Hexamethylenetetramine Research Articles

High-performance hybrid supercapacitor based on the porous copper cobaltite/cupric oxide nanosheets as a battery-type positive electrode material

In this work, CuCo2O4/CuO nanosheets (NSs) and CuCo2O4 oblique prisms (OPs) were synthesized at 130 °C with different amounts of hexamethyltetramine (HMTA) and reaction time through a hydrothermal method, and followed by an annealing treatment of precursors in air. The CuCo2O4/CuO NSs with 40 nm in thickness possessed a large specific surface area of 43.34 m2 g−1 and a mean pore size of 18.14 nm. The electrochemical tests revealed that the CuCo2O4/CuO NSs were belonged to the battery-type electrode material and exhibited a specific capacity of 395.55 C g−1 at the current density of 1 A g−1, higher than 258.16 C g−1 for CuCo2O4 OPs. A hybrid supercapacitor (HSC) was assembled with activated carbon (AC) as negative electrode and CuCo2O4-based materials as positive electrode. The CuCo2O4/CuO NSs//AC HSC exhibited a high energy density of 30.18 Wh kg−1 at a power density of 869.62 W kg−1, and showed a fantastic cycling performance with 105.22% capacity retention over 5000 cycles. In contrast, the CuCo2O4 OPs//AC HSC delivered an energy density 26.27 Wh kg−1 at 916.74 W kg−1. These impressive electrochemical properties indicate that CuCo2O4/CuO NSs may serve as a promising electrode material for the highly capable hybrid supercapacitors in the near future.

Effect of hexamethylene tetramine (HMTA) surfactant on the structural characteristics and photocatalytic activity of Cu-ZnO nanoparticle materials fabricated by the hydrothermal method

The experiment had fabricated and studied the properties of ZnO and Cu doped ZnO nanoparticles with the change of the hexamethylene tetramine surfactant content (HMTA) with molar ratio Zn2 +: HMTA = 1: x; x = 1, 2 and 4. The methods were used to study the characteristics of materials such as: XRD, raman shift, SEM, reflection spectrum. The results show that, when the content of surfactant HMTA increased (1-4 mol versus the moles of Zn2+), the size of the nanorods crystals of fabricated materials had reduced from 64.5 to 21.7 nm. The reflectance spectrum of Cu doped ZnO materials samples was lower in the visible light region compared to pure ZnO samples. The photocatalytic properties for decomposition of methylene blue organic dye of the Cu doped ZnO sample (with the greatest concentration of HMTA surfactant of 4 mol versus the moles of Zn2+) reached 98% after 40 minutes of ultraviolet light irradiation, with the rate constant k= 0,13261 min-1.

Methenamine hippurate compared with trimethoprim for the prevention of recurrent urinary tract infections: a randomized clinical trial.

The objective was to find an alternative treatment to a low-dose antibiotic for the prevention of recurrent urinary tract infections (UTI) and to evaluate the difference in rates of reinfection within 1year when treated with methenamine hippurate for prophylaxis compared with trimethoprim. We present a non-blinded randomized trial comparing methenamine hippurate with trimethoprim for the prevention of recurrent UTI at 12months after starting treatment. Women over 18 who had at least two culture-positive UTI in the prior 6months or three in the prior year were included. Ninety-two patients met enrollment criteria and were randomized to receive daily prophylaxis with methenamine hippurate or trimethoprim for a minimum of 6months. Both intent-to-treat and per-protocol analyses if patients received the alternative drug after randomization were analyzed using Student's t test, Mann-Whitney U test, Kaplan-Meier curves, log-rank test, and a logistic and multivariate regression model. The primary outcome of this study was culture-proven UTI recurrence by 12months after initiating prophylaxis. In the intent-to-treat analysis, we found no difference between groups in recurrent UTI, with a 65% (28 out of 43) recurrence in the trimethoprim group versus 65% (28 out of 43) in the methenamine hippurate group (p= 1.00). In the per-protocol analysis, 65% (26 out of 40) versus 65% (30 out of 46) of patients had UTI recurrences in the trimethoprim group versus the methenamine hippurate group (p= 0.98). Methenamine hippurate may be an alternative for the prevention of recurrent UTI, with similar rates of recurrence and adverse effects to trimethoprim.

