Chemical Transformation of B- to A-type Proanthocyanidins and 3D Structural Implications.

In nature, proanthocyanidins (PACs) with A-type linkages are relatively rare, likely due to biosynthetic constraints in the formation of additional ether bonds to be introduced into the more common B-type precursors. However, A-type linkages confer greater structural rigidity on PACs than do B-type linkages. Prior investigations into the structure-activity relationships (SAR) describing how plant-derived PACs with B- and complex AB-type linkages affect their capacity for dentin biomodification indicate that a higher ratio of double linkages leads to a greater interaction with dentin type I collagen. Thus, A-type PACs emerge as particularly intriguing candidates for interventional functional biomaterials. This study employed a free-radical-mediated oxidation using DPPH to transform trimeric and tetrameric B-type PACs, 2 and 4, respectively, into their exclusively A-type linked analogues, 3 and 5, respectively. The structures and absolute configurations of the semisynthetic products, including the new all-A-type tetramer 5, were determined by comprehensive spectroscopic analysis. Additionally, molecular modeling investigated the conformational characteristics of all trimers and tetramers, 1-5. Our findings suggest that the specific interflavan linkages significantly impact the flexibility and low-energy conformations of the connected monomeric units, which conversely can affect the bioactive conformations relevant for dentin biomodification.

Cavomycins A-C, Linear Oligomer Depsipeptides from an Annelid-Associated Streptomyces cavourensis.

Three unique linear oligomeric depsipeptides, designated as cavomycins A-C (1-3), were identified from Streptomyces cavourensis, a gut bacterium associated with the annelid Paraleonnates uschakovi. The structures of these depsipeptides were determined through a combination of spectroscopic methods and chemical derivatization techniques, including methanolysis, the modified Mosher's method, advanced Marfey's methods, and phenylglycine methyl ester derivatization. The unique dipeptidyl residue arrangements in compounds 1-3 indicate that they are not degradation products of valinomycin. Compound 2 and its methylation derivative 2a exhibited antiproliferative activity against PANC-1 pancreatic cancer cells with IC50 values of 1.2 and 1.7 µM, respectively.

Modulatory role of terminal monomeric flavan-3-ol units in the viscoelasticity of dentin.

Flavan-3-ol monomers are the building blocks of proanthocyanidins (PACs), natural compounds from plants shown to mediate specific biologic activities on dentin. While the stereochemistry of the terminal flavan-3-ols, catechin (C) versus epicatechin (EC), impacts the biomechanical properties of the dentin matrix treated with oligomeric PACs, structure-activity relationships driving this bioactivity remain elusive. To gain insights into the modulatory role of the terminal monomers, two highly congruent trimeric PACs from Pinus massoniana only differing in the stereochemistry of the terminal unit (Trimer-C vs. Trimer-EC) were prepared to evaluate their chemical characteristics as well as their effects on the viscoelasticity and biostability of biomodified dentin matrices via infrared spectroscopy and multi-scale dynamic mechanical analyses. The subtle alteration of C versus EC as terminal monomers lead to distinct immediate PAC-trimer biomodulation of the dentin matrix. Nano- and micro-dynamic mechanical analyses revealed that Trimer-EC increased the complex moduli (0.51 GPa) of dentin matrix more strongly than Trimer-C (0.26 GPa) at the nanoscale length (p < 0.001), whereas the reverse was found at the microscale length (p < .001). The damping capacity (tan δ) of dentin matrix decreased by 70% after PAC treatment at the nano-length scale, while increased values were found at the micro-length scale (~0.24) compared to the control (0.18 ; p < .001). An increase in amide band intensities and a decrease of complex moduli was observed after storage in simulated body fluid for both Trimer-C and Trimer-EC modified dentin. The stereochemical configuration of the terminal monomeric units, C and EC, did not impact the chemo-mechanical stability of dentin matrix.

Unprecedented Benzoquinone Motifs Reveal Post-Oligomerizational Modification of Proanthocyanidins.

