Silver Nanoparticle-Functionalized Postsynthetically Modified Thiol MOF UiO-66-NH-SH for Efficient CO2 Fixation.

Thiols are essential functional groups imparting unique properties, such as reactivity and selectivity, to many vital enzymes and biomolecules. The integration of electronically soft thiol groups within metal-organic frameworks (MOFs) yields elevated reactivity and a pronounced affinity for soft metal ions. However, the scarcity of thiol-based ligands and synthetic challenges hinder the advancement of thiol-based MOFs. To bypass the difficulties of synthesizing thiol MOFs by a direct reaction between thiol-based ligands and corresponding metal salts, postsynthetic modification (PSM) of MOFs is an efficient strategy to introduce thiol functionality. Herein, we have introduced Ag nanoparticles in postsynthetically modified thiol MOFs UiO-66-NH-SH (1) (synthesized by reaction between UiO-66-NH2 and thioglycolic acid) and UiO-66-NH-SH (2) (synthesized by reaction between UiO-66-NH2 and 3-mercaptopropionic acid) to synthesize a series of heterogeneous catalysts for CO2 fixation. Catalysts Cat 1-2 and Cat 3 - 4 were synthesized from UiO-66-NH-SH (1) and UiO-66-NH-SH (2), respectively, by using varying concentrations of silver (AgNO3). Catalyst Ag@UiO-66-NH-SH (1) (Ag = 3.45%; namely Cat 2) shows the highest efficiency for the catalytic conversion of propargylic alcohol and terminal epoxide to the corresponding cyclic carbonates. Finally, a rationalized reaction mechanism is proposed by correlating our results with the current literature. This work presents a viable strategy to utilize the thiol functionality of MOFs (avoiding the complexities associated with synthesizing thiol MOFs directly from thiol ligands) as a platform for introducing catalytically active metal centers and applying them as a heterogeneous catalyst for CO2 fixation reactions.

Thiol and thioether-based metal-organic frameworks: synthesis, structure, and multifaceted applications.

Metal-organic frameworks (MOFs) are unique hybrid porous materials formed by combining metal ions or clusters with organic ligands. Thiol and thioether-based MOFs belong to a specific category of MOFs where one or many thiols or thioether groups are present in organic linkers. Depending on the linkers, thiol-thioether MOFs can be divided into three categories: (i) MOFs where both thiol or thioether groups are part of the carboxylic acid ligands, (ii) MOFs where only thiol or thioether groups are present in the organic linker, and (iii) MOFs where both thiol or thioether groups are part of azolate-containing linkers. MOFs containing thiol-thioether-based acid ligands are synthesized through two primary approaches; one is by utilizing thiol and thioether-based carboxylic acid ligands where the bonding pattern of ligands with metal ions plays a vital role in MOF formation (HSAB principle). MOFs synthesized by this approach can be structurally differentiated into two categories: structures without common structural motifs and structures with common structural motifs (related to UiO-66, UiO-67, UiO-68, MIL-53, NU-1100, etc.). The second approach to synthesize thiol and thioether-based MOFs is indirect methods, where thiol or thioether functionality is introduced in MOFs by techniques like post-synthetic modifications (PSM), post-synthetic exchange (PSE) and by forming composite materials. Generally, MOFs containing only thiol-thioether-based ligands are synthesized by interfacial assisted synthesis, forming two-dimensional sheet frameworks, and show significantly high conductivity. A limited study has been done on MOFs containing thiol-thioether-based azolate ligands where both nitrogen- and sulfur-containing functionality are present in the MOF frameworks. These materials exhibit intriguing properties stemming from the interplay between metal centres, organic ligands, and sulfur functionality. As a result, they offer great potential for multifaceted applications, ranging from catalysis, sensing, and conductivity, to adsorption. This perspective is organised through an introduction, schematic representations, and tabular data of the reported thiol and thioether MOFs and concluded with future directions.

A thiol-containing zirconium MOF functionalized with silver nanoparticles for synergistic CO2 cycloaddition reactions.