Zeolitic imidazolate frameworks (ZIF‐8, ZIF‐67, and ZIF‐L) for hydrogen production

Hydride materials have good performance for hydrogen (H2) gas storage and release. The release of H2 gas from hydrides via the hydrolysis process can be improved or controlled using a catalyst. Herein, benzoic acid (BA) and hexamethylenetetramine (HMTA) modulate the synthesis of hierarchical porous zeolitic imidazolate framework‐8 (HFZIF‐8, Zn‐based metal organic frameworks [MOFs]), ZIF‐67 (Co‐based MOFs), and leaf‐like ZIF (ZIF‐L). The mechanistic study for the synthesis procedure of ZIF‐8 revealed an in situ synthesis of zinc hydroxide nitrate nanosheets (100‐ to 150‐nm thickness) with an interplanar distance of 0.97 nm between the layers of zinc hydroxide, Zn5(OH)82+. X‐ray diffraction (XRD) data indicated that benzoate ions replaced nitrate ions (2NO3−) between Zn5(OH)82+ layers leading to an increase in the interplanar distance (from 0.97 nm to 1.9 nm). Zinc hydroxide benzoate nanosheets showed a fast conversion into HPZIF‐8 at room temperature. The concentration of BA and HMTA tuned the porosity of HPZIF‐8, offering a hierarchical micropore–mesopore structure. The prepared materials increased the hydrolysis rate of sodium borohydride. ZIF‐8 and ZIF‐67 prepared using BA showed high catalytic performance in terms of efficiency and reaction time compared with other materials. The result's findings open new avenues for the synthesis of adequate materials for hydrogen generation via the hydrolysis of hydrides.

Excellent Toluene Sensing Properties Based on Monodispersed WO3 Nanoparticles

The preparation of size-controlled materials has shown remarkable potential with regard to their reinforced sensing performance. Herein, we report a facile solvothermal synthesis of dispersed WO3 nanoparticles with porous nanostructure caused by particle assembly. Various characterizations of the as-obtained samples were analyzed. Furthermore, the gas sensing properties of WO3 samples on volatile organic compounds were investigated. The results reveal that the gas sensors based on synthesized WO3 samples with suitable hexamethylenetetramine (HMT) amount and sintering treatment exhibit the highest response (132.0) towards 100 ppm toluene at the optimal working temperature of 225°C with fast response/recovery time (2 s/6 s), which is attributed to the porous structure of the sensing film and the high resistance caused by well crystallization and grain boundary among the nanoparticles.

Designing novel anticancer drug release vehicles based on mesoporous functionalized MCM-41 nanoparticles

Nanoparticles of mesoporous MCM-41 silica were synthesized, functionalized by 8-20% of hexamethylenetetramine (HMT) and employed as effective drug carriers. The carriers’ mesopores were filled with the cyclophosphamide (CP) anticancer medicine. The pore size, pore volume and surface area of pure MCM-41 were obtained equal to 32.54 Å, 0.89 cm3/g and 996.84 m2/g but they were noticeably decreased for the HMT-functionalized MCM-41 materials approving the HMT molecules were bound onto the surfaces and pores of such samples. The release of drug was performed in three neutral PBS, alkaline and acidic solutions. A sharply enhanced CP release was observed in approximately 24 h (burst release) while subsequently release of the drug was gradually boosted within 7 days indicating a sustained release behavior. The maximum drug release amount was measured in alkaline medium, moderate quantity in neutral solution and minimum value in acidic environment. The kinetic of the drug release was examined using the Korsmeyer-Peppas, Hixson-Crowel, Higuchi, first-order, and zero-order models and it was revealed that the CP release from the nanocarriers obeyed the Korsmeyer-Peppas model. Finally, it was decided that the MCM-41 sample containing 14% HMT was the most appropriate system as it had high/favorable quantities of drug loading plus drug release.

