Removal of heavy metal ions from wastewater using two-dimensional transition metal carbides.

Water is an indispensable material for human life. Unfortunately, the development of industrial activities has reduced the quality of water resources in the world. Meantime, heavy metals are an important factor in water pollution due to their toxicity. This study highlights the method for the capture of heavy metal ions from wastewater using the procedure of adsorption. The adsorption of toxic heavy metal ions (Pb2+, Hg2+, and Cd2+) on Ca2C as well as Cr2C carbide-nitride MXene monolayers is investigated using the density functional theory. We have carried out the optimization of the considered MXenes by nine DFT functionals: PBE, TPSS, BP86, B3LYP, TPSSh, PBE0, CAM-B3LYP, M11, and LC-WPBE. Our results have shown a good agreement with previously measured electronic properties of the Ca2C and Cr2C MXene layers and the PBE DFT method. The calculated cohesive energy for the Ca2C and Cr2C MXene monolayers are -4.12 eV and -4.20 eV, respectively, which are in agreement with the previous studies. The results reveal that the adsorbed heavy metal ions have a substantial effect on the electronic properties of the considered MXene monolayers. Besides, our calculations show that the metal/MXene structures with higher electron transport rates display higher binding energy as well as charge transfers between the metal and Ca2C and Cr2C layers. Time-dependent density functional analysis also displayed "ligand to metal charge transfer" excitations for the metal/MXene systems. The larger Ebin for the Pb@Ca2C as well as Pb@Cr2C are according to larger redshifts which are expected (Δλ = 45 nm and 71 nm, respectively). Our results might be helpful for future research toward the application of carbide-nitride MXene materials for removing wastewater pollutants.

N2 reduction to NH3 on surfaces of Co-Al18P18, Ni-Al21N21, Fe-B24N24, Mn-B27P27, Ti-C60 and Cu-Si72 catalysts.

CONTEXT: The abilities of Co-Al18P18, Ni-Al21N21, Fe-B24N24, Mn-B27P27, Ti-C60 and Cu-Si72 as catalysts for N2-RR to create the NH3 are investigated by theoretical levels. The ∆Eadoption and ∆Eformation of Co-Al18P18, Ni-Al21N21, Fe-B24N24, Mn-B27P27, Ti-C60 and Cu-Si72 are investigated. The ∆Eadsorption of N2-RR intermediates and ΔGreaction of reaction steps of N2-RR on Co-Al18P18, Ni-Al21N21, Fe-B24N24, Mn-B27P27, Ti-C60 and Cu-Si72 are examined. In acceptable mechanisms, the *NN → *NNH step is potential limiting step and *NN → *NNH step in enzymatic mechanism is endothermic reaction. The ∆Greaction of *NHNH2 → *NH2NH2 step on Co-Al18P18, Ni-Al21N21, Fe-B24N24, Mn-B27P27, Ti-C60 and Cu-Si72 are -0.904, -0.928, -0.860, -0.882, -0.817 and -0.838 eV, respectively. The Co-Al18P18 and Ni-Al21N21 have the highest ∆Greaction values for reaction steps of N2-RR. Finally, it can be concluded that the Co-Al18P18, Ni-Al21N21, Fe-B24N24 and Mn-B27P2 have acceptable potential for N2-RR by acceptable pathways. METHODS: The structures of Co-Al18P18, Ni-Al21N21, Fe-B24N24, Mn-B27P27, Ti-C60 and Cu-Si72 and N2-RR intermediates are optimized by PW91PW91/6-311+G (2d, 2p) and M06-2X/cc-pVQZ as theoretical levels in GAMESS software. The convergence for force set displacement of Co-Al18P18, Ni-Al21N21, Fe-B24N24, Mn-B27P27, Ti-C60 and Cu-Si72 and N2-RR intermediates are 1.5 × 105 Hartree/Bohr and 6.0 × 10-5 Angstrom. The Opt = Tight and MaxStep = 30 are considered to optimize Co-Al18P18, Ni-Al21N21, Fe-B24N24, Mn-B27P27, Ti-C60 and Cu-Si72 and N2-RR intermediates. The frequencies of Co-Al18P18, Ni-Al21N21, Fe-B24N24, Mn-B27P27, Ti-C60 and Cu-Si72 and N2-RR intermediates are calculated.

Navigating Adherence: Unraveling Factors Shaping Opioid Substitution Therapy Compliance.

