*2.2. Magnetic Behaviour*

Magnetic susceptibility (χM) data were measured on a powdered, restrained crystalline sample of **1** under a 0.1 T dc field in the T = 5–300 K temperature range. The temperature dependence of the χMT product is shown in Figure 6. At room temperature, the χMT value of 40.82 cm3 K mol-1 is close to the Curie constant expected for eight MnIII and four MnII ions, assuming a *g*-value of 2.00 (41.5 cm3 K mol-1). The χMT value remains approximately constant as the temperature is decreased until ~150 K, where it starts to decrease, reaching a minimum value of 13.27 cm3 K mol-1 at 5 K. This behaviour is indicative of the presence of predominantly weak antiferromagnetic interactions between the constituent metal ions. A fit of the 1/χM versus T data to the Curie–Weiss law afforded the Weiss constant, θ = −10 K. Magnetization measurements, performed in fields between 0.5–7 T (Figure 7), are in agreement with this observation, showing M increasing in a near linear like fashion with H, indicative of the field-induced population of low-lying excited states with larger magnetic moments. Previous magneto-structural correlations in alkoxide-bridged MnIII dimers in which the JT axes are coparallel, as seen in the central [Mn10] planar core (Figure 4), predict borderline and weak ferro- or antiferromagnetic exchange interactions, as observed [28]. No signals were observed in ac susceptibility measurements for data collected in the T = 1.8–10 K temperature range in frequencies up to 1500 Hz.

**Figure 6.** Plot of χMT vs T (o) and 1/χM vs T () in the range T = 5–300 K in an applied field of 0.1 T. The red line is a fit of the Curie–Weiss law. See text for details.

**Figure 7.** Field dependence of the magnetization (M) measured in the range T = 2–7 K and H = 0.5–7.0 T.


**1. Introduction**

The *Monascus*-fermented rice is the fermentation product of non-glutinous white rice with the fungus *Monascus*. It has been used for more than a thousand years in East Asian countries for producing rice wine, for flavoring, coloring and preservation of foods as well as a folk medicine for improving food digestion and blood circulation. Several species other than that isolated in 1895 and named *Monascus purpureus* in recognition of its purple colour, have also been widely used in making red wine and red-coloured foods [1]. These *Monascus* fermentation products are called Red Yeast Rice (RYR) in Western countries although the designation "yeast" is incorrect as *Monascus* is a filamentous fungus and not a yeast [2]. Other more accurate denominations like red fermented rice or red mold rice are also used but much more rarely. Today, the usage of *Monascus* rice products as colorant or flavour in foods, and for brewing red rice wine is permitted in many Asian countries but not in Europe. However, RYR extracts are largely sold in Western countries for their cholesterol-lowering effects.

A multitude of fungal secondary metabolites, phytosterols, isoflavonoids, fatty acids, pigments, monacolins and others, are produced during the fermentation process. Monacolins, in particular

monacolin K (MK), which is, in fact, lovastatin, the first marketed statin drug, inhibit the activity of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase. As a result, the endogenous synthesis of cholesterol is reduced and hence the elevated cholesterol level decreases. Many clinical studies demonstrated the efficacy of RYR in the treatment of hypercholesterolemia and its relative safety [3,4]. For similar cholesterol level reduction, the MK amount in clinically tested RYR is markedly lower than that used with prescription statin drugs [4]. This RYR potency is likely explained by the presence of monacolins other than MK and also by the improved dissolution rate and bioavailability of lovastatin when given as RYR [4,5]. However, adverse effects following RYR consumption have been reported; the nature of the symptoms and the targeted organs and systems are similar to those reported for statin drugs [6–9]. Considering the case reports gathered in the WHO Vigibase (82) [8] and those collected by four national health institutions (FDA (164) [8], French Nutrivigilance system (30) [6], Italian Surveillance system (52) [7] and Netherlands Pharmacovigilance Centre Lareb (74) [9]), the more frequent adverse effects are: (i) myalgias and related neuroskeletal complaints from 30% of FDA cases to 43% of Lareb cases, including cases of rhabdomyolysis in the five registries, (ii) gastrointestinal disorders which concern up to 23% of Italian cases, (iii) hepatobiliary disorders that affect from 9% of the WHO cases to 32% of the French cases, including severe adverse reactions as pancreatitis and acute hepatic failure, and (iv) skin and subcutaneous disorders which concern from 8% of French cases to 17% of Italian cases.

