Synthesis and Optical Properties of a Novel Hybrid Nanosystem Based on Covalently Modified nSiO2 Nanoparticles with a Curcuminoid Molecule.

A new curcuminoid molecule (3) has been designed and synthesized, containing a central -(CH2)2-COOH chain at the α carbon of the keto-enol moiety in the structure. The carboxylic acid group is added to react with exposed amino groups on silica oxide nanoparticles (nSiO2), forming an amide bond to attach the curcuminoid moiety to the nSiO2 covalently. The Kaiser test quantifies the functionalization degree, yielding 222 µmol of curcuminoid per gram of nanoparticles. The synthesized hybrid nanosystem, nSiO2-NHCO-CCM, displays significant emission properties, with a maximum emission at 538 nm in dichloromethane, similar to curcuminoid 1 (without the central chain), which emits at 565 nm in the same solvent. Solvent-induced spectral effects on the absorption and emission bands of the new hybrid nanosystem are confirmed, similar to those observed for the free curcuminoid (1). The new nanosystem is evaluated in the presence of kerosene in water, showing an emission band at 525 nm as a detection response. The ability of nSiO2-NHCO-CCM to change its fluorescence when interacting with kerosene in water is notable, as it overcomes the limitation caused by the insolubility of free curcuminoid 1 in water, allowing for the exploitation of its properties when connected to the water-stable nanosystem for future detection studies.

Covalent functionalization of MXenes for tribological purposes - a critical review.

Transition metal carbides, nitrides and carbonitrides (MXenes) have recently attracted notable attention in tribology and, particularly solid lubrication, due to their low shear strength and ability to form low-friction, wear-resistant tribo-layers. Their use as lubricant additives has only shown limited success due to their inherent hydrophilic character, causing a low phase-compatibility and dispersion-stability with pure base oils. To overcome this shortcoming and to boost MXenes' tribological performance as lubricant additive and reinforcement phase in composites, their tuneable surface chemistry moves into the focus of current research. Originating from chemical etching to synthesize MXenes, their outer surface contains a variety of surface terminations, which can function as anchoring points for molecules via covalent grafting/functionalization. By adopting an adequate functionalization strategy, this, in turn, can help to tailor MXenes' hydrophobicity, dispersion stability, restacking tendency, or oxidation resistance. This directly affects their dispersion stability in base oils and improves their phase compatibility with other matrix materials in composites, thus resulting in an enhanced tribological performance. Therefore, this review concisely summarizes the existing state-of-the-art regarding MXenes' covalent functionalization with a particular emphasis on tribological properties and needs, a topic, which has not been holistically reviewed yet. The first chapter sheds light on the existing synthesis approaches with detailed insights regarding the resulting surface terminations, which are crucial for the subsequent chemical functionalization. After summarizing strategies to increase their interlayer distance to improve the accessibility for chemical functionalization and the existing state-of-the art regarding MXene tribology, we critically discuss the existing functionalization strategies using different coupling agents (organosilanes, organophosphorus agents, aryldiazonium agents, among others). Subsequently, we emphasize on the crucial role of homogeneously distributed -OH surface terminations to guarantee the overall success of the functionalization approach and to boost the resulting tribological performance. Lastly, we address the existing challenges and derive future research directions. We anticipate that our article can serve as an excellent guide for MXenes' chemical functionalization, which can be useful in various applications including tribology thus paving the way towards enhanced physical and chemical properties of MXenes.

Surface enhanced fluorescence effect improves the in vivo detection of amyloid aggregates.

The ß-amyloid (Aß) peptide is one of the key etiological agents in Alzheimer's disease (AD). The in vivo detection of Aß species is challenging in all stages of the illness. Currently, the development of fluorescent probes allows the detection of Aß in animal models in the near-infrared region (NIR). However, considering future applications in biomedicine, it is relevant to develop strategies to improve detection of amyloid aggregates using NIR probes. An innovative approach to increase the fluorescence signal of these fluorophores is the use of plasmonic gold nanoparticles (surface-enhanced fluorescence effect). In this work, we improved the detection of Aß aggregates in C. elegans and mouse models of AD by co-administering functionalized gold nanorods (GNRs-PEG-D1) with the fluorescent probes CRANAD-2 or CRANAD-58, which bind selectively to different amyloid species (soluble and insoluble). This work shows that GNRs improve the detection of Aß using NIR probes in vivo.