Background and objective In drug-deaddiction programs, dropout is a major problem in any drug de-addiction program, as dependence is a chronic illness known to relapse frequently. Understanding factors that predict dropout can help design targeted interventions to promote follow-up. This study aimed to assess the various sociodemographic characteristics of opioid-dependent subjects on buprenorphine maintenance treatment and dropping out at or before the three-month follow-up period. Method In this study, the sociodemographic characteristics and quality of life (QOL) of 34 opioid-dependent subjects (males, 32, 94%; females, 2, 6%) on the day of their enrolment in an opioid substitution therapy (OST) center were assessed, and a comparison of sociodemographic and drug use pattern was made between those who followed up and those who dropped out by the end of three months. Results Statistical analysis of the various sociodemographic characteristics using appropriate tests yielded that predictors of good follow-up are younger age (F = 4.57907, P = 0.04008), better education (F = 5.07221, P = 0.031305), and being part of a nuclear family. Longer follow-up was associated with shorter opioid intake duration (F = 8.58908, P = 0.006195). Better social relationships, as evidenced by the social relationship domain score of QOL, predicted longer follow-up (F = 8.58908, P = 0.006195). Other characteristics analyzed did not yield significant associations. Conclusions The study unveils the complexity of opioid addiction recovery, revealing the interplay of age, education, family, addiction duration, and support, shaping one's resilience in recovery.

Desvenlafaxine-Triggered Acneiform Eruptions on the Hand: A Compelling Case Report.

A 45-year-old male developed a skin eruption after starting Desvenlafaxine for depressive symptoms associated with schizophreniform disorder. The patient developed a rash on the hand, hyperpigmentation, and itching, which resolved after discontinuing the medication. The Naranjo score suggested a probable link between desvenlafaxine and the skin reaction. Stable vital signs and normal labs supported this conclusion. The case underscores the importance of recognizing and reporting adverse drug reactions, even with generally safe medications like desvenlafaxine. Further research with larger samples is needed to explore this relationship in more depth.

Common Consequences of Uncommon Congenital Heart Disease: Exploring the Trilogy of Fallot With Infective Endocarditis and Cerebral Venous Thrombosis.

Trilogy of Fallot (ToF) is a rare congenital heart disease characterized by a combination of atrial septal defect, pulmonary stenosis, and right ventricular hypertrophy. It is more common in females and can cause symptoms such as cyanosis and breathlessness. ToF can lead to complications like thromboembolic events, including infective endocarditis (IE) and cerebral venous thrombosis (CVT). This case study discusses a nine-year-old female with ToF who also had IE and CVT. The patient recovered well following treatment with intravenous beta-lactam and aminoglycoside for IE and subcutaneous low-molecular-weight heparin for CVT.

Mechanical quantum analysis on the role of transition metals on the delivery of metformin anticancer drug by the boron phosphide nanotube.

We scrutinized the impact of doping of X atoms (X = Fe, Co, Ni, Cu, and Zn) on the metformin (MF) drug delivery performance of a BP nanotube (BPNT) using density functional B3LYP calculations. The pristine BPNT was not ideal for the drug delivery of MF because of a weak interaction between the drug and nanotube. Doping of the Zn, Cu, Ni, Co, and Fe into the BPNT surface raised the adsorption energy of MF from -5.3 to -29.1, -28.7, -29.8, -32.1, and -26.9 kcal/mol, respectively, demonstrating that the sensitiveness of the metal-doped BPNT increased after increasing the radius atomic of metals. Ultimately, there was an increase in the adhesion performance and capacity of the MF after X (especially Co atom) doping, making the nanotube suitable for MF drug delivery. The mechanism of MF reaction with the BPNT changed from covalent bonding in the natural environment to hydrogen bonding in the cancerous cells with high acidity.

Extraction of some essential amino acids using aqueous two-phase systems made by sugar-based deep eutectic solvents.

