformationally rich tetramethyl bisphosphonatocarbene with the CH bonds of the methyl groups leads to phosphaoxetane at room temperature, its fragmentation via a Wittig-type reaction during high vacuum flash pyrolysis (HVFP) results in dimethyl vinylphosphonate and methyl metaphosphate. The latter has been observed for the first time as an isolated entity.

Three cage-like polycyclic compounds, viz. exo-8-(trifluoromethyl)pentacyclo[5.4.0.0(2,6).0(3,10).0(5,9)]undecan-endo-8-ol, C12H13F3O, 5-(trifluoromethyl)-4-oxahexacyclo[5.4.1.0(2,6).0(3,10).0(5,9).0(8,11)]dodecan-3-ol, C12H11F3O2, and N-[exo-11-(trifluoromethyl)-endo-11-(trimethylsilyloxy)pentacyclo[5.4.0.0(2,6).0(3,10).0(5,9)]undecan-8-ylidene]aniline methanol solvate, C21H24F3NOSi.CH4O, were obtained from the corresponding oxo derivatives by nucleophilic trifluoromethylation with (trifluoromethyl)trimethylsilane in 1,2-dimethoxyethane solution in the presence of CsF. The crystal structures show that the addition of trifluoromethanide occurs exclusively from the exo face of the polycyclic ketones. Further examination of the crystal structures, together with that of the starting pentacyclo[5.4.0.0(2,6).0(3,10).0(5,9)]undecane-8,11-dione, C11H10O2, showed that increasing substitution at the 8- and/or 11-positions in the cage molecules increases the non-bonded intramolecular C...C distances at the mouth of the cage and changes the puckering of the five-membered rings involving the 8- and 11-positions from an envelope towards a distorted half-chair conformation. Intermolecular co-operative O-H...O hydrogen bonds in the endo-8-ol compound link the molecules into tetramers.

Matrix isolation spectroscopy allows the direct identification of ylide 1 and its cyclic isomer 2. They were obtained by pyrolysis of 1,2,4-trithiolane under high vacuum; the cyclic compound forms from 1 by thermal ring closure in a kinetically controlled reaction.

Reactions of the methylsulfinyl radical [CH3(O)S˙] with oxygen ((3)O2) in solid argon.

The atmospherically highly relevant methylsulfinyl radical (CH3(O)S˙) readily reacts with molecular triplet oxygen in cryogenic argon matrices containing small amounts of (3)O2. Comparison of experimental and computed IR- and UV/Vis spectra, including isotope exchange, show that the initially formed (3)O2 adduct has the structure of a peroxyl radical (CH3(O)SOO˙), which upon irradiation with UV light isomerizes to the methylsulfonoxyl radical (CH3SO3˙). The latter transforms into the methansulfonic acid radical (˙CH2SO3H) by irradiation with visible light. During the matrix photolysis small amounts of SO3 and the methyl radical were detected indicating competitive direct photodissociation.

Gas-phase generation and matrix isolation of the methylsulfonyl radical CH3SO2˙ from allylmethylsulfone.

The atmospherically highly relevant methylsulfonyl radical (CH3SO2(•)) was generated by high-vacuum flash pyrolysis (HVFP) of allylmethylsulfone and isolated in an argon matrix at 10 K; the allyl radical formed as the cofragment. Upon thermolysis, the methylsulfonyl radical undergoes partial decomposition, leading to substantial amounts of sulfur dioxide in the matrix. The title compound was characterized through the assignment of eight fundamental IR bands of its CD3 and (13)CH3 isotopologues and the excellent agreement with the B3LYP/6-311+G(3df,3pd) computed harmonic vibrational frequencies. The two most intense absorptions were found at 1267.1 and 1067.6 cm(-1). In extension of this study S-methyl methanethiosulfonate was found to be another suitable, although less efficient, precursor for the gas-phase generation of the methylsulfonyl radical.

Matrix isolation and spectroscopic properties of the methylsulfinyl radical CH3(O)S˙.

The atmospherically highly relevant methylsulfinyl radical CH3(O)S˙ was generated thermally under flash pyrolysis conditions and isolated in Ar matrices at 10 K; the allyl radical is a byproduct. CH3(O)S˙ and its D3- and (13)C-isotopologues were characterized through the excellent agreement between experimental and computed IR and UV/Vis spectra.

Functional group transformations in derivatives of 6-oxoverdazyl.