Nowadays, RYR is widely used as a cholesterol-lowering agent by patients with a proven or perceived intolerance to statins or by consumers, even without dyslipidemia or increased cardiovascular risk, interested in complementary and alternative medications to influence their lipid levels, as it is a common belief that "natural" products do not have side effects [4]. The RYR products are registered as dietary supplements (DS) and, despite their ever growing popularity, there is no uniform regulation regarding their content in monacolins, especially in MK, nor strict quality control. So, their efficacy and safety are unpredictable. Therefore, the development of analytical methods for the simultaneous determination of MK and other monacolins in RYR products is of great importance.

High performance or Ultra-high performance liquid chromatography (HPLC or UHPLC) with diode array detection (DAD) and/or mass spectrometry (MS) detection are regarded as the gold standard methods for the accurate identification and quantification of a wide range of components in RYR products, including monacolins and pigments [10–14]. Although sensitive and selective, they are usually time-consuming, require standard reference materials for quantitative analysis and may suffer from the occurrence of co-eluting interferences (matrix effects) which is a major drawback for MS quantification [15]. Proton Nuclear Magnetic Resonance (1H-NMR) is recognized as a method of choice for the analysis of complex mixtures (pharmaceuticals, biological media for instance) [16,17]. Indeed, it is highly reproducible, robust, and nonselective, thus allowing an unbiased overview of the sample composition as all the low molecular weight compounds in the solution (provided they bear 1H nuclei and are present at sufficient concentration) are detected simultaneously in a single run. It is also inherently quantitative because the area of each NMR resonance is directly proportional to the number of corresponding nuclei if spectra are recorded in fully relaxed conditions. Thus, at variance with other techniques, the response factor is not dependent on the molecular structure and there is no need for identical reference materials. Moreover, the sample preparation for NMR analysis is very simple as it requires dissolution (for solid products) or dilution (for liquid products) in an adequate deuterated solvent [16]. Lachenmeyer et al. [18] have already used 1H-NMR for the assay of the total quantity of monacolins in five RYR commercial products. They showed that the inhibitory effect of RYR on HMG-CoA reductase was all the more important as their monacolin content was high, but the monacolin contents they determined were not compared to those measured by an orthogonal analytical method.

The purpose of this study was to validate (or not) the 1H-NMR method for an accurate determination of the monacolin content in RYR DS by comparison with the well-established HPLC method and thus to control their quality. Therefore, 31 RYR DS were analyzed using 1H-NMR to establish their spectral signatures and to determine their monacolin contents based on the quantification of selected protons characteristic of the different monacolin chemical structures usually present. An UHPLC analysis with UV-Visible (UV-Vis) and MS detection was performed in parallel on the same 31 RYR DS in order to determine their chemical profiles and to quantify all the monacolins identified.

#### **2. Results and Discussion**


**2.4 Photodecolourisation studies**

*Gold Nanoparticles - Reaching New Heights*

**2.3 Characterisation of the catalysts**

*2.3.2 Transmission electron microscopy*

*2.3.3 BET surface area analysis*

*2.3.1 X-ray diffraction analysis*

product for Au/TiO2.

