Hot luminescence from single-molecule chromophores electrically and mechanically self-decoupled by tripodal scaffolds.

Control over the electrical contact to an individual molecule is one of the biggest challenges in molecular optoelectronics. The mounting of individual chromophores on extended tripodal scaffolds enables both efficient electrical and mechanical decoupling of individual chromophores from metallic leads. Core-substituted naphthalene diimides fixed perpendicular to a gold substrate by a covalently attached extended tripod display high stability with well-defined and efficient electroluminescence down to the single-molecule level. The molecularly controlled spatial arrangement balances the electric conduction for electroluminescence and the insulation to avoid non-radiative carrier recombination, enabling the spectrally and spatially resolved electroluminescence of individual self-decoupled chromophores in a scanning tunneling microscope. Hot luminescence bands are even visible in single self-decoupled chromophores, documenting the mechanical decoupling between the vibrons of the chromophore and the substrate.

Activating Electroluminescence of Charged Naphthalene Diimide Complexes Directly Adsorbed on a Metal Substrate.

Electroluminescence from single molecules adsorbed on a conducting surface imposes conflicting demands for the molecule-electrode coupling. To conduct electrons, the molecular orbitals need to be hybridized with the electrodes. To emit light, they need to be decoupled from the electrodes to prevent fluorescence quenching. Here, we show that fully quenched 2,6-core-substituted naphthalene diimide derivative in a self-assembled monolayer directly deposited on a Au(111) surface can be activated with the tip of a scanning tunneling microscope to decouple the relevant frontier orbitals from the metallic substrate. In this way, individual molecules can be driven from a strongly hybridized state with quenched luminescence to a light-emitting state. The emission performance compares in terms of quantum efficiency, stability, and reproducibility to that of single molecules deposited on thin insulating layers. Quantum chemical calculations suggest that the emitted light originates from the singly charged cationic pair of the molecules.

Green extraction of puromycin-based antibiotics from Streptomyces albofaciens (MS38) for sustainable biopharmaceutical applications.

Background: Microbial secondary metabolites have shown promise as a source of novel antimicrobial agents. In this study, we aimed to isolate, characterize, and evaluate the antimicrobial activity of compound from a novel Streptomyces albofaciens strain MS38. The objective was to identify a potential bioactive compound with broad-spectrum antimicrobial properties. Methods: The isolated strain MS38 on starch casein agar was characterized using morphological, physiological, and molecular identification techniques. The compound was obtained from the fermented broth through extraction with n-butanol and further purification using silica gel column chromatography and high-performance liquid chromatography (HPLC). Structural elucidation was conducted using Ultraviolet (UV), Infrared (IR), nuclear magnetic resonance (NMR), and mass spectrometry (MS) techniques. The antimicrobial activity was evaluated using the agar well diffusion method and the microplate Alamar blue assay (MABA). Results: The isolated strain MS38 was identified as novel S. albofaciens based on morphological characteristics and confirmed by 16S sequences analysis and MALDI-TOF MS. The compound obtained from the fermented broth exhibited substantial antimicrobial activity against a variety of pathogenic bacteria and fungi. Structural analysis revealed a complex chemical structure with characteristic functional groups indicative of potential antimicrobial properties. The compound demonstrated strong activity against both Gram-positive (Staphylococcus Spp.) and Gram-negative (Klebsiella pneumoniae and Escherichia coli) bacteria, as well as fungi, including Candida albicans and Trichophyton rubrum. Conclusion: This study successfully isolated and characterized a bioactive compound from a novel S. albofaciens MS38. The compound exhibited significant antimicrobial activity against a range of pathogenic microorganisms. These findings underscore the importance of exploring microbial biodiversity for the discovery of novel antimicrobial agents. This study contributes to the growing knowledge of microbial secondary metabolites with potential therapeutic value.

Synthesis and Surface Behaviour of NDI Chromophores Mounted on a Tripodal Scaffold: Towards Self-Decoupled Chromophores for Single-Molecule Electroluminescence.

This paper reports the efficient synthesis, absorption and emission spectra, and the electrochemical properties of a series of 2,6-disubstituted naphthalene-1,4,5,8-tetracarboxdiimide (NDI) tripodal molecules with thioacetate anchors for their surface investigations. Our studies showed that, in particular, the pyrrolidinyl group with its strong electron-donating properties enhanced the fluorescence of such core-substituted NDI chromophores and caused a significant bathochromic shift in the absorption spectrum with a correspondingly narrowed bandgap of 1.94 eV. Cyclic voltammetry showed the redox properties of NDIs to be influenced by core substituents. The strong electron-donating character of pyrrolidine substituents results in rather high HOMO and LUMO levels of -5.31 and -3.37 eV when compared with the parental unsubstituted NDI. UHV-STM measurements of a sub-monolayer of the rigid tripodal NDI chromophores spray deposited on Au(111) show that these molecules mainly tend to adsorb flat in a pairwise fashion on the surface and form unordered films. However, the STML experiments also revealed a few molecular clusters, which might consist of upright oriented molecules protruding from the molecular island and show electroluminescence photon spectra with high electroluminescence yields of up to 6×10-3 . These results demonstrate the promising potential of the NDI tripodal chromophores for the fabrication of molecular devices profiting from optical features of the molecular layer.