Aqueous two-phase systems (ATPSs) have long been recognized as versatile and efficient tools for the extraction of biomolecules, including amino acids. Recent advancements in the field have introduced a novel approach by utilizing deep eutectic solvents (DES) to form ATPs. This study aimed to determine the phase diagrams for an ATPS made of polyethylene glycol dimethyl ether 250 and two types of NADESs, namely choline chloride as a hydrogen bond acceptor (HBA), and either sucrose or fructose as a hydrogen bond donor (HBD) with a molar ratio of 1 : 2. The measured tie-line results revealed that the hydrogen bonds of NADES may not be entirely disrupted in aqueous solutions, and thus, these ATPSs act as ternary-like systems. Additionally, the binodal data were fitted using two semi-empirical equations, namely Merchuk and Zafarani-Moattar et al. equations. Furthermore, the ATPSs mentioned above were applied to extract three amino acids, namely l-arginine, l-phenylalanine, and l-tyrosine, and demonstrated good extraction levels. Finally, the Diamond-Hsu equation and its modified version were utilized to correlate the experimental partition coefficients of the amino acids. These advancements pave the way for the development of improved extraction methodologies and the exploration of new applications in the field of biotechnology, pharmaceuticals, and beyond.

Atypical Kawasaki Disease in a 16-Month-Old Baby: A Case Report and Literature Review.

Kawasaki illness is an inflammatory condition of small- to medium-sized vessels that primarily affects children. It affects the lymph nodes, skin, mucous membranes, and heart, especially the coronary arteries. Patients who lack the comprehensive clinical manifestations of classic Kawasaki disease (KD) are typically evaluated for incomplete KD. Such patients have persistent fever and lack one or more characteristic clinical signs. Here, we present a case of a 16-month-old baby presented with fever for nine days, excessive crying and irritability for four days, and refusal to feed for one day with pallor and developed lip cracking, mucositis, bilateral edema, and redness in the palms and soles followed by periungual desquamation. Lab evaluations revealed anemia, elevated white cell count, and c-reactive protein along sterile pyuria. Since the child became afebrile after ten days of illness, inflammatory marker levels decreased, and no coronary artery abnormalities were detected on 2D echocardiography, and the child was diagnosed with incomplete KD based on the clinical, laboratory, and radiological evaluations after ruling out all other possible causes. He was managed conservatively with low-dose aspirin, and the child was doing well on a two-month follow-up.

A Rare Case of Hypomyelinating Leukodystrophy and Its Management: A Case Report and Literature Review.

A subset of hereditary white matter disorders called hypomyelinating leukodystrophies (HLD) is characterized primarily by the absence of myelin deposition. Although the clinical presentation can be mild and the development of symptoms can occur in adolescence or adulthood, the majority of severe cases present during infancy and early childhood with significant neurological impairments. The clinical features vary from muscle stiffness to seizures and developmental delay. The detailed myelination process can be seen with magnetic resonance imaging (MRI), and many patients are diagnosed using MRI pattern recognition and next-generation sequencing (NGS) in most cases. Here, we report a case of an infant suffering from the hypomyelinating leukodystrophy-13 (HLD-13) variant, whose next-generation sequencing revealed a pathogenic homozygous variant.

A non-dominated sorting based multi-objective neural network algorithm.

Neural Network Algorithm (NNA) is a recently proposed Metaheuristic that is inspired by the idea of artificial neural networks. The performance of NNA on single-objective optimization problems is very promising and effective. In this article, a maiden attempt is made to restructure NNA for its possible use to address multi-objective optimization problems. To make NNA suitable for MOPs several fundamental changes in the original NNA are proposed. A novel concept is proposed to initialize the candidate solution, position update, and selection of target solution. To examine the optimization ability of the proposed scheme, it is tested on several benchmark problems and the results are compared with eight state-of-the-art multi-objective optimization algorithms. Inverse generational distance(IGD) and hypervolume (HV) metrics are also calculated to understand the optimization ability of the proposed scheme. The results are statistically validated using Wilcoxon signed rank test. It is observed that the overall optimization ability of the proposed scheme to solve MOPs is very good.•This paper proposes a method to solve multi-objective optimization problems.•A multi-objective Neural Network Algorithm method is proposed.•The proposed method solves difficult multi-objective optimization problems.

Localization and expression of Orexin B (OXB) and its type 2 receptor (OX2R) in mouse testis during postnatal development.