Enhanced Cellular Uptake of H-Chain Human Ferritin Containing Gold Nanoparticles.

Gold nanoparticles (AuNP) capped with biocompatible layers have functional optical, chemical, and biological properties as theranostic agents in biomedicine. The ferritin protein containing in situ synthesized AuNPs has been successfully used as an effective and completely biocompatible nanocarrier for AuNPs in human cell lines and animal experiments in vivo. Ferritin can be uptaken by different cell types through receptor-mediated endocytosis. Despite these advantages, few efforts have been made to evaluate the toxicity and cellular internalization of AuNP-containing ferritin nanocages. In this work, we study the potential of human heavy-chain (H) and light-chain (L) ferritin homopolymers as nanoreactors to synthesize AuNPs and their cytotoxicity and cellular uptake in different cell lines. The results show very low toxicity of ferritin-encapsulated AuNPs on different human cell lines and demonstrate that efficient cellular ferritin uptake depends on the specific H or L protein chains forming the ferritin protein cage and the presence or absence of metallic cargo. Cargo-devoid apoferritin is poorly internalized in all cell lines, and the highest ferritin uptake was achieved with AuNP-loaded H-ferritin homopolymers in transferrin-receptor-rich cell lines, showing more than seven times more uptake than apoferritin.

Broadening the scope of high structural dimensionality nanomaterials using pyridine-based curcuminoids.

We present a new heteroditopic ligand (3pyCCMoid) that contains the typical skeleton of a curcuminoid (CCMoid) decorated with two 3-pyridyl groups. The coordination of 3pyCCMoid with ZnII centres results in a set of novel coordination polymers (CPs) that display different architectures and dimensionalities (from 1D to 3D). Our work analyses how synthetic methods and slight changes in the reaction conditions affect the formation of the final materials. Great efforts have been devoted toward understanding the coordination entities that provide high dimensional systems, with emphasis on the characterization of 2D materials, including analyses of different types of substrates, stability and exfoliation in water. Here, we foresee the great use of CCMoids in the field of CPs and emphasize 3pyCCMoid as a new-born linker.

Effectiveness of eHealth-Based Psychological Interventions for Depression Treatment in Patients With Type 1 or Type 2 Diabetes Mellitus: A Systematic Review.

BACKGROUND: Comorbidity between diabetes mellitus and depression is highly prevalent. The risk of depression in a person with diabetes is approximately twice that of a person without this disease. Depression has a major impact on patient well-being and control of diabetes. However, despite the availability of effective and specific therapeutic interventions for the treatment of depression in people with diabetes, 50% of patients do not receive psychological treatment due to insufficient and difficult accessibility to psychological therapies in health systems. The use of information and communication technologies (ICTs) has therefore been proposed as a useful tool for the delivery of psychological interventions, but it continues to be a field in which scientific evidence is recent and controversial. This systematic review aims to update the available information on the efficacy of psychological interventions delivered through ICTs to improve depressive symptomatology in patients with diabetes. METHODS: A systematic review of the literature was performed following the PRISMA guidelines and using MEDLINE, Embase, PubMed, Web of Science, PsycINFO, Scopus, and Cochrane Library databases to search for randomized clinical trials of eHealth treatments for patients with diabetes and comorbid depression from 1995 through 2020. In addition, studies related to follow-up appointments were identified. Inclusion criteria were as follows: (a) randomized clinical trials (RCTs); (b) patients with type 1 and type 2 diabetes; (c) adult population over 18 years of age; (d) presence of depressive symptomatology assessed with standardized instruments; (e) treatments for depression based on established psychotherapeutic techniques and principles; (f) delivered through eHealth technologies. We did not limit severity of depressive symptomatology, delivery setting or comparison group (treatment as usual or other treatment). Two coauthors independently reviewed the publications identified for inclusion and extracted data from the included studies. A third reviewer was involved to discuss discrepancies found. The PEDro scale was used to assess the quality of the RCTs. No meta-analysis of the results was performed. The protocol used for this review is available in PROSPERO (Reg; CRD42020180405). RESULTS: The initial search identified 427 relevant scientific publications. After removing duplicates and ineligible citations, a total of 201 articles were analyzed in full text. Ten articles met the criteria of this review and were included, obtaining very good scientific quality after evaluation with the PEDro scale. The main results show that the eHealth psychological intervention for depression in patients with diabetes showed beneficial effects both at the end of treatment and in the short (3 months) and long term (6 and 12 months) for the improvement of depressive symptomatology. The methodology used (type of diabetes, eHealth technology used, recruitment context, implementation and follow-up) was very heterogeneous. However, all studies were based on cognitive-behavioral tools and used standardized assessment instruments to evaluate depressive symptomatology or diagnosis of MDD. Glycemic control was assessed by glycosylated hemoglobin, but no benefits were found in improving glycemic control. Only four studies included psychoeducational content on diabetes and depression, but none used tools to improve or enhance adherence to medical prescriptions or diabetes self-care. CONCLUSIONS: ICT-based psychological interventions for the treatment of depression in people with diabetes appear to be effective in reducing depressive symptomatology but do not appear to provide significant results with regard to glycemic control. Nonetheless, the scientific evidence reported to date is still very limited and the methodology very diverse. In addition, no studies have implemented these systems in routine clinical practice, and no studies are available on the economic analysis of these interventions. Future research should focus on studying and including new tools to ensure improvements in diabetes outcomes and not only on psychological well-being in order to advance knowledge about these treatments. Economic evaluations should also be undertaken to analyze whether these treatment programs implemented using eHealth technologies are cost-effective.

