1-Naphthylacetic acid appended amino acids-based hydrogels: probing of the supramolecular catalysis of ester hydrolysis reaction.

A 1-naphthaleneacetic acid-appended phenylalanine-derivative (Nap-F) forms a stable hydrogel with a minimum gelation concentration (MGC) of 0.7% w/v (21 mM) in phosphate buffer of pH 7.4. Interestingly, Nap-F produces two-component [Nap-F + H = Nap-FH, Nap-F + K = Nap-FK and Nap-F + R = Nap-FR], three-component [Nap-F + H + K = Nap-FH-K, Nap-F + H + R = Nap-FH-R and Nap-F + K + R = Nap-FK-R] and four-component [Nap-F + H + K + R = Nap-FH-K-R] hydrogels in water with all three natural basic amino acids (H = histidine, K = lysine and R = arginine) at various combinations below its MGC. Nap-F-hydrogel forms a nice entangled nanofibrillar network structure as evidenced by field emission scanning electron microscopy (FE-SEM). Interestingly, lysine-based co-assembled two- (Nap-FK), three- (Nap-FH-K and Nap-FK-R) and four-component (Nap-FH-K-R) xerogels exhibit helical nanofibrillar morphology, which was confirmed by circular dichroism spectroscopy, FE-SEM and TEM imaging. However, histidine and arginine-based two-component (Nap-FH and Nap-FR) and three-component (Nap-FH-R) co-assembled xerogels exhibiting straight nanofibrillar morphology. In their co-assembled states, these two-, three- and four-component supramolecular hydrogels show promising esterase-like activity below their MGCs. The enhanced catalytic activity of helical fibers compared to obtained straight fibers (other than lysine-based assembled systems) suggests that the helical fibrillar nanostructure is involved in ordering the esterase-like although all supramolecular assemblies are chemically different from one another.

Thianthrenation-promoted photoinduced alkene difunctionalization and aryl allylation with Morita-Baylis-Hillman adducts.

An organophotoredox-catalyzed alkoxyallylation of feed-stock olefins, through thianthrenation using a Morita-Baylis-Hillman adduct as an allylating agent, is described. Site-selective addition of MeOH to an alkene-thianthrenium salt and its subsequent conversion into a nucleophilic radical species forms the basis of this unique difunctionalization strategy. The scope is also expanded into radical aryl allylation.

Cationic and amphiphilic peptide-based hydrogels with dual activities as anticancer and antibacterial agents.

The emergence of peptide-based functional biomaterials is on the rise. To fulfil this purpose, a series of amphiphilic peptides, such as H2N-X-Met-Phe-C12H25, where X = L-lysine (CP1), X = L-histidine (CP2), and X = L-leucine (CP3), have been designed, synthesised, purified and fully characterised. Herein, we reported peptide-based supramolecular hydrogels with antibacterial and anticancer activities. An attempt has been made to investigate the antibacterial properties of these peptide-based hydrogels against Gram-positive (S. aureus and B. subtilis) and Gram-negative (E. coli and P. aeruginosa) bacteria. Investigations show that the L-lysine containing gelator, CP1, is active against both Gram-positive and Gram-negative bacteria and the L-histidine containing gelator, CP2, selectively inhibits the growth of Gram-negative bacteria. Interestingly, the L-leucine containing gelator, CP3, does not show any antibacterial properties. Moreover, the L-lysine containing gelator exhibits the best potency. Generation of reactive oxygen species (ROS) is a probable way to damage the bacterial membrane. To explore the cytotoxic properties and to determine the efficacy of the synthesized compounds in inhibiting cell viability, a comprehensive investigation was performed using three distinct cell lines: MDA-MB-231 (human triple-negative breast cancer), MDA-MB-468 (human triple-negative breast cancer) and HEK 293 (human embryonic kidney). Remarkably, the results of our study revealed a substantial cytotoxic impact of these peptide gelators on the MDA-MB-231 and MDA-MB-468 cell lines in comparison to the HEK 293 cells. Caspase 3/7 activity is the possible mechanistic path to determine the apoptotic rates of the cell lines. This finding emphasizes the promising potential of these peptide-based gelators in targeting and suppressing the growth of human triple negative breast cancer cells, while showing non-cytotoxicity towards non-cancerous HEK 293 cells. In a nutshell, these peptide-based materials are coming to light as next generation biomaterials.