Highly efficient N‐doped carbon supported FeSx‐Fe2O3 catalyst for hydrogenation of nitroarenes via pyrolysis of sulfurized N,Fe‐containing MOFs

Integrating MOFs as precursor, especially for employing N‐containing organic linkers, with sulfides is an effective method to prepare the highly efficient N‐doped carbon supported metal‐based catalysts for hydrogenation of nitroarenes. In this work, a N,Fe‐containing metal organic frameworks (MOFs; termed as MIL88‐HMTA) with spindle‐like structure was prepared via self‐assembly method, in which hexamethylenetetramine (HMTA) linker was introduced as N source. Subsequently, N‐doped carbon supported FeSx‐Fe2O3 catalyst (named FeSx‐Fe2O3@CN) was fabricated upon the pyrolysis of sulfurized MIL88‐HMTA. Catalytic experiments reveal that the FeSx‐Fe2O3@CN delivered excellent performance for hydrogenation of nitroarenes in comparison with those of catalyst without sulfidation process (Fe2O3@CN) and conventional MIL88 derived catalyst (Fe2O3@C). The XRD, TEM, SEM/EDX, Raman, UV, and XPS analyses have revealed that the developed FeSx‐Fe2O3@CN catalyst exhibited outstanding catalytic efficiency was ascribed to synergistic effect between FeSx and Fe2O3 species, abundant structural defects, more Fe‐Nx species, and strengthened decomposition ability of hydrazine hydrate (N2H4⋅H2O). Furthermore, the effect of sulfidation ratio (the mass ratio between thioacetamide and MIL88‐HMTA) towards preparation of the developed FeSx‐Fe2O3@CN on the catalytic activity of hydrogenation reaction was also systematically performed. Notably, the optimized catalyst (denoted as FeSx‐Fe2O3@CN‐8) exhibited unexpected performance and recyclability for hydrogenation of nitroarenes under mild condition. The pyrolysis of sulfurized N‐containing MOFs may present a facile approach for fabricating MOFs‐derived N‐doped carbon supported catalysts, which provides a potential application in heterogeneous catalytic reactions.

The Ugly Duckling Metamorphosis: The Ammonia/Formaldehyde Couple Made Possible in Ugi Reactions.

AbstractUgi reactions are still a challenge when the concomitant use of ammonia and formaldehyde is required. Herein, we propose a strategy to overcome this challenge using hexamethylenetetramine (HMTA) as a singular key for the employment of these two simple starting materials in the Ugi reaction. Acylaminoacetamide derivatives were prepared in good to excellent yields by this new methodology. The scope and optimization of the reaction conditions were investigated. This novel methodology was successfully applied in the synthesis of two different diketopiperazines (DKPs) using the Ugi/Deprotection+Activation/Cyclization (UDAC) method. A continuous flow approach was also used in this methodology.

A chromo-fluorogenic HMT sensor for Ag+ and the resultant HMT-Ag complex turn-off probe for F− in DMSO: experimental and theoretical studies

The photophysical properties of Hexamethylenetetramine (HMT) were investigated through physical methods and spectroscopically in dimethyl sulfoxide (DMSO) at ambient temperature. Evidently, HMT turned out as a sensor, selective and sensitive to silver ion (Ag+) only, among other cations, through colorimetric and fluorometric activities (observable by naked eye) and spectrally, both by UV-Vis and fluorescence spectroscopy. The resulting complex pedant (HMT-Ag) is highly responsive to the presence of fluoride ion (F−) in aqueous soluble DMSO, evidenced by changes in absorption spectra as well as fluorescence quenching, upon addition of the respective ions. Consequently, spectral changes induced by the addition of these ions, were consistently concomitant with colour changes, from colourless to light brown (HMT-Ag) to dark brown (HMT-Ag-F) in daylight condition, while bright light blue colour (HMT) to dark blue brownish (HMT-Ag) under UV-light conditions. The experimental results were complimented by theoretical studies, which are well within agreement of one another.