Scherrer equation,

1% Ag/TiO2, 0.15 g of AuCl3 for 1% Au/TiO2, 0.14 g of [Pt(NH3)4]Cl2 for 1% Pt/TiO2) taken in minimum amount of water was added to 10 g of synthesised TiO2 and was stirred at 70°C till the evaporation of the solvent. The colloidal solution was then irradiated with 125 W halogen lamp until complete reduction was observed visually by the formation of black precipitate for Ag/TiO2, Pt/TiO2 and purple coloured

Synthesised TiO2 and M/TiO2 photocatalyst were subjected to powder X-ray diffraction to confirm the crystalline size and the presence of the metal ion. The powder X-ray diffractograms were recorded using a X-ray diffractometer (PANalytical X'Pert Pro) with Cu Kα source having wavelength of 1.54 Å operating at 20 mA and 50 kV. The samples were scanned from 0.5–80° (2*θ*) for the confirmation of phase and presence of metal particles. The diameter of the metal particles was calculated from the (111) reflection of metal atom using Debye

d = Kλ/β Cos θ (1)

where d, diameter of the metal particle; K, constant; λ, wavelength of the X-ray

Particle size of the noble metals deposited on TiO2 was determined from electron micrographs taken by using transmission electron microscope (JEOL JEM-2010F) operating at 200 kV. A drop of alcoholic solution of the catalysts was placed on Cu grid and kept aside for about 45 s. Then transmission electron micrographs were recorded for the particles present on the grid. From the TEM images, average particle size of the catalysts was determined be taking minimum of 30 particles.

BET surface area analyser (Nova-Quantachrome 4200 e) was used to measure the surface area of all the catalysts. The measurement was done by using N2 as probe molecule at liquid nitrogen temperature (−190°C). Before the measurement, all the

Torr for 6 h. Linear portion

(1.54 Å); β, full width at half maximum; θ, angle of diffraction.

catalysts were degassed at 300°C at the pressure of 10−5

*2.3.4 Atomic absorption spectroscopic studies*

*2.3.5 UV-visible spectrophotometry*

of the BET plots was used for the determination of BET surface area.

The actual amount of metal content present in the synthesised catalysts (M/TiO2, M = Ag, Au and Pt) was determined using atomic absorption spectrophotometer (Perkin Elmer 2380) after digesting the photocatalysts in aqua regia.

UV-visible spectra of all the samples were recorded using UV-Vis double beam spectrophotometer (Hitachi U-2000) in the range 200–800 nm. The course of

**78**


**6. Optoelectronic applications**

2D materials have interesting properties for photonics and optoelectronics compared with other materials. 2D materials enables charge carrier generation by light absorption over a very wide energy spectrum including the ultraviolet, visible, short‐wave infrared (SWIR), near‐ infrared (NIR), mid‐infrared (MIR), far‐infrared (FIR), and terahertz (THz) spectral regimes [7]. Moreover, 2D materials have ultrafast carrier dynamics, wavelength‐independent absorption, tunable optical properties via electrostatic doping, low dissipation rates and high mobility, and ability to confine electromagnetic energy in small volumes [3]. Electrons in 2D crystals possess a valley degree of freedom (DOF) in addition to charge and spin [67]. 2D materials exhibit an anomalous Hall effect whose sign depends on the valley index effect (VHE). It implies that circularly polarized light excites electrons into a specific valley in the structure band, causing a finite anomalous Hall voltage whose sign is controlled by the helicity of the light [67]. The electronic structure changes at the edges of the 2D crystalline structure of MoS2 resulting in strong resonant nonlinear optical susceptibilities due to the translational symmetry breaking [68]. Graphene layers are used as electrodes with tunable work function, while TMDs are applied as photoactive material due to the strong light‐matter interaction and photon absorption. TMDs exhibit transparency, mechanical flexibility, and easy processing [7]. Also, they have the ability to tune the optical band gap by varying the number of monolayers to allow the detection and emission of light (electroluminescence) at different wavelengths. 2D materials present the photovoltaic effect, the photo‐thermoelectric effect, the bolometric effect, the photogating effect and the plasma‐wave‐assisted mechanism [3, 69]. Applications such as transparent electrodes in displays, photovoltaic modules, photodetectors, optical modulators, plasmonic devices, and ultrafast lasers have been developed [7]. 2D TMDs exploit their primary figure of merit and low room‐temperature photoluminescence quantum yield (QY) for applications such as light‐emitting diodes, lasers, and solar cells based on MoS2 [70].