Reaction of a Co(III)-peroxo complex with nitric oxide: putative formation of a peroxynitrite intermediate.

A Co(II) complex, [CoII(L)2(H2O)2](ClO4)2, 1, having a bidentate ligand L [L = bis(3,5-dimethylpyrazolyl)methane] has been synthesized. Complex 1 in acetonitrile solution at -40 °C, in the presence of H2O2 and NEt3, afforded the corresponding Co(III)-peroxo species, [CoIII(L)2(O22-)]+, as the transient intermediate 1a. Thermal instability precluded its isolation and further characterization. The addition of nitric oxide (NO) gas into the freshly prepared [CoIII(L)2(O22-)]+ in acetonitrile at -40 °C resulted in the corresponding Co(II)-nitrato complex, [CoII(L)2(NO3)](ClO4) (2). The reaction is proposed to proceed through a putative Co(II)-peroxynitrite intermediate 1b. It was evidenced by the characteristic phenol ring nitration reaction.

Effect of molar ratio and concentration on the rheological properties of two-component supramolecular hydrogels: tuning of the morphological and drug releasing behaviour.

Self-assembled supramolecular hydrogels offer great potential as biomaterials and drug delivery systems. Specifically, peptide-based multicomponent hydrogels are promising materials due to their advantage that their mechanical and physical properties can be tuned to enhance their functionalities and broaden their applications. Herein, we report two-component assembly and formation of hydrogels containing inexpensive complementary anionic, BUVV-OH (A), and cationic, KFFC12 (B), peptide amphiphiles. Individually, neither of these components formed a hydrogel, while mixtures with compositions 1 : 1, 1 : 2, and 2 : 1 (molar ratio) as A : B show hydrogel formation (Milli-Q water, at pH = 6.79). These hydrogels displayed a good shear-thinning behaviour with different mechanical stabilities and nano-fibrous network structures. The 1 : 1 hydrogel shows good cell viability for human embryonic kidney (HEK-293) cells and CHO cells indicating its non-cytotoxicity. The biocompatible, thixotropic 1 : 1 hydrogel with a nanofiber network structure shows the highest mechanical strength with a storage modulus of 3.4 × 103 Pa. The hydrogel is able to encapsulate drugs including antibiotics amoxicillin and rifampicin, and anticancer drug doxorubicin, and it exhibits sustainable release of 76%, 70%, and 81% respectively in vitro after 3 days. The other two mixtures (composition 1 : 2 and 2 : 1) are unable to form a hydrogel when they are loaded with these drugs. Interestingly, it is noticed that with an increase in concentration, the mechanical strength of a 1 : 1 hydrogel is significantly enhanced, showing potential that may act as a scaffold for tissue engineering. The two-component gel offers tunable mechanical properties, thixotropy, injectability, and biocompatibility and has great potential as a scaffold for sustained drug release and tissue engineering.

Sixth Ligand Induced HNO/NO- Release by a Five-Coordinated Cobalt(II) Nitrosyl Complex Having a {CoNO}8 Configuration.

Nitroxyl (HNO) and nitroxide (NO-) anion, the one-electron-reduced form of nitric oxide (NO), have been shown to have distinct advantages over NO from pharmacological and therapeutic points of view. However, the role of nitroxyl in chemical biology has not yet been studied as extensively as that of NO. Consequently, only a few examples of HNO donors such as Angeli's salt, Piloty's acid, or acyl- and acyloxynitroso derivatives are known. However, the intrinsic limitations of all of these hinder their widespread utility. Metal nitrosyl complexes, although few examples, could serve as an efficient HNO donor. Here, a cobalt nitrosyl complex of the {CoNO}8 (1) configuration has been reported. This complex in the presence of a sixth ligand [BF4-, DTC- (diethyldithiocarbamate anion), or imidazole] releases/donates HNO/NO-. This has been confirmed using well-known HNO/NO- acceptors like [Fe(TPP)Cl] and [Fe(DTC)3]. The HNO release has been authenticated further by the detection and estimation of N2O using gas chromatography-mass spectroscopy as well as its reaction with PPh3.