Proanthocyanidins (PACs) are complex flavan-3-ol polymers with stunning chemical complexity due to oxygenation patterns, oxidative phenolic ring linkages, and intricate stereochemistry of their heterocycles and inter-flavan linkages. Being promising candidates for dental restorative biomaterials, trace analysis of dentin bioactive cinnamon PACs now yielded novel trimeric (1 and 2) and tetrameric (3) PACs with unprecedented o- and p-benzoquinone motifs (benzoquinonoid PACs). Challenges in structural characterization, especially their absolute configuration, prompted the development of a new synthetic-analytical approach involving comprehensive spectroscopy, including NMR with quantum mechanics-driven 1H iterative functionalized spin analysis (HifSA) plus experimental and computational electronic circular dichroism (ECD). Vital stereochemical information was garnered from synthesizing 4-(2,5-benzoquinone)flavan-3-ols and a truncated analogue of trimer 2 as ECD models. Discovery of the first natural benzoquinonoid PACs provides new evidence to the experimentally elusive PAC biosynthesis as their formation requires two oxidative post-oligomerizational modifications (POMs) that are distinct and occur downstream from both quinone-methide-driven oligomerization and A-type linkage formation. While Nature is known to achieve structural diversity of many major compound classes by POMs, this is the first indication of PACs also following this common theme.

The Ethics of Publishing Biomedical and Natural Products Research.

Given that the essence of Science is a search for the truth, one might expect that those identifying as scientists would be conscientious and observant of the demands this places on them. However, that expectation is not fulfilled universally as, not too surprisingly, egregious examples of unethical behavior appear and are driven by money, personal ambition, performance pressure, and other incentives. The reproducibility-, fact-, and truth-oriented modus operandi of Science has come to face a variety of challenges. Organized into 11 cases, this article outlines examples of compromised integrity from borderline to blatant unethical behavior that disgrace our profession unnecessarily. Considering technological developments in neural networks/artificial intelligence, a host of factors are identified as impacting Good Ethical Practices. The goal is manifold: to raise awareness and offer perspectives for refocusing on Science and true scientific evidence; to trigger discussion and developments that strengthen ethical behavior; to foster the recognition of the beauty, simplicity, and rewarding nature of scientific integrity; and to highlight the originality of intelligence.

DESIGNER fraction concept unmasks minor bioactive constituents in red clover (Trifolium pratense L.).

In botanical extracts, highly abundant constituents can mask or dilute the effects of other, and often, more relevant biologically active compounds. To facilitate the rational chemical and biological assessment of these natural products with wide usage in human health, we introduced the DESIGNER approach of Depleting and Enriching Selective Ingredients to Generate Normalized Extract Resources. The present study applied this concept to clinical Red Clover Extract (RCE) and combined phytochemical and biological methodology to help rationalize the utility of RCE supplements for symptom management in postmenopausal women. Previous work has demonstrated that RCE reduces estrogen detoxification pathways in breast cancer cells (MCF-7) and, thus, may serve to negatively affect estrogen metabolism-induced chemical carcinogenesis. Clinical RCE contains ca. 30% of biochanin A and formononetin, which potentially mask activities of less abundant compounds. These two isoflavonoids are aryl hydrocarbon receptor (AhR) agonists that activate P450 1A1, responsible for estrogen detoxification, and P450 1B1, producing genotoxic estrogen metabolites in female breast cells. Clinical RCE also contains the potent phytoestrogen, genistein, that downregulates P450 1A1, thereby reducing estrogen detoxification. To identify less abundant bioactive constituents, countercurrent separation (CCS) of a clinical RCE yielded selective lipophilic to hydrophilic metabolites in six enriched DESIGNER fractions (DFs 01-06). Unlike solid-phase chromatography, CCS prevented any potential loss of minor constituents or residual complexity (RC) and enabled the polarity-based enrichment of certain constituents. Systematic analysis of estrogen detoxification pathways (ERα-degradation, AhR activation, CYP1A1/CYP1B1 induction and activity) of the DFs uncovered masked bioactivity of minor/less abundant constituents including irilone. These data will allow the optimization of RCE with respect to estrogen detoxification properties. The DFs revealed distinct biological activities between less abundant bioactives. The present results can inspire future carefully designed extracts with phytochemical profiles that are optimized to increase in estrogen detoxification pathways and, thereby, promote resilience in women with high-risk for breast cancer. The DESIGNER approach helps to establish links between complex chemical makeup, botanical safety and possible efficacy parameters, yields candidate DFs for (pre)clinical studies, and reveals the contribution of minor phytoconstituents to the overall safety and bioactivity of botanicals, such as resilience promoting activities relevant to women's health.

Geraniol-Derived Monoterpenoid Glucosides from Rhodiola rosea: Resolving Structures by QM-HifSA Methodology.