Boosting Light Emission from Single Hydrogen Phthalocyanine Molecules by Charging.

Interest in electroluminescence of single molecules is stimulated by the prospect of possible applications in novel light emitting devices. Recent studies provide valuable insights into the mechanisms leading to single molecule electroluminescence. Concrete information on how to boost the intensity of the emitted light, however, is rare. By combining scanning tunnelling microscopy (STM) and quantum chemical calculations, we show that the light emission efficiencies of an individual hydrogen-phthalocyanine molecule can be increased by a factor of ≈19 upon charging. This boost in intensity can be explained by the development of a vertical dipole moment normal to the substrate facilitating out-coupling of the local excitation to the far field. As this effect is not related to the specific nature of hydrogen-phthalocyanine, it opens up a general way to increase light emission from molecular junctions.

Light collection from a low-temperature scanning tunneling microscope using integrated mirror tips fabricated by direct laser writing.

We report on a cryogenic scanning tunneling microscope (STM) designed for single molecule studies, in which the light emitted from the tunneling junction is collected by an integrated optics on the tip. Using direct laser writing, the tip and the surrounding microscopic parabolic mirror are fabricated as one piece, which is small enough to collimate the collected light directly into an optical multimode fiber fixed inside the STM. This simple and compact setup combines high collection efficiency and ease of handling while not interfering with the cryostat operation, allowing uninterrupted measurements at 1.4 K for up to 5 days with low drift.

Improved antimicrobial compound production by a new isolate Streptomyces hygroscopicus MTCC 4003 using Plackett-Burman design and response Surface methodology.

An active strain, isolated from soil of Chhattisgarh, India, showed broad-spectrum antimicrobial activity against various pathogenic bacteria and fungi in glucose soybean meal broth. Strain was characterized as Streptomyces hygroscopicus MTCC 4003 based on 16S rRNA sequencing from Microbial Type culture Collection (MTCC), IMTECH, Chandigarh, India. Identification of the purified antimicrobial compound was done by using Infra-red (IR), Mass, Ultraviolet (UV), 1H and 13C nuclear magnetic resonance (NMR) spectra. Plackett-Burman design (PBD) and response surface methodology (RSM) methods were used for the optimization of antibiotic production. Effects of the four medium components soybean meal, glucose, CaCO3 and MgSO4 showed positive effect on antibiotic production, were investigated with the help of PBD. The individual and interaction effects of the selected variables were determined by RSM using central composite design (CCD). Applying statistical design, antibiotic production was improved nearly ten times (412 mg/L) compared with unoptimized production medium (37 mg/L).

Characterization of sucrose-glutamic acid Maillard products (SGMPs) degrading bacteria and their metabolites.

Two aerobic bacteria RNBS1 and RNBS3 capable to degrade and utilize sucrose-glutamic acid Maillard products (SGMPs) as carbon, nitrogen and energy source were isolated and characterized as Alcaligenes faecalis (DQ659619) and Bacillus cereus (DQ659620) respectively by 16S rRNA gene sequence analysis. In present study, mixed bacterial culture was found more effective compared to axenic culture RNBS1 and RNBS3 decolourizing 73.79%, 66.80% and 62.56% SGMPs, respectively. The SGMPs catabolizing enzyme was characterized as manganese dependent peroxidase (MnP) by SDS-PAGE yielding a single band of 43 KDa. Further, the LC-MS-MS and other spectrophotometric analysis have revealed that most of the SGMPs detected in control were diminished from bacteria treated samples. The disappearance of SGMPs from bacteria treated samples could be related with the degradation of SGMPs.

Multiple antibiotic resistance patterns of rhizospheric bacteria isolated from Phragmites australis growing in constructed wetland for distillery effluent treatment.