Fe-Catalyzed Hydroallylation of Unactivated Alkenes with Vinyl Cyclopropanes.

Catalytic, reductive C-C bond formation between alkenes and vinyl cyclopropane (VCP) through hydrogen atom transfer (MHAT) is developed. Despite VCP's use as probes in radical-clock experiments, translation of this manifold into synthetic methods for accessing elusive C-C bonds remains largely unexplored. This work represents the first foray into this front where the high chemoselectivity of MHAT for alkene over VCP was pivotal for realizing the strategy. This method exhibits a broad scope, high functional group tolerance, and useful applications.

Histidine-Containing Amphiphilic Peptide-Based Non-Cytotoxic Hydrogelator with Antibacterial Activity and Sustainable Drug Release.

A histidine-based amphiphilic peptide (P) has been found to form an injectable transparent hydrogel in phosphate buffer solution over a pH range from 7.0 to 8.5 with an inherent antibacterial property. It also formed a hydrogel in water at pH = 6.7. The peptide self-assembles into a nanofibrillar network structure which is characterized by high-resolution transmission electron microscopy, field-emission scanning electron microscopy, atomic force microscopy, small-angle X-ray scattering, Fourier-transform infrared spectroscopy, and wide-angle powder X-ray diffraction. The hydrogel exhibits efficient antibacterial activity against both Gram-positive bacteria Staphylococcus aureus (S. aureus) and Gram-negative bacteria Escherichia coli (E. coli). The minimum inhibitory concentration of the hydrogel ranges from 20 to 100 µg/mL. The hydrogel is capable of encapsulation of the drugs naproxen (a non-steroidal anti-inflammatory drug), amoxicillin (an antibiotic), and doxorubicin, (an anticancer drug), but, selectively and sustainably, the gel releases naproxen, 84% being released in 84 h and amoxicillin was released more or less in same manner with that of the naproxen. The hydrogel is biocompatible with HEK 293T cells as well as NIH (mouse fibroblast cell line) cells and thus has potential as a potent antibacterial and drug releasing agent. Another remarkable feature of this hydrogel is its magnification property like a convex lens.

Reaction of a nitrosyl complex of Mn(II)-porphyrinate with superoxide: NOD activity is favoured over SOD activity.

A five-coordinated {Mn(NO)}6 complex of Mn(II)-porphyrinate, [Mn(TMPP2-)(NO)], 1 {TMPPH2 = 5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin}, upon reaction with two equivalents of superoxide (O2-) in THF at -40 °C results in the corresponding MnIII-OH complex [MnIII(TMPP2-)(OH)], 2, via the formation of a putative MnIII-peroxynitrite intermediate. Spectral studies and chemical analysis suggest that one equivalent of superoxide ion is consumed to oxidize the metal center of complex 1 leading to [MnIII(TMPP2-)(NO)]+, while the subsequent equivalent reacts with [MnIII(TMPP2-)(NO)]+ to form the corresponding peroxynitrite intermediate. UV-visible and X-band EPR spectroscopic studies suggest the involvement of a MnIV-oxo species in the reaction, which forms through the O-O bond cleavage of the peroxynitrite moiety with concomitant release of NO2. The formation of MnIII-peroxynitrite is further supported by the well-established phenol ring nitration experiment. The released NO2 has been trapped using TEMPO. It should be noted that in cases of MnII-porphyrin complexes, the reaction with superoxide generally proceeds through a SOD-like pathway where the first equivalent of superoxide ion oxidizes the MnII center and itself is reduced to peroxide (O22-), while the subsequent equivalent of superoxide reduces the MnIII center with the release of O2. In contrast, here the second equivalent of superoxide reacts with the MnIII-nitrosyl complex and follows a NOD-like pathway.