Gold Nanoparticles Mediate Improved Detection of ß-amyloid Aggregates by Fluorescence.

The early detection of the amyloid beta peptide aggregates involved in Alzheimer's disease is crucial to test new potential treatments. In this research, we improved the detection of amyloid beta peptide aggregates in vitro and ex vivo by fluorescence combining the use of CRANAD-2 and gold nanorods (GNRs) by the surface enhancement fluorescence effect. We synthetized GNRs and modified their surface with HS-PEG-OMe and HS-PEG-COOH and functionalized them with the D1 peptide, which has the capability to selectively bind to amyloid beta peptide. For an in vitro detection of amyloid beta peptide, we co-incubated amyloid beta peptide aggregates with the probe CRANAD-2 and GNR-PEG-D1 observing an increase in the intensity of the fluorescence signal attributed to surface enhancement fluorescence. Furthermore, the surface enhancement fluorescence effect was observed in brain slices of transgenic mice with Alzheimer´s disease co-incubated with CRANAD-2 and GNR-PEG-D1. An increase in the fluorescence signal was observed allowing the detection of aggregates that cannot be detected with the single use of CRANAD-2. Gold nanoparticles allowed an improvement in the detection of the amyloid aggregated by fluorescence in vitro and ex vivo.

Silver nanoparticle synthesis in human ferritin by photochemical reduction.

Ferritin is a globular hollow protein that acts as the major iron storage protein across living organisms. The 8 nm-diameter internal cavity of ferritin has been used as a nanoreactor for the synthesis of various metallic nanoparticles different to iron oxides. For this purpose, ferritin is incubated in solution with metallic ions that enter the cavity through its natural channels. Then, these ions are subjected to a reduction step to obtain highly monodisperse metallic nanoparticles, with enhanced stability and biocompatibility provided by the ferritin structure. Potential biomedical applications of ferritin-nanoparticle complex will require the use of human ferritin to provide a safer and low-risk alternative for the delivery of metallic nanoparticles into the body. However, most of the reported protocols for metallic nanoparticles synthesis uses horse spleen ferritin as nanocontainer. Previous studies have acknowledged technical difficulties with recombinant human ferritin during the synthesis of metallic nanoparticles, like protein precipitation, which is translated into low recovery yields. In this study, we tested a novel photochemical reduction method for silver nanoparticle synthesis in human recombinant ferritin and compared it with the traditional chemical reduction method. The results show that photoreduction of silver ions inside ferritin cavity provides a universal method for silver nanoparticle synthesis in both recombinant human ferritin homopolymers (Light and Heavy ferritin). Additionally, we report important parameters that account for the efficiency of the method, such as ferritin recovery yield (~60%) and ferritin­silver nanoparticle yield (34% for H-ferritin and 17% for L-ferritin).

Correction: A new family of fullerene derivatives: fullerene-curcumin conjugates for biological and photovoltaic applications.

[This corrects the article DOI: 10.1039/C8RA08334G.].

Electric-field induced bistability in single-molecule conductance measurements for boron coordinated curcuminoid compounds.