Short X···N Halogen Bonds With Hexamethylenetetraamine as the Acceptor.

Hexamethylenetetramine (HMTA) and N-haloimides form two types of short (imide)X···N and X–X···N (X = Br, I) halogen bonds. Nucleophilic substitution or ligand-exchange reaction on the peripheral X of X–X···N with the chloride of N-chlorosuccinimide lead to Cl–X···N halogen-bonded complexes. The 1:1 complexation of HMTA and ICl manifests the shortest I···N halogen bond [2.272(5) Å] yet reported for an HMTA acceptor. Two halogen-bonded organic frameworks are prepared using 1:4 molar ratio of HMTA and N-bromosuccinimide, each with a distinct channel shape, one possessing oval and the other square grid. The variations in channel shapes are due to tridentate and tetradentate (imide)Br···N coordination modes of HMTA. Density Functional Theory (DFT) studies are performed to gain insights into (imide)X···N interaction strengths (ΔEint). The calculated ΔEint values for (imide)Br···N (−11.2 to −12.5 kcal/mol) are smaller than the values for (imide)I···N (−8.4 to −29.0 kcal/mol). The DFT additivity analysis of (imide)Br···N motifs demonstrates Br···N interaction strength gradually decreasing from 1:1 to 1:3 HMTA:N-bromosuccinimide complexes. Exceptionally similar charge density values ρ(r) for N–I covalent bond and I···N non-covalent bond of a (saccharin)N–I···N motif signify the covalent character for I···N halogen bonding.

Construction of 1D perovskite nanowires by Urotropin passivation towards efficient and stable perovskite solar cell

The instability issue of perovskite solar cells (PSCs) is still an unsettled problem that restricts its further commercialization. A hybrid dimension structure built by one-dimensional and three-dimensional perovskites (1D-3D) is an efficient strategy for improving the stability of PSCs. Herein, self-assembled 1D perovskite nanowires (1D-PNWs) have been successfully constructed by introducing a small amount of Urotropin (UTP) into the perovskite precursor solution used in a two-step preparation method that leads to passivate grain boundaries and thereby improves film crystallinity and reduced defects. The photovoltaic performance of the modified PSC at the optimum amount of UTP (5% molar percentage) has been significantly improved concerning the control devices due to the suppression of non-radiative recombination in the defects and GBs. The power conversion efficiency (PCE) of the optimum device increased from 11.47% to 19.15% with negligible hysteresis. This device was more stable than the control device, with only 5.08% PCE decline within 42 days in a relative humidity level of 38 ± 2 without encapsulation. This study introduces the 1D-PNW network growth by a self-assembly process to provide a feasible and effective strategy to fabricate cheap and extra stable perovskite solar cells.

Morphology controlled carbon aerogel with enhanced thermal insulation and mechanical properties: a simple route for the regulated synthesis

A simple route was proposed to prepare size-controlled carbon aerogel with superior thermal insulation and mechanical properties. Boron-modified phenolic resin (BPR) and hexamethylene-tetramine (HMTA) were crosslinked to build three-dimensional network structure initially followed by CO2 supercritical drying and carbonization. In order to regulate the microstructure of BPR aerogels, the best proportion of HMTA to BPR was confirmed as H/P = 1/5 based on the micromorphology performance in SEM. The interaction between HMTA and BPR was also studied by FTIR spectra, and microstructure evolution of the target product- carbon aerogels were illustrated by SEM technique. SEM patterns indicated that the carbon aerogels maintain a stable porous structure at 1000 °C (carbonization temperature), and pore size distribution were between 321∼612nm based on N2 adsorption-desorption method. The synthesis method is convenient and flexible, permitting a tailor of porous structure, mechanical strength, density and thermal conductivity by adjusting carbonization temperature and time. Consequently, the obtained carbon aerogel with high compressive strength (1.0∼2.3 MPa), low density (0.16∼0.26 g‧cm−3) and low thermal conductivity (0.023∼0.036 W m−l K−1) deserve to be a competitive candidate for high-temperature heat insulation material.