Metal ion-induced assembly of dipeptide-attached perylenediimide for fluorometric "turn on" detection of biologically important small molecule.

A dipeptide-appended perylenediimide (PDI-CFF) fluorescent molecule was designed, synthesized, and characterized. Though the molecule does not dissolve in any individual solvent, it dissolves well in an organic/water mixed solvent system such as tetrahydrofuran/water. This new fluorescent molecule was self-assembled in a tetrahydrofuran/water mixture to form both nanofibrous network structures and a nano ring structure. It has shown nanofibril morphology by the interactions with ferric ions (PDI-CFF/Fe3+ system) with diminishing fluorescent property. Interestingly, L-ascorbic acid (LAA) interacts with the PDI-CFF/Fe3+ system, showing turn-on fluorescence. Another interesting feature is that the minimum detection limits for Fe3+ ions and LAA are at the submicromolar levels of 6.2 × 10-8 and 3 × 10-8  M, respectively. Moreover, the fluorescent (10 µM) signals can be monitored by the naked eye under handheld UV lamp irradiation at 365 nm, and this is very convenient for the real application. In this study, the molecule offers the opportunity for processing these sequential fluorescence responses in order to fabricate a implication logic gate that includes NOT, AND, and OR simple logic gates using chemical stimuli (ferric ions and LAA) as inputs and fluorescence emission at 536 nm as output. The detailed mechanism of interactions of Fe3+ with PDI-CFF and LAA with the PDI-CFF/Fe3+ system is vividly studied by using Fourier transform infrared (FT-IR) analysis and fluorescence. Moreover, this new molecule was reusable for several times without significant loss of its activity. The construction of logic gates using biologically important molecules/ions holds future promise for the design and development of new bio-logic gates.

Amino acid containing amphiphilic hydrogelators with antibacterial and antiparasitic activities.

Nanoscale self-assembly of peptide constructs represents a promising means to present bioactive motifs to develop new functional materials. Here, we present a series of peptide amphiphiles which form hydrogels based on ß-sheet nanofibril networks, several of which have very promising anti-microbial and anti-parasitic activities, in particular against multiple strains of Leishmania including drug-resistant ones. Aromatic amino acid based amphiphilic supramolecular gelators C14-Phe-CONH-(CH2)n-NH2 (n = 6 for P1 and n = 2 for P3) and C14-Trp-CONH-(CH2)n-NH2 (n = 6 for P2 and n = 2 for P4) have been synthesized and characterized, and their self-assembly and gelation behaviour have been investigated in the presence of ultrapure water (P1, P2, and P4) or 2% DMSO(v/v) in ultrapure water (P3). The rheological, morphological and structural properties of the gels have been comprehensively examined. The amphiphilic gelators (P1 and P3) were found to be active against both Gram-positive bacteria B. subtilis and Gram-negative bacteria E. coli and P. aeruginosa. Interestingly, amphiphiles P1 and P3 containing an L-phenylalanine residue show both antibacterial and antiparasitic activities. Herein, we report that synthetic amphiphiles with an amino acid residue exhibit a potent anti-protozoan activity and are cytotoxic towards a wide array of protozoal parasites, which includes Indian varieties of Leishmania donovani and also kill resistant parasitic strains including BHU-575, MILR and CPTR cells. These gelators are highly cytotoxic to promastigotes of Leishmania and trigger apoptotic-like events inside the parasite. The mechanism of killing the parasite is shown and these gelators are non-cytotoxic to host macrophage cells indicating the potential use of these gels as therapeutic agents against multiple forms of leishmaniasis in the near future.

Ir-Catalyzed Ligand-Free Directed C-H Borylation of Arenes and Pharmaceuticals: Detailed Mechanistic Understanding.