Monoterpenoids are integral to the chemical composition of the widely used adaptogenic dietary supplement Rhodiola rosea. The present study expands the chemical space and stereochemical information about these taxon-specific constituents from the isolation and characterization of five geraniol-derived glucosides, 1-5. While 1 and 2 exhibited almost identical NMR spectra and shared the same 2D structure ascribed to the 4-hydroxygeraniolglucoside previously described as rosiridin, the NMR-based Mosher ester method revealed the enantiomeric nature of their aglycone moieties. This marks the first report of enantiomeric aglycones among geraniol derivatives. These findings also resolve the long-standing dispute regarding the absolute configuration of rosiridin and congeneric C-4 hydroxylated geraniols and may help explain incongruent bioactivity reports of R. rosea extract. Moreover, the three previously undescribed geranioloids 3-5 were fully characterized by extensive spectroscopic analysis. Quantum mechanics-driven 1H iterative functionalized spin analysis (QM-HifSA) was performed for all isolates and provides detailed NMR spin parameters, with adequate decimal place precision, which enable the distinction of such close congeners exhibiting near identical NMR spectra with high specificity. The outcomes also reinforce the importance of reporting chemical shifts and coupling constants with adequate decimal place precision as a means of achieving specificity and reproducibility in structural analysis.

Seco B-Type Oligomers from Pinus massoniana Expand the Procyanidin Chemical Space and Exhibit Dental Bioactivity.

Investigation of a pine bark extract for bioactive proanthocyanidin oligomers resulted in the isolation of structurally related dimeric seco B-type procyanidin derivatives, 1-5. This includes scalemic mixtures of gambiriin A1 (1a) and A2 (2a) and their newly described optical antipodes, ent-gambiriin A1 (1b) and ent-gambiriin A2 (2b), respectively, as well as a racemic mixture of the newly described (ent-)gambiriin A5 (3a/3b). Furthermore, the study now fully characterizes the previously reported optically pure dimers gambiriin B1 (4) and gambirflavan D1 (5), and characterized the novel seco B-type procyanidin trimer, 6 (gambirifuran C1). Thermal conversion of catechin in aqueous solution provided further evidence for the structures of 1-6 and led to the purification of semisynthetic 1a and 2a as well as additional dimers 7-10. Elucidating the structures of the natural dimers, 1-5, from comprehensive NMR and ECD data and synthetic evidence provided crucial reference points for establishing the structure of the seco B-type procyanidin trimer, 6. Serving as assigned building blocks, data from the dimers supported the 3D structural assignment of 6 based on NMR substituent chemical shift differences (s.c.s., syn. ΔδC) and component-based empirical ECD calculations. Within the newly characterized series of PAC-related molecules, 5 exhibited high dentin biomodification potential. In addition, considering the nomenclature issues and plausible biosynthetic pathways of this group of compounds led to a consolidated nomenclature of all currently known seco B-type procyanidins. These findings, thereby, expand the chemical space of bioactive catechin oligomers, which have promise as agents for the natural enhancement of dental biomaterials. Finally, the current knowledge of the chemical space of seco B-type procyanidin derivatives was compiled to the level of absolute configuration.

New Rufomycins from Streptomyces atratus MJM3502 Expand Anti-Mycobacterium tuberculosis Structure-Activity Relationships.

Four new rufomycins, compounds 1-4, named rufomycins 56, 57, 58, and 61, respectively, exhibiting new skeletal features, were obtained from Streptomyces atratus strain MJM3502 and were fully characterized. Compounds 1 and 2 possess a 4-imidazolidinone ring not previously encountered in this family of cyclopeptides, thereby resulting in a [5,17] bicyclic framework. The in vitro anti-Mycobacterium tuberculosis potency of compounds 3 and 4 is remarkable, with minimum inhibitory concentration values of 8.5 and 130 nM, respectively.

B-type Proanthocyanidins with Dentin Biomodification Activity from Cocoa (Theobroma cacao).

To enable translational studies, a scalable preparative isolation scheme was developed for underivatized cocoa (Theobroma cacao) proanthocyanidins (PACs), affording six all-B-type oligomeric PACs, including a new tetramer 4. Their structures, including absolute configuration, were unambiguously established by comprehensive spectroscopic and chemical methods. Evaluation of the PACs' dentin biomodification properties employed dynamic mechanical and infrared spectroscopic analyses in dentin bioassay models. PAC treatment enhanced the biomechanical strength of dentin by 5- to 15-fold compared to untreated dentin. Among the PAC agents, the pentamer, cinnamtannin A3 (6), led to the highest complex modulus value of 131 MPa, whereas the "branched" tetramer, 4, showed the lowest, yet still significant bioactivity. This study of specifically singly linked medium-length oligomeric PACs indicates that the linkage site is paramount in determining the potency of these PACs as dentin biomodifiers.