ZrC/C aerogel with high compressive strength by a carbothermic process

The ZrC/C aerogel is successfully prepared through copolymerization sols combined with carbothermal reduction method, using the ZrOC and phenol formaldehyde (PF) as the sols, and hexamethylenetetramine (HMTA) as cross-linker, respectively. The effects of heating treatment temperatures on physical and thermal properties of the aerogels are also investigated. XRD, SEM, and XPS measurements were adopted to characterize the morphology and microstructure of aerogels. Aerogels displayed low bulk density (0.262−0.379 g/cm3), relatively low thermal conductivity (0.0896−0.1064 W/m∙K), and high compressive strength (0.87–4.42 MPa). XRD results show that the aerogel is composed of ZrC and ZrO2 phases at 1400 °C and ZrC at 1500 °C or even high temperature, respectively, indicating that phase transformation of ZrO2 into ZrC. XPS results demonstrated that the element Zr, C, and O are based on ZrOC, ZrC, and ZrO valence band binding, respectively. ZrC/C aerogels with excellent physical and thermal properties may be used in high-temperature field soon.

Solar photocatalytic H2 production over CeO2-based catalysts: Influence of chemical and structural modifications

Different CeO2-based materials employed as unconventional photocatalysts for H2 production were here examined. The performances of bare CeO2 prepared by precipitation were compared with those of CeO2-WO3 composites synthetized by co-precipitation and surfactants-mediated precipitation. The bare CeO2 and the best CeO2-WO3 composite were treated with laser irradiation to investigate the modifications of cerium oxide due to this process. Considering the photocatalytic performance, the CeO2-WO3 composite prepared with the HMTA (hexamethylenetetramine) surfactant and irradiated with laser increased the H2 production up to 4 times compared to the bare CeO2, whereas the laser-modified CeO2 and the CeO2-WO3 synthetized by co-precipitation led to a smaller increase of H2 evolution (1.4 and 1.2 times higher than the as-prepared CeO2, respectively). On the basis of the characterization data (Raman, UV–vis Diffuse Reflectance, Photoluminescence, X-ray photoelectron spectroscopies, Transmission electron microscopy and N2 physisorption measurements) it was established that the addition of the HMTA gave higher WO3 dispersion, whereas the subsequent laser treatment facilitated the progressive incorporation of WO3 into CeO2, resulting in a more efficient doping process and a more defective CeO2. All these features were beneficial for the photoproduction of hydrogen. The tuning and the combination of the chemical and the structural modifications of ceria can be a promising route for the solar-driven photocatalysts designed for the green production of H2.

Case Study for the Predictive Environmental Risk Assessment of Hexamethylenetetramine Release to the Yodo River during a Massive Tsunami Attack

Untreated hexamethylenetetramine (HMT) was discharged into the Tone River in the central area of Japan, and the risk management plan in the watershed area has been strengthened because HMT is the precursor of formaldehyde (FA) regulated by Japanese water supply law. The release of HMT could occur not only in steady but also in unsteady environmental conditions. In this context, no quantitative environmental risk assessments have dealt with the combined events of FA precursor outflow and natural disasters, such as a massive tsunami attack. In this study, we estimated the time course changes of HMT concentrations at the near water treatment plant (WTP) intakes due to tsunami run-up in the river after HMT discharge from facilities along the river during a massive tsunami attack, then potential ecological and health impacts were estimated. This method has a strong analytical ability to reveal the relationship between wave source and inland water run-up in consideration of 3D density flow. For ecological risk, the half maximal effective concentration (EC50) was employed. We found that HMT concentration would not reach a level of concern even after the accident. For potential health risk in terms of the possible maximum inlet concentration of HMT at the WTP, the FA formation amount was 5.3 × 10−2 mg/L, which was below the water quality standard.