The orexins (OXs) were first reported in hypothalamus of rat, and they play an important role in diverse physiological actions. The OXs consist of orexin A (OXA) and orexin B (OXB) peptides and their actions are mediated via two G-protein-coupled receptors, orexin 1 receptor (OX1R) and orexin 2 receptor (OX2R), respectively. Presence of OXA and OX1R has been also reported in peripheral organs like reproductive tissues. These findings, therefore, highlight a possible role of OXs and their receptors in male reproductive health. Though, expression and localization of OXB and OX2R in the testis and their role in spermatogenesis are not finally clarified. Herein, we elucidated the localization and the patterns of expression of OXB and OX2R in Parkes mice testes during postnatal development. Results suggest that the precursor prepro-orexin (PPO), OXB and OX2R are expressed at the transcript and protein levels in mouse testis throughout the postnatal development. Immunostaining further showed the localization of OXB and OX2R both in interstitium and tubular compartments of the testis. On 7 day postpartum (7 dpp), only spermatogonia showed immunoreactivity of OXB and OX2R, while at 14, 28, 42 and 90 dpp, immunolocalization of OXB and OX2R were noted in the seminiferous tubules, especially in leptotene, pachytene spermatocytes, round and elongating spermatids, and in Leydig cells and Sertoli cells. The immunoreactivity of OXB and OX2R appeared to be stage-specific in adult mouse testis. The results suggest the expression of OXB and OX2R in mouse testis and their possible regulatory role in spermatogenesis and steroidogenesis.

Sub-Chronic Restraint Stress Suppresses Sexual Potency and Erection Efficiency by Targeting the Hypothalamic-Pituitary-Testicular Axis and the Nitric Oxide/Cyclic Guanosine Monophosphate/Phosphodiesterase 5α Pathway in Adult Rats.

INTRODUCTION: Male sexual potency and vigor are a complex neuroendocrine process and an important component of well-being. Psychological stress is one of the leading causes of male impotence worldwide. Therefore, to better understand the effects of psychological stress on male sexual potency, vigor, and the physiology of erection, we used the rat restraint stress (RS) model, which can most aptly simulate psychological stress. METHODS: Adult male SD rats were exposed to RS for 1.5 or 3 h/day for 30 days. Neuromodulators and hormones of sexual potency and penile erection were quantified using ELISA kit. The histoarchitecture of the penis was examined using Masson trichrome staining. Immunoblotting and immunofluorescence were used to assess the expression and immunolocalization patterns of penile erection markers. To assess sexual potency and vigor, a noncontact erection and a copulatory test were performed. RESULTS: RS exposure decreased the circulatory levels of gonadotropins and testosterone while increasing the serum corticosterone level. RS exposure altered the histomorphology of the penis by decreasing the smooth muscle/collagen ratio and increasing oxidative stress in penile tissue. Furthermore, RS adversely affected NO availability for penile erection by decreasing the neurotransmitter acetylcholine and other erection facilitatory markers such as p-Akt, nNOS, eNOS, and cGMP, while increasing the inhibitory marker PDE5α in the penis. RS exposure significantly reduced the frequencies of mount, intromission, and ejaculation, whereas it prolonged sexual exhaustion by increasing latencies of postejaculatory mount, intromission, and ejaculation. CONCLUSION: The current findings suggest that psychological stressors, such as RS, cause erectile dysfunction in adult male rats by modulating the hypothalamic-pituitary-testicular axis, oxidative balance, penile fibrosis, and the NO/cGMP/PDE5α pathway of penile erection.

Postnatal ontogeny of Neuromedin S and its receptors NMUR1 and NMUR2 expression in mouse testis.

Neuromedin S (NMS) is a well-known anorexigenic neuropeptide. Despite some reports of the presence of its transcript and precursor protein in testis, the expression and localization of NMS and its receptors during the postnatal development of mammalian testis remains elusive. We investigated the expression patterns and testicular localization of NMS and its receptors NMUR1 and NMUR2, during 5, 10, 20, 30, and 90 days of postnatal development, using real time PCR, immunoblot analysis and immunohistochemistry in mice. NMS and its receptors are present at all age groups at transcript level in mouse testis. At the protein level, NMS and NMUR2 are present in all age groups, whereas NMUR1 is present primarily in 30- and 90-day testis. Immunolocalization study showed that NMS and NMUR2 are expressed in spermatogonia, spermatocytes, Sertoli cells, and Leydig cells, in contrast to NMUR1 which is expressed exclusively in the Leydig cells of 30- and 90-day testis. The results also confirm the intranuclear localization of NMS in spermatogonia and spermatocytes. Although NMS-NMUR2 is expressed in Sertoli cells at all stages of the spermatogenic cycle, they showed a stage-specific expression pattern in spermatogonia and primary spermatocytes. In conclusion, NMS and its receptors NMUR1 and NMUR2 are expressed in the testis and may regulate spermatogenesis, possibly by modulating steroidogenesis and Sertoli cell function in the testis.