We have studied the single-molecule conductance of a family of curcuminoid molecules (CCMs) using the mechanically controlled break junction (MCBJ) technique. The CCMs under study contain methylthio (MeS-) as anchoring groups: MeS-CCM (1), the free-ligand organic molecule, and two coordination compounds, MeS-CCM-BF2 (2) and MeS-CCM-Cu (3), where ligand 1 coordinates to a boron center (BF2 group) and to a CuII moiety, respectively. We found that the three molecules present stable molecular junctions allowing detailed statistical analysis of their electronic properties. Compound 3 shows a slight increase in the conductance with respect to free ligand 1, whereas incorporation of BF2 (compound 2) promotes the presence of two conductance states in the measurements. Additional experiments with control molecules point out that this bistability is related to the combination of MeS- anchoring groups and the BF2 moiety within the structure of the molecules. Theoretical calculations show that this can be explained by the presence of two conformers once compound 2 is anchored between the gold electrodes. An energy minimum is found for a flat structure but there is a dramatic change in the magnitude and orientation of dipole moment (favouring a non-flat conformer in the presence of an external electric field) due to a conformational change of one of the terminal MeS- groups. The results thus point to an intricate interplay between the applied bias voltage and the molecule dipole moment which could be the basis for designing new molecules aiming at controlling their conformation in devices.

A new family of fullerene derivatives: Fullerene-curcumin conjugates for biological and photovoltaic applications.

The synthesis and characterization of a family of [60]fullerocurcuminoids obtained via Bingel reactions is reported. The new C60 derivatives include curcumin and curcuminoids with a variety of end groups. Preliminary biological experiments show the potential activity of the compound containing a curcumin addend, which exhibits moderate anti-HIV-1 and radical scavenger properties, but no anti-cancer activity. In addition, the new fullerocurcuminoids exhibit HOMO/LUMO energy levels that are reasonably matched with those of perovskites and when they were tested in perovskite solar cells (PSCs) as the electron transporting material (ETM), photoconversion efficiencies ranging from 14.04%-14.95% were obtained, whereas a value of 16.23% was obtained for [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) based devices.

An optimized low-cost protocol for standardized production of iron-free apoferritin nanocages with high protein recovery and suitable conformation for nanotechnological applications.

Ferritin is a globular protein that consists of 24 subunits forming a hollow nanocage structure that naturally stores iron oxyhydroxides. Elimination of iron atoms to obtain the empty protein called apoferritin is the first step to use this organic shell as a nanoreactor for different nanotechnological applications. Different protocols have been reported for apoferritin formation, but some are time consuming, others are difficult to reproduce and protein recovery yields are seldom reported. Here we tested several protocols and performed a complete material characterization of the apoferritin products using size exclusion chromatography, UV-vis spectroscopy, inductively coupled plasma optical emission spectrometry and dynamic light scattering. Our best method removes more than 99% of the iron from loaded holoferritin, recovering 70-80% of the original protein as monomeric apoferritin nanocages. Our work shows that pH conditions of the reduction step and the presence and nature of chelating agents affect the efficiency of iron removal. Furthermore, process conditions also seem to have an influence on the monomer:aggregate proportion present in the product. We also demonstrate that iron contents markedly increase ferritin absorbance at 280nm. The influence of iron contents on absorbance at 280nm precludes using this simple spectrophotometric measure for protein determination in ferritin­iron complexes. Apoferritin produced following our protocol only requires readily-available, cheap and biocompatible reagents, which makes this process standardizable, scalable and applicable to be used for in vivo applications of ferritin derivatives as well as nanotechnological and biotechnological uses.

The Calculating Boluses on Multiple Daily Injections (CBMDI) study: A randomized controlled trial on the effect on metabolic control of adding a bolus calculator to multiple daily injections in people with type 1 diabetes.

BACKGROUND: Although the insulin bolus calculator is increasingly being used by people with type 1 diabetes (T1D) on multiple daily injection (MDI) therapy, few studies have investigated its effects on glycemic control. The aim of this study was to determine whether adding this device to therapeutic intensification could further improve metabolic control. METHODS: A 4-month randomized controlled clinical trial was performed comparing subjects undergoing therapeutic intensification and either using the bolus calculator (Cb group) or not (active control [Co] group). Metabolic control, fear of hypoglycemia, and treatment acceptance were evaluated. RESULTS: In all, 70 people completed the study (42 in the Cb group, 28 in the Co group). There was a significant decrease in HbA1c in both the Cb and Co groups (-7 mmol/mol [-0.7 %] vs -4 mmol/mol [-0.4 %], respectively). There were no significant differences in HbA1c at baseline or the end of the study, or in the decrease in HbA1c, glycemia, or changes in blood glucose levels at the end of the study between the two groups. There was a significant increase in the number of participants with good metabolic control (HbA1c <58 mmol/mol [7.5 %]) in the Cb group (from 16.7 % to 40.5 %), but not in the Co group. The incidence of hypoglycemic events was reduced slightly but significantly only in the Cb group. There was no change in the fear of hypoglycemia at the end of the study. The bolus calculator was well accepted. CONCLUSIONS: In T1D, adding a bolus calculator to intensive MDI resulted in a significant improvement in metabolic control and slightly decreased the number of hypoglycemic episodes. Metabolic control also improved in the Co group.