Proanthocyanidin Tetramers and Pentamers from Cinnamomum verum Bark and Their Dentin Biomodification Bioactivities.

To enable the further exploration of structure-activity relationships (SARs) of proanthocyanidins (PACs) with dentin biomodification abilities, Cinnamomum verum was selected for scaled-up purification of mixed A-/B-type, medium-size PAC oligomers. Sequential purification by centrifugal partition chromatography (CPC), Sephadex LH-20, and semiprep HPLC chromatography yielded four underivatized tetrameric (5-8) and two pentameric (9-10) PACs. Their unambiguous structural characterization involved extensive spectral and chemical degradation approaches to show that epicatechin units are connected by plant-specific combinations of doubly linked A- and singly linked B-type interflavanyl bonds. The biomechanical properties (via dynamic mechanical analysis) and physicochemical structure (via infrared spectroscopy) were assessed to evaluate the biomodification potency of PAC-treated collagen in a preclinical dentin model. This study revealed that (4→8) versus (4→6) bonds in PAC interflavan linkages have limited influence on biomechanical outcomes of dentin. By exhibiting a 25-fold increase in the complex modulus of treated dentin compared to control, aesculitannin E (5) was found to be the most potent PAC known to date for enhancing the mechanical properties of dentin in this preclinical model.

Selective Preparation and High Dynamic-Range Analysis of Cannabinoids in "CBD Oil" and Other Cannabis sativa Preparations.

Much confusion exists about the chemical composition of widely sold Cannabis sativa products that utilize the cannabidiol (CBD) acronym and related terms such as "CBD oil", "CBD plus hemp oil", "full spectrum CBD", "broad spectrum CBD", and "cannabinoids". Their rational chemical and subsequent biological assessment requires both knowledge of the chemical complexity and the characterization of significant individual constituents. Applicable to hemp preparations in general, this study demonstrates how the combination of liquid-liquid-based separation techniques, NMR analysis, and quantum mechanical-based NMR interpretation facilitates the process of natural product composition analysis by allowing specific structural characterization and absolute quantitation of cannabinoids present in such products with a large dynamic range. Countercurrent separation of a commercial "CBD oil" yielded high-purity CBD plus a more polar cannabinoid fraction containing cannabigerol and cannabidivarin, as well as a less polar cannabinoid fraction containing cannabichromene, trans-Δ9-tetrahydrocannabinol, cis-Δ9-tetrahydrocannabinol, and cannabinol. Representatives of six cannabinoid classes were identified within a narrow range of polarity, which underscores the relevance of residual complexity in biomedical research on cannabinoids. Characterization of the individual components and their quantitation in mixed fractions were undertaken by TLC, HPLC, 1H (q)NMR spectroscopy, 1H iterative full spin analysis (HiFSA), 13C NMR, and 2D NMR. The developed workflow and resulting analytical data enhance the reproducible evaluation of "CBD et al." products, which inevitably represent complex mixtures of varying molecular populations, structures, abundances, and polarity features.

Galloylated proanthocyanidins in dentin matrix exhibit biocompatibility and induce differentiation in dental stem cells.

Aim: Grape seed extract contains a complex mixture of proanthocyanidins (PACs), a plant biopolymer used as a biomaterial to improve reparative and preventive dental therapies. Co-polymerization of PACs with type I collagen mechanically reinforces the dentin extracellular matrix. This study assessed the biocompatibility of PACs from grape seed extract on dental pulp stem cells (DPSCs) in a model simulating leaching through dentin to the pulp cavity. The aim was to determine the type of PACs (galloylated vs. non-galloylated) within grape seed extract that are most compatible with dental pulp tissue. Methodology: Human demineralized dentin was treated with selectively-enriched dimeric PACs prepared from grape seed extract using liquid-liquid chromatography. DPSCs were cultured within a 2D matrix and exposed to PAC-treated dentin extracellular matrix. Cell proliferation was measured using the MTS assay and expression of odontoblastic genes was analyzed by qRT-PCR. Categorization of PACs leaching from dentin was performed using HPLC-MS. Results: Enriched dimeric fractions containing galloylated PACs increased the expression of certain odontoblastic genes in DPSCs, including Runt-related transcription factor 2 (RUNX2), vascular endothelial growth factor (VEGF), bone morphogenetic protein 2 (BMP2), basic fibroblast growth factor (FGF2), dentin sialophosphoprotein (DSPP) and collagen, type I, alpha 1 (COLI). Galloylated dimeric PACs also exhibited minor effects on DPSC proliferation, resulting in a decrease compared to control after five days of treatment. The non-galloylated dimer fraction had no effect on these genes or on DPSC proliferation. Conclusions: Galloylated PACs are biocompatible with DPSCs and may exert a beneficial effect on cells within dental pulp tissue. The observed increase in odontoblastic genes induced by galloylated PACs together with a decrease in DPSC proliferation is suggestive of a shift toward cell differentiation. This data supports the use of dimeric PACs as a safe biomaterial, with galloylated dimeric PACs exhibiting potential benefits to odontoblasts supporting dentin regeneration.