Sub-chronic restraint stress exposure in adult rats: An insight into possible inhibitory mechanism on testicular function in relation to germ cell dynamics.

Psychological stress is now widely recognized as one of the major risk factors for male fertility. Its impact on the dynamics of testicular germ cells, however, has yet to be fully investigated. Therefore, we used the rat restraint stress (RS) model as a psychological stressor to assess the impact of psychological stress on testicular germ cell dynamics. Adult male SD rats were exposed to sub-chronic RS for 1.5 and 3 h per day for 30 days. The quality of cauda epididymis spermatozoa was adversely affected by RS exposure, and the frequency of spermatozoa with tail abnormalities was higher than that of spermatozoa with head abnormalities. RS exposure adversely affected testicular daily sperm production by disturbing the meiotic and post meiotic germ cell kinetics in the testis. The histomorphology of the testis was altered by loosening and vacuolization in the seminiferous epithelium, germ cell exfoliation and the presence of giant cells. Seminiferous tubules of stage I-VI and VII-VIII were severely affected in rats exposed to RS for 3 h. By interfering with steroidogenic enzymes, RS exposure disrupts testosterone biosynthesis. The testicular oxidative balance was also disturbed by RS exposure, which disrupted the levels/activities of lipid peroxidation, Nrf-2, superoxide dismutase and catalase. There was also an increase in caspase-3 activity and a decrease in the Bax-Bcl2 ratio. In conclusion, our findings suggest that psychological stressors like RS impair testicular functions in rats by disrupting germ cell dynamics, downregulating testicular androgenesis and increasing oxidative stress and apoptosis.

Anxiety among doctors during COVID-19 pandemic in a tertiary care center in India.

Background and Objectives: The ongoing pandemic of COVID-19 has a severe impact on the health-care system worldwide bringing doctors under immense pressure to work under stressful conditions. The main objective of this study was to assess anxiety among doctors and to understand the perceived causes of anxiety. Methodology: Questionnaires were made available to all willing doctors of SN Medical College, Agra; King George's Medical University, Lucknow, and GSVM Medical College, Kanpur, between May 12, 2020, and June 20, 2020 (during nationwide lockdown). The questionnaire consists of three main sections: details about respondents' working status, questions regarding respondents' reasons for concern, and Becks' Anxiety Inventory (BAI) scale. Results: Two hundred and fifty responses were received from about 599 doctors presented with the questionnaire. About 32% of the respondents have already done duties in COVID facilities and the rest are awaiting deployment at those facilities. Forty-two percent reported concern regarding transmitting the illness to close ones/loved ones/family members to be a cause of anxiety and 40% were worried about the quality of protective gear closely followed by examination-related worries. About 28.8% of the respondents scored >7 on BAI with 62.5% of these (18% of total respondents) reporting "moderate" levels of anxiety. Conclusions: Our findings underline the fact that pandemics such as COVID-19 cause significant levels of anxiety among doctors. The levels of anxiety differed for age, sex, and specialty. The perceived causes were the risk of transmitting to loved ones and concerns regarding protective gear. These outcomes highlight the need for early interventions to address anxiety and to provide support for doctors during such crises.

Enhanced Methanol Electro-Oxidation Activity of Nanoclustered Gold.

Size-selected 3 nm gas-phase Au clusters dispersed by cluster beam deposition (CBD) on a conducting fluorine-doped tin oxide template show strong enhancement in mass activity for the methanol electro-oxidation (MEO) reaction compared to previously reported nanostructured gold electrodes. Density functional theory-based modeling on the corresponding Au clusters guided by experiments attributes this high MEO activity to the high density of exposed under-coordinated Au atoms at their faceted surface. In the description of the activity trends, vertices and edges are the most active sites due to their favorable CO and OH adsorption energies. The faceted structures occurring in this size range, partly preserved upon deposition, may also prevent destructive restructuring during the oxidation-reduction cycle. These results highlight the benefits of using CBD in fine-tuning material properties on the nanoscale and designing high-performance fuel cell electrodes with less material usage.

An Intelligent Model for the Detection of White Blood Cells using Artificial Intelligence.