Butterfly and Nest‐Shaped Tp*‐W‐Cu‐S Cluster Monomers and Dimers with Hexamethylenetetramine as Ligand: Anion‐Dependent Structures and Nonlinear Optical Properties

Main observation and conclusionThe assembly of [Et4N][Tp*WS3] (1) with CuX (Tp* = hydridotris(3,5‐dimethylpyrazol‐1‐yl)borate; X = Cl, Br, and I) or [Cu(MeCN)4][PF6] in the presence of tetratopic ligand hexamethylenetetramine (HMT) afforded an array of four cluster‐based compounds, which are either neutral or anionic. These compounds include [Tp*WS3Cu3Cl2(HMT)] (2, monomer, neutral), [Tp*WS3Cu3Br2(HMT)] (3, monomer, neutral), [Tp*WS3Cu3I1.5(HMT)]2I (4, dimer, anionic), and [Tp*WS3Cu2(HMT)]2(PF6)2 (5, dimer, anionic). The size of the halogen is found to dictate the structures (2/3 versus 4), and the presence/absence of halogen also affects the utilization of coordinate site of HMT (4 versus 5) by creating more available Cu(I) site in the case of 5. The structures of 2—5 are also characterized using elemental analysis, Fourier‐transform infrared (FT‐IR) spectra, and ultraviolet‐visible (UV‐Vis) spectroscopy, with the dimeric structure of 5 also selected for the third‐order nonlinear optical (NLO) property investigations. The NLO measurement results suggest that the hyperpolarizability value (γ) of 5, reflecting its NLO properties as a neat material, features 2.12×10−30 esu, and it is comparable to other W/Cu/S cluster‐based molecular entities, rendering 5 a promising NLO‐active material.

Hierarchical porous N-doped carbon xerogels for high performance CO2 capture and supercapacitor

Novel microporous carbon xerogels (CX-HMTAs) with different morphologies and well-developed porosity were successfully fabricated. The hierarchical pore, surface structure, and nitrogen content could be easily controlled by adjusting the amount of hexamethylenetetramine (HMTA). The samples as-obtained exhibited high micropore volume and large specific surface area, which were applied as supercapacitor electrodes and CO2 capture materials. The CX-HMTA4 with a moderate concentration of HMTA (0.72 %) afforded the highest CO2 adsorption capability with 4.21 mmol g−1 at 273 K and 1 bar, and excellent ideal adsorption solution theory (IAST) selectivity with 70 for CO2/N2 capture at 298 K. Moreover, the CX-HMTA4 were simultaneously conducted as a supercapacitor electrode, and gave a maximum specific capacitance of 161 F g-1 and high stability (retained 99.4 % capacity after 1000 cycles) in 6 M KOH electrolyte at 1 A g-1, showed a great advance when compared with most reported benchmark carbon materials. The multifunctional porous carbon materials presented herein were facilely prepared without any activation, exhibiting considerable potentials for large-scale gas adsorption/separation and electrochemical energy storage.

Synthesis of high quality hydrothermally grown ZnO nanorods for photoelectrochemical cell electrode