An efficient method for Ir-catalyzed ligand free ortho borylation of arenes (such as, 2-phenoxypyridines, 2-anilinopyridines, benzylamines, benzylpiperazines, benzylmorpholines, benzylpyrrolidine, benzylpiperidines, benzylazepanes, α-amino acid derivatives, aminophenylethane derivatives, and other important scaffolds) and pharmaceuticals has been developed. The reaction underwent via an interesting mechanistic pathway, as revealed by the detailed mechanistic investigations by using kinetic isotope studies and DFT calculations. The catalytic cycle is found to involve the intermediacy of an Ir-boryl complex where the substrate C-H activation is the turnover determining step, intriguingly without any appreciable primary KIE. The method displays a broad range of substrate scope and functional group tolerance. Numerous late-stage borylation of various important molecules and drugs were achieved using this developed strategy. The borylated compounds were further converted into more valuable functionalities. Moreover, utilizing the benefit of the B-N intramolecular interaction of the mono borylated compounds, an operationally simple method has been developed for the selective diborylation of 2-phenoxypyridines and numerous functionalized arenes. Furthermore, the synthetic utility has been showcased with the removal of the pyridyl directing group from the borylated product to achieve ortho borylated phenol along with the ipso-borylation for the preparation of 1,2-diborylated benzene.

Reaction of a {Co(NO)}8 complex with superoxide: Formation of a six coordinated [CoII(NO)(O2-)] species followed by peroxynitrite intermediate.

A nitrosyl complex of cobalt(II) porphyrinate, [Co(F20TPP2-)(NO)], (F20TPPH2 = 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin) having {Co(NO)}8 configuration was synthesized and characterized by means of spectroscopic and structural analyses. Single crystal X-ray structure of the complex revealed the square pyramidal geometry around the cobalt center with a bent nitrosyl group. It reacts with superoxide (O2-) ion in CH2Cl2 at -40 °C to result in the corresponding nitrite (NO2-) complex. Involvement of a cobalt(II)-peroxynitrite intermediate is proposed in the course of the reaction. Moreover, spectroscopic studies suggested the formation of a transient six-coordinated [CoII(NO)(O2-)] species.

An acid-promoted pseudocine substitution manifold of γ-aminocyclopentenone enables divergent access to polycyclic indole derivatives.

We demonstrated γ-aminocyclopentenones to be a suitable surrogate for reactive cyclopentadienone via a pseudocine-substitution manifold. This approach enabled its orchestrated annulation with "tailored" bis-nucleophiles and to furnish complex ß,γ-annulated cyclopentanoids or indole-based polycyclic architectures. This strategy represents a generalized means for direct, regioselective and stereoselective ß,γ-functionalization of monosubstituted or unsubstituted aminocyclopentenones.

Can a Nitrosyl of a Mn(II)-Porphyrin Complex Release Nitroxyl/HNO?

In general, the nitrosyl complexes of Mn(II)-porphyrinate having the {Mn(NO)}6 configuration are not considered as HNO or nitroxyl (NO-) donors because of [MnI-NO+] nature. A nitrosyl complex of Mn(II)-porphyrin, [Mn(TMPP2-)(NO)], 1 [TMPPH2 = 5,10,15,20-tetrakis-4-methoxyphenylporphyrin], is shown to release HNO in the presence of HBF4. It is evidenced from the characteristic reaction of HNO with triphenylphosphine and isolation of the [(TMPP2-)MnIII(H2O)2](BF4), 2. This is attributed to the fact that H+ from HBF4 polarizes the NO group whereas the BF4- interacts with metal ion to stabilize the Mn(III) form. These two effects cooperatively result in the release of HNO from complex 1. In addition, complex 1 behaves as a nitroxyl (NO-) donor in the presence of [Fe(dtc)3] (dtc = diethyldithiocarbamate anion) and [Fe(TPP)(Cl)] (TPP = 5,10,15,20-tetraphenylporphyrinate) to result in [Fe(dtc)2(NO)] and [Fe(TPP)(NO)], respectively.

Unprecedented Reactivity of γ-Amino Cyclopentenone Enables Diversity-Oriented Access to Functionalized Indoles and Indole-Annulated Ring Structures.