Thiol-containing biomolecules, such as cysteine and glutathione, play essential roles in regulating the polarity and reactivity of the systems. Among functional MOFs, thiol MOFs, a subclass with a thiol group-containing ligand, are relatively less explored due to their synthetic challenges and stability and storage issues. Despite these drawbacks, they have many advantages due to the electronically soft thiol groups with strong reactivity and affinity toward soft metal ions. Herein, we have taken advantage of the affinity between thiol groups and a soft metal (Ag) by functionalizing a thiol MOF with Ag ions and finally synthesizing a silver nanoparticle-functionalized heterogeneous catalyst (Ag@Zr-DMBD). The Zr,Ag centre of the thiol MOF catalyst acts as an active centre and synergistically binds with the electron-rich oxygen atom of a terminal epoxide for efficient CO2 fixation to the corresponding cyclic carbonates under atmospheric CO2 pressure in 8 h. Finally, a rationalized reaction mechanism is proposed based on literature reports and current results. This work presents a viable strategy for using thiol MOFs as heterogeneous catalysts for CO2 fixation under mild conditions.

Anal sex and associated HIV-related sexual risk factors among female sex workers in Andhra Pradesh, India.

BACKGROUND: This study aims to understand the correlates of anal sex practices among female sex workers (FSWs) and examine the association of anal sex with HIV-related sexual risk factors in Andhra Pradesh, India. METHODS: A cross-sectional behavioural survey was conducted in 2011 among 795 FSWs aged 18 years or older. Probability-based cluster sampling was used to select respondents from sex work hotspots. RESULTS: One-quarter (23%) of FSWs had practiced anal sex in the last year. The odds of practicing anal sex were higher among FSWs aged 35 years or more than in those aged less than 25 years (adjusted odds ratio (AOR): 2.05, P<0.05), in those formerly married compared to those currently married (AOR: 1.88, P<0.01), in those having an income only from sex work compared to those having additional sources of income (AOR: 1.54, P<0.05), those reporting heavy alcohol consumption compared to those who did not (AOR: 2.80, P<0.01) and those who experienced violence compared to those who had not (AOR: 2.80, P<0.01). FSWs practicing anal sex were more likely to experience sexually transmissible infection (STI) related symptoms than those practicing only vaginal sex. There was no association between anal sex practice and condom use. CONCLUSIONS: Anal sex is associated with STI symptoms, a factor for HIV risk. HIV intervention programmes need to educate FSWs about the risks associated with anal sex.

Scale-up and coverage of Avahan: a large-scale HIV-prevention programme among female sex workers and men who have sex with men in four Indian states.

OBJECTIVE: Documenting the implementation of a public health programme as per its design is critical to interpretation of results from survey-led outcome and impact evaluation activities, the authors describe the scale-up and coverage of large-scale HIV-prevention services provided to female sex workers (FSWs) and high-risk men who have sex with men (HR-MSM) during the first 5 years of the Avahan programme in India. METHODS: Implementing NGO partner-generated denominator estimates from 70 districts were used to estimate the programme's intended coverage. Routine programme-monitoring data until December 2008 were used to describe the service and commodity availability, service utilisation to generate internal estimates of coverage. Coverage was validated in few districts using data from a cross-sectional survey. RESULTS: In December 2008, the estimated denominators for intended services were about 217,000 FSWs and 80,000 HR-MSM. By January 2007, 79% of eventual total clinics and 75% drop-in centres were established, and 83% of eventual peer educators were active. By month 48, sufficient condoms to cover all estimated FSW commercial sex acts were distributed free. By month 60, 75% of the estimated denominator intended to be covered was met monthly. 86% of FSWs and 67% of HR-MSM ever contacted had used sexually transmitted infections services at least once. Cross-sectional survey generated coverage results suggest that programme-monitoring data provide a proxy to coverage of services. CONCLUSION: Avahan's monitoring data show that Avahan achieved infrastructure scale by year 3 and high contact coverage through peers and with commodities by year 5 of implementation as per the design.