One-dimensional ZnO nanorods (ZnO NRs) have the edge over other nanostructures due to their unique properties. Current work fabricated ZnO NRs on pre-seeded ITO glass substrate through hydrothermal synthesis using customized hydrothermal set-up. The sources of Zn2+ and OH− ions were supplied continuously from zinc nitrate hexahydrate and hexamethylenetetramine (HMTA), respectively whereby the concentration of both precursors and the temperature of growth solution varied from 0.01 M to 0.05 M and from 80 °C to 120 °C, respectively. The impact of concentration and temperature variation on hydrothermal reaction and corresponding PEC cell performance is discussed. Field emission scanning electron microscopy (FESEM) results revealed that the morphology of prepared ZnO NRs arrays is concentration- and temperature-dependent. X-ray diffraction (XRD) reflected strong orientation along (002) direction for the hexagonal wurtzite ZnO NRs, and the film crystallinity greatly improved when the temperature increased. At optimal concentration and hydrothermal temperature, the ZnO NRs photoanode exhibited a bandgap value of 3.22 eV and achieved an impressive photocurrent density of 0.483 mA/cm2 that was attributed to the ordered rods alignment and improved optical properties. In addition, the electrochemical impedance spectroscopy (EIS) demonstrated optimized one-dimensional (1D) NRs sample showed better charge separation and transfer rate, which was two times larger than ZnO nanoparticles. The present work exhibited better photoelectrochemical performance than the other reported literature showing the high quality of ZnO NRs produced.

Effects of Modifiers on the Anti-wetting and Anti-icing Property of Aluminum Surface

The effects of modifiers on the anti-wetting and anti-icing property of the prepared rough aluminum surface were investigated. The rough aluminum substrates were obtained through electrochemical oxidization with 15 wt% sulfuric acid solution as the electrolyte at the constant current of 4 mA for 3 h. And then they were modified with octadecanoic acid (C18), polyethylene (PE), polystyrene (PS), polyethylene glycol (PEG) and hexamethylenetetramine (HMTA), respectively, whose surface free energies were 27.6, 31.0, 33.0, 61.6 and 70.0 mN/m, respectively. The contact angles (CA) were 154.6°, 128.4°, 127.6°, 5.0° and 0.0°, respectively, and the ice adhesion pressures were 15.9, 36.3, 55.9, 155.3 and 216.1 kPa, respectively. The ice adhesion strengths decrease along with the increasing anti-wetting property of aluminum surfaces and the decreasing of the surface energy of modifiers. These provide some new insights when designing the aluminum surface with anti-icing properties in some special applications.

Use of methenamine hippurate to prevent urinary tract infections in community adult women: a systematic review and meta-analysis.

BackgroundUrinary tract infections (UTIs) are often treated with antibiotics and are a source of antibiotic overuse.AimTo systematically review randomised controlled trials (RCTs) of adult women in the community with a history of recurrent UTIs and who use methenamine hippurate prophylactically.Design and settingSystematic review of women in the UK, Australia, Norway, and US (aged ≥18 years) with recurrent UTIs receiving methenamine hippurate against placebo or no treatment, and antibiotics.MethodThe authors searched three databases, clinical trial registries, and performed forward–backward citation analysis on references of included studies.ResultsSix studies involving 557 participants were included (447 were analysed). Of the six studies, five were published and one was an unpublished trial record with results, three compared methenamine hippurate against placebo or control, and three compared methenamine hippurate with antibiotics. For the number of patients who remained asymptomatic, methenamine hippurate showed a non-statistically significant trend of benefit versus antibiotics over 12 months (risk ratio [RR] 0.65, 95% confidence interval [CI] = 0.40 to 1.07, I2 49%), versus control over 6 or 12 months (RR 0.56, 95% CI = 0.13 to 2.35, I2 93%), and a non-statistically significant trend versus any antibiotic for abacteruria (RR 0.80, 95% CI = 0.62 to 1.03, I2 23%). A similar non-statistically significant trend of benefits for methenamine hippurate for the number of UTI or bacteriuric episodes was found, and a non-statistically significant difference in the number of patients experiencing adverse events between methenamine hippurate and any comparator, with a trend towards benefit for the methenamine hippurate, was identified. Antibiotic use and resistance were not consistently reported.ConclusionThere is insufficient evidence to be certain of the benefits of methenamine hippurate to prevent UTI. Further research is needed to test the drug’s effectiveness in preventing UTIs and as an alternative for antibiotic treatment for UTI.