Observation of an unexpected, Lewis acid promoted displacement of latent reactive γ-amino group on cyclopentenone presented unparalleled opportunity for enone functionalization and annulations with indole derivatives, which is developed in the current study. Herein, a vast range of C3/N-indolyl enones and indole alkaloid-like compound were accessed in excellent yields (up to 99 %) and selectivity through a one-pot operation. The mechanism most likely involves an unprecedented trait of Piancatelli-type rearrangement where influence of the gem-diaryl group appeared crucial.

Peptide-Based Gel in Environmental Remediation: Removal of Toxic Organic Dyes and Hazardous Pb2+ and Cd2+ Ions from Wastewater and Oil Spill Recovery.

A dipeptide-based synthetic amphiphile bearing a myristyl chain has been found to form hydrogels in the pH range 6.9-8.5 and organogels in various organic solvents including petroleum ether, diesel, kerosene, and petrol. These organogels and hydrogels have been thoroughly studied and characterized by different techniques including high-resolution transmission electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, and rheology. It has been found that the xerogel obtained from the peptide gelator can trap various toxic organic dyes from wastewater efficiently. Moreover, the hydrogel has been used to remove toxic heavy metal ions Pb2+ and Cd2+ from wastewater. Dye adsorption kinetics has been studied, and it has been fitted by using the Freundlich isotherm equation. Interestingly, the gelator amphiphilic peptide gels fuel oil, kerosene, diesel, and petrol in a biphasic mixture of salt water and oil within a few seconds. This indicates that these gels not only may find application in oil spill recovery but also can be used to remove toxic organic dyes and hazardous toxic metal ions from wastewater. Moreover, the gelator can be recycled several times without significant loss of activity, suggesting the sustainability of this new gelator. This holds future promise for environmental remediation by using peptide-based gelators.

Multicomponent, Tandem 1,3- and 1,4-Bisarylation of Donor-Acceptor Cyclopropanes and Cyclobutanes with Electron-Rich Arenes and Hypervalent Arylbismuth Reagents.

A tandem catalytic process for 1,3- and 1,4-bisarylation of donor-acceptor (D-A) cyclopropanes and cyclobutanes is disclosed. This strategy capitalizes on the use of two distinct sources of nucleophilic and electrophilic arylating agents, affording the formation of two new C-C bonds in an orchestrated multicomponent fashion with the aid of a catalytic Lewis acid. Mechanistic investigations have revealed it to be a stereoselective process, and products could be easily elaborated into other useful compounds.

Nitric Oxide Dioxygenase Activity of a Nitrosyl Complex of Mn(II)-Porphyrinate in the Presence of Superoxide: Formation of a Mn(IV)-oxo Species through a Putative Peroxynitrite Intermediate.

A nitrosyl complex of MnII-porphyrinate, [(F20TPP)MnII(NO)], 1 (F20TPPH2 = 5,10,15,20 tetrakis(pentafluorophenyl)porphyrin), was synthesized and characterized. Spectroscopic and structural characterization revealed complex 1 as a penta-coordinated MnII-nitrosyl with a linear Mn-N-O (180.0°) moiety. Complex 1 does not react with O2. However, it reacts with superoxide (O2-) in THF at -80 °C to result in the corresponding nitrate (NO3-) complex, 2, via the formation of a presumed MnIII-peroxynitrite intermediate. ESI-mass spectrometry and UV-visible and X-band EPR spectroscopic studies suggest the generation of MnIV-oxo species in the reaction through homolytic cleavage of the O-O bond of the peroxynitrite ligand as proposed in NOD activity. The intermediate formation of the MnIII-peroxynitrite was further supported by the well accepted phenol ring nitration which resembles the biologically well-established tyrosine nitration.

[3 + 2]-Annulation of Azaoxyallyl Cations and Thiocarbonyls for the Assembly of Thiazolidin-4-ones.

A base-promoted, efficient [3 + 2] annulation between azaoxyallyl cations and thiocarbonyls is reported for flexible access to highly functionalized thiazolidin-4-one derivatives in good to excellent yields. An intriguing feature of this method is the metal or Lewis acid free late-stage entry of distinct set of functional groups at C2 of thiazolidin-4-ones via substitution of a latent amino functional group. Overall, this approach constitutes a general platform for convenient access to this medicinally important scaffold.