Investigation of red clover (Trifolium pratense) isoflavonoid residual complexity by off-line CCS-qHNMR.

The importance of Trifolium pratense L. as a dietary supplement and its use in traditional medicine prompted the preparation of a thorough metabolite profile. This included the identification and quantitation of principal constituents as well as low abundant metabolites that constitute the residual complexity (RC) of T. pratense bioactives. The purity and RC of isoflavonoid fractions from standardized red clover extract (RCE) was determined using an off-line combination of countercurrent separation (CCS) and two orthogonal analytical methodologies: quantitative 1H NMR spectroscopy with external calibration (EC-qHNMR) and LC-MS. A single-step hydrostatic CCS methodology (Centrifugal Partition Chromatography [CPC]) was developed that fractionated the isoflavonoids with a hexanes-ethyl acetate-methanol-water (HEMWat) 5.5/4.5/5/5, v/v solvent system (SS) into 75 fractions containing 3 flavonolignans, 2 isoflavonoid glycosides, as well as 17 isoflavonoids and related compounds. All metabolites were identified and quantified by qHNMR spectroscopy. The data led to the creation of a complete isoflavonoid profile to complement the biological evaluation. For example, fraction 69 afforded 90.5% w/w biochanin A (17), with 0.33% w/w of prunetin (16), and 0.76% w/w of maackiain (15) as residual components. Fraction 27 with 89.4% w/w formononetin (13) as the major component had, in addition, a residual complexity consisting of 3.37%, 0.73%, 0.68% w/w of pseudobaptigenin (11), kaempferol (10) and pratensein (8), respectively. Despite the relatively high resolving power of CPC, and not unexpectedly, the chromatographic fractions retained varying degrees of the original metabolomic diversity. Collectively, the extent of metabolomic diversity should be recognized and used to guide the development of isolation strategies, especially when generating samples for bioactivity evaluation. The simultaneous structural and quantitative characterization enabled by qNMR, supported by LC-MS measurements, enables the evaluation of a relatively large number of individual fractions and, thereby, advances both the chemical and biological evaluation of active principles in complex natural products.

Paradoxical effects of galloyl motifs in the interactions of proanthocyanidins with collagen-rich dentin.

Plant-derived proanthocyanidins (PACs) mediate physicochemical modifications to the dentin extracellular matrix (ECM). The structure-activity relationships of PACs remain largely unknown, mostly due to the varied complex composition of crude extracts, as well as the challenges of purification and mechanistic assessment. To assess the role of galloylated PACs as significant contributors to high yet unstable biomodification activity to the dentin ECM, we removed the galloyl moieties (de-galloylation) via enzymatic hydrolysis from three galloyl-rich PAC-containing extracts (Camellia sinensis, Vitis vinifera, and Hamamelis virginiana). The biomechanical and biological properties of dentin were assessed upon treatment with these extracts vs. their de-galloylated counterparts. An increase in the complex modulus of the dentin matrix was found with all extracts, however, the crude extract was significantly higher when compared to the de-galloylated version. Exhibiting the highest content of galloylated PACs among the investigated plants, Camellia sinensis crude extract also exhibited the biggest relapse in mechanical properties after one-month incubation. De-galloylation did not modify the damping capacity of dentin ECM. Moreover, PAC-mediated protection against proteolytic degradation was unaffected by de-galloylation. The de-galloylation experiments confirmed that gallic acid in galloylated rich-PAC extracts drive stronger yet significantly less sustained mechanical effects in dentin ECM.

Do Certain Flavonoid IMPS Have a Vital Function?