Multiscale Approach to the Study of the Electronic Properties of Two Thiophene Curcuminoid Molecules.

We studied the electronic and conductance properties of two thiophene-curcuminoid molecules, 2-thphCCM (1) and 3-thphCCM (2), in which the only structural difference is the position of the sulfur atoms in the thiophene terminal groups. We used electrochemical techniques as well as UV/Vis absorption studies to obtain the values of the HOMO-LUMO band gap energies, showing that molecule 1 has lower values than 2. Theoretical calculations show the same trend. Self-assembled monolayers (SAMs) of these molecules were studied by using electrochemistry, showing that the interaction with gold reduces drastically the HOMO-LUMO gap in both molecules to almost the same value. Single-molecule conductance measurements show that molecule 2 has two different conductance values, whereas molecule 1 exhibits only one. Based on theoretical calculations, we conclude that the lowest conductance value, similar in both molecules, corresponds to a van der Waals interaction between the thiophene ring and the electrodes. The one order of magnitude higher conductance value for molecule 2 corresponds to a coordinate (dative covalent) interaction between the sulfur atoms and the gold electrodes.

Precisión del diagnóstico de depresión en pacientes con diabetes mellitus tipo 1 / Accuracy of diagnosis of depression in patients with Type 1 diabetes mellitus

Este estudio valora la precisión que tiene el clínico (Médico Especialista en Endocrinología y Nutrición: MEEN) al realizar el diagnóstico de depresión en pacientes con diabetes mellitus tipo 1 (DM1). Participaron 11 MEEN y 153 pacientes con DM1. El diagnóstico de depresión se realizó mediante la entrevista estructurada SCID-1 y la valoración del clínico. De la muestra inicial se seleccionaron aleatoriamente 50 pacientes (imponiendo la condición de que estuviera compuesta por 25 pacientes con depresión y 25 sin depresión). Los resultados muestran que los clínicos realizaron un mayor porcentaje de diagnósticos negativos (paciente sin depresión) que positivos (paciente con depresión). Un porcentaje considerable de pacientes con depresión no fueron diagnosticados (25%). Parece, pues, necesario dotar a los clínicos de protocolos adecuados para evaluar la presencia de este trastorno en DM1, así como continuar la investigación sobre el proceso diagnóstico para la toma de decisiones clínicas (AU)

This study assesses the clinical accuracy of physicians (Specialists in Endocrinology and Nutrition: SEN) to make the diagnosis of depression in patients with Type 1 diabetes mellitus (DM1). This study involved 11 SEN physicians, and 153 patients with DM1. The diagnosis of depression was performed using the SCID-1 structured interview and clinical assessment. From the initial sample, 50 patients were randomly selected (imposing the condition that it was included 25 patients with depression and 25 without depression). The results show that clinicians performed a higher percentage of negative diagnoses (patients without depression) than positive ones (patients with depression). A significant percentage of patients with depression were not diagnosed (25%). It therefore seems necessary to provide adequate clinical protocols to evaluate the presence of this disorder in DM1, as well as continuing research into the diagnostic process for clinical decision making (AU)

[Accuracy of diagnosis of depression in patients with Type 1 diabetes mellitus]. / Precisión del diagnóstico de depresión en pacientes con diabetes mellitus tipo 1.

This study assesses the clinical accuracy of physicians (Specialists in Endocrinology and Nutrition: SEN) to make the diagnosis of depression in patients with Type 1 diabetes mellitus (DM1). This study involved 11 SEN physicians, and 153 patients with DM1. The diagnosis of depression was performed using the SCID-1 structured interview and clinical assessment. From the initial sample, 50 patients were randomly selected (imposing the condition that it was included 25 patients with depression and 25 without depression). The results show that clinicians performed a higher percentage of negative diagnoses (patients without depression) than positive ones (patients with depression). A significant percentage of patients with depression were not diagnosed (25%). It therefore seems necessary to provide adequate clinical protocols to evaluate the presence of this disorder in DM1, as well as continuing research into the diagnostic process for clinical decision making.