Susceptibility patterns of 12 different antibiotics were investigated against rhizospheric bacteria isolated from Phragmites australis from three different zones i.e. upper (0-5 cm), middle (5-10 cm), lower (10-15 cm) in constructed wetland system with and without distillery effluent. The major pollutants of distillery effluent were phenols, sulphide, heavy metals, and higher levels of biological oxygen demand (BOD), chemical oxygen demand (COD) etc. The antibiotic resistance properties of bacteria were correlated with the heavy metal tolerance (one of distillery pollutant). Twenty-two species from contaminated and seventeen species from non-contaminated site were tested by agar disc-diffusion method. The results revealed that more than 63% of total isolates were resistance towards one or more antibiotics tested from all the three different zones of contaminated sites. The multiple-drug resistance property was shown by total 8 isolates from effluent contaminated region out of which 3 isolates were from upper zone, 3 isolates from middle zone and 2 isolates were from lower zone. Results indicated that isolates from contaminated rhizosphere were found more resistant to antibiotics than isolates from non-contaminated rhizosphere. Further this study produces evidence suggesting that tolerance to antibiotics was acquired by isolates for the adaptation and detoxification of all the pollutants present in the effluent at contaminated site. This consequently facilitated the phytoremediation of effluent, which emerges the tolerance and increases resistance to antibiotics.

Melanoidins as major colourant in sugarcane molasses based distillery effluent and its degradation.

Melanoidins are natural condensation products of sugar and amino acids produced by non-enzymatic Maillard amino-carbonyl reaction taking place between the amino and carbonyl groups in organic substances. Melanoidins extensively exist in food products, drinks and wastewaters released from distilleries and fermentation industries. Melanoidins are very important from the nutritional, physiological and environmental aspects and due to their structural complexity, dark colour and offensive odor, these pose serious threat to soil and aquatic ecosystem that release of melanoidins cause increased load of recalcitrant organic material to natural water bodies. This then causes the problems, like reduction of sunlight penetration, decreased photosynthetic activity and dissolved oxygen concentration whereas on land, it causes reduction in soil alkalinity and inhibition of seed germination. Further, due to the possibility of complexation reactions of introduced melanoidins with metal ions, they could influence the biogeochemical cycle of many constituents in natural waters. This review presents an overview to dramatic progress to understand the synthesis, chemical structure and degradation pathway of melanoidins as well as microbial strategies for the degradation and decolourisation of melanoidins.

Investigation of the biotransformation of pentachlorophenol and pulp paper mill effluent decolorisation by the bacterial strains in a mixed culture.

Mixed culture of two bacterial strains Bacillus sp. and Serratia marcescens showed potential pentachlorophenol (PCP) degradation and decolorisation of pulp paper mill effluent. The physico-chemical quality of pulp paper mill effluent has been analyzed after 168 h incubation period degraded by mixed culture. The study revealed that it has decreased high load of BOD, COD, TS, TDS, TSS, sulphate, phosphate, total nitrogen, total phenols, metals and different salts (i.e. chloride, sodium, nitrate, potassium) at 168 h incubation period. PCP degradation in pulp paper mill effluent was confirmed by HPLC analysis. Mixed culture was found to degrade PCP up to (94%) present in pulp paper mill effluent with 1% glucose and 0.5% peptone (w/v) at 30+/-1 degrees C, pH 8.0+/-0.2 at 120 rpm in 168 h incubation period. The simultaneous release of chloride ion up to 1,200 mg/l at 168 h emphasized the bacterial dechlorination in the medium. The pulp paper mill effluent degradation was also supported by decline in pH, AOX (absorbable organic halides), color, D.O., BOD, COD and PCP. The analysis of pulp paper mill effluent degradation products by GC-MS analysis revealed the formation of low molecular weight compound like 2-chlorophenol (RT=3.8 min) and tetrachlorohydroquinone (RT=11.86 min) from PCP extracted degraded sample. Further, mixed culture may be used for bioremediation of PCP containing pulp paper mill waste in the environment.

Isolation and characterization of novel Serratia marcescens (AY927692) for pentachlorophenol degradation from pulp and paper mill waste.

Seven aerobic bacterial strains were isolated from pulp paper mill waste and screened for pentachlorophenol (PCP) tolerance on PCP containing mineral salt agar medium (MSM). The organism was characterized by 16S rDNA sequencing which showed 99.7% sequence similarity with Serratia marcescens. PCP degradation was routinely monitored with spectrophotometric analysis and further confirmed by HPLC analysis. Among seven strains, ITRC S7 was found to degrade up to 90.33% of 1.127 mM (300 mg/l) of PCP and simultaneous release of chloride ion (2.435 mM) emphasized the bacterial dechlorination in the medium in presence of glucose as an additional carbon and energy source under optimized condition within 168 h incubation. In absence of glucose bacterium was unable to utilize PCP indicating the phenomenon of co-metabolism. Bacterium was identified as S. marcescens (AY927692), was a novel and potential aerobic bacterial strain capable of degrading PCP in axenic condition. Further, this strain may be used for bioremediation of PCP containing pulp paper mill waste in the environment.