BACKGROUND AND OBJECTIVE: The automatic detection and counting of white blood cells (WBCs) play a vital role in the diagnosis of hematological diseases. Computer-aided methods are prevalent in the detection of WBCs because the manual process involves several complexities. In this article, a complete automatic detection algorithm to recognize the WBCs embedded in cluttered and complicated smear images of blood is designed. METHODS: The proposed algorithm uses the ellipse detection approach to approximate the presence of WBCs in the Blood. A newly designed artificial electric field algorithm with novel velocity and position bound (AEFA-C) is employed for this purpose. The problem of detection of WBCs is transformed into an optimization problem where the random candidate solutions (ellipses) are efficiently mapped. These candidate ellipses are mapped onto the edge map of the smear image, and a complete mapping is obtained using the AEFA-C algorithm. RESULTS: The effectiveness of the AEFA-C based detector is tested over the 60 smear images of the blood, having all the five types of WBCs or leukocytes. The developed algorithm obtained an overall detection accuracy of 96.90%. Further, the robustness test is performed on the same dataset which justifies that the technique can handle the different noises with the detection accuracy of 90.33%. Also, the comparative study of the proposed detection algorithm with the state-of-art detection algorithms is carried out. CONCLUSIONS: The experimental results demonstrate the efficiency of the proposed scheme for the detection of the WBCs in terms of detection accuracy, stability, and robustness and its outperformance over the state-of-art algorithms.

A platinum-nickel bimetallic nanocluster ensemble-on-polyaniline nanofilm for enhanced electrocatalytic oxidation of dopamine.

We report a new approach to design flexible functional material platforms based on electropolymerized polyaniline (PANI) polymer nanofilms modified with bimetallic nanoclusters (NCs) for efficient electro-oxidation of small organic molecules. Composition defined ligand free Pt0.75Ni0.25 NCs were synthesized in the gas phase using the Cluster Beam Deposition (CBD) technology and characterized using RToF, HAADF-STEM, XAFS and XPS. NCs were then directly deposited on PANI coated templates to construct electrodes. Dopamine (DP) molecules were used as a representative organic analyte and the influence of the NC-PANI hybrid atomistic structure on the electrochemical and electrocatalytic performance was investigated. The as prepared, nearly monodispersed, Pt0.75Ni0.25 NCs of ca. 2 nm diameter featuring a PtOx surface combined with a shallow platelet-like Ni-O(OH) phase formed a densely packed active surface on PANI at ultralow metal coverages. Electrochemical measurements (EIS and CV) show a 2.5 times decrease in charge transfer resistance and a remarkable 6-fold increase at lower potential in the mass activity for Pt0.75Ni0.25 NCs in comparison with their pure Pt counterparts. The enhanced electrochemical performance of the Pt0.75Ni0.25 NC hybrid's interface is ascribed to the formation of mixed Pt metal and Ni-O(OH) phases at the surface of the alloyed PtNi cores of the bimetallic NCs under electrochemical conditions combined with an efficient charge conduction pathway between NCs.

Titanium Nitride Nanodonuts Synthesized from Natural Ilmenite Ore as a Novel and Efficient Thermoplasmonic Material.

Nanostructures of titanium nitride (TiN) have recently been considered as a new class of plasmonic materials that have been utilized in many solar energy applications. This work presents the synthesis of a novel nanostructure of TiN that has a nanodonut shape from natural ilmenite ore using a low-cost and bulk method. The TiN nanodonuts exhibit strong and spectrally broad localized surface plasmon resonance absorption in the visible region centered at 560 nm, which is well suited for thermoplasmonic applications as a nanoscale heat source. The heat generation is investigated by water evaporation experiments under simulated solar light, demonstrating excellent solar light harvesting performance of the nanodonut structure.

Unravelling the nucleation mechanism of bimetallic nanoparticles with composition-tunable core-shell arrangement.

The structure and atomic ordering of Au-Ag nanoparticles grown in the gas phase are determined by a combination of HAADF-STEM, XPS and Refl-XAFS techniques as a function of composition. It is shown consistently from all the techniques that an inversion of chemical ordering takes place by going from Au-rich to Ag-rich compositions, with the minority element always occupying the nanoparticle core, and the majority element enriching the shell. With the aid of DFT calculations, this composition-tunable chemical arrangement is rationalized in terms of a four-step growth process in which the very first stage of cluster nucleation plays a crucial role. The four-step growth mechanism is based on mechanisms of a general character, likely to be applicable to a variety of binary systems besides Au-Ag.