Self-assembly and traveling wave ion mobility mass spectrometry analysis of hexacadmium macrocycles.

Self-assembly of 1,3-di(4'-terpyridinyl)arenes by using the labile tpy-Cd(II)-tpy (where tpy = 2,2':6',2''-terpyridine) connectivity afforded access to hexacadmium macrocycles in high yield. These supramolecular assemblies were characterized by traveling wave ion mobility mass spectrometry (TWIM-MS).

Distinguishing between Dexter and rapid sequential electron transfer in covalently linked donor-acceptor assemblies.

The syntheses, physical, and photophysical properties of a family of complexes having the general formula [M2(L)(mcb)(Ru(4,4'-(X)2-bpy)2)](PF6)3 (where M = Mn(II) or Zn(II), X = CH3 or CF3, mcb is 4'-methyl-4-carboxy-2,2'-bipyridine, and L is a Schiff base macrocycle derived from 2,6-diformyl-4-methylphenol and bis(2-aminoethyl)-N-methylamine) are described. The isostructural molecules all consist of dinuclear metal cores covalently linked to a Ru(II) polypyridyl complex. Photoexcitation of [Mn2(L)(mcb)(Ru((CF3)2-bpy)2)](PF6)3 (4) in deoxygenated CH2Cl2 solution results in emission characteristic of the 3MLCT excited state of the Ru(II) chromophore but with a lifetime (tau(obs) = 5.0 +/- 0.1 ns) and radiative quantum yield (Phi(r) approximately 7 x 10(-4)) that are significantly attenuated relative to the Zn(II) model complex [Zn2(L)(mcb)(Ru((CF3)2-bpy)2)](PF6)3 (6) (tau(obs) = 730 +/- 30 ns and Phi(r) = 0.024, respectively). Quenching of the 3MLCT excited state is even more extensive in the case of [Mn2(L)(mcb)(Ru((CH3)2-bpy)2)](PF6)3 (3), whose measured lifetime (tau(obs) = 45 +/- 5 ps) is >10(4) shorter than the corresponding model complex [Zn2(L)(mcb)(Ru((CH3)2-bpy)2)](PF6)3 (5) (tau(obs) = 1.31 +/- 0.05 micros). Time-resolved absorption measurements on both Mn-containing complexes at room-temperature revealed kinetics that were independent of probe wavelength; no spectroscopic signatures for electron-transfer photoproducts were observed. Time-resolved emission data for complex 4 acquired in CH2Cl2 solution over a range of 200-300 K could be fit to an expression of the form k(nr) = k0 + A x exp{-DeltaE/kB T} with k0 = 1.065 +/- 0.05 x 10(7) s(-1), A = 3.7 +/- 0.5 x 10(10) s(-1), and DeltaE = 1230 +/- 30 cm(-1). Assuming an electron-transfer mechanism, the variable-temperature data on complex 4 would require a reorganization energy of lambda approximately 0.4-0.5 eV which is too small to be associated with charge separation in this system. This result coupled with the lack of enhanced emission at temperatures below the glass-to-fluid transition of the solvent and the absence of visible absorption features associated with the Mn(II)2 core allows for a definitive assignment of Dexter transfer as the dominant excited-state reaction pathway. A similar conclusion was reached for complex 3 based in part on the smaller driving force for electron transfer (DeltaG0(ET) = -0.1 eV), the increase in probability of Dexter transfer due to the closer proximity of the donor excited state to the dimanganese acceptor, and a lack of emission from the compound upon formation of an optical glass at 80 K. Electronic coupling constants for Dexter transfer were determined to be approximately 10 cm(-1) and approximately 0.15 cm(-1) in complexes 3 and 4, respectively, indicating that the change in spatial localization of the excited state from the bridge (complex 3) to the periphery of the chromophore (complex 4) results in a decrease in electronic coupling to the dimanganese core of nearly 2 orders of magnitude. In addition to providing insight into the influence of donor/acceptor proximity on exchange energy transfer, this study underscores the utility of variable-temperature measurements in cases where Dexter and electron-transfer mechanisms can lead to indistinguishable spectroscopic observables.