Flavonoids are a vast group of metabolites that are essential for vascular plant physiology and, thus, occur ubiquitously in plant-based/-derived foods. The solitary designation of thousands of known flavonoids hides the fact that their metabolomes are structurally highly diverse, consist of disparate subgroups, yet undergo a certain degree of metabolic interconversion. Unsurprisingly, flavonoids have been an important theme in nutrition research. Already in the 1930s, it was discovered that the ability of synthetic Vitamin C to treat scurvy was inferior to that of plant extracts containing Vitamin C. Subsequent experimental evidence led to the proposal of Vitamin P (permeability) as an essential phytochemical nutrient. However, attempts to isolate and characterize Vitamin P gave confusing and sometimes irreproducible results, which today can be interpreted as rooted in the unrecognized (residual) complexity of the intervention materials. Over the years, primarily flavonoids (and some coumarins) were known as having Vitamin P-like activity. More recently, in a NAPRALERT meta-analysis, essentially all of these Vitamin P candidates were identified as IMPs (Invalid/Improbable/Interfering Metabolic Panaceas). While the historic inability to define a single compound and specific mode of action led to general skepticism about the Vitamin P proposition for "bioflavonoids," the more logical conclusion is that several abundant and metabolically labile plant constituents fill this essential role in human nutrition at the interface of vitamins, cofactors, and micronutrients. Reviewing 100+ years of the multilingual Vitamin P and C literature provides the rationales for this conclusion and new perspectives for future research.

Rufomycins or Ilamycins: Naming Clarifications and Definitive Structural Assignments.

Rufomycin and ilamycin are synonymous for the same class of cyclopeptides, currently encompassing 33 structurally characterized isolates and 9 semisynthetic derivatives. Elucidation of new structures prioritized the consolidation of the names and established the structures of four diastereoisomeric rufomycins with a 2-piperidinone, named rufomycins 4-7, including full 1H/13C NMR assignments. The characteristic HSQC cross-peak for the CH-5, the hemiaminal carbon in amino acid #5, allows assignment of the stereocenters C-4 and C-5 within this ring. Semisynthetic derivatives (rufomycinSS 1, 2, and 3) were prepared from a rufomycins 4 and 6 mixture to validate the structural assignments. Based on the X-ray crystal structures of rufomycins 2 and 4, considering the NMR differences of rufomycins 7 vs 4-6 compared to rufomycinSS 1 vs 2 and 3, and taking into account that two major conformers, A and B, occur in both rufomycinSS 2 and 3, structural modeling was pursued. Collectively, this paper discusses the NMR spectroscopic differences of the stereoisomers and their possible 3D conformers and correlates these with the anti-Mycobacterium tuberculosis activity. In addition, a look at the history prioritizes names and numbering schemes for this group of antibiotics and leads to consolidated nomenclature for all currently known members, natural and semisynthetic derivatives, and serves to accommodate future discoveries.

Unveiling structure-activity relationships of proanthocyanidins with dentin collagen.

OBJECTIVE: To elucidate the structure-activity relationships (SARs) of proanthocyanidins (PACs) with type I collagen using sixteen chemically defined PACs with degree of polymerization (DP) 2-6. METHODS: Under a dentin model, the biomimicry of PACs with type I collagen was investigated by dynamic mechanical analysis (DMA) and infrared spectroscopy. The dentin matrix was modified with PACs from Pinus massoniana [monomers (Mon-1 and Mon-2), dimers (Dim-1-Dim-4), trimers (Tri-1-Tri-4), tetramers (Tet-1-Tet-5), and hexamer (Hex-1)]. A strain sweep method in a 3-point bending submersion clamp was used to assess the viscoelastic properties [storage (E'), loss (E"), and complex moduli (E*) and tan δ] of the dentin matrix before and after biomodification. Biochemical analysis of the dentin matrix was assessed with FTIR spectroscopy. Data were statistically analyzed using one-way ANOVA and post-hoc tests (α = 0.05). RESULTS: DP had a significant effect on modified dentin moduli (tetramers ≈ trimers > hexamers ≈ dimers > monomers ≈ control, p < 0.001). Trimers and tetramers yielded 6- to 8-fold increase in the mechanical properties of modified dentin and induced conformational changes to the secondary structure of collagen. Modifications to the tertiary structure of collagen was shown in all PAC modified-dentin matrices. SIGNIFICANCE: Findings establish three key SARs: (i) increasing DP generally enhances biomimicry potential of PACs in modulating the mechanical and chemical properties of dentin (ii) the secondary structure of dentin collagen is affected by the position of B-type inter-flavanyl linkages (4ß â†’ 6 and 4ß â†’ 8); and (iii) the terminal monomeric flavan-3-ol unit plays a modulatory role in the viscoelasticity of dentin.