Transformations of functional groups, such as OCH2Ph, OCOPh, NO2 and I, in 1,3,5-triphenyl-6-oxoverdazyls 1a-1e were investigated in order to expand the range of synthetic tools for incorporation of the verdazyl system into more complex molecular architectures and to increase spin delocalization. Thus, Pd-catalyzed debenzylation of the OCH2Ph group or basic hydrolysis of the OCOPh group gave the phenol functionality, which was acylated, but could not be alkylated. Orthogonal deprotection of diphenol functionality was also demonstrated in radical 1c. Pt-catalyzed reduction of the NO2 group led to the aniline derivative, which was acylated. Attempted C-C coupling reactions to iodophenyl derivatives 1e and 5e were unsuccessful. Selected verdazyl radicals were characterized by EPR and electronic absorption spectroscopy, and results were analyzed with the aid of DFT computational methods.

Oxathiirane.

We describe the first preparation of the long-sought parent oxathiirane from sulfine through photochemical rearrangement with light at lambda = 313 +/- 10 nm in an Ar matrix at 11 K. Oxathiirane was characterized by the extraordinarily good agreement of experimentally measured and (unscaled) CCSD(T)/cc-pVTZ computed vibrational frequencies for both the perhydrogenated and perdeuterated species. The title molecule is ca. 10 kcal mol(-1) less stable than sulfine, in marked contrast to the isomer energy difference of dioxirane vs carbonyl oxide (ca. -25 kcal mol(-1)). This is due to the strong positive polarization (blue potential) versus the highly electronegative oxygen atom (red). The stability ordering and the relative energy differences of carbonyl versus thiocarbonyl groups underline the likely role oxathiiranes play in sulfur transfer reactions.

Prototypical triplet alkyl phosphonatocarbenes.

The current case study focuses on the generation, identification, and characterization of two representative mono- and disubstituted alkyl phosphonatocarbenes by means of matrix isolation techniques in conjunction with density functional theory [B3LYP/6-311++G(d,p)] and coupled cluster [CCSD(T)/cc-pVXZ, X = D, T] computations. The EPR measurements identify both carbenes as triplet ground-state species with D values of 0.660 and 0.623 cm(-1), respectively, exhibiting persistency toward intramolecular reactions (the EPR signal observable in perfluoromethylcyclohexane up to around 70 K for the disubstituted molecule). While the reaction of the carbene center of the conformationally rich tetramethyl bisphosphonatocarbene with the CH bonds of the methyl groups leads to phosphaoxetane at room temperature, its fragmentation via a Wittig-type reaction during high vacuum flash pyrolysis (HVFP) results in dimethyl vinylphosphonate and methyl metaphosphate. The latter has been observed for the first time as an isolated entity.

Trifluoromethyl derivatives of pentacyclo[5.4.0.0(2,6).0(3,10).0(5,9)]undecane.

Three cage-like polycyclic compounds, viz. exo-8-(trifluoromethyl)pentacyclo[5.4.0.0(2,6).0(3,10).0(5,9)]undecan-endo-8-ol, C12H13F3O, 5-(trifluoromethyl)-4-oxahexacyclo[5.4.1.0(2,6).0(3,10).0(5,9).0(8,11)]dodecan-3-ol, C12H11F3O2, and N-[exo-11-(trifluoromethyl)-endo-11-(trimethylsilyloxy)pentacyclo[5.4.0.0(2,6).0(3,10).0(5,9)]undecan-8-ylidene]aniline methanol solvate, C21H24F3NOSi.CH4O, were obtained from the corresponding oxo derivatives by nucleophilic trifluoromethylation with (trifluoromethyl)trimethylsilane in 1,2-dimethoxyethane solution in the presence of CsF. The crystal structures show that the addition of trifluoromethanide occurs exclusively from the exo face of the polycyclic ketones. Further examination of the crystal structures, together with that of the starting pentacyclo[5.4.0.0(2,6).0(3,10).0(5,9)]undecane-8,11-dione, C11H10O2, showed that increasing substitution at the 8- and/or 11-positions in the cage molecules increases the non-bonded intramolecular C...C distances at the mouth of the cage and changes the puckering of the five-membered rings involving the 8- and 11-positions from an envelope towards a distorted half-chair conformation. Intermolecular co-operative O-H...O hydrogen bonds in the endo-8-ol compound link the molecules into tetramers.

Thioformaldehyde S-sulfide (Thiosulfine).

Matrix isolation spectroscopy allows the direct identification of ylide 1 and its cyclic isomer 2. They were obtained by pyrolysis of 1,2,4-trithiolane under high vacuum; the cyclic compound forms from 1 by thermal ring closure in a kinetically controlled reaction.